روشي جهت طرح لرزه اي اقتصادي مبتني بر قابليت اطمينان سازه ها

An Economic Reliability-Based Seismic Design of Structures

بهينه سازي طرح لرزه اي مبتني بر قابليت اطمينان (RBDO) روشي است كه در حضور عدم قطعيت ها با ارضاء كردن قيود احتمالاتي مي تواند اقتصادي ترين طرح لرزه اي برآورده كننده سطح معيني از ايمني را ارائه كند. جهت اطمينان از برآورده شدن قيود احتمالاتي نياز است كه پاسخ هاي سازه با استفاده از تحليل هاي ديناميكي غيرخطي حاصل گردند. از سويي ديگر استفاده از تحليل هاي ديناميكي غيرخطي در روش RBDO منجر به افزايش هزينه محاسباتي سازه مي شود. در اين تحقيق روشي جهت طرح لرزه اي اقتصادي مبتني بر قابليت اطمينان ارائه مي شود. هدف روش پيشنهادي آن است كه ضمن اطمينان از برآورده شدن قيود احتمالاتي از طريق بكارگيري تحليل ديناميكي غيرخطي فزاينده، طرح لرزه اي اقتصادي را با هزينه محاسباتي معقول ارائه نمايد. روش پيشنهادي از طريق تعيين طرح بهينه روش طراحي مبتني بر نيرو (FBD) كه ضوابط مبتني بر قابليت اطمينان را نيز ارضاء كند، بدنبال برآورده كردن اهداف مذكور مي باشد. در روش FBD، طرح بهينه تابعي از مقدار ضريب رفتار است. روش پيشنهادي با تعيين ماكزيمم ضريب رفتار برآورده كننده قيود احتمالاتي، طرح بهينه اي از روش FBD كه منجر به برآورده شدن ضوايط مبتني بر قابليت اطمينان مي شود را ارائه مي كند. بمنظور ارزيابي توانايي روش پيشنهادي، طرح لرزه اي سازه چهار طبقه با سيستم قاب خمشي ويژه با استفاده از اين روش انجام شد. نتايج نشان داد كه روش در ارائه طرح لرزه اي اقتصادي برآورده كننده ضوابط مبتني بر قابليت اطمينان موفق بوده است.

The seismic design of the structures is subjected to uncertainties originating from various sources. To ensure that a safe design is achieved, the uncertainties must be considered in the seismic design process. The reliability-based seismic design is the proper approach that directly takes into account the uncertainties. In this approach the performance objectives are reliability-based seismic criteria expressed either in terms of an annual probability of exceeding a given performance level or in terms of a probability of exceeding a given performance level conditioned on the seismic intensity corresponding to a specific hazard level. It is obvious that the ultimate aim of the reliability-based seismic design of a building is not only to satisfy the reliability-based seismic criteria, but also to minimize initial or life-cycle cost. The reliability-based seismic design optimization (RBDO) is the method that achieves the most economic design satisfying the reliability-based seismic criteria (probabilistic constraints). However, the RBDO is less preferred. This is because to ensure that reliability-based seismic criteria are achieved, the statistics parameters of the seismic demand and capacity must be determined through the results of the nonlinear dynamic analyses. On the other hand, the use of the nonlinear dynamic analyses in the RBDO method can lead to the increase of the computational cost so that the personal computers require several years to run it. In this study, a method to produce the reliability-based economic seismic design is proposed. Reliability-based seismic criteria are expressed in terms of a mean annual probability of exceeding a given performance level. The main goals are to ensure satisfying the reliability-based seismic criteria through the use of the results of the incremental dynamic analyses and to produce the economic seismic design within reasonable computing time. The proposed method achieves the two goals through determining the optimum design of the force-based design method that satisfies the reliability-based seismic criteria. The optimum design of the force-based design method depends on the value of the response modification factor. The value of the response modification factor of a building, which leads to satisfying the reliability-based seismic criteria, is in the range of one to a maximum value. From an economic point of view, the desirable value of the response modification factor is the maximum one, which results in a minimum design base shear and accordingly in an economic design. In order to respond to the two main goals, the method aims to determine the maximum value of the response modification factor of a building so that leads to satisfying the reliability-based seismic criteria. The proposed method is used to produce the seismic design of a 4-story building for two reliability-based seismic criteria. The steel special moment resisting frame is considered as the lateral load resisting system in the studied building. The results reveal that the proposed method can efficiently produce the economic seismic designs satisfying the reliability-based seismic criteria within reasonable computing time.While the designed frame by Zacharenaki et al using existing RBDO method can not satisfy specifications of reliability and this is shown the ability and efficiency of the proposed method.