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Development of Self-Centering Steel Plate Shear Walls (SC-SPSW) Jeff Berman Assistant Professor University of Washington Slide 2 NEESR-SG: Steel Plate Shear Wall Research Jeff Berman and Laura Lowes Michel BruneauLarry Fahnestock K.C. Tsai Sponsored by NSF through the George E. Brown NEESR Program Rafael Sabelli Material Donations from AISC Graduate Students: UW: Patricia Clayton, David Webster UIUC: Dan Borello, Alvaro Quinonez UB: Dan Dowden Slide 3 Project Overview Resilient SPSW Analysis and Verification of Performance Subassemblage Testing Shake Table Testing Fill Critical Knowledge Gaps Cyclic Inelastic Tension Field Action SPSW Damage States and Fragilities Coupled SPSW Testing (MUST-SIM) ~43 Full-Scale Testing Slide 4 Motivation Current U.S. seismic design codes Life Safety and Collapse Prevention Maximum Considered Earthquake (MCE) U.S. Earthquakes since 1970 1 : Only 2 people per year die due to structural collapse $2 billion per year in economic loss 1 ATC-69 (2008) Haiti Earthquake (2010) US Northridge Earthquake (1994) Slide 5 Resilient SPSWs: Motivation Steel Plate Shear Walls (SPSWs): Thin web plates: tension field action High initial stiffness Ductile Distributed yielding Replaceable fuses (web plates) However, Damage in HBEs and VBEs not as easy to repair/replace How can we limit damage to HBEs and VBEs to provide a quicker return to occupancy following an earthquake? (Vian and Bruneau 2005) Slide 6 Resilient SPSW: SPSW+ PT Frame V SPSW 1 st Cycle 2 nd Cycle V PT V R-SPSW Plate yields Unloading Connection Decompression Connection Recompression Plates Unloaded Previous PT Connection Work: Garlcok et al. 2002, Christopoulos et al., 2002 Slide 7 SC-SPSW Research Overview Analytical Research Analysis and Verification of Performance Performance-Based Design Procedure System Behavior Subassembly Testing (U. of Washington) Experimental Research Shake Table Testing (U. at Buffalo) Full-scale Testing (NCREE, Taiwan) Slide 8 R-SPSW Mechanics Distributed loads on frame from web plates Compression of HBE from three components: PT Web plate loads on VBE Web plate loads on HBE Slide 9 Performance-Based Design V V 10/50 10/50 First occurrence of: PT yielding Frame yielding Residual drift > 0.2% REPAIR OF PLATES ONLY V 2/50 2/50 First occurrence of: PT rupture Excessive PT yielding Excessive frame yielding Excessive story drifts COLLAPSE PREVENTION 50/50 V 50/50 Plate yielding NO REPAIR V wind Connection decompression Slide 10 Analytical Model Nonlinear model in OpenSees SPSW modeled using strip method: Tension-only strips with pinched hysteresis Strips oriented in direction of tension field Slide 11 Analytical Model (cont.) PT connection model: HBE VBE Compression-only springs at HBE flanges Diagonal springs to transfer shear Rocking about HBE flanges Compression-only springs at HBE flanges Rigid offsets Shear transfer Diagonal springs PT tendonsTruss elements with initial stress (Steel02) Analytical ModelPhysical Model Slide 12 Dynamic Analyses 3 and 9 story prototypes based on SAC buildings: 4-6 SPSW bays Each model subjected to 60 LA SAC ground motions representing 3 seismic hazard levels 50% in 50 year 10% in 50 year 2% in 50 year Used OpenSeesMP to run ground motions in parallel on TeraGrid machines Processor = 0 Processor = 1 Processor = n-1 R-SPSW model Ranger Slide 13 Analytical Summary Results for typical 9-story SC-SPSW designed WITHOUT optional 50% in 50 year No repair performance obj. Performance Objectives: No plate repair ( Story drift < 0.5%) in 50/50 Recentering (Residual Drift < 0.2%) in 10/50 Story drift < 2.0% in 10/50 (represents DBE) Limited PT, HBE, and VBE yielding in 2/50 All performance objectives met !!! REPAIR OF PLATES ONLY COLLAPSE PREVENTION NO REPAIR V V 10/50 10/50 V 2/50 2/50 50/50 V 50/50 V wind Slide 14 UW Component Tests Reaction Blocks Roller to Allow Gap Opening Pin to Allow VBE Rotation Subassemblage Target Deformation of Specimen Laboratory Configuration Slide 15 R-SPSW Testing Development of tension field Connection decompression Residual web plate deformation after test Flag-shaped hysteresis Slide 16 Comparison of Parameters Change in number of PT strandsChange in web plate thickness Affects recompression stiffness, K r, due to change in PT stiffness Affects decompression moment KrKr Affects system strength and energy dissipation Affects post-decompression stiffness Slide 17 Comparison with Idealized Response More energy dissipation than assumed Some compressive resistance due to geometric stiffening 1 st Cycle 2 nd Cycle V SC-SPSW Plate yields Unloading Connection Decompression Connection Recompression Plates Unloaded Slide 18 Web Plate Behavior Study FE modeling Experimental testing Pins Residual Load ~25% of yield strength (Webster 2011) Slide 19 Comparison with Models Future improvements to strip model: Modify strain hardening rules to account for cyclic yielding Quantify compression in SPSW strip model OpenSees model With and without compressive resistance in strips Slide 20 Frame Expansion As PT connection decompresses, VBEs spread apart Can cause floor damage or increase frame demands if beam growth is restrained, especially at 1 st floor beam Garlock (2002) Kim and Christopoulos (2008) Slide 21 Accommodation of Frame Expansion Kim and Christopoulos (2008) Garlock (2007) Flexible collector beams connecting PT frame and composite slab Applies additional point loads along beam Damage to collector beams Sliding interface between slab and beams Eliminates slab restraint Slide 22 Elimination of Frame Expansion Rocking about HBE centerline (Pin) NewZ-BREAKSS Rocking about top flange only Slide 23 Testing at NEES@Buffalo Quasi-Static tests 1/3 scale, 3-story Various PT connection details Full plate and Strips Slide 24 Comparison of Behavior Flange rocking provides better re-centering because of decompression moment NewZ-BREAKSS prevents floor damage due to frame expansion. Slide 25 UB Shake Table Tests 6 degree-of-freedom shake table Same specimens as quasi-static tests Scheduled for completion in fall 2012 Slide 26 System-level Testing National Center for Earthquake Engineering (NCREE) in Taiwan 2-story, full scale SC-SPSW Single actuator Quasi-static loading Summer 2012 Slide 27 NCREE Specimens PT column base Column can rock about its flanges Slide 28 NCREE Specimens PT column base Column can rock about its flanges 2 specimens Flange rocking HBEs NewZ-BREAKSS Connection (Top flange rocking HBEs) Slide 29 Conclusions Performance-based design procedure developed for SC- SPSW: Elastic behavior during frequent events Web plate yielding and recentering during DBE events Collapse prevention during MCE events Analytical studies show SC-SPSWs are capable of meeting proposed performance objectives Experimental subassembly tests show simple models are conservative and have room for improvement Future testing will verify performance on system level Slide 30 Questions? 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