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Development of Self-Centering Steel Plate Shear Walls (SC-SPSW) Jeff Berman Assistant Professor University of Washington.

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Presentation on theme: "Development of Self-Centering Steel Plate Shear Walls (SC-SPSW) Jeff Berman Assistant Professor University of Washington."— Presentation transcript:

1 Development of Self-Centering Steel Plate Shear Walls (SC-SPSW) Jeff Berman Assistant Professor University of Washington

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

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

4 Motivation Current U.S. seismic design codes – Life Safety and Collapse Prevention – Maximum Considered Earthquake (MCE) U.S. Earthquakes since : – 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)

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)

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

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)

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

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

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

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

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

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

14 UW Component Tests Reaction Blocks Roller to Allow Gap Opening Pin to Allow VBE Rotation Subassemblage Target Deformation of Specimen Laboratory Configuration

15 R-SPSW Testing Development of tension field Connection decompression Residual web plate deformation after test Flag-shaped hysteresis

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

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

18 Web Plate Behavior Study FE modeling Experimental testing Pins Residual Load ~25% of yield strength (Webster 2011)

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

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)

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

22 Elimination of Frame Expansion Rocking about HBE centerline (Pin) NewZ-BREAKSS – Rocking about top flange only

23 Testing at Quasi-Static tests 1/3 scale, 3-story Various PT connection details Full plate and Strips

24 Comparison of Behavior Flange rocking provides better re-centering because of decompression moment NewZ-BREAKSS prevents floor damage due to frame expansion.

25 UB Shake Table Tests 6 degree-of-freedom shake table Same specimens as quasi-static tests Scheduled for completion in fall 2012

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

27 NCREE Specimens PT column base – Column can rock about its flanges

28 NCREE Specimens PT column base – Column can rock about its flanges 2 specimens – Flange rocking HBEs – NewZ-BREAKSS Connection (Top flange rocking HBEs)

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

30 Questions? Thank You 30


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