Nonlinear behavior of one-story one-bay steel frames with off-center bracings having different eccentricities

Steel bracing system is one of the structural systems utilized to resist the seismic loads. In off-center bracing system (OCBS), the diagonal bracing is not straight and the diagonal member is connected to the corner of the frame by another brace member, so the bracing system is formed by three brace members. In this study, the effect of the location of connection point of these three brace elements, in other words, the eccentricity of the OCBS was investigated. To this aim, one-story one-bay frame as a single degree of freedom system, having various height to span length ratios of 3/3, 3/5, 3/7, 4/3, 4/5 and 4/7, and having OCBS with various eccentricities (e1 and e2) of 0.1 to 0.9 were studied. For each frame system, two cases were adopted. In the first case, the eccentricity e1 was kept constant and possible e2 variations were considered while in the second one, the eccentricity e2 was maintained constant and possible e1 variations were taken into account. Thus, a total of 506 different cases were examined by means of the nonlinear pushover analysis. The results in terms of the capacity curve, maximum base shear capacity, and the initial stiffness of the frames were evaluated. It was observed from the results of the analysis that this great range of eccentricity values considered in the design of the OCBS had significant effects on the overall behavior of the frame structures under the lateral load.