Category: Limit State Method

The working stress method gives satisfactory performance at working load but no attention is given to the conditions that arise at the time of collapse of the structure. This method does not give exact margin of safety. This drawback was taken into account in the ultimate load or load factor method of design. But load factor method leads to excessive deflection and cracking. A more rational approach is given by limit state method of design which is a balanced combination of working stress and ultimate load design method. The limit state method of design is discussed in Section 5 of IS code 456:2000.
The object of limit state design is based on the concept of achieving an acceptable probability that a structure will not become unserviceable in its lifetime for the use for which it is intended. It should be able to withstand safety all the loads that are going to act on it throughout its life alongwith satisfying the serviceability requirements. To ensure proper degree of safety and serviceability, the design must include all relevant limit states.