Which design check belongs to LSM?

Factored action <= design strength

Which codes correspond to WSM and LSM?

IS 800:1984 for WSM and IS 800:2007 for LSM

IS 800:2007 for WSM and IS 800:1984 for LSM

IS 456 for WSM and IS 800 for LSM

How is failure treated in WSM compared with LSM?

WSM does not consider failure, LSM considers limit states of strength and serviceability

WSM considers limit states of strength and serviceability

Asked 3/21
2080 Chaitra · 4 marks
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Working stress vs limit state method

Short answer

WSM is based on elasticity with working loads and a single safety factor on stress. LSM considers ultimate and serviceability limit states, uses factored loads and partial factors on loads and material, idealizing steel as elastic-perfectly plastic, achieving more uniform reliability and economy.

Differentiate between the working stress method of design and the limit state method of design (with sketches).

Point	Working Stress Method	Limit State Method
Basis	Elastic theory	Behaviour up to failure and at service
Loads	Working (characteristic) loads	Factored loads $\gamma_f\times$ characteristic
Safety	One factor of safety on material stress	Partial factors $\gamma_f$ and $\gamma_m$
Design check	Stress $\le$ permissible stress	Factored action $\le$ design strength
Stress-strain	Linear elastic	Idealised (elastic-plastic)
Failure	Failure not considered	Limit states of strength and serviceability
Uniform safety	Not uniform	Nearly uniform reliability
Economy	Generally heavier	More economical
Code	IS 800:1984	IS 800:2007

 WSM                         LSM
 stress                      stress
  fy |      /                 fy |  ______ (plastic)
 0.6fy|----/  perm.           fd |-/
     |   /                       |/ design
     |__/____ strain             |________ strain

In WSM the structure is designed to keep stress below $0.6f_y$ under working load; in LSM it is designed so that the factored load does not exceed the design strength $f_y/\gamma_{m0}$ and deflection stays within limits.

✓ Answer checked by Claude Opus 5.5 (high effort)

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