Behavior of concrete-filled steel tubes subjected to axial impact loading

Investigations on concrete-filled steel tubular (CFST) members under static loads have been extensively reported. Still, limited researches have been conducted to investigate the behavior of CFST columns subjected to axial impact loading. This paper presents an experimental study on dynamic behaviors of twelve square and rectangular CFST stub columns subjected to axial impact loading using a drop-weight test apparatus. The instantaneous force and deformation states were recorded during the impact tests. Finite element (FE) models were established and verified using the experimental results and existing research data, in which the strain rate effects of steel and concrete were fully considered. Then the effects of cross-section shape, steel strength, concrete compressive strength, steel ratio and impact energy condition on the dynamic responses of the CFST stub columns were studied using the FE models. The experimental and analytical studies indicate that the circular CFST stub columns perform better than the square and rectangular ones. While, little difference can be found between the square and rectangular CFST stub columns. For all the three shaped CFST stub columns, the average platform impact force increases and the deformation decreases with the increase of steel strength, concrete compressive strength, steel ratio and section area. Based on the parameter studies, a simplified design method was proposed by establishing the relationship between the maximum axial displacement and the impact energy condition to predict the deformation response of CFST stub columns under axial impact.