Cold-formed Steel Special Bolted Moment Frames Capacity Design Requirements

Design provisions of the Cold-Formed Steel─Special Bolted Moment Frame (CFS─SBMF) system in the proposed AISI Seismic Standard (AISI S110) are developed such that energy dissipation in the form of bolt slippage and bearing in the bolted beam-to-column moment connections would occur during a major seismic event. Beams and columns are then designed following the capacity design principles to remain elastic. Based on the instantaneous center of rotation concept, this paper presents background information for the design provisions in the AISI standard for calculating the expected maximum seismic force in the beams and columns at the design story drift. This requires that the resistance from both the bolt slippage and bearing actions in the moment connection be computed. Design tables are provided to facilitate the design. The recommended seismic design procedure is also provided. INTRODUCTION The American Iron and Steel Institute (AISI) is in the process of developing a seismic design Standard for cold-formed steel, Standard for Seismic Design of Cold-Formed Steel Structural Systems─Special Bolted Moment Frames AISI S110 [AISI, 2007]. The first seismic force-resisting system introduced in the AISI seismic standard is termed Cold-Formed Steel─Special Bolted Moment Frames (CFS─SBMF). It is common that this type of one-story moment frames is composed of cold-formed Hollow Structural Section (HSS) columns and doublechannel beams. Beams are connected to the column by using snug-tight highstrength bolts; see Figure 1 for a typical moment connection detail. Cyclic testing of full-scale beam-column subassemblies [Uang et al., 2008] showed that the bolted moment connection can provide a high ductility capacity 1 Assistant Professor of Architecture and Architectural Engineering at Kyoto University, Kyoto, JAPAN, asato@archi.kyoto-u.ac.jp 2 Professor of Structural Engineering at University of California, San Diego, La Jolla, CA, cmu@ucsd.edu