Difference between WSM(Working Stress Method) and LSM(Limit StateMethod)

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S.NO. Working Stress Method(WSM) Limit State Method(LSM)
1. Follow Hooks law i.e. stress-strain diagram is linear. Does not follow Hooks law, hence stress-strain diagram is non linear.
2. All tensile stresses are taken by steel only and not by concrete. The tensile strength of concrete is ignored.
3. Factor of safety is used. Here partial safety factors are used.
4. It is based on deterministic approach i.e. original behavior of structure under real applied loads. It is based on probabilistic approach to design.
5. Here material strength is underestimated and loads are working loads. Here material strength is underestimated and loads are generally working loads with extra safety i.e. overestimated.
 6. WSM satisfies serviceability criteria but highly uneconomical. Major concern is Safety and Serviceability before failure.
 7.  The plane section before bending remains plane after bending means stress-strain diagram linear. Plane section before bending remains plane after bending means only strain diagram is linear.
 8.  Non-Cracking zone is generally considered.  Cracking Zone is considered.
 9.  There is a need of modular ratio.  There is no need of modular ratio.
 10.  Stresses from working loads are compared with permissible stresses.  Stresses obtained from design loads are compared with design strength.
 11.  It is based on elastic theory.  It is based on plastic theory.


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Arbaj Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

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