BY HEMANTH KUMAR B S SSIT TUMKUR 1 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
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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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.