A Method for Performing Automated Plastic Mechanism Analyses of Steel Special Concentrically Braced Frames

Special concentrically braced frames (SCBFs) rely on yielding and buckling of the braces to achieve ductility of the system. AISC 341, Seismic Provisions for Structural Steel Buildings, requires designers to evaluate the columns, collectors, and connections in SCBFs for the capacity-limited seismic load effect associated with the expected strengths of the braces. In practice, especially for simple or regularly-shaped buildings, designers often compute these force demands by hand and manually combine them with the demands from other loads. However, for irregularly-shaped or atypical buildings, such as large industrial buildings without diaphragms or structures with unevenly distributed mass or stiffness, this can become an arduous task, especially during an iterative design process. The method described in this paper allows designers to automate a plastic mechanism analysis of an SCBF in an analysis model by imposing artificial self-straining (thermal) loads to emulate the capacity-limited seismic load effect.