Identification of Cracks

Q.1.ANSWER)

a)

 Type of Failure =Ductile flexural failure 

To prevent flexural failure, then beam should be well reinforced but not either over or under reinforced which lead to undesired failures regardless of the design of the section. There's nothing specifically provided to prevent such failures, care should be taken while calculating the loads for which the beam should sustain for its whole time-sensitive. Factor of safety plays major role for designing a well balanced section.

b) 

Type of Failure = Compression failure

The column can fail in compress due to the increase of the axial stress than its capacity. When the axial stress exceeds a certain amount resulting in concrete strain grerter than 0.0035 concrete will fail suddenly. It will be a sudden crushing of concrete.

Following methods can be used to prevent the column failure.

• Encasement or enlargement of the column cross section (jacketing).
• Cathodic protection to stop reinforcing steel corrosion.
• Re-alkalization of the reinforcing steel to stop corrosion.
• Chloride extraction to retard the reinforcing steel corrosion.
• Confinement using steel plate, carbon, or glass fiber materials.
• Addition of shear collars to increase the shear capacity of intermediate floors.
• Addition of a steel plate assembly to increase moment capacity.
• Supplemental columns.
• The application of a protection system to prevent future corrosion.

c)

Failure due to plastic hinge 

Q.2.ANSWER)

a)

 Type of Failure = Buckling 

When the applied load reaches the Euler load, sometimes called the critical load, the column comes to be in a state of unstable equilibrium. At that load, the introduction of the slightest lateral force will cause the column to fail by suddenly "jumping" to a new configuration, and the column is said to have buckled.

To prevent buckling of column there can be many ways:
1. tie the columns at half their length and so you will increase their strength 4 times.
2. reduce their tributary areas or increase the number of columns.
3. can vary the profile of the column with least area at ends and maximum at center. Like a bulged column.
4. can use the concept of BRBF frames which totally prevents buckling but it would be a costly idea.
5. can change the type of end connection that a particular column has. As the buckling of column depends on the type of end connections.

b) 

Type of Failure = Compression failure

Causes :

1. The load carried by the column is increased due to either increasing the number of floors or due to mistakes in the design.
2. The compressive strength of the concrete or the percent and type of reinforcement are not according to the codes’ requirements.
3. The inclination of the column is more than the allowable.
4. The settlement in the foundation is more than the allowable.

Remedies :

Reinforced column jacketing

It is one of the techniques used to improve or restore capacity of reinforced concrete column. The size of the jacket and the number and diameter of the steel bars used in the jacketing process depend on the structural analysis that was made to the column.

c)

Failure due to plastic hinge