بررسي اثر بيه‌ي عرشه در پاسخ ديناميكي پل با درنظرگرفتن اندركنش ديناميكي پل- قطار

Bridge Skewness Effect on the Dynamic Response of Bridges, Considering Dynamic Bridge- Train Interaction

در سال‌هاي اخير توجه به ديناميك پل‌هاي راه‌آهن به‌عنوان يكي از مقدمات ضروري جهت احداث خطوط قطارهاي سريع‌السير افزايش يافته است. در اين تحقيق، پاسخ ديناميكي پل راه‌آهن دوخطه يزدان از خط راه‌آهن قم ـ ساقه با بيه‌هاي مختلف ?، ??، ??، ?? و ?? درجه تحت بار قطار عبوري و تاثير بيه عرشه بر پاسخ ديناميكي سازه مورد بررسي قرار گرفته است. تحليل ديناميكي بر پايه يك مدل سه‌بعدي از مجموعه پل و قطار و اندركنش بين آن‌ها صورت گرفته است. با افزايش بيه پل مقدار فركانس مربوط به مد اول پل افزايش يافته و در حالت كلي پاسخ ديناميكي پل با افزايش بيه كاهش مي‌يابد. همچنين در سرعت‌هاي نزديك به تشديد، با عبور هر گروه از محور چرخ‌ها از روي پل، مقادير پاسخ‌ها به‌طور قابل ملاحظه‌يي افزايش مي‌يابد.

In recent years, interest in the dynamics of railway bridges, as necessary preliminaries for construction of high-speed railways, has increased rapidly. Increasing train speeds means that bridges are subjected to much higher dynamic effects. Therefore, the bearing capacity of structures must be increased in proportion to demand load, and dynamic effects must be considered in the structural design. In previous design methods, dynamic effects were often considered by introducing dynamic amplification factors, but, it can be seen that, in most cases, where train speed is more than 200 km/h, dynamic analysis of the bridge is required by increasing train speed. Correct understanding of the dynamics of railway bridges results in a realistic assessment of their structural responses under train loads. New bridge designs will be economical and also utilization of existing bridges will be proportional to their capacity. In this study, we have endeavored to specify the dynamic response of a double-track railway bridge to moving trains, and the influence of bridge skewness. Dynamic analysis is based on a three-dimensional model of bridge-train interaction. The Yazdan viaduct is an under construction bridge located on the Qom-Saghe double-track railway. It is also a simple span bridge with 22m span length that has been investigated under different skewness of 0, 15, 30, 45 and 60 degrees. To validate the accuracy of the model and the results of this study, a 30m span bridge from existing models in reputable international papers was used. The results of analysis demonstrated that the vertical displacement and acceleration of the bridge increase under high speed loads. At train speeds close to critical speed, due to moving axle groups, the bridge responses grew considerably as resonance occurred. Skewness was found to increase the fundamental frequency of the bridge, and with an increase in bridge skewness, the dynamic responses of the bridge decreased.