Evolution of truck weight limits and bridge live load models: evidence of impacts from Manitoba, Canada

Abstract

This research presents evidence of the impacts of truck size and weight regulation changes on bridge live load models, truck operating gross vehicle weights and bridge structure reliability, specifically focusing on the context of Manitoba, Canada. This work addresses previous research gaps and contributes knowledge to this topic by: (1) examining historical relationships between truck size and weight regulations and bridge design codes; (2) conducting a retrospective, longitudinal study using a unique time- series of truck weight data to provide insights about the magnitude and timing of the impacts of truck weight regulatory changes on truck operating gross vehicle weights; and (3) evaluating the reliability of typical bridge types designed according to modified live load models and subject to differing truck live loads. Key findings from this work include several insights and observations. First, while at times bridge codes are released in conjunction with expected regulation changes, there is often a delay in the issuance of revised design codes, thus highlighting the importance of assessing current changes to the truck fleet for future bridge code live load models. Second, truck carriers take advantage of increased truck weight limits; however, the truck configuration and type of commodity influences the sensitivity to the weight limit changes. Similarly, the timing of the response is dependent on the ease of implementation and immediate increases are observed for weigh-out commodities when fleet modifications are not required. Third, three bridge types designed to the previously unanalyzed live load model specified in Manitoba are found to maintain a level of safety for the girders that exceeds target code requirements with reliability indices ranging from 4.65 to 5.04, depending on the considered live load statistics. This indicates a potential capacity for the considered structure types to safely withstand increased traffic load effects. By studying specific topics influenced by truck size and weight regulation changes and providing evidence of the impacts on truck operating weights and bridge infrastructure, this thesis contributes new insights to address gaps in previous research. It highlights the importance of monitoring changing truck weights and configurations to maintain the level of safety of bridge infrastructure.