河口大桥施工过程剪力滞效应研究

Study of Shear Lag Effects of Hekou Bridge in Construction Process

兰州河口大桥为主跨360m的双塔双索面组合梁斜拉桥,主梁采用П形工字钢-混凝土组合梁,采用悬臂拼装法施工。为研究后续施工(施工步骤增加)对当前截面以及当前截面施工工况变化对已完成梁段剪力滞效应影响的规律,基于能量变分法及矩阵分析法,建立П形钢-混凝土组合梁斜拉桥截面任意位置剪力滞效应分析的有限梁段公式及剪力滞系数计算公式,并通过施工现场实桥试验对该桥施工过程中的剪力滞效应进行分析。结果表明:随着施工步骤的增加,截面应力分布更加均匀,剪力滞系数趋于平稳;施工步骤变化对腹板和翼板交界处剪力滞系数的影响较翼板中点处剪力滞系数大,腹板和翼板交界附近的剪力滞现象更加严重;施工工况变化对剪力滞的影响明显,同一截面不同工况剪力滞系数明显不同,甚至剪力滞特征(正、负剪力滞效应)也可能不同。

The Hekou Bridge in Lanzhou is a composite girder cable-stayed bridge with double pylons, double cable planes and with a main span of 360 m. The main girder of the bridge is the I I- shaped I-steel and concrete composite girder and is constructed by the cantilever assembling meth-od. To study the laws of the influences of the follow-up construction （the increased construction sequences） on the present section of the composite girder and the influences of the construction load case changing of the present section on the shear lag effects of the completed segments of the girder, the finite segment formula and the shear lag coefficient calculation formula for the shear lag effect analysis of the arbitrary positions of the section were established based on the energy varia-tion method and matrix analysis method. The bridge was tested at the site as well and according to the tests, the shear lag effects of the bridge in the construction process were analyzed. The results show that with the increase of the construction sequences, the stress distribution in the section of the composite girder of the bridge becomes more uniform and the shear lag coefficients tend to be stable. The influences of the changing of the construction sequences on the shear lag coefficients ofthe junctions of the webs and flange plates are greater than those on the shear lag coefficients of the middle points of the flange plates and the shear lag problems nearby the junctions of the webs and flange plates are more severe. The influences of the changing of the construction load cases on the shear lag are significant. In the same section, the shear lag coefficients of the different con-struction load cases are significantly different and even the shear lag characteristics （the positive and negative shear lag effects） might be different.