CIV4001-CIV4002 Intermediate Report - Research Proposal Template

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CIV 6020 Intermediate Report – Research Proposal

Department of Civil and Structural Engineering, University of Sheffield, 2012

Seismic Response of Reinforced

Concrete Structures with FRP

Strengthening

The University of SheffieldDepartment of Civil and Structural Engineering

CIV6020 Intermediate Report – Research Proposal

Candidate: MSc Structural Engineering

Supervisor: Prof. Kypros Pilakoutas



i

Abstract

The phenomenon of earthquakes has been far too old and the study on seismology has been

far too young to understand its true nature. The in depth-science of earthquakes has been a big

question since no can precisely predict when it is going to occur how it is going to occur and

what consequences in would bring into to the surface. Therefore it is very important in this

day and age to at least predict the outcome due to this on mad made structures. Many scientist

and seismologist and engineers have been working intensely on this subject because the

general consequence it brings is often catastrophic, devastating and fatal.

This MSc dissertation project briefly covers a basic study on earthquake loads and its

behaviour on reinforced concrete structures and its methods of failures to enable the reader to

understand a full picture of the response characteristics of a reinforced concrete structure.

This project mainly experiments a model which was chosen to be the Ecoleader Project n2

which is a seismically designed R/C frame structure used to test different strengthening

techniques to develop simple rational techniques for use in FRP strengthening on Beam-

Column joints to quantify their effectiveness on the response of the structure. Special cases of

Tsunami loadings on reinforced concrete structures are also reviewed. The main aim to

research this is to apply this loading condition onto this projects model if time permits.



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Table of Contents

List of Figures ........................................................................................................................... iii

1 Introduction ........................................................................................................................ 1

2 research aims and objectives .............................................................................................. 2

3 Literature review ................................................................................................................ 3

3.1 Background ................................................................................................................ 3

3.2 Seismic Capacity and Demand ................................................................................... 3

3.3 Failure of reinforced concrete structures to seismic loads ......................................... 4

3.3.1 Bond-Slip failure .................................................................................................... 4

3.3.2 Beam-Column Joint failure .................................................................................... 5

3.4 Existing seismic strengthening techniques ................................................................. 6

3.4.1 In-fill shear walls .................................................................................................... 7

3.4.2 External shear walls ............................................................................................... 7

3.4.3 RC jackets .............................................................................................................. 8

3.4.4 Steel jackets ............................................................................................................ 8

3.4.5 FRP Stengthening ................................................................................................... 9

3.5 Tsunami behaviour and its impacts on structures ...................................................... 9

4 Experiment and analysis ................................................................................................... 12

4.1 Seismic Response of Ecoleader frame on drain 3D-x .............................................. 12

4.2 Tsunami loading and analysis .................................................................................. 13

4.2.1 Hydrodynamic Force ............................................................................................ 13

5 pre-conclusion and results ................................................................................................ 14

6 References ........................................................................................................................ 15



iii

List of Figures

Figure 1 Example of Dissipative and non-dissipative global behaviour of structures [1] ......... 1

Figure 2 Damage on reinforcement column due to insufficient lap splice ............................... 2

Figure 3 ...................................................................................................................................... 3

Figure 4 General issues and causes for failure of reinforced concrete joints. ............................ 4

Figure 5 Typical Failure of Beam-Column Joint ....................................................................... 5

Figure 6- Change in the displacement demand and capacity of the structure after

strengthening [6] ................................................................................................................ 6

Figure 7 Reinforcement of in fill shear walls ............................................................................. 7

Figure 8 Application of external shear walls ............................................................................. 7

Figure 9 RC jacketing in beam-column joint ............................................................................. 8

Figure 10 Typical application of steel jacketing ........................................................................ 8

Figure 11- FRP strengthened frame ........................................................................................... 9

Figure 12- Uplift of water column due to earthquake .............................................................. 10

Figure 13- Tsunami wave generation ....................................................................................... 10

Figure 14- Tsunami wave with collected debris ...................................................................... 11

Figure 15 Damage on RC structures due to Tsunami water born objects ................................ 11

Figure 16- FRP strengthened Ecoleader frame ........................................................................ 12



1

1 INTRODUCTION

New lessons are always learnt earthquakes in intense magnitude. One of the common lessons

is learnt in many concrete structures around the world. In the days of rapid growth and

research in high performance material technology, the need for a ductile, strong, efficient

material is very essential to keep the world away from devastating results due to the curtsy of

natural disasters. The expertise show us that r/c structures strengthened with FRP are one of

the effective and efficient strengthening technique that can be adopted when its subjected

loads to seismic actions. In technical terms there are two primary methods in which the

seismic loads can be resisted:

Where the structure is constructed with large member sections that they are limited

only to take elastic stresses.

Where in a structure constructed of small sections, those are designed to create many

plastic hinges.

However, when the structure is made up of large sections it will be heavier in mass and they

may not have adequate margin for safety for unexpected larger earthquakes. This forms a

failure in brittle manner which can be catastrophic.

Figure 1 Example of Dissipative and non-dissipative global behaviour of structures [1]

Therefore to resist the earthquakes more efficiently and to increase the deformation capacity,

ductile behaviour will be most suitable option because it is almost impossible to predict the

forthcoming earthquake and its intensity hence in any event that the structure need to resist

and absorb more energy than its design, it will comfortably dissipate the energy with plastic

deformation of the structural elements.

March 11 2011, an earthquake of historic proportion strikes Japan on its east coast. The

massive 8.9 magnitude earthquake tears through the structures on a densely populated

neighbourhood. Minutes later a tsunami follows through the east coast carrying boats, yachts

and heavy structures with high velocity. It was recorded as one of the greatest natural disaster

tragedy in the modern times. It was an earthquake so powerful that it moved the earth from its

axis. Parts of Japan has gone 10ft out to the sea, parts of coast has dropped about 3ft. There



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are no mysteries in the event of this earthquake. Many people were able to survive due the

science and engineering understanding of earthquake behaviour and Tsunami, but this disaster

shows there is much more to learn for engineering purposes.

Another significant earthquake which led to crucial changes in engineering design standards

and codes is the 1995 Kobe earthquake. Many of the existing structures designed during that

time were in accordance with seismic design guidelines yet it had issues as inadequate lap

splice in longitudinal R/F, lack of confinement in critical hinge zones. These deficiencies can

significantly reduce the strength and ductility in R/C structures (Aboutha et al 1996).

Figure 2 Damage on reinforcement column due to insufficient lap splice [2]

2 RESEARCH AIMS AND OBJECTIVES

The main aim of this research is to review and analyse the response of the structure due to

earthquakes given in the frame tested under Ecoleader project with strengthening techniques

in critical regions. The 2nd phase of this research is to apply Tsunami loadings and impact

loading of water-born structures from Tsunami. In order to achieve these targets, the tasks are

broken down into as show in list below:

Reviewing the evolution and need for seismic resisting design and its structural

behaviour due to past significant events of earthquakes.

Understanding the behaviour of reinforced concrete structures under earthquake loads.

Review cases of failure of reinforced concrete structures and elements due to seismic

loads and understand the main causes of failures.

Understanding the behaviour of strengthening techniques in reinforced concrete

structures to increase ductility in critical regions.

Performing a Non-Linear analysis of the frame given Ecoleader project in Drain 3dx

for different peak ground acceleration with FRP strengthened at critical regions and

also a bare frame and compares the results.



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Study the phenomenon of Tsunami loading effects on reinforced concrete structures

and understand the behaviour of impulse loading due to water-born structures during a

Tsunami.

Application of Tsunami loads in to model in Drain 3dx and analyse results with a

frame strengthened with FRP.

3 LITERATURE REVIEW

3.1 Background

Existing reinforced concrete structures which were designed using only gravity loads or old

seismic standards should be modified on its structural configurations and material properties

to increase seismic performance. However information gathered from last few decades of

experimental and analytical studies from researches has given a rigid foundation of guidelines

for dealing with problems that are specific and in a logical manner due to high uncertainty on

the estimation of earthquake loads on structures.

Current seismic design accepts that damage will occur in moderate to large seismic events,

although attempts are made via special detailing and strengthening techniques to limit this

damage to specific plastic hinge zones. These zones, designed to sustain sever damage under

multiple cyclic rotations, tend to act like a fuse, essentially protecting the structure from

forming unfavourable mechanisms. Although this design philosophy ensures good protection

to occupants by preventing collapse, there is a strong likelihood a moderate to large

earthquake will render a structure irreparable. As a result, economic costs, both direct and

indirect, can be significant; this has been confirmed from recent earthquakes in the United

States (Northridge, 1994) and Japan (Kobe, 1995).

3.2 Seismic Capacity and Demand

Proportioning and detailing of critical

regions in earthquake-resisting structures

capacity have mainly been based on results

of tests on laboratory specimens tested in

shaking-table tests, pseudo dynamic tests

and quasi-static methods. Becauseearthquake loadings in these critical

Figure 3



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regions require additional requirements apart from proving sufficient strength and stiffness to

structural elements, a another basic requirement must be considered in the earthquake

resisting design which is ductility or inelastic deformation capacity. This is mainly because its

not economically feasible to design structures to behave elastically to strong-moderate

earthquakes [4]. Thus providing ductility in the critical regions will allow the structure to

dissipate most amount of energy by inelastic deformation as shown in Figure 3.

Since yielding at critically stressed regions and subsequent redistribution of forces to less

stressed regions is central to the ductile performance of a structure, good practice suggests

providing as much redundancy as possible in a structure.

3.3 Failure of reinforced concrete structures to seismic loads

Recent earthquakes such as Northridge and Kobe have exposed the vulnerability of reinforced

concrete structures. Most of the structures collapse and failure was caused most in Beam-

Column joints by brittle shear failure, lack of confinement and insufficient bond strength in

Longitudinal R/F as shown in Figure 4.

Figure 4 General issues and causes for failure of reinforced concrete joints. [4]

3.3.1 Bond-Slip failure

The behaviour of hysteric model of reinforced concrete structure mainly depends on the

behaviour of constituent materials and other factors related to the interaction between

concrete and reinforcement under cyclic loading. The demonstration of this interaction is the

relative slip between concrete and steel in the form of pull-out reinforcement from exterior

beam-column connections and also the due to large cracks in internal beam-column joints.



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During the design reinforced concrete elements it is assumed that perfect bond takes place.

This is true for low loads but when the load increases, cracking and breaking of bond happens

unavoidably and bond slip takes place in the beam. Near the cracks high bond stresses

develop causing relative displacement between reinforcement and concrete.

3.3.2 Beam-Column Joint failure

Current seismic design accepts that damage will occur in moderate to large seismic events,

although attempts are made via special detailing to limit this damage to specific plastic hinge

zones. These zones, designed to sustain severe damage under multiple cyclic rotations, tend to

act like a fuse, essentially protecting the structure from forming unfavourable mechanisms.

Figure 5 Typical Failure of Beam-Column Joint [5]

Although this design philosophy ensures good protection to occupants by preventing collapse,there is a strong likelihood a moderate to large earthquake will render a structure irreparable.

As a result, economic costs, both direct and indirect, can be significant; this has been

confirmed from recent earthquakes in the United States (Northridge, 1994) and Japan (Kobe,

1995). Generally, it is now recognised that beam-column joints can be critical regions in

reinforce concrete frames designed for inelastic response. the portions of columns that are

common to beams at their intersections are called beam-column joints. in reinforced moment

resistance frames, there are three common types of joints; exterior, interior, and corner joints

(uma and prasad, 2006).

A fundamental requirement of a reinforced concrete frame is that before joint failure, the

members should be able to develop their full capacity. to achieve this requirement, it is very

essential to verify the shear resistance and anchorage conditions of a reinforcement passing

through the joint region (penelis and kappos, 1997). Exterior beam-column joints are more

vulnerable than interior joints which are partially confined by beams attached to four sides of

the joint and contribute to the confinement.



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3.4 Existing seismic strengthening techniques

In the past a large number of reinforced concrete structures have been damaged by severe

earthquakes, and some of these structures have been repaired and strengthened. Several

examples of the repair and strengthening of reinforced concrete buildings damaged by

earthquakes have been reported in earthquake-prone countries. The need for the strengthening

of structures also arises in cases where existing structures must comply with more recent code

requirements. This was the case for a number of structures in Japan after the 1978 Miyagiken-

oki Earthquake.

In New Zealand there are many structures constructed before the 1970's that would have

inadequate response during a strong earthquake. Comparison of the design levels for

seismic lateral loads between previous codes and the current loading code (NZS 4203 [9])

indicates that buildings designed to the previous codes often do not satisfy the strength and

ductility requirements of the current loading code. Typical deficiencies of moment resisting

frames are: inadequate shear strength of columns and beam-column joints, and inadequate

flexural strength and ductility of columns (Brunsdon and Priestley, Park).

In the system strengthening , new elements are added to a building to enhance its global

stiffness. With an increase in the stiffness, the natural period of vibration of the building is to

decrease. This, in turn, will result in a decrease in the amount of horizontal displacement that

must be achieved by the building to resist earthquakes as shown in Figure-6. When the building has enough stiffness, it will no longer able to achieve the amount of displacement

which would cause it to collapse.

Figure 6- Change in the displacement demand and capacity of the structure after strengthening [6]



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3.4.1 In-fill shear walls

Among the global strengthening methods, addition of rc infill is the most popular one.

Many researchers have focused on the addition of infill rc walls and found that the installation

of rc infill walls greatly improves lateral load capacity and stiffness of the structure. even in

cases of application to damaged buildings, the infill method can yield satisfactory results

(canbay et al., 2003; sonuvar et al., 2004).

Figure 7 Reinforcement of in fill shear walls [6]

3.4.2 External shear walls

Although the use of shear walls becomes widespread due to the fact that they are effective

strengthening elements, they are also known to result in some difficulties hence they require a

great deal of demolition and construction works in the existing structure. Application of

external shear walls is an approach introduced to diminish such difficulties (sucuoglu,2006).

In this approach, shear walls are applied to the external facade of a building without

demolishing the existing infill walls. In that case, the shear wall can be placed in parallel with

or perpendicular to the existing frame members.

Figure 8 Application of external shear walls [6]



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3.4.3 RC jackets

One of the most frequently used methods for strengthening of the reinforced concrete

columns is the reinforced concrete jacketing (Figure-9). Jacketing which can be defined as the

confinement of the column with new and higher quality reinforced concrete elements may be

implemented for various purposes based on the type of deficiencies that the structural member

has. Columns subjected to brittle damages can be jacketed in order to enhance resistance

against shear and/or axial loads. In that case, although the purpose of jacketing is only to

increase axial load or shear strength, some changes will also occur in the bending stiffness

and moment capacity of the member after the jacketing application. By considering these

changes during the jacketing design, the jacketed section is ensured to achieve adequate shear

and axial load strength.

Figure 9 RC jacketing in beam-column joint [6]

3.4.4 Steel jacketsJacketing with steel elements is a practical method used frequently for various applications. A

typical steel jacketing application is presented in (Figure 10). Steel jacketing can readily be

used to especially enhance the shear strength of reinforced concrete elements. Located at the

corners of an element, L-profiles are coupled by means of steel plates and confined. With the

maintenance of continuity between storeys, steel jacketing can also be used to increase the

bending strength. Also, the maintenance of adequate strength between the steel element and

reinforced concrete element is inevitable for the improvement of bending capacity.

Figure 10 Typical application of steel jacketing [6]



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3.4.5 FRP Stengthening

In recent years, use of Fiber Reinforced Polymer has considerably become widespread in

strengthening applications. Fiber polymer fabrics that can be used to improve bending, shear

and axial capacities of the columns and beams may be manufactured from various materials

such as carbon, glass and aramid without an increase in the volume of the strengthened

member, significant improvements can be achieved in the capacity and ductility

characteristics of the element [6]. In (Figure 11), beam strengthening for a testing structure is

shown. These materials may practically be used for numerous purposes such as enhancement

of the flexural capacity of floor slabs and improvement of shear capacity of beams, columns

or shear walls.

Figure 11- FRP strengthened frame

In case FRP material is used like a longitudinal reinforcement, the additional flexural capacity

produced can easily be found by a simple calculation of cross-section. Calculations for

determining its contribution to the shear capacity is not very different from the conventional

reinforced concrete calculations. To measure enhancement in the axial capacity and change in

the ductility of the member, more complex calculations beyond the limits of basic reinforced

concrete knowledge are needed.

3.5 Tsunami behaviour and its impacts on structures

Earthquake does not only occur in the ground surface due to tectonic plate movement but also

be in the sea bed which displaces the water column above and originate waves as shown in

(Figure 10). These waves are commonly known as Tsunami.



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Regular sea waves by the wind are very different to tsunami waves. Wind blowing on the

surface of the sea can only move the upper layer of water, forming waves but not affecting

movement deeper down. The water particles moves in a circular motion which propagates the

wave along but deep down the sea particles don’t move. Therefore the strength of these waves

which reaches the shore mainly depends on the movement of the first few meters.

Figure 12- Uplift of water column due to earthquake

In the case of strong earthquake in the sea bed, the sea floor abruptly deforms and vertically

displaces the over lying water, the entire water column is disturbed by the uplift of the sea

floor. This sudden movement releases an impulse of energy which is transferred to the whole

column of water on the sea surface and the sea floor which moves the water particles deep in

the sea. And this wave of water approaches the shore with energy of an earthquake with a

destructive force far superior to an ordinary wave and that the cause which damages building

on other structures standing on its way despite the height and speed of the wave is low as seen

in (Figure 13).

Figure 13- Tsunami wave generation

Alarm systems are currently placed in Indian and Pacific oceans to send warnings when a

tsunami is generated. These waves are extremely fast up to 800km/h. The speed of the

tsunami wave depends on the depth of the water that is travelling through when approaching



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the shore therefore the tsunamis speed diminishes but the wave amplitude increases as it

approaches the shore as shown in (Figure-13).

During the Japan 2011 earthquake 95% of buildings were destroyed by Tsunami. As

witnessed heavy boats and cars were on top of buildings because as water pushes through

restricted areas in dense towns, its being tunnelled therefore it squeezes and increases its

height. Once the wave starts to move, it moves like glacier with collected heavy debris of

boats, trucks and cars including full scale houses as show in (Figure 14).

Figure 14- Tsunami wave with collected debris

Many RC buildings collapsed or were severely damaged due to the impact of massive objects

carried by the tsunami waves as shown in (Figure-15). However, tsunami field surveys have

reported that even improperly designed buildings that had only columns in the first-story (i.e.,

no infill walls) performed well during the Indian Ocean tsunami (Dias et al. 2006). Based on

tsunami field observations and research studies, new tsunami resistant buildings have been

constructed, where the lower level of the building would be elevated by means of RC

columns to allow the free flow of tsunami waves. However, these columns are very

vulnerable to impact from tsunami water-borne massive objects such as automobiles, barges,

boats, empty storage tanks and shipping containers (Ghobarah et al. 2006).

Figure 15 Damage on RC structures due to Tsunami water born objects [7]



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4 EXPERIMENT AND ANALYSIS

4.1 Seismic Response of Ecoleader frame on drain 3D-x

The investigated structure from the Ecoleader Project (No 2) as shown in (Figure 15) is used

as a case study structure to investigate the behaviour with bare frame and FRP strengthened

frame. The structure was constructed and tested on an AZALEE shaking table in laboratory

located in Saclay, France between October and November 2004 (Chaudat et al. 2005).

According to Chaudat et al. (2005), in order to simulate most of the existing buildings

in Europe, the structure was intentionally designed according to the old provisions of

building codes with poor detailing and no capacity design consideration.

Figure 16- FRP strengthened Ecoleader frame

The major objective of the Ecoleader project was to examine different techniques of

strengthening of the bare frame. Two different series of tests with different PGA levels

were performed on one-bay, two storey, full scale spatial RC structure: One on the bare

frame and the same frame with fibre reinforce polymer (FRP) strengthening (Chaudat et

al. 2005). The objective through this research project is to calibrate the data given as a

programmed file in Drain 3D-x to match with the experimental results. The fundamental

parameters which govern the accuracy are the beam-column joint properties. This will change

the overall behaviour of the structure. Initial analysis will be done to calibrate the results

using the bare frame properties. The second phase of this project is to input different

properties using strengthening techniques to improve the seismic performance under different

earthquake intensities from 0.05g-0.4g PGA.



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4.2 Tsunami loading and analysis

Building damage due to tsunami water-borne massive objects has been studied in seveal other

p, impact on a RC building with elevated lower level due to boats and shipping containers is

discussed. Nonlinear dynamic analysis of ecoleader RC frame systems is considered, namely

ordinary moment bare frame and FRP strengthened frame for high tsunami prone zones. At

the column impact section the displacement, shear force and moment-curvature responses are

investigated. In addition, the stress-strain behaviour of cover concrete, core concrete and

tension reinforcement at the impact section are studied. Finally, the behaviour of both frames

is compared.

Some of the main forces acting on structures due to a tsunami are breaking wave force,

buoyant force, hydrostatic force, surge force, hydrodynamic (drag) force and impact force due

to water-borne objects (Yeh 2006). In the present study, the dominant forces are the

hydrodynamic force and the impact force from tsunami water-borne massive objects.

4.2.1 Hydrodynamic Force

The hydrodynamic force FH exerted on first-story columns can be evaluated from:

F H =1/2. Ρ .C D.A.u2

Where ρ= fluid mass density,

CD = drag coefficient (2.0 for square columns),

u = tsunami flow velocity, and

A = wetted area of the object projected on the plane normal to the flow direction i.e., A hb = ,

in which h = flow depth and b = breadth of the object (FEMA 2000).

The estimation of time varying impact force on the structure is complex because the force

generated during the impact is influenced by the properties of the water-borne object, e.g.,

material properties, geometry, mass, velocity and orientation on impact; and the properties

of the structure itself, particularly its stiffness and inertia (Stronge 2000). In this study, the

impact force-time history is based on the impulse-momentum approach that equates the

change in linear momentum of the water-borne object and the impulse imparted on the

structure during the impact. This results in the following expression for the time varying

impact force FI:

where m = mass of the object, u = velocity of the object and t I = impact duration.



14

In Eqn above it is assumed that the velocity of the object before impact is the same as the

tsunami flow velocity u for the given inundation depth and that the linear momentum of

the object after impact is zero. The impact force-time history for the dynamic analysis is

assumed to be of triangular shape and the impact duration is taken as t I =0.1s following the

recommendation for RC construction in CCH (2000).

5 PRE-CONCLUSION AND RESULTS

Seismic performance of old buildings designed for old standards are vulnerable to both

seismic and tsunami load hazards. It was clearly seen the requirement of efficient

strengthening material to improve the performance of sub-standard buildings. Previous

research on the Ecoleader model using Drain 3D-x by using FRP and PTMS techniques reveal

significant change in overall structural behaviour. The analytical frequency dropped by 54%

for the first mode which is higher than the previous model by 10%. The analytical

results showed better agreement (by 15%) with the experimental results in contrast to the

previous model.

Considering the cases of previous research on the response of Tsunami loading due to water- born structures will be used in reference for this project. It shows that the peak displacement

due to a 1500 kg boat is more than 2.5 times the peak displacement due to impact of the 1200

kg boat at the same level. Degradation of the axial load carrying capacity, longitudinal bar in

tension has yielded and the maximum strain is 0.011 which is 5.5 times the yield strain due to

impact of the 1500 kg boat (Anil C, Kavinda 2008).



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6 REFERENCES

[1] ArcelorMittal Technical Brochure: Earthquake Resistant Steel Structures, Figure-3

[2] http://natgeotv.com.au/tv/seconds-from-disaster/episode.aspx?id=1875

[3] Seismic Design of Reinforced Concrete Structures, ASO OMER MOHAMAD AMINE,

1.4-1.6

[4] Repair and Strengthening of Reinforced Concrete Beam-Column Joints: State of

the Art by Murat Engindeniz, Lawrence F. Kahn, and Abdul-Hamid Zureick, ACI

structural journal technical paper

[5] http://www.engr.psu.edu/ae/newsletters/newsletter/Sp01/India.htm

[6] Seismic Strengthening of Reinforced Concrete Buildings Hasan Kaplan and Salih

Yılmaz Pamukkale University, Department of Civil Engineering Turkey

[7] Tsunami-Induced Loading on StructuresDan Palermo, Ph.D., P.Eng., and Ioan Nistor,Ph.D., P.Eng.

http://natgeotv.com.au/tv/seconds-from-disaster/episode.aspx?id=1875



http://www.engr.psu.edu/ae/newsletters/newsletter/Sp01/India.htm





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CIV4001-CIV4002 Intermediate Report - Research Proposal Template