Seismic Design and Performance Evaluation of Long-Span Special Truss Moment Frames

Abstract

The need for a very-long-span structure in sporting and industrial venues puts steel moment frames and braced frames at a disadvantage. In this regard, special truss moment frames (STMFs) can accommodate a large span by utilizing truss girders to provide high lateral stiffness. However, current seismic provisions for structural steel buildings do not allow STMFs’ span and truss depth to exceed 20 and 1.8 m, respectively. Moreover, when a very long span is used, the high axial forces induced by the gravity load could cause considerable ductility reduction of the chord members in the special segment. This paper presents a study on seismic behavior of long-span STMFs with double-channel truss members, a span length of 27.4 m, and a truss depth of 3.05 m. Plastic hinge models of double-channel sections considering the effect of high axial forces were developed based on experimental and nonlinear finite-element analysis (FEA) for both design basis earthquakes (DBEs) and near-collapse earthquakes or maximum considered earthquakes (MCEs). A design procedure for long-span STMFs using nonlinear pushover analysis is presented. The seismic performance of long-span STMFs was verified using the developed plastic hinge models as well as DBE and MCE ground motions through nonlinear time-history (NTH) analyses. According to the FEA results, a modification to the axial load limit in current seismic provisions for the chord members is recommended.