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Shape factor

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Form window results, go to “View Toolbox” Tab and select plastic axis, it give you the position of the X plastic (neutral) axis, which cut the free area in two equals part about Y-direction, and the position of the Y-plastic (neutral) axis, which cut the free area in two equals part about X –direction. If you check on the X-Plastic Area or Y-Plastic Area in the “View Toolbox” Tab, you will get graphically the X and Y plastic Areas. This feature is used by shape designer to compute the plastic section modulus Zpx and Zpy, with:



   My=sy* S             My: the Yield moment,

                         S: elastic section modulus


   Mp=sy* Zp    Mp: the plastic moment,

                       sy: the Yield stress:


Where f= Mp/My = Zp/S:  f is called the



Shape factor each section have two factors,

one in each direction fx and fy.

The value of f for wide flange beams is

typically in the range of 1.1 to 1.2.



If the elasto-plastic curve (s,e) is not symmetric about x axis (ie. The positive yield strength sy and the negative yield strength s’y has different absolute values), we have:






Where: y is measured from the plastic neutral axis. The location of the neutral plastic axis is not necessary the location which cut the free area in two equals part.



Stress-strain diagram of ductile steel material (not to scale)