Dynamic Stresses in Continuous Plate-Girder Bridges

This paper describes and presents results of the tests conducted on two three-span, continuous, plate-girder bridges in Oregon. Included herein are measurements of the deflection of the girders and strains in the girders, stringers, and floor beams under test vehicles. The test records provide values for the frequency of vibration, the frequency of strain oscillation, the amplitude of vibration, and the amplitude of strain oscillation. Test data are presented as curves, which show the variation of stress and deflection with the speed of the test vehicles. Comparisons are made with stresses and deflections computed according to existing specifications. Measured stresses, in general, are found to be lower than the computed values. Analytical work pertaining to theoretical frequencies and amplitudes of vibration is summarized. Good correlation was obtained between measured and computed frequencies of vibration. Computations relative to the amplitude of vibration do not provide a correlation with the measured values; however, they suggest that a substantial part of the vibration can be attributed to deck roughness. Measured strains are used to determine the degree of fixity of the ends of the floor beams, and measured deflections are used to evaluate the torsional rigidity of the structures.