Direct analysis of braced frames

Is there a procedure for utilizing the AISC direct analysis method in staad along with tension/compression only frame elements?

  • As of now, the DIRECT ANALYSIS implementation in STAAD cannot handle tension/compression only elements. This is our pipeline for development. For now, you need to use TRUSS specifications for the axial only members.



  • When it comes to designing per AISC 360, one thing to consider is when it is required to use the Direct Analysis method and when one of the alternatives can be used as well. AISC 360 requires that you use the Direct Analysis method if the ratio of second order drift in any story is greater than 1.5. Braced frames are usually so stiff that their drifts rarely exceed this, so the Direct Analysis method is not required and the Effective Length Method, for example, can be used instead. An advantage of the Direct Analysis method is that you don't have to calculate the effective length factor, K. But for Braced Frames K=1.0 anyway, so that advantage disappears. So unless you have unusually large drifts, for Braced Frames I recommend that you not use the Direct Analysis method, but use the Effective Length Method (which is described in Appendix 7 of AISC 360-10) and a value of K=1.0. That is a perfectly acceptable alternative.