Ultrasonic diagnostic load testing of steel highway bridges

This paper presents a new product, the SonicForce((TM)) Acoustic Strain Gauge (ASG), that utilizes a non-contact ultrasonic technology to measure applied strain requiring no paint removal and minimal surface preparation. After an overview of the ultrasonic technology is presented the results of a diagnostic test utilizing a prototype of the ASG will be discussed. The purpose of this test was to validate the Acoustic Strain Gauge as being functionally equivalent to the resistance strain gauge, and to demonstrate a cost effective enabling technology to the civil and structural engineering communities. The diagnostic test program was supervised by Dr. Abba Lichtenstien in accordance with accepted guidelines contained in the manual for ''Rating Bridges Through Testing'' For the purpose of this study the bridge superstructure was modeled and structural loading profiles were determined using both resistive and acoustic strain measurement techniques. Measured strains as determined by the ASG (correlation between the ASG and the resistance strain gauge was 0.998) were compared to theoretical loads in order to determine if the Rodeo Gulch superstructure was operating in a safe and reliable manner. Additionally, under the direction of Phil Fish (Wisconsin DOT), two pre-production ASGs were used to monitor accumulated cyclic loading. These test data are presented as a time series strip chart and rainflow histogram.