A Design Live Load Model for Long-Span Bridges Based on Traffic Data and Simulations

Abstract

Current design codes for long-span bridges rely on the conservative live load models developed based on the assumed severe traffic congestion scenarios. To properly consider the site-specific traffic environment in designs of long-span bridges, this study proposes a new live load model. First, traffic environments of long-span bridges are investigated to propose classifications according to the percentage of heavy vehicles and the occurrence frequency of traffic congestion. For multilane bridges, characteristic lanes (car, middle, and truck) are defined depending on their locations, and congested traffic flows are generated through microsimulation models to consider changes in vehicle speed and driving lanes. The traffic simulation produces live load samples, which provide a basis for a design lane load model and multiple presence factors for long-span bridges. As numerical examples, the live load effects of an actual bridge were estimated by the proposed live load model and compared with those in the current bridge design code of South Korea. The results show that the live load model of the existing code is overly conservative, whereas the proposed live load model reflects the actual traffic environments of long-span bridges effectively.