Recently, research works and utilization of fiber reinforced polymer FRP in
retrofitting of concrete have increased tremendously. It was shown that FRP
material is an effective method for strengthening of deficient reinforced concrete
members also it improves their performance. Several researches were conducted
to study the behavior of reinforced concrete beam strengthened by FRP and the
possible mode of failure.
Jinlong (2005) submitted an experimental and analytical
investigation on the behavior of FRP used to strengthening reinforced concrete
beams. He concluded that the externally bonding FRP plates to the tension zone
of reinforced concrete beams has been accepted as an efficient and effective
technique for flexural strengthening (Jinlong, 2005).
Arifovic and Taljsten (2008), investigated the mode
of failure of the reinforced concrete beams strengthened with FRP at the bottom
face subjected to bending, they concluded that the crack failure predicted due
to lower bound load and FRP should be extended along the critical crack region
(Arifovic and Taljsten, 2008).
Rahai et al. (2008), strengthened ten reinforced
concrete beams specimens by external CFRP strips glued at the bottom of beams
using different resins. The performance of these beams is then compared with
the non-damaged beams primarily strengthened to investigate the effectiveness
of CFRP. It was concluded that there is no difference between using CFRP with
epoxy resin and using CFRP with polyester resin in concrete beams (Rahai
et al., 2008).
Feilicetti and Domenico (2008) investigated the use
of epoxy resin in cracked concrete repair. The study conducted by using low-viscosity
slow-setting epoxy-resin injected in cracks initiated in 16 plain concrete beams
and tested in bending. It was shown that the treated specimens cracked in different
place at a higher failure load (Feilicetti and Domenico,
High Strength Concrete (HSC) is supposed to enhance the tensile strength of
concrete which give better performance comparing with the normal concrete. The
experimental researches show that the cracks in HSC members are initiated at
final stages of failure compared with normal concrete (Zain
et al., 2002).
Kang et al. (2010), investigated the effect
of adding fibers to reinforced concrete beam with HSC. The fiber volume ratio
varied from 0 to 5% was investigated by conducting bending tests and found that
the flexural tensile strength increased linearly with increasing the fiber volume
ratio (Kang et al., 2010).
The main objective of the present study is to investigate the effect of using
two method of placing FRP strips and epoxy resin as an alternative rehabilitation
methods used for steel-concrete composite beams having normal compressive strength
reinforced concrete deck and high compressive strength reinforced concrete deck
and their effect on flexural resistance, mid-span deflection and slip at ends
of steel-concrete composite beam.
MATERIALS PREPARATION AND EXPERIMENTAL TESTING METHODS
High performance concrete can be produced simply by using different mixing
proportions as a rational and simple procedure. Moreover, water reducing additives,
such as Flocrete, can be used to increase the concrete strength.
Locally available cement manufactured by Mass factory, in Sulaymania City,
Iraq is used with 20 mm maximum size aggregates from a location called Kanhash,
lies at about 60 km to the south of Mosul City is used. The cement, aggregate
and water used in concrete are tested and prepared before construction of composite
beam samples. Physical and chemical tests are conducted to ensure that the cement
complies with the requirements of Iraqi standards, (Iraqi
Specifications IQS No. 5, 1984) The chemical and physical tests results
of cement are shown in Table 1.
Local river sand is used as a fine aggregate in concrete, after applying a
sieve analysis and it was found to be complying with the British Standards-882
(B.S.882), with clay percentage 1.0% as shown in Table 2.
Local river gravel with maximum aggregate size of 20 mm, according to B.S.882
(BS 882, 1992), having a sieve analysis as shown in Table
2 is used as a coarse aggregate in concrete. Physical properties of coarse
and fine aggregate are shown in Table 3. A normal drinking
(tap water) is used for mixing of concrete.
In order to get the required compressive strength of concrete several mixes
are prepared. The final mix proportions (cement: sand: gravel/water) used with
a slump of (90 mm) for each type of used concrete, as shown in Table
4. A Flocrete, of 1% of cement weight in each mix, is added to the
high strength concrete mixes.
The NNF group denotes the concrete with normal compressive strength, having
an average cube compressive strength fcu = 25.8 MPa, without adding steel fiber
and NFC group denotes the concrete with normal compressive strength, having
average compressive strength fcu = 25.5 MPa, with steel fibers having aspect
ratio of 66 added to concrete. Two more groups were designed as a high compressive
strength concrete, having average compressive strength fcu = 56.8 MPa, for HNF
group cast without adding steel fibers to concrete and having average compressive
strength fcu = 57.1 MPa HFC groups cast with steel fibers added to concrete.
The last two groups represent a high strength concrete as stated by the ACI
- Code, 2011 (ACI, 2011; Aitcin and
In order to investigate the effect of fiber on compressive strength, a total
of nine standard concrete cubes, 150x150x150 mm, divided into three groups with
three fiber percentages 1.0, 1.5 and 2.0% are prepared and tested according
to standard method specified by ASTM specification (ASTM,
|| Physicochemical tests results of ordinary Portland cement
|| Gradation of aggregate
The fibers, shown in Fig. 1a, were placed in a 10 mm sieve
put and added gradually (spread) to concrete while mixing the concrete. The
test results show that, the optimum fiber percentage of 1.5% is chosen to be
The average concrete compressive strength is calculated by testing three standard
concrete cubes, 150x150x150 mm, (for each group) according to the method specified
by ASTM (2003). The results are listed in Table
5 with their standard deviation. The average results converted to standard
cylinder compressive strength (fc), by considering the standard cylinder
compressive strength equivalent to 80% of the standard cube compressive strength.
The composite beams having a total length of 2000 mm is composed of standard
hot rolled steel shape (W6X12), (AISC, 1994) connected
to 150 mm thickness concrete slab with 550 mm width, as shown in Fig.
An average steel yield strength (fy = 355 MPa) and ultimate strength of (fu
= 487 MPa) obtained from uniaxial tensile test of six strips taken from flange
and web of the steel section. The same test is carried out for the 10 mm diameter
reinforcement bars giving a yield strength (fy = 494MPa) and ultimate strength
of (fu. = 664 MPa). The results of steel section, reinforcement and concrete
strength are shown in Table 5. Using, uniaxial tensile test
results, the modulus of elasticity is found to be Es = 198650 MPa and Er = 198550
MPa for steel section and steel reinforcement, respectively. A total of 15 steel
headed stud mechanical shear connectors (12 mm diameter and 70 mm height, spaced
at 125 mm) are used for each sample to connect the steel section to the concrete
deck. An average yield strength and ultimate strengths of the connectors also
obtained from uniaxial tensile test, which show an average yield strength (fy
= 512 MPa) and ultimate strength of (fu. = 685MPa) an average of three samples.
The modulus of elasticity of stud connector, was found to be Est = 202200 MPa.
A total of twelve composite beams are constructed and tested at the civil engineering
laboratory, Mosul University, the samples are divided into four groups, each
of three beams. The headed stud shear connectors are welded to the flange of
each steel beam by qualified welders. The connectors spaced at 125 mm C/C, as
shown in Fig. 1c and d. A minimum reinforcement
area is used as a mesh with 10 mm bar diameter placed at the bottom of concrete
flange in both longitudinal and transverse directions. The concrete flange is
casted in wooden forms shown in Fig. 1c and d.
After concrete casting the concrete surfaces of the beams kept moist with wet
burlap for 3 days, then the wooden forms are removed and the specimens cured
in air-dry conditions. The composite beam specimens are simply supported at
its ends, with a span of 1900 mm between supports. A 500 kN hydraulic jack is
used to apply a two point monotonic load applied at top of concrete flange by
using a distribution beam and two cross shafts, generating the loading setup
shown in Fig. 2. This test setup generates two shear zones
near the ends and pure bending zone at the middle of the simply supported beam.
The gradually applied loads are monitored and recorded using a load cell. The
slip at ends of each beam was recorded at the end of each test and the deflections
at mid-span are recorded using transducer with an accuracy of 0.001 mm.
|| Physical properties of aggregate
|| Groups notations and mixes ratios
||Concrete cube compressive strength for groups NNF, NFC, HNF
and HFC, yield strength of steel section and yield strength of reinforcement
with standard deviations
|| Steel parts, steel fiber, wood form and concrete casting
of beam, (a) Steel fiber, (b) Geometry of composite beam, (c) Section, studs
and reinforcement and (d) Concrete casting
The present study used different compressive strength of concrete with or without
steel fibers added to concrete flange of the composite beam specimens in the
four groups. These specimens were tested to failure (referred to as original
specimens) and then the concrete flange of the same beams treated after failure
and retested using the same setup of the original test (referred to as rehabilitated
Three different methods of concrete deck treatment were used, depending on
the mode of failure observed after the original test. Each treatment method
is referred to depending on materials used and placing method of fiber reinforced
polymer. The treatments were carried out by placing Sikawrap-230C/45 strip having
tensile strength of 4120 MPa, (FRP strips), with 3 mm thickness, in the direction
of beam span (longitudinal direction) glued to concrete using Sikadure-330 Epoxy
with tensile strength of 31.5 MPa at 7-days, at the middle span of beam at top
and bottom of concrete flange with strip width 100 mm and length of 500 mm,
another method was suggested by placing the FRP strips in the direction perpendicular
to beam span (transverse direction) glued to concrete at the middle span of
beam, using three strips each strip with 100 mm width with 100 mm gap between
strips, surrounding the concrete deck along bottom, side and top of concrete
flange from both sides and finally a Sikadure-52 LV Epoxy Resin having tensile
strength of about 55 MPa at 4-days was injected in the cracks formed after testing,
as shown in Fig. 3c-e.
|| Beam test setup (Dimensions in mm), (a) Testing setup (longitudinal
section) and (b) Beam testing
|| Testing matrix and experimental results for the original
Therefore, each group after rehabilitation has three different types of specimens
named as, (Group Name-Type of Treatment), (For example, NNF-LFS (Normal compressive
strength No Fiber-treated by Longitudinal Fiber Strip), NNF-TFS (Normal compressive
strength No Fiber-treated by Transverse Fiber Strip) and NNF-ER (Normal compressive
strength No Fiber-treated by Epoxy Resin), etc.).
EXPERIMENTAL TESTS RESULTS
During testing of each composite beam specimens, the deflection at the mid-span
of the beam started and increased gradually with the increasing of the applied
load. The deflection is recorded at each load step and the slip between the
concrete deck and the steel section is measured for each beam at the end of
The cracks were initiated at the bottom of the concrete flange in most of the
specimens, at the early stage for all normal concrete groups and at more advanced
stages for high strength groups, due to the higher tensile strength of concrete
gained. The cracks are then extended further by increasing the applied load.
The final failure modes of the specimens are the flexural failure in concrete
flange after generating major cracks, as shown in Fig. 3a
and b. These failure modes are gained by positioning the load
to comply with the conclusions stated by Liang et al.
(2005) and Zain et al. (2002).
The deflection at mid span of the original composite beam specimens of the
four groups is recorded throughout loading stages up to failure of each beam.
The results of the original specimens are plotted in terms of load-deflection
curves, as shown in Fig. 4. The results in terms of yield
force, ultimate force, deflection (δ) at ultimate stage and slip at ends
at ultimate stages obtained from the original specimens tests of the four groups
are listed in Table 6.
|| Cracks generated and treatment in concrete deck, (a) Decks
cracks (Side), (b) Decks cracks (Top), (c) Longitudinal FRP strip,
(d) Transverse FRP strip and (e) Epoxy resin injection
|| Load-deflection curves of the original composite beam specimens
for the four groups, (a) Group NNF (original models), (b) Group NFC (original
models), (c) Group HNF (original models) and (d) Group HFC (original models)
|| Testing matrix and experimental results for the rehabilitated
After rehabilitations of the beams and conducting retests, the deflection at
mid span of the rehabilitated specimens of the four groups is also recorded
throughout loading stages up to failure of each beam. The results of the rehabilitated
specimens are plotted in terms of load-deflection curves, as shown in Fig.
5. The results in terms of ultimate force, defleultimate stage and slip
at ends at ultimate stages obtained from thction (δ) at e rehabilitated
specimens tests of the four groups are also listed in Table 7.
It was noticed that the failure of the rehabilitated specimens is due to cracks
initiated away from the treated area, at the end of FRP strips and near the
injected cracks. The percentages of ultimate loads, deflections and slips obtained
from the reloading of each beam after rehabilitation using the three suggested
methods are listed in Table 8.
The results of experimental test obtained from the original bending test for
the four groups listed in Table 6 show that, the maximum average
ultimate resistance of composite beam obtained by using high strength concrete
deck with steel fiber (group HFC), while the average ultimate resistance of
the other groups are shown to be less than the HFC group by about 1.4, 17.8
and 27.1% for groups HNF, NFC and NNF, respectively.
||Load-deflection curves of the rehabilitated composite beam
specimens for the four groups, (a) Group NNF (rehabilitated models), (b)
Group NFC (rehabilitated models), (c) Group HNF (rehabilitated models) and
(d) Group HFC (rehabilitated models)
|| Percentage of ultimate load, deflection and slip with respect
to original test values
These results comply with the conclusions stated by Zain
et al. (2002) which might be due to the higher tensile strength of
concrete gained in HSC group and increasing of interaction due to availability
of steel fibers.
The results show that the minimum average midspan deflection is obtained in
group HFC and the other group gives average midspan deflection more than the
HFC group by about 29.5, 9.3 and 23.1% for groups HNF, NFC and NNF, respectively.
The slips at ends of beam gives a minimum values in group HFC and the other
group gives average slip at ends more than the HFC group by about 18.8, 47.8
and 89.1% for groups HNF, NFC and NNF, respectively. These results agreed with
the conclusion stated by Luo et al. (2012) that
the concrete has the ability to transfer force after cracking (Luo
et al., 2012) and the presence of fiber would enhance these ability.
After treating the damaged composite beams, the beams are reloaded and the
results obtained listed in Table 7 show that the maximum average
ultimate resistance load and lesser average slip at ends is obtained in group
HFC, while a lesser average midspan deflection is obtained in group HNF. These
results comply with the conclusions stated by Jinlong (2005),
whom considered the FRP as one of the best alternatives used in strengthening
concrete structures (Jinlong, 2005).
The results obtained from reloading the four group specimens listed in Table
7 are compared to the original specimen's results listed in Table
6 and the percentages of ultimate loads, midspan deflection and slip at
ends with respect to the original values are listed in Table 8,
for the three different methods of treatment adopted. The values listed in Table
8 show that using longitudinal FRP gives ultimate resistance ranging from
93.8 to 100.5% from the original ultimate resistance of the four groups, as
well as the midspan deflection ranged from 29.5 to 84.9% from the original deflection
and the slip at ends ranged from 69 to 103% from the original slip. These results
might be obtained due to placing the FRP in the direction of moment and along
the cracks region which comply with the finding stated by Arifovic
and Taljsten (2008).
The results also show that using transverse FRP give ultimate resistance ranging
from 84.4 to 95.5% from the original ultimate resistance of the four groups,
as well as the midspan deflection ranged from 34.3 to 78.8% from the original
deflection and the slip at ends ranged from 67 to 91% from the original slip.
These results show that the FRP would be more effective if it placed in the
longitudinal direction which is not considered in the reviewed literature.
The results also show that using Epoxy Resin give ultimate resistance ranged
from 68.5 to 95.1% from the original ultimate resistance of the four groups,
as well as the midspan deflection ranged from 21.8 to 63.7% from the original
deflection and the slip at ends ranged from 90 to 110% from the original slip.
These results comply with those obtained by Feilicetti and
Domenico (2008), whereas new cracks were initiated after retesting of specimens.
These results show that treating composite beam using longitudinal FRP give
high ultimate resistance compared with the original test results.
Using results gained from experiments, the following conclusions are stated:
||The ultimate resistance of the composite beam is increased
by increasing compressive strength and/or adding steel fiber to concrete
deck comparing with the normal concrete without steel fiber of about 1.4
||Using HRC with steel fiber in concrete deck would decrease deflection
at midspan of about 9.3 to 29.5% as well as decrease slip at ends of composite
beams of about 18.8 to 89.1%
||Treating composite beam using longitudinal FRP give ultimate resistance
of about 93.8 to 100.5% compared with the original test results
||Treating composite beam using transverse FRP give ultimate resistance
of about 84.4 to 95.5% compared with the original test results
||Treating composite beam with Epoxy resin give ultimate resistance of about
68.5 to 95.1% compared with the original test results
||Treating composite beam using the three methods gives an ultimate resistance
with less deflection compared with the original samples
||Treating composite beam using the three methods gives an ultimate resistance
with less slip compared with the original samples
However, it is recommended to investigate composite beam with different length
failed in different modes and rehabilitated using FRP. Also, more detailed investigation
can be conducted in the future using finite element method to predict the ultimate
resistance of the composite beam rehabilitated using FRP.
This study is part of series of researches related to composite structures
constructed and tested in Material Laboratory-Civil Engineering Department,
College of Engineering, Mosul University. The authors would like to show their
appreciations to the Civil Engineering laboratory staff their cooperation and
the support of College of Engineering.