Fatigue Life of Weldment Details of Existing Orthotropic Steel Bridge Considering the Scour Effects

Abstract

During the service life of the orthotropic steel bridges (OSBs), fatigue damage accumulations could impact the safety and reliability of the bridges in their lifecycles. Fatigue damage evaluations of bridge weldments for the OSBs have been performed by many researchers for different loading scenarios and environmental conditions. During an extreme flooding event after many years of scour effects on bridge foundation, the foundation might fail and trigger the failure of the entire bridge. Many researchers have evaluated the effects of scour on the modal frequencies to monitor the depth of the foundation scour. For different dynamic characteristics of the bridges considering different soil and foundation conditions, it is not clear how the local stresses at the weld joints might be affected. In the present study, fatigue damage assessments of the bridge weld joints for the OSBs are conducted with the consideration of foundation scour of the bridges. First, a short span OSB is modeled in multiple length scales to balance computational costs and accuracy. The bridge welds are simulated in detail to capture the possible dynamic effects at these local structural details under different vehicle loadings. Soil springs are applied for the pile foundation, and the scour is simulated by releasing the soil springs. Using the hotspot stress method and the effective notch stress method, the revised equivalent stress ranges at the toe-deck crack, deck panel crack, floor beam crack, trough web crack, and root-deck crack are calculated. Based on the accumulated fatigue damages, reliability assessments of these cracks at different scenarios are performed. The fatigue life of the OSB is controlled by the cracks initiated at the floor beam-to-deck joints and the floor beam-to-rib joints. Considering foundation scour, the fatigue life of the weld joints is reduced by 22% at the maximum. The deterministic approach proposed in the specification is also used to predict the fatigue life of the weld joints. By introducing the effects of foundation scour, the fatigue life of the OSBs can be estimated more accurately.