Influence of Prestressing on the Fundamental Frequency of Uncracked Concrete Beams

Influence of Prestressing on the Fundamental Frequency of Uncracked Concrete Beams

In this study, a series of laboratory 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 bending vibrations under varying prestress forces. Numerical modeling results, based on the Euler-Bernoulli beam theory, were then compared with experimental data. It was shown that the fundamental frequency of uncracked PC beams is unaffected by increasing applied prestress force when these members are subjected to small second-order effects. Moreover, the compression-softening effect is prominent even if its classical decreasing trend is modified by variations in the concrete elastic modulus over time. The experimental results also confirmed that the fundamental frequency is not a reliable indicator of prestress losses in PC beams.