Parametric optimization of SIP connection geometry in CFS-MRF structures: A finite element study

The structural buildings should be designed to resist both static and dynamic loads. There are different types of structural systems that can support seismic loads. Moment-resisting frames (MRFs) are widely used for seismic purposes, relying on the plastic deformations occurring between the beam and column. The main problems of cold-formed steel sections in MRFs during seismic loads are premature local and distortional buckling, which cause severe damage under strong earthquakes, such as early loss of connection strength, low ductility, and low energy dissipation. This paper clarifies the performance of the CFS section with steel interconnected part (SIP) in moment-resisting frames (MRFs) in many aspects using finite element (FE) procedures. The study summarizes the required dimensions of SIP to achieve optimal behavior for the beam-column connection. Additionally, an advanced connection consisting of SIP and four pairs of out-of-plane stiffeners has been examined. The locations of the out-of-plane stiffeners have been carefully selected to stabilize the connection. A cantilever beam connection has been used to represent an MRF in an advanced way. The connection consists of 2 C channel back-to-back beams connected with a through plate with sixteen bolts. Numerical models have been developed and verified with experimental tests under both monotonic and cyclic loading. The characteristics and creation of the numerical model are well illustrated in this paper. Cyclic loading has been applied according to AISC protocol, which is used to test the performance of the steel connections, as well as to classify the connection according to different design codes. The results show that increasing the plastic moment capacity of the CFS section decreases the required SIP dimensions to achieve optimal behavior by the connection. Additionally, it has been found that using out-of-plane stiffeners in particular locations with SIP increases energy dissipation on average by 74 %. Using stiffeners with SIP can upgrade the classification of the connection from an ordinary or intermediate moment connection to a special moment connection without the need to increase the CFS cross-section area or reduce the slenderness ratio, which in turn reduces the overall costs of construction.