Seismic Response of Wood Shearwalls with Oversized Oriented Strand Board Panels
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SEISMIC RESPONSE OF WOOD SHEARWALLS WITH OVERSIZED ORIENTED STRAND BOARD PANELS by JENNIFER PATRICIA DURHAM BA.Sc, The University of British Columbia, 1995 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Civil Engineering We accept this thesis as conforming to the reauired standard , THE UNIVERSITY OF BRITISH COLUMBIA October, 1998 © Jennifer Patricia Durham, 1998 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of C'V't- £/u6-( >Q&fa£WC- The University of British Columbia Vancouver, Canada Date HCXJfcH66/^ ^ (^9g DE-6 (2/88) Abstract This thesis reports on an experimental study on the earthquake/seismic resistance of wood based shearwalls sheathed with oversized oriented strand board panels. This work extends from a previous study on walls subjected to quasi-static cyclic loading regimes by investigating the dynamic behaviour of this new wall system on a shake table. Monotonic, cyclic quasi-static and dynamic loading tests that included an applied dead load were performed on 2.44 m x 2.44 m shearwalls with standard (1.22 m x 2.44 m) and oversize (2.44 m x 2.44 m) oriented strand board panels. Measured and calculated properties for the 14 test walls are presented, which include the following: strength, stiffness and ductility values; energy dissipation values; and failure modes. This information was used to draw conclusions on the influence of panel size and panel-to-frame nail connection spacing on the behaviour of the shearwalls. Shearwalls constructed with single oversized panels (Type B) had an increase in capacity of 26% over regular walls (Type A) as measured by the maximum load reached in monotonic tests. Shearwalls constructed with single oversized panels and reduced nail spacing around the panel edges (Type C) had an increase in capacity of 104% over regular panel walls. The maximum loads measured in cyclic tests and the maximum base shears calculated in dynamic tests were in excellent agreement with the monotonic peak loads. Seismic Response of Wood Shearwalls with Oversized Oriented Strand Board Panels ii Abstract iii In dynamic testing, the Type C walls were not significantly damaged when subjected to the same ground motion that brought the Types A and B walls to failure. The wall with the oversized panel and reduced nail spacing was subsequently failed when subjected to the same ground motion scaled to a higher peak ground acceleration. Single oversized panel walls with reduced nail spacing dissipated roughly twice as much energy compared to the other two wall types whether tested cyclically or dynamically. Nail withdrawal was the dominant failure mode in all test types. A newly developed, relatively short cyclic test protocol was successful in producing the failure modes compatible with the failure modes observed in dynamic tests. Seismic Response of Wood Shearwalls with Oversized Oriented Strand Board Panels Table of Contents Abstract ii Table of Contents iv List of Tables vi List of Figures vii Acknowledgements x CHAPTER 1 Introduction 1 Objectives 6 Methodology 6 Organization 7 CHAPTER 2 Background 8 Function and Construction ofWood-based Shearwalls 8 Review of Shearwall Research 10 Monotonic and Static-Cyclic Testing 12 Procedures 12 Geometry 14 Precursory Work 15 Dynamic Testing 17 Connections 20 Modelling 22 Monotonic Models 23 Dynamic Models 27 Oriented Strand Board (OSB) 32 CHAPTER 3 Methodology 34 Analytical Studies 34 Seismic Response of Wood Shearwalls with Oversized Oriented Strand Board Panels iv Table of Contents v Analytical Program 35 Procedures 38 Static Tests 41 Setup 41 Procedures 43 Dynamic Tests 47 Setup 47 Procedures 49 CHAPTER 4 Analyses 55 Modified Program and Verification 55 CHAPTERS Test Results and Discussion 61 Static Tests 61 Results 61 Discussion 68 Dynamic Tests 72 Results 72 Analysis 80 Discussion 99 Summary 110 CHAPTER 6 Conclusions and Recommendations 112 Bibliography 116 Appendix A Dynamic Test Frame Schematics .... 123 Appendix B Analyses 125 Experimental Planning Studies 125 Sensitivity Studies 131 Comparison of Experiment Results and Analysis Results ...134 Summary 139 Seismic Response of Wood Shearwalls with Oversized Oriented Strand Board Panels List of Tables Table 3.1 Nail model parameters from SWAP 37 Table 3.2 Nail parameters for 2.67 mm dia., 50 mm long spiral nails 39 Table 3.3 List of tests with wall descriptions 54 Table 4.1 Modified SWAP results compared with original SWAP example results 56 Table 4.2 Analyses replicating experimental test by Dolan (1989) 58 Table 5.1 Results from static tests 62 Table 5.2 Summary: Analysis of static testing results 69 Table 5.3 Dynamic test results 75 Table 5.4 Summary: Analysis of dynamic testing results. 101 Table 5.5 Deviation of calculated dynamic peak shear from measured cyclic peak shear for each wall type. 102 Table 5.6 Energy dissipation for walls tested cyclically and dynamically 110 Table B.l Characteristics of analysis input accelerograms. 126 Table B.2 Analyses for planning experimental testing program 127 Table B.3 Analyses for completing sensitivity studies 134 Table B.4 Comparison between analytical and experimental first natural frequencies 135 Seismic Response of Wood Shearwalls with Oversized Oriented Strand Board Panels vi List of Figures Figure 2.1 Load-slip relationship for connectors in Foschi's model (1977) described by Equation 2.1 23 Figure 2.2 Shearwall model by Tuomi and McCutcheon (1978) 24 Figure 2.3 Shearwall model by Easly et al. (1982) 25 Figure 2.4 Shearwall model by Gupta and Kuo (1985) 26 Figure 2.5 Typical pinching of hysteresis loops in timber structures (highlighted) 27 Figure 3.1 Frame and panel displacement assumptions in SWAP 35 Figure 3.2 Nail model parameters from SWAP 37 Figure 3.3 East-West accelerogram from Joshua Tree Station - 1992 Landers California Earthquake 40 Figure 3.4 Static test setup schematic for 7.3 m wall (He, 1997) and photograph of 2.44 m wall in the setup 42 Figure 3.5 Cyclic testing protocol 45 Figure 3.6 Standard hold down attached to test wall 47 Figure 3.7 Schematic and photograph of dynamic test setup. 50 Figure 3.8 Close-ups of dead load pulley system 51 Figure 4.1 Drift results for Dolan (1989) wall input analyzed with modified SWAP 58 Figure 4.2 Comparison of drift time histories from a previous experiment (Latendresse and Ventura, 1995; Durham et al., 1996) and from the modified version of SWAP 59 Figure 5.1 Uplift during Test 1 63 Figure 5.2 Nails pulling out of the frame and pulling through the sheathing in Test 2 64 Figure 5.3 Test 4. a) Separation of sheathing and frame prior to test, b) Failure and relative movement at blocking. 65 Figure 5.4 Test 6 a) Bottom of studs bending after peak load was reached, b) Split stud at bottom corner 67 Figure 5.5 Failure along blocking in Test 8. Top panels show more damage 67 Seismic Response of Wood Shearwalls with Oversized Oriented Strand Board Panels vii List of Figures viii Figure 5.6 Load vs. drift curves for monotonic tests 71 Figure 5.7 Load vs. drift curves for cyclic tests compared to monotonic tests 73 Figure 5.8 Deviation of cable force from approximately 5.56 kN 74 Figure 5.9 First lateral natural frequency for wall with dead load in Test 11 76 Figure 5.10 Test 10b: a) Nail fatigue failures, b) Nails pull- through failures 77 Figure 5.11 Tests 10a, 10b, 1 Or: a) Damaged stud, b) Poor quality damaged stud, c) Minimal crushing at hold down connection 78 Figure 5.12 Crushing of panels in Test 14 80 Figure 5.13 Frame model for force calculations 81 Figure 5.14 Free body diagram of inertial mass K 84 Figure 5.15 Free body diagram of inertial mass platform 85 Figure 5.16 Free body diagram of vertical supports for inertial mass 87 Figure 5.17 Free body diagrams to determine the shear force transferred from the load transfer beam of the frame to the wall 90 Figure 5.18 Free body diagram of the shake table platform. Resultant forces in the link supports under the platform must be in the direction of the links at all times 91 Figure 5.19 Verification of earthquake input and measurements for Test 10a 98 Figure 5.20 Drift time histories for tests with 0.35 g peak ground acceleration 105 Figure 5.21 Acceleration time histories for tests with 0.35 g peak ground acceleration 106 Figure 5.22 Drift time histories for tests with 0.52 g peak ground acceleration 107 Figure 5.23 Acceleration time histories for tests with 0.52 g peak ground acceleration 107 Figure 5.24 Hysteresis loop for Test 11 (Type A), assuming 1% damping 108 Figure A.l Front view schematic of dynamic testing frame (measurements in mm) 123 Seismic Response of Wood Shearwalls with Oversized Oriented Strand Board Panels List of Figures Figure A.2 Side view schematic of dynamic testing frame (measurements in mm) 124 Figure B. 1 Drift time histories for Type A and Type C walls with different lengths 128 Figure B.2 Acceleration time histories for Type A and Type C walls with different lengths 129 Figure B.3 Changes in slope occur at the peak of each hysteresis loop (highlighted) 130 Figure B.4 Drift time histories showing the effect of varying the damping ratio in analyses of Type C walls 132 Figure B.5 Comparison between analytical and experimental monotonic behaviour 136 Figure B.6 Drift and acceleration response comparisons of analytical and experimental results for a Type C wall 138 Seismic Response of Wood Shearwalls with Oversized Oriented Strand Board Panels Acknowledgments "He who walks with the wise grows wise..." Proverbs 13:20, New International Version I would like to express my sincere thanks to all those who have provided help, advice and encouragement to me during the completion of this thesis.