Load effect of single-lane traffic simulations on long-span bridges

It is well acknowledged that long-span road bridges (about 50 m long and more) are
governed by congestion traffic rather than free-flow conditions. A conventional model
for the design of new long-span bridges is to place over the bridge a load model
representing a platoon of heavy vehicle with the gaps between them reduced to a
minimum. This assumption is too conservative for existing bridges, given the large
disruption costs faced by their closure for rehabilitation. In order to model the close
gaps between vehicles, characteristic of congested traffic, microsimulation is needed
to accurately capture drivers’ behaviour. In this work, a microsimulation model is
studied and found to replicate many different known forms of congestion. As a first
approach to the topic, single-lane simulations of identical vehicles have been carried
out in order to obtain load effect on a sample bridge. This load effect is studied with
reference to the form of traffic causing the load effect. It is found that the most
extreme load effect may not be caused by purely congested traffic but also by non-stationary congested conditions