Steel Design | Allowable stress design | Example

ASD (allowable strength design) is one of the oldest system that is being used for the design of steel, beams, columns, roof slab, trusses etc… In this method design remains within the allowable stress. Hence, in ASD a factor of safety applies to the strength of the material. So that structure will remain within the allowable stress level.

Allowable stress for both concrete and steel (that is used in concrete as a reinforced concrete) can be easily calculated from the equations.

For Concrete

     Where  is the compressive strength of concrete

For Steel

     Where is the yield strength of steel



A singly reinforced concrete section has a compressive strength = 60Mpa, and yield strength of the reinforced steel = 420 MPa


Design a bean using the allowable strength design method


As we have to use the allowable strength design method. Therefore, we will first find the allowable strength of concrete and steel by using formula 1 and 2.

  • For Concrete

f’c  = 60Mpa

    Fa = 27 MPa

  • For Steel

Fy = 420Mpa

  Fa = 210 MPa


In allowable strength design, factor of safety applies to the strength of reinforced concrete. Therefore, from the above results, it is very clear that in ASD, structure will be designed within the reduced value of stress not in the actual strength of reinforced concrete.


  1. eddfiguer June 9, 2012
  2. buy 4-mec February 27, 2013

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