Applied Science, Faculty of
Engineering, School of (Okanagan)
DSpace
UBCO
Saud, Deepak
Master of Applied Science - MASc
University of British Columbia
The jointed post-tensioned Precast Concrete (PC) shear walls are designed to rock around their base and self-center themselves upon unloading. One way to enhance ductility is by allowing controlled rocking at the wall-to-foundation connection using unbonded Post-tensioning (PT) tendons and mild steel rebars as energy dissipators in PC shear wall buildings. However, this jointed connection system is complex to build and time-consuming. Also, the jointed connection with grouted metal duct connections with deformed steel rebar as dowel rebar has limited ductility. A particular unknown exists about the force deformation capacity of grouted dowel connection. This thesis aims to investigate the local behavior of the PC wall through a novel connection using shape memory alloy (SMA) rebar and couplers. The study started with a numerical study to investigate the effects of various parameters (aspect ratio, axial load ratio, rebar types, and vertical reinforcement ratio) on the seismic response of the concrete shear walls reinforced with SMA bars at the base. Fifty-four finite element models of the RC walls reinforced with SMA rebars and steel were developed. The results were analyzed to evaluate the seismic behavior of SMA RC walls, which improved the understanding of SMA PC walls. Additionally, four coupler pullout tests and seven pullout tests of rebar in concrete blocks were carried out to investigate the effectiveness of the anchorage of the SMA rebar connected with the coupler and surrounding grout within a metal duct. The test results ensured the rebar was stressed beyond the superelastic strain range with very low slippage. Finally, three small-scale wall-to-wall connection test specimens were constructed and tested under monotonic loading to investigate the force-deformation response of the proposed anchoring system for SMA-reinforced PC wall-to-wall intersections. The result shows that specimens with the proposed connection consisting of SMA and couplers present higher yield displacement, yield and ultimate load capacity, and hardening ratio compared to the specimens with steel and couplers.
EXPERIMENTAL STUDY OF SHAPE MEMORY ALLOY CONNECTION IN PRECAST CONCRETE SHEAR WALLS FOR SEISMIC APPLICATIONS by Deepak Saud B.Tech., Motilal Nehru National Institute of Technology, 2012 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE COLLEGE OF GRADUATE STUDIES (Civil Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Okanagan) October 2024 © Deepak Saud, 2024 ii The following individuals certify that they have read, and recommend to the College of Graduate Studies for acceptance, a thesis entitled: EXPERIMENTAL STUDY OF SHAPE MEMORY ALLOY CONNECTION IN PRECAST CONCRETE SHEAR WALLS FOR SEISMIC APPLICATIONS submitted by Deepak Saud in partial fulfillment of the requirements of the degree of Master of Applied Science. Dr. Lisa Tobber, School of Engineering Supervisor Dr. M. Shahria Alam, School of Engineering Co-Supervisor Dr. Ahmad Rteil, School of Engineering Supervisory Committee Member Dr. Qian Chen, School of Engineering Supervisory Committee Member Dr. Mohamed Shehata, School of Engineering University Examiner iii Abstract The jointed post-tensioned Precast Concrete (PC) shear walls are designed to rock around their base and self-center themselves upon unloading. One way to enhance ductility is by allowing controlled rocking at the wall-to-foundation connection using unbonded Post-tensioning (PT) tendons and mild steel rebars as energy dissipators in PC shear wall buildings. However, this jointed connection system is complex to build and time-consuming. Also, the jointed connection with grouted metal duct connections with deformed steel rebar as dowel rebar has limited ductility. A particular unknown exists about the force deformation capacity of grouted dowel connection. This thesis aims to investigate the local behavior of the PC wall through a novel connection using shape memory alloy (SMA) rebar and couplers. The study started with a numerical study to investigate the effects of various parameters (aspect ratio, axial load ratio, rebar types, and vertical reinforcement ratio) on the seismic response of the concrete shear walls reinforced with SMA bars at the base. Fifty-four finite element models of the RC walls reinforced with SMA rebars and steel were developed. The results were analyzed to evaluate the seismic behavior of SMA RC walls, which improved the understanding of SMA PC walls. Additionally, four coupler pullout tests and seven pullout tests of rebar in concrete blocks were carried out to investigate the effectiveness of the anchorage of the SMA rebar connected with the coupler and surrounding grout within a metal duct. The test results ensured the rebar was stressed beyond the superelastic strain range with very low slippage. Finally, three small-scale wall-to-wall connection test specimens were constructed and tested under monotonic loading to investigate the force-deformation response of the proposed anchoring system for SMA-reinforced PC wall-to-wall intersections. The result shows that iv specimens with the proposed connection consisting of SMA and couplers present higher yield displacement, yield and ultimate load capacity, and hardening ratio compared to the specimens with steel and couplers. v Lay Summary Precast concrete (PC) building construction offers several advantages over traditional cast-in-place methods. These benefits include faster construction speed, improved quality, enhanced durability, and easier assembly on construction sites. The seismic performance of a PC shear wall building largely depends on the connections between the precast concrete elements, such as shear walls. This thesis proposes a novel connection using shape memory alloy (SMA) rebar and couplers for the PC shear wall to enhance building resilience. Various tests were conducted to investigate the local behavior of the PC shear wall using the proposed connection. The findings showed that the proposed connection presents a promising performance in seismic applications. vi Preface The research findings presented in this thesis were carried out by Deepak Saud under the supervision and guidance of Dr. Lisa Tobber and Dr. M. Shahria Alam at the University of British Columbia, Okanagan. It is worth noting that parts of the chapters of this thesis will be submitted for publication, as evidenced by the following list. Generative artificial intelligence (AI) was not used in the research work for any aspect of this thesis. Conference paper Parts of Chapter 3 were developed into a conference paper that I presented at the Canadian Society of Civil Engineering (CSCE) Conference in Whistler in May 2022. • Saud, D., Tobber, L., and Alam, M.S. (2022). Parametric study of slender shear walls reinforced with shape memory alloy bars. Proceedings of the Annual Conference of Canadian Society of Civil Engineering (CSCE) May 2022, Whistler, Canada. Journal paper Parts of the Chapters 5 and 6 were developed into a journal paper currently under preparation. • Saud, D., Tobber, L., Alam, M. S., Ahmadi M. H. and Zhou, L. (2024). Experimental study of shape memory alloy (SMA) connection in precast concrete shear walls for seismic applications. (Under preparation). vii Table of Contents Abstract ......................................................................................................................................... iii Lay Summary .................................................................................................................................v Preface ........................................................................................................................................... vi Table of Contents ........................................................................................................................ vii List of Tables ................................................................................................................................ xi List of Figures .............................................................................................................................. xii List of Symbols .......................................................................................................................... xvii List of Abbreviations ...................................................................................................................xx Acknowledgements .................................................................................................................... xxi Dedication ................................................................................................................................. xxiii Chapter 1: Introduction ................................................................................................................1 1.1 Background ..................................................................................................................... 1 1.2 Research goal and objectives .......................................................................................... 6 1.3 Thesis organization ......................................................................................................... 7 Chapter 2: Literature Review .......................................................................................................9 2.1 Introduction ..................................................................................................................... 9 2.2 Shape Memory Alloy .................................................................................................... 10 2.3 SMA in RC walls .......................................................................................................... 13 2.4 Ductile jointed PC walls ............................................................................................... 16 2.5 Summary ....................................................................................................................... 20 Chapter 3: Numerical Study on RC Walls Reinforced with SMA Rebars .............................21 viii 3.1 Introduction ................................................................................................................... 21 3.2 Numerical modelling .................................................................................................... 21 3.3 Modelling parameters ................................................................................................... 23 3.4 Result ............................................................................................................................ 26 3.4.1 Hysteretic response and trend ............................................................................... 26 3.4.2 Effect of reinforcement ratio ................................................................................. 31 3.5 Summary ....................................................................................................................... 34 Chapter 4: Design of the Novel SMA PC Wall Connection .....................................................36 4.1 Introduction ................................................................................................................... 36 4.2 Proposed system............................................................................................................ 36 4.2.1 Monotonic response of proposed wall system ...................................................... 38 4.2.2 Metal duct size and SMA length ........................................................................... 49 4.2.3 Load transfer mechanism and SMA coupler anchor ............................................. 50 4.3 Shear design across horizontal joints ............................................................................ 53 4.4 Summary ....................................................................................................................... 54 Chapter 5: Experimental Program ............................................................................................56 5.1 Introduction ................................................................................................................... 56 5.2 Material properties ........................................................................................................ 58 5.2.1 Steel rebar ............................................................................................................. 58 5.2.2 SMA rebar ............................................................................................................. 60 5.2.3 Concrete ................................................................................................................ 64 5.2.4 Grout ..................................................................................................................... 64 5.3 Coupler pullout test ....................................................................................................... 65 ix 5.3.1 Construction of the coupler pullout specimen ...................................................... 65 5.3.2 Test setup and instrumentation of the coupler pullout test ................................... 68 5.3.3 Expected result of the coupler pullout test ............................................................ 71 5.4 Pullout test of rebar in a concrete block ........................................................................ 72 5.4.1 Construction of the pullout test of rebar in a concrete block specimen ................ 72 5.4.2 Test setup and instrumentation of the pullout test of rebar in a concrete block ... 75 5.4.3 Issues during the pullout test of rebar in a concrete block .................................... 77 5.4.4 Expected result of the pullout test of rebar in a concrete block ............................ 78 5.5 Wall-to-wall connection test ......................................................................................... 78 5.5.1 Construction of the wall-to-wall connection specimen ........................................ 80 5.5.2 Test setup .............................................................................................................. 84 5.5.3 Loading protocol ................................................................................................... 85 5.5.4 Instrumentation ..................................................................................................... 86 5.5.5 Expected result of the wall-to-wall connection test .............................................. 89 5.5.6 Cost of SMA specimen ......................................................................................... 91 5.6 Summary ....................................................................................................................... 92 Chapter 6: Test Results and Discussion .....................................................................................93 6.1 Introduction ................................................................................................................... 93 6.2 Coupler pullout test results ........................................................................................... 93 6.3 Pullout test of rebar in a concrete block results .......................................................... 102 6.4 Wall-to-wall connection test results ............................................................................ 108 6.4.1 General response and failure modes ................................................................... 112 6.4.2 Force-displacement response .............................................................................. 115 x 6.5 Summary ..................................................................................................................... 120 Chapter 7: Conclusions and Recommendations .....................................................................123 7.1 Summary and conclusion ............................................................................................ 123 7.2 Limitations .................................................................................................................. 126 7.3 Research contribution ................................................................................................. 127 7.4 Recommendation for future study .............................................................................. 128 Bibliography ...............................................................................................................................129 Appendices ..................................................................................................................................138 Appendix A: Pictures from experimental testing .................................................................... 138 Appendix B: Pictures from material testing ............................................................................ 142 Appendix C: Mill certificates .................................................................................................. 145 Appendix D: Calculations ....................................................................................................... 152 xi List of Tables Table 2.1: List of experimental tests conducted on SMA RC shear wall ..................................... 16 Table 3.1: Parameters to study ...................................................................................................... 24 Table 3.2: Mechanical properties of SMA .................................................................................... 25 Table 5.1: Company provided steel rebar properties (Rebar Type 1) ........................................... 59 Table 5.2: Steel rebar properties (Rebar Type 1) .......................................................................... 59 Table 5.3: Steel rebar properties (Rebar Type 2) .......................................................................... 59 Table 5.4: Company provided NiTi properties (Mill certificate 1) .............................................. 61 Table 5.5: Company provided NiTi properties (Mill certificate 2) .............................................. 61 Table 5.6: NiTi properties ............................................................................................................. 62 Table 5.7: Coupler pullout test matrix .......................................................................................... 69 Table 5.8: Expected performance during coupler pullout test ...................................................... 72 Table 5.9: Pullout test of rebar in a concrete block matrix ........................................................... 77 Table 5.10: Expected performance during pullout test of rebar in a concrete block .................... 78 Table 5.11: Wall-to-wall connection test matrix .......................................................................... 84 Table 5.12: Expected performance during the wall-to-wall connection test ................................ 90 Table 6.1: Coupler pullout test results .......................................................................................... 94 Table 6.2: Pullout test of rebar in a concrete block results ......................................................... 103 Table 6.3: Wall-to-wall connection test results .......................................................................... 111 xii List of Figures Figure 1.1: Grouted dowel connection at a wall-to-foundation intersection (adapted from Seifi and Henry, 2019) ................................................................................................................................... 3 Figure 2.1: NiTi rebar ................................................................................................................... 11 Figure 2.2: 1D-superelastic model of SMA incorporated in FE Packages (adapted from Auricchio et al. 1997) ................................................................................................................... 12 Figure 2.3: Coupler ....................................................................................................................... 13 Figure 2.4: Gap opening at the wall foundation intersection ........................................................ 17 Figure 2.5: Flag-shaped hysteresis for a hybrid wall system ........................................................ 18 Figure 3.1: (a) Applied loading protocol (b) numerical model ..................................................... 22 Figure 3.2: Cross-section of wall model ....................................................................................... 25 Figure 3.3: Hysteresis trend for same aspect ratio and axial load ratio with varying rebar size (R = rebar size; A = aspect ratio; P = axial load ratio) ....................................................................... 27 Figure 3.4: Hysteresis trend for same rebar size and axial load ratio with varying aspect ratio (R = rebar size; A = aspect ratio; P = axial load ratio) ....................................................................... 29 Figure 3.5: Hysteresis trend for same rebar size and aspect ratio with varying axial load ratio (R = rebar size; A = aspect ratio; P = axial load ratio) ....................................................................... 30 Figure 3.6: Residual drift vs vertical reinforcement ratio ............................................................. 32 Figure 3.7: Normalized energy dissipation vs vertical reinforcement ratio .................................. 33 Figure 3.8: Drift at strength loss (θ80%) vs vertical reinforcement ratio ....................................... 34 Figure 4.1: (a) Proposed connection at wall-to-foundation intersection (b) flag-shaped hysteresis for the proposed system ................................................................................................................ 38 xiii Figure 4.2: Expected pushover response of the proposed system ................................................ 39 Figure 4.3: Yield point calculation ............................................................................................... 43 Figure 4.4: Ultimate point calculation (concrete crushing failure) ............................................... 46 Figure 4.5: Ultimate point calculation (rebar failure) ................................................................... 48 Figure 4.6: Load transfer from wall to connection ....................................................................... 51 Figure 4.7: Tensile force transfer from steel rebar to SMA rebar ................................................ 51 Figure 4.8: (a) Schematic of proposed anchor (b) SMA and coupler anchor (c) steel and coupler anchor ............................................................................................................................................ 53 Figure 5.1: (a) Coupler pullout test (b) pullout test of rebar in a concrete block (c) wall-to-wall connection test .............................................................................................................................. 57 Figure 5.2: Sample stress-strain response of a 12.7 mm smooth steel rebar (Type 1) ................. 60 Figure 5.3: SMA dogbone............................................................................................................. 63 Figure 5.4: SMA dogbone tensile test ........................................................................................... 63 Figure 5.5: Stress-strain response of SMA dogbone .................................................................... 64 Figure 5.6: (a) Coupler pullout specimen (a) detailing (b) SMA and coupler (c) steel and coupler....................................................................................................................................................... 66 Figure 5.7: SMA and coupler anchor preparation ........................................................................ 67 Figure 5.8: Pullout apparatus ........................................................................................................ 70 Figure 5.9: Coupler pullout test setup: (a) schematic (b) specimen in MTS 370 machine ........... 71 Figure 5.10: Pullout of rebar in a concrete block specimen (a) SMA and coupler (b) steel and coupler ........................................................................................................................................... 73 Figure 5.11: Pullout of rebar in a concrete block specimen detailing: (a) without ties (b) with ties....................................................................................................................................................... 74 xiv Figure 5.12: Pullout of rebar in a concrete block test setup: (a) schematic (b) specimen in MTS 370 machine .................................................................................................................................. 76 Figure 5.13: Walls connected with the proposed connection ....................................................... 79 Figure 5.14: Wall-to-wall connection specimen detailing ............................................................ 81 Figure 5.15: Construction steps .................................................................................................... 82 Figure 5.16: Wall-to-wall connection test specimens (a) CT1_SMA and CT3_Steel (b) CT2_SMA ..................................................................................................................................... 83 Figure 5.17: Wall-to-wall connection test setup: (a) schematic (b) specimen in MTS 370 machine....................................................................................................................................................... 85 Figure 5.18: Wire sensors position for CT1_SMA, CT2_SMA and CT3_Steel .......................... 87 Figure 5.19: LVDTs position for CT1_SMA and CT3_Steel ....................................................... 88 Figure 5.20: LVDTs position for CT2_SMA ............................................................................... 89 Figure 6.1: Rebar stress vs axial strain (CPT1_SMA and CPT2_SMA) ...................................... 95 Figure 6.2: (a) CPT1_SMA indentation on the SMA rebar and (b) location of rebar fracture inside the coupler .......................................................................................................................... 96 Figure 6.3: Rebar stress vs rebar slip (CPT1_SMA and CPT2_SMA) ......................................... 97 Figure 6.4: Rebar stress vs axial strain (CPT3_Steel and CPT4_Steel) ....................................... 98 Figure 6.5: Rebar stress vs rebar slip (CPT3_Steel and CPT4_Steel) .......................................... 99 Figure 6.6: Rebar stress vs axial strain (CPT2_SMA and CPT3_Steel) ..................................... 100 Figure 6.7: Top of the specimens after testing (a) CPT1_SMA (b) CPT2_SMA (c) CPT3_Steel (d) CPT4_Steel ............................................................................................................................ 101 Figure 6.8: (a) CPT1_SMA - premature failure (b) CPT2_SMA (c) CPT3_Steel (d) CPT4_Steel - ductile failure mode .................................................................................................................... 102 xv Figure 6.9: Rebar stress vs rebar slip (PT1_SMA and PT2_SMA_T) ....................................... 104 Figure 6.10: Rebar stress vs rebar elongation (PT1_SMA and PT2_SMA_T) .......................... 105 Figure 6.11: Top of the specimen after testing (a) PT1_SMA (b) PT2_SMA_T ....................... 106 Figure 6.12: Rebar stress vs rebar slip (PT3_Steel and PT4_Steel) ........................................... 107 Figure 6.13: Rebar stress vs rebar slip (PT5_Steel, PT6_Steel_T and PT7_Steel_T) ................ 108 Figure 6.14: Crack pattern for CT1_SMA specimen .................................................................. 113 Figure 6.15: Crack pattern for CT2_SMA specimen .................................................................. 114 Figure 6.16: Crack pattern for CT3_Steel specimen .................................................................. 115 Figure 6.17: Force-displacement response of CT1_SMA .......................................................... 117 Figure 6.18: Force-displacement response of CT2_SMA .......................................................... 118 Figure 6.19: Force-displacement response of CT3_Steel ........................................................... 119 Figure 6.20: Normalized force-elongation response ................................................................... 120 Figure A.1: Coupler pullout test (LVDT 1 touching the SMA rebar top) .................................. 138 Figure A.2: Pullout test of a rebar in a concrete block (a) top view (b) LVDT 1 touching the SMA rebar top during the testing ................................................................................................ 138 Figure A.3: Wall-to-wall connection test specimen left overnight in the MTS 370 machine .... 139 Figure A.4: LVDT position of wall-to-wall connection test specimen on (a) left (b) right side 140 Figure A.5: Failure mode and location (a) PT1_SMA – rebar slippage failure (b) PT2_SMA_T – rebar fracture failure (c) CT1_SMA – rebar slippage failure (d) CT2_SMA – rebar fracture ... 141 Figure B.1: Sample concrete cylinder for compressive strength test .......................................... 142 Figure B.2: Sample concrete cylinder for tensile test ................................................................. 142 Figure B.3: Grout cube compressive test .................................................................................... 143 Figure B.4: Steel rebar tensile test .............................................................................................. 143 xvi Figure B.5: SMA rebar tensile test ............................................................................................. 144 Figure C.1: 12.7 mm SMA mill certificate 1 (page 1) ................................................................ 145 Figure C.2: 12.7 mm SMA mill certificate 1 (page 2) ................................................................ 146 Figure C.3: 12.7 mm SMA mill certificate 2 .............................................................................. 147 Figure C.4: 12.7 mm smooth steel rebar mill certificate ............................................................ 148 Figure C.5: 10M steel rebar mill certificate ................................................................................ 149 Figure C.6: 16 mm steel plate mill certificate ............................................................................. 150 Figure C.7: Concrete mix design certificate ............................................................................... 151 xvii List of Symbols A = Aspect ratio Af = Austenite finish temperature of SMA Ag = Area of wall As = Area of rebar As = Austenite starting temperature of SMA b = Width of wall c = Neutral axis depth Cr = Equivalent compression force in concrete dc = diameter of coupler dm = diameter of metal duct E = Modulus of elasticity Ec = Modulus of elasticity of concrete Es = Modulus of elasticity of steel f'c = Compressive strength of concrete fc = Concrete compressive stress corresponding to ec fP1 = Austenite-to-martensite finishing stress of SMA Fe = Resultant lateral force Fr = Decompression force Fs = Force in rebar corresponding to fs fs = Stress in steel corresponding to es fT1 = Martensite-to-austenite starting stress of SMA xviii fT2 = Martensite-to-austenite finishing stress of SMA Fu = Ultimate force fu = Ultimate stress of rebar Fue = Estimated ultimate force Fy = Yield force fy = Yield stress of rebar fy-SMA = Austenite-to-martensite starting stress of SMA Fye = Estimated yield force H = Height of wall he = Height of wall at which resultant lateral force acts I = Moment of inertia Ki = Initial stiffness Kp = Post-yield stiffness L = Length of wall le = Length of energy dissipator Lm = Length of metal duct Md = Decompression moment N = Number of shear friction connections P = Axial load ratio Pf = Axial load V = Shear force Vmax = Maximum shear force Vr = Shear friction capacity at the horizontal joint xix θ80% = Cyclic degradation rotation ρv = Vertical reinforcement ratio f! = Material resistance factor for concrete c" = Cohesion stress s = Axial stress µ = Coefficient of friction l = Factor to account for low-density concrete µ = Ductility ratio d = elongation in SMA rebar g = Hardening ratio D = Lateral displacement q = wall drift (%) ec = Strain of concrete in compression ecu = Concrete crushing strain Dmax = Maximum lateral displacement Dr = Displacement at decompression force es = Strain of steel in tension Du = Ultimate displacement eu = Ultimate strain due = Estimated ultimate displacement Dy = Yield displacement ey = Yield strain xx List of Abbreviations ACI = American Concrete Institute ALAMS = Applied Laboratory for Advanced Materials & Structures ASSET = Advanced Structural Simulation & Experimental Testing ASTM = American Society for Testing and Materials CPCI = Canadian Precast / Prestressed Concrete Institutes CSA = Canadian Standards Association LVDT = Linear Variable Displacement Transducer NZS = New Zealand Standard NBCC = National Building Code of Canada NiTi = Nickel-Titanium / Nitinol PC = Precast Concrete PCI = Precast Concrete Institutes PT = Post-Tensioning PVC = Polyvinyl Chloride Plastic RC = Reinforced Concrete SMA = Shape Memory Alloy WS = Wire Sensors °C = Celsius xxi Acknowledgements I would like to express my sincere gratitude to my supervisors, Dr. Lisa Tobber and Dr. M. Shahria Alam, for their immense support and guidance during my M.A.Sc. studies. Furthermore, I would like to thank them for believing in me and providing me with the opportunity to pursue my graduate studies at the University of British Columbia. I am truly grateful for the inspiration and motivation they gave me to complete this work successfully. I would like to thank my supervisory committee members, Dr. Ahmad Rtiel and Dr. Qian Chen, for their valuable guidance and feedback. Their expertise and input have been invaluable in enhancing the quality of this thesis. I was privileged to be a member of two excellent research groups: the ASSET (Advanced Structural Simulation & Experimental Testing) group, led by Dr. Lisa Tobber, and the Applied Laboratory for Advanced Materials & Structures (ALAMS) group, led by Dr. Shahria Alam. I would like to thank all my fellow research mates for providing me with great research ideas while making my academic journey enjoyable and exciting. Moreover, I would like to acknowledge the financial support provided by the University of British Columbia through the University Graduate Fellowship, NSERC, CPCI and Mitacs Canada. Also, I would like to thank James Lockwood, Senior Engineer and Project Development Lead at Rapid-Span Structures, for providing support and guidance during the construction of specimens. xxii Lastly, I would like to express my deepest appreciation to my family for their love, support, and understanding throughout this academic journey. I am especially grateful to my wife, Anita Bhandari, for her constant encouragement, presence and love. xxiii Dedication I would like to dedicate this thesis to my family. 1 Chapter 1: Introduction 1.1 Background The precast concrete (PC) building construction method involves casting concrete elements in a controlled environment in certified precast plants. The concrete elements are then transported to the construction sites and assembled using connections to make buildings. This construction method has many advantages compared to the conventional cast-in-place methods due to its quality, durability, and ease of assembly on construction sites (CPCI, 2017). British Columbia and other parts of Canada are currently facing a housing shortage. Therefore, the need for rapid construction solutions is pressing. PC construction has emerged as a promising solution to address some of Canada’s urgent housing needs. Unlike cast-in-place construction methods, which can be time-consuming, PC construction significantly speeds up the construction process. This faster construction with PC can help meet the urgent demand for buildings. Furthermore, PC construction ensures high-quality and consistent concrete elements, making it a viable solution for Canada's building demand. In addition to rapid construction, buildings must be designed for seismic safety. British Columbia is situated in regions that are prone to significant seismic activities. As a result, buildings in British Columbia must be designed with strong lateral force-resisting systems to withstand the forces generated by earthquakes. One of the most commonly used systems in mid-rise and high-rise buildings for this purpose is reinforced concrete shear walls (referred to herein as walls), designed specifically to counteract the horizontal forces exerted during an earthquake. 2 These walls not only resist earthquake and wind loads but also support gravitational loads. During strong earthquake shaking, these walls designed following building codes have shown the system’s adequacy in preventing collapse and achieving life safety performance. However, previous earthquakes have demonstrated that some shear wall buildings designed according to this criterion suffered severe damage, especially in many mid-rise and high-rise reinforced concrete buildings (Elwood, 2013; Jünemann et al., 2016). The repair and retrofitting of these walls can be very costly or may require demolition due to the permanent deformation of the building. As seen in the 2010 Chile and 2011 Christchurch earthquakes, large-scale demolitions and reconstructions can have significant economic impacts, affecting a country's gross domestic product and overall economic stability. For instance, despite strict implementation of building codes, the 2011 earthquake in Christchurch, New Zealand, resulted in approximately NZ$40 billion in economic losses, equivalent to 20% of the country's gross domestic product, significantly impacting the nation's economy (Parker and Steenkamp, 2012). Therefore, shear walls should be designed to minimize damage to these structural elements, resulting in low or no permanent deformation in the buildings. This can be achieved if the building has a self-centering mechanism, which refers to the ability of the structural element or building to return to its original position after the release of external forces, such as earthquake forces (Tolou Kian and Cruz-Noguez, 2023). Thus, with minimum intervention, minor repair, and retrofitting, the building could be serviceable again without demolishing it. This highlights the necessity for structural safety design of buildings and life safety, considering all components, such as connections in PC shear wall buildings. The seismic performance of a PC building is highly dependent on the connections between the precast concrete elements, such as walls (Khaled A Soudki et al., 1995). Typical connections 3 observed in a PC shear wall building can be horizontal at the wall-to-foundation and wall-to-wall intersection. Horizontal connections commonly use grouted dowel connections to make wall-to-foundation and wall-to-wall connections using deformed steel rebars as dowels. Figure 1.1 shows the grouted dowel connection at a wall-to-foundation intersection. In this connection, the dowels are first embedded into the foundation before pouring the concrete. The dowels are then inserted into the voids of the walls created by the metal duct. Later, non-shrink grout is poured to fill the gap between the rebar and the metal duct. The grout is injected from the grout inlet until it comes out from the air outlet. These grout inlets and air outlets are placed in each metal duct. A dry pack is used to level and align the concrete elements and helps fill the gap. Figure 1.1: Grouted dowel connection at a wall-to-foundation intersection (adapted from Seifi and Henry, 2019) 4 The grouted dowel connections can be designed as emulative or jointed connections (NZS 3101, 2006). In a PC shear wall building with emulative connections, the strength of the connection is higher than the strength of the wall. However, in a PC shear wall building with jointed connections, the connections are weaker than the walls. In the case of jointed connections, failure is primarily concentrated on the connections. Conversely, emulative connections may result in localized yielding above the connections, reducing ductility compared to cast-in-place concrete shear walls. Similarly, the jointed connections show a lower ductility than the cast-in-place concrete shear walls. This highlights the limited ductility in existing grouted dowel connections. A jointed precast wall system is designed to rock around their base and self-center themselves upon unloading (Restrepo and Rahman, 2007). In this system, the unbonded post-tensioning (PT) tendons provide self-centering to the PC shear wall buildings. The construction of this system remains uncommon due to its complexity, causing increased time to build and high costs. Researchers (Smith and Kurama, 2014; Gu et al., 2019) used mild steel rebars as energy-dissipating rebars along with unbonded PT tendons to improve the ductility of PC shear wall buildings. However, they have shown that the mild steel rebars used in experiments have limited deformation capacity. Therefore, there is a need to develop an alternative connection with adequate ductility to construct PC shear wall buildings in high seismic regions. Further, this alternative proposed connection should be easy to construct and implement. Since the combination of 5 unbonded PT tendons and energy dissipators provides low residual strain after seismic loading the proposed connection should have a similar behavior. One of the solutions could be to use the shape memory alloy (SMA) rebars at the jointed connection instead of the unbonded PT tendons and mild steel rebars. SMA is an innovative material with a superelastic property. This material can return to its initial shape and position after removing the loading on the structure (Alam et al., 2008; Mohammadgholipour and Billah, 2023). This property of SMA will allow the connection to undergo large deformation without losing its strength within the superelastic range. Further, SMA can absorb and dissipate considerable energy during cyclic loading. Therefore, the self-centering system developed with the SMA connection at the wall-to-foundation and wall-to-wall intersections could significantly reduce the large permanent deformations and damages. This could help avoid demolition and reconstruction of buildings in high seismic areas. While this idea is promising, to the author’s knowledge, there have been no studies of SMA in PC wall connections. The thesis proposes a novel connection in the PC wall system that utilizes SMA rebars as a self-centering mechanism with reduced damage at the connection. The proposed ductile jointed PC wall system only has an SMA rebar as a connection. In this system, no unbonded post-tensioned tendons are used. The construction materials, such as metal ducts and grout, remain the same, with the SMA rebar being the only new element anchored by couplers. This ensures that material availability, constructability, and structural integrity stay consistent with standard industry practices. There are only a few changes in the new design, which is practical as the shear wall design and construction resemble conventional grouted dowel connection construction practice. 6 Additionally, the SMA and coupler assembly can be post-installed, simplifying and speeding up the process compared to unbonded PT tendon systems. While there is potential for such a system, there are still research gaps that need to be addressed. These include experimental investigations of the local behavior of the connection and anchoring system using an SMA rebar. Also, the limited experimental studies on SMA RC shear walls in the literature create a significant knowledge gap in our understanding of how shear walls with SMA rebar behave in seismic conditions. Before doing experimental studies, to gain a deeper understanding of the response of slender shear walls reinforced with SMA rebars, conducting a thorough numerical analysis of various parameters is crucial. This analysis should consider critical factors such as aspect ratio, axial load ratio, rebar types, and vertical reinforcement ratio. The insights gained from this numerical study can greatly support in selecting appropriate test specimen sections and understanding the responses. 1.2 Research goal and objectives The overarching goal of this thesis is to investigate the local behavior of the PC wall through a novel connection using superelastic SMA rebar and couplers. This goal is accomplished through the following three sub-objectives. • To determine the effects of various parameters (aspect ratio, axial load ratio, rebar types, and vertical reinforcement ratio) on the lateral response of the SMA-reinforced concrete shear walls using numerical analysis. • To experimentally investigate the effectiveness of the anchorage of the superelastic SMA rebar connected with the coupler and surrounding grout within a metal duct. 7 • To experimentally investigate the force-deformation response of the proposed anchoring system for SMA-reinforced PC wall-to-wall intersection. To achieve the aforementioned objectives, a numerical study and three different types of experimental tests are conducted. Firstly, the SMA-reinforced shear walls from the numerical study can show SMA’s excellent self-centering capabilities with minimal residual displacements. Secondly, based on these important numerical findings, the coupler pullout test and the pullout test of rebar in a concrete block are conducted experimentally to check the effectiveness of the proposed anchorage. The test results will ensure the rebar is stressed beyond the superelastic strain range with very low slippage. Finally, based on the significant findings from the two experimental tests, wall-to-wall connection tests are conducted using the proposed anchoring system under monotonic loading to investigate the force-deformation response. The three different types of experimental tests are carried out at the Structures Lab, University of British Columbia. 1.3 Thesis organization This thesis is organised into seven chapters with the following content. Chapter 1: Introduction contains the background, motivation, research goal and objectives, and thesis organisation. Chapter 2: Literature review presents a comprehensive literature review of precast concrete shear walls, SMA rebars and their use in different experimental studies on cast-in-place shear walls. The research gaps in the literature are presented, and the need for a novel connection using SMA as an energy-dissipating rebar for PC buildings is discussed. Chapter 3: Numerical study on RC walls reinforced with SMA rebars provides the numerical study to investigate the influence of various parameters (aspect ratios, axial load ratios, 8 reinforcement ratios, and types of SMA) on the hysteretic response of shear walls reinforced with SMA rebars. Chapter 4: Design of the novel SMA PC wall connection focuses on the design of a PC shear wall system using the novel connection. The various steps and equations involved in the design process are provided. Additionally, the system's load transfer mechanism is discussed. Chapter 5: Experimental program describes the overall experimental program, from constructing various test specimens, experimental setup, and loading protocol to instrumentation. Three different types of conducted tests are presented for evaluating the performance of SMA rebar and coupler anchors. The first two types of tests present the effectiveness of an anchorage system that uses SMA rebar and coupler. The third type of test discusses the local response of a section of the proposed system in Chapter 4. Chapter 6: Test results and discussion present the significant findings and results of the experimental tests described in Chapter 5. It also provides a detailed discussion of the experimental results. Chapter 7: Conclusions and recommendations present the summary and conclusions of the thesis. It also provides the limitations and recommendations for future studies. 9 Chapter 2: Literature Review 2.1 Introduction The ductility of the system plays a significant role in making buildings safer during earthquakes. For precast concrete (PC) shear wall buildings, the ductility mainly depends on the connections’ ability to withstand large deformation without significant force loss. One way to enhance ductility is by allowing controlled rocking at the wall-to-foundation intersection using unbonded post-tensioning (PT) tendons in PC shear wall buildings. However, this jointed connection system is complex to build, time-consuming and costly (Smith and Kurama, 2014; Gu et al., 2019). Also, the jointed connection with grouted metal duct connections has limited ductility. Consequently, there is a need for an alternative system that is easier to construct and provides adequate ductility. One potential solution involves using shape memory alloy (SMA) rebars in connections for PC shear wall buildings, which is a novel concept that has never been investigated. There have been limited studies on SMA RC shear walls and jointed ductile PC shear walls. Therefore, it is important to study the key aspects of SMA rebar, SMA rebar in RC shear walls, and ductile jointed walls to inform further research. The main purpose of this chapter is to provide a comprehensive literature review on the SMA rebar and its application in construction, as presented in the following section. Since SMA rebar is expensive compared to regular reinforcing bars, researchers have replaced steel rebar with SMA rebar only in critical regions. This chapter describes how various researchers have connected SMA rebars with regular steel rebars and utilized them in various structural elements, like columns, beam-column connections and walls. Finally, the findings from 10 the literature review will help identify key knowledge gaps in the SMA RC walls and ductile PC walls. 2.2 Shape Memory Alloy The shape memory alloy (SMA) has two unique properties: shape memory effect and super-elasticity. These two properties make SMA a smart material among other construction materials. The shape memory effect is the unique phenomenon by which SMA can recover its predetermined shape by heating even after large deformations. This property was first observed in gold-cadmium (Au-Cd) alloy during phase transformation (Ölander, 1932). The superelastic property of SMA can restore its initial shape spontaneously, even from its inelastic range upon unloading. This ability of SMA to recover permanent displacements under cyclic loading is beneficial in structural and earthquake engineering applications (Alam et al., 2007; Mohammadgholipour and Billah, 2023). In recent times, various types of SMAs, such as nickel-titanium (NiTi), copper-based (Cu-) SMA and iron-based (Fe-) SMA, have been developed and studied. The most appropriate type of SMA observed for structural applications is NiTi due to its ability to recover considerable strain, superelasticity, and excellent corrosion resistance (Janke, 2005). Figure 2.1 shows the NiTi rebar. NiTi can provide up to 10% recoverable strain with moderate energy dissipation during cyclic loading at room temperature (Fang et al., 2023). However, wider practical applications of NiTi in building construction are restricted due to high manufacturing costs and tedious machining processes (Alam et al., 2012; Muntasir Billah et al., 2022). While different compositions of SMAs are available, the Ni-Ti alloy is commonly available in the market and has also been found effective 11 in previous studies (Saiidi and Wang, 2006; Dina et al., 2023). However, alternative SMAs, such as Cu- and Fe-based alloys, are also gaining popularity because of their low production cost (Shrestha et al., 2013; Hong et al., 2024). One of the Fe-based SMAs, FeMnAlNi alloy, developed by (Omori et al., 2011) exhibits superelasticity in the range of NiTi, but at a low austenite finish temperature. This enables FeMnAlNi to function in the superelastic range, even at a low temperature (Billah and Alam, 2016). Figure 2.1: NiTi rebar Figure 2.2 shows the stress-strain behavior of SMA under reversed cyclic lateral loading at a constant temperature. When the load is applied to SMA, the material changes its form from austenite to a martensite state. Upon removal of the load, it reverts to its austenite state, enabling the material to regain its original shape and position. The SMA shows superelasticity when it is in the austenite state (Alam et al., 2008). Four parameters can represent the transformation, austenite-to-martensite starting stress (fy-SMA), austenite-to-martensite finishing stress (fP1), martensite-to-austenite starting stress (fT1) and martensite-to-austenite finishing stress (fT2). The one-dimensional stress-strain model of SMA, as shown in Figure 2.2, has been incorporated in finite element software packages such as SeismoStruct (SeismoSoft, 2022) because most civil engineering applications of SMA are related to rebars. 12 Figure 2.2: 1D-superelastic model of SMA incorporated in FE Packages (adapted from Auricchio et al. 1997) The superelastic SMA rebars are connected with steel rebars by mechanical couplers, as shown in Figure 2.3. This type of coupler was used to study SMA-steel hybrid RC columns (Alam et al., 2012). A similar coupler was also used to connect the SMA rebar with the steel rebar in the study of cast-in-place shear walls (Almeida et al., 2020). Some researchers (Abdulridha and Palermo, 2017; Tolou Kian and Cruz-Noguez, 2018) modified a similar coupler with 18 bolt heads in their studies for connecting SMA and steel rebars. In previous studies (Alam et al., 2010; Almeida et al., 2020), researchers have experimentally tested the coupler assembly connected with SMA and steel rebar to allow the SMA rebar to be stressed to its yield strength and achieve its full superelastic strain range. However, no experimental test has been conducted on only the SMA rebar and coupler anchor assembly. 13 Figure 2.3: Coupler In the past few decades, there has been some research on using SMA rebar in building construction. SMA rebars were successfully implemented in the plastic hinge regions of SMA RC elements, such as beam-column joints and columns representing RC bridge piers, by various researchers (Saiidi and Wang, 2006; Saiidi et al., 2007; Alam et al., 2008). However, only a few studies have been conducted on SMA rebars as potential reinforcements in the plastic hinge regions of shear walls (Abdulridha and Palermo, 2017; Cortés-Puentes et al., 2018; Cortés-Puentes and Palermo, 2018; Tolou Kian and Cruz-Noguez, 2018; Almeida et al., 2020). Further, no experimental test has yet been conducted using the SMA rebar as a connection to the PC wall. However, the SMA rebar as an energy-dissipating rebar is numerically studied in PC walls (Wang et al., 2019; Elnady and Jiang, 2024). 2.3 SMA in RC walls Researchers have recently started exploring using SMA rebars in RC shear walls. One of the main practical challenges is the anchorage issue between the smooth SMA rebar and the deformed steel rebar. To address this issue, researchers have used a mechanical coupler for connecting the SMA 14 rebar with the steel rebar. Another challenge is the higher cost of using SMA rebar than steel rebar. However, the cost can be reduced by using SMA at critical locations in the structural elements, such as shear walls. In the recent past, only five experimental studies were conducted on the SMA RC shear walls. Four experimental studies were performed to construct new SMA RC hybrid shear walls (Abdulridha and Palermo, 2017; Cortés-Puentes and Palermo, 2018; Tolou Kian and Cruz-Noguez, 2018; Almeida et al., 2020), while in one study, the SMA was used as a retrofitting element (Cortés-Puentes et al., 2018). In all the experiments, the performance of the SMA RC wall was compared with the traditional RC shear walls. In all five studies, the SMA rebars were placed at the boundary zone up to the length of the plastic hinge, connected by couplers with steel rebars at both ends. This intentional placement of SMA rebar is because RC shear walls subjected to bending experience the largest tensile strains at the boundary zones (Almeida et al., 2020; Hoult and De Almeida, 2022). Additionally, SMA rebars are only placed in the plastic hinge regions where the most significant inelastic deformations occur during seismic events (Shahnewaz and Alam, 2015; Soares et al., 2021). This targeted placement of SMA rebar in the shear wall reduces the quantity and associated costs of SMA rebar. Almeida et al. (2020) studied the SMA RC slender shear wall. They connected a 12 mm steel rebar with a 12.7 mm SMA rebar using a 33 mm coupler. They sheared off the screw’s head to reduce punching in the SMA rebar as suggested by previous studies (Alam et al., 2010). During their test of the RC SMA wall, they observed the sound of steel rebar fracture, which may have been caused by the SMA rebar slipping inside the coupler. Abdulridha et al. (2017) explored the behavior of 15 hybrid SMA RC slender walls, in which SMA rebar was connected to steel rebar using a modified coupler with eighteen bolts. In their study, one of the SMA rebars was fractured at the coupler location in the wall, which was due to the penetration of the bolt head into the SMA rebar. Therefore, there is a need for the proper SMA and coupler anchor system that can avoid penetration on SMA rebar and minimize SMA rebar slippage inside the coupler. Table 2.1 details experimental tests conducted in recent years on shear walls connected with SMA bars. In previous experimental tests conducted on SMA RC walls, the specimens were constrained with less than 4% axial load ratio (Pf/Agf'c) and an aspect ratio (height-to-length ratio of a shear wall) between 1.0 to 2.2 because of the laboratory size and equipment availability limitation. In Table 2.1, H represents the height of the wall, L is the length of the wall, Pf is the axial load, including the wall's self-weight, f'c is the compressive strength of concrete, Ag is the area of wall cross-section, and V is the peak force observed during the test. Most of these tests were only tested under quasi-static lateral loading, except the test done by Almeida et al. (2020), in which the walls were tested under both axial and quasi-static loading. Further, most experimental tests showed overturning due to an axial load (PfL/2VH) of less than 3%, except the test done by Almeida et al. (2020), which had 81%. The flexure failure mode was observed for the SMA RC shear walls, while the diagonal compression failure mode was observed for the two walls retrofitted with the SMA bracing system. 16 Table 2.1: List of experimental tests conducted on SMA RC shear wall Experimental Tests H/L Pf/Agf'c V/Agf'c PfL/2VH Almeida et al. (2020) 1.7 3.83% 1.43% 80.52% Kian et al. (2018) 2.0 0.08% 1.84% 1.05% Abdulridha et al. (2017) 2.2 0.17% 2.81% 1.35% Cortés-Puentes and Palermo (2018) 2.2 0.07% 1.13% 1.31% Cortés-Puentes et al. (2018) 1.0 0.19% 4.31% 2.25% 1.0 0.18% 7.75% 1.13% The limited experimental testing of SMA RC shear walls in the literature creates a significant knowledge gap in our understanding of how shear walls with SMA rebar behave in seismic conditions. Currently, there is only one study on SMA RC shear wall buildings with higher axial loads (Almeida et al., 2020). Considering that axial load ratios between 5% to 10% are common in mid-rise and high-rise shear wall buildings, there is a critical need to further understand the behavior of SMA in RC walls under important parameters such as high axial loads. This understanding could improve our knowledge and designs of ductile SMA PC walls. 2.4 Ductile jointed PC walls The jointed PC walls are designed to rock around their base and self-center themselves upon unloading (Restrepo and Rahman, 2007). Under lateral loads, axial stress from the wall's weight and unbonded post-tensioning (PT) tendons resist overturning and enable self-centering. The unbonded PT tendons, usually located in the center of the wall, generate most of the restoring force 17 when subjected to reversed cyclic lateral displacement loading. The wall’s weight contributes little to the restoring force compared to the unbonded PT tendons. These walls undergo lateral displacement (D) when subjected to lateral forces, forming a gap at their wall-to-foundation intersections, as shown in Figure 2.4. Researchers (Restrepo and Rahman, 2007; Smith and Kurama, 2014; Gu et al., 2019) placed mild steel rebars in the jointed PC walls to improve the seismic performance of the system, which is called a hybrid wall. As shown in Figure 2.4, a hybrid wall is a ductile jointed wall consisting of energy-dissipating rebars, such as mild steel rebars, along with unbonded PT tendons (NZS 3101, 2006). These mild steel rebars are designed to undergo repetitive tension compression to yield energy dissipation during cyclic loading. Figure 2.5 demonstrates the flag-shaped hysterical behavior of a hybrid wall system, where self-centering is provided by unbonded PT tendon and energy dissipation by mild steel rebars. Figure 2.4: Gap opening at the wall foundation intersection PC shear wallFoundationLateral ForceΔEnergy dissipatorsUnbonded PT tendonGapDry pack / grout 18 Figure 2.5: Flag-shaped hysteresis for a hybrid wall system Restrepo and Rahman (2007) placed energy dissipators as mild steel rebars at the wall and the foundation intersection in their studies. The authors calculated the length of the energy dissipator (le) such that the strain in the rebar at a gap opening does not exceed the strain at the tensile strength. They suggested that the provided length of the energy dissipator (lep) should be between 1.5 le to le. Similar concepts and ranges could be used while choosing the SMA rebar length in this thesis, as there is no explicit provision for SMA rebar in Canadian codes such as NBCC (CSA, 2019; NBCC, 2020) and CSA A23.3-19 (CSA, 2019). Despite numerous studies on the hybrid wall by various researchers (Kurama, 2002; Restrepo and Rahman, 2007; Smith and Kurama, 2014; Sritharan et al., 2015; Gu et al., 2019), its construction remains uncommon due to its complexity, which increases construction time and costs. DisplacementLateral forceSelf-centering byunbonded PT tendonEnergy dissipation by mild steel rebars Hybrid wall systemDisplacementLateral forceDisplacementLateral forceΔuFu 19 Furthermore, previous researchers (Smith and Kurama, 2014; Gu et al., 2019) have shown that the mild steel rebars used in experiments have limited deformation capacity. Few studies investigated the behavior of PC walls with grouted metal duct connections (Seifi et al., 2019). They conducted tests on PC walls with aspect ratios of 2 and 3, which showed rocking and flexural dominant behavior. The study considered critical parameters such as wall sizes of 150 mm and 200 mm, aspect ratios of 2 and 3, and axial load ratios of 0% or 5%, representing commonly used PC walls in low-rise buildings in New Zealand. The research showed that failure mechanisms varied with wall length and axial load ratios. In shorter walls with a low axial load ratio of 0%, failure was mainly due to the fracture of connection reinforcement. On the other hand, longer walls with a higher axial load ratio of 5% experienced concrete spalling, resulting in the detachment of the metal duct from the wall. However, the local behavior of the PC walls at the connection was unclear due to the complex interactions between wall geometry and applied axial loads. In recent years, there has been limited research on the localized behavior of grouted metal duct connections in PC walls. Pullout tests on dowel rebars in a grouted metal duct connection with varying reinforcement embedment lengths and metal duct types were studied (Elsayed et al., 2018). The results indicated consistent load capacities across specimens, with embedment lengths ranging from 10 to 16 times rebar diameter. A notable increase in ductility was observed when the embedment length was extended from 10 to 16 times the rebar diameter. Other researchers (Aragon et al., 2019) also conducted tests on grouted dowel connections with energy-dissipating rebars. Specimens with bond lengths exceeding 10 times the rebar diameter failed due to bar fracture, 20 which was considered a ductile failure, while specimens with inadequate bond length failed due to rebar pull-out. The metal duct type did not appear to influence the results as long as an adequate bond length was provided. There is no research on the localized behavior of grouted metal duct connection with SMA and coupler anchor systems. Therefore, there is a need to study the effectiveness of the SMA rebar anchor system in a metal duct. The jointed walls experience a force that crushes their base, a phenomenon known as toe crushing. However, this type of damage has already been extensively studied (Belleri et al., 2014; Gu et al., 2019; Restrepo and Rahman, 2007; Sritharan et al., 2015). A particular unknown exists about the force deformation capacity of grouted dowel connection. Therefore, there is a need to investigate the local behavior of energy-dissipating rebars, which is a critical aspect of wall behavior. 2.5 Summary This chapter provided a literature review on SMA rebar and discussed how it has been used in RC shear walls. Further, the chapter discussed the ductile PC shear walls. Limited research is available on the SMA RC shear walls and ductile jointed PC walls with grouted metal duct connections. The literature review on SMA RC walls showed that there is a gap in the behavior of walls with high axial load. To address this gap, the next chapter on the numerical study of RC shear walls reinforced with SMA rebars will discuss various significant parameters, such as axial load ratios, that affect the behavior of the wall. 21 Chapter 3: Numerical Study on RC Walls Reinforced with SMA Rebars 3.1 Introduction A comprehensive literature review in Chapter 2 showed that little experimental data is available on reinforced concrete (RC) shear walls connected with shape memory alloy (SMA) rebars. Further, it showed that only one study has been done on high axial loads on the SMA RC shear walls (Almeida et al., 2020). Most shear walls in actual buildings have an axial load ratio between 5% and 10%. The main purpose of this chapter is to further understand the behavior of SMA in RC walls under important parameters such as high axial load, as it could help improve our understanding of SMA precast concrete (PC) walls. Therefore, a numerical analysis is performed to understand the cyclic response of SMA RC shear walls. For this purpose, several finite element models were developed and subjected to axial and reverse cyclic lateral loading. The influence of various parameters, such as aspect ratios, axial load ratios, reinforcement ratios, and types of SMA, on the hysteretic response of SMA-reinforced shear walls is investigated. The chapter concludes by summarizing the findings from the numerical study. 3.2 Numerical modelling The three-dimensional finite element models of the shear walls were developed using a nonlinear analysis program, SeismoStruct (SeismoSoft, 2022). The shear walls were modelled using inelastic beam-column elements with rectangular cross-sections. This inelastic displacement-based frame element type was selected because it accurately captures deformations and is well-suited for nonlinear analysis, which is essential for simulating the complex behavior of walls under cyclic loading. This approach efficiently models flexural behavior, making it ideal for seismic 22 applications. The non-linear behavior of concrete and steel was modelled by the Mander model (Mander et al., 1988) and Menegotto and Pinto model (Menegotto, 1973). This steel model considers the Bauschinger effect, which is relevant for representing the stiffness degradation of the shear wall under cyclic loading. The superelastic SMA reinforcement was modelled with the available Auricchio and Sacco model (Auricchio et al., 1997) in SeismoStruct using the values provided in Table 3.2. The material models were accurately calibrated using the values shown in Table 3.2 for capturing the strength and stiffness degradation under cyclic loading. Static time-history analysis was performed to simulate the quasi-static behavior of shear walls under axial load and cyclic loading. The compressive strength of concrete and steel yield strength were 56 MPa and 470 MPa, respectively (Kolozvari et al., 2015). Figure 3.1 (a) shows the applied loading protocol on the numerical model shown in Figure 3.1 (b). The height of the various models was raised as per the aspect ratios (H/L), where H is the height of the wall and L is the length of the wall. The bottom of the wall was fixed. The reverse cyclic lateral loading incrementally increasing the drift amplitude was used as shown in Figure 3.1 (a). (a) (b) Figure 3.1: (a) Applied loading protocol (b) numerical model -1.5-1-0.500.511.520 10 20 30 40 50Drift (%)Loading stage (LS) 23 3.3 Modelling parameters Table 3.1 shows the four important parameters studied. The first parameter considered was the aspect ratio (H/L), which is the ratio of the height of the wall (H) to the length of the wall (L). Three different aspect ratio values (2, 3 and 4) were chosen to avoid shear failure and ensure the flexural dominant behavior of the shear wall. Furthermore, these aspect ratios (2, 3 and 4) are commonly found in mid-rise and high-rise shear wall buildings. The second parameter was the axial load ratio (Pf/Agf'c), which is the ratio of axial load applied to the wall due to gravity loads (Pf) to the axial load-carrying capacity of the wall that is equal to the compressive strength of concrete (f'c) multiplied by the wall gross cross-section area (Ag). Most shear walls in actual buildings have an axial load ratio between 5% and 10%. As a result, it is critical to determine the behavior of SMA RC walls made of higher aspect ratios under varying axial loading (5% and 10%). Therefore, these two axial load ratio values were selected. The third parameter was rebar types. Therefore, steel rebar and two types of SMA rebar (NiTi and FeMnAlNi) were selected. NiTi is the most suitable SMA for building construction because of its ability to recover significant strain, high superelasticity, and excellent corrosion resistance (Janke, 2005). However, NiTi has a higher cost than the other construction materials. FeMnAlNi is a cheaper promising alternative SMA composed of common metals and exhibits superelasticity in the NiTi range. The mechanical properties of two types of SMA (NiTi and FeMnAlNi), as shown in Table 3.2, were chosen from the previous studies (Alam et al., 2008; Omori et al., 2011). 24 Finally, the fourth parameter was vertical reinforcing ratios (ρv). As the behavior of the shear walls in bending is influenced by the outermost regions of the cross-section where confining reinforcement is provided (commonly known as boundary zone), the SMA rebars are placed only in such zones. Three different types of rebars - steel, NiTi and FeMnAlNi, of sizes #3 (11.3 mm), #5 (16 mm) and #7 (22 mm) were chosen to see the effects of an increase in the rebar area at the boundary zone. The vertical reinforcement ratio (ρv) was taken as the longitudinal reinforcement ratio of only one portion of the boundary zone, as shown in Equation 3.1. 𝜌# = 4 ´ (Area of rebar)150mm ´ 210mm ´ 100% 3.1 Table 3.1: Parameters to study Parameters Value a Aspect ratio (H/L) 2 3 4 b Axial load ratio (Pf/Agf'c) 5% - 10% c Types of rebars Steel NiTi FeMnAlNi d Vertical reinforcement ratio (𝜌#) 0.89% 2.48% 4.86% A total of 54 walls were analyzed (3 x 3 x 3 x 2 = 54 models) under axial and cyclic loading. A constant cross-section of 150 mm thick and 1200 mm long was considered for all shear wall models. This cross-section is referenced from a previous study (Kolozvari et al., 2015). The 10M (11.3 mm) steel rebars at a spacing of 125 mm were provided as longitudinal and transverse rebars in the wall web for all models, and 6.35 mm ties at a spacing of 50 mm were provided at the 25 boundary zones. Figure 3.2 shows the cross-section of the shear wall model and reinforcement detailing. Figure 3.2: Cross-section of wall model Table 3.2: Mechanical properties of SMA Mechanical properties NiTi FeMnAlNi Modulus of elasticity (E) 62.5 GPa 68 GPa Austenite-to-martensite starting stress (fy-SMA) 401 MPa 435 MPa Austenite-to-martensite finishing stress(fP1) 510 MPa 535 MPa Martensite-to-austenite starting stress (fT1) 370 MPa 335 MPa Martensite-to-austenite finishing stress(fT2) 130 MPa 170 MPa Superelastic plateau strain length (ε1) 6% 8% 26 3.4 Result A model was developed for each of the 54 combinations and each model was analyzed under axial and cyclic loading. The combination was named R#A#P#, where R = rebar size, A = aspect ratio and P = axial load ratio. For instance, R3A3P5 represents rebar size #3 (11.3 mm), aspect ratio 3 and axial load ratio 5%. To investigate the effects of various parameters on SMA-reinforced concrete shear walls, only one parameter was varied while the other parameters remained constant. 3.4.1 Hysteretic response and trend While assessing the various hysteretic responses for steel, NiTi and FeMnAlNi, interesting trends were observed. These trends are shown in Figure 3.3, Figure 3.4 and Figure 3.5. From the hysteretic plots, it can be observed that there is a significant difference in the hysteretic shapes of steel and SMA (NiTi and FeMnAlNi) shear walls. The shear walls with only steel reinforcing showed larger hysteresis “loops”, and for the majority of models, had residual deformations. Contrastingly, the SMA models had limited energy dissipation but showed minimal residual displacements, showcasing the SMA’s excellent self-centering capabilities. Figure 3.3 shows the different hysteresis for different vertical reinforcement ratios, a constant aspect ratio (A = 3), and a constant axial load ratio (Pf/Agf'c = 5%). In Figure 3.3, M represents the overturning moment due to lateral loading, Lw is the length of the wall, and P is the axial load. Also, the drift is taken as the ratio of permanent deformation over the height of the wall and is expressed in percentage. For all three rebar types, steel, NiTi and FeMnAlNi, an increase in vertical reinforcement ratio increased the wall’s lateral strength, leading to an increased overturning moment. However, this increased lateral strength also results in greater plastic deformations when 27 the wall yields, causing an increase in residual drift of the wall after the loads are removed. A similar result was observed in the previous study (Zhou et al., 2022). Therefore, in the steel shear wall models, a higher reinforcing ratio resulted in higher residual drifts. On the other hand, NiTi and FeMNAlNi shear walls showed low residual drift for all reinforcing ratios due to the SMA’s excellent self-centering abilities. Types of rebars Figure 3.3: Hysteresis trend for same aspect ratio and axial load ratio with varying rebar size (R = rebar size; A = aspect ratio; P = axial load ratio) Increase in rebar size 28 Figure 3.4 shows the different hysteresis for different aspect ratios, a constant reinforcing ratio of 2.48% (for rebar size #5), and an axial load ratio (Pf/Agf'c = 5%). For all three rebar types, steel, NiTi and FeMnAlNi, a higher aspect ratio resulted in lower stiffness, while a lower aspect ratio resulted in more energy dissipation (larger hysteretic loops) than a high aspect ratio. As the aspect ratio of a shear wall increased from 2 to 4, its behavior became more flexural-dominant, resulting in decreased stiffness and energy dissipation. The taller walls, with higher aspect ratios (H/L), exhibited behavior similar to cantilever beams, where bending becomes the primary deformation mode, inherently leading to lower stiffness than shear resistance. Furthermore, these taller walls are flexural-dominant, demonstrating less ductility and narrower hysteretic loops than the shorter walls during cyclic loading, thereby reducing energy dissipation. 29 Types of rebars Figure 3.4: Hysteresis trend for same rebar size and axial load ratio with varying aspect ratio (R = rebar size; A = aspect ratio; P = axial load ratio) Figure 3.5 shows the different hysteresis for different axial load ratios (Pf/Agf'c= 5% and 10%), a constant reinforcing ratio of 2.48% (for rebar size #5), and aspect ratio (A = 3). The higher axial load ratio (10%) resulted in a more pinched hysteresis (i.e., more prominent self-centering capability and led to earlier strength degradation compared with a low axial ratio (5%). The higher axial load ratio (10%) increased compressive stress, causing the concrete to crack earlier in the Increase in aspect ratio 30 wall, which resulted in decreased wall stiffness when subjected to axial and cyclic loading. Moreover, these earlier cracks, due to a high axial load ratio (10%), along with a reduction in wall stiffness, lead to pinched hysteresis loops with a narrower shape and less energy dissipation. Types of rebar Figure 3.5: Hysteresis trend for same rebar size and aspect ratio with varying axial load ratio (R = rebar size; A = aspect ratio; P = axial load ratio) Increase in axial load ratio 31 3.4.2 Effect of reinforcement ratio The residual drift is vital to determining the severity of building damage after an earthquake. It is taken as the ratio of permanent deformation over the height of the wall. Figure 3.6 shows the relationship between residual drift and vertical reinforcement ratio for steel, NiTi and FeMnAlNi at 5% and 10% axial load ratios. Figure 3.6 (a) and (d) show that residual drift was observed for all steel shear walls except for specimens with a reinforcing ratio of 0.89% (R3) and axial load ratio of 5%, where no residual drift was observed. This combination of a reinforcing ratio of 0.89% and an axial load ratio of 5% may have contributed to the steel shear walls' more elastic behavior, allowing them to return to their original shape after the load was removed. In all steel-reinforced shear walls, an axial load ratio of 10% had higher residual drifts than the axial load ratio of 5%. Further, the trend for the axial ratio of 5% walls showed that high vertical reinforcing ratios resulted in high residual drift. On the other hand, at an axial load ratio of 10%, walls with high vertical reinforcing ratios resulted in lower residual drift, except for R5A4P10, where the residual drift was low. In both axial load ratios of 5% and 10%, walls with a higher aspect ratio had lower residual drifts. This is because taller walls with higher aspect ratios are more flexible, which enables them to return to their original position more effectively during cyclic loading. The SMA-reinforced shear walls for an axial ratio of 5% showed no residual drift (i.e., Figure 3.6 (b) and (c)). This shows that the 5% axial load ratio combined with the inherent superelastic property of SMA rebar helps prevent permanent deformations during earthquake loading. In contrast, the axial load ratio of 10% showed small residual drifts at the lower reinforcing ratios 32 (i.e., Figure 3.6 (e) and (f)). The highest residual drift for SMA walls was about 0.2% for aspect ratio 3 specimen at 0.89% reinforcement ratio. The highest residual drift for steel walls was observed at around 1.4% for all three varying aspect ratios specimens, Figure 3.6 (d). Figure 3.6: Residual drift vs vertical reinforcement ratio Energy is the accumulation of hysteretic energy (i.e., inelastic force-deformation response) over all the cycles, which is normalized by the maximum shear force (Vmax) and the maximum displacement (Δmax). The normalized energy (Energy/Vmax/Δmax) was used to show energy dissipation capacity. Figure 3.7 shows that the normalized dissipated energy for steel is higher than the NiTi and FeMnAlNi at 5% and 10% axial load ratios. This is because the steel rebars absorb more energy through plastic deformation, while the SMA rebars can recover their shape after 33 unloading because of the inherent superelastic property. For steel-reinforced shear walls, energy dissipation was increased with the high reinforcement ratio due to increased lateral strength resulting in higher plastic deformation during cyclic loading. In contrast, there was low energy dissipation for shear walls with a high aspect ratio. Shear walls with NiTi and FeMnAlNi rebars showed low energy dissipation for high reinforcement ratios, as shown in Figure 3.7 (b, c, e, and f). The energy dissipation capacity of NiTi was slightly lower than that of FeMnAlNi. Overall, the NiTi and FeMnAlNi reinforced shear walls showed less than 50% of the energy dissipation than the steel-reinforced shear walls. Figure 3.7: Normalized energy dissipation vs vertical reinforcement ratio 34 The cyclic degradation rotation (θ80%) is the drift when the shear force is degraded to 80% of the maximum shear force. The value of θ80% is important as it represents the system ductility, a critical design parameter. For a 5% axial load ratio, no strength loss was observed in all three types of rebars. However, strength loss was observed for a 10% axial load ratio due to increased compressive stress, leading to the earlier concrete crack in the wall under axial and cyclic loading. Figure 3.8 shows the drift when the force degraded to 80% of the peak force. For a 10% axial load ratio, a higher reinforcing ratio resulted in a higher θ80%. Furthermore, higher rotation values were observed for the higher aspect ratios. Figure 3.8: Drift at strength loss (θ80%) vs vertical reinforcement ratio 3.5 Summary A detailed numerical study was performed with the force-deformation response and strain obtained from 54 models. The major conclusions drawn from the study are as follows: • The NiTi and FeMnAlNi reinforced shear walls showed minimal residual displacements, demonstrating SMA’s excellent self-centering capabilities. 35 • Significant residual drift was observed for steel shear walls except at a reinforcement ratio of 0.89% and an axial load ratio of 5%. In contrast, it was observed very low to none in NiTi and FeMnAlNi. • The NiTi and FeMnAlNi showed less energy dissipation than steel-reinforced shear walls at 5% and 10% axial load ratios. • No strength loss was observed at a 5% axial load ratio for all three rebar types. However, strength loss was observed for a 10% axial load ratio. 36 Chapter 4: Design of the Novel SMA PC Wall Connection 4.1 Introduction The numerical study in Chapter 3 demonstrated the excellent self-centering capacity of reinforced concrete (RC) shear walls connected with shape memory alloy (SMA) rebars. These SMA-reinforced shear walls exhibited very low residual deformation. However, a detailed design is necessary for precast shear walls connected with SMA rebars. Therefore, Chapter 4 will cover the proposed system for precast walls connected with SMA rebars, including design considerations, various equations for jointed walls with SMA rebars, and the load transfer mechanisms. Previous studies have shown that SMA rebar is connected to steel rebar using couplers; however, the proposed connection system utilizes only SMA and couplers. Additionally, the chapter will discuss the design of SMA and coupler anchors to be used in the grouted dowel connection. The main outcome of this chapter will be to propose an alternative novel connection using SMA rebars and couplers for the precast concrete (PC) shear wall. 4.2 Proposed system The chapter proposes a novel PC wall system which utilizes SMA rebars as a self-centering mechanism with reduced damage at the connection. The proposed precast wall system uses SMA rebars only; no unbonded post-tensioned tendons are used. The superelastic property of SMA allows the connection to withstand deformation without losing its strength within the superelastic range. Additionally, SMA rebars will have the ability to absorb and dissipate substantial energy during cyclic loading. As a result, the self-centering system, developed with the SMA connection 37 at wall-to-foundation and wall-to-wall intersections, has the potential to significantly reduce large permanent deformations and damages. The concept for the proposed connection is to use SMA rebar and couplers anchored inside the grouted metal duct. The SMA and coupler assembly will be prepared first, and then they will be post-installed at the intersections of the walls. The anchor assembly will be inserted first in the lower wall and positioned vertically with the help of wagon wheels inside the metal duct. After that, the top portion of the anchor will be inserted into the upper wall. A dry pack will be placed between the two walls. Further, the dry pack will help to seal the area around the metal duct. Later, the grout will be injected from the grout inlet placed at the lower wall, with a grouting machine until the grout comes out from the air outlet placed at the top wall. The process will also be simple and efficient for installing proposed connections for the precast walls at the construction site. Figure 4.1(a) illustrates the proposed connection at the wall-to-foundation intersection. The lateral force is applied along the wall height (H), while the resultant lateral force is assumed to be at a particular height (he). L refers to the wall length, and Pf is an axial load on the wall. Figure 4.1(b) displays the flag-shaped hysteresis response for the proposed system. The proposed connection with SMA rebar and couplers in the wall system will result in flag-shaped hysteretic behavior of the precast wall when the wall experiences earthquake loading. This is because of the superelastic property of the SMA rebars, which will result in very low residual deformation during unloading. In this proposed connection system, SMA rebar transfers load between the shear wall and the foundation. Therefore, a flag-shape response is expected. 38 (a) (b) Figure 4.1: (a) Proposed connection at wall-to-foundation intersection (b) flag-shaped hysteresis for the proposed system The process of designing the proposed system for precast wall connection involves several specific steps. First, the behavior of the proposed wall system needs to be analyzed, and then connection capacity needs to be determined. This is followed by assessing the SMA rebar area and strains and determining the length of the SMA rebar. 4.2.1 Monotonic response of proposed wall system Figure 4.2 shows the proposed wall's expected lateral force versus displacement response, which is plotted following the procedure outlined in ACI 550.7-19 (ACI, 2019a) and the shape of the curve is referenced from the previous study (Smith, 2012). When the part of the wall lifts off during lateral loading, the SMA rebar will be engaged in resisting forces. At this beginning point, the Dry pack / groutSMA and couplers anchor HLLateral forceResultant lateral force (Fe)hePfPC shear wallFoundationMetal ductDisplacementLateral force 39 force will be equivalent to the decompression force (Fr) and the displacement at the top of the wall (Dr) will be minimal. A little after the wall opens its gap from one corner, the SMA rebar will reach its yield load capacity (Fy), and the corresponding displacement observed at the top of the wall will be the yield displacement (Dr). Up to this point, there will be linear force-displacement response. When the wall is pushed further to its maximum capacity, it will fail due to either toe crushing or SMA rebar fracture. The toe-crushing type of failure has already been extensively studied (Belleri et al., 2014; Gu et al., 2019; Restrepo and Rahman, 2007; Sritharan et al., 2015). The toe crushing can be prevented by providing confinement reinforcement at wall corners. At this ultimate point, the force will be the ultimate force (Fu), and the ultimate displacement at the top of the wall (Du) will be maximum. Figure 4.2: Expected pushover response of the proposed system DisplacementLateral forceΔuFuΔyFySMA rebar yieldDecompression pointFrΔrToe crushing orSMA rebar fracture 40 Decompression point (Fr, Dr) The decompression point is identified as the beginning of a gap opening at the base of the wall (Aaleti and Sritharan, 2009). This point is determined when the stress in the extreme concrete fiber farthest from the rocking edge of the wall reaches zero. A linear strain distribution is assumed for the critical section due to the moment induced by the decompression force (Fr). The decompression moment, Md as shown in Equation 4.1 is calculated using the elastic flexural formula 𝜎 = $! × '!( . 𝑀) = 𝜎 × 𝐼𝑐) 4.1 Where Md is the decompression moment, 𝜎 is the stress in the wall due to the axial load, 𝜎 = *"+ × ,, Pf is axial load, L is wall length, b is wall width, cd is neutral axis depth, 𝑐) = +- , and I is the moment of inertia, 𝐼 = , × +#"- . Substituting the values of s, I and cd into Equation 4.2 and solving it yields the simplified Equation 4.3. 𝑀) = ( 𝑃.𝐿 × 𝑏) × (𝑏 × 𝐿/12 )𝐿2 4.2 𝑀) = 𝑃. × 𝐿 6 4.3 The decompression force (Fr) can be determined by dividing the decompression moment (Md) by the height (he) as shown in Equation 4.4. 𝐹0 = 𝑀)ℎ1 4.4 By substituting the value of Md from Equation 4.3 into Equation 4.4, the decompression force is determined as shown in Equation 4.5. 41 𝐹0 = 𝑃. × 𝐿6ℎ1 4.5 Assuming the precast wall will behave as the monolithic wall at the decompression force, the displacement at the top of the wall as shown in Equation 4.6 is calculated using a similar formula to the cantilever wall. Where Dr represents yield displacement, Fr is the decompression force, he is the height at which decompression force acts, E is the modulus of elasticity, and I is the moment of inertia. Yield point (Fy, Dy) The rebar at the end located at the uplift corner of the wall is assumed to be yielded to calculate the yield point (Fy, Dy). This means the end rebar is assumed to be strained to 0.75%, i.e. ey = 0.0075. The yield strain of SMA rebar is referenced from previous research (Alam et al., 2010). At this point, the strain in the compression fibre of concrete, ec, will be less than the concrete crushing strain, ecu. Three SMA rebars as dowels are assumed for the ease of yield point calculation as shown in the wall cross-section of Figure 4.3. Assuming the end SMA rebar is yielded, es3 = ey = 0.0075, the corresponding strain developed in the other SMA rebars and concrete will be es1 = es3 (c-d1) / (d3-c), es2 = es3 (d2-c) / (d3-c) and ec = es3 (c / (d3-c)). The neutral axis depth "c" from extreme compression fibre is calculated using the iterative method (Aaleti and Sritharan, 2009) or the sectional analysis software (Response-2000, 2000). The neutral axis depth “c” value depends on the axial load on the wall. Assuming the maximum stress developed in the concrete is about 40% of the maximum compressive stress (f'c) in the concrete, thus resulting in a linear stress-strain ∆0 = 𝐹0 × (ℎ1)/3 × 𝐸 × 𝐼 4.6 42 behavior (Brzev and Pao, 2009). The stress developed in the rebar and concrete corresponding to the strain will be fsi = esiEs (where i varies from 1, 2, 3) and fc = ecEc. Es and Ec are the modulus of elasticity in steel and concrete. Similarly, the force developed corresponding to the rebar stress will be Fsi = fsiAs, (where i varies from 1, 2, 3), and in concrete, it will be Cr = -1/2(fc)cb. Figure 4.3 shows the assumed wall cross-section, strains, stresses and forces to calculate the yield point. In the assumed wall cross-section, two dowels are placed at the boundary zone and one at the center. The yield moment (My) is shown in Equation 4.7. The moment of any point would be the same, but for simplification of the yield point calculation, it is taken about the center. The corresponding yield force (Fy) can be determined by dividing the yield moment (My) by the height (he) as shown in Equation 4.8. 43 Wall cross-section Strains Stresses Forces Figure 4.3: Yield point calculation 𝑀2 = 𝐶0 E𝑑- − 𝑐3H + 𝐹3" (𝑑- − 𝑑") + 𝐹3/ (𝑑/ − 𝑑-) 4.7 𝐹2 = 𝑀0 ℎ1 4.8 Where Fy represents the yield force, My represents the yield moment, Cr is the compression force in concrete, Cr = -1/2(fc)cb, f'c is the specified compressive strength of concrete, c is the neutral axis depth, b is the width of wall, d1, d2 and d3, are the distance of SMA rebars from the compression end of the wall, Fs1 and Fs3 are the forces in SMA rebars 1 and 3, and he is the height at which the resultant yield force acts. Ld1d2d3ces1es2ey = es3ec < ecufs1fs2bfy= fs3fc £ 0.4f'cFs1Fs2Fs3PCr 44 The elongation in the end SMA rebar (d3), is shown in Equation 4.9., which depends on the length of the SMA rebar (le) and the corresponding strain in the rebar (e3/ = e2). d/ = e3/ × 𝑙1 = e2 × 𝑙1 4.9 The wall drift q, in %, is calculated using Equation 4.10, where c is the neutral axis depth in mm and d3 is the distance of energy dissipator furthest from the wall edge in compression in mm. q = d/ / (𝑑/ − 𝑐) 4.10 The yield displacement at the top of the wall (Dy) is calculated using Equation 4.11, where H is the wall height in mm. D2 = q × 𝐻 4.11 Substituting the values of d3 and q from Equations 4.9 and 4.10 into Equation 4.11 and solving it gives the yield displacement, D2, as shown in Equation 4.12 D2 = ((e2 × 𝑙1) / (𝑑/ − 𝑐)) × 𝐻 4.12 Where Dy represents yield displacement, ey is the yield strain, le is the length of the SMA rebar, d3 is the distance of SMA rebar 3 from the compression end of the wall, c is the neutral axis depth and H is the height of the wall. Ultimate point (Fu, Du) The ultimate point (Fu, Du) could be determined by (i) assuming the proposed wall system failed due to toe crushing failure or (ii) assuming the proposed wall system failed due to SMA rebar fracture. Assuming the toe crushing failure where the concrete reached a crushing strain of 0.35% (i.e. ecu = 0.0035) on the extreme concrete compression fibre, the corresponding strain developed in the SMA rebars will be es1 = ecu (1 – d1/c), es2 = ecu (d2/c – 1), es3 = ecu (d3/c – 1). Assuming the 45 equivalent rectangular concrete stress distribution, a stress of a1f'c in the concrete is uniformly distributed over the block depth (a). The block depth (a) is equals to the product of b1 and c (a = b1c). Therefore, the equivalent compression force (Cr) will be equal to b1c(a1f'c)b, where a1, b1 are mathematical parameters defined by CSA A23.3-19 (CSA, 2019). Figure 4.4 shows the wall-cross section, strains, and stresses to calculate the ultimate point for the concrete crushing failure. The ultimate moment (Mu) is shown in Equation 4.13. The moment of any point would be the same, but for simplification, it is taken about the center. The corresponding ultimate force (Fu) can be determined by dividing the ultimate moment (Mu) by the height (he) as shown in Equation 4.14. 46 Wall cross-section Strains Stresses Forces Figure 4.4: Ultimate point calculation (concrete crushing failure) 𝑀4 = 𝐶0 E𝑑- − 𝑎2H + 𝐹3" (𝑑- − 𝑑") + 𝐹3/ (𝑑/ − 𝑑-) 4.13 𝐹4 = 𝑀4 ℎ1 4.14 Where Fu represents ultimate force, Mu represents ultimate moment, Cr is the equivalent compression force, Cr = b1c(a1f'c)b, a1, b1 are mathematical parameters, a1 = 0.85 – 0.0015f'c ³ 0.67 and b1 = 0.85 – 0.0025f'c ³ 0.67, c is neutral axis depth, fc is the resistance factor for concrete, f'c is the specified compressive strength of concrete, b is the width of wall, d1, d2 and d3, are the Ld1d2d3ces1es2es3ec = ecufs2bfs3a1f′cfs1a = β1cFs2Fs3PFs1Cr 47 distance of SMA rebars from the compression end of the wall, Fs1 and Fs3 are forces in SMA rebars 1 and 3, and a is the block depth, a = b1c. from the compression end of the wall, and he is the height at which ultimate force acts. Following similar equations to yield force from 4.9 to 4.11, the ultimate displacement, Du, corresponding to the ultimate force (Fu) is calculated and is shown in Equation 4.15 D4 = ((e3/ × 𝑙1) / (𝑑/ − 𝑐)) × 𝐻 4.15 Where Du represents ultimate displacement, es3 is the strain in the extreme rebar (3rd assumed rebar), le is the length of SMA rebar, d3 is the distance of SMA rebar 3 from the compression end of the wall, c is neutral axis depth and H is the height of the wall. Another possible ultimate failure of the proposed wall system will be due to the SMA rebar fracture. Figure 4.5 shows the ultimate point calculation based on the rebar fracture failure. When the wall is assumed to have failed due to SMA rebar fracture, the ultimate load capacity and displacement of the connection at the wall-to-foundation intersection depends on the maximum strain developed in the SMA rebar and its length. The ultimate load in SMA rebar, F’u is shown in Equation 4.16, which depends on the ultimate strength (fu) and rebar area (As). 𝐹′4 = 𝑓4 × 𝐴3 4.16 The ultimate elongation in SMA rebar (du), is shown in Equation 4.17. d4 = e34 × 𝑙1 4.17 Where esu signifies the ultimate strain and le stands for the length of the SMA. 48 The wall drift (q), is calculated using Equation 4.18. q = d4 / (𝑑/ − 𝑐) 4.18 The ultimate displacement at the top of the wall (Du) is calculated using Equation 4.19. D4 = q × 𝐻 4.19 Substituting the values of du and q from Equations 4.17 and 4.18 into Equation 4.19 and solving it gives the ultimate displacement as shown in Equation 4.20 D4 = ((e34 × 𝑙1) / (𝑑/ − 𝑐)) × 𝐻 4.20 Where Du represents ultimate displacement, esu is the ultimate strain, le is the length of the SMA rebar, d3 is the distance of SMA rebar 3 from the compression end of the wall, c is the neutral axis depth and H is the height of the wall. Figure 4.5: Ultimate point calculation (rebar failure) Lateral Forcec(d3 – c)d3!!ΔleHL" 49 4.2.2 Metal duct size and SMA length The grouted dowel connection can be designed according to the CPCI Design Manual (CPCI, 2017) or PCI Design Handbook (PCI, 2021). The minimum embedment length should be at least 300 mm for anchorage in the grouted metal duct (PCI, 2021). The embedment length should also satisfy the requirement of splice length for the vertical steel rebar of the shear wall (CSA, 2019). Therefore, the minimum embedment of the metal duct is calculated as per Equation 4.21. 𝐿5 = Minimum of (𝑙3678'1 or 300 mm) 4.21 Where Lm and lsplice represent the minimum embedment length of the metal duct and splice length for the vertical steel rebar, respectively. The splice length (lsplice) is 1.3 times the development length (ld) of the rebar. For the proposed connection, the diameter of the metal duct is selected based on the diameter of the coupler. According to the PCI Design Handbook (PCI, 2021), a minimum tolerance of 12.7 mm between the rebar and metal duct is required. Therefore, the minimum tolerance will be based on the coupler diameter to ensure the flow of grout inside the metal duct. The minimum diameter of the metal duct is shown in Equation 4.22. Additionally, as per the CPCI Design Manual (CPCI, 2017), the metal duct diameter should be at least three times the rebar diameter to ensure adequate construction tolerances and ease the erection of the wall. 𝑑5 = 𝑑' + 2 × (tolerance) 4.22 Where dm and dc represent the diameter of the metal duct and coupler, respectively. 50 The length of the SMA rebar in the proposed connection is determined by considering the maximum wall drift and maximum strain on the SMA rebar. The length of the SMA rebar, le, is calculated using Equation 4.23. 𝑙1 = de34 = 𝜃 × (𝑑/ − 𝑐)e34 4.23 Where d represents elongation in the SMA rebar, esu represents strain in SMA, q represents wall drift, c is the neutral axis depth and d3 is the distance of SMA furthest from the wall edge in compression. 4.2.3 Load transfer mechanism and SMA coupler anchor Figure 4.6 demonstrates the load transfer mechanism from the PC shear wall to the proposed ductile connection at the wall foundation intersection. When a lateral force (V) acts on the wall system, it generates a moment (M) that creates tension (T) and compression (C) forces at opposite ends of the wall as shown in Figure 4.6. Figure 4.7 shows the tensile force transfer from the steel rebar of the PC shear wall to the SMA rebar inside the metal duct of the connection. This means that the vertical rebars at the edge of the wall at the boundary zone transfer tension to the metal duct first through the bond stress developed between steel rebar, concrete and metal duct. Then, the tensile force is transmitted to the grout through bond stress developed between the grout and the metal duct. Finally, a bearing force is developed on the grout area below the coupler’s head. As a result, the tensile force is transferred to the SMA rebar. Therefore, providing adequate splicing length for the metal duct is important to ensure the force is transmitted effectively. 51 Figure 4.6: Load transfer from wall to connection Figure 4.7: Tensile force transfer from steel rebar to SMA rebar Lateral ForceVT CM(7) Tensile force on SMA rebar(6) Bearing force on grout(5) Bond stress b/w grout & metal duct(2) Bond stress b/w concrete & steel rebar(3) Bond stress b/w concrete & metal duct(4) Tensile force on metal duct (1) Tensile force on steel rebar 52 The proposed system consists of a new type of anchor using SMA rebar with two couplers assembly for connection design, as shown in Figure 4.8. Researchers used a similar coupler to clamp SMA rebar in their studies (Abdulridha and Palermo, 2017; Alam et al., 2012; Almeida et al., 2020; Cortés-Puentes et al., 2018; Tolou Kian and Cruz-Noguez, 2018). To prevent rebar slippage inside the coupler, all six screws of the coupler are proposed to clamp the SMA rebar securely. The number of screws might increase depending on the available size of the coupler for the rebar. Additionally, a high-strength epoxy will be applied to enhance adherence between the rebar and the internal surface of the coupler. Under loading conditions, the force will transfer from the rebar to the coupler, resulting in either rebar rupture or the slippage of rebar inside the coupler failure mode. The materials, such as metal duct and grout, are the same for the proposed precast wall system construction. Only the SMA rebar is new, which is connected by couplers. Therefore, material availability, constructability, and structural integrity remain the same as in industry practice. In conclusion, there are few changes in the new design, which is practical as the shear wall design and construction resemble conventional grouted dowel connection construction practice. 53 (a) (b) (c) Figure 4.8: (a) Schematic of proposed anchor (b) SMA and coupler anchor (c) steel and coupler anchor 4.3 Shear design across horizontal joints To ensure that the wall remains stable during loading, it is important to ensure that the designed shear friction capacity at the horizontal joint (Vr) is greater than the shear force at the joint (V). This helps prevent any significant horizontal slip of the wall and maintains its structural integrity. The shear design across horizontal joints equation can be written as shown in Equation 4.21. CouplerSMAorsmooth steel rebar 54 𝑉0 > 𝑉 4.24 The shear capacity of the connection (Vr) is determined by Equation 4.22, based on CSA A23.3-19 (CSA, 2019). 𝑉0 = l × f' × (𝑐" × 𝐴9" + µ × 𝐴3 × 𝑓2) 4.25 where l represents factor to account for low-density concrete, f' is the material resistance factor for concrete, 𝑐" is the cohesion stress, Ag1 is the rectangular wall cross-section area around the connection, As is the rebar area, µ is the coefficient of friction and fy is the rebar yield strength. The number of shear friction connections, N, is the ratio of shear force at the connection and shear capacity of the connection, as shown in Equation 4.15. 𝑁 = 𝑉/𝑉0 4.26 The above equations for determining the shear capacity of the connection are based on deformed steel rebars. However, no specific provisions or equations are available for calculating the shear capacity of smooth rebars such as SMA. Therefore, the same equations could be used to determine the shear capacity of the connection. However, it is important to note that because of the smooth surface of the rebar, the shear capacity may be reduced due to the reduction in bond stress. 4.4 Summary The chapter contributed to designing an alternative jointed wall system through a novel connection using SMA rebar and couplers. The monotonic response of the proposed wall system consisting of the new connection is discussed with various equations. The SMA and coupler anchor are 55 designed as per the available guidelines for the grouted dowel connection (CPCI, 2017; PCI, 2021), which are for the deformed steel rebar. The proposed novel connection will be tested to check the effectiveness of the anchor system and study the force-deformation response of the connection. In Chapter 5, the details about each type of specimen, construction, test setup, and testing procedures will be discussed. 56 Chapter 5: Experimental Program 5.1 Introduction To ensure the shape memory alloy (SMA) rebar fracture failure and the load transfer mechanism of the proposed system using SMA rebar and couplers described in Chapter 4, various tests need to be performed. Chapter 5 provides details of the experimental program conducted in a section of the proposed system. The chapter includes a discussion of the design of the test specimens, their material properties, and the construction process. It also covers the test setup and the testing program used for experimental evaluation. Figure 5.1 shows the three types of tests conducted to evaluate the performance of SMA rebar and coupler anchors. The tests included the coupler pullout test, the pullout test of rebar in a concrete block, and the wall-to-wall connection test. Each test is related to the next test, so the tests started from simple to complex. The first test was a coupler pullout test, shown in Figure 5.1(a) to make sure that the SMA rebar was stressed to its yield capacity and attained its full superelastic strain range. This test also helped identify the failure modes for the SMA rebar with a coupler. Four specimens were prepared for the coupler pullout test. The next step involved the pullout test of rebar in a concrete block, shown in Figure 5.1(b) to check the effectiveness of anchorage of the SMA rebar with the coupler and surrounding grout inside the metal duct. This test helped determine the amount of slip in the coupler and whether it had enough grip. It also helped check the failure modes of the SMA rebar with a coupler in the grouted metal duct. Seven specimens were prepared for the pullout test. Finally, a wall-to-wall connection test shown in Figure 5.1 (c), 57 was conducted to investigate the force-deformation response of wall-to-wall intersections. Three specimens were prepared for this connection test. (a) (b) (c) Figure 5.1: (a) Coupler pullout test (b) pullout test of rebar in a concrete block (c) wall-to-wall connection test Before conducting the three different types of tests mentioned above, material tests were performed to determine mechanical properties. The material tests also provided valuable information on the strength and strain of the rebar that was used to predict the expected results of the three different tests. 58 5.2 Material properties This section discusses the various materials used to construct the test specimens. Four different types of materials were used in total. The reinforcement materials included steel and NiTi rebars. Additionally, self-consolidating concrete and grout were used in the construction process and were also tested. 5.2.1 Steel rebar The 12.7 mm smooth steel rebar specimens were tested following the CSA G30.18 (CSA, 2021) and ASTM A370 (ASTM, 2016) standards. The specimens for tensile testing were 500 mm in length, with a 75 mm grip length at each end, resulting in a clear length of 350 mm. Each rebar specimen was subjected to a loading rate of 3.5 mm/min (with a range of 3.15 mm/min to 7.35 mm/min) throughout yielding and until strain hardening. A loading rate of 17.5 mm/min (range of 17.5 mm/min to 175 mm/min) was applied until rebar failure. The test specimens used two types of 12.7 mm smooth steel rebar. Mainly rebar type 1 is used in the coupler pullout test, pullout test of rebar in concrete block, and wall-to-wall connection test. Only the mill certificate of the rebar Type 1 was provided by the company and the results are shown in Table 5.1. Therefore, to validate the mill certificate result, the rebar test was done using an extensometer. The obtained test results of the steel rebar type 1 are shown in Table 5.2. The test results for yield strength, ultimate strength, and ultimate strain were 391 MPa, 517 MPa, and 27%, respectively. These results closely matched the mill certificate values of 373 MPa for yield strength, 526 MPa for ultimate strength, and 28% for ultimate strain. The stress-strain response of one of the 12.7 mm steel rebar type 1 is shown in Figure 5.2. Rebar type 2 is only used in the three 59 pullout test specimens. Therefore, only the yield and ultimate tensile strength of the rebar type 2 were necessary and measured accordingly. The obtained test results for the type 2 rebar are shown in Table 5.3. Table 5.1: Company provided steel rebar properties (Rebar Type 1) Yield strength (MPa) 373 Ultimate tensile strength (MPa) 526 Strain at rupture (%) 28 Table 5.2: Steel rebar properties (Rebar Type 1) Yield strength (MPa) 391 Yield strain (%) 0.19 Modulus of Elasticity (GPa) 206 Ultimate tensile strength (MPa) 517 Strain at rupture (%) 27 Table 5.3: Steel rebar properties (Rebar Type 2) Yield strength (MPa) 275 Ultimate tensile strength (MPa) 398 60 Figure 5.2: Sample stress-strain response of a 12.7 mm smooth steel rebar (Type 1) 5.2.2 SMA rebar Table 5.4 and Table 5.5 show the mechanical and chemical properties of the NiTi SMA provided by the company. The company provided two mill certificates, which are attached in Appendix C, and the test results are shown in Table 5.4 and Table 5.5. In the first mill certificate, the ultimate tensile strength and strain at rupture were 727 MPa and 18.1%, respectively (Table 5.4). Similarly, in the second mill certificate, the ultimate tensile strength and strain at rupture were 1076 MPa and 33.9%, respectively (Table 5.5). The difference between the first and second mill certificates was due to some factors, including rebar diameter, loading rate, material composition, and batch-to-batch variability. In the first mill certificate, the rebar diameter was 16 mm, while it was 6 mm in the second certificate. In the next chapter, Chapter 6 results and discussion, the coupler pullout 01002003004005006000 5 10 15 20 25 30Axial stress (MPa)Axial strain (%) 61 test, pullout test of rebar in a concrete block and wall-to-wall connection test results were closer to the first mill certificate, so the ultimate tensile strength and ultimate strain values are considered accordingly in the estimation of the test results. As per the company’s mill certificate, the Nitinol bars were heat treated to maintain the austenite material phase at a starting temperature (As) of -30°C for superelastic behavior in operational ambient temperatures above the finishing temperature of -10°C (Af). Table 5.4: Company provided NiTi properties (Mill certificate 1) Mechanical Properties Ultimate tensile strength 727 MPa Strain at rupture 18.1 % Austenite Start Temperature (As) -30 °C Austenite Finish Temperature (Af) -10 °C Chemical Properties Nickel 55.95 % Titanium Balance Table 5.5: Company provided NiTi properties (Mill certificate 2) Mechanical Properties Ultimate tensile strength 1076 MPa Strain at rupture 33.9 % Upper Plateau stress 412 MPa Lower Plateau stress 87 MPa Modulus of Elasticity 61 GPa Residual strain 0.205 % 62 The obtained test results of the NiTi SMA rebar are shown in Table 5.6. The SMA rebar was tested following ASTM F2516-22 (ASTM, 2022a) and ASTM E8/E8M-22 (ASTM, 2022b) standards at room temperature. A dogbone-shaped specimen of the SMA rebar was made using the ASTM E8/E8M-22 (ASTM, 2022b) standard, with a reduced diameter of 6 mm and a gauge length of 24 mm, as shown in Figure 5.3. The testing process included loading the rebar to 6% strain, unloading to 7 MPa, and then reloading until it failed to achieve the ultimate strength and strain. The NiTi SMA rebar tensile test setup is shown in Figure 5.4. The strain in the rebar is measured by the extensometer attached to the specimen. The specimen was loaded at a constant rate of 0.153 mm/min, which remained below the maximum allowable loading rate of 0.24 mm/min until it reached 6% strain. The specimen was then unloaded at a rate of 1.53 kN/min until it reached 7 MPa. The second loading cycle involved loading the specimen at a rate of 1.53 mm/min, which remained below the maximum allowable loading rate of 2.4 mm/min until it ultimately failed. The stress-strain response of the SMA rebar is shown in Figure 5.5. Table 5.6: NiTi properties Upper Plateau Stress (at 3% strain during first loading) 360.3 MPa Lower Plateau Stress (at 2.5% strain during unloading) 14.5 MPa Residual strain (at 7 MPa stress, after 6% strain) 2.24 % Yield strength 320 MPa Modulus of Elasticity 46 GPa Ultimate tensile strength 1112 MPa Strain at rupture 28.5 % 63 Figure 5.3: SMA dogbone Figure 5.4: SMA dogbone tensile test 64 Figure 5.5: Stress-strain response of SMA dogbone 5.2.3 Concrete The concrete used in the pullout test of rebar in a concrete block and wall-to-wall connection test was self-consolidating provided by the local precast plant. The mechanical properties of the concrete were determined according to the procedure outlined in the ASTM C39 (ASTM, 2009) and ASTM C496 (ASTM, 2011) standards. The 28-day concrete compressive and splitting tensile strengths (average values obtained on three identical 100 mm x 200 mm cylinders) were 62.52 MPa and 5.62 MPa, respectively. 5.2.4 Grout The grout used in the pullout test and connection test specimens is a high-strength, non-shrink grout, SikaGrout-212. The water-to-grout ratio was prepared per the specifications provided by 0200400600800100012000 5 10 15 20 25 30Axial stress (MPa)Axial strain (%) 65 the company. However, the water-to-grout ratio was kept to 0.16, which was within the recommended 0.18 (4.6 litres of water / 25 kg bag of grout). This 0.16 ratio was chosen to increase the mixture's viscosity without making it thicker and ensuring the grout flows inside the metal duct. The compressive strength of grout was determined as per the procedure outlined in ASTM C109 (ASTM, 2021) standard. The average 28-day compressive strength was 75.21 MPa. All specimens were cured for 28 days at ambient conditions in the curing room. 5.3 Coupler pullout test The main purpose of the coupler pullout test is to ensure that the SMA rebar is stressed to its yield capacity and attains its full superelastic strain range. This test will help determine how much the SMA rebar slips inside the coupler. It will also identify the failure modes for the rebar inside a coupler. It is the first time this test will be done in which all six screws are proposed to clamp the SMA rebar, maximizing clamping force and preventing rebar slippage failure inside the coupler. 5.3.1 Construction of the coupler pullout specimen For the coupler pullout test, the 12.7 mm SMA or steel rebar was 400 mm long and inserted inside the coupler’s full length. The internal diameter of the D250L bar lock L-series coupler is 20 mm, and it is 140 mm long. All six screws were used to clamp the rebar. Figure 5.6(a) shows the detailing, and Figure 5.6 (b) and Figure 5.6 (c) show the two types of test specimens of the coupler pullout tests. 66 (a) (b) (c) Figure 5.6: (a) Coupler pullout specimen (a) detailing (b) SMA and coupler (c) steel and coupler The method used to prepare the SMA or steel and coupler anchor involved smoothening the sharp ends of the screws, as shown in Figure 5.7(a), and making the ends flat to 3.5 mm in diameter, (Alam et al., 2010) as shown in Figure 5.7(b). Additionally, for the SMA and coupler anchor, the flat ends of the screws were curved out equal to the radius of the SMA rebar, as illustrated in Figure 5.7(c). To increase the surface roughness, the internal coupler surface and the entire length of the SMA or steel rebar inside the coupler were sandblasted (Almeida et al., 2020), as demonstrated in Figure 5.7(d) and Figure 5.7(e). In the case of SMA and coupler anchor, 1 mm thick rubber pads were inserted inside the coupler at the screw and SMA touching the surface to avoid the indentation 67 on SMA rebar, as shown in Figure 5.7(f). The bolt head was sheared off with the recommended minimum shear torque of 54 Nm as per the manufacturer’s specification, as shown in Figure 5.7(g). Additionally, to increase adherence between the rebar and the internal coupler, epoxy, a high-strength injectable mortar, was injected through the small hole at the coupler’s mid-length, as demonstrated in Figure 5.7(g) and Figure 5.7(h), ensuring that the epoxy was fully injected inside the coupler. (a) (b) (c) (d) (e) (f) (g) (h) Figure 5.7: SMA and coupler anchor preparation 68 Four specimens were constructed and tested to conduct the coupler pullout testing. The coupler pullout test specimens were named as "Coupler pullout test#_Material". For instance, CPT1_SMA represents coupler pullout test specimen 1 with SMA rebar. Two of these specimens were made using SMA and coupler (CPT1_SMA and CPT2_SMA), while the other two were made with smooth steel rebar and coupler (CPT3_Steel and CPT4_Steel). 5.3.2 Test setup and instrumentation of the coupler pullout test The crosshead speed applied to the SMA and coupler specimens followed the ASTM F2516-22 (ASTM, 2022a) standard, whereas the crosshead speed applied to the steel rebar and coupler specimens followed the ASTM E8/E8M-22 (ASTM, 2022b) standard. Table 5.7 provides the details of the coupler pullout tests. SMA rebar with coupler specimens (CPT1_SMA and CPT2_SMA) were subjected to loading at a constant rate of 0.153 mm/min until they reached 6% strain, after which they were unloaded at a rate of 1.5 kN/min to 7 MPa for the first cycle. The specimen was then loaded until failure at a rate of 1.53 mm/min. One specimen of smooth steel rebar and coupler (CPT3_Steel) was tested similarly to the SMA and coupler specimens to compare the results, while the other specimen (CPT4_Steel) was tested under tension load only. 69 Table 5.7: Coupler pullout test matrix Specimen Rebar Loading rate Load to 6% strain (mm/min) Unload (kN/min) Load to failure (mm/min) CPT1_SMA SMA 0.153 1.5 1.53 CPT2_SMA SMA 0.153 1.5 1.53 CPT3_Steel Steel 3.5 13.0 17.5 CPT4_Steel Steel 3.5 - 17.5 The coupler pullout test was tested under tension in an MTS machine using an apparatus. The test specimen was placed in a pullout apparatus of size 200 mm x 200 mm x 480 mm, as shown in Figure 5.8. Figure 5.9(a) shows the test setup, and Figure 5.9(b) shows the specimen in the MTS 370 machine. The rebar and coupler anchor were inserted through a 25 mm steel plate of pullout apparatus. This plate acted as a coupler reaction plate, allowing rebar tension. To measure the displacement (slippage) of the rebar inside the coupler, one Linear Variable Differential Transformer (LVDT) was employed at the top of the specimen (LVDT 1). Another LVDT was used to measure the rebar elongation at the bottom, as depicted in Figure 5.9. Two strain gauges were attached to the rebar to record its strain. The yield and ultimate load were measured by the MTS machine; thus, yield and ultimate stress were obtained. The yield stress was determined by dividing the yield load by the rebar cross-sectional area, while the ultimate stress was calculated by dividing the ultimate or maximum load by the rebar cross-sectional area. The assembled test specimens were 400 mm in length and weighed 1.15 kg. 70 Figure 5.8: Pullout apparatus 200 mm 200 mm 480 mm 71 (a) (b) Figure 5.9: Coupler pullout test setup: (a) schematic (b) specimen in MTS 370 machine 5.3.3 Expected result of the coupler pullout test The stress-strain relationship was expected to be linear up to yielding stress (fy). After yielding, there could be an increase in slippage of the rebar. The expected failure pattern during the testing was rebar rupture for the steel rebar and coupler pullout test. In contrast, rebar rupture or rebar 2 Strain gaugesLVDT 2LVDT 1CouplerSMA or smooth steel rebarApparatus 72 slippage failure could occur for the SMA rebar and coupler pullout test. The expected results of the tests are shown in Table 5.8. Table 5.8: Expected performance during coupler pullout test Specimen with rebar Yield stress (MPa) Ultimate stress (MPa) Failure Mode SMA 320 727 Rebar fracture / rebar slippage Steel (Type 1) 391 517 Rebar fracture 5.4 Pullout test of rebar in a concrete block The main purpose of the pullout test of a rebar in a concrete block is to check the effectiveness of the SMA rebar's anchorage with the coupler and surrounding grout inside the grouted metal duct placed in a concrete block. This test will help determine the coupler's slippage and whether it has enough grip. It will also check the failure modes of the SMA rebar with a coupler in the grouted metal duct placed in the concrete block. 5.4.1 Construction of the pullout test of rebar in a concrete block specimen The pullout test specimens were constructed with dimensions of 200 mm in length, 200 mm in width, and 325 mm in height. A 65 mm metal duct was placed in the center of each test specimen before casting concrete. After pouring the concrete, the SMA rebar or smooth steel rebar with the coupler head was post-installed, and a non-shrink grout with a strength of 75.21 MPa was filled inside the metal duct. At the active end (loading end), the SMA rebar or smooth steel rebar was inserted inside a PVC pipe to reduce the stress concentration effect on the concrete. This debonding 73 technique follows the recommendations of the ACI Committee 408 (ACI, 2003), which is necessary for preventing compression stresses induced by pullout testing that affect the bond behavior of the bar. Figure 5.10(a) and (b) shows the pullout test specimens with SMA and coupler anchor, and steel rebar and coupler anchor in concrete blocks. (a) (b) Figure 5.10: Pullout of rebar in a concrete block specimen (a) SMA and coupler (b) steel and coupler Seven specimens were constructed and tested for the monotonic pullout load testing. For SMA rebar with coupler specimens, one specimen included 6.35 mm ties and another specimen was prepared without ties. The ties were included to represent the part of the boundary element of the precast wall connection. For steel rebar and coupler specimens, three specimens without ties and two with ties were prepared. Specimens were named as "Pullout test#_Material_with / without 74 ties" for the pullout test of rebar in a concrete block. For instance, PT1_SMA_T represents pullout test specimen 1 with SMA and coupler anchor with ties under monotonic loading. Similarly, PT4_Steel represents test specimen 4 with steel and coupler anchor without ties under monotonic loading. The detailing of the pullout test specimen is shown in Figure 5.11. (a) (b) Figure 5.11: Pullout of rebar in a concrete block specimen detailing: (a) without ties (b) with ties ACI 318-19 (ACI, 2019b) recommends that the net bearing area for headed bars be at least 4 times the rebar area. The net bearing area is the difference between the head and rebar areas and plays a 150200150Metal duct Ø65200Coupler Ø333251501101407530303251501101407530306.35mmties @ 150mmSMA or smooth steel rebarCouplerVoidConcreteMetal ductGroutPVC pipe200 200200 200 75 significant role in deciding the anchorage strength. In a designed SMA rebar or smooth steel rebar with a coupler anchor pullout test specimen, the net bearing area is 5.6 times larger (726 mm2) than the rebar area (129 mm2). Additionally, the coupler diameter (33 mm) is 2.6 times larger than the SMA rebar diameter (12.7 mm). The bond capacity of this type of anchor depends on the coupler's cross-sectional area and height, as well as the embedment length. The overall head geometry of the coupler is responsible for transferring the tensile load to the grout below the head anchor. 5.4.2 Test setup and instrumentation of the pullout test of rebar in a concrete block The pullout test of rebar in a concrete block was tested under tension only in an MTS machine following a procedure similar to the ASTM C234 (ASTM 1988) standard. Figure 5.12(a) shows the test setup, and Figure 5.12(b) shows the specimen in the MTS 370 machine. The SMA or steel rebar was inserted through the bottom 25 mm steel plate in the pullout apparatus, which acted as a reaction plate to the concrete block to allow for tension in the rebar. The top LVDT placed at the unloaded end at the top of the specimen (LVDT 1) was used to measure the displacement (slippage) of the rebar inside the coupler in a concrete block. Another LVDT was clamped at the middle of the rebar at the bottom (LVDT 2), as shown in Figure 5.12. Additionally, two strain gauges were attached to the center of the rebar at the bottom to measure strain on the rebar. The assembled specimens weighed 31 kg and were approximately 325 mm long. A one-ton crane was used to lift the specimens and apparatus onto the MTS 370 machine. Table 5.9 provides the details of the pullout tests. The test was carried out with a uniform loading rate of 0.5 mm/min for the SMA rebar with coupler specimens (PT1_SMA and PT2_SMA_T), 1.0 mm/min for the steel rebar with 76 coupler specimens (PT3_Steel and PT4_Steel) and 2.0 mm/min for the steel rebar with coupler specimens (PT5_Steel, PT6_Steel_T and PT7_Steel_T) until failure. (a) (b) Figure 5.12: Pullout of rebar in a concrete block test setup: (a) schematic (b) specimen in MTS 370 machine LVDT 2LVDT 1CouplerSMA or smooth steel rebarApparatusMetal ductVoidConcreteGrout2 Strain gauges 77 Table 5.9: Pullout test of rebar in a concrete block matrix Specimen With / without ties Rebar yield strength (MPa) Rebar type Loading rate (mm/min) PT1_SMA Without ties 320 SMA 0.5 PT2_SMA_T With ties 320 SMA 0.5 PT3_Steel Without ties 391 Steel 1.0 PT4_Steel Without ties 391 Steel 1.0 PT5_Steel Without ties 275 Steel 2.0 PT6_Steel_T With ties 275 Steel 2.0 PT7_Steel_T With ties 275 Steel 2.0 5.4.3 Issues during the pullout test of rebar in a concrete block The two strain gauges were damaged when the specimen’s rebar was inserted through the apparatus's 25 mm central hole. Consequently, the stress and axial strain plots for the steel rebar could not be generated. Similarly, the LVDT 2 could not accurately record readings because the smooth steel rebar became thinner with higher elongation. Consequently, the clamp holding the LVDT 2 became loose and tilted due to its weight. Therefore, the rebar stress vs rebar elongation for LVDT 2 could not be plotted. However, in the case of the SMA rebar with a coupler, the LVDT 2 could provide the correct reading as the elongation of the SMA rebar was not as significant compared to the steel rebar. 78 5.4.4 Expected result of the pullout test of rebar in a concrete block There are several potential failure modes expected during the pullout test at grouted dowel connections, including rebar slip, slippage of SMA rebar, pullout failure and rebar fracture. Although rebar slip is a common failure mode in smooth rebar, the coupler, which acts as a head to the SMA rebar, will provide the necessary bearing force on concrete to prevent rebar slip. Another possible failure mode is the slippage of the SMA rebar inside the coupler. To prevent this, there are six screws in place to maximise clamping force. Pullout failure occurs when the embedded length of the rebar is too short, resulting in low bearing force due to low bond strength in grout and concrete. The most likely failure mode is rebar fracture, which happens when the applied tension load exceeds the tensile strength of the rebar. In the proposed SMA rebar with couplers anchor assembly, the rupture strength depends on the SMA rebar's tensile strength. The expected performance during the pullout test is given in Table 5.10. Table 5.10: Expected performance during pullout test of rebar in a concrete block Specimen with rebar Yield stress (MPa) Ultimate stress (MPa) Failure Mode SMA 320 727 Rebar fracture / rebar slippage Steel (Type 1) 391 517 Rebar fracture Steel (Type 2) 275 398 Rebar fracture 5.5 Wall-to-wall connection test The main purpose of the wall-to-wall connection test is to investigate the force-deformation response of the proposed anchoring system for SMA-reinforced PC wall-to-wall intersections. The 79 chapter considers a part of the wall-to-wall intersection to understand the local behavior. This part of the study represents the boundary element of the PC shear wall having a jointed ductile connection at wall-to-wall intersections, shown in Figure 5.13. When lateral loading is applied at the intersection of two walls, the selected section of the boundary element moves back and forth in the plane. The SMA rebar and couplers anchor assembly at the connection is placed to withstand both tension and compression loads during cyclic loading. The wall moves only upward, forming a gap and returning to its initial position. In reality, the concrete toe is crushed in the ultimate failure mode of the wall. However, the study aims to understand the behavior of the energy dissipation rebar within the metal duct of the proposed system. Therefore, the study limits the system's gap opening and closing in tension and focuses on how the rebar can handle it without exploring damage to the concrete in the compression range. Figure 5.13: Walls connected with the proposed connection Part of studyGroutSMA and couplers anchor Metal ductPC shear wallPC shear wall 80 5.5.1 Construction of the wall-to-wall connection specimen The wall-to-wall connection test specimens are 200 mm long, 200 mm wide and 1050 mm high as shown in Figure 5.14. The specimens' cross-section and detailing are illustrated in Figure 5.14. The different stages involved in creating the test specimens are sketched in Figure 5.15. Each specimen consists of two identical blocks comprising four 10M vertical steel rebars welded to a 25 mm steel plate for both top and bottom block specimens, Figure 5.15 (step 1). These vertical steel rebars are extended from the formwork to facilitate the welding of the plates. In the next step, 6.35 mm ties at a spacing of 150 mm around 10M steel rebars and a 65 mm metal duct at the middle of the four 10 M vertical rebars were placed before casting concrete as shown in Figure 5.15 (step 2). Once the concrete was poured to make identical concrete blocks, Figure 5.15 (step 3), the anchor with SMA rebar or smooth steel rebar and two couplers was post-installed. Later, a non-shrink grout filled the metal duct and gap between the two blocks as shown in Figure 5.15 (steps 4 to 6). 81 Figure 5.14: Wall-to-wall connection specimen detailing 105025mm plate16mm plate25mm grout512.525512.5Coupler Ø33Section AA'A'AB'B12.7 mm SMAorsmooth steel rebar 200Metal duct Ø65401204012.7 mm SMAorsmooth steel rebarMetal duct Ø65200Section BB'20040120402006.35 mm ties@ 150 mm10M rebar10M rebar6.35 mm ties@ 150 mmStep 110M steel rebar25 mm plate6.35 mm ties65 mm metal ductStep 2 Step 3Concrete block 82 Figure 5.15: Construction steps Three specimens were constructed for the test. The connection test specimens were named “Connection test#_Material”. For example, CT2_SMA represents connection test specimen 2 with SMA rebar under monotonic loading. Two specimens (CT1_SMA and CT2_SMA) were made using SMA rebar and coupler anchor. A specimen (CT3_Steel) with smooth steel rebar and coupler anchor was prepared to compare the results with the SMA rebar with the coupler anchor. The unbonded length of the SMA rebar in the anchor was designed considering the 2% and 1.5% global wall drift, which is directly linked to the unbonded length of the SMA rebar as described in the Step 4 Step 5 Step 612.7 mm SMA or smooth steel rebar33 mm coupler25 mm grout Non-shrink grout 83 previous section 4.2.2. The higher the wall's drift, the higher the unbonded length. The reviewed literature on various SMA RC shear walls and precast tests have employed the drift ratio within the 2% to 3% range. Therefore, the current study used a 2% and 1.5% drift ratio to ensure that the connection test specimen's size is appropriate for testing in the MTS machine. The detailing of three different types of connection test specimens is shown in Figure 5.16. The testing process involved three specimens subjected to monotonic loading. The details of the connection test are provided in Table 5.11. (a) CT1_SMA and CT3_Steel (b) CT3_Steel Figure 5.16: Wall-to-wall connection test specimens (a) CT1_SMA and CT3_Steel (b) CT2_SMA 10501401132511314075160.5160.575530105025 mm plate140147.525147.5140751251257560016 x 75 mm gripping plate25 mm groutSMA or smooth steel rebarGrout6.35 mm ties10M steel rebarMetal ductCoupler 84 Table 5.11: Wall-to-wall connection test matrix Specimen Wall drift (%) Unbonded length (mm) Rebar CT1_SMA 2.0 320 SMA CT2_SMA 1.5 250 SMA CT3_Steel 2.0 320 Steel 5.5.2 Test setup The wall-to-wall connection test was conducted under tension load between two concrete blocks on the MTS 370.50 machine with a capacity of 500 kN. The specimens were 1050 mm long and weighed 90 kg. They were lifted onto the MTS 370 machine using a one-ton crane and secured at both ends using flat-shaped hydraulic grips, ensuring adequate gripping length and minimum required pressure. Once clamped at the MTS machine, LVDTs and wire sensors were attached to the specimens. They were then connected to the data acquisition (DAQ) system and the instruments were calibrated before beginning the test. Figure 5.17(a) shows the test setup and Figure 5.17(b) shows the specimen in the machine before the test began. The tests were carried out using a displacement-controlled loading procedure. 85 (a) (b) Figure 5.17: Wall-to-wall connection test setup: (a) schematic (b) specimen in MTS 370 machine 5.5.3 Loading protocol For the monotonic test, the crosshead speed was applied as per the ASTM E8/E8M-22 (ASTM, 2022b). A displacement-based loading protocol was applied as per clause 7.6.4.3 Control Method C – crosshead speed control method for determining yield properties and clause 7.6.5 speed of 25 mm plate25 mm grout16 x 75 mm gripping plateConcrete block 1Concrete block 2 86 testing when determining tensile strength. A loading rate of 0.06 mm/min was applied up to yield force and 1mm/min until failure. 5.5.4 Instrumentation The instrumentation layouts for specimens are shown in Figure 5.18, Figure 5.19 and Figure 5.20. Two wire sensors and ten LVDTs were installed to record the local and overall displacement of the specimen. The two wire sensors (WS) were fixed to the ends of each specimen to ensure accurate data in case of grip slippage. WS (F) was fixed at the front, while WS (B) was placed at the back of the specimen. The LVDTs were clamped so that the instrument measures the displacement at different specimen sections. Five LVDTs were attached on the left and right sides of the specimen. The position of these LVDTs was intentionally alternated on the opposite sides to measure the displacement at each location accurately. The LVDTs and wire sensors were connected to the data acquisition system (DAQ), which was utilized to interpret the measured displacement and force responses. The MTS-embedded LVDT measured the total displacement of the specimen and axial force on the specimen. 87 Figure 5.18: Wire sensors position for CT1_SMA, CT2_SMA and CT3_Steel 1050Front viewWS (F)1050Back viewWS (B)WS (F) - wire sensor (front)WS (B) - wire sensor (back) 88 Figure 5.19: LVDTs position for CT1_SMA and CT3_Steel 10502351851812518185235 LP10LP09LP08LP07LP06Right side view4025Left side view4040702351851812518185235 LP01LP02LP03LP04LP051050 - wooden block- LVDT 89 Figure 5.20: LVDTs position for CT2_SMA 5.5.5 Expected result of the wall-to-wall connection test A gap opening in the middle of the specimen during the testing is expected. The middle grout section is the weakest for the wall-to-wall connection test specimens, consisting of only one unbonded SMA or steel rebar. Therefore, the ultimate strength and displacement are predicted corresponding to the weakest part of the specimen, as the rebar fracture failure mode is expected in the connection test specimens. The rebar is expected to elongate its unbonded length. The estimated yield and ultimate loads were determined by taking the rebar strength times the rebar area as shown in Equation 5.1 and Equation 5.2. The estimated ultimate displacement was 10502002201812518220200 LP10LP09LP08LP07LP0640254040702002201812518220200 LP01LP02LP03LP04LP051050 - wooden block- LVDTRight side viewLeft side view 90 determined by taking the ultimate strain times the unbonded length between the couplers as shown in Equation 5.3. The expected performance during the monotonic connection test is summarized in Table 5.12. 𝐹21 = 𝑓2 × 𝐴3 5.1 𝐹41 = 𝑓4 × 𝐴3 5.2 d41 = e4 × 𝑙1 5.3 where, fy is the rebar yield strength, fu is the rebar ultimate strength, As is the rebar area, eu signifies the ultimate strain, le stands for the unbonded length of the rebar, Fye represents the estimated yield load, Fue is the estimated ultimate load and due is the estimated ultimate displacement which will correspond to the maximum elongation in the rebar. Table 5.12: Expected performance during the wall-to-wall connection test Specimen As (mm2) le (mm) fy (MPa) fu (MPa) eu (%) Fye (kN) Fue (kN) due (mm) Failure Mode CT1_SMA 129 320 320 727 18.1 41.3 93.8 57.9 Rebar fracture / rebar slippage CT2_SMA 129 250 320 727 18.1 41.3 93.8 45.3 Rebar fracture / rebar slippage CT3_Steel 129 320 391 517 27 50.4 66.7 86.4 Rebar fracture 91 5.5.6 Cost of SMA specimen The cost associated with preparing the proposed wall-to-wall connection test specimen mainly depends on the cost of the SMA rebar. For this research study, a nickel-titanium (NiTi) alloy was selected because of its superior suitability for structural applications in building construction. NiTi offers several advantages, including significant strain recovery, high superelasticity, and exceptional corrosion resistance. However, the cost of NiTi rebar is substantially higher than that of conventional steel, with a purchase price of US$620.4/kg from the manufacturer for this study’s specimen construction. Although using NiTi rebar results in a substantially higher cost for individual wall-to-wall connection test specimens when compared to specimens constructed with smooth steel rebar, the overall cost impact on the entire building project is less significant. In the context of full-scale building construction, the cost of materials, labour and everything else will not make a significant difference in the whole building project, making using SMA in critical areas less impactful on the total budget. Previous studies have shown that integrating SMA in crucial locations within a building results in long-term benefits. These benefits include reducing structural and non-structural damage and minimizing the risk of injury and fatalities during seismic events (Aghajani and Asadi, 2023; Bruno and Valente, 2002). Therefore, while the initial investment in SMA rebar is higher, the long-term advantages, such as reduced post-earthquake repair costs and improved structural performance resulting in reduced economic loss and minimizing human risks associated with the 92 major earthquake, outweigh the initial costs. This makes SMA a cost-effective choice for owners and developers over the building's life cycle, especially in regions prone to seismic activity. 5.6 Summary This chapter provided detailed information about the three tests, which are the coupler pullout test, the pullout test of rebar in a concrete block and the wall-to-wall connection test. Accordingly, the methodological approach taken in specimen design and construction for each test is provided. In addition, testing setups, loading protocol and instrumentation plans are discussed. This chapter explored the expected performance of the three tests, concluding all tests are suitable for experimentation. In the next chapter, Chapter 6 will present and discuss the test results for each type of test. 93 Chapter 6: Test Results and Discussion 6.1 Introduction This chapter discusses the results of different tests proposed in the previous chapter, Chapter 5. The coupler pullout test results are presented first, followed by the pullout test of rebar in a concrete block and wall-to-wall connection test results. The four coupler pullout tests were conducted to ensure the rebar was stressed beyond its yield capacity in the proposed anchor system. Similarly, the seven pullout tests of rebar in a concrete block were conducted to check the effectiveness of SMA and coupler anchorage in grout inside the metal duct. Finally, the three wall-to-wall connection tests were conducted under monotonic loading to understand the response of the proposed novel connection at the wall-to-wall intersections. 6.2 Coupler pullout test results Four coupler pullout tests were conducted, and their results are presented and discussed below. Table 6.1 summarizes the coupler pullout test results. The initial two tests were performed on SMA and coupler anchor specimens. The first coupler pullout test specimen with SMA rebar (CPT1_SMA) exhibited premature failure, while the second specimen (CPT2_SMA) showed ductile failure. The premature failure of CPT1_SMA was caused by an indentation made by the flat head of the screw on the SMA rebar, resulting in high-stress concentration at the point of contact. This issue was prevented in CPT2_SMA by curving out the sharp ends of the screws to match the radius of the SMA rebar. Furthermore, a 1mm thick rubber pad was inserted inside the coupler between the coupler's screw and the SMA rebar to resolve the issue. The remaining two tests were conducted on steel and coupler anchor specimens (CPT3_Steel and CPT4_Steel). Both 94 specimens showed ductile failure. The rebar fracture location was inside the coupler for the CPT1_SMA specimen, whereas it was outside the coupler for the remaining three specimens (CPT2_SMA, CPT3_Steel and CPT4_Steel), as shown in Figure 6.8. Table 6.1: Coupler pullout test results Specimen Ultimate stress (MPa) Rebar slip at ultimate (mm) Failure mode Failure Location CPT1_SMA 422 0.5 Premature fracture Inside coupler CPT2_SMA 614 0.3 Rebar fracture Outside coupler CPT3_Steel 492 0.3 Rebar fracture Outside coupler CPT4_Steel 492 0.1 Rebar fracture Outside coupler Figure 6.1 shows the rebar stress vs axial strain of two tests, CPT1_SMA and CPT2_SMA. Specimen CPT1_SMA reached 6% strain in the first loading cycle and was unloaded to 7 MPa. However, it prematurely failed at 1.13% strain during the second loading cycle before reaching its superelastic strain (6% strain). This premature failure was due to the indentation made by the coupler’s screw on the SMA rebar resulting in stress concentration at the location. Figure 6.2(a) shows the indentation on the SMA rebar, and Figure 6.2(b) shows the location of the rebar fracture inside the coupler due to indentation. Despite the screw's head being flat, it caused penetration on the SMA rebar. To rectify this indentation issue, the second coupler pullout test specimen, CPT2_SMA, was prepared using the remaining piece of SMA rebar from the first test. As explained in detail in section 5.3.1, for CPT2_SMA, the sharp ends of the screws were curved out equal to the radius of the SMA rebar. Then, 1 mm thick rubber pads were inserted inside the 95 coupler at the screw and SMA touching the surface to avoid indentation on the SMA rebar. This SMA rebar piece was used since it failed before reaching the superelastic strain range. The length of the SMA rebar was 278 mm in CPT2_SMA, which was shorter than the previous specimen CPT1_SMA with 400 mm in length. The CPT2_SMA specimen reached 6% strain in the first loading cycle and was unloaded to 7 MPa. However, a residual strain of 0.75% was observed in the CPT2_SMA specimen. This was because of using the remaining piece of SMA rebar from the first test, CPT1_SMA. During the second loading cycle, the CPT2_SMA specimen exceeded its superelastic strain range, reaching 8.19% strain before rebar rupture. As a result, the SMA coupler anchor was made the same way for pullout and connection tests. Figure 6.1: Rebar stress vs axial strain (CPT1_SMA and CPT2_SMA) 01002003004005006007000 2 4 6 8 10Rebar stress (MPa)Axial strain (%)CPT1_SMACPT2_SMARupture 96 (a) (b) Figure 6.2: (a) CPT1_SMA indentation on the SMA rebar and (b) location of rebar fracture inside the coupler Figure 6.3 shows the rebar stress vs rebar slip of two tests, CPT1_SMA and CPT2_SMA. In both tests, initial slippage occurred due to the adjustment of the LVDT 1 needle positioned at the top of the rebar. The initial loading caused vibration in the specimen and apparatus, resulting in measurable slippage. In CPT1_SMA, an initial slippage of 0.10 mm was observed when the specimen was loaded to 6% strain. The corresponding stress in the rebar was 422 MPa. No further increase in slippage was noticed during unloading, and it remained constant at 0.10 mm slippage. During the second loading cycle, the slippage increased to approximately 0.5 mm by the end of the test. In contrast, the first loading cycle of CPT2_SMA showed a slippage of 0.30 mm at the same 6% strain, with a higher corresponding rebar stress of 614 MPa. Similar to CPT1_SMA, there was no increase in slippage upon unloading. In the second loading cycle, the slippage in CPT2_SMA increased to 0.35 mm, which was lower than the final slippage observed in CPT1_SMA. The results from the two tests show that CPT2_SMA had a higher stress capacity and demonstrated less overall slippage compared to CPT1_SMA. This was because of the 97 improved SMA and coupler anchor assembly, which involved curving out the sharp ends of the screws and inserting a 1 mm thick rubber pad in CPT2_SMA. Figure 6.3: Rebar stress vs rebar slip (CPT1_SMA and CPT2_SMA) Figure 6.4 shows the rebar stress vs axial strain of two tests, CPT3_Steel and CPT4_Steel. The axial strain was measured by the two strain gauges attached to the SMA rebar. The average yield strain and strength of CPT3_Steel and CPT4_Steel observed during the test were 0.16% and 340 MPa, respectively. In the first loading cycle of the CPT3_Steel specimen, the rebar was loaded to 6% strain and subsequently unloaded to a stress of 7 MPa, resulting in a residual strain of 5.5%. During the second loading cycle, the CPT3_Steel specimen reached 23.5% strain before rebar rupture occurred. In contrast, the CPT4_Steel specimen was subjected to tension loading only, 01002003004005006007000.0 0.1 0.2 0.3 0.4 0.5 0.6Rebar stress (MPa)Rebar slip (mm)CPT1_SMACPT2_SMA 98 reaching a maximum strain of 22.4% before rebar rupture occurred. The average ultimate strength observed for CPT4_Steel was 492 MPa. Figure 6.4: Rebar stress vs axial strain (CPT3_Steel and CPT4_Steel) Figure 6.5 shows the rebar stress vs rebar slip for the CPT3_Steel and CPT4_Steel tests. In both tests, initial slippage was observed because of the adjustment of the LVDT 1 needle at the top of the rebar due to the vibration on the specimen and apparatus during loading. For the CPT3_Steel specimen, a slippage of 0.17 mm was observed when loaded until 6% strain. During unloading, the slippage increased to 0.27 mm and then dropped to nearly 0.05 mm at 7 MPa. Later, after loading again, it increased to 0.3 mm before the rebar fractured. In contrast, in the CPT4_Steel specimen, it can be observed that the initial 0.1 mm slippage is due to the initial adjustment of the 01002003004005006000 5 10 15 20 25Rebar stress (MPa)Axial strain (%)CPT3_SteelCPT4_Steel 99 specimen, which remained constant throughout the testing. In contrast, the CPT4_Steel specimen exhibited an initial slippage of 0.1 mm due to the initial adjustment of the specimen, which remained constant throughout the test, indicating a more stable slip behavior than CPT3_Steel due to the tension loading only. Figure 6.5: Rebar stress vs rebar slip (CPT3_Steel and CPT4_Steel) Figure 6.6 compares the rebar stress versus axial strain of CPT2_SMA and CPT3_Steel tests under one cycle and load-to-failure loading conditions. The SMA and coupler specimen, CPT2_SMA, exhibited a significantly lower residual strain of 0.75% compared to the 5.5% residual strain observed in the steel and coupler specimen, CPT3_Steel. This important finding highlights the superior self-centering capacity of the SMA and coupler anchor, which exhibits 01002003004005006000.0 0.1 0.2 0.3 0.4Rebar stress (MPa)Rebar slip (mm)CPT3_SteelCPT4_Steel 100 low or negligible residual strain compared to the steel and coupler specimens. Such self-centering behavior is particularly advantageous for the PC shear wall systems as it eliminates the need for PT tendons to achieve self-centering, simplifying the structural design and enhancing overall performance. In the first loading cycle, the yield strain of the steel and coupler anchor specimen, CPT3_Steel, was relatively low, measuring 0.14%, compared to approximately 0.70% for the SMA and coupler anchor specimen, CPT2_SMA. Additionally, the observed energy dissipation capacity of CPT2_SMA was 369.61 kN/mm, in contrast to 618.54 kN/mm for the CPT3_Steel specimen. This indicates that the energy dissipation capacity of the steel and coupler anchor specimen, CPT3_Steel, was about 1.6 times higher than that of the SMA and coupler anchor specimen, CPT2_SMA. The ultimate strength of CPT2_SMA was 614 MPa, while it was 492 MPa for CPT3_Steel. Figure 6.6: Rebar stress vs axial strain (CPT2_SMA and CPT3_Steel) 01002003004005006007000 5 10 15 20 25Rebar stress (MPa)Axial strain (%)CPT2_SMACPT3_Steel 101 Figure 6.7 shows the top of the four specimens, CPT1_SMA, CPT2_SMA, CPT3_Steel and CPT4_Steel, after testing, showing very low slippage of rebar inside the coupler for the four tests. Figure 6.8 shows the failure modes and failure locations of the four specimens. (a) (b) (c) (d) Figure 6.7: Top of the specimens after testing (a) CPT1_SMA (b) CPT2_SMA (c) CPT3_Steel (d) CPT4_Steel 102 (a) (b) (c) (d) Figure 6.8: (a) CPT1_SMA - premature failure (b) CPT2_SMA (c) CPT3_Steel (d) CPT4_Steel - ductile failure mode 6.3 Pullout test of rebar in a concrete block results Seven tests were conducted; their results are presented and discussed below. Table 6.2 shows the summary of the test results. The first two tests were performed on SMA and coupler specimens (PT1_SMA and PT2_SMA_T), while the remaining five tests were performed with steel and coupler specimens (PT3_Steel, PT4_Steel, PT5_Steel, PT6_Steel_T and PT7_Steel_T). In the first Location of ductile failure Location of premature failure 103 SMA specimen, PT1_SMA, a rebar slippage failure mode was observed, and the failure location was inside the metal duct at the coupler. In the second SMA specimen, PT2_SMA_T, a rebar fracture failure mode was observed inside the coupler at the third screw from the loading end. The failure location and failure mode for PT1_SMA and PT2_SMA_T are shown in Appendix, Figure A.5 (a) and (b). For all five steel specimens, a rebar fracture failure mode was observed at the rebar. Table 6.2: Pullout test of rebar in a concrete block results Specimen Ultimate stress (MPa) Rebar slip at ultimate (mm) Failure mode Failure location Expected Ultimate stress (MPa) PT1_SMA 664 2.7 Rebar slippage Inside coupler 727 PT2_SMA_T 692 0.3 Rebar fracture Inside coupler 727 PT3_Steel 464 0.5 Rebar fracture At rebar 517 PT4_Steel 487 0.9 Rebar fracture At rebar 517 PT5_Steel 399 0.7 Rebar fracture At rebar 398 PT6_Steel_T 407 0.4 Rebar fracture At rebar 398 PT7_Steel_T 405 0.5 Rebar fracture At rebar 398 Figure 6.9 shows the rebar stress vs rebar slip of two test specimens, PT1_SMA and PT2_SMA_T, under tensile loading. In the PT1_SMA specimen, an initial slippage of about 0.3 mm was observed because of the adjustment of the LVDT 1 needle at the top of the rebar due to the vibrations on the specimen and apparatus during the early stages of loading. However, the slippage remains almost constant until 600 MPa stress. At this stress, the rebar slip increased to 0.5 mm with further loading, 104 and then it reached the maximum stress of 664 MPa, after which a significant rebar slippage of 2.7 mm was observed. In contrast, the PT2_SMA_T specimen showed no significant initial slippage and had a gradual increase in rebar slip to 0.1 mm until 620 MPa. Beyond this stress, the rebar slip reached a maximum of 0.3 mm before rebar fracture at an ultimate stress of 692 MPa. The addition of ties in the PT2_SMA_T specimen provided confinement to the SMA and coupler assembly, increasing the ultimate stress capacity by 4.22% compared to the PT1_SMA. The average stress of these two tests, PT1_SMA and PT2_SMA_T, was 678 MPa, compared to its expected ultimate stress of 727 MPa. Figure 6.9: Rebar stress vs rebar slip (PT1_SMA and PT2_SMA_T) 01002003004005006007008000.0 0.5 1.0 1.5 2.0 2.5 3.0Rebar stress (MPa)Rebar slip (mm)PT1_SMAPT2_SMA_T0.3mm 0.5mm 2.7mm 105 Figure 6.10 shows the rebar stress vs rebar elongation for the PT1_SMA and PT2_SMA_T specimens, where rebar elongation was measured by LVDT 2, clamped at the bottom. In the PT1_SMA specimen, a drop in rebar stress can be observed due to the slippage of the SMA rebar inside the coupler after the specimen reaches the maximum force. This slippage, accompanied by a loud noise, marked the failure of the specimen. However, no significant slippage was observed in the PT2_SMA_T specimen, which can be supported by the gradual increase in the stress before rebar failure. Figure 6.11 shows the tops of the two specimens after testing. Further examination by breaking the specimen confirmed that the PT1_SMA specimen experienced rebar slippage failure inside the coupler, while the PT2_SMA_T specimen failed by rebar fracture within the coupler at the third screw from the loading end, as shown in Figure A.5 (a) and (b). Figure 6.10: Rebar stress vs rebar elongation (PT1_SMA and PT2_SMA_T) 01002003004005006007008000 5 10 15 20 25 30 35 40Rebar stress (MPa)Rebar elongation (mm)PT1_SMAPT2_SMA_TRebar slippage 106 (a) (b) Figure 6.11: Top of the specimen after testing (a) PT1_SMA (b) PT2_SMA_T Figure 6.12 shows the rebar stress vs. rebar slip of two tests, PT3_Steel and PT4_Steel. Both tests ensured the steel rebar was stressed to its maximum capacity, and the maximum observed rebar slip was 0.5 mm for PT3_Steel and 0.9 mm for PT4_Steel. The observed stress in the rebar was 464 MPa and 487 MPa in the PT3_Steel and PT4_Steel specimens, respectively. The average stress of these tests, PT3_Steel and PT4_Steel, was 476 MPa, compared to its expected ultimate stress of 517 MPa. In both specimens, PT3_Steel and PT4_Steel, rebar fracture failure mode was observed at the rebar outside the concrete block. 2.7 mm slippage 0.3 mm slippage 107 Figure 6.12: Rebar stress vs rebar slip (PT3_Steel and PT4_Steel) Figure 6.13 illustrates the rebar stress versus rebar slip of three pullout tests: PT5_Steel, PT6_Steel_T and PT7_Steel_T. Each specimen was stressed to its maximum capacity, resulting in a maximum rebar slip of 0.7 mm for PT5_Steel, 0.4 mm for PT6_Steel_T, and 0.5 mm for PT7_Steel_T. The rebar's corresponding stresses were 399 MPa, 407 MPa, and 405 MPa for PT5_Steel, PT6_Steel_T, and PT7_Steel_T, respectively. The average stress in the three tests was 404 MPa, closely matching the expected ultimate stress of 398 MPa. The reduced rebar slip observed in the PT6_Steel_T and PT7_Steel_T specimens suggests that adding ties provided confinement, thereby influencing the slip behavior. Overall, these results demonstrated minor variations in rebar slippage while showing rebar fracture failure mode outside the concrete block at the rebar. 01002003004005006000.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Rebar stress (MPa)Rebar slip (mm)PT4_SteelPT3_Steel 108 Figure 6.13: Rebar stress vs rebar slip (PT5_Steel, PT6_Steel_T and PT7_Steel_T) 6.4 Wall-to-wall connection test results The previous four coupler pullout tests showed the rebar fracture failure would occur in the wall-to-wall connection test specimens. Further, the seven pullout tests in a concrete block confirmed that the rebar fracture or rebar slippage failure of SMA and coupler wall-to-wall connection specimens would occur inside the metal duct at the coupler, while the rebar fracture failure of the steel and coupler wall-to-wall connection specimens would happen in the middle of the specimen. Three wall-to-wall connection tests were conducted under monotonic loading. Sections 6.4.1 and 6.4.2 present and discuss the test results. Table 6.3 summarizes the connection test results under monotonic loading. The first two tests were performed on SMA and coupler wall-to-wall 01002003004005000.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Rebar stress (MPa)Rebar slip (mm)PT5_SteelPT6_Steel_TPT7_Steel_T 109 connection specimens (CT1_SMA and CT2_SMA), while the third test was performed with the steel and coupler connection specimen (CT3_Steel). The yield loads for specimens CT1_SMA, CT2_SMA, and CT3_Steel were 51.74 kN, 51.55 kN, and 43.45 kN, respectively. This shows that the CT1_SMA and CT2_SMA specimens demonstrated about a 20% increase in yield load capacity compared to the CT3_Steel specimen. Similarly, the ultimate loads for specimens CT1_SMA, CT2_SMA, and CT3_Steel were 94.31 kN, 74.10 kN, and 62.46 kN, respectively. This shows that the CT1_SMA and CT2_SMA specimens exhibited about 50% and 20%, respectively, higher ultimate load capacity than the CT3_Steel specimen. The yield displacements in CT1_SMA, CT2_SMA, and CT3_Steel, as shown in Figures 6.15, 6.16, and 6.17 are 5.60 mm, 5.30 mm, and 1.45 mm, respectively. This shows that the CT1_SMA and CT2_SMA specimens showed about 3.8 and 3.6 times higher yield displacement than the CT3_Steel specimen. The ultimate displacement observed for specimens CT1_SMA, CT2_SMA and CT3_Steel were 46.18 mm, 29.32 mm and 58.04 mm, respectively. The ductility ratio (μ) is calculated as the ratio of the ultimate displacement (Du) to the yield displacement (Dy). It quantifies the amount a material can deform plastically before breaking, providing an indication of its ductility. Researchers have demonstrated that in low to moderately seismic regions, PC connections require a ductility ratio of 4.0 (Khaled A. Soudki et al., 1995). Therefore, the proposed connection system using SMA rebar and couplers shows a ductile behavior, as the ductility ratio for CT1_SMA and CT2_SMA were 8.25 and 5.53, respectively. However, the ductility ratios of CT1_SMA and CT2_SMA specimens were 7.2 and 4.8 times lower than the CT3_Steel specimen. 110 This difference can be attributed to the significantly higher yield displacement observed in the SMA and couplers wall-to-wall connection specimens, in comparison to the steel and couplers wall-to-wall connection specimen. A similar lower ductility for the hybrid SMA wall than that of the RC steel wall was observed due to the significantly larger yield displacement of the hybrid SMA wall (Abdulridha and Palermo, 2017; Tolou Kian and Cruz-Noguez, 2018). The initial stiffness (Ki) is determined by dividing the yield force (Fy) by the yield displacement (Dy). It is also referred to as elastic stiffness or linear stiffness, representing the element's ability to resist deformation under an initial load. The initial stiffness in CT1_SMA, CT2_SMA, and CT3_Steel, was 9.73 kN/mm, 9.24 kN/mm, and 29.97 kN/mm, respectively. This shows that the initial stiffness of the steel and coupler connection system is about 31% higher compared to the SMA and coupler connection system. Post-yield stiffness (Kp) refers to the resistance of a concrete element to deformation after it has exceeded the yield point and entered the plastic deformation region. It quantifies the relationship between incremental increases in load and the corresponding incremental deformations in the post-yield phase. Understanding post-yield stiffness is essential for designing and analyzing concrete elements such as shear walls that undergo plastic deformation, ensuring they can withstand loads beyond their elastic limits without catastrophic failure. The post-yield stiffness (Kp) is calculated as the ratio of the difference in ultimate force (Fu) and yield force (Fy) to ultimate displacement (Du) and yield displacement (Dy). Mathematically, Kp = (Fu – Fy) / (Du – Dy). The post-yield stiffness in CT1_SMA, CT2_SMA, and CT3_Steel, observed was 1.05 kN/mm, 0.94 kN/mm, and 0.34 kN/mm, respectively. The CT1_SMA and CT2_SMA show more than 3.12 times and 2.79 times 111 higher post-yield stiffness compared to the CT3_Steel. This higher post-yield stiffness in SMA material might help design buildings by improving load distribution and compensating strengths when some structural elements have structural degradation to keep the required strength. The hardening ratio (g) is the ratio of post-yield stiffness (Kp) to the initial stiffness (Ki) of a material or concrete element. It measures the increase in strength of a material or concrete element after it has yielded. The hardening ratios for CT1_SMA, CT2_SMA, and CT3_Steel, were 0.11, 0.10 and 0.01, respectively. The CT1_SMA and CT2_SMA demonstrated more than 10 times higher than CT3_Steel. The higher hardening ratio of SMA and coupler anchor specimens means the material or concrete element gains more strength as it deforms plastically, which is an important consideration in material and structural design. Table 6.3: Wall-to-wall connection test results Specimen Fy (kN) Dy (mm) Fu (kN) Du (mm) μ Ki (kN/mm) Kp (kN/mm) g Failure mode Failure location CT1_SMA 51.74 5.60 94.31 46.18 8.25 9.24 1.05 0.11 Rebar slippage Inside coupler CT2_SMA 51.55 5.30 74.10 29.32 5.53 9.73 0.94 0.10 Rebar fracture Inside coupler CT3_Steel 43.45 1.45 62.46 58.04 40.03 29.97 0.34 0.01 Rebar fracture At the gap between two blocks 112 6.4.1 General response and failure modes During the monotonic loading test, all three specimens had a significant crack opening at the grouted joint between the two concrete blocks. The specimens failed due to the rebar slippage or fracture at different locations. The three different specimens' crack patterns are shown in Figure 6.14, Figure 6.15 and Figure 6.16. The connection test specimen with a smooth steel rebar anchor, CT3_Steel, showed necking before fracturing, as evident in the force-displacement behavior (Figure 6.19). In the specimens with SMA and couplers, rebar slippage failure occurred inside the coupler in the CT1_SMA specimen and rebar fracture failure inside the coupler at the second screw from the center grout end occurred in the CT2_SMA specimen. The failure location and failure mode for CT1_SMA and CT2_SMA are shown in Appendix, Figure A.5 (c) and (d). 113 Figure 6.14: Crack pattern for CT1_SMA specimen 114 Figure 6.15: Crack pattern for CT2_SMA specimen 115 Figure 6.16: Crack pattern for CT3_Steel specimen 6.4.2 Force-displacement response Figure 6.17, Figure 6.18, and Figure 6.19 show the force-displacement responses for three monotonic tests. The CT3_Steel specimen showed a higher elongation of 6.3% at the ultimate force, compared to the 4.8% and 2.8% elongation of CT1_SMA and CT2_SMA specimens. These 116 results indicate that the proposed wall system with steel and coupler connections has a significantly higher displacement capacity than those with SMA and coupler connections. For the CT1_SMA, the ultimate load (Fu) of 94.31 kN from the test closely matched the expected value (Fue) of 93.7 kN (based on the mill certificate 1 provided by the company). As discussed in section 5.2.2, the ultimate stress of SMA rebar in three different types of tests (coupler pullout test, pullout test of rebar in a concrete block and wall-to-wall connection test) aligned more closely with the values reported in the first mill certificate. Therefore, the ultimate tensile strength and ultimate strain values are considered when estimating the test results. During testing, a drop in force was noted due to slippage of the SMA rebar inside the coupler after the maximum load was reached, as shown in Figure 6.17. This slippage, accompanied by a loud noise, was later confirmed as the failure mode when the CT1_SMA specimen was broken apart, as depicted in Figure A.5(c). The estimated ultimate displacement (d41) of 57.9 mm, calculated using Equation 5.3, significantly differed from the observed displacement (d4) of 46.18 mm. This difference may be due to the confinement provided to the connection rebar by the surrounding grout, metal duct, and concrete. Also, the different elongation measurement methodologies for rebar test and wall-to-wall connection test specimens may have caused the difference. 117 Figure 6.17: Force-displacement response of CT1_SMA The CT2_SMA specimen experienced an early failure occurred due to the rebar fracture inside the coupler, resulting in an ultimate load (Fu) of 74.10 kN from the test compared to the expected value (Fue) of 93.7 kN (based on mill certificate 1) as shown in Figure 6.18. The CT2_SMA specimen was also broken to confirm the rebar fracture failure inside the coupler, which was at the second screw from the center grout end, as shown in Figure A.5 (d). However, the pullout test results of the SMA rebar showed adequate minimum embedment length. A significant difference in the estimated ultimate displacement (d41) of 45.0 mm (mill certificate) and observed ultimate displacement (d4) 29.32 mm is due to the early failure of the specimen. This early rebar fracture within the coupler limited the specimen’s ability to achieve the expected ultimate load and ultimate displacement. Fye = 41.3 kNFue = 93.7 kNdue = 57.9 mm0 1 2 3 4 5 60204060801000 10 20 30 40 50 60Elongation (%)Force (kN)Displacement (mm)Estimated yield loadEstimated ultimate loadEstimated ultimate displacement 118 Figure 6.18: Force-displacement response of CT2_SMA In the case of the CT3_Steel specimen, the ultimate load (Fu) of 62.46 kN from the test closely matched the expected value (Fue) of 66.7 kN (based on the material test result), as shown in Figure 6.19. However, a significant difference in the estimated ultimate displacement (d41) of 86.4 mm (material test result) and the ultimate displacement (d4) test result of 58.1 mm is observed. The difference in results could be attributed to the restraint offered to the connection rebar by the grout, metal duct, ties and concrete. Additionally, the differences in elongation measurement methods for rebar test and wall-to-wall connection test specimens may have contributed to the observed differences. Fye = 41.3 kNFue = 93.7 kNdue = 45.0 mm0 1 2 3 4 5 60204060801000 10 20 30 40 50 60Elongation (%)Force (kN)Displacement (mm)Estimated yield loadEstimated ultimate loadEstimated ultimate displacement 119 Figure 6.19: Force-displacement response of CT3_Steel As shown in Figure 6.20, all three specimens exceeded their estimated yield forces before failure. The maximum force (F) normalized by the estimated yield force (fy) for CT1_SMA, CT2_SMA, and CT3_Steel was 1.82, 1.43, and 1.30, respectively. This shows that the CT1_SMA specimen exhibited the highest strength beyond its estimated yield, followed by CT2_SMA and CT3_Steel specimens. Further, the CT3_Steel specimen showed strength degradation, which was not observed in CT1_SMA and CT2_SMA. Fye = 50.4 kNFue = 66.7 kNdue = 86.4 mm0 2 4 6 8 100204060800 10 20 30 40 50 60 70 80 90 100Elongation (%)Force (kN)Displacement (mm)Estimated yield loadEstimated ultimate loadEstimated ultimate displacement 120 Figure 6.20: Normalized force-elongation response 6.5 Summary This chapter provided the test results and discussion for each type of test, namely coupler pullout test, pullout test of rebar in a concrete block and wall-to-wall connection test. The coupler pullout test ensured the rebar was stressed to its yield capacity and attained its full superelastic strain range for SMA and coupler anchor specimens. The first SMA and coupler pullout test (CPT1_SMA) was conducted following the method suggested in the literature for anchoring the SMA rebar and coupler. However, the specimen failed prematurely at 1.13% strain during the second loading cycle due to the indentation made by the coupler’s screw on the SMA rebar that, resulted in high-stress concentration at that location. To address this issue, a 1 mm thick rubber pad was inserted inside the coupler at the screw and SMA rebar touching the surface in the second SMA and coupler 0.00.51.01.52.00 1 2 3 4 5 6 7F / fyElongation (%)CT1_SMACT2_SMACT3_Steel 121 pullout test (CPT2_SMA) to prevent indentation on the SMA rebar. Additionally, the sharp ends of the screws were curved out to match the radius of the SMA rebar. These corrective measures ensured that the rebar was stressed close to the ultimate stress of the SMA rebar, which is 727 MPa compared to 614 MPa. Moreover, the rebar rupture failure mode was achieved with minimal slippage of 0.3 mm. Similarly, in steel rebar and coupler pullout tests (CPT3_Steel and CPT4_Steel), rebar stress was 492 MPa, close to the ultimate stress of steel rebar, 526 MPa with an average slippage of 0.2 mm. Ductile failure mode was observed for both steel and coupler anchors. Furthermore, when compared with the one-cycle loading, CPT2_SMA showed a minimal residual strain of 0.75%, whereas CPT3_Steel showed a residual strain of 5.5%. This shows the superior self-centering capacity of the SMA and coupler specimen with low residual strain compared to the steel and coupler specimen. For the two pullout tests of SMA rebar in a concrete block (PT1_SMA and PT2_SMA_T), the proposed connection assembly reached near its ultimate stress, 727 MPa. The average maximum stress of the two tests was 678 MPa. However, rebar slippage failure with a slippage of 2.7 mm was observed in PT1_SMA, while rebar fracture failure with only 0.3 mm slippage was observed in PT2_SMA_T. Similarly, the rebar fracture failure outside the concrete block was observed in five pullout tests with a very low rebar slippage of less than 1 mm. All three wall-to-wall connection test specimens exceeded their predicted yield forces before reaching failure. The specimen with the steel and couplers connection, CT3_Steel, demonstrated necking followed by fracture at the gap between two blocks, while the specimens with the SMA and couplers connection, CT1_SMA, experienced rebar slippage failure inside the coupler, and 122 CT2_SMA, experienced rebar fracture failure inside the coupler. The two specimens, CT1_SMA and CT2_SMA, showed higher yield displacement, an average of 375% greater than that of the CT3_Steel specimen. Furthermore, the initial stiffness was about 31% lower for the specimens with SMA and couplers than that of the steel and coupler wall-to-wall connection specimen. However, the average hardening ratio was 250% higher for the SMA specimens than for the steel and coupler specimens. 123 Chapter 7: Conclusions and Recommendations 7.1 Summary and conclusion The main focus of the thesis was to investigate the local behavior of the precast concrete (PC) wall through a novel connection using shape memory alloy (SMA) rebar and couplers. To achieve this, a numerical study and three different types of experimental tests were conducted. The specific objectives achieved in this study are detailed below, along with a description of how these objectives were achieved in this thesis. The first objective of the study was to investigate the effects of various parameters (aspect ratio, axial load ratio, rebar types, and vertical reinforcement ratio) of the SMA-reinforced concrete shear walls on the seismic response using numerical analysis. To achieve this objective, fifty-four three-dimensional finite element models of the shear walls reinforced with SMA rebar (NiTi and FeMnAlNi) and steel were developed using SeismoStruct software (SeismoSoft, 2022). The major conclusions were drawn as follows: • The SMA-reinforced shear walls showed minimal residual displacements, demonstrating SMA’s excellent self-centering capabilities compared to the steel-reinforced walls. • At 5% and 10% axial load ratios, the SMA-reinforced shear walls showed less energy dissipation than steel-reinforced shear walls. • No strength loss was observed at a 5% axial load ratio for all three rebar types. However, strength loss was observed for a 10% axial load ratio. 124 The second objective of the study was to experimentally investigate the effectiveness of the anchorage of the SMA rebar connected with the coupler and surrounding grout within a metal duct. To achieve this objective, four coupler pullout tests and seven pullout tests of rebar in concrete blocks were carried out, as discussed in Chapters 5 and 6. The four coupler pullout tests were conducted to ensure that the rebar was stressed beyond the superelastic range, leading to ductile failure and low slippage, before placing the SMA and coupler anchor assembly in a concrete block. From these two different types of tests, the following conclusions were drawn: • Coupler pullout test: o The SMA rebar in the SMA and coupler anchor assembly exceeded the superelastic strain range by curving out the sharp ends of the screws to match the radius of the SMA rebar. This was done to prevent indentation on the SMA rebar and to avoid high-stress concentration that leads to premature failure of the SMA rebar and coupler assembly. Additionally, a 1 mm thick rubber pad was inserted inside the coupler between the coupler’s screw and the SMA rebar. o The SMA and coupler anchor specimen showed a low residual strain of 0.75% compared to the 5.5% residual strain by the steel and coupler anchor specimen under one cycle loading. The energy dissipation capacity of the steel and coupler anchor specimen was about 1.6 times higher than that of the SMA and coupler. o All four coupler pullout test specimens showed low or negligible rebar slippage, less than 0.5 mm, inside the coupler. • Pullout test of rebar in a concrete block: 125 o For the two pullout tests of SMA rebar in a concrete block, the rebar slippage failure inside the coupler occurred in the PT1_SMA specimen, while the rebar fracture failure inside the coupler at the third screw from the loading end occurred in the PT2_SMA_T specimen. The average stress for specimens with SMA rebar was 678 MPa, compared to its ultimate stress of 727 MPa. o In the PT1_SMA specimen, a slippage of 2.7 mm was observed, while PT2_SMA_T showed only 0.3 mm of slippage. This difference suggests a probable issue with the SMA and coupler anchor system during the specimen's construction. However, more tests are necessary to conclusively establish the effectiveness of the SMA and coupler anchor system within the metal duct. Comparatively, five pullout test specimens of steel rebar with a coupler in a concrete block showed very low slippage, measuring less than 1 mm. The third objective of the study was to investigate the force-deformation response of the proposed anchoring system for SMA-reinforced PC wall-to-wall intersections. To achieve this, three small-scale wall-to-wall connection test specimens were constructed and tested under monotonic loading. The following conclusions were determined. • All three specimens had a significant crack opening at the grouted joint between the two concrete blocks of the specimens, but they showed different failure modes at different locations. In the CT1_SMA specimen, rebar slippage failure occurred inside the coupler, while in the CT2_SMA specimen, rebar fracture failure occurred inside the coupler at the 126 second screw from the center grout end. However, rebar fracture failure occurred in the middle of the rebar outside the specimen for the CT3_Steel specimen. • Specimens with the proposed connection consisting of SMA and couplers present higher yield displacement but a lower ductility ratio. The yield displacement of the proposed connection with SMA and couplers was observed to be an average of 375% more than that of the steel and couplers connection specimen. Also, the yield and ultimate load capacity for specimens with SMA and couplers were 20% and 35% higher, respectively, compared to those with steel and couplers. • The initial stiffness was about 31% lower for the wall-to-wall connection specimens with SMA and couplers than for the steel and coupler wall-to-wall connection specimens. However, the average hardening ratio was 250% higher for the SMA and coupler specimens than for the steel and coupler specimens. 7.2 Limitations The study has the following limitations: • Specimens for the wall-to-wall connection test and pullout test of a rebar in a concrete block were designed based on the typical PC shear wall thickness, which is 200 mm. Due to this thickness limitation, the size of the metal duct was restricted, and the coupler and rebar sizes were selected accordingly. Therefore, the study considers only one rebar size, which is 12.7 mm, for both the SMA and smooth steel rebar in all three different types of tests. • For the pullout tests of a rebar in a concrete block, only one embedment length is considered due to the height of the coupler and pullout testing apparatus. 127 • For the present study, three wall-to-wall connection test specimens were tested under monotonic loading. However, wall-to-wall connection tests under tensile cyclic loading are also needed. 7.3 Research contribution The research study proposed an alternative novel connection utilizing shape memory alloy (SMA) rebar and couplers, which requires minor adaptations to current conventional grouted metal duct connection using deformed steel rebar construction practices. Most materials, such as metal ducts and grout, remain the same, with the SMA rebar being the only new element connected by couplers. Therefore, material availability, constructability, and structural integrity remain the same as in industry practice. There are only a few changes in the new design, which is practical as the shear wall design and construction resemble conventional grouted dowel connection construction practice. Additionally, the SMA and coupler assembly can be post-installed in the proposed connection, making the process faster and easier than the PC shear wall construction using unbonded PT tendons. Moreover, the proposed connection was also designed and tested to show the failure modes and mechanism. Importantly, this experimental study is the first to incorporate SMA rebar in precast concrete shear wall connections, highlighting its potential to impact earthquake-resistant structures' design and construction significantly. 128 7.4 Recommendation for future study The research study could be extended further by conducting a comprehensive study of the following recommendations: • The pullout test of rebar in a concrete block with different parameters such as embedment lengths, metal duct thickness, grout strength and rubber pad thickness can be studied. Further, cyclic tests can be performed on these specimens. • The wall-to-wall connection test specimens can be tested under tensile cyclic loading conditions using a similar set-up as suggested in the thesis. Lateral support around the specimen will be needed to limit the horizontal drift in the middle while testing the specimens. These tensile cyclic tests will help to understand the local behavior under seismic loading. The wall-to-wall connection test experimental program could be extended further under axial and lateral loadings with additional parameters in the future. • The wall-to-wall connection test data obtained from three monotonic tests from this thesis could be used for a detailed numerical study and modelling. It can be calibrated based on the present experimental studies of the thesis. • The large-scale PC wall specimens could be constructed and tested using the proposed ductile connection. The wall test study is crucial to understanding the cyclic behavior of PC shear walls connected with SMA rebars under axial and lateral loads. The results obtained from experimental testing will provide insights into the performance of precast shear walls connected with SMA rebar that can further help design and construct PC shear wall buildings in high seismic regions. 129 Bibliography Aaleti, S., Sritharan, S., 2009. A simplified analysis method for characterizing unbonded post-tensioned precast wall systems. Engineering Structures 31, 2966–2975. https://doi.org/10.1016/j.engstruct.2009.07.024 Abdulridha, A., Palermo, D., 2017. Behaviour and modelling of hybrid SMA-steel reinforced concrete slender shear wall. Engineering Structures 147, 77–89. https://doi.org/10.1016/j.engstruct.2017.04.058 ACI, 2019a. 550.7-19: Requirements for design of a special unbonded post-tensioned precast shear wall satisfying ACI 550.6 and commentary, Detroit, MI. ACI, 2019b. Building code requirements for reinforced concrete. ACI 318-19, Detroit, MI. ACI, 2003. Bond and development of straight reinforcing bars in tension. ACI 408R-03, Detroit, MI. Aghajani, M., Asadi, P., 2023. Life-cycle cost analysis of steel frames with shape-memory alloy based dampers. Structures 52, 794–812. https://doi.org/10.1016/j.istruc.2023.04.022 Alam, M.S., Moni, M., Tesfamariam, S., 2012. Seismic overstrength and ductility of concrete buildings reinforced with superelastic shape memory alloy rebar. Engineering Structures 34, 8–20. https://doi.org/10.1016/j.engstruct.2011.08.030 Alam, M.S., Youssef, M.A., Nehdi, M., 2008. Analytical prediction of the seismic behaviour of superelastic shape memory alloy reinforced concrete elements. Engineering Structures 30, 3399–3411. https://doi.org/10.1016/j.engstruct.2008.05.025 130 Alam, M.S., Youssef, M.A., Nehdi, M., 2007. Utilizing shape memory alloys to enhance the performance and safety of civil infrastructure: a review. Can. J. Civ. Eng. 34, 1075–1086. https://doi.org/10.1139/l07-038 Alam, M.S., Youssef, M.A., Nehdi, M.L., 2010. Exploratory investigation on mechanical anchors for connecting SMA bars to steel or FRP bars. Mater Struct 43, 91–107. https://doi.org/10.1617/s11527-010-9601-0 Almeida, J.P.D., Steinmetz, M., Rigot, F., De Cock, S., 2020. Shape-memory NiTi alloy rebars in flexural-controlled large-scale reinforced concrete walls: Experimental investigation on self-centring and damage limitation. Engineering Structures 220, 110865. https://doi.org/10.1016/j.engstruct.2020.110865 Aragon, T.C., Kurama, Y.C., Meinheit, D.F., 2019. Effects of Grout and Energy Dissipating Bar Properties on a Type III Grouted Seismic Connection for Precast Concrete Structures. PCIJ 64. https://doi.org/10.15554/pcij64.1-03 ASTM, 2022a. Standard Test Method for Tension Testing of Nickel-Titanium Superelastic Materials. ASTM F2516-22, ASTM International, West Conshohocken, PA. ASTM, 2022b. Standard Test Methods for Tension Testing of Metallic Materials. ASTM E8/E8M-22, ASTM International, West Conshohocken, PA. ASTM, 2021. Standard Test Method for Compressive Strength of Hydraulic Cement Mortars. ASTM C109/C109M-21, ASTM International, West Conshohocken, PA. ASTM, 2016. Standard Test Methods and Definition for Mechanical Testing of Steel Products. ASTM A370-16, ASTM International, West Conshohocken, PA. ASTM, 2011. Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens. ASTM C496/C496M-11, ASTM International, West Conshohocken, PA. 131 ASTM, 2009. Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens. ASTM C39/C39M-09, ASTM International, West Conshohocken, PA. Auricchio, F., Taylor, R.L., Lubliner, J., 1997. Shape-memory alloys: macromodelling and numerical simulations of the superelastic behavior. Computer Methods in Applied Mechanics and Engineering 146, 281–312. https://doi.org/10.1016/S0045-7825(96)01232-7 Belleri, A., Schoettler, M.J., Restrepo, J.I., Fleischman, R.B., 2014. Dynamic Behavior of Rocking and Hybrid Cantilever walls in Precast Concrete Building. ACI Structural Journal 111. https://doi.org/10.14359/51686778 Billah, A.H.M.M., Alam, M.S., 2016. Performance-Based Seismic Design of Shape Memory Alloy–Reinforced Concrete Bridge Piers. I: Development of Performance-Based Damage States. J. Struct. Eng. 142, 04016140. https://doi.org/10.1061/(ASCE)ST.1943-541X.0001458 Bruno, S., Valente, C., 2002. Comparative response analysis of conventional and innovative seismic protection strategies. Earthq Engng Struct Dyn 31, 1067–1092. https://doi.org/10.1002/eqe.138 Brzev, S., Pao, J., 2009. Reinforced concrete design: a practical approach, Updated. Pearson Custom Publishing, New York; Toronto; Cortés-Puentes, L., Zaidi, M., Palermo, D., Dragomirescu, E., 2018. Cyclic loading testing of repaired SMA and steel reinforced concrete shear walls. Engineering Structures 168, 128–141. https://doi.org/10.1016/j.engstruct.2018.04.044 132 Cortés-Puentes, W.L., Palermo, D., 2018. Seismic Retrofit of Concrete Shear Walls with SMA Tension Braces. J. Struct. Eng. 144, 04017200. https://doi.org/10.1061/(ASCE)ST.1943-541X.0001936 CPCI, 2017. Design manual: precast and prestressed concrete, Fifth edition. Canadian Precast/Prestressed Concrete Institute, Ottawa, Ont. CSA, 2021. Carbon steel bars for concrete reinforcement. CSA G30.18. Rexdale, ON: CSA. CSA, 2019. Design of concrete structures. CSA A23.3-19, Rexdale, ON. Dina, A.A., Ahmed, F.Z., Issa, M., El-kashif, K., 2023. Self-centric cyclic resistance of reinforced concrete shear wall with Shape Memory Alloy: Numerical and experimental large-scale model. Case Studies in Construction Materials 19, e02365. https://doi.org/10.1016/j.cscm.2023.e02365 Elnady, A.M., Jiang, H., 2024. Seismic Performance of an Earthquake Resilient Self-Centering Precast Reinforced Concrete Rocking Wall with External SMA Rods. Journal of Earthquake Engineering 28, 819–848. https://doi.org/10.1080/13632469.2023.2220049 Elsayed, M., Ghrib, F., Nehdi, M.L., 2018. Experimental and analytical study on precast concrete dowel connections under quasi-static loading. Construction and Building Materials 168, 692–704. https://doi.org/10.1016/j.conbuildmat.2018.02.140 Elwood, K.J., 2013. Performance of concrete buildings in the 22 February 2011 Christchurch earthquake and implications for Canadian codes. Can. J. Civ. Eng. 40, 759–776. https://doi.org/10.1139/cjce-2011-0564 Fang, C., Qiu, C., Wang, W., Alam, M.S., 2023. Self-Centering Structures Against Earthquakes: A Critical Review. Journal of Earthquake Engineering 27, 4354–4389. https://doi.org/10.1080/13632469.2023.2166163 133 Gu, A., Zhou, Y., Xiao, Y., Li, Q., Qu, G., 2019. Experimental study and parameter analysis on the seismic performance of self-centering hybrid reinforced concrete shear walls. Soil Dynamics and Earthquake Engineering 116, 409–420. https://doi.org/10.1016/j.soildyn.2018.10.003 Hong, K., Ji, S., Son, D., 2024. Fatigue behavior of RC beams strengthened with iron-based shape memory alloy rebars. Journal of Building Engineering 94, 109834. https://doi.org/10.1016/j.jobe.2024.109834 Hoult, R.D., De Almeida, J.P., 2022. Residual displacements of reinforced concrete walls detailed with conventional steel and shape memory alloy rebars. Engineering Structures 256, 114002. https://doi.org/10.1016/j.engstruct.2022.114002 Janke, L., 2005. Applications of shape memory alloys in civil engineering structures - Overview, limits and new ideas. Mater. Struct. 38, 578–592. https://doi.org/10.1617/14323 Jünemann, R., De La Llera, J.C., Hube, M.A., Vásquez, J.A., Chacón, M.F., 2016. Study of the damage of reinforced concrete shear walls during the 2010 Chile earthquake. Earthq Engng Struct Dyn 45, 1621–1641. https://doi.org/10.1002/eqe.2750 Kolozvari, K., Tran, T.A., Orakcal, K., Wallace, J.W., 2015. Modeling of Cyclic Shear-Flexure Interaction in Reinforced Concrete Structural Walls. II: Experimental Validation. J. Struct. Eng. 141, 04014136. https://doi.org/10.1061/(ASCE)ST.1943-541X.0001083 Kurama, Y.C., 2002. Hybrid Post-Tensioned Precast Concrete Walls for Use in Seismic Regions. pcij 47, 36–59. https://doi.org/10.15554/pcij.09012002.36.59 Mander, J.B., Priestley, M.J.N., Park, R., 1988. Theoretical Stress‐Strain Model for Confined Concrete. J. Struct. Eng. 114, 1804–1826. https://doi.org/10.1061/(ASCE)0733-9445(1988)114:8(1804) 134 Menegotto, M., 1973. Method of analysis for cyclically loaded RC plane frames including changes in geometry and non-elastic behavior of elements under combined normal force and bending. Presented at the Proc. of IABSE Symposium on Resistance and Ultimate Deformability of Structures Acted on by Well Defined Repeated Loads, 1973. Mohammadgholipour, A., Billah, A.M., 2023. Mechanical properties and constitutive models of shape memory alloy for structural engineering: A review. Journal of Intelligent Material Systems and Structures 34, 2335–2359. https://doi.org/10.1177/1045389X231185458 Muntasir Billah, A., Rahman, J., Zhang, Q., 2022. Shape memory alloys (SMAs) for resilient bridges: A state-of-the-art review. Structures 37, 514–527. https://doi.org/10.1016/j.istruc.2022.01.034 NBCC, 2020. National Building Code of Canada. Institute for Research in Construction, National Research Council of Canada, Ottawa, ON. NZS 3101, N.Z., 2006. Concrete Structures Standard, NZS 3101: 2006 The Design of Concrete Structures. New Zealand Standard, Wellington, NZ, Oceania. Ölander, A., 1932. An electrochemical investigation of solid cadmium-gold alloys. Journal of the American Chemical Society 54, 3819–3833. Omori, T., Ando, K., Okano, M., Xu, X., Tanaka, Y., Ohnuma, I., Kainuma, R., Ishida, K., 2011. Superelastic Effect in Polycrystalline Ferrous Alloys. Science 333, 68–71. https://doi.org/10.1126/science.1202232 Parker, M., Steenkamp, D., 2012. The economic impact of the Canterbury earthquakes. Reserve Bank of New Zealand Bulletin 75, 13–25. PCI, 2021. PCI design handbook: Precast and prestressed concrete. 8thed.Chicago: Precast/Prestressed Concrete Institute. 135 Response-2000, 2000. E.C. Bentz, Sectional Analysis of Reinforced Concrete Members, PhD thesis, Department of Civil Engineering, University of Toronto, Toronto, ON, Canada, 184 (2000). Restrepo, J.I., Rahman, A., 2007. Seismic Performance of Self-Centering Structural Walls Incorporating Energy Dissipators. J. Struct. Eng. 133, 1560–1570. https://doi.org/10.1061/(ASCE)0733-9445(2007)133:11(1560) Saiidi, M.S., Sadrossadat-Zadeh, M., Ayoub, C., Itani, A., 2007. Pilot Study of Behavior of Concrete Beams Reinforced with Shape Memory Alloys. J. Mater. Civ. Eng. 19, 454–461. https://doi.org/10.1061/(ASCE)0899-1561(2007)19:6(454) Saiidi, M.S., Wang, H., 2006. Exploratory study of seismic response of concrete columns with shape memory alloys reinforcement. ACI Structural Journal 103, 436–443. Seifi, P., Henry, R.S., Ingham, J.M., 2019. In-plane cyclic testing of precast concrete wall panels with grouted metal duct base connections. Engineering Structures 184, 85–98. https://doi.org/10.1016/j.engstruct.2019.01.079 SeismoSoft, 2022. SeismoStruct - A computer program for static and dynamic nonlinear analysis of framed structures. Available from URL: www.seismosoft.com. Shahnewaz, Md., Alam, M.S., 2015. Seismic Performance of Reinforced Concrete Wall with Superelastic Shape Memory Alloy Rebar, in: Structures Congress 2015. Presented at the Structures Congress 2015, American Society of Civil Engineers, Portland, Oregon, pp. 2230–2240. https://doi.org/10.1061/9780784479117.193 Shrestha, K.C., Araki, Y., Nagae, T., Koetaka, Y., Suzuki, Y., Omori, T., Sutou, Y., Kainuma, R., Ishida, K., 2013. Feasibility of Cu–Al–Mn superelastic alloy bars as reinforcement 136 elements in concrete beams. Smart Materials and Structures 22, 025025. https://doi.org/10.1088/0964-1726/22/2/025025 Smith, B.J., 2012. Design, analysis, and experimental evaluation of hybrid precast concrete shear walls for seismic regions. University of Notre Dame. Smith, B.J., Kurama, Y.C., 2014. Seismic design guidelines for solid and perforated hybrid precast concrete shear walls. pcij 59, 43–59. https://doi.org/10.15554/pcij.06012014.43.59 Soares, M.M., Palermo, D., Cortés-Puentes, W.L., 2021. Modelling of mid-rise concrete shear walls reinforced with superelastic shape memory alloys: Nonlinear analysis. Engineering Structures 247, 113049. https://doi.org/10.1016/j.engstruct.2021.113049 Soudki, Khaled A., Rizkalla, S.H., LeBlanc, B., 1995. Horizontal Connections for Precast Concrete Shear Walls Subjected to Cyclic Deformations Part 1: Mild Steel Connections. pcij 40, 78–96. https://doi.org/10.15554/pcij.07011995.78.96 Soudki, Khaled A, Rizkalla, S.H., LeBlanc, B., Eng, P., 1995. Subjected to Cyclic Deformations. PCI JOURNAL. Sritharan, S., Aaleti, S., Henry, R.S., Liu, K., Tsai, K., 2015. Precast concrete wall with end columns (PreWEC) for earthquake resistant design. Earthq Engng Struct Dyn 44, 2075–2092. https://doi.org/10.1002/eqe.2576 Tolou Kian, M.J., Cruz-Noguez, C., 2018. Reinforced Concrete Shear Walls Detailed with Innovative Materials: Seismic Performance. J. Compos. Constr. 22, 04018052. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000893 Tolou Kian, M.J., Cruz-Noguez, C.A., 2023. Plastic hinge length and inelastic rotational capacity of reinforced concrete shear walls detailed with Self-Centering reinforcement. Engineering Structures 279, 115518. https://doi.org/10.1016/j.engstruct.2022.115518 137 Wang, B., Zhu, S., Zhao, J., Jiang, H., 2019. Earthquake resilient RC walls using shape memory alloy bars and replaceable energy dissipating devices. Smart Mater. Struct. 28, 065021. https://doi.org/10.1088/1361-665X/ab1974 Zhou, L., Ye, A., Chen, F., 2022. Postearthquake Vertical Load-Carrying Capacity of Extended Pile Shafts in Cohesionless Soils: Quasi-Static Test and Parametric Studies. J. Bridge Eng. 27, 04022071. https://doi.org/10.1061/(ASCE)BE.1943-5592.0001918 138 Appendices Appendix A: Pictures from experimental testing Figure A.1: Coupler pullout test (LVDT 1 touching the SMA rebar top) (a) (b) Figure A.2: Pullout test of a rebar in a concrete block (a) top view (b) LVDT 1 touching the SMA rebar top during the testing 139 Figure A.3: Wall-to-wall connection test specimen left overnight in the MTS 370 machine 140 (a) (b) Figure A.4: LVDT position of wall-to-wall connection test specimen on (a) left (b) right side 141 (a) (b) (c) (d) Figure A.5: Failure mode and location (a) PT1_SMA – rebar slippage failure (b) PT2_SMA_T – rebar fracture failure (c) CT1_SMA – rebar slippage failure (d) CT2_SMA – rebar fracture Rebar slippage Rebar fracture 142 Appendix B: Pictures from material testing Figure B.1: Sample concrete cylinder for compressive strength test Figure B.2: Sample concrete cylinder for tensile test 143 Figure B.3: Grout cube compressive test Figure B.4: Steel rebar tensile test 144 Figure B.5: SMA rebar tensile test 145 Appendix C: Mill certificates Figure C.1: 12.7 mm SMA mill certificate 1 (page 1) 146 Figure C.2: 12.7 mm SMA mill certificate 1 (page 2) 147 Figure C.3: 12.7 mm SMA mill certificate 2 148 Figure C.4: 12.7 mm smooth steel rebar mill certificate 149 Figure C.5: 10M steel rebar mill certificate 150 Figure C.6: 16 mm steel plate mill certificate 151 Figure C.7: Concrete mix design certificate 152 Appendix D: Calculations 1. Length of SMA rebar for wall-to-wall connection test(a) For specimens CT1_SMA and CT3_Steelq = 0.02 (assumed wall drift ratio corresponding to yielding of critical SMA rebar) esu = 0.06 (SMA superelastic strain range 6%) d3 = 900 mm (distance of SMA rebar furthest from wall edge in compression) c = 120 mm (neutral axis depth calculated from simplified method) The length of the SMA rebar, le, is calculated as 𝑙1 = 𝜃 × (𝑑/ − 𝑐)e34 = 0.02 × (900 − 120)0.06 = 260 mm Dry pack/grout thickness between two concrete blocks = 25 mm Therefore, provided minimum length (lep) = 320 mm In the design of the energy dissipators, the length provided ranges between 1.5le £ lep £ le (Restrepo and Rahman, 2007) Check: lep / le = 1.23 (OK) Height of coupler = 140 mm Therefore, the total length of SMA rebar with two couplers (all 6 screws are used for clamping) lSMA = 320 + 2 (140) = 600 mm (b) For specimens CT2_SMAq = 0.015 (assumed wall drift ratio corresponding to yielding of critical SMA rebar) esu = 0.06 (SMA superelastic strain range 6%) 153 d3 = 900 mm (distance of SMA rebar furthest from wall edge in compression) c = 120 mm (neutral axis depth calculated from simplified method) The length of the SMA rebar, le, is calculated as 𝑙1 = 𝜃 × (𝑑/ − 𝑐)e34 = 0.015 × (900 − 120)0.06 = 195 mm Dry pack/grout thickness between two concrete blocks = 25 mm Therefore, provided minimum length (lep) = 250 mm In the design of the energy dissipators, the length provided ranges between 1.5l e £ lep £ le (Restrepo and Rahman, 2007) Check: lep / le = 1.28 (OK) Height of coupler = 140 mm Therefore, the total length of SMA rebar with two couplers (all 6 screws are used for clamping) lSMA = 250 + 2 (140) = 530 mm 2. Metal duct sizeAccording to the PCI Design Handbook (PCI, 2021), metal duct should have a minimum thickness of 0.51 mm (24 gauge) and a minimum tolerance of 12.7 mm between the rebar and metal duct is required. tolerance = 12.7 mm dc = 33 mm (diameter of D250L Barlock coupler) The diameter of the metal duct is selected based on the diameter of the coupler. 𝑑5 = 𝑑' + 2 × (tolerance) = 33 + 2 × 12.7 = 58.4 mm Therefore, provided a 65 mm diameter metal duct. 154 As per PCI Design Handbook (PCI, 2021), the minimum embedment length should be at least 300 mm for anchorage in the grouted metal duct. The embedment length should also satisfy the requirement of splice length for the vertical steel rebar of the shear wall (CSA, 2019). dSMA = 12.7 mm (diameter of SMA rebar) d10M = 11.3 mm (diameter of vertical 10M steel rebar) fy = 400 MPa f’c = 50 MPa 𝑙) = 0.45 × 𝑘" × 𝑘- × 𝑘/ × 𝑘: × 𝑓2 × 𝑑";$`𝑓′𝑐 𝑙) = 0.45 × 1 × 1 × 1 × 0.8 × 400 × 11.3√50 = 230.12 mm 𝑙3678'1 = 1.3 × 𝑙) = 299.16 mm A minimum embedment length of 300 mm is required to transfer the tensile load from 10M steel rebar to the metal duct. Therefore, provided an embedment length of metal duct (Lm) = 363 mm (CT1_SMA and CT3_Steel), and 328 mm (CT2_SMA)
Thesis/Dissertation
eng
Civil Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Tobber, Lisa
Alam, M. Shahria
Experimental study of shape memory alloy connection in precast concrete shear walls for seismic applications
Text