اثر زاویه اعمال زلزله و تحریک غیرهمزمان تکیه گاهی بر روی پل های قوسی بتن آرمه

با وجود رواج کاربرد پل های قوسی در مناطق لرزه خیز دنیا، رفتار لرزه ای این پل ها تاکنون مورد مطالعات محدودی قرار گرفته است. مطالعه حاضر به بررسی اثرات تغییر زاویه اعمال زلزله و تحریک غیرهمزمان تکیه گاهی بر پل های قوسی بتن مسلح می پردازد. چهار پل قوسی بتن آرمه ساخته شده در ایران به صورت سه بعدی مدلسازی شده و تحت تحلیل تاریخچه زمانی غیرخطی بر اساس 7 شتاب نگاشت قرار گرفتند که هریک از آن ها با تغییر زاویه در گام های 15 درجه اعمال شدند. تحریک غیرهمزمان تکیه گاهی نیز از طریق ایجاد تاخیر زمانی برای رکورد ورودی به هر تکیه گاه اعمال شد. نتایج نشان داد که افتادگی عرشه بیش از سایر پارامترها به زاویه اعمال زلزله حساس بوده است. افزایش نیروی محوری پای قوس در اثر رخداد زلزله تا 40 درصد مشاهده شد که بیشترین آن در حالت اعمال زلزله عرضی محاسبه گردید. اعمال تاخیر زمانی در تحریک تکیه گاه های سازه نیز منجر به حداکثر 10 درصد افزایش در معیارهای آسیب و حداکثر 5 درصد افزایش در نیروی محوری و لنگر خمشی پای قوس گردید.

effects of earthquake incidence angle and asynchronous support excitation on reinforced concrete arch bridges

arches are one of the most recognized structural forms, which are capable of transferring vertical loads to the supports through a compressive path. in addition to possessing desirable aesthetics, their force transfer mechanism makes arches especially suitable for materials that are weak in tension but strong in compression, such as concrete. with the advent of reinforced concrete, significant flexibility has been introduced to the design of concrete arches, due to which many reinforced concrete arch bridges have been built around the world, including in the high-seismicity regions. notable damage has been documented in several arch bridges during past earthquakes, such as the chi-chi or wenchuan earthquakes. in these earthquakes, undesirable cracking within the arch itself or in the lateral bracing elements was detected in arch bridges. certain aspects of seismic behavior of arch bridges are different from those in typical slab-on-girder bridges, including the significance of axial loads, which may change during earthquakes, sizable differences between in-plane and out-of-plane stiffness, and the use of piers with different heights. however, limited previous studies have addressed the seismic behavior of concrete arch bridges. in particular, the effect of earthquake excitation in directions other than the principal directions of arch bridges has not been sufficiently investigated. moreover, the effect of asynchronous support excitation has not been examined in detail for arch bridges. in the present study, the effects of earthquake incidence angle and asynchronous support excitation on reinforced concrete arch bridges are investigated. nonlinear 3-d models of four existing reinforced concrete deck-type arch bridges in iran were developed. the bridges had arch spans of 23, 35, 45 and 50 meters and were subjected to nonlinear time history analyses using seven acceleration records. the models incorporated nonlinear fiber-based elements for arch and piers and elastic elements for the bridge deck. the incidence angle was changed in 15 degrees increment between 0 and 90 degrees. moreover, the effect of asynchronous support excitation was investigated by means of introducing a time delay between excitation input for different supports. the relative displacement (drift) of the piers, the curvature ductility demands within the piers, the curvature ductility demand at different locations of the arch, and the displacement of the deck at the abutments (unseating) were used as damage indicators. the results showed that arch bridges were significantly more vulnerable to seismic loading in the transverse direction than in the longitudinal direction. unseating of the bridge deck from abutments and pier drifts were the most and the least sensitive damage parameter to the change in incidence angle, respectively. the unseating varied by 40 percent, whereas the maximum drift varied by 5 percent as a result of changes in the earthquake incidence angle. the axial force at the end points of the arch was found to change significantly during earthquake, with a maximum of 40 percent in case of 90-degree incidence angle. the effect of asynchronous support excitations was relatively small, with a maximum increase of 10 percent in damage indicators and 5 percent in the axial forces and bending moments.