Numerical evaluation of novel crashworthy devices for protection of RC piers subjected to vessel impact

The protection of bridge piers crossing navigation channels from the collisions of passing vessels is a critical issue nowadays, as vessel collision upon bridge piers has become one of the major threats to the safety of waterway bridges. This paper aims to develop a novel cost-effective crashworthy device, and to assess the effectiveness of the proposed device for protection of reinforcement concrete (RC) pier columns from vessel impact. The proposed protective device is comprised of a series of steel beams arranged in a frame-type manner with I-shaped cross-sections, where beam segments with reduced cross-sections are used to limit the plastic mechanism within certain structural components. The energy-dissipation capacity of the proposed device and its effectiveness for pier protection are thoroughly assessed by numerical approaches using general-purpose finite-element (FE) programs, where a barge is employed as the impacting vessel. Detailed non-linear FE models of the barge-device-pier system are developed and validated, and a parametric study is then conducted using the validated FE models with consideration of several important design parameters including barge impact velocity and geometric dimensions of the device. The numerical results show that the proposed device can absorb a large portion of impact energy during an impact event, which significantly reduces the magnitudes of impact forces transmitted to a protected RC pier column and attenuates the damage occurred to both the pier column and the impacting barge vessel. It is also found that the plastic deformation of the device can be effectively limited within the section-reduced beam segments whilst the remaining part remains elastic during impact, which would greatly facilitate the restoration of a damaged device after an impact event.