不封口钢管混凝土柱脚支承混凝土局部受压性能试验研究

针对端部不封口钢管混凝土的局部受压性能进行单调轴压试验研究及有限元分析。试件参数设置包括钢管的规格、支承体的混凝土尺寸、垫块的设置和配筋率等。试验及有限元分析表明：端部不封口钢管混凝土支承体顶面有压陷现象，其压陷现象与支承体的配筋率大小、不同局部受压面积比、垫块设置与否有关；对素混凝土支承体，其顶面压陷现象明显，并严重降低素混凝土的局部受压承载力；对配有间接钢筋的混凝土支承体，其顶面压陷现象不明显，对局部受压承载力影响不大，仍可按GB 50010-2010《混凝土结构设计规范》局部受压公式进行验算；当局部受压荷载满足GB 50010-2010中的要求时，不封口钢管混凝土支承体的压陷现象可以得到有效控制；局部受压截面通过局部承载力实测值与GB 50936-2014《钢管混凝土结构设计规范》公式对比可知，GB 50936-2014中建议的局部受压公式结果偏保守，柱脚环板下混凝土承载力也偏于保守。

Experimental research on local compression behavior of supporting concrete at unsealed bottom of concrete filled steel tubular column

Specimens test under monotonic uniaxial loading and FEM (finite element method) analysis have been investigated to the unsealed concrete filled steel tubular columns. The test parameters included steel pipe specification, size of concrete support, type of supporting bracket and reinforcement ratio. The results of tests and FEM analysis indicate that the depression of the top surface of bearing body of unsealed concrete filled steel tubular columns is related to the following parameters: the reinforcement ratio of bearing body, the area ratio of different local compression and the setting of supporting bracket. The top surface of concrete support under the unsealed concrete filled steel tubular column involves the phenomenon of depression which greatly decreases the local compression capability of plain concrete; top surface depression phenomenon is inconspicuous for concrete bearing body with indirect reinforcement and in such case, the local compression capacity still can be validated according to the formulas of local compression in GB 50010—2010 since the influence to local compression capacity is tiny; on the other hand, when local compression capacity satisfies GB 50010—2010, phenomenons of depression of unsealed concrete filled steel tubular columns can be effectively controlled; comparing the testing data and the formulas of local compression capacity in GB 50936—2014, the results indicate that the formulas of local compression and the bearing capacity of the annular concrete plate around column footing presented in GB 50936—2014 are conservative.