Experimental assessment of residual prestressing force in prestressed concrete beams through nondestructive tests

This work summarizes the outcomes of an experimental campaign carried out on pretensioned prestressed concrete (PC) beams, aimed at assessing the influence of varying prestressing levels on both static and dynamic structural parameters. Three 6m long PC beams were designed and tested in four-point bending, with increasing levels of applied load. At each load step, two nondestructive tests (NDTs) were carried out, namely dynamic free vibration and ultrasonic tests. Dynamic response was analyzed both in frequency and time domains, and non-linear parameters of vibration were assessed. Ultrasonic response data were analyzed too, specifically through the evaluation of ultrasonic signal attenuation, other than in terms of absolute ultrasonic pulse velocity. Additionally, load-carrying capacity, crack pattern, deflection and concrete strains were monitored during the test. Experimental evidences were then analyzed, showing how damage detection can be carried out.