PPT =RETROFITTING

Er. SHISH PAL

LECTURER IN CIVIL ENGINEERING

GOVT. POLYTECHNIC AMBALA CITY

1

Introduction

• Earthquake creates great devastation in terms of life, money

and failures of structures.

• Earthquake Mitigation is an important field of study from a

long time now.

• Seismic Retrofittingis a collection mitigation techniques for

Earthquake Engineering.

• It is of utmost importance for historic monuments, areas prone

to severe earthquakes and tall or expensive structures.

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Seismic Retrofitting

Definition

It is the modification of existing structures to make

them more resistant to seismic activity, ground motion,

or soil failure due to earthquakes.

The retrofit techniques are also applicable for other

natural hazards such as tropical cyclones, tornadoes and

severe winds from thunderstorms.

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When is Seismic Retrofitting

Needed ?The two circumstances are:-

Earthquake damaged buildings

Earthquake-vulnerable buildings (with no exposure to

severe earthquakes)

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Retrofit Performance Objectives

• Public safety only: The goal is to protect human life, ensuring

that the structure will not collapse upon its occupants or passers-

by, and that the structure can be safely exited. Under severe

seismic conditions the structure may be a total economic write-

off, requiring tear-down and replacement.

• Structure survivability: The goal is that the structure, while

remaining safe for exit, may require extensive repair (but not

replacement) before it is generally useful or considered safe for

occupation. This is typically the lowest level of retrofit applied to

bridges. 5Er. SHISH PAL

Retrofit Performance Objectives

(Contd.)Structure functionality: Primary structure undamaged and the

structure is undiminished in utility for its primary application.

Structure unaffected: This level of retrofit is preferred for

historic structures of high cultural significance.

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Need of Retrofitting in Existing

Earthquake Vulnerable Buildings

• Buildings have been designed according to a seismic code, but the

code has been upgraded in later years;

• Buildings designed to meet the modern seismic codes, but

• deficiencies exist in the design and /or construction;

• Essential buildings must be strengthened like hospitals, historical

monuments and architectural buildings;

• Important buildings whose services are assumed to be essential just

after an earthquake like hospitals;

• Buildings, the use of which has changed through the years;

Buildings that are expanded, renovated or rebuilt.

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Problems faced by Structural

Engineers are :-• Lack of standards for retrofitting methods

• Effectiveness of each methods varies a lot depending upon

parameters like type of structures, material condition, amount of

damage , etc.

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Basic Concept of Retrofitting

• The aim is at (CEB1997):-

Up gradation of lateral strength of the structure;

Increase in the ductility of the structure

Increase in strength and ductility

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Earthquake Design Philosophy

• Under minor but frequent shaking, the main members of the building

that carry vertical and horizontal forces should not be damaged; however

building parts that do not carry load may sustain repairable damage;

• Under moderate but occasional shaking, the main members may

sustain repairable damage, while the other parts of the building may be

damaged such that they may even have to be replaced after the

earthquake; and

• Under strong but rare shaking, the main members may sustain sever

(even irreparable) damage, but the building should not collapse.

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Classification of Retrofitting

Techniques

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Some Conventional ApproachesAdding New Shear Walls

Frequently used for retrofitting of non ductile reinforced concrete frame buildings.

The added elements can be either cast‐in‐place or precast concrete elements.

New elements preferably be placed at the exterior of the building.

Not preferred in the interior of the structure to avoid interior mouldings

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Some Conventional Approaches

(Contd.)Adding Steel Bracings

An effective solution when large openings are required.

Potential advantages for the following reasons:

Higher strength and stiffness,

Opening for natural light,

Amount of work is less since foundation cost may be minimized

Adds much less weight to the existing structure

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Adding Shear Walls and

Bracings

Fig: Effect of Adding Shear Walls and Bracings

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Adding Steel Bracings

Fig: RC Building retrofitted by steel bracing

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Some Conventional Approaches

(Contd.)• Jacketing (Local Retrofitting Technique)

Most popular method for strengthening of building columns

Types-1. Steel jacket, 2. Reinforced Concrete jacket,

3. Fibre Reinforced Polymer Composite(FRPC) jacket

Purpose for jacketing:

To increase concrete confinement

To increase shear strength

To increase flexural strength

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Jacketing

Fig: Column JacketingFig: Beam Jacketing

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Retrofit of Structures using Innovative

Materials

• Current research on advanced materials has mainly

concentrated on FRP composites.

• Studies have shown that externally bonded FRP

composites can be applied to various structural

members including columns, beams, slabs, and walls to

improve their structural performance such as stiffness,

load carrying capacity, and ductility.

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Effectiveness of FRPC as a Retrofitting

Material

Fig: A 3-D Model of aBuilding

Fig:ARetrofitApplication combining Conventional and Composites Retrofitting

(a) Wall Stresses

before

Retrofitting

(b) After

installation of

Steel Window

frames

(c) Additional

FRP

Retrofitting

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Base Isolation (or Seismic

Isolation)

Isolation of superstructure from the foundation is known as base

isolation.

It is the most powerful tool for passive structural vibration control

technique

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Concept of Base Isolation

• Significantly Increase the Period of the Structure and the

Damping so that the Response is Significantly Reduced.

Fig: Spectral Response for a Typical Base Isolation System

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Types of Base Isolations

• Base isolation systems which uses Elastomeric Bearings

• Base isolation systems with Sliding System

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Elastomeric Base Isolation Systems• This is the mostly widely used Base Isolator.• The elastomer is made of either Natural Rubber or Neoprene.

• The structure is decoupled from the horizontal components of the

earthquake ground motion

A layer with low horizontal stiffness is

introduced between the structure and the foundation.

Fig: Steel Reinforced Elastomeric Isolators

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Sliding Base Isolation Systems• It is the second basic type of isolators.

• This works by limiting the base shear across the isolator

interface.

Fig: Metallic Roller Bearing

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Spherical Sliding Base Isolators

• The structure is supported by bearing pads that have

curved surface and low friction.

• During an earthquake, the building is free to slide on the

bearings.

Fig: Spherical Sliding Base Isolator

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Friction Pendulum Bearing• These are specially designed base isolators which works on

the principle of simple pendulum.

• It increases the natural time period of oscillation by causing

the structure to slide along the concave inner surface through the

frictional interface.

• It also possesses a re-centering capability.

Fig: Cross-section of Friction Pendulum Bearing

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Friction Pendulum Bearing (Contd.)• Typically, bearings measure 3 feet in dia., 8 inches in height and weightbeing

• 2000 pounds

• Benicia Martinez Bridge, California is one of the largest bridges to date toundertake a seismic isolation retrofit.

• Largest seismic isolation bearings, measuring 13 feet in diameter, andweighing 40,000 pounds. They have a lateral displacement capacity of 53inches, a 5 million pound design dead plus live load, and a 5 second period.

• Fig: Bearing used in Benicia Martinez Bridge (left) and Benicia Martinez Bridge (right)

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Advantages of Base Isolation

• Isolates Building from ground motion

Lesser seismic loads, hence lesser damage to the structure.

Minimal repair of superstructure.

• Building can remain serviceable throughout construction.

• Does not involve major intrusion upon existing superstructure.

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CRACK REPAIR TECHNIQUES Epoxy-injection Grouting

Routing and Sealing

Flexible Sealing

Stitching

Providing additional Reinforcement

Drilling and plugging

Pre-stressing steel

Grouting

Dry packing

Surface Coatings

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CRACK REPAIR TECHNIQUES Epoxy-injection Grouting

Cracks as narrow as 0.002 in. (0.05 mm) can be bonded by the

injection of epoxy. The technique generally consists of

establishing entry and venting ports at close intervals along the

cracks, sealing the crack on exposed surfaces, and injecting the

epoxy under pressure. Epoxy injection has been successfully used

in the repair of cracks in buildings, bridges, dams, and other types

of concrete structures. However, unless the cause of the cracking

has been corrected, it will probably recur near the original crack.

The general procedure are given below.

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CRACK REPAIR TECHNIQUES

Clean the cracks: The first step is to clean the cracks that have

been contaminated; to the extent this is possible and practical.

Contaminants such as oil, grease, dirt, or fine particles of

concrete prevent epoxy penetration and bonding, and reduce the

effectiveness of repairs. Preferably, contamination should be

removed by vacuuming or flushing with water or other specially

effective cleaning solutions.

Seal the surfaces: Surface cracks should be sealed to keep the

epoxy from leaking out before it has gelled. A surface can be

sealed by applying an epoxy, polyester, or other appropriate

sealing material to the surface of the crack and allowing it to

harden. If a permanent glossy appearance along the crack is

objectionable and if high injection pressure is not required, a

strippable plastic surface sealer may be applied along the face of

the crack.31Er. SHISH PAL

CRACK REPAIR TECHNIQUES

When the job is completed, the surface sealer can be stripped

away to expose the gloss-free surface. Cementitious seals can

also be used where appearance of the completed work is

important. If extremely high injection pressures are needed,

the crack can be cut out to a depth of 1/2 in. (13 mm) and

width of about 3/4 in. (20 mm) in a V-shape, filled with an

epoxy, and struck off flush with the surface.

Install the entry and venting ports. Two methods are in general

use: Fittings inserted into drilled holes: This method was

the first to be used, and is often used in conjunction with V-

grooving of the cracks. The method entails drilling a hole into

the crack, approximately 3/4 in. (20 mm) in diameter and 1/2

to 1 in. (13 to 25 mm) below the apex of the V grooved

section.

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CRACK REPAIR TECHNIQUES

Bonded flush fitting: When the cracks are not V grooved , a

method frequently used to provide an entry port is to bond a fitting

flush with the concrete face over the crack. The flush fitting has an

opening at the top for the adhesive to enter and a flange at the

bottom that is bonded to the concrete.

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CRACK REPAIR TECHNIQUESMix the epoxy: This is done either by batch or continuous methods. Inbatch mixing, the adhesive components are premixed according to themanufacturers instructions, usually with the use of a mechanical stirrer,like a paint mixing paddle. Care must be taken to mix only the amountof adhesive that can be used prior to commencement of gelling of thematerial.

Inject the epoxy: Hydraulic pumps, paint pressure pots, or air- actuatedcaulking guns may be used. The pressure used for injection must beselected carefully. Increased pressure often does little to accelerate therate of injection. If the crack is vertical or inclined, the injection processshould begin by pumping epoxy into the entry port at the lowestelevation until the epoxy level reaches the entry port above. Forhorizontal cracks, the injection should proceed from one end of thecrack to the other in the same manner. The crack is full be maintained. Ifthe pressure can not be main.

epoxy is still flowing into unfilled portions or leaking out of the crack.

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CRACK REPAIR

TECHNIQUES

Remove the surface seal: After the injected epoxy has cured, the

surface seal should be removed by grinding or other means as

appropriate.

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CRACK REPAIR

TECHNIQUES

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CRACKS REPAIR BY

ROUTING AND SEALING• The Crack sealers should ensure the structural integrity and

service ability .in addition they provide protection from the

ingress of harmful liquids and gases.

• Routing and sealing of cracks can be used in condition

requiring remedial repair and where structural repair is not

necessary .the method consist of enlarging remedial repair and

where structural repair is not necessary . The method consist of

enlarging the crack along its length on exposed surface called

chasing or routing and sealing it with a suitable joint sealant.

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CRACKS REPAIR BY

ROUTING AND SEALING•This is a very common technique for crack treatment and is

relatively simple in comparison to the procedures and the training

required for epoxy injection .The procedure is most applicable to

flat horizontal surface such as floors and pavements. However this

method can be accomplished on vertical surface as well as on

curved surfaces.

•This method is used to repair both fine pattern cracks and larger

isolated cracks .a common and effective use is for waterproofing by

sealing cracks on the concrete surface where water stands or where

hydrostatic pressure is applied.

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CRACKS REPAIR BY

ROUTING AND SEALING• The sealant may be of sereval materials ,including epoxies silicones

urethanes poly sulfides asphaltic materials polymers mortars. Cement

grouts should be avoided due to the like hood of cracking .For floors

the sealant should be sufficiently rigid to support the anticipated

traffic.

•The procedure consists of preparing a groove at the surface ranging

in depth typically from 6 to 25mm.A concrete saw , hand tools or

pneumatic tools may be used .This groove is then clean by last or sir

blasting and allowed to dry . A sealant is placed into the dry groove

and allowed to curd.

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CRACKS REPAIR BY

ROUTING AND SEALING

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CRACKS REPAIR BY ROUTING

AND SEALING

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CRACKS REPAIR BY

ROUTING AND SEALING

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CRACKS REPAIR BY

STITICHING

•The stitching procedure consist of drilling holes on both

slides of the cracks cleaning the holes and an the legs of the

stitching dogs that span the cracks which either a non –shrink

grout or an epoxy bonding system .The stitching dogs

should be variable in length and orientation or both and

should be so located that the tension transmitted across the

cracks is not applied to single to a single plan but spread over

area.

•Stitching may be used when tensile strength must be

established across major cracks .stitching a crack tend to

stiffen the structure the overall structural restraint causing

concrete to cracks elsewhere.

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REPAIR OF CRACK STITCHING

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CRACKS REPAIR BY

STITCHING

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REPAIR BY PROVINDING

EXTRA RAINFORCEMENT Structurally deficient beams and columns are provided extra

reinforcing material at end section. The concrete cover is remove

and steel bar are welded for distance of L/5 for extra end bed

section is coverd with the help strength

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DRILLING AND PLUGGINGThis method consist of drilling down the length of the crack and

grouting its to from a key. A hole typically 50 to 75 mm in

diameter should be drilled. The drilled hole should be cleaned

made tight to be filled to be grout. The grout key to prevent

transverse movement of the section of concrete adjacent to the

crack. The key will be also reduce the heavy leakage through the

crack and loss if soil from behind the leaking wall.

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DRILLING AND PLUGGING

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USING STEEL PLATE

•In this technique Mild steel are glued to beam by epoxy

material for improve flexural and shearing strength of

the member main advantage of the technique are

simplicity and speed construction while the structure is

in used. The head does not reduce considerably and

additional weight edit to the structure by applying plate

very small

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USING STEEL PLATE

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GROUTINGGrouting is a process of injecting mixture of cement, sand

water at high pressure in the cracks, joints, voids etc.

Purpose of grouting:

To strengthen the porous Concrete

To prevent the seepage in dam and water retaining

structures

To reduce uplift pressure below dam

To fill the cracks in concrete structure

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GROUTINGProcedure for grouting:

Drilling of Grouting holes

For drilling grouting holes, equipment's like jack hammer, diamond drill, shot

drill etc are used. The choice of type of drilling equipment depends upon the

type of stone, size of hole and depth of hole.

Arrangement of grout pipes

Grout pipes of 4 to 5 cm dia and 45 to 90 cm length are inserted in the grout

holes. The space surrounding the pipe is filled with cement mortar. The top

end of the pipe is connected to the pump.

Cleaning of cracks

Before injecting grout mixture in the cracks, it is necessary to clean the cracks.

Inserting grout in holes

Normally grout is inserted in the holes at a pressure 0.65kg/cm2 36 depth hole.

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GROUTINGTypes of grouting:

1. Consolidation Grouting:

This type of grouting is used for shallow depthgrouting holes. Normally pressure below 3 kg/cm2 is

known as low pressure grouting.

2. Stage grouting:

When thick layers are to be grouted the total thickness of layer isdivided into stages of 1m each and grouting of each layer is carriedout one by one. Grouting of upper layer is started only after thegrout in the lower layer had properly set.3. Curtain Grouting:

This type of grouting is done to prevent the seepage of water belowfoundation of dam. Grouting holes are drilled in the upstream sideof dam in the bed rock and impermeable grout wall is created.

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CRACKING REPAIR BY

GROUTING•Based on grouting materials used there three types :

•Portland cement grouting

•Chemical grouting

•Epoxy grouting

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PORTLAND CEMENT

GROUTING • It is the process in which fine cement mortar (1:2) used to fill the crack

developed wall.

•For grouting a low pressure grouting pump is required to transfer the

grout in the wall required depth.

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CHEMICAL GROUTING•Chemical used for grouting are sodium silicate, urethanes and

acry lamide. Two or more chemical are combined to from gel, a

solid precipitate or a from as opposed to cement grout that

consist of suspension of a solid particles in a fluid. the

advantage of chemical grout include applicability in moist

environment and their ability to be applied in very fine crack.

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CHEMICAL GROUTING

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EPOXY METHOD•Epoxy Injection technique : Epoxy materials are

resinous binding material which posses high tensile

strength.

•Epoxy injection consist of high strength epoxy

material into the crack concrete filling the voids and

rebinding the affected members

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EPOXY METHOD

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PROVIDING SEISMIC BELT

•Belt are providing in building to preventopening of brick masonry walls particularlyat joint.

•Seismic belt are provided both side of wall above lintel of opening . if the height of story is 3.0m then one belt is sufficient, but the height is more than 3m then 2 belt are provided.

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SESMIC BELT

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•In this method mortar or concrete is conveyed through a

hose(pipe) under high pressure pneumatically on to the surface

to be treated called shortcrete method.

•For treating a damaged wall a layer of 75 mm thick layer of

shortcrete is sufficient to against earthquake.

SHORTCRETE METHOD OF

TREATMENT

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SHORTCRETE METHOD

OF TREATMENT

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BENEFIT OF RETROFITTING

•Saving on capital expenditure while benefiting from new

technologies

•Optimization of existing plant components

•Adaptation of the plant for new or changed products

•Increase in piece number and cycle time

•Guaranteed spare parts availability

•Reduced maintenance costs and increased reliabilit

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LIMITATIONS OF

RETROFITTING

•Lack of confidence of engineers and builders.

•Ignorance of general public.

•Disturbance during retrofitting work.

•Original importance and aesthetic value of building is

likely to be lost.

•Retrofitting sometimes causes reduction of usable space.

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Indian Codes for Earthquake Design

• IS: 1893-2002 (part-1) Criteria for Earthquake Resistant Design of Structures (Part 1 :

General Provision and Buildings) - Code of Practice

• IS: 4326-1993 Earthquake Resistant Design and Construction of Buildings – Code of

Practice

• IS: 13920-1993 Ductile Detailing of Reinforced Concrete Structures subjected to

Seismic Forces – Code of Practice

• IS: 13935-1993 Repair and Seismic Strengthening of Buildings – Guidelines

• IS: 13828-1993 Improving Earthquake Resistance of Low Strength Masonry

• Buildings - Guidelines

• IS: 13827-1993 Improving Earthquake Resistance of Earthen Buildings – Guidelines

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Conclusion

• Seismic Retrofitting is a suitable technology for protection of a

variety of structures.

• It has matured in the recent years to a highly reliable

technology.

• But, the expertise needed is not available in the basic level.

• The main challenge is to achieve a desired performance level at

a minimum cost, which can be achieved through a detailed

nonlinear analysis.

• Optimization techniques are needed to know the most efficient

retrofit for a particular structure.

• Proper Design Codes are needed to be published as code of

practice for professionals related to this field.67Er. SHISH PAL

REFRENCES:-

• Agarwal, P . and Shrikhande M.2006, Earthquake resist design of structure,

2nd edition, Prentice hall of India private limited ,New Delhi.

• EERI 1999, Lesson learnt over Time- Learning for Earthquake.

• Series volume II Innovative recovery in India, Earthquake engineering

research institute, Oakland (CA),USA.

• Murty, C.V.R , 2004, IITK-BMTPC Earthquake Tip NEW DELHI.

• Constantinou, Mc, syamn , M. D, TSOPELAS ,P., and Taylor, D.P., 1993

Fluid viscous dampers in application of seismic energy dissipation and

seismic isolation , ATC,-17, applied technology council ,san Francisco .

• Cardone , D . And dolce , M., 2003, seismic protection of light secondary

• Systems through different base isloation systems , journal of earthquake

engineering , 7(2) ,223-250.

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THANK YOU

69Er. SHISH PAL