Effects of axial load on nonlinear response of RC columns subjected to lateral impact load: Ship-pier collision

In this paper, the effects of axial load on dynamic responses and failure behaviors of reinforced concrete (RC) columns subjected to lateral impact loading are evaluated using numerical simulations in LS–DYNA. First, a series of numerical mass dropping impact tests are carried out on an axially loaded singular RC column to investigate the sensitivity of column impact response, internal force distribution, and plastic hinge location to the variability of the axial load. Also, a comparative study is done on the failure modes and impact responses of the column with different axial load ratios subjected to lateral impact loading at different elevations from the column base. It is found that the decrease of impact elevation causes the increase of initial peak impact force and changing the failure mode of the column from a global-flexure mode to the shear-flexural or global shear failure modes. In addition, a parametric study is carried out to quantify the relationships between the impact responses (including peak impact force, peak flexural moment, and plastic hinge location) and axial load ratio by varying of impact velocity for the column mid-span impacting scenarios. From the results, it is obtained that the increase of axial load ratio causes the increase of initial peak impact force and the internal forces of the column. Besides, it is found that the distance of plastic hinge locations from the column impact point (in particular, mid-span for parametric study) decreases in proportion to the increase of axial load ratio which causes the column failure localized at the impact zone. Moreover, to prove the axial load effects on the responses of an impacted structure in a realistic application, the finite element simulations of ship collision with a cable-stayed bridge pier in the cases with and without superstructure are developed in LS–DYNA. It is proved that the pier impact responses including impact force and internal forces have the greater values for the pier in the presence of the superstructure than those of isolated model. Also, The pier with superstructure tends to redistribute the impact load downward the pier substructure which leads to the increase of collision intensity, the severity of local damages, and shear failures.