Development of a portable total-stress measurement instrument
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] This research explores the application of ultrasonic stress measurement (USM) technologies to assess stress levels in gusset plates with the development of a small portable tool for in-situ condition assessment. The I-35W bridge in Minneapolis, Minnesota collapsed as a result of an overstressed (under-designed) gusset plate. Currently, the analytical tools used to assess the adequacy of gusset plates depend on assumed loading based on the intended design configuration of the bridge and conventional tools such as strain gages. The research team has previously developed a methodology for ultrasonic stress measurements in steel plates. This technology utilizes acoustic birefringence to analyze principal stresses. The birefringence measurement evaluates the normalized velocity difference of orthogonally polarized shear waves propagating through the plate. The birefringence varies proportionally as a function of strain in the steel. For verification, laboratory and field test were undertaken to compare ultrasonic stress measurements with stress measurements obtain via conventional strain gages. This project reports on research intended determine parameters and conditions necessary for total-stress measurements and the development of a portable tool that provides bridge engineers with quantitative, easy-to-interpret measurements of the in-situ forces carried in bridge members.
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