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

Observation:-

By observing the picture shown, we can understand that concrete crushed due the impact of the force.
And by concrete getting crushed we can also find reinforcement bars exposed out of the element.
Though the element had such an impact it does not seem like there is severe damage to the element.
The concrete in the element got spalled beyond the reinforcement which, as per observation from the image can be considered as the sign of rupture.
Though the element is affected beneath it is clear in the top which seems to be the supportive effect of the flange advantage from the slab.
And other point is, if crack is developed from bottom to top it shows sense that rebar yielding can occur in support bottom only.

Answer:-

From our observations we conclude that,
The failure occurred may be a form of flexural failure due to reversal of stress during earthquake.
During this stress reversal what happens is the support top experiences compression and the bottom support experiences tension.
The main point here is that the top compression on the element was managed by the advantage of the support from the slab to the element.
As we know steel reinforcement and the concrete combined as composite material acts as the structural support for the building.
As one of the material, the reinforcement got yielded this damage can be repaired.

Observation:-

In the shown image we observes the cracks along the edge of the beam and column.
As like the older situation we are not finding any crushing of material or the element.
But what we see is a crack due to some reason in the relation between the two elements.
Though hard crushing or rupture is not found.
We can see crack is developed through the structure and also the crack seems wider.
And the other major point is that the beam got separated from the column at joints.
Which is not a good sign of good relation between the elements.
And as told earlier concrete is not severely crushed.

Answer:-

As told in the observation there is poor relation between the elements joining.
We can come to a point that this is a beam pull out failure due to insufficient development length of reinforcement in joints.
In severe case of the earthquake at this same situation with severe horizontal movement of structure, the condition could have been worsen.
Like the beams could have got detached from the columns which is not at all acceptable by the structure leading to severe impact of the earthquake.
Now after such happening providing anchorage length between two existing concrete is very difficult and not advisable too.
So this damage cannot be repaired.

Observation:-

In the case from the image we can see that the cracks in the structure are exactly at the joints of the column and the beam.
And the crack has also got spread throughout its entire width.
And along with these elements the slab has also developed more cracks along the beam width direction.

Answer:-

After the observation, we can say that it is a plastic hinge failure.
The damage here has occurred only in the joint zone first of all.
The damage at the joint may be due to cyclic lateral loading and stress reversal at the joints.
And as we see the slab it has also participated to its best to handle the tension due to the force.
This we could note because here slab is severely cracked which means it has undergone tension with its flange condition.
But it could not control the damage.
In this case the joint can be strengthened.

Question 2:

Observation:-

In the image given we can find that, at the top of the column concrete has got damaged.
And the concrete is seen damaged all around the face of the column at the top of the column.
And also we can find that the beams are safe.
It seems the columns is placed at the edge of the building.
And other important thing can be noted is. It seems like a opening near the column.
Which can be understood by absence of walls.
It can probably be ground floor of the building, may left open for parking car and other movement access.

Answer:-

So, it is understood from the image that it is a soft storey failure.
Technically plastic hinge formation.
As said before, due to absence of infill walls at the ground floor, The plastic hinge 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.

Observation:-

In the image supplied the damage seems worse.
Here the concrete in the element has developed complete breakage diagonally.
As we can also see longitudinal reinforcements are intact but, Shear reinforcement spacing seems wider, which makes sense there may be lesser shear rebar provided.

Answer:-

Here we can say it is a pure shear failure.
Inadequate shear reinforcement certainly a reason for the concrete to take a high shear stress.

Observation:-

Here the column completely failed.
Majorly the failure seems to have happened at the top of the column.
And we can also find two slabs connected to the column, probably one at mid height of the column.
Here they have placed wooden supports which could be understood that may be post failure support.
Which cannot be a perfect solution but a temporary support may be.
This is to avoid complete collapse of the entire structure.

Answer:-

Here we can say it is a short column failure.
An additional beam or slab to the mid height of the column makes the column short on both remaining heights.
Which may lead to short column failure.
This type of failure is lead especially if the connection is unintentional and not accounted in design.
The failure given in the picture is not at all repairable.

Ship work like this
in your own course.