Identification of Cracks

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 crushed and the reinforcement is exposed.
• Concrete spalled beyond the reinforcement which may be a sign of rupture.
• Beam top portion looks the safe because of the flange advantages 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 experince compression and bottom experinxes tension.
• Top compression is managed by slab advantage. Bottom tension was not satisfied by the provided reinforcement.
• Since the reinforcement got yield, 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 look seperated from the columns at joints.
• Concrete is not severly crushed.

Answer:

• Its beam pull out failure due to insufficent development length of reinforcement joints.
• During earthquake, the horizontal movement of structuremakes this condition worse and detached the beam member from column.
• Providing anchorage length betwwen two existing concrete is very diffcult. 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 directrion.

Answer:

• Its a plastic hinge failure.
• The damage occured only in the joint zone first of all.
• Cuclic 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:What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate

a)

Observations:

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

Answer:

• Its a soft storey failure, technically plastic hinges formation.
• Due to absence o finfill walls at the ground floor, The plastic hinges 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 diagonally.
• Longitudinal reinfocements are intact.
• Shear reinforcement spacing looks wider( Which means probably lesser shear rebar provided)

Answer:

• Its a pure shear failure.
• Inadequate shear reinforcemnet compels concrete take all the shear stresses.

c)

Observations:

• Column failed compeletly.
• 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 aviod collapse of the entire structure.

Answer:

• Its 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 unitentional and not accounted in design.
• The failure given is not at all repairable.