Reliability index and parameter importance for bridge traffic loading definition changes

With the continued evolution of traffic loading specifications, safety classifications of bridge structures are subject to change, independent of the actual condition of the structures at that point in time. As investment decisions are often based on these safety classifications, a reclassification of safety level due to changing of traffic load definitions can lead to misinterpretation of the actual state of the structure, and thus lead to a misallocation of resources. Should a reclassification of safety occur after a change in traffic load specification, the question as to whether modern design codes are producing more or less robust bridges than previous design codes is raised. To investigate this, three bridge structures were assessed for evolving definitions of traffic load. Using deterministic and probabilistic methods, critical limit-states were assessed and the associated reliability indices and parametric sensitivity factors were determined and compared across various code specifications. This comparison allowed for the evaluation as to how the evolution of traffic load over time influences the computed safety of bridge structures.