To investigate the vertical prestress loss in concrete box girder webs with twice-tension, a rectangular thin plate test under twice-tension prestressed strand was conducted. At the same time, twice-tension vertical prestress loss used in a practical bridge was also tested, and was compared with the traditional vertical prestressed system using finishing rolling rebar. The test results have confirmed that the immediate vertical prestress loss can be reduced to less than 10% with the twice-tension technology, far less than that of finishing rolling rebar system. Twice-tension system can improve the efficiency of vertical prestress and shear reliability in box girder webs. At last, based on the test results, some factors that affect vertical prestress loss, including pipe roughness, compression of joint, deformation and retraction of anchorage, elastic compression of concrete, relaxation of tendons and creep and shrinkage of concrete, were discussed, and the corresponding methods of design taking value are proposed.%为了研究二次张拉钢绞线竖向预应力损失,进行了二次张拉钢绞线的矩形板试验,同时测试了采用二次张拉技术的实桥箱梁腹板竖向预应力的应力损失,并与传统的精轧螺纹钢竖向预应力体系进行比较.测试结果表明,采用二次张拉钢绞线技术后,箱梁腹板的即时竖向预应力损失基本上可以降低至10％以内,远小于精轧螺纹钢体系的竖向预应力损失率,可有效地提高箱梁腹板竖向预应力效率和抗剪可靠性.最后结合试验结果,探讨了管道摩阻、接缝压缩、锚具变形及回缩、弹性压缩、钢绞线松弛和混凝土收缩徐变等二次张拉竖向预应力各项损失的影响因素,并对各项二次张拉竖向预应力损失的设计取值方法提出了建议.
展开▼
