Journal of Steel & Structure

Journal of Steel & Structure

Evaluation of Response Modification Factor of BRB Systems Based on Structure Height

Document Type : Original Article

Authors
Department of Civil Engineering, University of Science and Culture, Tehran, Iran
Abstract
In current seismic design codes, the primary objective is to prevent structural collapse during strong earthquakes while allowing controlled damage in certain structural and non-structural components. This controlled damage mechanism provides considerable energy dissipation, which is a key factor in ensuring life safety. Most design codes formulate their requirements based on equivalent linear analyses. However, the lateral force distributions suggested by these codes such as the equivalent static method often lead to non-uniform inter-story drift demands, which may cause drift concentration in specific stories. Consequently, permanent deformations can develop in structural members due to inelastic responses. Buckling-Restrained Braces (BRBs) effectively address this issue by dissipating the majority of seismic input energy, thereby concentrating inelastic behavior within themselves and preventing the main structural members from entering the nonlinear range. Although seismic codes assign constant response modification factors (R) to different structural systems, numerous studies have shown that adopting a single fixed value can underestimate story drifts. This underestimation increases axial strain demand in BRBs and may result in residual deformations or soft-story mechanisms. In this study, the response modification factor is evaluated for diagonal and Chevron BRBF configurations in 4, 8, and 12-story buildings with both moment and pinned beam-to-column connections. The R-factors of these systems are proposed as functions of building height. Finally, the structural reliability of models designed with the calculated R-factors is compared against those designed using the constant values prescribed in Iranian Standard No. 2800. The results indicate that, due to the significant variation of R in BRBF systems (ranging from 4 to 13 depending on configuration), using constant values of 7 or 8 as recommended by Iranian and U.S. codes is not appropriate, particularly for structures with eight stories or more. Such simplification may underestimate seismic demands and consequently increase the probability of structural failure during earthquakes.
Keywords
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  • Receive Date 27 September 2025
  • Revise Date 20 November 2025
  • Accept Date 24 November 2025
  • First Publish Date 24 November 2025
  • Publish Date 23 September 2025