innovative techniques for seismic retrofit of reinforced

ACES Workshop: Innovative Materials and Techniques in Concrete Construction

October 10-12, Corfu, Greece

Innovative Techniques for Seismic Retrofit of Reinforced Concrete Joints

II.. BBedirhanogluedirhanoglu AA.. IIlkilki NN.. KKumbasarumbasarIstanbul Technical UniversityIstanbul Technical University



Contents

IntroductionIntroduction

Retrofit of Joints with CFRP sheetsRetrofit of Joints with CFRP sheets

Retrofit of Joints with prefabricated HPFRCC panelsRetrofit of Joints with prefabricated HPFRCC panels

ConclusionsConclusions



Introduction

1999

Kocaeli Earthquake



Introduction

Low quality of concrete ~10 MPa

Plain round bars ~220 MPa

Poor detailing

(no transverse bars)

(insufficient anchorage lengths)



Introduction

Purpose and scope

To improve the behavior of rc joints against earthquake excitations with applicable and realistic details.

Improvement Joints RetrofitStrength Exterior CFRP sheetsDuctility Low strength concrete Prefabricated HPFRCC panelsEnergy dissipation No hoops

Plain barsFull scale



Specimens



Specimens

4φ16

φ8/150

4φ16

4φ16

φ8/100

4φ16

2φ8

φ8/150/50 8φ16

φ8/100/45 8φ16

a

a

side view section a-a

ofwithoutneslab

top view ofspecimens without-of-plane beamand slab

section c-c

2x4φ16

φ8/100

section b-b

b

cc

Note: Dimensions are in mm, 1mm = 0.0394 in.

location of weldfor specimensJW1 and JW2

beam longitudinalreinforcement bended90-deg hook in the joint

Detail of beam top and bottom bars



Materials - Concrete

Mix-proportion (kg/m3)

Water Cement Sand Stone powder #1 Aggregate Admixture

239 170 698 414 747 1.8

Compression characteristics

0

2

4

6

8

10

0 50 100 150 200

Time (Days)

Com

pres

sive

Stre

ngth

(MP

a)

6.6

8.5 8.3

Ec180days= 13500 MPa



Materials – Reinforcing bars (plain round)

Diameter(mm)

Yield strength (MPa)

Yield strain

Maximum strength (MPa)

Strain corresponding to

maximum strength

Ultimate strength (MPa)

Ultimate elongation

16.05 325 0.0018 457 0.21 320 0.348.55 308 0.0016 411 0.20 265 0.44



Testing setup

roller supportsupport for loadingaxial load to thecolumn

rigid reinforcedconcrete plate

side view

MTS servo-controlledhydraulic actuator

reaction wall

hydraulic jack

load cellrollersupportswivel

back plate

swivelback plate

negativedirection

positivedirection

Column axial load: 0 – 12.5 – 25 – 50 - 62.5% of axial capacity



Testing setup

CDP10 CDP10 CDP10CDP25CDP25 CDP25 CDP25

CDP100 CDP100

1

3 2

CDP25

SDP200positive direction

SDP200positive directionnegative direction negative direction

CDP25CDP25CDP50

CDP25CDP25CDP50

CDP25CDP25CDP50

CDP25CDP25CDP50

CDP10



Behavior of reference specimens

F

crack open through the most ofthe section depthdue to slippage

of the beamlongitudinal bar

Pseudo-ductile behaviorNo strength degradation upto 4% driftStrength is below shear capacity of joint and flexural capacity of beam



Measure for prevention of concrete crushing in front of hooks



Behavior of specimens rehabilitated in terms of prevention of slip

020406080

100

0 0.02 0.04 0.06 0.08 0.1 0.12Drift ratio

Shea

r for

ce (k

N)

JO1JW1JW2

Calculated capacity corresponding to beam flexural failure



CFRP retrofit of joints

CFRP: 3800 MPa, 240 GPa, 1.55%, 0.176 mm and 330 g/m2




upper storycolumn

lower story column

piece-1

piece-2

piece-1piece-2

Step-1

Step-23 plies

3 plies

For specimens;

JC-F-3 and JWC-F-3




upper storycolumn

lower storycolumn

JWCFRP2 5 ply JWCFRP3 2 ply

J2DWCFRP for each face-1 ply

one 2700x200-mm piecefor each ply in each

diagonal direction

For specimens;

JWC-D-2 2 PliesJWC-D-5 5 PliesJWCP-D-(1+1) 1 Ply (for each face)



Retrofit application



Test results

-100

-80

-60

-40

-20

0

20

40

60

80

100

-0.1 -0.075 -0.05 -0.025 0 0.025 0.05 0.075 0.1

Drift ratio

Shea

r for

ce (k

N)

JOJC-F-3JWJWC-F-3JWC F 3 Contribution

of FRP

Contribution of welding and repair mortar

-100

-50

0

50

100

-0.1 -0.075 -0.05 -0.025 0 0.025 0.05 0.075 0.1

Drift ratio

Shea

r for

ce (k

N)

JWC-F-3

JWC-D-5

JWC-D-2



Test results

* FRP strains varied between 0.1% and 0.4% at peak load levels. FRP strains increased with increasing drift ratios and strains on FRP sheets in diagonal directions reached approximately 1.5%.

* It was seen that effective FRP strain can be considered as 0.4% in force based design of FRP retrofitted joints (approximately 25-30% of the ultimate FRP strain for this case)

* However, if displacement based design is carried out, FRP strains exceeding 0.4% can be considered, provided that FRP retrofit design is sufficient to obtain ductile behavior



Test results

* Joint shear strengths of reference specimens were between 0.42 and 0.52 √f'c.

* The failures of retrofitted specimens were basically due to shear failure of joint after FRP sheets were cut because of diagonal tension stresses in the joint core.

•Joint shear strengths of retrofitted specimens were around 0.70 √f'c.

•Anchorage of sheets on the columns were effective and sufficient.



0,τvb

τvc

Diagonal tension limit

σ1cσ1σ2

Loading

2α

−σN, −τv 0,−τv

−σN, τv

τv

σ

σ1

σ1 σ2

σ2

Principal joint stresses

σN

σN

2

1

τv

τv

Joint stresses

V

N

NExternal loads

22

1,2 2 2x y x y

xy

σ σ σ σσ τ

+ −⎛ ⎞= ± +⎜ ⎟⎝ ⎠

''

0.5 10.5

vc cc g

Nff A

τ = −c vcV b dτ= × ×

FRP fe f fF E Aε= × ×

sin 45FRP FRPV F= ×

t c FRPV V V= +

Theoretical consideration

, , ,t drift c drift c FRP drift FRPV k V k V= × + ×




Displacement

Capacity : Contribution of concrete

Demand for achieving flexural capacity of the beam

Capacity : Contribution of concrete and FRP composite

Contribution of FRP composite

Contribution of concrete

Shear Demand or capacity

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.00 0.02 0.04 0.06 0.08 0.10Drift ratio

Shea

r stre

ss c

apac

ity o

f con

cret

e /m

axim

um sh

ear s

tress

cap

acity

of

conc

rete

(Experimentally obtained for specimen JW)




0

100

200

300

400

500

0.00 0.02 0.04 0.06 0.08 0.10Drift ratio

Join

t she

ar fo

rce

(kN

)

JWPredicted shear capacity of the joint

Joint shear capacity corresponding to flexural moment capacity of the beam

0

100

200

300

400

500

0.00 0.02 0.04 0.06 0.08 0.10Drift ratio

Join

t she

ar fo

rce

(kN

)

JWC-F-3Predicted shear capacity of the joint


0

100

200

300

400

500

0.00 0.02 0.04 0.06 0.08 0.10Drift ratio

Join

t she

ar fo

rce

(kN

)

JWC-D-2Predicted shear capacity of the joint


0

100

200

300

400

500

0.00 0.02 0.04 0.06 0.08 0.10Drift ratio

Join

t she

ar fo

rce

(kN

)

JWC-D-5Predicted shear capacity of the joint


0

100

200

300

400

500

0.00 0.02 0.04 0.06 0.08 0.10Drift ratio

Join

t she

ar fo

rce

(kN

)

JWCP-D-(1+1)Predicted shear capacity of the joint




HPFRCC retrofit of joints

No Specimen Explanation Age (days) Retrofitting

1 JO Reference (without weld and repair mortar) 164 -

2 JW Reference (with weld and repair mortar)* 230 -

3 JHRetrofitted with HPFRCC (without weld and repair

mortar)280

40 mm thick precast HPFRCC

panel

4 JWHRetrofitted with weld, repair mortar and HPFRCC (with weld and repair mortar)*

28340 mm thick

precast HPFRCC panel



HPFRCC retrofit of joints

Lower-storycolumn

Upper-storycolumn

all dimensions are in mm

HPFRCC Plate500x500x40 mm

slabside

sidewithout

slab

JH and JWH



Materials - HPFRCC mix-proportions (kg/m3)

Cement Water Microsilica Silica sand Sand Steel fiber Admixture

925 204 186 557 278 314 33.6



Materials – steel fibers

Dramix ZP 30/0.55

Diameter, d (mm) 0.55

Length, l (mm) 30

Aspect ratio (l/d) 55

Density (kg/dm3) 7.85

Tensile strength (MPa) 1100

Cover N/A



Retrofit application



Test results



Test results

Maximum load at the t ip of the beam Drift rat io at fi rs t

Specimens Slab work in tension

-kN

Slab work in compress ion-

kN

Flexural crack at beam

Inclined crack at

joint

Diagonal defo rmation at 4% drift rat io (measured with LVDT in 480 mm

gage length on fro nt face, Fig. 10. a) *

ε lmax** ε l,% 4***

τv****

Limiting drift****

* (%)

Vjh/f`c (Slab in tension)

JO 65.8 53.3 1/1000 0.4/100 0.0064 0.0011 0.0012 1.53 6.3 0.19 JW 87.0 73.0 1/1000 1.0/100 0.0200 0.0017 0.0016 1.97 6.0 0.24 JHP 73.8 55.2 2/1000 2.0/100 -0.0030 0.0015 0.0014 1.70 10 0.21

JWH 85.3 84.0 1/1000 2.0/100 -0.0048 0.0017 0.0018 1.97 8.5 0.24



Test results

-100

-80

-60

-40

-20

0

20

40

60

80

100

-0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1

Drift ratio

Shea

r for

ce (k

N)

JOJHJWJWHJWH

Contribution of HPFRCC

Contribution of welding and repair




0

100

200

300

400

500

0 0.02 0.04 0.06 0.08 0.1Drift ratio

Join

t she

ar fo

rce

(kN

)

JWHPredicted shear capacity of the joint


0

100

200

300

400

500

0 0.02 0.04 0.06 0.08 0.1Drift ratio

Join

t she

ar fo

rce

(kN

)

JWPredicted shear capacity of the joint




Conclusions

Retrofitting the inadequately detailed reinforced concrete joints using FRP sheets or precast HPFRCC panels in an easily applicable manner can significantly increase the strength and drift capacity of joints.



Acknowledgments

Financial supports of;

TUBITAK (Project No: 106M054)ITU BAP (Project No: 31811)ISTONBETONSAYKS-BASFBEKSA

Assistance of;

Orkun IncecikKayhan KolcuCudi AsanAlican NartSüleyman Bedirhanoğluand other apprentices

For his valuable contribution in construction of the specimens master Salih Usta who recently passed away is also acknowledged.

THANK YOU

innovative techniques for seismic retrofit of reinforced

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