Buckling Prevented Variable Stiffness Knee Braced Steel Frame

A new configuration has been suggested for knee braced steel frames to avoid buckling of diagonal member. High performance of KBF is based on the plastic deformation of knee anchor. Buckling of diagonal member deranges this functionality and causes to reduction in ductility level and energy dissipation rate. Buckling effects on nonlinear static behavior of KBF under cyclic loading has been previously studied by author. Buckling of diagonal element can be avoided using buckling resistantdetails for axial member or more flexible sections for knee anchor. An alternate and more practical approach is utilization of variable stiffness knee elements. High energy dissipation rate of this system has been evidenced from the hysteretic response of its nonlinear analysis under static cyclic loading. Such a detail is practical using an auxiliary element parallel and in contact with the knee anchor. OpenSees Gap element and no-tension material have been employed to model the contact between the knee anchor and auxiliary element. Suggested technique has been used in nonlinear time history analysis of seismically excited multi storey KBFs under different earthquake records aiming to find the optimal composition of the proposed detail and to compare its performance with traditional KBF. Utilization of modified detail in case studies resulted in 29% reduction in maximum displacement response of seismically excited structure and more energy dissipation rate. Efficiency of the proposed mechanism is not sensitive to the frequency content and other characteristics of exciting earthquake

Keywords:

Knee Braced Steel Frame , Variable Stiffness Anchor , Buckling , Incremental Dynamic Analysis