Euler Buckling in Box Truss (RISA)

[shayneG]

I am currently working on a 37' long box truss in RISA, top and bottom chords L5x3x1/4 steel, with L2x2x1/4 bracing. I am applying wind and ice loads in which case the top and bottom chords fail. When I switch the chords to Euler buckling members the chords pass. I am not sure if Euler buckling is an accurate assumption to be making in this case or not. When can we consider a member to be Euler controlled as opposed to tens/comp?

Shayne C. Guenther

 

[JoshPlumSE]

Euler buckling members are really only intended to be used for tension only bracing. Usually when you've got a really slender single angle brace or pipe or such. It's probably most clear to define it as "tension only bracing". But, that can lead to iteration issues.... especially if there are load cases where the force level in these braces is very low.... The program could be iterating between 0.01 kips of tension and 0.01 kips of compression and get stuck in an infinite loop.

The "Euler Buckling" members were created to address those iteration problems. If the compression force is less than 52% of the theoretical euler buckling load for that member, then the program does not force another iteration. But, the program doesn't do a code check on it either.... That's because it is considered to be a tension member with a trivial amount of compression in it.