Impact of Overweight Vehicles (with Heavy Axle Loads) on Bridge Deck Deterioration

Bridge deck slabs develop compressive stresses from global flexural deformation and locally from high-level wheel loads when it is subjected to overweight trucks. This study quantified the impact of overweight vehicles with heavy axle loads on bridge decks using laboratory tests and numerical simulations. The laboratory tests focused on evaluating the impact of combined mechanical stresses and freeze-thaw cycles on the durability of air-entrained concrete. Concrete cylinders, after being cured in saturated limewater for 28 days, were subjected to various levels of compressive loads and then exposed to 300 freeze-thaw (F/T) cycles. Rapid chloride ion penetrability tests were conducted to evaluate the chloride permeability of the concrete samples. The laboratory test results indicated that the mechanical loading combined with freeze-thaw cycles significantly increased the permeability of air-entrained concrete and may accelerate the deterioration of concrete elements such as bridge decks. The observed permeability increase was due to the fact that higher compressive loads caused more extensive microcracks in concrete, and the damaged concrete further degrades under freeze-thaw cycles, which may have further opened and interconnected the microcracks. Bridge deck analyses were conducted to investigate stress distributions and stress levels in typical concrete bridge decks subjected to high axle loads. The numerical analyses using the idealized bridge models indicated that the normal stress in bridge decks in the transverse direction can be significantly affected by the thickness of bridge deck, the girder spacing, and the magnitude of the wheel loads. The analyses results also indicated that the normal stresses in the longitudinal direction may be calculated as the summation of the stresses due to global bending of the bridge superstructure under the truck loads, which can be estimated using typical design/rating procedures and the stress elevations near the wheel loads. The proposed equations may be used, in addition to the typical design/rating calculations, to capture the adverse stresses in bridge decks subjected to overweight trucks.