TECHNIQUES TO RESTORE ORIGINAL STRENGTH OF STRUCTURES

Structures are design for some intended use, and when it gets damaged, it is essential to restore original strength of building so that it can continue to serve the purpose. In case of un-reinforced load bearing masonry works, even a fine cracks can reduce its strength very largely. Therefore it is essential to locate the damages and repair them to restore the original strength of structures. These repair works can be done in many ways. We will discuss the techniques to carry out repairing work to restore the original strength of structures.

Techniques to Repair and Restore Strength of Structural Members:

1. Repair of Small cracks:

Cracks of small openings i.e. 0.075mm can be repaired by pressure injection of epoxy. The procedure for pressure injection is given below:

Clean the external surface thoroughly and make free from dust particles. Place the plastic ports along the crack surface on both sides of the member and secure it in place with an epoxy sealant. The center to center spacing of these ports may be approximately equal to the thickness of the element. When the sealant has cured, inject the epoxy resin beginning the lowest part of the crack at one part at a time in case of vertical or at one end of the crack in case it is horizontal structural member.

The injection of resin is continued till it starts to flow from the opposite side of the structural member at the corresponding port, or from the adjacent port on the same side of the member. Close the injection port at this stage, an continue injecting the epoxy resins at the next port and repeat the same procedure as discussed above.

It should be remembered that the distance between ports should be more closely spaced as the cracks gets smaller and pressure of injection should be higher. This is to ensure that epoxy is injected throughout the length of the crack. This technique is used for all types of structural elements- beams, columns, walls and floor units in masonry as well as concrete structures to restore the original strength.

2. Repair of Large cracks and crushed concrete:

Repair of large cracks (more than 6mm) and crushed concrete or masonry structural elements, following procedure may be followed:

1. Remove the loose material and clean the surface of the concrete cracks, and replace the crushed concrete or masonry with expansive cement mortar , quick setting cement or gypsum cement mortar.
2. Provide shear reinforcements wherever necessary in the region of repairs. Cover this reinforcement with mortar. This will provide strength as well as protection to the reinforcement.
3. For severely damaged concrete or masonry members, the complete damaged portion is removed and replaced with shear reinforcement (where necessary) and masonry as explained above.
4. In case walls and floor diaphragms are damaged, its repair can be done with ferro-cement. Steel mesh is provided on outside surface and fixed on the damaged surface by means of nailing or bolting and then covered with plaster or micro-concrete.

3. Repair of Fractured, excessively yielded and buckled structural member:

When a structural member is buckled or excessively yielded, its reinforcement would have buckled or elongated or excessively yielded. In such case, the structural member can be repaired by removing the damaged concrete portion and cutting the yielded portion of the reinforcement. Then new reinforcement bars are used as replacement and welded to the old portion of the reinforcement steel. Damaged concrete is replaced with fresh concrete. During this procedure, it may be necessary to provide temporary supports to the structures, as splicing of reinforcement without supports may collapse the structure.

If required, also provide additional reinforcement steels and shear reinforcements to prevent future buckling of structural members.

4. Repair of Fractured wooden members and joints:

Wooden structural members can be easily repaired. To restore the original strength structural members made of wood such as beams, columns, struts and ties can be done by splicing additional material. The weathered or rotten wood should first be removed. Nails, wood screws or steel bolts will be most convenient as connectors. It will be advisable to use straps to cover all such splices and joints so as to keep them tight and stiff.