Correct Answer - Option 2 : Torsion
Explanation:
The acceptable limit for the safety and serviceability requirements before failure occurs is called a “limit state.
In the limit state method, the structure shall be designed to withstand safely all loads liable to act on it throughout its life, it shall also satisfy the serviceability requirements, such as deflection and cracking.
There are two limit states:
i) Limit state of collapse: The limit state of collapse of the structure or part of the structure could be assessed from rupture of one or more critical sections and from buckling due to elastic or plastic instability or overturning.
Note:
The resistance to bending, shear, torsion and axial load at every section shall not be less than the appropriate values at that section produced by the most unfavourable combination of loads on the structures using the appropriate partial safety factors.
ii) Limit state of serviceability: It ensures that your designed structure is comfortable and useable enough for human use.
Note:
The serviceability limit state deals with vibrations and deflections (movements), as well as cracking and durability.
It might also involve limits to non-structural issues such as fire, acoustics and heat transmission.
As per IS 800: 2007, CL: 5.2.2.2, Limit State of Strength includes the following:
1. Fracture due to fatigue.
2. Brittle fracture.
3. Loss of Equilibrium of structure.
4. Loss of stability of structure.
Limit state of Serviceability includes the following:
1. Crack due to fatigue.
2. Repairable damage
3. Corrosion
4. Fire
5. Deformation and Deflections
6. Vibrations in structure
