NEES-Soft: Seismic Risk Reduction for Soft-Story Woodframe Buildings

NEES-Soft: Seismic Risk Reduction for Soft-Story Woodframe BuildingsJohn W. van de Lindt, University of AlabamaMichael D. Symans, Rensselaer Polytechnic InstituteXiaoyun Shao, Western Michigan UniversityWeichiang Pang, Clemson UniversityMikhail 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

SUNY at Buffalo: Prof Andre Filiatrault

Structural Solutions Inc.: Gary MochizukiU.S. Forest Products Lab.: Douglas RammerTipping Mar: David MarSouth Dakota State University: Prof Shiling PeiCal Poly – SLO: Charles Chadwell

The NEES-Soft Practitioner Advisory Committee (PAC)

Laurence Kornfield City of San Francisco - CAPSSKelly Cobeen WJESteve Pryor Simpson Strong TieTom Van Dorpe VanDorpe Chou Associates, Inc. Doug Thompson STB Structural EngineersDoug Taylor Taylor DevicesJanielle Maffeti California Earthquake AuthorityRose 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 ProjectDevelop 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 Wall7 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

First Floor

Ground Floor Plan

XY

10'-0" 10'-0"

1'-6" 1'-6" 1'-6" 7'-0"7'-0"

8'-0"

8'-0"

8'-0"

24'-0"

1

2

3

4

A B C

3'-4"10'-8"

Rev. 4-2 NEES-Soft (11.19.2011)

4"

3'-0" 3'-0"

H,G

H,G

EQx

EQx

H,G

H,G

H,G

H,G

H,G

H,G H,G

G,G

G,G

H,G H,G

H: Horizontal Wood SheathingG: Gypsum Wallboard

Typical Floor H: Horizontal Wood SheathingG: Gypsum Wallboard

Typical Floor Plan

XY

10'-0" 10'-0"

20'-0"

1'-6" 3'-0"7'-0"

8'-0"

8'-0"

8'-0"

24'-0

"

1

2

3

4

A B C

Bath

Bdrm 2

Bdrm 1Living Room

4'-8"

6'-4"

9'-4"

Kitchen

1

9'-2"3'-

0"

3'-0" 3'-0"

4"

Rev. 4-214'-0"

5'-6"

3'-0"

7'-0"

7'-0" 1'-6"

3'-0"

NEES-Soft (11.19.2011)

7'-0"

5'-6"

H,G

G,G

G,G G,G

G,G

G,G

G,G

G,G

EQx

EQx

H,G

H,G

H,G

H,G

H,G H,G

G,G

G,G

H,G H,G

1'-6"

4'-0"

6'-0"

3'-112"

1'-0"

2'-0"

1'-10

"3'-

0"

H,G

Floor Plans

Retrofit Type Target Verification

Steel Special Moment Frame (SSMF) or Inverted Moment Frame (IMF)

ATC 71.1

Wood Shear Walls

SSMF/IMF and Wood Shear WallsPerformance-Based Seismic RetrofitCross Laminated Timber (CLT)

Dampers

Retrofit Type Target Verification

Steel Special Moment Frame (SSMF) or Inverted Moment Frame (IMF) ATC 71.1

SSMF/IMF and Wood Shear Walls Performance-Based Seismic Retrofit

Knee-brace Other (only a limited numerical prediction being performed)

Phase 1– steel base frame

Phase 2 – first story constructed

Seismic Retrofits for the NEES-Soft Building

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)

Test Setup - Slow Pseudo Dynamic and Real-time

Cyclic test (CUREE Protocol) - Photos

Slow Pseudo Dynamic test

UA Hybrid Testing Results

-6 -5 -4 -3 -2 -1 0 1 2 3-10

-8

-6

-4

-2

0

2

4

6

8

10First Floor Wall HysteresisSlow Hybrid Test

Displacement(in)

For

ce(k

ip)

Test 3, 2500yr x3 mass

Test 2, 2500yrTest 1, 72yr

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

Conceptual plot of PSD hybrid test @ UB

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 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)- 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)

SAWS Shear Wall Model:Hysteretic responseof 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 (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)

DDD from previous work Pang et al, 2010

CM & CR

CM & CR

X

YZ

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 modesModal analysis for decoupled modesCombining modes to obtain the total displacementUsing 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

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

1st Story

Stiffness ratio over the height:K3 = 1.75 K;

K2 = 2.25 K;

K1 = 2.5 K;

2.05%

Regular building with Large in-plane Eccentricities

K1 / K2 = 1.11

K2 / K3 = 1.29

Unit weight for each floor: 30 psf

CM

CRex

ey

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

Prob

abili

ty o

f Exc

eeda

nce

Inter-story Drift Ratio (%)

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

1st Story

Error (%) = 3.5%

Target = 2.0%

CM

CR

ex

ey

Stiffness ratio over the height:K3 = 1.8 K;

K2 = 2.6 K;

K1 = 2.0 K;

1.93%

Soft-story Building with Irregularity over the height and in-plane

K1 / K2 = 0.77

K2 / K3 = 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

Prob

abili

ty o

f Exc

eeda

nce

Inter-story Drift Ratio (%)

Summary

BuildingEccentricity Fundamental

Period (sec) Sa @ MCE Drift (%)

Error (%)ex/Lx (%)

ey/Ly (%) Target Performance CDF Curve

Regular Building with Large in-plane Eccentricity 16.1 21.4 0.577 1.44g 2% / 50% NE 2.05 2.5

Soft-story Building with in-plane Eccentricity 12.5 16.7 0.489 1.5g 2% / 50% NE 1.93 3.50

Task Year 1 Year 2 Year 3

1. Hybrid Testing of Soft-Story Woodframe Building 1.1 1.2

2. 3-D Collapse Model Development 2.1

3. PBR Method for Soft Story 3.1 3.2 3.3

4. Evaluation of ATC-71.1 Retrofit Guidelines 4.1 4.2

5. Seismic Protection Systems for Higher Performance 5.1 5.2 5.3

6. Performance-Based Retrofit Guidelines 6.1

7. Project Advisory Committee 7.1

8. System Level Verification of Retrofit Procedures 8.1,2,3

9. Education, Outreach, and Technology Transfer 9.1

10. NEES Awardee Meetings (every 18 months) 10

12 - DOF Frame Element

(lower floor diaphragm)

12 - DOF Frame Element

(u pper 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

Incremental Dynamic Analysis (IDA) FEMA P-695 Far Field Ground Motions

ATC-63 / FEMA P-695 Far Field Ground motionsID Num M Year EQ Name Station Name

1 6.7 1994 Northridge Beverly Hills2 6.7 1994 Northridge Canyon Country-WLC3 7.1 1999 Duzce, Turkey Bolu4 7.1 1999 Hector Mine Hector5 6.5 1979 Imperial Valley Delta6 6.5 1979 Imperial Valley EI7 6.9 1995 Kobe, Japan Nishi-Akashi8 6.9 1995 Kobe, Japan Shin-Osaka9 7.5 1999 Kocaeli, Turkey Duzce

10 7.5 1999 Kocaeli, Turkey Arcelik11 7.3 1992 Landers Yermo Fire12 7.3 1992 Landers Coolwater SCE13 6.9 1989 Loma Prieta Capitola14 6.9 1989 Loma Prieta Gilroy15 7.4 1990 Manjil, Iran Abbar16 6.5 1987 Superstition Hills El17 6.5 1987 Superstition Hills Poe18 7 1992 Cape Mendocino Rio19 7.6 1999 Chi-Chi Taiwan, CHY10120 7.6 1999 Chi-Chi Taiwan, TCU04521 6.6 1971 San Fernando LA22 6.5 1976 Friuli Italy, Tolmezzo

Bi-axial ground motions

XY

Torsion

-1000

100200

300400 -200

0

200

400

6000

100

200

300

400

yx

z

0 5 10 15 20 25-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

Time(s)

Y R

oof

Drift

Roof Drift in Y direction - node#1&4 - EQ17

node#4

node#1

torsion

Node 4

Node 1

EQ ID 21, 1971 San Fernando Earthquake

Torsion

Soft-story drift and torsion are observed

IDA curves

0 5 10 150

0.5

1

1.5

2

2.5

3

3.5

Max. Resultant Interstory Drift (%)

Med

ian

Sa a

t N

atur

al P

erio

d (g

)

Maximum resultant Inter-Story Drift

EQs g=0o

EQs g=90o

16%median

84%

2 2x y

h

IDA Curves

0 2 4 6 8 10 12 14 16 18 200

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Max. Resultant Interstory Drift (%)

Col

laps

e P

roba

bilit

y

Collapse Diagram - Max Resultant Inter-Story Drift

Median Collapse drift 12~13%?

Collapse Fragility Curves maximum resultant inter-story drift

Code/ Methodology

Performance Level

Importance Factor

Target Drift

Hazard Level

DesignApproach

Retrofit Extent

RSeismic Response Coefficient

Base Shear (kips)m

Base Shear (kips)n

ASCE 7-10

Life Safety 1.0

2.5%

10%/50yr

Force Based EntireStructure 6.5

0.154 6.9a 16.5a

? 1.25 ? 0.192 8.7a 20.6a

? 1.5 2%/50yr 0.231 10.4a 24.7a

IEBC Collapse Prevention

1.0 2.5% 2%/50yr Force Based Ground

Level 20.375 32.5p 77.2p

1.25 0.469 40.7p 96.4p

1.5 0.563 48.8p 115.7p

ASCE 41

Collapse Prevention n/a 3% 2%/50yr

Performance Basedb

EntireStructure

n/a

DynamicAnalysis

- -

Life Safety n/a 2% 10%/50yr n/a - -

Immediate Occupancy n/a 1% 20%/50yr n/a - -

ATC 71-1 Collapse Prevention n/a 4%c

1.25%d 2%/50yre PerformanceBasedb

Ground Level n/a 1.920f

2.657g0.870h

1.129k 17-24 25-42

DDD

Collapse Prevention n/a 4% 2%/50yr

PerformanceBasedb

EntireStructure

n/a 1.527m 1.527n 45.6p 108.7p

Life Safety n/a 2% 10%/50yr n/a 0.342m 0.356n 10.2p 25.3p

Immediate Occupancy n/a 1% 50%/50yr n/a 0.148m 0.154n 4.4p 11.0p

a. Value includes ρ = 1.3b. Story drift displacement performancec. ground level target driftd. upper levels target drifte. 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 kipsk. Strength Coefficient based on second story strength in the X-direction (W = 82 kips)m.Based on total weight W = 35 kipsn. Based on total weight W = 82 kipsp. Vmax(Ultimate Capacity)

Summary of Current Methods

EOT – Educational Outreach

NEES Academy30 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 ModulesStand 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 Table2 months beginning Fall 20134-story full-scaleRetrofit order

PBSRATC 71.1Remove retrofits and collapse

Retrofit typesSMFCantilevered column (IMF)Dampers

Design just underway

Next Steps for NEES-Soft

NEES-Soft Retrofit building tests at UBConstruction phase in April 2013Test phase May – Oct 2013

DDD with torsionCompleted June 2012

PBSD for soft-storyCompleted August 2012

UC San Diego TestingAugust-Sept 2013

Update presentationsWCTE – Auckland, New Zealand; July

2012; next weekWCEE – Lisbon, Portugal; Sept 2012

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 LindtEmail: [email protected] [email protected]

½” scale model constructed by Prof Mikhail Gershfeld and students at Cal Poly Pomona.