Numerical investigation of hybrid UHPC columns subject to lateral impact

This paper presents extensive numerical and parametric studies on the dynamic performance of axially-loaded hybrid ultra-high-performance concrete (UHPC) columns subject to low-velocity impact loading. While existing studies have been performed on columns comprised fully of UHPC, the case of hybrid UHPC columns has not been fully explored. Hybrid columns involve the localised use of UHPC in combination with normal strength concrete (NSC) and can result in both performance and economic efficiencies. The present study uses Abaqus to develop a validated finite element (FE) model which allows exploration of key parameters such as impact location and energy, slenderness ratio and the length of the UHPC zone and their effect on hybrid column behaviour. It was found that localised adoption of UHPC at the predicted impact location significantly enhanced the performance and resulted in a change from brittle shear failure to flexural failure with minimal damage. The length of the UHPC segment was also found to have greater effect on columns with low reinforcement ratio. Meanwhile, the impact location was shown to have significant influence on the column response especially under a low pre-loading level. Hybrid columns experienced less displacement and higher plateau impact load under low impact energy. In comparison to the normal strength concrete column, the hybrid columns exhibited reduced mid-span displacement and increased impact load capacity which confirmed the ability of the UHPC segment to reduce the local damage resulting from the impact. In addition, in many cases, it was found that the application of higher pre-loading levels can provide an improvement in total impact performance of the hybrid columns. This is mainly attributed to the shifting of the pre-loading axis as a result of cracking at the top of the column ends. Finally, the presence of a UHPC segment with various lengths can change the location of the main (central) plastic hinge to the end of the UHPC segment, this reflects the ability of UHPC in improving the entire response of hybrid columns.