Pavement damage implications of Ontario Bridge Formula axle group weight limits

Abstract

The Ontario Bridge Formula (OBF) is the basis for the regulation of highway truck weights in Ontario. Allowable loads on tandem and tridem axle groups increase with increasing axle group spread. Analyses of the moments induced in simple-span bridges by the allowable axle group loads show that the moments increase with the increasing loads allowed on wider axle spreads. Pavement damage load equivalency functions developed from the Canroad pavement test series are used to estimate the. pavement damage impacts of these allowable axle loads. Relative pavement damage is shown to increase by 50% for the range of loads allowed on tandem axle groups and by 125 % for the load range allowed on tridems. If equal pavement damage were used for regulating axle group loads, then the range allowed for tandems would be 15 400–16 500 kg, instead of the OBF-allowed 15 400–19 000 kg; and 19 100–20 000 kg, instead of the OBF-allowed 19 500–28 600 kg, for tridems. Key words: highway bridges, highway pavements, bridge loads, trucks, load equivalencies.