مقايسه رفتار قاب‌‌هاي خمشي مركب (RCS) و فولادي تحت زلزله‌هاي حوزه نزديك گسل

Comparison between the Behavior of RCS and Concrete Moment Frames under Near Fault Earthquakes

بررسي رفتار سازه تحت زلزله ‌هاي حوزه نزديك به علت ماهيت ويژه اين زمين‌لرزه‌ ها در مقايسه با زلزله ‌هاي دور از گسل امري ضروري به نظر مي ‌رسد‌. در اين پژوهش به بررسي نياز ‌لرزه ‌اي سازه‌ هاي مركب RCS و فولادي تحت زلزله‌هاي حوزه نزديك گسل در مقايسه با زلزله‌هاي حوزه دور پرداخته شده است‌. به همين منظور تعداد 5 قاب خمشي مركب RCS و فولادي با شكل‌پذيري متوسط و در طبقات 4‌، 7‌، 10‌، 15 و 20 و 5 دهانه طراحي شد و سپس تحليل‌هاي ديناميكي توسط نرم افزار OpenSees بر روي سازه‌ها انجام شده است‌. نتايج بدست آمده در اين پژوهش نشان مي‌دهد كه هر چه تعداد طبقات بيشتر مي شود جابجايي سازه مركب از سازه فولادي كمتر مي شود. اختلاف ناشي از ركوردهاي نزديك و دور از گسل در محاسبه جابجايي و دريفت طبقات در سازه‌هاي فولادي به مراتب كمتر از اين اختلاف در سازه هاي مركب است. كه نشان مي دهد اثربخشي ركورد هاي نزديك گسل بر سازه هاي مركب بيشتر از سازه هاي معمول فولادي ست. افزايش دهانه به همراه افزايش ارتفاع سازه، بحراني بودن ركورد نزديك گسل بر جابجايي سازه مركبي كه تيرهايش شبيه سازه فولادي شده، را از بين مي برد.

The composite RCS moment resisting frame, includes concrete columns and steel beams, it has some advantages in comparison to ordinary steel and concrete moment resisting frames. Previous studies have shown that these systems, in case of preserving sufficient strength and needed ductility in seismic condition, could be effective in design and construction. In the previous research on these structures, studies were made on the frame and RCS connections but there has not been any study on the seismic assessment of the RCS structure with time history and for the near fault earthquakes considering the effect of span length, for adopting this type of structure. Investigating the structure behavior under near the fault earthquake, due to the special nature and characteristics of these earthquakes in comparison to the far fault earthquakes seems to be essential. For this purpose 5 composite RCS intermediate moment resisting frames with 4, 7, 10, 15 and 20 stories and 5 spans were designed and then nonlinear dynamic analysis was performed on the structures using the OpenSees software. The obtained results in this research show that with increase in the number of stories the displacement of composite structure decreases with respect to the steel structure. The difference due to near and far fault earthquakes in calculation of stories displacement and drift in steel structures is far lower with respect to this difference in composite structures. This shows that effectiveness of near fault records on composite structures is more than the ordinary steel structures. Increase in the span length together with increase in the structure height would diminish the criticality of near fault record concerning the displacement of a composite structure which its columns have been made similar to the steel structure.