Identification of Cracks

Question 1:

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 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. Bottom tension was not satisfied by the provided reinforcement.
◦ Since the reinforcement got yielded, it can not be repaired.

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 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.

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.
◦ But 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)

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.

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.

)

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.