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Curvature: An Indicator of the Mechanical Condition of Old Prestressed Concrete Bridges

Abstract The bearing capacity and therefore working life of prestressed concrete structures depends, in the main, on the persistence of the prestressing forces at a minimum level. However, it is difficult, if not impossible, to measure this characteristic and follow its evolution over time. The measurement of the curvature of certain strategic sections is more accessible, and is an indirect way of monitoring prestressing forces by locally detecting when critical thresholds are exceeded. This could be, for example, the beginning of the decrease of curvature under permanent load in a beam and slab bridge, or, for a hyperstatic structure, a “micro-crack flexion mode” being detected under traffic load. The choice of the area to be monitored is critical, and the analysis of the measured gross curvature—which is affected by many factors—must be made with the greatest of care. For more than two years, Laboratoire d'études et de recherche sur les matériaux (LERM)—a laboratory in the Société d'études techniques et économiques (SETEC Group) Group—has been carrying out an experiment of this nature by monitoring a post-tensioned prestressed-concrete independent-span viaduct (Viaducs Indépendants à Poutres Précontraintes - VIPP) using two curvature meters.