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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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Introduction
1999
Kocaeli Earthquake
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Introduction
Low quality of concrete ~10 MPa
Plain round bars ~220 MPa
Poor detailing
(no transverse bars)
(insufficient anchorage lengths)
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Specimens
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Measure for prevention of concrete crushing in front of hooks
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
CFRP retrofit of joints
CFRP: 3800 MPa, 240 GPa, 1.55%, 0.176 mm and 330 g/m2
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
CFRP retrofit of joints
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
CFRP retrofit of joints
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)
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Retrofit application
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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.
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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= × + ×
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Theoretical consideration
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)
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Theoretical consideration
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
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-D-2Predicted 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-D-5Predicted 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
)
JWCP-D-(1+1)Predicted shear capacity of the joint
Joint shear capacity corresponding to flexural moment capacity of the beam
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
HPFRCC retrofit of joints
Lower-storycolumn
Upper-storycolumn
all dimensions are in mm
HPFRCC Plate500x500x40 mm
slabside
sidewithout
slab
JH and JWH
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Materials - HPFRCC mix-proportions (kg/m3)
Cement Water Microsilica Silica sand Sand Steel fiber Admixture
925 204 186 557 278 314 33.6
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Retrofit application
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Test results
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
Theoretical consideration
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
Joint shear capacity corresponding to flexural moment capacity of the beam
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
Joint shear capacity corresponding to flexural moment capacity of the beam
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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.
ACES Workshop: Innovative Materials and Techniques in Concrete Construction
October 10-12, Corfu, Greece
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