Investigation of the Dynamic Amplification caused by Traffic Loading on Medium Span Bridges

P. Rattigan, A. González, and E. O'Brien (Ireland)


Dynamic modelling, traffic, bridge, loading


Modern bridge codes allow for a reduction of safety factors based on a better knowledge of the loads. This rational approach can lead to great savings in the design and assessment stages. Traffic loading is a clear example of a variable that can be modelled probabilistically using Weigh-In-Motion data. Then, a Monte-Carlo simulation using this traffic model can provide a more accurate estimation of the static characteristic bridge load effect. However, while this worst static case is carefully determined from simulations based on statistical traffic data, the worst dynamic effect is merely calculated multiplying the worst static effect by a dynamic amplification factor. This factor is necessarily a very conservative value since it must cover for many types of bridge structures and it ignores the structural dynamics and traffic characteristics of the site. The discrepancy between the methods to obtain worst static and dynamic load effects is clear. This paper analyses how to reduce the uncertainty associated to the dynamic load and how to benefit from the use of site-specific traffic loading to obtain a more realistic upper bound of not only the maximum static load effect but also the dynamic one.

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