On the structural safety of long-span bridges under traffic loadings caused by maintenance works

Abstract

Maintenance generally enhances bridge performance. However, the collapse of the I-35 W Highway Bridge over the Mississippi river in 2007 highlighted that maintenance work could generate adverse traffic load effects (LEs), resulting in a higher probability of structural failure. This study investigated the impact of maintenance work on the lifetime traffic loading and structural safety of long-span bridges. Maintenance works are classified according to their potential for causing lane closures and the presence of construction trucks on the bridge deck, wherein five loading scenarios are identified. Site-specific weigh-in-motion (WIM) data are used for traffic microsimulation over a long-span girder bridge carrying four-lane unidirectional traffic. Modified low-, medium-, and high-traffic volumes based on WIM data are considered. The traffic LEs were analyzed under the five scenarios and three traffic volumes, and the bridge safety was probabilistically evaluated with and without considering the impact of maintenance work. We showed that low and medium traffic flows with lane closures remain in free-flow states, considering that maintenance work poses no impact on lifetime LEs. However, under high traffic volume, lane closures cause congestion, and LEs under the one-lane closure scenario are even more adverse than those under slow-moving homogeneous congested traffic (the governing form in conventional design standards for long-span bridges). Furthermore, without considering the impact of maintenance work under high traffic volume, lifetime LEs may be underestimated by over 13% and the reliability index may be significantly overestimated. Consequently, maintenance works should be planned and executed so as to avoid undesirable loading situations.