Evaluation of Seismic Performance in Off-Center Bracing Systems: Crescent-Shaped versus Bilinear Configurations

Off-center braced frames present a novel approach to seismic-resisting systems in steel structures. Unlike traditional concentrically braced systems, the braces in this design are not straight. Instead, intentional eccentricity is introduced at the midpoint of the braces. This leads to a transition from a purely axial force behavior to a combined interaction of bending moment and axial force. As a result, the system demonstrates distinct energy dissipation characteristics and effectively prevents brace buckling, a common failure mode in traditional bracing systems. Moreover, it features a decoupled strength-stiffness behavior, offering the designer greater flexibility in defining the desired stiffness across different sections of the structure. Additionally, it allows for larger architectural openings. This paper introduces two distinct variations of off-center braced systems: a crescent-shaped configuration, resembling a segment of a circle, and a bilinear one, consisting of two straight lines connected at the center of the brace. To compare the seismic performance of these two configurations, a series of ۳-story braced frame models is developed, incorporating variations in the number of brace eccentricities. The initial design of these models follows seismic provisions for special concentrically braced frames, and a capacity-limited design methodology is then introduced to ensure that the eccentric braces function as energy-dissipating fuses. Nonlinear static pushover and nonlinear time history analyses are conducted, and a comprehensive comparison of the two configurations is presented, detailing their respective advantages and disadvantages.

کلیدواژه ها:

Concentrically braced frames ، capacity-limited design ، nonlinear analysis ، off-center bracing systems ، energy demand parameters