Evaluation of the Fatigue Strength of an Orthotropic Bridge Deck Detail Using Hot Spot Stress Approach

Paper in proceeding, 2010

The finite element method has become a predominant tool for fatigue design and analysis of welded joints and components, especially for complex structures. The use of the FEM in fatigue analysis is most often associated with the application of the structural hot spot stress approach rather than the traditional nominal stress method. The former is in general more accurate, particularly in the case of complex details. However, the accuracy of the method depends on several factors related to the finite element model, such as element type, mesh density and the method used to obtain the hot spot stress. Design recommendations given by design codes are directly applicable only to specific basic details. For some structural details with complex geometries and stress conditions, more detailed guidelines are needed in order to obtain an accurate estimation of the hot spot stress in these details.. An example, which is treated in this paper, is welded joints with cope holes in orthotropic bridges decks where it is not easy to separate the nonlinear stress caused by the notch at the weld toe from the stress concentration effect emanating from the hole in the detail. In this study, the application of the structural hot spot stress approach on a welded joint with cut-out holes in orthotropic bridge decks was investigated. Fatigue tests were carried out on full-scale specimens. In the analytical part, various finite element models created by shell and solid elements were investigated. Different weld modeling techniques to incorporate the weld itself into shell element models were also investigated. The results obtained from these models with different stress determination procedures including Battelle structural stress approach are compared with the results from experiments. The results from the FE analyses showed that the structural hot spot stresses obtained from the shell element models were unrealistically high when the welds were omitted. Also the way in which the welds are represented had a substantial influence on the magnitude of the hot spot stress in the detail. This study also provides valuable information on how finite element models can be detailed to obtain accurate load effects in details with cope holes similar to those considered in this study.