Multi-lane traffic load model of widening bridges considering lane load disparity

There is an increasing number of narrow bridges need widening to tackle road traffic growth. In the widening project, the superstructures of the new and existing bridges are generally connected. The current bridge widening guidelines require that standards used for the new bridge should be also applied for the existing bridge. However, the design standards of bridges subjected to traffic load have been significantly improved due to the increase of truck weight and truck volume over the past three decades. Consequently, many existing bridges may not meet the current standard and should be reconstructed. In reality, the existing and new bridges carry the fast-lane and slow-lane traffic respectively, and traffic loads have significant disparity across the multiple lanes, i.e. load level in the fast lane is smaller than that in the slow lane. Therefore, it is urgent to consider lane load disparity to investigate the traffic load effects in the new and existing bridges in these widening projects. In this paper, sitespecific multi-lane traffic loads were collected on a widening highway. A multi-lane traffic load model was proposed based on the coincident lane load effect approach, which considers lane load disparity. The proposed model is further employed to evaluate the differences of traffic load effects between the existing and new bridges, which are then compared with the calculated results based on the traffic load model in the current bridge design specification. Results indicate the old slabs fail to meet the requirements of the design specification, but they are safe when evaluate using the proposed multi-lane traffic load model. This conflict indicates the inaccurate of the current design specification model for some special applications such as widening bridges, and enhance the importance of proposing a multi-lane traffic load model from site-specific traffic data. The outcomes of the study could provide valuable recommendations on the retrofit or maintenance of the existing bridges in bridge widening projects.