Experimental investigation and improved FE modeling of axially-loaded circular RC columns under lateral impact loading

Abstract

Circular reinforced concrete (RC) columns have been widely used in the bridge structures (e.g., piers) due to their economic and functional advantages. However, RC columns are usually subjected to a lateral impact load under extreme loading conditions, especially under the collision event of an aberrant vehicle or vessel. Although a number of low-velocity impact tests on RC beams have been conducted, few experiments have been performed to clarify the dynamic behaviors of axially-loaded RC columns subjected to lateral impact loading. To this end, low-velocity impact tests on the axially-loaded circular RC columns are designed and conducted in this paper. Ten circular RC column specimens are fabricated with two different reinforcement ratios. Two out of these specimens are tested under static axial loading to determine their compressive resistances and the axial load levels applied in the impact tests. The other eight specimens with different axial load levels are tested under impact loading through the drop hammer test system at Hunan University. It is found that the applied axial loads have a great effect on the impact responses (e.g., impact forces, maximum and residual deformations) of the circular RC columns. Generally, the axial loads play a positive effect when the deformations of the column specimens are relatively small. On the contrary, the presence of an axial load exhibits catastrophic effects (e.g., complete collapse) in the case of the column with a low reinforcement ratio subjected to a high-energy impact. To further interpret the experimental data, the corresponding finite element (FE) models are developed for the impact simulation of axially-loaded RC columns. The conventional modeling used for RC beams is shown to have some disadvantages in the prediction of the impact-induced responses (e.g., resilient deformations) of the axially-loaded columns. For this reason, an improved FE modeling technique is proposed to simulate the axially-loaded RC columns subjected to impact loading. In the improved FE model, the concrete material model is modified to accurately consider the confinement effect of the spiral stirrup. The influences of both the bond-slip and crack closure behaviors on the impact-induced responses are also identified and considered in the improved FE models. The numerical results obtained from the improved models are in good agreement with the experimental data, indicating the applicability of the proposed FE modeling. These findings drawn from the experimental and numerical investigations can facilitate more reliable evaluation of a bridge structure with RC columns subjected to vehicle or vessel impacts.