بررسي قابليت خرابي پيش‌رونده در ساختمان‌هاي فولادي با سقف‌هاي مختلط

Investigation into the Potential of Progressive Collapse in Steel Buildings with a Composite Roof

بارهاي غيرعادي ناشي از حوادث طبيعي، خطاهاي اجرا و برخي مسايل ديگر مي‌توانند باعث به‌وجودآمدن خرابي پيش‌رونده در سازه‌ها شوند. بيشتر مطالعاتي كه در زمينهي ارزيابي خرابي پيش‌رونده در ساختمان‌هاي فولادي انجام شده است، مدل هاي دوبُعدي از قاب‌هاي فولادي هستند، كه در آنها توزيع سيستم‌هاي سقف در نظر گرفته نشده است و اين مورد مي‌تواند باعث كاهش دقت در مدل‌سازي موردنظر شود. در حالي كه كه درنظرگرفتن و محاسبه‌ي اثرات سه‌بُعدي و همچنين وجود دا‌ل‌هاي بتني در سقف‌هاي كامپوزيت، مي‌تواند نقش تاثيرگذاري در پاسخ سازه داشته باشد. به همين دليل در اين پژوهش مدل المان محدود سه‌بُعدي يك ساختمان فولادي 5 طبقه يك بار با درنظرگرفتن دال و بار ديگر بدون درنظرگرفتن دال با استفاده نرم‌افزار 11/6 Abaqus/CAE شبيه‌سازي شده و پتانسيل وقوع خرابي پيش‌رونده در آنها مورد ارزيابي قرار گرفته است. نتايج حاصل از تحليل‌ها نشان مي‌دهد كه درنظرنگرفتن دال به هنگام محاسبات مي‌تواند منجر به ايجاد خطا در ارزيابي پتانسيل وقوع خرابي پيش‌رونده در سازه شود .

Abnormal load due to natural events, implementation error and some other issues can lead to the occurrence of progressive collapse in structures. In the research undertaken so far, most have involved 2-D models and are based on bare steel frames without consideration of the contribution of the floor systems, which reduces the accuracy of the model. Consideration of the effects of three dimensional and concrete floor slabs can play a crucial role in the progressive collapse response. For this purpose, in this research, a 3-dimensional finite element model of a five story steel building was simulated by Abaqus/CAE 6.11 software; First, with consideration of the slabs, and next, without their consideration. Then, the potential for progressive collapse was simulated. The results of the analysis indicate that the lack of consideration of the slabs during computation can lead to errors in assessing the potential for progressive failure of structures. The following results can be concluded from this study: when a structure is subjected to unusual external loads, such as a motor vehicle collision, explosion of a bomb in a vehicle, etc., the most critical columns are located in the nearest frame to the outer frame of the structure. So, engineers should focus more on resistant design against progressive collapse, as it could be a key factor that has a significant role in reducing the progressive collapse potential. In progressive collapse evaluation, when external columns are removed and the structure is damaged, the closest columns to the external frame are critical. Also, after removing the columns in different modes, the loads are split between the adjacent members; hence, these members must have sufficient ability to withstand the additional forces. Therefore, the distribution of forces in these members, before and after column removal, can be seen by monitoring the axial force values for adjacent members of the removed column. Because all the members are designed to withstand earthquake loads and non-interference of related loads (i.e., earthquake ground motion) with progressive collapse, even by removal of the main load bearing members, other columns still have enough capacity to carry the existing loads.