ارزيابي شاخص اعتماد سازه‌يي فولادي قاب خمشي طراحي‌شده براساس آيين‌نامه‌ي فولاد ايران

Reliability Index Evaluation of MRF Steel Structures Designed According to Iranian Code

تيوري قابليت اعتماد، نقشي اساسي در ضوابط طراحي سازه‌ها ايفا مي‌كند و تحليل و طراحي سازه‌ها بر مبناي نظريه‌ي قابليت اعتماد، كه شاخه‌‌يي از تيوري عمومي احتمالات است، در سال‌هاي اخير توجه بسياري را به خود جلب كرده است. علت اين توجه، توانايي در مدل‌كردن عدم قطعيت در پارامترهاي بارگذاري و سازه‌‌يي از قبيل مشخصات مصالح، ابعاد هندسي، و تحليل غيرخطي سازه‌هاست. در اين نوشتار، براي محاسبه‌ي شاخص اعتماد سازه‌ها روشي ارايه شده است كه دو نكته‌ي مهم يعني ساده‌بودن و دقت روش در ارزيابي و محاسبه‌ي شاخص اعتماد سازه‌ها در نظر گرفته شده است. مقادير شاخص اعتماد به كمك نتايج حاصل از تحليل ديناميكي افزايشي و انتخاب ضريب شكل‌پذيري به عنوان معيار غيرخطي سازه محاسبه مي‌شود. براساس فرمول‌بندي ارايه‌شده، مقدار شاخص اعتماد به عنوان نمونه در سازه‌هاي فولادي قاب خمشي طراحي‌شده براساس آيين‌نامه‌ي فولاد ايران مورد ارزيابي قرار گرفته است.

Reliability theory, which itself is a part of general probabilistic concepts, plays a basic role in the design provisions of structures. In limit state or performance-based design, the structural reliability theory plays an essential role in setting the design criteria, as well as demonstrating the target reliability level appropriate to each society. Structural reliability is necessary for having a model that makes it possible to perform rational calculations in the presence of uncertainties in the various parameters encountered in loading parameters and those of structures such as material property, geometric dimensions and the nonlinear dynamic analysis procedure. Although several procedures for structural reliability evaluation, treating non-linear displacement responses, have been proposed, they require complex procedures that may not be used in the practical design process. In the present study, a ductility-based procedure is proposed to maintain both accuracy and simplicity, based on non-linear dynamic response analysis. The use of results of the nonlinear dynamic analysis for a few records to establish the seismic demand curve could be considered the computationally intensive part of the incremental dynamic analysis (IDA). The IDA is an emerging structural analysis method that offers thorough seismic demand and limit-state capacity prediction capability by using a series of nonlinear dynamic analyses under a suite of multiply scaled ground motion records. We used probabilistic tools, by applying the total probability theorem, in order to derive the hazard values for the ductility-based response. This study presents an analytical foundation for probability-based formats for seismic design and assessment of structures. In this study, a reliability assessment of six steel moment resisting frames (MRF), designed according to Iranian codes, is carried out. The reliability indices of these designed steel MRF structures are to be estimated using the present procedure, the ductility-based procedure.