ارزيابي تاثيرات تعيني و احتمالاتي نامعيني در مفاهيم محاسباتي ضريب رفتار قاب‌هاي خمشي بتن مسلح با مقاومت نهايي يكسان

Evaluation of Deterministic and Probabilistic Effects of Redundancy on the Response Modification Factor for RC Moment Resisting Frames with Equal Lateral Resistance

بيشتر پژوهشگران در ارزيابي رفتار سازه‌ها، مقاومت افزون از حد تسليم اولين عضو تا تسليم كلي سازه را ناشي از نامعيني دانسته‌اند و در برخي پژوهش‌ها اين بخش از مقاومت افزون به عنوان ضريب نامعيني معرفي شده است. از طرفي برخي ديگر از پژوهشگران، ضريبي را به عنوان ضريب نامعيني به طور مستقل از مقاومت افزون در فرمول‌بندي ضريب رفتار لحاظ كرده‌اند، كه مبتني بر تعداد قاب‌هاي لرزه‌بر و تيوري قابليت اعتماد سازه‌هاست. هدف از اين پژوهش، پاسخ به اين پرسش است كه آيا افزايش نامعيني به واسطه‌ي تاثيري كه در افزايش مقاومت افزون دارد، پديده‌اي مطلوب به حساب مي‌آيد يا اينكه به صرف افزايش تعداد قاب‌هاي لرزه‌بر و افزايش قابليت اعتماد سيستم، سازه رفتار مطلوب‌تري خواهد داشت. نتايج حاصل از اين پژوهش نشان مي‌دهد كه افزايش نامعيني در صورتي كه مقاومت افزون بيشتري در سازه ايجاد نكند، همواره نمي‌تواند موجب بهبود رفتار سازه‌هاي قاب خمشي شود.

The general opinion regarding the overstrength capacity of a structure is explained by the process of first local yielding to total failure being due to structural redundancy. Furthermore, results of some research indicate that this part of the overstrength capacity can be introduced as a redundancy reduction factor. On the other hand, some other research showed that an analytical parameter, according to the lines of vertical seismic framing and the theory of structural reliability, can be formulated as the redundancy reduction factor independent of the overstrength reduction factor in the analytical definition of the response modification factor. A general conceptual question is why structural redundancy has been regarded as a desirable property. Is it because making more overstrength capacity or just increasing the number of seismic resistant frames will make the structural behavior more desirable, as well as increasing the reliability of the systems? To answer these questions, six and nine floor three-dimensional reinforced concrete framed structures with the same story area and the same equal lateral resistance were designed. In this research, the essential parameters of the response modification factor for the studied structures were estimated numerically. Furthermore, by considering the strength factor as a random variable, both the deterministic and probabilistic effects of redundancy on the response modification factor were also evaluated. The results of this research illustrated that imposition of an increase in redundancy, where no more overstrength capacity will be made, might not improve the behavior of the framed structure. It is assumed that the same ultimate lateral resistance of structures that causes an increase, to a certain level, in redundancy, can also enhance both the ductility capacity and the inelastic capacity of structures. However, any further increase in the redundancy of that certain level might have a negative effect on the ductility capacity.