Assessment of Brazilian highway bridge live load models on five girders decks under free flow and traffic jam conditions

Abstract

The design of Brazilian highway bridges is based on the NBR 7188 code, which prescribes a live load model consisting of a 450 kN truck load and a distributed load of 5 kN/m2, both affected by an impact factor. Previous studies have shown that this load pattern does not adequately reproduce the effects of the real traffic. Two alternative load models that are more appropriate to represent actual Brazilian traffic effects were recently proposed; both were calibrated considering two-girder deck bridges, with span lengths up to 40 m. In such cases, the critical effects are associated with the free flow of heavy vehicles, including dynamic effects. This paper presents the procedures developed to assess the applicability of the previously proposed load models to five-girder bridges, with spans lengths ranging from 30 m to 50 m. For this span range, traffic jam scenarios are included in the analyses. The results indicate that the NBR 7188 load model is unsafe in several situations. Furthermore, one of the load models previously proposed was found to satisfactorily reproduce the effects of real traffic for this new set of bridges.