Abstract The performance of concrete-encased concrete-filled steel tube (concrete-encased CFST) subjected to low-velocity impact is investigated through experimental and numerical studies in this paper. A total of 40 concrete-encased CFST specimens, 20 square and 20 circular ones, are tested under a drop hammer apparatus. It shows that while the outer RC components have a shear-dominated failure mode, the core CFST deforms in a flexural pattern. The influence of tested parameters on the impact force and midspan deflection of the specimens is summarized. A finite element analysis (FEA) model is then established to investigate the shear mechanism of concrete-encased CFST under impact. A comparative study between a concrete-encased CFST member and an RC member shows that the core CFST component could effectively mitigate the shear failure of the outer RC section under impact due to its high shear resistance; meanwhile, the outer RC component could well protect the core CFST and reduce its flexural deformation. Such composite effects make the concrete-encased CFST members a desirable impact-resisting structure. Subsequently, a parametric study on the impact velocity shows that the debonding between outer RC and core concrete can be more prominent for the impact with a relatively higher velocity, and the use of shear studs is suggested for members under such circumstances.

中文翻译：

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混凝土包裹的 CFST 在低速冲击下的性能：抗剪分析

摘要 本文通过实验和数值研究研究了混凝土包裹钢管混凝土（concrete-encased CFST）在低速冲击下的性能。在落锤装置下测试了总共 40 个混凝土包裹的 CFST 试样，20 个方形和 20 个圆形。它表明，虽然外部 RC 组件具有剪切主导的失效模式，但核心 CFST 以弯曲模式变形。总结了试验参数对试件冲击力和跨中挠度的影响。然后建立有限元分析 (FEA) 模型来研究混凝土包裹的 CFST 在冲击下的剪切机制。混凝土包裹的CFST构件与RC构件的对比研究表明，核心CFST构件由于其抗剪强度高，可以有效减轻外RC截面在冲击下的剪切破坏；同时，外层的RC组件可以很好地保护核心CFST并减少其弯曲变形。这种复合效应使混凝土包裹的 CFST 构件成为理想的抗冲击结构。随后，对冲击速度的参数研究表明，在相对较高速度的冲击下，外层钢筋混凝土与核心混凝土之间的脱粘更为突出，建议在这种情况下对构件使用抗剪螺栓。外层RC组件可以很好地保护核心CFST并减少其弯曲变形。这种复合效应使混凝土包裹的 CFST 构件成为理想的抗冲击结构。随后，对冲击速度的参数研究表明，在相对较高速度的冲击下，外层钢筋混凝土与核心混凝土之间的脱粘更为突出，建议在这种情况下对构件使用抗剪螺栓。外层RC组件可以很好地保护核心CFST并减少其弯曲变形。这种复合效应使混凝土包裹的 CFST 构件成为理想的抗冲击结构。随后，对冲击速度的参数研究表明，在相对较高速度的冲击下，外层钢筋混凝土与核心混凝土之间的脱粘更为突出，建议在这种情况下对构件使用抗剪螺栓。