ارزیابی عملکرد لرزه ای پل های مصالح بنایی با استفاده از مدل پایه حرکت گهواره ای

پل‌های مصالح بنایی در برابر تحریک‌های لرزه‌ای آسیب‌پذیر بوده و عملکرد این سازه‌های ترد بر اثر اعمال بارهای لرزه‌ای نیاز به بررسی دقیق دارد. در این کار تحقیقی یک مدل ساده برای تحلیل دینامیکی این سازه‌ها پیشنهاد می‌شود که بر حرکت گهواره‌ای پایه در جهت عرضی پل مبتنی است. با استفاده از این مدل؛ تحلیل‌های غیرخطی تاریخچه زمانی این‌گونه پل‌ها به‌راحتی و به سهولت می‌تواند انجام گیرد. مدل پیشنهاد شده برای تخمین پاسخ‌های لرزه‌ای پل‌های مصالح بنایی بزرگ که به‌طور هم‌زمان تحت تاثیر تحریکات لرزه‌ای در جهت عرضی و قائم پل قرار گرفته‌اند مورد استفاده قرار می‌گیرد. نتایج حاصل از این پژوهش معلوم می‌نماید که در طی تحلیل لرزه‌ای پل؛ برای تخمین دقیق مقدار لغزش ناشی از برش و نیروی محوری پایه اثر مولفه قائم به همراه اثر مولفه افقی زلزله باید در نظر گرفته شود. با کاربرد مدل پیشنهادی برای بررسی بهسازی لرزه‌ای پل‌ها مشخص می‌گردد که عملکرد لرزه‌ای پل‌ها بر اثر افزایش میزان شکل‌پذیری عرشه به‌طور قابل‌توجهی بهبود می‌یابد.

Investigation on Seismic Performance of Masonry Arch Bridges Using Rocking Pier Model

Masonry bridges are vulnerable structural systems to the ground motion excitation that their survival in case of such incidents has to be studied in detail. In this work, a simplified model for dynamic analysis of masonry arch bridges based on rocking motion of rigid blocks is proposed. Using this model, nonlinear time integration analyses on these bridges can be done with ease and in a short time. Later, acceptance criteria for three cases of uncracked, fullyoperational and collapseprevention pier sections are developed for such bridges. The accuracy of proposed model in representing the behavior of a rocking system has been verified using the results of experimental studies on rocking motion of a masonryconcrete block reported elsewhere. The results show the suitability of the proposed model in representing rocking motion of rigid blocks. In a case study, the proposed model for masonry arch bridges was used in evaluation of seismic performances of a monumental masonry bridge subjected to both horizontal and vertical seismic actions. The study shows the importance of vertical component of ground motion in determination of internal forces and shearsliding deformation at the bottom of the bridge’s pier. The proposed model has also shown its ability in defining the effectiveness of a seismic retrofit approach for the same bridge system in a comparative study. According to this investigation, seismic performances of the bridge can be significantly improved in case of adding ductility to its deck assembly. To understand the capacity of bridge system in dealing with earthquake demands, a series of Incremental Dynamic Analyses (IDA) have been carried out on the rockingpier model of the bridge system using earthquake records. Considering the simplicity of rocking pier model, all the analyses on abovementioned bridge system have been carried out with ease and in a very short time. According to results, a bridge system subjected to bidirectional seismic actions (vertical and horizontal) has, unexpectedly, more capacity in dealing with seismic demands if it is compared with the same bridge system with unidirectional horizontal seismic excitation. Conversely, the sliding breakdown of the pier in case of bidirectional seismic actions is much higher than that in the case of unidirectional one. Moreover, significant reductions in the level of rotational pitch and shear sliding at rocking joint of the pier is expected in case of adding ductility to the deck of the bridge assembly. As it was expected, ductility in the bridge system also decreases the discrepancy of bridge responses with respect to different earthquake actions, which is attributed to the systems with higher energy dissipation potential.