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

In Chapter 3 of the Technical Reference Manual (American Concrete Design), under Section 3.5, in the 4th paragraph, you state that a PDELTA ANALYSIS is the appropriate way to account for slenderness effects during column design. You have the following additional statements in that paragraph :

 "To take advantage of this analysis, all combinations of loadings must be provided as primary load cases and not as load combinations. This is due to the fact that load combinations are just algebraic combinations of forces and moments, whereas a primary load case is revised during the pdelta analysis based on the deflections."

Can you explain the above statements in further detail?

These statements are provided to emphasize the fact that if you wish to carry out a PDELTA analysis for a load case where 2 or more previously defined load cases are combined, as for example, one case involving DEAD load and another involving WIND load, the right way to combine them is through the means of a REPEAT LOAD command, and not a LOAD COMBINATION command.  See Member Tension And Combination Load Cases for more details.