Direct Analysis and Design of Steel Frames Accounting for Partially Restrained Column Base Conditions

The 2005 AISC specification provides a new method for stability design of steel frame structures termed the direct analysis method (DM). This paper addresses the consideration of partial base fixity using the DM. A refined model of the column base moment-rotation response is developed using an adaptation of the component method (CM) of Eurocode 3 plus a representation of the foundation stiffness. The paper also summarizes and applies an extension of the DM for frames containing web-tapered members. An example clear-span gable frame is checked using several models of its nominally simple four-bolt base detail: ideally pinned, elastic based on G=10 from the AISC sidesway-uninhibited alignment chart, and elastic-perfectly plastic using the CM. It is demonstrated that the member strength unity checks and the frame deflections obtained by modeling of the column bases as elastic based on G=10 are accurate to slightly optimistic compared to the refined base model. It is found that the contribution of the signifi...