Seismic Evaluation and Retrofit of Beam- Column Joints of

1

FRP Retrofitting FRP Retrofitting -- 11

Seismic Evaluation and Retrofit of BeamSeismic Evaluation and Retrofit of Beam--Column Joints of MidColumn Joints of Mid--American BridgesAmerican Bridges

Part 1: Fiber Reinforced Polymer Retrofit Part 1: Fiber Reinforced Polymer Retrofit

Pedro F. Silva, Ph.D., P.E.Pedro F. Silva, Ph.D., P.E.GendaGenda Chen, Ph.D., P.E.Chen, Ph.D., P.E.

University of MissouriUniversity of Missouri--Rolla (UMR)Rolla (UMR)[email protected]@umr.edu

Geotechnical and Bridge Seismic Design WorkshopGeotechnical and Bridge Seismic Design WorkshopNew Madrid Seismic Zone ExperienceNew Madrid Seismic Zone Experience

October 28October 28--29, 2004, Cape Girardeau, Missouri29, 2004, Cape Girardeau, Missouri


Participants Participants

Pedro F. Silva, Ph.D., P.E.Pedro F. Silva, Ph.D., P.E.GendaGenda Chen, Ph.D., P.E.Chen, Ph.D., P.E.

Nick Nick ErecksonEreckson, M.S. Graduate Student , M.S. Graduate Student

2


Research Objectives

♦ Plastic hinges to form at the ends of the columns

♦ Beams protected against any significant flexural or shear inelastic actions

♦ Beam/column joints retrofitted in order to minimize inelastic rotations in the beam/column joint regions

Develop a Comprehensive Research Program to Establish the Seismic Retrofit of a Beam/Column

Joint According to Modern Seismic Design Principles Using CFRP Systems


Plastic Hinges Can Form Either in the Beams or Joints under Moderate Seismic Events

Current Design Deficiencies

♦ Excessive - Column flexural reinforcement

♦ Inadequate - Column shear reinforcement

♦ Inadequate - Beam shear reinforcement

♦ Inadequate - Beam flexural reinforcement

♦ Inadequate - Joint shear reinforcement

3


Evaluation of Bridge Structures

A-1) Ductile Flexural Response

A-2) Brittle Shear Response

A-3) Confinement of Plastic Hinge

A-4) Buckling of Longitudinal

Reinforcement

A) Column

B-1) Ductile Flexural Response

B-2) Brittle Shear Response

B) Bent Cap

C-1) Brittle Crushing of Diagonal Compression

Strut

C-2) Brittle Joint Shear Failure with

Reinforcement Pullout

C) Bent/Cap Joint

Performance Levels for a Typical Bent Cap/Column-bent Connection



35Steel Continuous871968A-2428


34Steel Continuous113.751971A-2430











(#)(#)(type)(feet)(Year)(#)

No. of Columns/Bent

No. of BentsGirder TypeMain Span

LengthYear BuiltBridge #

4



FAILFAILFAILA-2428

MARGINALFAILFAILA-3478

PASSFAILPASSA-2430

PASSFAILPASSA-2429

PASSPASSFAILA-2427

MARGINALFAILPASSA-2336

MARGINALMARGINALPASSA-2334

MARGINALMARGINALPASSA-2333

MARGINALFAILPASSA-2332

FAILMARGINALPASSA-2024

PASSMARGINALPASSA-1938

PASSMARGINALPASSA-1931

PASSPASSFAILA-1466

(PASS/ FAIL)(PASS/ FAIL)(PASS/ FAIL)(#)

Column ShearJoint Shear FailureFlexural Failure

Column Bent Cap Bridge #


♦ Unit 1 – Incremental retrofit at different performance levels

♦ Unit 2 – Complete retrofit before testing

Test Matrix

Design of Two Test Units for Evaluation of Retrofit of Beam/Column Systems Using

Carbon-FPP Composites

5


Prototype Structure

FRP Retrofitting FRP Retrofitting --1010

Top & Bot.Bars BentAt Ends

Center of Bent Cap

Bolts

5 - D25 (#8) -Top Reinf

610

D13 (#4) Hoops @ 120 o/c (0.40%)

D16 (#5) Stirrups@ 184 o/c

10 – D25 (#8) Bottom Reinf.

14 - D29 (#9)( ρl ≅ 3.5%)

50 Cover

610

880

1710

No Stirrups

152

1 - D16 (#5)(Each Side)

Longitudinal Section

6


740

0.61

D13 (#4) Hoops @ 120 o/c (0.40%)

880

14 - D29 (#9)( ρl ≅ 3.5%)

Beam & Column X-Sections

5 - D25 (#8) Top Reinf.D16 (#5) Stirrups

@ 184 o/c

10 – D25 #8) Bottom Reinf.Arranged in 2 Layers

1 - D16 (#5)(Each Side)


7



Demand Evaluation( )

( )

⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧+

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛

−=

⎪⎪

⎩

⎪⎪

⎨

⎧

−⋅

+⎟⎠⎞⎜

⎝⎛ −

−⋅

=

2P

2hH

HL

M

V

4DLP

2hH

DLLH

2M

M

b

OC

crB

1

b

oC

crB

Hc

h

C

b

A

C

Support Blocks

Column

Critical Section

Critical Section

h

DE F

G

D

lsls

L

H

L1P/2 P/2

Hc

h

C

b

Critical Section

h

G

D

lsls

L

L1

P

V

B

8


Material Properties

54194993Column

46094216BeamSpecimen

#2

36973525Column

53425026BeamSpecimen

#1

(psi)(psi)

Strength atTime of Testing

28 DayStrength

789

808

605

874

Yield Strength(ksi)

Bar#

Concrete Steel Rebar


0.00 1.00 2.00 3.00 4.00

Displacement Ductility

0.00

0.50

1.00

1.50

M /

M'y

Column Shear Capacity Evaluation

Unit ACI 318-02 UCSD

9


0.00 1.00 2.00 3.00 4.00

Curvature Ductility

0.00

0.50

1.00

1.50

2.00

M /

M'y

Beam Shear Capacity Evaluation

Negative Moment

Unit ACI 318-02 UCSD Demand


0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00

Curvature Ductility

0.00

0.50

1.00

1.50

2.00

2.50

3.00

M /

M'y

Positive Moment

Beam Shear Capacity Evaluation

Unit ACI 318-02 UCSD Demand

10


0.00 1.00 2.00 3.00 4.00


0.00

0.10

0.20

0.30

0.40

0.50

'C

Tf

ρ

Joint Principle Stresses Evaluation

Principal Tensile Stresses

0.29

0.42

Unit Joint Shear Failure Joint Shear Cracking


1 Column shear failure at µ∆ < 3 or onset of column cover concrete spalling

2 Onset joint shear failure at µ∆ > 2

Predicted Seismic ResponseUn-strengthened System

11


Column RetrofitSplicedCircular

14 - D29 (#9)( ρl ≅ 3.5%)

0.616 Plies

50mm Clear Gap

9 PliesN

o PliesIn LoadStud

3 Plies6 Plies

50mm Clear Gap

9 PliesN

o PliesIn LoadStud

3 Plies

( )CC

'

ujuj

Cuj fD

fε0.004ε0.10t −

=

Confinement (9 Plies)

Shear (2 Plies)

Retrofit Design Target µ∆=12.0

( )cotθDfπ0.5

VVVφV

tuj

PSCS

o

j

++−=


0.00 4.00 8.00 12.00


0.00

0.50

1.00

1.50

2.00

2.50

3.00

M /

M'y

Column Retrofit Evaluation

Unit Original Unit Retrofit ACI 318-02 UCSD

12


Carbon Fiber Reinforced Polymer (CFRP)

0.0065 in/plyNominal Thickness

24 in.Fabric Width

33,000 ksiTensile Modulus

1.67%Ultimate Rupture Strain

550 ksiUltimate Tensile Strength

Specimen # 1 and 2

Material Properties


Column

Retrofit

13


Joint Retrofit( ) ( )2

V2

HCFRP FFF +=

⎟⎟⎠

⎞⎜⎜⎝

⎛ −=

b

UCH 0.5h

0.5c0.7DTF

⎟⎠⎞

⎜⎝⎛ −

=0.5D

0.5cDTF UBV

ujj

CFRPjj fw

12

Ftn =

Joint Retrofit (3 Plies)

TCCC

FH

FV

TBL

CBL TBR

CBR

hB

Pull


JointRetrofit

14


Unit 2 – Retrofit Specimen

GFRP Anchors Layout CFRP Sheets Layout


Experimental Results

0 5 10 15 20 25 30Number of Cycles (#)

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

Disp

lace

men

tDuc

tility

( mD)

Loading LevelsLocations where dynamic testing was performedLocations where retrofit was added to the structure

(Specimen #1 Only)

V=1

9.43

k

V=38

.85

k

V=58

.28

k

Single Cyclesto First Yield

(LoadControl)

3 Cycles at EachDisplacement Level

Above Yield(Displacement Control)

m1.0

Dy=0.78"

m1.5

D=1.17"

m2.0

D=1.56"

m3.0

D=2.34"

m4.0

D=3.12"

m5.0

D=3.90"

m6.0

D=4.68"

m8.0

D=6.24"

m12.0

D=9.36"

0 5 10 15 20 25 30Number of Cycles (#)

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

Disp

lace

men

tDuc

tility

( mD)

0 5 10 15 20 25 30Number of Cycles (#)

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

Disp

lace

men

tDuc

tility

( mD)


(Specimen #1 Only)

V=1

9.43

k

V=38

.85

k

V=58

.28

k

Si


(Specimen #1 Only)

V=1

9.43

k

V=38

.85

k

V=58

.28

k

Single Cyclesto First Yield

(LoadControl)



m1.0

Dy=0.78"

m1.5

D=1.17"

m2.0

D=1.56"

m3.0

D=2.34"

m4.0

D=3.12"

m5.0

D=3.90"

m6.0

D=4.68"

m8.0

D=6.24"

m12.0ngle Cyclesto First Yield

(LoadControl)



m1.0

Dy=0.78"

m1.5

D=1.17"

m2.0

D=1.56"

m3.0

D=2.34"

m4.0

D=3.12"

m5.0

D=3.90"

m6.0

D=4.68"

m8.0

D=6.24"

m12.0

D=9.36"

15


-600

-400

-200

0

200

400

600

Late

ral l

oad

(kN

)

-102 -51 0 51 102Lateral Displacement (mm)

-12 -8 -4 0 4 8 12Displacement Ductility

Unit 2: Experimental Results

Life Safety MCE Reliable: µ∆= 6FU = 400kN

Occupational MCE Reliable: µ∆= 2FU=530kN

Cycles at Peak ∆max


Unit 2: Experimental Results

16


♦ Column shear capacity was enhanced by applying CFRP sheets in the hoop direction

♦ Strengthening of the joint region wasadequate in preventing joint shear failure

♦ Some level of strength degradation wasobserved in the joint region

♦ Main failure mode was characterized by fracture of the column long. reinforcement

Unit 2 - Conclusions


0.00 1.00 2.00 3.00Structural Natural

Period TN (sec)

0.00

1.00

2.00

3.00

Spec

tral

Acc

eler

atio

n (%

g) Distance From Fault Zone

1.6 km16 km160 km

6500.9116010001.3916.021302.991.60

VE(kN)

SA%g

Distance From NMSZ(km)

h

C

b

A

CColumn

BDE F

G

D

L

H

h

C

b

G

D

L

W

V

h

C

b

A

CColumn

BDE F

G

D

L

H

h

C

b

G

D

L

W

V

Elastic Shear Forces

0.31sec.T10.2mm∆

320kNF710kNW

N

Y

Y

==

==

Natural Period

17


New Madrid Seismic Zone


Life Safety MCE Reliable: µ∆= 6FU = 400kN

Occupational MCE Reliable: µ∆= 2FU=530kN sT25.1

T)1(1R −µ+= ∆

5354851.33Operational4002402.66Life Safety

160

5357521.32Operational4003782.61Life Safety

16

53516231.31Operational400 8322.55Life Safety

1.6

System Capacity

(kips)

Demand(kips)RPerformance

ObjectiveDistance From

NMSZ (km)

Seismic Demand

Response Modification Factor

18


♦ Column shear capacity was enhanced by applying CFRP sheets in the hoop direction

Adequate for any Seismic Level Hazard

♦ Strengthening of the joint region wasadequate in preventing joint shear failure

Life Safety: 16km from the NMSZ faultOperational: 160km from the NMSZ fault

Seismic Evaluation Conclusions

Documents

Seismic Evaluation and Retrofit of Beam- Column Joints of