Identification of Cracks

Question 1:

What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate

a)

Observation:

• 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 meams rebar yielding occures in support bottom only.

Ans:

• Its form of flexural failure due to reversal of stress during earthquake.
• During stress reversal, Support top experiences Compression and bottom experiences tension.
• Top commpression was managed by slab advantage.Bottom tenstion was not satisfied by the provided Reinforcement.
• since the reinforcement got yielded, it cannot gbe repaired.

b)

Observation:

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

Ans:

• Its Beam pull out failure due to insufficient development length of reinforcement in joint.
• During earthquake , the horizantal movement of structure makes this condition worse and detached from cloumn.
• providing anchorage length between two existing concrte is very difficult. So not repairable.

c)

Observation:

• 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.

Ans:

• Its a Plastic hinge failure.
• The damage occrred only in the joint zone first of all.
• Cyclic lateral loading and stress reversal the joint 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 controll the damage.
• The joint can be strengthened.

Question 2:

a)

Observation:

• 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.

Ans:

• 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)

Observation:

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

Ans:

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

c)

Observation:

• 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.

Ans:

• 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.