بررسي رفتار لرزه‌يي قاب‌هاي فولادي در سطوح خطر مختلف با روش زمان‌دوام

STUDY OF ENDURANCE TIME METHOD IN SEISMIC ASSESSMENT OF STEEL FRAMES AT DIFFERENT EXCITATIONS LEVELS

نياز به تحليل هاي سنگين و پر حجم ديناميكي غيرخطي و تاريخچه‌ي زماني در طراحي سازه ها براساس عملكرد، باعث شده است تا پژوهشگران كماكان در پي يافتن شيوه هاي جديدي براي بررسي عملكرد سازه تحت زلزله با شدت هاي مختلف باشند. در اين نوشتار، هدف بررسي توانمندي روش زمان‌دوام در پيش‌بيني رفتار لرزه‌يي قابهاي فولادي در سطوح مختلف خطر و همچنين ارايه‌ي روش زمان‌دوام به‌منزله‌ي روشي نوين و كاربردي، براي تعيين عملكرد قاب‌هاي فولادي با كمترين تعداد تجزيه و تحليل تاريخچه‌ي زماني است. براي اطمينان از صحت نتايج تجزيه و تحليل زماندوام در پيش‌بيني پاسخ‌هاي سازه، نتايج آن با نتايج تجزيه و تحليل تاريخچه‌ي زماني غيرخطي دو مجموعه‌ي شتاب‌نگاشت واقعي مقايسه و نشان داده شد كه در تمامي سطوح خطر مورد بررسي، توابع شتاب زمان‌دوام، پيش بيني مناسبي از رفتار سازه تحت زلزله‌هاي واقعي ارايه مي‌كنند. همچنين ملاحظه شد كه روش زمان‌دوام به شتاب‌نگاشتهاي انتخابي وابستگي ندارد.

In recent decades, most codes have placed a high value on the performance based design of structures. However, these methods are computationally complex and time-consuming, and have caused researchers to seek new and efficient methods to investigate the performance of structures under different intensities of seismic loading. In this paper, with endurance time (ET) analysis, we try to provide better insights into the dynamic behavior of structures at continuous performance levels and use them to evaluate the seismic performance of steel frames. By considerably reducing the number of time history analyses for assessment of structural responses at different intensities, the ET method can be a useful tool for executing the performance based design of structures. In other words, with just one analysis of the structure under ET acceleration, one can assess the structure at different performance levels. For more precise achievement, one can use 3 ET accelerations and consider the average of responses as the response of the structure. Endurance time analysis is based on time history analysis, however, in this method, the structure is subjected to a gradually intensifying acceleration function and different damage indices of the structure are evaluated through analysis time. The different duration of ET accelerations represents various intensities of earthquake at different hazard levels. For this purpose, various inelastic moment resisting steel frames were investigated at different hazard levels. In this research, the performance of structures under seismic excitation at different performance levels is evaluated, based on interstory drift ratios and story shear forces. To ensure the accuracy of the ET method, its results are compared with the results of a nonlinear time history analysis of two sets of ground motion. It was seen that the endurance time accelerogram leads to an almost proper prediction of structure behavior under various earthquake records. It is shown that ET predictions are not sensitive to selected ground motions. As an achievement, the endurance time method significantly decreases the amount of computation in each seismic evaluation analysis. In this research, ASCE-41 is used as the performance based design criterion.