Orthotropic steel decks (OSDs) are commonly used in bridge construction due to their material efficiency and strength. However, fatigue issues in welded joints remain a concern. Fatigue cracks often occur due to high stress concentrations, especially under heavy traffic loads. Current approaches of determining damage in a bridge are limited by the computational demands of Finite Element (FE) models to calculate stresses and the complexity of the fatigue verification. Consequently, there has been limited exploration of parametric optimization for OSDs. This research seeks to address this gap by developing a parametric model to assess the fatigue performance of OSDs according to the ROK version 2.0, the new Dutch Guideline, additionally focusing on identifying the influence of key design parameters through a parameter sensitivity analysis (PSA). This study aims to provide insights for optimizing OSDs to enhance fatigue resistance and design. Thereby aiming to increase material efficiency about OSDs and creating a parametric framework to determine damage in an OSD.

This resulted in the following research question: How can a parametric model be developed to assess the fatigue performance of Orthotropic Steel Deck bridges and what insights can be gained from analyzing the influence of key design parameters?

To answer this question, in part 1 a literature study is performed. This began by reviewing the theory of the OSD’s and fatigue, identifying the critical fatigue parameters which were expected to influence the incorporated directly ridden details. Furthermore, the Dutch regulations and state-of-the-art about automatizing of fatigue verifications were explored, after which a parametric model is developed.

Part 2 began by developing this model. Simplifications in the mesh and loading scheme are tested and applied to ensure the model is fast and sufficiently accurate. Utilizing various mesh sizes in different regions helps to reduce computation time by almost 300% while maintaining accuracy. Additionally incorporating symmetry in the loading scheme further reduces the computational time by about 127%. With this model, the first part of the main research question is answered. The model is used to find the governing details in the bridge within the design domain of the ROK [2]. The governing details are: the crack initiating at the weld toe located at the intersection of the trough and the deckplate, and the crack initiating at the weld root located at the intersection between the deckplate, trough and crossbeam. Which are respectively detail 1A and 1C of the ROK[2]. After this, a benchmark model is found to start the PSA and a sensitivity analysis is conducted for these previously mentioned details by systematically altering one parameter at a time (OAT).

Results of the PSA are distinguished for the two aforementioned details. For detail 1C, the deckplate thickness and trough top width influence the damage of the detail primarily, represented by respectively an exponential function and second order polynomial. The crossbeam thickness influences the damage by maximally 30% of the damage number of the benchmark, while this parameter is not included in the analytical solution. Other included parameters show small or negligible influence on the damage of detail 1C. The governing load position within the design domain is the transversal load distribution exactly above the middle of a trough. Furthermore, a difference in stiffness exists between two trough legs of the same
trough for detail 1C, significantly influencing the damage. The governing transversal location of detail 1C is at the trough leg closest to the main girder.

For detail 1A, by far the most influential parameter on the damage of this detail is the deckplate thickness, having a exponential influence. The trough center-to-center distance has the second greatest influence on the damage, this can be represented by a second order polynomial. The top trough width and crossbeam center-to-center account for a maximum influence of the damage number of 20% of the benchmark damage number. The influence of the other included parameters were small or negligible. The governing transversal location of detail 1A is, similarly to 1C, at the trough leg closest to the main girder.

The validation of the model shows a great difference in the difference in damage numbers obtained from version 2.0 of the ROK in comparison with version 1.4. Validation of the Goereese bridges therefore show damage numbers greater than 1 for the 2 aforementioned details. It is suggested to show extra attention to bridges designed with ROK version 1.4, or earlier versions, and to repair occurring cracks in a way that the local damage complies with the verification of ROK version 2.0. The parametric tool can play a useful part in this when expanded. Another future use case can be to support the goal of the Rijkswaterstaat of replacing the current labor-intensive fatigue calculation method with a table that outlines the dimensions of OSDs, by generating a large amount of data.