BYHEMANTH KUMAR B SSSIT TUMKUR

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JACKETING TECHNIQUES FOR RETROFITTING OF RC COLUMN AND BEAM

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MEANING OF RETROFITTING

GUIDELINES FOR RETROFITTING

GOALS AND OBJECTIVES OF RETROFITTING

JACKETING TECHNIQUES

COLUMN JACKETING

BEAM JACKETING

CONCLUSION

INTRODUCTION

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Modifying existing structures with additional or new component.

Intervention to increase the original strength and stiffness of the RC element.

WHEN

WHY HOW

RETROFITTING

MEANING OF RETROFITTING

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Arise at any time from the beginning of the construction phase until the end of the service life.

Construction phase

Service life

* Design errors* Deficient concrete production* Bad execution processes

* An earthquake* Fire, explosions* situations involving changes in the structure Functionality

WHEN ?

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Complete replacement is likely to be an increasing financial burden

Waste of natural resources

Reinforced concrete buildings and structures

Increase their load carrying capacities or enhance ductility under seismic loading.

WHY ?

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The choice of the repair and/or strengthening method depends on the structural behavior objectives.

HOW?

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Based on the results of the inspection, evaluate the performance of the structure

If the structure does not fulfill performance requirements proceed with design of the retrofitting

structure.

Appropriate retrofitting method

Evaluate the performance of the structure after retrofitting and verify that it will fulfill performance

requirements.

Inspect the existing structure

Identify the performance requirements for the existing structure

GUIDELINES FOR RETROFITTING

Giving unity to the structure.

Increasing the lateral strength and stiffness of the building

Eliminating sources of weakness or those that produce concentration of stresses.

Enhancement of redundancy in the number of lateral load resisting elements.

Goals and Objectives Of Restrengthening

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Purpose

concrete confinement

Shear strength

Flexural strength

Transverse reinforceme

nt

Longitudinal reinforcemen

t

JACKETING TECHNIQUES

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Reasons for strengthening of existing column

Addition of floors

Change of occupational usage

Aging due to deterioration, Corrosion

Errors in design / Construction

Settlement > Allowable

Inclination > Allowable

COLUMN JACKETING

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Column Jacketi

ng

Steel JacketingReinforced concrete

Jacketing

FRP Wrapping

1201/06/2013

Added concrete with longitudinal and transverse reinforcement

Reinforced Concrete jacketing

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CONTD…..

•Huge dead mass is added.

•The sizes of the sections are increased and the free available usable space becomes less.

•The stiffness of the system is highly increased.

•Longitudinal bars need to be anchored to the foundation and should be continuous through the slab.

•Requires adequate dowelling to the existing column.

•The speed of implementation is slow.

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Supporting the loads on columns by means of mechanical jacks

Preparation of column which is to be strengthened

Process of RC Jacketing

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Installing dowels for fastening the reinforcements around

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Installing new reinforcements

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Coating the surface with epoxy

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Pouring new concrete

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Details of RC Jacketing

Properties of

jackets

Width of jacket

Connectors

Match with the concrete of the existing structure.

Compressive strength greater than that of the existing structures

10 cm for concrete cast-in-place and 4 cm for shotcrete.

If possible, four-sided jacket should be used.

Distributed uniformly around the interface.

Better to use reinforced bars (rebar) anchored with epoxy resins of grouts.

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Longitudinal

reinforcement

Transverse reinforceme

nt

Shear stress

At least, 12 mm bar should be used at every corner for a four sided jacket.

Percentage of steel = 0.015 to 0.04

Spacing should not exceed six times of the width of the new elements

Designed and spaced as per earthquake design practice.

Minimum bar diameter used for ties is not less than 10 mm or 1/3 of the

diameter of the biggest longitudinal bar.

Provide adequate shear transfer mechanism to assured monolithic

behavior.

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STEEL JACKETING Involves a concrete-steel composite section by placing a skeleton made of steel angles and

straps

To prevent spalling off of the shell concrete.

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It is not used for columns in river, lake and seas.

Provides passive confinement to core concrete.

Encasing the column with steel plates and filling the gap with a non-shrink grout.

General thickness of grout = 25 mm.

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Process of Steel Jacketing

•Coating the steel bars with an epoxy material that would prevent corrosion.

•Installing the steel jacket with the required size and thickness, according to the design, and making openings to pour through them the epoxy material that would guarantee the needed bond between the concrete column and the steel jacket.

•Cleaning the reinforcement steel bars using a wire brush or a sand compressor.

•Removing the concrete cover.

• Filling the space between the concrete column and the steel jacket with an appropriate epoxy material

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Details of Steel Jacketing

Steel plate thickness

Shape of

jackets

Gap

At least 6 mm.

Rectangular jacketing, prefabricated two L-shaped panels

Gap between steel jacket and concrete column, 25 mm fill with cementations grout.

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Comprise fibers of high tensile strength within a polymer matrix such as vinylester or epoxy.

FRP WRAPPING

Involves wrapping of RC columns by high strength-low weight fiber

FRP sheets are wrapped around the columns, with fibers oriented perpendicular to the longitudinal axis of column, and are fixed to the column using epoxy resin.

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PROCESS OF FRP WRAPPING

Surface preparation

Remove dust and cement loose layer.

Repair of hairline cracks

Application of Primer

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BEAM JACKETING

Strength and stiffness of beams to resist gravity and seismic load.

Flexural resistance must be carefully computed to avoid the creation of a strong

beam-weak column system.

Jacketing of beam = one-sided jackets or 3 and 4 sided jackets.

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CONCLUSION

Improves the lateral load capacity of the building in a reasonably uniform and distributed way.

RC jacketing , leads to a uniformly distributed increase in strength and stiffness of columns, does not require specialized

workmanship, Disadvantage – Increase in dead weight.

Confinement of reinforced concrete columns with steel jackets can enhance the ductility as well as the ultimate strength of the

column, Disadvantage – corrosion.

The role of FRP for strengthening of existing or new reinforced concrete structures is growing at an extremely rapid pace

because of its advantages.

While jacketing a beam, its flexural resistance must be carefully computed to avoid the creation of a strong beam-

weak column system.