Identification of Cracks
Identification of Cracks
1) What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate?
a)
a). Observations:
- Concrete crushed and the reinforcement 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 slab.
- The crack develops from bottom to top means rebar yielding occurs in support bottom only.
Answer: -
- Its form of flexural due to reversal of stress during earthquake.
- During stress reversal, support top experiences compression and bottom experiences tension.
- Top compression is managed by slab advantage, bottom tension was not satisfied by the provided reinforcement.
- Since the reinforcement got yielded, it cannot be repaired.
b)
b). Observations:
- Cracks along beam-column edge.
- Cracks seem to have developed through the structure as it looks much wider.
- Beam looks separated from the column at joints.
- Concrete is not severely crushed.
Answer: -
- Its beam pulls out failure due to insufficient development length of reinforcement in joints.
- During earthquake, the horizontal movement of structure makes this condition worse and detached the beam member from column.
- Providing anchorage length b/w two existing concrete is very difficult, so not repaiable.
c)
c). Observations:
- Cracks are exactly at the joint of column-beam.
- Cracks in beam developed through its entire width.
- Slab also developed more cracks along the beam width direction.
Answer: -
- It’s a plastic hinge failure.
- The damage occurred 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 severely cracked means it has undergone tension with its flange condition), but unable to control the damage.
- The joint can be strengthened.
Question 2).
a)
a). Observations:
- Concrete damaged at top of a 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 means it is probably at ground floor, for parking car movement access.
Answer: -
- It’s a soft storey failure, technically plastic hinge formation.
- Due 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 concrete, it can either be repairable or non-repairable.
b)
b). Observations:
- Concrete developed complete breakage diagonally.
- Longitudinal reinforcement are intact.
- Shear reinforcement spacing looks wider ( which means probably lesser shear rebar provided)
Answer:
- It’s a pure shear failure.
- Inadequate shear reinforcement compels concrete takes all the shear stresses.
c)
c). Observations:
- Column failed completely.
- Failure at top of column.
- There are two slabs connected to the column, probably one at mid height of the column.
- The wooden piles might be a post failure support after column failed, providing temporary prop to avoid collapse of the entire structure.
Answer:
- 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 picture is not at all repairable.