预应力混凝土箱梁桥竖向预应力损失的实测与分析

基于某大跨预应力混凝土连续箱梁桥腹板竖向预应力的现场长期测试结果,对箱梁竖向预应力的各种损失进行了分析。结果表明:就所研究的情形而言,实测竖向预应力总损失可达其初始张拉应力的45%,锚具变形、钢筋回缩及接缝压缩等引起的损失占其总损失的53%。按现行公路桥规(JTGD62-2004)中确定纵向预应力损失的方法计算竖向预应力筋相应的各种损失,所得结果与相应各项损失的实测值基本吻合。对于竖向预应力传力锚固后损失的计算,收缩徐变模型的选取对其结果影响较大。此外还探讨了温度和后续荷载等因素对竖向预应力损失的影响,结果表明:后续荷载作用对竖向预应力损失的影响较小可予以忽略,而混凝土及孔道砂浆中水泥水化热造成的损失可达总损失的18.9%,因此必须予以考虑。

Vertical prestressing loss in the box girder of long-span PC continuous bridges

Based on the long-term field measurement of vertical prestress losses in the box girder of a long-span PC continuous bridge,a detailed analysis of the loss of the vertical prestressing is conducted.It shows that the total loss is about 45 percent of the jacking stress in vertical tendons,and the losses due to anchorage deformation,retraction of tendons and joint compression constitute a large percentage of the total loss.The calculation results,based on the Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts of China(JTG D62-2004),agree well with the measured results.For the calculated prestress losses after jacking,the model of creep and shrinkage of concrete plays a significant role.Other factors that influence the vertical prestress losses,such as temperature and subsequent loadings,are discussed.It is shown that the influence of the prestress losses due to subsequent loading can be ignored,and that the losses due to the hydration heat should be considered,which constitutes about 18.9 percent of the total loss.