A limit state is a state of impending failure beyond which a structure ceases to perform its intended function satisfactorily, in terms of safety or serviceability. The acceptable limit for the safety and serviceability requirements before failure occurs is called a limit state.

Two categories of limit states are considered in the design.

1. Limit state of collapse
2. Limit state of serviceability

Limit state of collapse:- It 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.

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.