Bridge roughness index as an indicator of bridge dynamic amplification

The concept of a road roughness index for bridge dynamics is developed. The international roughness index (IRI) is shown to be very poorly correlated with bridge dynamic amplification as it takes no account of the location of individual road surface irregularities. It is shown in this paper that a bridge roughness index (BRI) is possible for a given bridge span which is a function only of the road surface profile and truck fleet statistical characteristics. The index is a simple linear combination of the changes in road surface profile; the coefficients are specific to the load effect and span of interest. The BRI is well correlated with bridge dynamic amplification for bending moment due to 2-axle truck crossing events. A similar process can be used to develop a BRI for trucks with other numbers of axles or combinations of trucks meeting on a bridge.