Advance Retrofitting Techniques for Reinforced Concrete Structures

REVIEW PAPERS

ADVANCED RETROFITTING TECHNIQUES FOR REINFORCED CONCRETE STRUCTURES: A STATE OF AN ART REVIEW By * SOUMYA GORAI

** P.R. MAITI

* Research Scholar, Department of Civil Engineering, Indian Institute of Technology, Kharagpur, India. ** Associate Professor, Department of Civil Engineering, Indian Institute of Technology (BHU), Varanasi, India.

ABSTRACT Any technology or material has its limitations and to meet the new requirements new technologies have been invented and used over the ages. A large number of reinforced concrete structures located seismic prone areas are not capable of withstanding earthquake action according to the current coal provisions. Furthermore the seismic behaviour of the existing buildings are affected due to design deficiency, construction deficiency, additional loads, additional performance demand, etc. Recent earthquakes have clearly demonstrated an urgent need to upgrade and strengthen these seismically deficient structures. The retrofitting is one of the best options to make an existing inadequate building safe against future probable earthquake or other environmental forces. Retrofitting reduces the vulnerability of damage of an existing structure during a near future seismic activity. It aims to strengthen a structure to satisfy the requirements of the current codes for seismic design. The Significant amount of research work has been carried out in recent years to develop various strengthening and rehabilitation techniques to improve the seismic performance of structures. This paper aims to present of overview on different innovative and cost effective techniques of retrofitting for strengthening the damaged structures. Keywords: Jacketing, Shear Wall, Bracing, Shotcrete, Isolation. INTRODUCTION

against severe earthquake. The large strain energy

Earthquakes of varying magnitude have occurred in the

released during an earthquake travel as seismic waves in

recent past across the globe, causing extensive damage

all directions. These waves can be classified as body waves

to life and property. The recent earthquake (Nepal

consisting of P-waves (Primary) & S-waves (Secondary) and

Earthquake) that struck on 25th April,2015 destroyed

surface waves consisting of L-waves & Rayleigh waves. S-

Centuries old buildings at World Heritage Sites. Those

waves cause maximum damage to the structures by

buildings which were partly or totally destroyed have

vibrating the surface in horizontal and vertical direction

naturally to be rebuilt, and for safety in future, must be

(Duggal, 2007). The main types of damage in reinforced

constructed using adequate earthquake resisting

concrete structures due to earthquake are cracking in

measures according to the various Indian standards and

tension zone, diagonal cracking in the core and loss of

appropriate guidelines UNESCO and the Ministry of Culture

concrete cover, stirrups bursting outside and buckling of

began strengthening damaged monuments in danger of

main reinforcement. The complete replacement of such

collapsing before the monsoon season. Subsequent

buildings in a given area is just not possible due to a

restoration of collapsed structures, including historic houses

number of social, cultural and financial problems.

is planned.

Therefore, seismic strengthening of existing undamaged or

The seismic behaviour of the existing buildings is generally affected by their original structural inadequacies, material degradation due to aging and alterations carried out during use over time. These kind of structures cannot survive

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damaged buildings is a definite requirement. It will involve actions for upgrading the seismic resistance of an existing building so that it becomes safer under the occurrence of probable future earthquakes. Different Techniques have

i-manager’s Journal on Structural Engineering, Vol. 5 l No. 1 l March - May 2016

REVIEW PAPERS been used in the years to reinstate the structural integrity of

stiffness of the section can be obtained depending on the

the member by restoring or increasing its strength.

type of jacketing (Vaghani, 2014). There are several

Researchers across the globe are studying on the

techniques of jacketing of damaged structural elements.

retrofitting techniques those are advantageous and most

One of the most common technique is Reinforced

cost effective.

Concrete Jacketing (RCJ). In this process the existing

1. Aim & Objective

member is wrapped with concrete, reinforced with

In the present study an attempt has been taken to address the innovative retrofitting techniques for repair, restoration and strengthening of various types of reinforced concrete structure still date in existing literature. The main objective of

longitudinal steel and ties or with fabric wire. There are basically three methods of RCJ namely beam jacketing, column jacketing and beam column joint jacketing. The main advantages of RCJ is it increases the shear and

this study to describe the process and findings carried out

flexural capacity and easy to construct. Because of that it is

by the researchers across the globe on advanced

widely used techniques of retrofitting all over the world and

retrofitting techniques such as reinforced concrete

several kinds of research work has been done on the utilities

jacketing, steel jacketing, fiber reinforced polymer

of RCJ. Researchers have concluded that using of RCJ

composite jacketing, steel bracing system, addition of

considerably increases flexural and shear strength of

shear walls, seismic isolation system, shotcrete method

existing sections. Karayannis, Chalioris & Sirkelis (2008)

present in the current available literature. All the techniques

experimentally investigated and addressed a new type of

are systematically placed in this article to give a clear

RC jacket for external beam-column joint damaged by

understanding to the readers about repair and retrofitting

seismic excitations. This experimental program included 10

of RC structures.

exterior beam column joints (Figure 1) investigated under constantly increasing cyclic loads, then retrofitted with

2. Retrofitting Techniques 2.1 Reinforced Concrete Jacketing

proposed RC jackets and finally retested under same loading. The dissipated hysteretic energy area measured in

The main objective of jacketing is to increase the load

terms of the area of the full load–deformation envelopes of

carrying capacity of the structural elements against the

the original beam–column joints is compared with the

lateral load. A considerable increase in ductility and

hysteretic energy dissipation of the retrofitted specimens.

Figure 1. Application of RC jacketing to beam-column joint(Karayannis et al 2008)


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REVIEW PAPERS The comparisons of the seismic performance between the

the beam for strengthening purposes. Ready mix concrete

original and retrofitted specimens. The comparison of the

was used for RCJ. They have also done an analytical study

seismic performance between the original and the

to be compared with the experimental program. Minafò

retrofitted specimens indicated that all the retrofitted joints

(2015) presented an analytical approach to calculate the

using the proposed jacketing with light reinforcement

strength domain for RC jacketed columns and it was based

exhibited significantly enhanced behavior with respect to

on the stress-block approach. Author concluded that stress

the original specimen. The available structural system

block approach is suitable for the RC jacketed column

geometry and the building mass were not modified, and

section if all the parameters are well calibrated. The design

therefore the dynamic characteristics of the structure

procedure of RCJ of column is included in Indian

remain practically unaffected. Chalioris & Pourzitidis (2012)

Standard15988:2013.

applied self-compacting RCJ technique to shear

2.2 Steel Jacketing

damaged reinforced concrete beam. The thickness of the jacket is 25 mm and it encased the bottom part of the beam and the vertical side as well (U shaped jacket). The steel reinforcement of the jacket consists of small diameter mild steel longitudinal rebar and U-shaped stirrups. They have observed that the load bearing capacity and the overall structural performance of the jacketed beams was improved with respect to the initially tested specimens. Marlapalle, Salunke & Gore (2014) described the effectiveness of RCJ of beams and columns as per IS15988:2013. Author also mentioned the disadvantages of RCJ technique such as the available space is reduced due to the increase of section and a large amount of dead mass is added and the duration of implementation is very slow. Tahsiri, Sedehi, Khaloo & Raisi (2015) have observed from an experimental program that it increases the energy dissipation capacity and ductility too. Author have studied 12 strengthened and three reference specimen subjected to three point loading. Unidirectional laminates of Carbon Fiber Reinforced Polymer (CFRP) were glued to the soffit of

Steel jacketing refers to encasing the section with steel plates and filling the gap with non-shrink grout. It is a very effective method to remedy the deficiencies such as inadequate shear strength and inadequate splices of longitudinal bars at critical locations. But, it may be costly and its fire resistance has to be addressed. In practice the most commonly used strengthening technique is by steel strips and angles (a variety of steel). Steel Jacketing has been widely used in European Countries in the past centuries. Since the 1995 Hyogoken-Nanbu earthquake steel jackets are extensively used to enhance the shear capacity and ductility of the square reinforced concrete columns. Sakino & Sun (2000) produced a state-of-art report on the seismic behaviour of the retrofitted square RC columns based on the researches conducted in Japan. They established the stress strain relation of the concrete confined by steel jacket, described the method to evaluate the ultimate bearing strength and shear strength

Figure 2(a) Specimen ready for concrete pouring, (b)Specimen Strengthened with steel cage (Ruiz-Pinilla et al 2014)

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REVIEW PAPERS of the retrofitted columns under combined compression,

on seismic retrofit of existing reinforced concrete (RC)

bending & shear and produced the design formulae to

frames with fiber–reinforced polymer composite (FRPC)

calculate the deformation capacity of the retrofitted

jackets. FRPCs have two components; matrix and fiber. In

column. Ruiz-Pinilla, Pallarés, Gimenez & Calderón (2014)

the present context, thermosetting resins like epoxy or

experimented on 20 full scale interior beam column joints

polyethylene are used as matrix, while aramid, carbon and

(Figure 2) to determine the behavior of steel jacketing as a

glass fibers reinforce the matrix and lend strength to the

strengthening system for reinforced concrete framed

composite. The resin coheres and gives shape to the

structures. The main objective of this research was to

object, while fibers reinforce it. The result of such

determine the behavior of the strengthened beam-

combination is a light, flexible and strong composite

column joints designed originally for only gravity load. They

material.

have carried out the experiment with strong beam and

The advantages of FRPCs are,

weak columns under gravity load and cyclic load. In order to reach the conclusion author have prepared loaddisplacement envelope of all the specimens. It concluded that steel jacketing prevent column failure, increase the bending strength of column and the failure section is transferred to the next weakest zone. Belal, Mohamed & Morad (2015) investigated the behaviour of RC column

· FRPCs are non-metallic. Therefore, they are resistant to corrosion. · They have high strength to weight ratio. Therefore, for the same strength FRPC is considerably lighter. This eliminates requirements of heavy construction equipment and supporting structures.

strengthened with steel jacket technique. Seven

· FRPCs have high ultimate strain therefore they offer

Specimens were divided in two control un-strengthened

ductility to the structure, and they are suitable for

specimen and five strengthened specimens. Author

earthquake resistant applications.

worked on three variables, namely the shape of the main

Because of the aforesaid advantages FRPCs are

strengthening system, shape and size of the batten plates.

considered as the most favoured material in many

The specimens were placed in the loading system

strengthening applications. In some situation FRPCs are the

between jack head and steel frames. Author have carried

only plausible material that can be used as retrofitting

out FE modelling of the experimental program in ANSYS

material, especially where heavy material cannot get

12.0.Comparison between the experimental results and FE

access or closure of use is not practical. IS 15988: 2013

results were carried out. Author have prepared load vs

included the design procedure of strengthening by FRPC

deflection curve for each specimen for experimental

jacketing.

program as well as FE modelling. It have found that FE

Obaidat, Heyden & Dahlblom (2010) presented the effect

modelling had a good agreement with the experimental

of CFRP and CFRP/concrete interface in retrofitting

program. From this study Author have concluded that steel

concrete sections by using finite element analysis which

jacketing technique increased the load carrying capacity

was validated against laboratory experiment on eight

upto 20% and also observed that the mode of failure of the

beams. Two different models of CFRP were used in this

control specimens were brittle but strengthening with steel

study, in 1st model the CFRP material were considered as a

jacket changed the failure mode to more ductile.

linear elastic material and in the 2nd as linear orthotropic

2.3 Fiber Reinforced Polymer Composite (FRPC)

material. Two different models were used to represent the

Jacketing

interface between concrete and CFRP. In the first model

A number of attempts have been undertaken by the

the interface was modelled as a perfect bond while in the

researchers to identify the most suitable materials and

second it was modelled using a cohesive zone model.

appropriate techniques to strengthen the deficient

They have prepared load vs deflection curve for the results

structures. Many research studies have been conducted

obtained from FEM analysis and compared with the data obtained from the experimental work. There was a good


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REVIEW PAPERS agreement between FEM analysis and experimental work.

The first specimen was strengthened circular concrete

They have concluded that the use of CFRP laminates

segment and with CFRP in vertical & horizontal direction.

significantly influenced the behavior of retrofitted

Both of the specimen was subjected to the same loading.

specimens. The ultimate load increases with the length of

The crack pattern in concrete and CFRP was observed and

the CFRP. Moghaddam (2012) investigated the strength of

they have prepared load vs deflection curve, shear force

beam-column joints wrapped with FRP. At first the modelling

vs rotation curve. They concluded that for both the

and analysis of the beam-column joints with different kinds

specimen the performance of the joint are significantly

of FRP composites has been carried out in ABAQUS software

increased compared to theoretical calculation for

and after comparison with already done lab specimen the

identical specimen but the strengthened specimen

validation and precision of the work is considered. GFRP

performed better compared to repaired specimen.The

and CFRP laminates have been used as FRP composites.

wrapped CFRPs on the modified circular section reduces

The length of the FRP sheets and orientation of the fiber

the possibility of debonding of the fibers and also

have been varied. Vertical static point load and horizontal

performed to resist the shear load. Waghmare (2011)

cyclic loading have been applied at the tip of the column.

presented the guidelines regarding the material selection

The load vs displacement curve is produced for different

and techniques to be considered for RC, steel and FRP

models. He concluded that with the increase of the length

jacketing. He has listed the various technical aspects such

of FRP sheets from 200 mm to 600 mm the bearing

as width & thickness of the jackets, the minimum area of

capacity of the joints and ultimate displacement improve.

longitudinal reinforcement, a minimum area of transverse

Also by strengthening with CFRP more bearing capacity

reinforcement etc. for beam, column and beam-column

has been observed compared to GFRP. Hadi & Tran (2014)

joint jacketing. Eslami & Ronagh (2015) carried out

introduced a new method to retrofit exterior beam-column

Nonlinear Finite Element analysis of seismic response of

joint using segmental circular concrete cover with Carbon

reinforced concrete connections (Figure 4) retrofitted with

Fiber Reinforced Polymer (CFRP). They have cast two

externally bonded Carbon Fiber Reinforced and validated

identical RC T connections (Figure 3), one connection was

the result with the experimental program. Their study

strengthened and for the other connections a load was

comprised seven non-seismically detailed specimens, five

applied to the beam to cause serious failure and the failed

of which were retrofitted using CFRP sheets. Both

section was repaired with the same technique. The failed

monotonic and cyclic loadings were included in the

section was repaired by filling epoxy materials in cracks

loading of the specimens. The results of the nonlinear FE

and concrete cover was glued & it is wrapped with CFRP.

analyses developed in ANSYS were then validated against

Figure 3. Final Cracking pattern a) Strengthened Specimen b) repaired specimen (Hadi et al. 2014)

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REVIEW PAPERS the experimental results. Comparison of the experimental

retrofitted specimens. They concluded that application of

load-displacement curves with those obtained from the

CFRP sheets improves the resistance against shear failure

numerical analysis confirmed a good agreement

and increased the maximum applicable force upto 20% in

between both curves up to a moderate ductility demand

some cases and considerably improved top

far beyond the yielding point. So it was concluded that the

displacement. Saeed, Khanb, Ahmeda, Muhammad Ali &

suggested FE models can reliably predict the

Iqbal (2015) stated the technique of strengthening Low

performance of the original and retrofitted test specimens

Strength Concrete bridge piers by jacketing of CFRP. They

under monotonic and cyclic loadings.

constructed eight scaled down (1:4) LSC columns and

Bridges and viaducts are amongst the current structures

wrapped half of them with CFRP. The columns were then

that are subjected to severe damage under the seismic

subjected to Quasi-Static-Cyclic Load Tests and Free

force often causing partial failure and sometimes total

Vibration Tests in order to predict the behavior and the

collapse. In most of the cases, bridges safety is totally

efficiency of CFRP wrapping on circular columns having

dependent on the piers. So several studies for the ages are

LSC. The authors used Seismo Struct for analytical

carried out for the purpose of the safety of piers. Delgado,

modelling of bridge piers, based on seismic analysis of

Arêde, Vila, Pouca, Rocha, Costa & Delgado (2012)

various structures (Figure 5). They prepared the hysteresis

presented an experimental solution to retrofit hollow bridge

loops of various drift level for the un-retrofitted model and

piers with CFRP sheets to prevent shear failure. Prepared RC

the retrofitted model (one layer and two layers CFRP). For

hollow section piers with different transverse reinforcement.

evaluating the energy dissipation the area under the loops

A constant axial force was applied during the test and a

were calculated. They concluded that confining the

cyclic horizontal force was applied in a displacement

columns with CFRP enhanced the lateral load carrying

controlled manner. After the damage of the original

capacity significantly. They also observed that at the lower

specimen CFRP sheets were wrapped in the outer side

drift level the column dissipated comparatively lower

along the entire height in the form of hollow jacket. They

energy, but at higher drift levels, the same column started

observed the crack pattern and prepared the horizontal

dissipating more energy. This indicates that the confining

load vs top displacement curve for both the original and

effect produced by CFRP wrapping was more effective at higher drift level and dissipated more energy before failure. 2.4 Steel Bracing System Steel Braced frames are efficient structural systems for buildings subjected to seismic load and wind load. Steel bracing system provides strength, stiffness, ductility and energy dissipation. A school building in Japan was successfully retrofitted with steel bracing system after severe damage to short columns in Miyagi-ken-oki earthquake. A 12 storey building in Mexico was retrofitted after a small earthquake in 1980. Bracing system was included along the perimeter frames in the weak direction of the building. The retrofitted structures performed very well in the1985 earthquake. Steel braces should be arranged in such a way that centre line should pass through the centres of beam-column joints. The provisions for designing a steel bracing system is given in IS15388:2013.

Figure 4. Schematic diagram of a beam-column exterior joint wrapped with CFRP (Eslami et al. 2015)

Badoux & Jirsa (1990) have shown the design steps of the


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REVIEW PAPERS

Figure 5. Finite Element Modelling of Low Strength Concrete Bridge pier (Saeed et al. 2015)

steel bracing system in the form of flow chart and typical

stable hysteretic dissipation even at large amplitudes.

different types of bracing configuration. They have carried

Sarno & Manfredi (2010) studied the effectiveness of a

out an analytical study based on a previously done

seismic retrofitting scheme comprises buckling restrained

experimental research in which an RC frame with deep

braces placed along the perimeter frame of a

spandrel beam was retrofitted with steel bracing system

multistoreyed building. The sample RC existing framed

(Figure 6). The traditional steel braced frame has many

building is located near Naples, in South of Italy; the framed

disadvantages, the energy dissipation of traditional brace

structure was built in the early 1960s and it was designed for

is limited. Buckling restrained braces exhibit large and

gravity loads only. They prepared a 3D model of the

Figure 6. RC frame with deep spandrel beam was retrofitted with steel bracing system (Badoux et al. 1990)

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REVIEW PAPERS sample building as built and the retrofitted structure to

out on the addition of shear walls and it was found that

analyze the earthquake response. The FE package they

shear wall can greatly increase the lateral load capacity

utilized to assess the seismic performance of the sample

and stiffness of the structure. From the strengthening system

structures is Seismo Struct. The seismic performance of the

the existing partition walls are removed and shear walls are

existing and retrofitted structures was assessed through

made instead (Kaplan & Yılmaz, 2012). In such application

linear and nonlinear analyses, i.e. eigenvalue analysis,

shear walls bears most of the lateral loads and reduce the

nonlinear static analysis and nonlinear dynamic analysis.

displacement of the building and RC frames resists very low

They selected a set of seven code-compliant natural

amount of lateral loads due to shear wall-frame interaction

earthquake records and employed to perform inelastic

(Figure 7). Shear walls can also be constructed to the

history analyses at serviceability and ultimate limit states.

external face without demolishing the internal infill walls. In

After the comparison between as built and retrofitted

such cases shear walls are placed parallel with or

structure they concluded that both global and local lateral

perpendicular to the existing frame systems. Shear walls

displacements are considerably reduced after the seismic

can be made of reinforced concrete, steel and timber.

retrofit of the existing system. It was also found that, in the

Ismaei& Hassaballa (2013)carried out a FEA program to

braced frame, under moderate-to-high magnitude

examine the effectiveness of adding steel shear walls in

earthquakes, the average period elongation is about 30%,

residential building to increase the response against

while for the existing building the elongation is negligible

earthquake. They selected a three-story RC residential

(lower than 5%). As a result, BRBs are effective to improve

building, representing the majority of domestic buildings in

the ductility and energy dissipation of the sample building.

Sudan, for this research. The analysis was carried out in

M.Mazza, F. Mazza & Vulcano (2015) proposed design

SAP2000. The proposed building was analyzed for gravity

procedure for in proportion hysteretic damped braces

load, wind load and seismic load. The structure was

(HYDBs) in order to increase the performance level of

reanalyzed for the same load combination after adding

reinforced concrete in-elevation irregular framed building

steel shear walls having thickness 5mm, 7mm and 10mm

against specific level of seismic intensity. A numerical

in one direction along the full height of the building. They

investigation is carried out to check the effectiveness and

have observed a considerable reduction in the moment of

reliability of the procedure with reference to a six-storeyed

column and beam after adding steel shear walls. They

RC framed building, originally designed according to an

have concluded this retrofitting method can reduce the

old Italian seismic code (1996) for a medium-risk zone, later

seismic vulnerability of existing buildings in Sudan.

retrofitted by inserting of HYDBs to attain performance levels

2.6 Seismic Isolation Method

imposed by the current Italian code (NTC08) in a high-risk zone. The first two floors of the building were converted to

To reduce the potential damage caused by earthquakes,

office from residential which resulted vertical irregularity. To upgrade the test structure from a medium- to a high-risk seismic region, diagonal steel braces with hysteretic dampers (HYDs) were inserted at each storey. They derived two structural solutions from the infilled frame, by adopting proportional stiffness and strength (for damped braces infilled regular), and constant drift and shear ratios (damped braces infilled irregular) design criteria for HYDBs. 2.5 Addition of Shear Walls Addition of shear wall is the most popular strengthening method applied worldwide. Many researches were carried

Figure 7. Shear wall-frame interaction (MacLeod, 1970)


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REVIEW PAPERS past methods increased the building rigidity by adding shear walls or braced frames or jacketing systems. The "Seismic Isolation Method" is a very suitable and flexible approach for isolating the structure from the ground or isolating some part of the structure from the lower part reducing seismic shock propagation into the structure (www.bridgestone.com). This method reduces the chance of structural damage, also minimizes secondary damage to equipment inside the building such as computers, precision, instruments, medical equipment and communications systems. There are three types of Isolators (www.wikipedia.org)-

(b) Slider

2.6.1 Elastomeric Isolator It is made of sandwiches of soft rubber sheets and hard steel plates (Figure 8a). It works as a bearing to sustain the weight of the building and is able to move the building laterally. Soft rubber reduces the building vibration to slow shaking, and hard steel plate contributes to sustain the weight of the building. 2.6.2 Slider The slider has a coating of PTFE (polytetrafluoro-ethylene) and a stainless steel plate finished with a smooth surface. It

(c) Rotating ball bearing

works as bearing to sustain the weight of the building and is

Figure 8. Different kind of Seismic Isolation Method (www.oiles.co.jp/)

able to move the building laterally on the surface of the plate with a certain amount of friction (Figure 8b).

is able to move the building laterally without friction (Figure

2.6.3 Rotating ball bearing

8c).

It consists of ball bearings with retainers and rails or plates. It

Seismic isolators are the most powerful and popular tool to

works as a bearing to sustain the weight of the building and

protect a structure against devastating earthquake. Many researchers over the worldwide are studying the performance of base isolation systems. Feng & Chu (1996) developed an analytical model for seismically isolated viaduct near Osaka, Japan which experienced Kobe earthquake in 1995. The Matsunohama viaduct is four span continuous with a total length of 211.5 km. At first analytical model is developed and its accuracy is confirmed by comparing the simulated response to the recorded one during Kobe earthquake. Then they performed numerical simulation to examine the response of the Matsunohama viaduct to different ground motion with LRB, FPB (sliding steel bearing) or HDR (reinforced rubber bearing) isolators. They observed that installation of those

(a) Elastomeric isolator

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REVIEW PAPERS isolators significantly reduced the response acceleration of

surface provides the compactive effort necessary to

the bridge superstructure and pier deformation compared

consolidate the material and develop a bond to the

to the non-isolated bridge. Kawamura, Sugisak, Ogura,

substrate surface.

Maezawa, Tanak & Yajima (2000) reported about two

The shotcrete process is capable of placing repair

midrise RC buildings in Japan those were retrofitted by

materials in vertical and overhead applications without the

seismic isolation method. The two retrofitted buildings were

use of forms. The application of repair materials by the

located in the region where earthquake having Richter

shotcrete process should be considered whenever access

magnitude 7-8 were worried to occur in near future. It was

to the site is difficult, where the elimination of formwork

decided to apply the isolation system at 8th floor in the

provides economy, and where significant areas of

main building. Mid height portion of the 22 columns were

overhead or vertical repairs exist. This is the most

cut and lead rubber baring were installed (Figure 9). Base

conventional technique available for masonary structures.

isolation were adopted for the east buildings which were

The disadvantages of this method are time consuming to

supported on pile foundation on flat ground. Piles were cut

apply, reduction in available space, affects the asthetic

at their head and 7units of sliders and 14 units of rubber

view of the wall.

bearing were installed. They observed that for both the buildings fundamental time period in X and Y direction were increased considerably. In the main building the shear force above the isolators was reduced and in the lower structure the seismic load was also reduced by large amount. They concluded that this is the most effective technique for retrofitting as works can be done outside the structure and seismic performance is excellent. They also mentioned that clearance to neighboring buildings should be above 40 cm because of the large deformation and space are necessary for piping, staircase, elevator and escalator to follow the large displacement of the isolation story.

ElGawady, Lestuzzi & Badoux (2006) experimented on the in plane behaviour of the URM walls retrofitted using shotcrete. They constructed one-half scale single width walls using half-scale hollow clay brick masonry (HCM) units and a weak (M2.5) mortar. They had three specimens one reference specimen, 2nd specimen was retrofitted in one side by 40mm thick shotcrete, the 3rd one with 20mm thick specimen both side (Figure 10). A superimposed gravity load of approximately 30 kN was applied to the specimen using two external post-tensioning bars. The horizontal cyclic load was applied to the reinforced concrete head beam, which in turn distributed the force to the masonry panel. The typical cyclic loading consisted of a series of

2.7 Shotcrete Technique

force and displacement-controlled cycles. They prepared

Shotcrete is defined as concrete or mortar which is

the hysteresis loop for the control specimen and the

pneumatically conveyed at high velocity through a hose

retrofitted specimens. They concluded that the lateral

onto a surface. The high velocity of the material striking the

strength of the retrofitted specimen 3.6 times the same of the reference specimen. Retrofitting on double-side had more ductile failure and energy dissipation. Amiruddin, Hino, Yamaguch & Nakamura (2007) investigated the seismic behaviour of the RC piers retrofitted with polymer concrete mortar (PCM) shotcrete method (Figure 11). The piers were designed with a scale factor of 1:5 that of prototype bridge column. The effect of an earthquake on the column specimen was simulated by reversed cyclic loading. They have also carried out an analytical modelling in LUSAS finite element program. The load-deflection curve

Figure 9. Installation of isolator in column(Kawamura et al. 2000)

from FEM had a quite good agreement with experimental


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REVIEW PAPERS performance and current state of the structure is essential. References [1]. Duggal, S.K. (2007), “Earthquake Resistant Design of Structures”. New Delhi, India: Oxford University Press. [2]. Vaghani, M.V., Vasanwala, S.A., Desai, A.K., (2014). “Advanced Retrofitting Techniques for RC Building: A State of an Art Review”. International Journal of Current Engineering and Technology, Vol. 4, No. 2, pp. 579-584. Retrieved from http:// inpressco.com/category/ijcet. Figure 10. Application of shotcrete (Elgawady et al. 2006)

[3]. Karayannis, C.G., Chalioris, C.E., Sirkelis, G.M., (2008). “Local retrofit of exterior RC beam–column joints using thin RC jackets- an experimental study ”. Earthquake Engineering and Structural Dynamics, 37, pp. 727–746. [4]. Marlapalle, V.C., Salunke, P.J., Gore, N.G. (2014). “Analysis & Design of R.C.C. Jacketing for Buildings”. International Journal of Recent Technology and Engineering, Vol. 3, No. 3, pp. 62-63. [5]. Indian Standard 159881:(2013). “Seismic Evaluation and Strengthening of Existing Sreinforced Concrete Buildings”. Guideline, Bureau of Indian Standards, Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi.

Figure 11. Application of PCM shotcrete method to bridge column (Amiruddin et al.2007)

[6]. Minafò, G. (2015). “A practical approach for the strength evaluation of RC columns reinforced with RC

value. They observed that confinement with PCM

jackets”. Engineering Structures, Vol. 85, pp. 162-169.

increased the load carrying capacity by 136% in

[7]. Sakino, K. & Sun, Y. (2000). “Steel Jacketing for

experiment and 169% in finite element modelling.

improvement of column strength and ductility”. In the

Conclusion

Proceedings of 12th World Conference on Earthquake

Seismic retrofitting has now become a crucial issue. Recent

Engineering. Auckland, New Zealand.

occurrences of earthquakes in different parts of the world

[8]. Ruiz-Pinilla, J.G., Pallarés, F.J., Gimenez, E., Calderón,

have clearly demonstrated the urgency of repairing

P.A. (2014). “Experimental tests on retrofitted RC beam-

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REVIEW PAPERS ABOUT THE AUTHORS Mr. Soumya Gorai is currently pursing Ph.D. in the Department of Civil Engineering in Indian Institute of Technology Kharagpur. He received his M.Tech Department of Civil Engineering, Indian Institute of Technology (BHU) Varanasi and B.Tech, Department of Civil Engineering in National Institute of Technology, Durgapur.

Dr.P.R. Maiti is currently working as an Associate Professor in the Department of Civil Engineering in Indian Institute of Technology (BHU) Varanasi. He received his M.E Department of Structural Engineering, B.E. Department of Civil Engineering in Indian Institute of Engineering Science and Technology, Shibpur and Ph.D in Indian Institute of Technology Kharagpur.

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Advance Retrofitting Techniques for Reinforced Concrete Structures

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