a Gholizad - Civil Engineering Department, University of Mohaghegh Ardabili, Ardabil, Iran
p Kamrani
s Rahimi

Without concentration of damage in beam elements which carry gravity loads; Knee braced steel frames provide high ductility as in traditional eccentric braced frames. Furthermore, renewability of the knee element makes it more practical for retrofitting applications. High performance and reliability of this refurbishable system has been confirmed in previously published researches trying to get an optimal design for its configuration and components. Buckling of diagonal member which affects the hysteretic behavior of KBF under cyclic loadings has not been foreseen in previous evaluations of this system and shall be taken as a restraint in KBF optimal design. Buckling and post buckling behavior of axial members can be included via nonlinear analyses software. This may limit the size of yielding knee anchor and energy dissipation rate consequently. Resultant deficiency due to diagonal member buckling effect or knee element resizing has been evaluated through nonlinear analyses in this report. Buckling resistant elements can be utilized as diagonal members to avoid buckling. Another approach to compensate these deficiencies is utilization of some special details to provide variable stiffness for yielding knee anchor when diagonal member acts in compression or tension. Such a detail has been suggested in this article and its performance has been compared with alternate approaches. Analyses results imply that utilization of buckling resistant diagonal member provides the most energy dissipation rate. Variable stiffness knee element is the next preferable choice for vibration suppression. Plastic capacity of Knee member shall be limited to guarantee the diagonal element never buckles and yields assumed ductility level.

Steel Frame, Knee Braced Frame, Buckling, Optimum Design