Identification of Cracks
Aim: What is the mode of failure or damage of the beams in the figure above? Would you characterize the case as damage or as a failure? Are the damages repairable? Elaborate
Ans1:
a. Observations:
- In the figure we can see that the Beam has damaged more than column
- Concrete crushed and the reinforcement of beam bottom is exposed.
- Concrete spalled beyond the reinforcement which may be a sign of rupture.
- Beam top portion looks safe because of the flange advantage from the slab.
- The crack develops from bottom to top means rebar yielding occurs in support bottom only.
- The reinforcement is still active at the top.
From these observations we can conclude that
- Its form of flexural failure due to reversal of stress during earthquake.
- During the stress reversal, support top experiences compression and bottom experiences tension.
- Top compression is managed by slab advantage because the slab has concrete but the bottom tension was not satisfied by the provided reinforcement.
- So that the bottom reinforcement has yielded and it cannot be repaired.
- And it leads to the crushing of the concrete at the bottom.
b. Observations:
- Cracks along the Beam-column edge.
- Cracks seen to have developed through the structure as it looks much wider.
- Beam looks separated from the column at the joints.
- Concrete is not severly crushed.
From these observations we can conclude that
- Its beam pull out failure due to insufficient development length of reinforcement in joints.
- During earthquake, The horizontal movement of the structure makes this condition worse and detached to the beam member from the column.
- Providing anchorage length between two existing concrete is very difficulty. So it is not repairable.
c. Observations:
- Cracks are exactly at the joint of column-Beam.
- Cracks in Beam developed through its entire width.
- In fig. we can see slab is also developed more cracks along the beam width direction.
From these observations we can conclude that
- It is a plastic hinge failure.
- The damage occured only in the joint zone first of all.
- Cyclic lateral loading & stress reversal at the joints led to the damage.
- Even the slab participated to its best to handle the tension (Slab is severly cracked means it has undergone tension with its flange condition) But unstable to control the damage.
- The joint can be strengthened.
Ans2:
a. Observations:
- Concrete damaged at the top of the column.
- Concrete damaged all around the column face.
- Beams are safe.
- The location of column looks at edge of the building.
- No walls are built along the column beams it is probably at the ground floor, for parking car movement access.
From these observations we can conclude that
- It's a soft storey failure, Technically Plastic hinge formation.
- Dut to absence of infill walls at the Ground floor, The plastic hinge forms at the top of ground storey columns during lateral movement.
- Based on the development of crush of the concrete, it can either be repairable or Non-repairable.
b. Observations:
- Concrete developed complete breakage diagonally.
- Longitudinal reinforcements are intact.
- Shear reinforcement spacing looks wider (which means probably lesser shear rebar provideed).
From these observations we can conclude that
- It's a pure shear failure.
- Inadequate shear reinforcement compels concrete takes all the shear stresses.
c. Observations:
- Colums failed completely.
- Failure at the top of the column.
- There are two slabs connected to the column, probably one at the mid height of the column.
- The wooden piles might be a post failure support after column fialed, providing temporary prop toavoid collapse of the entire structure.
From these observations we can conclude that
- It's a short column failure.
- An additional slab or a beam connected to a column in mid height leads to this effect.
- This leads to failure especially if the connection is unintentional and not accounted in design.
- The failure given in the below picture is not at all repairable.