RETROFITTING OF EXISTING RCC MEMBERS DIFFERENT STRENGTHENING TECHNIQUES

SURAJ PRASANNA KUMAR

CE 5102-FALL 2015

INTRODUCTION

• Increasing resistant capacity of structure by various techniques.

• Prominent structural elements: Beams, Columns and slab.

• Deformation in elements.

• Restoring strength to its original condition.

• Release of stress on members.

• Seismic strengthening.

PROBLEMS FACED IN RCC STRUCTURES

• Damage to structural members.

• Excessive loading.

• Errors in design or construction.

• Modification of structural system.

• Seismic damage.

• Structural cracks.

• Corrosion due to penetration- honey combs.

RETROFITTING OR RECONSTRUCTION?

• Economical consideration.

• Immediate solution.

• Improved serviceability.

• Making buildings more suitable for intended use.

• More energy efficient - lowering related carbon emissions.

• Loads may be immediately applied, no cure time.

• Enhancement of strength to increase durability.

FACTORS INFLUENCING SELECTION

• Cost of Construction and maintenance.

• Environmental aspects.

• Clearance issues.

• Magnitude of strength to be enhanced.

• Time constraints.

• Existing concrete strength.

• Seismic effect consideration

• Accessibility to work areas.

FACTORS INFLUENCING SELECTION

• Cost of Construction and maintenance.

• Environmental aspects.

• Clearance issues.

• Magnitude of strength to be enhanced.

• Time constraints.

• Existing concrete strength.

• Seismic effect consideration

• Accessibility to work areas.

RETROFITTING TECHNIQUES

• Conventional techniques

o Section enlargement.

o External plate bonding.

o External post tensioning.

o Ferro cement covering.

o Grouting.

• Advanced strengthening techniques

o Fiber Reinforced polymer(FRP) composites.

SECTION ENLARGEMENT (RCC JACKETING)

• Entire cross section of member is increased.

• Additional structural reinforcement steel with shear stirrups.

• Process involves surface preparation, additional

reinforcement and concrete curing.

Advantages

• Enhanced strength.

• Increased shear capacity of columns.

• Technique is easy and it does not need special design

criteria.

CONTD.Disadvantages

• Increase in member cross section- less floor area.

• Increase dead weight due to extra steel and concrete.

• Prone to high level of corrosion.

• Requires more construction time as it involves curing.

• Production of dust and debris causes pollution and health

hazards.

• Needs shuttering, formworks, reinforced steel, concrete,

concrete pumps, vibrators, etc..,

EXTERNAL PLATE BONDING• Steel plates are attached to the surface of damaged members forming a

three phase steel composite system

• Acts as supplement to existing reinforcement.

Attachment of steel to concrete

o Adhesive connecting mechanism (glue).

o Bolting connecting mechanism.

Advantages

• Stress reduction due to the external steel plate.

• Enhances load bearing capacity.

• decreases chances of cracks and deflection.

CONTD.Disadvantages

• Increase in dead load.

• High installation cost due to heavy weight of steel plate.

• If there is any indications of corrosion in the reinforcement

this technique cannot be used.

• Susceptible to high level of premature de-bonding.

• Chances of corrosion is high.

• Bonding between concrete and steel plate.

• Reaction between epoxy adhesive and concrete.

EXTERNAL POST TENSIONING.

• High strength steel strands or pre-stressing tendons are used.

• Tendons are pulled and connected to anchor points on member.

• Very much suitable for retrofitting of bridges.

Advantages

• Ability to restress, destress and exchange any external pre-

stressing cable.

• Crack free members.

• Reduce deflection.

• High fatigue and impact resistance.

• Immediate enhancing of load bearing capacity.

CONTD.Disadvantages

• Usually requires a greater section depth.

• Exposed to environmental influences.

• Handling of the tensioning devices may be more

difficult.

• High cost.

• Prone to corrosion.

• Skilled person is needed for post tensioning

FERRO CEMENT COVERING

• composite material reinforced with wire mesh and cement mortar

modified with chemicals or polymers with closely spaced layer.

• Process involves surface preparation, orientation of wire mesh

and Ferro concrete finishing.

Advantages• Enhanced resistance to cracking• Capacity to carry heavy loads.• High flexural stiffness compared to ordinary cement.• Resistance to penetration of water.• Provide resistance to fire, corrosion and earthquake.

CONTD.Disadvantages

• Number of labor will be higher.

• Rust can be developed on reinforcement if not covered

properly by mortar.

• It is hard to do welding, screw, nut etc.., properly.

• Binding rod and mesh along can be time consuming.

• Proper curing is required.

• Increases dead weight.

RETROFIT BY GROUTING• Easiest process which involves placing of cementitious material

in to the cracks created from excessive loading in concrete

member.

• Pressure grouting is generally used.

• It is commonly used when honey combs are observed.

• Prevents reinforcement from corroding.

• Very low or no strength gained.

• After grouting proper curing has to be done but often it is

neglected.

• Not effective as other techniques.

ADVANCED STRENGTHENING TECHNIQUE

FIBER REINFORCED POLYMER

• Composite materials: polymer that is reinforced with fiber.

• Fiber reinforcement is to carry load along the length of the fiber, provide strength and stiffness.

• Flat layer contains an arrangement of unidirectional fibers fabrics embedded within a thin

layer of light polymer matrix material.

• Fibers usually use,

o RESINS= EPOXY/ POLYSTER/VINYLESTER.

o REINFORCEMENT(FIBRES)= CARBON/ GLASS/ ARAMID.

COMPOSITION OF FRP

EPOXYPOLYSTER VINYLESTER

RESINS

FIBRES

CARBONGLASS ARAMID

CARBON FIBER REINFORCED POLYMERType of composite material in which carbon constitutes the

fiber phase.

• High performance fiber polymer.

• It contains 93 to 95% of carbon.

• Each fiber is 5 to 10 microns in diameter.

• Twice as stiff as steel and five times as strong as steel.

• It is used to make aircrafts, spacecraft parts, racing car

bodies, bicycle frames etc.,

PROPERTIES OF CARBON FRP

• High tensile strength.

• CFRP is alkali resistant.

• Light weight.

• Corrosion resistant and chemically stable, hence best suitable for rehabilitation.

• High strength to weight ratio.

• Very low thermal conductivity.

• High ultimate strain, thus suitable to earthquake resistant application.

• Electrically, thermal resistance and is non magnetic.

• Fire resistant/ non flammable.

• High abrasion and wear resistance.

USE OF CFRP IN STRUCTURAL STRENGTHENINGCFRP STRIPS

• Performance of CRPF strips depend on the strength of adhesive used to bond the

strips to the concrete surface.

• Strong, ductile and durable structural system can be achieved.

• These are four times stronger than structural steel.

CFRP WRAPS

• Mainly used for corrosion control and retrofitting of rcc members.

•  resistance to collapse under earthquake loading

• In a circular column an increase in axial capacity is also achieved by wrapping.

•  the confinement of the CFRP wrap enhances the compressive strength of the

concrete and increase in load bearing strength.

• Immediate strength gain and open to traffic.

PROCEDURE

WHY THIS TECHNIQUE?

CARBON FIBER REINFORCED POLYMER

Disadvantages

• High initial cost.

• Lack of knowledge: absence of codes.

• Should be protected from UV radiation.

• Use od resins: problems with de-bonding.• Composites must be dried before repair because all resin matrices and some

fibers absorb moisture.

CONCLUSION

• CFRP are thin, strong, flexible, corrosion resistant and light weight. These properties makes

this technique suitable for all purpose compared to other conventional technique.

• High stiffness, high tensile strength, high chemical resistance, high temperature resistant and

fire resistant made CFRP one of the most popular material in retrofitting of RCC members.

• It possess strength up to five times that of steel being one third of its weight.

• Ease in process, less time consuming and increased resistance to deformation.

REFERENCES

• Traditional solutions for strengthening reinforced concrete slabs by dragoş banu and n.

ţăranu

• Decision selection technic for building strengthening methods a. okakpu1 and g.

ozay2,department of civil engineering, eastern mediterranean university, famagusta, via

mersin10, turkey

• Influence of using cfrp on damaged columns repaired with two different materials abbas s. al-ameeri 1* nisreen s. mohammed2 haider m. al-baghdadi 31(civil, engineering depart. / university of babylon, babylon city, iraq,)

• Behaviour of reinforced concrete columns confined with cfrp (carbon fiber reinforced polymer) c.k.rankoth

THANK YOU