Experimental Research on Mechanical Properties of Concrete-filled Double-skin Square Steel Tubular (Oblique Inside and Straight Outside) Columns Under Axial Compression
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摘要: 为研究内斜外正双重方钢管复合约束混凝土柱的轴压性能,设计8个组合柱试件和1个普通方钢管混凝土柱试件(SC1)进行轴心受压加载试验。变化参数包括内方钢管边长和壁厚、外方钢管壁厚、试件高宽比、芯柱面积比。试验观察了试件的受力破坏过程及形态,获取了荷载-位移全过程曲线,深入分析了各变化参数对试件破坏形态、轴压承载力、延性、耗能、刚度退化的影响规律。结果表明:组合柱试件在轴向压力作用下的破坏形态表现为塑性段弯曲失稳破坏和局部屈曲破坏,内钢管在核心混凝土与夹层混凝土的共同作用下产生连续不断的褶皱,而外钢管受到混凝土的挤压作用向外鼓曲,试件脱黏区域均出现了不同程度的鼓曲,较大的脱黏区域对试件最终破坏形态有明显影响。与试件SC1含钢率相近的组合柱试件,承载力提高了35%。组合柱试件荷载-位移曲线没有下降段,并表现出很好的塑性强化特性。增大内钢管边长,试件的初始刚度和峰值荷载均提高;受混凝土拌合不均的影响,增大钢管(内或外)壁厚,并没有提高试件峰值荷载,但能够有效改善试件后期的力学性能。高宽比增大到6的试件,受到二阶效应的影响,其破坏形态发生了改变,部分力学指标呈现不同程度的退化。在含钢率差别不大的情况下,增大试件芯柱面积比更能够发挥钢管与混凝土材料性能的优势。综合考虑内、外双重方钢管均对内部混凝土提供约束的计算方法,其计算值与实测值吻合良好。
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关键词:
- 内斜外正双重方钢管混凝土 /
- 柱 /
- 复合约束 /
- 轴压性能 /
- 破坏形态
Abstract: To investigate the mechanical properties of concrete-filled double-skin square steel tubular (oblique inside & straight outside) columns under axial compression, 8 composite column specimens and 1 ordinary concrete-filled square steel tubular columns specimen SC1 were prepared for the experiment. The parameters include the side length and thickness of inner square steel tube, the thickness of outer square steel tube, the slenderness ratio, and the core area proportion. In this study, the failure process and load-displacement curves were obtained. The failure modes, axial compressive bearing capacity, ductility, energy dissipation, stifness degradation and the effects of variable parameters on the mechanical properties of specimens were analyzed. The results showed that there were two failure modes:local buckling failure and bending failure in plastic plase. The inner tube showed continuous folds under the combined action of core concrete and sandwich concrete, while the outer tube heaved outward caused by the squeezing action of concrete. The steel tube bulged out in different degrees in the debonding area, and debonding area with large area and close distance had obvious influence on the final failure mode of the specimens. Compared with specimen SC1, the bearing capacity of composite column specimen with little difference in steel ratio had been increased by 35%. The load-displacement curves had no descending section and showed excellent plastic hardening characteristics. The initial stiffness and peak load of the specimen increased with the increasing of the width-thickness ratio of the inner steel tube. Affected by the uneven mixing of concrete, increasing the steel tube thickness (inside or outside) could effectively improve the mechanical properties of the specimen, but the peak load remained unchanged. Increasing the area ratio of core column could give full play to the advantages of steel tube and concrete when the steel content was not different. The calcuation method considering the effects of constratints of the superposition of double-skin square steel tube concrete on the inner was used to calculate the bearing capacity of specimens, which is in good agreement with the measured results. -
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