On the interface of stability and seismic design requirements for steel buildings

The 2005 AISC Specification stipulates analysis-and-design methods, with primary emphasis on the Direct Analysis Method (DM), to address stability requirements for steel framing systems. While the DM has important benefits over conventional methods, the interface of the AISC stability requirements and seismic design requirements in ASCE-7 is not fully established. For example, it is not clear how the DM should be combined with the equivalent lateral force procedure to determine member strength demands. It is not clear how the DM might be combined with the nonlinear static analysis procedure to evaluate post-elastic strength and deformation demands and overall system behavior. Clarification is needed on how the DM addresses different levels of seismic hazard. To examine these issues, a series of steel moment-resisting frame models were analyzed using the DM and several other analysis methods. The predicted post-elastic system behavior was compared against those obtained from distributed plasticity analyses that incorporated residual stresses and geometric imperfection. This paper describes key findings from these analyses.