Investigation of concrete-encased cross-shaped steel-filled BFRP-steel tube columns under lateral impact

This study aims to investigate the lateral impact resistance of the concrete-encased cross-shaped steel-filled BFRP-steel tube (CSBST) columns, which are suitable for bridge piers in humid and corrosive environments. Three CSBST specimens with different heights were subjected to drop-weight impact testing. The impact positions were set at an identical distance from one end support. One specimen was rotated by 45 degrees to evaluate the effect of impact direction. The experimental results elucidate the critical response characteristics of CSBST under lateral impact loads. Moreover, the effects of impact loadings, material properties, geometric dimensions, and boundary conditions were also explored based on finite element (FE) analysis. The numerical findings reveal that the impact force history curves of CSBST can be divided into the peak, plateau, and unloading stages corresponding to the localized response, overall deflection, and elastic recovery. The complete failure of CSBST was controlled by the tensile fracture of the steel tube, resulting in a sudden decline in the impact force during the plateau stage. Increasing the thicknesses of the BFRP-steel tube, enhancing the material properties of steel, and increasing the cross-sectional dimension can effectively improve the impact resistance of CSBST. In contrast, concrete strength and impact angle have minimal effect on impact performance. For a given impact loading, the maximum dynamic shear force and the ratio of maximum displacement to residual displacement are two key indicators for optimal design. The study emphasizes that while improving impact resistance is significant, it is equally vital to avoid over-design to prevent material waste.