ABSTRACT
As the traffic volume and vehicle load of highway bridges are continuously increasing around the world especially in developing countries, concrete bridges are subject to serious fatigue problems (Wang et al. 2012, Wang et al. 2013a). Under the coupled actions of traffic load and environments, damages and diseases such as concrete aging and mechanical behavior deterioration often appear after a certain period of service. Many concrete bridges collapse accidents caused heavy casualties and severe economic losses. Fatigue problem of concrete bridges is one of the most dominating reasons for structure failure (Tilly 1988).
In most developing countries, including China, reinforced concrete bridges were de-signed on the basis of allowable stress method in the 1960s and 1970s. In the past two decades, the high strength reinforcement and high performance concrete were widely used in bridges construction, which raised the ratio of live load to dead load, and more elements had a high level of stress. The initiation and accumulation of fatigue damage will lead to structural performance degradation. Therefore, the fatigue problems of concrete bridges are becoming more noticeable.
Fatigue and fracture study has been carried out on concrete bridge in USA and Europe since the 1960s. Based on fatigue failure mechanism of concrete bridges, fatigue life assessment approaches using S-N curves and fracture mechanics were proposed by Schläfli and Brühwiler to evaluate the fatigue safety of highway and railway bridges in Swiss (Schläfli & Brühwiler 1998). In China, the technology fusion of traffic load monitoring, dynamic strain monitoring, AE monitoring and fatigue life evaluation technique has been developed by Wang to evaluate fatigue life and fatigue service safety of concrete bridges (Wang et al. 2012, Wang et al. 2013).
In this paper, dynamic monitoring system was adopted to record strain history, and load spectrum was applied on typical reinforced concrete girder bridges. Then, reliability assessment methods based on linear cumulative damage theory and fracture mechanics were used to assess the fatigue performance of existing concrete girder bridges.
