Comparison between a destructive and a non-destructive method for evaluating residual prestressing in concrete beams

Prestressing techniques are widely adopted to build strategic structures, infrastructures and bridges. The safety and serviceability of prestressed concrete members depend on the effectiveness of prestressing. Consequently, the knowledge of residual prestressing during service life is a crucial aspect to consider. In this article, a comparison between a destructive and a non-destructive method to evaluate prestressing losses is described. The destructive approach is related to the “cracking re-opening” method according to the flexural capacity of the prestressed concrete beam under investigation. Conversely, the non-destructive method is based on the Timoshenko beam theory, in which the procedure estimates the residual prestressing by at least using one static small-deflection measured along the member axis. Also, the implementation of such a non-destructive method requires information regarding the flexural rigidity of the prestressed concrete beam. Specifically, the static deflected shape of a simply supported pre–tensioned concrete beam, and subjected to an additional vertical load, was measured during an experimental campaign which, in turn, was performed on prestressed concrete beams of different ages of curing. Concluding remarks including future research directions are illustrated at the end of the article.