In the field of civil engineering, it is often necessary to monitor constructions such as buildings or bridges to maintain their safety conditions. Non-destructive testing (NDT)methods outmatch other methods, because they do not influence the constructions performance. Static approaches are principally based on the experimental determination of flexural displacements. In this paper, two non-destructive methods are extended for the monitoring on prestress load in bridge beams. Both procedures require the knowledge of the flexural rigidity and of several deflections measured in given cross-sections along the beam under investigation, subjected to an additional vertical load. The extension of the NDT methods is verified by means of numerical tests on a PCI beam-type bridgewith parabolic tendon. Satisfactory estimates of the prestress loads are obtained when the displacement measurements are performed with accuracy and when higher II-order effects are actuated in the testing methods.