WHEEL LOADS FROM HIGHWAY BRIDGE STRAINS: FIELD STUDIES. RESEARCH REPORT

This paper describes further field measurements of the impact fraction, I, for the Six Mile Creek bridge, an 11.28m span composite steel and concrete girder bridge. It reports values in the range -0.19 to 1.25, consistent with those found in earlier studies. It also uses bridge strains to determine records of dynamic axle loads versus time for a standard truck and 123 service vehicles and subjects them to Fourier analysis. Although there is a general relationship between impact and the relative magnitude of the dynamic load components, this relationship is complex. There is no simple method to identify impactive vehicles. The field data has also been used to calibrate a simple vehicle model in which each axle load includes a dynamic load component which varies sinusoidally at the natural frequency of the bridge. This model has been used to predict upper bound values of I for bridges of varying span, with this dynamic component set at 4, 6 and 10 per cent. The resulting values are larger than those that have been commonly used, particularly for shorter spans (A).