اثر رفتار تابع زمان مصالح بر عملكرد عرشه پل‌هاي پيش‌تنيده طره‌اي

The Influence of Time Dependent Material Behavior on the Structural Performance of Prestressed Box Girder Bridge Superstructure

در اين مطالعه عوامل موثر بر گونه هاي رفتار تابع زمان مصالح، از جمله خزش، جمع شدگي، تغييرات مدول الاستيسيته بتن و همچنين پديده سستي فولادهاي پيش تنيدگي بر عملكرد عرشه پل هاي پيش تنيده طره‌اي در بازه زماني 35 ساله مورد بررسي قرار داده شده اند. به اين منظور، مدل اجزا محدود تفصيلي يك پل سه دهانه از انواع متداول پل‌هاي طره‌اي تهيه شده و آثار ساخت مرحله اي، رفتار تابع زمان مصالح، اعمال مرحله اي نيروهاي پيش‌تنيدگي و انواع افت‌هاي كوتاه مدت و بلندمدت در نيروهاي پيش تنيدگي، از طريق روش تحليل استاتيكي غيرخطي مورد مطالعه قرار گرفته‌اند. بر اساس نتايج مطالعات كمّي تفصيلي و نحوه تغييرات تنش ها و تغيير مكان ها در بازه زماني فوق الذكر، عوامل موثر بر عملكرد عرشه پلِ مورد بررسي شناسايي شده و ضمن تشريح ويژگي هاي رفتاري تابع زمان سازه عرشه، توصيه هاي طراحي و اصلاحي در زمينه ميزان پيش تنيدگي اوليه -به منظور ساخت و همچنين ميزان تاندون هاي پيوستگي لازم به نيت بهسازي اينگونه پل ها جهت بهبود رفتار بلندمدت عرشه پل ارايه گرديده است.

The time dependent material behavior is of particular importance in the study of the behavior of boxed girder prestressed concrete bridges. The stage by stage balanced cantilever method of construction of segmental bridge contributes further in their time dependent performance. In this work, in order to study the performance of cantilever prestressed concrete bridges in a time - span of 35 years, an attempt has been made to account for the factors and actions influencing the material time dependent behavior such as creep, shrinkage, the variation of elastic modulus and the loss of prestressing. For this purpose, a case study has been carried out on a three span continuous prestressed box-girder bridge. A three dimensional finite-element model has been constructed for the nonlinear stage by stage analysis taking into account the balanced cantilever construction method of segmental bridges, including the effects of loading history and material time-dependent behavior. The analysis results have been discussed in terms of the variation of stresses and displacements during the time span under consideration. Finally, the effect of the time dependent material behavior on the performance of the bridge has been demonstrated and some suggestions have been made to improve the time dependent behavior of such bridge superstructures in the construction of new bridges as well as the retrofit of existing bridges.