Applies To
	Product(s):	STAAD.Pro
	Version(s):	All
	Environment:	N/A
	Area:	Design
	Subarea:	American Steel Design
	Original Author:	Bentley Technical Support Group

What does the design parameter STIFF represent? 

The design parameter named STIFF is used in calculating allowable shear stress or shear capacity as per the AISC code. When the h/tw ratio ( terms explained below ) exceeds a certain code stipulated value, one may need to include web stiffeners to strengthen the web and thereby increase the shear capacity for the section. Sections of the AISC code like section F4 of the AISC 9th edition code or section G2 of the AISC 360-05 or the AISC 360-10 codes specify the relevant equations for allowable shear stress or capacities and how these are affected by the spacing of the stiffeners. These equations provided by the codes have a term called “a” which represents the clear distance between these transverse stiffeners. The STIFF parameter used in STAAD.Pro represents the term “a”. 

h= clear distance between flanges less the fillet radii for hot rolled sections

  = clear distance between flanges for welded sections

tw= thickness of the web