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NEES-Soft: Seismic Risk Reduction for Soft-Story Woodframe Buildings John W. van de Lindt, University of Alabama Michael D. Symans, Rensselaer Polytechnic Institute Xiaoyun Shao, Western Michigan University Weichiang Pang, Clemson University Mikhail Gershfeld, Cal Poly Pomona 2012 Quake Summit and NSF CMMI Awardees Conference Boston, MA; July 2012
The NEES-Soft Project Team • University of Alabama: Prof John W. van de Lindt; Pouria Bahmani, Ph.D. Student • Clemson University: Prof WeiChiang Pang; Ershad Ziaei, Ph.D. Student • Western Michigan University: Prof Xiaoyun Shao; Chelsea Griffith, M.S. Student • Rensselaer Polytechnic Institute: Prof Michael D. Symans, Prof David V. Rosowsky; Jingjing Tian, Ph.D. Student • Cal Poly – Pomona: Prof Mikhail Gershfeld; Robert McDougal. M.S. Student; Nathan Summerville, B.S. Student • SUNYat Buffalo: Prof Andre Filiatrault • Structural Solutions Inc.: Gary Mochizuki • U.S. Forest Products Lab.: Douglas Rammer • Tipping Mar: David Mar • South Dakota State University: Prof Shiling Pei • Cal Poly – SLO: Charles Chadwell
The NEES-Soft Practitioner Advisory Committee (PAC) • Laurence KornfieldCity of San Francisco - CAPSS • Kelly CobeenWJE • Steve PryorSimpson Strong Tie • Tom Van DorpeVanDorpe Chou Associates, Inc. • Doug ThompsonSTB Structural Engineers • Doug Taylor Taylor Devices • JanielleMaffetiCalifornia Earthquake Authority • Rose Grant State Farm Research
Motivation for NEES-Soft Community Action Plan for Seismic Safety (CAPSS) 43 to 80 percent of the multi-story wood-frame buildings will be deemed unsafe after a magnitude 7.2 earthquake 25% of these buildings would be expected to collapse Thousands of these buildings exist, many of them multi-family rentals ATC 71.1 Project Develop seismic retrofit requirements for soft-story wood-frame buildings in seismically active regions of the United States Focusing primarily on Northern and Southern California and the Pacific Northwest
NEES-Soft Project Summary NEES-Soft: Seismic Risk Reduction for Soft-Story Woodframe Buildings Five-university-industry National Science Foundation-funded collaboration Develop a better understanding the behavior of soft-story woodframe buildings under seismic loads through numerical analyses and experimental testing Provide experimental validation of ATC 71.1 concepts and PBSR approaches Characterize the improvement in seismic performance for an array of force-based and performance-based retrofit techniques Develop improved models of woodframe collapse mechanisms to better estimate the margin against collapse.
NEES-Soft Retrofit Testing NEES@UB Rxn Wall 7 months beginning April 2013 Full-scale slow pseudo-dynamic test Six actuators (6 DOF) One 2-bedroom apartment per floor Level 1 – two-car garage and storage space
Floor Plans H: Horizontal Wood Sheathing G: Gypsum Wallboard First Floor
Floor Plans H: Horizontal Wood Sheathing G: Gypsum Wallboard Typical Floor
Seismic Retrofits for the NEES-Soft Building Phase 1– steel base frame Phase 2 – first story constructed
NEES-Soft PSD and Real-time tests @UA Test Objectives: • to verify the developed psudodynamic (PSD) testing and hybrid testing methods and their application to wood frame structures for eventual expansion to full buildings at NEES@UB (completed) The first time hybrid testing of a wood frame structure. • to characterize the highly nonlinear seismic behavior of woodframe construction (underway) • to evaluate in real earthquake rate the enhanced seismic behavior of woodframe installed with viscous dampers (underway)
NEES-Soft PSD hybrid and Real-time tests @UA • Cyclic Tests: full CUREE protocol • Open Loop Hybrid Tests • to determine slow testing rate: 20 times slower was selected • to verify the developed continuous loading method • Closed Loop Hybrid Tests • Specimen 1: Loma Prieta Capitola (Completed) • Test 1: 72 year • Test 2: 2500 year • Test 3: mass x 3 and 2500 year • Specimen 2: Northridge-Beverly Hills(to be complete by Shao @ WMU remote control UA hybrid testing controller)
Slow PSD hybrid test @UB NEES Objective : to develop an increased understanding of the effects of first floor (soft-story) retrofits on the upper stories • Specimen: 3-dimensional (near) full scale model with and without retrofit • Numerical substructure: existing first story with various retrofits • Physical substructure: upper stories, full representation with construction details • Use six actuators to consider rotation
Performance-Based Retrofit using Energy Dissipation System • Performance-Based Retrofit • Increase damping in first story (and possibly stiffness) • May increase force transmitted to upper stories (imposes • limit on magnitude of damping in first story) • Expected performance level for design earthquake: • Fully Operational (FO) to Immediate Occupancy (IO) • Energy Dissipation System • Linear fluid viscous dampers • Peak force out-of-phase with peak displacement • Previously tested in wood structures • Location of Dampers • First story only • Along perimeter walls to provide contribution to torsionalresistance • Along both stiff and flexible wall lines • Displacement amplification system employed (scissor-jack)
Parametric Study of One-Story Inelastic • Structure with Energy Dissipation System • Two-way asymmetric w/rigid diaphragm • Biaxial ground motion • CR and CM are fixed • CSD varied EQ Motions - Canoga Park Station (moderate far-field) - Far-field EQ records from ATC-63 - Stronger component applied in X-direction - 4 walls (one on each side) - Wall materials: Exterior: Horiz. wood sheathing Interior: Gypsum wall board - 2 dampers along X- direction, (one each on north and south sides) - 2 dampers along Y- direction, (one each on west and east sides) EQ-X SAWS Shear Wall Model: Hysteretic response of conventional structure (no dampers) subjected to bi-axial Canoga Park motion. EQ-Y 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).
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 • Effect of Damper Location (CSD) • on Max. Inter-Story Drift Conventional CM 0.77 (0.2,-0.2) CR CSD @ Stiff Edge CSD @ Flexible Edge CSD @ Flexible Edge CSD @ Stiff Edge • 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 influenceon 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.
DDD with Torsion Procedure: Linear system (i.e. stiffness of lateral load resisting system element does not change during the analysis) Decoupling torsional modes from translational modes Modal analysis for decoupled modes Combining modes to obtain the total displacement Using spectral displacement to find the design stiffness of each lateral load resisting element Nonlinear system Using equivalent secant stiffness and damping ratio using method proposed by Filiatrault and Folz
Regular building with Large in-plane Eccentricities Stiffness ratio over the height: K3 = 1.75 K; K2 = 2.25 K; K1 = 2.5 K; K1 /K2 = 1.11 K2 /K3 = 1.29 Eccentricity ratio: ex = 4.82 ft ;Lx = 30 ft ex / Lx = 16.1% ey = 4.29 ft;Ly = 20 ft ey / Ly = 21.4% er= 6.45 ft CM CR ey ex Unit weight for each floor: 30 psf Earthquakes at MCE level (San Francisco) EQ forces applied in X-direction Target Drift = 2% for Prob. of Non-Exceedance of 50% Tn = 0.577 sec. Sa = 1.44g 1st Story Probability of Exceedance Target = 2.0% Error (%) = 2.5% 2.05% Inter-story Drift Ratio (%)
Soft-story Building with Irregularity over the height and in-plane Stiffness ratio over the height: K3 = 1.8 K; K2 = 2.6 K; K1 = 2.0 K; K1 /K2 = 0.77 K2 /K3 = 1.44 Eccentricity ratio for all stories: ex = 3.75 ft; Lx = 30 ft ex / Lx = 12.5% ey = 3.33 ft; Ly = 20 ft ey / Ly = 16.7% er= 5.02 ft CM CR ey ex Unit weight for each floor: 30 psf 1st Story Earthquakes at MCE level (San Francisco) EQ forces applied in X-direction Target Drift = 2% for Prob. of Non-Exceedance of 50% Tn = 0.489 sec. Sa = 1.5g Probability of Exceedance 1.93% Error (%) = 3.5% Target = 2.0% Inter-story Drift Ratio (%)
Frame Element F2F Element Soft Story (a) 6 - DOF Node 12 - DOF Frame Element (u pper floor diaphragm) Slave Node 6 - DOF Link Element 12 - DOF Frame Element (Shear Wall) (lower floor diaphragm) Slave Node (b) 3D Model for Collapse Analysis • 3D Model • Based on large deformation theory • Co-rotation • Geometric Nonlinearity • P-Delta Effect
Incremental Dynamic Analysis (IDA) FEMA P-695 Far Field Ground Motions X Y Bi-axial ground motions
Torsion Torsion EQ ID 21, 1971 San Fernando Earthquake Node 4 Node 1 Soft-story drift and torsion are observed
IDA Curves IDA curves
Collapse Fragility Curves maximum resultant inter-story drift Median Collapse drift 12~13%?
Summary of Current Methods Value includes ρ = 1.3 Story drift displacement performance ground level target drift upper levels target drift Maximum Considered Earthquake (MCE) Strength Coefficient based on ground story strength in the X-direction (W = 35 kips) Strength Coefficient based on second story strength in the X-direction (W = 35 kips) Strength Coefficient based on second story strength in the X-direction (W = 82 kips Strength Coefficient based on second story strength in the X-direction (W = 82 kips) Based on total weight W = 35 kips Based on total weight W = 82 kips Vmax(Ultimate Capacity)
EOT – Educational Outreach NEES Academy 30 minute on-line modules under development NS 10 – Classification, typical construction and behavior of soft story wood frame buildings NS 20 – Understanding of design options for retrofit of weak/soft story buildings NS 30 - Design example of weak/soft story retrofit using ATC 71.1 NS 40 - Design example of weak/soft story retrofit using direct displacement design methodology
EOT – Educational Outreach • NEES Academy - EOT Modules Stand alone educational content Could be incorporated into undergraduate and graduate online or hybrid courses. Moodle - NEES supported LMS (Learning Management System Modules allow for quicker and more efficient dissemination of information to various audience. Additional modules could be developed as needed
NEES-Soft Validation Testing NEES @ UCSD Shake Table 2 months beginning Fall 2013 4-story full-scale Retrofit order PBSR ATC 71.1 Remove retrofits and collapse Retrofit types SMF Cantilevered column (IMF) Dampers Design just underway
Next Steps for NEES-Soft NEES-Soft Retrofit building tests at UB Construction phase in April 2013 Test phase May – Oct 2013 DDD with torsion Completed June 2012 PBSD for soft-story Completed August 2012 UC San Diego Testing August-Sept 2013 Update presentations WCTE – Auckland, New Zealand; July 2012; next week WCEE – Lisbon, Portugal; Sept 2012
Thank you! Professor John W. van de Lindt Email: firstname.lastname@example.org Or email@example.com This material is based upon work supported by the National Science Foundation under Grant No. CMMI-1041631 (NEES Research) and NEES Operations. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the investigators and do not necessarily reflect the views of the National Science Foundation. ½” scale model constructed by Prof Mikhail Gershfeld and students at Cal Poly Pomona.