钢管约束活性粉末混凝土短柱承载力计算研究

Study on bearing capacity calculation of reactive powder concrete confined by steel tube short columns

活性粉末混凝土(RPC)具有超高强度但脆性较大,钢管约束可显著提高RPC的延性。采用全截面加载、仅对核心混凝土加载两种方式,对20根外径133mm的圆钢管约束RPC短柱开展轴心受压性能试验。分析了试件的破坏过程和特征、荷载-位移曲线和轴压承载力;探讨了加载方式、钢管径厚比和RPC强度对轴压性能的影响规律。结果表明:套箍系数大于0.9时,试件发生鼓曲破坏,其余则为剪切破坏;钢管厚度为4.5mm、6mm时,荷载-位移曲线会出现明显的下降段,钢管厚度为8mm、10mm时,曲线则平稳或者继续上升;试件整体轴压承载力大于钢、混凝土两种材料承载力的简单叠加,两种加载方式下的提高幅度分别为12%、24%。在试验基础上分析了钢管约束RPC短柱的工作机制和受力模型,结合双剪统一强度理论建立了短柱在两种加载方式下的轴压承载力计算方法,公式计算与试验结果的误差小于10%,适用性较好。

Reactive powder concrete(RPC) is a type of ultra-high concrete that has a relatively high brittleness. The ductility of RPC could be improved by confinement, and the use of RPC in composite RPC filled steel tube has become an important subject of research in recent years. By using the fully and partially loaded methods, twenty tests on the RPC confined by circular steel tube short columns with diameters of 133 mm under axial compression are conducted. Failure patterns, axial load-deformation curves and bearing capacity of specimens are studied, meanwhile, effects of loading methods, diameter-to-thickness ratios of steel tube and compressive strengths of RPC on the axial behavior are analyzed. Test results show that specimens display drum-shaped failure with confinement coefficients larger than 0.90, and other specimens with small coefficients display shear failure. There is a sudden drop after the peak load on the load-displacement curves for specimens with steel tube thickness of 4.5 mm and 6 mm, and a gradual increase after the peak load with the thickness of 8 mm and 10 mm. The ultimate capacity of composite specimens is higher than that of the sum of the load capacities of its individual constituents, and the confinement increases the load capacity by 12% and 24% for fully and partially loaded specimens respectively. The force mechanism and model of RPC filled steel tube columns are proposed based on the experimental results, and methods for calculating bearing capacity of composite columns are established by using the twin-shear unifiedstrength theory. The relative errors between calculated results and those of the model test are less than 10%, which indicates the proposed formulas are more applicable.