Fast EM stress sensors for large steel cables

This paper is focus on the applications of EM sensor on cable force measurement for large bridges. The sensors are entirely suitable for sheathed cables and require no physical contact with the cable itself. In order to meet the requirement of observing structure behavior under extreme events, a high sampling rate of EM technology has been developed. The sampling rate of the EM sensor can be as high as 0.1 Hz which is faster than the current available technology for sensor size of up to 250mm. Both laboratory and field calibrations were conducted. The relationship between the relative incremental permeability and tensile stress is derived from these calibrations. Field measurements on tendons for Stonecutters Bridge in Hong Kong demonstrate the reliability and accuracy of the EM stress sensors using the updated technology.