Challenge

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

Answer 1(a) :

Observation:

In this picture we observe that concrete gets damaged/ broken and reinforcement is visible at the bottom of the beam.
The concrete spalled beyond the reinforcement which indicates the segregation.
The top portion of the beam is not exposed due to covered by the slab projection so it’s looks safe and no major issue/ severe issue at the top of the beam.
Crack developed at the bottom and gradually increased towards the top. The pressure on the beam is more than its yielding point on the bottom support but the reinforcement is still active at the support top so there is no crack in the top of the beam.

Conclusion:

At the time of the earthquake, the stress on the beam is reversal, so this is a kind of flexural failure.
During the earthquake, the beam gets in the tension zone and the structure feels in compression due to the stress reversal support at the top.
Bottom reinforcement is not sufficient to resist the tension in the beam and the top compression is resisted by the slab due to the concrete
The bottom reinforcement of the beam lost its elastic limit, so it is impossible to repair the bottom crack.

Answer 1(b) :

Observation:

In this picture we observed the cracks developed in the column-beam corner
Looks like the crack is much wider and has developed through the column-beam joint
In the picture, the beam has separated from the column
In the picture shown, the concrete has not been crushed but only a crack generated.

Conclusion:

The reinforcement of the beam is not sufficient to anchor the vertical rebar of the column, that is insufficient development length of the rebar
Due to inadequate reinforcement, the beam is not bonded to the column that’s why the horizontal member gets detached from the vertical member during the earthquake
The lateral movement cannot be satisfied due to insufficient anchorage length of beam rebar so it keeps on separated from the column
It is very tough to provide the development length in casted concrete between two members, so it is not repairable

Answer 1(c) :

Observation:

Conclusion:

This is a plastic hinge failure, the deformation in the beam means no capability to resist the moment and it permits free rotation
The plastic hinge failure happens at the joint only, so the damage occurs in the junction
The main reasons for damage are cyclic lateral loading and stress reversal at the junction
As per the image, the slab has tried to handle the tension, but still it got cracked, so it is clear that the tension is more on the slab and the slab is unable to control the damage
To recover from the damage, we can strengthen the column-beam junction

Question 2:

Answer 2(a) :

Observation:

In this picture we observe that the column has damage from the top, bottom of the column is safe.
The damage is all around the face of the column
No damage found in the beam
No connected walls are along with column, so this could be the ground floor, probably the parking area
It is a most outer or external column of the building

Conclusion:

From these observations it's clear, that this is a soft storey failure, technically plastic hinge formation at column
Due to lateral movement in the building and the absence of walls, columns were affected because of a plastic hinge formed at the upper side of the ground floor
Based on spall out the concrete from the column and the severity of the column is to be decided either repairable or non-repairable

Answer 2(b) :

Observation:

The breakage of concrete has diagonally developed in the column, so this is not a crack it’s a completely crushed concrete detached from the column
Lateral and longitudinal reinforcements are visible. Rebar has not been damaged and has not separated
The clear vision of lateral reinforcement, i.e., shear links spacing is more than as per codel requirement which means that they have provided lesser shear reinforcement

Conclusion:

By observing the picture, we can conclude this is a pure shear failure because the crack is in a diagonal direction and the complete concrete had spalled and crushed
The shear reinforcements were not sufficient so it had detached and spalled throughout the column. It had compelled concrete to break down into pieces.

Answer 2(c) :

Observation:

From the given picture, we can observe that the column completely fail
Damage happens at the top of the column and the bottom of the column is safe
As per the picture, there are two slabs connected with the column and the space between both slabs is not the floor height so this is probably for mechanical equipment
The beam has been temporarily supported with the wooden piles after the column failure to avoid the collapse of the structure

Conclusion:

From the observation we can conclude that the failure is short column failure.
The column is attached to the intermediate slab and the height of the column is not similar then the other columns, so there is a heavy shear load on the column.
The intermediate slab load is unintentional and not accounted for in the design so this leads to the failure
This failure is not repairable

Ship work like this
in your own course.