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CHAPTER 2

LITERATURE REVIEW

2.1 HISTORICAL BACKGROUND OF COMPOSITE

CONSTRUCTION

Before modern Engineering and the ability to manipulate

concrete and steel, the world of architecture consisted of wood, adobe,

thatch and cave dwellings. The oldest known surviving concrete was

found in the former Yugoslavia and was thought to have been laid in

5,600 BC using red lime as the cement. The first major concrete users

were the Egyptians in around 2,500 BC and the Romans from 300 BC.

The Assyrians and Babylonians used clay as the bonding substance or

cement. The Egyptians used lime and gypsum cement. In 1756, British

Engineer, John Smeaton made the first modern concrete (hydraulic

cement) by adding pebbles as a coarse aggregate and mixing powered

brick into the cement. In 1824, English inventor, Joseph Aspdin

invented Portland Cement, which has remained the dominant cement

used in concrete production.

In 1830, a publication entitled, "The Encyclopedia of Cottage,

Farm and Village Architecture" suggested that a lattice of iron rods

could be embedded in concrete to form a roof. Eighteen years later, a

French lawyer named Joseph Louis Lambot created a sensation by

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building a boat from a frame of iron rods covered by a fine concrete

which he exhibited at the Paris Exhibition of 1855. Steel-reinforced

concrete was born then. William Wilkinson of Newcastle who applied

for a patent in 1854 introduced it as a building material for

"improvement in the construction of fireproof dwellings, warehouses,

other buildings and parts of the same". In 1867, Joseph Monier, a French

gardener took out a patent on some reinforced garden tubs and later

patented some reinforced beams and posts used for guardrails for roads

and railways. The first landmark building in reinforced concrete was

built by an American Mechanical Engineer, William E. Ward, in 1871-

1875. The house stands today in Port Chester, New York. In 1879, G. A.

Wayss, a German builder bought the patent rights to Monier's system

and pioneered reinforced concrete construction in Germany and Austria,

promoting the Wayss-Monier system. Austrian Engineers made great

developments in theory and practice in the 1890s, and the use of

structural steel shapes as reinforcement was developed.

The popularity of the process skyrocketed in the early 19th

century and soon, a majority of the developers all over the world was

using steel-reinforced concrete in the construction of their buildings.

The process has been refined over the years, constantly changing and

improving the formula for making high quality steel-reinforced

concrete. Many of the buildings located in industrialized nations use

steel-reinforced concrete to make the buildings stronger and able to

withstand the ravages of time and weather. Reinforcing the concrete that

will be used on the building adds tensile strength to the concrete,

making it much stronger and more flexible than regular concrete, which

helps to prevent cracking and breakage.

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However, with technological advancement, the exploitation of

concrete and steel in composite construction has become more and more

popular. This is because the combined effect of these two different

materials to form a single unit far exceeds the individual performance of

either one of these materials. An early example of composite

construction is the flitched timber beam where steel plates are bolted to

it to increase its strength and stiffness. In North America, the first

well-documented structural use of composite construction of rolled

beams embedded in concrete was in the Ward House, a private house,

completed at Port Chester, New York in 1877. The first systematic test

of composite columns was conducted at Columbia University by Burr in

the year 1908 (Burr 1912). In 1922, Mackay and colleagues conducted

the first test in Canada on composite floor panels, which comprised a

concrete slab with two encased I-beams (Mackay et. al. 1923).

During 1930s, composite structures were first applied in

highway bridge construction in Europe and North America. Built up

composite construction consisting of two or more structural steel

sections or cast iron encased with concrete, was used in the early

developments of composite structures. They were used long time before

the typical concrete encased single steel I- section, which became very

popular in the 1940s. In 1940s and 1950s, composite construction

started to develop rapidly, and solid concrete slabs with encased steel

beams were used extensively, with considerable composite action

allowed in some instances. The appearance and application of

mechanical shear connectors in late 1950s encouraged the development

of composite structural systems. Until the 1950s, fireproofing of the

steel- framework was achieved by encasing the steel columns in a low-

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strength mix of concrete but with no contribution of the concrete to the

strength of the column. Faber (1956) and Stevens (1959) performed tests

on encased columns that showed the economic advantage on using a

better-quality concrete that could allow the use of the columns as a

composite structural member.

In the year 1956, the Committee on Bridges and Structures of

the American Association of State Highway Officials (AASHO) issued

the first specification for the design of composite bridge superstructures

(Viest et. al. 1997); however, a thoroughly expanded version was

published in 1957. In December 1960, the joint ASCE-ACI Committee

issued tentative recommendations for the design and construction of

composite beams and girders for buildings, which later became the basis

for 1961 and 1963 AISC specification provisions for composite beams.

Since 1969, when the first typical specifications were recommended by

the AISC Specification, the use of composite structures has been

extensively employed in floor, roof, and highway bridge construction.

In 1969, Khan started using mixed steel- concrete into a single

system for the lateral load resisting system of mid and high-rise

buildings. One of his first applications features the use of composite

exterior columns and spandrel beams for a 20-storey mid-rise building

in Chicago. Griffis in 1986 recommended some design considerations

for composite- frame construction based on the two case studies

conducted on high-rise buildings with composite frame.

Recent development in composite construction occurred with

the invention of a new innovative reinforcement system termed

Prefabricated Cage System (PCS) proposed by Halil Sezen and

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Mohammad Shamsai of the Ohio State University. PCS has many

potential applications other than building columns; e.g., bridge piers,

abutments, pier caps, shear walls with PCS steel plates or with PCS

boundary elements, beams, piles, foundations, etc.

Since this investigation is meant for behaviour of a steel-

concrete composite beam with Prefabricated Cage as reinforcement,

which eventually acts as a concrete encased composite section, the

review has been done on the following areas,

Experimental and analytical studies conducted by

different researchers on steel-concrete composite beams.

Behaviour of concrete encased composite sections.

Studies performed on Prefabricated Cage Systems.

Deflection and ductility characteristics in reinforced

concrete and steel – concrete composite systems.

Confinement studies on the behaviour of concrete

confined by various reinforcement systems and slip

characteristics of different composite systems.

Finite element analysis of structures.

2.2 STUDIES ON COMPOSITE SYSTEMS

Russell Bridge and Jack Roderick (1978) examined the

behaviour of concrete encased steel composite columns made up of two-

channel sections with and without the conventional battens. A series of

tests was conducted on axially loaded pin ended composite columns.

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The results obtained were compared with the theoretical values obtained

from an inelastic analysis developed as an extension of the analytical

equations proposed by Roderick and Rogers.

Max Porter (1984) proposed design criteria for composite steel

deck slabs based on experiments. The author recommended design

procedures by utilizing the maximum strength concepts. For the slabs

failing in shear bond failure mode, a plot was made using the

parameters, cu 'fbd/V as ordinates and 'cf/'dL as abscissa.

A linear regression was then performed to determine the slope (m), and

the intercept (k), in order to provide an equation for the expected shear

capacity.

'c'

u fkL

dmbdV (2.1)

where Vu = Ultimate shear capacity

= reinforcement ratio (As/bd)

d = effective depth from the compression fibre to steel

deck centroid

fc´ = design concrete compressive strength

For flexure, the author suggested separate computations for

under reinforced and over reinforced sections. The recommended

effective composite moment of inertia for deflection is taken as an

average of the composite moments of inertia of cracked and uncracked

sections.

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Richard Nguyen (1991) conducted experimental investigations

on composite beams made of thin-walled, cold-formed steel-stiffened

channels and concrete subjected to shear and bending both individually

and combined to study the feasibility of using such beams as

reinforcement for the cast-in-place concrete beams. From the results, the

author concluded that by replacing the conventional steel reinforcing

bars with thin-walled, cold-formed steel sections of equal cross-

sectional areas, the ultimate strength of the composite beams in bending,

and shear can be achieved. Furthermore, the use of these composite

beams lead to considerable savings in cost and time of construction

without increasing the area of steel required for reinforcement. In

addition, the author developed preliminary empirical formulas to

compute the ultimate shear bond capacity of the composite thin-walled,

cold-formed steel-concrete beams and to predict the behaviour of these

beams under bending and combined bending, and shear stresses.

Deric John Oehlers (1993) studied the behaviour of steel

profiled sheets as permanent form work to the sides of the reinforced

concrete beams. From the test results, the author concluded that the

addition of profiled steel sheets to the sides of reinforced concrete

beams can substantially increase both their flexural and shear strength

without the loss of ductility, and this system does not prone to shear

bond failure at the profiled sheet-concrete beam interface. Moreover,

based on theoretical studies he suggested that the addition of side

profiled sheets will substantially reduce long term deflections due to

creep and shrinkage of the concrete and allow increases in the

span/depth ratio of about 20%.

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Brain Uy and Mark Andrew Bradford (1995a) carried out a

series of experiments on profiled composite beams. Test results

provided benchmark data for profiled composite beam construction and

also validated the hypothesis that profiled composite beams deflect less

than reinforced concrete beams under long-term loads when designed

for the same flexural strength. In addition, failure was found to occur

progressively through a combination of bond-slip failure and local

buckling of the steel sheeting.

A theoretical model for the cross-sectional behaviour of

profiled composite beams was then calibrated from the tests, and the

load-deflection characteristics of the model were found to agree with the

experimental results. A finite-strip model developed elsewhere predicted

the onset of local-buckling, which is in agreement with the experiments.

Ali Mirza et. al. (1996) reported a study on the steel composite

beam-columns in which steel shapes were encased in concrete with

second order effects were studied from 16 specimens loaded to failure.

Analyses based ACI 318, Eurocode 4 and finite-element modeling

procedures were compared to test results that provided further insight

into understanding the structural behaviour of such as beam-columns.

Madhusudhan Khuntia and Subhash Goel (1999) conducted

the experimental study of FRP encased steel joist composite beams.

They reported that this system has the great potential for use in the

seismic region and non seismic regions.

Saw and Richard Liew (2000) presented the design assessment

of encased I section and concrete filled composite columns based on the

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approaches given in Eurocode 4 Part 1.1, BS 5400: Part 5 and AISC

LRFD and concluded the design methods were mostly conservative

when compared with the test results.

Weng et. al. (2001) investigated the shear strength of concrete

encased I section. Important parameters such as the steel flange width,

stirrup ratio, concrete strength and applied axial load were considered in

the development of the method of the shear strength prediction. The

authors introduced a new term called “The critical steel flange ratio

(bf/B)cr” to distinguish the diagonal shear failure mode from the shear

bond failure mode.

= 1 0.17 1 + 0.073 + (2.2)

where,

bf = Width of steel flange

B = Gross width of the composite member

Fyh = Yield stress of transverse reinforcement

= Concrete compressive strength

= Ratio of transverse reinforcement

= Required axial compression or tension computed at

factored loads

= Gross area of RC member

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It was found that when the steel flange ratio (bf/B) of a

composite section is larger than the critical steel flange ratio (bf/B)cr, the

shear capacity will be governed by the shear bond failure mode and the

diagonal shear failure mode controls the shear capacity if the ratio of

(bf/B) is smaller than (bf/B)cr. The shear capacity predicted by the

proposed approach was compared with the values calculated by using

existing American and Japanese codes.

Weng et. al. (2002) constructed and tested nine full-scale

specimens to investigate the flexural and shear behaviour of concrete

encased steel beams. The test strength, load- deflection curve, crack

pattern, and failure mode of each specimen were recorded and studied

by the authors. The authors found the appearance of significant

horizontal cracks along the interface of steel flange and concrete,

referred to as the shear splitting failure in five tested specimens and also

observed that the steel flange width ratio, defined as the ratio of steel

flange width to gross section width, has a dominant effect on the shear

splitting failure of composite beams. They also predicted that the shear

splitting failure occurs when the steel flange width ratio of a composite

beam reaches 0.67 and the application of shear studs has a positive

effect on preventing this type of failure for beams with a large steel

flange ratio. In addition, the authors proposed a new method for

predicting the failure mode of composite beams, and the proposed

method gave satisfactory predictions when compared to the test results.

Finally, they derived a new equation for the design of the stirrups to

prevent shear splitting failure of naturally bonded composite beams.

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Jianguo Nie and Cai (2003) studied the effects of shear slip on

the deformation of steel-concrete composite beams. The equivalent

rigidity of composite beams was derived from which a general formula

to account for slip effects was then developed. They concluded that the

shear slip in partial composite beams has a significant contribution to

beam deformation, and the slip effects may result in stiffness reduction

up to 17% for short span beams.

Jianguo Nie et. al. (2004) conducted an experimental study on

behaviour of steel and high strength concrete composite beams. Seven

composite beams and one normal strength concrete beams were tested

under monotonic loading. The composite beams had higher initial

stiffness and very distinct post yielding characteristics than the normal

strength concrete beams. The authors concluded that for high strength,

concrete composite beams with full composite action, the elastic

stiffness calculated based on a transformed section gave reasonable

estimation of the initial stiffness.

Mark Lawson and Anthony Severirajan (2011) developed a

simplified method of elasto-plastic analysis of composite beams by

considering equilibrium of the composite cross section as a function of

its strain profile. A parabolic rectangular stress block for concrete was

used in the model with a declining concrete strength at strains exceeding

0.0035. They recommended that the 0.85 factor on the concrete strength

in Eurocode 4 may be set to 1.0 in elasto-plastic methods using the

above-said stress block.

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2.3 STUDIES ON PREFABRICATED CAGE SYSTEM

Mohammad Shamsai and Halil Sezen (2005) investigated the

confinement provided by PCS by comparing the results from six small-

scale column tests. The specimens were tested by axially loading the

concrete core. Furthermore, the authors studied the effects of PCS tube

thickness, the width and height of transverse and longitudinal steel on

the provided confinement and displacement capacity. From the test

results, the authors concluded that PCS provides much better concrete

confinement than a rebar reinforcement system and predicted that the

confinement provided by PCS is better than the confinement provided

by conventional rebar, and less than the confinement provided by tube.

They examined that the confinement was much affected by the opening

dimensions and less affected by the tube thickness. Besides, they found

that the confinement capacity decreases as the opening dimension

increases, whereas the confinement effect is the same whether the length

of the openings was increased or the width of the windows was

increased. They predicted that the final failure of PCS specimen was

always followed by the fracture of transverse steel.

Halil Sezen and Mohammad Shamsai (2006) experimentally

investigated the behaviour of PCS reinforced columns with normal

strength concrete. A total of 16 specimens were constructed and tested

to investigate the strength and displacement capacity of PCS reinforced

columns and was compared with those of equivalent rebar reinforced

specimens. From the test results, the authors concluded that PCS

reinforced specimens have similar elastic behaviour, comparable peak

strengths, and better performance in the residual strength section beyond

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the peak strength and were found to be more ductile and absorb more

energy than equivalent rebar reinforced specimens.

Moreover, the authors studied the effect of various parameters

such as plate thickness, number of longitudinal reinforcements,

transverse steel spacing and crossties, on the behaviour of PCS

specimens. Test results indicated that PCS reinforcement with thicker

tubes provides higher strength and better displacement capacity,

whereas the effects of parameters such as a number of longitudinal

reinforcement and transverse steel spacing on the overall behaviour are

not significant. Also, they recommended that crossties helps to prevent

the PCS tube from buckling and therefore, improves the confinement,

strength, and displacement capacity.

Mohammad Shamsai et. al. (2007) economically evaluated the

reinforced concrete structures with PCS reinforced columns, as it is one

of the major applications of PCS. Different parameters affecting the

economics of reinforcement systems were reviewed and a method for

estimating the cost and time savings of structures with PCS reinforced

columns were introduced. The method was applied to analyze a

reinforced concrete parking garage structure using different interest rates

and structural lifetimes.

From the investigations, the author concluded that using PCS

results in 33.3% time savings and 7.1% cost savings over rebar for each

column. Moreover, they predicted that PCS provides an average cost

saving of $220,543, which was equivalent to an average 3.6% savings

on total project cost, an average of 22.2% savings on total column costs

and provides a time saving of 116 days, which was equivalent to 20.4%

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savings on the total project time period, 33.3% savings on column’s

construction time period. Also they found that the cost savings were

directly proportional to annual interest rate and inversely proportional to

the lifetime of the structure. The authors also recommended that the

amount of cost savings is based on low quantity PCS production;

moreover, these cost savings should be even higher for mass production

of PCS reinforcement.

Halil Sezen and Mohammad Shamsai (2008) experimentally

investigated the axial strength, confinement, and displacement capacity

of 15 small-scale high-strength column specimens reinforced with PCS

and conventional reinforced concrete specimens. The authors evaluated

the behaviour of PCS specimens and compared with that of similar

rebar reinforced concrete columns and also investigated the effect of

several parameters such as steel tube thickness, opening dimensions,

number and spacing of longitudinal and transverse steel, on the strength

and displacement capacity. From the test results, they concluded that

small-scale column specimens reinforced with PCS and conventional

rebar have a comparable peak axial strengths and PCS specimens were

found to have a larger residual strength and deformation capacity.

The authors also concluded that the effect of steel plate

thickness on the strength and deformation capacity was not significant;

however, PCS reinforcement with very thin plate thickness resulted in

slightly smaller maximum strength. The number of longitudinal strips or

bars and the transverse reinforcement spacing did not have significant

effect on the behaviour of the specimens, provided the steel amount was

the same. The authors proposed a new model for concrete confined by

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PCS reinforcement and the calculated theoretical axial load–

displacement relations were compared with the experimental results.

The proposed model predicted the behaviour of PCS specimens

reasonably well.

2.4 STUDIES ON DEFLECTION AND DUCTILITY ON

RCC AND COMPOSITE BEAMS

Max Porter and Carl Ekberg (1976) explained the cold-formed

steel deck sections used in composite floor slabs. During the

construction phase, the steel deck serves as the structural load carrying

element. Design procedures were recommended for composite steel

deck-reinforced floor by utilizing the application of the maximum

strength concepts. The design capacity primarily was based upon the

computation of shear bond strength. However, the equation for flexural

capacities was also developed from the compatibility of strains and the

equilibrium of internal forces. Additional design considerations were

given on casting and shoring requirements, deflections and span/depth

relations. Deflection limitations follow the provisions of Section 9.5 of

the ACI building code. The recommended effective moment of inertia

for composite deck deflection limitations is taken as the average of

standard cracked and uncracked sections.

Vijaya Rangan (1982) proposed simple expression for

maximum allowable span-depth ratios for reinforced concrete beams

and one-way slabs based on Branson’s deflection computation method

as in ACI code. The proposed equation takes into account various

factors influencing deflections of reinforced concrete flexural members.

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Effective moment of inertia is expressed in terms of complex function

(k) of and as,

(2.3)

where,

= = Tensile steel ratio

= Compressive strength of concrete

= = Modular ratio

= 0.1955 0.111 > 0.045

= 0.0019 0.067 0.045

Peter Ansourian (1982) investigated the sagging rotation

capacity of composite beams consisting of a steel beam of, I section and

of a concrete slab attached by a shear connector. Experiments were

reported on four full scale composite beams in the range of the ductility

parameters ( ) from 0.65 to 3.0. This parameter is an index of the

degree of strain-hardening developed in the steel beam at the collapse.

Experiments were conducted for the minimum inelastic rotation and

deflection available at collapse. Examples were given of the application

of these expressions to design problems with continuous composite

beams. A minimum value of the ductility parameter was proposed for

which sufficient plastic redistribution was available for any combination

of spans and loadings.

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Pieter Pretorius (1985) developed a new simplified method for

long term deflection calculations of reinforced concrete members in

terms of immediate deflection. They concluded that immediate

deflections can be calculated using the transformed concrete sections.

For members without compression reinforcement long term deflections

can be determined from the following equations,

(2.4)

= ) (2.5)

= Creep factor proposed by Parrott

=Immediate deflection

=Neutral axis depth ratio

= = Reinforcement Ratio

=Long term deflection

=Modular ratio

Brain Uy and Mark Andrew Bradford (1995b) developed a

simple cross sectional analysis based on the routine mechanics of

materials to study the moment curvature response and hence the

ductility of profiled composite beams. Investigations were carried out on

the ramifications of various properties affecting the stiffness, strength

and ductility of profiled composite beam cross-section. They concluded

that the yield strength of the sheeting, area of tensile reinforcement, and

interfacial slip affected the ductility of the profiled beams.

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The member behaviour was then analyzed by using a simple

numerical integration technique to obtain deflections throughout a beam

and the results revealed that, although the increase in strength of cross-

section may affect the ductility, the latter may still remain fairly large

for all reasonable variations of material strengths and section geometries

so that plastic design and ductile failure are obtainable.

Wright (1995) presented a study on the local stability of filled

and encased steel sections. The author stated that the b/t ratios of

sections should be such that buckling will be resisted before a defined

stress or strain limit is reached. This study reviewed the determination of

b/t ratios for plates with various boundary conditions, including plates

that are in contact with a rigid medium such as concrete. The derivation

of b/t ratios for the buckling of web plates were subjected to bending

and shear. The energy method was used to equate the work required to

load the plate, to the work required to deform the plate into buckled

shape. Orthotropic plate theory and the flow theory of plasticity were

used to evaluate b/t ratios for plates subjected to uniaxial compression,

combinations of bending and axial loading and shear. It was concluded

that the strength and ductility of steel sections may be improved by

filling or encasing them with a stiff medium such as concrete.

Chien-Hung Lin and Feng-Sheng Lee (2001) investigated the

ductility of beams made with high workability high-performance

concrete and high-strength transverse reinforcement. The test parameters

included were concrete strength, an amount of tension reinforcement,

the amount of compression reinforcement and amount of transverse

reinforcement. They concluded that HPC beams exhibit better ductility

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than normal concrete beams. A decrease of tension reinforcement,

increase of compression reinforcement, increase of transverse

reinforcement and increase of stirrup strength improve the ductility

significantly. Use of high-strength transverse reinforcement with yield

strength greater than 60 ksi (414 MPa) increases the ductility and

reduces the amount of confining reinforcements required to achieve the

same ductility.

Ciro Faella et. al. (2003) adopted a numerical procedure

considering the nonlinear behaviour of shear connector to evaluate the

deflection of simply supported composite beams. This method assumed

different load-slip relationships for shear connectors in cracked slab.

Validation of the numerical procedure was done using the available

experimental results. A wide parametric analysis was performed with

reference to the evaluation of deflections for simply supported

composite beams. Finally, a simplified method to evaluate deflections

for beams with nonlinearly behaving shear connection was presented.

2.5 STUDIES ON CONFINEMENT

Soliman and Yu (1967) developed a stress- strain relationship

of bound concrete in flexure to understand the plastic deformation

capacity of critical regions reinforced with longitudinal and transverse

reinforcement. A generalized relationship was developed and expressed

as a function of spacing of binders, the ratio of the bound area to the

total area under compression, the size of binders and the shape of

concrete cross section. They concluded that the increase in the spacing

of the binders decreases the confining effect of binders. They also found

that an increase in the cross-sectional area of the binders increases the

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confining effect of binders. From the stress-strain curves, the property of

stress block for bound concrete for any extreme fibre was found.

Sundara Raja Iyengar et. al. (1970) presented the results of

axial compression tests on specimens where they chose size and shape

of test specimen and diameter and type of spiral wire as variable

parameters. They introduced a new factor called ‘Confinement Index’ to

define the confinement quantitatively. They found that the ultimate

strength and strain increased with confinement and linearly with

confinement index. The confinement was found effective only when the

pitch of binders is less than the least lateral dimension of the confined

specimen. They concluded that the circular spiral was most effective,

and the stirrups were least effective.

Mohamed Ziara et. al. (1995) examined both theoretically and

experimentally the flexural behaviour of structural concrete beams in

which confinement stirrups have been introduced in compression

regions. They proposed a method for the evaluation of the flexural

capacity of beams in which confinements of the compression regions

were present. They also outlined a method for the design of over

reinforced beams utilizing the ductility resulting from confinement.

They found that the presence of confinement increases the ductility of

the beams. They showed from the results that although the beams with

confinement were able to achieve a flexural capacity up to 246 percent

of the value corresponding to the maximum longitudinal reinforcement

ratio, they still failed in the ductile manner. They also found that in

beams, the stirrup spacing was reduced by 50 percent, the confining

36

stirrups delayed failure beyond the point at which spalling first occurred

in the cover concrete.

Mohamed Saafi et. al. (1999) investigated the performance of

concrete columns confined with carbon and glass fiber reinforced

polymer composite tubes. Type of fiber, thickness of tube and concrete

compressive strength were considered as test variables. Experimental

results proved that external confinement of concrete by FRP tubes can

significantly enhance the strength, ductility and energy absorption

capacity of concrete. Equations to predict the compressive strength and

failure strain as well as the entire stress-strain curves were developed.

The experimental results were compared with the analytical results

andproved satisfactory about the predictions of ultimate compressive

strength, failure strain and stress-strain response.

Esneyder Montoya et. al. (2006) proposed the constitutive

models for strength enhancement, concrete dilatation and a stress-strain

relationship for concrete in triaxial compression. Four simple categories

of confined concrete were defined by the authors based on the

confinement ratio and the concrete type. Three cylinders wrapped with

FRP fabric were tested in axial compression and modelled using in

house program. The analytical response of cylinders showed the

capacity of models and the non-linear finite-element program

reproduced the confined behaviour of concrete at the material level. The

set of constitutive models followed a compression field approach

suitable for implementation in non-linear finite element analysis

program.

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Lee et. al. (2010) conducted an experimental and analytical

study on the behaviour of concrete cylinders externally wrapped with

fiber-reinforced polymer composites and internally reinforced with steel

spirals. Totally, twenty four concrete cylinders with various confinement

ratios and type of confining steel were tested in pure compression. A

new empirical model to predict the axial stress-strain behaviour of

concrete confined with FRP and steel spirals was also proposed.

2.6 STUDIES ON SLIP CHARACTERISTICS

The load-slip characteristics of steel and concrete are an

important parameter in transferring the load in the composite system.

The areas which are considered to be useful to this research are dealt

with below.

Cem Topkaya et. al. (2004) reported about composite shear

stud strength at early concrete ages. Composite action between a

reinforced concrete deck and steel girders is usually achieved by making

use of the welded headed shear studs. A new push out test setup has

been developed. 24 tests were performed at concrete ages ranging from

4 h to 28 days. Test results were used to develop load-slip curves and

strength expressions. Furthermore, the variation of concrete properties

with time and the applicability of the existing code equations for

predicting early-age concrete stiffness were examined. Test results

revealed that shear transfer is achieved at very early concrete ages and

the rate of stiffness gained from the concert is greater than that of

strength.

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Mohamed Harajli, et. al. (2004), investigated the local bond

aspect between steel bars and concrete confined with ordinary transverse

steel. The test parameters included diameter of reinforcing bar, the ratio

of concrete cover to bar diameter and area of transverse reinforcement.

The results were compared with the results of similar specimens for

concrete confined either internally using steel fiber reinforcement or

externally using fiber-reinforced polymer (FRP) sheets. Based on these

comparisons, a unified expression for the local bond strength of

confined concrete was derived, and a general model for the local bond

stress-slip response was proposed and used to conduct an analytical

evaluation of the effect of confinement on development/ splice strength.

Lisa Feldman and Michael Bartlett (2005) carried out an

extensive experimental study on 252 pullout specimens to assess the

variability of steel-to-concrete bond of plain bar reinforcement. They

concluded that load-slip curves display a characteristic shape and

immediately after the maximum tensile load was reached, at a slip on

the order of 0.01 mm. They observed that the load got dropped off

markedly and then gradually with slip to a limiting residual load. They

found that this behaviour confirms the presence of two distinct bond

mechanisms: adhesion between concrete and steel before slip occurred,

and wedging of small particles that broke free from the concrete upon

the slip.

Valcuende and Parra (2009) examined the bond strength

between reinforcement steel and concrete, and the top bar effect in

self- compacting concrete. They found that at moderate load levels, SCC

performed with more stiffness, which resulted in greater mean bond

39

stresses. Furthermore, changed to the factor that took account of top-bar

effect for calculating the anchorage length of reinforcements was

proposed.

2.7 STUDIES ON FINITE ELEMENT ANALYSIS OF

STRUCTURES

Antonio Barbosa and Gabriel Ribeiro (1998) investigated the

possibilities of performing nonlinear finite element analysis of

reinforced concrete structures using ANSYS concrete model. They

performed a series of analysis of the same structure, exploring different

aspects of material modelling. The results of the analyses performed had

been compared to a load- deflection curve derived from an analytically

determined moment- curvature relationship. The authors concluded that

only nonlinear stress-strain relations for concrete in compression zone

had made it possible to reach the ultimate load and determine the entire

load – deflection diagram. They obtained satisfactory prediction of the

response of reinforced concrete structures in spite of the relative

simplicity of the analysed structure and of the employed models.

Fanning (2001) developed numerical models for the nonlinear

response of 3.0m ordinarily reinforced concrete beams and 9.0m

post-tensioned concrete beams, using ANSYS V5.5. The models

included a smeared crack analogy to account for the relatively poor

tensile strength of concrete, a plasticity algorithm to facilitate concrete

crushing in compression regions and a method specifying the amount,

the distribution and the orientation of any internal reinforcement. The

author recommended numerical modeling strategies and compared the

experimental load deflection responses for ordinary reinforced concrete

40

beams and post-tensioned concrete T-beams. Also he concluded that the

dedicated smeared crack model as an appropriate numerical model for

capturing the flexural modes of failure of reinforced concrete systems.

Santhakumar and Chandrasekaran (2004) carried out a

numerical study for retrofitted reinforced concrete shear beams using the

finite elements adopted by ANSYS. By taking advantage of the

symmetry of the beam and loadings, a quarter of the full beam was

modelled. The load deflection plots obtained from numerical study

showed good agreement with the experimental plots reported by Tom

Norris et. al. (1977). The author concluded that numerical study can be

used to predict the behaviour of retrofitted reinforced concrete beams

more precisely by assigning appropriate material properties. They also

presented the crack patterns in the beams and the effect of retrofitting in

uncracked and precracked beams.

Alper Büyükkaragöz (2010) conducted the experimental tests

on a beam strengthened by bonding with a prefabricated plate, which

has 80 mm thickness underneath and a control beam. The author

compared the experimental results with the results obtained from the

beam modelled with ANSYS finite element program. It was observed

that the results obtained from ANSYS finite element program are

considerably correlated with the results of the experiment. Also, he

concluded that the modeling that is made with ANSYS finite element

program can be useful for saving money and time in terms of the

specimen. And the design errors, which can be made in the design stage

or wrong material selection can be prevented. The author also

41

recommended that this way of modeling will be a guide for the further

experimental studies.

2.8 CRITICAL REVIEW

In the earlier investigations, steel – concrete composite beams

were carried out on conventional concrete slab over steel beam. Then

such type of construction was improved by using composite action by

means of shear connectors. Later on, built up composite construction

consisting of two or more structural steel sections encased in concrete

were used in order to overcome the problem of fire resistance.

Thereafter, more research works were carried out on concrete encased

sections consisting of two or more structural steel shapes that were

basically channels and angles that could be laced or battened together

forming one piece. Then came into picture the steel I-sections encased in

concrete. The literature available on conventional steel concrete

composite beams and concrete encased steel I-section provided

information on flexural behaviour.

In recent years, with the invention of a new reinforcement

system termed Prefabricated Cage System significant development

occurred in concrete encased steel composite construction. Mohammad

Shamsai (2005) carried out extensive research work on PCS reinforced

columns. The studies carried out on the steel-concrete composite beams

based on the available literatures (Delsye Teo et. al. 2006) clearly

indicates that so far significant work has not been carried out on

composite beams reinforced with prefabricated cage system. Hence, an

extensive experimental and analytical program is needed to capture the

behaviour of beams reinforced with Prefabricated Cage.

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2.9 SCOPE OF THE PRESENT RESEARCH

In the light of the above observations, an experimental and

analytical study on the behaviour of composite beams reinforced with

Prefabricated Cage is conducted through a series of tests. The objectives

of this study are:

1 To investigate the failure modes of Prefabricated Cage

Reinforced Concrete beams.

2 To study the deformation and ductile characteristics.

3 To develop an analytical model for flexural strength,

deflection at service stage and curvature ductility factor.

4 Compare the laboratory results with a numerical tool,

ANSYS 11.0.

The work plan of the entire research work is presented in the

following flowchart (Figure 2.1)

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Figure 2.1 Work Plan of the Research Work

Research Work

Numerical ModellingTheoretical InvestigationsExperimental Study

Study on CylindersConfined by Cage(25 x 3 specimens)

Bond Strength ofPerforated CR sheets

Embedded in Concrete(54 x 3 specimens)

Flexure Study on PCRCBeams

(36 x 3 specimens)

Ultimate MomentCarrying Capacity of

PCRC Beams

Deflection at serviceload of PCRC Beams

Curvature DuctilityFactor of PCRC Beams

Modelling of PCRCbeams usingANSYS 11.0

Compressive Strengthof Confined Concrete

Strain at UltimateCompressive Strengthof Confined Concrete

Deflection atservice load

Failure Load ofPCRC beams