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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
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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
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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
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