超大长宽比加劲型钢箱混凝土柱轴压性能分析

Analysis of Axial Compressive Performance of Stiffened Concrete-Filled Steel Box Column with Large Aspect Ratio

为研究加劲肋构造形式和截面长宽比对超大长宽比矩形钢箱混凝土柱轴压性能的影响,通过钢箱混凝土柱屈曲分析,预测其轴心受压时的屈曲模式,提出最小加劲刚度比简化公式,以优化开孔板加劲肋设计。在此基础上,以某高速公路匝道桥薄壁墩为例,设计3组(无肋、设置刚性加劲肋、设置柔性加劲肋,每组5个)矩形钢箱混凝土柱试件,采用Abaqus软件建立各试件有限元模型,分析各试件的破坏模式、混凝土轴向应力分布和轴压承载力。结果表明:无肋和设置柔性加劲肋时试件轴压破坏屈曲模式相同,设置刚性加劲肋可改变试件轴压破坏屈曲模式;与无肋矩形钢箱混凝土柱相比,若矩形钢箱混凝土柱沿壁长方向均匀设置加劲肋,达到极限荷载时截面大部分区域混凝土轴向应力分布均匀,有效限制钢板向外屈曲,提高了钢箱与混凝土的组合作用;钢箱混凝土柱承载力提高系数随截面长宽比的增大呈逐渐减小趋势,刚性加劲肋试件的承载力>柔性加劲肋试件的承载力>无肋试件的承载力,加劲肋与混凝土的黏结可使试件具有更高的极限承载能力;提出的最小加劲刚度比简化公式对加劲肋设计具有较好的指导作用。

The pattern of stiffeners and cross-sectional aspect ratio influence the axial compressive performance of rectangular concrete-filled steel box(CFSB)column.In this paper,buckling analysis is carried out to predict the failure modes of the rectangular CFSB column subject to axial compression,a simplified equation to calculate the minimum stiffening stiffness ratio is proposed to optimize the design of the perfobond leister(PBL)stiffeners.The thin-walled piers of a highway ramp bridge are used for case study.Three groups of rectangular CFSB column specimens were prepared,including five specimens without stiffeners,five specimens with rigid stiffeners,and five specimens with flexible stiffeners.The finite element models of these specimens were developed in Abaqus to analyze their failure modes,axial compression distribution in concrete and load bearing behaviors.It is shown that the columns without stiffeners and the columns with flexible stiffeners exhibit similar failure modes,implying that adding rigid stiffeners can change the failure modes of the columns under axial compression.Compared with the rectangular CFSB column without stiffeners,if the stiffeners are uniformly arranged along the length of walls of the rectangular CFSB column,the concrete axial compression in the most of the cross section is uniformly distributed under ultimate loads,which effectively restrict the outward buckling of steel plates and improve the composite action of the steel box and in-fill concrete.The improving coefficient of the load bearing capacity of the rectangular CFSB column is in inverse relation with the cross-sectional aspect ratio,and the load bearing capacities descend from the columns with rigid stiffeners,through columns with flexible stiffeners to columns without stiffeners.The bonding between stiffeners and concrete improves the ultimate load bearing capacity of the specimens.The proposed simplified equation to calculate the minimum stiffening stiffness sheds light on the design of the stiffeners in the rectangular CFSB column.