STRESS ANALYSIS OF CFRP STRENGTHENED SLABS SUBJECTED TO TEMPERATURE CHANGE

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 8, Issue 1, January 2017, pp.
Available online at http://www.iaeme.com/IJCIET
ISSN Print: 0976-6308 and ISSN Online: 0976
© IAEME Publication Scopus
STRESS ANALYSIS OF C
SLABS SUBJECTED TO T
Assistant Professor,
College of E
ABSTRACT
This paper includes an experimental and analytical investigation of flexural behavior of
reinforced concrete two-way slabs strengthened with CFRP sheets, CFRP bar due to
temperature change. Normal concrete was used to cast the slabs. The experimental work
includes testing of twelve reinforced concrete slab specimens with dimensions
(900mmx900mmx70mm). These slabs can be divided according to temperature change to three
groups at 23 ,45 and 80
according to strengthening to four groups each group contain three specimens, first group was
tested without strengthening acts as reference slabs (control), second group was reinforced
with (CFRP) bar, third group was strengthening with (CFRP) sheet 5cm each 10 cm and the
last group was strengthening with (CFRP) sheet 10cm each 20cm. The use of CFRP sheets
delays the appearance of the cracks by (60%
strengthening. The experimental results showed that the slabs reinforcement with CFRP bar
reduces the ultimate load carrying capacity by (0.61%
concrete slab. Also the experimental results show that the ultimate loads are increased by
about (0.61%-83.03%) for the slabs strengthened with CFRP sheets with respect to the
unstrengthened reinforced concrete slab (control slab). The increase in load carrying capacity
of slab due to temperature change was (36.36%
strengthening at 23 . The optimum a result was in the slabs strengthen by CFRP sheets 5cm
each 10cm at temperature
strengthen slabs . The numerical analyses present three
computer program (ABAQUS 6.13).
Key words: Temperature change, CFRP
Strengthening
Cite this Article: Abdul Ridah Saleh Al
CFRP Strengthened Slabs Subjected to Temperature Change
Engineering and Technology, 8(1), 2017, pp. 676
http://www.iaeme.com/IJCIET/issues.
IJCIET/index.asp 676
International Journal of Civil Engineering and Technology (IJCIET)
, pp. 676–684 Article ID: IJCIET_08_01_079
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=
6308 and ISSN Online: 0976-6316
Scopus Indexed
STRESS ANALYSIS OF CFRP STRENGTHENED
SLABS SUBJECTED TO TEMPERATURE CHANGE
Abdul Ridah Saleh Al-Fatlawi
essor, College of Engineering, University of Babylon
Dhoha Saad Hanoon
e of Engineering, University of Babylon, Iraq
way slabs strengthened with CFRP sheets, CFRP bar due to
al concrete was used to cast the slabs. The experimental work
each one content four specimens. Also slabs can be divided
) bar, third group was strengthening with (CFRP) sheet 5cm each 10 cm and the
delays the appearance of the cracks by (60%-74%) compared with slabs without
The experimental results showed that the slabs reinforcement with CFRP bar
reduces the ultimate load carrying capacity by (0.61%-15.67%) compared with reinforcement
83.03%) for the slabs strengthened with CFRP sheets with respect to the
of slab due to temperature change was (36.36%-51.5%) compared with the same
. The optimum a result was in the slabs strengthen by CFRP sheets 5cm
80 by increasing percentage (83.03%) compared without
strengthen slabs . The numerical analyses present three-dimension nonlinear model by using
computer program (ABAQUS 6.13).
emperature change, CFRP bar, CFRP sheet, Uniformly Distributed Load and
Abdul Ridah Saleh Al-Fatlawi and Dhoha Saad Hanoon
CFRP Strengthened Slabs Subjected to Temperature Change. International Journal of Civil
, 8(1), 2017, pp. 676–684.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=1
editor@iaeme.com
&IType=1
FRP STRENGTHENED
EMPERATURE CHANGE
University of Babylon, Iraq
way slabs strengthened with CFRP sheets, CFRP bar due to
al concrete was used to cast the slabs. The experimental work
each one content four specimens. Also slabs can be divided
) bar, third group was strengthening with (CFRP) sheet 5cm each 10 cm and the
74%) compared with slabs without
The experimental results showed that the slabs reinforcement with CFRP bar
15.67%) compared with reinforcement
83.03%) for the slabs strengthened with CFRP sheets with respect to the
51.5%) compared with the same slabs without
. The optimum a result was in the slabs strengthen by CFRP sheets 5cm
by increasing percentage (83.03%) compared without
near model by using
bar, CFRP sheet, Uniformly Distributed Load and
Fatlawi and Dhoha Saad Hanoon, Stress Analysis of
International Journal of Civil
asp?JType=IJCIET&VType=8&IType=1

Stress Analysis of CFRP Strengthened Slabs Subjected to Temperature Change
http://www.iaeme.com/IJCIET/index.asp 677 editor@iaeme.com
1. INTRODUCTION
The use of FRP to strengthen concrete structures has been a serious problem since the early 1990s.
The implementation of research activities to study the effect of temperature on CFRP reinforced
concrete structures. Aiello, et al. (1999)[1] studied the effects of thermal loads on the structural
performance of FRP reinforced concrete elements. The difference in transverse coefficient of thermal
expansion (CTE) between FRP and concrete causes the presence of tensile stresses within the concrete
and, eventually, the formation of cracks when the temperature increases. They address the evaluation
of temperature variations on concrete elements reinforced with AFRP and GFRP rebar , varying the
thickness of the concrete cover and the shape of the cross-section, in absence of transverse
reinforcement. Results obtained confirm the influence of temperature variations on the state of strain
and stress within FRP reinforced concrete elements and the necessity of a minimum concrete cover to
be provided in order to avoid the formation of through cracks. While Masmoudi, et al. (2005) [2]
presents the results of an experimental investigation to analyze the effect of the ratio of concrete cover
thickness to FRP bar diameter c/db on the strain distributions in concrete and FRP bars, using concrete
cylindrical specimens reinforced with a glass FRP bar and subjected to thermal loading from −30 to
+80°C. The experimental result shows that The minimum and maximum transverse strains for the five
FRP bar diameters tested in this study vary between −1,000 and −2,000 microstrain at −30°C and
between +1,000 and 2,500 microstrain at 80°C, respectively. This observation seems to be
independent of the concrete cover thickness, and as expected, the transverse strain of FRP bars is more
dependent on the temperature value at the interface of FRP bar/ concrete, since the test procedure
guarantees a stabilized temperature.
2. OBJECTIVE OF THIS STUDY
The objectives of the present work are:-
• Investigating experimentally the effect of temperature variation on the flexural capacity of two way RC
slabs.
• Investigating. Experimentally, the behavior of T.W RC slabs with strengthened with (CFRP sheet)
subjected to thermal load and static uniform loading.
• Investigating the effect of the different distribution of strengthening
• Finite element analysis by using ABAQUS program and comparing the results with those obtained
experimentally
3. MATERIAL PROPERTIES
3.1. Cement
Ordinary Portland cement was used in this study (Iraqi cement) This cement satisfies Iraqi
specifications No.5 (1984)[3].
3.2. Fine Aggregate (Sand)
Normal-weight natural sand obtained from Al-Ukhaider region was used as fine aggregate for concrete
mixes in this study. The obtained results indicated that the fine aggregate grading and the sulfate
content were within the limits of Iraqi specifications (No.45/1984)[4].
3.3. Coarse Aggregate (Gravel)
Natural crushed gravel from Al-Badra-wa-Jasan region with maximum size (17mm), was used in this
work. The crushed gravel was washed and cleaned by water for several times until the out washing

water clean then stored in air for surface to dry, and then stored in a saturated dry surface condition
before using.
3.4. Water
Using ordinary clean tap water for casting and curing all the slab specimens as well as for washing the
fine and coarse aggregate.
3.5. Steel Reinforcement
According to (ASTM 996 M-05) (2005) [5], deformed steel bars ( 8 mm ) in diameter were used as
reinforcement to test slab specimens obtained from China production.
3.6. Carbon Fiber Reinforced Polymer (CFRP) and Sikadur-330
The CFRP sheet used in the strengthening application was SikaWarp Hex-230C unidirectional flexible
sheets. The structural adhesive paste used for bonding the SikaWarp Hex-230C sheets to the concrete
substrate was Sikasdure-330 which is high-modulus high-strength two component (A and B) products.
3.7. CFRP Bar
The CFRP bar used in reinforcing of concrete.
4. CONCRETE MIX
In this work use Normal Concrete
4.1. Electrical -Thermal Oven
It is an electric oven consists of a total of heater in different special lengths. And the temperature
would be raising gradually from23 120 . Also there are temperature indicatore that are
showing degree of heat inside the oven. There are also thermal sensors placed inside the holes to
discover the extent of temperature model. Where the holes are placed on special divided aspects and
mid model. As show in Figure (1).
Figure 1 Electrical -Thermal oven
5. SPECIMENS DESCRIPTION
5.1. The Molds Preparation
A total of twelve two-way RC square slabs were cast and cured under laboratory conditions. All slabs
were casting in plywood mold to give two-way slab specimens with dimension (900 X 900) mm and
thickness (70 mm), and aspects of the mold is made of a plate thick (20mm) to insure that the two way
slab had a smooth surface.

5.2. Specimens Design
The specimens were designed to study the effect of temperature change (from23 to 80 ) on the
flexural response of strengthened RC two-way slabs by (CFRP bar , CFRP sheet). All of the test slabs
were of the same dimensions (900 mm * 900 mm * 70 mm), and had the same flexural reinforcement
with (5 ∅8mm in diameter) spaced at 15 cm c/c in x- and y-directions equivalent to reinforcement
ratio of (ρ = 0.00499) and similar arrangement (square mesh).
5.3. Supporting and Loading System
All slab specimens were tested in a universal testing machine, with maximum capacity of (2000 kN).
The slabs were simply supported over four (800mm) lines on all four sides (knife edge) resting on stiff
steel frame and subjected to a uniform load applied to the top face of slabs, Before the testing of all
slabs exposed to temperatures required by placing them inside the oven was manufactured for this
purpose as show in Figure (2).All four support lines were 50 mm from the slab edges, so the effective
span of the slab in both directions was 800mm.
Figure 2 Supporting base and load system
6. SPECIMEN IDENTIFICATION AND STRENGTHENING SCHEMES
The present study deals with twelve RC two way slab specimens were investigated in this research.
They were subjected to both mechanical loading and temperature variation from (23 to 80 ) . the
specimens can be divided into groups according to:
6.1. Temperature change ( )
• Four specimens subjected to
6.2. Strengthening Schemes
• Three slabs without strengthening (control)
• Three slabs reinforced with CFRP bars
• Three slabs externally strengthening with CFRP sheets (5cm each 10cm)
• Three slabs externally strengthening with CFRP sheets (10cm each 20cm).
Specimen shapes and Strengthening Schemes are shown in Figure (3).

Figure 3 Specimen shapes and Strengthening
7. CONCRETE CASTING AND CURING
The internal surfaces of cube, cylinder, prism, T.W molds are well cleaned and oiled to avoid adhesion
with concrete after hardening. Afterwards, the reinforcement is placed in the right position for all slab
molds.
8. THE MECHANICAL PROPERTIES OF HARDENED CONCRETE TESTS
In the hardened phase, only destructive test is done. Destructive testing are compressive strength (cube
& cylinder), splitting tensile strength, modulus of rupture, and stress-strain relationship (static
modulus of elasticity) .All the hardened properties of concrete for all specimens at 28 days are listed in
Table (1)
Table 1 Hardened Properties for Specimens
Group
Specimen
symbol cuf (Mpa)
'
cf (Mpa) ctf (Mpa) (Ec) (Mpa)*
1
S1 28.95 21.6 1.59 21983.1
S1c 24.27 20.01 2.54 21158.5
S1s-5cm 30.14 23.92 1.68 23133.5
S1s-10cm 32.39 24.16 1.37 23249.3
2
S2 27.48 20.67 2.2 21504.6
S2c 25.14 19.45 2.1 20860.3
S2s-5cm 24.56 19.3 2.2 20779.7
S2s-10cm 26.5 20.94 2.01 21644.6
3
S3 22.83 18.09 1.76 20117.8
S3c 25.59 20.5 1.42 21415.0
S3s-5cm 25.26 20.02 2.07 21163.8
S3s-10cm 27.21 21.68 2.45 220237

9. EXPERIMENTAL RESULT OF SLAB MODELS
9.1. General Behavior
All specimens were designed with a flexural reinforcement ratio of (0.499%) with a clear cover to the
reinforcement of 15mm, which is higher than the minimum reinforcement ratio required (0.0018) by
ACI building code.
9.2. First Cracking Loads
The first cracking loads (Wcr) which were obtained from. Generally, the visible first crack load of all
the specimens varied from (18%) to (43.85 %) of the experimental average ultimate loads.
9.3. Ultimate Load and Failure Modes
Table (2) provides a comparison for slabs with effect of temperature variation , effects of the
strengthening by using CFRP sheets on increasing the ultimate loads and failure modes with respect to
unstrengthened slab (control slab). The comparison is based on the ratio of the measured ultimate load
for each slab with respect to the ultimate measured load of the control slab.
Table 2 Ultimate load capacity in groups
Specimen Ultimate load
(kN/m2)
Increase in ultimate load (%)
S1 165 ------
S1c 150 -9.1
S1s-5cm 205 24.24
S1s-10cm 164 -0.6
S2 225 ------
S2c 164 -27.1
S2s-5cm 206 -8.4
S2s-10cm 164 -27.1
S3 250 ------
S3c 191 -15.1
S3s-5cm 302 20.8
S3s-10cm 260 4
9.4. Cracking Patterns
The cracking behavior of each group slab specimen was discussed in the following:
Group 1: Contains four specimens subjected to temperature (23 )

Group 2: Contains four specimens subjected to temperature(45 )
Group 3: Contains four specimens subjected to temperature(80 )

10. FINITE ELEMENT METHOD RESULTS
10.1. Ultimate Load and Ultimate Deflection
A comparison between the theoretical and experimental values of the first crack load, ultimate load
and ultimate deflection for all slabs models as shown in Table (3). The table shows a good agreement
between the theoretical and the experimental results.
Table 3 Experimental and theoretical, ultimate load and max. deflection.
Slab
Symbol
Temp.
Ultimate Load
(kN/m2) F.E./EXP.
(%)
Max.
Deflection
(mm)
F.E./EXP.
(%)
Exp. F.E Exp. F.E
S1
23
165 178.24 108.02 11.366 10.307 90.68
S1C 150 161.38 107.59 14.350 12.084 84.21
S1S-5cm 205 220.08 107.36 9.948 9.611 96.61
S1S-10cm 164 181.11 110.43 3.688 3.440 93.28
S2
45
225 251.94 111.97 20.061 17.215 85.81
S2C 164 179.16 109.24 16.547 13.740 83.04
S2S-5cm 206 230.02 111.66 4.040 3.700 91.58
S2S-10cm 169 193.19 114.31 12.059 12.091 100.26
S3
80
250 271.67 108.67 30.650 25.818 84.23
S3C 191 212.50 111.26 10.04* 6.332* 63.07
S3S-5cm 302 310.64 102.86 6.692** 3.917** 58.53
S3S-10cm 260 270.98 104.22 6.014
***
3.01*** 49.02
*Deflection at load 130 kN/m2
*** Deflection at load 180 kN/m2
***Deflection at load 140 kN/m2
11. CONCLUSION
• The experimental test results confirmed that the strengthening technique of (CFRP sheet) system is
applicable and can increase the ultimate capacity for strengthened of R.C two way slab. In this study,
the ultimate load capacity of the strengthened slabs ranged between about (24.24% for S1S-5cm to
83.03% for S3S-5cm) over the ultimate load capacity of the reference (unstrengthen) slab.
• The use of CFRP bar showed a decrease in stiffness. In this study the slab reinforced with CFRP bar
gave the minimum results in the ultimate load (-9.09% ,-0.61% and 15.76%) for (S1C,S2C,S3C)
respectively compared with the control solid slab S1.
• In this study, use CFRP sheet as strengthening the slabs, same amount of material strengthening but
different distribution. The group strengthening with CFRP sheet 5cm each 10cm is more stiffer than the
group strengthening with CFRP sheet 10cm each 20cm. But these two groups were affected by
temperature change, the ultimate load was increase when the temperature increased, this increasing is
about (24.24% at 23 to 83.03% at 80 ) for slab strengthening by CFRP sheet 5cm each 10cm and (-
0.61% at 23 to 57.58% at 80 ) for slab strengthening by CFRP sheet 10cm each 20cm compared
with the control slab (without strengthening and at 23 )
• The presence of CFRP sheet at the bottom tension zone surface reduced the tensile concrete strains, and
this reduction was reflected to strains in the bottom tension steel bar reinforcement (i.e., reducing the

tension steel bar strains), and this means increasing the tension strength and some tensile stresses would
be carried out by CFRP sheets.
• Using CFRP sheet as external strengthening had a significant effect on crack appearance and pattern of
the reinforced concrete two way slabs by delaying the crack appearance. The increase in cracking load
was about (62.5%) for slabs strengthening compared with the control slab in the same group.
• The three-dimensional finite element model used in the present study was able to simulate the
strengthened reinforced concrete two way slabs with (CFRP bar and CFRP sheet) with variable
temperature. The cracking loads, ultimate deflection and predicted ultimate loads were close to that
measured during the experimental testing with the maximum difference ratio in the ultimate load was
lower than (12%) for all the tested and analyzed slabs.
REFRENCES
[1] Aiello, M., Focacci, F., Huang, P .C., and Nanni, A. (1999), "Cracking of Concrete Cover in FRP
Reinforced Concrete Elements under Thermal Loads," Selected Presentation Proc., 4th
International Symposium on FRP for Reinforcement of Concrete Structures (FRPRCS4),
Baltimore, MD, Nov. 1999, pp. 233-243.
[2] Masmoudi, R., Zaidi, A., and Ge´rard, (2005), Transverse thermal expansion of FRP bars
embedded in Concrete. Journal of Com- posites for Construction, 9(5): pp 377–387.
[3] Iraqi Specification No. 5, , (1984), ”Portland Cement”, Baghdad.
[4] Iraqi Specification No. 45, "Natural Sources for Gravel that is Used in Concrete and Construction",
Baghdad, 1984.
[5] ASTM 996M, (2005), “Rail-Steel and Axle-Steel Deformed Bars for Concrete Reinforcement,”
Annual book of ASTM standards, Vol. 01.04, pp. 5.
[6] Javaid Ahmad and Dr. Javed Ahmad Bhat, Ductility of Timber Beams Strengthened Using CFRP
Plates, International Journal of Civil Engineering and Technology, 4 (5), 2013, pp. 42-54
[7] Dr.Salim T.Yousif , New Model of CFRP-Confined Circular Concrete Columns: An Approach,
International Journal of Civil Engineering and Technology (IJCIET), 4 (3), 2013, pp. 98-110

STRESS ANALYSIS OF CFRP STRENGTHENED SLABS SUBJECTED TO TEMPERATURE CHANGE

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