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Strengthening of Reinforced concrete Corbel Dr. Muhammad Abed Attiya

Strengthening of Reinforced concrete Corbel
Dr. Muhammad Abed Attiya
University of Kufa\ College of Engineering, Civil Department
E-mail: [email protected]
Corbel is a short structural element that cantilevers out from column/wall to support load. Generally, the corbel is casted monolithically with column/wall.
The followings are the major items show the behavior of the reinforced concrete corbel, as follows :

The shear span/depth ratio is less than 1.0, it makes the corbel behave in two-dimensional manner.
Shear deformation is significant is the corbel.
There is large horizontal force transmitted from the supported beam result from long-term shrinkage and creep deformation.
Bearing failure due to large concentrated load.
The cracks are usually vertical or inclined pure shear cracks.
The mode of failure of corbel are :
1- failure of the end anchorages of the tension tie , either under the load point or in the column.
2- failure of the compression strut by crushing or shearing.
3- local failures under the bearing plate.
The followings figure shows the mode of failure of corbel.

Reinforced concrete corbels likewise other structural members may subject to damage of cracking. As a result the efficiency of such structural member may reduce. For this purpose there is a need for strengthening to retrofit the corbel structural efficiency represented by load carrying capacity with an acceptable amount of deformation.
Different methods of strengthening technique were followed, different strengthening materials and bonding agents were attempted. Fiber reinforced polymers were found to be active materials for strengthening structural members. Test results indicate that concrete corbel reinforced with sufficient amount of flexural and shear reinforcements damaged by cracking can be repaired with CFRP sheets for a sufficient value of load capacity close to the load capacity of true corbel. However; the load enhancement of true reinforced concrete corbel after strengthening was found to be 28.3% using best CFRP sheet strengthening configuration provided to flexural and shear zones. It is worthy to note that fiber reinforced polymers are organic materials of high cost and using such materials for strengthening lead to the total high cost of the process. For this purpose there is good chance to develop other methods for strengthening provided that they become efficient and economic.

The figure above shows the way how the corbel cracks in case of overloading. The concrete of the short corbel is under a long term repeated tensile stress. In the first place the blue crack appears and the decisive destruction takes place along the line of the red crack. The transverse fastening together of the corbel completely eliminates the development of tensile forces and increases the load-carrying capacity of the corbel by about 500 % and prolongs its life span. The method of keeping taut a short strand is the technical know-how of PEEM Company. The performed work quality is verified by tens metric measurement through compressing the corbel of the column.
When fiber reinforced polymer (CFRP) laminates are used An increase of about (44.5- 60) % in the ultimate load has been obtained for specimens strengthening by inclined technique compared to the ultimate load of control corbel and (14.7 – 31.2)% for specimens strengthening horizontal technique. For corbels repaired with CFRP strips, an increase of (56%) with respect to the ultimate load of control corbel is achieved. Also the strengthened corbels show stiffer load deflection response than corresponding control corbels (un strengthened corbels).

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