Page 1 of 7

Journal for Studies in Management and Planning

Available at

http://edupediapublications.org/journals/index.php/JSMaP/

e-I SSN: 2395 -0463

Vol ume 02 I s s ue 9

September 2016

Available online: http://edupediapublications.org/journals/index.php/JSMaP/ P a g e | 171

Experimental and analytical study on GFRP

reinforced concrete deep beams

1Pamuru Mallemkondaiah, 14FF1D8705, p.malli.114@gmail.com

Mandava Institute of Engineering and Technology,

Vidya Nagar, Krishna District, Jaggayyapet, Andhra Pradesh, 521175

2Mr. D. Aditya Sairam, M-Tech. Associate Professor

Abs tract:

Corrosion of steel in reinforced concrete

structures is one of the biggest challenges faced by

the civil construction industry today. In reinforced

concrete structures, corrosion of steel reinforcement

due to harsh environmental conditions considerably

reduces the durability and life span of these

structures. To overcome this corrosion problem,

many new techniques have been tried and found to

be either expensive or ineffective. Fiber Reinforced

Polymer (FRP) materials in the form of solid bars

has been successfully tried as a substitute for steel

reinforcement in concrete structures.

FRP materials are anti-corrosive, have low

weight to strength ratio and are used for various

modern engineering applications. Considerable

research has been carried out to study the flexural

and shear behaviour of FRP reinforced slender

concrete beams. However, very little effort has been

taken to study the behaviour of Reinforced Concrete

(RC) deep beams reinforced with FRP rebars. This

work is an attempt to study the shear behaviour of

RC deep beams reinforced with Glass Fiber

Reinforced Polymer (GFRP) web reinforcement. A

concrete deep beam reinforced with FRP is

vulnerable to brittle failure under shear load

conditions as, individually, both concrete and FRP

have the tendency for brittle failure under shear

loading conditions.

As the FRP reinforcements which were

needed for this experimental work with required

dimensions were not commercially available, the

GFRP reinforcement bars and stirrups used in this

work were fabricated by a simple method devised by

the researcher called “Manual Fiber-Trusion”. The

main advantage of manufacturing GFRP

reinforcement by this method is that, the

reinforcement can be fabricated to any desired size

and shape with a combination of fiber volume

content of 75% and resin content of 25% without any

filler material being used. This increase in fiber

volume fraction in turn has substantially increas ed

the tensile strength of the GFRP reinforcement.

A deep beam is a structure whose depth is

comparable to its span. The failure in deep beams is

mainly due to shear rather than flexure. In this

experimental work, tests were conducted on thirteen

concrete deep beams with different configurations of

GFRP web reinforcement. The variable parameters

considered are the percentage of web reinforcements

and “shear span to depth” (a/d) ratio. All the other

parameters were kept constant. The thirteen deep

beams were cast with and without GFRP web

reinforcement and were tested in this work. The

testing was done in two stages - in the first stage, i.e.

in Series-I, nine deep beams were tested with a

“shear span to effective depth” ratio of 0.72 and the

results showed a substantial increase in the ultimate

shear load carrying capacity for deep beams

reinforced with GFRP web reinforcement when

compared to those without web reinforcement.

Considering this significant increase, four more deep

beams were cast in the second stage i.e. Series-II and

were tested with a “shear span to effective depth”

ratio of 1.08.

The results obtained from the experiments

conducted demonstrate that the GFRP web

reinforcements were more effective in increasing the

ultimate shear capacity of deep beam especially

when the “shear span to effective depth” (a/d) ratio

had a lower value.

The experimental results were also compared

with analytical “Strut-and-tie” models and the results

were found to be within the acceptable limits. The

Strut-and-Tie method of modelling is widely used in

the design of steel reinforced concrete deep beams.

This method was adopted due to its flexibility in

designing structures which are subjected to a

complex state of stress. The results obtained by STM

modelling in this work were found to be greater

compared to the experimental results. An attempt has

been made to propose a suitable modification in the

ACI 318-08 code so that it could be adopted for

design of GFRP reinforced concrete deep beams with

a small a/d ratio to obtain better results.

Finally, after analysis of the experimental results,

a design equation was formulated to predict the shear

carrying capacity of GFRP web reinforced deep

Page 2 of 7

Journal for Studies in Management and Planning

Available at

http://edupediapublications.org/journals/index.php/JSMaP/

e-I SSN: 2395 -0463

Vol ume 02 I s s ue 9

September 2016

Available online: http://edupediapublications.org/journals/index.php/JSMaP/ P a g e | 172

beams. The results obtained by using this equation

were found to be acceptable and so, this equation

may be adopted for predicting the shear load capacity

of deep beams reinforced with GFRP web

reinforcement and loaded within a small ‘shear span

to depth ‘ratio.

Keywords

Glass Fiber Reinforced Polymer (GFRP), Fiber- reinforced polymers (FRP), web reinforcement.

1. Introduction

Fiber-reinforced polymers (FRP) are composite

materials which are made of fibers embedded in

polymeric resin. The most commonly used synthetic

fibers are made of glass fiber (GFRP), carbon fiber

(CFRP) and Aramid fiber (AFRP). Some of the

commonly used resin matrices that bind the fibers

together to form a FRP composite material are

polyester, vinyl ester, and epoxy groups.

The excellent characteristics and advantageous

properties of FRP materials are good corrosion

resistance, high strength, low weight, non- magnetic

and non-conductivity, high fatigue resistance, ease of

handle at construction site and ease to cut and color

code. These outstanding characteristics of FRP

materials make them an ideal material of choice to be

used as a reinforcing material.

The fiber reinforced composite, which are used

for many engineering applications, are made of high

strength fibers embedded within a suitable matrix

material which is in the form of a resin, which

confines the fibers. The fibers are embedded and

bonded in polymeric resin through which it is

impregnated during its manufacturing process. The

fibers after impregnating in resin are cured to obtain

the end product called ‘Fiber Reinforced Polymer’

(FRP) material.

The fibers which take up the major part of the

FRP composite’s load are kept aligned in a particular

direction to counter the external applied forces. The

orientation of the fibers depends on the type and

position of the applied load for which it is designed.

The resin, functioning as matrix material, apart from

keeping the fibers in the correct position and

orientation, also facilitates the load transfer

mechanism between the external applied load and the

fibers. Added to this, the resin plays an important

role in protecting the fibers when exposed to extreme

environmental conditions.

Currently several types of fibers and resins are

commercially available. The type of fiber and resin

chosen for a particular FRP composite material

depends on factors such as cost, strength required

and their functional application. The most common

type of fibers used in FRP materials are Glass,

Carbon and Aramid fibers. These fibers are available

in different forms such as short chopped fibers,

roving, woven mat forms, etc.

Depending upon the application of the FRP

composites, the type of fiber and resin to be used is

selected. Among all the fibers, Glass fiber is the most

economically available fiber and is widely used in

civil engineering applications. Thus the ‘Glass Fiber

Reinforced Polymer’ (GFRP) has gained more

importance in Civil Engineering applications.

The resin in the form of polymer is mainly

classified under two different groups based on the

cross-link bond formation within the polymer during

polymerization. These polymers are grouped under

‘thermoset’ polymers and ‘thermoplastic’ polymers.

The ‘thermoset’ polymers are relatively stronger in

their performance due to the presence of cross-link

bonds which once formed cannot be broken. On the

other hand ‘thermoplastic’ polymers do not develop

these cross-links and hence they have relatively

lower strength and they can be melted easily by the

application of heat even after polymerization. The

most commonly used ‘thermoset’ polymers are

epoxies, polyesters, polyimides, etc. Among the

many ‘thermoset’ polymers the epoxy polymer has

been proved to perform well.

The ‘thermoplastic’ polymers are usually not

preferred for high strength applications in civil

engineering.

The need for exploiting the shear strength of FRP

deep beams has been felt necessary by earlier

researchers. Some researchers have attempted to

study the shear behavior of short beams whose ‘shear

span to effective depth’ ratio lies between 1.0 to 2.5.

There is no record of any experimental work done on

FRP reinforced deep beams till date. Since no

research study or experimental work was done on

FRP reinforced deep beams with ‘shear span to

effective depth’ ratio less than 1.0, the need was felt

to make an attempt to study FRP reinforced concrete

deep beams.

2. MODELLING OF GFRP BEAMS

Modelling of GFRP reinforced deep beams was

done using “strut and tie” method.

Strut-and-Tie Method : The Strut-and-Tie Method

(STM) is an analytical modelling method has

become a popular technique of designing due to its

flexibility.

The idea of the strut-and-tie method originated

from the truss analogy method. The design basis of

this method is a truss model which idealizes the flow

of force in a cracked concrete beam.

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Journal for Studies in Management and Planning

Available at

http://edupediapublications.org/journals/index.php/JSMaP/

e-I SSN: 2395 -0463

Vol ume 02 I s s ue 9

September 2016

Available online: http://edupediapublications.org/journals/index.php/JSMaP/ P a g e | 173

The Strut-and-Tie model has become one of the

most useful design methods for structures which are

subject to shear critical load conditions. They are

also preferred to be used at disturbed regions in the

concrete structure where the stress variation across

the section is non-linear.

Strut-and-Tie Modelling of steel reinforced

concrete deep beams has been extensively carried out

during the last few decades. This method of design

has been approved and adopted as a design method

in the code of practice in many countries.

Modelling Of GFRP Reinforced Deep Beams Using

STM:

Till date there is no design code available for

modelling FRP reinforced concrete structures using

STM. Hence, in this study, the deep beams

reinforced with GFRP web reinforcement were

modelled using the code ACI-318-05 meant for steel

RC structures. Finally, a comparative study between

the experimental and STM results was done to

evaluate the code’s compatibility with FRP

reinforcement. All the beams tested in this work

were modelled individually as the web

reinforcements differed from one another.

The entire beam is considered to be a disturbed

region or ‘D-region’ which has a shear span to depth

ratio of 0.72. Due to a shorter shear span and a

greater depth of the beams in this study, there were

constraints in modelling them. Since the strut angle

was restricted to be between 25o and 65o as

prescribed by the ACI 318-05 code, the beams were

modelled to have the simplest combination of struts

and ties that can be adopted for a simply supported

beam. Each beam was modelled with a combination

of two struts and two ties. This was advantageous

from the point of view that the simplest combination

of struts and ties was expected to give the best result.

Figure 1: Strut-and-Tie Model

The compressive strength of concrete played an

important role in checking the bearing strength in

each beam.

STM Results and Analys is of Modelled Beams

All the thirteen beams were modelled based on

the test results obtained by experimentation. Each of

the modelled deep beams was subjected to the

ultimate load obtained from experimental results to

study and evaluate its capacity. The forces in the

strut and tie members of the modelled beams were

calculated using the design equation of ACI 318 -05

Code of Practice for design. A typical model

designed for beam GFRDB-1 is shown in Figure 2.

Figure 2: STM Model of Beam GFRDB-1with

internal forces

The Strut-and-Tie method of modelling GFRP

reinforced deep beams which was developed using

the AC1-318 -05 code was found to be higher

compared to the experimental values of the tested

deep beams.

Although the STM results were found to be

greater, the STM method of modelling can be

adopted for GFRP reinforced deep beams by suitable

modification to minimize the gap between the

experimental and modelled results.

Materials and Its Properties:

The concrete used for casting was prepared in the

testing laboratory using a portable concrete mixture

machine. All the specimens which were tested were

cast by using cement concrete and the cement used

was confirming to the specification of IS 8112

(1989) code. The concrete was designed to achieve

the 28 day compressive strength of 40 N/mm2 (M40

Grade). The concrete mix proportion adopted was 1:

1.02: 1.93 with water/cement ratio of 0.38. The

material proportions per cubic meter of concrete:

1) 1059 kgs of coarse aggregate (maximum

size 20mm).

2) 560 kgs of natural river sand (sp.gr =2.53)