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Technical Session 10 (Wood Structures)2012 Quake Summit
Boston, MAJuly 12, 2012
Jingjing Tian, Ph.D. Student
Michael D. Symans, Assoc. Professor
Dept. of Civil and Environmental EngineeringRensselaer Polytechnic Institute
Effect of Plan Distribution of Energy Dissipation Devices on Seismic Response of
Soft-Story Wood-Framed Structures
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NEESR-CR: NEES-Soft: Seismic Risk Reduction for Soft-Story Wood Frame Buildings
John W. van de Lindt University of Alabama PI, Overall Project Manager
Michael Symans Rensselaer 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 EngineeringWestern Michigan Univ. 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 PersonnelIoannis
ChristovasilisNational Tech. Univ. of
Athens Senior Personnel
Douglas Rammer U.S. Forest Products Lab Senior PersonnelDavid Mar Tipping Mar Senior Personnel
Research supported by National Science Foundation CMMI Grant No. 1041631 (NEESR - Network for Earthquake Engineering Simulation Research)
Project Team
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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
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Seismic Response of Soft-Story BuildingsSoft-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.
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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)
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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)
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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)
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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
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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)
/ 0.2 and / 0.2x ye a e d
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 isadded 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)
Rigi
d-Ed
ge
Flex
ible
-Edg
e
10EQ-X
Flexible-Edge Deformation Rigid-Edge Deformation
10%sdx sdy
Effect of Plan Distribution onMax. Inter-story Drift
- One-story elastic structure (Tnx = Tny = 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
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Effect of Damper Magnitude on Max. Inter-story Drift / 0.5
/ 0.5sdx
sdy
e ae d
- 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.
10%sdx sdy
0% 30%sdx sdy
Rigid-Edge
Flexible-Edge
Flexible and Rigid Edge Deformations
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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).
/ 0.2 and / 0.2x ye a e d
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
SAWS Shear Wall Model:Hysteretic responseof conventional structure (no dampers)subjected to bi-axial Canoga Park motion.
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CSD moving
- One-story inelastic structure (Tnx = Tny = 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
mov
ing
/ 0.5sdxe a / 0.5sdxe a
/ 0.5sdye d
/ 0.5sdye d
Effect of Plan Distribution on Max. Inter-Story Drift
EQ-X
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Effect of Damper Magnitudeon 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.
0.2sdye d
/ 0.5sdye d
/ 0.5sdye d
EQ-X
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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 MassCR = 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).
/ 0.2 and / 0.2x ye a e d
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
SAWS Shear Wall Model:Hysteretic responseof conventional structure (no dampers)subjected to bi-axial Canoga Park motion.
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- One-story inelastic structure (Tnx = Tny = 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)
Effect of Plan Distribution on Max. Inter-Story Drift
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- One-story inelastic structure (Tnx = Tny = 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
mov
ing
in Y
CSD moving in X CSD moving in Y
Effect of Plan Distribution on Max. Inter-Story Drift: Far-Field Ground Motions
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Summary/ConclusionsGeneral 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 StructureMinimum inter-story drift of flexible wall lines (critical walls) obtainedwhen 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.
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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
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QUESTIONS?
