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Strengthening of timber beams using externally-bonded sprayed fibre reinforced polymers Talukdar, Sudip 2008

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STRENGTHENING OF TIMBER BEAMS USING EXTERNALLYBONDED SPRAYED FIBRE REINFORCED POLYMERS by  SUDIP TALUKDAR B.A.Sc., University of British Columbia, Vancouver, Canada, 2004  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in  THE FACULTY OF GRADUATE STUDIES (Civil Engineering)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  February 2008 © Sudip Talukdar, 2008  ABSTRACT The use of Fibre Reinforced Polymers (FRP) has grown in popularity in the construction industry. FRP has proven useful in the retrofit of various types of structural elements. It may be used for the strengthening of beams, the seismic upgrade of walls panels, as well as the jacketing of columns to provide confinement. There exist several methods of FRP application for the case of structural retrofits. These include the application of preprepared FRP mats, or application of FRP via the wet lay-up process. However, a new technique developed at the University of British Columbia allows for the application of FRP in the form of a spray.  Externally bonded Sprayed FRP (SFRP) is known to increase strength and energy absorption capacity of a retrofitted member as well as, or better than, FRP sheets. However, tests have primarily been carried out on concrete members only. An area of interest, into which not much research has been conducted, is the application of SFRP to timber. Timber bridges are extensively used in many parts of the world. Often due to remoteness and practical constraints, it is impossible to apply FRP sheets to retrofit these bridges. SFRP would be a much easier method of FRP application.  This study looked at the application of SFRP to Douglas Fir (D.Fir) Beam specimens subjected to 3-Point Flexural Loading only. The specimens were treated with either a water based (Borocol) or oil borne (Creosote) antifungal preservative prior to being sprayed with FRP. Different combinations of adhesives/bonding agents including Hydroxymethylated Resorcinol and Polymeric Isocyanates were used to try to develop a strong bond.  When considering using only chemical adhesives to obtain a proper bond between the two constituents of the composite, use of HMR is recommended for timber which is untreated or has been treated with a water borne preservative such as Borocol, while a pMDI adhesive such as AtPrime 2 is recommended for timber treated with an oil borne preservative such as Creosote. For Non Creosoted beams, adhesives did not generate as  ii  significant of a strength gain. For Creosoted beams, adhesives may be sufficient to generate significant strength gain when SFRP is applied to a beam. Considering that most structures in use would probably have been treated with a preservative similar to Creosote, in practice, AtPrime 2 or some other some sort of pMDI would probably be the adhesive of choice. Based on the results of the study, it is possible to say that the application of SFRP to retrofit/rehabilitate timber structures shows considerable promise. If a decent bond is achieved between the composite constituents, it is possible to substantially increase the ultimate flexural strength of the member, as well as drastically increase its ductility and energy absorption capacity. It is recommended that further tests be carried out using different types of loading schemes, geometrical configurations of SFRP, other types of anchorage, and development of a proper analytical model before the method is adopted for widespread use.  iii  ^  TABLE OF CONTENTS ^Abstract ^  ii  Table of Contents ^  iv  List of Tables ^  vii  List of Figures ^  viii  Acknowledgements ^ 1.0^Introduction and Research Significance ^  1  2.0^Background ^  3  ^2.1^Timber ^  4  2.1.1^Mechanical Properties of Timber ^  8  ^2.2^Fibre Reinforced Polymers ^  12  ^2.2.1^Polymer Matrix ^  12  ^2.2.2^Fibres ^  16  ^2.2.3^FRP Application Techniques ^  18  ^2.3^Adhesive Chemistry ^  20  ^2.4^Hydroxymethylated Resorcinol ^  23  2.5 Timber-FRP Bond Mechanisms ^  25  3.0^Previous Research ^  29  ^3.1^Reinforced Concrete-FRP Composites ^ ^3.2^Timber-FRP Composites ^  29  4.0^Experimental Program ^  35  31  ^4.1^Materials ^  35  ^4.1.1^Beam Species ^  35  ^4.1.2^Polyester Resin ^  36  ^4.1.3^Glass Fibre ^  37  ^4.1.4^Fungicides ^  38  ^4.1.5^Adhesives/Primers ^  39  ^4.2^Preparation ^  41  ^4.2.1^Sanding ^  41  ^4.2.2^Fungicide Application ^  42  iv  ^  4.2.3^HMR Preparation and Application ^  43  ^4.2.4^AtPrime 2 Application ^  45  ^4.2.5^SFRP Application Process ^  45  4.3^Specimen Testing ^ 5.0^Results ^  47 53  5.1^Three Point Flexural Test Analysis, Borocol Treated ^ 53  ^5.1.1^Beam A ^  53  ^5.1.2^Beam B ^  57  ^5.1.3^Beam C ^  59  ^5.1.4^Beam D ^  61  ^5.1.5^Beam E ^  64  5.2^Three Point Flexural Test Analysis, Creosote Treated ^ 65  ^5.2.1^Beam F ^  65  ^5.2.2^Beam G ^  68  ^5.2.3^Beam H ^  69  ^5.2.4^Beam I ^  71  ^5.2.5^Beam J ^  72  6.0^Discussion ^  74  6.1^Borocol Treated Beams ^  74  6.2^Creosote Treated Beams ^  77  6.3^Strain Analysis ^  78  6.4^Failure Mechanism ^  85  6.5^Simplified Strength Gain Model ^  88  6.6^Comparison to Other Studies ^  90  6.7 Other Comments ^  91  7.0^Conclusions ^  92  8.0 Recommendations for Future Work ^  95  ^References ^  98  Appendix A: Data from Flexural Beam Tests ^  103  Appendix B: Simplified Strength Gain Model ^  136  Appendix C: Sample Interfacial Shear Stress Calculation ^ 140  Appendix D: Predicted Ultimate Strengths ^  vi  142  LIST OF TABLES Table 1: Specified Strengths and Modulus of Elasticity of Timber in Different Directions ^ Table 2: Polymer Molecules ^  12  Table 3: Fibre Properties ^  17  Table 4: D.Fir Properties ^  36  Table 5: Resin Properties ^  36  Table 6: HMR Composition ^  39  Table 7: Specimen Testing Matrix for Static Loading ^ Table 8: Beam A Results ^  48  Table 9: Beam B Results ^  59  Table 10: Beam C Results ^  61  Table 11: Beam D Results ^  63  Table 12: Beam E Results ^  65  Table 13: Beam F Results ^  66  Table 14: Beam G Results ^  69  Table 15: Beam H Results ^  70  Table 16: Beam I Results ^  71  Table 17: Beam J Results ^  72  Table 18: Summary of Results, Non Creosoted ^  75  Table 19: Summary of Results, Creosoted ^  77  Table 20: Strains at failure, Gauge 3, Beams A-E ^  80  Table 21: Strains at failure, Gauge 3, Beams F-J ^  80  Table 22: Strains at failure, Gauge 1 vs Gauge 3 ^  81  Table 23: Strains at failure, Gauge 5 vs Gauge 7 ^  82  Table 24: Other Studies ^  89  vii  15  55  LIST OF FIGURES Figure 1: Cellulose Molecule ^  4  Figure 2: Hemicellulose Molecule ^  5  Figure 3: Lignin Molecule ^  5  Figure 4: Wood Cell Diagram ^  6  Figure 5: Tree Schematic ^  7  Figure 6: Bordered Pits in a Tracheid ^  8  Figure 7: Generalized Stresses on a Cube ^  9  Figure 8: Principal Axes of Wood ^  11  Figure 9: Unsaturated Polyester Resin ^  14  Figure 10: Wet Lay-Up Process ^  19  Figure 11: Spray FRP Process ^  20  Figure 12: Formation of Polyurethane via Isocyanate-Wood Reaction ^ 22 Figure 13: Formation of Polyurea via 2-step Isocyanate-Water Reaction ^ 22 Figure 14: HMR Molecule ^  23  Figure 15: Theoretical Wood-HMR Bonding Mechanism ^  24  Figure 16: Theoretical HMR-Isocyanate/PRF Bonding Mechanism ^ 24 Figure 17: Variations in Surface Wettability ^  27  Figure 18: Beam Specimens ^  35  Figure 19: Glass Fibres Applied to Beam ^  37  Figure 20: Fungicides, Borocol (L), Creosote (R) ^ Figure 21: HMR Constituents ^  38 40  Figure 22: AtPrime 2 Applied to Wood Surface ^  41  Figure 23: Belt Sander^  42  Figure 24: Wooden Beams Coated with Boracol ^  43  Figure 25: Color Change of HMR ^  43  Figure 26: Comparison of HMR Treated and Untreated Beam ^ 44 Figure 27: Application of AtPrime 2 to Beam ^ 45 Figure 28: Spray Gun ^  46  Figure 29: SFRP Application to Beam ^  47  viii  Figure 30: Static Test Setup ^  48  Figure 31: Cross Section of Reinforced Specimens Subjected to Static Testing ^ 49 Figure 32: Static Test Setup ^  49  Figure 33: Beam Dimensions and Instrumentation Diagram ^  50  Figure 34: Strain Gauges ^  51  Figure 35: Steel Plate and Load Cell ^  52  Figure 36: Beam A, Load vs. Displacement ^  54  Figure 37: Beam A, Gauge 2, Strains vs Load ^  55  Figure 38: Beam A, Gauge 1 vs Gauge 5 ^  56  Figure 39: Beam A, Gauge 2 vs Gauge 6 ^  56  Figure 40: Beam A, Gauge 3 vs Gauge 7 ^  57  Figure 41: Beam B, Load vs. Displacement ^  58  Figure 42: Beam B at failure ^  59  Figure 43: Beam C, Load vs. Displacement ^  60  Figure 44: Beam D, Load vs. Displacement ^  61  Figure 45: Beam D, at failure ^  62  Figure 46: Beam E, Load vs. Displacement ^  64  Figure 47: Beam F, Load vs. Displacement ^  65  Figure 48: Beam G, Load vs. Displacement ^  67  Figure 49: Beam H, Load vs. Displacement ^  68  Figure 50: Beam H, Just Prior to Failure ^  70  Figure 51: Beam I, Load vs. Displacement ^  70  Figure 52: Beam J, Load vs. Displacement ^  71  Figure 53: Comparison of Results, Non Creosoted ^  73  Figure 54: Comparison of Results, Creosoted ^  76  Figure 55: Non Linear Behavior Diagram ^  78  Figure 56: Gauge 2, Strains vs Load ^  81  Figure 57: Gauge 6, Strains vs Load ^  83  Figure 58: Debonding Diagram ^  85  ix  ACKNOWLEDGEMENTS  Firstly, I would like to acknowledge the guidance and support of my supervisor, Dr. Nemy Banthia. It has been a pleasure being his student, and his advice throughout this project has been invaluable.  I would also like to thank Dr. Sidney Mindess for agreeing to co read this thesis. His input has been invaluable and well received. Next I would like to acknowledge the contributions of Dr. Baidar Bakht, Mr. Friedl Brudermann, Dr. Douglas Gardner, Dr. John Newhook, and Dr. Thanasis Triantafillou, with all of whom I corresponded with via email, and whose comments and contributions were very much appreciated.  Thank you to my friends and colleagues in the UBC Civil Engineering Depal talent and especially the Materials Group. Your academic help and advice helped me complete this thesis, and your friendship and support has made my time here memorable.  I would like to acknowledge all the technical assistance I was provided with throughout this project. I would like to thank Mr. John Chandra and Mr. Gary Pinder of Johns Custom Fibreglass for helping with the preparation of my specimens, and Mr. Bill Leung, Mr. Scott Jackson, Mr. Harold Schrempp, Mr. Doug Smith, and Mr. John Wong in the Machine Shop for helping with the setup and instrumentation of my experiments. Also I would like to thank Ms. Susan Harper and Ms. Paula Parkinson for assisting me with preparing any chemicals and ensuring all my work was done in a safe manner.  Finally, last but not least, I would like to thank Ma and Baba for being the worlds most patient parents, and raising me to be the person I am today. Without you, I would not have completed this degree, and all that I have accomplished, I owe to you.  INTRODUCTION AND RESEARCH SIGNIFICANCE Changing social needs, upgrading of design standards, increased safety requirements and deterioration result in existing concrete, masonry, and timber structures such as bridges and buildings that are structurally deficient and need to be replaced or upgraded through strengthening (Triantafillou, 1998). Structures which have been excessively deteriorated may have undergone severe strength loss, and pose a serious threat to public safety. Therefore, it is imperative that structures be routinely inspected and any damage/deterioration be promptly rehabilitated, to avoid having to replace the bridge, or experiencing a catastrophic failure.  Disadvantages associated with traditional rehabilitation/retrofit techniques, such as use of bonded steel plates, have led researchers to develop new techniques, such as use of Fibre Reinforced Polymers (FRPs). FRPs offer an excellent combination of physical and mechanical properties, including low weight, immunity to corrosion, electromagnetic neutrality, ability to form long lengths, and excellent specific strength/stiffness.  A new technique has been developed at the University of British Columbia (UBC) by which FRP is applied in the form of a spray. Prior to application, the element surface is coated with a bonding agent/adhesive. Polymer is then sprayed out of a nozzle towards the surface. Attached to the nozzle is a fibre chopping device, which cuts the fibre into desired lengths and injects it into the spray stream along with the polymer. The FRP then impacts the surface and coats it. This application method is less labor intensive, less time consuming, and consequently, a highly cost effective option to consider when contemplating rehabilitation techniques.  1  Rehabilitation of existing structures has been regarded as a major area of FRP composite applications. Much research has gone into the retrofit of concrete with FRP, supplemented by successful field applications. However, research of FRP used to rehabilitate timber structures is much more limited, with very far fewer actual field applications. Structural timber members can be easily damaged by poor maintenance practices, and surface degradation due to overloading, pests, or weather conditions over years of use. Worldwide there are thousands of timber bridges in service, which will inevitably require replacement/retrofit. According to the 2005 'Report Card for Americas Infrastructure', there are 160570 bridges in the United States which are classified as structurally deficient. Approximately 7% of the national bridge inventory consists of timber bridges. If the same ratio of structurally deficient bridges applies to the timber bridge stock, this would mean well over 10000 timber bridges in the USA are structurally deficient. Instead of replacing the existing structures, applying SFRP reinforcement to the existing structures could be a more efficient solution.  The main objective of this study was to investigate whether or not application of SFRP to timber members is a feasible rehabilitation technique. This report will summarize the results of static flexural loading tests on Douglas Fir (D.Fir) beams treated with waterbased and oil-based preservatives. It is hoped that this work can be built upon such that ultimately, the study can be expanded and a definitive assessment as to the future of these types of composites can be made.  2  BACKGROUND Timber is a construction material with excellent properties for a variety of applications. Today, improved design methods, preservative treatment techniques, and advanced forms of timber construction enable some contemporary structures to be at least as permanent and economically competitive as those constructed from other materials. However as with any type of construction material, over time, timber can deteriorate due to environmental exposure, loading conditions, or may require upgrade due to code changes.  FRP composites can offer many advantages, and FRP is an obvious material to consider when deciding how to rehabilitate deteriorating wooden structures. The advent of Sprayed FRP as an application method allows for FRP to be applied in a less labor intensive and more cost effective way.  However, SFRP and timber are two highly dissimilar materials, both mechanically and chemically, and therefore SFRP should not be applied to a timber surface without first considering how to ensure that debonding does not occur at the interface between the two materials, either due to environmental conditions, or due to stresses imposed at the interface under loading. This section describes the two base composite materials as individual components, profiles materials which may be used to promote bonding between each component and details the difficulties associated with bonding and theoretically how to avoid premature delamination.  3  2.1^Timber  Wood is an organic material. When it is processed into a construction material, it is considered to be timber. It is also an anisotropic material, in that it has different and unique properties in each direction. On a molecular level, wood is made up primarily of cellulose, hemicellulose, lignin, and minor amounts of other extractives (Dinwoodie, 2000). Cellulose (Figure 1) is the most important component of wood. It is a linear polymer, composed typically of several thousand 13-d glucose units. The hydroxyl groups in each unit of glucose making up the cellulose cause it to behave as a polar molecule, and also allows for the generation of van der Waals and hydrogen bonding to adjacent molecules. Subsequently, cellulose molecules are able to attract adjacent cellulose molecules to create microfibrils. Microfibrils are threadlike bundles of cellulose molecules arranged parallel to each other, surrounded by lignin and hemicellulose, helping to bond them together. This orientation contributes to the higher tensile strength and toughness of wood (Dinwoodie, 2000). Hemicelluloses (Figure 2) are also polymeric molecules. However, they are built up from a variety of different sugar molecules rather than simply glucose, thus forming a branched, amorphous molecule. Lignins (Figure 3), on the other hand, have a complex, three dimensional structure, built up from phenyl propane units, linked in a variety of ways. Lignins, in particular, impart rigidity and compressive strength to the cell walls. The structure of lignins is not completely understood. However, it should be noted that like cellulose, both hemicellulose and lignin are polar molecules. Finally, the extractives do not form a part of the basic wood structure. They consist of a wide variety of chemical substances and are in part responsible for wood properties such as color, odor, taste, fungal and insect resistance and flammability (Dinwoodie, 2000).  Figure 1: Cellulose Molecule, (Dinwoodie, 1978)  4  •  — Oil OH OH^CII3  OH  COOH  OH ^ tvs.  HD O  13 '  ,.  1  0 "^Hi) OH^0  OH  Ote  n Figure 2: Hemicellulose Molecule, (Dinwoodie, 1978)  Figure 3: Lignin Molecule, (Dinwoodie, 1978)  Therefore, on a cellular level, wood maybe crudely modeled as being made of a bundle of cellulose fibres, embedded in a matrix of hemicellulose and lignin. The walls of these fibres are made up of microfibrils oriented in different ways (Figure 4).  5  S3 S2 S1  Figure 4: Wood Cell Diagram (Dinwoodie, 1978)  1.  The middle lamella (ML) is a lignin-rich layer which joins together the neighboring wood cells.  2.  The primary wall (P) is thin layer, with a random orientation of microfibrils.  3.  The Si layer is also relatively thin, consisting of 4 to 6 layers of microfibrils arranged in alternating right and left handed helices.  4.  The S2 layer is thick, making up most of the cell wall, with all microfibrils oriented in a right handed helix.  5.^The S3 layer is virtually identical to the Si layer.  Wood used in structural engineering applications is generally classified as softwood. Softwood is the wood of gymnosperms or those trees with needle-like leaves, which bear seeds in a woody cone. On a macroscopic level, as part of the trunk of a tree, wood can be divided into two regions, the sapwood region, and the heartwood region (Figure 5). The sapwood is responsible for the storage of food, and transportation of water/minerals to the crown of the tree. The tree increases its size as new wood cells are produced at the cambium, a zone of living cells lying between the bark and the sapwood. As the tree trunk increases in diameter, newer sapwood forms along the outer portion of the trunk, the older sapwood loses its ability to fulfill these tasks and is over time slowly converted into heartwood.  6  bark  diameter or tree  sapwood Witte to cream in colour) heartwood (brown to red in colour)  Figure 5: Tree Schematic (Tree Parts, 2008)  In softwood, 90% of cells are aligned on the vertical axis, while the remaining 10% are aligned in the horizontal plane in the form of long bands known as rays. Cells aligned vertically are known as tracheids. They are long and slim in geometry, and are primarily responsible for imparting strength to the trunk, as well as the conduction of water and minerals through the trunk to the crown. Rays on the other hand are made up of small block like cells known as parenchyma, and are mainly responsible for the storage of food material. Lateral transfer between tracheids is achieved through transportation through pits. Pits are small openings between adjacent tracheids allowing for fluid flow (Figure 6). Coupled with rays, pits form a complex capillary system which allows for fluids such as externally applied adhesives to penetrate deeply into the surface of wood.  7  '41114111011111  emess%  Figure 6: Bordered Pits in a Tracheid (Keey et al, 2000)  2.1.1 Mechanical Properties of Timber When a sample of timber is loaded in tension, compression or bending, the deformations obtained with increasing load are approximately proportional to the values of the applied load. This approximation is particularly true at lower levels of loading. Furthermore, this leads to the relationship:  f_v Where z is the strain deformation, o is the applied stress, and E is the constant known as -  the Modulus of Elasticity. Therefore, the Modulus of Elasticity can be approximated by taking the slope of the Stress vs. Strain curve at low levels of loading.  Similarly, within the elastic range of a material, shearing stress is proportional to shearing strain. This gives us the relationship:  C=  8  Where y is the shearing strain, ti is the shearing stress, and G is a constant known as the Modulus of Rigidity. Next, in general, when a body is subjected to a stress in one direction, the body will undergo a change in dimensions at right angles to the direction of the stress. The ratio of contraction or extension to the applied strain is known as Poissons ratio, and is given by: 0=  f2  Timber as a material is a highly orthotropic material, meaning that it has different orthotropic properties and strengths in different orthogonal directions. We can imagine a cube of material in a generalized stress condition as shown below:  A Yz  a  yy 0 ,  yx  Y X Figure 7: Generalized Stresses on a Cube (Dinwoodie, 1978)  Noticing that CYyz , cyz„ and a, are in fact shear stresses, we can write a generalized equation for orthotropic materials in matrix form as follows:  9  1 tix  ejar  -  _vyx _  _  - Hr  gz 1  vxr ges eye °Ix 6,7  sz  By  0  0  0  0  0  0  0  0  0  0  0 0  HA  17  0  0  0  0  0  0  0  1 2082:  0  0  0  0  0  az  1 20  CriX 115,  67aye  e'rZi Cry  1 2G  ,  The full derivation of this equation can be found in Dinwoodie, 2000. Clearly, this shows that the properties of an orthotropic material in one direction can influence the stresses in strains developed in an orthogonal direction. In general, this makes timber a very complex material. In applying the elements of orthotropic elasticity to wood and board materials made from wood, the assumption is made that the three principal elasticity directions coincide with the longitudinal (L), radial (R), and tangential (T) directions in the tree. Therefore, there are 9 independent constants which are required to specify the elastic behaviour of timber. These are the three Moduli of Elasticity (L,R and T), three Moduli of Rigidity (LT,LR and TR), and three Poissons Ratios (RT, LR and TL). These values of these constants are available in many timber textbooks, depending on the species of timber, and can thereby be used to determine stress-strain values of different species of timber.  10  Longitudinal  Figure 8: Principal Axes of Wood (Green et al, 1999)  There are several reasons for the varying orthotropic mechanical properties. One is the non homogenous nature of timber. A single piece may have varying densities throughout, and may have physical imperfections such as checks, shakes or knots which would vary the way stress is distributed throughout the specimen. The grain angle is also particularly important in influencing the stress-strain relationship within a specimen. Rotating the grain angle would result in the formation of transverse stresses within a piece. Also, a piece of timber is also significantly stronger along the fibre length, than orthogonal to the fibre direction. As it was explained in Section 2.1 that wood may be crudely modeled as being a bundle of cellulose fibres embedded in a matrix of hemicellulose and lignin. The linear, crystalline structure of cellulose allows it to form a stronger polymer, as opposed to the branched, less crystalline structure of hemicellulose and lignin. Therefore, as cellulose molecules are aligned along the fibre length, it makes sense that wood would have better strength properties along the fibre rather than orthogonal too it. Species of timber which are lower in hemicellulose and lignin would not hold together microfibrils as strongly, and therefore also tend to have weaker orthogonal strengths and shear strength parallel to the grain. The differences in strength are shown in Table 1.  11  Table 1: Specified Strengths and Modulus of Elasticity of Timber in Different Directions (CWC, 2005) Specified Strengths and Modulus of Elasticity for Structural Joist and Plank, Structural Light Framing, and Stud Grade Categories of Lumber (MPa)  Species identification D Fr-L  Hem-Fir  S-P-F  Compression  Grade  Bending at extreme fibre, f„  SS No. 1/No. 2 No. 3/Stud  16.5 10.0 4.6  1.9  SS No. 1/No. 2 No. 3/Stud  16.0 11.0 7.0  1.6  Longitudinal shear, 4  Parallel to grain, 4 19.0 14.0 4.6 17.6 14.8 7.0  SS No. 1/No. 2 No. 3/Stud SS No. 1/No. 2 No. 3/Stud  16.5 14.5 11.8 1.5 11.5 7.0 7.0 Northern 10.6 13.0 7.6 1.3 10.4 4.5 4.5 Note Tabulated values are based on the following standard conditions:  Modulus of elasticity  Perpendicubr to grain, Ca,  Tension parallel to grain, f,  E  Eos  7.0  10.6 5.8 2.1  12 500 11 000 10 000  8 500 7 000 5 500  4.6  9.7 6.2 3.2  12 000 11 000 10 000  8 500 7 500 6 000  8.6 5.5 3.2 6.2 4.0  10 500 9 500 9 000 7 500 7 000  7 500 6 500 5 500 5 500 5 000  5.3  3.5  2.0  6 500  4 000  (a) 286 mm larger dimension; (b) dry service conditions; and fr.) standard-term duration of load.  2.2^Fibre Reinforced Polymers  The use of Fibre Reinforced Polymers has been growing in popularity in the construction industry. FRP is a composite material comprising of a polymer matrix reinforced with fibres, usually of glass, carbon, or aramid (Williamson, 2002). Different fibres will have different strengths, stiffness and chemical properties. It is important to select a fibre such that it interacts optimally with the matrix it is embedded in. The types of polymer matrices used also vary. FRP composites often possess superior advantages such as high strength to weight ratio, high stiffness to weight ratio, tailorable mechanical and physical properties, weathering and corrosion resistance, and lower costs.  2.2.1 Polymer Matrix  Each type of polymer matrix offers benefits for particular applications. A polymer matrix falls into two categories: thermoplastics and thermosets. Raw thermoplastic resins can be heated and cooled repeatedly to change their state from liquid to solid and vice versa, while a thermoset resin cannot return to its original state. While thermoplastics such as 12  polyethylene, polystyrene, polypropylene, and thermoplastic polyesters have been used in the manufacture of wood fibre/polymer composites, thermosets are preferred as they are easier to process, have a low melting viscosity, good fibre impregnation, fairly low processing temperatures, and lower cost (Williamson, 2002). Commonly used polymers used for FRP matrices include polyesters, epoxies, vinyl esters, and phenolic resins. Polyesters are the most widely used class of thermosets in the construction market. They have a relatively low price, ease of handling, and a good balance of mechanical, electrical, and chemical properties. The most typical type of thermoset polyester is the unsaturated polyester resin (Figure 9). Unsaturated polyester resins are thermosetting, infusible, and insoluble materials. They can be formulated to different flexibilities and viscosities.  Compared to saturated polyester resins, unsaturated polyester resins contain reactive double bonds in the base polyester monomer, which are subsequently polymerized to allow for crosslinking between adjacent polymer chains. The mechanical properties of a given polyester resin are dependent on the density of crosslinks and the flexibility of the molecules between crosslinks. The crosslinking density and flexibility may be controlled in the resin synthesizing process. The greater the crosslinking density, the greater the viscosity and ultimate brittleness of the resin.  Unsaturated polyester resins are prepared in two steps. A linear polyester containing carbon-carbon double bonds in the polymer chain is composed and stabilized with an inhibitor. When the composition is ready for use, it is mixed with a catalyst system, compounded with fillers, reinforced with fibres, and crosslinked by the copolymerization of the unsaturated double bonds in the polyester. The polymerization takes place during the molding or lamination operations. In this respect, unsaturated polyester resins form ideal matrices for glass fibres.  Copolymerization occurs through the addition of an initiator (free radical) to break the double bonds linking carbon-carbon in the polymer chain. The most common initiator  13  used is Methyl Ethyl Ketone Peroxide (MEKP). As the amount of initiator being used is increased, so too will the reaction rate. Once the double bond has been broken, the carbon molecules are free to react with a cross linking monomer. The most widely used crosslinking monomer is styrene. By subsequent copolymerization of polyester double bonds with styrene a crosslinked structure is obtained in which polyester chains are linked by polystyrene bridges. The ratio of saturated to unsaturated components controls the degree of cross-linking and thus the rigidity of the product.  CH CH2)  0^a 1 :; C-0- Citi  0^0^C^0 IH 't II El^II^ ^II — 0 — C- C— C—C-0—C —C 11 —0-C i^11^11^2  H  CH  ^  c —0— 1-12  g.  0 H^II  CH3 II^II2  STYRENE BRIDGE  H H — C-0— c --c-0— 0— C- C— C I^ II H I^Ic^CHI 0  "2^  H C - 0 - CH— C —O—C-C—C—C-0 C— —0— 11 2 II^11 " 0^CH3 0^  c  H2^II0  (  0  CH3  ff cC H )  (H2C CH  Figure 9: Unsaturated Polyester Resin (Bureau et al, 2001)  Epoxy resins, first developed in the 1940s, have great versatility, high mechanical properties, high corrosion and chemical resistance, and good dimensional stability. Compared to polyester, epoxy resins shrink less and have higher strength /stiffness at moderate temperatures. They also cure slowly and are quite brittle after they are fully cured. Epoxy resins tend to be non polar (Williamson, 2002).  Vinyl Ester offers a transition in mechanical properties and cost between the easily processed polyesters and higher-performance epoxy resins. Compared to polyesters, vinyl ester resins shrink less and absorb less water and are more chemically resistant. Different  14  vinyl ester resins are available for different applications. Like most epoxies, vinyl esters are non polar (Williamson, 2002).  Phenolic resins are the predominately used adhesive system for the wood composite industry. Therefore, as a reinforcement of wood composites, FRPs manufactured using phenolic resin should be more compatible with the wood composite materials. Phenolic resins are usually dimensionally stable to temperature. They have excellent physical and mechanical durability. They also have a good adhesive property, low smoke production, and low flammability. Phenolic resins are usually modified using an elastomer or resorcinol. Phenol-Resorcinol Formaldehyde (PRF) resins are very popular as a resin matrix for FRP and as a binder in many other applications (Williamson, 2002). Table 2: Polymer Molecules (Banthia, 2003)  Resin Epoxy  Tensile Cure Specific Tensile Gravity Strength Modulus Shrinkage [GPa] iMPaj FA] '^li0^0^11 / \^r N.,/ /^I^I^\ \  1.201.30  55.00130.00  2.754.10  1.00-5.00  1.101.40  34.50103.50  2.103.45  5.00-12.00  1.121.32  73.0081.00  3.003.35  5.40-10.30  H^H^H^1I^(R and /e arc 11  complex  rullyiunctIonal \^ N — 11-^molecules) /  11  Polyester  ( it.,—(x1^0^0 I^,- -^II^II HC — 0 il^10^—02/0,— C-011 I^., H•C — 011  Vinyl Ester  0  Compared to wood, FRPs have a much higher tensile strength and stiffness. With their high strength and stiffness, the fibres carry the loads imposed on the composite, while the resin matrix distributes the load across all the fibres in the structure. The combination of reinforced fibres and resin matrix is more useful than the individual components (Williamson, 2002). The mechanical properties of fibre-reinforced polymer composites  15  are highly dependent on good load transfer from the fibres to the matrix material, which in turn is significantly impacted by the interface between the fibre and matrix. The compatibility between fibres and polymer matrix is the critical step for the manufacture of the fibre-reinforced polymers. Most fibre-reinforced polymer composites fail because of inadequate bonding at the interface between reinforcement and matrix resin.  2.2.2 Fibres The three commonly used fibres for producing FRPs for concrete applications are glass, synthetic fibres, such as aramid, and carbon/graphite. Their respective properties are provided in Table 2.  Chemically, glass fibres are constituted of Silica, Aluminum Oxide, and Magnesium Oxide. They have many advantages, including hardness, corrosion resistance, inertness, light weight, flexibility and low cost. All glass fibres have similar stiffness but different strength values and different resistance to environmental degradation. The commonly used glass fibres are E-glass (E for electrical), S-glass (S for strength), and C-glass (C for corrosion). Other types of glass fibres include D-glass (D for dielectric) and A-glass or AR-glass (AR for alkaline resistant). E-glass is the most commonly used glass fibre because it is the most economical for composites, offering sufficient strength at a low cost. Disadvantages of glass fibres include brittleness, low elastic modulus, reduction of tensile strength in the presence of water, and static fatigue (Williamson, 2002).  Carbon fibres, also called graphite fibres, are strong, lightweight, and chemically resistant. Carbon fibres are much stronger and stiffer than glass fibres. They have negative coefficients of thermal expansion, making them dimensionally stable. Carbon fibres are also good electrical conductors (Williamson, 2002). The major limitation factor for the application of carbon fibres is their cost. For carbon fibres used as reinforcement in composite materials, the fibres must go through several processing steps to ensure compatibility with matrix resin system. The first step involves oxidation or chemical treatment of the fibre surface to introduce functional groups (OH, NH2, COOH, etc.)  16  capable of interacting with matrix resin. The second step involves sizing or coating the oxidized fibre with a coupling agent, and/or resin precursor. Carbon fibre is currently produced in relatively limited quantities mostly via two manufacturing processes:  1)  Based on pitch (coal tar and petroleum products)  2)  Based on Polyacrylonitrile (PAN)  Pitch and PAN carbon fibres have properties that suit different applications. The most common carbon-fibre type is PAN, primarily for structural reinforcement because of its high tensile strength. Pitch fibres, on the other hand, offer designers a different profile. They are easily customized to meet specific applications. They often have a higher modulus, or stiffness than conventional PAN fibres, are intrinsically more pure electrochemically, and have higher ionic intercalation. Pitch fibres also possess higher thermal and electrical conductivity, and different friction properties (Carbon Fiber Research at UTSI, 2006).  Synthetic fibres are made by a process of aligning the polymer chains along the axis of the fibre. They can also exhibit very high strength and stiffness, good chemical resistance, and low density if a suitable process is used. The best-known polymer fibres are the aramid fibres, first commercialized by DuPont in 1971 under the trade name Kevlar. Kevlar fibres usually exhibit high specific strength and stiffness or high specific toughness. They also have a high thermal stability, low creep, and good chemical resistance. Disadvantages of aramid fibres include poor compression strength, susceptibility to moisture, UV and visible light (Williamson, 2002).  17  Table 3: Fibre Properties (Banthia, 2003)  FIBER TYPE  CARBON PAN High  Pitch  Strength High Modulus Ordinary High Modulus  Tensile Strength [MPa]  Modulus of Elasticity [GPa]  Elongation Coefficient of [%] Thermal Expansion [x106]  Poisson's Ratio  3500  200-240  1.3-1.8  (-1.2) to (-0.1)  25004000 780-1000 30003500  350-650  0.4-0.8  7 to 12  38-40 400-800  2.1-2.5 0.4-1.5  (-1.6) to (-0.9)  N/A  0.35  -0.2  ARAMID Kevlar 29 Kevlar 49  3620 2800  82.7 130  4.4 2.3  Kevlar 129  4210 (est.) 3450 2800  110 (est.)  --  N/A -2.0 59 N/A  172-179 130  1.9 2.3  N/A (-2.0), 59  3500  74  4.6  N/A  35003600 4900 18003500  74-75  4.8  5.0  0.2  87 70-76  5.6 2.0-3.0  2.9 N/A^,  0.22 N/A  Kevlar 149 Twaron Technora GLASS E-Glass S-Glass Alkali Resistant Glass  2.2.3 FRP Application Techniques FRP has proven useful in the retrofit of various types of structural elements. It may be used for the strengthening of beams through the application of FRP sheets to the tension face of the beam, seismic upgrade of wall panels by the application of FRP sheets, as well as the jacketing of columns with FRP to provide confinement. There exist a myriad of application methods for various different FRP uses. For the purposes of this discussion, we will limit FRP application methods to those primarily used in retrofit applications.  In most instances, the FRP is applied to the structural member in the form of a thin mat with continuous unidirectional fibres. The mat may be applied for the most desirable geometric configuration. The substrate and the mat are bound together through the  18  application of adhesives/bonding agents, and/or through mechanical linkage in the form of some sort of a mechanical anchoring system. A second method of FRP application is the wet lay-up process (Figure 10). In the wet lay-up process, the resin has a double function of adhesive for wood and matrix for the fabric reinforcement. First the substrate is gel coated with the resin. The fibre reinforcement is applied in the form of a fabric sheet. Prior to application it is submerged in and saturated with resin. The sheet is then applied onto the substrate using a hand roller and smoothed to remove air pockets (Vick, 1999). Upon drying the FRP/substrate will act as a composite material.  Resin (catalyzed) Hand roller  Fiber reinforcements  Gel coat Mold ^  Figure 10: Wet Lay-Up Process (Williamson, 2002)  In some circumstances, it is impractical to apply sheets due to geometrical/practical constraints. In such instances, it is desirable to apply the FRP in an alternate manner A novel technique has been pioneered at the University of British Columbia by which FRP is applied in the form of a spray. Although the SFRP system is not new technology (it has been used for years in the boat building and automotive industries) its application to the retrofit of structural members is unique. Prior to application, the element surface is coated with a bonding agent/adhesive. Polymer is then sprayed out of a nozzle towards the surface. Attached to the nozzle is a fibre chopping device, which cuts the fibre into desired lengths and injects it into the spray stream along with the polymer. The FRP then impacts the surface and coats it. A major advantage of this system is that the fibres are  19  oriented isotropically. Consequently, several layers of anisotropic FRP sheets may need to be applied in more than one direction to achieve the same action as one layer of FRP spray (Banthia and Boyd, 2000).  Figure 11: Spray FRP Process (Banthia, 2003)  2.3 Adhesive Chemistry Wood adhesives are polymeric materials that are capable of interacting physically or chemically, or both, with the surface of wood in such a manner that stresses are transferred between bonded members, hopefully without rupture of the adhesive or detachment of the adhesive from the wood. A detailed description of physical and chemical bond types is provided in Section 2.5.  Wood adhesives have existed for thousands of years. Originally, adhesives were derived from natural sources. Natural adhesives such as casein, animal blood, tree resin and animal waste were commonly used until recently as primary types of wood adhesives (Pizzi and Mittal, 1994).  However, over the past 50-60 years, tremendous research and effort has been conducted into the development of new types of synthetic adhesives. Today, highly durable synthetic adhesives produced from petrochemicals are available for the production of stronger, more efficient wood structures, as well as the production of engineered wood products such as glulam or plywood made from waste wood (Pizzi and Mittal, 1994).  20  The most common types of wood adhesives available today are Phenolic adhesives (Phenol Formaldehyde, Phenol Resorcinol Formaldehyde), Amino adhesives (Urea Formaldehyde, Melamine Urea Formaldehyde), and Polymeric Isocyanate (pMDI) adhesives (Conner, 2005).  Phenolic adhesives such as Phenol Formaldehyde (PF) are formed by the reaction of phenol with formaldehyde. By varying the amount of catalyst, reaction time, phenol to formaldehyde ratio, and temperature, a number of adhesive systems with different characteristics can be formulated. Other phenolic adhesives such as Phenol Resorcinol Formaldehyde (PRF) are formulated by simply incorporating resorcinol into the phenolformaldehyde reaction, or by replacing the phenol altogether. In any case, formaldehyde essentially acts as a driving mechanism, as the reaction of formaldehyde with phenol/resorcinol leads to the formation of hydroxymethylated derivatives of phenol. Over time, methylene linkages form between adjacent hyrdoxymethylated groups to form a 3-D polymeric network which cures to form a hardened resin.  Phenolic adhesives are often used in the production of engineered wood products, such as wafer board, plywood, or glulam. The hardened resin/adhesive is a durable, high strength complex, capable of withstanding cyclic changes in temperature and moisture, making for an excellent adhesive for use outdoors.  Amino adhesives form through the reaction of urea with formaldehyde. In the first stage of the reaction, formaldehyde is added to urea to form mono, di and tri hydroxymethylureas. This part of the reaction takes place under basic conditions. The pH of the complex is then decreased through the addition of an acid cure catalyst, which allows for condensation reactions to start via reaction of adjacent hydroxymethyl groups and amino nitrogens. The resulting hardened resin/adhesive is often used as a laminating adhesive, an adhesive for hardwood, or adhesive for furniture's. Unfortunately, Amino adhesives are not very moisture resistant (Pizzi and Mittal, 1994), and are usually limited to indoor applications only.  21  Polymeric Isocyanates are a particularly important class of adhesives because of their unique bonding properties with wood (Weaver and Owen, 1995). All isocyanates of industrial importance contain two or more isocyanate groups (—N=C=O) per molecule. At room temperature, pMDI is a clear brown liquid with a viscosity of about 0.5 Pa s and a low vapor pressure. It has an excellent shelf life as long as moisture is excluded. The adhesive properties of pMDI stem from the reactivity of the isocyanate groups. These groups react with compounds that have an active hydrogen, such as water, alcohols, and amines. Figures 12 and 13 show the common types of Isocyanate reactions. Heating increases the rate of this reaction, and at high temperatures the reaction can be extremely rapid. In addition to reacting with the moisture in wood to form polyureas, it is theoretically possible that covalent bonds form between hydroxyl groups in the wood and the isocyanate. These covalent bonds, to the extent that they form, act to anchor the polyurea to the wood and help bridge the gap between pieces of wood. R-NCO + HO-Wood 4 R-NH-CO-O-Wood Figure 12: Formation of Polyurethane via Isocyanate-Wood Reaction  R-NCO + H2O - R-NH-CO-OH -› R-NH 2 + CO2 Isocyanate Water^Carbamic Acid^Amine Carbon Dioxide  R-NCO +R-NH2 R-NH-CO-NH-R' Isocyanate Amine^Polyurea  Figure 13: Formation of Polyurea via 2-step Isocyanate-Water Reaction  Studies have shown that of the three major chemical components of wood, lignin is generally the most reactive with isocyanate (Weaver and Owen, 1995). In order to bond wood with non wooden materials, an adhesive which is able to chemically react with the surfaces of both materials must be selected. Although the adhesives mentioned above are capable of forming excellent bonds with wood, careful  22  research must be done to ensure that they are capable of forming bonds with a potentially dissimilar substrate.  2.4^Hydroxymethylated Resorcinol Hydroxymethylated Resorcinol (HMR) is a primer/coupling agent developed in the 1990's at the USDA Forest Service Products Laboratory. It consists of mono-, di-. and trihydroxymethylated resorcinol and oligomers of such molecules (Figure 14). It is prepared by reacting formaldehyde with resorcinol in a 1.5 molar ratio at mildly alkaline conditions.  HIldradmstIrMed^SW Moor  Figure 14: HMR Molecule, (Gardner, 2001)  HMR is a coupling agent which is able to react with different surface molecules of different materials, allowing it to be able to couple epoxy and other thermosetting adhesives to wood (Vick, 1995), (Christiansen and Vick, 2000). Therefore, epoxy/vinyl ester adhesives bond well to HMR primed wood, also allowing for either type of polymer to be used as a polymer matrix in wet-lay FRP (Vick 1995). The exact bonding mechanisms of HMR to wood and various types of polymers have not yet been confirmed, but several theoretical models exist. Figure 15 shows the theoretical bonding 23  mechanism of HMR to a wood surface. HMR is believed to bond to wood surfaces by forming ether linkages between hydroxymethyl groups of the coupling agent and primary alcohols of cellulose. Figure 16 shows the theoretical bonding mechanism of HMR to an Isocyanate adhesive, as well as to a Phenol Formaldehyde Resin (PRF) Adhesive. Note that in Figure 16, Bond A is a urethane linkage formed by the reaction of an isocyanate with the hydroxymethyl group of HMR, while Bond B is a methylene linkage allowing for bonding to PRF.  OH CH2OH  HAIR OH H— H Ether Linkage  Wood Figure 15: Theoretical Wood-HMR Bonding Mechanism, (Gardner, 2001)  0  I  RN^COCH2  B  OH  OH  CH2 A CH2O OH Ether Linkage —01.-^Hydrogen Bond  MO  HMR Treated Wood Figure 16: Theoretical HMR-Isocyanate/PRF Bonding Mechanism, (Gardner, 2001)  Many experiments involving HMR have shown that it can greatly increase the bonding capability of a variety of adhesives, including epoxy, vinyl ester and polyester to wood (Lyons and Ahmed, 2005). HMR has been shown to improve bonds between Copper 24  Chromate Arsenate (CCA) treated wood and adhesives as well. Finally, testing on wood treated with HMR has shown that HMR has the capacity to increase its resistance to delamination due to natural elements, including increases in temperature, or swelling/shrinkage due to moisture penetration (Richter and Steiger, 2005). Therefore, use of HMR may be advantageous when the wooden substrate is to be subjected to particularly harsh climates.  2.5 Timber FRP Bond Mechanisms -  If a proper bond is not attained between the FRP and original element, the FRP will be susceptible to premature delamination, composite action will not occur, and failure may occur upon the application of appreciable loading. Therefore, successful application of FRP to wood elements requires that a high quality, durable bond be developed between two dissimilar materials (Lopez-Anido et Al, 2000).  The dissimilarities are plentiful in number. While wood tends to have a heterogeneous surface chemistry, the surface chemistry of an FRP mat is much more homogenous. This tends to cause non uniform bonding to occur over the surface. Secondly, the surface of wood is highly porous, and the affinity of cellulose for water causes the wood to be highly hydrophilic (Vick, 1999). Consequently, water is easily absorbed into wood, causing it to swell and shrink. FRP on the other hand, is not porous at all. The cycle of wood swelling and shrinkage can tend to strain and break any bonds that have formed between the wood and the FRP. Furthermore, while wood is a polar material, due to the presence of polar molecules such as cellulose, hemicellulose and lignin, the FRP may or may not be polar depending on the polymer matrix used. Polar and non polar adherents will not bond together very easily, as it is much more difficult to form chemical bonds between their respective surfaces.  A proper bond is formed through a combination of mechanical bonds along with chemical bonding. Mechanical bonds are attained when surfaces are held together by an adhesive that has penetrated the porous surface while it is liquid, allowing the two  25  surfaces to anchor themselves to one another during solidification. Effective mechanical interlocking takes place when adhesives penetrate beyond the surface debris and damaged fibres into sound wood two to six cells deep. Deeper penetration into the fine microstructure increases the surface area of contact between adhesive and wood for more effective mechanical interlocking. If an adhesive penetrates deeply enough into sound wood and becomes rigid enough upon curing, the strength of the bond can be expected to exceed the strength of the wood (Vick, 1999). In the case of application of SFRP to wood only, this is the primary method of interfacial bonding between the two materials. The deeper the penetration of the SFRP resin into the wooden surface, the greater the interlock and the stronger the bond. Mechanical interlock may be also be enhanced artificially in several ways, such as through the provision of surface voids to promote adhesive penetration, the use of vacuum assisted resin infusion to promote surface absorption of the adhesive (Herzog, 2005), or by the provision of some sort of external mechanical anchorage device. Possible types of chemical bonds between FRP and wood include covalent bonds, Van der Waals bonds and hydrogen bonds. Hydrogen bonds and Van der Waals bonds are types of bonds formed between polar molecules when molecules with dipole moments attract each other electrostatically by lining up so that the positive and negative ends are close to each other. This is called dipole-dipole attraction. Covalent chemical bonds form when atoms of nonmetals interact by sharing electrons to form molecules. These covalent bonds are the strongest of chemical bonds; they are more than 11 times the strength of the hydrogen bond (Zumdahl, 1998). Chemical bonding is usually advanced by the provision of some sort of chemical adhesive or primer to the substrate surface. The presence of an adhesive may act as a medium allowing to dissimilar surfaces to bond together. For example, Surfaces A and B may not be able to form bonds with each other on their own. However, if Surface A and Surface B both bond with Adhesive C, then by applying Adhesive C to Surfaces A and B, reactions can occur between the adhesive and each of the respective surfaces, and upon curing of the adhesive, the two dissimilar surfaces will be able to bond together through  26  the medium of the rigid adhesive. A primer may serve to enhance the properties of a nadhesive, allowing the substrate surface to react more vigorously with the adhesive, or it may chemically alter the surface of the substrate, and allow it to bond to surfaces with which the substrate was previously unbondable. In the case of HMR and isocyanate, the isocyanate acts as the adhesive, reacting with wooden surfaces to form urethane bonds. The HMR simply enhances the properties of the Isocyanate by allowing for the formation of additional urethane linkages between the HMR molecules and the isocyanate adhesive.  Clearly there are inherent difficulties associated with trying to bond two dissimilar materials such as wood and FRP. However, when joined properly, it is possible to bond the two such that they form a very efficient composite. First, it is important to ensure that the adherent surfaces are properly prepared. Wood surfaces should be smooth, flat, and free of machine marks and other surface irregularities, including planar skips, and crushed, torn, and chipped grains. The smoother a surface is, the more easily it will be wetted when an adhesive is applied to it (Vick, 1999). Figure 17 clearly demonstrates the differences in surface wettability. The same piece of wood has been smoothened by three different amounts with sandpaper, A being non smoothened, C being the most smoothened. C displays the greatest wettability, as indicated by its small contact angle. However, as a note of caution, for wood surfaces, excessive sanding may damage the surface of the wood, and will also limit the amount of frictional interlock generated by adjacent adherents. Therefore, while wooden surfaces should be sanded, excessive sanding would in fact impede surface bonding.  Figure 17: Variations in Surface Wettability (Vick, 1999)  27  Next, the wood substrate should be free of burnishes, exudates, oils, dirt, and other debris. The greater the amount of contaminant present on the surface, the more difficult it will be to join the adherents, as the contaminant will be apt to interfere in the development of strong intermolecular bonds. For this same reason, woods that have been pretreated with chemicals such as Chromated Copper Arsenate (CCA), or oil based fungicides such as creosote, tend to form weaker bonds with other substrates (Herzog, 2004)). Metallic ions deposited from the application of CCA can interfere with the formation of chemical bonds between adhesives and substrates. Likewise, oil residue from creosote can prevent the formation of chemical bonding, as well as clogs up void space/pits at the outer surface of a wooden specimen preventing proper surface absorption of applied adhesives, and the development of mechanical interlock.  The type of wooden substrate selected may make a difference. Typically, woods which are of lower density will have higher porosity, and allow for adhesives to penetrate more deeply into their surfaces, forming a stronger bond between the two adherents (Vick, 1999). Additionally, certain species of softwoods are known to have greater amounts of pitting amongst adjacent tracheids, which would also promote penetration and absorption of resins/adhesives applied to the substrate surface.  28  3 PREVIOUS RESEARCH 3.1 Reinforced Concrete-FRP Composites Composites have gained widespread use as strengthening material for structures in applications where conventional strengthening techniques may be problematic. However, by far, the majority of applications and research work has been carried out on reinforced concrete (RC) structures. This fact is abundantly clear given that the majority of literature which has been written on FRP retrofitting concerns retrofitting of RC structures only. Although concrete and timber are different construction materials with independent mechanical characteristics, reviewing the nature of RC-FRP bonding provides insight into how to achieve a proper bond between FRP and timber.  Use of FRP in RC elements has been widespread. Bakis et al (2004) provided a state of the art review of FRP composites for construction, and detailed some of the applications. FRP strengthening has been used for flexural and shear strengthening of RC beams, confinement in structurally deficient RC columns, or upgrading of shear capacity of shear walls (Burwell et al, 2006).  Debonding of FRP from concrete occurs at two distinct interfaces. One is the interface between the concrete and the binder. The second is at the interface between the binder and the FRP. The interaction between the bond properties and the concrete cracking behavior is very complicated and directly influences the efficacy of the FRP strengthening. Therefore, the investigation of bond behavior and its effect is extremely important for the efficient application of FRP bonding technology. As described in Section 2.5, even for concrete, a good bond is developed through a combination of mechanical interlock and chemical bonds. Niu and Wu (2001) contended that debonding  29  propagation resembles in-plane shear/sliding fracture behavior in that FRP sheets are primarily loaded in tension and the adhesive layer is mainly in shear transferring stresses from the concrete to the FRP composites. As the binder transfers stresses between the two materials, the physical properties of this material and its interaction with the substrate and the FRP compatibility between the binder, the substrate and the FRP is key. Compatibility can be defined as a balance of physical, chemical, and electrochemical properties and dimensions between a repair material and the existing substrate that will ensure that the repair can withstand all the stresses induced by volume changes and chemical and electrochemical effects without distress and deterioration over a designed period of time (Emmons et al, 1993).  Buyukorturk et al (2004) provided an excellent summary of the reasons why one may choose retrofit using externally applied FRP, types of failure and the mechanisms behind FRP-RC debonding. In the case of RC beams, it was identified that failure may take place through (1) concrete crushing before yielding of the reinforcing steel, (2) steel yielding followed by FRP rupture, (3) steel yielding followed by concrete crushing, (4) cover delamination, (5) FRP delamination. Debonding of FRP strengthened members takes place in regions of high stress concentrations, which are often associated with material discontinuities and with the presence of cracks. Propagation path of debonding initiated from stress concentrations is dependent on the elastic and strength properties of the repair and substrate materials as well as their interfacial fracture properties. Crack propagation in one of the constituent materials is generally preferred over interface debonding in design of structural joints; however, the latter is often encountered, especially in cases of poor surface preparation or application. Saadatmanesh and Ehsani (1990) suggested that improper selection of adhesives might promote debonding failures.  Toutanji and Ortiz (2001) conducted a study on the effects of different surface preparation techniques on the bond interface between FRP sheets and concrete members. They concluded that externally bonded FRP sheets can increase the tensile strength and stiffness of RC specimens. They also concluded that water jet surface treatment of the  30  substrate produces a better interfacial bonding strength than surface treatment using a sander.  Finite Element (FE) modeling has been a key tool in trying to understand interfacial debonding behavior of FRP composites. Baky et al (2007) have provided an excellent description of all the different FE models that have been developed to try to understand the interfacial behavior of FRP strengthened RC beams. They also concluded their own analysis and determined that the maximum interfacial shear stress was seen to be dependent on the steel reinforcement ratio.  RC-FRP composite technology has advanced tremendously over the last few years. Researchers now have a good understanding of the topic, and of late, researchers have begun to review and question some of the initial guidelines/design manuals used to aid engineers in RC-FRP design. Harries and Aidoo (2006) reviewed the guidelines currently in place to mitigate debonding failures. They concluded that the current guideline used in the USA "ACI 440.2R-02- Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures" was generally adequate. The concurred with Smith and Teng (2002a, 2002b) that these models only show good predictive capacity using the data from which they were derived. Instead they recommended that these guidelines be reviewed and use a more generalized alternative proposed by Teng et al (2001). Ueda and Dai (2005) summarized and evaluated the existing test methods for evaluating the bond behavior of FRP sheet-concrete interfaces and introduced some updated modeling methods for the bond properties of the FRP sheet-concrete interfaces under various conditions.  3.2 Timber FRP Composites -  While the application of SFRP to timber is an entirely new technique, FRP composites have been studied and have been used in the past to successfully reinforce timber structures. Research on timber beams reinforced with FRP materials has increased beginning in the 1990's. Plevris and Triantafillou (1992) conducted an experimental and numerical investigation of beams reinforced with Carbon Fibre Reinforced Polymer  31  (CFRP) sheets, and concluded it was possible to increase the load carrying capacity of a specimen by increasing the area fraction of the fibre composite to an upper limit. Gentile (2000) looked at the flexural strengthening of timber bridge beams using Glass Fibre Reinforced Polymer (GFRP) rods. He found it was possible to increase the flexural strength and ductility using such a method. Dempsey and Scott (2006) evaluated the effect of mechanically fastening FRP strips to Southern Pine wood members, and concluded it was possible to increase ultimate moment, stiffness and ductility. The magnitude of each increase was partially dependant on fastener spacing. Johns and Lacroix (2000) looked at the application of GFRP and CFRP to commercial sawn lumber specimens. They concluded that the application of the strengthening material increases the effective strength of the wood, and has a greater effect on increasing strength of smaller, lower grade sections. Fiorelli and Dias (2003) conducted similar tests on pinewood beams, and compared their results to a theoretical model. They noted that use of reinforcement leads to an increase in ductility, particularly in the failure phase of a test.  Additionally, there have been numerous tests carried out on laminated timber beams. Gilfillan et al (2003) looked at experimental and theoretical results of reinforced Sitka Spruce laminated beams. Dagher et al (1996) investigated the benefits of reinforcing glulam beams made with Eastern Hemlock. Johnsson et al (2006) looked at the strengthening of glulam members by CFRP bars. Issa and Kmeid (2005) examined glulam beams reinforced with steel plates as well as CFRP. Dorey and Cheng (1996) and Hernandez et al (1997) conducted experiments on reinforced glulam, with the common finding between all these studies being that FRP materials can increase strength and ductility of glulam beams, and better utilize the compression strength of wood, by forcing failure in the compression zone at the top of the beam first, propagation of the failure downwards, finally followed by eventual rupture in the tensile zone and failure of the beam. Consequently, the mode of failure in reinforced specimens was a ductile one while failure was sudden and brittle in unreinforced specimens.  32  With regards to analytical modeling, pioneering work in determining stress-strain behavior of timber was carried out by Bazan (1980). He studied the relationship between tension, compression and bending strengths for clear wood, and proposed an idealized stress-strain relationship for wood with a bilinear relationship to represent the compression behavior. Buchanan (1990) modified this relationship slightly and used it to predict the bending strength of commercial timber. Bazan and Buchanans work formed the basis for Plevris and Triantifillou (1992) to develop an analytical model for TimberFRP composites taking into consideration non linear behavior. Similar work was done to try to predict ultimate flexural strength of old sawn lumber beams reinforced with CFRP laminates by Boai et al (2004). Gentile (2000) also explicitly developed a model to try to model failure of timber beams reinforced with GFRP rods. In all cases, it was found that when non linear behavior of timber is taken into consideration, it is possible to predict ultimate failure load with a very high level of accuracy.  It should be noted that in addition to laboratory studies of Timber-FRP composites, there have been successful field applications. The 39 year old Tourond Creek Bridge in Manitoba, Canada was the first timber bridge to undergo strengthening via reinforcement with GFRP bars. After rehabilitation, the 3 span, 23.3 meter structure is estimated to be at least 30% stronger. The province of Manitoba owns approximately 575 similar bridges, the majority of which are deficient in their load carrying capacity by today's standards. It is estimated that bridges similar to the Tourond Creek Bridge can be strengthened for about 15% of the cost estimated to completely replace it (Gentile et al, 1999).  There has also been much research conducted with regards to methods of improving the Timber-FRP bond itself. One of the most promising developments in Timber-FRP bond research is the development of Hydroxymethylated Resorcinol. Vick (1995) first published a paper detailing its successes in producing highly durable bonds to prevent delamination of FRP from HMR primed timber. The formulation was improved upon to prolong its shelf life in 2003 (Christiansen et al, 2003). Lyons and Ahmed (2005) conducted a comprehensive study on the factors that affect the bond between polymer composites and timber and concluded that HMR will improve bond strength except in dry  33  environmental exposure. Richter and Steiger (2005) confirmed that HMR can help overcome the problem of weak moisture stability of polyurethane and epoxy adhesives. Isocyanates are commonly used as wood adhesives. Weaver and Owen (1995) investigated the nature of Isocyanate-Timber bonding. Phanopoulos et al (1999) described the nature of isocyanate adhesion and penetration to timber and concluded that the bond is formed mainly through deep penetration and chemical interaction with lignin. Mufti et al (2001) conducted a series of experiments where a particular glue, Rotafix CB 10T was investigated for bonding GFRP's to timber sufaces treated with creosote. It was found that the interfacial shear strength was more than sufficient for most realistic loading cases. Finally, in addition to simply looking at chemical adhesion, Herzog et al (2005) investigated the durability of FRP-Timber composites fabricated using a pressure resin infusion system (ComPRIS). The fabrication method was found to produce materials with a shear strength equal to or greater than FRP composite sheets bonded with an epoxy resin.  34  4 EXPERIMENTAL PROGRAM This section begins by providing mechanical, chemical, and physical data for each of the different materials used in each experiment. This is followed by a detailed description of the test method, including information on material preparation, testing equipment, and loading schemes. 4.1^Materials  Following is a description of each of the materials that were used in the testing process. 4.1.1 Beam Species  Figure 18: Beam Specimens  The beam species selected was Douglas.Fir, procured from a local lumber yard (Figure 18). Douglas Fir is a commonly occurring softwood, which is often used for heavy construction applications. Its properties are given in Table 4:  35  Table 4: D.Fir Properties, (CWC, 2005 Property  Value  Flexural Strength  28 MPa 10000 MPa  Flexural Modulus  The beam dimensions were 305mm or 355mm in depth, 152mm in width, and 2438mm in length (Figure 31). These particular dimensions were chosen as they are typical of beam spans for many timber bridges currently in service in Eastern Canada. 4.1.2 Polyester Resin  The type of resin used throughout the experiment was the 713-6674 polyester resin manufactured by Hexion Specialty Chemicals Hexion 713-6674 is a general purpose unsaturated polyester resin having the properties given in the table below. Table 5: Resin Properties, (Product Bulletin, 2005) Property  Value  Flexural Strength Flexural Modulus Tensile Strength Tensile Modulus Tensile Elongation at failure  114 MPa 3620 MPa 60 MPa 3895 MPa 2%  Polyester resins are considered to be optimal for the spray process, as they are of low viscosity, and are able to form a stable matrix with glass fibres. Additionally, the ester groups present on polyester molecules present the opportunity for the formation of polar bonds between the wooden substrate and the resin itself.  36  4.1.3 Glass Fibre  Figure 19: Glass Fibres Applied to Beam  The type of fibre used throughout the experiment was ER2400JP6 Gun Roving, manufactured by Gibson Fibreglass. Glass roving is easy to chop, and forms a stable composite when embedded in a polyester matrix. Therefore, it is an ideal choice for use in SFRP applications. As fibre length increases, so too does the strength of the SFRP material. This effect can be attributed to better stress transfer and higher stress in the fiber, as the fibre length increases. A decrease in fibre length means that the stresses must be transferred from one fibre to another more often along the length of the composite. Such an increase in the number of stress transfers essentially increases the effect of the matrix on the overall composite strength since it is the matrix that must act as the stress transfer medium. It is this increased matrix contribution that induces greater non linearity in the stress strain response of SFRP material. Secondly, the longer the fibre length, the greater the surface area along which stresses can be transferred from matrix to fibre. Therefore, by increasing the fibre length, matrix-fibre interfacial stresses are decreased. So, in order to increase the strength of an SFRP layer, and minimize non linear response, a longer fibre length is desirable. Given the equipment that was available to conduct this experiment, 32 mm long fibre was the maximum possible cutting length, and was therefore selected as the fibre size (Figure 19).  37  However, practically speaking, it is worth noting that as fibre length increases, so too does fibre rebound. As the fibre length increases, it becomes more difficult to embed in a freshly sprayed system. Consequently, a large proportion of the fibre may simply bounce off the substrate surface. The phenomenon was noted by Banthia and Armelian (2002) only, in this case, the fibre was a constituent of a shotcrete spray rather than a SFRP spray. Consequently, in practice, it may be easier and more efficient to spray a shorter fibre length, and accept the decrease in SFRP strength. 4.1.4 Fungicides  Figure 20: Fungicides, Borocol (L), Creosote (R)  Boracol (Figure 20) is a wood preservative which is fungicidal and insecticidal with an added preventative mouldicidal effect; is fungicidal when used as a preventative treatment and fungicidal when used as an eradicant and effective in preventing mould on wood and stone as well as other absorbent surfaces. Boracol has been used for the shortterm remediation of commodities such as utility poles and has shown to add additional service life to such structures for about 8 years (Brudermann, 2006, pers. comm.). It is a waterbased formula, consisting of a clear solution of 19.6% disodium octaborate tetrahydrate and 1.0% didecyl dimethyl ammonium chloride in propylene glycol and water. It penetrates 3 -5 mm into the wood and establishes a reserve from where further penetration takes place.  38  The second type of fungicide used was the commonly used oil borne preservative known as Creosote (Figure 20). Creosote was a commonly used oil-borne preservative used on most structures constructed in the 1950's and 1960's. In addition to killing wood destroying organisms, it increases the dimensional stability of wood. It is toxic/carcinogenic to organisms which come in prolonged contact, and is therefore no longer recommended.  4.1.5 Adhesives/Primers  Three different combinations of chemical adhesives/primers were tested in order to promote bonding between the wood-FRP substrates. The first combination was to use an FRP primer resin known as AtPrime 2 on its own to prime the wooden surface prior to application of SFRP. The second combination allowed for the surface to first be primed with HMR, dried, and then coated with a layer of AtPrime. After application and drying of the AtPrime 2 coat, the SFRP was applied. The third combination was to apply the HMR on its own, and then apply the SFRP.  The properties of HMR have been discussed in Section 2.4. The compound was synthesized in the UBC Environmental Engineering Laboratory. It was synthesized using the following constituent chemicals: Table 6: HMR Composition  Composition aHNIR coupling agent Ingredient^ Parts by weight Water, deionized^ 90.43 Resorcinol, crystalline^ 3.34 Formaldehyde, 37 percent^ 3.79 Sodium hydroxide, 3 molar^ 2 .44 100.00 Total^  39  Figure 21: HMR Constituents  After all of the constituents (Figure 21) were combined, the compound was allowed to react for 4 h at room temperature on a stir plate, prior to application onto the substrate surface.  AtPrime 2 is an FRP primer resin developed by Reichold Inc. which serves to enhance secondary bonding performance (Martens et al, 1996). It was used to improve the SFRP to wood bond. AtPrime 2 is able to form a direct chemical bond with a variety of substrates including fully cured FRP, concrete, steel and many thermoplastics. AtPrime 2 cures through a moisture-activated mechanism that employs atmospheric humidity and molecular water on the substrate surface to cross-link the AtPrime 2 primer. It is prepared by mixing two constituent components together at a given ratio specified by the manufacturer. On a molecular level, it is classified as a pMDI adhesive. In this respect, it is highly conducive to be used as a wood adhesive, as pMDI adhesives are already extensively used as high strength adhesives in the manufacture of engineered wood products. The isocyanate group is easily able to react with polar molecules to form urethane linkages.  40  Figure 22: AtPrime 2 Applied to Wood Surface  Inhalation of Isocyanate spray or vapor can be hazardous. As the Isocyanate group is able to react with water molecules in human lungs, overexposure to Isocyanate based adhesives may be fatal. The hazards associated with such adhesives have led them being restricted in some countries. When using an adhesive such as AtPrime, it is essential that proper safety protocol be followed at all times.  4.2^Preparation Preparing the beams prior to testing was an involved and detailed process as outlined in this section.  4.2.1 Sanding #2 D.Fir Beams were first procured and delivered to the UBC Civil Engineering Materials Laboratory. The beams had been sitting outdoors in a lumber yard for an indefinite amount of time, and had been air dried. The beams were all in acceptable condition, and did not show any excessive amounts of cracking or surface deterioration.  41  The beams had been machine cut to dimensions of 152mm x 355mm x 2438mm or 152mm x 305mm x 2438mm. Consequently all surfaces of the beam were rough, and showed minor splintering. Additionally the surface was also very lightly coated with dirt/dust resulting from the outdoor exposure. The condition of the surface required sanding to smoothen the surface such that its wettability was maximized, as well as to remove any contaminants which would interfere with the bond.  Each surface to which SFRP was to be applied was sanded. Sanding was done with a belt sander loaded with a medium grit (#60) sandpaper (Figure 23). The smoother the surface, the greater the surface wettability. However, excessive sanding can damage the surface at a cellular level (Williamson, 2002), and will also hinder the formation of any frictional mechanical interlock at the interface. Therefore, by using a medium grit paper, an optimal combination of smoothness and interlock can be reached.  Figure 23: Belt Sander  4.2.2 Fungicide Application After the surfaces of each specimen had been sanded and brushed clean, Boracol fungicide was liberally applied with a paintbrush according to the manufacturers specifications (Figure 24). The fungicide was applied at the rate of 4.5 m 2 /l. Initially upon  42  application the surface turned to a light green tinge which gradually reverted back to a natural wood grain color. The beams were then allowed to sit for 10 days to allow for subsurface penetration of the liquid.  Figure 24: Wooden Beams Coated with Boracol  4.2.3 HMR Preparation and Application  Figure 25: Color Change of HMR (L- HMR immediately after start of reaction, R- HMR after 4h of reaction time)  43  HMR was prepared according to the foimula given in Section 4.1.5. After mixing together the individual liquid components, crystalline resorcinol was added to the blend, and placed on a stir plate. As soon as the resorcinol was added, the compound began to react, and over time changed from a clear liquid, to a reddish colored opaque solution (Figure 25). Studies have shown that HMR becomes effective after a 4 hour period, and has a maximum shelf life of 8 hours (Vick, 1995), (Christiansen and Vick, 2000). Therefore, it is imperative that the solution be applied to the wooden substrate within 4-8 hours of initial synthesis for the solution to have any effectiveness. Consequently, after being allowed to sit on the stir plate in a fume hood at STP for 4.5 hours, the solution was applied to the D.Fir beams with a paint brush, and then allowed to air dry. As specified, the solution was applied at the rate of 0.15 kg/m 2 .  Figure 26: Comparison of HMR Treated and Untreated Beam  Application of the HMR to the beam surface causes it to permanently change in color, from a natural wood grain, to a slight reddish tinge (Figure 26).  44  4.2.4 AtPrime 2 Application  AtPrime 2 was applied to each of the surfaces of the specimens to which SFRP was to be applied. Application was done as per manufacturer's specifications, with 1 kg covering approximately 10 m 2 . The compound was applied using a paint brush (Figure 27). After application, the AtPrime 2 was allowed to dry for 12 hours before application of SFRP onto the beam surface.  Figure 27: Application of AtPrime 2 to Beam  4.2.5 SFRP Application Process  Spraying was done off campus at a custom FRP fabrication shop, 'Johns Custom Fibreglass', located in Surrey, B.C.  A Venus-Gusmer H.I.S. Chopper Unit equipped with a Pro Gun spray gun was used in this project. It is portable equipment and can be moved to be used easily on site. The system contains three major parts; a resin pump which pumps the polyester resin from the drum, a catalyst pump which pumps the MEKP to the nozzle, and a spray chopper unit.  45  To run this equipment, a compressed air source with a minimum capacity of 0.5 m 3 /min is required. There is no need for electrical power supply unless used in cold weather conditions, in which case an electrical resin heater is required.  •••  Figure 28: Spray Gun  The resin and the catalyst are separately pumped into the spray gun. The catalyst content can be changed by making adjustments at the nozzle. For this study, a 3% MEKP initiator concentration was used. The MEKP concentration will affect the curing time for the spray. At the nozzle, there are inlets for air and the solvent. Air powers the chopper unit and the solvent is used to flush the resin and catalyst at the end of each period of operation. The glass roving is brought to the chopper unit. One of the rollers inside the chopper unit has evenly spaced blades which cuts the roving into a specified length. By changing this roller, the length of the chopped fibres can be changed. The chopper unit used in this project produced chopped fibres 32 mm in length. These fibres are forced out by air flow. The gun sprays the mixture of resin and catalyst with the chopped fibres onto the spraying surface. The final product is a 2-D randomly distributed fibre layer, encapsulated by a catalyzed resin. Although the operation of SFRP equipment is quite simple, being able to produce an exact thickness requires a skilled nozzleman. It is also important to note that corners of the specimen to which SFRP is being applied need to be  46  ground/rounded to allow for proper application and bonding between fibres applied to adjacent sides.  Figure 29: SFRP Application to Beam  After spraying, a ribbed aluminum compaction roller was used to force out any entrapped air voids, and work the material into a consistent thickness. Each pass with the spray gun applies a layer of approximately 2 mm to the surface of a specimen. Therefore, in order to achieve a surface thickness of 6 mm, 3 passes of spraying and rollering were required. On a typical beam, only 3 faces would be exposed and have spray accessibility. The top (compression) face would usually have load applied to it and be covered by a deck or some sort of load applying element. Therefore, in testing, only 3 faces were sprayed with SFRP prior to testing on each beam, the two side faces, and the bottom (tension) face.  Once the spray had been properly worked with the roller, and was of the desired thickness, the specimens were allowed to dry for 24 hours, allowing for the SFRP to harden, before being transported back to the lab.  4.3^Specimen Testing  For this report, beams were subjected to 3 point flexural tests only. 10 beams were subjected to 3 point flexural strength tests under quasi static loading conditions.  47  Figure 30: Static Test Setup  Specimen details are given in Table 7. As seen, Specimens A and F were kept as unsprayed control specimens against which data from the other specimens would be compared to. Specimens B and G were sprayed with 6mm thick SFRP with no additional mechanical anchorage or chemical adhesive applied to enhance bonding. Specimens C and H were first coated with AtPrime 2 only prior to application of 6mm SFRP, while Specimens D and I were coated with both HMR and AtPrime 2 prior to application of 6mm SFRP, with the expectation that the HMR would enhance the properties of the AtPrime. Specimen E and J were coated with HMR only prior to SFRP application. Table 7: Specimen Testing Matrix for Static Loadin Specimen A Specimen B Specimen C Specimen D Specimen E Specimen F Specimen G Specimen H Specimen I Specimen J  SFRP  Bonding Agent  Preservative  No Yes Yes Yes Yes No Yes Yes Yes Yes  No No AtPrime 2 only AtPrime 2 + HMR HMR only No No AtPrime 2 only AtPrime 2 + HMR HMR only  Borocol Borocol Borocol Borocol Borocol Creosote Creosote Creosote Creosote Creosote  48  [I, 6 mm FRP Spray 152mm x 355mm D.Fir Beam  --•-■ 152mm x 305mm D.Fir Beam  Figure 31: Cross Section of Reinforced Specimens Subjected to Static Testing  Testing equipment was located in the UBC Structures Laboratory. A Tinius Olsen Hydraulic Testing Machine, with a maximum capacity of 890 1(1\1 was used (Figure 30). The machine features a rigid frame on which a hydraulic load plate is attached. As the plate moves downward, upon contact with the specimen, a gradually incrementing point load is applied to the specimen. The rate at which the plate can be raised or lowered (and thus the rate of load incrimination) is controlled manually by the user. The specimen is supported on two steel base plates which can be adjusted laterally so as to provide supports for the beam (Figure 32). In all experiments, applied load on the specimen was incremented at the rate of approximately 130 N/sec. Load on the beam was incremented and data from the test was recorded until the beam failed in flexure.  Figure 32: Static Test Setup  49  Each beam was instrumented with strain gauges to determine what the actual surface strains were along various points on the specimen. Strain gauges are used to measure small deformations within a certain gauge length. Electrical strain gauges consist of a foil or wire bonded to the face of the specimen being tested. The strain gauge is bonded to the surface by an adhesive. When using strain gauges it is important to have a strong bond between the gauge and the member. The surface first should be carefully cleaned and prepared, and the adhesive must be properly applied and cured. An electric current is passed through the element, and as it is strained, the electrical resistance changes proportionally. As the surface deforms, the strain gauge also deforms, and consequently the resistance changes. Based on the resistance change, the actual surface strain can then be inferred. 30 mm, KFG-30-120-C1-11L 5M2R strain gauges (Figure 34), manufactured by Kyowa Electronic Instruments Co were used in all experiments. Gauge locations are indicated on Figure 33. ® Strain Gauge Displacement Pod  Figure 33: Beam Dimensions and Instrumentation Diagram  50  Figure 34: Strain Gauges  Load was applied onto each specimen by a vertical hydraulic loader. A load cell with 800 kN capacity was attached to the base of the loader to measure the applied load. A load cell is an electronic force measuring device commonly used in laboratory tests. In this device strain gauges are attached to a member within the load cell, which is subjected to axial loading or bending. An electrical voltage is input to the load cell and an output voltage is obtained. By knowing the relationship between force and the output voltage, the force can be determined by measuring the output voltage. A 150mm x 150mm x 25mm steel plate was placed on the surface of the 355mm deep specimen where the loading apparatus was to make contact (Figure 35). The steel plate is required so as to evenly distribute the load over a larger area, as opposed to allowing the load cell to come in direct contact with the beam, which would cause premature local crushing at the contact surface. As the loader continues to move downward, the load is incremented and in turn is measured by the load cell.  51  Figure 35: Steel Plate and Load Cell  The loading plate size was increased to 150mm x 200mm x 25mm for the 305mm deep specimens.  Maximum displacement of a beam subjected to 3 point flexural testing occurs at the load point. To measure this deflection, a displacement pod was attached to the beam.  52  5 RESULTS 5.1^Three Point Flexural Test Analysis, Borocol Treated  For this study, specimens were subjected to quasi-static 3-Point flexural tests only. The first set of tests were on beams which had been treated with Borocol preservative.  5.1.1 Beam A  Beam A was the control specimen. It was a beam which had been treated with fungicide, but had not been reinforced with any SFRP. Results from the other tests were compared against this test to determine what kind of improvement in properties had been achieved.  53  The Load vs. Displacement curve for this beam is given in Figure 36.  240 210 180  F  150  ..... 120 cs Cu 0 90 _.1 -  60 30 0 0  10^20^30 -  40  Displacement (mm) Figure 36: Beam A, Load vs. Displacement  The energy absorbed by the beam to failure was calculated by approximating the area under the Load vs. Displacement curve, and was found to be approximately 2.4 kJ.  The mode of failure was very much consistent with typical modes of failure for lumber specimens being subjected to a flexural load. The beam exhibited linear elastic behavior upto about 70% of the ultimate load. After this point, the beam began to exhibit inelastic behavior. The beam was observed to be crushing in the area around where the loading plate was located, causing the neutral axis of the beam to slowly move downwards. Finally, the beam failed due to rupture in the tension zone at the bottom of the beam.  54  Table 8: Beam A Results  Yielding Load (kN) (Approximate) 130  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  184.7  20.1  2.4  Analysis of strain gauge data seems to confirm the point at which the beam began to deform inelastically. The strains along a cross section of the beam were plotted to determine the location of the neutral axis. After about 130 kN it was found that the location of the neutral axis began to significantly deviate from its original location (Figure 37). After 130 kN compressive strains in the top half of the beam began to decrease, as compressive strains in the middle and bottom sections of the beam began to increase.  350 S 300 Ts 250 200 Cn 150 100 . E 50 CZ^0 fri l-5 -50 -100  1 — S pecimen A  Load (kN) Figure 37: Beam A, Gauge 2, Strains vs Load  Secondly, review of the strain gauge data confirmed the highly variable nature of a wooden specimen over its length. Placement of gauges (Figure 33) was such that theoretically, the strain in Gauge 1 should have equaled the strain in Gauge 5, Gauge 2 should have equaled that of Gauge 6 and Gauge 3 should have equaled that of Gauge 7. While the values were usually close, they were never totally equal. The most likely explanation of this phenomenon is the presence of imperfections such as splits, shakes or knots. Overall, while the beam displayed expected mechanical behavior, locally, the  55  mechanical characteristics were found to vary significantly along the cross section of the specimen.  1400 12100 1000 800  —Strain Gauge 1 —Strain Gauge 5  600  C75 400 200  0 0  50  100  150  200  Load (kN)  Figure 38: Beam A, Gauge 1 vs Gauge 5  900 800 700 600 I 500 — Strain Gauge 2  400  — Strain Gauge 6  300  7  ( ) 200 100 0 -100  U  2110  Load (kN)  Figure 39: Beam A, Gauge 2 vs Gauge 6  56  Figure 40: Beam A, Gauge 3 vs Gauge 7  5.1.2 Beam B  Beam B was reinforced with SFRP without any sort of additional bonding agent/primer being applied prior to its application.  57  The Load vs. Displacement curve for this beam is given in Figure 41:  240 210 180 2 150 4  cs 120 0 90  -  60 30 0 0^10^20^30^40  Displacement (mm) Figure 41: Beam B, Load vs. Displacement  The energy absorbed by the beam was calculated to be approximately 2.2 kJ.  This beam reinforced with SFRP exhibited an unconventional behavior compared to Beam A. This beam exhibited a totally linear response upto failure. Failure was sudden and totally unexpected. Upon reaching maximum load, SFRP in the vicinity of the load application point debonded rapidly, leading to a near instantaneous loss of load carrying capacity. Although the SFRP debonded off the sides of the beam, it in fact never ruptured, and was totally intact in the tension zone of the beam. Although failure was not totally catastrophic, it was essentially brittle in nature, in that failure occurred suddenly, and resulted in permanent inelastic deformation, despite the fact that the loading curve was totally linear.  58  Figure 42: Beam B at failure  The fact that the SFRP debonded off the sides of the beam, and the beam reached its maximum capacity before SFRP rupture indicates that the beam did not act as a true composite, and did not achieve its full potential. Table 9: Beam B Results  Yielding Load (kN) (Approximate) 210.1  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  210.1  22  2.2  Although the load carrying capacity of the beam increased over Beam A by approximately 13%, there was no significant gain in ductility, and therefore, the energy absorbed by the beam was actually less than that of Beam A. 5.1.3 Beam C  Beam C was reinforced with SFRP. Prior to SFRP application the beam had been coated with AtPrime 2 adhesive, in the hopes that it would delay the onset of SFRP delamination from the beam.  59  Unfortunately, during this test, there was a failure in the data acquisition system, resulting in incomplete data being recorded. The Load vs. Displacement graph is shown in Figure 43 for the test upto the point where the data acquisition system failed.  240 210 180 150 120 co 0 90 60 30 0 0^10^20^30^40  Displacement (mm) Figure 43: Beam C, Load vs. Displacement  Although data acquisition failed at 168.8 kN, it was possible to record the ultimate failure load from a manual gauge on the Olsen Testing Machine, at 181 kN. Therefore, there was no strength gain compared to Specimen A. It was not possible to record the ultimate displacement of the beam, but would be estimated somewhere around 25 mm, which would probably result in modest gains in ductility and energy absorption.  The mode of failure of the beam was observed to be similar to that of Beam B. As with Beam B, failure was initiated with debonding of SFRP in the vicinity of the load application point, however, this time the beam did have a mildly more ductile response,  60  and displayed some inelastic deformation even after debonding. However, given that failure was first initiated with SFRP delamination, it is fair to say that the beam had still not utilized its full potential, and did not act as a true composite structure. Table 10: Beam C Results  Yielding Load (kN) (Approximate)  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  140  181  Unknown*  Unknown*  *Due to Data Acquisition Failure  5.1.4 Beam D  Beam D was reinforced with SFRP. The beam itself had first been treated with HMR, and then coated with a thin layer of AtPrime 2 adhesive, to see the effect on the onset of SFRP delamination from the beam.  61  The Load vs. Displacement graph is shown in Figure 44:  240 210 180  F  150  ;-4 120 as 0 90 60 30 0 0^10^20^30  ^  40  Displacement (mm) Figure 44: Beam D, Load vs. Displacement  Beam D showed a significantly different mechanical response compared to Specimens A, B or C. In this case, the beam appeared to be much more ductile and had a significant increase in inelastic deformation. As with Beam C, it appeared to begin yielding at approximately 150 kN; however, this time, the SFRP did not debond from the surface of the specimen as quickly, and at failure, exhibited only mild debonding only in the vicinity of the load plate. The beam continued to deform under loading until the SFRP had actually ruptured in the tensile zone. Upon SFRP rupture, the beam failed instantaneously (Figure 45).  62  Given the fact that failure occurred upon SFRP rupture, rather than upon SFRP debonding, it is fair to say that the HMR-AtPrime 2 combination was much more successful in allowing the beam to act as a true composite to failure, as compared to the previously tested specimens, A, B or C.  Analysis of the strain gauge data seems to confirm that as the beam began to yield, there was a downward shift of the neutral axis within the beam. Please refer to Section 6.2 for a more detailed explanation of this phenomenon. As the tensile zone of the beam began to become more and more strained, fibres within the wooden section of the composite beam may have failed, resulting in a greater proportion of the stress being transferred to the SFRP coating. In this case, with the stress transfer, rather than debonding, the SFRP actually carried the load, and ultimately ruptured, rather than delaminate from the beam surface. Table I I : Beam D Results Yielding Load (kN) (Approximate) 150  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  215.2  31.6  4.8  63  The application of AtPrime 2 + HMR clearly enhanced the capacity of the composite beam, providing a 17% gain in strength, but more importantly, a 100% gain in energy absorbed. Clearly, when full composite action is achieved, the beam is much tougher and much more ductile. 5.1.5 Beam E  Beam E was reinforced with SFRP. This beam had only been treated with HMR primer prior to application of the SFRP. The Load vs. Displacement graph is shown in Figure 46:  240 210 180  2  -  150  120 as 0 90 ....1 60  10  30 0 0^10^20^30  Displacement (mm) Figure 46: Beam E, Load vs. Displacement  64  ^  40  Beam E showed mechanical characteristics very similar to Beam D. Yielding occurred at approximately 1501N. Like Beam D, the beam showed significant post yielding non linear behavior. Failure began with debonding of the SFRP in the region around the load application point, which was ultimately followed by failure via SFRP rupture.  Table 12: Beam E Results  Yielding Load (kN) (Approximate) 150  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  215.4  30.1  4.4  Use of HMR primer only, resulted in a 17% gain in ultimate strength, and an 83% gain in energy absorbed.  5.2^Three Point Flexural Test Analysis, Creosote Treated  5.2.1 Beam F  Beam F was the control specimen for the Creosoted specimens. Like Beam A, it was not reinforced with any SFRP. Results from the other creosoted beams were compared against this test to determine what kind of improvement in properties had been achieved.  65  The Load vs. Displacement curve for this beam is shown in Figure 47:  180 150 , 120 z — 90 a as J 60 -  30 0  0  ^  10^20^30^40 Displacement (mm)  Figure 47: Beam F, Load vs. Displacement Table 13: Beam F Results Yielding Load (kN) (Approximate) 108.7  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  108.7  13.1  0.6  The energy absorbed by the beam to failure was calculated by approximating the area under the Load vs. Displacement curve, and was found to be approximately 2.4 kJ.  The mode of failure of this particular control specimen was inconsistent with the Borocol treated control specimen. This particular beam showed practically no inelastic behavior, as failure was much more brittle and sudden. As the depth of the specimen was 50mm  66  less than that of the Borocol treated specimens, the ultimate and yielding loads of the Creosoted beams were less than those of the Borocol treated ones.  As Beam F is a control specimen against which the remaining reinforced beams would be compared against, it is important to try and determine how representative this beam is of a typical specimen. As discussed in Chapter 2, timber is an extremely variable material, and it is possible that this particular beam could be uncharacteristic of a typical specimen. Therefore, it could be underestimating, or overestimating the ultimate bending strength of the average D.Fir timber beam of this grade and these dimensions. Data from the Canadian Wood Councils Lumber Properties Research Project (Barett and Lau, 1994) can be used to determine the predicted the maximum bending stress and also the determine the percentile rank of the elastic modulus of the specimen. Calculations are shown in Appendix D. Based on the CWC data, the Elastic Modulus of the control specimen was determined to be in the top 33 percent rank (z-score=0.42), and the predicted ultimate bending strength was 28.45 MPa, while the actual ultimate bending strength was found to be 28.11 MPa. Given these results, it is believed that this control beam is a reasonable representation of an average #2 D.Fir beam.  67  5.2.2 Beam G  The Load vs. Displacement curve for this beam is shown in Figure 48:  180 150 120  z V  90  cu 60 30 0 0  ^  10^20^30^40 Displacement (mm)  Figure 48: Beam G, Load vs. Displacement  Beam G was sprayed with SFRP, and was not pretreated with any sort of adhesive to aid bonding. Even so, the beam exhibited a decent gain in strength over the control for the creosoted specimens (Beam F). What was most noticeable though, was the tremendous gain in energy absorbed by the beam (+460%).  During the test itself, it was clear that for the creosoted specimens, the SFRP on its own delaminates very quickly when it is not coupled with an adhesive. All of the delamination occurs in the compression zone of the beam. It is especially evident in the area around where the load is applied. Despite this delamination, the beam exhibited tremendous  68  resilience and showed an impressive amount of non linear deformation. Ultimately, the maximum strength of the beam was achieved before the SFRP failed by rupture. Table 14: Beam G Results Yielding Load (kN) (Approximate) 70  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  139.3  35.6  3.6  5.2.3 Beam H  The Load vs. Displacement curve for this beam is shown in Figure 49:  180 150 120 z _. — 90 co o ...] 60 30 0 0  ^  10^20^30^40 Displacement (mm)  Figure 49: Beam H, Load vs. Displacement  69  Beam H was sprayed with SFRP coupled with AtPrime 2 as an adhesive to enhance bonding. The presence of AtPrime 2 served to significantly reduce premature delamination. In fact, delamination of the SFRP from the substrate occurred only during the closing stages of the test when the beam was near failure. Also, delamination only occurred in the vicinity of the load application point (Figure 50).  Figure 50: Beam H, Just Prior to Failure  Use of AtPrime 2 on the Creosoted Specimen presented a totally different result than that of the Borocol treated specimen. Whereas with the Borocol treated specimen, the composite showed no strength gain, in the case of Creosoted specimens, the composite showed the highest amount of strength gain, of greater than 50%. It also exhibited significant non linear behavior, and ductility. The Beam failed before SFRP rupture.  Table 15: Beam 11 Results  Yielding Load (kN) (Approximate) 120  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  164.3  29.6  3.0  70  5.2.4 Beam I  The Load vs. Displacement curve for this beam is shown in Figure 51:  180 150 120  z — 90 co 0 —J 60 30  0 0  ^  10^20^30^40 Displacement (mm)  Figure 51: Beam I, Load vs. Displacement Table 16: Beam I Results  Yielding Load (kN) (Approximate) 80  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  112.4  29.9  2.5  Results from this test were quite surprising. The beam was treated with a combination of AtPrime 2 + HMR prior to SFRP application. This particular treatment preformed the best from the set of tests on the Borocol treated beams. However, for the Creosoted specimens, ultimately, this combination of adhesive and SFRP provided the least amount  71  of strength gain of only 3.4%. The presence of the SFRP however, still ensured a decent gain in ductility, of nearly 290%.  5.2.5 Beam J  The Load vs. Displacement curve for this beam is given in Figure 52:  180 150 120 z 90 Cu  0 —J  60 30 0  0^10^20^30^40  Displacement (mm) Figure 52: Beam J, Load vs. Displacement Table 17: Beam J Results  Yielding Load (kN) (Approximate) 120  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  147.3  26.7  2.3  72  Beam J was treated with HMR as a coupling agent only, prior to being sprayed with SFRP. The beam showed a significant strength gain as well as gain in ductility as compared to the control beam. During testing the beam showed some premature delamination in the compressive zone. Also of significance is the fact that of the Creosoted beams, this was the only one to show failure via SFRP rupture, meaning the composite had reached its maximum capacity.  73  6 DISCUSSION 6.1^Borocol Treated Beams  240  D B^ J, . • . .^4.,  210  •-:  i ...„--.  .......^-.....^E.  .'  ....•;#^.....••••'''.  .., -'  180  ... .'  i^ /1 ..•^  S  '.  A  /  150  1  0  /  .0 120 cts 0 90  J  . II  60  l  a  1  I^J.  i  1  1  J. 1,  ,,'  fl  : ir 0^j  30  a  rf  r • ti ,A  JP  0 0  10^20^30  Displacement (mm) Figure 53: Comparison of Results, Non Creosoted  74  40  Table 18• Summary of Results, Non Creosoted  Beam A Beam B Beam  C* Beam D Beam E  Ultimate Load (kN)  Ultimate Displacement (mm)  Energy Absorbed (kJ)  Load % Energy Increase Absorbed % over A Increase over A  184.7  20.1  2.4  -  -  -  210.1  22  2.1  13.8%  -12.5%  No  181.4  -  -  -1.8%  -  No  215.2  31.6  4.8  16.5%  100.0%  Yes  215.4  30.1  4.4  16.6%  83.3%  Yes  FRP Rupture  *Due to a data acquisition failure, displacements and strain gauge readings from Beam C were not properly recorded.  For Borocol treated beams, and likely for beams treated with similar water-borne preservatives, the use of AtPrime 2 (Beam C) on its own appears to be unsatisfactory. The ultimate flexural loading capacity of the beam treated with AtPrime 2 alone was actually less than that of the control specimen. Although data acquisition failed, it appeared that there would not be too much of a gain in ductility or toughness either. It seems as if although pMDI adhesives work well to bond wood to wood, they do not work as well in bonding FRP to wood.  Based on the results from this series of tests, it is possible to infer that HMR has the effect of significantly increasing the ductility and toughness of SFRP Strengthened Beams. Beams D and E were both treated with HMR, and it is clear from Figure 53/Table 18 that these beams are significantly more ductile than the others. In addition to simply trying to increase the flexural or shear strength of a beam, it may be equally important to increase ductility for improved seismic performance. Given that the HMR treated specimens ultimately failed through SFRP rupture, use of HMR appears to promote composite action in these beams.  Use of SFRP on its own without the aid of any sort of bonding agent/primer provided interesting results. Although there was a decent increase in flexural capacity, the ductility/toughness did not increase at all. The SFRP did not rupture, indicating full  75  composite action was not achieved. Therefore, given that a similar increase in flexural strength can be achieved along with a tremendous increase in ductility, for beams treated with Borocol or a similar water borne preservative, use of HMR as a bonding agent is recommended.  An interesting observation can be made regarding Beam A. Similarly to Beam F, Beam A is the control specimen against which other Borocol treated specimens were compared. As discussed in Section 5.2.1, information from the CWC Lumber Properties Research Project (Barett and Lau, 1994) can be used to predict the maximum bending stress of Specimen A. Based on the CWC data, the predicted ultimate bending strength was 18.63 MPa (Refer to Appendix D for calculation), while the actual ultimate bending strength was found to be 35 MPa. Therefore, it seems that this specimen may have been significantly stronger than the average #2 D.Fir Specimen of this size. Given that most specimens would likely be weaker than the control specimen tested, it would be fair to say that the improvement in strength properties of the retrofitted specimens may be underestimated when compared against this particular control specimen, and that had a more representative sample been chosen, the % load increase and % energy absorbed would have been greater.  76  ^  6.2^Creosote Treated Beams  180 H  150  J G  120  •-• ------------------  z ^90  ^  60 ^.„.  ^  30 / ^ 0 0^10^20^30^40  Displacement (mm)  Figure 54: Comparison of Results, Creosoted Table 19: Summary of Results, Creosoted  Beam F Beam G Beam H Beam I Beam J  Ultimate Load (kN)  Ultimate Displacement (mm)  Energy Absorbed (kJ)  108.7  13.1  0.6  -  -  -  139.3  35.6  3.6  28.2%  460.1%  No  164.3  29.6  3.0  51.1%  366.5%  No  112.4  29.9  2.5  3.4%  287.4%  No  147.3  26.7  2.3  35.5%  255.4%  Yes  Load % Energy Increase Absorbed % over F Increase over F  FRP Rupture  Figure 54 shows that as with the Borocol treated beams, the use of SFRP on Creosote treated beams significantly increased ductility, toughness and increased the load carrying capacity. Surprisingly SFRP seemed to perform even better on the Creosoted beams, as 77  the magnitude of the increase was much greater than for the Borocol treated beams. This result was contrary to expected performance, as the oil component of Creosote treatment was expected to retard bond formation. In some cases, it was evident that a poor bond had been formed in the compression zone of the beam, as the SFRP had almost completely delaminated off the beam surface. Yet, the SFRP continued to enhance the beams ductility and energy absorption capacity right to failure. Of interest was the performance of Beam G which only had been sprayed without any additional adhesive/bonding agent. Beam G ended up displaying the highest energy increase, and also showed notable strength gain. This was in complete contrast to the Borocol treated specimens.  The failure mechanism in the Creosoted beams was identical to that of the Borocol treated beams, in that failure initiated with crushing in the compression zone of the beam, and moves downwards until there was rupture in the tensile zone. A larger 150mm x 200mm x 25mm loading plate was used for testing these specimens, which minimized localized crushing at the loading point. This, in turn, appeared to delay the onset of delamination of the SFRP from the free edge around the loading area.  Unlike the first set of tests, the HMR appeared to now have little effect in improving the SFRP-Timber bond. The AtPrime 2 appeared to do a much better job of promoting adhesion between the two. The beam which was prepared with AtPrime 2 only (Beam H) showed the greatest increase in load capacity, and also provided an enormous increase in energy absorbed. It is unclear the exact mechanism by which AtPrime 2 increases its bonding capacity compared to the beams treated with Boracol, but clearly, it appears to work better in tandem with Creosote.  6.3 Strain Analysis When wood or timber is tested to failure in axial tension, the stress-strain relationship is fairly linear up to maximum load, and the wood fails in brittle tension. In axial compression, wood and timber are much more ductile materials, exhibiting a linear stress strain relationship up to a proportional limit, beyond which ductile yielding takes place. It  78  is this difference in the stress strain relationship between compression and tension which accounts for the non linear behavior of timber when it is subjected to a bending load. Non linear models which have been developed to try to predict failure load of timber beams typically propose an idealized stress strain relationship, with a bilinear relationship to represent the compression behavior. Figure 55 shows what happens to stresses and strains in a beam as it is subjected to a flexural load to failure.  ^ Centroidal axis  d  _._o_._._._._._._._._.  ad  Neutral cd axis^ Figure 55: Non Linear Behavior Diagram (Gentile, 2000)  If it is assumed that the elastic modulus of timber is the same in both tension and compression, then maximum tensile strains and maximum compressive strains in the beam will be equal, until the beam begins to yield in the compressive zone. At this point, the neutral axis of the beam begins to move down, and strains in the compressive zone increase rapidly, as the beam deforms inelastically in this area. The beam ultimately fails when fibres in the tensile zone reach their strain limit leading to a brittle rupture in the tensile zone.  However, it is important to realize that when SFRP reinforcement is added to the underside of the beam, its tensile strain carrying capacity increases. This leads to two important observations.  79  1)  The tensile strains in the reinforced specimens should be higher than the tensile  strains in the unreinforced specimens at failure.  2)  For the unreinforced specimens, inelastic deformation of the compressive zone of  the beam would generally lead to higher strains in the compressive zone then the tensile zone at failure. However, reinforced specimens have had their tensile strain carrying capacity increased, and therefore, reinforced specimens may exhibit a higher ultimate tensile strain then ultimate compressive strain at failure. Observation 1:  Observation 1 can be confirmed via strain gauge data. Consider strains at Gauge 3 for Beams A-E and then Beams F-J. Gauge 3 was attached to the underside of the beam, and therefore was in pure tension throughout the test. Please refer to Figure 33 for a diagram of the strain gauge locations. Please note that + strain indicates a compressive strain while strain indicates a tensile strain. Table 20: Strains at failure, Gauge 3, Beams A-E  Strains at failure: Gauge 3 Note:^Specimen^A^is unreinforced Specimen^A Specimen^B Specimen^C Specimen D Specimen E (pstrain) -  2148  (pstrain) -  2441  (pstrain)  (pstrain)  -  -  1866  (pstrain) -  2641  Table 21: Strains at failure, Gauge 3, Beams F-J  Strains at failure: Gauge 3 Note:^Specimen^F^is unreinforced Specimen^F Specimen^G Specimen^H Specimen I  Specimen J  (pstrain)  (pstrain)  (pstrain)  (pstrain)  (pstrain)  -1151  -1150  -1819  -1338  -1657  80  It becomes evident from Table 20 and Table 21 that the general trend is for tensile strains in the reinforced specimens (Specimens B-E, and G-J) to be greater than the unreinforced specimens (Beams A and F) at failure. Observation 2:  With regards to Observation 2, the trends are not as clear. Table 22: Strains at failure, Gauge 1 vs Gauge 3  Note:  Specimen A Strains at failure: Gauge is 1 (C) vs Gauge 3 (T)  unreinforced Specimen B Specimen C Specimen D  Specimen A (pstrain)  (istrain)  (pstrain)  Gauge 1  (pstrain) Specimen E  1209  1385  -  586  (pstrain)  2148  2441  -  1866  833  Gauge 3  Considering beams A through E, it appears that at failure, the tensile strain at failure is greater than the compressive strain. However, this would mean that as the beam is loaded to failure, the neutral axis of the beam moves upwards, rather than downwards.  To investigate further, strains at Gauge 2 were considered, and an interesting trend was noticed:  81  800 600 "—. 400  9  200  F  0  Ell -200 B  U) -400  Load (k N) Figure 56: Gauge 2, Strains vs Load  The neutral axis of a beam is the axis along which strain in the beam is equal to zero. For the beams tested, when each beam is unloaded, this axis is along the mid height of the beam. It seems that as load is increased, Beams A, D and E behave in an elastic manner, as the neutral axis remains approximately at mid height, with some minor fluctuation. However, when the beam begins to exhibit inelastic deformation (around 150 kN), strains at the neutral axis begin to deviate from 0 strain, and become compressive strains. This deviation indicates that the neutral axis of the beam has moved down, and more of the beam is beginning to deform in compression, rather than in tension. Beam B appeared to be the only exception to this phenomenon. In this case, it is clear from Figure 53 that this particular beam showed very little non linear behavior, and therefore the beam likely did not crush at all in the compression zone. Consequently, the neutral axis did not movie downwards as indicated by strains at Gauge 2. Therefore, data at the strain gauge along the original neutral axis, supports the theoretical hypothesis that as the beam is loaded to failure, it yields in the compressive zone, the original neutral axis begins to move down, the beam deforms non linearly in the compressive zone, and fails when the beam ruptures in the tensile zone. However, this contrasts with the actual readings at the top and bottom of the beams, which show that tensile strains at the bottom of the beam are far greater than the  82  compressive strains at the top, which would indicate that the neutral axis has moved upwards, rather than downwards from the original location.  In the effort to try and determine what is actually going on, data from Beams F-J are analyzed: Table 23: Strains at failure, Gauge 5 vs Gauge 7  Note:  Specimen F Strains at failure: Gauge is 5 (C) vs Gauge 7 (T)  unreinforced  Specimen  Specimen  Specimen H Specimen^I Specimen J  F (pstrain)  G (pstrain)  (pstrain)  (pstrain)  (pstrain)  751  1432  1726  881  1233  786  1585  951  2125  Gauge 5 Gauge 7  -  The trend in this set of data is not as clear, since for Beams G and H, strains are higher in the compressive zone of the beam at failure while for beams I and J, strains are higher in the tensile zone at failure. Therefore, as with beams A-E, data at the neutral axis of the section (Gauge 6) is analyzed.  83  •  •  600 500  400 9 300 46 • 200 • 100  F^ G  I ^0 -100 -200  it) '  0  n  Load (kN) Figure 57: Gauge 6, Strains vs Load  With the exception of Beam H, it seems that as load is incremented, and the beam exhibits non linear deformation, strains at the neutral axis again begin to deviate from 0 strain, and become compressive strains. Again, as with Beams A-E, this seems to support the hypothesis that as load is incremented, the neutral axis of the beam begins to move downwards all the way to failure.  Therefore, finally, given the data which was observed from strain gauges along the neutral axis it seems as if at the onset of inelastic behavior, the neutral axis of the beam begins to move down, and strains in the compressive zone increase and the beam ultimately fails when fibres in the tensile zone reach their strain limit leading to a brittle rupture in the tensile zone. Looking purely at data from the strain gauges located at the top and bottom of the beam may be misleading. It is important to remember that at the top of the beam (compressive) the strain gauge was applied directly to the substrate, while at the bottom of the beam (tensile), the strain gauge was applied to the SFRP after curing. The strain readings at the bottom of the beam may be somewhat deceptive. It seems that the presence of the SFRP at the bottom of the beam causes strains to be much higher in the immediate vicinity of the reinforcement. This phenomenon was also observed in data recorded by Gentile (1999). However, it is believed that tensile strains  84  within the timber are not as high as these tensile strains closer to and within the reinforcement. Therefore, while the rest of the beam behaves as predicted by Bazan (1980) or Buchanan (1990), maximum strains in and around the reinforcement will be higher than for an unreinforced beam.  6.4 Failure Mechanism Analysis of test data has shown that application of SFRP can result in increases in beam ductility, toughness and ultimate load carrying capacity.  Apparently, failure initiates when the beam begins to yield and starts to exhibit non linear displacement. At this point, the compression zone of the beam begins to crush. After some time, this crushing becomes quite apparent as the noise of fibres splitting and snapping can be heard. In the case of beams reinforced with SFRP, crushing in the compression zone can be seen as the laminate begins to debond from the surface of the beam and wrinkle (Figure 58). At the same time, strain gauge data confirms that the neutral axis of the beam begins to move lower and lower, and strains in the tensile zone begin to increase. Ultimate failure occurs with rupture and snapping of fibres in the tensile zone of the beam.  Analysis of the strain gauge data shows that in general, as the beam begins to display in elastic deformation, strains at the mid height of the beam begin to fluctuate (Figures 56 and 57), and tend to become compressive strains, which increase in magnitude as load is incremented. Figure 55 shows how this would happen, as the beam begins to go nonlinear, the neutral axis drops, lower and lower, and compressive strains in the region above the neutral axis increase.  85  F^  Debonding  L1^  U  Figure 58: Debonding Diagram  It appears the extent of delamination of SFRP from the compression zone has an effect on the ultimate strength of the beam. If the extent of delamination is substantial, the SFRP is not able to arrest the growth of fissures within the tensile zone of the beam, thereby allowing the beam to disintegrate rapidly. In short, delamination causes the beam to revert to its unretrofitted state. However, if the extent of delamination is lower, than the beam is able to act as a true composite. The tensile zone of the beam will not lose strength as quickly, as the SFRP will keep splitting of fibres in the tensile zone in check. Ultimately when stresses become too high, the SFRP will rupture, followed by instantaneous splitting of the wooden beam, and total failure of the composite.  The size of the loading plate has a serious effect on the extent of delamination in the compression zone. A 150mm x 150mm x 25mm steel loading plate had been used in Tests A-E. However, it became clear that the surface area of this plate was insufficient when the load was high enough to initiate yielding of the beam. The plate itself began to be crushed right into the surface of the beam, and at failure was usually embedded 20mm-25mm deep into the beam. Such crushing has two effects. First of all, it causes a very high stress to be concentrated in the vicinity of the SFRP laminate which would promote debonding. Secondly, localized crushing would physically shear the timber off of the laminate in the vicinity of the load plate, and promote free edge stresses. Therefore, use of a loading plate with a larger surface area would have been preferred, as a larger loading plate may have reduced crushing and delayed SFRP delamination in the compression zone of the beam.  86  The failure mechanism in the Creosoted Beams is identical to that of the Borocol treated beams, in that failure initiates with crushing in the compression zone of the beam, and moves downwards until there is rupture in the tensile zone. A larger 150mm x 200mm x 25mm loading plate was used for testing these specimens, which minimized localized crushing at the loading point. This in turn appeared to delay the onset of delamination of the SFRP from the free edge around the loading area.  Given the high strain capacity of the SFRP on its own, it is not clear whether sufficient anchorage can be achieved to force failure via SFRP rupture consistently. Overall, premature delamination of the SFRP from the adherent surface proved to be a consistent problem. The beam is able to utilize its full potential when it acts as a true composite. Thereby, the SFRP should not delaminate from the timber surface prior to failure. Premature delamination occurred several times for both the Creosoted and Borocol treated specimens. Interestingly, Beam H, which displayed the highest strength gain of the specimens tested also exhibited premature SFRP delamination. Therefore, theoretically, had a stronger bond been achieved, it is quite likely that the ultimate flexural strength of the beam would have been still higher.  After observations of the test, and analysis of the data, it is believed that delamination occurs due to a combination of the following reasons:  1)  The Existence of Interfacial Shear Stresses at the Timber-SFRP Interface:  These stresses cannot be avoided and will automatically be present when the beam is subjected to a load. If the amount of shear stress exceeds the bonding strength of the adhesive, the SFRP may delaminate prematurely, before the maximum flexural capacity of the composite has been reached.  2)  Material Incompatibilities:  The SFRP and timber each have different elastic moduli, and thereby would want to deform by different amounts under equivalent loading. This would be resisted by the build up of the additional shear stresses at the interface.  87  3)  Free Edge Effects:  A laminate in tension will have a build up of peel stresses at its free edge. Coupled with localized stresses which are generated in the vicinity of the loading plate, they may lead to premature peeling of the SFRP from the adherent surface.  4)  Face Wrinkling:  Occurs when the SFRP in the compression zone buckles and debonds from the adherent surface.  After reviewing the test data, reasons 2, 3 and 4 are believed to contribute the most towards delamination of the SFRP from the timber surface (Refer to Appendix C for interfacial shear stress calculation). Considering that significant strength gains were observed in beams which exhibited SFRP delamination, it is quite likely that if delamination can be avoided, the gains may be even more pronounced. Providing adequate anchorage in the compression zone around the loading point is critical, as this is where delamination will first occur. Localized stresses about the loading point can be partially mitigated by ensuring use of a proper sized loading plate. The delamination problem is quite complex, and due to the variety of reasons why it may occur, it is difficult to predict an exact delamination load. However, it was found that via simple use of chemical adhesives, it is possible to greatly delay the onset of delamination, and possibly avoid it all together. For the creosoted specimens, it was found that those composites which had bonded properly could be visually distinguished as the surface color of the SFRP was significantly darker, perhaps due to better resin infusion/chemical bonding with the substrate.  6.5^Simplified Strength Gain Model It is important to be able to predict the ultimate strength of SFRP-Timber composites if they are ever to be seriously considered for use in practice. Johns and Lacroix (2000) contended that the Simplified Transformed Section Model underpredicted strength for  88  FRP reinforced timber beams. Their results are confirmed in this set of experiments, as it was found that use of the model generally underestimated ultimate beam strength. The bending stress predicted by this method is found by transforming the composite section into a homogenous material based on the ratio n of their elastic moduli (Beer et al, 2002). The centroid and moment of inertia of the transformed equivalent section can then be calculated, and maximum bending stress is found via:  =  Where: a is the bending stress M - the moment at the neutral axis y - the perpendicular distance to the neutral axis I x - the area moment of inertia of the transformed section about the neutral axis x  The elastic modulus of the SFRP was taken from Solemani, 2006. Solemani had conducted tests on SFRP coupons identical in composition to the FRP spray that was used throughout this project. After analyzing the stress-strain response of SFRP coupons subjected to direct tensile tests, he concluded that the elastic modulus of the cured SFRP was 14 GPa.  Based on this calculation, a maximum load capacity of 127.5 kN is predicted for Beam H, when the actually load at failure was 164.3 kN (Refer to Appendix B for calculation details). This discrepancy is likely because the transformed section does not take into account nonlinear behavior. When a proper bond is formed, the composite may display significant nonlinear deformation, which would likely also lead to an increase in ultimate strength. Therefore, when trying to approximate ultimate strength, a more comprehensive approach is recommended such as that described in Gentile (2000) or Born et al (2004).  89  6.6^Comparison to Other Studies  Table 24 shows three projects that are most comparable in nature to this study: Table 24: Other Studies Study Name "Wood Members Strengthened with Mechanically Fastened FRP Strips" "Flexural Strengthening of Timber Beams using GFRP" "FRP Reinforced Wood as Structural Material"  Authors  Year  Method of Reinforcement  Dempsey and Scott  2006  Layers of GFRP, mechanically fastened with screws  Gentile et Al  2002  Plevris and Triantafillou  1992  % Strength Increase  2.9-51.3  GFRP bars, embedded into beams Wet Layed CFRP Laminates  25-50  11.3-59.1  All three studies dealt with reinforcement of sawn lumber with FRP. Dempsey and Scott (2006) along with Plevris and Triantafillou (1992) looked at application of FRP laminates to the substrates. The main difference was that Dempsey and Scott employed mechanical anchorage (hex head screws) to bind the laminate to the substrate, while Plevris and Triantafillou used a chemical adhesive (epoxy resin). Gentile et al (2002) on the other hand, used GFRP rods, which were embedded into the undersides of beams to provide flexural reinforcement. In general all three studies reported increases in ultimate strength along with significant increases in non linear deformation of their specimens. The mode of failure described in this study corresponded well with those reported in these three studies.  Given that in practice, beams in need of reinforcement would usually be creosote treated, from this study, it is best to consider the results from the creosoted treated beams. Therefore, from this study, SFRP strength increases are in the range of 3.4% to 51.1% depending on the type of adhesive used to bond the SFRP to the surface. Given this range of strength increase, it is fair to say that application of SFRP for retrofit compares quite reasonably to the traditional techniques employed in the three mentioned studies.  90  6.7 Other Comments The gain in ductility and energy absorption capacity afforded by the application of the SFRP is exceptional, and this characteristic could be utilized in applications such as seismic retrofit of structures, or stiffening of structures against wind loading. The type of strength gain that was observed in the Creosoted specimens was at par with and in some cases exceeded those from previous similar retrofit experiments. It is important to note that in practice, those sorts of bridges which would be in need of retrofit via FRP would likely be Creosoted or have some other sort of oil borne preservative treatment. Therefore, the types of strength and ductility gains obtained in the testing of the Creosoted specimens may be characteristic of what can actually be achieved in practice.  With regards to the physical structure of beams themselves, the strain gauges confirm the relative non uniformity of timber itself. The presence of flaws such as knots, splits and checks cause stress concentrations and non uniform stress distributions throughout the volume of the beam. As mentioned in Section 5.1.1, by geometry, Strains at Gauges 1 and 5 should have been equal, as should strains at 2/6 and 3/7. In some cases it was noticed that the actual neutral axis did not coincide with the theoretical neutral axis of the beam, and the position of the neutral axis of a given beam actually varied along its length.  91  7 CONCLUSIONS Based on the results of this study, it is possible to say that the application of Sprayed Fibre Reinforced Polymers to retrofit/rehabilitate timber structures shows considerable promise. If a decent bond is achieved between the composite constituents, it is possible to increase the ultimate strength of the member, and significantly increase its ductility.  The presence of FRP material appears to arrest crack opening, confine local rupture, and bridge local defects in timber, so that the timber can support higher nominal stresses and strains before failure.  It was found that delamination occurring in the compressive zone of the beam in the vicinity of where the load was applied led to a premature failure of the beam, before the SFRP would rupture, as full composite action was not achieved. When this delamination was delayed, full composite action was able to occur, and the beam failed via SFRP rupture. It was also noted that use of a wider loading plate for lab tests may minimize local stresses in the vicinity of where the load is applied and may prevent premature peeling and wrinkling. Significant strength gains were observed even in test specimens which exhibited premature delamination. If a better bond were to be achieved, these already significant gains could be even greater.  It is believed that delamination occurs due to a combination of the following reasons:  I)^The Existence of Interfacial Shear Stresses at the Timber-SFRP Interface 2)  Material Incompatibilities  3)  Free Edge Effects  92  4)^Face Wrinkling  Reasons 2,3, and 4 are believed to be the main reasons for delamination.  Failure of the SFRP-Timber composite beams initiates when the beam begins to yield and starts to exhibit non-linear distortion. At this point, the compression zone of the beam begins to crush. This may lead to debonding of the SFRP from the compression zone of the beam if an adequate bond is not achieved. As stresses continue to increase, strains in the tensile zone also increase. Ultimate failure occurs with rupture and snapping of fibres in the tensile zone of the beam.  Given the data which was observed from strain gauges along the neutral axis it seems as if at the onset of inelastic behavior, the neutral axis of the beam begins to move down, and strains in the compressive zone increase and the beam ultimately fails when fibres in the tensile zone reach their strain limit leading to a brittle rupture in the tensile zone. Looking purely at data from the strain gauges located at the top and bottom of the beam may be misleading. It seems that the presence of the SFRP at the bottom of the beam causes strains to be much higher in the immediate vicinity of the reinforcement. It is believed that tensile strains within the timber are not as high as these tensile strains closer to and within the reinforcement. Therefore, while the rest of the beam behaves as predicted by Bazan (1980) or Buchanan (1990), maximum strains in and around the reinforcement will be higher than for an unreinforced beam.  The Simplified Transformed Section model was found to generally underpredict the ultimate capacity of a sprayed composite beam specimen. This is believed to be a result of the increase in ductility and non linear behavior of the strengthened flexural elements.  When considering using only chemical adhesives to obtain a proper bond between the two constituents of the composite, use of HMR is recommended for timber which is untreated or has been treated with a water borne preservative such as Borocol, while a pM DI adhesive such as AtPrime 2 is recommended for timber treated with an oil borne  93  preservative such as Creosote. For Non Creosoted beams, adhesives did not generate as significant of a strength gain. For Creosoted beams, adhesives may be sufficient to generate significant strength gain when SFRP is applied to a beam.  Considering that most structures in use would probably have been treated with a preservative similar to Creosote, in practice, AtPrime 2 or some other some sort of pMDI would probably be the adhesive of choice.  The gain in ductility and energy absorption capacity afforded by the application of the SFRP is exceptional, and this characteristic could be utilized in applications such as seismic retrofit of structures, or stiffening of structures against wind loading. The type of strength gain that was observed in the Creosoted specimens was at par with and in some cases exceeded those from previous similar retrofit experiments. Gains in the Creosoted specimens were particularly average. Strength gains were between 3.4%-51.1% with an overall average gain of 29.6%. Gains in energy absorbed were between 255.4%-460.1% with an overall average gain of 342.4%.  94  8 RECOMMENDATIONS FOR FUTURE WORK Based on the results of this project, the applications of SFRP for the retrofit/rehabilitation of timber structures appear to show some promise. However, further research is required before drawing any definitive conclusions regarding the future prospects of this technique.  I)^It is important to remember that this project was limited to the response of the composite under static flexural loading only. When applied to a real life structure, in addition to static loading, the composite would most definitely be subjected to dynamic loading as well. In fact, if the SFRP were applied with the express purpose of retrofitting a structural component in order to improve its seismic performance, then response under dynamic loading would definitely need to be evaluated.  2)  As was explained in Section 2.5 wood has a high affinity for water, which causes it to shrink and swell. This volume distortion when wood is moistened and dried would increase stresses at the SFRP-Substrate interface, and could very well lead to premature delamination under any sort of loading. On the other hand, it is possible that the SFRP could act as a barrier, shielding the wooden surface from moisture and preventing any volumetric expansion. Regardless, the effect exposure to the elements has on the composite must be investigated in order to make a full and proper assessment of SFRP-Timber composite capabilities.  3)  There are currently a myriad of different types of adhesives/primers/anchoring techniques available which could potentially be used to enhance SFRP-Timber  95  bonding. While only two such chemicals were investigated here, there are many others which could potentially be investigated. Some examples are: a) Latex based adhesives, which are known to bond well to porous surfaces. b) Epoxy resins. There have been some studies conducted which show that epoxy resins can in fact be used to successfully bond GFRP to different structural elements, including timber (Mufti et al, 2001). c) Vinyl Ester. While Polyester is usually used as a polymer matrix for glass fibres, Vinyl Ester can also be used to form a stable composite as well. Non polar Vinyl Ester could possibly develop stronger bonds with an oil based preservative, such as creosote. d) Mechanical Anchorage. From the results of these tests, it is clearly possible to predict where delamination is most likely to occur under static loading. Delaying ,  the onset of delamination is a key to increasing the overall flexural strength of the composite. Mechanical Anchorage could easily be applied to the substrate surface in the areas where delamination is predicted with the effect of likely increasing the flexural strength significantly. Mechanical Anchorage could simply be applied in the form of nails or screws, or even in the form of composite based anchors.  4)  Spraying three sides of the beam allowed for the laminate to be better anchored to the substrate compared to if only the bottom had been sprayed. This may have prevented premature delamination of the SFRP from the bottom of the beam. However, it still may be worthwhile to try alternate spray configurations so that an optimal design can be finalized. Given that delamination initiates in the compression zone, leaving the compression zone unsprayed would provide an insight into just how effective the spray is in preventing timber crushing under compressive stress.  5)  It is important to be able to accurately predict what the ultimate failure load of a SFRP-Timber composite would be. It has been demonstrated that use of the Simplified Transformation Model is insufficient. Development of a model which  96  takes into account non-linear behavior of timber would be recommended. Literature suggests that such a model would be much more precise and accurate.  There are also practical considerations which have to be met regarding the cost effectiveness or ease of application of SFRP composites. Such concerns would probably be alleviated via a field demonstration project. 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"Kiln-Drying of Lumber". Springer, Berlin.  100  Lopez-Andio, R., Gardner, D. J., Hensley, J. L., 2000. "Adhesive Bonding of Eastern Hemlock Glulam Panels with E-Glass/Vinyl Ester Reinforcement". Forest Products Journal, 50(11): 43-47. Lyons, J.S., Ahmed, M., 2005. "Factors Affecting the Bond Between Polymer Composites and Wood". Journal of Reinforced Composites and Plastics, 24(4): 405-412. Martens, R., Siegel, M., Linares, F., 1996. "Secondary Bond Strength of FRP to a Variety of Substrates". NACE Corrosion Symposium, Buffalo, NY. Mufti, A. A., Bakht, B., Svecova, D., Adams, T., 2001. "Evaluation of Glue for Bonding FRP Laminates on Timber Beams Treated with Creosotes". 29th CSCE Annual Conference, Victoria, BC. Niu, H., Wu, Z., 2006. "Effects of FRP-Concrete Interface Bond Properties on the Performance of RC Beams Strengthened in Flexure with Externally Bonded FRP Sheets". Journal of Materials in Civil Engineering, 18(5):723-731. Phanopoulos, C., Marcinko, J.J., Buckley, C., 1999. "The Nature of Isocyanate to Wood Adhesion, and the Locus of Resin Penetration". Institute of Materials Conference, London, UK. Pizzi, A., Mittal, K.L., 1994. "Handbook of Adhesive Technology". Marcel Dekker Inc. New York, NY. Plevris, N., Triantafillou, T., 1992. "FRP-Reinforced Wood as Structural Material". Journal of Materials in Civil Engineering, 4(3): 300-317. Product Bulletin, 2005, Hexion 713-6674 [Brochure], Columbus, 01-1. Richter, K., Steiger, R., 2005. "Thermal Stability of Wood-Wood and Wood-FRP Bonding with Polyurethane and Epoxy Adhesives". Advanced Engineering Materials, 7(5): 419-426. Saadatmanesh, H., Ehsani, M.R., 1990. "Fiber Composites can strengthen beams". Concrete International: Des Constr, 12(3):65-71. Solemani, R., 2006. "Sprayed Glass Fiber Reinforced Polymers in Shear Strengthening and Enhancement of Impact Resistance of Reinforced Concrete Beams". PhD Thesis, University of British Columbia. Smith, S.T., Teng, J.G., 2002a. "FRP-strengthened RC beams. I: review of debonding strength models". Engineering Structures, 24:385-395.  101  Smith, S.T., Teng, J.G., 2002b. "FRP-strengthened RC beams. II: assessment of debonding strength models". Engineering Structures, 24:397-417. Teng, J., Smith, S.T., Yao, J., Chen, J.F., 2001. "Intermediate crack induced debonding in RC beams and slabs." Construction and Building Materials, 17(6-7):447-462. Toutanji, H., Ortiz, G., 2001. "The effect of surface preparation on the bond interface between FRP sheets and concrete members". Composite Structures, 53:457-462. Tree parts (Image), 2008. Retrieved January 28, 2008 from http://www.state.sc.us/forest/reftree.htm Triantafillou, T., 1998. "Composites: A New Possibility for the Shear Strengthening of Concrete, Masonry, and Wood". Composites Science and Technology, 58(8): 1285-1295. Vick, C.B., 1995. "Hydroxymethylated Resorcinol Coupling Agent for Enhanced Adhesion of Epoxy and Other Thermosetting Adhesives to Wood", Wood Adhesives Symposium, USDA Forest Service, Forest Products Laboratory. Maidson, WI. Vick, C.B., 1999. "Adhesive Bonding of Wood Materials" in "Wood Handbook: wood as an engineering material". USDA Forest Service, Forest Products Laboratory. Madison, WI. Weaver, W.F., Owen, N.L., 1995. "Isocyanate-Wood Adhesive Bond". Applied Spectroscopy, 49(2): 171-176. Williamson, T.G., 2002. "APA Engineered Wood Handbook". McGraw-Hill. USA. Zumdahl, S., 1998. "Chemical Principles". Houghtin Mifflen. Boston, MA.  102  APPENDIX A: DATA FROM FLEXURAL BEAM TESTS  Energy absorbed by each specimen was found by calculating the area under each Load vs. Displacement curve. This was done by numerically approximating the area under the curve using the trapezoid rule.  Beam A:  Load  Displacement  Incremental Energy Absorbed  0.47 10.06 20.03 30 39.96 50.02 60.09 70.15 80.21 90.18 99.86 110.96 119.98 130.04 140.01 149.98 160.04 170.01 179.97 184.72  0.5 -1.01 1.5 2.51 2.01 4.01 3.51 5.52 5.52 6.53 7.03 7.53 8.53 10.04 9.54 12.55 13.55 14.56 18.07 20.08  -7.95015 37.76295 25.26515 -17.49 89.98 -27.5275 130.8912 0 86.04695 47.51 52.705 115.47 188.7651 -67.5125 436.43495 155.01 166.67525 614.2149 366.51345  Sum:  2392.76475  Yielding Load (kN) (Approximate) 130  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  184.7  20.1  2.4  104  Beam B:  Load 0.37 9.23 20.13 29.73 39.89 50.23 59.84 70.18 79.97 90.12 100.1 109.7 120.23 130.01 139.8 149.96 160.48 170.64 179.88 189.85 199.82 210.16  Displacement 0.91 2.92 3.42 4.42 5.93 6.93 7.43 8.44 9.44 10.95 10.95 12.96 12.46 13.96 14.46 15.47 15.97 16.98 17.98 18.98 20.49 22  Incremental Energy Absorbed 9.648 7.34 24.93 52.5631 45.06 27.5175 65.6601 75.075 128.41795 0 210.849 -57.4825 187.68 67.4525 146.3288 77.61 167.2156 175.26 184.865 294.20085 309.5349  Sum:  2199.7258  Yielding Load (kN) (Approximate)  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  210.1  210.1  22  2.2  105  Beam C:  Yielding Load (kN) (Approximate)  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  140  181.4  Unknown  Unknown  Beam D:  Load 1.29 10.34 20.31 29.92 40.08 50.05 60.2 69.99 79.97 89.94 100.1 110.25 120.23 130.01 140.17 149.96 160.12 169.9 180.06 190.03 200.19 210.16 215.15  Displacement 0 0.5 2.01 2.51 3.01 4.02 4.52 5.02 6.03 7.03 7.53 8.03 10.04 9.04 10.04 11.05 11.05 13.56 15.06 17.57 20.59 26.61 31.63  Incremental Energy Absorbed 2.9075 23.14075 12.5575 17.5 45.51565 27.5625 32.5475 75.7298 84.955 47.51 52.5875 231.6324 -125.12 135.09 146.51565 0 414.1751 262.47 464.46295 589.2322 1235.1535 1067.5281  Sum:  4843.6536  Yielding Load (kN) (Approximate)  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  150  215.2  31.6  4.8  106  Beam E:  Load 0.228 10.02 20.052 30.072 40.092 50.004 60.024 70.164 80.076 89.988 99.9 110.028 120.06 129.972 139.992 150.012 159.924 170.064 180.204 190.332 200.016 210.276 215.4  Displacement 0 0.25 1.24 1.98 2.72 3.21 4.45 5.19 6.18 6.67 7.41 7.91 9.14 9.64 10.38 11.86 13.34 15.32 18.29 20.51 26.69 29.4 30.14  Incremental Energy Absorbed 1.281 14.88564 18.54588 25.96068 22.07352 68.21736 48.16956 74.3688 41.66568 70.25856 52.482 141.50412 62.508 99.88668 214.60296 229.35264 326.68812 520.14798 411.29496 1206.17532 555.94566 157.50012  Sum:  4363.51524  Yielding Load (kN) (Approximate)  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  150  215.4  30.1  4.4  107  Beam F:  Load  Displacement  Incremental Energy Absorbed  0.7125 10.4375 20.8875 31.325 41.7625 52.2125 62.8875 72.85 83.4125 93.7375 104.0625 108.6875  0 1.73 2.97 4.45 5.44 6.67 8.4 9.89 11.12 12.6 12.85 13.1  9.64475 19.4215 38.63725 36.1783125 57.794625 99.5615 101.1244375 96.1014375 131.091 24.725 26.59375  Sum:  640.8735625  Yielding Load (kN) (Approximate) 108.7  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  108.7  13.1  0.6  108  Beam G:  Load  Displacement  Incremental Energy Absorbed  0.2473958 10.377604 20.885417 31.276042 41.653646 52.03125 62.669271 72.916667 83.424479 93.815104 104.19271 114.57031 124.96094 135.33854 139.29688  0 0.99 1.98 3.21 4.2 6.18 6.92 8.89 10.38 11.86 13.09 15.32 20.26 30.88 35.58  5.259375 15.47519531 32.07929687 36.10019531 92.74804687 42.43919271 133.5521484 116.4741536 131.1572917 121.7748047 243.9207682 591.6421875 1382.190234 645.3932292  Sum:  3590.20612  Yielding Load (kN) (Approximate)  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  70  139.3  35.6  3.6  109  Beam H:  Load  Displacement  Incremental Energy Absorbed  0.00 9.97 19.94 30.02 39.99 49.96 60.04 69.89 79.98 90.18 100.15 110.35 120.08 130.17 140.14 150.1 159.95 164.34 154.85  0 1.73 3.21 4.44 5.93 6.91 8.15 9.38 10.62 11.85 12.84 14.33 16.06 18.53 19.51 20.26 22.97 24.46 29.64  8.62405 22.1334 30.7254 52.15745 44.0755 68.2 79.90695 92.9194 104.6484 94.21335 156.8225 199.32195 309.05875 132.4519 108.84 420.11775 241.59605 826.7021  Sum:  2992.5149  Yielding Load (kN) (Approximate)  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  120  164.3  29.6  3.0  110  Beam I:  Load 0.24 65.38 75.83 85.90 97.4125 102.75 106.9 110.825 114.7375 112.3625  Displacement 0 8.16 10.13 12.6 15.08 16.06 17.3 18.78 21.99 29.9 Sum:  Incremental Energy Absorbed 267.699 139.082 199.730375 227.3075 98.079625 129.983 161.1165 362.0278125 898.1805 2483.206313  Yielding Load (kN) (Approximate)  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  80  112.4  29.9  2.5  1 11  Beam J:  Load 0.12 9.97 20.05 30.02 40.11 50.07 60.04 70.24 80.33 90.06 100.26 110.11 120.08 131.83 139.89 147.25  Displacement 0 1.98 3.71 4.94 6.67 8.15 9.14 10.87 12.35 13.34 14.58 16.06 17.3 18.28 21.5 26.68 Sum:  Incremental Energy Absorbed 9.9891 25.9673 30.79305 60.66245 66.7332 54.50445 112.6922 111.4218 84.34305 117.9984 155.6738 142.7178 123.4359 437.4692 743.6926 2278.0943  Yielding Load (kN) (Approximate)  Ultimate Load (kN)  Maximum Deflection (mm)  Energy Absorbed (kJ)  120  147.3  26.7  2.3  112  Summary: Ultimate Load (kN)  Ultimate Displacement (mm)  Energy Absorbed (kJ)  Load % Increase  Energy Absorbed % Increase  184.7 210.1 181.4 215.2 215.4  20.1 22 31.6 30.1  2.4 2.2 4.8 4.4  13.8% -1.8% 16.5% 16.6%  -12.5% 100% 83.3%  Yes Yes  Ultimate Load (kN)  Ultimate Displacement (mm)  Energy Absorbed (kJ)  Load % Increase  Energy Absorbed % Increase  FRP Rupture?  Beam H  108.7 139.3 164.3  Beam I  112.4  Beam J  147.3  13.1 35.6 29.6 29.9 26.7  0.6 3.6 3.0 2.5 2.3  28.2% 51.1% 3.4% 35.5%  460.1% 366.5% 287.4% 255.4%  Beam A Beam B Beam C Beam D Beam E  Beam F Beam G  113  FRP Rupture? No No  No  No No  Yes  Strain Gauge Data:  Strain Gauge  Following are plots of strain values across sections of each beam, for while the beam is deforming linearly. Please note that NEGATIVE strains indicate TENSION, while POSITIVE strains indicate COMPRESSION. Please note that highlighted values indicate the beam was deforming in a plastic manner, and therefore, these values were not plotted on the strain distribution graph.  114  Beam A: Section A Strain Distribution Gauge^Gauge 1 2  35 106 200 270 376 470 575 634 739 833 927 1009 1080 1150 1221 1256 1268 1268 1209  12 0 -23 -12 -47 -47 -35 -47 -47 -47 -47 -35 -47 -23 -23 70 129 211 305  Gauge 3  Load  -12 -117 -223 -340 -446 -563 -681 -775 -880 -986 -1080 -1232 -1338 -1455 -1585 -1714 -1855 -2019 -2148  0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180  Specimen A, Section A, Strain Distribution Graph  -  kN kN 20 kN 30 kN  6  -  kN  —.-50 kN —+-  60 kN  —70 kN 500^1000^1500  80 kN 90 kN 100 kN  -8  110 kN  Strain  120 kN 130 kN _  115  Section B Strain Distribution Gauge 5  Gauge 6  Gauge 7  Load  35 117 200 282 376 446 563 610 704 810 869 951 998 1080 1115 1185 1209 1221 1232  47 59 82 117 129 176 211 235 270 305 305 352 387 434 493 540 669 716 810  23 -59 -141 -211 -305 -376 -470 -540 -622 -693 -775 -880 -962 -1033 -1139 -1232 -1350 -1467 -1585  0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180  Specimen A, Section B, Strain Distribution Graph  —o-0 kN —5— 10 kN 20 kN 30 kN —3c-40 kN —41-50 kN —1-- 60 kN —70 kN 80 kN 90 kN 100 kN 110 kN  Strain  120 kN 130 kN  116  Beam B:  Section A Strain Distribution Gauge 1 0 47 106 188 247 317 376 446 505 564 658 705 752 822 892 963 1022 1069 1139 1209 1303 1385  Gauge 2 0 0 -47 -47 -58 -94 -105 -105 -152 -164 -199 -188 -199 -223 -234 -246 -258 -258 -270 -258 -293 -281  Gauge 3 0 -94 -223 -329 -481 -587 -681 -810 -916 -1033 -1139 -1268 -1397 -1491 -1596 -1714 -1819 -1937 -2054 -2183 -2312 -2441  Load 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210  Specimen B, Section A, Strain Distribution Graph  -  0 kN 10 kN 20 kN 30 kN  E 0 a)  -  kN  +  50 kN  + 60 kN —70 kN  .E  o O 0. 2 :o • E .2 E  - 80 kN 90 kN  is  100 kN  0 ID O .0  110 kN  -J 0  120 kN 130 kN 140 kN Strain  150 kN —160 kN  Due to a data acquisition failure, strains across Section B were not properly recorded for Beam B.  118  Beam C: Due to a data acquisition failure, strains for Beam C were not properly recorded to failure.  119  Beam D:  Section A Strain Distribution Gauge 1 0 70 140 187 258 340 446 551 622 692 751 821 880 939 997 1056 1115 1032 986 939 868 586  Gauge 2 0 23 0 0 -12 -24 -12 0 0 -24 -35 -59 -71 -71 -106 -118 -129 -35 35 117 246 610  Gauge 3 0 -70 -117 -199 -246 -317 -387 -422 -469 -563 -645 -727 -786 -845 -915 -986 -1068 -1197 -1291 -1408 -1584 -1866  Load 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210  Specimen D, Section A, Strain Distribution Graph  0 kN 10 kN E  20 kN  w  30 kN  E 0  -X-  a) LT)  4 0 kN 50 kN  -0  47  ^ 60 kN  O  — 70 kN  a) 0. 2 2 -1 E 0 "r – o . 0  500^1000^1500  80 kN 90 kN 100 kN 110 kN  co  120 kN 130 kN 140 kN 150 kN  Strain  120  •  Section B Strain Distribution Gauge 5 0  12 117 176 247 329 411 481 575 646 716 763 845 880 951 1010 1056 939 892 787 716 470  Gauge 6  0 0 0 -23 -12 0 12 24 35 12 12 12 0 0 0 -12 0 71 129 200 305 517  Gauge 7  0 -70 -141 -211 -282 -376 -434 -505 -563 -634 -728 -798 -892 -974 -1056 -1139 -1209 -1350 -1455 -1608 -1784 -2101  Load  0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210  Specimen D, Section B, Strain Distribution Graph -  kN  -is- 10 kN 20 kN  E  0  30 kN  -a RS •  0 CL  kN  -  50 kN  -  2 :o E  +  -  60 kN  —70 kN  • E -1  o  -  0  w .0  80 kN 90 kN 100 kN  rn  110 kN  lC  L9  120 kN 130 kN Strain  140 kN 150 kN  121  Beam E: Section A Strain Distribution Gauge 1 0 58 129 246 328 411 493 587 657 657 739 798 857 915 950 1009 1021 1056 1044 1033 868 833  Gauge 2 0 -23 -12 0 12 -12 12 -12 24 -117 -82 -70 -70 -70 -35 -12 47 106 164 258 540 634  Gauge 3 0 -93 -187 -328 -375 -504 -575 -704 -809 -927 -986 -1091 -1220 -1314 -1396 -1490 -1690 -1772 -1948 -2065 -2429 -2641  Load 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210  Specimen E, Section A, Strain Distribution Graph  -  kN  -4-10 kN  E  20 kN  E 0  30 kN -4-40 kN  -o  - 4-50 kN ^ 60 kN 0 `.45'  CL  72 -2000^-1500 E  -1000^-500  —70 kN 500^1000^1500  0  80 kN 90 kN 100 kN  0 -J  110 kN  rn  120 kN  3  co CD  130 kN 140 kN  -8  150 kN  Strain  122  Section B Strain Distribution Gauge 5 0 83 200 259 364 435 517 646 728 810 916 951 1092 1127 1268 1291 1291 1303 1268 1186 799 611  Gauge 6 0 0 36 -11 36 24 24 94 47 71 106 71 141 106 165 130 188 282 423 552 881 1022  Gauge 7 0 -94 -164 -317 -376 -469 -610 -646 -775 -951 -1009 -1150 -1185 -1338 -1397 -1561 -1667 -1831 -1972 -2136 -2570 -2934  Load 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210  Specimen E, Section B, Strain Distribution Graph -  kN 10 kN 20 kN  E  0  30 kN  4.■  40kN  a)  -  co  —0— 50 kN  as '5 0 2 E CC0 E -2000^-1500^-1000^-500 0  —4-60 kN 1 500^1000^1500  a) _o  —70 kN 80 kN 90 kN 100 kN  a)  a)  110 kN  fa  CD  120 kN 130 kN 140 kN 150 kN  123  Beam F: Section A Strain Distribution Gauge 1 0 106 188 270 352 493 587 646 752 810 904  Gauge 2 0 12 12 -12 -12 47 23 12 59 59 59  Gauge 3 0 -129 -258 -399 -493 -587 -704 -857 -986 -1068 -1151  Load 0 10 20 30 40 50 60 70 80 90 100  Specimen F Section A, Strain Distribution Graph -  0kN  —E-10 k N  • ,lir e.  20 k N  -  ^ 2 O  -o  E  -1 )00  -1000  ,.  -500,4/  //V  I  I  30 k N 40 kN  500  1000  0  —6-- 50 kN -  60 kN  —70 kN 80 k N  Stra i n  90 kN 100 kN  Due to a data acquisition failure, strains across Section B were not properly recorded for Beam F.  124  Beam G:  Due to a data acquisition failure, strains across Section A were not properly recorded for Beam G. Section B Strain Distribution Gauge 5 0 105 235 364 493 622 728 868 986 1103 1232 1338 1432  Gauge 7 0 -105 -164 -270 -375 -504 -587 -610 -634 -692 -763 -763 -786  Gauge 6 0 24 12 0 47 71 94 153 177 223 247 294 282  Load 0 10 20 30 40 50 60 70 80 90 100 110 120  Specimen G, Section B, Strain Distribution Graph  r  ,-----  -o • •E' .  ca a) fa  2  2  1,  •E  • E ra to -1 00 o a) o  •  .00,40••••00001 „••00,•••• _500  -500  0 kN  —s-10 kN 20 kN 30 k N  10 0  )K-- 4 0 kN  —  —co-- 50 kN  E 2  -  60 k N  —70 kN Strain  125  Beam H: Section A Strain Distribution Gauge^Gauge 1 2 0 0 164 -12 293 0 493 -12 645 -12 856 35 986 35 1162 35 1326 35 1479 24 1631 24 1807 71 1901 35 2065 35 2218 35 2183 106 2171 176  Gauge 3 0 -118 -200 -305 -458 -517 -646 -751 -857 -998 -1127 -1197 -1338 -1456 -1561 -1667 -1819  Load 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160  Specimen H, Section A, Strain Distribution Graph 0  • o a) a. M -a  6  -  4  -  0 kN 10 kN 20 kN  2  a E  30 kN  as o o • E o) 2  —*-40 kN  -  1 00  500  -500:4•0",/!. ■I  1000  0  -  50 kN 60 kN  =  —70 kN 80 kN Strain  126  •  Section B Strain Distribution Gauge 5  0 118 259 364 482 622 728 869 939 1057 1174 1327 1385 1503 1597 1667 1726  Gauge 6  0 0 -11 -23 -47 12 -11 0 -23 -47 -47 -11 -47 -47 -23 0 12  Gauge 7  0 -164 -329 -481 -646 -751 -892 -1056 -1209 -1362 -1491 -740 -904 -1068 -1233 -1409 -1585  Load  0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160  Specimen H, Section B, Strain Distribution Graph  o a)  -  cn • o  —NI— 10 kN  -  • 0_  20 kN  2 v 0  U  30 kN c d  0  II  O .0  72, E rn  kN  kN -  50 kN t^ 60 kN  "  co  —70 kN 80 kN Stra in  127  Beam 1:  Due to a data acquisition failure, strains across Section A were not properly recorded for Beam 1. Section B Strain Distribution Gauge 5 0 82 200 247 352 458 540 646 704 787 881  Gauge 6 0 12 47 71 94 129 165 212 282 388 482  Gauge 7 0 -141 -247 -352 -376 -446 -563 -657 -810 -904 -951  Load 0 10 20 30 40 50 60 70 80 90 100  Specimen I, Section B, Strain Distribution Graph  -  kN  —a— 10 kN 20 kN 30 kN —)K-- 40 kN -  50 kN  ^ 60 kN —70 kN 80 kN Strain  128  •  Beam J: Section A Strain Distribution Gauge 1 0 82 223 305 446 575 680 809 915 1044 1162 1291 1326 1490 1479  Gauge 2 0 -35 -70 -106 -129 -164 -199 -211 -258 -246 -270 -258 -270 -258 -188  Gauge 3 0 -83 -247 -341 -458 -564 -669 -810 -904 -1022 -1151 -1233 -1362 -1527 -1657  Load 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140  Specimen J, Section A, Strain Distribution Graph  -  -0. 6  30 kN kN  • o cl) -o  -  •0 E  o  10 kN 20 kN  • •E'  0 0 -1  0 kN  4.," ,  00  -1000  50 kN  --- 60 kN  - 08.14/^ii  o6  .0  to o  0  —70 kN 80 kN  E 0) 2  a, '  90 kN  CU  100 kN Stra in  129  110 kN 120 kN  Section B Strain Distribution Gauge 5 0 118 200 282 388 505 587 681 787 869 975 1092 1174 1245 1233  Gauge 6 0 -24 -47 -59 -59 -71 -71 -82 -71 -71 -59 -24 -12 47 59  Gauge 7 0 -153 -270 -446 -599 -716 -869 -1010 -1150 -1280 -1409 -1561 -1726 -1890 -2125  Load 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140  Specimen J, Section B, Strain Distribution Graph  0 kN —  r  -  10 kN  20 kN 30 kN 40 kN —t-50 kN ^ 60 kN 00 -1500^-1000 ^_7_500  —70 kN 80 kN 90 kN 100 kN  Strain  110 kN 120 kN  130  Gauge 1 Strains vs Load  1600 1400  ♦  1200 1000  7,1  •  800  •  600  ca  400 200  •  .1: K  ♦ ♦ • ■ • • -,. ■  -  11  ■  ♦  .,_  ♦  ♦ ♦ ♦ ,__..".  • " ■ ■  is  it  i''''  • Specimen A  ■ Specimen B Specimen D Specimen E  ''-  ....  0 0  50  ^ ^ ^ 100^150 200 250 Load (kN)  Gauge 2 Strains vs Load 800 600 E 400 co 17') 200  -  • Specimen A  .  C 0  ^.  (7)  -200  ■ Specimen B Specimen C  ,.___,...^_^ . . . •. ___, .___•••^•^ -,,,^ ••__^  •^ •^• ■ us** 1d ti 0 ''' 'I^It ^ ■ ■^111 ■ ...  -  )^  Specimen E  150^200^2 0 III  a a  . ,  -400 Load (kN)  Gauge 3 Strains vs Load  100^150^200^250 • Specimen A  •  ■ Specimen B  Specimen C Specimen E  Load (kN)  131  Gauge 4 Strains vs Load 2000 1500 1000 500  to  tz^0  - — —50-^ • • ra I A a lio_k_it )^  -500 . ffs  -1000  ti"  -1500  ito  •  i  , 200 a a • •  a---^  1--13--lia  •  • Specimen A • Specimen B ^ 2 0 Specimen D  1  Specimen E  -2000 -2500 Loa d (kN)  Gauge 5 Strains vs Load 2000 1800 1600 :E. 1400 .12 1200 Tr1 1000 . a 800 .6‘3 600 (0 400 200  ---  o  Ar L .^...;^•7;  PP  IN^  •  •  •  II  a  • Specimen A  4"--.  • Specimen B Specimen D  i,',  _41,_■40 __ *2  .: It -  Specimen E  r*  .  ,  tr■  0 0  50^100^150  200  ^  250  Loa d (kN)  Gauge 6 Strains vs Load 1200 1000 800 600 •c 400 200  ,-, ••• • • v^  200  •  ••  • Specimen A  •• • •  a a 50^011 • •  n  it°  Loa d (kN)  132  ▪ Specimen B Specimen D Specimen E , al  ssi 200^250  ▪•  Gauge 7 Strains vs Load 500 0  A^ 100 ^150_^200^250  -500 WI -1000 () • -1500  ♦ Specimen A  ♦  Specimen D  • -2000 Cl)  Specimen E  -2500 -3000 -3500 Load (kN)  Gauge 1 Strains vs Load  2500 2000  ♦ Specimen G  //) 1500  x x  c 1000 . (U  x a  500 0  0  ^  is  1---- X--  Specimen F Specimen H  x  :• •  Specimen I x Specimen J  50^100^150  ^  200  ^  250  Load (kN)  Gauge 2 Strains vs Load  ♦ Specimen F ■ Specimen G Specimen H  a  la  • ■  ▪  Specimen I  ■  x Specimen J n^n  X X X x 50 ^ AOX x x  Load (kN)  133  x 150  Gauge 3 Strains vs Load 0 -200 -400 -600 cts -800 71; z -1000 c -1200 ;)- -1400 -1600 -1800 -2000  —50-  1  100  150-  20 0 • Specimen F  * , * 4 ' s____s_w_ a  ■ Specimen G Specimen H Specimen I  x x  Specimen J x  Load (kN)  Gauge 4 Strains vs Load 3000 2500  ■ ■  2000 1500 1000  •  0  ■Ck X  it_  ■  ■  ■  500  ■  a  • Specimen F  ■  ■ Specimen G  Specimen H Specimen I  * •r * • ♦ • •7-  x  6.) *  -500  X  x Specimen J  X 180 3;  x  2 0  3`___ JK 150  -1000 Load (kN)  Gauge 5 Strains vs Load 2000 1800 1600 1400 co 1200 u; • 1000 • 800 600 Cl) 400 200  r  .  r X  r7  X  • *  r■  •  a  -PI-  3:  3:  •  It_ IN^3:  • Specimen F  _K-  x_ ___X__IC  ■ Specimen G  i 1  X  x .  i  Specimen I  •  x Specimen J  0 0  50  Specimen H  100 Load (kN)  134  150  200  Gauge 6 Strains vs Load 600 500 400  • Specimen F  *IT? 300  ■ Specimen G  200 •  a  100  c15^0 1^F. -100  •• : •,  Specimen H  )  I  x x  a  x %) xx  x  r  Specimen I x Specimen J  x^x-  x1b0  150  2( 0  -200  Load (kN)  Gauge 7 Strains vs Load  100  0 • Specimen F  17)  -1000  Specimen G Specimen H  • -1500  ■ Specimen I X Specimen J  -2000  Load (kN)  135  APPENDIX B: SIMPLIFIED STRENGTH GAIN MODEL  ^  Consider the Creosote Control Specimen, Beam F: First, determine Elastic Modulus, ^:= 28 MPa Consider a point on the L v D curve where the beam is still linear elastic, L = 20 kN P := 20 kN 1:= 2.438m^b 0.152m d := 0.305 m  ,^,3 c := —^I := — D 2^12 6 (Gauge 3) E := 258 .10 —  a := E •c M -c  E •c  1 P -1-c  E -E  8 -1  P -1 -c 8 •E  E  E = 1.002 x 10  10  Pa  E := 10GPa Next, determine Ultimate Strength, Consider the point on the L v D curve where the beam fails, L = 108.7 kN P := 108.7 kN :-  :=  M  •C  I  P .1-c  4 .1  = 2.811 x 10 "Pa  137  Now we know the Elastic Modulus and Ultimate Strength of the Unreinforced Wood, using the Simplified Transformation Model, we try to determine Ultimate Strength of the Composite. 152  6. Actual Section  TransCormecl Section  The section is transformed by taking the ratio of the Elastic Modulus of FRP to the Elastic Modulus of the Creosoted wood, and multiplying the horizontal dimensions of the FRP by that ratio. ^n := EEFRP E ms, := 10 GPa EFRP := 14 GPa ms, n = 1.4 Now that we know the dimensions of the transformed section, find the centroid and moment of inertia of the new section: I 305mm ^+ (229.6mm)• (6mm)- (308mm) ( 168.8mm) • ( 305mm) • \ ^2 Y  (168.8mm)• (305mm) + (229.6mm)- (6mm)  y = 0.157 m  138  2^ (305.nm )^ 1 3 I 3 I:= — -(168.8-nn)-(30510 + (168.8mr)-(30570^y + -(229.6nn)-(6mrr) + (229.6nm) .(6mrr) -(308mm- y) : 12  2  Mc :-  I  P -c I = 4.316 x 10  -4  m  4  := 28 MPa 1 := 2.438 m^c :=  P :=  311 mm 2  a.44 1.c  P = 127.494 kN  139  APPENDIX C: INTERFACIAL SHEAR STRESS  Trans formed FRP  The interface between the FRP and the timber is where shear stresses build up, the length of this perimeter is: t := 305mm + 305mm + 152mrr The area of the FRP is:  A:= (8.4m•305mm) + (229.6mm6mril A = 6.502 x 10  -3  m  2  The centroid of the FRP is: r 305mm) 305mrn (8.4mm).(305mm) + (8.4mm) -(305mm) •(^ + (229.6mm) -(6mm) -(308mm) 2 2 Y (8.4mm) -(305mm) + (8.4mm) -(305mm) + (229.6mm) -(6mm) The maximum load supported by any of the creosoted beams was Beam H, 164.34 kN 164.34 kN V :— ^ 2 4 V= 8.217 x 10 N 4.316 x 10 4 m 4^Q:=^— 156.6mm) t 0.762 m n -I^I  V -Q • t  q = 46.862 kPa  141  APPENDIX D: PREDICTION OF ULTIMATE STRENGTHS  Determination of Beam Strength: Beam A Done by analyzing data from Beam A (Control Specimen):  C Y max :—  M max.c^b  := 6 in d := 14 in  G  max -  P-1- c  I  1:= — -b•d 12  P := 184.7 kN^1:– 2.44m^c 7in  I = 1372in  3  4  Gmax = 35 MPa (Therefore, this is the strength of the unreinforced timber to be used in all calculations)  Determination of Elastic Modulus: Done by analyzing data from Beam A (Control Specimen): Consider a point on the Load vs Displacement Graph where the curve is still linear: Try Section A, load applied is 50 kN: E:= —  E:–  P-I-c  P^50 kN^I := 2.44^c 7in  8-I-c  E = 8.4 GPa  143  I = 1372in 4^E := 563 -10  —6  a := 11038MPa  Given in Table 3.5.2 in 'Canadian Lumber Properties', for D.Fir, 38x235  P 5 := 6998 MPa^#2,  G P5 P 5 := G 1.645)t  1.645  Assuming a standard normal distribution where P5 is the 5th percentile value  1.1 = 2.456x 103 -MPa Ew := a + z•vi^Now,  determine the percentile rank of the Elastic Modulus of the given specimen.  E N, := 8400 MPa  Ew -  Z ^  z —1.074 F(z) := 0.142^Taken  from standard normal distribution table  Therefore, the percentile rank of the Elastic Modulus = 1-(2)(0.142) = 0.716 Now we calculate the Ultimate Compression Strength (UCS) and Ultimate Tensile Strength (UTS) of the given specimen: Table 1.25 in 'Canadian Lumber Properties' k := 2.51 m 1 := 21.65 := 11.37 (  x- x0  k  F(z) := 1 — e  x := 21.62 MPa^(UCS)  Table 1.13 in 'Canadian Lumber Properties' k := 1.70 m 1 := 18.41 x 0 := 3.97 /^ k  x-N0  F(z) := 1 — e  ^  m1  x := 10.08 MPa^(UTS)  Now, calculate Ultimate Compression Strength and Ultimate Tensile Strength taking into account size factors: For three point bending, 1 L,  ^•L k+1  1 L, ^ • 2438min 10+ 1 L ec = 221.636 • mm^Compression 1 L et := 5.9 + 1 2438 mm  L et = 353.333 -min^Tension k 1 := 10 L ucs := 4267mm^  Given in Chapter 3 of Canadian Lumber Properties k 2 := 9.1^d UCS^235 mm UCS := 21.62 MPa^d := 355 mm 1  fCU  k i^k2 ( LUCS^I d UCS -UCS ^d L ec  145  ^  fcu^27.773 •MPa  ^k 1^5.9 LUTS := 3683 mm^  Given in Chapter 3 of Canadian Lumber Properties  ^k 2^4 . 4 d UTS := 235 mm d := 355 mm  UTS := 10.08 MPa 1 — k (  f  f  :–  1  -UTS L UTS Let  1 _ k2 dUTS \  j  d^i  UTS  7 1.365x 10 Pa  k 3 :=^10  f [(k3 + 1) m •  c := 0.5  K3 taken from Gentile, 1999, while for an unreinforced beam, the neutral axis is at the midheight of the beam, therefore, c = 0.5  k3 .ftu  fm = 18.601 • MPa  146  Determination of Beam Strength: Beam F Done by analyzing data from Beam F (Control Specimen):  b := 6in^d := I 2in P := 108.11\ 1  1 :=-- — -b-d 12  1 = 864in  ^  I := 2.44rr^c := 6in  3  4 c  a max :–  CS  P-I•c max := 4.1  a max = 28.099MPa  Determination of Elastic Modulus: Done by analyzing data from Beam F (Control Specimen): Consider a point on the Load vs Displacement Graph where the curve is still linear: Try Section A, load applied is 50 kN:  E :=  P := 20k1\  1 := 2.44rr^c := 6in  1 := 864n 4^c := 258.10  E 81•c E = 10.02GPE  147  6  := 11038 MPa  Given in Table 3.5.2 in 'Canadian Lumber Properties', for #2, D.Fir, 38x235  P 5 := 6998 MPa  — P5 1-1  P 5 := a — 1.6451.1  1.645  Assuming a standard normal distribution where P5 is the 5th percentile value  = 2.456x 10 3 •MPa Ew  +  Now, determine the percentile rank of the Elastic Modulus of the given specimen. Note that the Elastic Modulus was calculated in Appendix B  E N, := 10000 MPa Ems, -6 z ^  z = —0.423 F ( z) := 0.337^Taken  from standard normal distribution table  Therefore, the percentile rank of the Elastic Modulus = 1-(2)(0.337) = 0.326 Now we calculate the Ultimate Compression Strength (UCS) and Ultimate Tensile Strength (UTS) of the given specimen: Table 1.25 in 'Canadian Lumber Properties' k := 2.51 m 1 := 21.65 x 0 := 11.37 k  0  X  F(z) := 1 — e -  1-11, )  x := 26.56 MPa^(UCS)  Table 1.13 in 'Canadian Lumber Properties' k := 1.70 m 1 := 18.41 x0 := 3.97 \k  F(z) := 1 — e^  ml ,  x := 14.88 MPa^(UTS)  Now, calculate Ultimate Compression Strength and Ultimate Tensile Strength taking into account size factors: For three point bending, Le ^•1 +1  L cc  1 2438 mm 0+1  Lec = 221.636 .mm^Compression 1  Let^5.9 + 1 243$ mm L et = 353.333 -mm^Tension k 1 := 10^Lucs := 4267 mm  Given in Chapter 3 of Canadian Lumber Properties k 2 := 9.1 d UCS^235 mm  UCS := 26.56 MPa^d := 305 mm 1^1 (  LUGS  fC U^  L ec  \ I  2  d UCS k  ^d  UCS  fcti = 34.692 • MPa  k 1 := 5.9^L UTS^3683 mm  Given in Chapter 3 of Canadian Lumber Properties  k 2 := 4.4^d UTS^235 mm UTS := 14.88 MPa^d := 305 mm  ftu  1^1 k,^k2 ( L UTS^( d UTS Let  • UTS  7  ftu = 2.086x 10 Pa  k 3 := 10^c^0.5^K3 taken from Gentile, 1999, while for an unreinforced  beam, the neutral axis is at the midheight of the beam, therefore, c = 0.5 (k3 + 1)  fm :-[  k3  1 . 0u  fm = 28.422 • MPa  

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