Get PPT here What is the WSM method? In the working stress method, the stress-strain curve is assumed to be linear to the yield stress. To overcome the problems and damages due to uncertainty in design, permissible stress is kept as a fraction of the yield stress. As factor of safety is the ratio of yield stress to working stress, the members of the structure are sized to keep stresses within the permissible value. The working stress method is the oldest systematic analytical design method. Although IS 800-2007 gives more details and preferences to limit state method, it also permits the use of the working stress method wherever the limit state method is not practically adaptable. In Limit State Method, structure should be able to carry and withstand all the loads which will act on it throughout its life. Structure should not suffer total collapse under any kind of accidental loads such as explosions.