Seismic Performance of a Full Scale Soft Story Woodframed Building with Energy Dissipation Retrofit Jingjing Tian, Ph.D. and Michael D. Symans, Ph.D. Dept. of Civil and Environmental Engineering Rensselaer Polytechnic Institute Mikhail Gershfeld, P.E., Ph.D. Dept. of Civil Engineering Cal Poly Pomona Pouria Bahmani and John van de Lindt, Ph.D. Dept. of Civil and Environmental Engineering Colorado State University Tenth National Conference on Earthquake Engineering (10NCEE) Anchorage, Alaska July 2014 1
Approaches to Soft Story Retrofit No Retrofit Stiffness Retrofit Damping Retrofit Low accelerations High deformations in ground story Low deformations in upper stories Increased accelerations Reduced deformations in ground story Increased deformations in upper stories Decreased accelerations Reduced deformations in ground story Increased deformations in upper stories Response less sensitive to value of natural period 2
Target Performance: FEMA P 807 and NEES Soft Seismic Hazard Level Performance Level Target Drift Limit (%) PNE (%) Target Drift Probability of Non Exceedance Retrofit Approach Retrofit Scope FEMA P 807 MCE (Default) 2%/50yr Standard Performance Short Return Period 50%/50yr DBE 10%/50yr NEES Soft PBSR MCE 2%/50yr Higher Performance DBE 2%/50yr MCE 2%/50yr OSL (Default) IO LS CP IO LS High Deformability Low Deformability 4 1.25 1 2 4 1 2 80 50 50 80 50 50 Adding strength/stiffness Ground story only Adding strength/stiffness Ground Story + (Upper Stories) Adding Damping Ground Story + (Upper Stories) 3
Full Scale Seismic Testing at NEES UCSD Building Properties: Plan dimensions: Story height: Seismic weight: Shear walls: 38 ft 24 ft 8 ft 10 3/4 in. 134 kips Exterior: Horizontal Wood Siding (HWS) Interior: Gypsum Wall Board (GWB) Southeast Corner Test Phases: 1) Cross Laminated Timber (CLT) Panel retrofit (P 807) 2) Steel Moment Frame (SMF) retrofit (P 807) 3) Special Steel Moment Frame (SSMF) retrofit (PBSR) 4) Damper retrofit (PBSR) 5) No retrofit (test to collapse) Ground Motions: 1989 Loma Prieta earthquake Gilroy Station record, 0 component (G03000) Northeast Corner 1992 Cape Mendocino earthquake Rio Station record, 360 component (RIO360) Scaling: 42% DBE, 100% DBE, 150% DBE 4
Energy Dissipation Retrofit: Damper Frames Toggle Braced Damper Frame u, F Linear Viscous Damper C axial = 0.26 kip sec/in Force Capacity: 4 kips Stroke Capacity: 4 in. extension 2 in. compression Geometry Aspect ratio = 2.4 A = 37.75 in B = 89.14 in C = 74.96 in D = 2 in E = 20.24 in = 57.53 degrees = 20.14 degrees Nonlinear Displ. Amplification Displ. Amplification 2.6 Avg. = 1.6 1.1 Extension Compression Frame Drift (in.) Average Amplification Damper Displacement: 1.6 Damper Force: 1.6 Frame Damping Coeff: 2.5 5
PBSR Design of NEES Soft UCSD Test Building CM CSD Neglecting modal coupling: sdx 62% Estimated damper frame cost: $9/ft 2 Ground Story Floor Plan (Damper Retrofit) Effect of Damper Magnitude on Peak Drift Upper Story Floor Plan (Shear Wall Retrofit) PBSR Design Criteria Satisfied < 2% 6
Implementation of Dampers and Shear Walls Damper Retrofit in Ground Story Shear transfer connection South wall line North wall line FVD closeup view Shear Wall Retrofit in Upper Stories Wood structural panel Anchor Tie down System (ATS) at end posts for uplift restraint Shear wall locations NOTE: Designed for prior test phase which used SSMF retrofit. Not necessarily optimal for damper retrofit. Retrofit along line A 7
Seismic Tests Evolution of modal periods WN ID Phase Seismic Test ID GM PGA (g) (g) Hazard Level T U 14 G03000 0.269 0.5 50%/50 42% DBE V W Phase 4 Damper Retrofit 15 16 G03000 RIO360 0.645 0.596 1.2 1.2 10%/50 10%/50 X 17 G03000 0.967 1.8 2%/50 Y 18 RIO360 0.894 1.8 2%/50 Z DBE MCE MCE Rio360 Record; Damper Frame #7 Dampers fully engaged (max. uplift and lateral slippage in.) 8
Seismic Test Results Peak inter story drift in X direction (%) Displacement profiles in X direction Test 14 Test 15 Test 16 Test 17 Test 18 Story 1 0.210 0.585 0.457 0.943 0.784 Story 2 0.309 0.695 0.928 0.996 1.280 Story 3 0.446 0.999 1.301 1.410 1.843 Story 4 0.075 0.163 0.285 0.282 0.424 50%/50. % DBE: 10%/50 % MCE: 2%/50 δ % Performance objective (drift limits) met in all cases except one. Substantially increased width of hysteresis loop for soft story (increased energy dissipation capacity). Minimal Y direction displacements (dampers suppressed torsion response) Overturning restraint system was effective (lateral displacement due to bending % of total displ.) MCE Rio360 Record 9
Effects of Damping Retrofit Comparison to Unretrofitted Structure Soft Story Drift Comparison to stiffness based retrofit SSMF 77% reduction FVD Energy MCE RIO360 record : 40% In NEES Soft project, SSMF and FVD systems were not designed to compete with each other but rather to meet common PBSR objective MCE RIO360 Record : 60% Damping system provides ratedependent energy dissipation in ground story, leading to similar inter story drifts but smaller peak base shear force 10
Shake Table Test 18 MCE Rio 360 Motion Seismic Test 18 MCE Rio 360 (Phase 4) 11
Ongoing Work: Narrow Damper Frames Source: Schott, F.H, Lee, D.A., Karns, J. and Symans, M.D. (2014). "Sustainability in Soft Weak Open Front Buildings," Proc. of Tenth National Conf. on Earthquake Engineering (10NCEE), Anchorage, Alaska, July, 2014. Drag strut /Link Earthquake Input Lateral Support of Frame and Panels Braced Frame with Damper (32 x 93 ) Damper and Amplification Mechanism Structural Stiffness provided by premanufactured HardyFrame Wall Panel Foundation Source: J. Karns, Mitek. Seismic Testing at UCSD 3 frame configurations Two distinct sizes for single family and multifamily construction Displ. Amplification 5 Collaboration between MiTek and Taylor Devices for implementation of dampers in light framed construction. Currently under consideration for retrofit of soft story building in San Francisco 12
Conclusions Energy Dissipation Retrofit Provides stable, non degrading source of energy dissipation Protects the soft story (minimizing damage by controlling drift response) while limiting the transfer of forces to upper stories Rate Dependent Energy Dissipation Provides high damping forces at low displacements, precisely at time that structure provides minimal lateral resistance. At peak displacements, the rate dependent forces are zero and thus do not add to the peak restoring forces in the structure, leading to significant reduction in peak base shear force. Torsion Control Strategic distribution of dampers in plan minimizes torsional response Multi Story Retrofit (high performance retrofit) Damper retrofit in first story combined with upper story shear wall retrofit results in high performance system (<2% peak drift for MCE level motion with 50% PONE). First Story Only Retrofit (low performance retrofit) Per hybrid testing at NEES UB, energy dissipation retrofit can be used for first story only retrofits consistent with FEMA P 807 Guidelines (<4% peak drift for MCE level 13 motion with 80% PONE).
Acknowledgements NEES-Soft Project Team NEESR-CR: NEES-Soft: Seismic Risk Reduction for Soft-Story Wood Frame Buildings John W. van de Lindt Michael Symans Weichiang Pang Mikhail Gershfeld Xiaoyun Shao Colorado State University Rensselaer Polytechnic Institute Clemson University Cal State University, Pomona Civil Engineering Western Michigan Univ. PI, Overall Project Manager Co-PI, Performance-Based Seismic Retrofit Co-PI, Advanced Numerical Modeling Co-PI, Design of Test Specimens Co-PI, Hybrid Test Coordinator Andrei Filiatrault University at Buffalo Senior Personnel David Rosowsky Rensselaer Polytechnic Institute Senior Personnel Gary Mochizuki Structural Solutions, Inc. Senior Personnel Ioannis National Tech. Univ. of Christovasilis Athens Senior Personnel Douglas Rammer U.S. Forest Products Lab Senior Personnel David Mar Tipping Mar Senior Personnel NEES UCSD NEES UB NSF CMMI Grant No. 1041631 14