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

摘要

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 significant initial stiffness of typical bases to the overall frame response is limited by the connection strength.