預力混凝土為現今橋梁結構之主體，而預力損失的估算為預力橋梁設計的重要指標之一。本研究旨在探討後拉法預鑄節塊箱型梁在施工中之混凝土應變及相關預力損失，同時利用ACI 209、CEB-FIP MC78與CEB-FIP MC90預測混凝土應變。本研究對高雄港聯外高架橋新生路北段第四單元(U4)進行混凝土應變監測，且針對B14跨橋梁進行預力損失估算，並與設計單位所提供之有效預力進行比較。
在施工中對預鑄節塊進行應變監測，可發現節塊於預鑄場澆鑄生產後，節塊中較厚的腹版區域受水化熱影響產生100x10-6的拉伸應變，而其餘較薄區域受混凝土乾縮現象影響產生100~160x10-6的壓縮應變。在施拉預力過程中可量測到170~270x10-6的瞬時彈性應變，並加以推估各跨節塊的混凝土彈性模數。在預力施拉完成後，節塊在三個月內產生160~290x10-6的壓應變，其潛變發展趨勢與圓柱試體潛變架所測得之潛變有一比例關係。
在預力損失評估中，B14跨橋梁三個月內的內置預力損失為580~1000kg/cm2，佔初始預力的3.6%~6.5%；外置預力損失為792kg/cm2，佔初始預力的5.5%，兩者均在設計容許值以內。

Prestressed concrete is the primary construction material of bridges nowadays, and prediction of presress losses is one of the critical factors considered in design of bridges. This thesis aims at studying the behavior of post-tensioning precast segmental bridge box-girder and prestress losses during the construction. Meanwhile, the ACI 209、CEB-FIP MC78 and MC90 codes are used to predict the strain of concrete. In experimental study, the prestress losses in unit four (U4) of Kaohsiung Port Viaduct was monitored and compared with design effective prestress.
After concrete segments fabrication, the thicker regions of concrete segments effected by heat of hydration and generated 100x10-6 tension strain, while the rest of thinner regions affected by shrinkage and generated 100~160x10-6 compressive strain. In the process of prestress tensioning, the elastic strain 170~270x10-6 was measured and the modulus of elasticity of box-girder was then estimated. After finishing the prestress, the concrete strains of the box segments were significantly affected by creep effect and generated 160~290x10-6 compressive strain within three months.
In the assessment of prestress losses, the box-girder in B14 span generated 580~1000 kg/cm2 internal prestress losses, accounting for 3.6%~6.5% of the initial prestress and 792 kg/cm2 external prestress losses, accounting for 5.5% of the initial prestress within three months.

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