Difference between WSD and USD design

structural engineering books

There is certainly some differences between WSD (WORKING STRESS DESIGN) and USD ( ULTIMATE STRESS DESIGN). The differences are stated below:

Difference between WSD and USD design


  • Stress condition of structural member under working load is given attention.
  • Full strength of material is not utilized and is reduced by a factor.
  • Stresses calculated are within the elastic limit.
  • Is less economical than USD.


  • Focuses on the strength capacity of the members at conditions corresponds to failure.
  • Material properties are assessed and used in design.
  • Loads are multiplied by a factor.
  • More economical

stress diagram

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