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Technical Session 10 (Wood Structures) 2012 Quake Summit Boston, MA July 12, 2012 Jingjing Tian, Ph.D. Student Michael D. Symans, Assoc. Professor Dept. of Civil and Environmental Engineering Rensselaer Polytechnic Institute Effect of Plan Distribution of Energy Dissipation Devices on Seismic Response of Soft-Story Wood-Framed Structures 1 Slide 2 NEESR-CR: NEES-Soft: Seismic Risk Reduction for Soft-Story Wood Frame Buildings John W. van de Lindt University of AlabamaPI, Overall Project Manager Michael SymansRensselaer Polytechnic Institute Co-PI, Performance-Based Seismic Retrofit Weichiang Pang Clemson University Co-PI, Advanced Numerical Modeling Mikhail Gershfeld Cal State University, Pomona Co-PI, Design of Test Specimens Xiaoyun Shao Civil Engineering Western Michigan Univ. Co-PI, Hybrid Test Coordinator Andrei FiliatraultUniversity at BuffaloSenior Personnel David Rosowsky Rensselaer Polytechnic Institute Senior Personnel Gary MochizukiStructural Solutions, Inc.Senior Personnel Ioannis Christovasilis National Tech. Univ. of Athens Senior Personnel Douglas RammerU.S. Forest Products LabSenior Personnel David MarTipping MarSenior Personnel Research supported by National Science Foundation CMMI Grant No. 1041631 (NEESR - Network for Earthquake Engineering Simulation Research) Project Team 2 Slide 3 Outline Seismic response and energy dissipation retrofit for soft-story buildings Energy dissipation retrofit Damper type and location Displacement amplification system Numerical Simulations Summary of parametric study of linear simplified model Nonlinear analysis of simplified model Summary and Future work 3 Slide 4 Seismic Response of Soft-Story Buildings Soft-Story Buildings: - Stiffness irregularity due to first story having large openings in perimeter walls and minimal interior walls and upper stories having small openings and many interior walls. - First story acts as a base isolation system in that it protects the upper stories through its flexibility. 4 Slide 5 Seismic Retrofit Strategies Conventional Retrofit Increase stiffness/strength of soft story Tends to increase forces transmitted to upper stories Thus, need to avoid overstrengthening soft story Expected performance level for design earthquake: Shelter-in-Place (structure serves as shelter but may have significant damage) Performance-Based Retrofit Increase damping in first story (and possibly stiffness) May increase force transmitted to upper stories Expected performance level for design earthquake: Fully Operational (FO) to Immediate Occupancy (IO) 5 Slide 6 Energy Dissipation Retrofit Damper Type Linear fluid viscous dampers Linear: Peak force out-of-phase with peak displ. Pure energy dissipation Design and analysis procedures exist Previously tested in wood structures Damper Location First story only Perimeter walls to increase torsion resistance Along both stiff and flexible wall lines Displacement amplification system (scissor-jack) 6 Slide 7 Damper Displacement Amplification System: Scissor-Jack Bracing Scissor-jack bracing assembly in "Olympic House and Park Building" in Nicosia, Cyprus Fluid Viscous Damper Model of FVD within scissor-jack bracing Simplified Model - Neglect flexibility of bracing members - Neglect damper stiffness - Result: Amplification factor = 4 (based on geometry of narrow garage door walls used in soft story building model) Source: Hanson and Soong (2001) 7 Slide 8 Numerical Simulations One-Story Elastic Structure (Review of Main Findings) Two-way asymmetric Linear elastic shear walls; Linear viscous dampers Uniaxial and biaxial ground motions Parametric Study (using Matlab) to evaluate effects of damping plan distribution and damping magnitude One-Story Inelastic Structure Two-way asymmetric Nonlinear shear walls; Linear viscous dampers Uniaxial and biaxial ground motions Parametric Study (using SAWS2.1 + SAWS2.1-IDA) to evaluate effects of damping plan distribution and damping magnitude 8 Slide 9 CM = Center of Mass CR = Center of Rigidity (located at ; similar to location for NEES-Soft test specimen) CSD = Center of Supplemental Damping (location varies) EQ-X Parametric Study of One-Story Linear Elastic Structure with Energy Dissipation System - Two-way asymmetric w/rigid diaphragm - Uniaxial ground motion - CR & CM Fixed - CSD Varied Since a damping system is added to the inherent damping (5% assumed in all modes) with intent of protecting structural framing system, structure behavior is assumed to be linear elastic. Northridge EQ Motions - Rinaldi Receiving Station (strong near-field) - Newhall County Fire Station (moderate near-field) - Canoga Park Station (moderate far-field) 9 Rigid-Edge Flexible-Edge Slide 10 EQ-X Flexible-Edge Deformation Rigid-Edge Deformation Effect of Plan Distribution on Max. Inter-story Drift - One-story elastic structure (T nx = T ny = 0.5 sec) - Uniaxial ground motion (Rinaldi 228) - Drift normalized w.r.t. value when CSD is at CR - Fixed damping magnitude: CSD @ Rigid Edge CSD @ Flexible Edge Moving CSD away from CR and toward CM: - Reduces drift along flexible edge (minimizes translation AND torsion). - Increases drift along rigid edge but rigid edge drift not main concern. - Overall, plan-wise distribution of damping has strong influence on structure response 10 Slide 11 Effect of Damper Magnitude on Max. Inter-story Drift - One-story elastic structure - Uniaxial ground motion (CP 106) - Drift normalized w.r.t. value when - Fixed CSD: EQ-X Increasing Magnitude of Damping: - Monotonically reduces drift along both flexible and rigid edges (minimizes translation AND torsion). - Strongest influence is on flexible edge - Rate of drift reduction largest for small damping ratios. - Transmission of damper forces to wood framing system and into foundation may impose limitation on damper magnitude. Rigid-Edge Flexible-Edge Flexible and Rigid Edge Deformations 11 Slide 12 Parametric Study of One-Story Inelastic Structure with Energy Dissipation System - Two-way asymmetric w/rigid diaphragm - Uniaxial ground motion - CR & CM Fixed - CSD Varied Northridge EQ Motions - Newhall County Fire Station: NCF90+NCF360 (moderate near-field) - Canoga Park Station: CP106+CP196 (moderate far-field) CM = Center of Mass CR = Center of Rigidity (located at ; similar to location for NEES-Soft test specimen). CSD = Center of Supplemental Damping (location varies in Y- direction). EQ-X - 4 walls (one on each side) - 2 dampers along X- direction, (one each on north and south sides) - Wall materials: Exterior: Horiz. wood sheathing Interior: Gypsum wall board 12 SAWS Shear Wall Model: Hysteretic response of conventional structure (no dampers) subjected to bi-axial Canoga Park motion. Slide 13 CSD moving - One-story inelastic structure (T nx = T ny = 0.5 sec) - Uniaxial ground motion (CP106) - Fixed total damping magnitude: Damping coefficient along X- direction is 5 kips-sec/in Moving CSD from flexible edge to stiff edge: - Increases drift along flexible edge (due to both translation AND torsion). - Reduces drift along stiff edge. - Overall, damper location (plan-wise distribution) has strong influence on structure response. - The optimized CSD location is approximately -0.2d in Y- direction (for a range of motions). CSD moving 13 Effect of Plan Distribution on Max. Inter-Story Drift EQ-X Slide 14 Effect of Damper Magnitude on Max. Inter-Story Drift - One-story inelastic structure - Uniaxial ground motion (CP 106) - Damper magnitude for both dampers increased at same rate from 0 to 5 kips-sec/in. - CSD location fixed ( ). Increasing Magnitude of Damping: - Monotonically reduces drift along all wall lines (minimizes both translation AND torsion). Rate of drift reduction largest at small damper magnitudes. - Transmission of damper forces to wood framing system and into foundation may impose limitation on damper magnitude. 14 EQ-X Slide 15 Parametric Study of One-Story Inelastic Structure with Energy Dissipation System - Two-way asymmetric w/rigid diaphragm - Biaxial ground motion - CR and CM Fixed - CSD varies EQ Motions - Canoga Park Station (moderate far-field) - 22 Far-field EQ records from ATC-63 - Stronger component applied in X-direction CM = Center of Mass CR = Center of Rigidity (located at ; similar to location for NEES-Soft test specimen) CSD = Center of Supplemental Damping (location varies in X- and Y-direction). EQ-X EQ-Y - 4 walls (one on each side) - 2 dampers along X- direction, (one each on north and south sides) - 2 dampers along Y- direction, (one each on west and east sides) - Wall materials: Exterior: Horiz. wood sheathing Interior: Gypsum wall board 15 SAWS Shear Wall Model: Hysteretic response of conventional structure (no dampers) subjected to bi-axial Canoga Park motion. Slide 16 - One-story inelastic structure (T nx = T ny = 0.5 sec) - Biaxial ground motion (CP106+CP196) - Fixed total damping magnitude: Damping coefficient along each direction is 5 kips-sec/in Moving CSD from CR towards, and beyond, CM: - The maximum structural responses generally decreases (reducing translation AND torsion). - Damper location (plan-wise distribution) has strong influence on structure response. - For a range of ground motions, the optimized CSD location is approximately at the coordinate (0.2, -0.2), which is symmetric with CR about CM. CR CM CSD @ Stiff Edge CSD @ Flexible Edge CSD @ Flexible Edge CSD @ Stiff Edge Conventional 0.77 (0.2,-0.2) 16 Effect of Plan Distribution on Max. Inter-Story Drift Slide 17 - One-story inelastic structure (T nx = T ny = 0.5 sec) - Biaxial ground motion (22 far-field records) - Fixed damping magnitude: damping coefficient along each direction is 2.5 kips-sec/in Moving CSD from CR towards CM: - Maximum drift varies non-monotonically. - Damper location (plan-wise distribution) has strong influence on structure response. - Optimized CSD location: X = 0.1~0.2 Y = -0.2~-0.1 CSD location (x,-0.2)CSD location (0.2,y) CSD moving in X CSD moving in Y 17 CSD moving in X CSD moving in Y Effect of Plan Distribution on Max. Inter-Story Drift: Far-Field Ground Motions Slide 18 Summary/Conclusions General Conclusion Plan distribution of energy dissipation system (location of CSD) has strong influence on maximum inter-story drift response of both linear and nonlinear soft-story structures. Linear Elastic Structure Minimum inter-story drift of flexible wall lines (critical walls) obtained when CSD is as far as possible from CR in direction toward CM (ideally, at corner of structure, although damping cannot physically be concentrated at a single point). Nonlinear Structure - Minimum inter-story drift of flexible wall lines (critical walls) obtained when CSD is far from CR in direction toward CM but NOT as far as possible. - Near-optimal choice for plan distribution of dampers is to position them such that the CSD is symmetric with respect to the CR about the CM. 18 Slide 19 19 Numerical - Extend parametric analyses to multi-story inelastic structures with different wall materials (SAWS2.1/SAWS2.1-IDA/Matlab) - Extend analyses to consider near-field ground motions - Investigate seismic retrofit consisting of combined stiffening and damping Numerical/Experimental - Evaluate performance of damper/stiffening retrofit relative to conventional (primarily stiffening) retrofits Experimental - Real-time hybrid testing of full-scale shear walls with dampers at University of Alabama - Hybrid testing of 3-story full-scale building using virtual dampers at NEES-UB - Shake table testing of 4-story full-scale building using physical dampers at NEES-UCSD On-Going/Future Work Slide 20 20 QUESTIONS?