Behavior of FRP Wrapped Rectangular RC Columns with Shape Modification Mr

Behavior of FRP Wrapped Rectangular RC Columns
with Shape Modification
Mr. Prashant P. Saykar
PG Student, Department of Civil Engineering
Sinhgad College of Engineering,
Pune, India
[email protected]

Abstract: Fiber reinforced polymers are successful
alternative that have numerous advantages over
traditional reinforcement methods giving structures a
longer service life. The glass fiber reinforced polymer
has significantly enhances the strength and ductility of
concrete by forming perfect adhesive bond between
concrete and the wrapping material. The research work
on FRP confined circular column under the axial and
eccentric compression loading has been done in past few
years. In this project, behaviour of concrete columns
confined by the GFRP (Glass Fiber Reinforced
Polymers) jacket was investigated through analytical
method. For this purpose, total 12 rectangular columns
of different cross-section were taken for analysis. In this
dissertation, 12 columns divided in to three groups of
two, two, and eight columns. There are three groups of
column first and second groups were reference columns.
The third group consist of four subgroups depending on
aspect ratio of rectangular shape of column viz. 1:1.25,
1:1.5, 1:1.75, and 1:2. Columns were modified in shape
by using segmental cover. Each subgroup consist of two
columns. The height of all columns were 700 mm.
Comparative study using finite element based software
was carried out with previous available literature.

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Keyword: Ductility; Eccentricity; GFRP Confinement;
High strength; Rectangular columns.

1 Introduction
Most of the previous studies reported so far
investigation the behaviour of concentric load as well as
eccentric load. This paper investigates further in this
direction with addition of shape modification.

Mr. P. B. Kodag
Department of Civil Engg.,
Sinhgad College of Engineering,
Pune, India

Experimental investigation carried out by Rahul
Raval and Urmil Dave 1 on effectiveness of GFRP
wrapped square, rectangular and circular column. In
results they were concluded GFRP shows increment in
load carrying capacity. Square and rectangular section
columns were found to experience lesser increment in
strength as compared to that of circular columns. Riad
benzaid et.al 2 done experimental research on
behaviour of square column confined with GFRP
flexible wrap. The parameters which were considered in
this experiment were number of composite layers and
the corner radius for square shape. They concluded that
columns with GFRP wrap increase load carrying
capacity, more axial load carrying capacity & increase
column ductility.

M.N.S. Hadi et.al 3 explores new technique to
maximize GFRP efficiency. They use GFRP
confinement for square concrete columns,
circularisation using segmental circular concrete covers.
After experimental study researchers concluded that
GFRP confinement reduce ultimate load coming on
column. Steel stripe provide alternative for concrete
confining. M.N.S. Hadi 4 has done another
experimental work on FRP wrapped columns under
eccentric loading. Researcher used three groups one
with reference and another two represent CFRP and
GFRP. Author found that FRP composite can
significantly increase the strength of concrete column.
Both concentrically and eccentrically, the CFRP
wrapped columns resulted in higher loads and ductility
compared to GFRP wrapped and steel reinforced
columns.
M. N. S. Hadi 5 did experimental work using
concrete segmental cover on square columns. He used
two reference columns group one normal square column
and all four corner round column. Other two groups
consist CFRP wrapped and steel strip columns. At end,
author concluded that all confined specimen showed
high load carrying capacity compared with unconfined

specimen. Among all three group CF achieved highest
load carrying capacity followed by group SF.
Problem with CFRP is high cost, CFRP cost almost 6
times greater than GFRP sheets. The studies under taken
in the past concentrated on studying FRP confined
columns subjected to concentrated loads and also most
of the studies have been limited to circular cross-
sections and square columns. In view of this scarcity our
goal is to study the behaviour of GFRP wrapped
rectangular columns having different cross-section
subjected to eccentric loading.

2 GLASS FIBER REINFORCED POLYMER
GFRP (Glass Fiber Reinforced Polymers) material is a
type of composite material that is increasingly used in
the construction industry in recent years. Due to their
light weight, high tensile strength, and corrosion
resistance and easy to implementation makes these
material preferred solutions for strengthening method of
reinforced concrete structural elements, typical form
shown in Fig. 1

Fig 1 Typical form of glass fiber
2.1 Advantages of GFRP
FRP composites are different from steel in that they
possess properties that can vary in different directions
(anisotropic) whereas steel has similar properties in all
directions (isotropic).
GFRP have many other superior properties over
conventional materials like: ultra-high strength,
corrosion resistance, light weight, high fatigue
resistance, nonmagnetic, high impact resistance, and
durability.

2.2 Disadvantages of FRP
Due to the moisture effect matrix softening occur which
leads to hydrolysis cause reduction dominant properties
of composite, such as shear strength, stiffness, and
mechanical properties.
Due to change in temperature mechanical properties of
composite decreases, hence at low temperature
premature brittle failure observed in structural members.
2.3 Applications of FRP
GFRP systems provide a very practical tool for lateral
strengthening and retrofit of concrete structures, and are
appropriate for:
Flexural strengthening
Shear strengthening
Column confinement and ductility improvement

2.4 Type of GFRP

E-glass – Alkali free, highly electrically resistive glass
made with alumina-calcium borosilicates. E-glass is
known in the industry as a general-purpose fiber for its
strength and electrical resistance.

S-glass – High strength glass made with magnesium
aluminosilicates. Used where high strength, high
stiffness, extreme temperature resistance, and corrosive
resistance is needed.

C-glass – Corrosive resistant glass made with calcium
borosilicates. Used in acid corrosive environments.

E glass fiber is the most commonly used fiber in the
fiber reinforced polymer composite industry. In this
work E-glass fiber properties are used. Table 1 shows
properties of E glass fiber.

E-GFRP sheets properties

1 Thickness(mm) 0.43
2 Tensile strength(Mpa) 2060
3 Modulus of elasticity(Gpa) 70-90
4 Density(gms/m3) 900
5 Young’s Modulus of
Elasticity(N/mm2)
75,900
6 Specific gravity 2.56
Table 1 Properties of E-GFRP sheets
3 Numerical Modelling
The computation of loads acting on body and
deformation caused due to that body gives us the
collapse analysis of that body. In current project finite
element model is developed to know the behaviour of
innovative rectangular column under compressive loads
as well as eccentric loads. Eccentric lode applies at 40
mm from the center of column. The results obtained
from finite element model are compared with

experimental tests. The FE model was generated using
modelling software and finite element software.
For these modeling 12 short columns divided in to
three groups of two, two, and eight columns is carried
out. There are three groups of column first and second
groups consist reference columns. The third group
consists of four subgroups depending on aspect ratio of
rectangular shape of column viz. 1:1.25, 1:1.5, 1:1.75,
and 1:2.
3.1 Model Making
For this work various parts of columns created
separately and assemble together in creo software. There
are four model parts generated includes bar, stirrups,
concrete box and GFRP outer cover.
1 Reinforcing bar has 10 mm diameter and 700 mm
long. Material used for bar is steel fe415. Here 415 is
minimum yield strength in N/mm2. Fig 2 shows
reinforcing bar part

Fig 2 Reinforcing part
2 Stirrups used having diameter 6 mm but length of
stirrups vary with aspect ratio and similar steel
properties as bar. Stirrups paced in longitudinal
direction of columns having 200 mm c/c distance. Fig 3
show stirrups

Fig 3 Stirrups
3 Concrete box this is made up with properties of
concrete. M20 grade concrete properties are used.
During modeling inside concrete material remove to
create space for insert bar and stirrups when assemble
together.
Fig

Fig 4 Concrete box
4 Outer GFRP cover is small thickness part having 0.43
mm thickness. Length varies with aspect ratio and this
part use as outside cover to strengthening columns.

Fig 4 GFRP cover

3.2 Columns Assembly
1 Reference columns first group has two rectangular
columns sizes 120 x 150 x 700 mm are generated in
modeling software. There is no additional segmental
concrete of GFRP cover are used. Fig 2 shown
rectangular column.

Fig 5 a) Top view b) Front view of rectangular column
2 In second group two rectangular columns all four
edges are rounded. Columns size 120 x 150 x 700 group
columns. No additional cover provided in these
columns.

Fig 6 a) Top view b) Front view round edge rectangular column
3 In third group having four subgroups size and
segmental cover varies with columns size.
First subgroup consist two columns having aspect ratio
1:1.25. Columns size 120 x 150 x 700 mm with
segmental concrete cover 12 mm at shorter side and 20
mm at larger side are provided. One layer GFRP wrap
having thickness 0.43 mm wrapped around columns
periphery.

Fig 7 a) Top view b) Front view 120 x 150 rectangular column with cover and GFRP
Second subgroup consist two columns having aspect
ratio 1:1.5. Columns size 120 x 180 x 700 mm with
segmental concrete cover 12 mm at shorter side and 20
mm at larger side are provided. One layer GFRP wrap
having thickness 0.43 mm wrapped around columns
periphery.

Fig 8 a) Top view b) Front view 120 x 180 rectangular column with cover and GFRP
Third subgroup consist two columns having aspect ratio
1:1.75. Columns size 120 x 220 x 700 mm with
segmental concrete cover 12 mm at shorter side and 25
mm at larger side are provided. One layer GFRP wrap
having thickness 0.43 mm wrapped around columns
periphery.

Fig 9 a) Top view b) Front view 120 x 210 rectangular column with cover and GFRP
Fourth subgroup consist two columns having aspect
ratio 1:2. Columns size 120 x 240 x 700 mm with
segmental concrete cover 12 mm at shorter side and 25
mm at larger side are provided. One layer GFRP wrap
having thickness 0.43 mm wrapped around columns
periphery.

Fig 10 a) Top view b) Front view 120 x 240 rectangular column with cover and GFRP

4 Experimentation
There are two type loading taken in to consideration,
first one axial loading and another one eccentric
loading. For this work all modeling software file save in
to IGS and stp format then this file import in to finite
element software. After importing geometry each part
has need to specific material properties. Concrete and
steel properties available but there are no GFRP
properties so create new material and all GFRP
properties include in outer cover. Pressure applies at top
surface area of column while bottom surface consider as
fix. Eccentric loading applies 40 mm apart from the
center of column. Use split command and draws line
and applies load on that line to get eccentric loading.
References
1 Rahul Raval and Urmil Dave, “Behavior of GFRP
wrapped RC Columns of different shapes”, Elsevier
Procedia Engineering, 51 (2013), pp-240-249.
2 Riad Benzaid, Nasr?Eddine Chikh ; Habib Mesbah,
“Behavior of square concrete column confined with
GFRP composite warp”, Elsevier Procedia Engineering,
54 (2013), pp-365-376.
3 Lei, X., Pham, T. M. ; Hadi, M. N. S., “Behaviour
of CFRP wrapped square RCcolumns under eccentric
loading”, Structural Engineering Conference, pp-1-8,
Australia.
4 Muhammad N.S. Hadi “Comparative study of
eccentrically loaded FRP wrapped columns”, School of
Civil, Mining and Environmental Engineering,
University of Wollongong, NSW 2522, Australia
5 Muhammad N. S. Hadi, M.ASCE1; Thong M.
Pham2; and Xu Lei3″New Method of Strengthening
Reinforced Concrete Square Columns by Circularizing
and Wrapping with Fiber-Reinforced Polymer or Steel
Straps” journal of composites for construction © asce /
march/april 2013 / 229

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