Wheel Loads from Highway Bridge Strains: Field Studies

This paper describes further field measurements of the impact fraction, I, for Six Mile Creek Bridge, an 11.28‐m‐span composite steel and concrete grider bridge. It reports values between $-0.19\mathrm{and}1.25\text{,}$ consistent with those found previously. 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 relationship between impact and the 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 proposed in a companion paper, in which each axle load includes a dynamic load component that 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%. The resulting values are larger than those that have been commonly used, particularly for shorter spans.