An ultrasonic stress measurement (USM) instrument was developed that provides bridge engineers with quantitative measurements of the total in-situ stresses in bridge members. The total stress measured includes dead load, residual, and live load stresses. This new technology is a significant improvement over other stress measurement technologies such as strain gages, which are not capable of measuring the in-situ residual or dead load stresses in a bridge member. The USM instrument developed is a portable, battery-operated system designed to be suitable for practical stress measurement in the field. The USM instrument provides a tool that helps engineers assess bridge safety by providing the capability to measure the in-situ forces in bridge members, reducing the uncertainty associated with theoretical estimates based on design drawings and assumed load distributions.
The USM instrument was tested in the laboratory and through field testing that verified the accuracy of the total stress measurement. Laboratory testing was used to determine key acoustic properties of common bridge steels, and to test and develop the USM instrument. The field test consisted of measuring the shear stresses in a gusset plate of a truss bridge under different loading conditions. It was found that the USM was capable of accurately determining the total stress in the gusset plate. This project developed a first-generation prototype that represents a significant step toward the creation of a portable stress measurement instrument. Future implementation plans include additional field testing and commercialization of the technology.