Evaluation of residual prestress levels on beam bridge elements using a non-destructive and a destructive method.

Abstract Residual prestress levels are a crucial parameter when assessing the state of existing prestressed concrete elements on bridges. Large deflections and cracking may be caused by significant long-term prestress losses, affecting the bridge serviceability state and, in some cases, even producing its collapse. Obtaining a reliable measurement of such parameters is usually a complicated task, as it often involves the complete dismantlement and posterior destructive testing of the bridge element. Researchers have developed and applied several destructive and non-destructive methods (e.g., crack moment, decompression load, strand cutting, exposed strand, drilled hole, and saw cuts). However, despite these advances, there is still no reliable technique, as each case is affected by multiple parameters such as materials, construction methodology, maintenance, or weather conditions. This thesis aims to find a practical application replicable for existing bridges, specifically in the Italian context. A non-destructive method (saw-cuts) and a destructive method (strand cutting) are applied to several precast prestressed concrete beams with lengths of around 20 m. The tested beams are taken from the dismantled Corso Grosseto Viaduct in Turin, in the BRIDGE|50 research project scope. The applied methods are the “saw-cuts” method which measures the strains generated by completely isolating a small concrete block in the inferior section of a PC beam by saw-cutting it, the strains can then be related to the residual prestress force; and the “strand cutting” method that consists in completely exposing a prestressed strand, which is cut to obtain its prestressing stress. In the end, the purpose of this thesis is to bring an objective comparison between the results obtained using the non-destructive and destructive methods.