Fatigue damage evaluation of cutout details in steel bridges

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School of Engineering | Doctoral thesis (article-based) | Defence date: 2023-10-17
Degree programme
63 + app. 75
Aalto University publication series DOCTORAL THESES, 155/2023
Fatigue damage is one of the most common and dangerous damage types in steel bridges, and many bridges are facing the challenge of ageing and its subsequent hazard risks. For steel bridges, the fatigue-prone details can be generally classified into two categories, welded and unwelded details. For welded details, the mechanism of fatigue crack initiation can be attributed to the initial weld defect introduced by the welding process, while for the unwelded structural details, the primary reasons for the fatigue crack initiation are distinguishable compared to that of welded ones. Fatigue damages in typical orthotropic steel decks are mostly found at rib-to-deck joints, rib-to-floor beam connections, butt weld connections, etc. In rib-to-floor beam connections, though the fatigue cracks initiated at welded joints and cutouts are both extensively observed, the latter attracts less attention, and its fatigue evaluation method is still not yet clear. Therefore, in this dissertation, the fatigue damage evaluation of cutout is performed. The primary goal of the research is to evaluate the possibility of fatigue crack initiation, and this overarching goal is further divided into three sub-goals: to detect the fatigue crack initiation in its early stage, to find a reliable theoretical method that is consistent with the civil engineering practice for predicting their fatigue lives, and to numerically predict their fatigue lives. To achieve these subgoals, laboratory fatigue tests on notched specimens with notch radii that are used in real bridges were first conducted, and for some specimens, the surface roughness parameters were also measured during the fatigue test. The surface roughness evolutions during the fatigue load were obtained, and effective crack detection parameters were also found. The prediction of fatigue life using the theory of critical distance was conducted, and a new formulation of critical distance-fatigue life relationship was proposed and validated with experimental data. In the numerical modelling prediction for fatigue, a new SWT model-based algorithm for the fatigue crack initiation life prediction of notched details in the high-cycle fatigue regime was proposed by considering the cycle-by-cycle fatigue damage accumulation, and the damage model was implemented by employing the UDMGINI subroutine written with Fortran code. A good agreement between the predicted fatigue initiation life and experimental results was confirmed. This study yielded three main conclusions regarding the assessment of fatigue in cutout details within the high-cycle fatigue regime. Firstly, the statistical surface roughness parameters proved effective in detecting fatigue crack initiation. Secondly, a new logarithmic formulation of the critical distance-fatigue life relationship was proposed. Lastly, a new SWT model-based algorithm for the fatigue crack initiation life prediction of notched details in high-cycle fatigue regime was proposed. These three key findings can serve as a foundation for evaluating fatigue damage in cutout details and make significant contributions to bridge engineering.
Supervising professor
Lin, Weiwei, Prof., Aalto University, Department of Civil Engineering, Finland
Thesis advisor
Markou, Athanasios, Dr., Aalto University, Finland
fatigue life prediction, fatigue crack detection, theory of critical distance, surface roughness, numerical simulation
Other note
  • [Publication 1]: Hao, Rui; Lehto, Pauli; Lin, Weiwei. 2023. Critical distance-based fatigue life evaluation of blunt notch details in steel bridges. Journal of Constructional Steel Research, volume 201, pages 1-16. ISSN 0143-974X.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202301021064
    DOI: https://doi.org/10.1016/j.jcsr.2022.107738 View at publisher
  • [Publication 2]: Hao, Rui; Wen, Zongyi; Xin, Haohui; Lin, Weiwei. 2023. Fatigue life prediction of notched details using SWT model and LFEM-based approach. Materials, volume 16, pages 1-16.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202303222476
    DOI: https://doi.org/10.3390/ma16051942 View at publisher
  • [Publication 3]: Hao, Rui; Lin, Weiwei. Evolution of surface roughness of notched steel details under fatigue loading. Submitted for journal publication