Despite the increasing popularity of cable-stayed bridges, no accurate or simple method is available for directly measuring the stresses (forces) in the cable stays. The measurement of the forces is important for monitoring excessive wind or traffic loadings, to gage the redistribution forces present after seismic events, and for detecting corrosion via loss of the cross section. It is planned to develop a remote (portable) magnetoelastic sensor for the direct measurement of stress in steel cables and tendons. A magnetoelastic sensor based on a cylindrical solenoidal geometry, which is suitable for installation at the time of construction or winding in-situ for existing cables has been developed at the University of Illinois at Chicago. The technique is based upon the dependence of the magnetic properties of structural steels directly related to the state of stress. The magnetic properties are measured by subjecting the steel to a pulse or periodic magnetising field. Changes in flux through circuits surrounding or adjacent to the steel allow the magnetic properties to be measured. Accuracy within 1% (against a load cell) in the temperature range of -40 (F) to 140(F) are routinely achieved with different sizes of sensor below the elastic limit. These sensors have been accepted for field testing during the construction of several projects. This project will investigate avenues to extend the magnetoelastic measurement principles to a new sensing circuit which does not require winding it around the cable. It is portable and reusable. It is highly desirable to perform the stress measurement using this coil geometry in the post-yield regime for damage assessment of cables due to unanticipated loadings.
