Question

Briefly discuss the significance of two main factors (list those 2 factors) in strength limit state design method used for safety in the context of a real-world structural steel design example.

Answer 1

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 ensures they wil not reach limit states and not become unfit for the function they are intended.

There are two main limit states:

(i) limit state of collapse and

(ii) limit state of serviceability

(i) Limit state of collapse deals with the strength and stability of structures subjected to the maximum design loads out of the possible combinations of several types of loads. Therefore, this limit state ensures that neither any part nor the whole structure should collapse or become unstable under any combination of expected overloads.  

(ii) Limit state of serviceability deals with deflection and cracking of structures under service loads, durability under working environment during their anticipated exposure conditions during service, stability of structures as a whole, fire resistance etc.The deflection under serviceability loads of a building or a building component should be such that, they do not impair the strength of the structure or components or cause damage to finishing.