Bridge Rating System

Long-span suspension bridges begin to deteriorate once they are built and continuously accumulate damage during their service life due to natural hazards and harsh environments such as typhoons, earthquakes, highway road vehicles, trains, temperature and corrosion. To ensure the serviceability and safety of longspan suspension bridges, bridge rating systems are often adopted by bridge management authorities as guidance in determining the time intervals for inspection and the actions to be taken in the event of defects being identified. Regular bridge inspection is one of the most important maintenance programmes to achieve desirable solutions to maintain satisfactory infrastructure performance from the long-term economic point of view. Nevertheless, most of the currently used bridge rating methods for long-span suspension bridges are based on practical experience with some engineering analyses. On the other hand, SHM technologies have gained rapid development in recent years (Mufti, 2001; Wenzel, 2009). SHM systems have been designed and installed in a number of long-span cablesupported bridges to monitor their serviceability and safety, including the Tsing Ma Bridge (Wong et al., 2001a; 2001b). However, the measurement data obtained from the SHM system have not been fully utilized for the current bridge rating. There is insufficient link between the bridge rating method and the SHM system to fulfil the common goals. In this regard, this chapter presents an SHM based bridge rating method for inspection of long-span suspension bridges. The fuzzy based analytic hierarchy approach (F-AHP) is employed, and the hierarchical structure for synthetic rating of each structural component of a bridge is proposed. The criticality and vulnerability analyses are performed largely based on field measurement data from the SHM systems to offer relatively accurate condition evaluation of the bridges and to reduce uncertainties involved in the existing rating method. The procedures for determining relative weighs and fuzzy synthetic ratings for both criticality and vulnerability are then suggested. The fuzzy synthetic decisions for inspection are made in consideration of the synthetic ratings of all structural components. Finally, the SHM based bridge rating method is applied to the Tsing Ma suspension bridge as a case study.