ارزيابي سطح عملكرد لرزه‌‌يي سازه‌هاي فولادي قاب خمشي براساس اهميت آنها مطابق استاندارد 2800 ايران

Seismic Performance of Steel Moment Frames Based on their Importance According to the Iranian Seismic Code

طراحي لرزه‌‌يي در بسياري از آيين‌نامه‌ها، از جمله استاندارد 2800 ايران، بر اساس روش نيرويي است. در اين روش براي ارتقا سطح عملكرد ساختمان‌ها، نيروي وارد بر آنها با افزايش ضريب اهميت ساختمان (I) افزايش داده مي‌شود. از آنجا كه در روش نيرويي، رفتار سازه در حوزه‌ي غيرارتجاعي مشخص نيست، ميزان و محل آسيب سازه در سطوح عملكرد متفاوت براي طراح نامعلوم خواهد بود. در اين نوشتار با استفاده از تحليل‌هاي استاتيكي غيرخطي، سطح عملكرد سازه‌هاي طراحي‌شده براساس استاندارد 2800 ايران برآورد و نسبت ضريب اهميت سازه‌هاي مورد مطالعه در سطوح عملكرد مختلف بررسي و ارزيابي شده است. در نهايت، مقدار ضريب اهميت مورد نياز براي سطوح عملكرد موردنظر برآورد شده است. نتايج به‌دست‌آمده نشان‌دهنده‌ي آن است كه سازه‌هاي بلندمرتبه با اهميت متوسط و سازه‌هاي با اهميت خيلي زياد جواب‌گوي سطح عملكرد موردنظر نيستند و نياز به افزايش مقدار ضريب اهميت آن‌ها دارند.

The current Iranian Seismic Code, for seismic loading and analysis of structures, (Standard no. 2800) considers linear elastic analysis to be adequate for structural and seismic response prediction for a majority of structures. In this regulation, an importance factor, I, is considered to improve the performance of buildings based on their importance. Linear analysis is inadequate for observing structural performance during earthquakes, because proper seismic behavior and the stability of structures are not just governed by strength; structures need to resist determined amounts of force and should be able to displace determined amounts of displacements. On this basis, it is expected that by using importance factor, I, in linear analysis, the structures will behave properly, and after earthquakes, will present a desired level of performance. New seismic regulations, such as FEMA 356 and the Iranian Seismic Rehabilitation Guideline, use a performance-based design method; nonlinear analysis methods are the main tools of these codes. Also, the main objective of this research is to evaluate the seismic performance of buildings, with different importance levels, designed according to the Iranian Seismic Code, using the Iranian Seismic Rehabilitation Guideline. In this research, a set of structures, with different categories of occupancy and different numbers of stories, are designed according to the Iranian Seismic Code. The seismic performance levels of the mentioned structures are evaluated using nonlinear static analysis (pushover), based on the Iranian Seismic Rehabilitation Guideline. The results show that the low- and medium-rise buildings behave to a life safety (LS) performance level. In high-rise buildings, with medium importance, the required performance level (LS) is not achieved, and in very high importance (essential) buildings, the required performance level (IO) is not achieved. Therefore, increasing the importance factor, I, does not necessarily lead to improvement in performance levels, but leads to an increase in structural weight; this could be a non-economic decision. By using non-linear analysis in parts of the structure, in which performance level is not met, the structure would be strengthened and achieve the required level of performance.