Cyclic Behaviour of the Knee Braced System Considering the Type of Knee Joint

In recent years, the use of braced frame systems has been expanded to achieve a stiff and ductile structures in high seismic zones. Among the various types of bracing systems, the knee bracing system has been specially considered for seismic design in steel structures. In this system, the diagonal member provides the system’s stiffness, and the knee member as a fuse, provides the ductility and prevents the buckling of diagonal member; Thus, it is expected that the stiffness and ductility of the structures will be remained simultaneously. In this study, the knee braced frames modelled using finite element method under statically cyclic loading. The effect of different types of the joints between the diagonal members to the knee member on cyclic behaviour of the knee bracing system was investigated. Three fixed joints were: the diagonal connected to flange of a continuous knee member (KBF1), the diagonal connected to the web of discontinuous knee member (KBF2) and the diagonal connected to the web of discontinuous knee member with stiffener (KBF3). The results showed that KBF3 model had better performance in terms of ductility, energy absorption and ultimate capacity. Besides, the elastic stiffness of KBF2 and KBF3 joints were approximately the same.