带球冠形脱空缺陷的钢管混凝土构件拉弯试验和承载力计算方法研究

Mechanical behavior and design approach of concrete filled steel tubes with circular-segment gap under combined actions of tension and bending

为研究球冠性脱空缺陷对钢管混凝土拉弯性能的影响机理,完成了24根钢管混凝土试件在拉弯作用下的试验研究,包括16根带球冠形脱空缺陷试件和8根无脱空对比试件,考察了脱空率和偏心率对带球冠形脱空缺陷试件的承载力、拉力-位移关系曲线、弯矩-曲率关系曲线、应变发展的影响规律。试验结果表明:随着脱空率的增大,带脱空缺陷试件的承载力有所降低;随着偏心率的增大,脱空缺陷对钢管混凝土承载力的不利影响趋于显著。建立了带脱空缺陷的钢管混凝土拉弯构件的有限元分析模型,其计算结果和试验结果吻合良好。采用有限元模型对带脱空缺陷构件的工作全过程进行了分析,揭示了脱空缺陷对钢管与混凝土之间相互作用的影响机理,并对脱空率、混凝土强度、钢材强度和含钢率等重要影响因素开展了参数分析,分析结果表明:随着脱空率的增大、钢管混凝土拉弯承载力总体呈线性下降的趋势,降低混凝土强度、提高钢材强度和含钢率对承载力下降幅度的影响并不显著。最后,基于参数分析结果提出了考虑球冠形脱空缺陷影响的钢管混凝土拉弯承载力简化计算公式。

To study the influential mechanism of circular-segment gap on concrete filled steel tubes(CFSTs) under combined actions of tension and bending, a total of 24 CFSTs members, including 16 CFSTs members with circular-segment gap and eight counterparts without gap, were tested under eccentric tension. The effects of gap ratio and eccentric ratio on ultimate strength, tensile force versus tensile displacement, bending moment versus curvature and strain development of CFSTs with gap were experimentally investigated. It shows that the ultimate strength tends to decrease with the increase of gap ratio, and the unfavorable influence of gap tends to be more significant with the increase of eccentric ratio. Meanwhile, a finite element analysis(FEA) model was established to model the CFSTs with gap under combined actions of tension and bending, and the numerical results agree well with the test ones. By the FE model, the behavior of CFSTs with gap during the whole loading process was analyzed, and the influential mechanism of gap on the interaction between steel tube and concrete was revealed. A series of parametric studies were also conducted to investigate the effects of gap ratio, concrete strength, steel strength and steel ratio on the ultimate strength of CFSTs with circular-segment gap. It is found that the ultimate capacity of CFSTs under combined actions of tension and bending tends to decrease with the increase of gap ratio, and the effects of concrete strength, steel strength and steel ratio on the reduction of ultimate capacity is less significant. Finally, a simplified formula to predict the ultimate strength of CFSTs under combined actions of tension and bending with considering the effect of gap was proposed.