Effective Prestressing Force Testing Method of External Prestressed Bridge Based on Frequency Method

A practical project is taken for the example to analyze the application of frequency method in the effective prestress test of external prestressed bridge. In the process of solving the dynamic differential equation of tension cable, the effects of boundary conditions on the natural frequencies of external prestressed tendons are analyzed. The analysis results show that the fundamental frequency of the prestressed tendons under fixed boundary condition is higher than that under hinged-support support boundary condition, and the relative variance decreases with the increase of tensioning force. With the same tensioning force, the relative variance decreases with the increase of cable length. In the practical test, only the upper and lower bound limits can be obtained according to the measured prestressed tendon frequencies, while the real effective prestress values are between them. For external prestressed tendons, a kind of short tension cable, the frequency method can produce certain error in calculating the effective prestress.