Vibration-based continuous monitoring of tensile loads in cables and rods: System development and application

The estimation of axial load in prismatic members using flexural vibrations has been investigated for long. Several methods are available in the literature. They take advantage of experimental estimates of the parameters of flexural modes to solve an inverse problem and identify the axial loads in the presence of a number of assumptions and eventual additional unknowns. These methods represent a valuable solution for the estimation of the tensile force in operation. A common drawback is the need to periodically carry out a modal identification test, usually exciting the member by an impact hammer and manually processing the collected dataset. This makes these techniques suitable for periodic checks rather than continuous monitoring. Taking advantage of the most recent developments in the field of Operational Modal Analysis (OMA), an automated system for continuous monitoring of axial loads based on dynamicmeasurements has been developed. After a review of the methods for vibration-based axial load identification, the development of the monitoring system for continuous tensile load estimation is discussed in its relevant aspects. Some experimental results obtained after the installation of the monitoring system on one of the cables of a sample arch steel roof are finally illustrated for validation purposes.