Ohuchi, Hajime

Saito, Hisashi

Tanigchi, Masaki

Tsunokake, Hisao

Osaka City University Repository

Mem. Fac. Eng., Osaka City Univ., Vol. 49, pp. 51-58 (2008)
Shear Strengthening by Ductile Fiber Reinforced Cementitious Composite Jacketing
Hisashi SAITO*, Masaki TANIGUCHI**, Hisao TSUNOKAKE*** and Hajime OHUCHI****
(Received September 30, 2008)
Synopsis
Present study focuses on verifYing shear strengthening effect by DFRCC jacketing around existing members.
In this study, a series of experimental tests have been conducted followed by Finite Element nonlinear analyses. It
is concluded as following; I) Horizontal cracks dominate in the DFRCC jacketed section independently with
existing member with diagonal shear crack in which no particular bond treatment between existing and jacketing
surfaces, 2) FE nonlinear analyses can predict experimental results up to the ultimate, 3) DFRCC shear
strengthening effect can be predicted by the JSCE fonTlula with considering the tensile strength ofDFRCC.
KEYWORDS: Ductile Fiber Reinforced Cementitious Composite, Shear Strengthening Effect, Repair, Retrofit,
Finite Element nonlinear analyses
1. INTRODUCTION
Ductile Fiber Reinforced Cementitious Composite (DFRCC) is a material with significant tensile ductility
due to fiber bridging effect through multiple cracks I). This material has been applied to the practice for not only
repair but energy dissipation material as well. In the material cost it has disadvantage compared with ordinal
reinforced concrete. However, when considering repair and retrofit application, it is potentially competitive to use
that material with appropriate quantity by panel adding or winding on the surface of existing structure. Focusing
on seismic retrofit application, few studies have been found, especially on shear strengthening 2).
In these back grounds, present study focuses on verifying shear strengthening effect by DFRCC jacketing
arow1d existing members. In this study, a series of experimental tests have been conducted followed by Finite
Element (FE) nonlinear analyses; I) selection of DFRCC mix proportion, 2) uni-axial tensile test on composite
action between reinforced concrete (RC) and DFRCC panel, and 3) loading tests of DFRCC jacketed member up
to shear failure, and 4) FE nonlinear analyses for test result prediction and also for additional numerical
experiment.
*
**
***
****
Graduate Student, Department of Civil Engineering
Obayashi Coporation, Japan
Research Associate, Department of Civil Engineering
Professor, Department of Civi I Engineering
-51-
2. UNI-AXlAL TENSILE TEST OF DFRCC
2.1 Test Procedure
Uni-axial tensile test is calTied out for three types of mix proportions focused on selection of DFRCC mix
proportions. Test parameters are three types of mix proportions as listed in Tab.I. Uni-axial tensile test is
carried out with these mix proportions. These mix prop0l1ions are evaluated from tensile toughness aspect. The
utilized chopped fiber is PYA (Pry Vinyl Alcohol) with O.04mm of diameter, l2mm of length, l.6MPa of tensile
strength and 40GPa of elastic modulus. Test specimen dimension is dumbbell model as shown in Fig.l, i.e.
1OOx lOOmm of edge section, R350 cw-ve section and 60x lOOmm of center section. Measurements are load and
four displacement gauges.
2.2 Test Result
Fig.2 represents stress strain relationship obtained in uni-axial tensile test, where stress is defined as load
divided by cross section area and strain is as averaged displacement divided by measured length. Tensile
touglmess is evaluated by the strain at which descending stress reaches initial crack strength. In these mix
proportions, more tensile toughness obtained is Type-3 of mix proportions, which is used in the following tests.
Tab.l Mix Proportion
W/(C+FA) SIC VI Unit Quantity (kg/m3)
(%) (%) (vol.%) W C FA S PVA VA SP
Type-I 1.5 413 918 0 459 19.5 1.4 I
Type-2 45 50 440 781 195 391 26 0 I
2.0
Type-3 458 815 204 407 26 0.4 10
(NOTE) W/(C+FA): Water by BInder Ratio, SIC: Sand by Cement RatIO, VI: FIber Volume FractIOn
W: Water, C: Cement , FA: Fly Ash, S: Fine Aggregate, PVA: Pry Vinyl Alcohol Fiber
VA: Viscorsity Imprement, SP: Superplasticizer
100
1 D
Fig.l Test Specimen of Un i-axial Tensile Test
t
20 6020
~n35i
Curve Section: RJ~OJJ. 115:
~ · ~~l~:::~auge B"'lOO\ 400
115
Urn! mm 35:
J
I
1
I
!
4r-~~~~r==========;--,
.'" \ --Type-I (Two Specimens)
I'L~.·-· - -"" ----- Type-2 (Four Specimens)
3 f{r.", _._i'--~\; ,,---Type-] (Four Specimens) _
~ VY,'" - '"" • .C'i:l ~'I_/">~I""'''-''' ", r .. .......... A-.....·~ \:,,' ',,'" 'P~ I" , ..........:: ...... ,> ... , \ \, " " .........I ~ ..,1 \\" 'I . __.~-.. -'1
"--' ? \\ "'\ . ,......... .
gJ - '\ . " -, I
I!)
...
ci5
1
o I 1.5 2
Strain (%)
Fig.2 Stress Strain Relationship of
Uni-axial Tensile Test
3. UNI-AXIAL TENSILE TEST ON COMPOSITE ACTION
3.1 Test Procedure
Uni-axial tensile test of composite element with RC and DFRCC is carried out focusing on composite
action. In this test, composite action is evaluated from tensile stress of DFRCC and crack distribution. Fig.3 and
-52-
Tab.2 shows dimension of test specImen and sunllilary of composite action respectively. DFRCC panel is
bonded to RC section with epoxy. At the end of specimen, steel plate is placed with welded 10mm diameter
rebar distributed to specimen. Test parameter is type of bond (Overall Bond: type A, Paltial Bond: type B) and
the thickness of DFRCC panel (t=10, 20 and 30mm). Measurements are load, four displacement gauges and
four stain gauges of rebar surface.
Type of Bond Thickness of
Specimen (Bond Area*) DFRCC Panel
t(mm)
A-IO Overall Bond 10
A-20 (type A: - - ) 20
A-30 30
B-IO Partial Bond 10
B-20 (type B: ••••.• ) 20
B-30 30
(*) reffer to Flg.3
Steel Plate
Tab.2 Summary of Composite Action
Rebar(DIO)
Concrete
foRce
Partial Bond (type B)
t
-+- : Load Direction
_ : Strain Gauge (Concrete Surface)
_ : Strain Gauge (Rebar Surface)
_"' : Displacement Gauge
Unit:mm
Overall Bond (type A)
Fig.3 Test Specimen on Composite Action
3.2 Test Result
Fig.4 shows stress strain relationship of DFRCC. Strain is average four displacement gauges. Here, stress
of DFRCC is defined as follows;
(1)
where (JDFRCC= stress of DFRCC (N/mm"), P= measured load (N), Es= elastic modulus of rebar (N/nm12), E:s=
measured strain of rebar, A s= section area of rebar (mm2), ADFRCC = section area of DFRCC panel(mm2). No
significant difference is observed between specimens with toughness in 10nml thickness specimens. In 20nllil
thickness specimens, A-20 specimen exceeds maximum stress more than B-20 specimen. However, no
difference is almost strain in maximum stress. Additionally, B-20 specimen of softening branch after maximwn
stress is more gradual than A-20 specimen. In 30lllin thickness specimens, B-30 specimen exceeds maximwll
stress and strain in maximwn stress more than A-30 specimen. Therefore, in case of partial bond, it is asswned
that tensile toughness ofDFRCC can be brought out more effective in comparison with overall bond.
Fig.S illustrates pattern diagrams of crack distribution in test tennination of type A and B specimens. In
type A specimens, a crack from RC section distributes into DFRCC section without another crack distribution as
shown in Fig.S(a), that means localized crack opening. On the other hands, in type B specimens, some crack
distributions are observed as shown in Fig.S(b).
From the composite element test, in case of DFRCC jacketing to RC, tensile toughness can be demonstrated
more effective if type of bond is partial bond. Additionally, the thickness of DFRCC is demonstrated more than
20nllil.
-53-
(a) Type A Specimens (Overall Bond)
(b) Type B Specimens (Partial Bond)
Fig.S Pattem Diagrams of Crack Distribution
DFRCC
DFRCC
RC
-A-IO ----8-10
- A-20 ---- 8-20
-A-30 ---- 8-30
\/~"~"""
" ......._.../~, .. \ ......
,.......... '\. "
, ,
r-."\I!'.r-, ,'\.'\., ,... ,.- ... - ..............
, "
... ~\, ,-' "'-"'--... ..
" ' ... _-----:
o 0.2 0.4 0.6
Strain COlo)
Fig.4 Stress Strain relationship of DFRCC
4. TEST AND FE-NONLINEAR ANALYSES ON DFRCC JACKETING MEMBER
4.1 Test on DFRCC Jacketing Member
4.1.1 Test Procedure
Fig.6 illustrates test specimens and measurements. Core RC of the specimen is the same all dimension.
Test specimens are made to precede shear failure by using four main rebar of D22(SD295). Jacketing is
reinforced with DFRCC or RC. In the case, no special bond treatment is interface between core RC and
jacketing based on test result in section 3. Additionally, thickness of DFRCC jacketing is 20 and 30mm. For
comparison, specimen of RC jacketing is designed as shear capacity rises more than the specin1en of DFRCC
30mm jacketing. Design shear capacity is calculated by equation (2)1),3);
Veu = Vee + Ves + Vel
Vee = 0.20ifi· V'-10-00-/-d . if;::. bwd
Ves = (A,.Jwy / Ss ) . d / 1.15
Vel = (ftyd / tan fJ,J . 2td / 1.15
(2)
where Vee= core RC contribution of shear capacity, Ves= stirrup contribution of shear capacity, Vcr DFRCC
contribution of shear capacity,j'e= compression strength of concrete(MPa), pw= tensile main rebar ratio, bll'=
web width(mm), d= effective depth(mm), Aw= section area of stirrup (mm\};vy= yield strength of stirmp (MPa),
Ss= spacing of stirrup (mm),ftyr tensile yield strength ofDFRCC (MPa), fJu= crack angle to member axis (this
study:fJu=45 degree), t= thickness ofDFRCC (mm). Tab.3 shows summary of test specimen and design shear
capacity. TabA shows material properties. Measurements are load, six displacement gauges, eight strain gauges
of main rebar, twelve PI displacement gauges (except COO specimen), two strain gauges of concrete and eight
strain gauges (only RC50 specimen). PI displacement gauge sets up 45 degree to member axis. Crack is
observed to every 0.2 times design shear capacity.
-54-
P700
4-D22
SD295
I
-0-e;e-G-
Unit: mm
(c) Core RC
[ffi'!lJ : Strain Gauge (Concrete)
~ : Displacement Gauge
::::::nrn:= : PI Displacement Gauge
P
£
t---
- Uf
.. 0
w
.=
o
~~i
~ 200+2t_J
,~DIO
I
----{)O;Oo-
(a) DFRCC Jacketing
D6
,.170~I~Q_1I0~-:' :
iL 2711 --l...~ 270 --~-lN-~
(b) RC Jacketing
300
rr:m : Strain Gauge (Main Rebar and Stirrup)
Fig.6 Test Specimen and Measurements
Tab.3 Summary of Test Specimen and Design Shear Capacity
Thickness of
Design Shear Capacity
Jacketing CoreRC
Jacketing
Total
Specimen RC DFRCC
I Vee V es Vel Veil
(nun) (kN) (kN) (kN) (kN)
COO - 68.5 - 68.5
DFR20 20 70.3 - 28_3 98.5
DFR30 30 70.6 42.4 113.0
RC50 50 66.3 72.7 - 140.8
Tab.4 Material Properties
Main Rebar Stirrup
Core Concrete
Jacketing
(D22) (D 10) (DFRCC or Concrete)
Specimen
E s fy E s fy E e Ie E e fry Ie
(GPa) (MPa) (GPa) (MPa) (GPa) (MPa) (GPa) (MPa) (MPa)
coo 29.9 33.3 - - -
DFR20 - - 30.7 36.0 15.7 48.8
185 335 3.01
DFR30 30.8 36.5 15.6 49.0
RC50 169 369 30.3 34.4 32.0 - 37.3
(NOTE) E s: Elastic Modulus of main rebar and stirrup,fy: Yield Strength of main
rebar and stirrup, E c: Elastic Modulus of concrete and DFRCC,fo': Tensile
Yield Strength of DFRCC,fc: Compressive Strength of concrete and DFRCC
-55-
4.1.2 Test Result
Fig.7 illustrates crack distribution ofDFR20 and RC50 (crack width represents line thickness). Black and
red line shows the crack of jacketing and core RC respectively. Fig.S represents mean shear sh'ess drift angle
relationship. Specimen COO reaches maximum load after diagonal shear crack occurs, and brittle failure occurs.
Specimen DFR20 is increased the load after diagonal shear crack occurs. Afterward, multiple cracks are
observed DFRCC jacketing, and DFR20 gets to failure by 10% descent from maximum load because of the
crack is localized. Crack distribution of the jacketing is different from core RC. Specimen DFR30 is more
gradual than softening branch of DFR20. On the other hand, DFR30 is similar to DFR20 in ten11S of crack
distribution. In Specimen RC50, maximum load reaches after diagonal shear crack occurs and the stinup of RC
jacketing yield. RC50 occurs brittle failure because of rupturing stirrup ofRC jacketing.
In all specimens, the crack distribution of jacketing is different from that of core RC. Horizontal crack
tends to occur in jacketing. Fig.9 illustrates the mechanism that horizontal crack of jacketing OCClli'S. Core RC
expands to vertical direction due to diagonal shear crack. Additionally, there is no particular bond treatment of
core RC and jacketing, and jacketing act tensile force of vertical direction with core RC expansion. Therefore, it
is assumed that jacketing occur horizontal crack.
-~~==~=~TI-
•• • ••• 0' _ • • • '-\"_~ •••
, I
_: --~-~~-_:~~~-~ ::;~~?
(a) DFR20
- Core RC
- Jacketing
(b) RCSO
Fig.7 Crack Distribution
--coo
--DFR20'
--DFR30.
--RC50
0.0 I 0.02 0.03
Drift Angle (rad)
Fig.S Mean Shear Stress Drift Angle Relationship
Expansion due to
Diagonal Crack
Fig.9 Mechanism on Crack of Jacketing
-56-
4.2 FE-Nonlinear Analyses on DFRCC Jacketing Member
4.2.1 Analytical Procedure
Fig.10 represents analytical model ofDFR20, where concrete and DFRCC are modeled by
quadrilateral elements and main rebar are modeled by truss elements. The joint of y direction benveen core RC
and DFRCC jacketing is rigid at the only upper and lower flange, but that of x direction free. Incremental
vertical displacement is provided as shown in Fig.10. Tri-linear stress strain relationship model is assumed for
DFRCC based on uni-axial tensile test result shown in Fig.n.
4.2.2 Analytical Result
Fig.12 represents crack distribution of DFR20 in maximum load. In the test, the center of DFRCC jacketed
section is occurred. On the other hand, in the analysis, the crack occms to an upper and lower flange. But FE
nonlinear analysis can predict horizontal crack of jacketing. Fig.13 shows shear force displacement relationship.
Though initial stiffness is slightly different from test result, FE nonlinear analysis can predict test result up to
the maximum load.
0 Core Concrete 0 : Laadi ng Plate
I' Lx 0 DFRCC : l\IIain Rebar
Displacement
Fig.10 Analytical Model of DFR20
Strain (%)
Fig.n Stress Strain Relationship of DFRCC
~..------l--Test Result
- Analytical Result
I.
Fig.12 Crack Distribution
Core RC
---Z
CSIOO
v
~
o
u..
2 3 456
Displacement (mm)
Fig.13 Shear Force Displacement Relationship
-57-
4.3 Shear Strengthening Effect by DFRCC Jacketing
Fig.14 shows shear strengthening effect obtained by tests and experimental analyses. Here, the result of
additional numerical experiment is also shown besides test results on DFRCC jacketing member. Additional
numeric experiment assumes 10 and 40mm thickness of DFRCC jacketing. The strengthening component is
calculated by equation (2). In COO and DFR30 specimens, shear capacity by experimental analyses are larger
than the test results by 10%. However, in DFR20 and RC50 specimens, shear capacity by experimental analyses
correspond to the test results. Good agreement is obtained between test and analytical results. As a result,
DFRCC shear strengthening effect can be evaluated by the JSCE formula (dotted line ofFig.14).
200.----,---.,---------,-----,
....
ro
~ 50-
[/)
• Test Result
I:'::. Analytical Result
- - - JSCE Formula
o 20 40 60 80 100
Strengthening Component( Vel or Vse ) (kN)
Fig.14 Shear Strengthening Effect
5. CONCLUDING REMARK
Present study is concluded as followings.
(I) Horizontal cracks dominate in the DFRCC jacketing section independently with existing member with
diagonal shear crack in which no particular bond treatment between existing and jacketing surfaces.
(2) FE nonlinear analyses can predict experimental results up to maximum load.
(3) DFRCC shear strengthening effect can be predicted by the JSCE formula with considering the tensile
strength ofDFRCC.
REFERENCES
1) Japan Society of Civil Engineering: Recommendations for Design and Construction of High Performance
Fiber Reinforced Cement Composite with Multiple Fine Crack, Concrete Library, 2007
2) K.Wakita, K.Kosa, H.Goda and A.Ogawa: Experiment of seismic reinforcement effect for partial use of
High Performance Cement Composite, Proceeding of JCI, Vo1.29, pp.1441-1446, 2007
3) Japan Society of Civil Engineering: Standard Specifications for Concrete Structures, Structural Perfonnance
Verification, 2002
-58-


Shear Strengthening by Ductile Fiber Reinforced Cementitious Composite Jacketig

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Shear Strengthening by Ductile Fiber Reinforced Cementitious Composite Jacketig

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