Stress Monitoring of Prestressed Steel Strand Based on Magnetoelastic Effect Under Weak Magnetic Field Considering Material Strain

Abstract

Prestressed steel strands are critical components of prestressed structures, which determine the bearing capacity of the structures. The prestress loss of steel strands causes the bearing capacity to decline. To monitor the stress of prestressed steel strands, a stress monitoring method based on the magnetoelastic effect was proposed. The influence of the material strain was considered to improve monitoring accuracy. To do the monitoring, a coil-based sensor, using a small excitation current to generate a necessary magnetic field, was employed. The sensor converted the stress into inductance. An experimental system was set up, and two batches of specimens were tested. The experimental results showed that the measured inductance was stable and repeatable. There was a nonlinear relationship between the inductance and the stress. Strands of different batches need to be calibrated separately to obtain the inductance-stress equation. Based on the calibration equation and measured inductance, the stress of strands could be calculated. The difference between the calculated stress and the actual stress was small. Besides, to improve the accuracy and ease of the construction, the self-induction coil of the senor should be one layer and with moderate turns.

Prestress Monitoring of Internal Steel Strands Using the Magnetoelastic Inductance Method

“…According to the Biot-Savart theory, the coil of the magnetoelastic inductance sensor [16] can be regarded as a solenoid. The solenoid has a radius of r, a length of l m , and turns of n. Assuming that the magnetic field distributes uniformly along the coil's axis, the magnetic field in the coil (B) can be expressed as Eq.…”

“…In stage 2, ΔL still increased with the tension increment, but the changing rate of the ΔL began to decrease. This decrease was caused by the reduction of the sectional area of the steel strand [16]. Since there existed a relationship between ΔL and the tension, the sensor inductance could be used to characterize the prestress.…”

“…Thus, the MIM could be used to monitor the prestress of the internal steel strand. Additionally, the prestress calculation and analysis method [16,21] proposed for the external steel strand could be directly used. Because the measured inductance can be affected by uncertainties, a fuzzy preprocessing would be necessary to perform [22,23].…”

“…Due to the small size of the MIM sensor, the MIM method could be used for prestress monitoring. Experimental research was conducted on external steel strands [16]. Because the internal steel strands are wrapped by grouting material, the working condition of the MIM sensor is different.…”

A Passive Wireless Differential Sensor for in-Situ Early Detection of Periprosthetic Joint Infection

“…Magnetoelastic (ME) transduction has been employed in a broad range of sensing applications such as stress/strain measurements [6][7], pH sensing [8], cell growth monitoring [9], metal ion detection [10], and immunoassay for pathogens [11][12] and biomarkers [13]. With inherent passive wireless characteristics, ME sensors are highly suitable for implantable applications such as integration with orthopedic implants to monitor possible structural failures [14] and with biliary stents to monitor sludge accumulation and restenosis [15].…”