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

Significance 

It is necessary to maintain transport infrastructures to optimize and improve their performance. Bridges, for example, undergo continuous deterioration process for which maintenance and repair works are needed to detect and prevent potential failures. However, maintenance works can increase the traffic load beyond the limits, thus contributing to bridges’ failure or even collapse. Evidence was the collapse of the I-35 W Highway Bridge in Minneapolis undergoing maintenance in 2007. During the maintenance works on this bridge, two lanes were closed and construction materials were stockpiled on the bridge deck. Thus, in addition to altering the normal traffic flow, the bridge collapsed due to additional weight due to the maintenance works. The failure was also attributed to inadequate inspection and undersized gusset plates. This case showed that maintenance works could induce detrimental traffic loading scenarios on bridges that are worth investigating to establish their effects on lifetime loading and safety.

Common scenarios of traffic load effects on bridges are based on the classification of independent scenarios. The traffic load effects are derived from different independent loading scenarios. For traffic loading of small and medium span bridges, the critical and independent scenarios depend on the presence of trucks and the number of trucks, respectively. In contrast, that of long-span bridges depend on free traffic flow and congestion. Nevertheless, traffic loading scenarios during maintenance works, especially those requiring heavy construction machines and lane closure, are quite different. Since such maintenance works are conducted on numerous occasions during the service life of bridges, it is imperative to consider the importance of these events for accurate prediction of lifetime load effects.

Herein, Professor Junyong Zhou and Dr. Liwen Zhang from Guangzhou University and Professor Colin Caprani from Monash University investigated the impact of maintenance works on lifetime traffic loading and structural safety of long-span bridges. In their approach, maintenance work was classified based on event probability and traffic input uncertainty (whether or not the works required construction trucks or lane closure) to determine independent traffic loading scenarios. Site-specific weigh-in-motion (WIM) data were utilized for traffic microsimulation of the five identified scenarios considering three different traffic volumes: modified low-, medium- and high-traffic volumes. The simulation was performed over a girder bridge carrying four-lane unidirectional traffic. An analysis of the traffic load effects and evaluation of the bridge safety in the presence and absence of maintenance work was performed. Their work is currently published in the journal, Engineering structures.

The research team showed that low and medium traffic volume remained in a free flow state even with lane closure because the maintenance work had no impact, and the conventional design standards governed any adverse effects. In contrast, under high traffic volume, lane closure due to maintenance resulted in congestion, producing load effects that were more detrimental compared to that under slow-moving but congested traffic. Excluding the impact of maintenance works could lead to underestimation of bridge lifetime load effects by over 13% under high traffic volume. Closing one of the four lanes during minor maintenance was found to pose detrimental effects than closing two lanes during major maintenance works because the latter reduced traffic intensity. Furthermore, the location and layout of the works need to be carefully identified because they can potentially generate adverse load effects than normal traffic congestion.

In summary, the new study is the first to evaluate traffic loading scenarios that bridges are likely to undergo during their service lifetime, considering the contribution of maintenance works. The effects of maintenance work on structural safety and lifetime load effects of long-span bridges were quantified. The authors emphasized the need for proper planning of maintenance works during bridges’ design, maintenance, and management. This could ensure structural safety by avoiding severe loading scenarios and associated safety risks. In a statement to Advances in Engineering, the authors said their study contributes to traffic control strategies for improving the performance of bridges.

Reference

Zhou, J., Caprani, C., & Zhang, L. (2021). On the structural safety of long-span bridges under traffic loadings caused by maintenance worksEngineering Structures, 240, 112407.

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