With the continuous growth of traffic load, maintenance has become the main task of various management departments. The cable force loss is directly related to the long-term service performance and life of the bridge. The wireless electro-mechanical impedance (EMI) technique based on PZT transducer attracts more and more attention due to its simple operation, fast detection speed, and wide application range. In this paper, the PZT transducers were coupled to the surface of the nut of the cable to monitor the cable force. Then the influence of the number of EMI sampling points (i.e., 250, 500, 1000) on the RMSD was investigated. The feasibility of the wired and wireless EMI method applied on the cable force monitoring was verified. The results show that the peak of the impedance curve shifted to the right with the increase of the force. The sampling points had little influence on the normalized RMSD. Therefore, the smaller sampling points could be selected to reduce power consumption. The PZT transducer has a strong potential to have a uniform sensitivity coefficient for a member under test. © Tongji University Press 2024.

Extensive research has shown that iron-based shape memory alloys (Fe-SMA) can be used as prestressing materials in new reinforced concrete (RC) structures or existing RC structures. Currently, the Fe-SMA is thermally activated using various methods, including resistive heating, infrared, fire torch, propane torch, and heating jacket. Among them, resistive heating is a relatively better method with a wide range of applications and a short activation time. However, for the resistive heating method, the influences of the current magnitude and the activation time on the temperature distribution and the generated recovery stress in the Fe-SMA are still unclear, which restricts the field application of the Fe-SMA. The self-prestressing behavior of the Fe-SMA involves multiple physical fields such as electric currents, temperatures, and mechanics. This paper developed a multi-physical finite element model to simulate the self-prestressing behavior of the Fe-SMA when it is used as a strengthening material. The model is verified by the experimental results reported in literatures. The results show that the model can accurately predict the temperature distribution and the recovery stress of Fe-SMA strengthened RC beams. Furthermore, the model helps choose the appropriate activation current magnitude and activation time needed to achieve the design prestressing value in the Fe-SMA, reducing the risk of thermal damage to concrete caused by constant high temperatures. This study provides a constructive guideline for the field application of the Fe-SMA. © Tongji University Press 2024.

The tensile stress caused by the diffusion of the prestress in the post-tensioned anchorage zone will Induce premature cracks at the end anchorage zone of prestressed concrete structures. Indirect steel reinforcements are usually adopted to resist tensile stress. However, too dense indirect reinforcements often have an adverse effect on the casting quality of the concrete. In light of the above, it is proposed in this paper to replace the conventional steel spiral stirrup with the newly developed iron-based shape memory alloy (Fe-SMA) spiral stirrup, which can generate hoop confinement through its shape memory effect (SME). The extra hoop confinement provided by the Fe-SMA spiral stirrup could theoretically improve the cracking resistance of the anchorage zone. A finite element model using ABAQUS was established to simulate the compression performance of a concrete prism with the Fe-SMA spiral stirrup, and the model was verified by theoretical calculation results. The transverse stresses along the tendon path under different hoop prestressing levels in the elastic stage were compared. Moreover, the load-displacement curves and the cracking of the overall anchorage zone were also investigated. The results showed that using the Fe-SMA spiral stirrup can effectively improve the anti-crack performance of the anchorage zone. © Tongji University Press 2024.