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 otom tension was not Satisfied by ineorOvided reinforcement.
• Since the reinforcement got yielded. it can not be repaired.

b) 

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.
• 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.

b)  

Observations:

• Concrete developed complete breakage diagonaly.
• 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.

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.