Applies To
	Product(s):	STAAD.Pro
	Version(s):	All
	Environment:	N/A
	Area:	Steel Design
	Subarea:	IS 800:2007
	Original Author:	Surojit Ghosh

***WARNING : MEMBER - XXX IS SLENDER AND CANNOT BE CHECKED FOR MOMENT FORCES. IF THERE
IS ANY BENDING, THEN BE AWARE THAT THERE IS NO CAPACITY FOR THOSE FORCES.
***NOTE : ONLY WIDE FLANGE SHAPES WITH SLENDER WEBS CAN BE CHECKED FOR BENDING.

As mentioned in cl.3.7.2(d), slender section should be designed either according to IS801 code or with reduced section property. For wide flange section, the option to design slender section is implemented if only the web is slender, flange is non-slender. If the flange class of any section is slender, the design of that section is incomplete. Program calculates the axial and shear capacity only. If there is any bending, capacity is not calculated and the section is not checked against bending and interaction. A warning message is displayed for this and the overall design ratio is set to infinity. 

In summary, following the recommendation if IS800:2007 code, STAAD.Pro doesn’t allow flange slender section design. Since STAAD.Pro 20.07.11.82 version, if the flange class is slender, the warning message is displayed in all TRACK output and the critical design ratio is set to infinity so that member fails in design check. This will intimate the user about the fact that the member design is incomplete. The section size needs to be increased such that the flange class is non-slender.