Experimental study on the fundamental frequency of prestressed concrete bridge beams with parabolic unbonded tendons

In this study, a laboratory experiment–based testing program was conducted on a large-scale high-strength Prestressed Concrete I (PCI) beam with a parabolic unbonded tendon, capable of simulating a typical prestressed bridge member. Specifically, the simply supported PCI beam was subjected to free transverse vibrations with different prestress forces to demonstrate that its fundamental frequency was unaffected by such force. A reference model, describing the behavior of the PCI beam as a combination of two substructures interconnected, i.e., a compressed concrete Euler–Bernoulli beam and a tensioned parabolic cable, predicts no change in fundamental frequency with increasing prestress force when variation of the concrete's initial elastic modulus over time is taken into account. The large-scale experimental results confirmed that fundamental frequency is not an appropriate parameter for prestress loss prediction in concrete bridge beams with parabolic unbonded tendons. Accordingly, subsequent studies will be conducted for improving a static nondestructive testing method for such detection in concrete bridges.