三向预应力混凝土斜拉桥箱梁裂缝研究

为分析混凝土水化热和三向预应力钢筋张拉顺序对斜拉桥预应力箱梁施工裂缝的影响,建立了嘉陵江大桥空间有限元实体模型,通过模拟现场实测温度场和选取3种不同的预应力钢筋张拉工序,分析水化热和预应力钢筋张拉顺序对箱梁顶板、底板和腹板受力特性的影响,并对比分析结果和实际裂缝情况。结果表明:水化热是嘉陵江大桥箱梁底板和腹板产生施工裂缝的一个重要原因;但是单纯的水化热不能使腹板产生裂缝。横向和竖向预应力钢筋滞后纵向1～2个节段张拉的施工工艺使得底板施工前期拉应力增长较快;且使得腹板在施工过程中拉应力变大。因而,预应力钢筋张拉顺序成为嘉陵江大桥箱梁底板和腹板产生施工裂缝的另一个重要原因,但是预应力钢筋张拉顺序对箱梁最终状态应力影响很小。

Analysis on Construction Cracks in Box Girder ofthe Three-dimensional Prestressed Concrete Cable-stayed Bridge

In order to analyze the influence of hydration heat reaction of concrete and tension sequence of three-dimensional prestressed tendons on construction cracks of prestressed box girder of cable-stayed bridge, a spatial finite element solid model of Jialing River Bridge is established in this paper. Based on simulating the measured temperature field and choosing three different tension procedures of prestressed tendons, the influence of hydration heat reaction and tension sequence of prestressed tendons on the mechanical characteristics of the top, base and web plates of box girder is analyzed, which are associated to the actual cracks of Jialing River Bridge. The results showed that: the hydration heat reaction is an important reason for the construction cracks on the base plate and web plate of the Jialing River Bridge. However, Single hydration heat reaction can not cause cracks in the web plate. The construction technology of transverse and vertical prestressed tendons tensioned later than longitudinal prestressed tendons for 1-2 segments makes the tensile stress of base plate increase rapidly in the early stage of construction, and makes the tensile stress of web plate become larger in the construction. Therefore, the tension sequence of prestressed tendons is another important reason for the construction cracks on the base and web plates of the box girder of Jialing River Bridge. However, the tension sequence of prestressed tendons has little effect on the tensile stress of ultimate construction state of prestressed concrete box girder.