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 get damage/ broken and reinforcement are visible at the bottom of beam.
The concrete spalled beyond the reinforcement that is indicates the segregation.
The top portion of beam is not exposed due to covered from the slab projection so it’s look safe and no major issue/ severe issue in the top of the beam.
Crack developed in bottom and gradually increasing towards the top. The pressure on 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 top of beam.

Conclusion:

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

Answer 1(b)

Observation:

In this picture we observed the cracks developed in column-beam corner
Looks like the crack is much wider that have developed through the column-beam joint
In the picture, the beam has separated from the column
In picture shown, the concrete has not the crushed but only 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, beam 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 beam means no capability to resist the moment and its permit to free rotation
The plastic hinge failure is happened at the joint only, so the damage occurs in the junction
The main reason of damage are cyclic lateral loading and stress reversal at the junction
As per the image, the slab has tried for handle the tension, but still it got cracked, so it clear that the tension is more on the slab and slab is unable to control 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 column is safe.
The damage is all around the face of column
No damage found in beam
No connected walls are along with column, so this could be ground floor, probably parking area
It is a most outer or external column of the building

Conclusion:

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

Answer 2(b)

Observation:

The breakage of concrete has diagonally developed in column, so this is not a crack it’s a completely crushed and concrete detached from column
Lateral and longitudinal reinforcements are visible. Rebar has not damaged and 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 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 breakdown into pieces.

Answer 2(c)

Observation:

From the given picture, we can observe that the column is completely fail
Damage happen at top of column and bottom of column is safe
As per picture, there are two slabs connected with the column and the space between both slab is not the floor hight so this is probably for mechanical equipment
The beam has temporary 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 with intermediate slab and the height of column is not similar then the other columns, so there is the heavy shear load on the column.
The intermediate slab load is unintentional and not accounted in the design so this leads to the failure
This failure is not repairable

Ship work like this
in your own course.