日本建築学会大会学術講演梗概集	 （関東）	 2015 年	 9	 月	 23019

Crack Width Evaluation of RC Members Reinforced with Braided AFRP Bars
(Part 1: Pullout and Tensile Bond Test of AFRP Bars)○Toshiyuki KANAKUBO *Regular member
Regular member
Regular member
Slippage
Tensile bond test

RA7S·RA13S(Sand-coated type)Fig.1 Tested reinforcement
Table 1 List of reinforcement
IDDiameter(mm)

Sectional area(mm2)RA7·RA7S
RA13·RA13S

8.10
13.51

51.50
143.28

Elasticmodulus(kN/mm2)
63.7
71.2

Table 2 Mechanical properties of concreteCompressivestrength(N/mm2)
37.2Tensile strength(N/mm2)

Elastic modulus(kN/mm2)

2.67

26.9

Unbond region

AFRP Rod

100LVDT

Teflon sheet

Steel plate80(100,120)
Reaction plate
Loading direction

coupler

Fig.1. Details and loading method of pullout bond test
40 250

250

200

1680
200 200250

250 40LVDT

33 54 33
Pi-gauge

120

Slit

420

420

420

420

Specimen with 120mm x 120mm,reinforced with RA7 and RA7S

Unit: mmFig.2. Details and loading method of tensile bond test

Crack Width Evaluation of RC Members Reinforced with Braided AFRP Bars
(Part 1: Pullout and Tensile Bond Test of AFRP Bars)― 37 ―

RA7·RA13(Normal surface)

Bond region

1. Introduction
AFRP bars as an alternative to the steel reinforcements haveadvantages to no-corrosion, high tensile strength and use inelectromagnetic fields. However, AFRP bars with its low elastic
modulus and bond stiffness may cause a lager crack width ofconcrete and it is difficult to grasp the characteristics of crack
width due to the AFRP bars with a variety of surface textures
such as braided ones.
The purpose of this study is to propose theoretical calculationformulas to predict crack width of RC members reinforced withAFRP bars based on the relationship between reinforcement
strain and slip at the loaded end which deduced by previousstudy1) . Pullout bond test and tensile bond test were conductedat the same time to investigate the adaptability of the proposed
formulas.
2. Experimental Program
2.1Tested reinforcement and concrete
Fig.1. shows the tested reinforcement with two types of surface.
One is normal braided surface and another one is the sandcoated type. Table 2 and Table 3 show the list of reinforcement
and the mechanical properties of concrete respectively. Samebatch of concrete was used for both two tests.
2.2 Outline of pullout bond test
Pullout bond test was conducted for obtaining the bond stress –slip relationship (bond constitutive law) between AFRP bar andconcrete. Specimen details and loading method is shown in Fig.
1. The specimen is a rectangular concrete block with height of100mm. One rod is arranged in the central position of the block.
The bond length is set to 32mm for RA7 and RA7S, or 52mmfor RA13 and RA13S. The main parameters are reinforcement
type and the sectional area of concrete block which varies as
80mm x 80mm, 100mm x 100mm and 120mm x 120mm. Threesame specimens for each parameter were tested. The monotonic
pullout load was applied until the slippage reached to 20 mm or
concrete failed by splitting. The pullout load and the slippage at
the free end were measured.
2.3 Outline of tensile bond test
The purpose of tensile bond test is to obtain measured crack
width to compare with calculated value by the proposed
formulas. Specimen and loading method is shown in Fig.2. 144d bBond stress
Pullout bond test80(100,120)

Crack width
AFRP bars

Shuai HAO **Hitomi OKAZAKI***

Toshiyuki KANAKUBO, Shuai HAO,Hitomi OKAZAKI

Bond stress(N/mm2)

151510105 Concrete section size:
80x80mm
Reinforcement:
RA7051012315

Loaded end slip(mm)5 Concrete section size

12380x80mm
Reinforcement
RA7S02051015

Loaded end slip(mm)20Fig.3. Bond stress – slip relationship of pullout bond test
Table 3 Test results of pullout bond test (RA7·RA13)
SectionMaximumSlip at max.
size
AFRP barbond stressbond stress(mm)(N/mm2)(mm)
RA711.45
5.1880x80
RA13－*－
RA712.28
4.79
100x100
RA13－
－
RA7
13.78
4.83
120x120
RA13－－*Did not appear till concrete splitting
Table 4 Test results of pullout bond test (RA7S·RA13S)
Section
size
(mm)
80x80
100x100
120x120

AFRP bar

Slippingbond stress*(N/mm2)

Slip at slippingbond stress(mm)

RA7S

11.91

0.17

RA13S

10.43

0.17

RA7S

10.85

0.15

RA13S

8.83

0.19

RA7S

10.71

0.21

RA13S

10.67

0.19

*Definition is explained in part 280x80mm
RA780x80mm
RA7SFig.4. Crack pattern of tensile bond test specimen
100100RA13RA13S

Tensile load(kN)

8080Tensile load(kN)

Bond stress(N/mm2)

Pi-gauges were set on the specimen along axial direction tomeasure crack width. Specimens are subjected to tensile load
until it reaches to a particular value in order to ensure the AFRP
bar may not be broken. The main parameters are reinforcement
type and the sectional area of concrete as same as ones in thepullout bond test. To make sure crack appears before AFRP bar
broken, three slits were conducted in two specimens (120mm x120mm, reinforced with RA7and RA7S) before loading as
shown in Fig.2. The section area at slit is as same as 80mm x80mm.
3. Test Results
3.1 Test results of pullout bond test
Fig.3 shows two examples of bond stress – slip relationship ofpullout bond test and each figure includes three same specimens.
Comparing with two figures, it can be found that surface ofAFRP bars determines the characteristic of bond constitutive law.
Sand-coated type shows higher bond stiffness. Bond stressincreased again after the maximum value. It is considered thatthe lugs as the surface shape of braided bars move toward toloaded end, and cause a mechanical occlusion. Table 3 and Table
4 show the test results of pullout bond test. It can be found thatthe sectional size of concrete block and the diameter of bar does
not have large influence to those values.
3.2 Test results of tensile bond test
Two examples of final crack patterns after loading are shown inFig. 4. It is remarkable that the higher bond stiffness leads larger
numbers of cracks. The whole test results indicate that crack
spacing increases as the sectional size becomes larger. Examplesof tensile load versus total deformation curves are shown in Fig.
5. The straight lines from the origin indicate the relationship forbare reinforcement. Tension stiffening effect can be found in all
the specimens. The effect becomes higher with the concrete
sectional size increasing. The curves show several drops oftensile load at which a new crack takes place.
4. Conclusions
A pullout bond test is carried out to obtain the bond constitutive
law. From the test results it can be found that surface of AFRP
bars determines the characteristic of bond constitutive law.
Tensile bond test has also been conducted. It is remarkably thatbond phenomenon between concrete and reinforcement
determines the characteristic of crack patterns.
Acknowledgement
AFRP bars were provided by Fibex Co., Ltd.
References
1) Kanakubo T., Yamato N., Crack Width Prediction Method
for Steel and FRP Reinforcement Based on Bond Theory,
Journal of Advanced Concrete Technology, Vol. 12(2014),
No. 9, pp. 310-3196040200604080x80mm
100x100mm
120x120mm
Bare bar

1020
Total deformation(mm)2030

080x80mm
100x100mm
120x120mm
Bare bar

1020
Total deformation(mm)30Fig.5. Tensile load – total deformation curve* Dept. of Engineering Mechanics and Energy, Univ. of Tsukuba, Assoc. Professor** Dept. of Engineering Mechanics and Energy, Univ. of Tsukuba, Graduate Student*** Dept. of Engineering Mechanics and Energy, Univ. of Tsukuba, Graduate Student― 38 ―