A multi-scale finite element model of Tsing Ma Bridge for hot spot stress analysis

Failure due to fatigue damage is an important failure mode for large suspension bridges and welded connections are usually identified as one of the most vulnerable locations for accumulative fatigue damage of steel bridges. The hot-spot stress approach has been successfully used for the fatigue evaluation of welded joints. Traditionally a structural analysis using a global FE model is first conducted to determine the critical locations, based on which a local analysis is then carried out to obtain the hot-spot stress distribution that is the basis of fatigue status assessment process. Alternatively, a multi-scale model is proposed by using the mixed dimensional coupling method merging typical detailed joint geometry models into the global model so that the hot-spot stress can be directly output through a single step of analysis. As a case study, a multi-scale model of Tsing Ma Bridge was developed accordingly and the calculated results were compared with those of the global structural model and the structural health monitoring data with respect to first few order natural frequencies and vertical displacement at GPS level sensor-installed locations, and hot spot stress situation combined with stress concentration factors at a typical intersection joint. The comparison results show that the multi-scale model output agrees well with those of the global model and the monitoring data within the acceptable range, indicating that, at the same engineering level, the developed multi-scale model is more convenient and yet appropriate for the purpose of hot spot stress analysis in fatigue evaluation.