I am using RAM Elements and add lateral torsional bracing and positive flange bracing causes the stress ratio due to torsion to skyrocket (from 0.93 to 427000). Shouldn't the bracing restrict the torsional forces? Have I modeled something incorrectly?
You checked CLT Restraint and entered a short Lb_pos?
If so I would probably need to see the model. It might be something particular to the shape, the design code, or your version.
CLT is unchecked, Lb pos and L Torsion are both fixed at ten feet. I have uploaded the model.
I re-ran it with some substitute sections for the pipe columns and I still get the high torsion stress.
The original torsion forces were small, less than 1 k-ft, so the simple solution might be to turn off the DG9 code check options. I tested segmenting the chords (just 1548 and 1551) and that also worked.
Answer Verified By: Kevin Hurtt
Seth, you mentioned that you would normally segment a truss chord. Why is that? The physical member configuration does simplify several things as far as model organization, so is there a disadvantage or even an analysis concern with doing that? I thought that as long as one accounted for the unbraced lengths and releases appropriately, there wouldn't be a problem using physical members.
Trusses often have panel points at irregular intervals so the unbraced length of each segment varies. For that reason I prefer to model the chord in segments.
Ah, OK. Just wanted to see if there was something I wasn't aware of that might affect our designs. We like boringly repetitive panel layouts when we design trusses, but even if we do have some variance, like some 6', 8', or 10' panels, we'll just specify that max unbraced length for the chord member to cover us for any later adjustments. Thanks!