Magneto-Elastic Sensors for Postearthquake Damage Detection in Steel Structures

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9724948 Wang In this project, research is conducted toward development of a method of direct stress measurement based on the measurement of magnetization characteristics of ferro-magnetic structural materials. It has been shown that the magnetization characteristics of ferro-magnetic materials are related to the stress level, and a number of successful magneto-elastic sensors have been designed by researchers around the world. Most of these sensors are cylindrical in design and are primarily designed for measuring force and stress in cylindrical specimens. This is sometimes seen as a severe deficiency, since the bast majority of structural elements in a typical structure are planar (girders and beams, plates and decks) and the specimen under investigation cannot be enclosed within the sensor. A novel planar sensor design will be achieved using the concept of magnetic reluctance measurement for stress analysis. The sensor design philosophy emphasizes the ability to make stress measurements in the post yield region of the structure. The research consists of the following tasks: 1) design of sensors that can operate in the postyeild zone, 2) development of a residual stress sensor capable of detecting yielding, 3) development of a surface mountable planar sensor design in contrast to a cylindrical design, and 4) development of a suitable constitutive model for determination of permeability-stress relationships for sensor design and calibration. The proposed sensor is flexible and can be utilized for a variety of structural monitoring schemes, force measurement of inplanar and circular cross-sections, monitoring of prestress loss in bridge girders, and postearthquake evaluation of structural members. ***