مقاله انگلیسی رایگان در مورد کمانش پویای مهاربندی ها در قاب های مهاربندی شده – وایلی 2017

Stability of members under static and dynamic loading conditions has been studied in the past.1-3 Studies on dynamic stability of compression elements such as columns and rods can be broadly categorized into 2 main subcategories3 : parametric resonance and stability under impulsive actions. A rod might experience parametric resonance when it is subjected to a harmonic axial force with an oscillation frequency that has a certain relation to the natural frequency of the member.3-7 The second subclass is concerned with the stability of compression members under impulsive actions such as the impact of a mass, a rapidly applied axial force, or an imposed boundary velocity.8-20 A brief summary of these studies, which are mostly conducted prior to the 1980s, can be found in Galambos3 and Simitses,21 while more recent studies in this active field of research can be found in Hao et al, Ji and Waas, Mimura et al, Motamarri and Suryanarayan, Morozov et al, and Kuzkin and Dannert.22-28 The common consensus in the above studies is that, under impulsive actions, the axial force of a member can easily exceed its static critical load. External impulsive actions that can cause axial strain rates of the order of 10−1 to 102 s −1 in a rod are generally considered as low‐velocity excitations while actions with a resulting axial strain rate of 102 to 106 s −1 as high‐velocity excitations. 3 Investigation of high‐velocity excitations, which are typically encountered under impact or blast conditions, is out of the scope of the current study. Previous studies9,13,19,26,29-32 have shown that, in low‐velocity excitations with low to moderate compression speeds, the expected buckled shape is identical to the fundamental buckling mode observed in a quasi‐static case; however, for high compression speeds, higher buckling modes might also be excited. During strong ground motions, brace members in steel concentrically braced frames (CBFs) exhibit rapid shortenings and elongations leading to repeated cycles of buckling in compression and yielding in tension. When a rod is subjected to rapid shortening, due to the inertia effect of the rod’s mass, it will take a certain amount of time for the member to deflect laterally and buckle, and within this time period, the axial force of the rod can exceed its Euler load significantly.9 Similarly, it is possible for braces of a CBF to exhibit loads above their static buckling load (ie, to experience dynamic overshoot). Previous experimental and analytical results9,25,26,28,32 have shown that such dynamic overshoots can range from a few percent to hundreds of times the Euler buckling load. In a brief study by Tada and Suito,33 it was also demonstrated that the buckling and postbuckling behaviors of truss structures could notably differ under dynamic and static analysis. It is worth noting that the study was, however, conducted considering monotonic loads and rather low compressions speeds (<15 mm/s).