考虑非均匀收缩徐变的PC箱梁桥时变性能

为研究箱梁顶板、底板及腹板厚度差异引起的非均匀收缩徐变效应,分析了某三跨预应力混凝土(PC)连续箱梁桥时变性能.考虑混凝土抗压强度、弹性模量的时变性,分别建立模拟实际悬臂施工顺序的实体单元及梁单元有限元模型,比较成桥后在均匀及非均匀收缩徐变下的结构变形、混凝土应力和钢束应力.同时将长期挠度、钢束应力与相应规范值进行对比,并估算了车辆荷载及非均匀收缩徐变导致跨中底板出现拉应力和裂缝的时间.结果表明,与均匀收缩徐变相比,非均匀收缩徐变对跨中长期下挠影响较小,而对混凝土应力影响较大,在箱梁设计中应予以考虑.

Time-dependent behavior of PC box girder bridges considering non-uniform shrinkage and creep

The time-dependent behavior of a typical three-span prestressed concrete (PC) continuous box girder bridge was analyzed to investigate the effect of non-uniform shrinkage and creep due to thickness differences among webs and top and bottom flanges in box girders. Considering time-varying effects of compressive strength and elasticity modulus of concrete, finite element models which simulated cantilever-construction by solid and beam elements were developed, respectively. A comparative study on structural displacement, concrete stress and tendon stress caused by uniform and non-uniform creep and shrinkage after bridge completion was peformed. Meanwhile, long-term deflection and tendon stress were compared with relevant values which were calculated according to the standard. And the time when tensile stress and crack resulting from vehicle load and non-uniform creep and shrinkage in the bottom flange appeared was estimated. The results show that compared with uniform creep and shrinkage, non-uniform creep and shrinkage have smaller influence on the long-term deflection at midspan, and have greater effect on the concrete stress, which should be concerned in design of box girders.