Causes of Mechanical Damage to Alabama Bridge Decks

Excessive damage to Alabama bridge decks that required premature bridge replacements prompted the Alabama Department of Transportation to sponsor an extensive study of the causes of severe deck damage. The mechanical causes of damage, such as the use of slender decks and heavy truck loadings, the magnitudes of service load stresses, and how progressive damage occurs were addressed. Such causes are particularly important for decks constructed in the southern United States, where damage caused by deicing salts and freeze-thaw is not as prevalent as it is in northern U.S. states. To assess the significance of these factors, five damaged decks and five reasonably undamaged decks, as controls, were investigated. Studies conducted on these bridge decks included condition surveys, weigh-in-motion surveys, finite-element analyses, and load tests. The observed damage predominantly consisted of severe transverse cracking at the top surface of the decks. Although restraint of deck shrinkage strains by girders occurred at some of the damaged decks, thus initiating cracking, damage appears to be progressive, and major factors determined from the study to contribute to damage include slender decks, lack of longitudinal reinforcement, aggregate selection, and high axle group loadings.