Nithyapriya N P
Department of Civil Engineering
College of Engineering Trivandrum
Kerala, India
nithyapriyanp1997@gmail.com
Shalu R F
Department of Civil Engineering
College of Engineering Trivandrum
Kerala, India
shalurf@cet.ac.in
Anandlal R
Department of Civil Engineering
College of Engineering Trivandrum
Kerala, India
anandlal@cet.ac.in
Abstract Now a days fiber-reinforced polymer (FRP)
confinement is one of the most important techniques used for
the strengthening and repairing of concrete structures. In the
case of columns, the square/rectangular columns show less
effectiveness towards FRP confinement compared with circular
columns due to their flat sides and sharp corners. So the
strengthening of square/rectangular columns needs more
attention than circular columns. The performance of
square/rectangular columns can be improved by modifying the
shape of columns before FRP wrapping. The researches show
that varying the corner radius of non-circular columns
improves the confinement area and thereby increase the
confinement efficiency of FRP. Recently, curvilinearization
technique was developed in which slightly curved sides are
provided to existing square/rectangular sections before
application of FRP. Circularisation is also another shape
modification method in which the existing square columns are
modifying into circular sections by using segmental concrete
covers before the FRP wrapping process. This paper mainly
deals with these shape modification techniques in the carbon-
fiber-reinforced polymer (CFRP) confined square columns.
Keywords concrete column; square column; circular
column; fiber reinforced polymer; carbon fiber reinforced
polymer; shape modification; corner radius; corner rounding;
curvilinearization; circularisation; failure modes; compressive
strength; stress-strain responses; hoop strain; confinement
efficiency; size effect; net spacing; core concrete; crumb rubber
concrete; cross-section
I. I
NTRODUCTION
In real conditions, existing concrete columns may require
strengthening because of different reasons such as upgrading
the use of the current structure, modification in design codes,
and correction of errors that happened during construction.
The compressive strength and ductility can be effectively
increased by confining the concrete columns with fiber-
reinforced polymer (FRP) [1-4, 16, 30-34, 68-69, 71-75].
High resistance to corrosion and chemical effects, high
strength-to-weight ratio, etc. are the major advantages of FRP
[5]. There are different types of FRP among them glass,
carbon, aramid, and basalt fiber reinforced polymers are
common. For strengthening applications, carbon-fiber-
reinforced polymer (CFRP) is mostly used because of its high
strength and less weight [6-7]. Considering the concrete
columns, the presence of flat sides and sharp corners make the
square/rectangular columns less effective towards FRP
confinement [8-11]. It is because the stress distribution
becomes non-uniform on the sides and more concentrated at
the edges [8, 12-15]. A method to improve the confinement
efficiency is increasing the jacket thickness, but it is not
economical. Changing the cross-section of the
square/rectangular columns before FRP strengthening can
improve the performance of the columns as compared with the
columns without any shape modification [12-13, 16-23, 60].
The concept of shape modification was introduced by
Seible and Priestely in which a rectangular RC column was
retrofitted with an elliptical shell jacket [70]. Several studies
have been done with shape modification of the non-circular
columns.
II. STRENGTHENING OF CONCRETE COLUMNS BY
FRP
A. General
Commonly used strengthening methods in RC structures
includes the application of an external layer of a metallic plate,
textile-fiber sheet, wire mesh, post-tensioning concrete, or
steel jacketing, and injection of epoxy [24-27]. FRPs are used
for strengthening RC members results in better performance
as compared with other techniques and that have commonly
been practiced recently [1-4, 28-29].
B. Fiber-reinforced polymer (FRP)
FRP is a composite material made up of a polymer matrix
reinforced with fibers such as glass, carbon, aramid, or basalt
[28-29]. The performance of confined columns is also
depending on the type of FRP, the number of layers, etc. [35-
37]. Due to less weight, and high strength and resistance to
fatigue and creep failure, CFRP is used mostly for the
strengthening applications of structures [38-41]. Fig. 1 shows
the schematic diagram of an FRP composite material.
C. Types of Strengthening Techniques in Concrete Columns
by FRP
External bonding of FRP laminates and near-surface
mounting (NSM) of FRP bars/strips can strengthen the
concrete columns[42-48]. Among these two, external
wrapping is commonly used. External FRP wrapping can be
done by different methods such as wrapping of fabric,
Fig. 1. Typical composite geometry of FRP [41]
22
Government College of Engineering Kannur (GCEK)
Electronic copy available at: https://ssrn.com/abstract=3780531
22
Government College of Engineering Kannur (GCEK)
Electronic copy available at: https://ssrn.com/abstract=3780531