Numerical investigation on the dynamic behavior of UHPFRC strengthened rocking concrete bridge piers subjected to vehicle collision

The nonlinear dynamic responses of UHPFRC-strengthened monolithic and rocking concrete bridge piers with different configurations including the rocking monolithic pier (RMono), rocking segmental piers with four (RSeg4), and eight (RSeg8) are numerically investigated in this study. Different rocking piers subjected to vehicle collisions with variations of the UHPFRC cover thickness (tU), length (LU), and its strengthening scheme are investigated using finite element (FE) simulations in LS-DYNA. From the evaluation of the piers constructed with normal concrete (NC) under different Vimp, it was found that the segmental piers experience higher recoverability and lower peak impact and internal forces compared to the Mono and RMono piers, however, they suffered more severe concrete spalling at the corners and edges of the segments due to the segment’s slippage. Also, the RMono pier demonstrates better impact resistance with a displacement recoverability of 55% against a high-velocity vehicle impact with Vimp = 140 km/h and withstands collapse compared to the total collapse of the Mono and segmental piers. In addition, it is found that the increase of tU from 80 mm to 160 mm had a more positive effect on the impact resistance and damage mitigation of the Mono and the RMono piers than its effect on the performances of segmental piers. As a result, the residual displacement of the RMono pier decreased by 60% while enhancing its residual shear force by 33%, and the residual bending moment by 64%. Also, the residual displacements of the RSeg4 and RSeg8 piers decreased by 75% and 80%. The Mono pier with Scheme-2 and a UHFRC cover of 80 mm resulted in lower impact force by 42%, lateral displacement by 43%, peak shear force by 22.5%, and bending moment by 31% than those of Scheme-1. Besides, the use of UHPFRC cover for the column-footing and column cap-beam connections in addition to the whole height of the RMono pier (Scheme-3) significantly reduces the concrete spalling damage level at the column base. Moreover, it is found that the use of UHPFRC for all the edges of the column segments in addition to the bottom zone of the RSeg4 and RSeg8 piers (Scheme-4) considerably mitigates the spalling damages and enhances the recoverability of the segmental piers by 67% and 63%, respectively compared to performances of these piers when using Scheme-1 and Scheme-2.