Fatigue damage prognosis for long-span steel bridges is of the utmost importance in bridge maintenance and management. In this study, a multi-scale fatigue damage prognosis algorithm is developed to calculate the trans-scale fatigue damage accumulation of newly-built long-span steel bridges under vehicle loading. The necessity and procedure of establishing a multi-scale finite element (FE) model of a newly-built long-span bridge for fatigue damage prognosis are first introduced. The future vehicle loading on the bridge is forecasted using the recorded weigh-in-motion (WIM) data and the agent-based traffic flow micro-simulation method. Then, the multi-scale fatigue damage prognosis algorithm is developed based on the multi-scale FE model and using the future vehicle loading. Finally, the proposed algorithm is applied to a newly-built long-span cable-stayed bridge for the time period from 2010 to 2020. The results show that the macro-scale fatigue damage accumulation and micro-scale short crack evolution of the critical components of the bridge can be simultaneously predicted and visualized. The proposed algorithm can be used as a numerical tool for fatigue damage prognosis of steel bridges where (or near where) WIM station is installed.

Current numerical methods cannot simulate well three-dimensional (3D) fracture process of solids. In order to study 3D fracture process of brittle-like materials and improve crack growth path prediction accuracy, a method is developed based on continuum damage mechanics and finite element method. In the developed method, damage is computed by homogenizing stress or strain in the preset characteristic field for reducing the spurious mesh sensitivity. Meanwhile, an additional procedure is used to consider the unstable and competing fracture process, which can be used to consider stress redistribution due to local damage evolution during the fracture process simulation. In addition, a damage model of concrete is also developed and used to describe material damage. Finally, 3D fracture process of two numerical examples, were simulated and compared with the experimental results by using the developed method. The 3D crack growth path and macroscopic mechanical behaviors can be predicted by the developed method coupled with a damage model. From the comparison, the effectiveness and modeling capability of the developed method are verified, which can be used to study 3D fracture mechanisms of concrete-like materials.