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۱EVALUATION OF BUCKLING PREVENTION METHODS FOR KNEE BRACINGS
نویسنده(ها): ، ،
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۷
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.<\div>

۲Performance of Friction Damper for Dynamic Response Reduction of Seismically Excited Knee Braced Steel Frames
نویسنده(ها): ،
اطلاعات انتشار: نهمین کنگره بین المللی مهندسی عمران، سال
تعداد صفحات: ۸
High performance and reliability of refurbish able knee braced steel frames has been confirmed in previous researches trying to get an optimal design for its configuration. Buckling of diagonal member which affects the hysteretic behavior of KBF under cyclic loadings has not been foreseen in previousevaluations of this system. This deficiency can be improved by utilization of adjustable rotary friction damper device (FDD) as knee element. Diagonal element buckling can be prevented considering a suitable value for FDD sliding threshold moment (Mf). Nonlinear time history analyses have beenperformed to evaluate the response of single story KBF subjected to seismic record. Optimal Mf in FDD has been chosen for these analyses. Roof displacement and acceleration, base shear and diagonal element’s buckling status have been compared in KBF and FKBF with different configurations. More than 89% displacement response reduction has been earned for the FKBF without considerable increase in base shear<\div>

۳Buckling Prevented Variable Stiffness Knee Braced Steel Frame
نویسنده(ها): ،
اطلاعات انتشار: نهمین کنگره بین المللی مهندسی عمران، سال
تعداد صفحات: ۷
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<\div>
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