Identification of Cracks

Identification of cracks

In the construction industry the issues of fatigue cracks in structures are crucial since they may lead to structural failure. These cracks are not only ugly to the eyes but can pose a great threat to the foundation if not diagnosed and repaired early enough. So in this blog let me share with you some tips on how to determine the existence of structural crack and the kind of crack usually seen in buildings.

Structural Cracks -

These are the cracks that are found at the structural parts of a building including the foundation, walls, floors and ceilings as a result of some conditions like temperature changes, soil movement and other conditions.

Structural cracks may arise due to

• Incorrect design

• overloading of the structural components

• Overloading of the soil in which the building is constructed.

Nonstructural cracks -

Nonstructural cracks are generally due to internal forces developed in the buildings on account of the changes in the size of building components due to

a. Moisture variation

b. Temperature variation

c. Effect of gasses, liquid, and solids on the building.

Question 1: What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate

a)

OBERVATIONS :

In this picture concrete crushed and the reinforcement is exposed.

In this picture there is concrete spalled (break into smaller pieces) 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 (lack strength )occurs in support bottom only.

ANSWER :

Its 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.

Since the reinforcement got yielded, it can be repaired. 

 b) 

OBERVATIONS :

In this picture there is crack along Beam-Column edge.

In this picture there is cracks seem to have developed through the structure as it looks much wider.

Beam looks separated from the column at joints.

In this picture concrete is not severely crushed.

ANSWER :

This type of problem arise when its Beams 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.

Solution for this kind of problem is to provide anchorage length between two existing concrete is very difficult. So not repairable.

 c) 

OBERVATIONS : 

In this picture cracks are exactly at the joints of column-Beam.

In this picture cracks in beam developed through its entire width.

Slab also developed more cracks along the beam width direction.

ANSWER :

From the observation we understand that it is a plastic hinge failure.

The damages occurred only in the joints zone first of all.

Cyclic lateral loading & 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 under gone tension with its flange condition), but unable to control the damages.

The joints can be strengthened.

Question 2: What is the mode of failure or damage of the beams in the figure above? Are the damages repairable? Elaborate

a)  

OBERVATIONS : 

From the above picture we can observe concrete damaged at top of a column.

From the above picture we can observe concrete damaged all around the column face.

From the above picture we can see that the beams are safe.

The locations of column looks at edge of the building.

No walls are built along the column means it is probably at ground floor, for parking cars movement access.

ANSWER :

From this observation it is clear that it's a Soft failure, Technically Plastic hinge formation.

Due to absence of infill walls at the ground floor, the plastic hinge forms at the top of ground storey column during Lateral movement.

Based on the development of crush of concrete, it can be repairable or Non- repairable.

b)  

OBERVATIONS :

Concrete developed complete breakage diagonally.

Longitudinal reinforcement are intact.

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

ANSWER :

From this observation we can say that it's a Pure Shear failure.

Inadequate shear reinforcement compels concrete takes all the shear stresses

c) 

OBERVATIONS :

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.

ANSWER :

From the observation we can say that it is Short Column failure.

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.

The failure given in the picture is not at all repairable.