Difference Between Limit State Method and Working Stresses Method

 In the context of structural engineering, the Limit State Method (LSM) and the Working Stress Method (WSM) are two different approaches to design that are defined by the Indian Standard (IS) codes.

The Working Stress Method (WSM) is an older approach to design that was widely used in India until the 1980s. It is based on the concept that a structure is safe as long as the stresses produced in the structure under the working loads are below a certain limit known as the allowable stress. The allowable stress is calculated by dividing the ultimate strength of the material by a factor of safety. The factor of safety is a value that is used to ensure that the structure is safe even if there are uncertainties in the design and construction process.

The Limit State Method (LSM) is a more recent approach to design that was introduced in the 1980s. It is based on the concept that a structure is safe as long as it satisfies certain limit states, which are conditions in which the structure is no longer able to perform its intended function. The limit states are defined based on the performance requirements of the structure and the possible failure modes that may occur. The design is carried out by ensuring that the probability of failure under the limit states is very low.

In summary, the key difference between the Limit State Method and the Working Stress Method is that the former is a more modern and advanced approach to design that takes into account the limit states of a structure, while the latter is an older approach that is based on allowable stresses. The IS codes for both methods have been developed to ensure the safety of structures, but the LSM is more commonly used today due to its ability to take into account a wider range of failure modes and performance requirements.

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