扁平钢箱梁U肋加劲板的加载偏心

Study on Force Eccentricity of U-Rib Stiffened Plate of Flat Steel Box Girder

以一座主跨1 088 m扁平钢箱梁斜拉桥为例,分析了扁平钢箱梁U肋加劲板加载偏心的大小及对U肋加劲板稳定承载力的影响。首先采用包括梁单元和板壳单元的混合建模方法建立全桥有限元模型,在计算加载偏心的梁段采用壳单元,其他部位采用梁单元。根据有限元方法求得U肋加劲板截面的应力分布,利用积分方法计算U肋加劲板的内力和加载偏心,并将加载偏心对承载力的影响等效为初始几何弯曲。研究结果表明,U肋加劲板的加载偏心率约为0.17,最大为0.35,相当于L/250的初始弯曲,该值远大于规范规定的最大几何偏心,因此计算扁平钢箱梁U肋加劲板稳定承载力时需考虑加载偏心的影响。

Initial force eccentricity of stiffened plates with U-ribs of flat steel box girders for cable-stayed bridges and its effects on the ultimate strength of the stiffened plates were analyzed with the example of a cable-stayed bridge of 1 088 m main-span.The bridge structure was modelled using beam elements and shell elements in the analysis.The segments with initial force eccentricity were modelled using shell elements and the others parts were modelled using beam elements.The stress distribution on U-rib stiffened plate was obtained by FEM method and then the inner force and initial load eccentricity of the stiffened plates were calculated by the intergration of the sectional stress on the plates.The effects of the initial force eccentricity on the ultimate strength of the stiffened plates were considered as equivalent geometrical imperfection.The results showed that the initial eccentricity of the stiffened plates was about 0.17 and the maximum value was 0.38 and it equals to a geometrical imperfection of L/250.The equivalent geometrical imperfection value is much greater than those suggested by some design codes for steel bridges.Therefore,the force eccentricity must be taken into account in the ultimate strength estimation of the stiffened plates of flat steel box girders.