Dynamic Stresses in Continuous Plate Girder Bridges

This paper describes and presents results of tests conducted by the Bureau of Public Roads and the Oregon State Highway Department on two three-span continuous plate girder bridges in Oregon. Measurements include deflection of the girders and strain in the girders, stringers and floor beams under test vehicles approximating the AASHO H20-S16-44 truck at speeds of 5 to 45 miles per hour. The test records provide values of frequency of vibration, amplitude of vibration, and amplitude of strain oscillation. Test data are presented in curves showing variation of stress and deflection with speed. Comparisons are made with stresses and deflections calculated according to existing specifications. Measured stresses in general are found to be lower than calculated values. Analytical work pertaining to theoretical frequencies and amplitudes of vibration is summarized. A good correlation was obtained between measured and computed frequencies of vibration. Calculations relative to the amplitude of vibration do not provide a correlation with the measured values; however, they strongly 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.