Safety Assessment of Widened Bridges Considering Uneven Multilane Traffic-Load Modeling: Case Study in China

Several bridges now require widening owing to the continuous development of road transport. However, the standard of traffic load in design specifications has been enhanced. Consequently, old bridges may not meet the safety requirements of current design specifications and, therefore, must be reconstructed or retrofitted. However, the old structures in widened bridges carry fast-lane traffic loads, which are relatively low due to uneven multilane traffic loads. This paper reports a case study conducted on a Chinese highway widening project for comprehensively evaluating the structural safety of multislab widened bridges using code-based deterministic and reliability-based probabilistic approaches. In the deterministic evaluation, previous and current Chinese bridge designs and other national codes were employed. Meanwhile, in the probabilistic assessment, an uneven multilane truckload modeling was implemented based on site-specific traffic data. Subsequently, bridge safety under normal traffic conditions with all lanes open and occasional traffic conditions with lane closure was investigated. The results indicate that most old slabs, especially those closer to medial dividers, are unsafe under the current Chinese design specifications. However, a site-specific assessment under normal traffic conditions indicates that these old slabs possess adequate security reserves, except that the side slab close to the junction requires safety. Further analyses conducted with occasional traffic conditions demonstrated that closing fast lanes does not affect the safety of slabs. Conversely, closing slow lanes significantly affects the safety of inner old slabs, which should be prohibited or addressed with strict weight restrictions. These results can be beneficial for future bridge widening projects.