带球冠形脱空缺陷椭圆钢管混凝土短柱轴压性能与受力机理分析

Structural Performance and Mechanical Analysis of ECFST Short Column with the Spherical-Cap Gap Under Axial Compression

椭圆钢管混凝土组合构件因具有良好的套箍约束效果、灵活的主次轴刚度分布以及优越的建筑美学效果,近年来被逐渐应用于大跨空间、重载桥梁等实际工程中。然而由于材料特性、施工工艺和服役环境等因素的影响,钢管混凝土结构可能出现脱空缺陷问题,但目前尚未见有关脱空缺陷对椭圆钢管混凝土构件受力性能影响的分析报道。基于带球冠形脱空缺陷椭圆钢管混凝土短柱轴压性能试验,建立了考虑椭圆截面特征和脱空缺陷影响的精细化有限元分析模型。研究了钢材强度、混凝土强度、脱空率、长短轴比和径厚比等诸多因素对其承载力、刚度和延性的影响规律,揭示了球冠形脱空对椭圆钢管混凝土轴压短柱破坏模式、典型荷载-位移曲线、应力-应变分布以及接触应力的影响机制,提出了考虑球冠形脱空影响的椭圆钢管混凝土短柱轴压承载力简化计算公式,并验证了其准确性。研究结果表明,球冠形脱空的出现会显著削弱钢管与混凝土之间的相互作用,进而降低椭圆钢管混凝土短柱的承载力、刚度及延性,且脱空区接触应力的消失可能导致局部钢管率先发生鼓曲凹陷以及脱空区混凝土的脆性破碎。研究结果可为实际工程中带球冠形脱空缺陷椭圆钢管混凝土结构的评估与防治提供科学依据。

In recent years,the elliptic concrete-filled steel tube(ECFST) member has been gradually applied to large-span spatial structures,heavy-haul bridges and other practical projects because of its advantages in good constraint effect, flexible axis distribution,and superior architectural aesthetics. However,concrete gap imperfections are observed in CFST structures due to some negative factors in material properties,construction technology and the service environment. In contrast,the influence of the spherical-cap gap on the mechanical properties of ECFST members has never been reported. Based on the axis compression test of ECFST short columns with the spherical-cap gap(ECFST-SG),a finite element model is established considering the effect of the elliptical cross-section characteristics and the spherical-cap gap in this paper. The influence of critical parameters,such as material strength,gap ratio,radius-thickness ratio and aspect ratio,on the axial compressive resistance,stiffness and ductility of the ECFST-SG column is analyzed. The influencing mechanism of the spherical-cap gap on the failure mode,load-displacement curve,stress and strain distribution and contact stress of the ECFST stub column is revealed. A simplified formula for predicting the axial compressive resistance of the ECFST-SG columns,considering the impact of the spherical-cap gap,is presented,and its accuracy is verified. Research results indicate that the spherical-cap gap significantly weakens the interaction between the elliptical steel tube and the core concrete,therefore,the resistance,stiffness and ductility of the ECFST columns are respectively decreased. The absence of contact stress around the spherical-cap gap may lead to the local buckling of the steel tube and the brittle collapse failure of the core concrete in this region.The research results may provide a scientific basis for evaluating and treating ECFST columns with spherical-cap gaps in practical engineering.