Abstract
Steel strands are widely used in cable stay or suspension bridges. The safety and stability of steel strands are important issues during their operation period. Steel strand is subjected to various types of prestress loss which loosens the wedge anchorage system, negatively impacting the stability of the structure and even leading to severe accidents. In this paper, the authors propose a time reversal (TR) method to monitor the looseness status of the wedge anchorage system by using stress wave based active sensing. As a commonly used piezoceramic material, Lead Zirconate Titanate (PZT) with a strong piezoelectric effect is employed. In the proposed active sensing approach, PZT patches are used as sensors and actuators to monitor the steel strand looseness status. One PZT patch is bonded to the steel strand, one PZT patch is bonded to the wedges, and another PZT patch is bonded to the barrel. There are three different interfaces of the wedge anchorage system to monitor the steel strand looseness status. In the first method, the PZT patch on the steel strand is used as an actuator to generate a stress wave and the PZT patch on the wedge is used as a sensor to detect the propagated waves through the wedge anchorage system. In the second method, the PZT patch on the steel strand is used as an actuator to generate a stress wave and the PZT patch on the barrel is used as a sensor to detect the propagated waves through the wedge anchorage system. In the third method, the PZT patch on the wedges is used as an actuator to generate a stress wave and the PZT patches on the barrel is used as a sensor to detect the propagated waves through the wedge anchorage system, of which the looseness will directly impact the stress wave propagation. The TR method is utilized to analyze the transmitted signal between PZT patches through the wedge anchorage system. Compared with the peak values of the TR focused signals, it can be found that the peak value increases as the wedge anchorage system tightness increases. Therefore, the peak value of the TR focused signal can be used to monitor the tightness of the steel strand. In addition, the experimental results demonstrated the time reversal method’s reliability, sensitivity and anti-noise property.
Highlights
The long-span prestressed concrete bridge has many advantages, such as large span capacity, strong seismic capacity, convenient construction and little maintenance work
The obtained under amplifier and was transmitted the PZT 1, which was pasted on the steel strand
The results indicated that the focused value of the received signal based on the time reversal technique through three different contact surfaces can reflect the tightness of the prestressed steel strand
Summary
The long-span prestressed concrete bridge has many advantages, such as large span capacity, strong seismic capacity, convenient construction and little maintenance work. Developed a time reversal enabled pulse-position modulation method to effectively solve the multipath propagation problem of stress-wave based communication in concrete structures. Van Damme et al [56] introduced a combination of time reversal acoustic and nonlinear elastic wave spectroscopy to monitor the surface crack of steel structures. The piezoelectric ceramic transducer is a new type of stress monitoring method with the advantage of non-destructive, long-term and stable stress monitoring, and adapting to the construction status of prestressed steel strands is a good way to substitute the traditional monitoring means. The time reversal method based on piezoceramic was used for active monitoring of the wedge anchorage system. Experimental results clearly demonstrate that the proposed time reversal technique can monitor the loading status of the wedge anchorage system with excellent repeatability and strong anti-disturbance ability
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