Identification of Cracks
Week 1-Assignment 1-Module 3
Aim: To determine the mode of failure or damage to the beams and check if such damages are repairable or not for the given photos.
1.a)
Observation:
- 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:
- It’s a form of Flexural failure 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 while the Bottom tension was not satisfied by the provided reinforcement.
- It cannot be repaired since the reinforcement got yielded.
- b)
Observation:
- 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 pull 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 between two existing concrete is very difficult. So not repairable.
1.c)
Observation:
- 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.
2.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 crash of concrete, it can either be repairable or non-repairable.
2.b)
Observations:
- Concrete developed complete breakage diagonally.
- Longitudinal reinforcements 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.
2.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.