Ijciet 06 10_002

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 6, Issue 10, Oct 2015, pp. 15-24 Article ID: IJCIET_06_10_002
Available online at
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=10
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
BEHAVIOR OF SHORT CONCRETE
COLUMNS REINFORCED BY CFRP BARS
AND SUBJECTED TO ECCENTRIC LOAD
Prof. Dr. Nameer A. Alwash and Ahmed Hamid Jasim
Civil Engineering, College of Engineering, Babylon University-Iraq
ABSTRACT
This paper focused to study the behavior of short concrete column
reinforced by CFRP bars and subjected to eccentric axial load. It was based
on ten concrete columns with normal concrete. All columns were identical in
size and the nominal dimensions. The model dimensions selected in the present
investigation was a square section of 140*140mm and a total length of
820mm. The length between corbels (middle portion) was 400mm, for
eccentric loaded columns, variable values of eccentricity (e) were studied
herein. Three of columns were cast as control specimens or for the purpose of
comparison, one without reinforcement and two with longitudinal steel
reinforcement, the other specimens were as longitudinal reinforced by CFRP
bars.
The behavior of these columns will be quantified by conducting axial
load–moment (P-M) and load–deflection (P-Δ) response analysis, the latter is
used to study the secondary column effect. Additionally, the failure
mechanisms of these columns will also be identified and quantified.
Ultimately, The experimental results were studied and compared with data
published by a nonlinear three dimensional finite element (F.L.) analyses have
been used to analyze the tested columns, This has been done by using the
available computer program (ABAQUS/Standard 6.13.). The study concludes
that the CFRP bars contribute about 14.51% of column capacity under axial
load. For Column reinforced with CFRP bars gave some decrease in ultimate
load 3.78% under axial load with respect to the column reinforced with steel
bars, while it gave clear increase in ultimate load 38.21% under load
eccentricity e/h values (0.857). It can be concluded that using CFRP
reinforcement has a significant effective on ultimate load capacity of columns
with high eccentricity.
Key words: Short Concrete Column, CFRP Bars, eccentricity.

Cite this Article: Prof. Dr. Nameer A. Alwash and Ahmed Hamid Jasim.
Behavior of Short Concrete Columns Reinforced by CFRP Bars and Subjected
To Eccentric Load. International Journal of Civil Engineering and
Technology, 6(10), 2015, pp. 15-24.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=10
1. INTRODUCTION
Corrosion of the reinforcement is one of the major reasons for deterioration of
reinforced concrete structures with conventional steel. Fiber reinforced polymer
(FRP) composites can be a solution to overcome the corrosion problem of reinforced
concrete structures which is exposed to harsh environmental conditions. The common
types of FRP composites for concrete construction include carbon, glass, and aramid
;CFRP, GFRP, and AFRP respectively. In addition to be corrosion resist, FRP
composites possess light weight, nonmagnetic and strength comparable or greater to
that of steel strength depending on the types (Choo, C.C.2005) (1)
.
2. LITERATURE REVIEW
Paramanantham (1993) (2)
tested seventeen 8 x 8 x 72 in. (200 x 200 x 1800 mm)
concrete beam-columns reinforced with GFRP bars. From the results of experiments
he reported that GFRP bars would be stressed up to 70 percent of its ultimate strength
in pure flexure, and up to 20 to 30 percent in compression.
3. PROGRAM OF THE WORK
The experimental program was intended to focus the behavior of concrete columns
with a square section reinforced with CFRP longitudinal bars and subjected to
eccentric axial load. It was based on ten concrete columns with normal concrete cast
in laboratory of Civil Engineering Department of Babylon University. All columns
were identical in size and the nominal dimensions. The model dimensions selected in
the present investigation was a square section of 140*140mm and a total length of
820mm. The length between corbels (middle portion) was 400mm, see figure (1). For
eccentric loaded columns, variable values of eccentricity e were studied herein. The
test specimen details are summarized in table (1), each column is identified by
symbols where the first two symbols set describe the kind of longitudinal
reinforcement; (CF) refers to carbon fiber reinforced polymers bars, (PC) denotes
plain concrete without reinforcement while (ST) denotes main steel reinforcement.
The third symbol is a number that refers to the value of load eccentricity in mm. The
forth symbol describes the average compressive strength (fc`) according to
experimental compressive strength result of concrete specimens of columns; (A)
refers to fc`=29.5 MPa.

Behavior of Short Concrete Columns Reinforced by CFRP Bars and Subjected To Eccentric
Load
Table 1 Details of the tested columns specimens.
Column
designation
Longitudinal
reinforcement
Longitudinal
reinforcement
ratio ρ %
Eccentricity
e (mm)
e/h
(mm)
CF0A 4 ∅ 6 0.646 0 0
CF1A 4 ∅ 6 0.646 1 0.071
CF2A 4 ∅ 6 0.646 2 0.143
CF4A 4 ∅ 6 0.646 4 0.286
CF6A 4 ∅ 6 0.646 6 0.429
CF8A 4 ∅ 6 0.646 8 0.571
CF12A 4 ∅ 6 0.646 12 0.857
ST0A 8 ∅ 5 0.649 0 0
ST12A 8 ∅ 5 0.649 12 0.857
PC0A - - 0 0
Figure 1 CFRP reinforced column details (All dimensions in mm).
The columns (except PC0A) contained the same transverse reinforcement of
deformed bars with 4.5mm and spaced at 92mm as well as the corbels reinforced well
to prevent premature failure at this portion of the specimens during the tests and to
concentrate the failure in the middle portion.
4. MATERIAL PROPERTIES
Steel Reinforcement: two types of steel reinforcing bars were used in the tested
columns of this study: first, deformed steel bar nominal diameter Ø10mm were used
as corbel reinforcement. Second, deformed steel bars nominal diameter Ø5mm were
used as transverse ties and longitudinal reinforcement. The results of testing steel
reinforcement are summarized in table (2).

Table 2 Specification and test results of steel reinforcing bars
Nominal diameter
(mm)
Measured
diameter (mm)
Yield stress
(MPa)
Ultimate strength
(MPa)
5 4.5 525 720
10 9.5 600 725
CFRP Reinforcement: Aslan 201 series were used in this study, as standard product.
Features of CFRP bars are sand coating and helical wrap surface. The nominal
diameter is 6 mm which was used to reinforce the CFRP RC column specimens in the
longitudinal directions. Table (3) represents the results of tests as which provided
from the manufacturer of the CFR Pbars.
Table 3 Aslan 200 mechanical properties.
Nominal
Diameter
(mm)
Nomina
l Area
(mm2
)
Guaranteed Tensile
Strength (f*fu )
(MPa)
Ultimate
Tensile
Load
(kN)
Tensile
Modulus of
Elasticity(GPa)
Ultimate
Strain
(%)
6 31.67 2241 70.8 124 1.81%
5. THE TEST RIG AND EQUIPMENT
Columns were tested in a vertical position and under compressive eccentric loading
with hinged-hinged end conditions up to failure. The applied load are measured by a
hydraulic machine with capacity of 670 kN, the load was applied with a loading
increment rate of about 10% of estimated ultimate load of column. During the test of
the columns, the main characteristics of their structural behavior were measured at
every stage of loading. The load at first crack as well as the ultimate failure load. The
measurements, which were recorded during the tests, are the following: strain in
concrete and displacements. The linear variable differential transducers (LVDT) with
0.0001mm accuracy were used to measure the lateral deflection at the tension side of
column in mid-height. Figure (2) shows testing column.
Figure 2 shows testing column.

Load
6. RESULT AND DISCUSSIONS
6.1 First Cracking Load and Cracks Pattern
The visible first cracking load (Pcr) and ultimate load(Pu) which are obtained from
experiments are presented in table (4).From this table, one can see the visible first
crack load of all the specimens varied from (9.4%) to (80.1%) ultimate loads. This big
change in the proportions is due to the compressive strength, and eccentricity of load.
The columns with concentric load or small eccentricity were under compression stress
and therefore the cracks need big load to appear. Because the stress is concentrated
near the supports so cracks appear firstly in the supports (corbel area). Whereas the
first cracks appear in the tension face at middle of column or near of it when the
column under high eccentricity of loading due to the concrete tensile stress reaches
the ultimate tensile strength.
The experimental results of columns indicate that the CFRP bars contributed
14.51% of column capacity for CF0A under axial load comparison with column
PC0A. On the other hand, when making a comparison between the columns that
reinforced with steel and CFRP bars show that the column reinforced with CFRP bars
gave some decrease in ultimate load 3.78% under axial load with respect to the
column reinforced with steel bars, while it gave clear increase in ultimate load
38.21% under load eccentricity 12cm that agreed to e/h values (0.857).
Table 4 Test results of the ultimate load and the first crack load and location of first crack.
Column's
Symbol
Ultimate load
Pu (kN)
First crack load
Pcr (kN)
(Pcr/Pu)
%
Location of first crack
load
PC0 503 333 66.2 corbel
ST0 595 204 34.3 corbel
CF0A 576 350 60.8 corbel
CF1A 531.55 425.8 80.1 corbel
CF2A 458 320 69.9 corbel under loading
CF4A 272 60 22.1 mid-height
CF6A 193 50 25.9 15cm above mid-height
CF8A 125 30 24 mid-height
CF12A 74 15 20.3 9cm above mid-height
ST12A 53 5 9.4 mid-height
6.2. Deflection
Lateral displacements measurements at mid-height were taken until the ultimate load.
The recorded loads, lateral displacement at mid-height of Columns CF1A, CF2A,
CF4A, CF6A, CF8A, CF12A and ST12Aare presented in figure (3).

Figure 3 Load - Lateral Displacement at mid-height of the columns.
Based on figure (3), the following observations can be seen for tested columns:
In general the experimental load versus mid-height lateral deflection behavior was
noticed to have three distinguished stages; The first is being an initial straight portion
of the load-deflection curve representing the elastic stage, the second is a nonlinear
portion with distinct change in slope with increasing deflections (elastic-plastic stage),
and the third is also a nonlinear portion but has characteristics in which a slight
increase in load results in a larger deflection (represent the plastic stage).
Lateral deflection at mid-height of column increases whenever load eccentricity
increases.
6.3. Failure Modes of Test Specimens
The manners of failure of all test columns specimens are listed in table (5).Failure
mode of the specimens CF0A, CF1A and CF2A occurred suddenly due to cleavage of
the concrete and simultaneous rupturing some of the longitudinal CFRP bars. Also,
for the specimen CF4A failure occurred suddenly due to spalling of concrete cover. In
addition, the failure of specimen CF6A occurred gradual due to spalling of concrete
cover, all above specimens failure can be classified as compressive failure mode.
Whereas failure manner of the remaining specimens CF8A, CF12A, and ST12A were
gradual expanding in the tension zone and reduction in compression zone even the
remaining outermost concrete crumbles. Therefore CF8A can be classified as
combined failure mode and CF12A and ST12A as concrete tension failure mode.
0
50
100
150
200
250
300
350
400
450
500
550
600
0 2 4 6 8 10
LoadkN
Lateral Displacement mm
CF1A
CF2A
CF4A
CF6A
CF8A
CF12A
ST12A

Load
Table 5 Manners of failure of test columns specimens.
Column's Symbol Failure Mode at Ultimate Failure State
PC0A Cleavage of the concrete Sudden
ST0A
Cleavage of the concrete and simultaneous
buckling of the longitudinal steel
Sudden
CF0A, CF1A, CF2A
Cleavage of the concrete and simultaneous
rupturing of CFRP bar
Sudden
CF4A Progressive concrete crushing Sudden
CF6A Progressive concrete crushing Gradual
CF8A Combined concrete failure Gradual
CF12A, ST12A concrete tension failure Gradual
7. ULTIMATE LOAD-MOMENT OF COLUMNS REINFORCED
BY CFRP BARS
A comparison between the ultimate load-moment of the tested columns and finite
element analysis using the available computer program (ABAQUS /Standard 6.13.)
are shown in table (6) and figure (4).
Table 6 Ultimate load-moment comparison between experimental and finite element of
columns (ρ=0.646%, fc`=29.5MPa)
Column's
Symbol
e
(mm)
Experimental F.E. ABAQUS Percentage
difference%PukN Mu kN.m PukN Mu kN.m
CF0A 0 576 0 596.2 0 -3.51
CF1A 10 531.55 5.3155 481.5 4.815 9.46
CF2A 20 458 9.16 398.4 7.968 13.01
CF4A 40 272 10.88 274.4 10.976 -0.88
CF6A 60 193 11.58 186 11.16 3.63
CF8A 80 125 10 129.6 10.368 -3.68
CF12A 120 74 8.88 72.72 8.7264 1.73
Pure moment as a beam 0 7.249

Figure 4 Ultimate load-moment interaction diagram of experimental and finite element of
columns (ρ=0.646%, fc`=29.5MPa)
The table (6) shows the ultimate load - moment results of experimental and F.E.
ABAQUS of columns that reinforced with CFRP bar, as well as the table displays the
percentage increase or decrease in the ultimate load-moment of finite element analysis
with respect to tested columns. One can see that the maximum percent of difference is
13.01% and minimum percent of difference is -3.68%. These results show an
acceptable agreement between the finite element and experimental results of tested
columns, with underestimated ultimate load from finite element analysis which is
preferable.
8. PARAMETRIC STUDY
The main objective of this section is to investigate the effect of several important
parameters on the behavior of concrete column. These parameters include percent of
CFRP reinforcement of column (ρ) and compressive strength of concrete. Where (ρ =
Acf/ Ag), Ag and Acfare the gross column cross sectional area and area of CFRP
reinforcement, respectively.
8.1. CFRP Reinforcement Ratio ρ
In order to investigate the effect of ρ on the ultimate load-moment behavior of
column, three different CFRP bar ratios namely ρ = 0.6463%, 1.4543% and 2.5857%
respectively were studied and the other properties are the same for the considered
column. Figure (5) shows the effect of ρ on ultimate load-moment of column.
0
50
100
150
200
250
300
350
400
450
500
550
600
650
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
PukN
Mu kN.m
Experimental
F.E.

Load
Figure 5 Effect of (ρ) on ultimate load-moment interaction diagram of column (fc`=29.5
MPa).
As shown in figure (5), increasing the CFRP reinforcement ratio ρ enhances the
behavior of concrete column reinforced by CFRP bar clearly, and this may reaches
(52%) for the considered cases.
8.2 Compressive Strength
In order to investigate the effect of (fc`) on the ultimate load-moment behavior of
column three different fc` (25, 29.5 and 33.465MPa) were adopted. Figure (6) show
the effect of fc` on ultimate load-moment of column.
Figure 6 Effect of fc` on ultimate load-moment interaction diagram of column.
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
PukN
Mu kN.m
F.E. ρ=0.6463%
F.E. ρ=1.4543%
F.E. ρ=2.5857%
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
PukN
Mu kN.m
F.E. fc`=33.465 MPa
F.E. fc`= 29.5 MPa
F.E. fc`= 25 MPa

As shown in figure (6), increasing the concrete compressive strength enhances the
behavior of concrete column reinforced by CFRP bar clearly. However, such
enhanced is not significant in case of high eccentricities.
9. CONCLUSIONS
Based on the results obtained from the experimental work, finite element analysis, the
following conclusions are drawn;
 CFRP bars contribute about 14.51% of column capacity under axial load.
 Column reinforced with CFRP bars gave some decrease in ultimate load 3.78% under
axial load with respect to the column reinforced with steel bars, while it gave clear
increase in ultimate load 38.21% under load eccentricity e/h values (0.857). It can be
concluded that using CFRP reinforcement has a significant effective on ultimate load
capacity of columns with high eccentricity.
 The general behavior of the finite element models which were analyzed by
(ABAQUS/Standard 6.13) shows good or acceptable agreement with the
experimental results. Maximum difference in ultimate load was (13.01%).
 Failure mode of the columns under pure compression condition occurre suddenly due
to cleavage of the concrete and simultaneous rupturing some of the longitudinal
CFRP bars, with increasing in eccentricity of load tension zone will appear and
expand at the expense of compression area and the occurred failure changes from
suddenly due to spalling of concrete cover to gradual due to spalling of concrete
cover, (all these failure can be classified as compressive failure mode), with high
eccentricity gradual expanding in the tension zone and reduction in compression zone
even the remaining outermost concrete crumbles.
REFERENCES
[1] Choo, C. C., "Investigation of Rectangular Concrete Columns Reinforced or
Prestressed with Fiber Reinforced Polymer (FRP) Bars or Tendons " Doctoral
Dissertation, College of Engineering at the University of Kentucky, 2005,1 pp.
[2] Paramanantham, N. S., “Investigation of the Behavior of Concrete Columns
Reinforced with Fiber Reinforced Plastic Re-bars,” MS thesis, Lamar University,
Beaumont, TX, 1993, Cited in 1.
[3] Samir A.Al Mashhadi and Ahmed Hassan Hadi. Strengthening Reinforced
Concrete One Way Slabs by Overlay Technique & Using CFRP. International
Journal of Civil Engineering and Technology, 5(2), 2014, pp. 52 – 70.
[4] Adnan Ibrahim Abdullah, Dr. Muyasser M. Jomaa'h and Dr. Alya'a Abbas Al-
Attar. Flexural Behavior of Fiber Reinforced Concrete I- Beams Strengthened
with (CFRP). International Journal of Civil Engineering and Technology, 5(1),
2014, pp. 47 – 60.
[5] 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.
[6] Yaman S.S. Al-Kamaki, Riadh Al-Mahaidi and Azad A. Mohammed. Behavior
of Concrete Damaged By High Temperature Exposure and Confined with CFRP
Fabrics. International Journal of Civil Engineering and Technology, 5(8), 2014,
pp. 148 - 162.

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