| Applies To | |||
| Product(s): | STAAD.Pro | ||
| Version(s): | All | ||
| Environment: | N/A | ||
| Area: | American Steel Design | ||
| Subarea: | Slenderness Failure | ||
| Original Author: | Bentley Technical Support Group | ||
The steel design output indicates a slenderness failure (KL/r exceeds allowable). Why? The axial force on the member is very small.
The code has requirements which say that the KL/r ratios for a member should not exceed certain allowable limits. For members subjected to tensile forces, the code suggests one limit, and for members subjected to compressive forces, there is another limit.
This check does not consider the amount of the axial force. It only looks at the sign of the force to determine if it is a tensile force or compressive force.
In most codes, this is the first check STAAD does on a member. If the member fails the check, no further calculations are done for that member.
So, STAAD performs these checks by default. However, the code does not offer any guidelines on what must be the minimum magnitude of the axial force for the member to become a candidate for this check.
So, in STAAD, two parameters are available - one called MAIN and another called TMAIN if you wish to bypass this check (TMAIN is available for some codes only). Please refer to the list of Design Parameters for the code you are using to check how these two parameters can be set to bypass the slenderness checks. For example for the AISC codes, MAIN can be set to 1 for bypassing the slenderness check in compression and TMAIN can be set to 1 to bypass the slenderness check in tension. For IS 800 2007 code, these would have to be set to -1 for the respective checks to be bypassed.