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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.

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Presentation on theme: "NEES-Soft: Seismic Risk Reduction for Soft-Story Woodframe Buildings John W. van de Lindt, University of Alabama Michael D. Symans, Rensselaer Polytechnic."— Presentation transcript:

1 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

2 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 SUNY at 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

3 The NEES-Soft Practitioner Advisory Committee (PAC) Laurence Kornfield City of San Francisco - CAPSS Kelly Cobeen WJE Steve Pryor Simpson Strong Tie Tom Van Dorpe VanDorpe Chou Associates, Inc. Doug Thompson STB Structural Engineers Doug Taylor Taylor Devices Janielle Maffeti California Earthquake Authority Rose Grant State Farm Research

4 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

5 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.

6 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


8 Floor Plans First Floor H: Horizontal Wood Sheathing G: Gypsum Wallboard

9 Typical Floor H: Horizontal Wood Sheathing G: Gypsum Wallboard Floor Plans

10 Retrofit TypeTarget Verification Steel Special Moment Frame (SSMF) or Inverted Moment Frame (IMF) ATC 71.1 Wood Shear Walls SSMF/IMF and Wood Shear Walls Performance-Based Seismic Retrofit Cross Laminated Timber (CLT) Dampers Retrofit TypeTarget Verification Steel Special Moment Frame (SSMF) or Inverted Moment Frame (IMF)ATC 71.1 SSMF/IMF and Wood Shear WallsPerformance-Based Seismic Retrofit Knee-braceOther (only a limited numerical prediction being performed) Phase 1– steel base frame Phase 2 – first story constructed Seismic Retrofits for the NEES-Soft Building

11 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)

12 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)

13 Test Setup - Slow Pseudo Dynamic and Real-time

14 Cyclic test (CUREE Protocol) - Photos

15 Slow Pseudo Dynamic test

16 UA Hybrid Testing Results

17 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

18 Conceptual plot of PSD hybrid test @ UB

19 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 torsional resistance Along both stiff and flexible wall lines Displacement amplification system employed (scissor-jack)

20 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 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) - 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) 20 SAWS Shear Wall Model: Hysteretic response of conventional structure (no dampers) subjected to bi-axial Canoga Park motion.

21 Effect of Damper Location (CSD) on Max. Inter-Story Drift - 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) 21

22 DDD from previous work Pang et al, 2010

23 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

24 Eccentricity ratio: e x = 4.82 ft ; L x = 30 ft  e x / L x = 16.1% e y = 4.29 ft; L y = 20 ft  e y / L y = 21.4% e r = 6.45 ft 1 st Story Stiffness ratio over the height: K 3 = 1.75 K; K 2 = 2.25 K; K 1 = 2.5 K; 2.05% Regular building with Large in-plane Eccentricities K 1 / K 2 = 1.11 K 2 / K 3 = 1.29 Unit weight for each floor: 30 psf CM CR exex eyey Target = 2.0% Error (%) = 2.5% 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 Probability of Exceedance Inter-story Drift Ratio (%)

25 Eccentricity ratio for all stories: e x = 3.75 ft ; L x = 30 ft  e x / L x = 12.5% e y = 3.33 ft ; L y = 20 ft  e y / L y = 16.7% e r = 5.02 ft 1 st Story Error (%) = 3.5% Target = 2.0% CM CR exex eyey Stiffness ratio over the height: K 3 = 1.8 K; K 2 = 2.6 K; K 1 = 2.0 K; 1.93% Soft-story Building with Irregularity over the height and in-plane K 1 / K 2 = 0.77 K 2 / K 3 = 1.44 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 Unit weight for each floor: 30 psf Probability of Exceedance Inter-story Drift Ratio (%)

26 Summary Building Eccentricity Fundamental Period (sec) Sa @ MCE Drift (%) Error (%) e x /L x (%) e y /L y (%) Target PerformanceCDF Curve Regular Building with Large in-plane Eccentricity16.121.40.5771.44g2% / 50% NE2.052.5 Soft-story Building with in-plane Eccentricity12.516.70.4891.5g2% / 50% NE1.933.50

27 12-DOF Frame Element (lower floor diaphragm) 12-DOF Frame Element (upper floor diaphragm) 6-DOF Node 6-DOF Link Element (Shear Wall) Slave Node Slave Node (b) (a) Soft Story F2F Element Frame Element 3D Model Based on large deformation theory Co-rotation Geometric Nonlinearity P-Delta Effect 3D Model for Collapse Analysis

28 Incremental Dynamic Analysis (IDA) FEMA P-695 Far Field Ground Motions ATC-63 / FEMA P-695 Far Field Ground motions ID NumMYearEQ NameStation Name 16.71994NorthridgeBeverly Hills 26.71994NorthridgeCanyon Country-WLC 37.11999Duzce,Turkey Bolu 47.11999HectorMine Hector 56.51979ImperialValley Delta 66.51979ImperialValley EI 76.91995Kobe,Japan Nishi-Akashi 86.91995Kobe,Japan Shin-Osaka 97.51999Kocaeli,Turkey Duzce 107.51999Kocaeli,Turkey Arcelik 117.31992LandersYermo Fire 127.31992LandersCoolwater SCE 136.91989LomaPrieta Capitola 146.91989LomaPrieta Gilroy 157.41990Manjil,Iran Abbar 166.51987SuperstitionHills El 176.51987SuperstitionHills Poe 1871992CapeMendocino Rio 197.61999Chi-ChiTaiwan, CHY101 207.61999Chi-ChiTaiwan, TCU045 216.61971San FernandoLA 226.51976FriuliItaly, Tolmezzo Bi-axial ground motions X Y

29 Torsion Node 4 Node 1 EQ ID 21, 1971 San Fernando Earthquake Torsion Soft-story drift and torsion are observed

30 IDA curves IDA Curves

31 Median Collapse drift 12~13%? Collapse Fragility Curves maximum resultant inter-story drift

32 Code/ Methodology Performance Level Importance Factor Target Drift Hazard Level Design Approach Retrofit Extent R Seismic Response Coefficient Base Shear (kips) m Base Shear (kips) n ASCE 7-10 Life Safety1.0 2.5% 10%/50yr Force Based Entire Structure 6.5 0.1546.9 a 16.5 a ? 1.25?0.1928.7 a 20.6 a ?1.52%/50yr0.23110.4 a 24.7 a IEBC Collapse Prevention 1.0 2.5%2%/50yrForce Based Ground Level 2 0.37532.5 p 77.2 p 1.250.46940.7 p 96.4 p 1.50.56348.8 p 115.7 p ASCE 41 Collapse Prevention n/a3% 2%/50yr Performance Based b Entire Structure n/a Dynamic Analysis -- Life Safetyn/a2% 10%/50yrn/a -- Immediate Occupancy n/a1% 20%/50yrn/a -- ATC 71-1 Collapse Prevention n/a 4% c 1.25% d 2%/50yr e Performance Based b Ground Level n/a 1.920 f 2.657 g 0.870 h 1.129 k 17-2425-42 DDD Collapse Prevention n/a4%2%/50yr Performance Based b Entire Structure n/a1.527 m 1.527 n 45.6 p 108.7 p Life Safety n/a2%10%/50yrn/a0.342 m 0.356 n 10.2 p 25.3 p Immediate Occupancy n/a1%50%/50yrn/a0.148 m 0.154 n 4.4 p 11.0 p a.Value includes ρ = 1.3 b.Story drift displacement performance c.ground level target drift d.upper levels target drift e.Maximum Considered Earthquake (MCE) f.Strength Coefficient based on ground story strength in the X-direction (W = 35 kips) g.Strength Coefficient based on second story strength in the X-direction (W = 35 kips) h.Strength Coefficient based on second story strength in the X-direction (W = 82 kips k.Strength Coefficient based on second story strength in the X-direction (W = 82 kips) m.Based on total weight W = 35 kips n.Based on total weight W = 82 kips p.V max (Ultimate Capacity) Summary of Current Methods

33 Code/MethodologyStrengthsLimitations ASCE 7-10 Simplified approach Currently accepted by all jurisdictions Response modification factor is based on engineering judgment Requires entire building to be retrofitted to meet standards for new building IEBC Only requires retrofit of ground story, no requirements for upper stories Does not consider increased damage to upper floors Requires lower R value Only meets Collapse Prevention level of performance Requires use of Ω to calculate ground level forces Requires 25% increase in calculated deflection ASCE 41 Used to determine structural deficiencies Designer chooses level of performance required for structure Requires in-depth analysis Requires extensive data collection involving destructive testing Overly sophisticated for application ATC 71-1 Only requires retrofit of ground story Limits damage in upper stories Utilizes existing strength in non-structural finishes Needs to be verified Application limited to weak story buildings Requires software (Weak Story Tool) to be less time consuming DDD Designer chooses level of performance Meets both safety and damage limitations Allows for the consideration of drift limits without use of nonlinear pushover analysis Time consuming compared to force-based methodologies Design process requires backbone curves to estimate shear wall behavior Does not yet consider torsion Strengths and Limitations

34 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

35 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

36 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

37 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

38 Thank you! 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. Professor John W. van de Lindt Email: Or ½” scale model constructed by Prof Mikhail Gershfeld and students at Cal Poly Pomona.

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