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

AIM: TO IDENTIFY the mode of failure or damage of the beams in the given figure

a)

Type: From the above image we can say that, this Crack is formed due to flexural failure in beams.

Reason: The cracks which are formed as a result of flexural stress is called as flexural crack.

Damage is caused due to insufficient of reinforcement or concrete.

The flexural strength, known as modulus of rupture, bend strength, or fracture strength, is a material property, defined as the stress in a material just before it yields in a flexure test. The flexural strength represents the highest stress experienced within the material at its moment of rupture. It is measured in terms of stress.

Solution:

These cracks can be controlled by providing proper tension reinforcement. This failures steel must be provided at top/bottom of beam. These damages are repairable, while repairing this we need to remove pipes, wires and turn off the water and power connection. It can be repaired by adding cement to the damaged part.

b)

Type: From the above image we can say that, this type of Cracks are formed due to high slump concrete, and aslo due to the mistakes done in the construction and honeycombing in concrete.

Reason: Beams and columns carry heavy load.

Solution: To avoid cracks in concrete, avoid using high slump concrete. Concrete of moderate slump (less than 5 inches) results in less cracking. High slump concrete can only be used if it is controlled by concrete admixtures or designed such that segregation and bleeding of concrete is controlled. Concrete admixtures such as water reducers or super plasticizers can be used to increase slump while reducing addition of water content. Air entertained concrete can also be produced to increase slump especially when concrete is to be subjected to freeze and thaw cycles. The honeycombing occurs when the fine mortar fails to thoroughly fall and fill the gaps created by the coarse aggregate. As mentioned previously, poor concrete consolidation is usually the top cause of honeycombing, along with poor vibration, improper ratio of fine to coarse aggregate, dry concrete and construction conditions that are not up to standard.

c)

Type: From the above image we can say that, this type of Crack is formed due to the beam-column joint failure.

Reason: In the strong column-weak beam design, beams are expected to form plastic hinges at their ends and develop flexural overstrength beyond the design strength. The high internal forces developed at plastic hinges cause critical bond conditions in the longitudinal reinforcing bars passing through the joint and also impose high shear demand in the joint core. It occured due to high shear forces during seismic activity. If it is not properly repaired excessive loss in strength,then structure will collapse.

Question 2:

a)

Type: From the above image we can say that, this Crack is formed due to the flexural failure of a column or failure in column due to buckling.

Reason: Columns have the most important role in all structural members of a building. Buckling is the sudden change in shape of a structural component under load. If a structure is subjected to gradually increase in load ,member may suddenly changes the shape.

Solution: According to the base civil engineering concept, columns failure wants to be occurring after bears and the other components damages. Performance of existing buildings in earthquakes indicates that the bears are less vulnerable to damage during earthquakes and their damage appears to be less critical to performance as compared with that of columns and column-beam joints.

b)

Type: From the above image we can say that, this Crack is formed due to Shear failure in column.

Reason: Lateral loads in a structure are carrying by vertical elements such as columns and shear walls. Size of columns is increased in direction of shear to increase shear capacity. High shear forces are attracted by shorter columns. These failures occur during earthquake at open ground floor level.

Solution: Lateral loads are generated by winds, earthquake loads, from retaining structures, etc. Shear links are provided to columns based on the shear forces excreted on them. Further, the size of the columns is increased in the direction of shear to increase the shear capacity.

c)

Type: From the above image we can say that, this Crack is formed due to the short column failure.

Reason: Failure of column usually occurs due to anyone of the following stresses developed in the column. Short column will fail only because of direct compressive stress developed in the column or we can also say that short column will usually fail due to direct compression or crushing.

In Short Columns, failure takes place due to yielding and we define this phenomenon as CRUSHING, Short Columns are classified based upon Slenderness Ratio which is the ratio of the effective length (Length between point of zero moments) and least lateral dimension of the column.