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A Performance-Based Approach for Loading Definition of Heavy Vehicle Impact Events

Wednesday, April 3, 2019 - 17:30

Based on bridge failure data compiled by the New York State Department of Transportation, collision, both caused by vessels and vehicles, is the second leading cause of bridge failures after hydraulic. The current AASHTO-LRFD (2012) specification recommends designing a bridge pier vulnerable to vehicular impacts for an equivalent static force of 600 kips (2,670 kN) applied in a horizontal plane at a distance of 5.0 feet above the ground level. This report presents a performance-based approach for designing a bridge pier subject to impact by a tractor-semi-trailer weighing up to 80,000 lb based on an extensive experimental and computational investigation. The mechanics and modes of failure of bridge pier bents during vehicular impacts are investigated through two pendulum impact tests on a large scale physical model of a three-column bent system. The parameters of the computational model are calibrated to these two tests and further validated through comparisons to other published small-scale impact tests. Through extensive numerical simulation of heavy vehicle (tractor-semitrailer) impacts on piers, the impact force time histories are proposed in the form of analytical triangular pulse functions. The parameters of these functions are derived through numerical regression based on the simulation results. A performance-based approach that relates demands (in terms of the applied force time histories) and capacity (in terms of acceptable shear distortion and plastic rotation) is proposed for the design of bridge piers vulnerable to heavy vehicle impact. Since many collision failures have been observed to be dominated by shear failure, the proposed performance-based approach uses capacity design concepts from earthquake engineering to mitigate collapse by minimizing shear distortion of piers impacted by heavy vehicles.  The report is available online from FHWA at https://www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/18062/18062.pdf