Seismic Performance Assessment and Retrofit of Non-Ductile RC

Frames with Infill WallsP. Benson ShingIoannis KoutromanosAndreas StavridisMarios KyriakidesSarah BillingtonKaspar Willam

NEES & PEER Quake SummitSan Francisco, October 8-9, 2010

Masonry-Infilled RC Frames

• Complicated structural systems. • Additional complexity introduced for older

construction, where shear failures are expected in concrete columns.

• Mixed performance in past earthquakes.

Collaborative research project to develop understanding of behavior, modeling techniques and retrofit schemes for masonry-infilled frames.

Cyclic Behavior of Infilled Frames

Single-Story, single-bay, non-ductile reinforced concrete frames, infilled with solid brick masonry panel, tested at CU Boulder by Willam et al.

280mm 3380mm 280mm

1870mm

370mm

#2 @ 265mm stirrups8 #5 bars

280mm

280mm

= 156kN

Lateral displacement

W2

= 156kNW2

#2 @ 265mm stirrups8 #5 bars

280mm

280mm

Lateral displacement

280mm3380mm280mm

1870mm

370mm

912mm836mm

610mm

794mm

= 156kNW2

= 156kNW2

Cyclic Behavior of Infilled Frames

Modeling Scheme

• Plane stress smeared cracking continuum elements to describe distributed cracking & crushing.

• Interface elements to describe strongly localized cracks as well as mortar joint cracking-sliding.

Modeling Approach – RC Columns

Triangular smeared crack element

Interface element to model discrete cracks

Cracks are modeled in discrete and smeared fashion.

Stavridis and Shing, 2010

Modeling Approach – Infill Panels

Anticipated cracking pattern mainly runs through the mortar joints, with some brick splitting cracks

Interface (for possible splitting cracks)

Quadrilateral smeared crack elements (each elem. = half brick)

Interface (for bed joints) Interface (for head joints)

Stavridis and Shing, 2010

Smeared Crack Element

Uncracked material: Failure surface combines Von Mises criterion with a tension cutoff criterion.

c

c

2

p pe o c o 2

1p 1p

2ε 2εσ =f + f' f

ε ε

σe

cf'

of

σ2e

ε1p ε2p εp

σe

mf'

of

σ2e

2

p pe o m o 2

1p 1p

2ε 2εσ =f + f' f

ε ε

e 2e p m 2e p 2pp m 2e

mσ σ + r f' σ 1-exp ε ε

r f' σ

-m

1

m1

e 2e p c 2e p 2pp c 2e

mσ = σ + r f' σ 1 exp ε - εr f' - σ

- - -

p cr f'c

c

2

p pe o c o 2

1p 1p

2ε 2εσ =f + f' f

ε ε

σe

cf'

of

σ2e

ε1p ε2p εp

σe

mf'

of

σ2e

2

p pe o m o 2

1p 1p

2ε 2εσ =f + f' f

ε ε

e 2e p m 2e p 2pp m 2e

mσ σ + r f' σ 1-exp ε ε

r f' σ

-m

1

m1

e 2e p c 2e p 2pp c 2e

mσ = σ + r f' σ 1 exp ε - εr f' - σ

- - -

p cr f'

Failure surface of uncracked materialNonlinear isotropic hardening-softening law for effective strength

σ1

σ2

σe

ft

ftσe

Originally formulated by Lotfi and Shing (1992)

Smeared Crack Element

Cracked material: Orthotropic stress-strain law:

ε1ε2

fc

ft

ε

σ

Secant stiffness unloading/reloading

Initial stiffness unloading/reloading

Exponential softening

Parabola

Exponential softening

Interface Element

Local coordinate system

initialfinal

Yield surface (Lotfi and Shing 1994)

σ

ττ2 – μ2(σ – s)2 – 2r(σ – s) = 0

d = del + dpl + dg

Displacement vector:

so

co = μ2so + 2roso2

μο

1

μr1

μ, r, s: strength parameters

ο

14

2

3

n

t

elastic

plastic

geometric

Tensile Stress vs. Normal Crack Opening

Koutromanos and Shing (2010)

Interface Elementσ

dndn1 dn2

σ

dndn1 dn2

σ

dndn1 dn2

σ

dndn1 dn2

σ

dndn1 dn2

σ

dndn1 dn2

σ

dndn1 dn2

σ

dndn1 dn2

Loading-unloading

Reloading

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 20 40 60 80 100 120

Normal Displacement (μm)

Tens

ile S

tres

s (M

Pa) Experiment

Analysis

Joint Dilatation & Compaction

100-psi Normal Compression

Shear

Axial Compression

Interface Element

Test on mortar joint by Mehrabi and Shing (1994)

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-10 -5 0 5 10

Shear Displacement (mm)

Shea

r Str

ess

(MPa

)

experimentanalysis

-3.0-2.5-2.0-1.5-1.0-0.50.00.5

-10 -5 0 5 10

Shear Displacement (mm)

Nor

mal

Dis

plac

emen

t (m

m)

experimentanalysis

Verification – Quasi-static Tests

-2.5-2.0-1.5-1.0-0.50.00.51.01.52.02.5

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

drift ratio (%)

V/W

ExperimentAnalysis

-2.5-2.0-1.5-1.0-0.50.00.51.01.52.02.5

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

drift ratio (%)

V/W

ExperimentAnalysis

Verification – Quasi-static Tests

Shake Table Test 1

EASTWEST

Prototype 3-story Building

R/C frame with solid brick infill panels, representing design practice in California in the 1920s.

Slab with joists

1 2

A

B

C

D

22’

18’ 318’

22’

22’

El Centro NS Record, 1940 Imperial Valley Earthquake

Gilroy 3 000 Record, 1989 Loma Prieta Earthquake

Base Acceleration Time Histories

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0 10 20 30 40

Acc

eler

atio

n (g

)

time (sec)-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0 10 20 30 40A

ccel

erat

ion

(g)

time (sec)

Motion Sequence

Trial Motion

1 Gilroy 40%2 Gilroy 67%3 Gilroy 67b%4 Gilroy 83%5 Gilroy 91%6 Gilroy 100%7 Gilroy 120%8 El Centro 250%

Stavridis et al, 2010

Specimen Damage

Motion Drift Damage

G40 0.01% None

G67 0.10% Slight

G67b 0.12% Slight

G83 0.28% Moderate

G91 0.40% Moderate

G100 0.55% Important

G120 1.06% Severe

E250 -  Collapse

After G67 ( = DE level)

Bottom Story Response

Motion Drift Damage

G40 0.01% None

G67 0.10% Slight

G67b 0.12% Slight

G83 0.28% Moderate

G91 0.40% Moderate

G100 0.55% Important

G120 1.06% Severe

E250 -  Collapse

After G91 ( = MCE level)

Bottom Story Response

Specimen Damage

Motion Drift Damage

G40 0.01% None

G67 0.10% Slight

G67b 0.12% Slight

G83 0.28% Moderate

G91 0.40% Moderate

G100 0.55% Important

G120 1.06% Severe

E250 -  Collapse

After G120

Bottom Story Response

Specimen Damage

Final Test - Collapse

El Centro 250% Motion

Verification – Shake Table Test 1

• Response is examined for a sequence of 5 motions: Gilroy 67% (twice), 83%, 91%, 100%, 120%.

• Initial stiffness-proportional Rayleigh damping:

0.005

0.000

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.0450.050

0.0 0.5 1.0 1.5 2.0

T(s)

ζ

Bottom Story Drift Time HistoriesG67 Motion

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

3 4 5 6

time (sec)

drift

ratio

(%)

ExperimentAnalysis

G67b Motion

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

27 28 29 30

time (sec)

drift

ratio

(%)

ExperimentAnalysis

G83 Motion

-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

51 52 53 54

time (sec)

drift

ratio

(%)

ExperimentAnalysis

G91 Motion

-0.40-0.30

-0.20-0.100.00

0.100.20

0.300.40

75 76 77 78 79

time (sec)

drift

ratio

(%)

ExperimentAnalysis

G100 Motion

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

99 100 101 102

time (sec)

drift

ratio

(%)

ExperimentAnalysis

G120 Motion

-0.80

-0.40

0.00

0.40

0.80

1.20

123 124 125 126

time (sec)

drift

ratio

(%)

ExperimentAnalysis

G120 Motion

Bottom Story Hysteretic PlotsG67 motion G67b motion G83 motion

G91 motion G100 motion G120 motion

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

-0.10 -0.05 0.00 0.05 0.10

drift ratio (%)

norm

aliz

ed s

hear

, V1/W

ExperimentAnalysis

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

-0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20

drift ratio (%)

norm

aliz

ed s

hear

, V1/W

ExperimentAnalysis

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

-0.30 -0.20 -0.10 0.00 0.10 0.20 0.30

drift ratio (%)

norm

aliz

ed s

hear

, V1/W

ExperimentAnalysis

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

-0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 0.40

drift ratio (%)

norm

aliz

ed s

hear

, V1/W

ExperimentAnalysis

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

-0.60 -0.40 -0.20 0.00 0.20 0.40 0.60

drift ratio (%)

norm

aliz

ed s

hear

, V1/W

ExperimentAnalysis

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

-1.20 -0.80 -0.40 0.00 0.40 0.80 1.20

drift ratio (%)

norm

aliz

ed s

hear

V1/W

ExperimentAnalysis

After G91

Cracking Pattern

Experiment Analysis

After G100Experiment Analysis

Cracking Pattern

After G120Experiment Analysis

Cracking Pattern

Panel with ECC retrofit

Shake Table Test 2

Anchors (1’ x 1’ grid)

Unbonded dowels (with grease)

Dowels

Application of ECC Retrofit

Application of ECC Retrofit

ECC Retrofit Behavior1/5 scale specimens tested quasi-statically at Stanford University by Kyriakides and Billington.

No retrofit

Drift (%)

Late

ral L

oad

(kN

)

Unretrofitted Wall

Retrofitted Wall

With ECC Retrofit

crush

Damage at Specimen

Frame/panel separation

Epoxy injections at major cracks

Second Story Strengthening

1 layer of Tyfo BC

1 layer of Tyfo SEH-51A System Oriented Vertically

1 layer of Tyfo SEH-51A System, Oriented Horizontally

12”

12”

GFRP overlay (by Fyfe Co.)

Trial Motion

1 Gilroy 40%2 Gilroy 67%3 Gilroy 83%4 Gilroy 91%5 Gilroy 100%6 Gilroy 120%7 Gilroy 150%8 El Centro 150%9 El Centro 200%

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0 0.2 0.4 0.6 0.8 1.0

SA (g

)

period (sec)

G40G67G83G91G100G120G150

Motion Sequence

DE

MCE

T1 before testing

T1 after testing

Effectiveness of 2nd Story Repair

Before FRP Retrofit After FRP Retrofit

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Drift Ratio (%)

V 2/W

G50G67G83

G91G100

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5

Drift Ratio (%)

V 2/W

G40G67G83G91G100G120G150E150E200

-1.2-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.01.2

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

Drift Ratio (%)

V 1/W

G40G67G83G91G100G120G150E150E200

Bottom Story Response

Motion Drift Damage

G40 0.09% Slight1

G67 0.15% Slight

G83 0.17% Slight

G91 0.19% Slight

G100 0.24% Slight

G120 0.34% Moderate

G150 0.65% Severe

E150 0.52% Severe

E200 0.67% Severe

1Damage due to previous motions

specimen 1 peak

specimen 1 peak

Final Damage

Failure of top ECC/frame shear dowel connection

joint failure

Signs of delamination

Shear/sliding Crack at Bottom Story

Failure of shear dowels

• Infills can significantly increase the lateral strength of a non-ductile frame, thus improving seismic performance.

• Retrofit using ECC overlay increased the resistance of the infilled frame, however it may not always be possible to increase ductility.

• Repair based on epoxy injection/GFRP is fast and efficiently restores the strength of an infill panel.

Conclusions

• The proposed analysis methodology offers satisfactory agreement with recorded data in terms of global response quantities and failure mechanism.

• Further numerical investigation of system performance for different configurations is feasible.

Conclusions

- Research sponsored by NSF (under the Network for Earthquake Engineering Simulation Research Program).

- Professional Advisory Panel: Joe Maffei, John Kariotis, David Breinholtz, Michael Valley, Gregory Kingsley, Ronald Mayes.

- Johnson Western Gunite Company.- Fyfe Co. (Scott Arnold).

Acknowledgements

• Questions?

Thank you