مقاومت در برابر خرابي پيش‌روند‌ي ساختمان‌هاي بتني با شكل‌پذيري‌هاي مختلف

Progressive Collapse Resistance of RC Framed Buildings with Different Ductilites

اطمينان از سازه هميشه به عنوان يك اصل براي مهندساني كه مسيول طراحي پروژه هاي عمراني بوده اند، مطرح بوده است. يكي از مكانيزم هايي كه در دهه هاي اخير توجه به آن افزايش پيدا كرده است، خرابي پيش رونده است. از اين رو در اين پژوهش، با استفاده از آيين نامه‌ي GSA به بررسي ميزان مقاومت خرابي پيش رونده در ساختمان هاي طراحي‌شده با شكل پذيري هاي مختلف بر طبق آيين نامه هاي ايران پرداخته شده است. ساختمان ها پس از طراحي براي بارگذاري هاي متداول، توسط دو روش تحليل استاتيكي و ديناميكي غيرخطي براي حالت هاي مختلف حذف ستون تحليل شده اند. براساس بارگذاري هاي تعريف‌شده در GSA، قاب خمشي معمولي و متوسط به ترتيب اضافه مقاومتي در حدود 80 و 33 درصد دارند. ولي با توجه به ضوابط راهنماي GSA، قاب خمشي ويژه‌ي طراحي‌شده براساس آيين نامه هاي ايران، قادر به تحمل بارهاي مربوط به خرابي پيش رونده نبوده و برخي از حالت هاي حذف ستون در آن منجر به خرابي شده است. در واقع اين‌گونه مي توان بيان كرد كه يك طراحي لرزه‌يي ويژه، هنگامي كه شكل پذيري بيشتري در مقايسه با طراحي معمولي دارد، الزاماً عملكرد بهتري تحت فرآيند حذف ستون نخواهد داشت.

The reliability of structures under different loading conditions is the main objective of civil engineers. Experiments show that buildings may be vulnerable to blast air pressure and localized failures that occur in them. The cause of the explosion could be accidental or intentional, e.g., happened by terrorist attacks on public or private buildings. Progressive collapse is a catastrophic phenomenon which has been of greatest interest to many researchers and engineers during the last decade. Therefore, in this study, RC framed structures designed in accordance with Iranian design codes are evaluated using the GSA guidelines in order to investigate their progressive collapse potential. A five-story building is used to evaluate the impact of structural ductility on the progressive collapse that has a regular plan. The building blocks are designed for low, medium, and high ductile moment frames. In this study, the performance evaluation of progressive collapse conducted on buildings, and it shall include three different locations for removal of columns in the building plan. In addition to assessing the impact of locating columns in different locations, column removal is performed in stories 1, 3, and 5. In fact, in every building, there are 9 column removal scenarios; all these scenarios are analyzed for both methods of static and dynamic analyses. The structures are designed according to the conventional Iranian design codes, and afterwards evaluated using both nonlinear dynamic and nonlinear static analyses following different column removals. The column removals’ static and dynamic analyses to assess the buildings are designed by different ductilities; it is concluded that the potential progressive collapse of the special moment frames is very much more than intermediate and ordinary moment frames. Based on the load combination specified by the GSA, ordinary and intermediate frames can withstand collapse up to overload factors of 1.8 and 1.33, respectively. On the contrary, the special moment-resisting frame cannot resist against progressive collapse, and several column removals lead to collapse. In fact, this may suggest that a special seismic design, while more ductile compared to an ordinary design, does not necessarily have a better performance under a column removal scenario.