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Decision support system for construction cycle design 1987

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DECISION SUPPORT SYSTEM FOR CONSTRUCTION CYCLE DESIGN b y GORDON KI-WAI LAW THESIS SUBMITTED IN PARTIAL FULFILLMENT THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CIVIL ENGINEERING We accept this thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA APRIL 1987 © Gordon Ki-Wai Law, 1987. I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . DEPARTMENT OF C I V I L ENGINEERING The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5 D a t e : A P R I L 1987 i i ABSTRACT The objective of this thesis is to develop a conceptual design of a computerized environment for detailed design of construction a c t i v i t i e s associated with projects characterized by s i g n i f i c a n t r e p e t i t i o n . High-rise building construction is used as the example of r e p e t i t i v e construction projects. The construction cycle design of a t y p i c a l f l o o r structure is studied to gain an understanding of the d i f f i c u l t y and complexity involved in the a c t i v i t y design process. Modeling technigues currently used in construction planning, modeling technigues developed in the f i e l d of operations research, and assembly l i n e balancing technigues used in i n d u s t r i a l engineering are reviewed to determine their a p p l i c a b i l i t y for detailed construction cycle design. o Using the concept of decision support systems developed in the f i e l d s of management science and knowledge engineering for solving i l l - s t r u c t u r e d and i l l - d e f i n e d problems, a conceptual design of a decision support system for construction cycle design is developed. i i i TABLE OF CONTENTS ABSTRACT i i LIST OF FIGURES ix ACKNOWLEDGEMENT xi 1. INTRODUCTION 1 1.1 Tra d i t i o n a l Approach to Construction Planning. 2 1.2 Repetitive Construction and Construction Planning 3 1.3 Need for A c t i v i t y Design Tools for F i e l d Management 4 1.4 Research Objective and Approach 5 2 . TERMINOLOGY 7 2.1 Hierarchical Levels in Construction Management 8 2.2 Terminology for Information Representation ... 10 2.2.1 Work Breakdown Structure in "Assemblies" 11 2.2.2 Work Breakdown Structure in Work/Component "Categories" 12 3. CYCLE PLANNING IN R E P E T I T I V E CONSTRUCTION PROJECTS 14 3.1 The Typical Construction Cycle 15 3.2 The Construction Cycle Planning Problem 16 3.2.1 Design Parameters and Decision Variables 17 3.2.2 Need for An A c t i v i t y Design Environment 24 i v 4. E X I S T I N G M O D E L S F O R C O N S T R D C T I O N P L A N N I N G 26 4.1 Deterministic Models 26 4.1.1 Bar Charts 26 4.1.2 C r i t i c a l Path Method (CPM) 29 4.1.3 Line-of-Balance (LOB) 31 4.1.4 Time Space Scheduling Method (TSM). 34 4.1.5 Multiple A c t i v i t y and Crew Balance Charts 37 4.2 P r o b a b i l i s t i c Models 39 4.2.1 Uncertainties in The Construction Environment 39 4.2.2 Queuing Models 40 4.2.3 Discrete Event Simulation 42 4.2.4 Monte Carlo Simulation 44 4.2.5 Program Evaluation and Review Technique (PERT) 45 4.2.6 Decision CPM 46 4.2.7 Graphical Evaluation and Review Technique (GERT) 46 4.2.8 Project Length Analysis and Evaluation Technique (PLANET) ... 47 4.2.9 P r o b a b i l i s t i c Networking Evaluation Technique (PNET) 48 4.3 Mathematical Programming Techniques 49 4.4 Current Practice in Construction Modeling .... 50 5.0 P R O D U C T I O N P L A N N I N G A N D A S S E M B L Y L I N E B A L A N C I N G ( A L B ) 55 5.1 Production Planning 56 5.2 Assembly Line Production 57 5.2.1 Line Balancing Procedure 58 V 5.2.2 Example of Line Balancing 59 5.3 Assembly Line Balancing Algorithms 63 5.3.1 System Constraints 64 5.3.2 P r i o r i t i e s of Work Element Assignment 64 5.3.3 Balanced Assignment and Smoothing . 65 5.3.4 Variable Element Time 66 5.3.5 Element Sharing, Multiple Manning and Multiple Stations 66 5.3.6 Related A c t i v i t i e s 67 5.3.7 Other Considerations 68 5.4 Assembly Line Balancing and Construction Cycle Design 69 5.4.1 S i m i l a r i t i e s Between ALB and Construction Cycle Design 69 5.4.2 Differences Between ALB and Construction Cycle Design 70 5.5 Application of ALB to Construction Cycle Design 73 5.5.1 Limitations of ALB Algorithms 74 5.5.2 Application of ALB Pri n c i p l e s to Construction Cycle Design 76 6 . DECISION SUPPORT SYSTEM (DSS) FOR ACTIVITY DESIGN 78 6.0 Objectives 78 6.1 The Creative Human Decision Making Process ... 80 6.2 Decision Support Systems for Decision Making . 82 6.3 Decision Support System (DSS) for A c t i v i t y Design 83 6.3.1 Module 1 - Problem Recognition .... 89 6.3.1.1 Representation of Project Information 89 vi 6.3.2 Module 2 - Problem D e f i n i t i o n 91 6.3.2.1 Current Practice and Problem D e f i n i t i o n 91 6.3.2.2 Problem D e f i n i t i o n and The DSS .... 92 6.3.2.3 Problem D e f i n i t i o n and Computer Input Format 93 6.3.3 Module 3 - Solution Formulation ... 95 6.3.3.1 Review and Select Construction Technologies 97 6.3.3.1.1 Current Practice and Selection of Technologies 98 6.3.3.1.2 Selection of Technologies and The DSS 98 6.3.3.1.3 Attributes of Construction Technologies 100 6.3.3.2 Define Construction Operations .... 104 6.3.3.2.1 Defining an Operation 105 6.3.3.2.2 Defining Related Operations 105 6.3.3.2.3 Redefining Operations 107 6.3.3.3 Sequence Defined Operations 110 6.3.3.3.1 Operations Sequence and The P-Matrix 110 6.3.3.3.2 Operations Sequence and Lag Calculations 112 6.3.3.3.3 Repetitive Construction and The P-Matrix 112 6.3.3.3.4 Sequencing Operations with The P-Matrix 114 6.3.3.4 Estimate and Assign Resources 115 6.3.3.4.1 Current Practice and Resource Assignment 116 6.3.3.4.2 ALB and Estimation of Resource Requirements 118 vi i 6.3.3.4.3 Assigning Labour Crews 121 6.3.3.4.4 Assigning Special Resources 123 6.3.4 Module 4 - Solution Analysis 126 6.3.4.1 Current Practice in Resource Analysis and Cycle Design 126 6.3.4.2 C r i t i c a l Path Method for Solution Analysis 128 6.3.4.3 Presentation of Analysis Results .. 129 6.3.4.3.1 C r i t i c a l Path Analysis Results .... 129 6.3.4.3.2 Status of Committed Resources 130 6.3.4.3.3 Work Schedules for Labour Crews and Special Resources 131 6.3.5 Module 5 - Design Improvement and Enrichment 138 6.3.5.1 D i f f i c u l t i e s in Improving An A c t i v i t y Design 138 6.3.5.2 An Approach to Solution Improvement 139 6.3.5.3 Solution Improvement and The Multiple Operation Time Chart ... 142 6.3.5.4 Instructions to Manipulate The Multiple Operation Time Chart ... 143 7. CONCLUSIONS AND RECOMMENDATIONS 146 7.1 Conclusions 146 7.2 Recommendations for Future Research 148 7.2.1 Computer Programming and F i e l d Application 148 7.2.2 Graphics Interface for Cycle Design 148 7.2.3 Integration with Other Management Functions 149 7.2.4 Integration with Other Modeling Technigues 150 v i i i 7.2.5 Detailed Planning of Construction Cycle Operations 151 BIBLIOGRAPHY 152 i x LIST OF FIGURES 4.1 Fenced bar chart of a warehouse project 28 4.2 Precedence diagram of a warehouse project 28 4.3 Line-of-Balance modeling technique 33 4.4 Time Space diagrams 36 4.5 Multiple a c t i v i t y chart of a building cycle 38 4.6 Current application of CPM in construction planning 54 5.1 Example of a 20-element assembly production process 60 5.2 Suggested balance to the assembly production process 62 6.1 Creative human decision making process 81 6.2 Problem recognition, problem d e f i n i t i o n and solution formulation 87 6.3 Solution analysis and design improvement and enrichment 88 6.4 Problem d e f i n i t i o n 94 6.5 Review and select construction technologies 99 6.6 Review work tasks of construction technology 103 6.7 Defining an operation 108 6.8 Defining related operations 109 6.9 Sequencing operations - the P-Matrix 111 6.10 Estimate and commit resource pools 120 6.11 Assigning labour crews to operations 124 6.12 Assigning special resources to operations 125 6.13 C r i t i c a l path analysis results 134 6.14 Resource Status Table 135 X 6.15 Select crews and special resources to report in M.O.T. chart 136 6.16 Multiple Operation Time (M.O.T.) chart 137 6.17 General Rules for design improvement 141 x i ACKNOWLEDGEMENTS I want to express my sincere gratitude to Dr. A. D. Russell, my supervisor, for his valuable advice, guidance and encouragement throughout my studies. I greatly appreciate his e f f o r t s and time in reviewing this thesis and the valuable suggestions to improve the content. My thanks are extended to Dr. W.F. Caselton for reviewing this thesis. Acknowledgement is most g r a t e f u l l y extended to the Canada Mortgage and Housing Corporation who has provided the scholarship which enabled me to pursue graduate studies at the University of B r i t i s h Columbia. A special thank you to professors, friends and colleagues who have given me valuable advice and much treasured support and encouragement during this study. 1 1 . INTRODUCTION Construction projects are t r a d i t i o n a l l y developed by owners or users who are concerned about the functional and aesthetical aspects of the f a c i l i t i e s and rarely consider the d i f f i c u l t i e s in producing the desired end products. The construction industry must develop construction methods and technologies that can e f f i c i e n t l y , economically and safely produce the desired physical f a c i l i t i e s . Most construction projects are of r e l a t i v e l y short duration and l i t t l e scope is offered for economies of scale through mass production. Therefore, general contracting firms and subcontractors concentrate their a c t i v i t i e s within limited areas in order to master the s k i l l s and technologies associated with their s p e c i a l i z a t i o n and to reduce unit costs to an extent that they can stay in business. Expertise in their specialized areas is developed by learning through practice; in-depth analysis of construction a c t i v i t i e s is rarely considered except when a construction a c t i v i t y i s new and has s i g n i f i c a n t impact on o v e r a l l project cost and completion time, when problems develop during construction and threaten completion of the project, or when the a c t i v i t y is to be repeated a s i g n i f i c a n t number of times (say greater than twelve to f i f t e e n times). 2 1.1 TRADITIONAL APPROACH TO CONSTRUCTION PLANNING Current construction planning methods being used, such as the c r i t i c a l path method, provide higher management with information on construction deadlines and resource requirements of projects. Such information also provides goals and objectives towards which f i e l d management personnel are expected to work, although they are not provided with a t a c t i c a l plan, such as a detailed short cycle schedule, to achieve them. F i e l d management personnel, who are concerned with the methods of accomplishment required to meet goals imposed by higher management, must focus their e f f o r t s at the production level of the construction process. Their immediate concerns are the commitment of resources, the method and seguence of construction operations and the elimination of delays and i d l e resources. They are interested in a much more detailed breakdown of construction a c t i v i t i e s as a mean of revealing potential delays and imbalances a f f e c t i n g the rate of construction. A more detailed analysis of construction a c t i v i t i e s also provides them with information useful for tracking and c o n t r o l l i n g valuable resources. Day-to-day operational plans of construction a c t i v i t i e s are rarely considered and studied in d e t a i l and in a systematic manner. Rather, they are either i m p l i c i t in the adoption and modification of past methods or developed by s i t e managers and construction superintendents in the f i e l d 3 during construction of the f a c i l i t i e s . Detailed descriptions of day-to-day construction operations reside in the minds of key s i t e personnel. It is generally accepted that s i t e managers and construction superintendents w i l l have enough experience and s k i l l s to achieve the goals set for the project in an e f f i c i e n t manner. However, the management trai n i n g environment through which s i t e management personnel are expected to acguire these s k i l l s is extremely uneven and tie d to t r a d i t i o n and h i s t o r i c a l precedents. The rapid advance in construction technologies often reduces the usefulness of past experience. 1.2 R E P E T I T I V E CONSTRUCTION AND CONSTRUCTION PLANNING Repetitive construction projects, which include mass housing development, high-rise building, highway, bridge and tunnel projects, are characterized by standardized design for a large number of t y p i c a l sections. The high degree of repetition in these project types allow savings in cost and time achieved through highly detailed construction planning to be multiplied; problems that result from poor planning w i l l , however, propagate and magnify as a project progresses. For example, in the production of a t h i r t y story building, savings in the construction of a t y p i c a l f l o o r w i l l be multiplied t h i r t y times; i d l e time of resources resulting from poor planning w i l l also be multiplied t h i r t y t imes. 4 1.3 NEED FOR ACTIVITY DESIGN TOOLS FOR F I E L D MANAGEMENT Existing planning models which originated for management at the organizational and project levels f a i l to meet the detailed needs of management at the construction s i t e . This problem is well recognized by p r a c t i t i o n e r s in the construction industry and has been addressed by authors in the construction l i t e r a t u r e . Peer [98] stated that: "None of the network methods includes in i t s algorithm and c a l c u l a t i o n any consideration for solving the p r a c t i c a l organization problems of the production process on s i t e . " [98] Dabbas and Halpin [27] further stated that: "Methodologies and systems which address problems at the l e v e l of f i e l d decision making and control are less abundant. In p a r t i c u l a r , systems for analyzing construction operations at the technological l e v e l have not received as much attention as higher l e v e l systems." [27] The t r a d i t i o n a l approach to construction planning does l i t t l e to encourage innovations in the design of construction a c t i v i t i e s in order to benefit from advances in construction technologies. Also, this approach deals with problems only when they actually arise during the construction process when i t is often either too late or too costly to make changes. 5 To encourage the detailed design of construction a c t i v i t i e s before resources are actually committed and to deal with problems before they arise in the f i e l d , a planning system which caters to the needs of s i t e management personnel must be developed. Such a system should be able to provide information useful for tracking and c o n t r o l l i n g valuable resources, should be easy to use and should be able to respond to the dynamic environment of the construction s i t e . 1 . 4 RESEARCH OBJECTIVE AND APPROACH The objective of this thesis is to develop a conceptual design of a computerized environment for detailed design of construction a c t i v i t i e s with emphasis on a c t i v i t i e s associated with projects characterized by s i g n i f i c a n t r e p e t i t i o n . The a c t i v i t y design environment would a s s i s t construction management personnel to systematically analyze and design construction a c t i v i t i e s resulting in t a c t i c a l plans to achieve goals set for a construction project. The environment would also allow construction management personnel to apply personal judgment, i n t u i t i o n and c r e a t i v i t y in the a c t i v i t y design process. In chapter two, the terminology used throughout the thesis is presented. In chapter three, the construction cycle planning problem in high-rise construction projects is described to 6 gain an understanding of the d i f f i c u l t i e s and complexity involved in designing a construction a c t i v i t y . In chapter four, e x i s t i n g models for construction planning described in the l i t e r a t u r e are reviewed and studied to determine their a p p l i c a b i l i t y for detailed a c t i v i t y design. In chapter f i v e , the assembly l i n e balancing technigue described in the i n d u s t r i a l engineering l i t e r a t u r e is studied to determine whether i t can be adapted for design of construction a c t i v i t i e s . In chapter s i x , a brief overview of the process of decision making is described. Then, the process of a c t i v i t y design is described by flow charts and f i v e modules: problem recognition, problem d e f i n i t i o n , solution formulation, solution analysis, and design improvement and enrichment. F i n a l l y , a conceptual design of an a c t i v i t y design environment is described in terms of computer input/output formats and interaction between the computer and the decision maker. Chapter seven presents thesis conclusions and recommendations for future research. 7 2. TERMINOLOGIES One of the f i r s t problems encountered in the study of construction planning is the lack of a consistent terminology with which to describe construction processes. In this chapter, the terminology used for describing the construction process at the production l e v e l of the project management hierarchy w i l l be introduced and w i l l be used consistently in this thesis. Terminology associated with two approaches to work breakdown structures used in the a c t i v i t y design environment w i l l also be described. 2.1 HIERARCHICAL L E V E L S IN CONSTRUCTION MANAGEMENT In the management of construction projects, a hi e r a r c h i c a l structure exists because of the differences in the concerns of management personnel at head o f f i c e and at the construction s i t e . The hierarchy can be roughly divided into three l e v e l s : organizational, project and production. At the organizational l e v e l , management is concerned with the legal and business structure of a firm, the various functional areas of management, and the interaction between head o f f i c e and f i e l d management personnel performing these functions. It is also concerned with the a project's t o t a l 8 c o s t , d u r a t i o n , and c a s h f l o w i n r e l a t i o n t o t h e p o r t f o l i o o f o t h e r p r o j e c t s . A t t h e p r o j e c t l e v e l , management i s c o n c e r n e d w i t h p r o j e c t d e f i n i t i o n , c o n t r a c t u a l and l e g a l o b l i g a t i o n s , and b r e a k d o w n o f t h e p r o j e c t i n t o a c t i v i t i e s f o r t i m e , c o s t and r e s o u r c e c o n t r o l . Management a t t h e p r o d u c t i o n l e v e l , w h i c h i s d e s c r i b e d as s i t e / f i e l d management i n c h a p t e r o ne, i s c o n c e r n e d w i t h t h e s e l e c t i o n o f e f f i c i e n t c o n s t r u c t i o n methods and t e c h n o l o g i e s , t h e commitment o f r e s o u r c e s and t h e d a y - t o - d a y p r o g r e s s o f c o n s t r u c t i o n a t t h e s i t e . C o n s t r u c t i o n p l a n n i n g a t t h e p r o d u c t i o n l e v e l c a n i n v o l v e t h r e e l e v e l s o f d e t a i l : (1) A c t i v i t y An a c t i v i t y i s a t i m e a nd r e s o u r c e c o n s u m i n g e l e m e n t o f a p r o j e c t . I t i s n o r m a l l y d e f i n e d f o r t h e p u r p o s e o f t i m e and c o s t c o n t r o l by a p l a n n e r / s c h e d u l e r , e s t i m a t o r , o r c o s t e n g i n e e r . I t i s u s u a l l y r e l a t e d t o t h e c o n s t r u c t i o n o f a d i v i s i o n o f t h e p h y s i c a l f a c i l i t y by a s e q u e n c e o f o p e r a t i o n s . An a c t i v i t y i s u n i q u e and must be c o m p l e t e d o n c e . An e x a m p l e o f an a c t i v i t y i s t h e c o m p l e t i o n o f t h e f l o o r s t r u c t u r e o f a t h i r t y s t o r y h i g h - r i s e b u i l d i n g . (2) O p e r a t i o n A c o n s t r u c t i o n o p e r a t i o n r e p r e s e n t s a c o l l e c t i o n o f work t a s k s r e l a t e d t o e a c h o t h e r t e c h n o l o g i c a l l y . I t i s c l o s e l y r e l a t e d t o t h e c o n s t r u c t i o n method and c a n 9 be r e p e t i t i v e in nature. The duration of an operation is measured in hours or days. An example of an operation is the forming of a section of a f l o o r slab using say a tower crane, 2 general labourers, 10 carpenters and 1 foremen. (3) Work Task A work task is the basic descriptive unit of the construction process. If a work task is broken down into components, human factor considerations or detailed eguipment motions are involved. A work task should be a readily i d e n t i f i a b l e component of a construction operation. Its description must be so clear that any member of a construction crew can readily grasp and v i s u a l i z e what is involved in the work task. Work tasks are therefore the basic building blocks of operations. An example of a work task is i n s t a l l i n g a support bracket of a section of slab formwork. Another term that w i l l be used in this thesis is as s i g n m e n t which is a c o l l e c t i o n of work tasks or operations s p e c i f i c a l l y assigned to a crew member or a crew. Of the h i e r a r c h i c a l levels described, only the production level i s pertinent to the a c t i v i t y design problem. Discussions in this thesis w i l l concentrate at the production l e v e l . 10 2 .2 TERMINOLOGY FOR INFORMATION REPRESENTATION Information representation is one of the most important elements in any problem solving environment. In the a c t i v i t y design environment, which w i l l be developed in this thesis, the physical f a c i l i t y being constructed has to be broken down into smaller units. The terminology employed in representing this information must be consistent to ensure proper communication between the computer and management personnel. Systematic work breakdown structures described in the construction management l i t e r a t u r e , can provide the terminology needed to represent the above information. In the paper "Work Breakdown Structures in Construction", Ponce-Campos and Ri c c i [64] described a work breakdown structure (WBS) as: "a systematic approach to subdividing an e f f o r t into i t s components and/or end product." [64] In other words, a work breakdown structure is a systematic approach to represent the manner in which a physical f a c i l i t y and i t s components are constructed. The approaches to work breakdown structure in physical assemblies and in work categories w i l l be adopted. The terminology described below w i l l be used in discussions of the a c t i v i t y design environment. 11 2.2.1 WBS IN P H Y S I C A L " A S S E M B L I E S " The f i r s t task in any problem solving process is defining the problem in a clear and precise manner. In a construction project, the problem definition process involves defining the dimensions of the physical f a c i l i t y in detail. The following terminology wi l l be used for problem definition in the activity design environment being developed. T o t a l - A s s e m b l y : denotes the physical f a c i l i t y to be delivered at completion of the project as defined by the total scope of work in the contract documents. A s s e m b l y G r o u p : denotes a grouping of physical assemblies with similar functions and represents a significant portion of a building or structure; e,g superstructure, substructure, south-wing, north-wing. A s s e m b l y : denotes a meaningful subdivision of an assembly group; e.g. a floor elevation, a sub-grade elevation. S u b - A s s e m b l y : denotes a horizontal division of an assembly group or an assembly; e.g. the north-wing of the superstructure, bay 13 of a floor elevation. 12 Assembly (subassembly) Component: denotes one of the components of an assembly (subassembly); e.g. slab, columns, walls, and cores are components of a floor elevation assembly. 2.2-2 WBS IN WORK/COMPONENT "CATEGORIES" Construction operations are labour intensive processes. Solution formulation involves defining the operations or work which are to be performed to construct the physical f a c i l i t y . Operations can be categorized by the trade performing the work or the physical components on which work is being performed. The following terminology w i l l be used in the solution formulation process in the activity design environment being developed. Category Group: denotes a grouping of components by disciplines or trades; e.g. c i v i l / s i t e , concrete, metal. Category: denotes a grouping of components by functions under the same category group; e.g. under the category-group of concrete, we can have supported slabs, grade slabs, cores, columns, footings, and walls. Category Component: denotes the material or sub-component that make up an identifiable project 13 component; e.g. in the concrete component we can have form-work, rebar, concrete, and misc. metals. Category Sub-Component: denotes a process in each work category component; e.g. [form-work] is composed of [form-work installation] and [form-work dismantling] processes. 14 3. CYCLE PLANNING IN R E P E T I T I V E CONSTRUCTION PROJECTS In order to understand the process involved in designing a construction a c t i v i t y , in this chapter the decision making process involved in designing t y p i c a l construction cycles in high-rise construction projects w i l l be used as an example to i l l u s t r a t e the complexity of the a c t i v i t y design problem. The t y p i c a l construction cycle in a high-rise building construction project is often simply i d e n t i f i e d as a single a c t i v i t y in the project network; for example, the a c t i v i t y of form and pour the f i f t h f l o o r . The design of a construction cycle can therefore be i d e n t i f i e d with the design of a construction a c t i v i t y . Thus, the terms a c t i v i t y design and construction cycle design w i l l be used interchangeably in this thesis. The t y p i c a l construction cycle in a high-rise building construction project w i l l f i r s t be described and the problems and objective of construction cycle design are discussed. Then, the design parameters and variables w i l l be studied. F i n a l l y , statements w i l l be made regarding the goal of the construction cycle planning problem and the need of a construction cycle design environment. 15 3.1 T H E T Y P I C A L C O N S T R U C T I O N C Y C L E The construction of a high-rise building consists of construction of the substructure and superstructure. Construction of the superstructure often accounts for a major portion of the t o t a l project duration. The construction of the superstructure can be roughly divided into the following groups of a c t i v i t i e s : (1) s t r u c t u r a l , (2) e l e c t r i c a l , (3) mechanical, and (4) building f i n i s h e s . The s t r u c t u r a l a c t i v i t i e s form the most s i g n i f i c a n t group of a c t i v i t i e s as other a c t i v i t i e s cannot proceed unless the s t r u c t u r a l components are complete. The s t r u c t u r a l a c t i v i t i e s are characterized by a sequence of operations which are carried out to produce a t y p i c a l f l o o r structure. The sequence of operations are repeated a number of times u n t i l the building structure is completed. Because of the c y c l i c nature of the repeated sequence of operations, they are c o l l e c t i v e l y c a l l e d the " t y p i c a l cycle". Since the f l o o r structures must be completed before the other a c t i v i t i e s mentioned above can begin, the s t r u c t u r a l a c t i v i t i e s often appear as " c r i t i c a l " in the project network. The rate at which a t y p i c a l f l o o r structure is produced therefore governs how fast the other a c t i v i t i e s can progress. This fact has been well recognized and most general contractors perform the s t r u c t u r a l a c t i v i t i e s with their own work-force; the other groups of a c t i v i t i e s which involve intermittent use of special trades are often subcontracted to contractors spe c i a l i z e d in those p a r t i c u l a r 16 areas. Since the s t r u c t u r a l group of a c t i v i t i e s the concentrate on the s t r u c t u r a l a c t i v i t i e s form the c r i t i c a l following discussions w i l l a c t i v i t i e s . 3.2 THE CONSTRUCTION CYCLE PLANNING PROBLEM Once the project is awarded to a construction firm, the project manager, construction manager, s i t e superintendent, and sometimes the s i t e foremen w i l l meet to discuss how the buildfhg is to be constructed. The major concern is meeting the project c r i t e r i a in the most e f f e c t i v e manner in terms of time, money, labour, materials, and equipment u t i l i z a t i o n . The "time" objective is therefore met at the expense of the "cost" of the committed resources. In order to use the committed resource e f f e c t i v e l y , the f i e l d management personnel must choose the most appropriate construction technologies and methods. In the t r a d i t i o n a l approach to construction planning, the construction cycle for a f l o o r structure often appears in the project network as a single a c t i v i t y ; for example, the a c t i v i t y of form and pour f l o o r slab with a duration of f i v e days. Even though the construction methods and technologies are discussed in project meetings, because of the lack of a proper construction planning system, they are often mentioned only in general terms, and are rarely analyzed and documented in a systematic manner. Problems with the chosen construction 17 methods and technologies are dealt with only as they appear during the construction process. 3 . 2 . 1 DESIGN PARAMETERS AND DECISION VARIABLES To i l l u s t r a t e the decision process and understand the complexity involved in designing a construction a c t i v i t y , some of the parameters and decision variables in the design of the construction cycle of a t y p i c a l f l o o r structure in a high-rise building project w i l l be discussed. (1) Cycle Time In order to meet the target date for delivery of the finished product, management must make a decision regarding the time reguired to construct a t y p i c a l f l o o r , i . e . cycle time. This decision often evolves into a time-cost trade-off problem: a reduced cycle time can be achieved at the expense of more expensive eguipment, a larger labour pool and increased overtime cost. However, cycle time can also be shortened by proper operation planning to reduce i d l e time of labour and eguipment and through selection of e f f e c t i v e eguipment and forming technology. The cycle time for a f l o o r structure w i l l influence and is influenced by the selection of forming and material handling technologies, material, eguipment and labour usage and seguencing of operations. 18 F o r m i n g T e c h n o l o g i e s Formwork cost represents one of the major and most variable portion of the cost in the structure cycle. It normally accounts for 33% to 55% of the t o t a l concrete placement cost (Fintel [25]); the cost of the r i g i d l y s p e c i f i e d concrete and r e i n f o r c i n g s t e e l normally do not vary to any s i g n i f i c a n t extent. Cost of concrete placement depends on the proper sequencing of operations, e f f e c t i v e use of over-time, e f f i c i e n t work space d i v i s i o n and a l l o c a t i o n and selection of appropriate material handling equipment, a l l of which are related to the forming system selected and how the system is implemented. Conventional b u i l t - i n - p l a c e formwork is used normally only in highly complicated non-reusable forming or the opposite extreme of simple, undemanding formwork. In low-rise building construction projects where expensive l i f t i n g equipment is not f e a s i b l e , an entire story may be formed and later disassembled and passed up to the next fl o o r through shafts or outside the building after the concrete has acquired the minimum strength. Reusable formwork is used in large r e p e t i t i v e projects such as high-rise building projects. The economy of the formwork w i l l depend on: (1) the f i r s t cost of formwork, either rental or custom b u i l t , (2) cost of non-reusable parts, (3) number of reuses, (4) 19 cost of erecting and s t r i p p i n g , and (5) cost of cleaning, repairing, and modifications. The ganging of forming sections and the choice of shoring system (horizontal or v e r t i c a l ) must also be studied in terms of their implications of their cost, time, and labour reguirements and impacts on other operations. M a t e r i a l s T r a n s p o r t a t i o n Experience in high-rise construction projects has indicated that proper scheduling of major l i f t i n g eguipment such as the tower crane is c r u c i a l to the time and cost performance of a project. The choice of l i f t i n g equipment depends on the s i t e conditions and the purposes for which they are intended. For most high-rise building projects, their locations in busy commercial areas prohibit the use of mobile crane; consequently, tower cranes are most often used. Being an expensive piece of equipment, only one is normally used except in projects with large plan areas and the required reach necessitates the use of two or more tower cranes. Capacities of the l i f t i n g equipment w i l l be governed by the maximum reach and weight required to be l i f t e d . Conversely, the capacity of the crane may l i m i t the size of formwork sections that can be transported. The l i f t i n g equipment w i l l be used for the transport of heavy forming sections, prefabricated concrete or r e i n f o r c i n g s t e e l components, and placement 20 of concrete when a crane and bucket system is chosen. Most of these operations are c r i t i c a l in the structure cycle. Thus careful planning and study of the equipment schedule is required to avoid delay or interruption of operations. C o n c r e t e Placement Next to formwork, concrete placement is the most costly item and is labour intensive. The choice of placement method has a s i g n i f i c a n t impact on the economy and qu a l i t y of the concrete placed. The e f f i c i e n c y of the operation is often measured in terms of the rate of placement in volume of concrete placed per unit time. The most frequently used systems of concrete placement are pumping, crane and bucket, and material hoists. For large projects, integrated systems of material hoists, conveyor bel t s , and motorized buggies might be used. The use of high-early strength concrete can reduce the curing time and thus allows the forms and shores to be reused more often. Use of super-plasticizers w i l l s i g n i f i c a n t l y reduce the time reguired for placement and f i n i s h i n g . In fact, decisions pertaining to the selection of concrete additives and non-destructive testing to determine strength can be central to the design of the s t r u c t u r a l cycle. 21 (5) P r e f a b r i c a t i o n of Components Prefabrication of structure components, such as concrete stairways, column reinforcing steel cages, and use of welded reinfor c i n g s t e e l mesh, often allows the corresponding operations to be carried out in more e f f i c i e n t manners by allowing them to proceed in p a r a l l e l rather than sequentially. Prefabricated components, however, need to be transported to the work location and thus have to compete with other operations for use of l i f t i n g equipment; moreover, prefabricated components and on-site prefabrication processes occupy s i t e areas needed for material storage and other purposes. (6) Breakdown and Sequence of Operations Decisions made on forming, material transportation, and concrete placement technologies determine to some extent the l i s t of operations reguired to be carried out. The decision maker can choose to break down the f l o o r structure into smaller sections and decide the sequence in which they are to be constructed. He can decide to form the whole f l o o r and then place the concrete or he can decide to form half a f l o o r , place the concrete, and then form and place the rest of the f l o o r ; similar decisions can be made for other operations such as construction of the elevator cores. 22 Decisions on how the f l o o r structure is to be broken down and constructed determine the number of sets of forms required. Careful sequencing of the corresponding operations is necessary to ensure smooth transitions between operations and to minimize i d l e time for labour and equipment resources. (7) S c h e d u l i n g of S u b - T r a d e s Operations performed by sub-trades, though not studied in d e t a i l by general contractors, are d i s t i n c t operations which take up time and space during the construction process. Sub-trades must be scheduled to come on s i t e only when the p a r t l y - f i n i s h e d product is ready for their p a r t i c u l a r operations. C o n f l i c t s between sub-trades a r i s i n g from limited work space and need for the same l i f t i n g equipment must be avoided as they impose delay costs to the sub-trades and subsequently to the general contractor. (8) Number of Crews, Crew S i z e s , and Crew Mix Decisions on forming, material handling, and concrete placement technologies, prefabrication of components, and the breakdown of the f l o o r structure together define the set of operations and tasks involved in construction of the f l o o r structure. The tasks involved in each operation subseguently define the labour types, and the sizes and mixes of each crew requ i red. 23 The production rate required to achieve the desired cycle time w i l l , up to certain l i m i t s , be proportional to the crew s i z e . Multiple crews can be used to speed up the construction operations, but at the expense of more sets of forms and more crowded work space. Extra s h i f t s and/or over-time can also be used to shorten cycle time but not without the associated costs. Use of Resources and Crew Assignment Given the pool of resources, the decision maker must determine the schedules for each major piece of equipment and work assignments for each crew and each individual member of a crew so as to achieve the expected productivity rate with maximum e f f i c i e n c y . If the desired production rate cannot be achieved with the given pool of resources, changes in the size of the resource pool and/or in the construction technology must be contemplated. Operations that use shared resources must be scheduled to minimize queuing delays. Decisions have to be made on the p r i o r i t i e s given to various operations when c o n f l i c t s of equipment usage a r i s e . For the case of limited work space, the work schedule of each crew must be c a r e f u l l y developed to avoid over-crowding. 24 (10) I d e n t i f y i n g C r i t i c a l O p e r a t i o n s and P r o c e s s e s Once the construction operations have been defined and assigned to various crews and equipment, operations that are c r i t i c a l and w i l l potentially disturb the smooth progress of the construction process must be identified. Any expected problems should be analyzed and studied and the corresponding correction plans developed, i f time and cost allow, before they actually happen in the f i e l d . 3 . 2 . 2 NEED FOR AN ACTIVITY DESIGN ENVIRONMENT From the above discussions, we can identified the following characteristics of the construction cycle design problem: (1) multiple objectives: time, cost, and effectiveness and efficiency of committed resources; (2) trade-offs between multiple objectives such as time and cost within product quality constraints; (3) a large number of variables, such as choice of technologies, choice of construction methods and sequence of operations, and the commitment and use of resources, that together determine the effectiveness of the subsequent production schedule; (4) a large number of possible values for each variable and a large number of feasible variable value combinations. 25 The ultimate objective of the construction cycle design process is to maximize p r o f i t s through the selection of a time and cost e f f e c t i v e solution. This require the evaluation of a l l possible design alternatives. However, because the linkages between them are not pr e c i s e l y known and because of the i n a b i l i t y to define a l l of the decision variables in quantitative term, we do not have a closed form production function that link a l l the design variables and the design objective. An optimal solution cannot be obtained by a deterministic mathematical process. The problem must be solved by management personnel who understand the design objective and the complex linkages between the design variables, and by applying experience, personal judgment and i n t u i t i o n in the solution design process. Although a deterministic mathematical procedure is not available to determine the best design a l t e r n a t i v e , i t is possible to create an environment in which the construction management personnel can readily explore the design alternatives and generate an action plan to be used in the f i e l d . The conceptual design of an ' a c t i v i t y design environment w i l l be described is chapter s i x , after the review of modeling techniques being used in construction planning and i n d u s t r i a l engineering in chapters four and f i v e . 26 4. EXISTING MODELS FOR CONSTRUCTION PLANNING In order to develop a construction cycle planning framework, the exis t i n g models used in construction planning w i l l f i r s t be reviewed to determine their a p p l i c a b i l i t y for detailed construction cycle design. 4-1 DETERMINISTIC MODELS 4.1.1 BAR CHARTS The bar (or Gantt) chart was developed by Henry L. Gantt (1861-1919) for i n d u s t r i a l production management in the early 1900's. The basic intentions are: (1) to set down the steps (influenced by technical r e s t r i c t i o n s ) , stages, or phases of work that must be followed in order to bring a project to f r u i t i o n , and (2) to enable the planner to monitor and track status of the project. Since i t s introduction, the bar chart has received wide acceptance from management in many d i s c i p l i n e s for graphically portraying project plans and work progress. The basic modeling concept of the bar chart is the representation of a project work item ( a c t i v i t y ) with a time scaled bar whose length represents the planned duration of the work item. It 27 can be located in calendar time to indicate the schedule for st a r t i n g , execution and completion of the project work item i t represents. The scaled length of the bar is also used as a graphical base on which to plot actual performance toward completion of the work item. Ingenious use of the bar chart provides management with useful project information on ov e r a l l scheduling, use of resources and productivity. The major advantage of the bar chart model is that i t is simple and easy to understand and update, and thus has been widely used by construction personnel at a l l levels in the management hierarchy. However, the model f a i l s to show det a i l s of the technologies involved in the construction operations and the i n t e r - r e l a t i o n s of project work items. The nature of the i n t e r - r e l a t i o n s among work items have to be deduced by users. Used by i t s e l f , the bar chart is inadequate for solving the complex problems that construction management personnel often face today. In general, construction projects are now analyzed using more sophisticated models and the output is displayed in bar chart format for easy understanding by f i e l d personnel. Melin and Whitetaker [83] devised a graphic representation, the fenced bar charts (figure 4.1), which retains the s i m p l i c i t y of the bar chart model but shows the network logic found in precedence or arrow diagrams. Other techniques including the 1ine-of-balance and multiple a c t i v i t y chart have their o r i g i n in the bar chart modeling rationale. 28 S MOVE IN I ORDER AND DEL . REBRR 10 PLACE fTEBPfl E [7 CLEAR SITE B EXCAVATE 3 ORDER ANO P E L . STRUCT. STEEL 11 CAST FOOTINGS 13 ERECT URLLS • i t l M POUR FLOOR 4. ORDER ANO DEL . UIN00U5 5 ORDER ANO DEL . EQUIP. I < I I I I I I I 15 PLACE ROOF 17 INSTALL E0U1PTMENT 16 INSTALL UlNDOUslia CLEAN UP "itl. 8 15 22 2 9 5 12 19 26 S 12 19 26 2 9 JAN79 FEB79 MAR79 APH79 16 23 30 7 H MAY 79 Figure 4.1: F e n c e d b a r c h a r t o f a warehouse p r o j e c t S o u r c e : M e l i n and W h i t e t a k e r [ 8 3 ] , p. 501 ORDER REBAR S ORDER STEEL ORDER EQUIP. 0 06 9 3 07 10 MOVE CLEAR IN SITE . 0 9 10 10 5 l i 3 9 10 oe 20 29 10 30 EXCAVATE PLACE REBARS H 10 25 25 9 30 CAST ROOFING POUR FLOOR 40 13 69 69 19 79 ERECT PLACE WALLS ROOF 40 29 69 69 10 75 0 0 0 04 99 65 16 70 ORDER INSTALL WINDOWS WINDOWS ' 19 99 70 70 5 75 INSTALL EQUIP. ACTV ITT DESCRIP. CLEAR UP ES - EARLY START EF - EARLY FINISH 10 • ACTIVITY IDENTIFICATION LF - LATE FINISH LS - LATE START DU • ACTIVITY DURATION TF - TOTAL FLOAT Figure 4.2: P r e c e d e n c e d i a g r a m o f a warehouse p r o j e c t S o u r c e : M e l i n and W h i t e t a k e r [ 8 3 ] , p. 500 29 4.1.2 CRITICAL PATH METHOD (CPM) The c r i t i c a l path method, originated in 1957 by James E. Kelly of UNIVAC and Morgan R. Walker of duPont, represents a project plan by a network model that depicts the logic of the construction plan. Two types of graphs, the precedence ( a c t i v i t y on node, figure 4.2) and the arrow ( a c t i v i t y on arrow) diagrams have been used, with the former now being preferred. The network model uses labeling techniques to assign a variety of attributes to the model such that a wide spectrum of problems can be treated graphically. Preparing a CPM network usually involves the following steps: 1. L i s t the a c t i v i t i e s (or work items). 2. Establish the durations of and the resources reguired for each a c t i v i t y . 3. Develop the network l o g i c , i . e . precedence r e l a t i o n s . 4. Find the c r i t i c a l path and n o n - c r i t i c a l paths. 5. On a time frame, develop resource usage histograms for each type of resource for the whole project. 6. Level resources within acceptable l i m i t s for the project. 7. Re-schedule sta r t times of a c t i v i t i e s to s u i t resource l e v e l i n g . 8. Iterate through 3 to 7 u n t i l a " s a t i s f a c t o r y " solution is achieved. 30 The major advantages of the c r i t i c a l path method are as follows: 1. Logic restraints are c l e a r l y shown on the diagram whereas assumptions were necessary when bar charts were used for control. 2. It stimulates more detailed planning by the contractor which usually results in better coordination, fewer delays, fewer claims and e a r l i e r project completion. 3. It permits evaluation of the impacts of anticipated and actual changes of project conditions on the contractor's work. 4. It can be used to provide progress and payment data. 5. Updating permits refinement of occupancy dates, needed delivery dates for owner furnished items and the f i n a l completion dates. 6. An additional advantage of the c r i t i c a l path method is the easy access to numerous computer software packages developed for use in the construction industry. Several of these packages integrate the project scheduling function with material procurement, cost control and accounting functions. Despite the numerous advantages of the c r i t i c a l path method, i t has not been welcomed by many construction personnel because of i t s r e l a t i v e complexity. The network diagram and i t s modeling rules cannot be e a s i l y understood by untrained personnel. Updating of the project network is 31 also tedious for large projects. Even when much of the redrafting and computational work is performed with the assistance of computers, the vast amount of computer printout generated is not welcomed and is often not e a s i l y comprehensible by s i t e personnel. B i r r e l l [11] c r i t i c i z e d the c r i t i c a l path method for not being able to represent the more r e a l i s t i c " h e u r i s t i c " process of construction planning. 4.1.3 LINE-OF-BALANCE (LOB) The l i n e of balance (LOB) is a scheduling technique developed by the U.S. Navy in the early 1900s. It was f i r s t applied to i n d u s t r i a l manufacturing and production control where the objective was to evaluate the flow rates of finished products in a production l i n e . Three diagrams are used in the LOB technique: (1) The production diagram, as shown in figure 4.3(a), represents the i n t e r - r e l a t i o n s of the assembly operations for a single unit of the finished product. It is the representation of the technological constraints on the operations and shows the operations reguired to produce a single unit, such as a t y p i c a l f l o o r structure of a high-rise building project. (2) The objective diagram, as shown in figure 4.3(b), is used to plot the planned number of units produced versus time. For a mass housing development project, 32 the objective diagram may show the expected number of housing units produced in each week or month. (3) The progress diagram, as shown in figure 4.3(c), indicates the numbers of units for each of the subassemblies which should be completed by s p e c i f i c dates. It takes the form of a v e r t i c a l bar graph; each bar represents an operation shown in the production diagram; the length of a bar indicates the actual number of units of the corresponding subassembly produced to date. Actual progress is compared to the "l i n e of balance" (or balance l i n e ) , a l i n e produced from the production and objective diagrams. It corresponds to the le v e l of progress needed for each operation at the p a r t i c u l a r date to achieve the objective. The l i n e of balance method focuses on monitoring the current status of an a c t i v i t y r e l a t i v e to i t s scheduled status so that corrective action can be i n i t i a t e d where and when required. 33 -V 0 m- - v — A 1 | S u b c o n t r a c t p a r t P u r c h a s e p a r t \ ^ S u b a s s e m b l y c o m p l e t i o n / \ U n i t c o m p l e t i o n M o n t h s p r i o r t o u n i t c o m p l e t i o n Figure 4.3(a): Production diagram - - 70 - - Feb. 1 Fig 4.3(b): Objective diagram Fig 4.3(c): Progress diagram Figure 4 . 3 : Line-of-Balance modeling technigue Source: Johnston [57], p. 250 34 4 . 1 . 4 TIME SPACE SCHEDULING METHOD (TSM) The time space scheduling method described by Stradal and Cacha [123], has been labeled by other authors also as "linear scheduling method (LSM) " (Johnston [57]), "linear planning chart" (Russell [114]), " v e r t i c a l production method (VPM)" (O'Brien [93]), and "flow l i n e method" (Cormican [23]). This scheduling technique has some relationship to the LOB technique. TSM emphasizes a diagram similar to the objective diagram for planning purposes while LOB places emphasis on the balance l i n e of the progress diagram. The label "Time Space Scheduling Method" is chosen because the scheduling technique shows c l e a r l y the locations or "space" where each corresponding a c t i v i t y take place in a given "time". The TSM diagram graphs time versus location where location is e s s e n t i a l l y a measure of progress. Location can be measured in many ways. In high-rise building projects the measure is flo o r s whereas in mass housing development projects the appropriate unit is housing units. Time can be measured in terms of hours, days, weeks, or months, as is appropriate to the project time and l e v e l of d e t a i l desired in the schedule. Stradal and Cacha [123] has described the use of TSM diagrams for studying the e f f e c t of double s h i f t s and change in production rates of construction operations on the number of formwork sets required. O'Brien [93] has used TSM diagrams to study the fl o o r cycle of a high-rise building; 35 the a v a i l a b i l i t y of sc a f f o l d i n g for bricklayers and close-in requirement for sheetrock contractors were studied and rates of progress of d i f f e r e n t trades were synchronized to produce a s a t i s f a c t o r y schedule. The most s i g n i f i c a n t advantage of TSM is the s i m p l i c i t y with which i t can convey a detailed working schedule. Further, the r e s p o n s i b i l i t i e s of individual crews can also be separated and represented by their corresponding progress 1i nes. Authors who advocate the use of TSM stress the importance of "balanced" production lines such that i d l e time for valuable resources is minimized. At the a c t i v i t y l e v e l , the Time-Space diagram indicates the "desired" rates of progress for various a c t i v i t i e s (see figure 4.4(a)). This model indicates the "desired" end result but how to achieve i t is l e f t to the management. One disadvantage of the TSM, sim i l a r to that of the bar chart model, is the d i f f i c u l t y of i d e n t i f y i n g l o g i c relationships between a c t i v i t i e s . Another disadvantage of TSM is that i t can become complicated and confusing to untrained personnel when the number of a c t i v i t i e s is large, the sequence of a c t i v i t i e s is complex and when production rates vary from location to location (see figure 4.4(b)). 36 Figure 4.4(a): A simple Time-Space diagram Source: O'Brien [93], p. 115 DAVf Figure 4.4(b): A more complex Time-Space diagram Source: Stradal and Cacha [123], p. 454 Figure 4 . 4 : Time-Space diagrams 37 4.1 . 5 MULTIPLE ACTIVITY AND CREW BALANCE CHARTS Halpin and Woodhead [43] described the Multiple A c t i v i t y Chart (figure 4.5) used to coordinate a c t i v i t i e s with crew allocations and to schedule delivery and material handling systems. It consists of a series of v e r t i c a l bars. A v e r t i c a l bar is used for each crew, hoist, or crane unit involved. Each v e r t i c a l bar portrays the work assignment and schedule for a labour crew or a major piece of equipment. The work assignments for each crew or equipment are arranged such that they occur in a common length or building cycle. The bars are then analyzed to see i f there is c o n f l i c t of locations or in use of shared equipment. Crew Balance Charts are similar to multiple a c t i v i t y charts except the former model focuses on the internal operation of a p a r t i c u l a r crew and each bar is used to represent individual crew member work assignments and sequences. Crew balance charts can also be used for work improvement purposes. By changing the size of the work crew and rearranging work assignments to crew members, unnecessary overload and i d l e time can be minimized to produce the most e f f i c i e n t crew s i z e . These models are only conceptual models of the real system and include no quantitative or a n a l y t i c a l techniques to a s s i s t management to determine the set of work assignments to various crews. They are helpful in the evaluation of operation sequencing and the t o t a l labour contribution of each working trade. They provide a clear 38 statement of work assignments and sequences not available from other models. Dismantling Form forms Erection Dismantle Erect fcxmi forms B Area * A Area ( Stack B > ' Dismantle Erect forms forms C Art* I * 8 Are* Slack C > 1 Dismantle Erect forms n forms 0 Area c i S C Area Slack D • Dismantle Erect forms forms A Area >- 0 Area * o 1 Stack A Steel Crew Unload Son Sort Unload Sort Unload Sort Concrete Inspect Pour C Finish •Clean up Inspect Pour D Finish Clean up Inspect Pour A Finish Clean up Inspect Pour 8 Finish Clean up Crane R. Steel Concrete Bucket pour C Lift lurms Windows R. Steel Concrete Bucket • pour 0 Lift forms Windows R. Steel Concrete Bucket pour A Lift forms Windows R. Steel Concrete Bucket pour 8 Lift forms Windows 'Available for other tasks. Windows Set windows Stack Set windows Stack Set windows Stack Set windows Stack Hoist Mortar Available* Mortar Bricks Mortar Available Mortar Available Mortar Available Bricks Mortar Available Masonry Lay brick 0 Slack Layout /» Lay brick A Stack Layout f Lay brick B Stack Layout C Lay brick C Slack Layout D Figure 4 . 5 : Multiple activity chart for a building cycle Source: Halpin and Woodhead [43], p 37 39 4.2 PROBABILISTIC MODELS 4.2.1 UNCERTAINTIES IN THE CONSTRUCTION ENVIRONMENT P r o b a b i l i s t i c models have been used for construction planning because of the dynamic construction environment. Uncertainties in both external and internal elements of a project influence the accuracy of estimates for a c t i v i t y durations. Ahuja and Nandakumar [2] i d e n t i f i e d the following l i s t of stochastic elements that affect the accuracy of a c t i v i t y duration estimates: 1. learning curve 11. foundation conditions 2. weather 12. design schedule 3. space congestion 13. drawing approval schedule 4. crew absenteeism 14. inspection schedule 5. regulatory requirements 15. i n e f f e c t i v e supervision 6. design changes and rework 16. i n e f f i c i e n t consultant 7. economic a c t i v i t y l e v e l 17. material delivery schedule 8. labour unrest 18. transportation schedule 9. crew interfacing 19. union problems 10. project complexity 20. legal problems Carr [19] included weather conditions and Ashley [7] included learning curve effects in their models. Ahuja and Nandakumar [2] included seven elements (weather, space congestion, crew absenteeism, regulatory requirements, 40 design changes and rework, economic a c t i v i t y levels and labour unrest), which they considered to be the most s i g n i f i c a n t influences on a c t i v i t y duration estimates in their model PRODUF (PROject Duration Forecast). 4 . 2 . 2 QUEUING MODELS The word "queue" in French means " l i n e " , and queuing theory provides techniques for analyzing the eff e c t that waiting in l i n e has on various s i t u a t i o n s . Erlang is considered to have l a i d the groundwork for many of the e a r l i e s t technigues of queuing analysis from 1909 through 1920. Queuing theory remains an area of active research. It has been applied to various situations across a wide spectrum of d i f f e r e n t d i s c i p l i n e s : telecommunications, vehicular t r a f f i c , machine repair/maintenance, inventory control and storage, material handling, computer networking, hospitals, and counter services for many d i s c i p l i n e s . The simplest queuing model can be represented by a system of demand and services. The individual items that demand services are c a l l e d the customers; the f a c i l i t i e s that provide the services demanded are ca l l e d servers. Customers may enter the network at any p a r t i c u l a r server, proceed through according to their needs and leave the system after the required services are received. An example is a f l e e t of hauling trucks (customers) which require loading by a loader (server) - see G r i f f i s [41]. 41 Queuing theory provides mathematical solutions for simple systems and provides measures of effectiveness of the system being modeled. Examples of these measures for a simple concrete delivery system in a construction type project are: (1) Average number of units in the queue, e.g. average number of concrete trucks waiting to be emptied. (2) The average waiting time or delay before service begins, e.g. the average waiting time for each concrete truck before i t is emptied. (3) The p r o b a b i l i t y that the t o t a l delay can be greater than some value, e.g. the pr o b a b i l i t y that a concrete truck has to wait more than a certain period of time before i t can be emptied. (4) Expected i d l e time of t o t a l service f a c i l i t y , e.g. the u t i l i z a t i o n of valuable resources such as labour and tower crane. Through study of these system e f f i c i e n c y measures, decisions can be made regarding: (1) Securing additional service f a c i l i t i e s , e.g. i n s t a l l i n g additional l i f t i n g equipment (additional tower crane, hoist, or using a concrete pump with higher capacity). (2) Rearranging e x i s t i n g service f a c i l i t i e s , e.g. changing layout of delivery routing system to reduce t o t a l concrete truck waiting time. 42 (3) E s t a b l i s h i n g a s c h e d u l e t o r e d u c e i d l e t i m e o f t h e s e r v i c e f a c i l i t i e s , e . g . s h a r i n g t h e c r a n e a n d o t h e r l i f t i n g e q u i p m e n t w i t h o t h e r c r e w s and t r a d e s t o i n c r e a s e i t s u t i l i z a t i o n . S o l u t i o n s t o s i m p l e q u e u i n g m o d e l s c a n be o b t a i n e d f r o m t a b l e s . However, m a t h e m a t i c a l s o l u t i o n s f o r t h e more c o m p l e x q u e u i n g s i t u a t i o n s i n l a r g e c o n s t r u c t i o n p r o j e c t s a r e n o t r e a d i l y o b t a i n a b l e . 4.2.3 D I S C R E T E EVENT SIMULATION S i m u l a t i o n i s a p r o c e d u r e i n w h i c h e x p e r i m e n t s a r e p e r f o r m e d on t h e m o d e l o f a s y s t e m i n o r d e r t o d e t e r m i n e how t h e s y s t e m w o u l d r e s p o n d t o c h a n g e s e i t h e r i n i t s s t r u c t u r e o r i n i t s e n v i r o n m e n t . I t i s a p r o c e d u r e by w h i c h s y s t e m o u t p u t s a r e d e f i n e d and a n a l y z e d as l o g i c a l and m a t h e m a t i c a l f u n c t i o n s o f s y s t e m i n p u t v a r i a b l e s and p a r a m e t e r s . T h e r e a r e many g e n e r a l p u r p o s e s i m u l a t i o n l a n g u a g e s , s u c h as GPSS, SIMSCRIPT, SLAM, GASP. H i g h l e v e l l a n g u a g e s s u c h as t h e CYCLONE ( H a l p i n [ 4 4 ] ) w e re d e v e l o p e d e s p e c i a l l y f o r c o n s t r u c t i o n p r o j e c t s . S i m u l a t i o n has been a p p l i e d t o numerous p r o b l e m s s u c h as f a c i l i t y d e s i g n and p r o d u c t i o n p l a n n i n g and s c h e d u l i n g ( M e l l i c h a m p [ 8 4 ] ) , m a t e r i a l h a n d l i n g and d i s t r i b u t i o n ( P h i l l i p s [ 1 0 2 ] ) , and h i g h - r i s e c o n s t r u c t i o n ( H a l p i n [ 4 4 ] ) . I n g e n e r a l , s i m u l a t i o n h a s t h e f o l l o w i n g a d v a n t a g e s : 43 1. It allows managers to experiment with the system in order to determine which external factors are important and how they interact. 2. Decision makers are forced to examine a l l foreseeable elements of the model in d e t a i l during the process of designing a simulation model. 3. Simulation allows decision makers to experiment with d i f f e r e n t strategies without the risk of disturbing the real system. Many authors in the construction management l i t e r a t u r e recommend that simulation should be used to model construction operations because other models cannot treat the learning curve e f f e c t s , come-back delays, weather, and other stochastic project variables and parameters which arise in the complex and exposed environment of construction projects. Simulation is a powerful tool that can be used r e l i a b l y to simulate most of the complex situations that cannot be studied by other modeling technigues. However, models developed using the techniques are generally "custom-made" and can be applied only to the s p e c i f i c project situations which they represent. Use of the simulation technique also requires knowledge of a simulation language. Mathewson [79] has suggested the use of a "(simulation) program generator" to reduce the programming e f f o r t required; however, further research and development in this area are required. 44 4 . 2 . 4 MONTE CARLO SIMULATION Monte C a r l o method i s a s i m u l a t i o n t e c h n i q u e w h e r e b y v a l u e s f o r random v a r i a b l e s a r e s a m p l e d f r o m d i s t r i b u t i o n s and c o m b i n e d t o d e t e r m i n e p r o p e r t i e s o f t h e s y s t e m u n d e r s t u d y . I t c a n be u t i l i z e d t o g e n e r a t e d u r a t i o n s f o r e a c h a c t i v i t y i n a p r o b a b i l i s t i c n e t w o r k by r a n d o m l y c a l c u l a t i n g a f e a s i b l e v a l u e f r o m t h e d i s t r i b u t i o n t h a t r e p r e s e n t s p o s s i b l e o u t c o m e s f o r t h e a c t i v i t y . Once g e n e r a t e d , t h e d u r a t i o n s a r e t r e a t e d as d e t e r m i n i s t i c and t h e n o r m a l c r i t i c a l p a t h c a l c u l a t i o n s a r e p e r f o r m e d . The p r o c e d u r e i s r e p e a t e d many t i m e s , k e e p i n g s t a t i s t i c s on e a c h p r o j e c t e d p r o j e c t d u r a t i o n and t h e number o f t i m e s i n d i v i d u a l a c t i v i t i e s were c r i t i c a l . The r e s u l t s o f t h e s i m u l a t i o n p r o v i d e an u n b i a s e d p r o j e c t i o n o f t h e p r o j e c t c o m p l e t i o n - t i m e d i s t r i b u t i o n and an i n d i c a t i o n o f t h e " c r i t i c a l i t i e s " o f e a c h a c t i v i t y . No a s s u m p t i o n i s made a p r i o r i on t h e s h a p e o f t h e f i n a l d i s t r i b u t i o n . I t p r o v i d e s a r e l i a b l e p r o f i l e e v e n i f t h e f i n a l d i s t r i b u t i o n i s d o m i n a t e d by a few a c t i v i t i e s , p r o v i d e d a c t i v i t i e s a r e n o t c o r r e l a t e d . However, i t o f t e n r e q u i r e s a l a r g e number o f s i m u l a t i o n s t o p r o d u c e an a c c u r a t e p r o j e c t i o n o f t h e p r o f i l e o f t h e f i n a l d i s t r i b u t i o n and t h u s r e q u i r e s l a r g e amounts o f c o m p u t i n g t i m e . I n a d d i t i o n , t h e r e i s no me a s u r e by w h i c h one c a n e s t i m a t e t h e number o f s i m u l a t i o n s r e q u i r e d . 45 4.2.5 PROGRAM EVALUATION AND REVIEW TECHNIQUE (PERT) The major difference between PERT and CPM is the assumption of d i s t r i b u t i o n s for a c t i v i t y durations for PERT. The o r i g i n a l developers of PERT chose a beta d i s t r i b u t i o n to estimate the shape of the a c t i v i t y duration d i s t r i b u t i o n . Given the most likely(m), o p t i m i s t i c ( a ) , and pessimistic(b) estimates of an a c t i v i t y duration the mean and standard deviation of the a c t i v i t y duration are approximated by: mean = (b - a) / 6 standard dev. = (a + 4m + b) / 6 The developers of PERT claimed that the beta d i s t r i b u t i o n was chosen for i t s f l e x i b i l i t y . However, Elmaghraby [33] proved that the above approximations actually r e s t r i c t the shape of the d i s t r i b u t i o n function. After the expected a c t i v i t y durations are estimated, the mean-time-to-completion of the project is computed by treating the estimated a c t i v i t y durations as deterministic. The assumption that the resulting d i s t r i b u t i o n of the project duration w i l l tends normal, because of the "central l i m i t theorem", is then made. In making the above approximation and ignoring the correlations of network paths, the resulting estimates on expected project durations become optimistic, i . e . underestimated. 46 4.2.6 DECISION CPM Decision CPM networks (Naaman [90]) are characterized by having both deterministic a c t i v i t y nodes and decision nodes. The decisions taken at the decision nodes depend on the outcomes of events which are not known with certainty in advance. Completion of the network can be achieved through a number of possible optimal paths. The optimal path can be determined by a lengthy integer programming procedure or an acceptable path can be determined by more economical int e r a c t i v e h e u r i s t i c procedures. This model forms the basis of more complex ones, such as GERT discussed below. 4.2.7 GRAPHICAL EVALUATION AND REVIEW TECHNIQUE (GERT) GERT, Graphical Evaluation and Review Technique, developed by Pritsker and Happ (Pritsker and Happ [104], [105]), represents a considerable extension to the PERT/CPM network modeling technique. It makes possible the representation and simulation of less r e s t r i c t i v e network types. The special features of GERT include user definable a c t i v i t y time d i s t r i b u t i o n s , p r o b a b i l i s t i c branching, multiple outcomes, feedback, sel f - l o o p i n g , and other complex node r e a l i z a t i o n l o g i c s ; therefore complex models of systems with random variable components can be replicated. Execution of the model is performed by Monte Carlo type simulation 4 7 p r o c e d u r e s . M o d e l o u t p u t s a r e d e s c r i p t i v e r a t h e r t h a n o p t i m i z i n g and s y s t e m i m p r o v e m e n t s a r e p e r f o r m e d by t r i a l a nd e r r o r . B e c a u s e o f t h e c o m p l e x i t y o f t h e m o d e l i n g l o g i c w i t h GERT, t h e m o d e l o f a g i v e n s y s t e m i s d i f f i c u l t t o d e v e l o p and u n d e r s t a n d . 4.2.8 PROJECT LENGTH ANALYSIS AND EVALUATION TECHNIQUE (PLANET) The i d e a f o r PLANET (Kennedy and T h r a l l [ 6 2 ] ) a r o s e f r o m c o n s i d e r a t i o n o f t h e p r o b l e m s f a c e d by NASA i n a d m i n i s t r a t i o n o f t h e S p a c e S h u t t l e P r o g r a m t o meet p r o m i s e d d e a d l i n e s . I n o r d e r t o meet them u n d e r l i m i t e d f u n d s , i t i s e s s e n t i a l t o d e t e r m i n e a c t i v i t i e s w h i c h a r e c r i t i c a l o r s l a c k s u c h t h a t r e s o u r c e s c a n be " s t o l e n " f r o m t h e s l a c k a c t i v i t i e s t o e x p e d i t e t h e c r i t i c a l o n e s . PERT was n o t c o n s i d e r e d t o be a v i a b l e t e c h n i q u e as t h e summing o f mean and v a r i a n c e s o v e r t h e c r i t i c a l p a t h t e n d s t o p r o d u c e an o p t i m i s t i c mean c o m p l e t i o n t i m e . The a s s u m p t i o n o f a b e t a d i s t r i b u t i o n f o r a c t i v i t y d u r a t i o n i n PERT a l s o may n o t be g e n e r a l e n o u g h . GERT d e v e l o p e d by P r i t s k e r and Happ a l l o w s t h e u s e r t o c h o o s e f r o m n i n e p r o b a b i l i t y d i s t r i b u t i o n s . H owever, t h e o r i g i n a l v e r s i o n o f GERT d i d n o t i n c l u d e a n a l y s i s o f t h e c r i t i c a l p a t h . K ennedy and T h r a l l [62] t h e r e f o r e d e v e l o p e d PLANET w h i c h u s e s t h e Monte C a r l o s i m u l a t i o n a p p r o a c h t o a m o d i f i e d GERT m o d e l i n g t e c h n i q u e w i t h c r i t i c a l p a t h a n a l y s i s 48 at each simulation and thus allows feedback, looping, and the inclusion of large variances in the development/testing type a c t i v i t i e s . 4.2.9 P R O B A B I L I S T I C NETWORKING EVALUATION TECHNIQUE (PNET) PERT considers a c t i v i t y durations as random variables. However, the required project duration is determined s o l e l y on the basis of the mean c r i t i c a l path and subsequently the expected completion time for a given network is underestimated. Monte Carlo simulation can be used to solve the problem but i t requires considerable computing time. These are the observations that motivated Ang and Abdelnour [4] to develop PNET. The technique employed considers the correlations between d i f f e r e n t paths which arise from the sharing of a c t i v i t i e s which PERT has previously ignored. Ang and Abdelnour [4] stated that j o i n t p r o b a b i l i t i e s c o r r e l a t i n g the paths are d i f f i c u l t to calculate except for the cases of 0% or 100% c o r r e l a t i o n . They then proposed a scheme for sel e c t i n g representative paths. The project completion-time p r o b a b i l i t y can then be calculated as the product of the p r o b a b i l i t i e s of these paths. As the technique is a n a l y t i c a l , i t is be more economical and e f f i c i e n t than the Monte Carlo simulation technique. 49 4 . 3 MATHEMATICAL PROGRAMMING TECHNIQUES In addition to the modeling techniques described above, other mathematical models have been described in the operations research l i t e r a t u r e . Of these, linear programming and dynamic programming have been applied to construction problems. Most applications of mathematical programming techniques described in the construction and i n d u s t r i a l engineering l i t e r a t u r e have been applied to problem of optimal resource allo c a t i o n s (Coskunoglu [24]) and network duration compression (Perera [100]). Extensive research and development work has also been done in the area of in d u s t r i a l engineering. The "Economic Scheduling Path" described by Riggs [110] and the "Multiple Objective Shortest Path Problem" described by White [130] are based on these mathematical programming techniques. Even though mathematical programming techniques allow an optimal solution to be i d e n t i f i e d from a large number of alte r n a t i v e s , they have the following disadvantages for construction related problems: (1) In most si t u a t i o n s , the project objectives, variables, and constraints cannot be ea s i l y reduced to mathematical form. (2) The e f f o r t , cost, and time si t u a t i o n into mathematical to reduce a problem equations are often 5 0 excessive for use in construction planning on a day-to- day basis. (3) The time required to modify a developed model is often too long. The mode is therefore not responsive to the dynamic project conditions at the production l e v e l s . ( 4 ) The models developed with this techniques are not comprehensible to management at the production l e v e l . 4 . 4 C U R R E N T P R A C T I C E I N C O N S T R U C T I O N M O D E L I N G Deterministic modeling techniques have gained acceptance in construction because of their r e l a t i v e s i m p l i c i t y . Among the deterministic models described, the c r i t i c a l path method is the only a n a l y t i c a l model that can be used for systematic time analysis of construction projects and a c t i v i t i e s . The application of the c r i t i c a l path method in construction planning is shown in figure 4 . 6 and has been b r i e f l y described in section 4 . 1 . 2 . Although the c r i t i c a l path method places no r e s t r i c t i o n on the l e v e l of d e t a i l at which planning is to be carried out, t r a d i t i o n a l l y , i t has been applied at the a c t i v i t y l e v e l , i . e . the smallest element treated is an a c t i v i t y . The construction process is f i r s t broken down into the major a c t i v i t i e s , a c t i v i t y duration and resource requirement estimates are then assigned to each a c t i v i t y . For example, an a c t i v i t y can be defined as: form and pour a complete 51 fl o o r slab in f i v e days employing 5 carpenters, 4 masons, 2 general labourers and the tower crane. In the process, i m p l i c i t management decisions have been made regarding the choice of construction technologies and crew assignments to carry out the operations involved in each a c t i v i t y . The input data are then analyzed using CPM and constrained resource analysis and l e v e l i n g algorithms. W i l l i s [131] reviewed the developments in resource constrained scheduling algorithms and stated that: 11. . . . resource constrained scheduling algorithms have focused on algorithm qu a l i t y using project duration as the only c r i t e r i o n . They have assumed fixed a c t i v i t y duration, fixed resource requirements over the a c t i v i t y durations and fixed resource l i m i t s over time." There is .... "the p r a c t i c a l need for f l e x i b i l i t y in the d e f i n i t i o n of resource constraints and requirements ...." [131] W i l l i s further described the " p r a c t i c a l requirements" of a system for analysis of resource constrained projects. They include: (1) s t a b i l i t y in re-scheduling of a resource constrained project such that there w i l l be no d r a s t i c changes to the o r i g i n a l schedule; (2) variable resource requirements over time and variable resource constraints over time; (3) f a c i l i t y to allow an a c t i v i t y to be fixed in time; 52 (4) f a c i l i t y to allow stretching and squashing of act i vi t ies; (5) f a c i l i t y to allow consideration of variable resource requirements over the duration of an a c t i v i t y ; and (6) f a c i l i t y to allow assignment of alternative resources. The requirements simply indicate that the current approach to construction process modeling using CPM has f a i l e d to model a l l of the p r a c t i c a l or r e a l i s t i c aspects of the construction planning process. The current approach assumes constant resource requirement over an a c t i v i t y duration such that in the example used e a r l i e r , the assigned labour resources and the tower crane have to be assigned "exclusively" to the a c t i v i t y of form and pour f l o o r slab. This is u n - r e a l i s t i c because some of the assigned resources are required for only part of the a c t i v i t y duration. For example, the general labourers might be required only to clean and o i l the formwork at the st a r t and end of the a c t i v i t y and the tower crane might be needed only for about three hours each day. Current constrained resource scheduling methods neglect the p o s s i b i l i t y of using over time and a second s h i f t to eliminate resource c o n f l i c t s . They do not allow a c t i v i t y durations and assigned resources to be modified i n t e r a c t i v e l y . In other words, the need exists for a more " f l e x i b l e " framework to treat the elements that the current approach to construction modeling f a i l s to capture. 53 In addition, decision making processes, such as the choice of construction technologies and crew assignments, which are only implicit in the current approach to construction planning, must be treated. ^ START ^ L i s t of A c t i v i t i e s ) and P - r e l a t l o n s / A c t i v i t y Durations 7 1/ C r i t i c a l Path Ana l y s i s <^ ##, > I m p l i c i t Management Decisions 1. Choice of technologies and construction methods 2. Resource a l l o c a t i o n and crew assignments Pr o j e c t Duration A c t i v i t y S t a r t / F i n i s h Dates Resource Analys I s \ rES 1 Constrained Resource AssIgnment 1 Pro} ect Schedule To S i t e Management^ ^ STOP ^ 0 Z Set Resource / A Figure 4 . 6 : Current application of CPM in construction planning 55 5. PRODUCTION PLANNING AND ASSEMBLY LINE BALANCING R u s s e l l [114] h a s s t a t e d : b u i l d i n g c o n s t r u c t i o n i s c h a r a c t e r i z e d by a l a r g e number o f r e p e t i t i v e a n d n o n - r e p e t i t i v e a c t i v i t i e s , e a c h o f s h o r t d u r a t i o n .... d e s p i t e t h e b e s t e f f o r t s by owners and a r c h i t e c t s t o d i s t i n g u i s h one p r o j e c t f r o m a n o t h e r , t h e r e i s s u b s t a n t i a l s i m i l a r i t y among p r o j e c t s i n t e r m s o f s y s t e m s and a c t i v i t y b r e a k down." A s h l e y [7] s t a t e d t h a t : " M u l t i p l e - u n i t , m u l t i p l e - f l o o r , o r l i n e a r l y p r o g r e s s i v e p r o j e c t s r e s e m b l e a s s e m b l y l i n e p r o c e s s e s i n t h e i r s t r u c t u r e o f a s m a l l s e t o f t a s k s i n r e p e a t i n g s e q u e n c e . " D a v i s [31] s t a t e d : "The a s s e m b l y - l i n e b a l a n c i n g p r o b l e m i s c o n c e r n e d w i t h r e p e t i t i v e o p e r a t i o n s and l a r g e numbers o f i d e n t i c a l p r o d u c t s . " The a b o v e and o t h e r a u t h o r s h a v e n o t e d t h e s i m i l a r i t i e s b e t w e e n t h e r e p e t i t i v e a c t i v i t y d e s i g n p r o b l e m and t h e a s s e m b l y l i n e d e s i g n p r o b l e m . H o w e v e r , few h a v e s t u d i e d and s u g g e s t e d w h e t h e r t h e a p p r o a c h u s e d by i n d u s t r i a l e n g i n e e r s f o r a s s e m b l y l i n e d e s i g n p r o b l e m s c a n be a p p l i e d t o t h e d e s i g n o f r e p e t i t i v e a c t i v i t i e s . I n t h i s c h a p t e r , t h e a s s e m b l y l i n e p r o d u c t i o n p r o c e s s and t h e l i n e b a l a n c i n g p r o b l e m a r e s t u d i e d i n some d e t a i l . The s i m i l a r i t i e s and d i f f e r e n c e s b e t w e e n r e p e t i t i v e c o n s t r u c t i o n and a s s e m b l y p r o d u c t i o n w i l l be a n a l y z e d t o d e t e r m i n e w h e t h e r a s s e m b l y l i n e b a l a n c i n g t e c h n i q u e s c a n be a p p l i e d t o c o n s t r u c t i o n c y c l e p l a n n i n g . 56 5.1 PRODUCTION PLANNING Many o f t h e p l a n n i n g m o d e l s u s e d i n c o n s t r u c t i o n , s u c h as b a r c h a r t and l i n e - o f - b a l a n c e , h a v e t h e i r o r i g i n i n t h e f i e l d o f p r o d u c t i o n p l a n n i n g f o r t h e m a n u f a c t u r i n g i n d u s t r y . P r o d u c t i o n i s a wor d t h a t d e s c r i b e s m a t e r i a l s c h a n g e d by t o o l s , w h i c h c o u l d be d e s c r i b e d as c o n t r o l l e d f o r c e s u s e d t o o p e r a t e on t h e e n v i r o n m e n t t o b r i n g a b o u t g o a l - o r i e n t e d c h a n g e . P r o d u c t i o n m a n a g e r s a r e f a c e d w i t h t h e p r o b l e m s o f p l a n n i n g , e x e c u t i o n , and c o n t r o l o f o p e r a t i o n s i n t h e p r o d u c t i o n p r o c e s s t o e n s u r e t h a t t h e r e s u l t s o f t h e o p e r a t i o n s a r e o f a g r e e d q u a n t i t y , on s c h e d u l e and o f s p e c i f i c q u a l i t y and c o s t . Schmenner [117] c l a s s i f i e d t h e p r o d u c t i o n p r o c e s s e s as f o l l o w s : (1) Job Shop - g e n e r a l l y c u s t o m p r o d u c t s ; e . g. a m a c h i n e s h o p t h a t p r o d u c e s m e t a l o r p l a s t i c p a r t s w h i c h a r e a s s e m b l e d i n t o o t h e r m a c h i n e s . (2) Batch Flow - l o t s o f p r o d u c t s g e n e r a l l y d e s i g n e d i n - h o u s e ; e.g. a c l o t h e s f a c t o r y t h a t m a n u f a c t u r e s p r o d u c t s w h i c h h a v e t o meet o r d e r s o f a w i d e v a r i e t y o f m a t e r i a l s , m o d e l s , and s i z e s . (3) Worker-Paced Assembly Line - m o s t l y s t a n d a r d p r o d u c t s b u t w i t h o p p o r t u n i t i e s f o r s e l e c t e d o p t i o n s ; e.g. a f a s t f o o d r e s t a u r a n t w h ere a s t a n d a r d l i s t o f f o o d i s s e r v e d b u t c e r t a i n o p t i o n s , s u c h as h a m b u r g e r w i t h no o n i o n o r p i c k l e s , a r e p o s s i b l e . 57 (4) Machine-Paced Assembly Line - same p r o d u c t m i x as i n (3) b u t t h e p r o d u c t i v i t y i s more d e p e n d e n t on t h e e q u i p m e n t as co m p a r e d t o (3) w h i c h i s more l a b o u r i n t e n s i v e ; e.g. a a u t o m o b i l e p r o d u c t i o n l i n e , o r a c o n v e y o r a s s e m b l y l i n e o f e l e c t r o n i c p r o d u c t s . M a c h i n e - p a c e d a s s e m b l y l i n e s a r e o f t e n s i m p l y r e f e r r e d t o a s " a s s e m b l y l i n e s " . (5) Continuous Flow - s t a n d a r d p r o d u c t s w i t h l i t t l e o r no c u s t o m i z a t i o n p o s s i b l e ; u s u a l l y n o t p r o d u c e d i n d i s c r e t e u n i t s and s o h a v e t o be m e a s u r e d i n t o n s , b a r r e l s , e t c ; e . g . a p a p e r m i l l o r a p e t r o l e u m p r o c e s s i n g p l a n t w h ere p r o d u c t i v i t y i s o n l y d e p e n d e n t on t h e t y p e o f raw m a t e r i a l s and t h e c a p a c i t i e s o f p r o c e s s i n g e q u i p m e n t . 5.2 ASSEMBLY LINE PRODUCTION H e n r y F o r d ( 1 863-1947) i s u s u a l l y c r e d i t e d w i t h t h e c r e a t i o n o f t h e " a s s e m b l y l i n e e r a " when t h e f i r s t a u t o m o b i l e was i n t r o d u c e d . The b a s i c i d e a o f t h e a s s e m b l y l i n e i s d e c o m p o s i t i o n o f t h e end p r o d u c t i n t o s u b a s s e m b l i e s , and s u b - s u b a s s e m b l i e s , and s o on down t h e l i n e u n t i l t h e s m a l l e s t i n d i v i s i b l e component i s r e a c h e d . I f t h i s s u b d i v i s i o n i s r e v e r s e d , we c a n d e f i n e t h e o p e r a t i o n s o r work t a s k s ( t h e b a s i c i n d i v i s i b l e u n i t o f work t h a t c a n n o t r a t i o n a l l y be f u r t h e r s u b d i v i d e d ) w h i c h a r e n e c e s s a r y t o g r o u p t h e com p o n e n t s i n t o s u b a s s e m b l i e s , and s o o n , u n t i l 58 t h e end p r o d u c t i s r e a c h e d . B e c a u s e o f t h e l i n e a r a s p e c t o f t h i s p r o c e s s i t i s known as t h e a s s e m b l y l i n e p r o d u c t i o n p r o c e s s . 5 . 2 . 1 LINE BALANCING PROCEDURE B a l a n c i n g an a s s e m b l y l i n e n o r m a l l y i n v o l v e s t h e f o l l o w i n g number o f s t e p s : (1) The i n d u s t r i a l e n g i n e e r must d e s c r i b e what h a s t o be done i n d e t a i l , i n c l u d i n g t h e d e s c r i p t i o n s o f j o b e l e m e n t s . (2) E a c h o f t h e j o b e l e m e n t s i s a s s i g n e d a t i m e w h i c h i s o f t e n d e t e r m i n e d by r e f e r e n c e t o e s t a b l i s h e d s t a n d a r d o r by s p e c i a l s t o p w a t c h s t u d i e s . (3) Once t i m e s a r e a s s i g n e d t o s p e c i f i c j o b e l e m e n t s , t h e e n g i n e e r r e v i e w s them w i t h t h e r e l e v a n t s u p e r v i s o r s on t h e p r o d u c t i o n l i n e t o d e t e r m i n e w h e t h e r o r n o t t h e y a r e r e a s o n a b l e . C h a nges a r e made as r e g u i r e d . (4) Once a g r e e m e n t i s r e a c h e d , t h e r e l e v a n t i n f o r m a t i o n i s u s e d t o b a l a n c e work l o a d s among t h e w o r k e r s . One way t h i s i s done i s by t a k i n g work e l e m e n t s f r o m one w o r k e r and p l a c i n g them w i t h a n o t h e r . 59 (5) The i n i t i a l balance is studied for reasonableness and adjustments are made u n t i l the l i n e is s a t i s f a c t o r i l y balanced. (6) The "paper" balance is then ready for t r i a l on the factory f l o o r . The engineer, supervisors, and workers a l l become involved in this a c t i v i t y . If actual element times are larger than predicted, help w i l l be given to the worker to improve time - by changing the layout of the work sta t i o n , adding fi x t u r e s or other equipment, changing production methods, or reducing the t o t a l work assignment by re-balancing the assembly l i n e . 5.2.2 EXAMPLE OF LINE BALANCE The keys to l i n e balance are (1) breaking down a complex product and production process into i t s component pieces and tasks and (2) juggling the coordination of these pieces and tasks so that the process is smooth and no bottlenecks are b u i l t into i t . An example of a 20-element assembly production process is shown i s figure 5.1. Figure 5.1(a): Precedence network of work elements ESTIMATED TIME ESTIMATED TIME JOB ELEMENT (minutes) JOB ELEMENT (minutes) 1 0.65 11 1.10 2 0.11 12 1.75 3 0.37 13 0.94 4 0.75 14 0.62 5 0.10 15 0.45 6 0.58 16 0.81 7 0.25 17 0.87 8 1.01 18 1.60 9 1.17 19 0.60 10 0.43 20 0.83 Figure 5.1(b): Job elements and estimated element times Figure 5.1: Example of a 20-element assembly production process Source: Schmenner [117], p. 97 61 The objective is to use the information given to develop a flow l i n e process capable of turning out 300 units of the product in an eight hour day. The suggested possible means of developing the process can be summarized as follow: Total job element time = Sum (element time a l l elements 1 to 20) = 14.99 minutes Total production minutes req'd / working day = 14.99 min/unit x 300 units = 4497 minutes Assume a 7.5 hour work day (450 min) Number of workers req'd/ working day = 4497 min. / (450 min./worker) = 10 workers For perfect balance: "Control cycle time" = (14.99 minutes/unit) / 10 worker = 1.5 minutes The following is a suggested solution to the assembly balancing problem: 62 WORK STATION JOB ELEMENTS TOTAL TIME/UNIT (minutes) BALANCE DELAY (minutes) 1 1,2,4 1.51 -0.01 2 3,5,6,7 1.30 0.20 3 8,10 1.44 0.06 4 9,12 1.46 0.04 5 9,12 1.46 0.04 6 13,14 1.56 -0.06 7 11 1.10 0.40 8 15,17 1.32 0.18 9 16.18 1.21 0.29 10 16.18 1.21 0.29 11 19.20 1.43 0.07 F i g . 5-2: Suggested balance to the assembly l i n e production process Source: Schmenner [117], p. 98 Observations pertaining to this solution are: Eleven work stations are reguired instead of ten because of the i n a b i l i t y to meet the ideal "perfect balance. " Some stations have been overloaded while some station, are under-utilized r e s u l t i n g in unproductive i d l e time. Stations 4, 5, 9 and 10 have workers working on every other unit in order to solve the problem of "over- cycle" (note that the times of job elements 12 and 18 are 1.75 and 1.60 respectively which are over the control cycle time. If only one worker was assigned to work on element 12 or 18, bottlenecks would occur. 63 5.3 ASSEMBLY LINE BALANCING ALGORITHMS In general, the objectives in designing an assembly li n e process are to minimize the number of groupings or work stations with a given cycle time, or to minimize the cycle time for a given number of stations subject to certain r e s t r i c t i v e constraints. Two approaches to the assembly l i n e balancing problem have been adopted by manufacturing production management - the a n a l y t i c a l approach (Akagi [3], Wilson [132]) which give an "optimal" solution and the h e u r i s t i c approach (Arcus [5], Raouf et a l [109], Tonge 126]) which gives an "acceptable" solution. The a n a l y t i c a l approach employs integer programming technique which most authors agree to be demanding in terms of mathematical modeling e f f o r t . The h e u r i s t i c approach is the application of s e l e c t i v e routines that reduce the size of a problem u n t i l i t is manageable by manual or computer operations. Sensible rules are used to simulate the decision-making pattern of human beings when they operate unaided in the system. Another reason for the use of h e u r i s t i c s for the ALB problem is that the number of possible groupings of work elements is so large that an exhaustive enumeration scheme is u n - r e a l i s t i c . 64 5.3.1 SYSTEM CONSTRAINTS S i m i l a r t o a c o n s t r u c t i o n p r o c e s s , an a s s e m b l y p r o d u c t i o n l i n e i s a l s o s u b j e c t e d t o c e r t a i n p r e c e d e n c e o r t e c h n o l o g i c a l c o n s t r a i n t s , i . e . t h e work t a s k s h a v e t o be p e r f o r m e d i n a s p e c i f i c o r d e r . I n a d d i t i o n , z o n e c o n s t r a i n t s may a r i s e b e c a u s e o f t h e p h y s i c a l l o c a t i o n o f s p e c i a l i z e d e q u i p m e n t o r t h e o p e r a t o r , o r b e c a u s e o f h e a l t h o r s a f e t y r e g u l a t i o n s . 5.3.2 PRIORITIES OF WORK ELEMENT ASSIGNMENT Tonge [126] g i v e s a l i s t o f t h e r u l e s t h a t c a n be u s e d t o a s s i s t i n t h e a s s i g n m e n t o f work e l e m e n t s t o work s t a t i o n s : (1) C h o o s e t h e t a s k w i t h t h e l a r g e s t t i m e . (2) C h o o s e t h e t a s k w i t h t h e most " i m m e d i a t e " f o l l o w e r s . T h i s i n c r e a s e s t h e number o f t a s k s a v a i l a b l e f o r a s s i g n m e n t t o t h e n e x t s t a t i o n . (3) C h o o s e a t a s k r a n d o m l y . (4) C h o o s e t h e t a s k w h i c h became a v a i l a b l e f i r s t f o r a s s i g n m e n t . (5) C h o o s e t h e t a s k w h i c h became a v a i l a b l e l a s t f o r a s s i g n m e n t . (6) C h o o s e t h e t a s k w i t h t h e most f o l l o w e r s ( i n c l u d i n g f o l l o w e r s t o i t s i m m e d i a t e f o l l o w e r s ) . T h i s r u l e a l s o 65 increases the number of tasks available for assignment to the next s t a t i o n . (7) Choose the task for which the sum of i t s times plus the times of it's followers is the largest (Helgeson and Birnie [48] c a l l e d this the ranked p o s i t i o n a l weight). (8) Number the tasks such that a l l followers of a task have a higher number, assigning a number a r b i t r a r i l y when necessary. Choose the task with the lowest number (following a suggestion of Jackson [53]). (9) Number a l l tasks with no predecessors as 1. If the highest number assigned to any immediate predecessor of a task is n, number that task n + 1. Then choose the task with the lowest number (based on the approach of Kilbridge and Wester [63]). Numerous assignment rules were also recommended by other authors; Raouf et a l [109] suggested giving p r i o r i t i e s to work elements which are on the c r i t i c a l path. 5.3.3 BALANCED ASSIGNMENT AND SMOOTHING Another problem often discussed is that of a "balanced" work assignment such that no station is overworked while another station may have an excessive amount of " i d l e delay". This is measured by the smoothness index (proportional to the sum of the squares of id l e delays at each work station) as discussed in Moodie and Young [88]. 6 6 The s m o o t h n e s s o f a b a l a n c e c a n be i m p r o v e d by " t r a d i n g and t r a n s f e r " o f work e l e m e n t s b e t w e e n s t a t i o n s . 5.3 .4 VARIABLE ELEMENT TIMES The p r o b l e m o f v a r i a b l e work e l e m e n t t i m e s w ere r e c o g n i z e d by some a u t h o r s . M o o d i e and Young [88] d e s c r i b e d an a l g o r i t h m t o c o n s i d e r v a r i a b l e work e l e m e n t t i m e s by i n c l u d i n g t h e a v e r a g e s and v a r i a n c e s o f work e l e m e n t t i m e s and t h e p r o b l e m b a l a n c e d a g a i n s t a u s e r s e l e c t e d " c o n f i d e n c e l e v e l " . M a n s o o r [77] d i s c u s s e d t h e u s e o f a wage i n c e n t i v e scheme t o e n s u r e w o r k e r p r o d u c t i v i t y . L a t e r , M a n s o o r [74] a l s o d i s c u s s e d t h e p r o b l e m i n t e r m s o f t h e s e l e c t i o n o f N o p e r a t o r s o u t o f a p o o l o f M a v a i l a b l e o p e r a t o r s a c c o r d i n g t o t h e i r p e r f o r m a n c e r a t i n g s t o j u s t meet t h e d e s i r e d p r o d u c t i o n l e v e l . 5.3.5 ELEMENT SHARING, MULTIPLE MANNING AND MULTIPLE STATIONS Some a u t h o r s ( A r c u s [ 5 ] , A k a g i e t a l [ 3 ] ) d i s c u s s e d t h e us e o f m u l t i p l e m a n n i n g o f a work s t a t i o n o r " p a r a l l e l " b a l a n c i n g t o s o l v e t h e p r o b l e m when a work e l e m e n t c a n n o t r e a l i s t i c a l l y be b r o k e n down f u r t h e r s u c h t h a t t h e e l e m e n t t i m e i s l e s s t h a n t h e c y c l e t i m e . A k a g i e t e l f o r m u l a t e d t h e p r o b l e m i n t h e manner t h a t a w o r k e r c a n move b e t w e e n 67 stations in order to a s s i s t another worker with an element when the work at his station is complete (element sharing). Sarker et a l [116] formulated the problem to allow p a r a l l e l work stations to increase e f f i c i e n c y and productivity and to reduce cycle time below the greatest element time. 5 . 3 . 6 RELATED A C T I V I T I E S Arcus [5], in his description of COMSOAL, treated the problem by proposing to assign the work elements according to f i v e programs: 1. use no c r i t e r i o n , 2. group tasks by workers p o s i t i o n , 3. group task by tools, 4. group tasks by unit's p o s i t i o n , or 5. any combination of the above c r i t e r i a . This problem, in f a c t , was studied by Tonge [126] as early as 1960 and later discussed by Agrawal [1]. Agrawal stated that: "An assembly operation may be considered to be related to some operations and unrelated to others. The relationship can be by ways of their belonging to the same subassembly, interdependent on one another .... The algorithm employed w i l l be a l l o t t i n g a set of related operations to a worker (or workers) as against the usual operation-by- operation allotment " [1] 68 The "relatedness" of a set of work elements is determined by the precedence l i n k s . Agrawal proposed an algorithm which forms f e a s i b l e sets (total operation time less than the given cycle time) of related operations s t a r t i n g from the end of the precedence network; the sets are then assigned with p r i o r i t y given to the sets with the largest t o t a l times. Tonge [126] exploited the structure of a network and related the work elements into "sets" and "chains" and employed an h i e r a r c h i c a l approach to the task assignment problem. In phase one of his approach, men are assigned to a group of work elements instead of the t y p i c a l assignment of work element to work station or men; thus the t o t a l work element time in any grouping is limited by the t o t a l men available instead of the "available station time". In phase two of his approach, the assignment procedure then follows the t y p i c a l procedure of assigning work elements to each individual station or man. 5.3.7 OTHER CONSIDERATIONS The following concepts were also discussed by Mariotte [78] : B a t c h i n g and b a n k i n g using an e x t r a - s h i f t or over- time for a short period of time. 69 M u l t i p l e L i n e s o r m u l t i p l e s h i f t s t o i n c r e a s e p r o d u c t i o n r a t e . O f f - l i n e s t a t i o n s and subassembly l i n e s where c e r t a i n work e l e m e n t s a r e p e r f o r m e d b e f o r e t h e y a r e j o i n e d w i t h t h e m a j o r a s s e m b l y . 5 . 4 ASSEMBLY LINE BALANCING AND CONSTRUCTION CYCLE DESIGN 5 . 4.1 SIMILARITIES BETWEEN ALB AND CONSTRUCTION CYCLE DESIGN The two p l a n n i n g f u n c t i o n s r e s e m b l e e a c h i n t h a t b o t h p r o c e s s e s c o n s i s t o f s e t s o f r e p e t i t i v e t a s k s t o p r o d u c e a l a r g e number o f s i m i l a r o r i d e n t i c a l f i n i s h e d p r o d u c t s . They a l s o r e s e m b l e e a c h o t h e r i n t h a t t h e managers a r e c o n c e r n e d w i t h : (1) f o r m u l a t i o n o f o p e r a t i o n s and w o r k s t a s k s t o be c a r r i e d o u t t o p r o d u c e t h e f i n i s h e d p r o d u c t s w i t h i n p r o j e c t c o n s t r a i n t s ; (2) c h o i c e o f t e c h n o l o g i e s , c h o i c e o f e q u i p m e n t , and l a y o u t o f work s i t e t o c a r r y o u t t h e o p e r a t i o n s i n t h e most e f f i c i e n t and e f f e c t i v e manner; (3) b a l a n c e d a s s i g n m e n t o f t h e i d e n t i f i e d o p e r a t i o n s and work t a s k s t o work s t a t i o n s o r w o r k e r s ; 70 (4) i m p l e m e n t a t i o n o f a p r o d u c t i o n p l a n and m o n i t o r i n g o f o p e r a t i o n s a t t h e work s i t e ; and (5) d e v i s i n g p r o d u c t i o n method i m p r o v e m e n t s t o i n c r e a s e p r o d u c t i v i t y , l o w e r p r o d u c t i o n c o s t , and r e d u c e c y c l e t i m e f o r e a c h u n i t . 5.4.2 DIFFERENCES BETWEEN ALB AND CONSTRUCTION CYCLE DESIGN B o l i n q [12] d e s c r i b e d r e p e t i t i v e c o n s t r u c t i o n p r o j e c t s as s e q u e n t i a l c r e w s y s t e m s and s t a t e d t h a t a s e q u e n t i a l c r e w s y s t e m : " c o n s i s t s o f two o r more c r e w s f o l l o w i n g one a n o t h e r i n a f i x e d s e q u e n c e t o c o m p l e t e a p a r t i c u l a r t a s k on a u n i t b e i n g c o n s t r u c t e d . U n i t s i n t h e s e s y s t e m s a r e o f t e n l a r g e and r e l a t i v e l y i m m o b i l e as compa r e d t o t h o s e p r o c e s s e d by t y p i c a l p r o d u c t i o n s y s t e m s I n t h e s e q u e n t i a l s y s t e m , t h e f i r s t c r e w b r i n g s new u n i t s i n t o t h e s y s t e m and t h e r e m a i n i n g c r e w s p r o c e s s t h e s e u n i t s as t h e y become a v a i l a b l e . C rews p e r f o r m t h e i r a s s i g n e d work i n a f i x e d s e q u e n c e w i t h r e s p e c t t o one a n o t h e r , and u n i t s a r e p r o c e s s e d by e a c h c r e w i n t h e same o r d e r as t h e y e n t e r t h e s y s t e m . " [12] B o l i n q has g i v e n a good summary o f t h e d i f f e r e n c e s b e t w e e n a r e p e t i t i v e c o n s t r u c t i o n p r o j e c t and a t y p i c a l a s s e m b l y p r o d u c t i o n l i n e b u t s t o p p e d s h o r t o f s u g g e s t i n g an 71 algorithm for the construction context. The differences between the two systems can be summarized as follows: (1) Units in construction projects are large and immobile; worker have to travel along the workface as construction progresses. (2) Unit in r e p e t i t i v e construction units can be considered to be introduced into the system when work by the f i r s t crew is i n i t i a t e d . In-process inventory is limited to a small number of units; buffer stock of the main assembly is non-existent in most projects. This make the proper balance of crew assignments more c r i t i c a l to avoid unnecessary interruption and i d l e time. (3) Factory type assembly l i n e production produces large numbers of smaller items for an extended period of time; feedback on the effectiveness of the production process can be collected more quickly and modifications for improvement can also be implemented more quickly and e a s i l y . Any e f f o r t expended on improvement of balance w i l l pay back in future improvements in productivity. In construction projects, there might not be s u f f i c i e n t time to study and implement improvements to the production design once the i n i t i a l design is implemented. This requires optimization of the i n i t i a l design and, where possible, certain f l e x i b i l i t y in the construction process should be maintained to accommodate changes or improvements. 72 (4) B e c a u s e o f t h e s i z e o f t h e u n i t , u n n e c e s s a r y r e l o c a t i o n o f w o r k e r s l o w e r s p r o d u c t i v i t y s i g n i f i c a n t l y . A s s i g n m e n t o f work e l e m e n t s t h e r e f o r e h a s t o t a k e i n t o c o n s i d e r a t i o n t h e r e l a t e d n e s s s o as t o r e d u c e r e l o c a t i o n o f w o r k e r s f r o m one a r e a t o a n o t h e r . R e l a t e d n e s s i s , h o w e v e r , d i f f i c u l t t o be c l e a r l y d e f i ned. (5) The work e l e m e n t s o f c o n s t r u c t i o n p r o j e c t s a r e o f t e n r e s t r i c t e d by r e q u i r e m e n t s f o r s p e c i a l t r a d e s o r e q u i p m e n t , and l i m i t e d s p a c e a t t h e work f a c e . T h e s e i m p o s e s a d d i t i o n a l c o n s t r a i n t s on t h e work a s s i g n m e n t p r o c e s s . (6) I n c o n s t r u c t i o n p r o j e c t s , b e c a u s e o f t h e s i z e o f t h e u n i t b e i n g p r o d u c e d , m u l t i p l e m a n n i n g i s t h e norm r a t h e r t h a n t h e e x c e p t i o n u n l e s s t h e o p e r a t i o n s a r e b r o k e n down i n t o t h e f i n e r d e t a i l s o f work t a s k s . (7) B e c a u s e o f t h e l a r g e s i z e o f an u n i t and t h u s t h e l o n g e r p r o c e s s i n g t i m e o f o p e r a t i o n s , e l e m e n t s h a r i n g c a n be a c h i e v e d more e a s i l y i n c o n s t r u c t i o n p r o j e c t s . (8) The way t h e u n i t c a n be p r o d u c e d i s more f l e x i b l e ( o r r a t h e r l e s s w e l l d e f i n e d ) i n c o n s t r u c t i o n p r o j e c t s and t h e i n p u t o f e x p e r i e n c e i s t h e r e f o r e d e s i r a b l e i n t h e c o n s t r u c t i o n c y c l e d e s i g n p r o c e s s . T h i s may n e c e s s i t a t e an i n t e r a c t i v e p r o g r a m w h i c h p r o m p t s t h e u s e r f o r d e c i s i o n s . (9) B e c a u s e o f t h e c o m p l e x i t y and s k i l l d e p e n d e n c e o f c o n s t r u c t i o n o p e r a t i o n s as c o m p a r e d t o t h e more r o u t i n e 73 m o t i o n s f o r an a s s e m b l y l i n e , c o n s t r u c t i o n o p e r a t i o n s a r e more s u s c e p t i b l e t o i n t e r r u p t i o n s due t o v a r i a b l e e l e m e n t t i m e s and t h u s c o n t i n u i t y i s d i f f i c u l t t o m a i n t a i n . The c y c l e d e s i g n s y s t e m f o r c o n s t r u c t i o n p r o j e c t s must t h e r e f o r e be e a s y t o m a n i p u l a t e and r e s p o n s i v e t o c h a n g e s a t t h e work s i t e . 5.5 APPLICATION OF ALB TO CONSTRUCTION CYCLE DESIGN B e c a u s e o f t h e more s t a b l e e n v i r o n m e n t o f t h e m a n u f a c t u r i n g i n d u s t r y and t h e a v a i l a b i l i t y o f l a r g e r p r o d u c t l i n e r u n s , more e f f o r t has been p u t i n t o d e v e l o p i n g b e t t e r methods and c o m p u t e r p r o g r a m s f o r p r o d u c t i o n p l a n n i n g and c o n t r o l . R e l a t i v e l y w e l l d e f i n e d m a n u f a c t u r i n g p r o c e d u r e s f a c i l i t a t e more s y s t e m a t i c a p p r o a c h e s t o a n a l y s i s of p r o d u c t i o n o p e r a t i o n s . The s i m i l a r i t i e s b e t w e e n a s s e m b l y l i n e p r o d u c t i o n and r e p e t i t i v e c o n s t r u c t i o n p r o j e c t s i n d i c a t e t h a t a s s e m b l y l i n e b a l a n c i n g t e c h n i q u e s m i g h t f i n d a p p l i c a t i o n t o t h e c o n s t r u c t i o n c y c l e d e s i g n p r o b l e m . D e s i g n of c o n s t r u c t i o n c y c l e s a t t h e p r o d u c t i o n l e v e l h o w e v e r h a v e more s t r i n g e n t work a s s i g n m e n t c o n s t r a i n t s t h a n t h e d e s i g n o f an a s s e m b l y p r o d u c t i o n l i n e b e c a u s e o f t h e p h y s i c a l s i z e o f and i m m o b i l i t y o f a s s e m b l y u n i t s i n c o n s t r u c t i o n p r o j e c t s , t h e r e q u i r e m e n t s o f s k i l l e d o p e r a t o r s o f s p e c i f i c t r a d e s and h e a v y e q u i p m e n t t o p e r f o r m t h e r e s p e c t i v e o p e r a t i o n s , t h e more f l e x i b l e c o n s t r u c t i o n methods and t h e more d y n a m i c p r o j e c t e n v i r o n m e n t . 74 5.5.1 L I M I T A T I O N S OF ALB ALGORITHMS E v e n t h o u g h e x t e n s i v e r e s e a r c h and d e v e l o p m e n t h a v e been done i n d e s i g n i n g good a s s e m b l y l i n e b a l a n c i n g a l g o r i t h m s , t h e l a r g e number o f p r o d u c t i o n c o n s t r a i n t s and t h e g r e a t number o f p o s s i b l e a s s i g n m e n t r u l e s make i t d i f f i c u l t t o d e v i s e an a l g o r i t h m t o s u i t a l l s i t u a t i o n s and a c c o u n t f o r a l l p o s s i b l e a l t e r n a t i v e s i n o r d e r t o o p t i m i z e t h e a s s e m b l y l i n e d e s i g n . M o o d i e [ 8 6 ] , q u o t i n g s t a t i s t i c s f r o m a p a p e r p u b l i s h e d i n 1 9 6 9 , s t a t e d t h a t : 8 1 % o f t h e b a l a n c i n g i s done e i t h e r m a n u a l l y o r by t r i a l and e r r o r m e t h o d s . A p p a r e n t l y , i n d u s t r i a l a p p l i c a t i o n s do n o t a l w a y s f i t i n t o t h e mo l d o f s p e c i f i c c o m p u t e r i z e d a s s e m b l y l i n e b a l a n c i n g p a c k a g e s . A c o m p u t e r o r i e n t e d m e t h o d o l o g y , w h i c h o f f e r s t h e i n d u s t r i a l e n g i n e e r t h e a b i l i t y t o c o m b i n e t h e m a n u a l methods w i t h t h e power o f t h e c o m p u t e r , i s i n t e r a c t i v e p r o g r a m m i n g . where an e n g i n e e r , who i s f a m i l i a r w i t h t h e a s s e m b l y o f t h e p r o d u c t c a n u s e h i s i n s i g h t s , i n g e n u i t y , and p e r c e p t i o n s i n c o n j u n c t i o n w i t h t h e power o f t h e c o m p u t e r , t o a c h i e v e a g o o d , w o r k a b l e , a s s e m b l y l i n e b a l a n c e . " and ".... t h e p r u d e n t a n a l y s t who knows s o m e t h i n g a b o u t t h e r e l a t i o n s h i p s b e t w e e n t h e e l e m e n t s w h i c h i s n o t g i v e n i n t h e p r e c e d e n c e m a t r i x [86] M o o d i e t h e n d e s c r i b e d an i n t e r a c t i v e p r o g r a m w h i c h does n o t u s e any s p e c i f i c l i n e b a l a n c i n g a l g o r i t h m s b u t s i m p l y u s e s t h e c o m p u t e r t o g u i d e t h e t h e d e c i s i o n maker t h r o u g h 75 t h e m a n u a l l i n e b a l a n c i n g p r o c e s s and p r o v i d e s f e e d b a c k t o t h e a n a l y s t t o show t h e i m p l i c a t i o n s o f d i f f e r e n t d e c i s i o n s . The a b o v e s t a t e m e n t s made by M o o d i e and h i s c h o i c e o f a more s i m p l i s t i c a p p r o a c h t o t h e p r o b l e m i n d i c a t e t h a t a s s e m b l y b a l a n c i n g a l g o r i t h m s and h e u r i s t i c s f a i l t o c a p t u r e a l l t h e f a c t o r s w h i c h i n f l u e n c e t h e l i n e d e s i g n i n t h e m a n u f a c t u r i n g e n v i r o n m e n t . I n o r d e r t o c a p t u r e some o f t h e f a c t o r s and r e s t r i c t i o n s t h a t a r e " f a r more e x t e n s i v e t h a n j u s t t h o s e d e s c r i b e d by t h e p r e c e d e n c e d i a g r a m " , S c h o f i e l d [118] i n t h e L i n e S e q u e n c i n g P r o g r a m d e v e l o p e d a t N o t t i n g h a m U n i v e r s i t y (NULISP) u s e s a s e t o f h i g h l e v e l " i n s t r u c t i o n s " t o c o n t r o l t h e l i n e b a l a n c i n g p r o c e d u r e s a f t e r t h e l i s t s o f work t a s k s and p r e c e d e n c e r e l a t i o n s h i p s h a v e been d e f i n e d . E x a m p l e s o f t h e commands a r e : JOIN* < l i s t o f work t a s k s > - d e f i n e t h e s e t o f work t a s k s t o be p e r f o r m e d by t h e same o p e r a t o r o r a t t h e same work s t a t i o n . FIX* < t a s k number) AT* < s t a t i o n number) - a s s i g n t h e s p e c i f i e d t a s k t o be p e r f o r m e d by a p a r t i c u l a r o p e r a t o r w i t h s p e c i a l s k i l l e d o r a t a p a r t i c u l a r work s t a t i o n e q u i p p e d w i t h s p e c i a l i z e d m a c h i n e r y . MULTI* <no. o f o p e r a t o r s ) AT* < s t a t i o n number) s p e c i f y t h e p a r t i c u l a r work s t a t i o n t o be manned by a c e r t a i n number o f o p e r a t o r s . 76 CYCLE* < d e s i r e d p r o d u c t i o n r a t e > - d e f i n e t h e d e s i r e d c y c l e t i m e f o r p r o d u c t i o n o f one u n i t o f t h e a s s e m b l e d p r o d u c t . 5.5.2 APPLICATION OF ALB PRINCIPLES TO CONSTRDCTION CYCLE DESIGN D e s p i t e t h e more s t r i n g e n t work a s s i g n m e n t c o n s t r a i n t s i n d e s i g n i n g c o n s t r u c t i o n o p e r a t i o n s and t h e l i m i t a t i o n s o f c u r r e n t l y a v a i l a b l e ALB a l g o r i t h m s , t h e f o l l o w i n g p r i n c i p l e s e m p l o y e d i n t h e d e s i g n o f a s s e m b l y p r o d u c t i o n l i n e s c a n be a p p l i e d t o c o n s t r u c t i o n c y c l e p l a n n i n g : (1) E s t i m a t i o n of R e s o u r c e R e q u i r e m e n t s f o r P e r f e c t B a l a n c e The e x a m p l e o f l i n e b a l a n c e f o r a 20 e l e m e n t s a s s e m b l y p r o d u c t i o n d e s c r i b e d i n s e c t i o n 2.2 o f t h i s c h a p t e r i l l u s t r a t e s a s i n g l e i t e r a t i o n o f t h e m a n u a l l i n e b a l a n c i n g p r o c e d u r e . The f i r s t s t e p a f t e r t h e work t a s k s and p r e c e d e n c e r e l a t i o n s h i p s h a v e been d e f i n e d i s e s t i m a t i o n o f t h e number o f s t a t i o n s o r o p e r a t o r s r e q u i r e d t o meet t h e d e s i r e p r o d u c t i o n r a t e o f 300 u n i t s e a c h e i g h t h o u r d a y . The e s t i m a t i o n t h e n becomes a d e s i g n o b j e c t i v e f o r t h e d e c i s i o n m a k e r . The number o f o p e r a t o r s c a n be i n c r e a s e d when p e r f e c t b a l a n c e c a n n o t be a c h i e v e d . T h i s p r o c e s s i s c a l l e d b a c k w a r d p l a n n i n g . 77 I n t h e t r a d i t i o n a l a p p r o a c h t o c o n s t r u c t i o n p l a n n i n g , b a c k w a r d p l a n n i n g i s s e l d o m m e n t i o n e d i n t h e c o n s t r u c t i o n l i t e r a t u r e and i t i s o n l y p e r f o r m e d by f i e l d p e r s o n n e l i n an i n f o r m a l manner. T h i s i s b e c a u s e t h e p r o d u c t i v i t i e s i n c o n s t r u c t i o n o p e r a t i o n s a r e h i g h l y i n f l u e n c e d by s p e c i f i c p r o j e c t c o n d i t i o n s and b e c a u s e o f t h e d i f f i c u l t y o f a c h i e v i n g p e r f e c t l y b a l a n c e d d e s i g n s . E s t i m a t i o n o f r e s o u r c e r e q u i r e m e n t s i s t h e r e f o r e d e p e n d e n t on p a s t e x p e r i e n c e o f t h e p r o j e c t m anagers and s u p e r i n t e n d e n t s i n v o l v e d and t h e r e i s no g u i d e l i n e f o r p o s s i b l e i m p r o v e m e n t t o o v e r a l l p r o j e c t p r o d u c t i v i t y ; e s t i m a t i o n s on r e s o u r c e r e g u i r e m e n t s u n d e r p e r f e c t l y b a l a n c e d c o n d i t i o n s c a n p r o v i d e t h i s g u i d e l i n e . (2) S p e c i a l I n s t r u c t i o n s f o r I n t e r a c t i v e C o n s t r u c t i o n C y c le Design As d e s c r i b e d by S c h o f i e l d [ 1 1 8 ] , t h e e l e m e n t s i n v o l v e d i n t h e d e s i g n o f a s s e m b l y p r o d u c t i o n l i n e a r e f a r more e x t e n s i v e t h a n any s i n g l e p r o g r a m c a n r e a l i s t i c a l l y i n c l u d e . The e l e m e n t s i n v o l v e d i n t h e d e s i g n o f c o n s t r u c t i o n o p e r a t i o n s a r e e v e n more e x t e n s i v e as d i s c u s s e d t h e t h e p r e v i o u s s e c t i o n . The u s e d o f i n s t r u c t i o n s t o c o n t r o l t h e l i n e b a l a n c i n g p r o c e d u r e s as d e s c r i b e d by S c h o f i e l d c a n a l s o f i n d a p p l i c a t i o n s i n t h e c o n s t r u c t i o n c y c l e d e s i g n p r o b l e m . A p p l i c a t i o n s t h e o f a b o v e p r i n c i p l e s i n a d e c i s i o n s u p p o r t s y s t e m f o r c o n s t r u c t i o n c y c l e d e s i g n a r e d e s c r i b e d i n c h a p t e r s i x . 78 6. DECISION SUPPORT SYSTEM (DSS) FOR ACTIVITY DESIGN 6.0 OBJECTIVES T r a d i t i o n a l a p p r o a c h e s t o p r o b l e m s o l v i n g h a v e e m p h a s i z e d t h e u s e o f d e t e r m i n i s t i c q u a n t i t a t i v e m o d e l i n g t e c h n i q u e s w h e r e b y s o l u t i o n s c a n be g e n e r a t e d by s o l v i n g c l o s e d f o r m f u n c t i o n s t h a t l i n k a l l t h e d e s i g n v a r i a b l e s w i t h t h e d e s i g n o b j e c t i v e . I n c h a p t e r t h r e e , we ha v e s t a t e d t h a t t h e a c t i v i t y d e s i g n p r o b l e m c a n n o t be d e f i n e d by a c l o s e d f o r m f u n c t i o n ; d e s i g n s o l u t i o n s t h e r e f o r e d e p e n d on t h e e x p e r i e n c e , p e r s o n a l j u d g m e n t and i n t u i t i o n o f t h e management p e r s o n n e l i n v o l v e d i n t h e a c t i v i t y d e s i g n p r o c e s s . I n t h i s c h a p t e r , d e c i s i o n m a k i n g p r o c e s s e s and d e c i s i o n s u p p o r t s y s t e m s d e s c r i b e d i n t h e i n d u s t r i a l e n g i n e e r i n g and management s c i e n c e l i t e r a t u r e a r e f i r s t s t u d i e d t o a s s i s t i n t h e d e v e l o p m e n t o f an u n d e r s t a n d i n g o f t h e p r o c e s s e s i n v o l v e d i n d e s i g n i n g a c o n s t r u c t i o n a c t i v i t y . A c o n c e p t u a l d e s i g n o f a d e c i s i o n s u p p o r t s y s t e m w h i c h w o u l d p r o v i d e t h e n e e d e d a c t i v i t y d e s i g n e n v i r o n m e n t i s t h e n d i s c u s s e d i n t e r m s o f f i v e m o d u l e s - p r o b l e m r e c o g n i t i o n , p r o b l e m d e f i n i t i o n , s o l u t i o n f o r m u l a t i o n , d e s i g n a n a l y s i s , and d e s i g n i m p r o v e m e n t and e n r i c h m e n t . 79 I n d e a l i n g w i t h t h e p r o b l e m r e c o g n i t i o n m o d u l e , o n l y b r i e f s t a t e m e n t s a r e made r e g a r d i n g t h e p r o b l e m o f i n f o r m a t i o n r e p r e s e n t a t i o n . The f a c i l i t y t h a t a s s i s t s i n t h e p r o c e s s o f d e t a i l e d p r o b l e m d e f i n i t i o n by d e f i n i n g t h e p h y s i c a l d i m e n s i o n s o f t h e s u b a s s e m b l i e s and work c a t e g o r y c o m p o n e n t s i s d e s c r i b e d . A s y s t e m a t i c f o r m a t f o r d e s c r i b i n g c o n s t r u c t i o n t e c h n o l o g i e s t h a t c a n a s s i s t management p e r s o n n e l i n c o m p a r i n g and s e l e c t i n g t h e a p p r o p r i a t e c o n s t r u c t i o n t e c h n o l o g y i s p r e s e n t e d . I n p u t d a t a s t r u c t u r e s t h a t p e r m i t r e a l i s t i c f o r m u l a t i o n o f d e s i g n s o l u t i o n s a r e d e s c r i b e d . The p r i n c i p l e s o f a s s e m b l y l i n e b a l a n c i n g a r e a d o p t e d f o r e s t i m a t i n g r e s o u r c e r e q u i r e m e n t s t o g u i d e management p e r s o n n e l i n t h e r e s o u r c e a s s i g n m e n t p r o c e s s . L a b o u r r e s o u r c e s a r e a s s i g n e d as c r e w s r a t h e r t h a n as i n d i v i d u a l w o r k e r s . R e s o u r c e s c a n be a s s i g n e d t o an o p e r a t i o n f o r p a r t o f t h e o p e r a t i o n d u r a t i o n . The c r i t i c a l p a t h method and m u l t i p l e a c t i v i t y c h a r t s a r e a d o p t e d t o a s s i s t i n t h e s o l u t i o n a n a l y s i s and t h e d e s i g n i m p r o v e m e n t and e n r i c h m e n t p r o c e s s e s . E x a m p l e s o f h i g h l e v e l i n s t r u c t i o n s a r e a l s o d e s c r i b e d t o a l l o w management p e r s o n n e l t o m o d i f y t h e o p e r a t i o n s c h e d u l e m a n u a l l y a n d t o i m p r o v e t h e p r e l i m i n a r y d e s i g n and t o p r o d u c e t a c t i c a l p l a n s , c a l l e d t h e m u l t i p l e o p e r a t i o n t i m e (M.O.T.) c h a r t s , f o r u s e i n t h e f i e l d . 80 6.1 THE CREATIVE HUMAN DECISION MAKING PROCESS. A systematic approach to the decision making process as described by Salvendy [115] is represented by figure 6.1 and involves the following steps: (1) P r o b l e m D e f i n i t i o n (and R e c o g n i t i o n ) Understanding the s i t u a t i o n and recognizing the need for a decision. This step involves searching, obtaining, processing and examination of raw data to i d e n t i f y and define the problem. (2) P r o b l e m S o l v i n g ( S o l u t i o n F o r m u l a t i o n ) Developing, inventing, and analyzing possible courses of action to solve the problem defined. This step involves the process of conceptualizing the problem, drawing on past experience, adapting experience to the new s i t u a t i o n , and developing and creating new solutions for the defined problem. (3) Idea S c r e e n i n g ( S o l u t i o n A n a l y s i s ) Choosing the best solution from the set of possible courses of action generated in the problem solving process. This step involves testing the set of 81 p o s s i b l e s o l u t i o n s f o r f e a s i b i l i t y and c h o o s i n g t h e most e f f e c t i v e s o l u t i o n . Idea E n r i c h m e n t ( D e s i g n Improvement) P r e p a r i n g t h e s o l u t i o n f o r a c t i o n . T h i s s t e p i n v o l v e s e x a m i n i n g t h e c o u r s e o f a c t i o n c h o s e n i n t h e i d e a s c r e e n i n g p r o c e s s f o r f u r t h e r i m p r o v e m e n t . A b r o a d f o c u s i s m a i n t a i n e d a n d common-sense i s e m p l o y e d t o d e v e l o p a t a c t i c a l p l a n t o be f o l l o w e d i n c a r r y i n g o u t t h e s o l u t i o n . - S i t u a t i o n PROBLEM DEFINITION (1) P r o b l e m D e f i n e d PROBLEM SOLVING (2) Many I d e a s IDEAS SCREENING (3) — B e s t I d e a IDEA ENRICHMENT (4) - A c t i o n F i g . 6.1: C r e a t i v e human d e c i s i o n m a k i n g p r o c e s s 82 6 . 2 D E C I S I O N S U P P O R T S Y S T E M S A N D D E C I S I O N M A K I N G In the la s t decade, extensive research and development have taken place in the f i e l d s of management science and knowledge engineering. The objective is to develop expert systems that can simulate the decision making process of human "experts" in problem solving. However, many researchers, such as Godin [40], r e a l i z e that computers cannot completely replace human experts in the decision making process and advocate a "symbiotic" human-machine relationship whereby: "The computer churns through vast numbers of computations in employing the embedded scheduling h e u r i s t i c s , but when i t needed help ( i . e . when the he u r i s t i c s proved too simple), the human was close at hand to provide very f l e x i b l e , i n s i g h t f u l assistance." [40] The above system is also described as the "Interactive Decision Support System" (IDSS for short). The IDSS allows decision makers to more closely follow their behavioral process, draw on experience and apply personal judgment and i n t u i t i o n in the decision making process; the computer performs the functions of data and information processing and quantitative analysis. The IDSS, however, cannot a s s i s t decision makers in making q u a l i t a t i v e decisions such as those involved in conceptual designs and innovations. To meet the s p e c i f i c needs of q u a l i t a t i v e decision making. Young [135] proposed the "Right-Brained or Total 83 DSS" (TDSS f o r s h o r t ) f o r c r e a t i v e d e c i s i o n m a k i n g . W h i l e Young has d e s c r i b e d i n d e t a i l t h e c o n c e p t u a l d e s i g n o f a t o t a l d e c i s i o n s u p p o r t s y s t e m , w i t h s p e c i a l e m p h a s i s on t h e q u a l i t a t i v e a s p e c t s o f t h e d e c i s i o n m a k i n g p r o c e s s , i t i s t o o e x t e n s i v e f o r a p p l i c a t i o n t o t h e c o n s t r u c t i o n a c t i v i t y d e s i g n p r o b l e m a t t h e p r e s e n t s t a g e o f r e s e a r c h and d e v e l o p m e n t i n t h e c o n s t r u c t i o n i n d u s t r y . B a s e d on c u r r e n t u n d e r s t a n d i n g s o f t h e human d e c i s i o n m a k i n g p r o c e s s and t h e c o n c e p t o f i n t e r a c t i v e d e c i s i o n s u p p o r t s y s t e m s , a c o n c e p t u a l d e s i g n f o r an a c t i v i t y d e s i g n e n v i r o n m e n t i s d e v e l o p e d i n t h e f o l l o w i n g s e c t i o n s . 6.3 DECISION SUPPORT SYSTEM FOR ACTIVITY DESIGN The a p p r o a c h t a k e n i n t h e c o n c e p t u a l d e s i g n o f t h e d e c i s i o n s u p p o r t s y s t e m f o r a c t i v i t y d e s i g n i s r e p r e s e n t e d by t h e f l o w c h a r t s i n f i g u r e 6.2 and f i g u r e 6.3. T h e s e c h a r t s r e f l e c t r e a l i s t i c a l l y t h e p r o c e s s c a r r i e d o u t by c o n s t r u c t i o n management p e r s o n n e l i n d e s i g n i n g c o n s t r u c t i o n a c t i v i t i e s . The d a t a b a s e management s y s t e m (DBMS) shown r e q u i r e s e x t e n s i v e and p r e c i s e d e f i n i t i o n o f d a t a s t r u c t u r e s and w i l l n o t be d i s c u s s e d i n t h i s t h e s i s . B u i l d i n g on t h e d i s c u s s i o n s i n s e c t i o n s 6.1 and 6.2, t h e a c t i v i t y d e s i g n p r o c e s s w i l l be r o u g h l y d i v i d e d i n t o f i v e m o d u l e s : 84 Module 1 - P r o b l e m R e c o g n i t i o n T h i s m odule r e p r e s e n t s t h e p r o c e s s i n w h i c h f i e l d management p e r s o n n e l draw on a body o f i n f o r m a t i o n t o f a m i l i a r i z e t h e m s e l v e s w i t h t h e t y p e o f p r o b l e m s r e p r e s e n t e d by t h e c u r r e n t s i t u a t i o n . I t a l s o a l l o w s them t o s t u d y t h e d i f f i c u l t i e s a s s o c i a t e d w i t h t h e p a r t i c u l a r t y p e o f p r o b l e m s and how s i m i l a r p r o b l e m s h a v e been s o l v e d i n t h e p a s t . S o l u t i o n s t h a t w o r k e d i n t h e p a s t c a n t h e n be a d a p t e d f o r t h e c u r r e n t s i t u a t i o n . Module 2 - P r o b l e m D e f i n i t i o n The f i r s t s t e p i n p r o b l e m s o l v i n g i s d e f i n i n g t h e p r o b l e m . F o r c o n s t r u c t i o n a c t i v i t y d e s i g n , t h e d i m e n s i o n s o f t h e a s s e m b l y and s u b a s s e m b l i e s o f t h e p h y s i c a l f a c i l i t y t o be c o n s t r u c t e d must be d e f i n e d . U s i n g t h e s e d i m e n s i o n s , t h e s c o p e o f work t o be e x e c u t e d c a n be d e t e r m i n e d . D e t a i l e d d e f i n i t i o n o f p r o b l e m d i m e n s i o n s a l s o a l l o w s r e s o u r c e r e q u i r e m e n t s t o be e s t i m a t e d a c c u r a t e l y and f a c i l i t a t e s t h e s t u d y o f d e s i g n a l t e r n a t i v e s . Module 3 - S o l u t i o n F o r m u l a t i o n A f t e r t h e p r o b l e m has been d e f i n e d , f i e l d management p e r s o n n e l h a v e t o f o r m u l a t e a p r e l i m i n a r y a c t i v i t y d e s i g n . T h i s p r o c e s s i n v o l v e s s e l e c t i n g t h e a p p r o p r i a t e c o n s t r u c t i o n t e c h n o l o g i e s , d e f i n i n g and s e g u e n c i n g c o n s t r u c t i o n 85 o p e r a t i o n s t o p r o d u c e t h e p h y s i c a l a s s e m b l y u n i t , and e s t i m a t i n g and c o m m i t t i n g t h e r e s o u r c e s - l a b o u r , h a r d w a r e , e q u i p m e n t and work s p a c e , t o p e r f o r m t h e d e f i n e d o p e r a t i o n s . Module 4 - S o l u t i o n A n a l y s i s The p r e l i m i n a r y d e s i g n s o l u t i o n must t h e n be a n a l y z e d by c o m p u t e r r o u t i n e s f o r f e a s i b i l i t y and e f f e c t i v e n e s s . The d e f i n e d v a l u e s o f d e s i g n p a r a m e t e r s and v a r i a b l e s a r e p r o c e s s e d and a n a l y z e d t o p r o d u c e an o p e r a t i o n s s c h e d u l e . I d l e t i m e a n d c o n f l i c t s o f r e s o u r c e s must be i d e n t i f i e d and c o m m u n i c a t e d t o management p e r s o n n e l f o r a p p r o p r i a t e m o d i f i c a t i o n s t o t h e p r e l i m i n a r y d e s i g n . Module 5 - Design Improvement and Enrichment T h i s m o d u l e r e p r e s e n t s t h e p r o c e s s t h r o u g h w h i c h f i e l d management p e r s o n n e l s e e k t o i m p r o v e t h e p r e l i m i n a r y d e s i g n by s o l v i n g p r o b l e m s i d e n t i f i e d i n t h e s o l u t i o n a n a l y s i s p r o c e s s . W h e t h e r t h e i d e n t i f i e d p r o b l e m s c a n be s o l v e d e f f e c t i v e l y d e p e n d s on t h e e x p e r i e n c e , j u d g m e n t and i n t u i t i o n o f t h e management p e r s o n n e l . The f i n a l d e s i g n t h a t r e s u l t s f r o m t h e d e s i g n i m p r o v e m e n t p r o c e s s c a n be a n a l y z e d f o r c o s t e f f e c t i v e n e s s . I t e r a t i o n s t h r o u g h m odule 3 and m o d u l e 4 t o s t u d y o t h e r d e s i g n a l t e r n a t i v e s m i g h t be r e q u i r e d t o p r o d u c e a d e s i g n s o l u t i o n t h a t i s a c c e p t a b l e i n t e r m s o f b o t h t i m e and c o s t . F i n a l l y , e l e m e n t s t h a t a r e n o t 86 n o r m a l l y c o n s i d e r e d i n t h e a c t i v i t y d e s i g n p r o c e s s c a n a l s o be i n c l u d e d i n t h e f i n a l d e s i g n t o p r o d u c e t a c t i c a l p l a n s - s h o r t c y c l e s c h e d u l e , c r e w a s s i g n m e n t s , e q u i p m e n t s c h e d u l e s and s u b - t r a d e s s c h e d u l e s , t h a t c a n be f o l l o w e d i n t h e f i e l d t o a c h i e v e t h e g o a l s s e t f o r a c o n s t r u c t i o n p r o j e c t . The i s s u e s i n v o l v e d i n e a c h m o d u l e a r e d i s c u s s e d and a d d r e s s e d i n t h e f o l l o w i n g s e c t i o n s . T h r o u g h t h i s p r o c e s s , a c o n c e p t u a l d e s i g n o f a d e c i s i o n s u p p o r t s y s t e m f o r a c t i v i t y d e s i g n w i l l be d e s c r i b e d . E x a m p l e s o f d a t a s t r u c t u r e s and c o m p u t e r i n p u t / o u t p u t f o r m a t s t h a t c a n be u s e d i n t h e a c t i v i t y d e s i g n e n v i r o n m e n t a r e a l s o p r e s e n t e d . 3 O a a r n x o o c IT n »0 so o a n Rl X o H M z M o z t SO O 09 r n 3 SO RI O o ft z o z 3 o o a r RI W o n a H M o z o 3 a > M o z Specifications Construction DrawIngs T \ Quantity / Survey / — Rev leu \ Construction Mathods / Break Down to Smaller Units D e f i n i t i o n of Unit Dimensions Select Construction Technolog Jes I Grouping of Operations DefIne P-Matrlx Review I Construct I \ Methods (Select from Standard P-Matrlces / J a > > a > Ui m 3 > Z > ra 3 Rl Z CA * Ui H Rl 3 O CO 3 cn F i g u r e 6.2 CO Figure 6.3 co co 89 6.3.1 MODULE 1 - PROBLEM RECOGNITION 6.3.1.1 REPRESENTATION OF PROJECT INFORMATION I n t h e d e s i g n o f c o n s t r u c t i o n a c t i v i t i e s , f i e l d management p e r s o n n e l h a v e t o draw on t h e i r e x p e r i e n c e w i t h s i m i l a r p r o j e c t s and a p p l y t h e i r k n o w l e d g e o f c o n s t r u c t i o n m ethods and t e c h n o l o g i e s . The s u c c e s s o f a p r o j e c t i s t h e r e f o r e h i g h l y d e p e n d e n t on t h e e x p e r i e n c e and k n o w l e d g e o f t h e k e y management p e r s o n n e l . The a b i l i t y t o r e p r e s e n t e x p e r i e n c e and k n o w l e d g e h e l p e n s u r e t h a t t h e a c o n t r a c t i n g f i r m ' s a b i l i t y t o compete i s n o t a f f e c t e d by t u r n - o v e r i n i t s k e y management p e r s o n n e l . E x p e r i e n c e and k n o w l e d g e r e p r e s e n t e d i n p r o p e r f o r m a t s c a n a l s o be u s e d t o p r o v i d e an e n v i r o n m e n t f o r t r a i n i n g l e s s e x p e r i e n c e d c o n s t r u c t i o n management p e r s o n n e l . E x p e r i e n c e and k n o w l e d g e c a n be r e p r e s e n t e d by two c l a s s i f i c a t i o n s o f p r o j e c t i n f o r m a t i o n : (1) b r o a d q u a l i t a t i v e d e s c r i p t i v e s t a t e m e n t s , and (2) d e t a i l e d q u a n t i t a t i v e d a t a . The f o r m e r r e p r e s e n t s i n f o r m a t i o n w h i c h c a n h e l p management p e r s o n n e l q u i c k l y i d e n t i f y t h e p a s t p r o j e c t t h a t most c l o s e l y r e p r e s e n t t h e p r e s e n t s i t u a t i o n . I t i n c l u d e s d e s c r i p t i o n s o f i n n o v a t i o n s and c r e a t i v e d e s i g n s w h i c h w o u l d o t h e r w i s e be l o s t a m i d s t t h e q u a n t i t a t i v e p r o j e c t d a t a . I t c o u l d be i n t h e f o r m o f b r i e f s t a t e m e n t s 90 d e s c r i b i n g t h e o v e r a l l p r o j e c t p e r f o r m a n c e , p r o d u c t i o n s y s t e m s and t e c h n o l o g i e s e m p l o y e d , o p e r a t i o n s c a r r i e d o u t , and t h e d i f f i c u l t i e s , s o l u t i o n s and i n n o v a t i o n s i n v o l v e d i n a p r o j e c t . The l a t t e r t y p e o f d e t a i l e d q u a n t i t a t i v e i n f o r m a t i o n a r e d e m a n d i n g i n t e r m s o f c o m p u t e r s t o r a g e and d a t a b a s e m a i n t e n a n c e . E x a m p l e s o f t h i s t y p e o f i n f o r m a t i o n a r e t h e d e t a i l e d d i m e n s i o n s o f p r o j e c t a s s e m b l y and s u b a s s e m b l y c o m p o n e n t s , o p e r a t i o n d e f i n i t i o n s and c r e w a s s i g n m e n t s . A t p r e s e n t , few c o n s t r u c t i o n f i r m s h a v e o r g a n i z e d r e c o r d s o f p a s t p r o j e c t s ; t h e body o f i n f o r m a t i o n o n l y r e s i d e s i n t h e m i n d s of k e y management p e r s o n n e l . F o r t h i s r e a s o n and t h e l i m i t e d s c o p e o f t h i s t h e s i s , no d e t a i l s o f t h i s m o d u l e w i l l be d e s c r i b e d i n t h e a c t i v i t y d e s i g n e n v i r o n m e n t b e i n g d e v e l o p e d . I t i s h o p e d t h a t t h e a c t i v i t y d e s i g n e n v i r o n m e n t w i l l a l s o a c t as a t o o l by w h i c h p r o j e c t i n f o r m a t i o n c a n be c o l l e c t e d and p r o c e s s e d f o r f u t u r e r e f e r e n c e . 91 6.3.2 MODULE 2 - PROBLEM DEFINITION The l e v e l o f d e t a i l i n w h i c h a p r o b l e m i s d e f i n e d w i l l a f f e c t how r e a l i s t i c and e f f e c t i v e t h e s u b s e q u e n t d e s i g n s o l u t i o n i s . A c o n s t r u c t i o n p r o j e c t c a n be d e f i n e d by t h e d i m e n s i o n s o f i t s s u b a s s e m b l y c o m p o n e n t s , e .g. a r e a and t h i c k n e s s o f e a c h bay o f a f l o o r s l a b , and t h e d i m e n s i o n s o f e a c h work c a t e g o r y c o m p o n e n t , e . g . t h e r e b a r c o n t e n t s o f t h e f l o o r s l a b s u b a s s e m b l i e s . T h i s d e f i n i t i o n p r o c e s s a s s i s t s i n i d e n t i f y i n g t h e work t a s k s r e q u i r e d t o c o n s t r u c t t h e p h y s i c a l p r o d u c t . T h e s e work t a s k s c a n t h e n be g r o u p e d and a s s i g n e d t o c o n s t r u c t i o n o p e r a t i o n s . 6.3.2.1 CURRENT PRACTICE AND PROBLEM DEFINITION M o d e l i n g t o o l s and s y s t e m s c u r r e n t l y a v a i l a b l e f o r c o n s t r u c t i o n p l a n n i n g do n o t p r o v i d e t h e f a c i l i t y by w h i c h management p e r s o n n e l c a n d e f i n e t h e p r o b l e m i n t h e d e t a i l d e s c r i b e d a b o v e . I n t h e a c t i v i t y p l a n n i n g p r o c e s s , t h e f i e l d management p e r s o n n e l f i r s t d i v i d e t h e t y p i c a l p h y s i c a l a s s e m b l y i n t o s u b a s s e m b l i e s a l o n g l o g i c a l b r e a k s , s u c h as t h e c o l u m n l i n e s ; t h e s u b a s s e m b l i e s a r e t h e n a s s i g n e d i n g r o u p s t o t h e c o r r e s p o n d i n g c o n s t r u c t i o n o p e r a t i o n s . The q u a n t i t i e s o f work i n e a c h o p e r a t i o n must be c a l c u l a t e d m a n u a l l y o r d e r i v e d f r o m v a l u e s p r o d u c e d by t h e e s t i m a t o r . I n o r d e r t o i d e n t i f y t h e most e f f e c t i v e c o n s t r u c t i o n method f o r a c o n s t r u c t i o n a c t i v i t y , one h a s t o e x p e r i m e n t w i t h 92 d i f f e r e n t g r o u p i n g s o f t h e s u b a s s e m b l y u n i t s , t h u s c h a n g i n g t h e work c o n t e n t o f t h e o p e r a t i o n s . E v e r y t i m e t h e g r o u p i n g s of s u b a s s e m b l i e s a r e c h a n g e d , t h e work t a s k s a s s i g n e d t o t h e c o r r e s p o n d i n g o p e r a t i o n s w i l l c h a n g e and t h u s t h e work q u a n t i t i e s a n d t h e r e s o u r c e r e q u i r e m e n t s o f o p e r a t i o n s w i l l h a v e t o be r e c a l c u l a t e d . 6.3 . 2 . 2 P R O B L E M D E F I N I T I O N AND T H E DSS One o f t h e o b j e c t i v e s o f t h e d e c i s i o n s u p p o r t s y s t e m f o r t h e P r o b l e m D e f i n i t i o n m o d u l e i s t o p r o v i d e an e n v i r o n m e n t i n w h i c h t h e p r o b l e m c a n be d e f i n e d i n d e t a i l by s p e c i f y i n g t h e d i m e n s i o n s o f e a c h s u b a s s e m b l y component and e a c h work c a t e g o r y c o m p o n e n t . The f o l l o w i n g b e n e f i t s c a n be a c h i e v e d by d e f i n i n g t h e p r o b l e m i n t h i s d e t a i l e d manner: (1) U s i n g t h e d i m e n s i o n s s p e c i f i e d , s i m p l e r o u t i n e s c a n be u s e d by t h e c o m p u t e r t o c a l c u l a t e a c c u r a t e l y t h e work c o n t e n t s o f and t h u s t h e r e s o u r c e s r e q u i r e d t o p e r f o r m t h e c o n s t r u c t i o n o p e r a t i o n s ; t h e r e s o u r c e r e q u i r e m e n t s c a l c u l a t e d c a n be u s e d t o a s s i s t i n t h e r e s o u r c e a s s i g n m e n t p r o c e s s . (2) B e c a u s e t h e work c o n t e n t o f t h e o p e r a t i o n s c a n be c a l c u l a t e d by c o m p u t e r , d i f f e r e n t ways o f g r o u p i n g t h e s u b a s s e m b l i e s f o r c o n s t r u c t i o n i n t h e s o l u t i o n f o r m u l a t i o n p r o c e s s c a n be s t u d i e d r e a d i l y . 93 (3) By d e f i n i n g t h e d i m e n s i o n s a s s e m b l y u n i t , t h e i m p a c t d i m e n s i o n s o f n o n - t y p i c a l a s s e s s e d . and work c o n t e n t o f e a c h of d i f f e r e n c e s i n t h e a s s e m b l y u n i t s c a n be 6.3.2.3 PROBLEM DEFINITION AND COMPUTER INPUT FORMAT F i g u r e s 6.4(a) and 6.4(b) show t h e p r o c e s s o f d e f i n i n g t h e d i m e n s i o n s o f a t y p i c a l a s s e m b l y component. The name t o be u s e d i n d e s c r i b i n g t h e a s s e m b l y d i v i s i o n s ( o r u n i t s ) and t h e t o t a l number o f s i m i l a r u n i t s i n t h e p r o j e c t a s s e m b l y g r o u p a r e e n t e r e d . T h i s i s f o l l o w e d by d e t a i l e d d e f i n i t i o n o f t h e d i m e n s i o n s o f t h e s u b a s s e m b l y c o m p o n e n t s and t h e work c a t e g o r y c o m p o n e n t s . The d i m e n s i o n s o f t h e t y p i c a l a s s e m b l y a r e f i r s t e n t e r e d . Any a s s e m b l y d i v i s i o n w i t h d i m e n s i o n s t h a t d e v i a t e s f r o m t h a t o f t h e t y p i c a l d i v i s i o n c a n t h e n be i d e n t i f i e d and m o d i f i e d . I n t h e e x a m p l e shown, t h e a r e a s e n t e r e d a r e u s e d t o c a l c u l a t e t h e r e s o u r c e s r e q u i r e d f o r f o r m w o r k and c o n c r e t e f i n i s h i n g o p e r a t i o n s , t h e r e b a r c o n t e n t i s u s e d t o c a l c u l a t e t h e r e s o u r c e s r e q u i r e d f o r t h e r e b a r i n s t a l l a t i o n o p e r a t i o n , and t h e p r o d u c t i v i t y f a c t o r ( P r o d v ' F.) i s u s e d t o r e f l e c t p o s s i b l e d i f f i c u l t i e s i n v o l v e d i n c o n s t r u c t i n g t h e s u b a s s e m b l y , e . g . f o r m i n g o f a i r r e g u l a r l y s h a p e d a r e a , w h i c h w i l l r e d u c e t h e r a t e o f c o n s t r u c t i o n . F i g u r e 6 . 4 ( a ) : S e l e c t a s s e m b l y c o m p o n e n t t o d e f i n e ASSEMBLY DEFINITIONS : SUPERSTRUCTURE Enter Name of Assembly D i v i s i o n : I E l e v . 1 Enter Tota l Number of Assembly D i v i s i o n s : I 25 1 S e l e c t Assembly Component to De f ine : SLAB > " ' - S U B % " \ COLUMNS ELEV. CORE WALLS F i g u r e 6 . 4 ( b ) S p e c i f y d i m e n s i o n s o f s u b a s s e m b l y a n d work c a t e g o r y c o m p o n e n t s T Y P I C A L ASSEMBLY COMPONENT DIMENSIONS Assembly Component : SLAB I Bay ) A-1 A-2 B-1 B-2 B-3 B-4 B-5 C-4 C-5 I Area 1 2 < M̂  > 90 100 100 100 65 100 100 100 85 (Slab Thkn. < mm > 150 200 200 200 150 200 200 200 150 [Rebar Content ! < tons/M 2 > 1.0 I.I .1 .9 .1 .1 .1 .0 Copy Dlmeslons to Other Assembly D i v i s i o n s : Y e s / No Modify Dimensions In Assembly D i v i s i o n : Y e s / No Enter Assembly D i v i s i o n No. to Modify : t 24 1 IProdv' F .J 0.90 1.00 1 .00 1.00 0.60 1 .00 1.00 1 .00 0.85 F i g u r e 6 . 4 : P r o b l e m d e f i n i t i o n 95 6 . 3 . 3 MODULE 3 - SOLUTION FORMULATION As s t a t e d i n s e c t i o n 4.5, c u r r e n t p r a c t i c e i n c o n s t r u c t i o n p l a n n i n g f a i l s t o m o d e l c o n s t r u c t i o n a c t i v i t i e s i n a r e a l i s t i c manner. F o r e x a m p l e , i t assumes t h a t r e s o u r c e c o n s u m p t i o n has t o be c o n s t a n t o v e r t h e e n t i r e d u r a t i o n o f a c o n s t r u c t i o n o p e r a t i o n . I t a l s o f a i l s t o c o r r e c t l y m o d e l t h e a c t u a l c o n s t r u c t i o n a c t i v i t y d e s i g n p r o c e s s . F o r e x a m p l e , l a b o u r r e s o u r c e s h a v e t o be a s s i g n e d a s i n d i v i d u a l w o r k e r s r a t h e r t h a n as c r e w s . The o b j e c t i v e o f t h i s m o d u l e i s t o p r o v i d e a p r o b l e m s o l v i n g e n v i r o n m e n t t h a t r e f l e c t s t h e r e a l i t i e s o f c o n s t r u c t i o n a c t i v i t i e s a s p r a c t i c e d i n t h e f i e l d . The s o l u t i o n f o r m u l a t i o n p r o c e s s h a s been d i v i d e d i n t o t h e f o l l o w i n g p r o c e s s e s : (1) R e v i e w and s e l e c t c o n s t r u c t i o n t e c h n o l o g i e s ; (2) D e f i n e o p e r a t i o n s ; (3) S e q u e n c e d e f i n e d o p e r a t i o n s ; and (4) E s t i m a t e and a s s i g n r e s o u r c e s . Some o f t h e f e a t u r e s i n c o r p o r a t e d i n t o t h e f o r e g o i n g p r o c e s s e s a r e as f o l l o w s : (1) A d a t a s t r u c t u r e f o r r e p r e s e n t i n g c o n s t r u c t i o n t e c h n o l o g i e s i s d e s c r i b e d . The c o m p u t e r i z e d r e c o r d o f c o n s t r u c t i o n t e c h n o l o g i e s c a n be u s e d t o a s s i s t 96 management i n c o m p a r i n g d i f f e r e n t c o n s t r u c t i o n t e c h n o l o g i e s i n t h e s o l u t i o n s e l e c t i o n p r o c e s s . (2) By u s i n g t h e d e t a i l e d d e f i n i t i o n o f p h y s i c a l d i m e n s i o n s o f s u b a s s e m b l i e s and work c a t e g o r y c o m p o n e n t s d e v e l o p e d i n t h e P r o b l e m D e f i n i t i o n m o d u l e , o p e r a t i o n s a r e d e f i n e d by s e l e c t i n g t h e s u b a s s e m b l i e s t o be i n c l u d e d i n t o t h e work c o n t e n t o f t h e o p e r a t i o n s . (3) The s e q u e n c i n g o f o p e r a t i o n s d e s c r i b i n g an a c t i v i t y i s d e f i n e d i n m a t r i x f o r m a t f o r c l a r i t y . The l a g s i n t h e p r e c e d e n c e r e l a t i o n s b e t w e e n o p e r a t i o n s c a n be d e f i n e d as a p e r c e n t a g e o f t h e c o r r e s p o n d i n g o p e r a t i o n d u r a t i o n . (4) U s i n g t h e p r i n c i p l e s o f a s s e m b l y l i n e b a l a n c i n g , t h e r e s o u r c e s r e q u i r e d t o p e r f o r m c o n s t r u c t i o n o p e r a t i o n s a r e e s t i m a t e d by c o m p u t e r t o a s s i s t i n t h e r e s o u r c e a s s i g n m e n t p r o c e s s . (5) L a b o u r r e s o u r c e s a r e a s s i g n e d t o o p e r a t i o n s as c r e w s r a t h e r t h a n as i n d i v i d u a l w o r k e r s . R e s o u r c e s c a n a l s o be a s s i g n e d t o an o p e r a t i o n f o r a p e r c e n t a g e o f i t s d u r a t i on. 97 6.3.3.1 REVIEW AND SELECT CONSTRUCTION TECHNOLOGIES I n a c o n s t r u c t i o n p r o j e c t , t h e c h o i c e o f p r o d u c t i o n t e c h n o l o g y i s o f p r i m e i m p o r t a n c e . I t a f f e c t s t h e p r o d u c t i o n r a t e o f t h e c o n s t r u c t i o n o p e r a t i o n s and t h u s t h e c y c l e t i m e . I t a l s o i m p o s e s c e r t a i n c o n s t r a i n t s on l a b o u r r e s o u r c e a s s i g n m e n t s b e c a u s e o f p o s s i b l e minimum c r e w s i z e r e q u i r e m e n t s . E a c h t e c h n o l o g y a l s o has a s s o c i a t e d c o s t s . The c h o i c e o f c o n s t r u c t i o n t e c h n o l o g y t h e r e f o r e o f t e n e v o l v e s i n t o a t r a d e - o f f p r o b l e m b e t w e e n a c t i v i t y p r o d u c t i o n r a t e ( t i m e ) and c o s t . A p r o d u c t i o n t e c h n o l o g y t h a t h a s a h i g h e r u n i t p r o d u c t i o n r a t e , h o w e v e r , m i g h t n o t be a p p r o p r i a t e f o r a c e r t a i n s i t u a t i o n and w i l l n o t i n c r e a s e t h e o v e r a l l p r o d u c t i o n r a t e o f an a c t i v i t y e v e n a t t h e e x p e n s e o f t h e e x t r a c o s t . W h e t h e r a t e c h n o l o g y w i t h a h i g h u n i t p r o d u c t i o n r a t e i s a p p r o p r i a t e d e p e n d s on w h e t h e r t h e o p e r a t i o n s c a n be p r o p e r l y b a l a n c e d . F o r e x a m p l e , t h e o v e r a l l p r o d u c t i o n r a t e o f an a c t i v i t y , s a y c o n s i s t i n g o f two o p e r a t i o n s i n p a r a l l e l , w i l l n o t be i n c r e a s e by i n c r e a s i n g t h e p r o d u c t i o n r a t e o f one o p e r a t i o n a l o n e , r a t h e r , t h e p r o d u c t i o n r a t e s o f b o t h o p e r a t i o n s must a l s o be i n c r e a s e d p r o p o r t i o n a t e l y , i . e . t h e a c t i v i t y d e s i g n must be b a l a n c e d , i n o r d e r t o b e n e f i t f r o m u s i n g t e c h n o l o g i e s w i t h h i g h e r u n i t p r o d u c t i o n r a t e s . i. 98 6.3.3.1.1 CURRENT PRACTICE AND SELECTION OF TECHNOLOGIES C u r r e n t l y a v a i l a b l e c o n s t r u c t i o n p l a n n i n g t e c h n i q u e s and s y s t e m s do n o t p r o v i d e management t h e f a c i l i t y t o s t u d y a l t e r n a t i v e c o n s t r u c t i o n t e c h n o l o g i e s and s e l e c t t h e most s u i t a b l e one. I n s t e a d , c o n s t r u c t i o n p e r s o n n e l draw on t h e i r own k n o w l e d g e o f a v a i l a b l e c o n s t r u c t i o n t e c h n o l o g i e s and do l i m i t e d f o r m a l s t u d y o f one o r two a l t e r n a t i v e s a t b e s t . T h i s l a t t e r p r o c e s s i n v o l v e s r o u g h e s t i m a t e s o f t e c h n o l o g y c o s t s and r e s o u r c e r e g u i r e m e n t s . T h i s a p p r o a c h d o e s l i t t l e t o e n c o u r a g e i n n o v a t i o n s and c o n s i d e r a t i o n s o f new d e v e l o p m e n t s i n c o n s t r u c t i o n t e c h n o l o g i e s . 6.3.3.1.2 SELECTION OF TECHNOLOGY AND THE DSS To f a c i l i t a t e t h e s t u d y o f a l t e r n a t i v e c o n s t r u c t i o n t e c h n o l o g i e s , a v a i l a b l e t e c h n o l o g i e s must be c l a s s i f i e d by t h e work c a t e g o r i e s t h e y a r e i n t e n d e d f o r and c o d e d i n a s y s t e m a t i c f o r m a t t o a l l o w c o m p a r i s o n and a c c u r a t e e s t i m a t i o n o f c o s t and r e s o u r c e r e q u i r e m e n t s . I n t h e f o l l o w i n g d i s c u s s i o n , a d a t a s t r u c t u r e i s s u g g e s t e d f o r c o d i n g and s t o r i n g c o n s t r u c t i o n t e c h n o l o g i e s i n a c o m p u t e r d a t a b a s e . The a t t r i b u t e s u s e d f o r c l a s s i f y i n g and d e s c r i b i n g c o n s t r u c t i o n t e c h n o l o g i e s a r e a l s o d e s c r i b e d . 99 F i g u r e 6 . 5 ( a ) : S e l e c t t e c h n o l o g y by work ca t e g o r y Select Work Category-Group to Review Technologies : CONCRETE CIVIL/SITE CONCRETE SUB-TRADES OTHERS Select Work Category : FORMWORK FORMWORK REBAR POURING CURING FINISHING Select Assembly Component : SLAB S L A B " ' ,' *"i COLUMNS ELEV. CORE WALLS F i g u r e 6.5(b): Compare and s e l e c t t e c h n o l o g y Select Slab Formwork System: EFCO F l o a t i n g S lab I System! t Unit Production 1 I Hardware ) I Crew Make-Up 1 [ Rate 1 [ U n i t Cost ] [ Ratios ) < M2/Mn-hr > < cnd$/M2 > < Carpenter > < Gen. Labr > EFCO Floating' j 4.8 37.50 0.9 0.1 FORM-Ezy 6.4 47.75 0.8 0.2 Review detailed descriptions of selected technology : Yes / No F i g u r e 6 . 5 : R e v i e w and s e l e c t c o n s t r u c t i o n t e c h n o l o g i e s 1 0 0 6.3.3.1.3 A T T R I B U T E S OF CONSTRUCTION TECHNOLOGIES F i g u r e s 6.5(a) and 6.5(b) show t h e c o m p u t e r i n p u t f o r m a t s u s e d t o a s s i s t i n s e l e c t i n g a l t e r n a t i v e c o n s t r u c t i o n t e c h n o l o g i e s . The f o l l o w i n g a t t r i b u t e s u s e d i n s e l e c t i n g c o n s t r u c t i o n t e c h n o l o g y a r e n o t e d : ( 1 ) Work C a t e g o r y G r o u p , C a t e g o r y a n d A s s e m b l y C o m p o n e n t T h e s e a t t r i b u t e s , as shown i n f i g u r e 6 . 5 ( a ) , i d e n t i f y t h e work c a t e g o r y f o r w h i c h t h e c o n s t r u c t i o n t e c h n o l o g y i s i n t e n d e d . They a r e u s e d f o r c l a s s i f y i n g c o n s t r u c t i o n t e c h n o l o g i e s . C o n s t r u c t i o n t e c h n o l o g i e s c a n t h e n be r e t r i e v e d by t h e s y s t e m u s e r f o r c o m p a r i s o n s by s p e c i f y i n g t h e i r c l a s s i f i c a t i o n s . The work b r e a k d o w n s t r u c t u r e by wo r k / c o m p o n e n t c a t e g o r i e s d e s c r i b e d i n c h a p t e r two c a n be u s e d as a c l a s s i f i c a t i o n scheme f o r c o n s t r u c t i o n t e c h n o l o g i e s ; a c o m p r e h e n s i v e scheme h a s n o t been d e v e l o p e d i n t h i s t h e s i s . (2) U n i t P r o d u c t i o n R a t e , H a r d w a r e U n i t C o s t a n d Cr e w Make-Up R a t i o s U n i t P r o d u c t i o n R a t e d e s c r i b e s t h e t i m e r e g u i r e d t o 2 3 p l a c e a s i n g l e u n i t (M , M , e t c ) o f a c o n s t r u c t i o n o p e r a t i o n u s i n g t h e s e l e c t e d t e c h n o l o g y . I t d e t e r m i n e s t h e 101 production rate of the operation. In the decision support system for a c t i v i t y design, i t is used to calculate the resource requirements to achieve a s p e c i f i e d operation duration. Higher productivity can be achieved usually only at the expense of higher cost; in other words, the construction technology selection process is a trade-off between time and cost. For the example shown in figure 6.5(b), the higher productivity of FORM-Ezy is achieved at the expense of a higher hardware cost. The cost associated with a construction technology is two-fold: hardware cost and labour cost. Hardware Unit Cost represents the cost for either renting or f a b r i c a t i n g the system hardware. Labour cost would be best s p e c i f i e d separately, because hourly labour rates would depend on the geographic location of the project and other project conditions. Crew Make-Up Ratios i d e n t i f y the ratios of the numbers of men reguired for each labour type in employing the construction technology. For example, to dismantle and 2 i n s t a l l a 240 M f l o o r slab using the EFCO Floating form 2 2 w i l l require 50 man-hours (240 M / 4.8 M /Mn-hr) - 45 carpenter-hours (50 Mn-hr x 0.9) and 5 general labourer- hours (50 Mn-hr x 0.1). The rental cost of formwork w i l l be $9,000.00 (240 M2 x $37.50). Displaying the three attributes of construction technologies side-by-side can a s s i s t management in selecting 1 0 2 an a p p r o p r i a t e t e c h n o l o g y f o r t h e p r e l i m i n a r y d e s i g n s o l u t i o n . O t h e r a t t r i b u t e s u s e f u l i n t h e a c t i v i t y d e s i g n p r o c e s s , s u c h as minimum c r e w s i z e r e q u i r e m e n t s and t h e work t a s k s i n v o l v e d , c a n a l s o be i n c l u d e d i n t h e a t t r i b u t e l i s t . F o r e x a m p l e , t h e s y s t e m u s e r may w i s h t o r e v i e w t h e work t a s k s i n v o l v e d i n a c o n s t r u c t i o n m e t h o d , as shown i n F i g u r e s 6.6. I n g e n e r a l , b r e a k d o w n s o f c o n s t r u c t i o n t e c h n o l o g i e s t o t h i s l e v e l o f d e t a i l a r e n o t r e a d i l y a v a i l a b l e ; t h e r e f o r e , t h e i r t r e a t m e n t i s n o t p u r s u e d f u r t h e r i n t h i s t h e s i s . 1 0 3 F i g u r e 6 . 6 ( a ) : R e v i e w w o r k t a s k s o f s e l e c t e d t e c h n o l o g y - p a g e 1 EFCO F l o a t i n g Slab Formwork S y s t e m W o r k T a s k s : L i t e r a t u r e F i l e N o . : S l b F m - 0 1 2 P a g e 1 o f 3 S l a b F o r m w o r k D i m e n s i o n : 2 0 M b y 10 M B a y ** I N S T A L L AND D I S M A N T L E FORM ** No. of Unit Total < a l l t i m e I n m i n u t e s > Units Time Time Comments 01 S e t r o l l e r s u p p o r t b r a c k e t a h e a d 8 4 0 3 2 0 0 2 L o w e r s u p p o r t b r a c k e t s & f o r m 8 15 1 2 0 0 3 S t r i p s l a b e d g e h a n d r a i l (1 e n d ) 1 3 0 3 0 0 4 A t t a c h t u g g e r w i n c h 1 3 0 3 0 0 5 P o s i t i o n r o l l i n g s c a f f o l d 1 15 15 0 6 R o l l s l a b f o r m o u t t o p i c k - p o i n t s 1 3 0 3 0 0 7 C r a n e h o o k u p 4 p o i n t s 4 5 2 0 0 8 S l a b s w i n g - o u t a n d r e s e t 1 2 0 8 0 4 M e n & C r a n e 0 9 C l e a n a n d o l 1 f o r m 7 8 4 s f 6 / 1 0 0 s f 4 6 1 0 1 n s t a I I f 1 1 l e r p a n e 1 1 9 0 1 8 0 2 men 6 . 6 ( b ) : R e v i e w w o r k t a s k s o f s e 1 e c t e d t e c h n o l o g y - p a g e 2 EFCO F l o a t i n g Slab Formwork S y s t e m W o r k T a s k s : ** S P L I T T I N G O F FORM ** No. of Unit Total < a l l t i m e I n m i n u t e s > Units Time Time 11 R e m o v e 1 b o l t a t b e a r i n g b l o c k s 4 5 2 0 12 A t t a c h t u g g e r w i n c h 1 3 0 3 0 13 P o s i t i o n r o l l i n g s c a f f o l d 1 15 15 14 R o l 1 s l a b f o r m o u t 1 3 0 3 0 15 C r a n e h o o k u p 4 p o i n t s 4 5 2 0 1 6 S l a b s w i n g o u t a n d r e - s e t 1 2 0 8 0 17 I n s t a l l 1 " b o l t a t b e a r i n g b l o c k s 4 5 2 0 P a g e 2 o f 3 Comments 4 M e n & C r a n e F i g u r e 6 . 6 : R e v i e w work t a s k s o f c o n s t r u c t i o n t e c h n o l o g y S o u r c e : Economy Forms C o r p o r a t i o n , Des M o i n e s , I o w a , USA. 1 0 4 6.3.3.2 DEFINE CONSTRDCTION OPERATIONS C o n s t r u c t i o n o f a f l o o r a s s e m b l y u n i t i s a c c o m p l i s h e d by c o m p l e t i o n o f a l l t h e s u b a s s e m b l y c o m p o n e n t s d e f i n e d i n t h e p r o b l e m d e f i n i t i o n p r o c e s s . The s i m p l e s t c o n s t r u c t i o n method i s t o c o n s t r u c t t h e w h o l e f l o o r a s s e m b l y as a s i n g l e s e c t i o n ; f o r e x a m p l e , t h e f o r m w o r k and r e b a r i n s t a l l a t i o n f o r t h e c o m p l e t e f l o o r s l a b a r e c o m p l e t e d b e f o r e c o n c r e t e i s p o u r e d and f i n i s h e d . A l t h o u g h s i m p l e , t h i s method c o u l d h a v e an u n d e s i r a b l y l a r g e c y c l e t i m e and c o u l d be a c c o m p a n i e d by c o n s i d e r a b l e i d l e t i m e f o r k e y t r a d e s . To s h o r t e n c y c l e t i m e and b e c a u s e o f o t h e r e c o n o m i c c o n s i d e r a t i o n s , t h e f l o o r a s s e m b l y i s o f t e n c o n s t r u c t e d i n s e v e r a l m a j o r s e c t i o n s . F o r e x a m p l e , a f l o o r a s s e m b l y c a n be d i v i d e d i n t o f i f t e e n s u b - a s s e m b l i e s , s a y , B a y - A l t o Bay-C5. C o n s t r u c t i o n o p e r a t i o n s c a n be p e r f o r m e d i n t h r e e s e c t i o n s o f f i v e b a y s . The f o r m w o r k and r e b a r c a n be i n s t a l l e d i n t h e f i r s t s e c t i o n , c o n c r e t e c a n t h e n be p o u r e d and f i n i s h e d i n t h e f i r s t s e c t i o n w h i l e f o r m w o r k and r e b a r a r e b e i n g i n s t a l l e d i n t h e s e c o n d s e c t i o n and s o on u n t i l c o n s t r u c t i o n of t h e f l o o r a s s e m b l y i s c o m p l e t e d . By c o n s t r u c t i n g t h e f l o o r a s s e m b l y i n t h r e e s e c t i o n s , f e w e r f o r m w o r k u n i t s c o u l d be r e q u i r e d and c y c l e t i m e c o u l d be r e d u c e d . C h a n g e s i n c o n s t r u c t i o n method w i l l r e q u i r e t h e d e f i n i t i o n s o f c o n s t r u c t i o n o p e r a t i o n s t o be c h a n g e d . F o r e x a m p l e , i f t h e f l o o r a s s e m b l y i s c o n s t r u c t e d i n t h r e e s e c t i o n s i n s t e a d o f a s i n g l e s e c t i o n , t h e o p e r a t i o n , s a y 105 I n s t a l l Slab Formwork, has to be redefined as three operations, say, I n s t a l l Slab Formwork Section #1, I n s t a l l Slab Formwork Section #2 and I n s t a l l Slab Formwork Section #3. 6.3.3.2.1 DEFINING AN OPERATION The process of defining an operation is shown in figures 6.7(a) and 6.7(b). An operation is f i r s t i d e n t i f i e d by i t s work categories as shown in figure 6.7(a). The process of id e n t i f y i n g the operation by i t s work categories can f a c i l i t a t e c o l l e c t i n g project information for cost accounting of the current project and for estimating the costs of similar projects in the future. After the operation is i d e n t i f i e d by i t s work categories, the defined dimensions of the subassembly components and work category components, e.g. the dimensions of the f l o o r slab subassemblies, and rebar contents in each subassembly, can be retrieved. The user can then define the work assignment of an operation by sel e c t i n g the respective subassemblies to be included in the operat i on. 6.3.3.2.2 DEFINING RELATED OPERATIONS Construction operations that belong to d i f f e r e n t work categories can be related to each others by their work assignments, i . e . the same or similar groups of 106 subassemblies are assigned to the operations. In the example shown in figures 6.8(a) and 6.8(b), the rebar operation RbrSlb-1, Rebar Floor Slab Section #1, is related to the formwork operation InsSlbFm-1, I n s t a l l Slab Formwork Section #1. Normally, both operations have to be defined by assigning selected subassemblies to the operations. Thus, a set of f l o o r slab subassemblies, say A-1, A-2, B - l , B-2, and C-1, have to be assigned to the formwork operation, InsSlbFm-1. The assignment process must then be repeated by assigning, once again, the f l o o r slab assemblies A-1, A-2, B - l , B-2, and C-1 to the rebar operation, RbrSlb-1. In the a c t i v i t y design environment developed, operations related in the above manner can be defined conveniently as i l l u s t r a t e d in figure 6.8. The operation to be defined is f i r s t related to an already defined operation. The work assignment of the related operation is then retrieved, the user can accept the already defined work assignment or add or delete sub-assemblies as reguired. The quantity of work of the defined operation is then calculated using the work category component dimensions s p e c i f i e d in the Problem D e f i n i t i o n module. In the example shown, the work assignment of the rebar operation, RbrSlb-1 has been related to the formwork operation, InsSlbFm-1, the quantity of rebar to be i n s t a l l e d can be calculated from the rebar content of the subassemblies s p e c i f i e d in the problem d e f i n i t i o n process. 107 6.3.3.2.3 REDEFINING OPERATIONS An o p e r a t i o n c a n be r e d e f i n e d u s i n g a c o m p u t e r i n p u t / o u t p u t f o r m a t s i m i l a r t o f i g u r e 6 . 7 ( b ) , by a d d i n g o r d e l e t i n g s u b a s s e m b l i e s f r o m t h e a s s i g n m e n t o f an o p e r a t i o n . U s i n g t h i s new d e f i n i t i o n , t h e c o m p u t e r c a n r e c a l c u l a t e t h e t o t a l q u a n t i t y o f work and r e s o u r c e r e g u i r e m e n t s . How t h e s e c a l c u l a t e d r e s o u r c e r e q u i r e m e n t s a r e u s e d i n g u i d i n g t h e r e s o u r c e a s s i g n m e n t p r o c e s s i s d e s c r i b e d i n s e c t i o n 6.3.3.4. F i g u r e 6.7(a): S e l e c t o p e r a t i o n to d e f i n e Select Work Category-Group : CONCRETE CIVIL/SITE CONCRETE SUB-TRADES OTHERS Select Work Category : SLAB SLAB COLUMNS ELEV. CORE WALLS Select Work Category Component : FORMWORK FORMWORK REBAR DELIVERY CURING FINISHING Select Work Category Sub-Component : INSTALL INSTALL DI SMANTLE Enter Name of Operation : I InsSlbFm - 1 1 Enter Description : [ I n s t a l l s l a b formwork B A Y < A 1 , A 2 , B 1 , B 2 , C 1 > 1 Selected Slab Formwork System : EFCO F l o a t i n g Slab Change selected system : No / Yes F i g u r e 6.7(b): A s s i g n s u b a s s e m b l i e s t o an o p e r a t i o n Operation : InsSlbFm - 1 I n s t a l l s l a b formwork B A Y < A 1 , A 2 , B 1 . B 2 . C I > Selected Slab Formwork System : EFCO F l o a t i n g S lab Move cursor and press <Enter>/<Del> to Include/remove assembly. t Bay 1 ( Area 1 IProdv' Fl 2 A - 1 90 0.90 A - 2 100 1.00 B - 1 100 1.00 B - 2 100 1.00 B-3 65 0.60 B-4 100 1.00 B-5 100 1.00 C - 1 90 0.90 F i g u r e 6 . 7 : D e f i n i n g an o p e r a t i o n F i g u r e 6.8 ( a ) : S e l e c t r e l a t e d o p e r a t i o n t o d e f i n e Select Work Category-Group : CONCRETE CIVIL/SITE CONCRETE SUB-TRADES OTHERS Select Work Category : SLAB SLAB COLUMNS ELEV. CORE WALLS Select Work Category Component : REBAR FORMWORK REBAR DELIVERY CURING FINISHING Enter Name of Operation : I RbrSlb-1 1 Enter Description : I S lab Rebar BAY<A1 ,A2,B1 ,B2,C1 > 1 Enter Related Operation : t InsSlbFm-l ] Selected Slab Rebar System : I n s t a l l In p lace Change selected system : No / Yes F i g u r e 6.8 ( b ) : Review and modi fy a s s i g n m e n t of o p e r a t i o n Operation : RbrSlb-1 Related to : InsSlbFm-l Rebar S lab BAY<A1,A2,B1,B2,CJ> Selected Slab Rebar System : I n s t a l l In p lace Move cursor and press <Enter>/<Del> to include/remove assembly. I Bay 1 A - l A-2 B-1 B-2 B-3 B-4 B-5 C-1 (Rebar Content! < tons/M 2 > . 0 .1 [Prodv* F! 0 . 9 0 1 . 0 0 • • • • 1 .00 1 .00 0 . 6 0 1 .00 1 . 0 0 1 .00 F i g u r e 6 .8: D e f i n i n g r e l a t e d o p e r a t i o n s 1 1 0 6.3.3.3 SEQUENCE DEFINED OPERATIONS 6.3.3.3.1 OPERATIONS SEQUENCE AND THE P-MATRIX O p e r a t i o n s d e f i n e d t o c o n s t r u c t p h y s i c a l a s s e m b l i e s must be p e r f o r m e d i n a s p e c i f i e d b u t n o t n e c e s s a r i l y u n i q u e s e q u e n c e w h i c h i s g o v e r n e d by t e c h n o l o g i c a l and o t h e r p r o j e c t c o n s t r a i n t s . D e t e r m i n i n g t h e b e s t s e q u e n c e i s a d e s i g n p r o b l e m i n i t s e l f , t h e s o l u t i o n o f w h i c h r e q u i r e s c o n s i d e r a b l e c o n s t r u c t i o n e x p e r i e n c e . The s e q u e n c e o f o p e r a t i o n s i s d e f i n e d by i d e n t i f y i n g t h e i m m e d i a t e p r e d e c e s s o r s o r i m m e d i a t e s u c c e s s o r s o f e a c h o p e r a t i o n . I n i n d u s t r i a l e n g i n e e r i n g , t h e P - m a t r i x ( o r p r e c e d e n c e m a t r i x ) i s o f t e n u s e d t o r e p r e s e n t t h e s e g u e n t i a l r e l a t i o n s b e t w e e n o p e r a t i o n s . T h i s m a t r i x f o r m a t has t h e a d v a n t a g e o f s i m p l i c i t y and c l a r i t y . H owever, when t h e number o f o p e r a t i o n s and t h u s t h e s i z e o f t h e m a t r i x i n c r e a s e s , t h e p r o c e s s o f m a n u a l l y s e a r c h i n g f o r t h e i m m e d i a t e p r e d e c e s s o r s o r s u c c e s s o r s c a n become t e d i o u s . T h i s p r o b l e m c a n be s o l v e d by a d d i n g a c o l u m n o r a comment l i n e on t h e s c r e e n t h a t shows t h e i m m e d i a t e s u c c e s s o r s o f t h e o p e r a t i o n u n d e r t h e c u r s o r . The p r o c e s s o f s e q u e n c i n g d e f i n e d o p e r a t i o n s i n m a t r i x f o r m a t i s shown i n f i g u r e 6.9. I l l Enter A c t i v e Assembly D i v i s i o n : [ 4 1 ENTER IMMEDIATE SUCCESSORS OF OPERATION: IType(s) of r e l a t i o n ; Lag In (^duration) or (hr:mln)l Type: 1 = FS, 2 = SF, 3 = SS, 4 = FF Oprat lon Assm* 1 . D . D i v . 2 3 4 5 6 7 8 9 1 DsmSIbFm-l 3 i;0 0 0 0 0 i;0 0 0 2 InsSlbFm-1 4 * I;0 0 0 0 0 0 0 3 RbrS lb -J 4 * 3;80* i;0 0 0 0 0 4 SIvSlb-l 4 • 0 0 0 0 5 CncrSlb-1 4 • 0 0 0 6 CureSlb-1 4 » 0 0 0 7 1nsSlbFm-2 4 » 0 8 RbrSlb-2 4 * 9;80* 9 SlvSlb-2 4 • Operation: RbrSlb -1 Successors: 3, SlvSlb-1; 4, CncrSlb-1; F i g u r e 6 .9: S e g u e n c i n g o p e r a t i o n s - t h e P - M a t r i x 1 1 2 6.3.3.3.2 OPERATIONS SEQUENCE AND LAG CALCULATIONS T h e r e a r e f o u r t y p i c a l s e q u e n t i a l r e l a t i o n s h i p s , n a m e l y f i n i s h - t o - s t a r t , s t a r t - t o - f i n i s h , s t a r t - t o - s t a r t , and f i n i s h - t o - f i n i s h . E a c h r e l a t i o n s h i p i s f u r t h e r d e s c r i b e d by a l a g v a l u e . T r a d i t i o n a l l y , t h e s e l a g v a l u e s a r e e n t e r e d i n t i m e u n i t s , e.g. 1 d a y . When o p e r a t i o n d u r a t i o n s a r e c o n s t a n t p a r a m e t e r s , t h i s i s a u s e f u l way o f d e s c r i b i n g l a g s . I n r e a l i t y , h o w e v e r , o p e r a t i o n d u r a t i o n s a r e d e c i s i o n v a r i a b l e s . T h u s , when t h e l a g i s d e f i n e d i n t i m e u n i t s , e v e r y t i m e a cha n g e i s made t o t h e o p e r a t i o n d u r a t i o n , t h e l a g must be r e c a l c u l a t e d m a n u a l l y . To f a c i l i t a t e t h e p r o c e s s o f c h a n g i n g t h e d u r a t i o n s o f o p e r a t i o n s , i t i s s u g g e s t e d t h a t l a g s be e n t e r e d as p e r c e n t a g e s o f o p e r a t i o n d u r a t i o n s . When t h e o p e r a t i o n d u r a t i o n s a r e c h a n g e d , t h e c o m p u t e r c a n a u t o m a t i c a l l y r e c a l c u l a t e t h e l a g v a l u e s t o be u s e d i n t h e n e t w o r k a n a l y s i s . 6.3.3.3.3 REPETITIVE CONSTRUCTION AND THE P-MATRIX A r e p e t i t i v e c o n s t r u c t i o n p r o j e c t i s c h a r a c t e r i z e d by a number o f i d e n t i c a l o r v e r y s i m i l a r a s s e m b l y u n i t s . C o n s t r u c t i o n o f an a s s e m b l y u n i t i s i n i t i a t e d by one cre w t h a t p e r f o r m s an o p e r a t i o n a t t h e l o c a t i o n w h i c h w i l l be o c c u p i e d by t h e p h y s i c a l f a c i l i t y . O t h e r c r e w s t h e n f o l l o w t o c a r r y o u t t h e o p e r a t i o n s r e q u i r e d t o c o m p l e t e t h e c o n s t r u c t i o n o f t h e a s s e m b l y . T h i s i s t h e s e q u e n t i a l c r e w 113 s y s t e m d e s c r i b e d by B o l i n q [ 1 2 ] . The c o m p l e t e s e q u e n c e of o p e r a t i o n s r e q u i r e d t o c o n s t r u c t a t y p i c a l a s s e m b l y i s c a l l e d t h e " t y p i c a l c y c l e " . E v e n t h o u g h t h e t y p i c a l c y c l e c a n be i d e n t i f i e d as a d i s t i n c t s e q u e n c e o f o p e r a t i o n s , c o n s t r u c t i o n o f t h e a s s e m b l y u n i t s a r e n o t i n d e p e n d e n t o f e a c h o t h e r . I n t h e c o n s t r u c t i o n o f a h i g h - r i s e b u i l d i n g , f o r e x a m p l e , w h i l e some c r e w s a r e s t i l l p e r f o r m i n g t h e i r a s s i g n e d o p e r a t i o n s i n a c o n s t r u c t i o n c y c l e , t h e c r e w t h a t has i n i t i a t e d and c o m p l e t e d i t s o p e r a t i o n ( s ) i n t h e p a r t i c u l a r c y c l e c o u l d h a v e i n i t i a t e d a n o t h e r c o n s t r u c t i o n c y c l e . T h u s , two o r more c o n s t r u c t i o n c y c l e s c a n be i n p r o g r e s s a t any one t i m e and o v e r l a p e a c h o t h e r . F o r e x a m p l e , w h i l e t h e f o r m w o r k d i s m a n t l i n g c r e w s a r e w o r k i n g on t h e 3 r d c o n s t r u c t i o n c y c l e ( o r 3 r d f l o o r a s s e m b l y ) , t h e f o r m w o r k i n s t a l l i n g c r e w c o u l d be w o r k i n g on t h e 4 t h c o n s t r u c t i o n c y c l e ( o r 4 t h f l o o r a s s e m b l y ) . The smooth t r a n s i t i o n o r r e a s s i g n m e n t o f l a b o u r c r e w s f r o m one c y c l e t o t h e n e x t i s c r i t i c a l t o a v o i d i n g i d l e t i m e and r e s o u r c e c o n f l i c t s . To i d e n t i f y c l e a r l y t h e i n t e r f a c e b e t w e e n c y c l e s and t h e t r a n s i t i o n f r o m one c y c l e t o t h e n e x t , t h e s p e c i f i c a s s e m b l y d i v i s i o n ( u n i t ) on w h i c h an o p e r a t i o n i s b e i n g p e r f o r m e d must be i d e n t i f i e d . The e x t e n t t o w h i c h t h e o p e r a t i o n s i n e a c h d i v i s i o n must be d e f i n e d i n t h e P - m a t r i x d e p e n d s on t h e d e g r e e t o w h i c h t h e c y c l e s o v e r l a p . The o p e r a t i o n s d e f i n e d i n t h e P - m a t r i x must d e s c r i b e t h e c o m p l e t e c o n s t r u c t i o n c y c l e o f an a s s e m b l y u n i t . 114 I n a d d i t i o n , a s m a l l number o f n o n - t y p i c a l a s s e m b l y u n i t s e x i s t s f o r most r e p e t i t i v e p r o j e c t s . S o m e t i m e s , t h e d e v i a t i o n s o f t h e s e n o n - t y p i c a l u n i t s m i g h t be s i g n i f i c a n t enough t o r e q u i r e m o d i f i c a t i o n t o t h e t y p i c a l c o n s t r u c t i o n c y c l e d e s i g n . T r a n s i t i o n s b e t w e e n n o n - t y p i c a l and t y p i c a l c o n s t r u c t i o n c y c l e s must a l s o be c o n s i d e r e d i n t h e c y c l e p l a n n i n g p r o c e s s . 6 . 3 . 3 . 3 . 4 SEQUENCING OPERATIONS WITH THE P-MATRIX F i g u r e 6.9 shows an e x a m p l e o f s e q u e n c i n g t h e d e f i n e d o p e r a t i o n s i n m a t r i x f o r m a t . The c o n s t r u c t i o n c y c l e d e s i g n o f t h e 4 t h f l o o r a s s e m b l y i s b e i n g f o r m u l a t e d . The t o t a l work q u a n t i t i e s f o r e a c h o p e r a t i o n c a n be c a l c u l a t e d a u t o m a t i c a l l y f r o m t h e s u b a s s e m b l y and c a t e g o r y - c o m p o n e n t d i m e n s i o n s o f f l o o r a s s e m b l y d i v i s i o n s 3 and 4 d e f i n e d i n t h e p r o b l e m d e f i n i t i o n p r o c e s s . The o p e r a t i o n DsmSlbFm-1, D i s m a n t l e S l a b Formwork S e c t i o n #1, o f t h e 3 r d f l o o r a s s e m b l y (Assm 1 D i v . 3) i s i d e n t i f i e d as t h e i m m e d i a t e p r e d e c e s s o r t o t h e o p e r a t i o n I n s S l b F m - l , I n s t a l l S l a b Formwork S e c t i o n #1, o f t h e 4 t h f l o o r a s s e m b l y (Assm' D i v . 4 ) . The o p e r a t i o n R b r S l b - 1 , R e b a r S l a b S e c t i o n #1 has a S t a r t - t o - S t a r t r e l a t i o n w i t h t h e o p e r a t i o n S l v S l b - 1 , I n s t a l l S l e e v i n g s i n S l a b #1, w i t h a l a g of 80% t h e d u r a t i o n o f R b r S l b - 1 . 115 6 . 3 . 3 . 4 ESTIMATE AND ASSIGN RESOURCES The p u r p o s e f o r e v a l u a t i n g d i f f e r e n t c o n s t r u c t i o n t e c h n o l o g i e s and methods i s t o d e s i g n t h e most e f f e c t i v e s o l u t i o n , i n t e r m s of l a b o u r , h a r d w a r e and s p e c i a l e q u i p m e n t c o s t s , w i t h i n t i m e and o t h e r p r o j e c t c o n s t r a i n t s . The c o s t o f l a b o u r a c c o u n t s f o r a m a j o r p o r t i o n o f t h e t o t a l c o s t o f any c o n s t r u c t i o n p r o j e c t . T h e r e f o r e , c a r e f u l p l a n n i n g i s r e q u i r e d t o e l i m i n a t e l a b o u r i d l e t i m e . Use o f h a r d w a r e and s p e c i a l e q u i p m e n t must be m a x i m i z e d t o m i n i m i z e t h e c o s t . Work s p a c e c o n s t i t u t e a n o t h e r r e s o u r c e t h a t h a s t o be managed c a r e f u l l y . P r o p e r s i t e p l a n n i n g h e l p s e n s u r e t h a t a l l c o n s t r u c t i o n o p e r a t i o n s c a n p r o g r e s s i n a smooth manner. D e t a i l e d s i t e p l a n n i n g r e q u i r e s t h e u s e o f s c h e m a t i c m o d e l s and a g r a p h i c s i n t e r f a c e b e t w e e n t h e c o m p u t e r and t h e s y s t e m u s e r . T r e a t m e n t o f t h i s r e s o u r c e i s b e y o n d t h e s c o p e o f t h i s t h e s i s . I n t h e a c t i v i t y d e s i g n e n v i r o n m e n t d e v e l o p e d , work s p a c e , h o w e v e r , c a n be t r e a t e d as a s p e c i a l r e s o u r c e t o be s h a r e d by c o n s t r u c t i o n o p e r a t i o n s . The o b j e c t i v e o f t h i s s u b s e c t i o n i s t o d e s c r i b e a f a c i l i t y t h a t a s s i s t s i n t h e r e s o u r c e a s s i g n m e n t p r o c e s s . An e n v i r o n m e n t i s p r o v i d e d where r e s o u r c e s c a n be a s s i g n e d i n a manner t h a t r e f l e c t s t h e a c t u a l c o n s t r u c t i o n p r o c e s s . The p r o c e s s e s o f e s t i m a t i n g r e s o u r c e r e q u i r e m e n t s and a s s i g n i n g l a b o u r c r e w s and s p e c i a l r e s o u r c e s t o p e r f o r m t h e c o n s t r u c t i o n o p e r a t i o n s w i l l be d e s c r i b e d . The p r i n c i p l e s o f a s s e m b l y l i n e b a l a n c i n g h a v e been a d o p t e d f o r e s t i m a t i o n o f 116 r e s o u r c e r e q u i r e m e n t s . L a b o u r r e s o u r c e s a r e a s s i g n e d as c r e w s r a t h e r t h a n as i n d i v i d u a l w o r k e r s . H a r d w a r e and work s p a c e a r e c o n s i d e r e d as s p e c i a l r e s o u r c e s and c a n be a s s i g n e d t o a c o n s t r u c t i o n o p e r a t i o n . R e s o u r c e s c a n be a s s i g n e d t o an o p e r a t i o n f o r p a r t o f i t s d u r a t i o n . 6.3.3.4.1 CURRENT PRACTICE AND RESOURCE ASSIGNMENT C u r r e n t l y a v a i l a b l e c o n s t r u c t i o n m o d e l i n g t e c h n i q u e s and s y s t e m s f a i l t o a s s i s t d e c i s i o n m a k e r s i n r e s o u r c e a l l o c a t i o n b e c a u s e o f t h e i r i n a b i l i t y t o r e f l e c t t h e a c t u a l p r o c e s s o f l a b o u r a s s i g n m e n t . The f o l l o w i n g a d d i t i o n a l p r o b l e m s w i t h t h e c u r r e n t p r a c t i c e o f r e s o u r c e a s s i g n m e n t c a n be i d e n t i f i e d : (1) I n t h e t r a d i t i o n a l a p p r o a c h t o c o n s t r u c t i o n p l a n n i n g , d u r a t i o n s a r e f i r s t a s s i g n e d t o c o n s t r u c t i o n a c t i v i t i e s f o r a CPM a n a l y s i s , and t h e n r e s o u r c e s a r e a s s i g n e d c o n s i s t e n t w i t h t h e s e d u r a t i o n s t o p e r m i t a r e s o u r c e a n a l y s i s . T h e s e r e s o u r c e r e q u i r e m e n t s a r e c a l c u l a t e d m a n u a l l y f r o m q u a n t i t y t a k e - o f f d a t a and s t a n d a r d p r o d u c t i v i t y d a t a . T h e i r e s t i m a t i o n t o meet a " t a r g e t c y c l e t i m e " i s p a r t o f t h e p r o c e s s o f t e n i d e n t i f i e d as b a c k w a r d p l a n n i n g , i . e . s e t t h e d u r a t i o n , t h e n a l l o c a t e t h e r e s o u r c e s t o a c h i e v e i t . C u r r e n t l y a v a i l a b l e c o n s t r u c t i o n m o d e l i n g t e c h n i q u e s and s y s t e m s f a i l t o a s s i s t i n t h e b a c k w a r d p l a n n i n g p r o c e s s . 117 (2) In adopting currently available modeling techniques and systems, labour resources have to be assigned as individual workers; for example, 4 carpenters and 1 general labourer could be assigned to i n s t a l l slab formwork. No proper i d e n t i f i c a t i o n is given to labour groups to allow them to be tracked as a unit from operation to operation. In r e a l i t y , labour crews are formed and assigned to carry out certain sets of operations. Once the crews are formed, their members work together for extended periods of time except when conditions reguire some crews to be s p l i t temporarily. (3) Currently available construction modeling techniques and systems also f a i l to r e f l e c t the actual resource assignment process because they require resources to be assigned to an operation for i t s complete duration. In practice, certain resources are employed by a construction operation only for part of i t s duration; for example, the tower crane may be required for only two hours during the eight hour duration of the formwork dismantling operation. One way to treat this problem is by decomposing an operation into sub- operations such that resources can be assigned to one of the sub-operations instead of the complete operation. The process, however, increases the number of operations defined and make the network lo g i c more d i f f i c u l t to comprehend. 118 I n t h e f o l l o w i n g s u b s e c t i o n s , t h e p r o b l e m s i d e n t i f i e d w i l l be t r e a t e d . 6 . 3 . 3 . 4 . 2 ALB AND ESTIMATION OF RESOURCE REQUIREMENTS I n t h e a s s e m b l y l i n e b a l a n c i n g p r o c e d u r e d e s c r i b e d i n c h a p t e r 5, " p e r f e c t - b a l a n c e " i s u s e d as t h e o b j e c t i v e t o e s t i m a t e t h e t o t a l r e s o u r c e p o o l r e g u i r e d . A l t h o u g h p e r f e c t b a l a n c e c a n n o t u s u a l l y be a c h i e v e d i n t h e d y n a m i c c o n s t r u c t i o n e n v i r o n m e n t , and e v e n i n t h e more s t a t i c m a n u f a c t u r i n g e n v i r o n m e n t , i t s e r v e s as a g o a l and a benchmark i n f o r m u l a t i n g an e f f e c t i v e d e s i g n s o l u t i o n . When more r e s o u r c e s a r e r e q u i r e d t h a n t h e e s t i m a t e d v a l u e s u n d e r p e r f e c t b a l a n c e , i t i n d i c a t e s t h a t f u r t h e r i m p r o v e m e n t t o t h e d e s i g n m i g h t s t i l l be f e a s i b l e . T h i s p r i n c i p l e w i l l be u s e d t o a s s i s t i n t h e b a c k w a r d p l a n n i n g p r o c e s s o f r e s o u r c e a s s i gnment. F i g u r e 6.10(a) shows a c o m p u t e r i n p u t f o r m a t t h a t c a n be u s e d i n t h e a c t i v i t y d e s i g n d e c i s i o n s u p p o r t s y s t e m . The work c a t e g o r y g r o u p o f t h e a c t i v i t y i s f i r s t i d e n t i f i e d . U s i n g t h e d i m e n s i o n s o f s u b a s s e m b l i e s and work c a t e g o r y c o m p o n e n t s f r o m t h e p r o b l e m d e f i n i t i o n p r o c e s s , and u s i n g t h e u n i t p r o d u c t i o n r a t e s o f t h e s e l e c t e d p r o d u c t i o n t e c h n o l o g i e s , t h e c o m p u t e r c a n c a l c u l a t e t h e t o t a l man-hour r e q u i r e m e n t s f o r e a c h t r a d e t o c o n s t r u c t t h e a s s e m b l y u n i t . By d i v i d i n g t h e t o t a l man-hour r e q u i r e m e n t s by t h e t a r g e t c y c l e t i m e , t h e numbers o f men r e q u i r e d f o r e a c h t r a d e c a n 119 be c a l c u l a t e d . T h e s e number c a n t h e n be f i n e t u n e d by t h e u s e r t o r e f l e c t c o n s i d e r a t i o n s w h i c h c a n n o t be q u a n t i f i e d . I n t h e e x a m p l e shown, t h e t o t a l r e s o u r c e r e q u i r e m e n t s f o r t h e C o n c r e t e work c a t e g o r y g r o u p , w h i c h i n c l u d e a l l o p e r a t i o n s i n a t y p i c a l h i g h - r i s e s t r u c t u r e c y c l e t h a t a r e n o r m a l l y p e r f o r m e d by t h e g e n e r a l c o n t r a c t o r , a r e c a l c u l a t e d . The numbers o f men r e q u i r e d f o r e a c h l a b o u r t y p e a r e r o u n d e d and a r e u s e d as t h e maximum r e s o u r c e l e v e l s f o r t h e s t r u c t u r e c y c l e . The g o a l f o r t h e management i s t h e n t o b a l a n c e t h e c o n s t r u c t i o n o p e r a t i o n s s u c h , t h a t t h e t o t a l l a b o u r r e s o u r c e s u s e d by t h e o p e r a t i o n s w i l l be b e l o w t h e s e l e v e l s . S p e c i a l r e s o u r c e s s u c h as a t o w e r c r a n e a n d p r e f a b r i c a t i o n a r e a s a r e n o t n e c e s s a r i l y a c t i v e f o r t h e c o m p l e t e c o n s t r u c t i o n c y c l e d u r a t i o n . C o n s e q u e n t l y , t h e a s s u m p t i o n o f p e r f e c t b a l a n c e c a n n o t be u s e d t o e s t i m a t e t h e t o t a l r e s o u r c e r e q u i r e m e n t s . The d e c i s i o n maker must u s e h i s p e r s o n a l j u d g m e n t o r draw on h i s e x p e r i e n c e t o a s s i g n t h e maximum l e v e l s o f m a j o r e q u i p m e n t and h a r d w a r e . An e x a m p l e o f a c o m p u t e r i n p u t f o r m a t f o r a s s i g n i n g maximum l e v e l s o f s p e c i a l r e s o u r c e s i s shown i n f i g u r e 6 . 1 0 ( b ) . I n t h i s f i g u r e , [ C o s t / U n i t ] i n d i c a t e s t h e c o s t f o r e m p l o y i n g t h e r e s o u r c e p e r t i m e u n i t and i s u s e d i n c o s t a n a l y s i s o f t h e d e s i g n s o l u t i o n ; [Max. U n i t ] i n d i c a t e s t h e maximum number o f u n i t s a v a i l a b l e . F i g u r e 6 . 1 0 ( a ) : E s t i m a t e and a s s i g n l a b o u r poo l 120 Estimate by Work Category-Group : Yes / No Select Work Category-Group : CONCRETE CIVIL/SITE CONCRETE Formwork Rebar Pour Ing Finishing To ta l : (Carpenter ! 240 20 260 (Masonry! (Steel Wkrl (Gen. L a b r l 80 112 192 160 160 Enter Desired Cycle Time : ( 35) HOURS / DAYS Estimated Resource Requirements (If perfectly balanced) 7.4 5.5 Enter Resource Pool [ 8 1 1 6 1 Enter Special Resource Pool : ' Ye$ / No 4.6 ( 5 J 20 10 80 8 118 <Mn-Hr> 3.4 <Man> t 4 1 <Man> F i g u r e 6 . 1 0 ( b ) : A s s i g n s p e c i a l r e s o u r c e pool SPECIAL RESOURCE POOL : II.D.l [Type! [Description] Tcrane Equipment Tower Crane CncrPmp Equipment Concrete Pump SlbFm Hardware EFCO Floating Slab Form ClmnFm Hardware EFCO Modular Column Form ZonSI WorkZone Storage Yard Zone 1 ZonW2 WorkZone Active Work Zone 2 [Cost/Unltl [Max. Units! $1000.00 / Day $125.25 / Hour $750.00 / Week $375.00 / Week 1 1 10 9 1 1 F i g u r e 6.10: E s t i m a t e and a s s i g n r e s o u r c e p o o l s 121 6 . 3 . 3 . 4 . 3 ASSIGNING LABOUR CREWS F i g u r e s 6.11(a) and 6.11(b) show how l a b o u r r e s o u r c e s c a n be a s s i g n e d i n a r e a l i s t i c manner. I n f i g u r e 6 . 1 1 ( a ) , t h e l i s t o f d e f i n e d o p e r a t i o n s a r e r e t r i e v e d and d i s p l a y e d t o t h e u s e r . A f t e r an o p e r a t i o n has been s e l e c t e d f o r r e s o u r c e a s s i g n m e n t , t h e u s e r i s p r o m p t e d t o e n t e r t h e o p e r a t i o n d u r a t i o n . U s i n g t h e ALB p r i n c i p l e t h e l a b o u r r e s o u r c e s r e q u i r e d t o p e r f o r m t h e o p e r a t i o n w i t h i n t h e s p e c i f i e d d u r a t i o n c a n be c a l c u l a t e d by t h e c o m p u t e r b a s e d on t h e work a s s i g n m e n t o f t h e o p e r a t i o n and t h e s e l e c t e d c o n s t r u c t i o n t e c h n o l o g y . C r e w s a r e t h e n f o r m e d , u s i n g t h e c a l c u l a t e d r e s o u r c e r e q u i r e m e n t s as t h e g u i d e l i n e , and a s s i g n e d t o p e r f o r m t h e o p e r a t i o n . By i d e n t i f y i n g t h e c o m m i t t e d r e s o u r c e as c r e w s , t h e s e q u e n c e o f o p e r a t i o n s p e r f o r m e d by e a c h c r e w c a n be i d e n t i f i e d f o r p r o d u c t i v i t y c o n t r o l and s t u d y . The f o l l o w i n g s c a s e s i n r e s o u r c e a s s i g n m e n t a r e w o r t h y o f n o t e : (1) Crews assigned to more than one operation O p e r a t i o n s t h a t do n o t o v e r l a p i n t i m e c a n be p e r f o r m e d by t h e same c r e w ; f o r e x a m p l e , w i t h i n a f i v e day c o n s t r u c t i o n c y c l e , a f o r m w o r k c r e w c a n p e r f o r m t h e o p e r a t i o n o f i n s t a l l i n g s l a b f o r m w o r k on one day and p e r f o r m t h e o p e r a t i o n o f i n s t a l l i n g b u i l d i n g c o r e f o r m w o r k on n e x t . F o r t h i s c a s e , t h e management c a n a s s i g n t h e same cr e w t o two o r more o p e r a t i o n s . As o p e r a t i o n s t h a t s h a r e t h e same 122 c r e w c a n n o t o v e r l a p i n t i m e , t h e y a r e t r e a t e d as h a v i n g f i n i s h - t o - s t a r t r e l a t i o n s h i p s i n t h e n e t w o r k a n a l y s i s . (2) Mixed Crew and M u l t i p l e Crews The t e r m m i x e d c r e w i s u s e d t o d e s c r i b e a c r e w made up o f more t h a n one l a b o u r t y p e s . I n t h e e x a m p l e shown i n f i g u r e 6.11, a m i x e d c r e w o f 3 c a r p e n t e r and 1 g e n e r a l l a b o u r e r c a n be f o r m e d t o i n s t a l l t h e s l a b f o r m w o r k s e c t i o n . H o wever, t h i s w o u l d mean t h a t t h e g e n e r a l l a b o u r w i l l be i d l e more t h a n 50% o f t h e t i m e . To s o l v e t h i s p r o b l e m , one c a n a s s i g n a c r e w o f 3 c a r p e n t e r s f o r t h e c o m p l e t e o p e r a t i o n d u r a t i o n and a cr e w o f 1 g e n e r a l l a b o u r e r f o r 50% o f t h e t i m e . T h i s c a s e c a n t h e n be i d e n t i f i e d as a m u l t i p l e - c r e w a s s i g n m e n t one. The u s e o f t h e a s s i g n m e n t p r o c e d u r e t h e n a l l o w s t h e g e n e r a l l a b o u r t o be a s s i g n e d t o a n o t h e r o p e r a t i o n when no l o n g e r n e e d e d . To s o l v e t h e s e c o n d p r o b l e m i n t h e t r a d i t i o n a l a p p r o a c h t o c o n s t r u c t i o n p l a n n i n g and t o a l l o w l a b o u r r e s o u r c e s t o be e m p l o y e d more e f f e c t i v e l y , t h e a d d i t i o n a l a t t r i b u t e s o f [ D u r a t i o n , L a g ] a r e d e f i n e d f o r e a c h crew a s s i g n m e n t . D u r a t i o n i n d i c a t e s t h a t t h e a s s i g n e d c r e w i s t o be e m p l o y e d o n l y f o r t h i s s p e c i f i e d p e r i o d o f t i m e o r p e r c e n t a g e o f t h e o p e r a t i o n d u r a t i o n ; l a g i n d i c a t e s t h e t i m e when t h e cr e w w i l l be e m p l o y e d i n t e r m s o f t i m e f r o m t h e s t a r t o f t h e o p e r a t i o n ; e x a m p l e s a r e d e s c r i b e d i n t h e n e x t s e c t i o n . 123 6 . 3 . 3 . 4 . 4 ASSIGNING SPECIAL RESOORCES Figures 6.12(a) and 6.12(b) show the computer input formats for assigning special resources to construction operations. A l i s t of the special resource type i d e n t i f i e d can be retrieved and the corresponding resources assigned to the sp e c i f i e d operation. For the example shown in figure 6.12(a), the tower crane is to be employed in the operation InsSlbFm-l after 20% of the operation is completed and for 40% of the t o t a l operation duration. In the example shown in figure 6.12(b), ten units of the hardware SlbFm (EFCO slab formwork) are available, f i v e units are assigned to the operation InsSlbFm-l. The resource is employed for 100% of the operation duration. F i g u r e 6 . 1 1 ( a ) : S e l e c t o p e r a t i o n to a s s i g n r e s o u r c e s 124 CREW and SPECIAL RESOURCE ASSIGNMENT Select from operation l i s t : InsSlbFm-l INol 1 I 2 3 4 5 6 11.D.l ir»sF«iSlb-1 RbSlb-1 SlvSlb- l CncrSlb-1 CureSIb-1 DsmFmSIb-1 [Description! Install Slab Formwork BAY<A1,A2,B1,B2fC1> Rebar Slab BAY<A1,A2,B1,B2,C1> Mechanical Sleevings BAY<A1,A2,B1,B2,C1> Pour Concrete Slab BAY<A1,A2,B1,B2,C1> Cure Concrete Slab BAY<A1,A2,B1,B2,C1> Dismantle Slab Formwork BAY<A1,A2,B1,B2,C1> F i g u r e 6 . 1 1 ( b ) : A s s i g n l abour crew to meet t a r g e t o p e r a t i o n d u r a t i o n Operation : InsSlbFm-l Min. Crew Size : 3 I n s t a l l Slab Formwork BAY<A1,A2.B1,B2,C1,C2> Neglect : No / Yes 2 Content : 480 M RESOURCE POOL : [Carpenter] To ta l : 8 Balance : ' 5 CREW FORMED : SlbFrmCrw-1 3 SIbRbCrw-l [Masonry! (Steel Wkr! [Gen. L a b r l 6 5 4 <Man> Enter Desired Operation Duration : [ 7 1 HOURS / DAYS Estimated Resource Requirements : 2.5 0.5 <Man> ASSIGN CREW : ( SlbFmCrw-1 ! 3 I Enter IDuratlon;Lag! <$duratlon or hr:mln> : I 100*;0 ] ADD ANOTHER CREW : No / Yes ASSIGN SPECIAL RESOURCES : No / 'Yes ' F i g u r e 6 . 1 1 : A s s i g n i n g l a b o u r c r e w s t o o p e r a t i o n s F i g u r e 6 . 1 2 ( a ) : S e l e c t s p e c i a l r e s o u r c e type t o a s s i g n Operation : InsSlbFm-1 I n s t a l l S lab Formwork BAY<AI,A2,B1,B2,C1,C2> ASSIGN SPECIAL RESOURCES : EQUIPMENT HARDWARE WORK-ZONE Select EQUIPMENT from l i s t : TCrano [I.D.J (Description) (Cost/UnltJ [Max. UnltsJ TCrano Tower Crane $1000.00 / Day 1 Enter No. of Units to be Assigned : [ 1 J Enter [Duratlon;Lagl <ifdurotlon or hr:mln> : ( 20Jf;40£ 1 ASSIGN ANOTHER SPECIAL RESOURCE : No / J F i g u r e 6 . 1 2 ( b ) : A s s i g n s p e c i a l r e s o u r c e s t o o p e r a t i o n Operation : InsSlbFm-1 I n s t a l l S lab Formwork BAY<A1,A2,B1,B2,C1,C2> ASSIGN SPECIAL RESOURCES : EQUIPMENT HARDWARE Select HARDWARE from l i s t : SlbFm II.D. 1 SlbFm ClmnFm (Description) EFCO Floating Slab Form EFCO Modular Column Form WORK-ZONE (Cost/Unl+1 $750.00 / Week $375.00 / Week Enter No. of Units to be Assigned : [ 5 1 Enter (DuratIon;Lagl <$durat!on or hr:mln> : ASSIGN ANOTHER SPECIAL RESOURCE : fNo"| / Yes [ 100*;0 ) [Max. Unltsl 10 F i g u r e 6.12: A s s i g n i n g s p e c i a l r e s o u r c e s t o o p e r a t i o n s 126 6.3.4 MODULE 4 - SOLUTION ANALYSIS As m e n t i o n e d i n s e c t i o n 6.2, t h e r e l a t i o n s h i p b e t w e e n t h e c o m p u t e r and t h e d e c i s i o n maker i n a d e c i s i o n s u p p o r t s y s t e m c a n be d e s c r i b e d as s y m b i o t i c . I n o t h e r w o r d s , t h e c o m p u t e r a n d t h e d e c i s i o n maker d e p e n d on e a c h o t h e r t o s o l v e a p r o b l e m . I n t h e d e s c r i p t i o n o f t h e d e c i s i o n s u p p o r t s y s t e m f o r a c t i v i t y d e s i g n , t h e c o m p u t e r f u n c t i o n s m a i n l y t o p r o v i d e an e n v i r o n m e n t i n w h i c h management p e r s o n n e l c a n f o r m u l a t e a d e s i g n s o l u t i o n i n a r e a l i s t i c manner. A n o t h e r m a j o r f u n c t i o n o f t h e c o m p u t e r i s t o a n a l y z e t h e d e s i g n s o l u t i o n f o r m u l a t e d by t h e u s e r i n o r d e r t o p r o d u c e an o v e r a l l s c h e d u l e . C o n f l i c t s b e t w e e n o p e r a t i o n s i n u s i n g s h a r e d r e s o u r c e s must be i d e n t i f i e d and t h e e f f e c t i v e n e s s i n u s i n g r e s o u r c e s must be d e t e r m i n e d . F i n d i n g s f r o m t h e a n a l y s i s must be c o m m u n i c a t e d t o t h e u s e r f o r p o s s i b l e m o d i f i c a t i o n and i m p r o v e m e n t . 6.3.4.1 CURRENT PRACTICE IN RESOURCE ANALYSIS AND CYCLE DESIGN T r a d i t i o n a l l y , r e s o u r c e s a r e a s s i g n e d t o a c t i v i t i e s and r e s o u r c e p r o f i l e s a r e p r o d u c e d t o s t u d y t h e l a b o u r r e s o u r c e u s a g e . I f a r e s o u r c e p r o f i l e i n d i c a t e s t h a t t h e r e s o u r c e u s a g e f l u c t u a t e s t o o much o r t h a t t h e maximum l e v e l o f a r e s o u r c e e x c e e d s t h e maximum l e v e l a v a i l a b l e , t h e n 127 management must make t h e a p p r o p r i a t e d e c i s i o n s t o s o l v e t h e p r o b l e m . Some p r o b l e m s c a n be r e s o l v e d t h r o u g h t h e u s e o f l e v e l l i n g and a l l o c a t i o n a l g o r i t h m s w h i c h r e l y on t h e u s e o f a c t i v i t y f l o a t s t o a c h i e v e s p e c i f i e d o b j e c t i v e s - c o n t i n u i t y o f r e s o u r c e u s a g e , h o w e v e r , i s g e n e r a l l y n o t c o n s i d e r e d a d e s i g n o b j e c t i v e by most a l g o r i t h m s . The g o a l i n c o n s t r u c t i o n c y c l e d e s i g n i s t o a c h i e v e a b a l a n c e d c y c l e . I n o t h e r w o r d s , t h e g o a l i s t o e l i m i n a t e a l l f l o a t s b e t w e e n o p e r a t i o n s s o t h a t t h e y c a n p r o g r e s s s m o o t h l y w i t h o u t i n t e r r u p t i o n . An u n i n t e r r u p t e d c y c l e d e s i g n a l s o i n d i c a t e s t h a t t h e r e s o u r c e s l e v e l w i l l r e m a i n s c o n s t a n t . The u s e f u l n e s s o f r e s o u r c e l e v e l l i n g f o r d e s i g n i n g c o n s t r u c t i o n c y c l e s i s t h e r e f o r e q u e s t i o n a b l e . W h i l e a r e s o u r c e c o n s t r a i n e d s c h e d u l i n g a l g o r i t h m m i g h t be a b l e t o r e s o l v e c o n f l i c t s i n u s i n g s h a r e d r e s o u r c e s , i t i s o n l y a c h i e v e d by i n t e r r u p t i n g and d e l a y i n g c o n s t r u c t i o n o p e r a t i o n s ; i n d o i n g s o , i t d e f e a t s t h e g o a l o f a b a l a n c e d c y c l e . A t p r e s e n t , t h e r e i s no a l g o r i t h m t h a t c a n g u a r a n t e e t h a t a b a l a n c e d c y c l e d e s i g n c a n be o b t a i n e d . The s y s t e m u s e r must d e p e n d s on h i s e x p e r i e n c e , p e r s o n a l j u d g m e n t and i n t u i t i o n , a s s i s t e d by t h e c o m p u t e r , t o f o r m u l a t e a s a t i s f a c t o r y c y c l e d e s i g n . The r e s u l t s o f t h e s o l u t i o n a n a l y s i s and t h e f o r m a t s i n w h i c h t h e y c o u l d be p r e s e n t e d a r e d e s c r i b e d i n s e c t i o n s 6.3.4.2 and 6.3.4.3 b e l o w . How 128 t h e s e r e s u l t s c a n be u s e d t o i m p r o v e t h e b a l a n c e o f t h e c y c l e d e s i g n i s d i s c u s s e d i n s e c t i o n 6 . 3 . 5 . 6.3.4.2 CRITICAL PATH METHOD FOR SOLUTION ANALYSIS Of t h e a n a l y t i c a l m o d e l s r e v i e w e d i n c h a p t e r s f o u r and f i v e , t h e c r i t i c a l p a t h method i s t h e s i m p l e s t method t h a t c a n p e r f o r m t h e r e q u i r e d a n a l y s i s and r e q u i r e s t h e l e a s t p r o g r a m m i n g e f f o r t . D i s c r e t e e v e n t s i m u l a t i o n and d e t e r m i n i s t i c m a t h e m a t i c a l p r o g r a m m i n g t e c h n i q u e s c o u l d a l s o be u s e d t o p e r f o r m t h e r e q u i r e d a n a l y s i s and p r o v i d e t h e r e q u i r e d i n f o r m a t i o n . H o w e v e r , b o t h r e q u i r e e x c e s s i v e p r o g r a m m i n g e f f o r t f o r d a y - t o - d a y u s e i n t h e f i e l d and b o t h r e q u i r e s o p h i s t i c a t e d s i m u l a t i o n and m a t h e m a t i c a l p r o g r a m m i n g s o f t w a r e t o r e s i d e i n t h e d e c i s i o n s u p p o r t s y s t e m . I n a d d i t i o n t o i t s s i m p l i c i t y , t h e c r i t i c a l p a t h method has t h e a d v a n t a g e o f h a v i n g been u s e d i n t h e c o n s t r u c t i o n i n d u s t r y f o r an e x t e n d e d p e r i o d o f t i m e and t h e u n d e r l y i n g c o n c e p t s a r e c o m p r e h e n s i b l e t o p r o j e c t management p e r s o n n e l . The c r i t i c a l p a t h method i s t h e r e f o r e a d o p t e d as an a p p r o p r i a t e a n a l y t i c a l t o o l f o r t h e d e c i s i o n s u p p o r t s y s t e m . H o w e v e r , b e c a u s e of t h e need t o c o n s i d e r t h e o v e r l a p p i n g o f c o n s t r u c t i o n c y c l e s , a s s t a t e d i n s e c t i o n 6 . 3 . 3 . 3 , a d d i t i o n a l c o m p u t e r r o u t i n e s m i g h t be n e e d e d . T h e s e r o u t i n e s w i l l n o t be t r e a t e d i n t h i s t h e s i s . 129 6.3.4.3 PRESENTATION OF ANALYSIS RESULTS A f t e r t h e t e n t a t i v e s o l u t i o n h a s been a n a l y z e d , t h e r e s u l t s h a v e t o be c o m m u n i c a t e d t o t h e u s e r s o t h a t s o l u t i o n r e f i n e m e n t c a n t a k e p l a c e . T h r e e t y p e s o f o u t p u t c a n be i d e n t i f i e d : (1) c r i t i c a l p a t h a n a l y s i s r e s u l t s , (2) s t a t u s o f c o m m i t t e d r e s o u r c e s , and (3) work s c h e d u l e s f o r l a b o u r c r e w s and s p e c i a l r e s o u r c e s . 6.3.4.3.1 CRITICAL PATH ANALYSIS RESULTS C r i t i c a l p a t h a n a l y s i s r e s u l t s c a n be p r e s e n t e d i n s e v e r a l f o r m a t s . C u r r e n t p r a c t i c e u s e s t a b u l a r o u t p u t s and b a r c h a r t s . The a c t i v i t y i n f o r m a t i o n i n c l u d e s : e a r l y s t a r t t i m e ( E S T ) , l a t e s t a r t t i m e ( L S T ) , e a r l y f i n i s h t i m e ( E F T ) , l a t e f i n i s h t i m e ( L F T ) , f r e e f l o a t (FF) and t o t a l f l o a t (TF) . F i g u r e 6.13 r e p r e s e n t one of t h e f o r m a t s i n w h i c h c r i t i c a l p a t h a n a l y s i s r e s u l t s c a n be p r e s e n t e d . A c t i v i t y p l a n n i n g a t t h e p r o d u c t i o n l e v e l r e q u i r e s t i m e u n i t s t o be i n h o u r s and m i n u t e s . Two a t t r i b u t e s t h a t c a n be u s e d t o a s s i s t t h e u s e r i n t h e d e s i g n i m p r o v e m e n t p r o c e s s h a v e been i d e n t i f i e d i n t h e t a b l e : (1) [ F F / D u r a t n ] - t h e r a t i o o f f r e e f l o a t t o t h e o p e r a t i o n d u r a t i o n . I t i n d i c a t e s t h e p e r c e n t a g e o f t i m e t h a t t h e c r e w a s s i g n e d t o t h e o p e r a t i o n w i l l be i d l e , p r e s u m i n g a l l o p e r a t i o n s s t a r t a t t h e i r e a r l i e s t t i m e . H owever, u n a v a i l a b i l i t y o f r e s o u r c e s may p r e c l u d e t h e 130 e a r l y s t a r t o f an o p e r a t i o n . Crew a s s i g n m e n t s t h e r e f o r e i m p o s e a d d i t i o n a l c o n s t r a i n t s on t h e c r i t i c a l p a t h n e t w o r k l o g i c - h a v i n g t h e same cr e w a s s i g n e d t o two o p e r a t i o n s i m p o s e s a f i n i s h - t o - s t a r t r e l a t i o n b e t w e e n them. (2) [ L b r C o s t / D u r a t n ] - t h e r a t i o o f t o t a l l a b o u r c o s t o f t h e o p e r a t i o n t o t h e o p e r a t i o n d u r a t i o n . I t p r o v i d e s a r o u g h e s t i m a t e o f how much l a b o u r c o s t c o u l d be s a v e d by e l i m i n a t i n g t h e i d l e t i m e o f an o p e r a t i o n . When t h e c y c l e d u r a t i o n has t o be s h o r t e n e d , t h i s r a t i o may h e l p i n d i c a t e w h i c h c r i t i c a l o p e r a t i o n w i l l c o s t l e s s t o s h o r t e n . The e x a c t amount o f s a v i n g o r c o s t , h o w e v e r , d e p e n d s on t h e method c h o s e n t o a c h i e v e t h e o b j e c t i v e . 6 . 3.4 . 3.2 STATUS OF COMMITTED RESOURCES I n o r d e r t o i d e n t i f y a l l c o n f l i c t s i n r e s o u r c e u s a g e , one n o r m a l l y has t o s t u d y t h e p r o f i l e s o f e a c h r e s o u r c e t y p e . When t h e number o f r e s o u r c e t y p e s a s s i g n e d i s l a r g e , t h i s p r o c e s s c a n become t e d i o u s . F i g u r e 6.14, t h e r e s o u r c e s t a t u s t a b l e , shows how summary i n f o r m a t i o n r e g a r d i n g t h e u s a g e o f s p e c i a l r e s o u r c e s - e q u i p m e n t , h a r d w a r e and work a r e a s , c a n be r e p r e s e n t e d i n t a b u l a r f o r m w h i c h c a n h e l p i d e n t i f y p r o b l e m a r e a s . The [ A c t i v e Time] and [ % I d l e ] i n d i c a t e how e f f e c t i v e l y t h e r e s o u r c e s a r e b e i n g u s e d . F o r e x a m p l e , t h e p r e f a b r i c a t i o n a r e a , l a b e l l e d P f Z o n e - A l , i s o c c u p i e d f o r 27 131 hours and is unoccupied for 8 hours (or 24%) of the 35 hours cycle. C o n f l i c t s in using the resource can also be id e n t i f i e d and the operations that are competing for i t are l i s t e d to guide the user in resolving c o n f l i c t s . In the example shown, c o n f l i c t s in using the tower crane are indicated; between 15:00 - 16:00 (working hours are measured from sta r t of the construction c y c l e ) , the operations RbrClm-Sl and InsSlbFm-3 both require the use of the tower crane; between 17:00 - 18:00, the operation InsSlbFm-3 is again competing with RbrClm-S2 for the tower crane. This information, together with use of the multiple a c t i v i t y chart described in the next section, can help management id e n t i f y quickly the problems and alternative solutions. 6.3.4.3.3 WORK SCHEDULES FOR LABOUR CREWS AND SPECIAL RESOURCES F i e l d management personnel need detailed t a c t i c a l plans to di r e c t labour crews and to schedule special resources in order to perform the construction operations for a given cycle. In the DSS for construction cycle design being developed, labour resources are assigned as crews rather than as individual workers. The multiple operation time (M.O.T.) chart shown in figure 6.16 i l l u s t r a t e s how the multiple a c t i v i t y chart described in section 4.1 can be adapted to provide detailed work schedules for crews and special resources. 132 The m u l t i p l e a c t i v i t y c h a r t i s a m o d e l i n g t e c h n i g u e i n t r o d u c e d i n i n d u s t r i a l e n g i n e e r i n g f o r work method s t u d i e s and f o r s t u d y i n g t h e b a l a n c e o f work a s s i g n m e n t s i n a s s e m b l y p r o d u c t i o n l i n e s . A l t h o u g h i t h a s been m e n t i o n e d i n t h e c o n s t r u c t i o n management l i t e r a t u r e ( H a l p i n and Woodhead [ 4 3 ] , N i c h o l i s [ 9 1 ] ) , no c o m p u t e r i z e d a p p l i c a t i o n i n c o n s t r u c t i o n p l a n n i n g h a s been d e s c r i b e d . I t c a n show t h e s e q u e n c e s o f o p e r a t i o n s p e r f o r m e d by e a c h c r e w a l o n g s i d e e a c h o t h e r and i s t h e r e f o r e u s e f u l f o r s t u d y i n g and i m p r o v i n g t h e b a l a n c e o f work a s s i g n m e n t s and i n r e s o l v i n g c o n f l i c t s i n t h e u s a g e o f s h a r e d r e s o u r c e s . The M.O.T. c h a r t c a n be d e r i v e d f r o m t h e c r i t i c a l p a t h a n a l y s i s r e s u l t s . An o p e r a t i o n i s p l o t t e d by i t s s t a r t and f i n i s h t i m e u n d e r t h e cre w ( o r c r e w s ) t h a t i s a s s i g n e d t o p e r f o r m i t . T h u s , a c o l u m n i n t h e M.O.T. c h a r t r e p r e s e n t s a work s c h e d u l e f o r t h e c o r r e s p o n d i n g l a b o u r crew o r s p e c i a l r e s o u r c e . F l o a t s , o r i m p e r f e c t b a l a n c e o f c o n s t r u c t i o n o p e r a t i o n s a r e shown as i d l e t i m e ( I DLE f o r l a b o u r c r e w s and AVA I L A B L E f o r s p e c i a l r e s o u r c e s ) . B r e a k s c a n a l s o be shown t o i n d i c a t e c o f f e e and l u n c h t i m e s . A l t h o u g h n o t shown i n t h e g i v e n e x a m p l e , i t i s a l s o p o s s i b l e t o i n d i c a t e c o n f l i c t s i n u s i n g s h a r e d r e s o u r c e s , s u c h as t h e t o w e r c r a n e and work a r e a s . How t h e M.O.T. c h a r t c a n be u s e d f o r d e s i g n i m p r o v e m e n t w i l l be d i s c u s s e d i n s e c t i o n 6.3.5. To f a c i l i t a t e t h e s t u d y o f i n t e r a c t i o n s b e t w e e n l a b o u r c r e w s and s p e c i a l r e s o u r c e s , t h e u s e r c a n e n t e r t h e o r d e r i n w h i c h t h e s e l e c t e d c r e w s and s p e c i a l r e s o u r c e s a r e t o be 133 r e p o r t e d , as shown i n f i g u r e 6.15. F o r e x a m p l e , t h e work s c h e d u l e s f o r two work a r e a s c a n be s e l e c t e d f o r d i s p l a y s i d e by s i d e t o d e t e r m i n e w h e t h e r o v e r c r o w d i n g i n one a r e a c a n be e l i m i n a t e d by a s s i g n i n g c e r t a i n o p e r a t i o n s t o t h e o t h e r work a r e a , o r by c h a n g i n g t h e s e q u e n c e o f c o n s t r u c t i o n o p e r a t i o n s . * * C R I T I C A L P A T H A N A L Y S I S R E S U L T S * * A c t i v i t y Duration: 3 6 : 3 0 Operation 1.0. EST LST EFT LST FF Duratn FF Dura+n Lbr Cos1 Duratn I n s S l b F m - l ( E l e v . 4 ) 0 : 0 0 0 : 0 0 7 : 0 0 7 : 0 0 0 0 : 0 0 7 : 0 0 0 . 0 0 $ 1 1 2 . 5 0 l n s S l b F m - 2 ( E l e v . 4 ) 7 : 0 0 7 : 0 0 1 4 : 0 0 1 4 : 0 0 0 0 : 0 0 7 : 0 0 0 . 0 0 $ 1 1 2 . 5 0 l n s S l b F m - 3 ( E l e v . 4 ) 1 4 : 0 0 1 4 : 0 0 2 1 : 0 0 2 1 : 0 0 0 : 0 0 7 : 0 0 0 . 0 0 $ 1 1 2 . 5 0 R b r C w - 1 ( E l e v . 5 ) 2 4 : 0 0 2 4 : 0 0 2 8 : 0 0 2 8 : 0 0 0 0 : 0 0 4 : 0 0 0 . 0 0 $ 8 7 . 5 0 R b r C w - 2 ( E l e v . 5 ) 2 8 : 0 0 2 5 : 0 0 3 3 : 0 0 3 5 : 0 0 2 : 0 0 * • • • 5 : 0 0 « • • • 0 . 4 0 • • • « $ 8 7 . 5 0 Figure 6.13: C r i t i c a l path a n a l y s i s r e s u l t s 13 S P E C I A L RESOURCE STATUS C y c l e Time : 35:00 R e s o u r c e I . D . PfZone-A1 PfZone-A2 WrkZon-E3 A c t i v e * l d l e Max T ime A v a i l xx:xx 27:00 30:00 35:00 x.xx 0.24 0.15 0.00 M a x . U s e d T C r a n e ConfI l e t s : 15:00 - 16:00 17:00 - 18:00 RbrC lm-S l ; InsSlbFm-3 InsSlbFm-3; RbrClm-S2 Figure 6.14: R e s o u r c e S t a t u s T a b l e MULTIPLE OPERATION TIME CHART : Report to : Screen / P r i n t e r Report ALL Crews/Resources : Yes / No Select Crews/Resources to Report : Crew/1 Crew/2 Crew/3 Crew/4 Crew/5 Crew/6 Crew/7 Crew/8 FmCrw#1 FmCrw#2 RbrCrw#1 RbrCrw#2 CnCrCrw/1 TCrane GenLbr#1 PfZon#1 Crew/Resource I.D. Descr ip t ion FmCrw#1 Formwork crew /I, 6 carpenters, 1 general labour FnCrw#2 Formwork crew #2, 5 carpenters CnCrCrw#2 Concrete finishing and clean-up crew, 3 masons, 1 general labour i g u r e 6.15: S e l e c t crews and s p e c i a l resources to report i n M.O.T. cha M U L T I P L E O P E R A T I O N T I M E C H A R T A C T ' V A C T ' L T I M E T I M E 111 121 131 141 151 F u C r w / l FnCr«/2 R b r C r w / l R b r C r w / 2 C n c r / 1 161 T C r o n e 171 181 G o n L b r / l P f Z o n / l Day 1 0 : 0 0 7 :00 7:30 8 : 0 0 8 : 3 0 9 : 0 0 9 : 3 0 10:00 10:30 11:00 II :30 12:00 12:30 1:00 1:30 2:00 2:30 3:00 7:00 3 :30 Day 2 Q j/nS | b,FjH~ 1 iiaatBtoiaa l a a a i u i i i t i a aaamam*.amjtm itaBiadaio ( E l e v . 3) InsSlbFm-1 PfCwRbr-1 P f C l m R b r - S l P r C l m s ( E l e v . 4) ( E l e v . 5) ( E l e v . 5) ( E l e v . 5) DsmSIbFm-2 x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x A V A I L A B L E I O L E InsSlbFm-1 cIis«Diaiai C l e a n - U p A V A I L A B L E E l e v . 3 P f C l n r t b r - S I i , ( E l e v . 3) P fCwRbr -2 P f C l m R b r - S 2 ( E l e v . 5) ( E l e v . 5 ) V as -« -*a* • a • a I D L E P f C l m R b r - S 2 I n s S l b - F m - . Y . _ . 7:00 7 :00 7:30 8 : 0 0 8 :30 9 : 0 0 9 : 3 0 10:00 10:30 11:00 11:30 12:00 12:30 1:00 1:30 2 :00 2:30 3 :00 14:00 3:30 Day 3 DsmS I bFm-2 «••..««.«. P f C l m R b r - S 2 A V A I L A B L E ( E l e v . 3) l n s S l b F m - 2 R b r S l b - 1 ( E l e v . 5 ) P rCrWIs ( E l e v . 4) ( E l e v . 4) ( E l e v . 5) P fC lmf)br -S2 Y DsmSlbFm-3 P f C l m R b r - S 3 ( E l e v . 5) P r C r W I s I O L E P i C l m R b r - S 3 l n s S l b F m - 2 L A V A I L A B L E x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x ( E l e v . 3) V Y Y......... I D L E l n s S l b f M - 2 14:00 7:00 7:30 8 : 0 0 8 :30 9 : 0 0 9 : 3 0 10:00 10:30 11:00 11:30 12:00 12:30 1:00 1:30 2:00 2:30 3:00 21 :00 3 :30 Q$jnS I bFlB - 3 Ba>oBBBa»a«« laniaiiiDii ••aaaistmii mammmmmaaa ( E l e v . 3) l n s S I F m - 3 R b r S l b - 2 R b r C l m - S l P r S l b - 1 ( E l e v . 4) ( E l e v . 4) ( E l e v . 3) ( E l e v . 4) V DsmClmFm-SI 1 R b r C l m - S l P r S I b 1. . I n s S l b F m - 3 I D L E x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x ( E l e v . 3) InsClmFm-SI ( E l e v . 5) RbrC lm-S2 ( E l e v . 5) Y V i . 1131 *br( I < i . . . . . . . . A V A I L A B L E R C l m - S 2 DsmClmFm-SI I n s S l b F m - 3 JL....... Day 4 2 1 : 0 0 7:00 7:30 8 : 0 0 8 : 3 0 9 :00 9 : 3 0 10:00 10:30 11:00 11:30 12:00 12:30 1:00 1:30 2:00 2:30 3 :00 28 :00 3 :30 O . T . 4 :00 4 :30 5:00 Eaaansaaaaa sans•anasue a n a a i a i a a a i i s a s a a a s a a B InsCwFm-l R b r S l b - 3 R b r C l m - S 3 P r S l b - 2 ( E l e v . 5) ( E l e v . 4) ( E l e v . 5) ( E l e v . 4) DsraClmFm-S2 ( E l e v . 3) InsCImFm-S3 x x x x x x ( E l e v . 5) x x x x x x R b r C l m - S 3 P r S l b - 2 l nsC*Fm- l assasaaiDii I D L E B E s a a s a a a a a A V A I L A B L E DsmClmFm-S2 i InsCwFm-2 ( E l e v . 3) x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x a s . s s s a V B a a lnsCwFm-2 I D L E V v i l a i s a i s a a a BiBasaaaaa RbrCw-1 ( E l e v . 5) RbrCw-1 ( E l e v . 5) Bsasaasaaaa A V A I L A B L E Y Day 3 2 8 : 0 0 7:00 7:30 8 : 0 0 8 : 3 0 9 :00 9 : 3 0 10:00 10:30 11:00 II :30 12:00 12:30 1:00 1:30 2:00 2:30 3 :00 35 :00 3 :30 sat a a at teat at * as BE a a a c s s B B B i s : caasaaBSBaa a a a B i a s s a o a A V A I L A B L E < a a DsmClmFm-S3 ClsCwFm-1 RbrCw-2 RbrCw-2 P r S l b - 3 P r S l b - 3 ( E l e v . 3) ( E l e v . 5) ( E l e v . 5) ( E l e v . 5) ( E l e v . 4) lnsClmFm-S3 ( E l e v . 3) e s s a a a a B B B B ClsCwFm-2 y Y a a a s s c a a a a a a s SB 3 statist i , CIsCwFm-1 . . . . . . . . . . . DsmClmFm-S3 A V A I L A B L E ^ I D L E a o i s a a a a a D i ClsCwFm-2 x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x DsroSlbFm-l ( E l e v . 4) ( E l e v . 5) I D L E I D L E 1 A V A I L A B L E Y F i g u r e 6.16: M u l t i p l e O p e r a t i o n Time (M.O.T.) C h a r t 138 6.3.5 MODULE 5 - DESIGN IMPROVEMENT AND ENRICHMENT 6.3.5.1 DIFFICULTIES IN IMPROVING AN ACTIVITY DESIGN A b a l a n c e d c y c l e i s n o t u s u a l l y a c h i e v e d i n t h e i n i t i a l d e s i g n s o l u t i o n . The i n i t i a l s o l u t i o n must be m o d i f i e d t o r e s o l v e r e s o u r c e c o n f l i c t s and t o i m p r o v e e f f e c t i v e n e s s o f r e s o u r c e u s a g e . The d e s i g n i m p r o v e m e n t p r o c e s s i s t h e most i m p o r t a n t and y e t most c o m p l e x p r o c e s s i n d e s i g n i n g a b a l a n c e d c o n s t r u c t i o n c y c l e . As s t a t e d i n c h a p t e r t h r e e , t h e d e s i g n p a r a m e t e r s and v a r i a b l e s a r e l i n k e d t o e a c h o t h e r b u t t h e l i n k a g e s c a n n o t be d e f i n e d p r e c i s e l y . B e c a u s e o f t h e c o m p l e x l i n k a g e s , c h a n g i n g t h e v a l u e o f a d e s i g n v a r i a b l e c o u l d h a v e a s i g n i f i c a n t e f f e c t on t h e o v e r a l l c y c l e d e s i g n . F o r e x a m p l e , i n a s s i g n i n g o v e r - t i m e t o an o p e r a t i o n t o e l i m i n a t e c o n f l i c t s i n u s i n g a s h a r e d r e s o u r c e , t h e s t a r t t i m e s and f i n i s h t i m e s o f t h e s u c c e s s o r s t o t h e o p e r a t i o n m i g h t be a f f e c t e d and c o u l d c a u s e c o n f l i c t s b e t w e e n o t h e r o p e r a t i o n s f o r s h a r e d r e s o u r c e s . A d d i n g t o t h e c o m p l e x i t y i s t h e number o f d e s i g n v a r i a b l e s t h a t c a n be m o d i f i e d t o s o l v e a g i v e n p r o b l e m ( s e e f i g u r e 6 . 3 ) . F o r e x a m p l e , c o n f l i c t s i n u s i n g s h a r e d r e s o u r c e s c a n be e l i m i n a t e d by: (1) a s s i g n i n g o v e r - t i m e o r e x t r a s h i f t s t o one o r more o f t h e o p e r a t i o n s c o m p e t i n g f o r t h e s h a r e d r e s o u r c e ; 139 (2) s p e e d i n g up an o p e r a t i o n by i n c r e a s i n g t h e c r e w s i z e s o t h a t t h e o p e r a t i o n c a n u s e t h e s h a r e d r e s o u r c e a t an e a r l i e r t i m e ; (3) c h a n g i n g t h e c o n s t r u c t i o n t e c h n o l o g y of one o r more o p e r a t i o n s . F o r e x a m p l e , a c o n c r e t e pump c o u l d be u s e d f o r p o u r i n g c o n c r e t e i n o r d e r t o f r e e t h e t o w e r c r a n e f o r o t h e r o p e r a t i o n s ; (4) a c o m b i n a t i o n o f t h e a b o v e c o u r s e s of a c t i o n . E a c h f e a s i b l e c o u r s e o f a c t i o n must be c a r e f u l l y c o n s i d e r e d i n o r d e r t o s e l e c t t h e c o u r s e o f a c t i o n w h i c h i s most c o s t e f f e c t i v e and d o es n o t s e r i o u s l y u p s e t t h e o r i g i n a l o p e r a t i o n s s c h e d u l e . The l a t t e r c o n c e r n h a s been i d e n t i f i e d by W i l l i s [131] as t h e r e q u i r e m e n t o f " s t a b i l i t y i n r e - s c h e d u l i n g " and h a s been d i s c u s s e d i n s e c t i o n 4.5. 6.3.5.2 AN APPROACH TO SOLUTION IMPROVEMENT The n a t u r e o f t h e a c t i v i t y d e s i g n p r o b l e m p r e c l u d e s a r e a l i s t i c , s o l v a b l e m a t h e m a t i c a l p r o g r a m m i n g f o r m u l a t i o n . C o n s e q u e n t l y , a t r i a 1 - a n d - e r r o r a p p r o a c h t o p r o b l e m s o l v i n g i s r e q u i r e d . A m a n u a l p r o c e s s t e n d s t o be t e d i o u s and t h e s o l u t i o n o b t a i n e d i s i n g e n e r a l l e s s a c c u r a t e t h a n t h a t o b t a i n e d by c o m p u t e r r o u t i n e s . So t h e g o a l becomes t o c r e a t e an e n v i r o n m e n t w h i c h u s e s t h e power of t h e c o m p u t e r t o i d e n t i f y p r o b l e m s , s u g g e s t s o l u t i o n s , a n a l y z e them, and 140 i n c o r p o r a t e t h e e x p e r i e n c e , j u d g m e n t and i n t u i t i o n o f t h e u s e r and a n a l y z e p o t e n t i a l i m p r o v e m e n t s . The c r i t i c a l p a t h a n a l y s i s r e s u l t s as shown i n f i g u r e 6.13 and t h e r e s o u r c e s t a t u s t a b l e c a n be u s e d t o i d e n t i f y c o n f l i c t s i n u s i n g s h a r e d r e s o u r c e s and t h e c o m p e t i n g o p e r a t i o n s . By s t u d y i n g t h e M.O.T. c h a r t t o g e t h e r w i t h t h e P - M a t r i x , t h e u s e r c a n g a i n i n s i g h t s i n t o t h e p o s s i b l e i m p a c t o f a c o u r s e o f a c t i o n on t h e o v e r a l l c y c l e d e s i g n . A f t e r an o p e r a t i o n h a s b een c h o s e n f o r m o d i f i c a t i o n , t h e c o m p u t e r c a n s u g g e s t a l i s t o f p o s s i b l e c o u r s e s o f a c t i o n ( s e e F i g u r e 6 . 1 7 ) . The c o m p u t e r c a n t h e n g u i d e t h e u s e r t o p a r t i c u l a r s t e p s o f t h e s o l u t i o n f o r m u l a t i o n p r o c e s s a c c o r d i n g t o t h e a c t i o n s e l e c t e d . T h i s i s t h e n f o l l o w e d by a n a l y s i s and t h i s p r o c e s s i s r e p e a t e d u n t i l a s a t i s f a c t o r y d e s i g n i s a c h i e v e d . 141 Modify Operation : R b R C w-2 ( E l e v . 5) 1 . R e - D e f i no L a b o u r Crew 2. Re-Schedule Operations 3. Re-AssIgn Resources 4. Assign Over-Time 5. Add Extra Shift 6. Change Production Technology 7. Prefabricate Components Select Action to Take : 1 1 1 F i g u r e 6.17: G e n e r a l r u l e s f o r d e s i g n i m p r o v e m e n t 142 6.3.5.3 SOLUTION ENRICHMENT AND THE M.O.T. CHART Any m o d e l o f a p r o b l e m s i t u a t i o n i s n e c e s s a r i l y a s i m p l i f i c a t i o n o f r e a l i t y . F o r t h e a c t i v i t y d e s i g n e n v i r o n m e n t b e i n g d e v e l o p e d , a l t h o u g h e m p h a s i s h a s been p u t on m o d e l i n g t h e p r o b l e m and t h e d e c i s i o n p r o c e s s i n t h e most r e a l i s t i c m anner, n o t a l l of t h e p r o j e c t e l e m e n t s h a v e b e e n t r e a t e d . E x a m p l e s o f t h e s e e l e m e n t s a r e : (1) I n c l u s i o n o f I n f r e q u e n t Work T a s k s and O p e r a t i o n s Many work t a s k s and i n f r e q u e n t o p e r a t i o n s i n a c o n s t r u c t i o n p r o j e c t a r e n o t n o r m a l l y s c h e d u l e d . E x a m p l e s o f t h e s e i n c l u d e d e l i v e r y o f s t o c k m a t e r i a l s s u c h as r e b a r and t i m b e r s , g e n e r a l c l e a n - u p and m a i n t e n a n c e o f e q u i p m e n t . I n c l u s i o n o f t h e s e s m a l l e r and n o n - r e g u l a r o p e r a t i o n s i n t h e c y c l e p l a n n i n g t e n d s t o c o m p l i c a t e i t s d e s i g n . However, t h e s e work t a s k s and o p e r a t i o n s must be p e r f o r m e d and c a n n o t be n e g l e c t e d . F o r e x a m p l e , i f t h e i n v e n t o r y o f r e b a r and t i m b e r s a r e n o t w e l l m a i n t a i n e d and o r g a n i z e d , t h e p r o d u c t i v i t i e s o f t h e r e i n f o r c i n g and f o r m w o r k c r e w c a n be a d v e r s e l y a f f e c t e d . (2) A s s i g n i n g D i f f e r e n t B r e a k s t o D i f f e r e n t Crews An a d d i t i o n a l t o o l f o r f i e l d management t o remove c o n f l i c t s i n t h e u s a g e o f s h a r e d r e s o u r c e s i s by 143 a s s i g n i n g b r e a k s t o d i f f e r e n t c r e w s a t d i f f e r e n t t i m e s . I f managed c a r e f u l l y t h e p r o c e s s c a n h e l p t o e l i m i n a t e i d l e t i m e and i m p r o v e t r a n s i t i o n s b e t w e e n o p e r a t i o n s . (3) A s s i g n m e n t o f T e m p o r a r y H e l p t o O p e r a t i o n s C u r r e n t l y a v a i l a b l e m e t h o d o l o g i e s and s y s t e m s f o r c o n s t r u c t i o n p l a n n i n g r e q u i r e r e s o u r c e s t o be a s s i g n e d t o an o p e r a t i o n f o r i t s e n t i r e d u r a t i o n . I n t h e a c t i v i t y d e s i g n e n v i r o n m e n t p r o p o s e d h e r e i n , r e s o u r c e s c a n be a s s i g n e d t o an o p e r a t i o n f o r p a r t o f i t s d u r a t i o n . F o r e x a m p l e , f r o m s t u d y o f t h e M.O.T. c h a r t , management m i g h t d e c i d e t o a s s i g n an i d l e g e n e r a l l a b o u r e r t o an o p e r a t i o n t o r e d u c e t h e d u r a t i o n o r s i m p l y t o e n s u r e t h a t a c r i t i c a l o p e r a t i o n c a n be c o m p l e t e d i n t i m e . 6 . 3 . 5 . 4 I N S T R U C T I O N S TO M A N I P U L A T E T H E M . O . T . C H A R T To i m p r o v e t h e i n i t i a l s o l u t i o n and t o i n c l u d e e l e m e n t s n o t c o n s i d e r e d a t t h e o u t s e t i n t h e p r o b l e m d e f i n i t i o n and s o l u t i o n f o r m u l a t i o n p r o c e s s e s , t h e s y s t e m u s e r s h o u l d be a l l o w e d t o m a n i p u l a t e t h e M.O.T. c h a r t t o o b t a i n a more r e a l i s t i c work s c h e d u l e t h a t c a n be f o l l o w e d a t t h e c o n s t r u c t i o n s i t e . S c h o f i e l d [118] has d e s c r i b e d t h e u s e o f h i g h l e v e l i n s t r u c t i o n s t o c a p t u r e some o f t h e f a c t o r s and r e s t r i c t i o n s 144 t h a t a r e " f a r more e x t e n s i v e t h a n j u s t t h o s e d e s c r i b e d by t h e p r e c e d e n c e d i a g r a m " i n t h e L i n e S e q u e n c i n g P r o g r a m d e v e l o p e d a t N o t t i n g h a m U n i v e r s i t y ( N U L I S P ) . A s i m i l a r s e t of i n s t r u c t i o n s c o u l d be u s e d i n t h e c o n s t r u c t i o n c y c l e d e s i g n d e c i s i o n s u p p o r t s y s t e m t o t r e a t t h e e l e m e n t s d e s c r i b e d e a r l i e r . H e r e a r e some e x a m p l e s o f p o s s i b l e commands: Commands f o r a s s i g n i n g and r e m o v i n g l a b o u r c r e w s b r e a k s s o as t o e l i m i n a t e c o n f l i c t s i n u s i n g s h a r e d r e s o u r c e s o r t o e n s u r e a smooth t r a n s i t i o n b e t w e e n o p e r a t i o n s . [ASSIGN] [BREAK] <name> TO <crew I.D./ALL> FROM <hr:mn> TO <hr:mn> [REMOVE] [BREAK] <crew I.D.> <name> [MOVE] [BREAK] <crew I.D.> <name> TO <hr:min> Command f o r a s s i g n i n g o v e r - t i m e t o o p e r a t i o n s i n o r d e r t o e l i m i n a t e c o n f l i c t s i n u s i n g s h a r e d r e s o u r c e s o r t o c r a s h t h e d u r a t i o n s o f c r i t i c a l o p e r a t i o n s . [ASSIGN] [O.T.] TO <crew I.D./ALL> FROM <hr:min> TO <hr:mi n> Commands f o r a s s i g n i n g and r e - a s s i g n i n g d e f i n e d o p e r a t i o n s o r i n f r e q u e n t work t a s k s and o p e r a t i o n s , s u c h as g e n e r a l c l e a n - u p and o t h e r s i t e m a i n t e n a n c e w o r k , t o i d l e r e s o u r c e s . 145 [ASSIGN] [JOB] <name / o p e r a t i o n I.D.> TO < r e s o u r c e I.D.> FOR <hr:min> [REMOVE] [JOB] <crew I.D.> <name / o p e r a t i o n I.D.> Command f o r m a n u a l l y c r a s h i n g an o p e r a t i o n w i t h o u t r e d e f i n i n g i t . I n r e v i e w i n g t h e M.O.T. c h a r t , t h e u s e r m i g h t d e c i d e t h a t t h e p r o d u c t i o n r a t e o f a p a r t i c u l a r o p e r a t i o n c a n be i n c r e a s e d s l i g h t l y w i t h o u t a s s i g n i n g a d d i t i o n a l r e s o u r c e s . T h i s command a l l o w t h e b y p a s s o f more t e d i o u s p r o c e s s e s . [CRASH] < o p e r a t i o n I.D.> BY <hr:min.> Command s i m i l a r t o [CRASH] b u t i t i s u s e d f o r m a n u a l l y s t r e t c h i n g t h e d u r a t i o n o f an o p e r a t i o n . [STRETCH] < o p e r a t i o n I.D.> BY <hr:min> Command w h i c h a l l o w s t h e s y s t e m u s e r t o r e t u r n f r o m t h e ma n u a l mode t o t h e s y s t e m g u i d e d mode ( F i g u r e 6 . 1 7 ) . [RETURN] The i n s t r u c t i o n s d e s c r i b e d a b o v e p r o v i d e f l e x i b i l i t y t o t h e u s e r and p e r m i t t h e a p p l i c a t i o n o f jud g m e n t and i n t u i t i o n t o " e n r i c h " an a c t i v i t y d e s i g n by i n c l u d i n g e l e m e n t s n o t c o n s i d e r e d i n t h e s o l u t i o n f o r m u l a t i o n p r o c e s s . The m o d i f i e d d e s i g n c a n be' r e a n a l y z e d , i f r e q u i r e d , and t h e M.O.T. c h a r t p l o t t e d f o r u s e i n t h e f i e l d . 146 7. CONCLUSIONS AND RECOMMENDATIONS 7.1 CONCLUSIONS The c o n c e p t u a l d e s i g n o f a d e c i s i o n s u p p o r t s y s t e m f o r a c t i v i t y d e s i g n d e v e l o p e d i n c h a p t e r s i x meets t h e o b j e c t i v e s e t f o r t h i s t h e s i s by p r o v i d i n g an e n v i r o n m e n t i n w h i c h management p e r s o n n e l a t t h e p r o d u c t i o n l e v e l c a n d e s i g n r e p e t i t i v e c o n s t r u c t i o n c y c l e s . T h i s s y s t e m s p e c i f i c a t i o n p r o v i d e s a p l a n n i n g e n v i r o n m e n t t h a t r e a l i s t i c a l l y r e f l e c t s and c a p t u r e s t h e d e c i s i o n m a k i n g p r o c e s s t h a t c o n s t r u c t i o n management p e r s o n n e l m e n t a l l y go t h r o u g h , a l b e i t i m p e r f e c t l y , i n d e s i g n i n g c o n s t r u c t i o n a c t i v i t i e s . The i n f o r m a t i o n c a p t u r e d i n t h e f o r m u l a t i o n o f a d e s i g n s o l u t i o n f o r a g i v e n s i t u a t i o n c a n be u s e d f o r f u t u r e r e f e r e n c e and f o r e d u c a t i n g l e s s e x p e r i e n c e d management p e r s o n n e l . The d e c i s i o n s u p p o r t s y s t e m c a n f u n c t i o n as a medium w h e r e b y management p e r s o n n e l c a n s y s t e m a t i c a l l y d e f i n e a p r o b l e m and document and a n a l y z e t h e i m p a c t o f c e r t a i n d e c i s i o n s on t h e a c t i v i t y d e s i g n ; no s o p h i s t i c a t e d a l g o r i t h m i s e m p l o y e d t o s e e k " o p t i m a l " d e s i g n s o l u t i o n s . I t p r o v i d e s an e n v i r o n m e n t i n w h i c h management c a n d e f i n e a p r o b l e m and f o r m u l a t e d e s i g n a l t e r n a t i v e s i n a r e a l i s t i c manner. 147 By r e c o r d i n g c o n s t r u c t i o n t e c h n o l o g i e s i n a s y s t e m a t i c f o r m a t , t h e s y s t e m u s e r c a n compare and e x p e r i m e n t w i t h d i f f e r e n t t e c h n o l o g i e s and s e l e c t t h e most a p p r o p r i a t e ones f o r c o n s t r u c t i o n . The d e c i s i o n s u p p o r t s y s t e m p r o v i d e s a c c u r a t e e s t i m a t e s o f r e s o u r c e r e q u i r e m e n t s f o r u s e i n t h e r e s o u r c e a s s i g n m e n t p r o c e s s . L a b o u r r e s o u r c e s c a n be a s s i g n e d as c r e w s ; work a r e a s a r e t r e a t e d as a s p e c i a l r e s o u r c e t o p e r m i t c o n s i d e r a t i o n o f s i t e p l a n n i n g i n t h e a c t i v i t y d e s i g n p r o c e s s . R e s o u r c e s c a n a l s o be a s s i g n e d f o r o n l y p a r t o f an o p e r a t i o n ' s d u r a t i o n . R e s u l t s f r o m a n a l y s i s o f t h e i n i t i a l d e s i g n s o l u t i o n a r e p r e s e n t e d i n f o r m a t s , t h e r e s o u r c e s t a t u s t a b l e and t h e m u l t i p l e o p e r a t i o n t i m e c h a r t , t h a t c a n h e l p management p e r s o n n e l i d e n t i f y p r o b l e m s w i t h t h e d e s i g n and f o r m u l a t e i m p r o v e m e n t s t o i t . I n s t r u c t i o n s c a n be u s e d t o p r o v i d e t h e f l e x i b i l i t y f o r c o n s t r u c t i o n management p e r s o n n e l t o c o n s i d e r e l e m e n t s n o t u s u a l l y i n c l u d e d i n t h e s o l u t i o n f o r m u l a t i o n p r o c e s s and t o p r o d u c e t a c t i c a l p l a n s t h a t c a n be f o l l o w e d a t t h e f i e l d l e v e l . 148 7.2 RECOMMENDATIONS FOR FUTURE RESEARCH 7.2.1 COMPUTER PROGRAMMING AND F I E L D A P P L I C A T I O N T h i s t h e s i s h as been l i m i t e d t o t h e c o n c e p t u a l d e s i g n o f a d e c i s i o n s u p p o r t s y s t e m f o r a c t i v i t y d e s i g n . The p r o p o s e d s y s t e m has n o t been programmed f o r c o m p u t e r a p p l i c a t i o n . I n o r d e r t o t e s t w h e t h e r t h i s d e c i s i o n s u p p o r t s y s t e m c a p t u r e s f u l l y t h e r e a l i t i e s o f c o n s t r u c t i o n p r o c e s s e s and i s a c c e p t a b l e t o c o n s t r u c t i o n management p e r s o n n e l a t t h e p r o d u c t i o n l e v e l , a p r o t o t y p e s y s t e m must be d e v e l o p e d a n d t e s t e d . O n - s i t e d o c u m e n t a t i o n o f t h e d e t a i l e d d e c i s i o n p r o c e s s i n v o l v e d i n d e s i g n i n g a c o n s t r u c t i o n c y c l e i s a l s o r e q u i r e d . H i s t o r i c a l p r o j e c t i n f o r m a t i o n and a v a i l a b l e c o n s t r u c t i o n t e c h n o l o g i e s s h o u l d be c a t e g o r i z e d i n f o r m a t s s u i t a b l e f o r c o m p u t e r a p p l i c a t i o n . 7.2.2 GRAPHICS I N T E R F A C E FOR C Y C L E DESIGN I n c e r t a i n t y p e s o f p r o j e c t , s u c h as h i g h - r i s e c o n s t r u c t i o n and mass h o u s i n g d e v e l o p m e n t p r o j e c t s , t h e t y p i c a l a s s e m b l y c a n be d e f i n e d by r e l a t i v e l y s i m p l e g e o m e t r y and a s t a n d a r d i z e d s e t of b u i l d i n g c o m p o n e n t s . F o r t h e s e t y p e s o f p r o j e c t s , i t i s p o s s i b l e t o d e s i g n a g r a p h i c s i n t e r f a c e f o r p r o b l e m d e f i n i t i o n and s o l u t i o n f o r m u l a t i o n . F o r e x a m p l e , i n a h i g h - r i s e c o n s t r u c t i o n p r o j e c t , t h e p l a n 149 of a t y p i c a l f l o o r can be defined graphically and the building components, such as columns and beams, can be selected from a l i s t and located in the plan. The dimensions of each subassembly and components can then be entered d i r e c t l y on the fl o o r plan. The f l o o r plan thus defined can also be used for s i t e planning and for studying flyform layouts. 7.2.3 INTEGRATION WITH OTHER MANAGEMENT FUNCTIONS The process of designing a construction cycle at the production l e v e l i s part of the t o t a l project management process. The a c t i v i t y design function must be integrated with other project management functions so that relevant information, such as construction expenditures can be collected and use in project cost accounting and other functions. Integration of the decision support system with the estimating function can reduce the t o t a l e f f o r t required for problem d e f i n i t i o n . Russell [114] has i l l u s t r a t e d how the a c t i v i t y design function relates to other functions in the t o t a l project management system for re p e t i t i v e construction projects. One of the requirements for integration of project management functions is the standardization of work breakdown structures for a l l levels of the project management hierarchy. The work breakdown structures described by Ponce-Campos and Ricci [103] can be used as a 150 f r a m e w o r k by w h i c h t h e r e q u i r e d s t a n d a r d i z a t i o n c a n be a c h i e v e d . 7.2.4 INTEGRATION WITH OTHER MODELING TECHNIQUES T a k e n i n d i v i d u a l l y , e x i s t i n g m o d e l s c a n n o t be u s e d t o s o l v e t h e c o n s t r u c t i o n c y c l e d e s i g n p r o b l e m . However, i t i s p o s s i b l e t o make u s e o f them i n t h e d e c i s i o n s u p p o r t s y s t e m f o r a n a l y z i n g d e s i g n a l t e r n a t i v e s . F o r e x a m p l e , s i m u l a t i o n and a n i m a t i o n c a n be u s e d t o c o m m u n i c a t e t h e i m p a c t s o f c e r t a i n d e c i s i o n s t o t h e s y s t e m u s e r i n a more d y n a m i c a n d e f f e c t i v e manner and d e t e r m i n i s t i c m a t h e m a t i c a l p r o g r a m m i n g t e c h n i q u e s , s u c h as l i n e a r p r o g r a m m i n g , c o u l d be u s e d t o s o l v e s u b - p r o b l e m s o f t h e a c t i v i t y d e s i g n p r o b l e m . S i m u l a t i o n and m a t h e m a t i c a l p r o g r a m m i n g t e c h n i q u e s , h o w e v e r , r e q u i r e s e x c e s s i v e p r o g r a m m i n g e f f o r t t h a t p r o h i b i t s i t f r o m d a y - t o - d a y u s e i n t h e f i e l d . The p r o g r a m m i n g e f f o r t r e g u i r e d w i l l be g r e a t l y r e d u c e d i f " p r o g r a m g e n e r a t o r s " w h i c h c a n i n t e r p r e t t h e n e t w o r k l o g i c and t h e n g e n e r a t e t h e p r o g r a m s r e q u i r e d f o r s i m u l a t i o n and m a t h e m a t i c a l a n a l y s i s c o u l d be d e v e l o p e d . 151 7.2.5 DETAILED PLANNING OF CONSTRUCTION CYCLE OPERATIONS One t o p i c t h a t h a s n o t been d i s c u s s e d i n d e t a i l i n t h i s t h e s i s i s t h e a s s i g n m e n t o f work t a s k s w i t h i n d e f i n e d c r e w s , i n o t h e r w o r d s , t h e d e t a i l e d d e s i g n o f t h e o p e r a t i o n s i n a c o n s t r u c t i o n c y c l e . T h i s p r o c e s s i s a s s i g n e d t o t h e u s e r . F o r e x a m p l e , i n a s s i g n i n g a t o w e r c r a n e t o t h e f o r m w o r k i n s t a l l a t i o n o p e r a t i o n s a y t h i r t y m i n u t e s a f t e r t h e o p e r a t i o n h a s s t a r t e d and f o r a p e r i o d o f one and a h a l f h o u r s , t h e u s e r h a s m e n t a l l y d e c i d e d t h a t c e r t a i n s e t o f work t a s k s has t o be p e r f o r m e d p r i o r t o u s e o f t h e c r a n e and t h a t a n o t h e r s e t o f work t a s k s r e q u i r e s u s e o f t h e c r a n e f o r 90 m i n u t e s . The o p e r a t i o n d e s i g n p r o c e s s i n v o l v e s a s s i g n i n g t h e s e t o f work t a s k s a s s o c i a t e d w i t h t h e c o n s t r u c t i o n t e c h n o l o g y s e l e c t e d ( s e e f i g u r e s 6.6(a) and 6 . 6 ( b ) ) t o i n d i v i d u a l c r e w members. A t p r e s e n t , few p r o d u c t i o n o p e r a t i o n s , e x c e p t t h o s e d o c u m e n t e d by s p e c i a l i z e d h a r d w a r e s u p p l i e r s , s u c h as t h e Economy Forms C o r p o r a t i o n , h a v e been d o c u m e n t e d t o t h i s l e v e l o f d e t a i l . To c o l l e c t and document t h e r e g u i r e d i n f o r m a t i o n , p r o d u c t i o n method s t u d y t e c h n i q u e s d e s c r i b e d i n t h e i n d u s t r i a l e n g i n e e r i n g l i t e r a t u r e , s u c h as t i m e - l a p s e p h o t o g r a p h y , c o u l d be u s e d . 152 BIBLIOGRAPHY [1] Agrawal, P.K., "Related A c t i v i t y Concept in Assembly Line Balancing", International Journal of Production Research, v 23 n 2, Mar/Apr 1985, pp 403-421. [2] Ahuja, H. and Nandakumar, V., "Simulation Model to Forecast Project Completion Time", Journal of Construction Engineering and Management, ASCE, v 111 n 4, Dec 1985, pp 325-342. 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