Identification of Cracks

Q.1) WHAT IS THE MODE OF FAILURE OR DAMAGE OF THE BEAM IN THE FIGURE ABOVE? ARE THE DAMAGES REPAIRABLE? ELABORATE

1a) 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 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 cannot be repaired.

1b) 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 put off 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.

1c) Observations:

• Cracks are exactly at the joint of Columns Beam.
• Cracks in Beam developed through its entire width.
• Slab also developed more cracks along the beam width direction.

Answer:

• It is a plastic hinge failure.
• The damage occurred only in the joint zone first of all.
• Cyclic lateral loading & stress reversed 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.

Q.2) WHAT IS THE MODE OF FAILURE OR DAMAGE OF THE BEAM IN THE FIGURE ABOVE? ARE THE DAMAGES REPAIRABLE? ELABORATE

2a) 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 be either be repairable or Non-repairable.

2b) Observations:

• Concrete developed complete the 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.
• So it is not repairable.

2c) 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.