Assessment and strengthening of prestressed damaged beams

The paper describes the evaluation of the actual conditions, the repairing design criteria and procedures, and the final validation tests carried out on a high damaged prestressed beams of the viaduct “Fiumara of Tito” on the highway RA005 Sicignano-Potenza in Basilicata - Italy. In the first phase several release tests have been performed on damaged beams with the aim of evaluating the residual prestressing stress acting both on concrete and on tendons. In particular, the tests on concrete have been carried out by extracting cores which have been previously instrumented with strain-gages; in a similar way, the strands were tested by gluing a micro strain-gage on a singular wire of a strand and the cutting the wire itself. The test results were used for optimising the design of an adjunctive prestressing system, consisting in 4 external unbounded cables and in a continuous FRC reinforcing of the bottom wing. The tensioning procedure of the external cables of each beam was then monitored by strain-gages installed on concrete at mid span, by load cells to measure the force applied by the cables, and by measuring the vertical deflection using laser optical levels. The validation of the repairing works was finally performed by static load acceptance tests, performed using the same apparatus previously adopted for the tensioning monitoring.