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Development of Self-Centering Steel Plate Shear Walls (SC-SPSW)

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Presentation on theme: "Development of Self-Centering Steel Plate Shear Walls (SC-SPSW)"— 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 Larry Fahnestock Michel Bruneau Graduate Students: UW: Patricia Clayton, David Webster UIUC: Dan Borello, Alvaro Quinonez UB: Dan Dowden K.C. Tsai Rafael Sabelli Sponsored by NSF through the George E. Brown NEESR Program Material Donations from AISC

3 Project Overview a ~43° Resilient SPSW
Analysis and Verification of Performance Subassemblage Testing Shake Table Testing Full-Scale Testing Fill Critical Knowledge Gaps a ~43° Cyclic Inelastic Tension Field Action SPSW Damage States and Fragilities Coupled SPSW Testing (MUST-SIM)

4 US Northridge Earthquake (1994)
Motivation Current U.S. seismic design codes Life Safety and Collapse Prevention Maximum Considered Earthquake (MCE) U.S. Earthquakes since 19701: Only 2 people per year die due to structural collapse $2 billion per year in economic loss US Northridge Earthquake (1994) Haiti Earthquake (2010) 1 ATC-69 (2008)

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
VSPSW VPT D D VR-SPSW Unloading Plate yields Connection Decompression Plates Unloaded 1st Cycle 2nd Cycle D Connection Recompression Previous PT Connection Work: Garlcok et al. 2002, Christopoulos et al., 2002

7 SC-SPSW Research Overview
Analytical Research Performance-Based Design Procedure Analysis and Verification of Performance 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
V2/50 D2/50 First occurrence of: PT rupture Excessive PT yielding Excessive frame yielding Excessive story drifts Collapse Prevention V10/50 D10/50 First occurrence of: PT yielding Frame yielding Residual drift > 0.2% Repair of Plates Only V D50/50 V50/50 Plate yielding No Repair Vwind Connection decompression D

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: Compression-only springs at HBE flanges Rocking about HBE flanges Shear transfer Diagonal springs PT tendons Truss elements with initial stress (Steel02) HBE VBE Rigid offsets Physical Model Analytical Model Compression-only springs at HBE flanges Diagonal springs to transfer shear

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 Ranger R-SPSW model Processor = n-1

13 Analytical Summary All performance objectives met !!!
Results for typical 9-story SC-SPSW designed WITHOUT optional 50% in 50 year “No repair” performance obj. V D V10/50 D10/50 V2/50 D2/50 D50/50 V50/50 Vwind 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 No Repair Collapse Prevention Repair of Plates Only All performance objectives met !!!

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

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

16 Comparison of Parameters
Change in number of PT strands Change in web plate thickness Kr Affects recompression stiffness, Kr, due to change in PT stiffness Affects decompression moment Affects system strength and energy dissipation Affects post-decompression stiffness

17 Comparison with Idealized Response
1st Cycle 2nd Cycle VSC-SPSW D Plate yields Unloading Connection Decompression Recompression Plates Unloaded More energy dissipation than assumed Some “compressive” resistance due to geometric stiffening

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

19 Comparison with Models
OpenSees model With and without compressive resistance in strips Future improvements to strip model: Modify strain hardening rules to account for cyclic yielding Quantify compression in SPSW strip model

20 Kim and Christopoulos (2008)
Frame Expansion As PT connection decompresses, VBEs spread apart Garlock (2002) Kim and Christopoulos (2008) Can cause floor damage or increase frame demands if beam growth is restrained, especially at 1st floor beam

21 Accommodation of Frame Expansion
Garlock (2007) Flexible collector beams connecting PT frame and composite slab Applies additional point loads along beam Damage to collector beams Kim and Christopoulos (2008) 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 NEES@Buffalo
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 2 specimens
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 Thank You To provide insight into my background, here are some projects I’ve worked on Questions?

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