بررسي ضوابط آيين نامه براي تيرهاي پيوند متوسط در بادبندهاي خارج محور

STUDYING CURRENT PROVISIONS FOR INTERMEDIATE LINKS IN EBFS

در بين انواع تيرهاي پيوند، رفتار تيرهاي با طول كوتاه به علت جذب انرژي بالاتر و شكل پذيري بهتر بيشتر مورد توجه قرار گرفته است. اما الزامات معماري در بسياري از مواقع استفاده از تيرهاي با طول متوسط و بلند را ناگزير مي سازد. علاوه‌بر اين، نتايج گزارش‌شده از تحقيقات پيشين مويد ناايمن‌بودن برخي از نمونه ها با طول متوسط و ارضانشدن ضوابط آيين نامه براي آنهاست. براي بررسي دقيق تر ضوابط آيين نامه ‌يي در اين تحقيق، تعدادي تير پيوند با طول متوسط با استفاده از روش اجزا محدود مدل‌سازي و ضوابط آيين نامه‌يي اين نوع تيرها و تاثير پارامترهاي مختلف بر رفتار آنها بررسي شده است. در انتها با توجه به نتايج مشاهده‌شده، توصيه هايي براي طراحي تيرهاي متوسط به‌منظور حصول اطمينان از رفتار مطمين تر آنها ارايه شده است.

Among different link types, short links are always considered the best alternative due to their better energy dissipation capacity and ductility. But, architectural limitations, in some cases, leave no choice other than intermediate and long links. Furthermore, the results of recent studies have revealed some non-conservative behavior of intermediate links, i.e. they do not satisfy the provisions. To investigate the validity of the current provisions for intermediate links, some separated link beams are modeled here, and the effect of different parameters on their performance are studied. The boundary conditions of models are selected so they could realistically reflect link behavior in a real structure. The concerned links are modeled using the finite element method in the ANSYS program. Verifying the modeling approach with previous experimental, as well as analytical, works, stiffener spacing, thickness, slenderness ration of web and flange, link length, section, and other significant parameters on link performance, are inserted in the study, and their role in link behavior are investigated. Considering the intended aim of the paper, monotonic loading is not suitable, and cyclic loading according to protocols prescribed by codes like AISC2005, ATC24, etc, were applied to the models. By analyzing model outputs, the hysteretic behavior of the links is extracted and the plastic rotation capacity of links, that is, the main parameter utilized to judge link behavior, is deduced. Also, the graphical outputs of models, such as displacement, and elastic and plastic strains, at different load steps, are used to support the results. Stiffener spacing and position (whether they are provided on one or two sides of the web) and the web slenderness ratio are discerned as the most effective parameters on the behavior of intermediate links. The current plastic rotation capacity considered for intermediate links is shown to be unreliable for specified length ratios of these links. Finally, some design suggestions have been provided for these types of link.