APPLICATION OF ELECTROMAGNETIC-ACOUSTIC TRANSDUCERS FOR NONDESTRUCTIVE EVALUATION OF STRESSES IN STEEL BRIDGE STRUCTURES

This report presents the results of a study to (1) assess the applicability of electromagnetic-acoustic transducers for nondestructive evaluation of stresses in bridge structures and (2) evaluate the new ultrasonic instruments as an effective technique for stress surveys in bridge structures. Field tests were performed on two bridges, one a simply supported design and the other an integral backwall bridge. Residual stress measurements were made on a vertical scanline in the web at midspan of a simply-supported bridge. Live load measurements were made by determining the normalized change in arrival times of surface waves propagating between two transducers mounted on the bottom flange. Good agreement between strain gage and ultrasonic data was obtained, both for the time-history of strain and also for the equivalent stress range. The ultrasonic equipment for live load measurements is portable and easily installed. Unlike strain gage installation, ultrasonic measurements could be made without paint removal.