Identification of Cracks

Ans 1)

a)

Observations:

• Concrete crushed and the reinforcement is exposed.
• Concrete spelled beyond the reinforcement which may be a sign of rupture.
• Beam top portion looks safe because of the flange advantage from slab.
• The cracks develops from bottom to top means rebar yielding occurs in support bottom only.

Mode of failure:

• Its form of flexursl failure due to reversal of stress during earthquake.
• During stress reversal,Support top experience 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 can not be repaired.

b)

Observations:

• Cracks alog beam-column edge.
• Craacks seem to have developed through the structure as it looks much wider.
• Beam looks separated from the column joints.
• Concrete is not severely crushed.

Mode of failure:

• Its beam pill 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 it is not repairable.

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.

Mode of failure:

• It is a Plastic hinge failure.
• The damge occurred only in the joint zone first of all.
• Cyclic lateral loading and 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 or repairable.

Ans 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 the edge of the building.
• No walls are built along the column means it is probably at ground floor, for parking car movement access.

Mode of failure:

• It is 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)

Observations:

• Concrete developed complete breakage diagonally.
• Longitudinal reinforcements are intact.
• Shear reinforement spacing looks wider (which means probably lesser shear rebar provided).

Mode of failure:

• It is a pure shear failure.
• Inadequate shear reinforcements compels concrete takes all the shear stresses.
• It can not be repaired.

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.

Mode of failure:

• It is 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.