Nonlinear Behaviour of Mid-rise Steel Buildings with Gate Braced Frames

Off-center or gate braced frames are a special configuration of inverted V bracing with non-straight diagonal members that are made of two elements connected to the corner of the frame by another member. This arrangement is characterized by an eccentricity of the intercepted bracing as respect to the straightness of the theoretical working length of the diagonal members in chevron configuration. These types of braced frames permit larger openings with significant advantages in terms of architectural functionality. The seismic performance of gate braced frames differs from that of traditional chevron braced frames, because of the out-of-straightness eccentricity of bracing members and the position of the corner-to-brace connecting element. Therefore, in this paper, a numerical parametric study based on both nonlinear static pushover and dynamic time-history analyses is presented and discussed in order to examine the influence of brace-to-brace detailing on seismic response of this structural typology. The results showed that the initial stiffness, the strength and the interstorey drift demand are very sensitive to the out-of-straightness eccentricity of bracing.