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

Utilizing DFF in STAAD only helps one check the local deflection. What if I want to check the drift of a column / beam frame?

If my joint displacement printout says that joint of a column/beam joint has moved 1.42 inch in the global X, then my drift ratio is 18x12/1.42 = 152.11, but the "dff" says 1072 for the same column, then where is the dff being measured?

When the DFF parameter is specified, the deflection checks during steel design are performed on the basis of so called "local axis deflection", not the nodal displacements in the global axis. For this reason, it is not possible to include storey drift checks into the steel design calculations at present.

If you want additional information on local axis deflection, please refer to example # 13, and Section Technical Reference of STAAD Commands > TR.44 Printing Section Displacements for Members in the STAAD.Pro Help.