Determination of Stay-Cable Forces Using Highly Mobile Vibration Measurement Devices

Abstract

Vibration measurements are an established method for determining the tension force of stay cables. Whereas stay cables are structural members exhibiting significant geometrical nonlinearities, their behavior can be linearized to approximate their vibration characteristics. Based on measured natural frequencies, the cable force can thus be identified. This paper presents methods to facilitate such force identification using highly mobile measurement equipment—namely, modern microelectromechanical systems (MEMS)–based acceleration sensors connected to battery-operated microcontrollers as well as those integrated in smartphones. The paper systematically investigates the accuracy of measurement data obtained from such systems and the effect on the tension force calculated. It is shown that sensor resolution and sampling rate directly affect the accuracy of the force measurement and are discriminating criteria between competing systems. Furthermore, a study of the amplitude of excitation arising from manual and ambient wind excitation shows that resolution limitations of the sensor may prohibit a reliable identification of natural frequencies. A novel smartphone-based software framework is presented, which integrates measurements from the different types of sensor systems. Furthermore, it allows use of nonlinear finite-element–based analyses for the cable-force identification. The proposed methodology and implementation were validated on cables of the Queensferry Crossing during construction, for which direct force measurements were available to compare with vibration-based results. The technology has shown potential to allow very simple and cost-effective yet accurate tension-force measurements.