A novel smart steel strand based on optical-electrical co-sensing for full-process and full-scale monitoring of prestressing concrete structures

As the main load bearing component, the steel strand has a significant impact on the safety of civil infrastructure. Real-time monitoring of steel strand stress distribution throughout the damage process is an important aspect of civil infrastructure health assessment. Hence, this study proposes an optical-electrical co-sensing (OECS) smart steel strand with the DOFS and CCFPI embedded in. It can simultaneously measure small strains in the initial damage phase with high accuracy and obtain information in the large deformation phase with relatively low precision. Several experiments were carried out to test its sensing performance. It shows both DOFS and CCFPI have good linearity, repeatability and hysteresis. In comparison to DOFS, CCFPI has a relatively lower accuracy and resolution, but a large enough measurement range to tolerate the large strain in the event of a steel strand failure. To verify the reliability of the proposed smart steel strand in real structures, the strand strain distribution in the full damage process of bonded prestressed beams under four-point bending loading was monitored using the smart steel strand as a prestressing tendon. The strain measured by the OECS steel strand is shown to reflect the deformation and stiffness variation of prestressed beams under different load.