Identification of Cracks

ANSWERS

1.

a) Observations

• Concrete is crushed at the bottom and the reinforcement is exposed.
• Concrete is spalled beyond the reinforcement which may be a sign of rupture.
• The beam top portion looked safe because of the flange advantage from the slab.
• The crack developed from bottom to top means rebar yielding occurs in support only.

Conclusions

• It's a form of Flexural failure due to the reversal of stress during an earthquake.
• During stress reversal, the top support experiences Compression, and the Bottom experiences Tension.
• Top compression is managed by Slab Advantage. Bottom tension wasn't satisfied by the provided reinforcement.
• Since the reinforcement got yielded, it can't be repaired.

b) Observations

• Cracks are 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 isn't severely crushed.

Conclusions

• It's Beam pull-out failure due to insufficient development length of reinforcement in joints.
• During an earthquake, the horizontal movement of the structure makes this condition worse and detaches the beam from the column.
• Providing anchorage length between two existing concrete is very difficult. So, it isn't repairable.

c) Observations

• Cracks are exactly at the joint of the column beam.
• Cracks in the beam developed through its entire width.
• The slab also developed more cracks along the beam width direction.

Conclusions

• 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 damage.
• Even the slab did its best to handle the Tension (The 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 the top.
• Concrete damaged at all around the Column face.
• Beams are safe.
• The location of the column looks at the edge of the building.
• No walls are built along the column means it's probably on the Ground floor for Parking car movement.

Conclusions

• It's a Soft storey failure. Technically Plastic hinge formation.
• Due to the absence of infill walls on 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 reinforcement is intact.
• Shear reinforcement spacing looks wider (which means probably lesser shear rebar provided).

Conclusions

• It is a Pure shear failure.
• Inadequate shear reinforcement compels concrete to take all the shear stresses.

c) Observations

• Column 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 post-failure support after the column failed, by providing a temporary prop to avoid collapse of the entire structure.

Conclusions

• It's a Short column failure.
• An additional slab or a beam connected to a Column in the mid-height leads to this effect.
• This leads to failure especially if the connection is unintentional and not accounted for in the design.
• The failure given in the picture isn't at all repairable.