مطالعه موردي يك ساختمان بتن آرمه مقاوم در برابر زلزله تحت اثر بارگذاري انفجار

The Study of an Earthquake-Resistant Reinforced Concrete Building under the Blast Loading

با توجه به حوادثي كه در گوشه و كنار دنيا به وقوع پيوسته، مشخص شده رفتار ساختمانها تحت اثر بارهاي انفجار به دليل خصوصيات متفاوت اين نوع بارگذاري با بارهاي ديگر يكسان نيست. از آنجايي كه بيشتر شهرهاي ايران به دليل موقعيت ممتاز استراتژيكي و برخورداري از منابع طبيعي خداداي سرشار، همواره در معرض تهديدهاي خارجي قرار دارند، لزوم شناخت تهديدات و نحوه مقابله با آنها چون حملات تروريستي، انتحاري و بمب بر مهندسان سازه الزامي است و ساختمانها بايد براي چنين خطراتي محاسبه شوند. با توجه به جايگاه ويژه سازه‌هاي بتن ‌مسلح در صنعت ساختمان كشور و گستردگي استفاده از سيستم هاي ساختماني خمشي بتن‌مسلح در ساختمانهاي طراحي شده و آسيب‌پذيري اين نوع سيستم‌هاي ساختماني در برابر بارهاي انفجار، هدف از اين تحقيق بررسي دقيق پاسخ يك ساختمان بتن‌آرمه نه طبقه مقاوم در برابر زلزله تحت اثر بارگذاري ضربه‌اي و انفجار مي‌باشد. از آنجايي كه فرض مي‌گردد سازه مذكور در ناحيه با لرزه‌خيزي بسيار زياد قرار دارد ابتدا سازه مذكور تحت اثر نيروهاي لرزه‌اي بهسازي شده، آنگاه سازه بهسازي شده تحت اثر بارهاي انفجار قرار مي‌گيرد. دو طرح بهسازي شامل بهسازي قابهاي خمشي بتن‌آرمه و بهسازي با اضافه نمودن ديوارهاي برشي پيشنهاد مي‌گردد. نتايج تحليل اجزا محدود غيرخطي نشان مي‌دهند كه بهسازي قابهاي خمشي به طور قابل-ملاحظه‌اي اثرات تخريبي انفجار و به دنبال آن انهدام پيشرونده را كاهش مي‌دهد. نتايج همچنين نشان مي‌دهند كه بهسازي با اضافه نمودن ديوارهاي برشي در كاهش خسارات ناشي از انفجار موثر مي‌باشد اما در قياس با بهسازي قابهاي بتن‌آرمه تاثير كمتري دارد.

Given the incidents occurred around the world, it has been identified that due to the different characteristics of blast loads, the behavior of structures under these loads are not the same as the other loads. Because of the strategic privileged position of most cities of Iran and rich natural resources, external threats are exposed. Hence, structural engineers need to understand the risks and how to deal with such terrorist attacks and suicide bombings. Building structures should also be designed for such dangers. In many earthquakes and blasts, most of the deaths have occurred due to collapsing of buildings than due to any direct effect of the earthquakes or blasts. Therefore, it is of primary importance to ensure that buildings will not collapse which requires a considerable enhancement in the ductility of the building. The behavior of structures against impulsive loads is affected by structural charac-teristics that are also important for seismic resistance. Deformability, strength, stiffness, and stability of the structural framing system and elements and resistance to progressive collapse are factors that play important roles on the stability of buildings under both blast and seismic loads. The significance of these structural parameters on blast resistance of reinforced concrete buildings should be assessed through structural analysis. Due to the special position of reinforced concrete in the construction industry, widespread use of moment resisting frame systems in building structures and vulnerability of this type of building systems against blast loads, the objective of this study is to evaluate the exact response of a seismic rehabilitated nine-story reinforced concrete building to the impact load. Assuming the structure is located in an area with high seismicity, first, the building is rehabilitated under the seismic forces, then, the rehabilitated building is subjected to the blast load. Two strengthening scheme, including strengthening of reinforced concrete frames and strengthening with adding shear walls are proposed. Each strengthening plan is then analyzed for its response to the blast loading. The blast and progressive collapse analyses demonstrate that the strengthening plan of moment resisting frame would significantly reduce the amount of blast-induced damage and subsequent progressive collapse, compared with the response of the original building. The results also show that the strengthening plan with shear walls is effective but compared with the strengthening of moment resisting frame is less effective in reducing blast and progressive collapse damage. It can be seen that strengthening of perimeter elements enhanced the performance of the building subjected to blast loading.