Comparison of the Behavior of Steel Structures with Concentric and Eccentric Bracing Systems

Over the years bracings were used as part of an effective lateral load resisting system to enhance stiffness and reduce deformation. Structures need to be strong and at the same time ductile. Besides they also need to be economical and constractable. In recent years with increased concerns about seismic activities more research had been carried out to find the response of structures to seismic forces. The main objective of this study is to investigate the behavior of Concentric and Eccentric Braced (CBF, EBF) steel frames by using linear dynamic, nonlinear time history and nonlinear static pushover analysis. Hence it was decide to investigate the two basic types of bracing systems, X-shape and Λ-shape. Earthquake impact on structure depend on many factors include structures height, number of story, each story height and number of bays on plan. For this reason design and performance analyses were carried out on 4, 8 and 12 story buildings with 3x3 symmetric and 3x5 asymmetric bays on plan. According to ASCE7-10, the value of the deflection amplification factor coefficient (cd) depends on the type of bracing. This study indicated that it also depends on the number of floors but it is independent from number of bays. In all structures, the initial stiffness of CBF was more than that of EBF. Pushover graphs show that EBF braces have more ductility than CBF. Target shift is larger in both directions for EBF when compared to those of CBF. On the other hand, for 3x3 bays increase in the number of floors lead to increase in the target shift for both CBF and EBF. Keywords: Eccentric Brace Frame, Concentric Brace Frame, Linear dynamic analysis, Nonlinear Dynamic Time History Analysis, Pushover Analysis