AISC Direct Analysis Method with RISA 3D

This video illustrates the process for conducting the Direct Analysis Method for steel structures per the 15th Edition of the AISC Steel Construction Manual (AISC 360-16, Specifications for Structural Steel Buildings, Chapter C). This video performs design according to LRFD, though the ASD procedure is similar.

The primary benefit of performing structural analysis per the Direct Analysis Procedure is that the effective length factors K for all columns can be assumed equal to 1. Thus, the effective column length is equal to the unbraced length.

The necessary features for the Direct Analysis Method are:
1) Stiffness Reductions: apply 80% stiffness to all stiffnesses that contribute to the stability of the structure, plus an additional reduction to flexural stiffness of members with high compressive loads.
2) Second-Order Analysis: consider both P-Delta (capital Delta, accounting for deflections at column ends) and P-delta (lowercase delta, accounting for deflections along the lengths of columns) effects.
3) Notional Loads: lateral loads that account for structural imperfections, equal to 0.002 times the factored gravity loads on each story.