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An experimental investigation of the behaviour of connections in thin precast concrete panels under earthquake… Kallros, Mikael Kaj 1987

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AN EXPERIMENTAL  INVESTIGATION OF THE BEHAVIOUR  OF CONNECTIONS IN THIN PRECAST CONCRETE PANELS UNDER EARTHQUAKE LOADING By MIKAEL KAJ KALLROS B.A.Sc.(Civil),  The U n i v e r s i t y  of B r i t i s h Columbia, 1985  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES CIVIL ENGINEERING DEPARTMENT  We accept t h i s t h e s i s as conforming to the r e q u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA April  1987  © Mikael Kaj K a l l r o s ,  1987  In presenting  t h i s t h e s i s in a p a r t i a l  f u l f i l m e n t of the  requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t freely  a v a i l a b l e for reference  and study. I f u r t h e r agree  that permission for extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s or her r e p r e s e n t a t i v e s .  It i s  understood that copying or p u b l i c a t i o n of t h i s  thesis for  financial  written  gain  s h a l l not be allowed without my  permission.  Department of CIVIL ENGINEERING The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5  Date : A p r i l  15, 1987  i i ABSTRACT  I n v e s t i g a t i o n s of connections f o r p r e c a s t concrete panel b u i l d i n g s have shown that i t i s d i f f i c u l t  to design an  embedded connection that w i l l perform w e l l under earthquake l o a d i n g . Some t y p i c a l connections use studs or  reinforcing  bars embedded i n the edge of the p a n e l . These are then welded or b o l t e d to an adjacent p a n e l . During  earthquake  l o a d i n g the c r u s h i n g of concrete around the embedment u s u a l l y leads to premature l o s s of s t r e n g t h and  s t i f f n e s s of  the connection before s i g n i f i c a n t d u c t i l i t y can develop. I t has been found that connection performance improves with i n c r e a s i n g panel t h i c k n e s s . The behaviour concrete panels was  of embedded connections i n v e s t i g a t e d . The  in t h i n precast  i n t e n t was  to improve  connection design d e t a i l s and to develop a simple method of p r e d i c t i n g connection s t r e n g t h s with panel t h i c k n e s s e s of mm  to 75  50  mm.  S i x t e e n c o n n e c t i o n s of s i x d i f f e r e n t types were t e s t e d . Three were t e s t e d m o n o t o n i c a l l y and  t h i r t e e n were t e s t e d  under r e v e r s e d c y c l i c l o a d i n g . C e r t a i n types of connections can be used to t r a n s f e r earthquake loads between t h i n concrete panels as long as they have adequate s t r e n g t h . Methods f o r p r e d i c t i n g s t r e n g t h of connections are d i s c u s s e d . The t e s t e d should not be r e l i e d on to develop  the  connections ductility.  iii TABLE OF CONTENTS PAGE # ABSTRACT  ii  TABLE OF CONTENTS  i i i  LIST OF TABLES  viii  LIST OF FIGURES  ix  LIST OF PHOTOGRAPHS  xiii  ACKNOWLEDGEMENTS  xvi  CHAPTER 1 - INTRODUCTION  1  1.1. GENERAL  1  1.2. OBJECTIVES AND SCOPE  2  CHAPTER 2 - REVIEW OF CONNECTION DESIGNS FOR PRECAST CONCRETE  4  2.1. INTRODUCTION  4  2.2. CONNECTION BEHAVIOUR DURING EARTHQUAKES  4  2.3. TYPES OF CONNECTIONS  6  2.3.1. CAST IN PLACE CONNECTIONS  6  2.3.2. DRY CONNECTIONS  8  2.3.2.1. MECHANICAL CONNECTORS  10  2.3.2.2. WELDED CONNECTIONS  10  2.3.2.2.1. EMBEDDED CONNECTIONS WITH RIGID WELD PLATES 2.3.2.2.2. EMBEDDED REBAR CONNECTION  12 15  2.3.2.2.3. EMBEDDED CONNECTIONS WITH DUCTILE WELD PLATE 2.4. LOCATION OF CONNECTIONS  24 26  iv 2.5. CONCLUDING REMARKS  26  CHAPTER 3 - EXPERIMENTAL MATERIALS AND SPECIMEN PREPARATION  27  3.1. INTRODUCTION  27  3.2. FORM  29  3.3. CONCRETE  31  3.3.1. CONCRETE MIXING AND CASTING PROCEDURE  31  3.3.2. TEST RESULTS OF CONCRETE MIXES  33  3.4. STEEL  37  3.4.1. REINFORCING MESH  37  3.4.2. SPECIMEN SUPPORT PLATE  37  3.4.3. CONNECTION STEEL  39  3.5. TYPES OF CONNECTIONS 3.5.1. REBAR #1 BENT TO 45 DEGREES.  45 45  3.5.2. REBAR #1 BENT TO 45 DEGREES AND WELDED TO AN ANGLE  47  3.5.5. ANGLE WELDED TO REINFORCING MESH  51  3.5.6. REVERSED ANGLE WELDED TO REINFORCING MESH  51  CHAPTER 4 - LABORATORY TEST DETAILS  55  4.1. INTRODUCTION  55  4.2. ASSUMPTIONS MADE FOR THE TESTS  58  4.3. TEST RIG  58  4.4. LOADING AND DATA ACQUISITION SYSTEM  63  4.5. USE OF THE DATA ACQUISITION SYSTEM  67  4.5.1. OPERATION OF MTS SERVO-CONTROLLER  67  4.5.2. OPERATION OF NEFF 620  67  V  4.5.3. OPERATION OF PDP-11/10 4.6. TEST MEASUREMENTS  67 68  4.6.1. LOAD MEASUREMENT  68  4.6.2. DISPLACEMENT MEASUREMENT  68  4.6.2.1. CONNECTION DISPLACEMENT  70  4.6.2.2. SIDEWAYS MOVEMENT  73  4.6.2.3. SPECIMEN ROTATION  73  4.6.3.4. MOVEMENT OF HYDRAULIC JACK  77  4.7. LOADING PROCEDURE CHAPTER 5 - EXPERIMENTAL  RESULTS  77 79  5.1. INTRODUCTION  79  5.2. DETAILS OF CONNECTIONS TESTED  80  5.2.1. REBAR #1 AT 45 DEGREES  80  5.2.1.1. TEST #1  81  5.2.1.2. TEST #2  87  5.2.1.3. TEST #6  90  5.2.2. REBAR #1 AT 45 DEGREES WELDED TO AN ANGLE  94  5.2.2.1. TEST #3  94  5.2.2.2. TEST #4  102  5.2.2.3. TEST #5  104  5.2.3. REBAR #2 AT 4 5 DEGREES WITH SHORT RECESS  111  5.2.3.1. TEST #7  111  5.2.3.2. TEST #8  120  5.2.3.3. TEST #13  126  5.2.4. REBAR #2 AT 45 DEGREES IN A 75 MM THICK SLAB 5.2.4.1. TEST #11  130 130  vi 5.2.4.2. TEST #12  140  5.2.4.3. TEST #14  146  5.2.5. ANGLE WELDED TO REINFORCING MESH  151  5.2.5.1. TEST #9  151  5.2.5.2. TEST #15  161  5.2.6. REVERSED ANGLE WELDED TO REINFORCING MESH 165 5.2.6.1. TEST #10  165  5.2.6.2. TEST #16  176  CHAPTER 6 - DISCUSSION, CONCLUSIONS AND FUTURE SCOPE  182  6.1. INTRODUCTION  182  6.2. DISCUSSION  183  6.2.1. BEHAVIOUR OF THE CONNECTIONS DURING CYCLIC LOADING  183  6.2.2. BEHAVIOUR OF CONNECTIONS DURING MONOTONIC LOADING  184  6.2.3. STRENGTH OF CONNECTIONS  186  6.2.3.1. MAXIMUM MEASURED STRENGTHS  186  6.2.3.2. STRENGTHS AT FAILURE  187  6.2.3.3. CALCULATED STRENGTHS  187  6.2.3.3.1. SEPARATE REBAR AT 45 DEGREES.  187  6.2.3.3.2. CONNECTIONS WELDED TO REINFORCING MESH.  191  6.2.3.3.2.1. TYPE A  192  6.2.3.3.2.2. TYPE B  192  6.2.3.3.3. CALCULATED CONNECTION STRENGTHS  195  vii 6.2.3.4. INFLUENCE OF CONCRETE STRENGTH ON CONNECTION STRENGTHS  201  6.2.4. TYPES OF CONNECTION FAILURES  204  6.2.5. DISPLACEMENT OF THE CONNECTIONS  206  6.2.6. SIDEWAYS MOVEMENT OF THE CONNECTIONS  207  6.2.7. CONNECTION DETAILS  208  6.2.7.1. PANEL THICKNESS  208  6.2.7.2. PANEL RECESS  209  6.2.7.3. ANGLE WELDED TO CONNECTION  209  6.3. CONCLUSION  209  6.4. FUTURE SCOPE  210  REFERENCES  213  viii LIST OF TABLES  TABLE #  PAGE #  3.1. MIX PROPORTIONS  32  3.2. COMPRESSION STRENGTHS OF CYLINDERS  34  3.3. YIELD AND ULTIMATE STRESSES  41  6.1. MAXIMUM CONNECTION STRENGTHS  185  6.2. MEASURED CONNECTION STRENGTH AT FAILURE  188  6.3. CALCULATED CONNECTION STRENGTHS  196  6.4. CALCULATED CONNECTION STRENGTHS  197  6.5. MOVEMENTS OF CONNECTIONS  205  ix  LIST OF FIGURES  FIGURE # 2.1.  PAGE #  A connection t y p i c a l to those t e s t e d by Aswad Ref. [ 8 ] .  9  2.2. T y p i c a l Mechanical  connection.  11  2.3. D e t a i l s of the connections t e s t e d , showing the arrangements of the studs.  13  2.4. D e t a i l s of connections r e p o r t e d i n Ref. [ 8 ] .  16  2.4. Continued  17  2.5. Types of connections t e s t e d i n Ref. [ 4 ] .  19  2.5. Continued  20  2.5. Continued  21  2.5. Continued  22  2.6. Model developed 2.7. Connection  i n Ref. [ 4 ] .  t e s t e d i n Ref. [ 1 2 ] .  23 25  3.1. Spec imen  28  3.2. Forms f o r specimens  30  3.3. Compression s t r e n g t h s of c y l i n d e r s  36  3.4. Support  40  plate  3.5. Y i e l d and U l t i m a t e S t r e s s e s of S t e e l  43  3.6. L o a d - d e f l e c t i o n curves f o r rebar #2  44  3.7. Rebar #1 at 45 degrees  46  3.8. Rebar #1 at 45 degrees  welded t o angle  48  3.9. Rebar #2 at 45 degrees  with small recess  49  3.5. Rebar #2 at 45 degrees  with small recess  49  X  3.10.  Rebar #2 at 45 degrees with a recess i n a thicker slab  50  3.11.  Angle welded to r e i n f o r c i n g mesh  53  3.12.  Reversed angle welded t o r e i n f o r c i n g mesh  54  4.1.  Test r i g  4.2. Test  r i g separated  56 into parts.  59  4.2. Continued  60  4.3.  69  L o c a t i o n s of the LVDTs.  4.4. LVDT mounting f o r connection 4.5.  displacement.  LVDT mounting f o r sideways movement and specimen rotation.  5.1.  71  74  L o a d - d e f l e c t i o n curve  f o r Test  #1.  83  5.2. L o a d - d e f l e c t i o n curve  f o r Test  #2.  88  5.3.  f o r Test  #6.  91  L o a d - d e f l e c t i o n curve  5.4. Sideways movement of connection f o r Test  (Test #6).  5.5.  L o a d - d e f l e c t i o n curve  #3.  5.6.  Sideways movement of connection  5.7.  Cracking p a t t e r n f o r Test  5.8.  L o a d - d e f l e c t i o n curve  97  5.9.  Load a p p l i c a t i o n p o i n t s f o r Rebar #1 with angle.  (Test #3).  #3.  f o r Test  92  98 99  #4.  5.10.  L o a d - d e f l e c t i o n curve  5.11.  Sideways movement of the connection  5.12.  L o a d - d e f l e c t i o n curve  5.13.  Sideways movement of connection  5.14.  L o a d - d e f l e c t i o n curve  5.15.  Sideways movement of connection  5.16.  L o a d - d e f l e c t i o n curve  103  f o r Test #5.  107 (Test #5).  f o r Test #7. (Test #7).  f o r Test #8. (Test #8).  f o r Test #13.  106  108 113 114 122 123 127  xi 5.17.  Sideways movement of connection  (Test #13).  5.18.  L o a d - d e f l e c t i o n curve  5.19.  Enlargement of the l o a d - d e f l e c t i o n curve f o r  f o r Test #11.  Test #11. Sideways movement of connection  5.21.  L o a d - d e f l e c t i o n curve  5.22.  Sideways movement of connection  5.23.  L o a d - d e f l e c t i o n curve  5.24.  Enlargement of the l o a d - d e f l e c t i o n curve f o r  (Test #11).  f o r Test #12. (Test #12).  f o r Test #14.  #14.  Sideways movement of connection  5.26.  L o a d - d e f l e c t i o n curve  5.27.  Enlargement of the l o a d - d e f l e c t i o n curve f o r  (Test #14).  f o r Test #9.  #9.  Sideways movement of connection  5.29.  L o a d - d e f l e c t i o n curve  5.30.  Enlargement of the l o a d - d e f l e c t i o n curve f o r  (Test #9).  f o r Test #15.  #15.  142 147  149 153  155 162  163  5.31.  Sideways movement of connection  5.32.  L o a d - d e f l e c t i o n curve  5.33.  Enlargement of the l o a d - d e f l e c t i o n curve f o r  (Test #15).  f o r Test #10.  Test #10.  164 167  168  5.34.  Sideways movement of connection  5.35.  L o a d - d e f l e c t i o n curve  5.36.  Enlargement of the l o a d - d e f l e c t i o n curve f o r  (Test #10).  f o r Test #16.  Test #16. 5.37.  141  154  5.28.  Test  134  148  5.25.  Test  132  133  5.20.  Test  128  Sideways movement of connection  169 178  179 (Test #16).  180  xii 6.1. Forces i n rebar c o n n e c t i o n .  190  6.2. Forces i n connection welded to r e i n f o r c i n g mesh (perpendicular c r a c k i n g ) .  193  6.3. Forces i n connection welded t o r e i n f o r c i n g mesh (diagonal c r a c k i n g ) .  194  6.4. Measured versus C a l c u l a t e d s t r e n g t h s .  198  6.5. Measured versus C a l c u l a t e d s t r e n g t h s .  199  6.6. F a i l u r e versus C a l c u l a t e d s t r e n g t h s .  200  6.7. F a i l u r e versus C a l c u l a t e d s t r e n g t h s .  202  6.8. Connection  203  s t r e n g t h s versus C y l i n d e r s t r e n g t h s .  6.9. Forces p e r p e n d i c u l a r to c o n n e c t i o n .  212  xiii LIST OF PHOTOGRAPHS  PHOTOGRAPH #  PAGE #  3.1. Concrete t e s t c y l i n d e r  38  3.2  46  Rebar #1 at 45 degrees  3.3. Rebar #1 at 45 degrees welded t o angle  48  3.4. Rebar #2 at 45 degrees with a short recess  49  3.5. Rebar #2 at 45 degrees with a r e c e s s i n a thicker slab  50  3.6. Angle welded t o r e i n f o r c i n g mesh  53  3.7. Reversed angle welded to r e i n f o r c i n g mesh  54  4.1. Test r i g  57  4.2. MTS c o n t r o l l e r and NEFF 620.  64  4.3. PDP-11/10 computer t e r m i n a l .  65  4.4. LVDTs measuring  72  4.5. LVDT measuring 4.6. LVDTs measuring  connection displacement. sideways movement. specimen  rotation.  75 76  5.1. Small crack along bottom l e g (Cycle #1 +79 kN).  84  5.2. Bottom corner f a l l i n g o f f (Cycle #2 +91 kN).  85  5.3. Connection a t f a i l u r e  (Cycle #3 +74 kN).  86  5.4. Connection at f a i l u r e  (Cycle #1 -44 kN).  89  5.5. Connection at f a i l u r e  (Cycle #6 +59 kN).  93  5.6. Bending of top bar (Cycle #11 +40 kN).  100  5.7. Connection at f a i l u r e  (Cycle #13 +32 kN).  101  5.8. Connection at f a i l u r e  (Cycle #5 +50 kN).  109  5.9. Connection at f a i l u r e  (Cycle #5 +50 kN).  110  5.10. C y c l e #4 -50 kN (Test #7).  115  xiv 5. 1 1 . C y c l e #4 -87  kN  (Test #7) .  1 16  5. 12. Cycle #4 -87  kN  (Test #7).  1 17  5. 13. C y c l e #5 + 56 kN  (Test #7) .  1 18  5. 14. C y c l e #5 + 32 kN  (Test #7) .  1 19  5. 15. Connection at f a i l u r e  (Cycle #16  -38  kN) .  1 24  5. 16. Connection at f a i l u r e  (Cycle #16  -38  kN) .  1 25  5. 17. Connection at f a i l u r e  (Cycle #1 + 42 kN) .  1 29  5. 18. Cycle #10  -79  kN  (Test #11).  1 35  5. 19. Cycle #12  + 65 kN  (Test #11).  1 36  5. 20. Cycle #12  + 77 kN  (Test #11).  1 37  5. 21 . C y c l e #12  -59  kN  (Test #11).  1 38  5. 22. Connection at fa i l u r e (Cycle #13 5. 23. Tension corner  f a l l i n g off  + 67 kN) .  ( C y c l e #1 +97  1 39 kN).  143  5. 24. Top corner f a l l i n g o f f (Cycle #1 + 75 kN) .  144  5. 25. Connection at f a i l u r e  (Cycle #1 + 75 kN) .  1 45  5. 26. Connection at f a i l u r e  (Cycle #15  1 50  5. 27. C y c l e #4 -41  + 62 kN) .  kN  (Test #9) .  156  5. 28. C y c l e #7 + 51 kN  (Test #9) .  1 57  5. 29. Cycle #7 + 51 kN  (Test #9) .  158  5. 30. Cycle #9 -29  kN  (Test #9) .  159  5. 31 . Cycle #9 -29  kN  (Test #9) .  1 60  5. 32. Cycle #2 + 42 kN  (Test #10).  170  5. 33. Cycle #2 + 42 kN  (Test #10) .  171  5. 34. Cycle #4 + 60 kN  (Test #10) .  172  5. 35. Cycle #6 + 56 kN  (Test #10) .  1 73  5. 36. Cycle #6 + 56 kN  (Test #10).  174  5. 37. Cycle #7 -14  (Test #10) .  1 75  kN  Cycle #11 + 42 kN (Test #16).  ACKNOWLEDGEMENTS  The author wishes t o thank Dr. R.A. Spencer valuable  for h i s  guidance i n the p l a n n i n g and i n the i n v e s t i g a t i o n  c a r r i e d out i n t h i s t h e s i s . The author i s proud t o have been a s s o c i a t e d with Dr. Spencer  i n t h i s work.  Thanks a r e extended t o the t e c h n i c i a n s  i n the  l a b o r a t o r y , e s p e c i a l l y B. M e r k l i e , G. K i r s c h , D. Postgate and W. Schmit  for their assistance  i n making the t e s t  equipment. The author i s g r a t e f u l f o r f i n a n c i a l support from the Prestressed  Concrete I n s t i t u t e , Chicago,  Illinois.  Mikael K. K a l l r o s  1  CHAPTER 1  INTRODUCTION  1.1.  GENERAL P a n e l i z e d or p r e c a s t concrete  experienced  c o n s t r u c t i o n has  phenomenal growth i n the past decade. T h i s  growth i s f u e l e d by a combination of two f a c t o r s . One i s the s t a n d a r d i z a t i o n of design and manufacturing and the second i s the i n c r e a s e i n f l e x i b i l i t y it use  and speed of e r e c t i o n which  o f f e r s . Precast b u i l d i n g s were i n i t i a l l y  developed f o r  i n e s s e n t i a l l y nonseismic r e g i o n s . T h e i r use has,  however, spread  to zones of high seismic r i s k  Europe, Japan and the S o v i e t Union before  i n America,  their  seismic  behaviour has been s t u d i e d i n depth. The expanding use of p r e c a s t concrete  b u i l d i n g s i n seismic regions  p r e s e n t i n g new c h a l l e n g e s resistant  i s therefore  i n the area of earthquake-  design.  Research on p r e c a s t concrete  b u i l d i n g s during  recent  years has l e a d to s i g n i f i c a n t advances towards a b e t t e r understanding  of both component and system behaviour  earthquakes. Despite questions for  t h i s progres s ,  there s t i l l  remain some  t o be answered about the seismic design  p r e c a s t concrete b u i l d i n g s .  during  procedures  2 Attempts to r e s i s t the f o r c e s w i t h i n the l i m i t s of the elastic During  response  are uneconomic f o r most concrete  buildings.  l a r g e ground a c c e l e r a t i o n s dynamic f o r c e s equal to  the l a t e r a l load c a p a c i t y of the s t r u c t u r e may  be induced i n  the s t r u c t u r e . T h i s can l e a d to y i e l d i n g or p l a s t i c deformations In  i n some of the c r i t i c a l areas i n the  order to prevent  l a r g e earthquake,  s e r i o u s damage and  l o s s of l i f e d u r i n g a  i t i s t h e r e f o r e necessary to ensure that  the p o s t - e l a s t i c deformations structural  structure.  can occur without a complete  collapse.  A d u c t i l e connection between two  p r e c a s t panels  h e l p to ensure a safe s t r u c t u r e . The earthquake  can  damage i n  p r e c a s t concrete panel b u i l d i n g s occurs i n most cases along the j o i n t s . The panels themselves little  u s u a l l y d i s p l a y very  damage. However, some of the energy  an earthquake T h i s energy  can be d i s s i p a t e d through  the panel  during  joints.  d i s s i p a t i o n can be achieved by d e s i g n i n g the  connections i n such a way displacement  generated  that they can, even during s e v e r a l  c y c l e s , deform i n e l a s t i c a l l y without  fracture  while m a i n t a i n i n g at the same time t h e i r u l t i m a t e c a p a c i t y .  1.2.  OBJECTIVES AND  SCOPE  The main o b j e c t i v e s of t h i s r e s e a r c h are : a) To develop  improved connection d e t a i l s f o r members with  t h i n f l a n g e s i n earthquake buildings.  r e s i s t a n t p r e c a s t concrete  3 b) To develop r a t i o n a l methods of a n a l y s i s and design of connections  f o r members with t h i n f l a n g e s i n earthquake  r e s i s t a n t precast concrete  buildings.  Chapter 2 d i s c u s s e s some of the e x i s t i n g types of connections and t h e i r  locations.  Chapter 3 c o n t a i n s a d e s c r i p t i o n of the experimental m a t e r i a l s , e x p l a i n s how the v a r i o u s m a t e r i a l s were prepared and g i v e s a d e s c r i p t i o n of the d i f f e r e n t  types of  connections. Chapter 4 d e s c r i b e s the t e s t  r i g , the measurements  taken d u r i n g the t e s t , the l o a d i n g procedure and the data a c q u i s i t i o n and c o n t r o l  system.  Chapter 5 c o n t a i n s the r e s u l t s of the l a b o r a t o r y t e s t s for the v a r i o u s types of c o n n e c t i o n s . The r e s u l t s a r e presented through the use of graphs, t a b l e s and p i c t u r e s . Chapter 6 presents a d i s c u s s i o n of the experimental r e s u l t s , a comparison with t h e o r e t i c a l c a l c u l a t i o n s and suggestions f o r f u t u r e r e s e a r c h .  4  CHAPTER 2  REVIEW OF CONNECTION DESIGNS FOR  2.1.  PRECAST CONCRETE  INTRODUCTION Embedded concrete connections must meet an  of  assortment  design and performance c r i t e r i a . A connection must have  the s t r e n g t h to r e s i s t  the f o r c e s to which i t w i l l  be  exposed d u r i n g i t s design l i f e t i m e . Some of these f o r c e s are dead l o a d s , l i v e l o a d s , wind l o a d s , earthquake l o a d s , and water p r e s s u r e s , volume changes and  loads due  soil  to  i n s t a b i l i t y . At the same time, the connections must a l s o be able to accommodate r e l a t i v e l y  l a r g e deformations.  Designing  good connection d e t a i l s a l s o i n v o l v e s b a l a n c i n g c o n t i n u i t y and d u c t i l i t y A review  with good economics and ease of c o n s t r u c t i o n . of connection behaviour  during earthquakes i s  presented. A number of the e x i s t i n g connections are along with the l o c a t i o n s of the  2.2.  reviewed  connections.  CONNECTION BEHAVIOUR DURING EARTHQUAKES C o n s t r u c t i n g concrete b u i l d i n g s out of p r e c a s t  in earthquake prone regions of the world  r a i s e s many  q u e s t i o n s i n earthquake r e s i s t a n t d e s i g n . The ductility  of the connections  panels  s t r e n g t h and  between the p r e c a s t panels  will  5  s i g n i f i c a n t l y a f f e c t the behaviour b u i l d i n g d u r i n g an earthquake. most cases observed [1].  of a p r e c a s t concrete  The earthquake  damage i s i n  to take p l a c e along the connection  lines  T h i s happens mainly because the s t r e n g t h of the  connection  i s r a r e l y comparable to the s t r e n g t h of the  surrounding p a n e l . The d e t e r i o r a t i o n of the region around the connection under c y c l i c  l o a d i n g c o n t r i b u t e s to f u r t h e r  r e d u c t i o n i n the r e s i s t a n c e of the c o n n e c t i o n . performance of the connections and the  The  i n the w a l l s and  roof diaphragms w i l l t h e r e f o r e be c r i t i c a l  i n the  floor  in r e s i s t i n g  earthquakes. It i s d e s i r a b l e f o r the diaphragms to r e s i s t  f o r c e s without y i e l d i n g , which r e q u i r e s t h a t the  earthquake connections  remain e l a s t i c . T h i s r e q u i r e s a connection which can continue to c a r r y the f o r c e s due i n a d d i t i o n can handle earthquake.  to dead and  the dynamic f o r c e s induced by the  W a l l s , on the other hand, may  be assumed to  y i e l d under the a c t i o n of l a t e r a l loads due The design procedure presented  l i v e loads, and  to  earthquakes.  f o r a b u i l d i n g of t h i s type i s  i n the PCI Design Handbook [2] and  the CPCI M e t r i c  Design Handbook [ 3 ] . A s t a t i c a n a l y s i s u s i n g e q u i v a l e n t lateral  f o r c e s shows that the connections between adjacent  panels i n the shear w a l l s and diaphragms w i l l be subject to r e v e r s i n g shear  f o r c e s a c t i n g p a r a l l e l to the edge of the  panel during the earthquake and  [ 4 ] , Connections  between w a l l  f l o o r or roof diaphragm u n i t s w i l l be s u b j e c t to s i m i l a r  f o r c e s . In a d d i t i o n , the connections w i l l a l s o have to  6  resist  pullout  f o r c e s a c t i n g both i n the plane of the panels  and p e r p e n d i c u l a r t o them. During an earthquake any connection might a l s o be s u b j e c t t o secondary a d d i t i o n to those p r e d i c t e d by the s t a t i c  forces in  analysis.  Spencer and Tong [5] showed that the use of connections i n shear w a l l s having an a c t u a l s t r e n g t h higher than the s t r e n g t h assumed i n the design i s unconservative and can l e a d to an unsafe b u i l d i n g . T h i s was i l l u s t r a t e d  by the  r e s u l t s of a n o n - l i n e a r a n a l y s i s of the response  of a one  s t o r y box-type p r e c a s t s t r u c t u r e d u r i n g a moderate earthquake. Designing a b u i l d i n g with r e l a t i v e l y static  lateral  will yield  low e q u i v a l e n t  f o r c e s and i n c o r p o r a t i n g connections which  i n an earthquake  can be made both economical and  s a f e . T h i s i s the case i f the connections have an a c t u a l s t r e n g t h s i m i l a r to that assumed i n the design and can undergo the necessary  2.3.  inelastic  displacements.  TYPES OF CONNECTIONS There are v a r i o u s types of connections which can be  classified  as f o l l o w s .  2.3.1. CAST IN PLACE CONNECTIONS These connections are a l s o c a l l e d  wet c o n n e c t i o n s .  A f t e r the panels are p l a c e d i n p o s i t i o n , r e i n f o r c e d or u n r e i n f o r c e d c a s t - i n - p l a c e concrete i s used to form the j u n c t i o n between the p a n e l s . The connection area w i l l o f t e n  7  be h e a v i l y congested  with reinforcement so i t i s a d v i s a b l e  to use small aggregate  and mixes with high slump. The  p r o p e r t i e s which i n f l u e n c e the s t r e n g t h and performance of wet  connections  a) Concrete  include :  s t r e n g t h - of both the panels and the c a s t i n  place connections. b) Connection  reinforcement - t h i s i n c l u d e s the  location  and type of s t e e l w i t h i n the c o n n e c t i o n . c) P r e p a r a t i o n of panel s u r f a c e - the s u r f a c e can p l a i n , c a s t e l l a t e d or  be  grooved.  d) Force t r a n s v e r s e to connection - can be from  gravity  loads or p o s t - t e n s i o n i n g . e) Shear connectors - p l a c e d i n the j o i n t to r e s i s t f o r c e s i n the The  joint.  shear t r a n s f e r  through adhesion,  shear  i n wet  c o n n e c t i o n s can be achieved  f r i c t i o n , dowel a c t i o n and d i r e c t  bearing.  However, the bond between p r e c a s t and c a s t - i n - p l a c e c o n c r e t e w i l l o f t e n be destroyed during the c o n s t r u c t i o n p r o c e s s . T h i s along with creep and shrinkage e f f e c t s e l i m i n a t e s the adhesion unless a clamping  and  friction  effectively  t r a n s f e r mechanisms  f o r c e , a c t i n g normal to the connection  face, i s a p p l i e d [6]..  T h i s clamping  through e x t e r n a l compressive  f o r c e can be s u p p l i e d  f o r c e s , p o s t - t e n s i o n i n g or  transverse mild s t e e l . It i s also e s s e n t i a l  i n wet  connections to develop t r a n s v e r s e s t e e l beyond both s i d e s of the f a i l u r e plane  [7].  8 2.3.2. DRY CONNECTIONS The most common type of dry shear connections a r e made up of embedded s t e e l shapes anchored  i n t o the p r e c a s t  members by studs or r e i n f o r c i n g b a r s . The connection  i s then  f i n i s h e d by b o l t i n g or welding a separate s t e e l p i e c e to the embedded s t e e l shapes. A v a r i e t y of mechanisms a r e used i n the dry connections t o t r a n s f e r shear between p a n e l s . The shear  f o r c e s can be t r a n s f e r r e d through  bearing of the s t e e l  shapes, shear of the connecting elements, shear of the b o l t s or through  shear of the weld,  f r i c t i o n between b o l t e d  plates. Martin and Korkosz [7] p o i n t out that dry connections should be designed c o n s e r v a t i v e l y f o r e a r t h q u a k e - r e s i s t a n t c o n s t r u c t i o n . They say that longer weld l e n g t h s , a d d i t i o n a l anchorage of r e i n f o r c i n g bars and lower a l l o w a b l e s t r e s s e s are j u s t i f i e d presence performed  for cyclic  l o a d i n g e s p e c i a l l y with the  of f o r c e s normal t o the shear c o n n e c t i o n . T e s t i n g by Aswad [8] shows that the a p p l i c a t i o n of one k i p  pull-out. f o r c e normal t o a connection can reduce the u l t i m a t e shear c a p a c i t y by 1/3. A normal f o r c e of t h i s  size  can e a s i l y be reached d u r i n g e r e c t i o n or caused by e f f e c t s of shrinkage and temperature. one Aswad t e s t e d can be seen  A c o n n e c t i o n s i m i l a r t o the i n F i g u r e 2.1.  1  Figure 2 . 1 . A connection t y p i c a l to those t e s t e d by Aswad Ref. [ 8 ] .  2.3.2.1. MECHANICAL CONNECTORS These connections are u s u a l l y made up of b o l t s and v a r i o u s i n s e r t s . P o s t - t e n s i o n i n g or high t e n s i o n b o l t s may a l s o be used i n these types of dry connections. One example of a mechanical Drescon-Concordia  connection  i s the  system [ 9 ] . T h i s type of connection  uses  s t e e l p l a t e or a s e c t i o n with s l o t t e d holes which i s f r i c t i o n b o l t e d to the s t e e l  i n s e r t s . These i n s e r t s are  anchored i n t o the concrete p a n e l s . A t y p i c a l connection i s shown i n F i g u r e 2.2. The s l o t t e d holes are made t o accommodate the manufacturing  and e r e c t i o n t o l e r a n c e s with  a d d i t i o n a l c l e a r a n c e t o absorb energy by s l i p p i n g . T e s t s showed that with s l o t t e d h o l e s , the f r i c t i o n a l  movement  c o u l d g i v e the d e s i r e d energy d i s s i p a t i o n without  causing  i n e l a s t i c y i e l d i n g of the m a t e r i a l s . The main f e a t u r e of such a connection  i s t h e r e f o r e the  a b i l i t y t o c o n t r o l the s l i p p a g e of the j o i n t . T h i s can be achieved by s e l e c t i n g the a p p r o p r i a t e j o i n t s u r f a c e and the a p p r o p r i a t e c l e a r a n c e f o r the s l o t t e d h o l e s . P r o p e r l y designed, severe  the connection would be expected  to s l i p during  seismic e x c i t a t i o n s but not under s e r v i c e l o a d s .  2.3.2.2. WELDED CONNECTIONS These connections  have s t e e l embeddments, u s u a l l y bars  or p l a t e s , which are w e l l anchored i n t o the concrete  panels  These embeddments are s i t u a t e d a t p o i n t s , along the panel  11  weld afltr traction  0  CD  -connecting pkrte Q) red. washers U— IrtMrt  anchors  -joint  INSERT  ELEVATION -connecting piati -bolts (ASTM A325) -ins«rt  X CONNECTING PLATE  nuts welded to Insert  panel  SECTION  wall panels connecting angles  bolts connecting angles insert wall panel  (ASTM  A325)i  insert wall panel SECTION  Figure 2.2. T y p i c a l Mechanical connection.  12 edges, where the connections can e a s i l y be welded to one another. A t h i r d s t e e l p i e c e i s u s u a l l y used i n order t o make the welding of the two connections e a s i e r . When the p r e c a s t j o i n t s are welded t o g e t h e r , they can immediately be s u b j e c t e d to f u l l  l o a d i n g . T h i s w i l l e f f e c t i v e l y shorten the  construction period. Previous research has suggested  a number of d i f f e r e n t  connection d e s i g n s . These i n c l u d e : a) Embedded connections with r i g i d weld p l a t e s . b) Embedded rebar c o n n e c t i o n s . d) Embedded connections with d u c t i l e weld p l a t e connections.  2.3.2.2.1. EMBEDDED CONNECTIONS WITH RIGID WELD PLATES Spencer and N e i l l e  [10] r e p o r t e d t e s t s on t h i s type of  c o n n e c t i o n . They performed r e v e r s e d c y c l i c t e s t s on headed stud connectors. T y p i c a l connections are shown i n F i g u r e 2.3.  The shear  f o r c e s were a p p l i e d i n the l o n g i t u d i n a l  d i r e c t i o n of the connection angle, as shown i n F i g u r e 2.3. Connection  A1 was loaded m o n o t o n i c a l l y to f a i l u r e while the  other f i v e connections were loaded at f r e q u e n c i e s i n the range of 0.01 to 0.02 Hz. Spencer and N e i l l e r e p o r t e d that f a i l u r e of the connections was preceded by p r o g r e s s i v e c r u s h i n g and s p a l l i n g of the concrete above and below the a n g l e . They a l s o observed  p r o g r e s s i v e t e n s i o n c r a c k i n g p a r a l l e l t o the  13  OETAILS  CONNECTION  PANEL  OF STUDS 4  REINFORCEMENT  Al  6'  A2.A3 t'x3* /gL«lZ'LONG • 3  , , I  LL  B1 a'xj'x^glxu'lONG-  =....  B2 sVx^Lxir/lONG-  B3 3x2x /gLx10'LONG 3  Figure 2.3. D e t a i l s of the connections  t e s t e d i n Ref.  showing the arrangements of the studs.  [10],  14 angle but at the same time s e v e r a l inches away from i t . F a i l u r e of connections A1 and B1 occured when a l a r g e block of  concrete surrounding the studs broke away. The other  connections f a i l e d when one of the studs broke o f f c l o s e to the weld. The f a c t that the weld between the stud and the angle f a i l e d  i n four of the connectors  suggests that the  weld i s a weak p o i n t i n the c o n n e c t i o n . Hawkins [11] suggests that f i f t y  percent of the studs should be a b l e to  c a r r y the maximum l o a d on the u n i t . The  f o l l o w i n g c o n c l u s i o n s were reached by Spencer and  N e i l l e [10]. a) The PCI procedures  f o r c a l c u l a t i n g the u l t i m a t e design  s t r e n g t h of these connections under s t a t i c conservative  loading give  results.  b) The s t r e n g t h of the connections i n the f i r s t l o a d i n g up to y i e l d  w i l l be approximately  c y c l e s of  the same as  the s t r e n g t h i n monotonic l o a d i n g . c) I f c y c l i c limit,  l o a d i n g i s continued above the s t a b i l i t y  the s t r e n g t h of the connections w i l l  fall  an i n c r e a s i n g number of c y c l e s , and the y i e l d envelope  w i l l tend to approach the s t a b i l i t y  d) The d e f l e c t i o n s reached before f a i l u r e to  twentyfour  strength limit.  were from  times the t h e o r e t i c a l e l a s t i c  with  seven  deflection  corresponding t o the design u l t i m a t e s t r e n g t h . e) These connections, i f p r o p e r l y designed and d e t a i l e d , appear to be s u i t a b l e f o r use i n e a r t h q u a k e - r e s i s t a n t b u i l d i n g s designed as box-type systems.  15  2.3.2.2.2. EMBEDDED REBAR CONNECTION T h i s type of connection i s made up of s t e e l  reinforcing  bars which a r e c a s t i n t o the edge of the p a n e l s . There are s e v e r a l design advantages with t h i s type of c o n n e c t i o n compared to those using studs. Some of these are : a) A l a r g e r s u r f a c e area i s a v a i l a b l e f o r welding the r e i n f o r c i n g bars to the angle. T h i s means lower  weld  s t r e s s e s and a r e d u c t i o n i n the chance of p u l l i n g out the c o n n e c t i o n . b) There i s a longer development of the bars i n t o the p r e c a s t members. T h i s reduces  the chance of p u l l i n g out  the c o n n e c t i o n . Aswad [8] t e s t e d a s e r i e s of connections u s i n g s i z e double of c y c l i c  full-  tee shapes. The t e s t s d i d not cover a wide range  t e s t s because the main o b j e c t i v e s were to d i s c o v e r  the f a i l u r e c a p a b i l i t i e s of the connections and t o measure the r e l a t i v e s l i p between adjacent p r e c a s t elements.  In most  cases the l o a d was a p p l i e d m o n o t o n i c a l l y during s e v e r a l s t e p s . D e t a i l s of some of the connections can be seen i n F i g u r e 2.4. The c y c l i c carried  t e s t s , performed  by Aswad [ 8 ] , were not  f a r enough to give much i n s i g h t  behaviour  i n t o the dynamic  of the c o n n e c t i o n s . The major o b s e r v a t i o n was that  the connections s u b j e c t e d to the c y c l i c major s t i f f n e s s d e t e r i o r a t i o n a f t e r  loads showed no  three c y c l e s .  16  Figure 2.4.  D e t a i l s of connections  reported  in Ref.  [8],  Figure 2.4. Continued  18  Another i n v e s t i g a t i o n performed c o n s i s t e d of c y c l i c anchored  by Spencer  shear t e s t s on a v a r i e t y of  i n t o concrete panels. The  t e s t e d are shown i n F i g u r e 2.5.  the c a l c u l a t i o n s can be seen  connections  types of c o n n e c t i o n s  Spencer [4] d i s c u s s e d design  methods f o r c a l c u l a t i n g the s t r e n g t h of these under both monotonic and c y c l i c  [4]  connections  l o a d i n g . The models used f o r  i n F i g u r e 2.6.  A comparison  made between the measured s t r e n g t h values and  was  the c a l c u l a t e d  strength values. The  f o l l o w i n g c o n c l u s i o n s were reached by Spencer [ 4 ] .  a) Loading c y c l e s i n the e l a s t i c  range do not reduce  the  s t r e n g t h of the c o n n e c t i o n s . b) The nominal  s t r e n g t h of the connections can be  using the models shown i n F i g u r e c) The  the nominal  inelastic d) The  2.6.  s t r e n g t h of the c o n n e c t i o n s , with the rebar  i n t o the connection at 45 degrees, of  found  falls  s t r e n g t h under c y c l i c  running  to about 50 %  loading into  the  range.  s t r e n g t h of the c o n n e c t i o n s , with the rebar  i n t o the connection at 90 degrees, 50 % of the nominal the i n e l a s t i c  falls  s t r e n g t h under c y c l i c  to l e s s  running than  loading into  range. These connections were not  recommended f o r use  i n s i t u a t i o n s where they might  loaded past t h e i r e l a s t i c  be  limit.  e) The connection with a recess i n the panel edge and a s t r a i g h t embedded bars appears simulated earthquake  loading.  to perform  best under  Figure 2 . 5 .  Types of connections t e s t e d i n Ref. [ 4 ] ,  Figure 2.5. Continued  21  F i g u r e 2.5. Continued  22  Figure 2.5. Continued  Figure 2.6. Model developed in Ref. [4].  24 f) Panel t h i c k n e s s and c o n c r e t e q u a l i t y can have a marked e f f e c t on the behaviour  of the c o n n e c t i o n s .  2.3.2.2.3. EMBEDDED CONNECTIONS WITH DUCTILE WELD PLATE Saxena [12] performed  t e s t s on t h i s type of c o n n e c t i o n .  He t e s t e d a system which used a d u c t i l e s t e e l connector r e p l a c e the r i g i d  to  p l a t e or bar normally used to connect  adjacent c o n n e c t i o n s . In h i s connection a s t e e l pipe with a longitudinal s l i t  was  welded between embeddments i n adjacent  precast panels. A s p l i t  pipe connector  can be seen  in F i g u r e  2.7. The a) The  f o l l o w i n g c o n c l u s i o n s were reached by Saxena [12] : split  pipe connection i s able to accommodate the  r e l a t i v e movement between panels due temperature b) The  split  to shrinkage  and  changes.  pipe connection l i m i t s the f o r c e s that  develop during dynamic l o a d i n g which leaves the panels l a r g e l y undamaged. c) S l i g h t  i n a c c u r a c i e s i n the dimensions  of the p r e c a s t  panels during c a s t i n g can be accommodated when the pipe i s welded i n p o s i t i o n on  site.  25 /•  Figure 2.7.  -pre-cast Panel  Connection t e s t e d in Ref.  [12].  26 2.4. LOCATION OF CONNECTIONS In p r e c a s t panel c o n s t r u c t i o n there are b a s i c a l l y  five  l o c a t i o n s i n which the connections can d i s s i p a t e energy d u r i n g an earthquake. a) Connection  These l o c a t i o n s are :  between f l o o r  panels.  b) H o r i z o n t a l connections between w a l l p a n e l s . c) V e r t i c a l connections between w a l l p a n e l s . d) Connections  between f l o o r and w a l l p a n e l s .  e) Connections  between foundations and w a l l p a n e l s .  2.5. CONCLUDING REMARKS It should be noted that the types of connections used in the i n d u s t r y vary w i d e l y . Most of them are designed e m p i r i c a l l y and have not been s t u d i e d e x p e r i m e n t a l l y or t h e o r e t i c a l l y . T h e i r u l t i m a t e s t r e n g t h and seismic l o a d i n g behaviour  would t h e r e f o r e g e n e r a l l y not be known. More  r e s e a r c h i n the area of dynamic p r o p e r t i e s of c o n n e c t i o n s , utilizing desi rable.  embedded s t e e l s e c t i o n s , would t h e r e f o r e be  27  CHAPTER 3  EXPERIMENTAL MATERIALS AND  SPECIMEN PREPARATION  3 . 1 . INTRODUCTION A t o t a l of s i x t e e n specimens were prepared i n the M a t e r i a l s Laboratory of the C i v i l E n g i n e e r i n g Department at the U n i v e r s i t y of B r i t i s h Columbia.  The  s i x t e e n specimens  were prepared from m a t e r i a l s o b t a i n e d from v a r i o u s l o c a l suppliers. Each of the specimens was form. The  forms were b u i l t  a s e c t i o n of a double-tee was  poured  cast  i n a reusable plywood  to model as c l o s e l y as p o s s i b l e , f l a n g e ( F i g u r e 3 . 1 . ) . The  section  out of concrete mixed i n the l a b o r a t o r y . A l l  specimens were r e i n f o r c e d with a welded wire mesh and had a s o l i d s t e e l support p l a t e c a s t i n t o one the s t e e l support p l a t e was  s i d e . The purpose  to h o l d the specimen i n the  t e s t i n g frame d u r i n g the t e s t i n g procedure. The were cast  different  connections  i n t o the o p p o s i t e s i d e of the specimens.  of the t e s t i n g program was  of  The  aim  to examine the behaviour of s i x  types of connections d u r i n g c y c l i c l o a d i n g .  In order to study a number of d i f f e r e n t c o n n e c t i o n s , only two or three specimens were c a s t with the same  28  F i g u r e 3.1. Specimen  29  connection type. I t i s t h e r e f o r e not p o s s i b l e to conduct s t a t i s t i c a l comparison of the  3.2.  formwork for the specimens c o n s i s t e d of 19  plywood and  50 mm  x 100 mm  f o r easy and e f f i c i e n t  (nominal)  mm  lumber b o l t e d together  s t r i p p i n g . Two  i d e n t i c a l forms were  i n order to speed up the c a s t i n g p r o c e s s . One  forms was 25 mm  connections.  FORM The  built  m o d i f i e d for specimens 11,  15 and  of the  16. These were  t h i c k e r than the other specimens. D e t a i l s of the  can be seen i n F i g u r e The  s i d e opposite the connection was  s e c t i o n was  100 mm.  The  made 19 mm  t h i c k e r part was  thicker  thicker  made i n an attempt  to model the t r a n s i t i o n between the flange and the web r e a l double-tee  beam. The  The  in a  wider part a l s o provided more  f o r the s t e e l p l a t e which was  specimen i n the t e s t i n g  forms  3.2.  than the r e s t of the specimen. The width of t h i s  cover  a  used to hold the  frame.  forms were thoroughly  o i l e d before the c o n c r e t e  p l a c e d . T h i s was  done i n order to make the s t r i p p i n g  e a s i e r . Care was  a l s o taken to prevent  the j o i n t s d u r i n g the c a s t i n g  any  procedure.  leakage  was  process  through  30  V'Y'Y.'''''''''  1500 mm I I I  T  I  50  mm  777 111  inn?  |*— 50 mm 19 mm  70 mm  700 mm  1  100 mm  4*  100 mm Opening for support p l a t e  Figure 3.2. Forms f o r specimens  31 3.3. CONCRETE 3.3.1. CONCRETE MIXING AND  CASTING PROCEDURE  The c o n c r e t e mixed i n the l a b o r a t o r y was designed f o r a compressive  s t r e n g t h of 30 MPa.  The  f o l l o w i n g m a t e r i a l s were  used f o r the mixture (the mix p r o p o r t i o n s can be found i n Table 3.1.)  :  a) Cement - Type 10 normal kg paper  s t r e n g t h cement s u p p l i e d i n 40  bags.  b) Sand - I n d u s t r i a l f i n e sand s u p p l i e d i n 36 kg paper bags. c) G r a v e l - Assortment  of s i z e s , up to 10 mm  in size.  The  g r a v e l came i n 36 kg paper bags. However, bagged g r a v e l was  not a v a i l a b l e f o r mixes 11, 15 and  for these mixes was  16. The  gravel  obtained from a separate p i l e .  g r a v e l i n t h i s p i l e a l s o had a maximum aggregate of  10 mm  The  size  but had a s l i g h t l y h i g h e r moisture c o n t e n t .  d) Water - O r d i n a r y tap water. The cement, aggregates and water were weighed and s t o r e d i n separate c o n t a i n e r s . The  i n g r e d i e n t s f o r the  concrete were then mixed together i n a pan-type mixer, i n the f o l l o w i n g order : a) Coarse and f i n e aggregates were poured  i n t o the mixer.  b) The aggregates were batched t o g e t h e r . c) Cement was  added to the aggregates.  d) The cement was e) Water was  batched together with the aggregates.  added to the mix.  TABLE 3.1.  MIX PROPORTIONS  MIX #  TEST #  CEMENT (lb)  SAND (lb)  GRAVEL (lb)  WATER (lb)  1  2  40  80  1 40  20  2  1  40  80  1 40  20  3  4  40  80  1 40  20  4  3  40  80  1 40  20  5  6  40  80  1 40  20  6  5  40  80  1 40  20  7  8  40  80  1 40  20  8  7  40  80  1 40  20  9  13  40  80  1 40  20  10  9  40  80  1 40  20  1 1  14  60  120  210  30  12  15  40  80  1 40  20  13  10  40  80  1 40  20  14  16  40  80  1 40  20  15  12  60  120  210  30  16  1 1  60  1 20  210  30  33 f)  The whole combination was mixed f o r approximately  10  minutes. A f t e r the mixing was completed, in  the form and was  Care was  the concrete was p l a c e d  compacted by means of a v i b r a t i n g  table.  taken not to d i s t u r b the r e i n f o r c i n g mesh and  connection d u r i n g the p l a c i n g of the c o n c r e t e . Three c y l i n d e r s were a l s o c a s t from each mix 28 day compressive  the  test  in order t o check  the  s t r e n g t h of the concrete mixtures. The  s u r f a c e s of the specimens were f i n i s h e d with a trowel and both the form and the c y l i n d e r s were covered with a p l a s t i c sheet to prevent moisture l o s s e s d u r i n g the f i r s t form was was  day.  disassembled during the second day and the  moved i n t o the moisture room f o r f u r t h e r  The  specimen  curing.  3.3.2. TEST RESULTS OF CONCRETE MIXES Before the specimens were c a s t , the slump and the a i r content of the mixture was  recorded. A summary of these  r e s u l t s are a v a i l a b l e i n Table 3.2.  U n f o r t u n a t e l y , the a i r  meter d i d not work p r o p e r l y f o r the f i r s t  seven mixes. I t  can a l s o be seen i n the t a b l e that the slump and a i r content for  mixes 11, 15 and  16 were q u i t e d i f f e r e n t  from the other  mixtures. T h i s i s most l i k e l y caused by the d i f f e r e n t aggregate which was The  coarse  used f o r them.  r e s u l t s of the 28 day compressive  c y l i n d e r s can be seen i n Table 3.2. r e l a t i o n s h i p s between the average  s t r e n g t h s of the  In F i g u r e 3.3.  compression  the  s t r e n g t h s of  TABLE 3.2.  COMPRESSION STRENGTHS OF CYLINDERS  MIX  CYLINDER  #  #  STRENGTH (lb)  STRENGTH (MPa)  AVRG. STRE. (MPa)  SLUMP  1  1  92300  50.64  50.64  63.5  (1 )  2 2 2  1 2 3  91 300 78000 98600  50.09 42.80 54. 1 0  49.00  63.5  (1)  3 3 3  1 2 3  89800 95000 96100  49.27 52. 1 2 52.73  51 .37  57.2  (1)  4 4 4  1 2 3  75600 83600 75500  41.48 . 45.87 42.92 41 .42  63.5  (1)  5 5 5  1 2 3  85900 77400 69800  47. 1 3 42.47 38.30  42.63  63.5  (1 )  2-A 1 -A 3-A  6 6 6  1 2 3  85300 96100 88200  46.80 52.73 48.39  49.31  57.2  (1 )  4-A 5-A 6-A  7 7 7  1 2 3  93600 86800 92400  51 .36 47.62 50.70  49.89  50.8  (1)  8 8 8  1 2 3  68200 76000 87800  37.42 41 .70 48. 1 7  42.43  44.5  1.9  9 9 9.  1 2 3  92000 85000 95500  50.48 46.64 52.40  49.84  44.5  1 .8  10 10 10  1 2 3  87800 91000 104000  48.17 49.93 57.06  51 .72  31 .8  1.7  (mm)  AIR CONTENT (%)  PIC. #  4-B  TABLE 3.2. CONTINUED  MIX  CYLINDER  #  #  STRENGTH (lb)  STRENGTH (MPa)  AVRG. STRE. (MPa)  1 1 1 1 1 1  1 2 3  99600 101000 80600  54.65 55.42 44.22  51 .43  19.1  12 12 12  1 2 3  81000 90400 105800  44.44 49.60 58.05  50.70  44.5  1 .7  1-B  13 13 13  1 2 3  77000 68000 67200  42.25 37.31 36.87  38.81  44.5  1.9  3-B  14 14 14  1 2 3  101000 89000 101200  55.42 48.83 55.53  53.26  38. 1  1.7  15 15 15  1 2 3  82800 90300 99400  45.43 49.54 54.54  49.84  19.1  2.3 (2)  16 16 16  1 2 3  88800 110000 89400  48.72 60.35 49.05  52.71  19.1  2.2 (2)  (1) A i r meter not working. (2) G r a v e l taken from separate p i l e .  SLUMP (mm)  AIR CONTENT (%)  2.7 (2)  PIC. #  5-B  6-B  2-B  Compression strengths of cylinders Average compression  i  i  i  1  2  6  i  i  i  i  3  4  5  .  i  i  i  i  7  8  9  Mix #  i  strength  •  •  •  11 15 16  •  >  •  10 12  13 14  37 the d i f f e r e n t mixtures are shown. T h i s f i g u r e shows that the average compression  s t r e n g t h s are f a i r l y  uniform but w e l l  above the design s t r e n g t h of 30 MPa. A l l of the compression cylinders failed  i n an e x p l o s i v e f a i l u r e , c a u s i n g small  p i e c e s of concrete to f l y o f f . About 80 % of the c y l i n d e r s failed  i n a c o n i c a l shaped  failed  i n a d i a g o n a l mode. Photograph  t y p i c a l compression  f a i l u r e mode. The remaining ones 3.1. i l l u s t r a t e some  results.  3.4. STEEL 3.4.1. REINFORCING MESH The main reinforcement f o r the specimens c o n s i s t e d of a welded wire mesh. The mesh was produced  from 8.89 mm  diameter p l a i n wire p i e c e s which were welded together making 152 mm x 152 mm squares. The l o c a t i o n of the wires was kept the same f o r a l l specimens.  A t e n s i o n t e s t performed  set  a y i e l d s t r e n g t h of 530 MPa and  of wire p i e c e s produced  on a  an u l t i m a t e s t r e n g t h of 660 MPa.  3.4.2. SPECIMEN SUPPORT PLATE The support p l a t e was made of o r d i n a r y f l a t  s t e e l 100  mm wide and 8 mm t h i c k . 75 mm of the p l a t e was c a s t i n t o the back of the specimen  and the wire mesh was welded t o the  p l a t e . In the middle and a t both ends of the p l a t e , short  38  Photograph 3.1. Concrete t e s t  cylinder  39 p i e c e s were welded to the edge of the long p l a t e . These p i e c e s had 22 mm b o l t holes through the support p l a t e can be found The  the middle. A sketch of  i n F i g u r e 3.4.  support p l a t e was chosen as the means f o r mounting  the specimens i n the t e s t apparatus  to a v o i d clamping the  specimens at the ends. Compression on the ends of the specimens, d u r i n g t e s t i n g , might have prevented propagating  from the connections  cracks from  along the edge of the t e s t  spec imen.  3.4.3. CONNECTION STEEL Ordinary  1OM G40.21-300W weldable  r e i n f o r c i n g s t e e l was  used f o r four of the connections. The f i r s t  s i x connections  were made from one 6.0 meter l e n g t h of rebar. A d i f f e r e n t l e n g t h of rebar, obtained from a d i f f e r e n t  s u p p l i e r , was  used f o r the other c o n n e c t i o n s . The rebar used f o r the f i r s t six  connections w i l l be r e f e r r e d to h e r e a f t e r as Rebar #1  and the rebar used f o r the other connections as Rebar #2. The y i e l d and u l t i m a t e strengths of the two rebars were q u i t e d i f f e r e n t as can be seen i n Table 3.3. The measured values were a l s o higher than the expected  values f o r a 300W  steel. The  rebar used i n the connections  was bent  to a d e s i r e d  shape ( d i s c u s s e d l a t e r ) . A l o a d i n g p l a t e was welded t o the connection before the specimen was t e s t e d . A s e t of t e n s i o n t e s t s were performed on the f o l l o w i n g rebar systems :  40  22 mm  dia. 150 mm  200 mm  100 mm  Figure 3.4. Support p l a t e  TABLE 3.3.  YIELD AND ULTIMATE STRESSES  REBAR SYSTEMS  YIELD STRESS (MPa)  ULTIMATE STRESS (MPa)  REBAR #2 STRAIGHT BAR  409. 2  689.5  REBAR #2 BAR BENT ONCE  387. 0  676. 1  REBAR #2 BAR BENT FIVE TIMES  347. 0  680.6  471 .5  688.6  489. 3  698.4  REBAR #2 MILL SPECIFICATIONS  445. 0  674.0  REBAR #1 STRAIGHT BAR  596. 4  971 .5  WIRE IN REINFORCING MESH  530. 0  660.0  REBAR #2 P-IECES WELDED TO THE BAR REBAR #2 PIECES WELDED TO THE BAR AND BENT ONCE  42 a) S t r a i g h t r e b a r . b) Rebar bent once t o 30 degrees and then s t r a i g h t e n e d . c) Rebar bent  f i v e times to 30 degrees and then  straightened. d) Two 25 mm rebar p i e c e s were welded 50 mm apart t o the s i d e of a s t r a i g h t  rebar.  e) Two 25 mm rebar p i e c e s were welded 50 mm apart t o the s i d e of a rebar bent once to 30 degrees and then s t r a ightened. The e f f e c t on the rebar's y i e l d s t r e s s , due to bending 3.5.  s t r e s s and u l t i m a t e  and h e a t i n g , can be seen i n F i g u r e  and F i g u r e 3.6. The f i g u r e s show that bending  rebar decreases  of the  the y i e l d s t r e n g t h s l i g h t l y , while h e a t i n g  the rebar i n c r e a s e s the y i e l d s t r e n g t h . The y i e l d  strength  i n c r e a s e s f u r t h e r when the rebar i s both bent and heated. However, no n o t i c e a b l e change i s observed  i n the u l t i m a t e  s t r e n g t h . F i g u r e 3.5. a l s o d i s p l a y s the d i f f e r e n t the l o a d - d e f l e c t i o n curves  shapes of  f o r the f i v e cases. The  d i f f e r e n c e s i n the y i e l d s t r e n g t h s can be a t t r i b u t e d t o aging. The aging process  i n low-carbon s t e e l s , such as rebar,  can be d i v i d e d i n t o two types: quench aging and s t r a i n aging. Quench aging occurs when low-carbon s t e e l s are r a p i d l y c o o l e d down from temperatures lower c r i t i c a l  s l i g h t l y below the  temperature of the s t e e l . The r e s u l t of the  r a p i d c o o l i n g down i s an i n c r e a s e i n s t r e n g t h and hardness and a decrease  i n the d u c t i l i t y of the s t e e l .  |\  I Yield stress  \//A  Ultimate stres  45 S t r a i n aging occurs when low-carbon s t e e l or c o l d worked at room temperature.  i s deformed  When the s t e e l i s  deformed or c o l d worked, i t s s t r e n g t h and hardness i s i n c r e a s e d while the d u c t i l i t y  3.5.  i s decreased.  TYPES OF CONNECTIONS Six d i f f e r e n t types of connections  of them were made out of bent  were prepared.  Four  rebar. Some had an angle  welded t o the rebar. Two types used an angle welded d i r e c t l y to the r e i n f o r c i n g mesh. Some of the connection designs f o r specimens 7-16 were based on the r e s u l t s of t e s t s t e s t s were conducted  1-6. These  before specimens 7-16 were f a b r i c a t e d .  3.5.1. REBAR #1 BENT TO 45 DEGREES. T h i s connection c o n s i s t e d of a p l a i n rebar p l a c e d along the edge of the specimen with two l e g s bent degrees.  Each l e g was 300 mm long and the s e c t i o n of the  connection 3.7.  i n a t 45  running along the edge was 200 mm long. F i g u r e  and Photograph 3.2. show t h i s  connection.  A drawback with t h i s connection type  i s that part of  the specimen's edge had to be c h i s e l e d o f f i n order to expose the rebar, before the l o a d i n g p l a t e c o u l d be s u c c e s s f u l l y welded to the rebar. T h i s connection would t h e r e f o r e be d i f f i c u l t  to weld to another  connection.  46  1400  mm  1  Figure 3.7. Rebar #1 at 45 degrees  Photograph 3.2. Rebar #1 at 45 degrees  47 3.5.2. REBAR #1 BENT TO 45 DEGREES AND WELDED TO AN ANGLE S i m i l a r to the previous c o n n e c t i o n , except  that a 50 mm  x 50 mm x 200 mm long angle was welded to the rebar. F i g u r e 3.8.  and Photograph 3.3. show t h i s  connection.  The major b e n e f i t of t h i s type of connection  i s the  ease with which the connection can be welded to an adjacent connection.  3.5.3. REBAR #2 BENT TO 45 DEGREES WITH SHORT RECESS S i m i l a r to connection  #1, except  that a 20 mm x 20 mm x  200 mm long recess was made i n order t o expose the s i d e of the rebar. F i g u r e 3.9. and Photograph 3.4. show t h i s connection. Since the s i d e of the bar, along the edge of the specimen, i s exposed i n t h i s type of connection  i t w i l l be  e a s i e r to weld two f l a n g e s t o g e t h e r .  3.5.4. REBAR #2 BENT TO 45 DEGREES WITH A RECESS IN A THICKER SLAB S i m i l a r to connection  #1, except  that t h i s  connection  had a 25 mm x 25 mm recess along the l e n g t h of the specimen. The  t h i c k n e s s of the s l a b was a l s o 75 mm,  compared to 50 mm  for the other specimens. F i g u r e 3.10. and Photograph 3.5. show t h i s  connection.  Photograph 3.3. Rebar  #1 at 45 degrees welded to angle  49  Photograph 3.4. Rebar  #2 at 45 degrees with small  recess  50  1400  Figure  3.10  mm  Rebar  #2  at  45  in a thicker  P h o t o g r a p h 3.5.  Rebar #2 recess  degrees with a  recess  slab  at  45  degrees with a  in a thicker  slab  51 The major b e n e f i t d e r i v e d from using t h i s connection i s the added concrete cover over the c o n n e c t i o n . The recess a l s o makes i t e a s i e r t o weld two connections  together.  3.5.5. ANGLE WELDED TO REINFORCING MESH T h i s connection had a 20 mm x 20 mm x 200 mm long angle welded t o the outermost  wire of the r e i n f o r c i n g mesh. The  outer wire, running p a r a l l e l with the s i d e of the specimen, was a l s o c u t c l o s e t o the ends of the a n g l e . The r e i n f o r c i n g wire had t o be c u t o f f s i n c e i t was too c l o s e t o the edge of the specimen. Removing the wire w i l l however reduce the shear c a p a c i t y of the specimen. F i g u r e 3.11. and Photograph 3.6.  show t h i s c o n n e c t i o n . One b e n e f i t with t h i s connection i s that no e x t r a p i e c e  of rebar i s needed. The connection i s a l s o easy t o weld t o another one.  3.5.6. REVERSED ANGLE WELDED TO REINFORCING MESH T h i s connection had a 20 mm x 20 mm x 200 mm long reversed angle welded t o the outermost  wire of the  r e i n f o r c i n g mesh. Since the angle was r e v e r s e d , the outermost  wire was 50 mm i n t o the s l a b and was t h e r e f o r e not  cut o f f . F i g u r e 3.12. and Photograph 3.7. show t h i s connection. T h i s connection would be p r e f e r a b l e over the p r e v i o u s one  s i n c e a l l of the r e i n f o r c i n g strands can be kept  intact.  Two  f l a n g e s with t h i s connection can a l s o be e a s i l y  together.  welded  53  25  600  mm  mm  50  1  50 mm  Figure  3.11. A n g l e welded  Photograph  to reinforcing  3.6. A n g l e welded  mesh  to r e i n f o r c i n g  mesh  mm  54  55  CHAPTER 4  LABORATORY TEST DETAILS  4.1. INTRODUCTION A t o t a l of s i x t e e n connections were t e s t e d S t r u c t u r a l E n g i n e e r i n g Laboratory of the C i v i l  i n the Engineering  Department a t the U n i v e r s i t y of B r i t i s h Columbia. During the t e s t i n g , the specimens were h e l d v e r t i c a l l y  i n the t e s t r i g  (see F i g u r e 4.1. and Photograph 4.1.). A s t e e l p l a t e with a narrow spacer was welded to the c o n n e c t i o n s . A displacement controlled hydraulic  jack, mounted with i t s a x i s v e r t i c a l i n  the t e s t r i g , a p p l i e d e i t h e r a monotonic or a r e v e r s e d cyclic  load to the s t e e l p l a t e . A l l connections were loaded  i n t o the i n e l a s t i c connection  range, and t e s t i n g continued u n t i l  each  failed.  The v e r t i c a l displacement  and the sideways movement of  the c o n n e c t i o n s were measured r e l a t i v e to the c o n c r e t e and load-displacement  curves were recorded f o r each t e s t . The  data was recorded with a NEFF 620 data a c q u i s i t i o n  system  which was c o n t r o l l e d by a PDP-11/10 minicomputer. The data f i l e s were t r a n s f e r r e d at the end of each t e s t , through the UBC Amdahl computer, to a PC computer where they were processed.  56  i:  \Y\4  Reaction  frame  i  Top c o n t r o l rod  Figure 4.1.  Test r i g  Photograph 4.1. Test  rig  58  4.2.  ASSUMPTIONS MADE FOR It  THE  TESTS  i s assumed that the connections  system w i l l  i n a p r e c a s t panel  behave i n more or l e s s the same f a s h i o n as  d i d i n the t e s t . During earthquake e x c i t a t i o n , a c t i o n w i l l occur  i n the c r i t i c a l  inelastic  regions around the  c o n n e c t i o n s . A d u c t i l e connection w i l l that the i n e l a s t i c deformation  then h e l p to ensure  i s l i m i t e d to the  connection  zone. I t i s t h e r e f o r e assumed t h a t the panels w i l l the e l a s t i c range while the n o n - l i n e a r behaviour to the  4.3.  they  remain i n  i s limited  connections.  TEST RIG The  t e s t r i g which was  seen i n F i g u r e 4.1.  used i n the l a b o r a t o r y can  and Photograph 4.1.  This test  be  r i g can  be  d i v i d e d i n t o s e v e r a l separate p a r t s : a) Reaction  frame - T h i s frame c o n s i s t e d of two  columns which were p l a c e d 2.5  m apart  5.5  m long  (Figure 4.2.(a)).  These columns were b o l t e d to the concrete f l o o r and  had  a l a r g e c r o s s beam between them. The purpose of the c r o s s beam was  to hold the h y d r a u l i c jack i n a v e r t i c a l  posit ion. b) Support  column - T h i s 1.6  the concrete f l o o r and  m h i g h column was  served as the support  b o l t e d to f o r the  C>  o 0)  li  Spacer oo  o  Angle  0  o  (a) Reaction frame  (b) Support column  Mild s t e e l Top control rod  (c)  side control rod  Figure  4.2. Test  strip  1  (d) Load  plate  r i g separated i n t o p a r t s .  Figure 4.2. Continued  61 specimens, h o l d i n g them i n a v e r t i c a l p o s i t i o n (Figure 4.2.(b)).  The  three c o n t r o l rods were a l s o b o l t e d to  the column. c) H y d r a u l i c capacity  jack - The  (Figure 4.2.(a)). A l o a d c e l l  c a p a c i t y was end  h y d r a u l i c jack had  attached  of the jack was  to one  end  a 100  Kip  with the same  of the jack. The  b o l t e d to the bottom of the  beam through a c l e v i s which allowed  cross  the jack to swing  about an a x i s p a r a l l e l to the c r o s s beam. The  jack  t h e r e f o r e r e s t r a i n e d from moving sideways but was to move towards or away from the d) Yoke - The  yoke c o n s i s t e d of two  jack was  was free  specimen. s i d e arms which were  welded to a top c r o s s beam ( F i g u r e 4 . 2 . ( e ) ) . hydraulic  other  The  connected to the yoke with a b o l t  through the c r o s s beam. The were connected to an  two  s i d e arms of the yoke  i n v e r t e d T-shape.  e) I n v e r t e d T-shape - T h i s piece c o n s i s t e d of a c r o s s beam with a v e r t i c a l hollow 4.2. ( f ) ) . A short arm c r o s s beam. One short arms and hollow  c o n t r o l arm was  attached  c o n t r o l rod was one  c o n t r o l arm.  rod was  welded to i t ( F i g u r e to each end of  attached  the  to each of  connected to the top of  the the  These three c o n t r o l arms formed a  p a r a l l e l o g r a m l i n k a g e that c o n s t r a i n e d the T-shape to remain v e r t i c a l when i t moved up and beam had  down. The  cross  s i x b o l t h o l e s through the middle. These were  used to t r a n s f e r the load from the c r o s s beam to the l o a d i n g p l a t e which was  attached  to the c o n n e c t i o n .  The  62 i n v e r t e d T-shape was a t t a c h e d t o the yoke by a 19 mm diameter  p i n through  each of the short arms.  f ) Loading p l a t e - A 300 mm x 125 mm x 20 mm p l a t e was welded to each c o n n e c t i o n . A m i l d s t e e l s t r i p was welded down the middle  i n order t o a c t as a spacer  between the connection and the l o a d i n g p l a t e (Figure 4.2.(d)). The p l a t e was welded t o the connection the specimen was l i f t e d  before  i n t o the t e s t r i g . P r i o r to the  s t a r t of each t e s t , the c r o s s beam of the i n v e r t e d Tshape was b o l t e d t o the l o a d i n g p l a t e with s i x b o l t s . A small aluminum angle was b o l t e d t o the top of the l o a d i n g p l a t e and served as the r e f e r e n c e p o i n t f o r the LVDTs. g) C o n t r o l rods - These three rods were pinned between the i n v e r t e d T-shape and the specimen support  column  (Figure 4 . 2 . ( c ) ) . These rods formed a p a r a l l e l o g r a m l i n k a g e which prevented  the i n v e r t e d T-shape's c r o s s  beam from r o t a t i n g . T h i s prevented  the a p p l i c a t i o n of  moments t o the connections and ensured  that they were  s u b j e c t e d only to d i r e c t shear l o a d i n g . h) Spacer - T h i s p i e c e served as a spacer between the specimen and the support column (Figure 4.2.(b)). A l a r g e angle with b o l t holes matching the specimen support p l a t e was attached to one s i d e of the spacer.  63 4.4. LOADING AND DATA ACQUISITION  SYSTEM  The l o a d i n g and data a c q u i s i t i o n system c o n s i s t e d of four major components : a) MTS s e r v o - c o n t r o l l e d load system. b) A NEFF 620 data a c q u i s i t i o n system. c) A PDP-11/10 minicomputer. d) UBC Amdahl  computer.  The MTS load system was used to apply the l o a d . The a p p l i e d load and the c o r r e s p o n d i n g displacements were recorded with the NEFF and the PDP. The data f o r each t e s t was t r a n s f e r r e d with the Amdahl computer  to a PC computer  where i t was subsequently processed. Photographs 4.2. and 4.3. show p a r t of the system. Some of the f e a t u r e s of the data a c q u i s i t i o n system can be seen below : The MTS s e r v o - c o n t r o l l e d load system c o n t r o l s : a) Speed of l o a d i n g . b) D i r e c t i o n of l o a d i n g . c) Movement  of the h y d r a u l i c  jack. I t can be moved  under  e i t h e r stroke or load c o n t r o l . d) Type of o s c i l l a t o r y motion. A f u n c t i o n generator can produce e i t h e r a sawtooth or a s i n e f u n c t i o n f o r use as the command s i g n a l .  Photograph 4.2. MTS c o n t r o l l e r and NEFF 620.  65  Photograph 4.3. PDP-11/10 computer  terminal.  66 The NEFF 620 p r o v i d e s : a) S i g n a l c o n d i t i o n i n g f o r up to 64 t r a n s d u c e r s . b) S e l e c t i o n of the channels  to be measured.  c) Measurement of the v o l t a g e f o r the s e l e c t e d d) D i g i t a l output  channels.  r e p r e s e n t i n g the v o l t a g e and the channel  selected.  The PDP-11/10 p r o v i d e s : a) C o n t r o l of the NEFF, i n c l u d i n g s e l e c t i o n of channel to be read and the command  to read the channel.  b) C o n t r o l to stop and s t a r t at  the data a c q u i s i t i o n  system  any time d u r i n g the t e s t .  c) P r o c e s s i n g of data from the NEFF using a program w r i t t e n i n BASIC. The program can compute and p r i n t r e s u l t s f o r p r e - s e l e c t e d channels during the t e s t . d) Storage of measured v o l t a g e s on a d i s k . e) F i l e  t r a n s f e r to the UBC Amdahl computer.  The Amdahl computer p r o v i d e s : a) C a p a b i l i t y t o process the data t r a n s f e r r e d from the PDP-11/10 minicomputer. b) F i l e  t r a n s f e r to a PC computer.  67 4.5. USE OF THE DATA ACQUISITION SYSTEM A short d e s c r i p t i o n of the o p e r a t i o n s which are r e q u i r e d t o o b t a i n data  f o r the t e s t s f o l l o w s . For more  comprehensive d e s c r i p t i o n s , please see the a p p r o p r i a t e system manuals.  4.5.1. OPERATION  OF MTS SERVO-CONTROLLER  a) Set the a p p r o p r i a t e c a l i b r a t i o n  factors.  b) Connect the leads t o the NEFF. c) S e l e c t a p p r o p r i a t e f u n c t i o n on f u n c t i o n  generator.  d) Set speed and d i r e c t i o n of l o a d i n g .  4.5.2. OPERATION  OF NEFF 620  a) Connect the leads from the LVDTs and the MTS to the f r o n t  controller  panel.  b) Set the f r o n t panel  switches  to t h e i r  appropriate  settings.  4.5.3. OPERATION a) Prepare  OF PDP-11/I 0  one RK05 d i s k with the necessary  b) Load and run the BASIC software c) Prepare  language  software. processor.  and run the data a c q u i s i t i o n program f o r the  particular  application.  d) Store the measured data on the d i s k .  68 e) Transmit  the data f i l e s  t o the UBC Amdahl computer f o r  further processing.  4.6. TEST MEASUREMENTS The  load and the displacement  v o l t a g e s were recorded  with the NEFF data a c q u i s i t i o n system and the PDP-11/10 computer d u r i n g the t e s t s . During the t e s t s the l o a d d e f l e c t i o n curves were a l s o p l o t t e d on a X-Y r e c o r d e r . T h i s was done i n order t o have a v i s u a l c o n t r o l over the l o a d and the d e f l e c t i o n of the c o n n e c t i o n .  4.6.1. LOAD MEASUREMENT The  load a p p l i e d t o the connection was recorded with a  100 K i p l o a d c e l l which was s i t u a t e d between the h y d r a u l i c jack and the yoke. The l o a d c e l l  was c a r e f u l l y  calibrated  before the t e s t i n g program s t a r t e d . The obtained c a l i b r a t i o n f a c t o r was then used t o c a l c u l a t e the a p p l i e d l o a d during t e s t i n g and data p r o c e s s i n g .  4.6.2. DISPLACEMENT MEASUREMENT Four d i f f e r e n t  s e t s of displacements  measured by l i n e a r v a r i a b l e d i f f e r e n t i a l (LVDT's).  These displacements  ( F i g u r e 4.3.) were transformers  were :  a) The up and down movement of the connection r e l a t i v e t o the concrete specimen (LVDT #1 and LVDT #2).  69  LVDT # 4  F i g u r e 4.3.  Locations of the LVDTs.  70  b) The sideways movement of the connection r e l a t i v e t o the concrete specimen c) The displacement to the t e s t  floor  (LVDT #3). and r o t a t i o n of the specimen  relative  (LVDT #4 and LVDT #5).  d) The movement of the h y d r a u l i c j a c k . At the beginning of each t e s t , the LVDTs were c a l i b r a t e d and the c a l i b r a t i o n  f a c t o r s were s t o r e d i n a f i l e  which was used during f u r t h e r data p r o c e s s i n g . The LVDTs were c a l i b r a t e d by measuring the v o l t a g e s f o r s e v e r a l known displacements. From these v o l t a g e s an average f a c t o r was c a l c u l a t e d  calibration  f o r each LVDT.  4.6.2.1. CONNECTION  DISPLACEMENT  The movements of the connections were measured by two LVDTs. The maximum t r a v e l d i s t a n c e of these LVDTs was -12.5 mm  to +12.5 mm.  One LVDT was mounted on each s i d e of the  specimens ( F i g u r e 4.4. and Photograph 4.4.). The LVDTs were supported  from a reusable seat s i t u a t e d at the back of the  specimens because no c r a c k i n g was expected The  in this region.  reusable LVDT seats were b o l t e d to the specimen  two h o l e s . These holes were d r i l l e d  through  through  the specimens  a f t e r they had cured. The movements of the connections r e l a t i v e to the concrete panels were measured from an aluminum angle which was b o l t e d t o the top of the l o a d i n g p l a t e . The v o l t a g e readings from each LVDT was recorded  Top view  LVDTs  Side view  LVDTs  F i g u r e 4.4. LVDT mounting  f o r connection  displacement.  Photograph  4.4.  LVDTs measuring  connection  displacement.  73 separately  i n the data f i l e  but the l o a d - d e f l e c t i o n curves  were based on the average of the two  readings.  4.6.2.2. SIDEWAYS MOVEMENT The  sideways movement of the connections was  with one LVDT which was  supported  measured  from the c r o s s beam of the  i n v e r t e d T-shape (Figure 4.5.(a) and Photograph 4.5.). T h i s part of the t e s t equipment was  b o l t e d to the p l a t e which  welded to the embedded s t e e l c o n n e c t i o n . The probe was that was  lightly  displacement  s p r i n g loaded a g a i n s t an aluminum p l a t e  glued to the c o n c r e t e . The maximum t r a v e l d i s t a n c e  of the LVDT was taken  was  -25.4  mm  to +25.4 mm.  T h i s measurement  i n order to see the sideways movements of  connections  the  rebar to the surrounding concrete d u r i n g  v a r i o u s steps of the c y c l i c  was  the  tests.  4.6.2.3. SPECIMEN ROTATION Two  LVDTs were used to r e c o r d the r o t a t i o n  displacements  and  of the specimen r e l a t i v e to the t e s t  floor  (Figure 4.5.(b) and Photograph 4.6.). The movement of the support  column was  a l s o checked. These measurements were  used to check the s t r e n g t h of the support p l a t e which cast  i n t o the back of the specimen. One  LVDT was  the f r o n t edge of the specimen and the other one  was  p l a c e d at was  placed  at the back edge. The maximum t r a v e l d i s t a n c e of these LVDTs was  -12.5  mm  to +12.5  mm.  74  Figure 4.5. LVDT mounting and specimen  f o r sideways movement rotation.  Photograph 4.5. LVDT measuring sideways movement.  76  Photograph 4.6. LVDTs measuring specimen  rotation.  77 4.6.3.4. MOVEMENT OF HYDRAULIC JACK The  movement of the h y d r a u l i c  LVDT b u i l t  i n t o the jack  LVDT was -75 mm t o +75  jack was recorded  by an  i t s e l f . The maximum t r a v e l of t h i s  mm.  4.7. LOADING PROCEDURE The hydraulic  specimens were loaded j a c k . The v e r t i c a l  by a s e r v o - c o n t r o l l e d  shear f o r c e a p p l i e d by the jack  was e i t h e r monotonic or reversed loaded  c y c l i c . The monotonic t e s t s  the connections i n one d i r e c t i o n u n t i l  These monotonic t e s t s were performed i n order t h e i r maximum strengths  with the strengths  cyclic  failed.  to compare  of s i m i l a r  connections which were t e s t e d under c y c l i c The  they  loading.  t e s t s u s u a l l y began with s e v e r a l c y c l e s of  l o a d i n g to about 70 % of the estimated monotonic c a p a c i t y of the connections.  The load was then i n c r e a s e d with an  increment of about 5 % of the c a p a c i t y . At t h i s new level  the l o a d was again  load  c y c l e d u n t i l no f u r t h e r d e f l e c t i o n  was n o t i c e d . T h i s sequence was then continued  u n t i l the  connections f a i l e d completely or u n t i l the s t r e n g t h  fell  substantially. The  t e s t i n g procedure was q u a s i - s t a t i c with each c y c l e  t a k i n g s e v e r a l minutes. The l o a d a p p l i e d to the connection c o u l d be h e l d constant order  to allow  s e v e r a l times during  each c y c l e i n  the specimen t o be examined. The amount of  d e f l e c t i o n and load placed  on the connection  was v i s u a l l y  c o n t r o l l e d by watching an X-Y r e c o r d e r .  The load  reversal  p o i n t s were a l s o manually s e l e c t e d by watching the curve on the X-Y r e c o r d e r . X-Y r e c o r d e r ,  In a d d i t i o n to the curve recorded on the  s e l e c t e d values were a l s o p r i n t e d by the  computer d u r i n g  the t e s t . These readings were s e l e c t e d  manually a t c r i t i c a l p o i n t s by depressing  the Return button  on the computer keyboard. The values were at the same time stored could the  i n a separate f i l e on the PDP-11/10 d i s k . T h i s  file  l a t e r be used t o reproduce the l o a d - d e f l e c t i o n curve,  sideways movement and the specimen r o t a t i o n f o r each  test.  79  CHAPTER 5  EXPERIMENTAL RESULTS  5.1.  INTRODUCTION T h i s chapter d i s c u s s e s i n d e t a i l the r e s u l t s of the  t e s t s performed i n the l a b o r a t o r y . The l o a d i n g of each connection connection by formulae Two  behaviour  d u r i n g the  i s d e s c r i b e d and the measured  s t r e n g t h i s compared to the s t r e n g t h c a l c u l a t e d which are d i s c u s s e d i n s e c t i o n 6.2.3.3.  curves are given f o r each c o n n e c t i o n . One  shows the  l o a d a p p l i e d to the connection versus the movement of the connection  r e l a t i v e to the surrounding  specimen. The  curve shows the sideways movement of the connection to the specimen. The formulae Two  s t r e n g t h values c a l c u l a t e d by  are i n d i c a t e d with l i n e s on the  relative the  graphs.  separate s t r e n g t h values were c a l c u l a t e d  p l o t t e d on the l o a d - d e f l e c t i o n curves  other  f o r the  and  connections  which were f a b r i c a t e d from separate r e i n f o r c i n g bars  (see  s e c t i o n 6.2.3.3.1.). These l i n e s were denoted : a) Fy  - Where the measured y i e l d s t r e s s f o r the rebar, as d e l i v e r e d , was  used to c a l c u l a t e  V . n  80 b) Fyw  - Where the y i e l d s t r e s s f o r the rebar that c o l d bent to 30 degrees, welded was  Two  was  s t r a i g h t e n e d and  used to c a l c u l a t e  then  V . n  s t r e n g t h values were c a l c u l a t e d and a l s o p l o t t e d on  the l o a d - d e f l e c t i o n curves f o r the connections which were welded s t r a i g h t to the r e i n f o r c i n g mesh of the specimens. a) Ca - Type A, p e r p e n d i c u l a r c r a c k i n g (see s e c t i o n 6. 2. 3.3.2.1.). b) Cb - Type B, d i a g o n a l c r a c k i n g (see s e c t i o n 6*2»3*3»2«2«)»  5.2.  DETAILS OF CONNECTIONS TESTED Six d i f f e r e n t types of c o n n e c t i o n s were t e s t e d i n the  l a b o r a t o r y . A comprehensive d e s c r i p t i o n , of the can be found  i n s e c t i o n 3.5.  S e c t i o n 6.2.  d i s c u s s e s the r e s u l t s of the t e s t s . The  connections  summarizes and  types of  connections  were :  5.2.1. REBAR #1 AT 45 DEGREES T h i s type of connection c o n s i s t e d of a p i e c e of rebar with two  l e g s bent  so as to enter the specimen at 45  to the edge. The p o r t i o n p a r a l l e l specimen was  200 mm  degrees  to the edge of the  long and each of the l e g s was  300  mm  l o n g . For more d e t a i l s on t h i s connection see s e c t i o n 3.5.1. A t o t a l of three specimens were f a b r i c a t e d and t e s t e d with t h i s type of c o n n e c t i o n . The  later  r e s u l t s were :  81 5.2.1.1. TEST #1 The  l o a d - d e f l e c t i o n curve  f o r t h i s t e s t can be seen i n  Figure 5.1. Photograph 5.3. shows the connection  after  f a i l u r e . The f o l l o w i n g o b s e r v a t i o n s were noted during the testing  ( Cy stands f o r C y c l e ) :  Cy 01 + 79 kN  - a crack opened up along the top s i d e of top reinforcing leg. - a small crack c o u l d a l s o be n o t i c e d along the bottom l e g (Photograph  5.1.).  - small concrete p i e c e s were s p a l l i n g o f f along the v e r t i c a l p o r t i o n of the bar (Photograph Cy 01 -17 kN  5.1.).  - no change.in  the l o a d but i t was  observed  that the panel moved s l i g h t l y . Cy 01 -94 kN  - the crack around the top s i d e of the connection  l e g opened up a b i t more.  - a crack opened up at the top at the l e v e l of the support Cy 02 +91  kN  plate.  - a l a r g e p i e c e of c o n c r e t e f e l l o f f a t the bottom corner of the connection  (Photograph  5.2.) . - a longer crack opened up along the bottom leg of the rebar. Cy 02 -78 kN  - l a r g e p i e c e s of concrete were f a l l i n g o f f . - a dialgauge attached t o the bottom corner of the panel showed a sideways movement of  82  around 0.5  inches towards the back s i d e of  the p a n e l . - no c r a c k i n g was v i s i b l e on the bottom s i d e of the p a n e l . Cy 03 +75  kN  - the rebar broke suddenly at the bottom corner of the connection  (Photograph 5.3.).  - the break occurred at the end of the weld between the rebar and the l o a d i n g p l a t e .  83  Figure 5.1.  Load- d e f l e c t i o n  curve for Test  #1.  Photograph 5.1. Small crack along bottom l e g (Cycle #1 + 79 kN).  Photograph 5.2. Bottom corner f a l l i n g  off  (Cycle #2 +91 kN).  86  Photograph 5.3.  Connection at f a i l u r e  (Cycle #3 + 74  kN).  87  5.2.1.2. TEST #2 The  l o a d - d e f l e c t i o n curve  f o r t h i s t e s t can be seen i n  F i g u r e 5.2. Photograph 5.4. shows the connection f a i l u r e . The f o l l o w i n g o b s e r v a t i o n s were noted  after  during  testing : 0  Cy 01 +89 kN  - a crack along the rebar became  visible  ( S i m i l a r to Photograph 5.1.). - the top corner of the specimen moved 2.5 mm r e l a t i v e to the support post  (measured with  a dialgauge). Cy 01 -44 kN  - the connection  failed  suddenly.  - the f a i l u r e of the connection  took p l a c e at  the end of the weld between the rebar and the l o a d i n g p l a t e  (Photograph  5.4.).  - the crack along the top l e g opened up a b i t more. - a concrete p i e c e (100 mm x 100 mm)  f e l l of  along the bottom rebar l e g ( S i m i l a r to Photograph 5.2.).  88  (0  u in  o  o  o  -<  Figure  o  o  o  o  o  o  o  o  o  o I  5.2. Load- d e f l e c t i o n  o I  o I  o I  o I  o I  o I  curve for Test  o I  o I  #2.  1  I  89  Photograph 5.4.  Connection at f a i l u r e  (Cycle #1  -44  kN).  90 5.2.1.3. TEST #6 The  l o a d - d e f l e c t i o n curve  f o r t h i s t e s t can be seen i n  F i g u r e 5.3. The sideways movement of the connection  i s shown  in F i g u r e 5.4. Photograph 5.5. shows the connection  after  f a i l u r e . The f o l l o w i n g o b s e r v a t i o n s  were noted d u r i n g the  testing : Cy 03 +42 kN  - no v i s i b l e c r a c k i n g at t h i s  Cy 04 +60 kN  - some concrete connection  load.  a t the bottom corner  fell  of the  o f f ( S i m i l a r t o Photograph  5.2). Cy 04 -56 kN  - the top l e g of the connection  broke suddenly  at end of the weld between the rebar and the loading p l a t e . - at t h i s p o i n t the d i r e c t i o n of the l o a d was reversed. Cy 05 +59 kN  - the bottom l e g f a i l e d at the end of the weld (Photograph 5.4.). - only one l e g c o n t r i b u t e d to the s t r e n g t h d u r i n g t h i s c y c l e s i n c e the other d u r i n g the p r e v i o u s c y c l e .  l e g broke  91  Figure 5.3.  L o a d - d e f l e c t i o n curve for Test  #6.  o CO  o o  o o a» oo  F i g u r e 5.4.  o ^  o  CD  o m  o  o  o  4 n w  o H  o  o  o  I •*-»  CMI  o I co  5 I  0  m I  o  o  I  I  CD  Sideways movement of connection  o  00 I  o a>  (Test  o o  #6).  93  Photograph 5.5. Connection at f a i l u r e  (Cycle #6 +59  kN).  5.2.2. REBAR #1 AT 45 DEGREES WELDED TO AN ANGLE T h i s connection was  of the same type as the p r e v i o u s  one. The only d i f f e r e n c e was angle was  that a 50 mm  x 50 mm  x 200  mm  welded to the r e i n f o r c i n g bar. For more d e t a i l s  see s e c t i o n 3.5.2. In t o t a l three specimens of t h i s type were f a b r i c a t e d . Two  of these were t e s t e d under c y c l i c  the specimens was  l o a d i n g while one  t e s t e d m o n o t o n i c a l l y . The  of  r e s u l t s were :  5.2.2.1. TEST #3 The  l o a d - d e f l e c t i o n curve  F i g u r e 5.5.  The  in F i g u r e 5.6. f a i l u r e . The  f o r t h i s t e s t can be seen i n  sideways movement of the connection Photograph 5.7.  shows the connection  i s shown after  f o l l o w i n g o b s e r v a t i o n s were noted during  the  testing : Cy 01  - c r a c k i n g n o i s e s c o u l d be heard  from the  specimen. Cy  02  e l a s t i c behavior, no change i n c r a c k i n g .  Cy  04  when the connection was  loaded upwards, a  small crack along the top end of the became s l i g h t l y  larger  when the connection was  angle  (See F i g u r e 5 . 7 . ( a ) ) . loaded downwards, a  crack at the bottom end of the angle opened up a l i t t l e  b i t (See F i g u r e  5.7.(b)).  95 Cy 07 -66  kN  - the crack at the top opened up more. - some concrete f e l l the connection  Cy 08 +67  kN  of at bottom corner of  (See F i g u r e 5 . 7 . ( c ) ) .  - the concrete corner above the angle f e l l o f f (See F i g u r e  5.7.(d)).  - some concrete a l s o f e l l corner of the Cy 09 +69  kN  o f f at the bottom  angle.  - l a r g e p i e c e s of the concrete bottom corner of the angle  fell  o f f at the  (See F i g u r e  5.7.(e)). Cy 09 -65  kN  - more concrete f e l l  o f f at the c o r n e r s .  - the panel moved sideways d u r i n g maximum load. Cy  10 -42  kN  - the weld between the angle and connection  rebar suddenly  the  began to f a i l  at  the top end of the angle. - a d d i t i o n a l concrete was the connection Cy  11 +40  kN  s p a l l i n g o f f around  rebar.  - the f a i l u r e of the weld between the and the angle  progressed.  - the top bar was loading  bending  (Photograph  - the bottom bar was applied  rebar  a l o t d u r i n g upward  5.6.). p u l l i n g out due  to the  tension.  - a d d i t i o n a l concrete s p a l l i n g o f f around the connection  rebar.  96  Cy 13 +32  kN  - f a i l u r e of the c o n n e c t i o n due to p u l l o u t of t e n s i o n l e g (Photograph 5.7.).  98  o cn  o "  o  o  o  o  o  o  o  o  o  o  o  o I  o I  o I  o I  o I  Figure 5 . 6 . Sideways movement of connection  o I  o I  o I  (Test  o I  ~ I  #3).  1  (a)  (b)  1 (d)  (c)  J (e)  Figure 5.7. Cracking p a t t e r n f o r Test  #3.  100  Photograph 5.6. Bending of top bar (Cycle #11  +40  kN).  Photograph 5.7. Connection at f a i l u r e  (Cycle #13  +32  kN).  102 5.2.2.2. TEST #4 The  l o a d - d e f l e c t i o n curve  f o r t h i s monotonic t e s t can  be seen i n F i g u r e 5.8. The f o l l o w i n g o b s e r v a t i o n s were noted during t e s t i n g : Cy 01 -85 kN  - the upper corner r o t a t e d o u t . - the concrete a t the bottom corner of the connection was c r u s h i n g . - a crack opened up under the bottom c o r n e r .  Cy 01 -87 kN  - bond f a i l u r e around the top l e g of the connection  rebar.  - p a r t of the weld between the connection rebar and the angle broke at the t o p corner due  to the sideways movement of the  connection. - the bottom rebar l e g bent  sideways and down  without much c r u s h i n g of the c o n c r e t e  103  Figure 5.8.  Load - d e f l e c t i o n  curve for Test  #4.  1 04 5.2.2.3. TEST #5 In t h i s t e s t the l o a d i n g p l a t e was welded to the back s i d e of the angle  (Figure 5.9.). T h i s means t h a t the l o a d  was a p p l i e d at a s l i g h t l y d i f f e r e n t was a p p l i e d t o the two p r e v i o u s The l o a d - d e f l e c t i o n curve  l o c a t i o n from where i t  tests. f o r t h i s t e s t can be seen i n  F i g u r e 5.10. The sideways movement of the connection i s shown i n F i g u r e 5.11. Photographs 5.8. and 5.9. show the connection a f t e r f a i l u r e . The f o l l o w i n g o b s e r v a t i o n s were noted d u r i n g t e s t i n g : Cy 02 +45 kN  - cracks appeared at the top corner of the connection  (Similar to Figure 5.7.(a)).  - no v i s i b l e c r a c k i n g a t the bottom corner of the Cy 02 -43 kN  connection.  - cracks appeared at the bottom corner of the connection  (Similar to Figure  5.7.(b)).  - the concrete was pushed away from around the edges of the a n g l e . Cy 03 +44 kN  - more c r a c k i n g at the c o r n e r s of the connection.  Cy 04 +46 kN  - p a r t s of the concrete had f a l l e n o f f around the angle  ( S i m i l a r to F i g u r e s 5.7.(b) and  (c)). - the connection c o u l d move up and down q u i t e freely.  105 - c o u l d see l a r g e t w i s t i n g of the angle as connection was  the  loaded up and down.  - each c y c l e caused  10-20  mm  long c o n c r e t e  p i e c e s to s p a l l o f f along the l e g s of the r e i n f o r c i n g bar which was connection Cy 05 +50  kN  (Photograph  - the connection of  5.8.).  f a i l e d by complete exposure  the t e n s i o n l e g of the  (Photograph  used f o r the  5.9.).  connection  106  1 Angle  Connection rebar  b)  F i g u r e 5.9.  Test #5  Load a p p l i c a t i o n p o i n t s f o r Rebar #1  with angle.  10  F i g u r e 5.10.  L o a d - d e f l e c t i o n curve f o r Test  #5.  1 o  S  S  S  P  S  S  2  S  2  c  2  0  0  0  i  0  i  0  0  i  °  c  3  i  i  i  o  igure 5 . 1 1 . Sideways movement of the connection  o i  o i  o i  Y  (Test # 5 ) .  Photograph 5.8.  Connection at f a i l u r e  (Cycle #5 +50  kN).  P h o t o g r a p h 5.9.  Connection at f a i l u r e  ( C y c l e #5 +50  kN).  5.2.3. REBAR #2 AT 45 DEGREES WITH SHORT RECESS T h i s connection was s i m i l a r t o the connection i n s e c t i o n 5.2.1. The only d i f f e r e n c e was that a 20 mm x 200 mm  x 20 mm  r e c e s s was c a s t beside the r e i n f o r c i n g bar along  the edge of the specimen. For more d e t a i l s see s e c t i o n 3 • 5« 3 • In t o t a l three specimens were f a b r i c a t e d . Two of these were t e s t e d under c y c l i c  l o a d i n g while one of the specimens  was t e s t e d m o n o t o n i c a l l y . The r e s u l t s were :  5.2.3.1. TEST #7 The  l o a d - d e f l e c t i o n curve  f o r t h i s t e s t can be seen i n  F i g u r e 5.12. The sideways movement of the connection i s shown i n F i g u r e 5.13. Photographs 5.10. to 5.14. show the connection d u r i n g t e s t i n g and at f a i l u r e . The f o l l o w i n g o b s e r v a t i o n s were noted during t e s t i n g : Cy 03 -78 kN  - a small part of the top corner above the recess f e l l o f f .  Cy 04 -50 kN  - small p i e c e s of c o n c r e t e at both c o r n e r s was f a l l i n g o f f (Photograph  Cy 04 -87 kN  5.10.).  - a loud c r a c k i n g sound c o u l d be heard  from  the specimen. - a l o t of concrete was f a l l i n g o f f a t both c o r n e r s of the connection and  5.12.).  (Photographs 5.11.  1 12 Cy 05 +56  kN  - the concrete was  f a l l i n g o f f around the  t e n s i o n l e g of the  connection.  - the top rebar l e g was corner Cy 05 +32  kN  (Photograph  bending  f r e e l y at the  5.13.).  - the weld between the connection bar and l o a d i n g p l a t e was  beginning  to f a i l  the  from the  corners. - the t e n s i o n l e g of the connection p u l l i n g out without (Photograph  any  5.14.). The  i n c r e a s e i n the l o a d connection  f a i l e d when the bottom t e n s i o n l e g totally  exposed.  was  finally was  F i g u r e 5.12.  L o a d - d e f l e c t i o n curve f o r Test  #7.  Displacement (mm)  Photograph 5.10. Cycle #4 -50 kN (Test #7).  116  Photograph 5.11. Cycle #4 -87 kN (Test #7).  1 17  Photograph 5.12. Cycle #4 -87 kN (Test #7).  Photograph 5.13. Cycle #5 +56 kN (Test #7).  119  Photograph 5.14. Cycle #5 +32 kN (Test #7).  120  5.2.3.2. TEST #8 The  l o a d - d e f l e c t i o n curve  f o r t h i s t e s t can be seen i n  F i g u r e 5.14. The sideways movement of the connection i s shown i n F i g u r e 5.15. Photographs 5.15. and 5.16. show the connection a f t e r  f a i l u r e . The f o l l o w i n g o b s e r v a t i o n s were  noted d u r i n g t e s t i n g : Cy 02  - only a small crack was v i s i b l e a t the c o r n e r s of the connection  (Similar to  Photograph 5.1.). Cy 05  - the c r a c k s a t the c o r n e r s propagated a d d i t i o n a l 5-10  an  mm.  Cy  10  - the c o r n e r s were c r a c k i n g f u r t h e r .  Cy  11 +70 kN  - p a r t of the concrete around the top corner of  the connection  fell  o f f ( S i m i l a r to  Photograph 5.11.). Cy  12 -52 kN  - p a r t of the concrete around the bottom corner f e l l o f f . - the bar bent  outwards at the end of the weld  between the rebar and the l o a d i n g p l a t e . T h i s made i t p o s s i b l e f o r the bar at the compression  corner t o bend f u r t h e r without  c r u s h i n g the concrete  ( S i m i l a r t o Photograph  5.13.). Cy  15 +31 kN  - p a r t of the concrete s p a l l e d o f f around the bottom l e g of the c o n n e c t i o n .  121 Cy  15 -53 kN  - the corner of concrete around the top l e g spalled o f f .  Cy  16 -38  kN  - the top l e g of the connection (Photograph  rebar broke  5.15.).  - at t h i s p o i n t the l o a d d i r e c t i o n  was  reversed. Cy  17 +22  kN  - the bottom l e g of the connection p u l l e d out ( S i m i l a r to Photograph  5.7.).  F i g u r e 5.14.  L o a d - d e f l e c t i o n curve f o r Test  #8.  Photograph 5.15.  Connection at f a i l u r e  (Cycle #16  -38  kN).  125  P h o t o g r a p h 5.16.  Connection at f a i l u r e  (Cycle  #16  -38  kN).  5.2.3.3. TEST #13 The  l o a d - d e f l e c t i o n curve f o r t h i s monotonic t e s t can  be seen i n F i g u r e 5.16. The sideways movement of the connection  i s shown i n F i g u r e 5.17. Photograph 5.17. shows  the connection a f t e r f a i l u r e . The f o l l o w i n g o b s e r v a t i o n s were noted d u r i n g t e s t i n g : Cy 01 +93 kN  - a small p i e c e of concrete f e l l top corner of the connection  o f f a t the  (Similar to  Photograph 5.10.). Cy 01 +68 kN  - the bottom t e n s i o n corner f e l l o f f . - more c o n c r e t e f e l l  o f f a t the top corner  ( S i m i l a r to Photograph 5.11.). Cy 01 +42 kN  - the connection  f a i l e d by p u l l o u t of the  t e n s i o n l e g of the rebar  (Photograph  5.17.)  12  (N:>0  F i g u r e 5.16.  P^OT  L o a d - d e f l e c t i o n curve f o r Test  #13.  128  F i g u r e 5.17.  Sideways movement of connection  (Test  #13).  129  Photograph 5.17.  Connection at f a i l u r e  (Cycle #1 +42  kN).  130 5.2.4. REBAR #2 AT 45 DEGREES IN A 75 MM THICK SLAB T h i s connection was s i m i l a r to the connection i n s e c t i o n 5.2.1. The only d i f f e r e n c e s were that the s l a b was 75 mm  t h i c k and i t had a 25 mm x 25 mm  recess which was c a s t  along the entire-edge of the specimen. For more d e t a i l s see section  3.5.4.  In t o t a l three specimens were f a b r i c a t e d . Two of these were t e s t e d under c y c l i c  l o a d i n g while one of the specimens  was t e s t e d m o n o t o n i c a l l y . The r e s u l t s were :  5.2.4.1. TEST #11 The  l o a d - d e f l e c t i o n curve f o r t h i s t e s t can be seen i n  Figure 5.18. F i g u r e 5.19. d i s p l a y s an enlargement of the f i r s t c y c l e s of the l o a d - d e f l e c t i o n curve. The sideways movement of the connection  i s shown i n F i g u r e 5.20.  Photograph 5.18. to 5.22. show the connection d u r i n g the t e s t i n g and at f a i l u r e . The f o l l o w i n g o b s e r v a t i o n s were noted d u r i n g t e s t i n g : Cy 08 -81 kN  - small p i e c e s of concrete were f a l l i n g o f f at the c o r n e r s of the c o n n e c t i o n . - c o u l d see the connection  rebar bending at  the 45 degree c o r n e r s . Cy  10 +77 kN  - a concrete p i e c e cracked o f f at the top corner of the c o n n e c t i o n .  131 - a l a r g e gap c o u l d be seen at the corner under the bottom l e g of the c o n n e c t i o n . T h i s was Cy  10 -79  kN  caused  by the bending  11 +74  kN  rebar.  - the bottom corner of the connection (Photograph  Cy  of the  f e l l off  5.18.).  - the concrete was  s p a l l i n g o f f around the  bottom t e n s i o n l e g . - the top bar was  bending  a l o t at the  45  degree bend ( S i m i l a r to Photograph 5.13.). Cy  12 +65  kN  - a l a r g e p i e c e of concrete s p a l l e d o f f along the middle  of the connection  (Photograph Cy  12 +77  kN  - more bending  5.19.). of the l e g at the  side of the bar Cy  12 -59  kN  rebar  (Photograph  compression  5..20.).  - the t e n s i o n l e g of the connection broke at end of weld between the l o a d i n g p l a t e and the r e i n f o r c i n g bar  (Photograph  5.21.).  - at t h i s p o i n t the d i r e c t i o n of the l o a d  was  reversed. Cy  13 +67  kN  - the t e n s i o n l e g of the connection p u l l e d (Photograph  out  5.22.).  - only one of the l e g s was  c o n t r i b u t i n g to the  load s i n c e the other l e g broke during the previous c y c l e .  Displacement  (mm)  13  F i g u r e 5.19.  Enlargement of the l o a d - d e f l e c t i o n Test  #11.  curve f o r  Displacement (mm)  OO  135  136  Photograph 5.19. C y c l e #12 +65 kN (Test #11).  Photograph 5.20. Cycle #12 +77 kN (Test #11).  138  Photograph 5.21. Cycle #12 -59 kN (Test #11).  139  Photograph 5.22.  Connection at f a i l u r e  (Cycle #13  + 67  kN).  5.2.4.2. TEST The  #12  l o a d - d e f l e c t i o n curve  be seen i n F i g u r e 5.21. connection  The  f o r t h i s monotonic t e s t  sideways movement of the  i s shown i n F i g u r e 5.22.  the connection a f t e r  can  f a i l u r e . The  Photograph 5.25.  shows  following observations  were noted during t e s t i n g : Cy 01 +95  kN  - a crack developed  at the compression  Cy 01 +97  kN  - a concrete p i e c e (100x150 mm) around the t e n s i o n corner  fell  corner. o f f from  (Photograph  5.23.). Cy 01 +70  kN  - no change i n the c r a c k i n g of the c o n c r e t e . - the top l e g of the connection was  bending  a  lot. - the bottom l e g was than 45 Cy 01 +75  kN  s t r a i g h t e n i n g out to l e s s  degrees.  - the top corner of concrete was (Photograph  f a l l i n g off  5.24.).  - more of the concrete around bottom corner fell  off .  - the weld was  f a i l i n g at the bottom corner  between the load p l a t e and  the  connection  rebar. - the t e n s i o n l e g broke at the end of the weld (Photograph  5.25.).  1  to  o  o  o  o  o  o  o  o  o  o  o  o  o  I  o  I  o  I  o  I  o  I  o  I  o  I  F i g u r e 5.21. L o a d - d e f l e c t i o n curve f o r Test  o  I  o  I ~  #12.  142 o CO  F i g u r e 5.22.  Sideways movement of connection  (Test  #12).  Photograph 5.23.  Tension corner f a l l i n g o f f  (Cycle #1 +97  kN).  144  \i  Sim CVCLE  Photograph 5.24.  J  Top corner f a l l i n g o f f (Cycle #1 +75  kN).  Photograph 5.25.  Connection at f a i l u r e  (Cycle #1 +75  kN).  5.2.4.3. TEST #14 The  l o a d - d e f l e c t i o n curve  f o r t h i s t e s t can be seen i n  F i g u r e 5.23. An enlargement of the f i r s t d e f l e c t i o n curve  c y c l e s of the l o a d -  i s shown i n F i g u r e 5.24. The sideways  movement of the connection  i s d i s p l a y e d i n F i g u r e 5.25.  Photograph 5.26. shows the connection a f t e r  f a i l u r e . The  f o l l o w i n g o b s e r v a t i o n s were noted d u r i n g t e s t i n g : Cy  12 +91 kN  - small c r a c k s were v i s i b l e around the top corner of the c o n n e c t i o n . - a small gap c o u l d be seen between the concrete and the legs of the connection a t the c o n n e c t i o n  corners.  Cy  1  3 + 94 kN  - the top corner of the concrete f e l l o f f .  cy  1  3 -93 kN  - the bottom corner f e l l o f f .  Cy  1  4 + 86 kN  - movement of the l e g s at the c o r n e r s , but no additional cracking.  Cy  1  4 + 78 kN  - a l a r g e p i e c e of concrete f e l l tension  Cy  1  4 -69 kN  - another tension  Cy  1  5 + 62 kN  o f f a t the  corner. p i e c e of concrete f e l l  o f f at the  side.  - the top t e n s i o n l e g broke a t the end of the weld (Photograph  5.26.).  147  Figure  5.23.  L o a d - d e f l e c t i o n curve f o r Test  #14.  o  o  o  o  o  o  o  o  o  o  *-*  Figure 5.24.  o  o  o I  o I  o I  o I  o I  o I  o I  o I  o I  -<  Enlargement of the l o a d - d e f l e c t i o n curve f o r Test  #14.  F i g u r e 5.25.  Sideways movement of connection  (Test  #14).  150  P h o t o g r a p h 5.26.  Connection at f a i l u r e  ( C y c l e #15  +  151 5.2.5. ANGLE WELDED TO REINFORCING MESH T h i s connection  was made up out of a 50 mm x 50 mm x  200 mm angle which was welded s t r a i g h t to the r e i n f o r c i n g mesh i n the specimen. For more d e t a i l s see s e c t i o n 3.5.5. In t o t a l two specimens were f a b r i c a t e d . Both of these were t e s t e d under c y c l i c  l o a d i n g . The r e s u l t s were :  5.2.5.1. TEST #9 The  l o a d - d e f l e c t i o n curve f o r t h i s t e s t can be seen i n  Figure  5.26. An enlargement of the f i r s t c y c l e s i s shown i n  Figure  5.27. The sideways movement of the connection  displayed  in Figure  the connection observations Cy  04 -41 kN  is  5.28. Photographs 5.27. t o 5.31. show  during  t e s t i n g and at f a i l u r e . The f o l l o w i n g  were noted during - diagonal  testing :  cracks opened up on both s i d e s of  the s l a b (Photograph 5.27.). - no concrete  was f a l l i n g o f f at l o a d l e v e l s  of -40 kN to +40 kN. Cy  07 +51 kN  - the diagonal  cracks  was enlarged  and they  appeared to go s t r a i g h t through the specimen (Photographs 5.28. and 5.29. the arrows i n the photographs i n d i c a t e the d i r e c t i o n of l o a d i n g which opened up the c r a c k s ) . - the angle l i f t e d up p a r t of the concrete above the angle when the load was a p p l i e d upwards.  1 52 - a gap was opened at the bottom edge of the angle d u r i n g upward l o a d i n g . - small p i e c e s of concrete were f a l l i n g o f f at both ends of the angle. Cy 08 +38 kN  - a l a r g e p i e c e of concrete f e l l  o f f from the  back s i d e of the specimen. Cy 09 -29 kN  - the c o n c r e t e at both ends of the angle had fallen  o f f (Photograph  5.30.).  - at t h i s p o i n t the s t r e n g t h of the connection was generated  by bending  the r e i n f o r c i n g  bars which were p e r p e n d i c u l a r to the connection  (Photograph  - the c o n n e c t i o n  finally  5.31.). f a i l e d when the bars  broke away from the angle.  153  Figure  5.26. L o a d - d e f l e c t i o n  curve for Test  #9.  1 54  (K3l)  igure  P'Ol  5.27. Enlargement of the l o a d - d e f l e c t i o n curve f o r Test  #9.  1 55 o CO  - S3  -8  oo  -  a a a a O  «S  O.  o  - CO  - CJ  i  Figure  i  i  i  o  o o o o o  Q  O  O  CO CD  5.28.  i  CO IO  i—r O  O  O  O  I  O  O  I  O  I  cu I  i—i—i—r  i—i—r O  t  O  I  Sideways movement of connection  O  I  O  I  O  I  O  I — >  (Test #9).  m  —«  156  Photograph 5.28. C y c l e #7 +51 kN (Test  158  Photograph 5.29. Cycle # 7 +51 kN (Test #9).  159  P h o t o g r a p h 5.30.  Cycle  #9  -29  kN  (Test  #9).  Photograph 5.31. C y c l e #9 -29 kN (Test  #9).  161 5.2.5.2. TEST The  #15  l o a d - d e f l e c t i o n curve  f o r t h i s t e s t can be seen i n  F i g u r e 5.29.  An enlargement of the f i r s t c y c l e s i s shown i n  F i g u r e 5.30.  The  displayed  sideways movement of the connection i s  i n F i g u r e 5.31.  The  f o l l o w i n g o b s e r v a t i o n s were  noted d u r i n g t e s t i n g : Cy 05 +52  kN  - a d i a g o n a l crack opened up s t r a i g h t the s l a b from the bottom of the  through  angle  ( S i m i l a r to Photograph 5.27.). Cy 05 -52  kN  - a d i a g o n a l crack opened up s t r a i g h t the s l a b from the top of the  through  angle.  - the d i a g o n a l c r a c k s opened up one a f t e r other d u r i n g the next connection was slightly  kN  four c y c l e s when the  c y c l e d . The  cracks appeared  l a r g e r with each c y c l e ( S i m i l a r to  Photographs 5.28. Cy 09 +47  the  and  - a piece of concrete  5.29.).  fell  o f f at the  top  fell  o f f at the bottom  corner. Cy 09 -47  kN  - a p i e c e of concrete corner.  Cy  10 -17  kN  - p i e c e s of concrete f e l l  o f f on back s i d e of  the s l a b ( S i m i l a r to Photographs 5.30.  and  5.31.). - the connection  f a i l e d when the  bars broke o f f from the  angle.  reinforcing  162  (K3i)  F i g u r e 5.29.  p-Bo-r.  L o a d - d e f l e c t i o n curve  f o r Test  #15.  16  o o •**  o  o  o  o  o  o  o  o  o  o  o i  o i  o i  o i  o i  o i  o i  o i  o i  Y  igure 5.30. Enlargement of the l o a d - d e f l e c t i o n curve f o r Test  #15.  164 o CO  - 8  -Si  a a, *»  a m  a«  o m o. •» Q  \ 1  8  1  1  cp o o> oo  o  F i g u r e 5.31.  1  1  1  h  . 1  1  1  1  1  1  1  1  1  1  1  1  i  i  i  i  i  i  i  i  i  Sideways movement of connection  (Test  CM  CM  I  #15).  165 5.2.6. REVERSED ANGLE WELDED TO REINFORCING MESH T h i s connection was made up out of a 50 mm x 50 mm x 200 mm  r e v e r s e d angle which was welded s t r a i g h t to the  r e i n f o r c i n g mesh i n the specimen. For more d e t a i l s see section  3.5.6.  In t o t a l two specimens were f a b r i c a t e d . Both of these were t e s t e d under c y c l i c  l o a d i n g . The r e s u l t s were :  5.2.6.1. TEST #10 The l o a d - d e f l e c t i o n curve f o r t h i s t e s t can be seen i n Figure 5.32. An enlargement of the f i r s t  c y c l e s i s shown i n  F i g u r e 5.33. The sideways movement of the connection i s d i s p l a y e d i n F i g u r e 5.34. Photographs 5.32. to 5.37. show the c o n n e c t i o n during t e s t i n g and a t f a i l u r e . The f o l l o w i n g o b s e r v a t i o n s were noted during t e s t i n g : Cy 02 +42 kN  - a diagonal crack on the f r o n t side of the specimen opened up from the top of the angle when the connection was loaded upward. A s i m i l a r crack developed from the bottom of the angle when the specimen was loaded downwards  (Photograph 5.32.).  - on the back s i d e of the specimen, the c r a c k s developed from the opposite ends of the angle (Photograph 5.33.). - the corners above and below the angle were also cracking.  166 Cy 04 +60 kN  - the c r a c k s opened up more at the higher l o a d (Photograph  Cy  06 +56 kN  5.34.).  - the corner above the angle cracked o f f (Photograph  5.35.).  - l o a d i n g down, the bottom corner cracked o f f (Photograph  5.36.).  - the connection t w i s t e d q u i t e a b i t when the load was a p p l i e d . T h i s was caused t h i n metal Cy  07 -17 kN  by the  i n the a n g l e .  - the connection  f a i l e d when the bar which was  p a r a l l e l t o the angle y i e l d e d at both ends of  the angle  (Photograph  5.37.).  167  F i g u r e 5.32.  L o a d - d e f l e c t i o n curve f o r Test  #10.  168 KO  I  i o  o  i o  i o  i o  i o  i o  i o  i o  1  i o  o  i o  -*  o  I  (.M3T)  i  i o  I  o  I  i—i—i—i—i—r T  i o  I  o  I  o  I  o  I  o  I  o  I  V  P^o-i  igure 5.33. Enlargement of the l o a d - d e f l e c t i o n curve f o r Test #10.  169 CM  a a  a a o  o o  o o o o co I N e fi  O O O O O  •* n  w  (K>t)  F i g u r e 5.34.  -i  O  I  O CM  I  O CO  Q ^  I I  O 10  I  O co  I  O t»  I  o co  I  o  5  o o  I *p  P-BOT;  Sideways movement of connection  (Test  #10).  Photograph 5.32. Cycle #2 +42 kN (Test #10).  Photograph 5.33. C y c l e #2 +42 kN (Test #10).  Photograph 5.34. Cycle #4 +60 kN (Test #10).  Photograph 5.35. Cycle #6 +56 kN (Test #10).  174  Photograph 5.36. Cycle #6 +56 kN (Test  #10).  Photograph 5.37. Cycle #7 -14 kN (Test #10).  176 5.2.6.2. TEST The  #16  l o a d - d e f l e c t i o n curve  f o r t h i s t e s t can be seen i n  F i g u r e 5.35.  An enlargement of the f i r s t  F i g u r e 5.36.  The  c y c l e s i s shown i n  sideways movement of the connection i s  d i s p l a y e d i n F i g u r e 5.37.  Photograph 5.38.  connection at f a i l u r e . The  shows the  f o l l o w i n g o b s e r v a t i o n s were noted  during t e s t i n g : Cy 06 +60  kN  - some small p i e c e s of. concrete f e l l o f f at both ends of the a n g l e . - small d i a g o n a l c r a c k s showing up on  both  s i d e s of the specimen. Cy 07 +72  kN  - l a r g e r c r a c k s opened up on both s i d e s of the s l a b . The c r a c k s behaved s i m i l a r l y to the c r a c k s i n the p r e v i o u s specimen Photographs 5.32.  Cy 08 +72  kN  and  ( S i m i l a r to  5.33.).  - more l a r g e c r a c k s opened up on both s i d e s of the specimen. - the s i d e of the angle that was  welded to the  l o a d i n g p l a t e t w i s t e d i n and out when the load was c y c l e d . Cy  10 +62  kN  - the corners above and below the  angle  cracked o f f ( S i m i l a r to Photographs and Cy  11 +42  kN  5.35.  5.36.).  - the bar p a r a l l e l to the angle y i e l d e d at both ends of the  angle.  a l a r g e p i e c e of c o n c r e t e f e l l  o f f on  back s i d e of the specimen around the r e i n f o r c i n g bars (Photograph 5.38.).  178  F i g u r e 5.35.  L o a d - d e f l e c t i o n curve f o r Test  #16.  180  CM  (K31)  PWOTC  F i g u r e 5.37. Sideways movement of connection  (Test  #16).  181  Photograph 5.38. Cycle #11 + 42 kN (Test #16).  182  CHAPTER 6  DISCUSSION, CONCLUSIONS AND FUTURE SCOPE  6.1. INTRODUCTION T h i s i n v e s t i g a t i o n was i n i t i a t e d to develop  improved  d e t a i l s and r a t i o n a l methods of a n a l y s i s f o r a connection f o r use i n a t h i n  flange of an element i n an  earthquake  r e s i s t a n t b u i l d i n g . I t was assumed d u r i n g the t e s t i n g of the connections that the f l a n g e remained e l a s t i c while the nonl i n e a r behaviour The  was r e s t r i c t e d to the c o n n e c t i o n .  r e s u l t s of the i n v e s t i g a t i o n are summarized and  d i s c u s s e d i n t h i s chapter. The c o n c l u s i o n s presented are based  on the experimental o b s e r v a t i o n s of the behaviour of  the c o n n e c t i o n s during t e s t i n g and the measured f o r c e s and deformations. The recommendations f o r f u r t h e r study are a l s o based  on the r e s u l t s d i s c u s s e d here.  183 6.2. DISCUSSION  6.2.1. BEHAVIOUR OF THE CONNECTIONS DURING CYCLIC LOADING The c y c l i c  t e s t i n g of each connection began with  s e v e r a l c y c l e s of l o a d i n g w i t h i n the e l a s t i c in  Loading  t h i s range, up to about 80 % of the p r e d i c t e d s t r e n g t h of  the c o n n e c t i o n , appeared to  range.  to cause only minor c r a c k i n g c l o s e  the c o r n e r s of the c o n n e c t i o n s . In each case,  i n i t i a l c y c l e s produced  s t a b l e and narrow  curves and d i d not appear t o reduce the connections  these  load-deflection  the s t r e n g t h of any of  ( F i g u r e s 5.18. and 5.23.).  The connections f a i l e d e i t h e r by bar f a i l u r e or by s p a l l i n g when the connections were loaded i n t o the i n e l a s t i c range. The bar f a i l u r e s g e n e r a l l y o c c u r r e d a t very small deflections  ( F i g u r e s 5.1. and 5.2.). For the connections  that f a i l e d by s p a l l i n g , the s t i f f n e s s f e l l  g r a d u a l l y while  the width of the l o a d - d e f l e c t i o n curves i n c r e a s e d ( F i g u r e s 5.5. and 5.14.). S u c c e s s i v e c y c l e s of i n e l a s t i c for  these connections caused  displacement  i n c r e a s e d c r a c k i n g which was  followed by a p r o g r e s s i v e l o s s of c o n c r e t e around the embedded b a r . The bar c a r r y i n g compression at  tended  t o buckle  t h i s p o i n t and became i n e f f e c t i v e . T h i s gave some of the  connections a reduced but r e l a t i v e l y increasing  i n e l a s t i c displacements  s t a b l e s t r e n g t h with  ( F i g u r e s 5.5., 5.14. and  5.29..). However, other connections showed r e l a t i v e l y l o s s of s t r e n g t h with i n c r e a s e d displacement  little  (Figure 5.18.).  184 The connections that were welded s t r a i g h t to the specimen's r e i n f o r c i n g mesh l o s t most of t h e i r l o a d c a r r y i n g c a p a c i t y a f t e r a few c y c l e s i n the i n e l a s t i c  range ( F i g u r e s  5.26. and 5.32.). At t h i s p o i n t the specimens were a l s o s e v e r e l y cracked. In g e n e r a l , the connections  fabricated  from embedded rebar with the lower y i e l d s t r e s s  (Rebar  behaved b e t t e r than s i m i l a r connections f a b r i c a t e d rebar with higher y i e l d s t r e s s  (Rebar  #2)  from  #1). Both of the above  c o n n e c t i o n s a l s o behaved b e t t e r than those i n which the r e i n f o r c i n g mesh was used as p a r t of the c o n n e c t i o n .  6.2.2. BEHAVIOUR OF CONNECTIONS DURING MONOTONIC LOADING Three of the connections were t e s t e d m o n o t o n i c a l l y (see Tabie 6.1.). The maximum load f o r these connections reached  j u s t before the concrete around the compression  corner of the connection cracked o f f (see Photograph The  was  5.2.).  l o a d - d e f l e c t i o n curves f o r these connections had a  f a l l i n g branch which was formed d u r i n g i n c r e a s e d i n e l a s t i c displacement. The s t r e n g t h of the connections remained at a l e v e l of about 60 % of the maximum s t r e n g t h u n t i l a d e f l e c t i o n of about 10 to 20 times the d e f l e c t i o n at the maximum s t r e n g t h was reached  ( F i g u r e 5.21.).  None of the connections t h a t were welded s t r a i g h t to the r e i n f o r c i n g mesh were t e s t e d m o n o t o n i c a l l y . Of the other c o n n e c t i o n s , the connections that were f a b r i c a t e d from the rebar with the lower y i e l d  stress  (Rebar  #2) again behaved  Table 6.1. MAXIMUM CONNECTION STRENGTHS  CONNECTION TYPE  y  REBAR # 1  REBAR # 1 WITH ANGLE  REBAR # 2  REBAR # 2 7 5 mm SLAB  ANGLE TO MESH  REV. ANGLE TO MESH  POSITIVE STRENGTH (kN)  TEST #  NEGATIVE STRENGTH (kN) i  1  CYCLES AT MAXIMUM  1(.__  _  1i  # OF CYCLES IN TEST  1  90.64  -93.94  2  3  2  88.60  -50.32  1  1  6  60.85  -56.41  4  5  3  69.31  -67.33  10  13  4  0.00  -89.92  1  MONOTONIC  5  50.36  -46.26  6  6  7  88.76  -77.19  4  5  8  70.52  -85.31  1 1  16  13  93.93  0.00  1  MONOTONIC  1 1  81 .62  -81.34  8  13  12  97.57  0.00  1  MONOTONIC  14  93.60  -92.99  13  15  9  50.99  -73.66  8  9  15  59.82  -65.26  9  1 1  10  60.66  -63.36  4  7  16  76.45  -73.49  9  1 1  b e t t e r than the connections f a b r i c a t e d from the rebar with the higher y i e l d  stress  (Rebar #1).  6.2.3. STRENGTH OF CONNECTIONS  6.2.3.1. MAXIMUM MEASURED STRENGTHS The maximum measured p o s i t i v e and negative s t r e n g t h s f o r the d i f f e r e n t connections a r e given i n Table 6.1. A comparison of these s t r e n g t h values shows the the maximum and minimum s t r e n g t h s are u s u a l l y s i m i l a r i n magnitude. The t a b l e does not show a l a r g e v a r i a t i o n between the maximum s t r e n g t h s of the connections that were f a b r i c a t e d from the two d i f f e r e n t  s t r e n g t h r e b a r s . The t a b l e a l s o shows the  c y c l e d u r i n g which the maximum s t r e n g t h s occurred and the number of c y c l e s to f a i l u r e . A comparison of these c y c l e numbers and the maximum s t r e n g t h s f o r each connection shows that while the y i e l d s t r e s s does not seem t o have a l a r g e e f f e c t on the connection s t r e n g t h i t does appear to a f f e c t the number of c y c l e s to f a i l u r e . The connections made from Rebar #2, which had the lower y i e l d  s t r e s s appeared  able to s u s t a i n more l o a d i n g c y c l e s at lower a f t e r the maximum s t r e n g t h s had been reached, made from Rebar #1.  t o be  load l e v e l s , than  those  187 6.2.3.2. STRENGTHS AT FAILURE The  usable connection s t r e n g t h s a t f a i l u r e can be seen  in Table 6.2. The usable connection s t r e n g t h was estimated as f o l l o w s . I f the connection f a i l e d suddenly, at f a i l u r e  the s t r e n g t h  f o r l o a d i n g i n one d i r e c t i o n was taken as the  l o a d measured immediately  before f a i l u r e and the s t r e n g t h  f o r l o a d i n g i n the other d i r e c t i o n was taken as the l o a d at the end of the previous h a l f c y c l e . I f the connection  failed  g r a d u a l l y , one value of s t r e n g t h at f a i l u r e was taken as the s t r e n g t h a t the end of the l a s t c y c l e was s t i l l and  i n which the c a p a c i t y  i n c r e a s i n g when the d e f l e c t i o n went through zero  the other was taken as the s t r e n g t h a t the end of the  p r e v i o u s h a l f c y c l e . The monotonic t e s t s were c o n s i d e r e d to have f a i l e d when the connection rebar broke or when the s t r e n g t h had f a l l e n to 50 % of the maximum s t r e n g t h . Table 6.2. a l s o shows the number of c y c l e s to f a i l u r e f o r the c o n n e c t i o n s and the number of c y c l e s t o maximum s t r e n g t h .  6.2.3.3. CALCULATED STRENGTHS The c a l c u l a t e d shear s t r e n g t h s f o r the two d i f f e r e n t types of connections were obtained by the f o l l o w i n g two procedures.  6.2.3.3.1. SEPARATE REBAR AT 45 DEGREES. A procedure f o r c a l c u l a t i n g the shear s t r e n g t h of t h i s type of connection i s given i n [1] and [ 2 ] . As shown i n  188 Table 6.2. MEASURED CONNECTION STRENGTH AT FAILURE  CONNECTION TEST CYCLES FAILURE TYPE AT TYPE # MAXIMUM REBAR # 1  REBAR # 1 WITH ANGLE  REBAR # 2  REBAR # 2 75 mm SLAB  ANGLE TO MESH  REV. ANGLE TO MESH  STRENGTH PREVIOUS CYCLES AT MAXIMUM TO FAILURE STRENGTH FAILURE (kN) (kN)  1  2  BAR  3  74.35  -77.70  2  1  BAR  1  -50.32  88.60  6  4  BAR  5  59.90  -56.41  3  10  SPALLING  13  32.26  -43.86  4  MONO.  SPALLING  1  -51.00  5  6  SPALLING  6  50.36  -46.26  7  4  SPALLING  5  -56.14  88.75  8  1 1  16  22.26  -37.40  BAR  13  MONO.  SPALLING  1  41 .72  1 1  8  SPALLING  12  77.00  12  MONO.  BAR  1  73.09  14  13  BAR  15  9  8  BAR  15  9  10 16  -69.93  61 .77  -69.30  8  32.60  -73.66  BAR  10  42.34  -65.26  4  BAR  6  -55.79  55.56  9  BAR  1 1  44.54  -63.53  189 F i g u r e 6.1., each l e g c o n t r i b u t e s t o the s t r e n g t h of the c o n n e c t i o n . I f each l e g i s assumed to y i e l d when the connection  fails,  then  C = T = A  b  * F  [1]  y  where A^ i s the c r o s s s e c t i o n a l area of the rebar and F i s v  the y i e l d s t r e n g t h . When the two l e g s are a t 45 degrees, the connection V V  n  n  the s t r e n g t h of  is:  = Sqrt(2) * A  * F  fa  [2]  y  However, t h i s approach f o r c a l c u l a t i n g the s t r e n g t h must be m o d i f i e d when the concrete  i s l o s t around the l e g s  by s p a l l i n g . At t h i s p o i n t the compression i n e f f e c t i v e and the expected  shear  l e g becomes  s t r e n g t h i s 0.5 * V . n  Two separate values were c a l c u l a t e d and p l o t t e d on the l o a d - d e f l e c t i o n curves  f o r t h i s type of c o n n e c t i o n . These  were denoted Fy and Fyw (see s e c t i o n 5.1. f o r d e f i n i t i o n of the  terms). It  has been suggested  by Spencer [4] that the above  approach must be m o d i f i e d f o r a connection with an angle welded to the connection fail  rebar. Before the connection can  the c o n c r e t e bearing a g a i n s t the end of the angle must  be pushed o f f . The f o r c e Fp r e q u i r e d t o f a i l  this  concrete  was found t o be given by F  p  = A  p  * f c  [3]  F i g u r e 6.1.  Forces i n rebar c o n n e c t i o n .  191  where Ap i s the area of the recess formed by the angle and f c  i s the concrete c y l i n d e r s t r e n g t h . The shear  strength  under monotonic l o a d i n g w i l l t h e r e f o r e be given by V  n  = Sqrt(2) * A  b  * Fy + A  p  * f c  However, t h i s approach does not seem to be v a l i d  [4] for thin  p a n e l s . For the panels s t u d i e d i n t h i s i n v e s t i g a t i o n , the s t r e n g t h of the connections  that had an angle welded to the  rebar was p r e d i c t e d with formula  [ 2 ] , T h i s can be e x p l a i n e d  by the f a c t that a f t e r only a few c y c l e s the c o n c r e t e a t the ends of the angle had cracked o f f and the connection worked as a normal rebar  connection.  6.2.3.3.2. CONNECTIONS WELDED TO REINFORCING MESH. During the t e s t i n g of the specimens which used connections, through  i t was observed  that cracks developed  these straight  the specimens. These c r a c k s s t a r t e d a t the ends of  the connections  and extended from the edge of the f l a n g e  towards the t h i c k e n e d p o r t i o n of the specimen, which r e p r e s e n t s the web. The c r a c k s appear t o be c o n s i s t e n t with a f l e x u r a l mode of f a i l u r e , with the maximum t e n s i l e  strain  at the edge of the flange and the n e u t r a l a x i s a t flange-web junction. Some of the c r a c k s that developed  d u r i n g the t e s t i n g  extended from the end of the connections  s t r a i g h t a c r o s s the  flange t o the web. These c r a c k s were c a l l e d type A. Other  c r a c k s were seen to extend from the end of the connections across the web at approximately 45 degrees. These c r a c k s were c a l l e d type B. Pauley, P r i e s t l e y and Synge [13] r e p o r t e d s i m i l a r d i a g o n a l crack development d u r i n g t e s t i n g of squat s h e a r w a l l s . Types A and B represent the two extreme cracking cases.  6.2.3.3.2.1. TYPE A The procedure  f o r c a l c u l a t i n g the connection shear  s t r e n g t h f o r type A c r a c k i n g i s given i n [5] and shown i n F i g u r e 6.2. as Ca = Pi*F *(D /2)*2*((W-A )+(W-A )+...)/W) y  b  1  where Fy i s the y i e l d s t r e n g t h ,  2  i s the diameter of the  bar, W i s the panel width and A-| , A , 2  to the r e i n f o r c i n g  [5]  ... are the d i s t a n c e s  bars from the panel edge.  The bars p a r a l l e l t o the c o n n e c t i o n which were part of the r e i n f o r c i n g mesh extended a c r o s s these types of c r a c k s . The above formula i s d e r i v e d by assuming that a l l the bars c r o s s i n g the crack y i e l d and that the y i e l d s t r e n g t h of the steel  is F . v  6.2.3.3.2.2. TYPE B The procedure  f o r c a l c u l a t i n g the shear s t r e n g t h of  t h i s type of connection i s given i n [6] and shown i n F i g u r e 6.3. as  193  Ca = P i * F  y  * (D /2)~2 * ((A, + A b  2  + A3 + A )/W) 4  Ca = Connection c a p a c i t y Fy = S t e e l y i e l d D  b  stress  = Diameter of rebar  F i g u r e 6.2. Forces i n connection welded to r e i n f o r c i n g mesh (perpendicular c r a c k i n g ) .  194  Cb = P i * F  y  * (D /2)~2 * ((B, + B b  Cb = Connection  Figure  + B  3  + B )/W) 4  capacity  F  y  = Steel y i e l d  stress  D  b  = Diameter of  rebar  6.3.  2  Forces i n connection (diagonal  welded to r e i n f o r c i n g mesh  cracking).  195 Cb = P i * F * ( D / 2 r 2 * ( (L-B ) + (L-B ) + . . . )/W) y  where F  y  b  1  i s the y i e l d s t r e n g t h , D  [6]  2  b  i s the diameter of the  bar, W i s the d i s t a n c e from the edge of the flange to the p o i n t where the diagonal compression s t r u t  i s assumed t o  meet the web and B , B 2 , ... are the d i s t a n c e s from the 1  r e i n f o r c i n g bars  from t h i s p o i n t .  The above formula  i s d e r i v e d by assuming that a l l the  bars c r o s s i n g the crack y i e l d and that the y i e l d s t r e n g t h of the s t e e l i s F . However, y  to a connection  i t i s assumed that bars  parallel  do not c o n t r i b u t e to i t s s t r e n g t h . T h i s i s a  c o n s e r v a t i v e assumption which i s l i k e l y to be true when there are a number of connections  along a f l a n g e .  6.2.3.3.3. CALCULATED CONNECTION STRENGTHS The c a l c u l a t e d strengths and the measured maximum s t r e n g t h s are shown i n Table  6.3. and 6.4. Table  d i s p l a y s the s t r e n g t h values obtained  6.3.  from using formula  [2]  f o r both Fy and Fyw. Both c a l c u l a t e d values are a l s o p l o t t e d on the l o a d - d e f l e c t i o n curves Table  f o r each t e s t  6.4. shows the values obtained  ( s e c t i o n 5.2.).  by formulas [5] and  [ 6 ] . F i g u r e 6.4. shows the r e l a t i o n s h i p between the measured s t r e n g t h and the c a l c u l a t e d s t r e n g t h f o r the  connections  (using Fy and C a ) . Figure 6.5. shows the r e l a t i o n s h i p between the measured s t r e n g t h and the c a l c u l a t e d s t r e n g t h f o r the connections  (using Fyw and Cb). Figure 6.6. shows  Table 6.3. CALCULATED CONNECTION STRENGTHS  CONNECTION TYPE REBAR # 1  REBAR # 1 WITH ANGLE  REBAR # 2  REBAR # 2 7 5 mm SLAB  POSITIVE STRENGTH (kN)  NEGATIVE STRENGTH (kN)  STRENGTH USING Fy (kN)  1  90.64  -93.94  84.34  98.50  2  88.60  -50.32  84. 34  98.50  6  60.85  -56.41  84.34  98.50  3  69.31  -67.33  84.34  98.50  4  0.00  -89.92  84.34  98.50  5  50.36  -46.26  84.34  98.50  7  88.76  -77. 1 9  57.70  69.20  8  70.52  -85.31  57.70  69.20  13  93.93  0.00  57.70  69.20  1 1  81 .62  -81.34  57.70  69.20  12  97.57  0.00  57.70  69.20  14  93.60  -92.99  57.70  69.20  TEST #  STRENGTH USING Fyw (kN)  Table 6.4. CALCULATED CONNECTION STRENGTHS  CONNECTION TYPE ANGLE TO MESH  REV. ANGLE TO MESH  POSITIVE STRENGTH (kN)  NEGATIVE STRENGTH (kN)  STRENGTH USING Ca (kN)  9  50.99  -73.66  39.20  62.02  15  59.82  -65.26  39.20  62.02  10  60.66  -63.36  59.00  53.00  16  76.45  -73.49  59.00  53.00  TEST #  STRENGTH USING Cb (kN)  Measured versus Calculated strength  • A  Rebar #1 + Rebar #2 75 mm  Calculated strength (kN) Rebar #1 with Angle o Rebar #2 vr. Recess X Angle to mesh V Rev. angle to mesh  Measured  • A  Rebar #1 + Rebar #2 75 m m  versus  Calculated  strength  Calculated s t r e n g t h (kN) Rebar #1 -with Angle o Rebar #2 yr. Recess X Angle to m e s h V Rev. angle to m e s h  Failure versus Calculated strength Using Fy or Ca  0 +  20  40  60  80  100  Calculated strength (kN) Rebar #1 -with Angle o Rebar #2 YT. Recess X Angle to mesh v" Rev. angle to mesh  201 the  r e l a t i o n s h i p between the f a i l u r e strength  calculated  strength  and the  f o r the connections (using Fy and C a ) .  F i g u r e 6.7. shows the r e l a t i o n s h i p between the f a i l u r e strength (using By  and the c a l c u l a t e d  strength  Fyw and Cb). comparing the v a l u e s i n the t a b l e and examining the  graphs and the l o a d - d e f l e c t i o n can  f o r the connections  be seen that  curves f o r a l l the t e s t s , i t  the models used f o r the c a l c u l a t i o n s work  reasonably w e l l . However, as p o i n t e d out i n s e c t i o n 6.2.3.1., the agreement was not good enough to c o n f i r m  that  the maximum s t r e n g t h s depended on the value of F . The y  models d e s c r i b e d predict  above are c o n s i d e r e d to be adequate t o  the a c t u a l maximum s t r e n g t h  used w i t h the a c t u a l  of the connections when  F . y  6.2.3.4. INFLUENCE OF CONCRETE STRENGTH ON CONNECTION STRENGTHS F i g u r e 6.8. shows a graph of the c y l i n d e r  s t r e n g t h s and  the connection s t r e n g t h s . An examination of the graph reveals the  no d i r e c t r e l a t i o n s h i p between the two s t r e n g t h s f o r  specimens which had an embedded r e i n f o r c i n g f o r the  connection i n a d d i t i o n the  to the mesh i n the p a n e l . However,  graph seems to i n d i c a t e some r e l a t i o n s h i p between the  plotted  strength  values f o r the two types of connections  that were welded s t r a i g h t to the r e i n f o r c i n g mesh.  This  r e l a t i o n s h i p can be i n f e r r e d s i n c e the t e n s i l e r e s i s t a n c e of the c o n c r e t e c o u l d  contribute  to the s t r e n g t h ,  as a  Failure  versus  Calculated  strength  Using F J T V or Cb  • A  Calculated strength (kN) Rebar #1 + Rebar #1 with Angle o Rebar #2 nr. Recess Rebar #2 75 mm X Angle to mesh V Rev. angle to mesh  M  O  Connection lO. C  strength  vs. Cylinder  str.  -Metve lorvtc-  100  fD  Monotonic  cn  Monotonic  co  90  O O 3 3  fD  O  80  H  70  H  rt  O 3  W rr  n  fD  3  iQ rr  60  3*  cn < fD i-l  50  cn  c  ijebar  cn O  40  Rebar  #1 Rebar #1 TV. Angle Rebar  H  #2  75mm  A  n  g  l  e  #2 ReY.  3 &  Anglle  fD r-t  30  in  rt  —I  1  fD  3  lO  rr  3*  •  Cylinder str.  (MPa)  i  2  6  1  1  1  1  3  4  5  1  I  1  1  7  8  9  1  l  I  "I  I  11 15 16  Mix g A Connection  st.  1  1  10 12  1  1  1  13 14  (kN)  cn  to o CA)  204 secondary  e f f e c t , during the t e s t s of these  connections.  6.2.4. TYPES OF CONNECTION FAILURES The connection f a i l u r e s can be d i v i d e d i n t o two general t y p e s . The f i r s t  and most common type was the bar f a i l u r e ,  while the second was f a i l u r e caused  by s p a l l i n g . The f a i l u r e  types f o r each of the t e s t e d connections are l i s t e d  i n Table  6.2. The without  bar f a i l u r e s f o r Rebar #1 occurred  suddenly,  warning, at r e l a t i v e l y h i g h loads and with a very  small connection displacement. T h i s sudden f a i l u r e was most l i k e l y caused  by the high y i e l d  s t r e s s of the rebar which  made the rebar very b r i t t l e . The d e f l e c t i o n s at f a i l u r e f o r the t e s t s can be found The  i n Table 6.5.  bar f a i l u r e s f o r Rebar #2 took p l a c e a f t e r the  connection rebar had been bent back and f o r t h s e v e r a l times. T h i s i n d i c a t e s that t h i s rebar was much more d u c t i l e which means that the bar f a i l u r e s would occur at much higher d e f l e c t i o n s and u s u a l l y not before some concrete had s p a l l e d off  from around the c o r n e r s of the connections. Spalling  f a i l u r e s occurred only i n the connections  which were made from a separate rebar. The f a i l u r e s were a r e s u l t of one of the connection l e g s p u l l i n g out from the specimen (see Photograph 5.7.). T h i s type of f a i l u r e happened g r a d u a l l y with more and more of the connection legs exposed with each c y c l e . The connections f a i l e d when the l a s t p i e c e of the r e i n f o r c i n g  l e g p u l l e d out.  Table  6.5.  MOVEMENTS OF CONNECTIONS  CONNECTION TEST FAILURE TYPE TYPE '#  REBAR  #1  REBAR # 1 WITH ANGLE  REBAR # 2  REBAR # 2 75 mm SLAB  ANGLE TO MESH  REV. ANGLE TO MESH  DEFLECTION SIDEWAYS MAXIMUM AT MAXIMUM MOVEMENT SIDEWAYS FAILURE DEFLECTION FAILURE MOVEMENT (mm) (mm) (mm) (mm)  1  BAR  1.45  1.45  2  BAR  -0.42  -0.92  6  BAR  -0.03  -3.09  1.25  5.83  26.44  26.44  3  SPALLING  9.43  10.22  4  SPALLING  -9.02  -9.02  5  SPALLING  5.86  10.95  11.35  25.18  7  BAR  -0.06  3.44  4.11  18.39  8  BAR  5.64  -8.43  16.21  23.38  13  SPALLING  15.97  17.52  19.64  19.64  11  SPALLING  11.88  12.28  9.04  16.22  12  BAR  14.35  14.35  17.68  17.68  14  BAR  12.20  14.48  6.42  11.12  9  BAR  5.38  11.23  1.96  12.00  15  BAR  6.13  15.82  2.06  16.24  10  BAR  -0.18  5.53  -0.03  -1.30  16  BAR  -0.01  -6.49  -6.75  -7.55  206 The connections that were welded s t r a i g h t to the r e i n f o r c i n g mesh f a i l e d when the s t e e l mesh y i e l d e d  i n the r e g i o n around  i n the r e i n f o r c i n g  the c o n n e c t i o n s . The  f a i l u r e d i d not however take p l a c e before there had been e x t e n s i v e c r a c k i n g around  the connections and c o n s i d e r a b l e  l o s s of c o n c r e t e . Diagonal c r a c k s a l s o developed connection corners s t r a i g h t  from the  through the specimen (see  Photographs 5.28. and 5.29.). These c r a c k s extended  a l l the  way towards the back of the specimens.  6.2.5. DISPLACEMENT OF THE CONNECTIONS The displacement c a p a c i t y of the connections should be compared t o the r e q u i r e d displacement c a p a c i t y i n an earthquake  which w i l l depend on the s t r e n g t h of the b u i l d i n g  and the i n t e n s i t y of the earthquake.  The c a l c u l a t e d  response  of a one s t o r y panel s t r u c t u r e with a shear w a l l connection model s u b j e c t e d to a moderately  severe earthquake i s  d i s c u s s e d by Spencer  and Tong [ 5 ] . They found that the  maximum displacement  at roof l e v e l v a r i e d from about  15 mm  f o r a s t r u c t u r e with strong shear w a l l s i n which the c o n n e c t i o n s remained  elastic  to 40 mm  for a building  with  weaker w a l l s i n which the connections were loaded w e l l the i n e l a s t i c  into  range. I t was a l s o assumed that s t r e n g t h of  the c o n n e c t i o n s c o u l d f a l l  to about  50 % of the o r i g i n a l  value at maximum displacement. Spencer  and Tong [5] showed that the shear  v between the w a l l panels was  displacement  v = x * (b/h)  [7]  where b was the panel width, h was the height t o roof  level  and x was the displacement at roof l e v e l . The displacement of an i n d i v i d u a l connection w i l l  then be 0.5 * v. For the  b u i l d i n g they analysed, the r a t i o of b/h was 0.44 which meant that the l a r g e s t displacement connection would be approximately 9.0  capacity required for a  0.44*0.50*40 mm or about  mm. The above displacement can be compared to the  connection displacement at f a i l u r e and the maximum connection displacement which can be found i n Table 6.5. The v a l u e s show that the connections i n the 75 mm c o u l d be used  in buildings  loaded i n t o the i n e l a s t i c  specimens  i n which the connections would be range  with the lower y i e l d s t r e s s  i n an earthquake.  (Rebar  The rebar  #2) behaved again a l s o  b e t t e r than the rebar with the higher y i e l d s t r e s s ( R e b a r #1 ).  6.2.6. SIDEWAYS MOVEMENT OF THE CONNECTIONS The  sideways  movement of the connections at f a i l u r e and  at the maximum movement can be seen sideways  i n Table 6.5. The  movement i s a l s o p l o t t e d versus the load f o r each  t e s t and can be found small sideways  i n s e c t i o n 5.2. The graphs  show very  movements d u r i n g the i n i t i a l c y c l e s of the  t e s t s . However, with i n c r e a s i n g number of c y c l e s the sideways  movement was growing.  T h i s i s mainly the r e s u l t of  208 the t h i n cover around the connection r e i n f o r c i n g bars which o f f e r s minimal  r e s t r a i n t a g a i n s t sideways movement of the  connection under c y c l i c l o a d i n g . Another reason  f o r the sideways movement c o u l d be the  f a c t that the connection rebar was not p l a c e d e x a c t l y i n the middle  of the specimens. The bars i n the r e i n f o r c i n g mesh  and the connection rebar were together c e n t e r e d i n the specimen  (see F i g u r e 3.9.). T h i s meant that the connection  rebar was p l a c e d s l i g h t l y o f f c e n t e r .  6.2.7. CONNECTION DETAILS  6.2.7.1. PANEL THICKNESS A comparison of the r e s u l t s obtained f o r the 75 mm t h i c k specimens with the r e s u l t s f o r the 50 mm  thick  specimens i n d i c a t e s that the t h i c k e r specimens behave b e t t e r during l o a d i n g c y c l e s . The t e s t s show that the t h i c k e r specimens l o s e l e s s concrete around the connection r e i n f o r c i n g . T h i s i s mainly due t o the t h i c k e r cover the r e i n f o r c i n g bars. The connections  i n the t h i c k e r  specimens can a l s o maintain a higher l o a d l e v e l  without  f a i l u r e and the connections experience much lower movement.  over  sideways  209 6.2.7.2. PANEL RECESS The  type of connection that had a short recess beside  the connection  r e i n f o r c i n g appeared to perform  b e t t e r than  the other types of connections d u r i n g the t e s t i n g . The recess a l s o works b e t t e r than the longer one  short  since t h i s  preserves the concrete at the connection c o r n e r s . Another f u n c t i o n of the recess i s to expose the s i d e of the rebar the specimen can e a s i l y be welded to another  so  specimen.  6.2.7.3. ANGLE WELDED TO CONNECTION The main f u n c t i o n of the angle welded to the reinforcing  i s to make the attachment to an  connection e a s i e r . The  any  s i n c e the concrete around the  angle w i l l be s p a l l e d o f f a f t e r the f i r s t  6.3.  adjacent  angle does not however add  s t r e n g t h to the connection  connection  few  cycles.  CONCLUSION  a) Good q u a l i t y c o n t r o l of the s t e e l that goes i n t o the connections  is essential. Brittle  f a i l u r e s of the  connections, which are more l i k e l y with h i g h  yield  s t r e n g t h bars, are not d e s i r a b l e . b) A t h i c k e r  flange w i l l behave b e t t e r during earthquake  l o a d i n g s i n c e there i s more cover around  the  r e i n f o r c i n g . A t h i c k e r flange i s a l s o l e s s during transport.  fragile  210 c) The design s t r e n g t h of a connection should be taken as 50 % of the expected maximum c a p a c i t y of the c o n n e c t i o n . The spacing between connections can be reduced  i n order to reduce  the l o a d on each c o n n e c t i o n .  d) Loading c y c l e s i n the e l a s t i c reduce  range do not seem t o  the c a p a c i t y of the c o n n e c t i o n s .  e) The connections with a recess i n the panel edge and embedded bars at 45 degrees under simulated earthquake  appear to perform  l o a d i n g . These connections  can a l s o be e a s i l y a t t a c h e d t o an adjacent f) Connections  best  i n which an angle  connection.  i s welded d i r e c t l y to the  r e i n f o r c i n g mesh are not recommended s i n c e they damage the r e i n f o r c i n g s t e e l and cause severe c r a c k i n g i n the flange  itself.  g) The models used t o p r e d i c t the connection s t r e n g t h a r e adequate f o r p r e d i c t i n g the lower  l i m i t of the  connection s t r e n g t h s .  6.4.  FUTURE SCOPE The  r e s e a r c h d e s c r i b e d i n t h i s d i s s e r t a t i o n c o v e r s only  a small p a r t of the o v e r a l l o b j e c t i v e of p r e d i c t i n g the behaviour  of p r e c a s t concrete b u i l d i n g s under  earthquake  l o a d i n g . Based on the r e s u l t s of t h i s study, the f o l l o w i n g suggestions are made f o r f u r t h e r r e s e a r c h on the behaviour of embedded rebar connections i n t h i n f l a n g e s .  21 1 a) T e s t s should be performed where the connections  were  c y c l e d at lower loads f o r a longer p e r i o d of time. T h i s would show the e f f e c t of f a t i g u e on the c o n n e c t i o n s . b) A l a r g e number of s i m i l a r connections  should be t e s t e d  in order to e s t a b l i s h a s t r e n g t h d i s t r i b u t i o n . c) Connections  should be t e s t e d under c y c l i c  l o a d i n g while  a p e r p e n d i c u l a r f o r c e i s simultaneously a p p l i e d to the c o n n e c t i o n . T h i s p e r p e n d i c u l a r f o r c e should be a p p l i e d p e r p e n d i c u l a r to the plane of the f l a n g e , and i n the plane of the f l a n g e , p e r p e n d i c u l a r to the edge (see forces  and P , F i g u r e 6 . 9 . ) . 2  combined a p p l i c a t i o n of these  The e f f e c t of the  f o r c e s should a l s o be  i n v e s t i g a t e d . Both the a b i l i t y of the connection to resist  these  f o r c e s and t h e i r e f f e c t on the shear  c a p a c i t y are important understood.  and need to be b e t t e r  212  F i g u r e 6.9. Forces p e r p e n d i c u l a r to c o n n e c t i o n .  213  REFERENCES  1.  S.V. Polyakov et a l . . I n v e s t i g a t i o n i n t o Eartquake R e s i s t a n c e of Large Panel B u i l d i n g s . Proc. F o u r t h World Conference on Earthquake E n g i n e e r i n g , Santiago, C h i l e 1969, V o l . 1.  2.  PCI Design Handbook. 3rd Ed., P r e s t r e s s e d Concrete I n s t i t u t e , Chicago, 1985.  3.  M e t r i c Design Handbook. 1st Ed., Canadian Concrete I n s t i t u t e , Ottawa, 1982.  4.  R.A. Spencer. Earthquake R e s i s t a n t Connections f o r Low Rise P r e c a s t Concrete B u i l d i n g s . Seminar on P r e c a s t Concrete C o n s t r u c t i o n i n Seismic Zones, Tokyo, October 27-31, 1986, pp. 61-81.  5.  R.A. Spencer and W.K.T. Tong. Design of a One-Story Precast Concrete B u i l d i n g f o r Earthquake Loading. Proc. E i g h t World Conference on Earthquake E n g i n e e r i n g , San F r a n c i s c o 1984, pp. V o l V, pp. 653-660.  6.  J.M. Becker and C. L o r e n t e . Seismic Design of P r e c a s t Concrete Panel B u i l d i n g s . Proc. Workshop on Earthquake R e s i s t a n t R e i n f o r c e d Concrete B u i l d i n g C o n s t r u c t i o n , U n i v e r s i t y of C a l i f o r n i a at Berkeley, J u l y , 1977.  7.  L.D. M a r t i n and W.J. Korkosz. Connections f o r P r e c a s t P r e s t r e s s e d Concrete B u i l d i n g s . T e c h n i c a l Report No. 2, P r e s t r e s s e d Concrete I n s t i t u t e , Chicago, March, 1982.  8.  A. Aswad. S e l e c t e d P r e c a s t Connections: Low-Cycle Behaviour and S t r e n g t h , Proc. 2nd U.S. N a t i o n a l Conference on Earthquake E n g i n e e r i n g , S t a n f o r d U n i v e r s i t y , C a l i f o r n i a , August 22-24, 1979.  9.  W.F. Dawson and M. Shemie. B o l t e d Connections as a S u b s t i t u t e f o r on S i t e Welding and Wet J o i n t s i n Precast Concrete. Proc. Canadian S t r u c t u r a l Concrete Conference, Ottawa 1977, pp. 269-289.  10.  R.A. Spencer and D.S. N e i l l e . C y c l i c T e s t s of Welded H e a d e d S t u d Connections. PCI J o u r n a l , May-June, 1976, V o l . 15, No. 1, pp. 67-78.  Prestressed  214 11.  N.M. Hawkins. S t a t e - o f - t h e - A r t Report on Seismic R e s i s t a n c e of P r e s t r e s s e d and P r e c a s t Concrete S t r u c t u r e s : Part 2 - P r e c a s t Concrete, PCI J o u r n a l , January-February, 1978, V o l . 23, No. 1, pp. 40-58.  12.  R.P. Saxena. An Experimental I n v e s t i g a t i o n of a P r e c a s t Concrete Connection. M.Ap.Sc. T h e s i s , Department of C i v i l E n g i n e e r i n g , U.B.C., September 1983.  13.  T. Paulay, M.J.N. P r i e s t l e y and A . J . Synge. D u c t i l i t y i n Earthquake R e s i s t i n g Squat S h e a r w a l l s . ACI J o u r n a l , July-August, 1982, V o l . 79, No. 4, pp. 257-269.  

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