Identification of Cracks
Answer for 1.a)
Mode of Failure: Concrete crushed and the reinforcement is exposed. Its form of Flexure Failure. Flexural failure has occured due to reversal of Stresses during the earthquake. At support, due to stress reversal top of the beam experiences compression and bottom of the beam experiences Tension.
Top compression is managed by the Flange action of Slab. Whereas the Tensile stresses at bottom were not satisfied by the reinforcement provided at the bottom of the beam. This has resulted from yielding of the reinforcement, which can be seen from the provided picture in 1.a.
Since the reinforcement has yielded, it can not be repaired
Answer for 1.b)
It is observed that cracks at the beam column edge have formed. It is beam pullout failure due to insufficient development/anchorage length of reinforcement at the joint. The horizontal movement of structure due to earthquake may lead to complete detaching of beam from column.
Repairing the damage by providing anchorage length is not possible as the two concrete surfaces are old.
Answer for 1.c)
Major crack is observed exactly at the joint of Column & Beam. Minor cracks are observed across the depth of beam and lenght of slab. It is Plastic hinge failure. Due to Cyclic lateral loading and stress reversal at the joint damage has resulted. Due to flange action of Slab, few cracks are visible in slab also.
As the concrete has not spalled beyond reinforcement, joint can be strengthened. But the damage cannot be reversed.
Answer for 2.a)
It is observed that the concrete at the top of the column is damaged all around its face. But the beam is safe. By this it can be inferred that it is soft storey failure due to Plastic hinge formation. As the infill walls are absent, it has led to strong beam and weak column mode of failure.
By providing infill walls, further damage can be avoided. But it depends on the level of damage concrete has undergone.
Answer for 2.b)
From the picture it is observed that longitudinal reinforcement is intact (has not bulged) whereas spacing of shear reinforcement is more than recommended. Due to this concrete was was subjected to shear stress. The crack is in diagonal direction. As a result, it has led to Shear failure. Shear strength of Concrete is very less when compared to that of steel.
As the concrete has undergonce failure, the structure/damage is not repairable.
Answer for 2.c)
It is seen that there are two slabs connected to the column, one at the roof height and another at mid height of column. The column has failed due to Short column effect. The additional slab/beam at mid height was not accounted in the design and has lead to this failure.
This type of damages cannot be repaired.