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CHAPTER 2

LITERATURE REVIEW

2.1 GENERAL

Structures are expected to deform inelastically when subjected to

severe earthquakes, so seismic performance evaluation of structures should be

conducted considering post-elastic behavior. Therefore, a nonlinear analysis

procedure must be used for evaluation purpose as post-elastic behavior cannot

be determined directly by an elastic analysis. Moreover, maximum inelastic

displacement demand of structures should be determined to adequately

estimate the seismically induced demands on structures that exhibit inelastic

behavior.

Various simplified nonlinear analysis procedures and approximate

methods to estimate maximum inelastic displacement demand of structures

are proposed in literature. The widely used simplified nonlinear analysis

procedure, pushover analysis is discussed in detail.

2.2 PUSHOVER ANALYSIS

Pushover analysis is an approximate analysis method in which the

structure is subjected to monotonically increasing lateral force with an

invariant height-wise distribution until a target displacement is reached.

Pushover analysis consists of a series of sequential elastic analyses,

superimposed to approximate the force-displacement curve of the overall

15

structure. A two or three dimensional model which includes bilinear or

trilinear load-deformation diagrams of all lateral force resisting elements is

first created and gravity loads are applied initially.

The structure is subjected to predefined lateral load patterns which

are distributed along the building height. The lateral forces are increased until

some members yield. The structural model is modified to account for the

reduced stiffness of yielded members and lateral forces are again increased

until additional members yield. The process is continued until a control

displacement at the top of building reaches a certain level of deformation or

structure becomes unstable. The roof displacement is plotted with base shear

to get the global capacity curve Figure 2.1.

Figure 2.1 Illustration of a Pushover Analysis

(Rui Carneiro Barvos and Ricardo Almeida 2005)

16

Pushover analysis can be performed as force-controlled or

displacement controlled. In force-controlled pushover procedure, full load

combination is applied as specified, i.e, force-controlled procedure should be

used when the load is known (such as gravity loading). Also, in force-

controlled pushover procedure some numerical problems that affect the

accuracy of results occur since target displacement may be associated with a

very small positive or even a negative lateral stiffness because of the

development of mechanisms and P-delta effects.

The published reports ATC 40 (1996) and FEMA 273 (1997)

highlighted the non-linear static pushover analysis. It is an efficient method

for the performance evaluation of a structure subjected to seismic loads. The

step by step procedure of the pushover analysis is to determine the capacity

curve, demand curve and performance point. These reports deal with

modeling aspects of the hinge behavior, acceptance criteria and procedures to

locate the performance point.

The seismic performance of non-ductile reinforced concrete framed

buildings, in regions of low to moderate seismic forces was evaluated by

Kunnath et al (1995). The detailing configurations included in the analysis

were discontinuous positive flexural reinforcement, lack of joint shear

reinforcement and inadequate transverse reinforcement for column core

confinement. When the buildings were subjected to a moderate level

earthquake, the buildings suffered significant but not severe damages. The

beams were more damages than the columns, except in the lower storey levels

of the nine storey structure.

Javeed Munshi and Satyendra Ghosh (1997) evaluated the seismic

performance of a code designed 12-storey reinforced concrete building. The

global and local inelastic behaviors of the building in the two orthogonal

17

directions were studied under several earthquake ground motions. Nonlinear

concrete behavior, including stiffness degradation and strength loss caused by

cracking, crushing of concrete and yielding of steel was simulated by using

the fiber beam-column element of the DRAIN-2D program. Pushover

analysis was used to determine the global ductility of the structure. It was

found that weak coupling between the walls resulted in large ductility

demands, which can be directly reduced by increasing the wall strength.

Jaswant et al. (1997) studied nine different models of the building.

The buildings were considered to be located in seismic zone III. Linear elastic

analysis was performed for the models of the building using ETABs analysis

package. Two different analyses were performed on the models of the

building considered in this study, namely the equivalent static analysis and

the multi model dynamic analysis. Finally suggested that, the buildings are

located in Zone-III will exhibit poor performance during a strong earthquake.

This hazardous feature of Indian RC frame buildings needs to be addressed

immediately and necessary measures should be taken to improve the

performance of the buildings.

Helmut Krawinkler and Seneviratna (1998) discussed that, the

pushover analysis would be a great improvement over presently employed

elastic evaluation procedures and they also pointed out that a carefully

performed pushover analysis would provide insight into structural aspects that

control performances during severe earthquakes. Further it was concluded

that, for structures that vibrate primarily in the fundamental mode, the

pushover analysis would provide good estimates of global as well as local

inelastic, deformation demands. These analyses also expose design

weaknesses that may remain hidden in an elastic analysis.

18

Ashraf Habibullah and Stephen (1998) described the use of

SAP2000 for the performing a pushover analysis of a simple three

dimensional building. SAP2000 is a state-of-the-art, general purpose, and

three dimensional structural analysis programs. SAP2000 has static pushover

analysis capabilities which were fully integrated into the program; allow

quick and easy implementation of the pushover procedures for both two and

three dimensional frames.

Mwafy and Elanashai (2000) owing to the simplicity of inelastic

static pushover analysis, a comparison study was made between inelastic

dynamic analysis and inelastic static pushover analysis for 12 reinforced

concrete buildings of different characteristics. The analysis was carried out

using natural and artificial earthquake records. It was found that the static

pushover analysis was more appropriate for low rise and short period framed

structures. For well designed buildings but with structural irregularities, the

result of the procedure also shows good correlation with the dynamic

analysis.

Sudhir K. Jain and Rahul Navin (2000) studied the seismic

strengthening of multistorey reinforced concrete frames which were assessed

by means of non-linear pseudo static analysis of four bays, three, six and nine

storey frames were designed for seismic zones I to V as per Indian codes. The

over strength increases as the number of storeys decreases; over strength of

the three storey frame was higher than the nine storey frame. Further, interior

frames have higher over strength as compared to exterior frames of the same

building. These observations were significant for seismic design codes which,

at present do not take into account the variation in over strength.

19

Elnashai (2001) analyzed the dynamic response of structures using

static pushover analysis. The significance of pushover analysis as an

alternative to inelastic dynamic analysis in seismic design and assessment

were discussed. New developments towards a fully adaptive pushover method

accounting for spread of inelasticity, geometric non-linearity, full multi-

modal, spectral amplification and period elongation within a framework of

fiber modeling of materials were discussed and preliminary results were

given. These developments lead to static analysis results that were closer than

ever to inelastic time-history analysis.

A modal pushover analysis procedure for estimating seismic

demands for buildings was developed by Chopra and Goel (2002). The modal

pushover analysis was applied to a nine-storey steel building to determine the

peak inelastic response and it was compared with rigorous non-linear

response history analysis. It was concluded that the modal pushover analysis

was accurate enough for practical application in building evaluation and

design.

Santoshkumar et al. (2003) studied the evaluation of multistorey

buildings with and without considering the stiffness of infill located in

zone III. The study compromised of seismic loads, gravity load analysis and

lateral load analysis as per the seismic code for the bare and infill structure by

considering different analytical models, and their evaluation was carried out

using pushover analysis. The results in terms of natural periods, lateral

deformation and ductility ratio were compared for the different building

models. It was concluded that the performance point of all the building

models considered for the study falls before the life safety point. Hence the

buildings need not be retrofitted. Base shear capacity was observed to be

20

greater than the design base shear; therefore the building has safe under

design basis earthquake.

Mela et al. (2003) a basilica type church was analysed in order to

assess its structural behaviour and seismic vulnerability. For this purpose, an

effective two step procedure was used, consisting of a) three dimensional

static and dynamic linear analysed of the structural complex, and b) two

dimensional non-linear pushover analysis of the single macro elements. The

comparison between demands versus capacity was carried out for all

transversal and longitudinal macro elements of the church, allowing a direct,

though approximate and assessment of the seismic safety level of the church.

The insertion of rigid diaphragms, which represents a widely used retrofit

technique, was also investigated.

Mehmet Inel and Hayri Baytan Ozmen (2006) studied the effect of

plastic hinges in nonlinear analysis of reinforced concrete buildings. Pushover

analysis was carried out for four as well as seven storied reinforced concrete

buildings to represent low and medium rise buildings. The frames were

modeled with default and user defined hinge properties to study possible

differences in the results of pushover analysis. Comparison of response was

also made in terms of base shear capacity, displacement capacity and

deformation of hinges. User defined plastic model was found to be effective

than the default hinge model. From the above discussion it was concluded

that comparative studies were made between pushover analysis and inelastic

time history analysis in evaluating the performance of existing building but,

no comparison study was found between pushover analysis and Demand to

Capacity Ratio (DCR) method of analysis.

21

Kasim Armagan Korkmaz et al. (2007) studied a three storied RC

frame structure with different amount of masonry infill walls were considered

to investigate the effect of infill walls on earthquake response of these types

of structures. Pushover curves were obtained for the structures using non-

linear analysis for SAP 2000. From the pushover curves, storey displacement,

relative storey displacement, maximum plastic rotations were determined.

Regarding the analysis results, the effects of irregularities were determined in

the structural behavior under earthquake.

Sadjadi et al. (2007) presented an analytical approach for seismic

assessment of RC frames using nonlinear time history analysis and pushover

analysis. The analytical models were validated against available experimental

results and used in a study to evaluate the seismic behaviour of these five

storied frames. It was concluded that both the ductile and the nominally

ductile frames behaved very well under the considered earthquake, while the

seismic performance of the ground floor structure was not satisfactory. After

the damaged ground floor frame was retrofitted the seismic performance was

improved.

Zine et al. (2007) conducted the Pushover analysis for reinforced

concrete structures designed according to the Algerian code. The main output

of a pushover analysis was in terms of response demand versus capacity. If

the demand curve intersected the capacity envelope near the elastic range,

Figure 2.2(a), then the structure had a good resistance. If the demand curve

intersects the capacity curve with little reserve of strength and deformation

capacity Figure 2.2(b), then it can be concluded, that the structure would

behave poorly during the imposed seismic excitation and need to be

retrofitted to avoid major damage or collapse in future.

22

(a) Safe Design (b) Unsafe Design

Figure 2.2 Typical Seismic Demand versus Capacity (Zine et al. 2007)

Ramkumar and Baskar (2008) examined the structural evaluation

of RC building when located in various zones of India. Response spectrum

analyses were carried out for all seismic zones in India considering with and

without infill stiffness. Pushover analysis was carried out to produce a

pushover curve consisting of capacity spectrum, demand spectrum and

performance point. Pushover analysis showed that performance of the

building components and also the maximum base shear carrying capacity of

the structures for various zones.

Kadid and Boumrkik (2008) conducted study on three framed

buildings with five, eight and twelve storeys respectively were analyzed.

Most of the hinges developed in the beams and a few in the columns but with

limited damage as shown in Figure 2.3. The results obtained in terms of

demand, capacity and plastic hinges give an insight into the real behavior of

structures.

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Figure 2.3 Hinge Patterns of Five Storey Building for Different

Displacement Levels (Kadid and Boumrkik 2008)

Anil Babu et al. (2008) conducted vulnerability analysis on two

existing multistorey buildings. Gravity load analysis, response spectrum

analysis and pushover analysis were performed. The capacity of each member

was obtained and compared with the demand. The result showed the level of

vulnerability of the buildings. The first building, which was in zone III, was

able to sustain the gravity load. The second building, located in zone IV,

however was adequate under gravity load. But, under earthquake load,

demands on some of the members crossed their capacities.

Ramesh Kumar and Baskar (2008) evaluated a G+7 RC framed

building using linear and non-linear analysis under earthquake loading. Two

types of analysis were employed namely, response spectrum analysis and

pushover analysis. The building was assumed to be placed in various zones of

India. Response spectrum analyses were carried out for all seismic zones in

India considering with and without infill stiffness. Pushover analysis was

carried out to produce a pushover curve consists of capacity spectrum,

demand spectrum and performance point. Response spectrum analyses

showed that most of the building components (beams and columns) were

24

failed in zone IV and V. Pushover analyses showed that the storey

displacement exceeded maximum permissible limit for zone IV and V. From

this evaluation, it was concluded that the structure must be retrofitted in zones

IV and V. The structure was provided with inverted V-bracing system and it

was again analyzed. The structure with inverted V-bracing system sustained

more lateral load and satisfied the codal requirements under those zones.

Mehdi Poursha et al. (2009) presented a new pushover procedure

which can take into account higher-mode effects. The procedure, which had

been named the consecutive modal pushover procedure, utilizes multi-stage

and single-stage pushover analyses. The final structural responses were

determined by enveloping the results of multi-stage and single-stage pushover

analyses. The procedure was applied to four special steel moment-resisting

frames with different heights. A comparison between estimates from the

consecutive modal pushover procedure and the exact values obtained by

nonlinear response history analysis, as well as predictions from modal

pushover analysis, had been carried out. It was demonstrated that the

consecutive modal pushover procedure was able to effectively overcome the

limitations of traditional pushover analysis, and to accurately predict the

seismic demands of tall buildings.

Mehanny and El Howary (2010) evaluated the seismic assessment

of ductile versions of low to mid-rise moment frames located in moderate

seismic zones was carried out through comparative trial designs of two

(4 and 8-story) buildings adopting both space and perimeter framed

approaches. Code-compliant designs, as well as a proposed modified code

design relaxing design drift demands for the investigated buildings, were

examined to test their effectiveness and reliability. Vulnerability curves for

the frames were generated corresponding to various code-specified

performance levels. However, the study suggested that more consistent

25

reliability for designed structures would be achieved by disaggregating the

force reduction factor into its static and dynamic parts and that code default

values of this factor for some building types would be better reduced for a

more reliable performance.

Shahrin Hossain (2011) followed the procedures of ATC 40 in

evaluating the seismic performance of residential buildings in Dhaka. The

present study investigated as well as compared the performances of bare

frame, full infilled and soft ground storey buildings. For different loading

conditions resembling the practical situations of Dhaka city, the performances

of these structures were analysed with the help of capacity curve, capacity

spectrum, deflection, drift and seismic performance level. The performance of

an in filled frame was found to be much better than a bare frame structure. It

is found that, consideration of effect of the infill leads to significant change in

the capacity. Investigation of buildings with soft storey showed that soft

storey mechanism reduced the performance of the structure significantly

and makes them most vulnerable type of construction in earthquake prone

areas.

Dinesh J. Sabu and Pajgade (2012) concentrated on seismic

evaluation of existing reinforced concrete building. Seismic analysis was

carried out for existing reinforced concrete building. The reinforcement

provided in building was compared with all the three formats of modeling

i. e. bare frame modeling, brick infill frame modeling and infill + soil

effect interaction model. After all the study, the following conclusions were

drawn.

The strength of the existing structure could be enhanced to the

required level and it would definitely improve the seismic

resistance capacity of the building required for zone III.

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The concrete jacketing method was easy, effective and

economical method for improving the seismic resistance

capacity of the member and building as well.

About 30% to 40% less reinforcement required in building

with brick infill + soil interaction effect as compared to bare

frame in ground storey. And relatively less difference in

reinforcement in other upper storey.

Ramaraju et al. (2012) carried out the nonlinear analysis (pushover

analysis) for a typical six storey office building designed for four load cases,

considered three revisions of Indian (IS: 1893 and IS: 456) codes. In that

study, nonlinear stress–strain curves for confined concrete and user-defined

hinge properties as per Eurocode 8 were used. A significant variation was

observed in base shear capacities and hinge formation mechanisms for four

design cases with default and user-defined hinges at yield and ultimate. This

may be due to the fact that, the orientation and the axial load level of the

columns cannot be taken into account properly by the default-hinge

properties. Based on the observations in the hinging patterns, it was apparent

that the user-defined hinge model was more successful in capturing the

hinging mechanism compared to the model with the default hinge.

2.3 CONCLUSIONS

Many guidelines are reviewed for linear, non-linear analysis and

the seismic evaluations of the structures are also discussed. Most of the

researchers have reviewed that the buildings were assumed to be placed in

various zones of India and carried out the investigation on the non-linear

analysis (pushover analysis) and compared the performance of the building

components, maximum base shear capacity of the structures located in the

27

various zones. Many papers considered different amount of masonry infill

walls to investigate the effect of infill walls on earthquake in response to the

structures. SAP2000, ETABS and IDARC-2D software’s were mainly used to

find out the seismic evaluation and performance of the structures. All these

studies require further research not based on assumptions, but in real terms it

is essential to consider existing reinforced concrete structures under seismic

evaluation.

2.4 SEISMIC RETROFITTING OF STRUCTURES

There are three types of deficiencies in a building, which have to be

accounted for by the retrofitting engineer: (i) inadequate design and detailing

(ii) degradation of material with time and use and (iii) damage due to

earthquake or other catastrophe. The retrofit engineer is expected to estimate

the deficiency resulting from all the three sources, suggest a retrofit scheme to

make up for the deficiencies and demonstrate that the retrofitted structure will

be able to safety resist the future earthquake forces expected during the

lifetime of the structure. These papers present a brief review of the available

methods and techniques for retrofitting of RC building.

ASCE (2000) the intent of this standard, Guideline for Condition

Assessment of the Building Envelope, is to provide a guideline and

methodology for assessing the condition and performance of existing building

envelope systems and components and identifying problematic and

dysfunctional elements. It applies equally to a building's envelope or portion

whose primary purpose may be to serve as the supporting structural system of

the building. This standard assists the investigator in developing a logical

approach to this assessment by establishing an assessment procedure

including investigation, testing methods and a form for the report of the

condition assessment. Since any evaluation will also involve "professional

28

judgment", a section providing guidance is included. Both consultants and

clients will find this standard to be a useful source of information on

assessing building envelope systems.

FEMA 172 (1992) the handbook described the techniques

that engineers could use to solve a variety of seismic rehabilitation

problems in existing buildings, a broad spectrum of building types and

building components (both structural and nonstructural). Techniques are

illustrated with sketches and the relative merits of the techniques are also

discussed.

This publication FEMA 156 and FEMA 157 (1994 and 1995)

presented a methodology to estimate the costs of seismic rehabilitation

projects at various locations in the United States. The above edition was

based on a sample of almost 2,100 projects, with data collected by using a

standard protocol, strict quality control verification and a reliability rating. A

sophisticated statistical methodology applied to this database yields cost

estimates of increasing quality and reliability as more and more detailed

information on the building inventory is used in the estimation process.

FEMA 308 (1999) suggested practical guidance for the repair,

upgrade of earthquake damaged concrete and masonry wall buildings. Target

audiences were design engineers, building owners, officials, insurance

adjusters and government agencies. The publication contained sections on

performance based repair design, repair technologies, categories of repair and

nonstructural considerations. The last section included repair guides, which

provided outline specifications for typical repair procedures.

Murty (2002b) discussed how the existing buildings could become

seismically deficient when (a) seismic design code requirements are upgraded

29

since the design of these buildings with an older version of the code;

(b) seismic design codes are deficient and (c) designers lack understanding of

the seismic behavior of structures. Indian buildings built over the past two

decades were deficient because of items (a), (b) and (c) above.

Three levels of improvement in the existing RC frame buildings

were possible, namely (a) repair (b) restore and (c) strengthen. The

consequence of any prescribed method of the retrofitting were (a) adding

brick masonry walls in all possible bays in ground storey (b) jacketing of all

RC columns in ground storey only, (c) adding steel diagonal braces in some

bays in ground storey and (d) infilling existing RC frame with RC structural

walls in some bays in ground storey only. In all cases, foundation

strengthening may be essential. The seismic capacity of the building should

be quantitatively evaluated based on its effectiveness from the points

of view of strength, stiffness and ductility Sometimes, a retrofit scheme

may have better performance than the damaged structure, but still may be

poor; the retrofit scheme that assures at least a basic ductility is preferable to

the others.

Sudhir K. Jain and Srikant (2002) concept of pushover analysis was

becoming a popular tool in the profession for design of new buildings,

seismic evaluation of existing buildings and developing appropriate strategy

for seismic retrofitting of buildings. It was shown how this analytical

technique could be useful in deciding seismic retrofitting strategy and

techniques.

Richard White and Khalid Mosalam (2002) evaluated the

procedures and retrofit strategies for existing reinforced concrete framed

buildings were designed primarily for gravity loads. Selected evaluation and

rehabilitation methods were reviewed, including portions of the 1996 NEHRP

30

guidelines for seismic rehabilitation of buildings. New research resulted for

predicting the behaviour of masonry infilled frames was presented, and

general research issues were suggested.

Yogendra Singh (2003) studied and discussed that, a large number

of existing buildings in India were severely deficient against earthquake

forces and the number of such buildings was growing very rapidly. This was

highlighted in the past earthquake. Retrofitting of any existing building was a

complex task and requires skill, retrofitting of RC buildings was particularly

challenging due to complex behavior of the RC composite material. The

behavior of the buildings during earthquake depends not only on the size of

the members and amount of reinforcement, but also to a great extent on the

placing and detailing of the reinforcement. The construction practices in India

resulted in severe construction defects, which made the task of retrofitting

even more difficult.

Shailesh Agrawal and Ajay Chourasia (2003) performed the

nonlinear static analysis of RC building using pushover approach before and

after retrofitting. The comparison of strength parameters and pushover curve

indicated that there was increase in ductility. As regards to stiffness of the

building, it was seen that it remains more or less same up to linear stage,

while in nonlinear stage every point increased both in capacity and the

deformation after retrofitting. The strength of the building was correlated with

base shear, the net enhancement in strength after retrofitting.

Amar Prakash and Thakkar (2003) studied the seismic retrofitting

of an existing fourteen storied RC building frame located in seismic zone IV.

The study included seismic evaluation and retrofitting of RC framed building,

by using steel bracing and infill masonry walls. The seismic performance of

two retrofitting techniques such as steel bracing (V, diamond and cross

31

pattern) and infill walls were relatively compared. Among three patterns of

steel bracing, cross pattern shows better performance than ‘V’ and diamond

bracing patterns.

Chandrasekaran et al. (2003) conducted studies on 150 year old

building, Ganga Mahal located in Assi Ghat and Sanskrit University of

Varanasi. The buildings were mathematically modeled and analyzed for its

structural behavior. The suggested measures of structural strengthening for

these heritage structures were based on the understanding of the detailed

studies conducted by the authors on the failure pattern of various structures

during earthquakes in India.

Ashutosh V. Mahashabde et al. (2003) identified an efficient

retrofitting method for reinforced concrete buildings. Two buildings such as

one open ground storey with infills and the other by partial open ground

storey with infills, which were damaged in the January 2001 Bhuj earthquake,

were subjected to static pushover analysis with code specified design shear

distribution. The observed failure modes conform to the actual structural

damages sustained by the buildings during that earthquake. The selected

methods of retrofitting were a) Jacketing of columns in the ground storey,

b) Structural walls in the ground storey of some selective panels, and

c) Structural walls for all the stories in some panels. These three basic

schemes were used in combination for ascertaining an economical method

giving the maximum strength and ductility. Of all the methods studied, the

combination of column jacketing in ground storey and shear wall throughout

the height of the building with selective strengthening of upper storey frame

members, give the most economic and desirable performance.

FEMA 395-397 (2003), FEMA 398 and FEMA 399 (2004)

described administrators with information to assess the seismic vulnerability

32

of school buildings, hospital building, office building and apartment building,

retail building and to implement a program of incremental seismic

rehabilitation. Increase in the number of seismically resistant buildings in all

areas of identified earthquake risk.

The guidelines given by Durgesh C. Rai (2005) were intended to

provide a systematic procedure for the seismic evaluation of buildings, which

could be applied consistently to a rather wide range of buildings. This

document also discussed some cost effective strengthening schemes for

existing older buildings which were identified as seismically deficient during

the evaluation process.

Giusepe Oliveto and Massimo Marleta (2005) gave the traditional

methods of seismic retrofitting. Modern methods and philosophies of seismic

retrofitting, including base isolation and energy dissipation devices, were

reviewed. The presentation was illustrated by case studies of actual buildings,

where traditional and innovative retrofitting methods were applied.

The document by Durgesh C. Rai (2006) highlighted a higher

degree of damage in a building could be expected during an earthquake, if the

seismic resistance of the building was inadequate. The decision to strengthen

it before the occurrence of an earthquake depends on the building’s seismic

résistance. The structural system of the deficient building should be

adequately strengthened, in order to attain the desired level of seismic

resistance.

Lakshmanan (2006) conducted pushover analysis for the structures

using SAP 2000 evaluating the various repair strategies, for the improvement

of the seismic performance of RC structures. The behaviors of repaired beams

and beam column joints were discussed. It was observed that an inherent

33

deficiency in the detailing of the beam-column joints gets reflected even after

repair, though the performance factors indicate significant improvement. Two

of the logical extensions show that the repair would not be as effective in

these cases.

Kaustubh Dasgupta and Murty (2006) identified an efficient

retrofitting method for existing open ground storey RC frame buildings.

A two dimensional RC frame has designed as non-ductile. Detailing was

subjected to nonlinear static pushover analysis. The RC frame was retrofitted

by three methods. a) Concrete jacketing of columns in the ground storey,

b) Brick masonry infill in the ground storey and c) RC structural wall in the

ground storey panel. Of all the methods studied the use of structural wall in

the ground storey panel gave the maximum strength and ductility.

Seki et al. (2007) gave the seismic evaluation and retrofitting

procedures of reinforced concrete buildings based on JICA technical

cooperation project in Romania. The content covered i) an outline of the

seismic evaluation; history and comparison of Romanian seismic design

codes with the Japanese seismic evaluation guidelines, ii) an outline of the

retrofitting techniques which were transferred from Japan to Romania and

structural tests for retrofitting techniques employed in Romania and

iii) retrofitting details that were used by JICA/NCSRR in the retrofitting

design of two vulnerable buildings in Bucharest.

Alexander G. Tsonos (2008) made a study to evaluate retrofitting

methods which address particular weaknesses that are often found in

reinforced concrete structures, especially older structures, namely the lack of

sufficient flexural and shear reinforcement within the columns and the lack of

adequate shear reinforcement within the joints. Thus, the use of a reinforced

concrete jacket and a high-strength fibre jacket for cases of post-earthquake

34

and pre-earthquake retrofitting of columns and beam–column joints was

investigated experimentally and analytically. The effectiveness of the two

jacket styles was also compared.

Ei-Sokkary and Galal (2009) investigated analytically the

effectiveness of different rehabilitation patterns in upgrading the seismic

performance of existing nonductile RC frames structures. The study

investigated the performance of two RC frames (with different heights

representing low and high rise buildings) with or without masonry infill was

rehabilitated and subjected to three types of ground motion records. The

ground motion records represented earthquakes with low, medium and high

frequency contents. Three models were considered for the RC frames: bare

frame, masonry infilled frame with soft infill and masonry infilled frame with

stiff infill. Four rehabilitation patterns were studied namely; 1) introducing a

RC shear wall, 2) using steel bracing, 3) using diagonal FRP strips (FRP

bracings) in the case of masonry infilled frames, and 4) wrapping or partially

wrapping the frame members (columns and beams) using FRP composites.

Incremental dynamic analysis was conducted for the studied cases. The

seismic performance enhancement of the frames was evaluated in terms of the

maximum applied peak ground acceleration resisted by the frames, maximum

inter storey drift ratio, maximum storey shear-to-weight ratio and energy

dissipation capacity.

Ryan J. Williams et al. (2009) presented a methodology that can be

used to make informed decisions on whether or not to retrofit structures for

seismic events based on the expected economic benefit due to retrofitting.

The seismic fragility of a given structure as well as the seismic hazard at a

specific building location was incorporated into the decision-making process.

The prescribed methodology was used to study two identical reinforced

concrete buildings, one located in Memphis, Tennessee and one in

35

San Francisco, California. The probabilities of failure and generalized

reliability indices were calculated for the identical structures in both

locations. A parametric analysis was performed to determine the effects that

achievable loss reduction, investment return period, and retrofit cost have on

the economic feasibility of seismic retrofitting in Memphis and San

Francisco. A case study was conducted to find the impact of a modest retrofit

strategy applied to the identical buildings in Memphis and San Francisco. The

probabilities of failure and generalized reliability indices were calculated for

the retrofitted building in both locations and compared to the corresponding

values for the original buildings. The results of the parametric analysis and

case study were used to determine the effects of building location on retrofit

feasibility.

Savitha et al. (2009) studied performance based seismic evaluation

of building models namely: bare frame, soft storey, retrofitted building with

unreinforced masonry infill and increased stiffness of columns and different

locations in open ground storey for G+2, G+5and G+ 8, storey’s located in

seismic zone III. The buildings were designed by gravity loads which were

analyzed by equivalent static method using ETAB and nonlinear version 9

software. The seismic vulnerability of building was assessed by carrying out

non linear static pushover analysis at immediate occupancy, life safety and

collapse prevention performance levels. Comparative study of two retrofit

techniques was made by comparing the values of natural period, base shear,

lateral displacement, storey drift, ductility and also performance of buildings

were checked at their respective failure modes and target displacement levels.

The investigation concluded that, the buildings designed as per IS: 456-2000

provisions using limit state method of design were inadequate for seismic

load combination as per IS: 1893-2002 (Part-I) code provisions. The

performance of the buildings having non- ductile moment resisting frames

could be improved by adding infill walls or increasing stiffness of ground

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columns. The retrofitting techniques addition of infill walls and increase in

stiffness of ground columns, out of three different locations at the

intermediate portion i.e. at the middle bays gave better performance than that

of at central core and peripheral bays.

Cengizhan Durucan and Murat Dicleli (2010) focused on a

proposed seismic retrofitting system configured to upgrade the performance

of seismically vulnerable reinforced concrete buildings. The proposed seismic

retrofitting system was composed of a rectangular steel housing frame with

chevron braces and a yielding shear link connected between the braces and

the frame. The retrofitting system was installed within the bays of an RC

building frame to enhance the stiffness, strength and ductility of the structure.

The proposed seismic retrofitting system and a conventional retrofitting

system using squat infill shear panels were used in an existing school and an

office building. Nonlinear time history analyses of the buildings in the

original and retrofitted conditions were conducted for three different seismic

performance levels to assess the efficiency of the proposed seismic

retrofitting system. The analyses results revealed that the building retrofitted

with the proposed seismic retrofitting system had a more stable lateral

force–deformation behaviour with enhanced energy dissipation capability

than that of the one retrofitted with squat infill shear panels

Niroomandi el al. (2010) reported on the results of an investigation

into the effectiveness of FRP retrofitting the joints in enhancing the seismic

performance level and the seismic behaviour factor (R) of ordinary RC

frames. The flexural stiffness of FRP retrofitted joints of the frame was first

determined using nonlinear analyses of detailed Finite Element models of

RC-joint–FRP composite. The results showed that the performance level and

the seismic behaviour factor of the FRP retrofitted RC frame were

significantly enhanced in comparison with the original frame and were

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comparable with those of the steel-braced frame. It was also found that using

FRP at joints may upgrade an ordinary RC frame to an intermediate and even

a high ductility frame.

Yuksel et al. (2010) conducted the experimental studies on the

behaviour of bare and Carbon Fiber Reinforced Polymer (CFPR)-retrofitted

infilled RC frames with different bracing configurations. Quasi-static

experimental results were presented and discussed on six 1/3rd -scaled infilled

RC frames that were retrofitted using CFRP material in various schemes. The

test results showed a significant increase in the yield and ultimate strength

capacities of the frames with a decrease in relative story drifts, especially in

the cross-braced and the cross diamond-braced type of retrofitting schemes.

The energy dissipation capacities of the retrofitted frames turned out to be

more than those of the bare infilled frame, thus reducing the seismic demand

imposed on the frames. The cross diamond-braced type of retrofitting scheme,

which was positioned on the infill wall and outside the beam–column

connection regions of RC frame, showed the best behaviour among the other

schemes. This scheme not only prevented brittle shear failures of the infill

wall, but also prevented the transfer of additional forces to the weak and

brittle beam–column connections.

Chien-Kuo Chiu and Wen-Yu Jean (2011) proposed an estimating

procedure that can be used to set the optimal seismic level in the seismic

retrofit design for a low rise RC building was proposed. Along with damage

control, cost of maintenance over the remaining service life was also

considered in this estimating procedure. Furthermore, combination of

upgrading rates in terms of yielding acceleration and the ductility capacity of

the single degree of freedom system were also suggested to the designer of

the retrofit. Although the structure in the case study was limited to a low rise

RC building in Taipei, the optimal seismic retrofit level calculated via the

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same procedure can be derived and utilized when making decisions about

how to set the upgrading rates in structural capacities in the seismic retrofit

design based on economic considerations.

Yuichi Sato et al. (2011) presented a three-dimensional Finite

Element Analyses on all-frame model of a three-story reinforced concrete

(RC) building damaged in the 1999 Taiwan Chi-Chi Earthquake. Non-

structural brick walls of the building acted as a seismic resistant element

although their contributions were neglected in the design. Hence, the entire

structure of a typical frame was modelled and static and dynamic nonlinear

analyses were conducted to evaluate the contributions of the brick walls. The

results indicated that brick walls improved frame strength although shear

failures were caused in columns shortened by spandrel walls. Then, the

effectiveness of three types of seismic retrofits was evaluated. The maximum

drift of the first floor was reduced by 89.3%, 94.8% and 27.5% by Steel-

confined, Full-RC and Full-brick models respectively. Finally, feasibility

analyses of models with soils were conducted. The analyses indicated that the

soils elongate the natural period of building models although no significant

differences were observed.

Pavan Kumar et al. (2012) comprehensive review of materials and

techniques used for seismic retrofitting of RC framed building located in

seismic zone -V were discussed briefly using SAP 2000 software. The

document highlighted a higher degree of damage in a five storied building is

expected during an earthquake. Keeping the view of constant revision of the

seismic zones in India, lack of proper design and detailing of structures

against earthquake the methods of seismic retrofitting were reviewed by

identifying weak points. Modern methods and philosophies of seismic

retrofitting like energy dissipation devices and materials were reviewed.

Finally conclude that, wrapping techniques were prescribed in this study.

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which are light in weight, economical and to increase the ductility of elements

in order to prevent the progressive collapse of building such that people can

easily escape to outside from building with in safe time.

Gopen Paul and Pankaj Agarwal (2012) conducted an experimental

and analytical study on single storey RC model. A seismic evaluation of four

storeys two dimensional frames designed with previous IS codes had also

been carried out to investigate the effect of retrofitting technique. On the basis

of this study, the existing four storey RC frame building in seismic zone IV,

designed and constructed using previous Indian standards was found

inadequate to withstand the present day code requirement. The experimental

pushover analysis of the frame model showed that there was an increase in

effective stiffness, yield load and ultimate load of about 3.4, 2.9 and 2.7 times

respectively due to inclusion of infill wall whereas the above three parameters

increases about 17, 11.6 and 14.7 times respectively due to addition of steel

bracing. The analytical pushover analysis of the four storey frames also

showed that there was a increase in effective stiffness, yield load and ultimate

load of about 1.5, 1.6 and 1.8 times respectively due to inclusion of infill wall

whereas the above three parameters increases about 16, 4 and 5 times

respectively due to addition of steel bracing. For fully confined infill, the

equivalent strut model specified in FEMA 356 gives a reasonable prediction

on both un-cracked stiffness and lateral strength of masonry infilled panel

frame.

Hamood Alwashali and Masaki Maeda (2012) investigated the

damage of several low-rise RC buildings caused by the Great East Japan

earthquake in Sendai city. The selected building was evaluated to have high

seismic capacity, index (Is) > 0.7, using Japanese Standard for Seismic

Evaluation of Existing RC Buildings. Causes of the damage were discussed.

Moreover, pushover analysis was carried out to those buildings. In general,

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pushover analysis predicted well the damage level but there were some

differences in plastic hinge locations when compared to the actual damage.

Masaki Maeda et al. (2012) highlighted the investigation of

reinforced concrete building structures. Japanese RC building showed good

performance for saving lives on Great Japan Earthquake. However, a number

of retrofitted buildings and buildings that had been evaluated to be safe had to

be evacuated after the earthquake. Some of these buildings are going to be

demolished because the repairs are too costly. This issue is one that requires

attention. Good correlation was observed between calculated seismic capacity

Is-index and observed damage. Most of the buildings with Is-values lower

than 0.6 were vulnerable to moderate and severe damage. Most of the

buildings are with Is-values higher than 0.7 escaped severe damage.

Moreover, buildings designed according to current seismic design code had

minor damage in structural members.

Praval Priyaranjan (2012) attempted to evaluate an existing

building located in Guwahati (Seismic zone -V) using equivalent static

analysis. Indian Standard IS-1893:2002 (Part-1) was followed for the

equivalent static analysis procedure. Building was modeled in commercial

software STAAD Pro. Seismic force demand for each individual member was

calculated for the design base shear as required by IS-1893:2002.

Corresponding member capacity was calculated as per Indian Standard

IS456:2000. Deficient members were identified through demand-to-capacity

ratio. A number of beam and column elements in the first floor of the present

building were found to be deficient that needs retrofitting. A local retrofitting

strategy was adopted to upgrade the capacity of the deficient members. The

study showed that steel jacketing is an efficient way to retrofit RC members

to improve flexure as well as shear capacity.

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Waiel Mowrtage and Vail Karakale (2012) presented a new

concept on collapse prevention of existing RC buildings during a seismic

event. The idea is to install steel panels in specified locations in the structure

to reduce inter-story drifts. The panels are expected to work as a fuse in an

electric circuit when a major earthquake occurs; the panels will attract the

seismic forces and they may totally damaged but they will prevent severe

damage in the main structural system. The proposed panels were light-weight,

easy to handle and can be constructed very quickly. Moreover, they are cheap

and do not need formwork or skilled workers. To test the concept, a half-

scale, single-story three dimensional reinforced concrete frame specimen was

constructed at the shake-table laboratories of the Kandilli Observatory and

Earthquake Research Institute of Bogazici University and subjected to

recorded real earthquake base accelerations. The amplitudes of base

accelerations were increased until a moderate damage level is reached. Then,

the damaged RC frames was retrofitted by means of steel panels and tested

under the same earthquake. The seismic performance of the specimen before

and after the retrofit was evaluated using FEMA356 standards and the results

were compared in terms of stiffness, strength and deformability. The results

have confirmed effectiveness of the proposed retrofit scheme in future.

2.5 CONCLUSIONS

Many guidelines are reviewed regarding seismic rehabilitation

of buildings of different cases. Some of the researchers discussed the

various seismic retrofitting methods for existing building. The strengthening

methods carried out by most of the researchers were concrete jacketing of

columns of ground floor, brick masonry infill in the ground floor, X and V

bracing, shear wall, FRP of beams and columns. All these topics require

further research, as it is essential for seismic retrofitting of existing reinforced

concrete structures.