Evaluation of the True Behavior of the End Supports in the Carbajal de la Legua Old Bridge

Bridges are prone to bearing deterioration due to aging, environmental causes and/or traffic overloading, and, as a result, a bridge originally designed as simply supported may be behaving differently due to changes in support conditions. The latter can lead to damage, not only to the bearings, but also to the rest of the structure due to unforeseen variations in the distribution of internal forces. In this paper, static load testing is used to evaluate the true behavior of the boundary conditions of an existing bridge and how they affect the overall structural response. The subject of investigation is a 16 m span concrete bridge subjected to the forces applied by a truck loaded with quarry aggregate. Static measurements are obtained for four positions of the truck and used to tune a mathematical model of the bridge until achieving an accurate resemblance with the experimental data. Boundary conditions are idealized with linear rotationary springs, which allow considering all possible degrees of rotational restraint at both end supports. It is shown how those values of the spring constants that best fit the measurements for a single loading case can be misleading and differ significantly from the optimal solution found combining all loading cases together.