12

CHAPTER 2

LITERATURE REVIEW

2.1 GENERAL

For understanding the seismic behavior of precast concrete

structures, the study of behavior of joints is of great importance as the

connections form the weakest link in the structure. Experimental studies are

necessary as it gives the realistic response of the structure. But Finite Element

Modeling as gained importance as experimental investigations though

accurate can be time consuming and costly. The use of Finite Element

packages to model the structural elements is faster and cost effective. Hence,

many parameters can be studied by modeling the structural elements using

Finite Element packages. Several researchers worldwide have investigated the

behaviour of precast beam-column connections under earthquake loading both

experimentally and analytically. A detailed review of the literature has been

carried out to understand the behaviour of precast beam column connections

under cyclic loading. Among these the most significant literatures are briefly

summarized in this chapter. The finite element modeling related to precast

beam-column modeling related work are also reviewed.

13

2.2 OVERVIEW OF LITERATURE

2.2.1 Studies on Experimental Investigations of Precast Beam

Column joints under Seismic Loading

2.2.1.1 Wet Connections

Bull and Park (1986) investigated the performance of cast-in-place

reinforced concrete moment resisting frames incorporating precast prestressed

concrete U- beam shells subjected to seismic loading. The precast beams

acted as permanent formwork and were not connected by steel to the

cast-in-place concrete of the beam or column. Three full scale exterior beam

column subassemblies were tested. It was concluded that the two specimens

that were designed for seismic loading was satisfactory and can be used in

ductile seismic resisting frame. The third specimen that was designed without

special provisions for seismic loading was suitable for non seismic resisting

frames where the seismic loads are carried by walls and other structural

systems.

Cheok and Lew (1991) attempted to develop moment resisting

precast concrete connections in seismically active regions by testing four one-

third scale monolithic concrete beam-to-column connections. Two were

designed according to the 1985 Uniform Building Code (UBC) Seismic zone

2 criteria and two according to UBC zone 4 criteria. In addition, two precast

post-tensioned concrete beam-to-column connection similar in design to the

monolithic zone 4 specimens were tested. It was concluded that post-

tensioned precast concrete beam-column connections are strong and as ductile

as the monolithic connections, for high seismic regions. However, the per

cycle and cumulative energy dissipation characteristics, of the precast beam-

column connections could be improved.

14

Cheok and Lew (1993) tested eight 1/3-scale model precast beam to

column interior connections under cyclic loading. In general, the precast

concrete specimens had higher storey drifts at failure and higher initial

stiffness than monolithic specimens. The measured maximum concrete

strengths exceeded the calculated values and performed as well as monolithic

specimens in most cases. The cumulative energy dissipated to failure by

precast specimens was greater than that of monolithic specimens.

Castro et al (1994) investigated the seismic performance of a newly

developed precast system with the concrete members at the ends and the bar

connections are located at the middle of the precast members where the

stresses are small. Tests were conducted on nine two-thirds scale interior

beam-column joints including a monolithic specimen. The behaviour with

respect to bending strength of the beams, the shear strength and bond

deterioration at the beam column joint core and energy dissipation were

studied. It was concluded that precast concrete specimens can sustain

inelastic deformations under cyclic loading and can be ductile as cast-in-situ

specimens.

Loo and Yao (1995) conducted experimental investigations on

eighteen half scale interior connection models to evaluate their strength and

ductility properties under static and repeated loading. Eighteen half scale

models were fabricated, making six groups of two precast specimens (Type A

and Type B) and one monolithic specimen. The perspective view of the

connection Type A and Type B are shown in Figures 2.1 and 2.2 respectively.

All models had the same dimensions but different concrete strengths and / or

steel ratios. It was concluded that under both static and repeated loading, the

precast connections attained a higher flexural strength than monolithic

connections. The precast connection types under repeated loading, possessed

larger energy absorbing capacities than monolithic models.

15

Figure 2.1 Perspective View of Type A Connection (Loo and Yao, 1995)

Figure 2.2 Perspective View of Type B Connection (Loo and Yao, 1995)

16

Stone et al (1995) developed a hybrid precast system, which was

designed to have the same flexural strength as a conventionally reinforced

system with the same beam size. The hybrid system was self-centering and

displayed essentially no residual drift. The hybrid system had a very large

drift capacity. The hybrid system dissipated more energy per cycle than the

conventional system for upto 1.5 percent drift. The concrete in the hybrid

suffered negligible damage, even at drifts up to 6 percent.

Restrepo et al (1995) conducted tests on six assemblages of

perimeter frames under quasi static cyclic reversed loading. Four units were

connected at the beam midspan and two units were connected at the beam-to-

column joint region. Units 1, 2 and 3 had connections between precast

concrete elements at mid span of beams consisting of overlapping hooks or

straight splices in cast-in-situ concrete showed excellent performance under

cyclic loading. Unit 4 had strong regions at the ends of the precast beams and

a diagonally reinforced cast-in-place connection region at the beam midspan,

with diagonal bars connected by bolted steel plates welded to the bars. The

test of this unit showed limited ductility response due to the bursting forces

that had not been considered in the initial design. It showed full ductility after

the damaged region was repaired by adding transverse reinforcement and

bearing rods at the bend of the diagonal reinforcement. Unit 5 had the precast

concrete placed between the columns and a cast-in-place concrete joint core

between the ends. Unit 6 had precast concrete beam element passing the

column and the longitudinal column bars grouted in vertical corrugated ducts

in beam-to-column joint region. Both Unit 4 and 5 showed excellent

performance in terms of strength and ductility.

Preistly and MacRae (1996) tested two ungrouted post-tensioned

precast concrete beam to column sub-assemblages under cyclic reversals of

inelastic displacements. One sub-assemblage represented an exterior joint

17

while the other was an interior joint of a one-way prestressed concrete frame.

The test specimens were designed with gradually reduced beam and joint

shear reinforcement compared with equivalent monolithic joints, but with

special spiral confinement of the beam plastic hinge regions. Both

subassemblages performed well, with only minor damage upto drift ratios of 3

percent. It was concluded that satisfactory seismic performance can be

expected from well designed ungrouted precast, post-tensioned concrete

frames.

Stanton et al (1997) studied a precast framing system with precast

elements connected by unbounded post –tensioning steel and bonded

reinforcing bars. The behavior was compared with a pair of conventional

monolithic; cast-in-place frames. It was concluded that a hybrid system can be

designed to have the same flexural strength as a conventionally reinforced

system with members of the same size. The shear resistance of the hybrid

system was superior to that of a conventionally reinforced frame. The hybrid

system was self centering and displayed no residual drift and had very large

drift capacity. It dissipated more energy per cycle than conventionally

reinforced frame up to a drift of 1.5 percent. It was also observed that damage

in the hybrid system was minimal.

Elliot et al (1998) studied the behavior of structural beam to column

connections in precast concrete skeletal and portal structures. The types of

connections adopted for beam to column testing is shown in Figure 2.3. In

most of the connections, ductile modes of failure were observed. The authors

concluded that the frame stability can be enhanced by utilizing the strength

and stiffness of precast concrete beam to column connections in a semi rigid

frame analysis. This method was found for internal connections but not for

edge connections.

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Figure 2.3 Types of Connections Used in Precast Beam to Column

Tests (a) Billet (b) Welded Plate ( Elliot et al, 1998)

Vasconez et al (1998) developed a high energy absorbing joint for

precast concrete structures in seismic zones. The material of the joint was a

High Performance Fibre Reinforced Cement Composite (HPFRC) matrix. The

FRC based connection design was successful in making the connection act as

a plastic hinge by spreading the yielding from centre to the interfaces. The

steel fibres used in cast-in-place connection lead to an increase in strength,

energy capacity, stiffness, displacement and rotation capacities. There was a

decrease in damage and shear deformations. Steel fibres were found to be

more effective in improving the response of the joint than polyvinyl alcohol

fibres. It was also observed that reducing the confinement provision of the

ACI by 50 percent in steel fibre reinforced connections resulted in improved

behaviour compared to normal RC specimens with full confinement.

19

Alcocer et al (2002) conducted experiments on two full scale beam-

column precast concrete joints under uni-directional and bi-directional

loading that simulated earthquake type loadings. The most relevant feature of

the connection is that conventional mild steel reinforcing bars or prestressing

strands, rather than welding or special bolts, were used to achieve beam

continuity. Specimen design followed the strong-column–weak-beam

concept. Beam reinforcement was purposely designed and detailed to develop

hinges at the joint faces and to impose large inelastic shear force demands

into the joint. As expected, the joint controlled the specimen failure. In

general, the performance of both beams-to-column connections was

satisfactory. Joint strength was 80 percent of that expected for monolithic

reinforced concrete construction. Specimen behavior was ductile due to hoop

yielding and bar pullout, while strength was nearly constant up to drifts of 3.5

percent.

Khaloo and Parastesh (2003) studied four types 2/5 scale model

precast connection and one monolithic concrete beam-column connections. In

the precast specimen, the load was transferred in the spliced reinforcement by

a combination of lap splicing and end anchorage of bars. The end portions of

the beams were designed in the form of a channel that sat on the column

bearing area and carried the shear stresses due to the slab. Then the

connection length region is grouted to form the monolithic connection. The

main variables of this study were the level of axial load of the column,

spacing of beam stirrup in the connection length region, gravity load on the

beam and use of steel fibre in grout of the connection region. The authors

concluded that all the specimens were capable of providing strength, ductility,

and storey drift and energy dissipation comparable with that of reference

specimen. A reduction in the axial load, the use of steel fibre region in grout

of the connection length region significantly increased the ductility, storey

drift, strength and energy absorption of the precast connection. The presence

20

of concentrated gravity loads on beams increased the strength, ductility and

storey drift as compared with reference specimen.

Khaloo and Parastesh (2003) carried out an experimental study to

investigate a simple moment-resisting precast concrete beam-column

connection under cyclic inelastic loading. Four precast beam-column

connections and one monolithic connection were tested. The variables

examined were the connection length of reinforcements and presence of

transverse bars at mid height of connection. It was concluded that the

reduction in connection length reduced strength, ductility and energy

absorption. The failure mode changed toward partial separation and slippage

of bond between the precast concrete beam and the cast-in-place grout. The

presence of transverse bars in the connection length enhanced the seismic

behavior of the precast connection system.

Blandon and Rodriguez (2005) conducted experimental study of a

half-scale two storey precast concrete structure built with a dual structural

system (combination of structural walls and frames). A typical feature in

some of the beam to column connections in the test structure was that the

beam bottom longitudinal bars in the joint region were poorly anchored. The

test structure was subjected to simulated seismic loading until the structure

reached failure. The responses of the precast structural elements and their

connections during testing, including beam to column connections, column to

foundation connections and the diaphragms were observed. A pull-out was

observed in the beam bottom bars. Due to this failure pattern, the use of dual

structural systems is a promising solution for the construction of seismic

resisting precast concrete building. In a dual system, the deformation demands

in the beam to column connections of the frame subsystem can be

significantly reduced when compared with the case the case of a building built

21

with frames only system for resisting lateral loads. As a result, the frame

system could be designed for limited ductility.

Joshi et al (2005) performed experiments on two precast and an

equivalent monolithic exterior beam-column joint sub-assemblage specimen.

The schemes for the anchorage of beam bars were different in the two set of

specimens. In the first type of detailing, a single U-bar is used as top and

bottom beam reinforcements as shown in Figure 2.4. The other type of

detailing conforms to the Indian Standard Code for ductile detailing of

reinforced concrete sections as shown in Figure 2.5. In precast specimens, the

connectivity of reinforcement bars between beam and column was achieved

by welding the exposed bars of the components in the point region. Under

displacement–controlled pseudo-static loading, the monolithic specimen with

beam bars anchored into the column performed better than the monolithic

specimen with continuous U-bars as beam reinforcement. The cumulative

energy dissipation for the monolithic specimen with continuous U-bar

reinforcement was more than the other monolithic specimen. The precast

specimens with beam bars anchored into the column performed better than the

corresponding monolithic beam. The precast specimen with continuous U-

bars as beam reinforcement performed worse than the corresponding

monolithic specimen, due to high average strength and stiffness deterioration.

Of the two precast specimens, the one with the beam bars anchored into the

column with the welding of the lap splices performed better than the one with

continuous U-bars as beam reinforcement.

22

Figure 2.4 Details of the Reinforcement of the First Specimen

(Joshi et al 2005)

Figure 2.5 Details of the Reinforcement of the Second Specimen (Joshi

et al 2005)

Korkmaz and Tankut (2005) investigated the seismic behaviour of

the connection detail proposed by an industrial partner and the specimens

with improved details, in order to develop a moment resisting precast concrete

beam to beam connection. In this study, six beam–beam connection

23

subassemblies were tested under reversed cyclic loading simulating severe

earthquake action. The first specimen was a monolithic specimen used as a

reference specimen and tested to define the reference behaviour. The second

specimen was a precast specimen, which was detailed by a company

specializing in precast concrete production. The remaining specimens were

modified according to the results of the formerly tested specimens. All of the

specimens were identical in dimensions. All test specimens were 1/2.5 scaled

models of the improved connection details used in the highly critical

earthquake zones. The behavior of the precast members was compared with

that of the reference one and with the others. Though the original connection

did not perform well, the modified precast connection showed satisfactory

performance and was recommended for use in seismic zones.

Rodriguez and Blandon (2005) tested a half-scale two-storey

precast concrete building incorporating a dual system representing a parking

structure in Mexico City under simulated cyclic loading. The observed global

response showed that showed the importance of the reinforced concrete wall

participation in the response. This participation led to an important reduction

in the deformation demands in the critical section of the precast frame

members. The displacement ductility demand was found to be higher in the

wall sub-system than in the frame sub-system of the dual system. Some of the

beam to column details that had substandard reinforcing details had poor

deformation capacity. But the observed and calculated deformation demands

in these connections were not critical since they were significantly reduced by

the wall interaction.

Khoo et al (2006) tested two full scale precast concrete sub-frames

in which the connection are constructed on the beam span and kept away from

the column faces so as to avoid coinciding with the plastic hinge regions

during seismic excitations. The variable examined was the connection detail.

24

One connection was composed of overlapping 90° hooks. All the beams

longitudinal bars were spliced using such hooks and the overlaps started at

about ‘1.8d’ from the column face where‘d’ is the effective beam depth. Two

sets of stirrups spaced at 120mm were installed at the overlapping hooks. The

other connection consisted of overlapping 180° hooks starting at ‘1.75 d’ from

the column face. The stirrups were similar to that of the first connection. It

was concluded that the precast concrete frames were capable of matching the

overall performance of the monolithic connections and thereby providing

moment resisting behavior.

Chun et al (2007) assessed the effectiveness of headed bars

terminating in exterior beam-column joints. Nine inter storey and five roof-

level joint specimens were tested under reversed cyclic loading. The primary

test parameters were the anchorage type, size and arrangement of the beam

bars and the heads and the detailing provided for roof joints. The test results

indicated that hysteretic behaviour of exterior joints constructed with headed

bars was similar or superior to joints constructed and tested with hooked bars.

Head size with a net area of three to four times the bar area was sufficient to

anchor the beam reinforcement effectively within the exterior beam column

joint. It was also concluded that in addition to providing vertical U-bars at

roof joints, heads on column bars should extend beyond the beam top bars to

provide improved behavior.

Nishiyama and Wei (2007) conducted cyclic load tests on seven

precast, prestressed concrete beam to column joint assemblages. The

experimental parameters studied were location of tendon anchorage,

prestressing steel content in the beam section, concrete compressive strength

and to investigate the shear strength of the beam to column joint. It was

concluded that maximum load capacities for test units with inside anchorages

were 9% to 13% less than specimens with anchorage outside the joint core.

25

Joint shear deformation was less in the test units with outside anchorage than

in test units with inside anchorage. Damage to the beam to column joint

assemblages and the decay of the maximum capacities of the test units were

due not only to joint shear failure but also to anchorage deterioration of the

prestressing steel.

Xue and Yang (2010) studied the behavior of precast concrete

connections in a moment resisting frame under cyclic loading. The

connections studied were exterior connection, interior connection, T

connection and knee connection. It was observed that Knee connections were

less effective when compared to other connections. All the connections

exhibited strong column-weak beam failure mechanism. It was concluded that

all the connections performed satisfactorily in seismic conditions with respect

to strength, ductility and energy dissipation capacity.

2.2.1.2 Dry Connections

Dolan and Pessiki (1984) demonstrated that the behaviour

characteristics of a welded monotonically loaded precast concrete connection

can be simulated using models. Tests of one-quarter scale models of a single

beam to column connection were conducted. Good agreement was found

between the strength and the normalized moment rotation response of the

model and the prototype. The effects of weld quality and design eccentricities

had similar consequences in both model and prototype.

Ochs and Ehsani (1993) tested five precast beam to column

subassemblies under simulated earthquake type loading. The columns

included steel plates or angles embedded in the columns and beams which

facilitated field erection. Various connection details were studied. One

connection was a monolithic specimen and four were precast specimens.

Specimen P1 and PR1 consisted of two fabricated T-sections embedded in the

26

column. Each T-section had three holes to allow for the passing of the column

longitudinal bars. Four No.7 standard 90 degree hooks were welded to the T-

sections to provide adequate anchorage of the plate within the joint. The beam

end included two large single angles to which longitudinal reinforcement was

welded. The beam angles were welded to column section with fillet welds

over full width of the beam. Specimen PR1 differed from P1, as additional

intermediate reinforcement in the form of U-shaped No.6 bars was used. For

specimens P2 and PR2 the connection was similar to that of specimen P1 and

PR1. The only change made was that on the lower side a straight plate which

extended from the column face was utilized instead of a T-section. It was

concluded that precast concrete specimens performed similarly to that of

monolithically cast concrete connection. The precast column was strong

enough to force a plastic hinge away from the column face. The critical part

of the precast connections was the welded beam bars as they initiated the

failure of specimens. It was also observed that the intermediate reinforcing

bars in the precast concrete specimens had less effect on the capacity of the

specimen early in the test, however as the test progressed, these bars

contributed to the specimen capacity.

Ersoy and Tankut (1993) tested precast concrete beams with dry

joints designed for multistory buildings located in a seismic area under

reversed cyclic loading. The original beam consisted of two steel plates one at

top, the other at the bottom, welded to the anchored steel plates in the column

bracket and the beam. The design was later revised by adding side plates. The

main variables were presence of side plates and joint width. The authors

concluded that the joint width is an important parameter and therefore

tolerances should be checked carefully during erection. The strength, stiffness

and energy dissipation of the member with side plates were comparable to

those of monolithic member.

27

Englekirk (1995) developed an energy absorbing ductile connector

that can be to construct a seismic moment resisting frame of precast concrete

components. The ductile connector was a ductile rod which was the yielding

element. The function of the ductile rod was to accommodate post yield

system deformations. Two types of ductile rods were used (i) milled and (ii)

cast. It was suggested that the rod bearing transfer mechanism could be

improved by increasing the bearing area and adding a confining plate at the

face of the column. It was observed that the strain hardening characteristics of

the material used in the casting were better than that used in milled rod.

Priestley et al (1999) tested a large-scale five-storey precast

concrete building constructed to 60 percent scale under simulated seismic

loading. It was concluded that behaviour of the structure was extremely

satisfactory, with only minimal damage in the shear wall direction, and no

significant strength loss in the frame direction, though it was tested to drift

levels upto 4.5 %, more than 100 percent higher than the design drift level.

The different precast connections adopted are shown in Figure 2.6(a) to (d).

Spieth et al (2004) presented the results of an experimental study

together with companion of analytical modeling of two distinctly different

precast concrete beam to column connections. The first consists of precast

concrete beams with armored end connections connected directly to the

column, while the second is a connection offset away from the column at

about the 1/8 point within the span. In both cases, the beams were connected

via un-bonded post-tensioned high strength prestressing thread bars to a

prestressed concrete column. Lateral loading tests were conducted up to ±4%

drift with and without supplementary mechanical energy dissipators. The

results show that the non-linear moment-rotation performance can be

accurately modeled. From this study it was concluded, that with appropriate

28

armouring of the precast members, damage can be avoided to the connection,

while the entire structure is self-centered following an earthquake.

a) Hybrid Post Tensioned Connection

b) Pretensioned Connection

Figure 2.6 Different Precast Connections Adopted (Priestley et al 1999)

29

c) TCY-Gap Connection

d) TCY Connection

Figure 2.6 (Continued)

30

Ousalem et al (2009) studied the seismic performance of an

assembled precast high strength concrete beam with a simple and innovative

lap splice connection in high rise buildings. The flexibility variation along the

lap splice connection of the beam, which involves a reduced profile, was also

investigated. The lap splice connection, located at beam mid span was

connected by transverse bolts. The authors concluded that the beams under

reversed cyclic loading proved to be ductile and failure occurred outside the

lap splice connection similar to monolithic ordinary reinforced concrete

beams. The flexural stiffness varied along the lap splice connection of the

assembled beam and declined at the transition section of the reduced profile

under large loading. The reduction in the effective flexural stiffness at the

location of the transition section did not jeopardize the performance of the

assembled precast beam within the design limits.

Ousalem et al (2009) investigated the seismic performance of two

precast high strength reinforced concrete exterior beam-column joints

subjected to varying high axial levels. High grade steel bars were used as

reinforcement. Splice grout-sleeves and mechanical anchors were used in

columns and beams respectively. The maximum axial tension level in the

columns was 90% of the yield strength of the main bars. It was concluded that

the tested specimens under high axial tension loads performed well and

showed stable response with the lateral storey drift angle of 3%, exhibited

appropriate response characteristics, lateral force resistance and energy

absorption capacity. The bond deterioration of the beam main bars in joints

subjected to varying axial load was higher under axial tension load than under

axial compression load. The mechanical anchors were very effective and no

sign of concrete crushing was observed within lateral storey drift of 2%.

Kaplan et al (2009) tested a typical pin connected precast concrete

frames strengthened with external shear walls under reversed cyclic imposed

31

drift at a constant rate. The experiments showed that the structure with shear

walls showed increased lateral stiffness and lateral load resisting capacity and

provided an effective diaphragm for the structure.

2.2.1.3 Hybrid Connections

Dolan et al (1987) tested a two bay by two storey moment resisting

frame which included several moment resisting connections. The various

types of connections adopted were (i) beam to column connection using

welded plates for the positive and negative connections (ii) beam to column

connections using continuous reinforcing through the column and cast-in-

place topping and positive moment connection using welded plates (iii)

connection using bolts (iv) a precast beam constructed into a cast-in-place

column (v) a precast beam post-tensioned to a column (vi) a precast beam

installed on a grouted dowel (vii) a precast beam made continuous using

DYWIDAG threaded bars screwed into couplers cast in the column. It was

concluded that all the connections developed strengths and were considered

strong enough for their intended use. The bolted connection was found to

exhibit energy dissipation similar to monolithic connections.

Ertas et al (2006) presented the test results of four types of ductile,

moment-resisting precast concrete frame connections and one monolithic

concrete connection, all designed for use in high seismic zones. The

performances of the precast concrete connections subject to displacement

controlled reversed cyclic loading were compared with that of the monolithic

connection. The precast concrete connections tested were subdivided into

three groups namely cast-in-place, composite with welding, and bolted. The

cast-in-place connections were located in either the beam or the column of the

precast concrete subassemblies. The composite connection is a common detail

used in the Turkish precast concrete industry. Two bolted specimens without

corbels were also tested. Through these tests, the responses of different

32

connection types under the same loading pattern and test configuration were

compared. Comparisons of performance parameters, such as energy

dissipation and ease of fabrication, revealed that the modified bolted

connections may be suitable for use in high seismic zones.

Ozden and Ertas (2007) presented the test results on post-tensioned,

precast concrete moment-resisting, beam-column connections containing

different mild steel reinforcement contents. In the experimental program, five

hybrid connections were tested under displacement controlled reversed cyclic

loading. Each hybrid connection was compared with the test result of the

reference monolithic subassembly in terms of connection strength, stiffness

degradation, energy dissipation, and permanent displacement. The response of

post tensioned, precast concrete hybrid connections approached that of the

monolithic subassembly as the mild steel reinforcement content increased.

Connection capacities were well predicted by the joint gap opening approach.

The design assumptions of hybrid connections are best satisfied with a 30%

mild steel reinforcement contribution to the connection’s flexural capacity.

Kulkarni and Li (2009) conducted experimental and finite element

method investigation of hybrid steel-concrete beam-column joints subjected

to seismic loading. Four prototype specimens of beam-column joints with

slabs were tested under reversed cyclic loading. Two were cast-in-place

concrete specimens, and two were precast concrete specimens constructed

with hybrid connections. The rectangular column simulated two different

structural combinations, one was strong column-weak beam and another was

weak columns-strong beam. Both were tested to evaluate how the connection

details of the different systems influenced the strength of the joints. It was

observed that the precast concrete achieve consistent hysteretic loops

throughout the cyclic loading and behaved well compared with cast-in-place

connections. The top reinforcement of precast concrete specimens was

stressed to a higher level than cast-in-place concrete top reinforcement during

33

seismic loading, but a lower state of stress level can be achieved in precast

concrete construction with an increase in plate thickness of the hybrid

connection. The hybrid connection with a strong column-weak beam system,

an axial load between zero and 0.2fc´ Ag enhances performance. For the

connections with a weak column-strong beam system, the axial load ranging

from zero to 0.1 fc´Ag, where fc´ and Ag are cylinder compressive strength and

gross area of column respectively. The increase in plate thickness, the hybrid

connection was capable of carrying the required storey shears and the energy

dissipation of the joint increases. The Finite Element analysis and

experimental results were found to be good agreement.

Li et al (2009) conducted experimental and analytical investigations

of hybrid-steel concrete connections. Four full scale specimens, included one

cast-in-place and three precast specimen were tested under cyclic load

reversals. The critical parameters influencing the joint’s behavior such as

continuation of beam bottom reinforcement, column axial load, the size and

embedded length of the angle sections are varied and their effects including

possible implications on code specifications are discussed. Experimental

observations showed that precast specimens under cyclic loading experienced

no abrupt damage within the joint core region and therefore, the final failure

was not controlled by the capacity of the joint core. The precast specimen’s

performance was good at exhibiting adequate ductile behavior under seismic

loading and it also agreed well with cast-in-place specimen. Embedment of

the steel sections in the joint greatly enhanced the strength of the joint core

with the specimens carrying storey shears up to a ductility factor of 3.5. Beam

to column connection of precast specimens was sufficiently stiff and ductile

and effectively resisted both shear forces and bending moments. Joint core

regions of the precast specimens were adequately confined by the

incorporated steel sections, providing significantly high degree of restraint

34

and reducing the joint core deformation under reversed cyclic loading. The

Finite Element analysis results compared well with the experimental results.

Thinh et al (2009) tested a new type of precast unbounded post-

tensioned exterior beam-column joint of a long span frame under the

simultaneous action of gravity load and cyclic load. Four specimens were

tested. The first specimen was designed with shear bracket that resisted the

shear force induced by designed gravity load. The second specimen was

designed without shear bracket. The third specimen was designed with shear

bracket to resist shear force induced by gravity load which is 1.5 times of that

of the first specimen. The fourth specimen was designed similar to the first

specimen, but had the slab and spandrel beam. It was concluded that specimen

with shear bracket exhibited good hysteretic behavior with small residual

deformation. Specimen without shear bracket experienced large beam slip.

Excessive crushing of the slab together with fracture of slab reinforcement

caused deterioration of strength with large residual deformation. It was

proposed that the design of shear bracket and inverted U-shaped steel box

should be modified to prevent the deformation of these parts under the action

of very large gravity load and cyclic load.

2.2.2 Studies on Analytical Investigations of Precast Elements

2.2.2.1 Beam Elements

Faherty (1972) studied a simply supported reinforced and

prestressed concrete beam loaded with two symmetrically placed concentrated

transverse loads using the finite element method of analysis. The nonlinear

analysis considered the concrete nonlinear properties, the linear bond slip

relation with a destruction of the bond between the steel and concrete, and

bilinear steel properties. The transverse loading was incrementally applied

whereas the dead load, release of the prestressing force, the elastic prestress

35

loss, the time dependent prestress loss, and the loss of tensile stress in the

concrete as a result of concrete rupture were applied as single loading

increments. The results for the reinforced and prestressed beam showed that

deflections computed using the finite element model compared well with the

experimental results.

Barbosa and Ribeiro (1998) analysed a simply supported reinforced

concrete beam subjected to uniformly distributed load using finite element

package ANSYS. Due to transversal and longitudinal symmetry, a quarter of

the beam was modeled. Reinforcement was modeled as discrete reinforcement

and smeared reinforcement. Each type had been analyzed four times with four

different material models. Linear elastic behavior for both concrete and steel

was adopted for the first model, the former capable of cracking in tension and

crushing in compression. In the second model, crushing of compressed

concrete was disabled and an elastic perfectly plastic model based on

Drucker-Prager yield criterion had been used instead. A multilinear uniaxial

stress-strain relation, simulating a parabolic curve represented concrete

compressive behavior in the third model. Finally, crushing had been

associated to the multilinear stress-strain curve in order to compose the fourth

compression model for concrete. It was concluded that satisfactory prediction

of the response of reinforced concrete structures were obtained for all the

models.

Fanning (2001) conducted nonlinear analysis of reinforced and

post-tensioned concrete T-beams using finite element package ANSYS.

Quarter and half models were modeled for reinforced and post-tensioned

concrete T-beams respectively. SOLID65 element and LINK8 element were

used to model concrete and internal reinforcement. Discrete reinforcement

was favoured over the alternative smeared stiffness capability as it allowed

the reinforcement to be precisely located whilst remaining a relatively coarse

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mesh for the surrounding concrete medium. For formulating the model for

post-tensioned beam LINK8 element was used for the post-tensioning cables,

with the remaining internal reinforcing bar modeled using distributed smeared

stiffness approach. The numerical model predicted well the nonlinear load-

deflection response of the beams upto failure. The finite element model

predicted the crack pattern similar to the test beam. It was concluded that for

capturing the flexural modes of failure of reinforced concrete systems, the

smeared crack model was an approximate numerical model.

Kachlakev et al (2001) studied the behavior of four concrete beam

members with externally bonded Carbon Fiber Reinforced Polymer (CFRP)

fabric using ANSYS. SOLID65 element, LINK8 element, SOLID46 element

and SOLID45 element were used to model concrete, steel reinforcement, FRP

composites and steel plates respectively. Symmetry allowed one quarter of

the beam to be modeled. It was concluded that in the load strain plots, the

strain in the linear stage from the FE analysis correlated well with those from

the experimental data. The yield load of steel from FE analysis was 14%

lower than that of the test results. In the linear range, the load deflection plot

was stiffer when compared to the experimental results. The first cracking

loads obtained form ANSYS was higher than the test data. ANSYS

underestimated the ultimate load of the beams by 5% to 24%.

Hu et al (2004) conducted numerical analysis using ABAQUS

finite element program to predict the ultimate load carrying capacity of

rectangular reinforced concrete beams strengthened by fibre reinforced

plastics applied at the bottom or on both sides of the beams. The steel

reinforcing bars, plain concrete and fibre reinforced plastics was simulated

using appropriate constitutive models. The influences of fibre orientation,

beam length and reinforcement ratios on the ultimate strength of the beams

were investigated. The behaviors of the beams with high and low

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reinforcement ratios and strengthened with FRP at the bottom are not

influenced by the length of the beam significantly. The beams with high

reinforcement ratios and strengthened with FRP at the bottom had more

cracks at the central region than those with low reinforcement ratios. With

the same FRP layers, the ultimate strengths and the numbers of cracks of the

beams strengthened by FRP on both sides were much less than those

strengthened by FRP at the bottom.

Santhakumar et al (2004) conducted numerical study to simulate

the behavior of retrofitted reinforced concrete shear beams. The study was

carried out on the unretrofitted RC beam designated as control beam and RC

retrofitted using carbon fibre reinforced plastic (CFRP) composites with ±45º

and 90º fibre orientation. The finite elements adopted by ANSYS were used

for this study. A quarter of the full beam was modeled by taking advantage of

the symmetry of the beam and loadings. When compared with the

experimental models showed 8% increase in the ultimate load for control

beam and uncracked retrofitted beam and 8% decrease in the ultimate load for

precracked retrofitted beam. At the ultimate stage all the numerical models

show less deflection especially the precracked retrofitted beam showed 31%

less deflection.

Wolanski (2004) studied the flexural behavior of reinforced and

prestressed concrete beams using finite element analysis ANSYS. SOLID65

element and LINK8 were used to model the concrete and whereas SOLID45

was used to simulate the steel plate for loading area and supports. The

SOLID65 element required both linear isotropic and multilinear isotropic

material properties to properly model concrete. The multilinear isotropic

material used the Von Mises failure criteria along with William Warnke

model to define the failure of concrete. Deflections and stresses at the

centerline along with initial and progressive cracking of the finite element

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model compared well with the experimental data. The failure mechanism of

the reinforced and prestressed concrete beam was modeled well and the

failure load was close to the experimental results.

Ibrahim and Mubarak (2009) studied the behavior of externally

prestressed continuous concrete beams subjected to symmetrical static

loading. A numerical model based on the finite element method using

ANSYS. The elements SOLID65 and LINK8 were used to model concrete

and steel reinforcement. The prestress in the finite element was given as an

initial strain in the link element. SOLID45 element was used for steel plates at

the support and loading location to avoid stress concentration problems. The

anchorage zone was modeled as steel plate which was connected to the tendon

element. The finite element analysis showed good agreement with the

experimental results throughout the entire range of behavior and failure mode.

Ibrahim and Mahmood (2009) presented an analysis model for

reinforced concrete beams externally reinforced with fibre reinforced polymer

(FRP) laminates using finite elements method adopted by ANSYS. The finite

element models are developed using a smeared cracking approach for

concrete and three dimensional layered elements for the FRP composites. The

results obtained from the ANSYS finite element analysis were compared with

the experimental data. The comparisons were made for load-deflection curves

at mid-span; and failure load. The results from finite element analysis were

calculated at the same location as the experimental test of the beams. The

accuracy of the finite element models is assessed by comparison with the

experimental results, which are to be in good agreement. The load-deflection

curves from the finite element analysis agree well with the experimental

results in the linear range, but the finite elements results are slightly stiffer

than that from the experimental results. The failure load obtained from the

numerical solution for all beams is slightly smaller than experimental load.

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The maximum difference in ultimate loads for all cases is 7.8%. The final

loads for the finite element models are the last applied load step before the

solution diverges due to numerous cracks and large deflections.

Chansawat et al (2009) developed three-dimensional finite element

model to simulate the behavior of full scale reinforced concrete beams

strengthened with glass and carbon fibre reinforced polymer sheets. It

consisted of an unstrengthened control beam, a flexural strengthened beam,

shear strengthened beam and shear and flexural strengthened beam. For

concrete eight node isoparametric elements with a smeared crack approach

was used and FRP composites were modeled as three dimensional layered

elements. Analysis results were compared with data obtained from full-scale

beam tests through the linear and nonlinear ranges up to failure. It was

concluded that FE models could identify qualitatively trends observed in the

structural behavior of the full-scale beams. The predicted crack initiation

patterns resembled the failure modes observed for the full-scale tests.

Buyukkaragoz (2010) studied the strengthening of the beam by

bonding with prefabricated plate and a control beam. ANSYS finite element

program was used for modeling. SOLID65 element was used for the concrete

model in the reinforced concrete beam model. In this study Hognestad

concrete was used due to lack of confinement for the concretes. The stress-

strain obtained from the model was used in the definition of the multi-linear

isotropic material. In addition, the William Warnke failure model was used in

the definition of concrete. The steel was defined as bilinear isotropic based on

Von Mises yielding criteria. LINK8 element was used to define reinforcement

in ANSYS. In the model, epoxy was used to bond the prefabricated plate to

the beam. SOLID46 element was used for epoxy in the program. SOLID46 is

layered version of the 8-node structural solid (SOLID45) designed to model

layered thick shells or solids. Reinforcement and stirrups were modeled with

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discrete method by constituting element definition from mesh nodes

constructing the concrete. The results obtained from ANSYS finite element

program were similar to the experimental behavior of the beams.

Obaidat et al (2010) presented a finite element analysis of eight RC

beams retrofitted with Carbon Fibre Reinforced Polymer (CFRP). The

commercial numerical analysis tool ABAQUS was used and different

material models were evaluated. Linear elastic isotropic models were used for

CFRP and a perfect bond model and a cohesive bond model was used for the

concrete-CFRP interface. A plastic damage model was used for the concrete.

The finite element analysis results showed good agreement with the

experimental data regarding load-displacement response, crack pattern and

debonding failure mode when cohesive bond model was used. The perfect

bond model failed to capture the softening behavior of beams. There was no

significant difference between the elastic isotropic and orthotropic models for

the CFRP.

2.2.2.2 Beam Column Joints

Marcakis and Mitchell (1980) attempted to develop a rational

analytical model capable of predicting the ultimate capacity of a variety of

embedded steel member precast connections. The development of this

analytical model is based on the results of a series of experiments in which the

different variables like effect of column axial load, effect of additional welded

reinforcement, effect of shape of embedded member were studied. A series of

experiments indicated that the analytical model conservatively predicted the

capacity of connections with axial load levels less than 75 percent of the pure

axial load capacity of the column. All the specimens tested with low axial

loads failed in the concrete and exhibited ductile behaviour. For higher levels

of axial load a significant decrease in the ductility was observed. If larger

ductility is required, the connection can be designed such that failure takes

41

place in the embedded steel member. The analytical model has been used to

prepare a series of non-dimensionalized design curves for connections with or

without additional welded reinforcement.

Camarena (2006) conducted the finite element analysis of interior

precast prestressed beam column connection under seismic loading using

finite element package DIANA. The behavior of concrete was modeled with

total strain based constitutive model. A bilinear stress-strain relationship that

consisted of a elastic part, a yield part and a part with hardening was used for

ordinary reinforcement. For the reinforcement an elastic plastic model was

used both in tension and compression with Von Mises yield criterion. The

rubber pad was modeled with a linear elastic stress strain relation with a

Poisson’s ratio close to 0.5. For the mortar a total strain model was used

similar to one for concrete. The author concluded that the structural response

of the ductile beam-column connection of jointed systems under imposed

lateral loads was satisfactory. Damage to the beams was minimal; most of the

cracks were limited to the regions close to the interface and the concrete

cover. There was no loss of prestress in the secondary tendons. The structure

achieved a drift of 4% which was higher than the drift of 2 to 3% that is

normally assumed in the design of structures.

Mostofinejad and Talaeitaba (2006) proposed a finite element

modeling for nonlinear analysis of an exterior reinforced concrete joint

covered with fibre reinforced plastics (FRP) overlays. The model consisted of

the effects of anchorage slip and anchorage extension of the steel

reinforcement in the connection zone. ANSYS finite element package was

used for the nonlinear analysis. For modeling concrete, longitudinal

reinforcement and FRP composites, the elements used were SOLID65,

LINK8 and SOLID45 were used. The transverse reinforcement was modeled

as smeared reinforcement. The anchorage slip and the anchorage extension of

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the reinforcement were modeled using nonlinear spring model. The exterior

beam-column joints, the end supports of the top and bottom columns were

fixed and monotonic concentrated load was applied to the tip of the beam.

Finer meshes were chosen for the connection region due to the probability of

stress concentration and more cracking. To perform the nonlinear analysis, the

load was applied step by step and the modified Newton Raphson method was

used for the solution. The effects of debonding of FRP laminates in FE

analysis were eliminated by limiting the maximum strain in FRP laminates.

The results of the numerical analysis were found to compare well with the

experimental results.

Kulkarni et al (2008) carried out a non-linear finite element

analysis of hybrid-steel concrete connections. The critical parameters

influencing the joint behavior, such as axial load on column, the connection

plate thickness and continuation of beam bottom reinforcement were varied

and their effects, especially implication on code specifications were studied.

In the study, the specimens were analysed using DIANA software. Two

dimensional plane stress elements were used to simulate the concrete and

steel plates, while reinforcing bars were modeled as truss elements. In

material modeling, the concrete models were based on nonlinear fracture

mechanics to account for cracking, and plasticity models were used for the

concrete in compression and steel reinforcement. Comparison with the

experimental results indicated that the finite element models used were

suitable. The failure modes, ultimate ductility capacities, deformations and

cracking patterns correlated well with experimental results.

Pirmoz and Danesh (2009) studied the effect of the seat angle

stiffness on moment-rotation response of the bolted top-seat angle

connections using finite element method ANSYS. All components of the

connection such as the beam, column, angles and bolts head are modelled

43

using eight noded SOLID45 elements and bolt shanks are modelled using

SOLID64 elements, which can apply a thermal gradient on it to pretension the

bolts. The effect of interactions between components, such as slippage of

bolts and frictional forces, are modelled using surface contact algorithm.

ANSYS can model contact problems using contact pair elements CONTA174

and TARGE170, which pair together in such a way that no penetration occurs

during the loading process. Thus the effect of adjacent surface interactions,

including angle-beam flange, angle/beam flange-bolt head/nut, bolt hole-bolt

shank and effect of friction, are modelled using the mentioned contact

elements. Bolt heads and nuts were modelled as hexagons, and were similar to

their actual shape. To consider the frictional forces, Coulomb’s coefficient

was assumed to be 0.25, which had better agreement with test results. The FE

method cannot model the fracture or cracking of the material because two

elements cannot be separated and thus the material fracture is not considered.

In the finite element analysis the difference between test data and numerical

models grows in nonlinear portion of curves. A major cause is the nonlinear

constitutive laws for materials, especially for situations where only uniaxial

values of the stress-strain curves were available.

Kaya and Arslan (2009) analytically modeled three precast beam to

column connections connected as post-tensioning and the cast-in-place beam

to column connections using ANSYS finite element program. In the analytical

models: model sizes, material properties, the loading program and the

boundary conditions were similar to the test specimens. A smeared crack

model was selected to define the cracked concrete. Full bond was assumed

between the concrete and steel. For this reason additional bond element was

defined between the concrete and steel. A discrete model was used for the

analytical models. For this study, Hognestad concrete model was used for due

to lack of confinement for concrete. William-Warnke failure model was used

in the definition of concrete. The results of the experimental tests and

44

analytical analysis showed that the performance of the prestressed

connections were adequate for load capacity but the analytical models initial

and 1.5% storey drift stiffness differed from the test specimens. The reason

for this behavior was the difference in the loading programs applied to the

analytical and experiment models. Loading was applied as load-controlled

steps to the analytical models. However, for the specimens it was applied as

load-controlled step at the beginning and then displacement-control steps

were used. Some parameters necessary for modeling concrete, reinforced steel

and prestressed strands may not be determined sufficiently such as the

concrete fracture parameters. For the effect of the concrete on the behavior of

the model to be fully reflected, all the concrete properties, including the

modules of elasticity, compressive stress, tension stress and poisson ratio

must be carefully determined. Figure 2.7 shows the Reinforcement details of

the precast beam column specimens.

Figure 2.7 Reinforcement Details of the Precast Beam Column

Specimens (Kaya and Arslan, 2009)

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Hawileh et al (2010) developed three dimensional nonlinear finite

element model to predict the behavior of precast hybrid beam-column

connection subjected to cyclic loading. The precast joint was modeled using

three dimensional solid elements and surface-to-surface contact elements

between the beam/column faces and interface grout in the vicinity of the

connection. The solid element SOLID65 was used to model the concrete. The

primary reinforcement post-tensioned strands and mild steel reinforcement

bars were modeled as solid elements SOLID185 because they were debonded

from the adjacent concrete surfaces in the vicinity of the connection. The

regular beam and column reinforcement are discretized using the discrete spar

elements. Perfect bond was assumed between the reinforcing steel and

concrete element. In this structure, the beam and column faces are in contact

with the interface grout, and there was also contact between the mild steel

bars and grout in the vicinity of the connection. Two element types

CONTA174 and TARGE170 were used for the contact and target surfaces

since the contact were between the two different surfaces. Surfaces with finer

mesh were designated as contact surface while surfaces with coarser meshes

were considered target surfaces. Results showed that the response envelope

from the finite element analysis correlated fairly well with the experimental

results. Good correlation existed in all stages of lateral cyclic loading.

Isometric view of the finite element model of the connection is shown in

Figure 2.8.

Ozden and Ertas (2010) presented an alternative section analysis

and hysteretic modeling for the response of precast concrete hybrid

connections which had different level of mild steel contributing to the

connection flexural capacity. It was suggested that the well known classical

reinforced concrete section analysis approach cannot be directly applied to the

precast concrete hybrid connections due to the strain compatibility between

the concrete sections and the partially bonded mild steel and the unbounded

46

prestressing tendons. The authors proposed a section analysis in which

initially the moment rotation behavior of the hybrid connection was modeled

by providing a new debonding length formulation for mild steel. A hysteretic

response was proposed by considering the residual displacement that was

measured during the hybrid connection subassemlage tests. It was observed

that the moment rotation envelope model and the cyclic response behavior

model both exhibited satisfactory agreement with the previously published

test results.

Figure 2.8 Isometric View of the Finite Element Model of the

Connection (Hawileh, 2010)

Sen et al (2010) conducted a finite element analysis for studying

the effectiveness of retrofitting technique called “strip wrapping technique”

for using carbon fibres (FRP) for strengthening of RC beam-column

connections damaged due to various reasons. The emphasis was mainly for

material modeling of the composite layered reinforced concrete structure

which took into account the stress-strain behavior of concrete tension

stiffening and the cracking of concrete. SOLID65, PIPE16 and SHELL63

were the elements used for discretising concrete, reinforcing bars and carbon

fibres respectively. The analytical programme confirmed the externally

47

bonded Fibre Reinforced Polymer (FRP) using carbon fibre with a new

technique called strip wrapping technique was a promising and a viable

solution towards enhancing the strength and stiffness characteristics of the

beam-column joints.

Wang et al (2010) conducted a nonlinear analysis of steel concrete

composite beam to concrete filled steel tubular column joints. In this study,

elastoplastic constitutive model based on the increment theory was used to

describe the constitutive relation of concrete. The model used William

Warnke five parameter yield criterion, uniform strength criterion and

associated flow criterion. A simplified Varma’s model was taken as the

constitutive relation for steel which considered dynamic hardening and local

buckling. SOLID65 was used to simulate concrete. This finite element model

can simulate wrapped tension cracking, crush, plastic deformation and creep

of concrete in three orthogonal directions. SHELL181 element was used to

simulate wrapped steel, strengthened ring and steel tubular. This finite

element model can simulate stress stiffening and large deformation of these

materials. LINK8 element which was the tension-compression element along

the axis was chosen to simulate the bar. COMBIN39 element was used to

simulate the contact and slip between wrapped steel, steel tubular and

concrete. The hysteresis curves of FEA calculation and the experimental

values were found to match well during the elastic stage. The authors

observed that because of the different loading mechanism and the difference

of finite element model and the specimen, the differences of them increased

under cyclic loading. However, the shape rules of the curves remained the

same.

Dere and Dede (2011) studied the failure behavior and crack

formation of a reinforced concrete frame under monotonic and reversed cyclic

lateral loading by three dimensional nonlinear finite element analysis using

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ANSYS software. Concrete was modeled as SOLID65 element. For modeling

reinforcement smeared reinforcement option was preferred as it was easy and

reliable. The load displacement envelopes obtained from ANSYS analysis and

experimental data were compared and found to be in good agreement with

each other. The crack profiles obtained from ANSYS model compared with

that of the experiments. The finite element model showed larger number of

cracks but the crack locations compared well with the experiments.

2.2.2.3 Precast Wall, Slab and Column

Xiao and Flaherty (2000) conducted finite element analysis of slab

column connections. The ANSYS finite element package was used for

modeling. SOLID65 element was used to model concrete. This element can

represent both linear and nonlinear behavior of the concrete. The flexural

reinforcement was defined using smeared reinforcement approach. The

compressive stress-strain relationship represented using two types of curves.

Firstly, a bilinear curve (perfectly plastic model) and secondly a multi-linear

curve (strain softening curve) was used. The main focus of this analysis was

to model the load deflection behavior of the specimen. The nonlinear

procedures of the finite element package cannot handle negative gradients in

the stress-strain curve, therefore the stress was not allowed to fall before

failure occurred. Hence the curve upon yielding was maintained horizontal up

to failure or was given a slight positive gradient to help converge of the

solution. The numerical investigations provided good agreement between the

predicted and the measured test results of the ultimate load and the associated

deflection.

Belakhdar (2008) developed a nonlinear finite element model for

evaluating the behavior of reinforced concrete slabs strengthened with shear

bolts under transverse load. The concrete was modeled as eight noded brick

elements. The flexural reinforcement and the shear bolts were modeled as

49

truss elements. A perfect bond was assumed between the brick element and

truss element. The nonlinear behavior of concrete in compression was

simulated by an elastio-plastic work-hardening model and in tension a

suitable post-cracking model based on tension stiffening and shear retention

models were employed. The steel was simulated using an elastic-full plastic

model. The validity of the theoretical formulations and the program used was

verified through comparison with available experimental data and the

agreement had proven to be good.

Kheyroddin and Naderpour (2008) conducted an analytical and

parametric study on the effectiveness of using externally bonded steel plates

and Fibre Reinforced Polymer (FRP) on reinforced concrete shear walls as a

retrofit technique to improve the seismic behavior. The solid element

SOLID65 in the ANSYS program was used in the analysis. The plasticity

model for concrete was based on the flow theory of plasticity, Von Mises

yield criterion, isotropic hardening and associated flow rule. The shear

transfer coefficient t represented conditions of the crack face. The value of t

ranges from 0 to 1.0, with 0 representing smooth crack and 1.0 representing

rough crack. The shear transfer coefficient used for this study was equal to

0.2. The shear transfer coefficient for a closed crack was taken as 1.0. The

externally bonded steel plates were modeled as SOLID45 element. A layered

solid element, SOLID46 was used to model FRP composites. From

verification against the experimental data it was concluded that the finite

element program can be used to simulate the whole load deformation curve,

the elastic part, the initiation of cracking, shear cracks and crushing fairly

well.

Tavio and Tata (2009) presented a non-linear finite element

modeling and analysis of rectangular normal strength reinforced concrete

columns confined with transverse steel under axial compressive loading. The

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columns were modeled as discrete elements using ANSYS nonlinear finite

element software. Concrete and reinforcement were modeled as 8 noded

SOLID65 elements and 3D- LINK8 bar elements respectively. The non-linear

constitutive law of each material was also implemented in the model. The

results indicate that the stress-strain relationships obtained from the analytical

model using ANSYS are in good agreement with experimental data. This was

confirmed with the insignificant difference between the analytical and

experimental results (i.e) 5.65 and 2.8 percent for the peak stress and strain at

peak stress, respectively. The actual stress-strain relationship, the strength

gain and ductility improvement have also been confirmed to be satisfactory.

2.3 SUMMARY

From the literatures, it is observed that the precast connections can

be detailed as strong as that of the monolithic connections. It is also

understood that the dry connections have better energy dissipation

characteristics. Hence, for the present study seven types of simple mechanical

connections have been adopted for the experimental investigations under

reversed cyclic loading. From the literatures, it was decided to use the finite

element package ANSYS for modeling. Information about the elements to be

used in modeling the various materials was also studied. It was concluded

that, for modeling precast connection in ANSYS the most appropriate

elements to be used are SOLID65, LINK8, CONTACT174, TARGET170,

and SOLID45. Also data input in material model to simulate concrete to

behave in multi-linear, elastic and inelastic stages are decided from the

literature study. From the experience of past researchers, possibilities and

reasons of error and approximations were also studied. The advanced

methodologies can be adopted for the better modeling and analysis of various

structural elements.