Hi All,
I am just checking a truss top chord beam for torsion using code AISC-1989. The staad file is attached herewith.
In the staad file, i made two model. LHS model is a normal truss with concentrated vertical loads. RHS model is similar to LHS model, but i used the eccentricity d2 to move the load point from the center of its web, so that the torsion moment can be developed automatically. I checked the reactions of both models and the reactions are same, in addition RHS model are having Mx reactions at its supports, which is satisfactory. Stress ratios for all the members excluding top chord are the same between both the models. The stress ratio is varies only in the top chord and i noticed there is a huge increase in the axial force in the RHS model. And the failure was noticed due to clause H1-1, which is no relation with torsion (In AISC-1989 no torsion requirements were considered under Chapter-H).
So we are really confused and need Bentley response on the followings.
1. Is Staad handling torsion design of members as per AISC-1989 and DG-9?
2. Why the actual axial stress on the top chord are increased drastically, when i apply a concentrated force with an eccentricity by using d2 option?
3. If Staad is handling torsion design as per AISC-1989, then why the reports and calculations are not generated, even if i use TRACK 2 command? How to check and substantiate that the Staad is considering it correctly?
Your earliest response is highly appreciated.