Quasi-X-braced steel moment frames (QXB-MFs) evaluation using analytical and numerical methods.

Typical concentrically braced frames (CBFs), such as cross-braced (X-braced) frames, are commonly used to provide resistance against lateral loads. These systems are prone to buckling under compression, resulting in instability before reaching the yield strength. In other words, this bracing system exhibits an asymmetric behavior in tension and compression that undermines its energy dissipation capacity during excitation and leads to substantial damage to the structural and non-structural members. In an attempt to improve these shortcomings, this study introduces the novel quasi-X-braced frames. The stiffness and stability of the quasi-X-braced steel moment frames were evaluated by novel analytical and numerical methods. Drawing on strain energy concepts and Castigliano's theorem, this study presents an accurate analytical formulation for the lateral elastic stiffness of two-dimensional single-span and one-story quasi-X-braced steel moment frames (QXB-MFs). In this regard, all effective parameters, including the axial and shear loads and bending moments of all members, were taken into account. The proposed relation was validated with results from different cases using OpenSees. The error between the elastic stiffness results of the developed relation and the finite element numerical analysis was found to be negligible. Also, the seismic performance of QXB-MF systems was investigated according to the FEMA P695 methodology for near-field and far-field ground motion records compared with the intermediate moment frame. The results showed that using quasi-X braces in the intermediate moment frame improves the seismic performance of this system. [ABSTRACT FROM AUTHOR]