Experimental determination of dynamic allowance for traffic loading in bridges

Bridge codes adopt values for dynamic allowance in traffic load models that are necessarily conservative
to cover for an entire range of bridges with different mechanical characteristics, boundary conditions, and the large
number of uncertainties associated to the vehicle-bridge interaction problem. A further level of conservatism occurs
due to the independent manner in which the governing static load and the corresponding allowance for dynamics are
specified. In particular, certain bridges are not susceptible to high levels of vehicle-bridge interaction when loaded
by a critically heavy vehicle or a critical combination of vehicles. Recent advances in Bridge Weigh-In-Motion
technology allow not only to collect information on the weights, spacings and speeds of the traffic loads traversing a
bridge, but also to separate the maximum static strain from the total measured strain using a filtering procedure. In
this paper, maximum static and total load effects are collected and analysed for three different sites as part of the
European project ARCHES (6th RTD framework programme). Bridge measurements are used to discuss the
dynamics of the most frequent truck classes and the entire traffic sample. The measurements reveal a decrease in
percentage increment in dynamics and a reduction on the variability of the dynamic increment as the static load
effect increases. This phenomenon can be of particular relevance in the assessment of the dynamics of extreme
loading cases.