Magnetic Resonance Enhanced Prestress Monitoring for Prestressed Tendons

A high sensitivity prestress monitoring method by the magnetic resonance (MR) effect was proposed in this work. An experiment on prestress monitoring in the life cycle was carried on. The results showed that, after the initial tensioning, the induced voltage was determined by the prestress instead of the prestress history as usual. Moreover, under the higher excitation magnetic field, the MR method owned weaker hysteresis and higher stability. The sensitivity was increased by 125.58% to 0.0194% /kN, which was close to four times the sensitivity of the magnetoelastic method. Obtaining the induced voltage-prestress relationship by laboratory calibration, the prestress monitoring errors corresponding to the construction stage and the operation stage were 8.9% and 10.9%, respectively. When the prestress is monitored only in the operation stage, the prestress monitoring error was reduced to 9.1% by using the self-calibration method. Since the proposed method can monitor the prestress varied within 100% design prestress, the proposed method can be used for short cables with a large stress amplitude.