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CHAPTER 2

LITERATURE REVIEW

2.1 GENERAL

Several researchers worldwide have investigated the behaviour of

reinforced cement concrete columns and beam-column joints of moment

resisting building under earthquake loading. A detailed review of literature

has been carried out to understand the influence of non-conventional detailing

of reinforcement on the behaviour of structural elements. Among these the

most significant literature are briefly summarised in this chapter. The past

efforts and recent contributions in finite element modelling of concrete

structural elements and material modelling related to this thesis work are also

reviewed.

2.2 OVERVIEW OF LITERATURE

2.2.1 Studies on Performance of Columns Under Seismic Loading

Wight and Sozen (1975) tested twelve concrete column specimens

under a series of load reversals and observed the benefit of the axial load

which delayed the decay in strength and stiffness of columns under cyclic

loading. They found that enough transverse reinforcement is needed for

confining the core and hence to reduce the strength and stiffness loss.

Abrams (1987a) studied the effect of axial load on the reversed

lateral cyclic loading of columns and found that the additional axial load

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increased the stiffness, flexural strength and shear capacity. The author found

that the shape of the hysteretic loop was influenced by the range of axial force

variation and the rate of change of axial force with lateral deflection.

Saatcioglu and Ozcebe (1989) tested full-scale columns under

slowly applied lateral load reversals. Test parameters were axial load,

confinement reinforcement and deformation path. They reported increased

stiffness degradation and early strength degradation with addition of axial

loads. The authors concluded that selection of a proper confinement

configuration is a more feasible approach than the reduction in hoop spacing

alone to achieve the same level of ductility.

Sakai and Sheik (1989) presented a state-of-the-art report on

concrete confinement defining the status of the problem and future direction

of work. Topics discussed include properties of confined concrete, behaviour

of confined sections and columns including plastic hinge regions, and a

critical evaluation of the design code provisions.

Azizinamini et al (1992) conducted full scale testing of columns

with different transverse reinforcement details and found that the flexural

capacity of columns increased with axial load but ductility reduced

substantially. They found that six bar diameter extension of hook is sufficient

to produce adequate displacement ductility. Test results indicate that increase

in the amount of transverse reinforcement improves the ductility.

Aycardi et al (1994) tested gravity load designed column specimens

under simulated seismic loading, with low and high level axial forces and

with and without lap splices, representing interior and exterior columns at

floor slab and beam soffit levels. The failure of the columns were flexurally

dominated resulting in buckling of column reinforcement in the case of high

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axial loads and low cycle fatigue of the longitudinal bars in the case of low

axial loads. The maximum strength was observed when interstorey drift was

between 2% and 3% and subsequently, strength decreased with additional drifts.

Mo and Wang (2000) conducted experiments on RC columns with

various tie configurations by reversed cyclic loading. They proposed

transverse reinforcement configuration with alternate ties to improve the

seismic performance.

Elwood and Moehle (2003) observed that the lateral displacement

or drift of a reinforced concrete column at axial failure was dependent upon

and directly proportional to the spacing of transverse reinforcement and the

axial stress developed within the column. Further, it was noted that the lateral

drift experienced by the columns at axial failure was dependent upon and

inversely proportional to the amount of axial load exerted on the columns.

The performance of columns under seismic loading is also influenced by the

secondary moment due to drift.

Turer and Akyuz (2003) made a case study and suggested that the

diagonal tension crack at the upper end of the column is due to a combination

of inferior material quality, inadequate transverse reinforcement, and

insufficient column confinement. Insufficient structural resistance combined

with the poor construction quality and detailing causes catastrophic failure of

the structures.

Flores (2004) studied experimentally the behaviour of columns

under seismic loading to understand the progression of damage and

mechanisms causing collapse in shear-critical reinforced concrete columns.

Based on the test results, the authors developed analytical models to predict

the drift capacity of columns.

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Montes et al (2004) studied the impact of optimal longitudinal

reinforcement on the curvature ductility capacity of column sections. An

approach for determining an acceptable reinforcement by means of

reinforcement sizing diagram has been described. The authors concluded that

the curvature ductility capacity enhanced for the case of optimal longitudinal

reinforcement relative to the values computed for conventionally reinforced

columns.

Mark et al (2008) developed a nonlinear conjugate gradient search

method for finding the optimal reinforcement of a rectangular reinforced

concrete cross section. The authors suggested the use of the model for

sections subjected to uniaxial or biaxial bending.

As per the literature reviewed on behaviour of columns under

cyclic shear loading, it was concluded that adequate transverse reinforcement

and appropriate longitudinal reinforcement will provide better ductility,

stiffness and strength to the column elements of the buildings. The research

by Montes et al (2004) indicated that the use of optimal reinforcement

improves the curvature ductility of columns than that of higher percentage of

reinforcement. Hence the effects of percentage of longitudinal reinforcement

and orientation of ties on the behaviour of columns under cyclic shear loading

are experimentally studied as a preliminary part in this project work.

2.2.2 Studies on Performance of Beam-Column Joints and Non-

Conventionally Detailed Structural Elements Under Seismic

Loading

Paulay and Binney (1974) conducted experimental studies on the

short reinforced concrete coupling beams by providing the principal

reinforcement diagonally instead of in the conventional form. The authors

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designed the diagonal reinforcement based on the assumption that the shear

force resolves itself into diagonal tension and compression. Initially, the

diagonal compression is transmitted by concrete and the compression

reinforcement makes no significant contribution. When diagonal tension bars

are loaded to yield range, wide cracks are formed and these cracks remain

open even after the removal of loading. When the reversed load is applied as

during an earthquake, these bars are subjected to large compressive force and

may yield even before the cracks formed previously are closed. As equal

amount of steel was provided in both the diagonal band, the loss of

contribution of concrete will not affect the strength of the beam. Thus the use

of inclined reinforcement prevents brittle failure in short coupling beams.

Uzumeri (1977) tested exterior beam-column sub assemblages

under high constant axial compressive forces and concluded that the large

axial compressive force applied to the concrete struts was detrimental to the

joints.

Paulay et al (1978) studied the behaviour of interior joints from the

experimental data base. They concluded that total shear force at the joint

should be carried by the diagonal strut and truss mechanism. The major

contribution is from strut mechanism, which is to be diminished after the

plastic hinge formation at beam near joint interface. The stirrup and

intermediate column bars can provide the strut mechanism. The diameter of

the column bars should not be excessive to avoid bond failure.

Meinheit and Jirsa (1981) carried out experimental investigations to

evaluate the factors influencing the shear capacity of the beam-column joints.

The parameters considered were (i) size and spacing of transverse

reinforcement in the joints, (ii) percentage of column longitudinal

reinforcement, (iii) axial load on columns, (iv) effect of transverse beams and

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(v) aspect ratio of joints. Their conclusions were (1) transverse reinforcement

in the connection improved the shear capacity, (2) unloaded transverse beams

improved the shear capacity, (3) column axial load had no influence on

ultimate shear capacity of joints, (4) connection geometry had no influence on

shear strength of joints, as far as shear area of the connection remained

constant.

Minami and Wakabayashi (1984) provided diagonal reinforcement

in short columns which were failing in shear and found better performance

than with conventional reinforcement. The authors found that shear resistance

of columns was improved by developing additional truss mechanism from the

diagonal reinforcement. The shear strength of columns increased with

increase in the yield tensile force of diagonal reinforcement. For the

diagonally reinforced columns, the failure mode changed from shear to

flexural failure and hysteresis curves changed to spindle shape having high

energy dissipation capacity.

Durrani and Wight (1985) carried out experiments on interior

beam-column joints subjected to reversed cyclic loading. The objective of the

studies were to evaluate the effect of the amount of joint hoop reinforcement

and joint shear stress on strength degradation, loss of stiffness, energy

dissipation, shear deformation of joints, and the slippage of beam and column

bars through the joint. The authors found that a combination of lower joint

shear stress and a moderate amount of joint reinforcement was more effective

than a combination of a higher shear stress level and a heavily reinforced joint

for higher energy dissipation. A minimum column to beam flexural strength

ratio of 1.5 was recommended for design. The slippage of beam bars was

observed to be dependent on the joint shear stress level and confinement of

joint core, and hence member end rotation due to slippage was recommended

to be included in the nonlinear dynamic analysis.

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Ehsani and Wight (1985) tested six exterior beam-column

subassemblies with and without transverse beams and slab and compared their

behaviour. The parameters investigated included the flexural strength ratio

(ratio of flexural capacities of the columns to that of the beams), the

percentage of transverse reinforcement used within the joints and the shear

stress in the joints. In the case of specimens where the flexural strength ratio

is one or less, hinges are formed in the columns. The flexural strength ratio is

reduced significantly due to contribution of the slab longitudinal

reinforcement. It was found that the transverse beams are subjected to a

combination of bending and torsion loading. The confinement of a joint in the

specimen with transverse beam and slab improved significantly over a similar

specimen without transverse beam or slab.

Durrani and Zerbe (1987) tested six exterior beam-column

subassemblies. Out of these specimens one was without transverse beams, one

was with transverse beams and the other four were with transverse beams and

slab. As the columns were designed to be stronger than the beams, the

flexural hinges formed in the beams in all the specimens. It was found that the

specimens with slab showed higher flexural strength than the specimen

without slab. The stiffness of the specimens with slab is 60 % to 70 % higher

than that of the specimens without slab. It was also shown that the loss of

stiffness in specimens with slab is gradual and is not affected significantly by

the different slab widths. Also the specimens with slab dissipated

approximately 40 % more energy than the specimens without slab.

Zerbe and Durrani (1989) studied the behaviour of beam-column

connections under earthquake type loading by testing indeterminate frame sub

assemblies. The specimens used for testing were plain two-bay substitute

frame with beam and column alone. Any restriction to the elongation of the

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main beams and the accompanying axial compression were observed to affect

the response of the connections. It was reported that the joint shear in both

interior and exterior connections increased while the column to beam flexural

strength ratio reduced. The lateral resistance was reported to have increased

significantly. A procedure to account for the presence of axial compression in

the main beams in the design of beam-column connections was presented

based on the observed mechanism of lateral load resistance and the observed

behaviour of the connections.

Paulay (1989) used the laws of statics to demonstrate the

disposition of internal forces in beam-column joints. It was shown that due to

joint shear forces, which result in extensive diagonal cracking of the core

concrete, significant orthogonal tensile forces are generated. Also, as in the

case of linear elements, joint shear reinforcement is necessary to sustain a

diagonal compression field rather than to provide confinement to compressed

concrete in a joint core. The author concluded that (1) After diagonal

cracking; diagonal compression forces transmitted by concrete alone are

unconditional prerequisites of statically admissible shear transfer within a

joint. The purpose of joint shear reinforcement is to sustain such mechanisms.

(2) To restrict excessive joint dilation, which may significantly increase

storey drift, orthogonal tensile forces within a joint core must be resisted

primarily by reinforcement additional to beam and column bars that pass

through the joints. (3) Under typical earthquake actions, beams dilate rather

than confine joint cores unless it runs in transverse direction. Therefore,

provided that the flexural reinforcement in a beam passes through or is

anchored within the column, the width of a beam relative to the width of a

column is an irrelevant quantity in terms of joint performance.

Leon (1990) investigated the performance of interior joints with

respect to joint shear stress and beam anchorage lengths. Different levels of

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joint shear stress and anchorage length were arrived by changing the column

depth. The author stated that, when the anchorage lengths are large, even the

minimum shear reinforcement required for column confinement was adequate

to give good cyclic behaviour. Also it was proved that the assumption of rigid

joints in moment resisting frame is valid only if the anchorage lengths are

equal or exceed 28 bar diameters.

Alameddine and Ehsani (1991) conducted reversed cyclic loading

test on high strength concrete corner beam-column subassemblies. The test

result shows that lower shear stress with adequate joint confinement were

necessary to ensure good performance of joints and to move the hinging zone

away from joints. It was also shown that properly designed high-strength

reinforced concrete connections exhibit ductile hysteretic response. The

minimum flexural strength ratio of column to beam, 1.4 was also applicable to

high strength joint to ensure the formation of plastic hinges in the beam rather

than in columns.

Pantazopoulou and Bonacci (1992) studied the mechanics of beam -

column joints in laterally loaded structures and lead to formulation based on

compatibility of strain and stress equilibrium within the core. They developed

algebraic expressions relating the average joint shear stress and the associated

joint shear distortion. The model made by them showed that shear strength of

a joint depends on usable compressive strength of concrete as well as the

presence of shear hoops.

Tsonos et al (1992) conducted tests on external beam - column

connections using inclined reinforcing bars under seismic conditions.

Specimens with conventional reinforcement (type s) and specimens with

crossed inclined bars and hoop reinforcement (type x) provided in joint region

were evaluated. In type x specimens, four numbers of intermediate vertical

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joint shear reinforcement were replaced by four cross-inclined bars bend

diagonally across the joint core. The development length for both types of

bars was equal. The variables were the amount of inclined bars, the ratio of

the column-to-beam flexural capacity and the joint shear stress. The authors

found that the exterior joints with inclined bars had high shear resistance and

least deterioration than specimens designed as per code recommendations.

They concluded that the inclined bars introduce an additional new mechanism

of shear transfer and diagonal cleavage fracture was avoided for those

specimens.

Agbabian et al (1993) studied the effect of axial column load on the

shear capacity of beam-to-column connections. They observed that the axial

column load has a marked effect on the shear deformation capacity, yield

point, cracking pattern, ultimate capacity and ductility of the panel zone. They

tested three interior beam column sub assemblages with ten per cent, five per

cent and zero per cent axial load capacity. Test results indicated that the

overall displacement response of the sub assemblages decreased by 22 per cent for

a decrease in the axial load from ten to five per cent of the squash load.

Bonacci and Pantazopoulou (1993) studied the influence of key

variables such as axial load, concrete strength, presence of transverse beams

and bond demand on the behaviour of joints using results of a database study

compiled from published literature. The study consisted of a detailed

description of the parametric dependence of joint behaviour using mechanical

model developed by the authors. A design guideline was proposed to

proportion the column size such that the intensity of bond demand inside the

joint, (bond index) is kept low.

Veerendra Kumar and Mohammed Shamim (1999) carried out

experiments on beam column joints subjected to axial compression and

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uniaxial bending. The effects of column axial load, shear and tension

reinforcement in the beam on the performance of joints were studied. It was

found that the efficiency of joints increases with the increase in axial load on

column and with the increase in tensile and shear reinforcement in the beam.

The authors found that increase in shear reinforcement decreases ultimate

deflection of beam column joints and this reduction was significant in higher

percentage of tensile reinforcement in beams. They reported that increase in

shear reinforcement in beam increases the ultimate strength of joints at higher

axial load levels.

Tsonos (2000) investigated the improvement of earthquake

resistance of exterior reinforced concrete beam column connection with

vertical hoops in the joint region and compared with the response of similar

specimens constructed with the vertical joint shear reinforcement required by

Eurocode 8 and NZS 3101:82. The author concluded that vertical joint hoop

reinforcement gives more effective reinforcing pattern for sustaining the

vertical joint shear force than the intermediate column bars. He also

concluded that sub assemblages with vertical hoops in the joint region have

increased strength, stiffness and energy dissipation.

Murty et al (2001) tested the exterior beam column joints subjected

to static cyclic loading. They conducted experiments by changing the

anchorage detailing of beam reinforcement and shear reinforcement detailing.

The experiment revealed that anchoring the beam bars in to the column is

essential in developing a good hysteretic response in the frame. They

governed the sequence in which member capacities will be attained, nature of

the failure mode, and the overall energy dissipation potential of the system.

They stated that diagonal compression strut will carry shear force in the joint

core, only when the horizontal shear stress is limited to a value less than the

compressive strength of the concrete core when it is extensively cracked

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under load reversals. Their work emphasizes the need for larger joint sizes

and extra shear reinforcement in the joint. They reported that the practical

joint detailing using hairpin-type reinforcement is a competitive alternative to

providing closed ties in the joint region.

Bakir and Boduroglu (2002) developed a methodology for

predicting the failure modes of monotonically loaded reinforced concrete

beam-column joints. The authors concluded that the design charts gave

accurate predictions of failure modes.

Sathish Kumar et al (2002) studied the hysteretic behaviour of

lightly reinforced concrete exterior T shaped beam to column joint sub

assemblages detailed as per IS 13920:1993 and providing additionally two

pairs of cross reinforcement on joints having development length to beam

from joint face on one end. The parameters studied were effect of joint

rotation, column axial load, cross reinforcement in the joint and the

percentage of longitudinal reinforcement in the beam. They concluded that (1)

allowing free joint rotation is beneficial and leads to an increase in the

ductility and energy dissipation capacity of RC Frames. (2) the use of cross

reinforcement in the joints reduces the damage in the joint region but stiffness

of the joints leading to crack formation at the beam to column joint line

thereby reducing the ductility and energy dissipation capacity of the frame.

(3) The presence of axial load in the columns not only increases the strength

and ductility but also reduces the damage in the joint region.

Bakir (2003) conducted a parametric study of shear resisting

mechanism of exterior joints from experimental database. After doing a

multiple linear regression analysis a design equation for joint shear force was

developed considering the effect of inclined bars. The author concluded that

this equation was an improvement on existing code recommendations.

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Murty et al (2003) experimentally studied the beam column joints

in frames common in pre seismic code / gravity-designed reinforced concrete

(RC) frames buildings by changing the anchorage detailing pattern of beam

reinforcement and providing hairclip-type bends as confining reinforcement.

Exterior RC joint sub assemblages were studied with four details of

longitudinal beam bar anchorage and three details of transverse joint

reinforcement. All the specimens showed low ductility and poor energy

dissipation with excessive shear cracking of the joint core. They explained the

importance of carefully designed beam column joints for the satisfactory

performance during strong seismic shaking of RC frame buildings. The

authors found that beam reinforcement with American Concrete Institute

(ACI) Standard hook along with hairclip-type bend stirrup at joint region was

the preferred combination.

Subramanian and Rao (2003) studied the behaviour and design of

two, three and four member beam column joints and explained the past

experimental investigations in the detailing of the joints. The authors also

explained some of the incorrect design and construction practices of beam

column joints. They reported that the efficiency of joint detail improved (1)

when inclined bars are added to take up the tensile forces at the inner corners,

(2) when thickness of the adjoining members are different and (3) when the

length ratio of the two legs is changed from 1 to 2.

Uma and Meher Prasad (2003) presented a new analytical model

for beam column joints to represent the shear behaviour within the joint panel

zone by establishing shear stress - shear deformation history envelope with

salient response points, which forms the backbone for the primary curve of

the strength - deformation model for joints in non-linear dynamic analysis

computational tool. The authors also discussed the procedure to accommodate

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the effect of bond-slip of the longitudinal bars passing through the joints in

predicting the beam column joint behaviour under reversed cyclic loading

reflecting the seismic conditions.

Tsonos (2004) conducted an experimental study to find the

improvement of the earthquake resistance of RC beam-column joints with

inclined bars under the influence of P- effect. An analytical model was

developed for predicting ultimate shear strength of joints subjected to

earthquake-type loading, variable axial load and P- effect. The axial load

change and P- effect causes significant deterioration of joint element. The

author concluded that inclined bars in the joint region were effective for

reducing the unfavorable impact of P-effect and axial load change.

Jing et al (2004) conducted experiments on interior joints by

changing the beam reinforcement-detailing pattern at the joint core. Diagonal

steel bars in the form of “obtuse Z” were installed in two opposite direction of

the joint. The authors found that the non-conventional pattern provided was

suitable for joints in regions of low to moderate seismicity. Anandavalli et al (2005) carried out experiments on full scale

exterior beam column joints and assessed the seismic capacity of the existing

joints in the nuclear power plant structures which were detailed as per IS:

13920:1993. Test results revealed that there is a significant contribution due

to shear deformation on the total deformation suffered by the joint.

Hwang et al (2005) investigated the effect of joint hoops on the

shear strength of exterior beam-column joints. They found that major function

of the joint hoop is to carry shear as tension tie and to constrain the width of

tension crack. They suggested that lesser amount of joint hoops with wider

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spacing could be used without significantly affecting the performance of

joints.

Karayannis et al (2005) investigated the behaviour of exterior beam

column joints with continuous rectangular spiral reinforcement as shear

reinforcement in the joint region. The authors concluded that the usage of the

rectangular spiral reinforcement significantly improves the seismic capacity

of external beam-column connections.

Asha and Sundararajan (2006) experimentally investigated the

behaviour of exterior beam column joints with detailing as per IS 13920: 1993

under seismic conditions. They evaluated the specimens with reinforcement

provided in joint region namely, square hoop (SH), square spiral (SS), circular

hoop (CH), circular spiral (CS) and substandard detail (SD, i.e., without any

hoop) in terms of load - displacement relation, ductility, stiffness, load ratio

and cracking pattern. They finally concluded that the specimen with SS

confinement in joint region showed high strength, spindle shaped hysteretic

loop with large energy dissipation capacity, higher stiffness and highest

cumulative energy dissipation.

Alva et al (2007) tested four exterior beam - column joints under

reversed cyclic loading. The variables are the joint transverse reinforcement

and concrete compressive strength. The authors concluded that concrete

compressive strength is the major factor that governs the joint shear capacity.

They also found that increasing the number of stirrups increases the joint

shear capacity.

Sarkar et al (2007) reviewed the design procedures for the RC beam

column joints under seismic loading with a special emphasis on three

international codes of practice viz. ACI 318M-02, NZS 3101: 1995 and prEN

1998-1: 2003. It was pointed out that there is an urgent need to revise IS

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13920 suitably, in terms of (i) Minimum column width, (ii) Column/beam

flexural strength ratio, (iii) Estimation of shear demand, (iv) Assessment of

shear strength, design and detailing of shear reinforcement. It was found that

the New Zealand code gives the most conservative recommendation, followed

by Euro code. Although the ACI code, relatively less conservative, gives

many recommendations that are practical. It was strongly recommended that,

at the very least, the provisions given in ACI 318M-02, may be adopted in

IS 13920.

Tsonos (2007) studied experimentally the performance of beam-

column sub assemblages of modern structures. The test results indicate that

current design procedures could sometimes lead to excessive damage of the

joint regions.

Chalioris et al (2008) investigated the effectiveness of cross

inclined bars (X bars) as joint shear reinforcement in exterior reinforced

beam-column connections under cyclic deformations. The arrangement of

cross inclined bars consisted of the cross inclined bars alone and in

combination with common stirrups or vertical bars. The authors found

enhanced cyclic performance and improved damage mode with flexural

hinges at beam-joint interface.

Karayannis and Sirkelis (2008) investigated the behaviour of

exterior beam-column joints repaired or/ and strengthened with a combination

of epoxy resin injections and carbon-fibre-reinforced plastics. The authors

concluded that the technique of epoxy resin injections is appropriate for the

total rehabilitation of the joints seismic capacity, since no damage have been

observed at the joint area of the specimens after the repair.

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The anchorage length requirements for beam and column bars, the

provision of transverse / confining reinforcement, the role of stirrups in shear

transfer at the joint, the design and detailing of the joints are the main issues

found. From the literature reviewed it seems that the major role of ties is to

resist the shear force in the joint core. The study of using additional cross

inclined bars at the joint core shows that the inclined bars introduce an

additional new mechanism of shear transfer and diagonal cleavage fracture at

joints was avoided. In spite of the wide accumulation of test data the influence

of cross inclined bars on shear strength of joints has not been mentioned in

major international codes. Hence in the present work the confining

reinforcement are arranged in non-conventional ways by providing diagonal

bars on two faces of joints and their performance are compared with

transverse reinforcement detailing as per the current code of practices viz., IS

456 and IS 13920 incorporating the proposed revisions(Jain and Murty

2005(a) and (b)).

2.2.3 Studies on Finite Element Modelling of Concrete Structural

Elements

An extensive description of previous studies on the application of

the finite element method to the analysis of reinforced concrete structures and

the underlying theory and the application of the finite element method to the

analysis of linear and nonlinear reinforced concrete structures is presented in

excellent state-of-the art reports by the American Society of Civil Engineers

in 1982 (ASCE 1982).

Barbosa and Ribeiro (1998) investigated the possibilities of

performing nonlinear finite element analysis of reinforced concrete structures

using ANSYS concrete model. In this study, nonlinear stress-strain relations

for concrete in compression were made to reach the ultimate load and

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determine the entire load-deflection diagram. The good results attained

suggest that, in spite of the relative simplicity of the analyzed structure and of

the employed models, satisfactory prediction of the response of reinforced

concrete structures may be obtained.

Fanning (2001) constructed the finite element models of 3.0 m

ordinarily reinforced concrete beams and 9.0 m post-tensioned concrete

beams, using the Solid65 element in ANSYS. The internal reinforcement

were modelled using three dimensional spar elements with plasticity, Link8,

embedded within the solid mesh. According to the author, the models

accurately captured the nonlinear flexural response of these systems up to

failure. It was found that the optimum modelling strategy, in terms of

controlling mesh density and accurately locating the internal reinforcement

was to model the primary reinforcing in a discrete manner. The author

concluded that the dedicated smeared crack model is an appropriate numerical

model for capturing the flexural modes of failure of reinforced concrete

systems.

Damian et al (2001) studied finite element modelling of reinforced

concrete structures strengthened with Fibre Reinforce Plastic (FRP)

laminates. A three-dimensional finite element model of the bridge was

developed to examine the structural behavior before and after applying FRP

laminates. Nonlinear finite element analysis was performed using the ANSYS

program. SOLID65, LINK8, and SOLID46 elements represented concrete,

discrete reinforcing steel bars, and FRP laminates, respectively. The

comparisons between ANSYS predictions and field data were made in terms

of concrete strains. The Finite Element (FE) bridge model very well predicts

the trends in the strains versus the various truckload locations.

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Maeck and De Roeck (2002) developed a finite element model to

simulate the dynamic behaviour of cracked reinforced concrete.

Reinforcement and concrete were explicitly modelled as well as the interface

layer, where the force transfer between both materials is established. They

reported that discrete approach stands closer to physical reality than the

smeared crack approach, as it reflects the localised character of cracking.

Lowes and Altoontash (2003) developed a model to represent the

response of reinforced-concrete beam-column joints under reversed-cyclic

loading. The model was implemented as a four-node 12 degree-of-freedom

element that is appropriate for use with typical hysteretic beam-column line

elements in two-dimensional nonlinear analysis of reinforced concrete

structures (http://opensees.berkely.edu). This model represented the

mechanisms that determine the inelastic beam-column joint behaviour

through the combined action of one-dimensional shear-panel, bar-slip, and

interface-shear components. Constitutive relationships were developed to

define the load-deformation response of the joint model on the basis of

material, geometric and design parameters. Comparison of simulated and

observed response for a series of joint subassemblies with different design

details indicates that the model proposed by the authors is appropriate for

simulating response under earthquake loading.

Santhakumar et al (2004) simulated the behaviour of retrofitted

reinforced concrete (RC) shear beams. The study was carried out on the

unretrofitted RC beam designated as control beam and RC beams retrofitted

using carbon fibre reinforced plastic (CFRP) composites. The effects of

retrofitting on uncracked and precracked beams were also studied. The finite

elements adopted by ANSYS were used in this study. The authors reported

that the load deflection plots obtained from numerical study show good

agreement with the experimental plots.

29

Qi Zhang (2004) presented the application of the finite element

method for the numerical modelling of punching shear failure mode using

ANSYS. The author investigated the behaviour of slab-column connections

reinforced with Glass Fibre Reinforced Polymers (GFRPs). SOLID65 and

LINK8 elements represented concrete and reinforcing steel bars respectively.

A spring element, Link10, along the edge, was included in this study to reflect

the actual setup of slab-column connection. A quarter of the full-size slab-

column connections, with proper boundary conditions, were used in ANSYS

for modelling. Concrete constitutive relationship included the elastic-perfectly

plastic model, crack condition and crush limit. GFRP reinforcement was

defined linear elastic. Spring supports were the compression only elements.

The author reported that general behaviour of the finite element models

represented by the load-deflection plots at centre show good agreement with

the test data. However, the finite element models showed slightly more

stiffness than the test data in both the linear and nonlinear ranges.

Qi Zhang and Hussein (2004) constructed the finite element model

for GFRP-reinforced concrete slabs under static loading, short duration

impact loading including blast waves (soft impact) and falling rocky block

(hard impact). A full-size slab-column connection model, with proper

boundary conditions, was constructed using ANSYS. A static analysis was

conducted first to verify the accuracy of the model. The concrete constitutive

model included the elastic-perfectly plastic model, crack condition and crush

limit. GFRP reinforcement was defined as a linear elastic material. Good

agreement with the test data was obtained. Under blast wave impact, the

maximum amplitude of displacement and reaction force was proportional to

the overpressure. The periods of oscillated displacement were similar to the

period of the first mode in the modal analysis; however, the displacement due

to high overpressure exhibits much more disorderly than those with low

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overpressure, and the reaction force with high pressure decays much slower

than the others.

Hegger et al (2004) used a nonlinear finite element analysis

program ATENA to investigate the behaviour of exterior and interior beam-

column joints. The model was calibrated using the test results. The concrete

was modelled with nine-node isoparametric shell elements, while discrete

bars were used to model the reinforcement. Only half of the system was

modelled through the thickness such that the symmetry conditions were used.

The program ATENA assumes full bond between the reinforcement and

concrete. Thus, the actual bond behaviour was represented by the

deformations of the elements surrounding the reinforcing bars and a finer

mesh was used within the joint. Because of the expected stress concentrations,

the intersections of the beam and column compression zones were also

modelled using a finer mesh. An idealised elastic, fully plastic stress-strain

curve was used for material modelling of reinforcing bar. The authors

concluded that the most important factors affecting the shear capacity of

exterior beam-column connections are the concrete compressive strength, the

joint slenderness of the connection, the beam reinforcement (ratio, detailing

and anchorage) and the amount of stirrups inside the joint.

Wolanski (2004) investigated the use of the finite element method

for the analysis of reinforced and pre-stressed concrete beams. A mild steel

reinforced concrete beam with flexural and shear reinforcement was analysed

to failure and compared to experimental results to calibrate the parameters in

ANSYS. The deflections and stresses at the centerline along with initial and

progressive cracking of the finite element model were comparable with

experimental data obtained from a reinforced concrete beam. The failure

mechanism of a reinforced concrete beam was modelled quite well and the

failure load predicted was very close to the failure load measured during

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experimental testing. Deflections and stresses at the zero deflection point are

modelled well using a finite element package. The load applied to cause

initial cracking of the prestressed concrete beam compares well with hand

calculations. Flexural failure of the prestressed concrete beam was modelled

well using the finite element package, and the load applied at failure was very

close to hand calculated results.

Bakir and Boduroglu (2005) applied nonlinear softened truss model

for membrane elements on beam-column joints incorporating the effect of

bond slip. The authors suggested that the revised model gives very accurate

predictions of shear strength of joints.

In this section, the finite element modelling of reinforced concrete

elements using different packages, and their comparison with experimental

investigations are also reviewed. Considering the capabilities of the finite

element software package ANSYS, the same was adopted for the present

work. The finite element analysis includes modelling of the column with

different percentage of longitudinal reinforcement and exterior joints of

reinforced concrete with conventional and non-conventional reinforcement

detailing.

2.3 SUMMARY

A brief review of literature has been presented under three divisions

as, performance of columns under seismic loading, behaviour of beam -

column joints and non-conventionally detailed structural elements under

seismic loading and finite element modelling of concrete structural elements.

From the literature reviewed, it is observed that optimum percentage of

longitudinal reinforcement in columns, and usage of a better non-conventional

detailing pattern for exterior joints are to be investigated to get earthquake

resistant framed structures.