Identification of Cracks
1Q]
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.
MODE OF FAILURE: -
It is 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.
It occurs when the beam is under-reinforced; the reinforcement ratio in the beam is low than balanced reinforced ratio.
CONCLUSION: -
Since the reinforcement got yielded, it cannot 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.
MODE OF FAILURE: -
It is Beam Pull out failure due to insufficient development length of reinforcement in joints.
Bond stress between the bar and surrounding concrete is insufficient to prevent the bar from slipping slightly.
Consequently, bar will not be able to generate full tensile stress and section will not be able to generate the full moment of resistance and concrete will crack.
During Earthquake, the horizontal movement of structure makes this condition worse and detached the beam member from column
CONCLUSION: -
Providing anchorage length between two existing concrete is very difficult.
So, it is 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.
MODE OF FAILURE: -
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 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.
CONCLUSION: -
The joint can be strengthened.
2Q]
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.
MODE OF FAILURE: -
It is a Soft Storey failure, Technically plastic hinge formation.
Soft storey is a situation when the upper levels of a building is stiffer than the lower storey. This can result in undesirable performance of the building.
A soft storey has inadequate shear resistance or inadequate ductility (energy absorption capacity) to resist earthquake induced building stresses.
Due to absence of infill walls at the Ground floor, the plastic hinge forms at the Top of ground storey columns during lateral movement.
CONCLUSION: -
Based on the development of crush of concrete, it can either be repairable or Non-repairable.
B)
OBSERVATIONS: -
Concrete developed complete breakage diagonally.
Longitudinal reinforcements are intact.
Shear reinforcement spacing looks wider
(which means probably lesser shear rebar provided)
MODE OF FAILURE: -
It is a Pure Shear Failure.
When there are no shear walls, columns carry these lateral loads. If no adequate shear links, these types of column failure could occur.
Lateral loads are generated by winds, earthquake loads, from retaining structures, etc.
Inadequate shear reinforcement compels concrete took all the shear stresses.
Failure causes mainly due to the lack of links in the area where there are higher shear forces.
CONCLUSION: -
It is not repairable.
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
MODE OF FAILURE: -
It is a Short Column Failure
The short columns are stiffer compared to long columns.
More the stiffness of any structural element, less will be its flexibility to undergo any sort of deformation. More is the stiffness, more will be the force required to bring any deformation.
If the short columns are not designed to take such large force, damage is caused to the column and hence the structure is affected.
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.
CONCLUSION: -
The failure given in the picture is not at all repairable.