بررسی خرابی پیش‌رونده در ساختمان‌های فولادی بلندمرتبه دارای سیستم دوگانه قاب خمشی ویژه و مهاربند کمانش‌ناپذیر

در این مقاله خرابی پیش‌رونده سازه های بلندمرتبه دارای سیستم دوگانه قاب خمشی فولادی و مهاربند کمانش ناپذیر با در نظر گرفتن سناریوهای خرابی متعدد بررسی می شود. مهاربندهای فولادی از نوع (هشت8 هفت7) و شورون می باشند که در دهانه‌های کناری و گوشه نصب شده اند. مهاربند کمانش‌ناپذیر به علت رفتار مناسب در کشش و فشار و همچنین منحنی هیسترزیس نسبتاً متقارن، عملکرد لرزه ای مناسبی دارد. چهار نوع سازه با سیستم قاب خمشی ویژه فولادی دارای مهاربند کمانش‌ناپذیر در دهانه‌های گوشه و کناری با آرایش (هشت8 -هفت7) و شورون(v) ، دارای کاربری های مسکونی و تجاری  مورد بررسی قرار گرفته است. بر اساس مطالعات عددی مقاله حاضر، ضعیف‌ترین عملکرد در میان سازه های مورد بررسی مربوط به سازه دوگانه با مهاربند کمانش ناپذیر (هشت8 هفت7) در گوشه و بهترین عملکرد مربوط به سازه دوگانه با مهاربند کمانش ناپذیر شورون در دهانه کناری بوده است. درعین‌حال عملکرد سیستم های مورد بررسی برای حالت های مهاربند شورون در دهانه گوشه و مهاربند (هشت8 هفت7) در دهانه کناری تا حد زیادی مشابه یکدیگر می باشد. به‌علاوه، در تمامی سناریوهای حذف تک‌ستون، مقدار خیز در سازه‌هایی که ستون حذف شده در دهانه مهاربندی قرار نداشته است به میزان قابل‌توجهی (تقریباً 1.5 تا 3 برابر) بزرگ‌تر از خیز سازه دارای سناریوی حذف برای ستون واقع در دهانه مهاربندی می باشد.

Investigating Progressive Collapse in High-Rise Dual Special Steel Moment-Resisting Frames and Buckling-Restrained Braces

In the recent decades designing buildings against progressive collapse has been subjected to growing attention. In progressive collapse, the failure of one single structural member is transmitted to other members resulting in collapse of the entire loadresisting system of the building. Progressive collapse in buildings can be triggered by diverse factors such as accidental gas blast, impact between vehicles and one of the columns, etc. It is, thus, of great importance to design a building to withstand such catastrophic collapse. In this manner, in the design process, the building is subjected to different failure scenarios of single elements, e.g. a column, and investigate whether the failure spread to the remaining parts of the structure. While a substantial effort has been devoted to design earthquakeresilient structures based on the current seismic codes and stateoftheart researches in earthquake engineering, still further studies are required to investigate the resistance of structures against progressive collapse.In this research the progressive collapse of dual special steel momentresisting frames and bucklingrestrained braces, as an earthquakeresilient structural system for highrise buildings, has been numerically investigated considering several failure scenarios. Bucklingrestrained braces have been considered to provide appropriate seismic performance due to fair tensile and compressive behavior as well as almost symmetrical hysteresis response. In the performed numerical analyses, progressive collapse in four highrise residential and commercial 20story buildings with dual special steel momentresisting frames and bucklingrestrained braces with different configuration, such as (combined VInverted V) and (V) located in the corner and edge bays is studied, regarding different failure scenarios. The abovementioned scenarios include the removal of a corner or edge column in the first or fifteenth floor, as well as the removal of two edge columns of the braced bays in the first or fifteenth floor. The numerical models were verified against existing published experimental and numerical results before being applied to the analytical cases. This is achieved by comparing the results reproduced by the numerical tool to the previously published results regarding both cyclic analysis, at the subassembly level, and timehistory analysis, at the structural level.The adopted numerical models were based on Finite Element (FE) simulation of the structures taking into account both material and geometric nonlinearities. The Inelastic forcebased plastic hinge frame element type in SeismoStruct software was used to model beam and column elements, while Inelastic forcebased frame element type elements was implemented to model the nonlinear behavior along the bucklingrestrained braces. Each of the bracing elements consisted of three parts, including: a middle part to simulate the core as well as transition and elastic segments of bracings, and two end parts with large stiffness to simulate the panel zone and gusset plates. Rayleigh damping was also selected to model the damping in timehistory analyses of the progressive collapse process. The performance criteria for all the members and connections were selected according to ASCE/SEI 4117.Based on the obtained results, the peak vertical deflection of the top node of the removed column was approximated to be as large as 6.5 cm, and collapse was observed in one of the numerical models (commercial building contains Xbracing in the corner bays). The dual structure with Xbracing in the corner bays represents the weakest performance, while the best performance was related to the case of Vbracing in the edge bays, and the Vbracing in the corner bays and Xbracing in the edge bays have shown similar behaviors. In addition, in all the single column removal scenarios, the peak value of deflection in the cases in which the column removal was not located at the bracing bays was significantly greater, approximately 1.5 to 3 times larger, compared to those of column removals in the bracing bays.