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

NEESR-SG: Steel Plate Shear Wall Research

Larry Fahnestock K.C. Tsai Jeff Berman and Laura Lowes Graduate Students: UW: Patricia Clayton, David Webster UIUC: Dan Borello, Alvaro Quinonez UB: Dan Dowden Sponsored by NSF through the George E. Brown NEESR Program Michel Bruneau Rafael Sabelli Material Donations from AISC

Project Overview

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

• •

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) US Northridge Earthquake (1994) Haiti Earthquake (2010)

• •

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)

Resilient SPSW: SPSW+ PT Frame

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

SC-SPSW Research Overview

Analytical Research System Behavior Performance-Based Design Procedure Analysis and Verification of Performance Experimental Research Subassembly Testing (U. of Washington) Shake Table Testing (U. at Buffalo) Full-scale Testing (NCREE, Taiwan)

• •

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

Performance-Based Design

V V 2/50 V 10/50 NO REPAIR V 50/50 Plate yielding REPAIR OF PLATES ONLY COLLAPSE PREVENTION First occurrence of:  PT yielding  Frame yielding  Residual drift > 0.2% First occurrence of:  PT rupture  Excessive PT yielding  Excessive frame yielding  Excessive story drifts V wind Connection decompression D D 50/50 D 10/50 D 2/50

Analytical Model

• • Nonlinear model in OpenSees SPSW modeled using strip method: • • Tension-only strips with pinched hysteresis Strips oriented in direction of tension field

Analytical Model (cont.)

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

• • •

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 Ranger

•

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 V 2/50 V 10/50 V V 50/50 V wind NO REPAIR REPAIR OF PLATES ONLY COLLAPSE PREVENTION D 50/50 All performance objectives met !!! D 10/50 D 2/50 D

UW Component Tests

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

Development of tension field

R-SPSW Testing

Connection decompression Flag-shaped hysteresis Residual web plate deformation after test

Comparison of Parameters

Change in number of PT strands Change in web plate thickness

K r • Affects recompression stiffness, K r , due to change in PT stiffness • Affects decompression moment • Affects system strength and energy dissipation • Affects post-decompression stiffness

Comparison with Idealized Response

V SC-SPSW Plate yields Connection Decompression Unloading Plates Unloaded Connection Recompression D 1 st Cycle 2 nd Cycle • • More energy dissipation than assumed Some “compressive” resistance due to geometric stiffening

Web Plate Behavior Study

FE modeling

Residual Load

Experimental testing

Pins ~25% of yield strength (Webster 2011)

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

Frame Expansion

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

Accommodation of Frame Expansion

• Flexible collector beams connecting PT frame and composite slab – Applies additional point loads along beam – Damage to collector beams • Garlock (2007) Sliding interface between slab and beams – Eliminates slab restraint Kim and Christopoulos (2008)

Elimination of Frame Expansion

• Rocking about HBE centerline (Pin) • NewZ-BREAKSS – Rocking about top flange only

Testing at NEES@Buffalo

• • • • Quasi-Static tests 1/3 scale, 3-story Various PT connection details Full plate and Strips NewZ-BREAKSS Conn.

Flange Rocking Centerline Rocking

Comparison of Behavior

NewZ-BREAKSS Conn.

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

Flange Rocking

• • •

UB Shake Table Tests

6 degree-of-freedom shake table Same specimens as quasi-static tests Scheduled for completion in fall 2012

System-level Testing

• National Center for Earthquake Engineering (NCREE) in Taiwan – 2-story, full scale SC-SPSW – Single actuator – Quasi-static loading – Summer 2012

NCREE Specimens

• PT column base – Column can rock about its flanges

NCREE Specimens

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

•

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

Thank You

Questions?

30