RC Jacketing

SEISMIC RETROFITTIMG(RC Jacketing)

Group #8

M.E. Structures

Earthquake

A sudden violent shaking of the ground, typically causing great destruction, as a result of movements within the earth's crust or volcanic action.

Structural failures

Civil engineers duty

Provide solutions1. Safety2. Practical3. Cost efficient4. List goes on…

Seismic Retrofit solutions

Retrofitting:

The strengthening and enhancement of the performance of

deficient structural elements in a structure or a structure as

a whole is referred to as retrofitting. Retrofitting means

structural strengthening of a building to a Pre- defined

performance level, whether or not an earthquake has

occurred.

Seismic Retrofit solutions (conti…)



Introduction (conti…)

Various Materials for Retrofitting

1. Grouts like cement sand grout, polymer grout

2. Bonding Agents like epoxy treatment

3. Replacement and Jacketing Material like FRP, steel plate bonding and ferrocements.

When, why and how

When??The need to rehabilitate a structure may arise at any time from the beginning of the construction phase until the end of the service life. During the construction phase, it may occur because of

design errors; deficient concrete production; bad execution processes.

When??

During the service life, it may arise on account of:

an earthquake; an accident, such as collisions, fire,

explosions; situations involving changes in the structure

functionality; the development of more demanding code

requirements.

Why??

The decision to rehabilitate must be made only after the inspection of the structure, its structural evaluation and a cost/benefit study of the different solutions

Non destructive testing

Why??

How?

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

The strengthening techniques for reinforced concrete structures can be divided into:

1. addition of new structural elements;2. strengthening of the existing structural elements.

Jacketing

Jacketing is the most popularly used method for strengthening of building columns. The most common types of jackets are steel jacket, reinforced concrete jacket, fibre reinforced polymer composite jacket, jacket with high tension materials like carbon fibre, glass fibre etc.

Purpose of jacketing

To increase concrete confinement by transverse fibre reinforcement, especially for circular cross-sectional columns,

To increase shear strength by transverse fibre reinforcement,

To increase flexural strength by longitudinal fibre reinforcement provided.

Jacketing (Technical Considerations)

The main objective of jacketing is to increase the seismic capacity of the moment resisting framed structures. In almost every case, the columns as well as beams of the existing structure have been jacketed.

In comparison to the jacketing of reinforced concrete columns, jacketing of reinforced concrete beams with slabs is difficult yielding good confinement because slab causes hindrance in the jacket.

FRP Jacketing

Fibre-reinforced plastics are a category of composite plastics that specifically use fibre materials to mechanically enhance the strength and elasticity of plastics.

The original plastic material without fibre reinforcement is known as the matrix.

FRP Jacketing

Types of Fiber reinforced plastics Carbon fiber material Glass fibre material Aramid fiber material

FRP Jacketing

fibre reinforced polymer composite jackets for seismic strengthening of columns are winded with high strength carbon fibres around column surface to add spiral hoops

FRP jacketing

Confinement is of high degree because carbon fiber is of high strength and high modules of elasticity are used;

The carbon fibre has light weight and rusting does not occur.

Steel Jacketing

Reinforced Concrete Jacketing

Reinforced concrete jacketing can be employed as a repair or strengthening scheme. Damaged regions of the existing members should be repaired prior to their jacketing. Rehabilitated sections are designed in this way so that the flexural strength of columns should be greater than that of the beams.

Jacketing procedure of RC columns

Added longitudinal reinforcement.

1. Anchoring to footing: Generally, in the case of RC jacketing, the steel longitudinal reinforcing bars of the added jacket can be anchored to the original footings.

2. Crossing the slab: When continuity between floors of the RC jacketing is required, holes must be provided in the slab to allow the longitudinal bars of the jacket to pass through.


Interface surface treatment1. Increasing surface roughness: hand chipping, sand-blasting, jack-

hammering, electric hammering, water demolition, iron brushing, etc

2. Surface pre wetting: . It has been indicated that an excessively dry substrate can absorb too much water from the repairing material, causing excessive shrinkage. Excessive humidity on the substrate can close the pores and prevent the absorption of the repairing material. A saturated substrate with a dry surface may be considered the best solution.

3. Application of bonding agents:The values of the shear and tension strength of the interface reduced when the epoxy resin was applied on the sand-blasted surfaces, contrarily to what happened when other roughening methods were used.


Addition of steel connectors: The use of steel connectors is of extreme importance in the case of precast RC beams with in situ cast slabs

Addition of concrete: Normally the added concrete has a maximum aggregate dimension of about 2mm because of the lack of space in the jacket. This is due to its diminished thickness associated with the volume occupied by the added steel reinforcement. It is also for this reason that a self-compacting concrete (SCC) is frequently used.



With this rehabilitation method, a significant increase of strength and/or ductility can be achieved. This technique can consequently be used to achieve these objectives, but also to correct the overall behaviour of the structure.

Alcocer & Jirsa(1990) studied the response of RC frames redesigned by jacketing. The specimens were tested applying a bi-directional cyclic loading. The authors have concluded that jacketing may change the structural concept from a strong beam–weak column to a strong column–weak beam concept. They state that, by jacketing the most damaged element, the column, the strength and the stiffness were 35 and 45%, respectively, of the values obtained with the redesigned undamaged structure.

RC jacketing : Structural behaviour

Alcocer(1993) states, in his experimental study on RC frame connections rehabilitated by jacketing, that, by jacketing the most damaged elements, the columns and joint, the strength at 2% drift and the stiffness at 0.5% drift were 63 and 52%, respectively, of the values obtained with the undamaged specimen.


Rodriguez & Park(1994), performed simulated seismic load tests on damaged and undamaged RC columns strengthened by jacketing to investigate the increase of strength, stiffness and ductility achieved. They state that the strength and stiffness of the columns repaired by jacketing were up to three times those of the as-built columns

The effect of previous damage and the different reinforcing details used, had no significant influence on the overall seismic performance of the jacketed columns.


Conclusion

The RC jacketing strengthening method, unlike other techniques, leads to a uniformly distributed increase in strength and stiffness of columns. The durability of the original column is also improved, in contrast to the corrosion and fire protection needs of other techniques where steel is exposed or where epoxy resins are used. Finally, this rehabilitation procedure does not require specialized workmanship. All those reasons make RC jacketing an extremely valuable choice in structural rehabilitation. The structural behaviour of a building rehabilitated by RC jacketing of the columns, like any other strengthening technique, is highly influenced by details.

a non shrinkage concrete should be adopted with characteristics of a selfcompacting, high-strength and high-durability concrete.

References

Aguilar J, Juarez H, Ortega R & Iglesias J. The Mexico earthquake of September 19, 1985. Statistics of damage and retrofitting techniques in reinforced concrete buildings affected by the 1985 earthquake. Earthquake Spectra 1989: 5(1): 145–151.

Alcocer SM. RC frame connections rehabilitated by jacketing. Journal of Structural Engineering 1993: 119(5): 1413–1431.

Alcocer S & Jirsa J. Assessment of the response of reinforced concrete frame connections redesigned by Jacketing. Proceedings of the 4th US National Conference on Earthquake Engineering 1990: 3: 295–304.

Rodriguez M & Park R. Seismic load tests on reinforced concrete columns strengthened by jacketing. ACI Structural Journal, March–April 1994: 91(2): 150–159.

Rodriguez M & Park R. Repair and strengthening of reinforced concrete buildings for earthquake resistance. Earthquake Spectra 1991: 7(3): 439–459.

www.google.com www.sciencedirect.com

http://www.google.com/

http://www.sciencedirect.com/

Documents

RC Jacketing