Vulnerability assessment and performance improvement strategies for bridges subjected to vehicular collision

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Oppong, Kofi
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Shafei, Behrouz
Phares, Brent
Alipour, Alice
Sturgill, Roy
Hsu, Ming-Chen
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Civil, Construction, and Environmental Engineering
The collision of vehicles into bridges is a recurring event on roads and highways. AASHTO’s provision for vehicular collision involves designing the pier or abutment for an equivalent static force (ESF) of 2,670 kN (600 kip), or redirecting or absorbing the collision load using an embankment or a safety barrier. The ESF specified for design by AASHTO was determined from full-scale crash tests of vehicle collisions between rigid columns and 36.3 metric ton (80.0 kip) tractor-semitrailers traveling at 80.5 km/h (50 mph). There is the need for other impact velocities to be investigated other than 80.5 km/h (50 mph) because the average speed limit on highways in the US is 113 km/h (70 mph). Furthermore, the 129 km/h (80 mph) speed limit is common on interstate highways. Similar to the AASHTO LRFD bridge design manual, the Eurocode provides guidelines for vehicular collision into bridges. The pertinent information provided by the Eurocode involves the design of superstructures for over-height vehicle collision. The ESF design value specified by the Eurocode is 500 kN (112 kip), and this value was obtained by utilizing the formula for hard impact. This design value does not consider the characteristics of the impacting objects, nor the bridge superstructures subject to over-height collision. The design force only accounts for a truck’s direct over-height impact and does not include the impacts originating from the cargo encroaching the vertical clearance of the overpass. Furthermore, to ensure that the bridge girders impacted by over-height vehicles are not compromised, it is essential to have an accurate assessment of the impact-induced loading demand. It is also crucial to be able to predict the degree of bridge damage due to vehicle collisions. Therefore, head-on and over-height vehicle collisions into bridge substructures and superstructures are investigated in this study. The use of full-scale physical tests for this study was not possible due to lack of resources and therefore finite element modeling (FEM) is utilized throughout. The FEMs are all validated with experimental data from the literature before simulations are conducted. The results from the FEM simulations led to the estimation of collision loads on concrete bridge piers and girders from head-on and over-height vehicle collisions. The behavior and vulnerability of bridges during vehicular collisions are recorded in various figures and tables, and discussed. The use of ultra-high-performance concrete (UHPC) in mitigating damage caused from over-height collision into concrete girders is investigated. The discussion concluded that UHPC was an excellent material to use in the fabrication of girders for new bridge constructions, and was an excellent material to use for bridge girder retrofitting. Finally, three different foam materials in the form of energy absorbing composite panels were attached to concrete bridge girders to evaluate their performance in mitigating damage to bridge superstructures from over-height collisions. Various foam panel dimensions and densities were tested and the results revealed that each of the three foam materials performed well under conducive conditions, with two of the foam panels exhibiting excellent energy absorption capabilities that would be useful for over-height vehicle collision damage mitigation of concrete bridge girders.
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