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)

Observations:

• Concrete is crushed and the reinforcement is exposed.
• Concrete is damaged/spalled more than the reinforcement level and we can see elements changed darker which may be signs of rupture.
• The beam top portion looks safe because of the flange advantage from the slab.
• The crack develops from bottom to top means rebar yielding occurs in the support bottom only.

Answer:

• It is a form of Flexural failure due to the reversal of stress during an earthquake.
• During stress reversal, the Support top experiences compression and the 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 can not be repaired.

b)

Observation:

• Cracks are formed along the Beam-Column edge.
• Cracks seem to have developed through the structure as it looks much wider.
• The beam looks separated from the column at the joints.
• Concrete is not severely crushed.

Answer:

• Its beam pull-out failure is due to insufficient development length of reinforcement in joints.
• During an earthquake, The horizontal movement of the structure makes this condition worse and detached the beam member from the column.
• It required development length with sufficient length can resist the structure from this kind of failure. But, providing anchorage length between two existing concrete is very difficult. So it cannot be repaired.

c)

Observation:

• Cracks occurred exactly at the joint of column-Beam.
• In a beam, cracks are developed through its entire width.
• The 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 and stress reversal at the joints led to the damage.
• Even the slab participated in its best to handle the tension i.e, the slab is severely cracked means it has undergone tension with its flange condition but is unable to control the damage.
• The joint can be strengthened.

Question 2: What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate

a)

Observation:

• Concrete damaged at top of a column.
• Concrete is damaged all around the column face.
• The beams are safe.
• The location of the column looks like it is at the edge of the building.
• No walls are built along the column means it is probably on the Ground floor, for parking car movement access.

Answers:

• It is a Soft storey failure, Technically a 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 crushed 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 shear rebar provided.

Answers:

• It's a pure shear failure.
• Inadequate shear reinforcement compels concrete to take all the shear stresses.

c)

Observation:

• The column failed completely.
• Failure at top of the column.
• There are two slabs connected to the column, Probably one at mid-height of the column.
• The wooden piles might be post-failure support after the column failed, Providing a temporary prop to avoid the collapse of the entire structure.

Answers:

• It is a short-column failure.
• An additional slab or 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 for in the design.
• The failure given in the picture is not at all repairable.