Identification of Cracks

1)

What is the mode of failure or damage of the beams in the figure below? Are the damages repairable? Elaborate

a)

b)

c)

Ans.

a)

Observations:-

Concrete crushed and the reinforcement is fully exposed

Concrete fall up to the rebars 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

Conclusions:-

Its form of flexural failure due to reverse of stress during earthquake

During stress reversal 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

Since the reinforcement got yielded , it cannot be repaired

b)

Observations:-

The cracks are formed along Beam- Column edge

The cracks seem to have developed through the structure as it looks much wider

Beam looks separated from the column at joints

Concrete is not severally crushed

Conclusions:-

It’s a Beam pull out failure due to insufficient development length of reinforcement in joints

During earthquake, the horizontal movement of structure makes this condition worse and detached the beam member from column

Providing anchorage length between two existing concrete is very difficult. So it is not repairable

c)

Observations:-

The cracks are exactly at the joint of column and Beam

Cracks in Beam developed through its entire width

Slab also develop more cracks along the beam width direction

Conclusions:-

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 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

Here the joint can be strengthen,hence repairable

2)

a)

b)

c)

Ans

a)

Observations:-

Concrete damaged at top of the column

Concrete damaged all-round the column face

Beams are safe

The location of column looks edge of building

No walls are built along the column means it is probably at ground floor,For parking car movement access

Conclusions:-

It is a soft story failure, technically plastic hinge formation

Due to absence of infill walls at the ground floor, the plastic hinge forms at the top of ground story column during lateral movement

Based on the development of crush of concrete it can be either repairable or unrepairable

b)

Observations:-

Concrete developed complete breakage diagonally

Longitudinal reinforcement are intact

Shear reinforcement spacing looks wider (which means probably lesser shear rebar provided)

Conclusions:-

It is pure shear failure

Inadequate shear reinforcement compels concrete takes all the shear stresses

Repairable to a extend

c)

Observations:-

Column failed completely

Failure at top of column

There are two slabs connected to columns, probably one at mid of the column

The wooden rods may be added as a failure support after column failed, providing temporary prop to avoid collapse of the entire structure

Conclusions:-

It is a short column failure

An additional slab or a beam connected to a column in mid height leads to its effects

This leads to failure especially if the connection is unintentional and not accounted in designs

This failure in picture is unrepairable