Identification of Cracks

CHALLENGE 01

1.

a)

Observation:

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

Answer:

• It's 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 yeilded, it cannot be repaired.

b)

Observation:

• Cracks along beam-column edge.
• Cracks seem to have developed through the structure as it looks much wider.
• Beam looks seperated from the column at joints.
• Concrete is not severly crushed.

Answer:

• It's Beam Pull out failure due to insufficient developement lenght of reinforcement in joints.
• During earthquake, the horizontal movement of structure makes this condition worse and detached the beam member from the column.
• Providing the anchorage length between the two existing concrete is very difficult. So, it is not repairable.

c)

Observation:

• Cracks are excatly 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 occured only in 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, but unable to control the damage.
• The joint can be strengthened.

2.

a)

Observation:

• Concrete damaged at the top of a column.
• Spalling of concrete occurs all around the column face.
• Beams are safe.
• The location of looks at edge of the building.
• No walls are built along the column means it is probably at the ground floor, for parking car movement access.

Answer:

• It's a Soft storey failure, technically plastic hinge formation.
• Due to the 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 cursh or spall of concrete, it can either repairable or non-repairable.

b)

Observation:

• Concrete developed complete breakage diagonally.
• Longitudinal reinforcements are intact.
• Shear reinforcement spacing looks wider, which means probably lesser shear reinforcement provided.

Answer:

• It's a Pure Shear failure.
• Inadequate shear reinforcement compels concrete takes all the shear stress.

c)

Observation:

• Concrete failed completely.
• Failure at the top of cloumn.
• 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 non accounted in design.
• The failure given in the picture is not at all repairable.