July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 11

NEESR-SGNEESR-SGSeismic Performance Seismic Performance Assessment and Retrofit of Non-Assessment and Retrofit of Non-Ductile RC Frames with Infill Ductile RC Frames with Infill WallsWalls

P. Benson Shing, Jose Restrepo, and Andreas StavridisUniversity of California, San Diego

Kaspar Willam, Sivaselvan Mettupalayam, and Ben BlackardUniversity of Colorado, Boulder

Sarah Billington and Marios KyriakidesStanford University

George E. Brown, Jr. Network for Earthquake Engineering Simulation

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 22

2000 Kocaeli, Turkey Earthquake (EERI)

Performance IssuesPerformance Issues

• Non-uniform infill –Non-uniform infill – open bottom storyopen bottom story

• Asymmetric Asymmetric stiffeningstiffening introducing torsionintroducing torsion

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 33

Beneficial Influence of InfillBeneficial Influence of InfillNegro et al. (1996)

Bare Frame

Infilled Frame

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 44

Main IssueMain Issue

Brittle shear failure of columnsBrittle shear failure of columns Strength degradation of infill Strength degradation of infill

and columns leading to soft and columns leading to soft story mechanismstory mechanism

Soft Story

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 55

Questions to be AnsweredQuestions to be Answered

What is the threshold ground motion What is the threshold ground motion level beyond which an infilled frame level beyond which an infilled frame will have undesirable performance?will have undesirable performance?

How can we raise this threshold with How can we raise this threshold with cost-effective strengthening?cost-effective strengthening?

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 66

State of the PracticeState of the Practice

Lack of reliable analysis tools for Lack of reliable analysis tools for sound engineering decisions sound engineering decisions

Contribution of infill walls to seismic Contribution of infill walls to seismic resistance difficult to assessresistance difficult to assess

Lack of proven cost-effective Lack of proven cost-effective strengthening methods for infill wallsstrengthening methods for infill walls

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 77

Complicated Failure Complicated Failure MechanismsMechanisms

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 88

Frame-Panel InteractionFrame-Panel Interaction

Weak Infill

Strong Infill

Frames Tested byMehrabi et al. (1994)

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 99

Project DeliverablesProject Deliverables

Improved analysis methods for Improved analysis methods for performance assessmentperformance assessment

Rational assessment procedure Rational assessment procedure considering contribution of infill wallsconsidering contribution of infill walls

Validated cost-effective Validated cost-effective strengthening methods to enhance strengthening methods to enhance system-level performancesystem-level performance

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 1010

Research ApproachResearch Approach

Assessment of Existing Modeling Methods

Improved Analysis Methods

Small-Scale Tests on Strengthening Methods

Medium-Scale Tests on Single-Story Frames

Large-Scale Tests on Multi-Story Frames

Component Performance System Performance

Retrofit Methods

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 1111

Rational Assessment Rational Assessment ProcedureProcedure

Does the building need strengthening considering the

contribution of infill walls?

Can it be economically and adequately strengthened without additional load resisting systems?

Addition of new loading resisting systems

Infill and/or column strengthening

DoneNo

Yes

NoYesPe

rfo

rman

ce A

sse

ssm

en

t

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 1212

Retrofit MethodsRetrofit Methods

Engineered Cementitious Engineered Cementitious Composites (ECC) for infill Composites (ECC) for infill strengtheningstrengthening

FRP overlay or sprayFRP overlay or spray

Infill wall-to-beam connectionInfill wall-to-beam connection

Column strengtheningColumn strengthening

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 1313

ECC Overlay (Stanford U.)ECC Overlay (Stanford U.)

A

A A-A

ECC

Shear connector

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 1414

Small-Scale Tests at Small-Scale Tests at StanfordStanford

Prism Tests

Flexural Tests

In-plane Wall Tests

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 1515

2/3-Scale Single-Story Frame 2/3-Scale Single-Story Frame TestsTests(Colorado NEES Site)(Colorado NEES Site)

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 1616

Tentative Test Matrix for Tentative Test Matrix for Single-Story SpecimensSingle-Story Specimens

Specimen InfillWall

WallOpenings

ColumnRetrofit

Wall Retrofit

1 Y N N N

2 Y N N ECC/Connectors

3 Y Y N N

4 Y Y N ECC

5 Y Y N FRP or Spray FRP

6 Y N Y HPFRCC, FRP or Spray FRP

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 1717

Full-Scale Shake Table Full-Scale Shake Table TestsTests(UCSD NEES Site)(UCSD NEES Site)

• Frame with solid infill.

• Frame with solid infill and retrofit.

• Frame with infill openings and retrofit.

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 1818

Analysis MethodsAnalysis Methods

Advanced computational models for Advanced computational models for detailed analysis (CU-Boulder)detailed analysis (CU-Boulder)

Limit analysis methods accounting for Limit analysis methods accounting for multiple failure scenariosmultiple failure scenarios

Simplified strut models for time Simplified strut models for time histories analysishistories analysis

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 1919

Evaluation of Existing Evaluation of Existing ModelsModels

Effect of Infill

0

10

20

30

40

50

60

70

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Displacement, in

Load, ki

ps

Bareframe

Frame w/ Infill

Tests by Mehrabi et al. (1994)

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 2020

Comparison of ProgramsComparison of Programs

0 20 40 60 80 100 120

0

20

40

60

80

100

FEAP

DIANA

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5 3

Lateral Displacement (in)

Late

ral L

oad

(kip

s)

STANFORDCOLORADOUCSDExperimental

Stanford: DIANAColorado: ABAQUSUCSD: FEAP

PrincipalTensile Strain

Crack and Crushing

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 2121

Infill Joint Modeling with Infill Joint Modeling with FEAP ElementFEAP Element

Shear

Axial Compression

Failure Surface

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 2222

Infilled Frame Analysis Infilled Frame Analysis (FEAP)(FEAP)

-1.5 -1 -0.5 0 0.5 1 1.5

-60

-40

-20

0

20

40

60

Displacement, in

Forc

e, Kip

s

Single Story Single Bay Concrete Frame with I nfi ll

Finite Element Model

Experiment

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 2323

Additional Modeling WorkAdditional Modeling Work

Parametric studies to examine influence Parametric studies to examine influence of model parametersof model parameters

Calibration of simplified analytical modelsCalibration of simplified analytical models

Predictive analysis and assessment with Predictive analysis and assessment with new experimental resultsnew experimental results

Model improvementModel improvement

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 2424

Project TeamProject Team

Benson ShingBenson ShingJose RestrepoJose RestrepoAndreas StavridisAndreas Stavridis

Kaspar WillamKaspar WillamSivaselvan MettupalayamSivaselvan MettupalayamBen BlackardBen Blackard

Sarah BillingtonSarah BillingtonMarios Marios

KyriakidesKyriakides

Rutherford & ChekeneRutherford & Chekene

Joe MaffeiJoe MaffeiBill HolmesBill HolmesBret LizundiaBret Lizundia

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 2525

Professional Advisory PanelProfessional Advisory Panel

Joe Maffei, R&C (Chair)Joe Maffei, R&C (Chair) Dave Brieholz, BQEDave Brieholz, BQE John Kariotis, K&AJohn Kariotis, K&A Ron Mayes, SGHRon Mayes, SGH Paul Murray, PSDGPaul Murray, PSDG Mike Valley, MKAMike Valley, MKA Greg Kingsley, KLAGreg Kingsley, KLA

Ron Hamburger, SGH

July 21-23, 2006July 21-23, 2006 NEES Annual MeetingNEES Annual Meeting 2626

Thank You