# Seismic Design Procedure for Low-Rise Cold-Formed Steel-Special Bolded Moment Frames
## 1 Introduction  
The American Iron and Steel Institute (AISI) published the \"Standard for Seismic Design of Cold-Formed Steel Structural Systems\" in 2007 [1]. This standard introduced cold-formed steel-special bolted moment frames (CFS-SBMFs) as the first seismic force-resisting system. CFS-SBMFs consist of double-channel beams and square hollow structural section (HSS) columns that are connected by snugly tightened high-strength bolts. This type of moment frame is designed for one-storey construction only, as seen in Figure 1. The frame's ductility is provided through slippage and bearing in the bolted beam-to-column moment connections. The beams and columns remain essentially elastic according to the capacity design principles. Although CFS-SBMFs were initially intended for applications on industrial platforms, some designers have used them to design single-storey buildings. However, using this type of moment frame for structures that are over one storey in height is not currently permitted by ASCE 7 [2]. CFS-SBMFs, which were introduced in AISI S-110, were initially developed by [PERSON] and [PERSON] [3]. Their structural performance and mathematical modelling for the prediction of their inelastic behaviours were also verified and validated by [PERSON] and [PERSON] [4, 5]. [PERSON] et al. studied configurations of double-channel beams and the reinforcement effects by testing and using numerical simulations to increase their strength and ductility [6, 7, 8]. [PERSON] et al. conducted full-scale testing of built-up beams with bolted connections for comparison with the numerical simulation results [9]. [PERSON] et al. continued to conduct numerical simulationsof double-channel beams with several cross-sectional shapes and reinforcement effects to improve their ductility performance with bolted joints [10]. These studies referred to the AISI framing system and similarly focused on how to provide ductility. However, they mainly focused on improving the ductility of built-up beams with bolted end connections to spread the plasticity over the connected members, which is not part of the design concept of CFS-SBMFs. It is crucial to clarify and develop a method of providing ductility in cold-formed steel members. Cold-formed steel members are composed of relatively slender elements; therefore, expecting ductility from them is insufficient, and reinforcement is needed when they are treated similarly to heavy sections (i.e., compact sections). However, reinforcement methods that can be demonstrated in quantitative ways are still under development, and further studies are required. [PERSON] et al. surveyed full-scale back-to-back built-up beams under monotonic and cyclic loading to demonstrate the structural performance of the members [11]. It was also mentioned that cold-formed steel members themselves cannot provide ductility, and drastic strength deterioration will happen in monotonic and, especially, cyclic loading. [PERSON] examined the seismic performance of cold-formed steel houses but did not include the moment-resisting frame system depicted in Figure 1[12]. Moreover, due to the lack of ductility in cold-formed steel members themselves, small ductility reduction factors (i.e., behaviour factors) are used in designs. As a result, the design force that will be used to determine the members will be large. Figure 1: Original bolted AISI connection [1]: (**a**) 2D drawings; (**b**) 3D configuration; (**c**) closeup of the bolted connection. This study aims to extend the use of CFS-SBMFs to multi-storey low-rise buildings and create a new moment connection detail for connecting beams and columns that can be utilised in multi-storey building frames. Moreover, a design procedure for beam-to-column connections will be presented for this system to resist seismic forces, which guarantees the potential for ductility from the bolted connections and not from the beams or columns.