對大跨徑的橋梁而言，預應力系統為重要的受力部分，橋體的變位量往往與預應力的損失有關。而預應力的損失原因除了乾縮潛變、錨定端滑移等，裂縫的擴展也可能造成預應力的損失。裂縫的生成擴展方向及速度，源自許多因素。本研究透過相關數值模擬，以及預應力混凝土梁振型模態。利用監測數據之變位曲線，再與數值模擬進行比對，透過反算分析估算出劣化箱型梁之剩餘預力。用利用估算出之現有預力值及呆載重使用裂縫擴展模擬判斷現場結構裂縫劣化主要原因。;For the long-span bridge, the prestressed system is an important part of the force, and the displacement of the bridge body is often related to the loss of prestress. In addition to shrinkage and creep, the cause of the loss of prestressing, the direction and speed of the formation and expansion of the slip crack at the anchor end are derived from many factors. In this study, the relevant numerical simulation and the vibration mode of the prestressed concrete beam are adopted. Then compare with the numerical simulation, through the inverse calculation analysis to decompose the prestressed of the extension box-girder. The crack propagation simulation is used to judge the cracks of the on-site structure by using the existing prestressed value and the dead load.
