تعيين بار نهايي گسيختگي پل هاي سنگي قوسي به كمك مدل رفتاري مناسب مصالح

Determination of ultimate failure load of stone arch bridges by using consistent material models

در سال‌هاي اخير، مدل‌سازي مناسب پل‌هاي قوسي سنگي به‌دليل نقش مهم آنها در سيستم ريلي كشورمان مورد توجه بسيار پژوهشگران قرار گرفته است. در اين نوشتار، به‌منظور بررسي بار نهايي گسيختگي اين پل‌ها، از مدل المان محدود سه‌ بعدي استفاده و سيستم به 2 بخش: قوس باربر و خاكريز تقسيم شده است. مدل‌هاي رفتاري مناسب خاك و سنگ براساس مدل‌هاي اصطكاكي خميري همراه با سطوح تماس اصطكاكي بين بلوك‌هاي بنايي كه سختي افزاينده‌ دارند، نياز مبرم به شناسايي دارند. همچنين نقش ديوارهاي پيشاني به‌منزله‌ي قيد تغييرمكان افقي خاكريز روي پل در بهبود مكانيسم گسيختگي پل نبايد ناديده گرفته شود. به‌منظور صحت‌سنجي مدل پيشنهادي، پل پرستوود با نرم‌افزار المان محدود مدل و فقط 3/1? خطا در مقدار بار نهايي تجربي آن نتيجه شده است.

In recent years, great interest has been shown towards effective modeling of masonry arch bridges. However, the issue of an efficient model is in controversy among researchers with contrasting strategies. The fact that there are a great number of stone arch bridges in Iran (about 3300) most of which are serving the railway network, makes the issue very crucial in terms of roads network vulnerability due to their unknown behaviors against usual and unusual loads. In this paper, a nonlinear 3D finite element method is employed in order to determine the ultimate failure load of stone arch bridges. Most of these bridges are composed of three structural parts; arch barrel, backfill and spandrel walls. However, because of simplifications in modeling masonry arch bridges in some researches, spandrel walls are neglected. Efficient description of material properties of these parts has great influences on the accuracy of the resulting ultimate failure load. The experience has shown that elastic modeling of these systems could not yield a reasonable behavior. Also, even if only nonlinear models of different contacts are used, in some cases the analysis results would not be satisfactory. It is understood that accurate results could be achieved even by simple Mohr-Coulomb models for the barrel arch and spandrel walls. At the same time Drucker-Prager material law for the backfill, along with appropriate modeling of the contact surfaces of different materials should be used. It is shown that hardening stiffness in pressure over-closure of hard contacts should not be neglected. In addition, the important role of spandrel walls has to be accounted for in a 3D analysis model. Indeed, the former improves the bridgeʹs failure mechanism, whereas the latter restrains the bridgeʹs lateral deformations. To validate the proposed model, the actual failure test on the Prestwood Bridge is considered. According to the actual failure test, the proposed model is subjected to a load at the quarter point of the bridge span. Despite other models, the aforementioned modeling strategy could yield similar collapse mechanism as that of the prototype, and the ultimate failure load is achieved with only 1.3 percent error in respect to the experimental one.