External magnetization based elasto-magnetic sensing technology for tension monitoring of aged PSC structures

Abstract

The prestressed concrete (PSC) girder bridge is most commonly used bridge type for short and/or medium-span bridge. However, if the tension of the prestressing (PS) tendon of PSC girder is loosen due to deterioration or damage of tendon, it can be collapse suddenly. Therefore, it is necessary to monitor the tension of internal PS tendon to maintain the PSC girder bridge. But in the case of an aged bridge without a built-in sensor, there is no way to monitor the tension of the internal tendon. To monitor the residual prestress of aged PSC girder bridge, this study proposed an external magnetization based elasto-magnetic (EXEM) sensing technique. To magnetize the PS tendon of PSC girder, the EXEM sensor system was designed through theoretical study and finite element analysis. The EXEM sensor was fabricated according to the design, and the proposed method was verified through scaled-down PSC girder test. The EXEM sensor system was installed symmetrically on after the end of tapered section of the girder. After installation, the magnetic response of PS tendon was measured while applying tensile stress step by step. Also, temperature compensation was applied to remove the effect of temperature caused by the resistance of the solenoid. Through numerical analysis and actual experiments, it was confirmed that the tendons inside a PSC type I girder can be magnetized using the EXEM sensor system. Moreover, the residual prestress can be diagnosed by measuring the magnetic response change due to tension using the proposed EXEM sensing technique.