OF CURVATURE ON FLEXURAL PERFORMANCE OF GFRP REINFORCED CONCRETE BEAM
Department of Civil Engineering, University
of Moratuwa, Katubedda , Moratuwa, Sri Lanka.
Department of Civil Engineering, University of
Moratuwa, Katubedda , Moratuwa, Sri Lanka.
Abstract: Ageing of infrastructure is one of the biggest challenges Engineers
facing nowadays. A main problem in deteriorating the life of reinforced
concrete structure is corrosion of the reinforcing steel due to this the
industry is moving towards the fibre reinforcement methods. Fibre Reinforced
Polymer (FRP) bar, a non-corrosive material which is a viable substitute for
steel in preventing the corrosion. Carbon Fibre Reinforced Polymer and Glass Fibre
Reinforced Polymer bars are emerged as promising alternative to traditional
steel with excellent result in terms of corrosion resistance. In case of GFRP,
they have high tensile strength and light in weight but they are brittle in
compression and have lower stiffness than steel reinforcement. Although GFRP
technology has been use for several years, some countries do not have adequate
knowledge to use this technology effectively. Many studies are going on using GFRP bars as
alternative material for steel. GFRP bars behave linearly elastic up to failure
and concrete beam reinforced with GFRP bars exhibit a lower post-cracking
bending stiffness comparing with steel and steel reinforcement cannot be used
at all situations because of its high elastic modulus. Although the flexural
performance of concrete beam using GFRP bars has been extensively studied,
there have not been much studies so far addressing the effects of curvature on
flexural performance of concrete beam reinforced with GFRP bars. Therefore the present study addresses on gaining an insight in to
the flexural behaviour performance of GFRP Reinforced curved concrete beam.
Keywords: GFRP; curved beam; flexural performance;
Fibre Reinforced Polymer (GFRP) is a composite material made of polymer
reinforced with fibres. GFRPs are commonly used in harsh environment on
Bridges, outside garages, off shore structures, aerospace, automotive marine
and construction industries. Corrosion of steel is and the oxidation of iron in
moisture condition leads to the spalling of concrete which intern reduce the
strength of the structure. Reducing this corrosion effects GFRP is usable due
to its non-corrosive nature. These
GFRP bars have high tensile strength, low weight to strength ratio, good
fatigue resistance and good non-magnetic properties. Although the use of
GFRP has become a popular reinforcement material in the recent construction which is cheaper than other FRP bars and hence its
transportation cost also getting reduced.
Designing with GFRP
does not required any special kind of knowledge, it is similar as reinforcement
considerable number of studies that have been carried out on flexural
performance of concrete beam using GFRP. An experimental study has been carried
out by G.Naveen kumar to investigate the effect of reinforcement ratio, cracks
patterns, deflection nature and other parameters related to flexural behaviour
of GFRP concrete beam. It was observed that the GFRP reinforced beam undergoes
more deflection for small loads. (G Naveen Kumar
and Karthik Sundaravadivelu, 2017) .There are some
other observation has been made in studies done by S.Yamini roja which
indicated that the crack forming load was found early in GFRP reinforced beam
due to its low modulus of elasticity and mainly they fail in flexural zone due
to cracks. (S. Yamini Roja1,
P. Gandhi2, DM. Pukazhendhi2 and R. Elangovan3, 2014) Further studies
carried out by M.B.Varma, stated that GFRP bars having roving shows more
flexural strength than plain GFRP bars. (M.B.Varma, 2011) Although there have
been many studies conducted on GFRP bars but due to its limitation of
serviceability criteria the usage of GFRP bars limited and nowadays it’s very
important to go for curved structure specially in bridge structures using GFRP.
Nature of GFRP bars
GFRP bars are generally manufactured by
the pultrusion process using thermoset polymeric resins with 75% glass fibre
composition. GFRP fibres are anisotropic and have high tensile strength and
also have linear stress-strain behaviour.()
Figure 1: Tensile properties of steel
and various FRP bars (Pilakoutas.K,
Generally the mechanical properties of
glass fibre reinforced polymer reinforcements are influenced by the
characteristics, orientation and shape of the particular fibre, fibre/matrix
volumetric ratio, on the manufacturing processing of the fibre and the bonding
at the interface between fibres and matrix. The placement of the fibres in place, transferring and distributing stresses through fibres,
bringing a lateral support against buckling under compression and protect fibres from abrasion and surrounding
environment are done by the resin matrix.
When considering the usage of fibre in
civil engineering applications, the durability and the capacity because it is
very important to maintain the structural performance in the severe changing
environmental conditions where they are in use. There are three different
phases of material such as fibre, resin and interface. The durability of FRP
reinforcing rods is related to these phases. As the constructions will be
exposed to various environments which leads to the deteriorations and
degradations. This will lead to the reduction in the long term durability and
Due to non-corrosive nature of GFRP it
is advantageous for civil infrastructures especially in marine and salt
environment. Increasing the GFRP reinforcement ratio is key factor for
enhancing load carrying capacity and controlling deflection (Ashour AF). Due to low elastic
modulus, GFRP concrete beam shows higher deflection and larger crack widths
comparing to the steel reinforced structure. (Toutanji HA).GFRP bars have
relatively low stiffness in comparison with steel, which results in large
deflections. They show a brittle behaviour than the traditional steel
reinforcements. This often makes the limit of deflection and crack width at
service loads the governing criteria in design of members (440).
strength of beam reinforced with GFRP is more than normal RC structure. Two factors
decides the flexural strength of concrete beam reinforced with GFRP.
of fibre (M.B.Varma, 2011)
flexure behaviour of GFRP reinforced beams depends on the low modulus of
elasticity and the rupture strain of the beams. In a balanced reinforced
section, when the compression concrete reaches its maximum, the tensile
reinforcement reaches its ultimate strength.
The ultimate load of 23% for beam prototype reduced and failure of beam
is under flexure by using GFRP as the main reinforcement. When replacing GFRP
as the main and shear reinforcement, it showed 33% reduction in ultimate load
and the beam showed shear failure. The GFRP reinforced beam failures occurs due
to the bond failure between GFRP rods and the concrete and reduced post
cracking stiffness. The shear strength of beam changes in a significant level
due to the effect of using GFRP rods in transverse direction. Even if we
increase the strength of concrete, there won’t be any significant change in the
strength of beam. The change in the ratio of longitudinal reinforcement decides
the mode of failure. (G Naveen Kumar
and Karthik Sundaravadivelu, 2017)
strength is determined by the formula
Pf x L/b d2 (1)
Flexure strength (MPa), Pf is Central point load through two point loading
system( KN),b is Width of beam in mm and d is Depth of beam in mm. (M.B.Varma, 2011)
load-deflection behaviour of the normal strength and high strength concrete GFRP
RC beams under static loading displayed a bi-linear response. GFRP RC beams
designed as over-reinforced with 1.0% and 2.0% reinforcement ratio showed signs
of reserve capacity or “ductility” prior to total failure. (Matthew Goldston, 2016)
direct pull out test between GFRP and concrete shows the failure of GFRP rod
layers. Also it reveals that the increment in diameter of the bar decreases the
strength of the bond. The concrete beams reinforced with the GFRP bars shows
more strain and deflection values. When observing the behaviour of stress
strain graphs for this, the curve is linear before cracks and beam behaves
linearly with the reduced stiffness after cracks. (G Naveen Kumar and Karthik Sundaravadivelu, 2017)
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