Longitudinal Multiple Presence of Trucks on Continuous Bridge Spans

In designing and evaluating roadway bridges in the surface transportation infrastructure, truck load is a major variable to account for. For daily operation, truck load also is a primary factor. Trucks on continuous spans were studied, with a focus on their behavior of longitudinal multiple presence in the same lane(s). Current US specifications include provisions for how to account for such multiple presence, and these provisions have evolved over the years. However, the basis for the provisions and their changes have not been well documented. An unprecedentedly large number of high-quality in-motion truck weight data were gathered in eight states across the US and used to investigate trucks’ longitudinal multiple presence behavior. A new approach to analyzing each platoon of trucks recorded in traffic was developed for this purpose. Each random platoon’s total load effect was identified, covering every truck in the platoon, to obtain reliable statistics of the maximum load effects. Results show that longitudinal multiple presence increases with truck volume and span length. Relevant current AASHTO provisions therefore were found to be conservative or overconservative. Accordingly, it was concluded that lower longitudinal multiple presence factor values for evaluation and design are more justifiable. These results may be used by bridge owners and engineers for realistic load rating and design, for more-uniform structural safety and cost effectiveness. This is consistent with the top two goals of the AASHTO Committee on Bridges and Structures’ strategic plan for extending bridge service life and assessing bridge condition.