Superload Evaluation of the Bonnet Carré Spillway Bridge

Abstract

The passage of overloads that require special permitting is a common occurrence. Prior to the passage of such an overload, a simplified computer analysis is generally conducted to predict the expected behavior of the bridge. This paper addresses the field evaluation of three superloads that crossed the Bonnet Carré Spillway Bridge in Louisiana. Emphasis is placed on comparisons between the expected and actual behavior due to rotational restraint, live load distribution, the stiffening effect of bridge rails, and other factors. Finite-element modeling was conducted and the approach taken along with the results obtained are described. One important conclusion was that the longitudinal configuration of the axle loads supplied by the hauler was configured differently than indicated on the permit. While the gross load was accurate, the distribution between sets of axles varied considerably from those assumed in the permitting process. To minimize the potential for damage to bridges it is therefore recommended that axle loads be weighed prior to the passage of such overloads.