Feasibility study of estimating PCI beam stiffness using free vibration testing

Nondestructive testing methods were widely proposed for the evaluation of flexural rigidity of beams belonging to frame or truss structures. By contrast, the experimental identification of the stiffness of prestressed concrete bridge beams was less studied. In this work, a series of dynamic experiments were conducted on a large–scale Prestressed Concrete I (PCI) beam with a straight unbonded tendon. Specifically, the simply supported PCI beam was subjected to free vibration tests with different prestress forces. Subsequently, the experimental data were compared with analytical results based on the first–order Euler–Bernoulli beam theory. It was proved that the fundamental frequency of the PCI beam obtained by free vibration testing is not an appropriate indicator to estimate the prestress losses. Vice versa, the fundamental frequency could be a reliable parameter to evaluate the PCI beam stiffness for engineering applications of structural health assessment in the field.