Question

What are the different limit states of design as per IS 456: 2000?

a. Limit state of failure

b. Limit state of damage

c. Limit state of collapse

d. Limit state of serviceability

1. a and d
2. b and c
3. c and d
4. a and b

Answer 1

Correct Answer - Option 3 : c and d

Explanation:

Limit State Method:

• Limit states are the acceptable limits for the safety and serviceability requirements of the structure before failure occurs. 
• The design of structures by this method will thus ensure that they will not reach limit states and will not become unfit for the use for which they are intended. 
• Limit State Design requires two principal criteria to be satisfied:

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.
• 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: 

• Limit state of serviceability of prestressed concrete should satisfy cracking, deflection, and maximum compression also.

• The crack width & deflection should not exceed the permissible limit and the maximum compressive force also should not exceed the strength of concrete.