Monitoring Damage in PC Slabs by Modal and Ultrasonic Tests

. The effectiveness of modal and ultrasonic tests for monitoring the damage in precast prestressed concrete slabs was experimentally investigated. Four slabs with two different span lengths and corresponding modes of failure (interfacial shear and flexural failures) were subjected to loading steps until failure. The variations in fundamental natural frequency, damping ratio, ultrasonic pulse velocity (UPV), and ultrasonic wave attenuation in relation to the damage severity and failure mode were investigated and compared. It was observed that the natural frequency was sensitive to flexural crack development. A significant change in the damping ratio was obtained in the slabs with moderate damage. The UPV was not affected by a moderate degree of interfacial shear damage and a low degree of flexural damage; however, it was strongly related to the progression of flexural damage at the severe stage. Among the various indexes, ultrasonic wave attenuation was most sensitive to the development of damage. The method could detect interfacial-shear and flexural cracks at an early stage.