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Fatigue Analysis of Steel Bridge Details: Hot Spot Stress Approach Open Access

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This research successfully applies the hot spot stress approach to steel highway bridges for fatigue evaluation of welded details subject to in-plane stress or out-of-plane distortion. The existing nominal stress approach addresses distortion only qualitatively and is unable to deal with novel geometries. The hot spot stress approach provides an alternative that is more predictive in analysis and more reliable, as well as covering a wider range of geometries and loading modes. This approach has been used successfully for welded details in various engineering fields with limited prior application to bridge engineering.This work develops a hot spot stress approach for fatigue design of steel bridges. The approach's accuracy, safety, sensitivity to element mesh quality and density, and ease of application is evaluated. To obtain hot spot stress data essential to deriving the stress-life curve necessitated a re-analysis of the nominal data associated with current fatigue classification in terms of hot spot stress. To perform this re-analysis, guidelines had to be developed to perform and interpret finite element methodology. These guidelines are based on a round-robin study that assesses the performance of five element types and six hot spot stress computation rules, validated with measured strain data from static pull tests of typical welded details. The soundness of the derived stress-life curve is checked by a ten-fold cross-validation analysis.The round-robin results together with the measured strain data show that the 20-noded reduced integration element using coarser finite element meshes is best suited for hot spot stress analysis. The surface extrapolation rules are easier to implement and validate and should be put into immediate use. Re-analysis of the existing nominal data in terms of the hot spot stress allows elimination of empirically derived multiple categories and the derivation of a unique master curve for all detail types irrespective of their geometry and loading modes. The hot spot stress approach facilitates the use of FEM in design, provides a method to quantify secondary distortion stresses, eliminates the need for a fatigue catalogue, and permits full analysis of industry's latest configurations.

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