Seismic evaluation of concentrically braced steel frames equipped with yielding elements and BRBs

Abstract

As a way of increasing lateral load resistance, Concentrically Braced Frames (CBFs) are employed in steel structures. Structures with CBF display high lateral stiffness and experience lesser story drifts than structures with Moment Resisting Frame (MRF). Despite the advantages, there are some major problems in the performance of the braced frames, such as low capacity in energy dissipation, buckling of conventional brace members, and degradation of strength and stiffness. To increase the energy dissipation of braced frames, central yielding elements in the intersection of braced members have been proposed in the past. In this study, BRB elements were placed in the bracing system to improve energy dissipation and lateral stiffness and to reduce buckling in the bracing. Designing a structure that includes the stated lateral-load-resisting system necessitates seismic performance parameters to be evaluated. As the study's main purpose, by pursuing the FEMA P695 methodology, seismic parameters, including response modification factor, over-strength factor, and deflection amplification factor (R-, Ω-, and Cd-factor), are specified. Several archetypes with various properties were considered to reflect the possible application of this bracing system. Based on FEMA P695, static pushover analyses are implemented to establish over-strength factors for archetypes. Subsequently, Incremental Dynamic Analyses (IDA) are implemented to specify Adjusted Collapse Margin Ratios (ACMRs). Finally, the acceptance of the abovementioned assumed factors for the system is scrutinized by comparing ACMRs values with the values which are acceptable in FEMA P695.