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Numerical modeling of cold-formed steel sheathed shear walls under lateral loading

Topçuoğlugil , Yağmur
Cold-formed steel (CFS) structural systems have been used increasingly in seismically active regions. Shear walls consisting of CFS framing and sheathing panels constitute one type of lateral force resisting system for such CFS framed buildings. The purpose of this study is to develop an efficient numerical model to predict the lateral load response of shear walls that are framed with CFS profiles and sheathed with oriented strand board (OSB) panels. Numerical modeling of shear walls was conducted in OpenSees platform. Fastener-based approach incorporating nonlinear fastener model for screw connections was adopted. Screw connections were modeled by using a special hysteretic material model capable of softening, strength degradation, and cyclic pinching called as Pinching4. Parameters required to define this hysteretic model were based on a series of monotonic and cyclic loading tests conducted on OSB-to-CFS screw connections. Additionally, a complementary test program was carried out on OSB specimens to determine the in-plane shear properties of OSB sheathing panels. Shear wall model was verified with full-scale experimental data in terms of strength, stiffness and pinching characteristics. Then, a parametric study by utilizing the verified model was conducted in order to investigate the influence of various parameters such as local fastener behavior, fastener spacing, rigidity of stud-track connection, stiffness of CFS framing members, stiffness of hold-down members and the level of gravity loading on overall wall response. Seismic force modification (R) factors, including ductility related force modification factor (Rµ) and overstrength related force modification factor (RΩ), were calculated by using the bilinear force-displacement response determined from the numerically determined hysteretic response of several shear walls following the Equivalent Energy Elastic-Plastic (EEEP) approach.