Steel Orthotropic Bridge Decks (OBDs) are widely used in long-span and movable bridges. Fatigue resistance analysis plays an important role in the design or assessment of OBDs. One possible fatigue failure is the crack initiating from the weld root of stiffener-to-deck plate connections at crossbeams. A full-scale experimental investigation in this study using a 20 mm thick deck plate with a dimension of 9.4 m × 5.1 m, including three crossbeams, represents the modern designed OBDs. The experiments show an arrest of crack propagation with a final crack depth of approximately 75% of the deck plate thickness. On the contrary, through thickness cracks develop in deck plates of 10 or 12 mm. Hot spot stress based fatigue detail categories (DC) using various failure criteria derived from the tests. Analysis with the effective notch stress shows that the DC has low sensitivity to the amount of weld penetration. The results of analyses with the eXtended Finite Element Method (XFEM), employed to analyse the fatigue crack propagation path and crack arrest, are in line with the experimental study.

The welding process induces residual stresses because of the non-uniform heating and cooling of the material. Residual stresses are known to influence fatigue crack growth. However, studies addressing both the formation of residual stress – giving a realistic multi-directional stress and strain field – and redistribution of residual stresses due to crack growth in the case of a surface crack have not been found. The extended finite element method was employed in this study to evaluate the stress intensity factors of a planar, growing crack in a welded T-joint with and without welding induced residual stresses. The initial residual stress field was taken from a welding simulation using the finite element method. The redistribution of the residual stress field due to crack growth was studied in addition to the shape and growth rate of the planar crack. The study shows that, in agreement with experimental evidence, the external stress ratio has a significant influence in the absence of residual stress but it does not have a significant influence in the presence of residual stress. The current study gives insight into the cause of this observation.

Fatigue cracks in the stiffener-to-deck plate connections of orthotropic bridge decks, initiating from the weld toe or root and propagating into the stiffener or weld throat, are experimentally and numerically studied. A statistical analysis of the structural stress is carried out using the experimental data. Automatic welded specimens show a significantly higher fatigue resistance than manual welded ones for both details of the study. Including results in the literature, the characteristic fatigue resistances appear larger than the values in current standards and range between 100 and 160 MPa. A proposal for the fatigue resistance values is given for design purposes. The effective notch stress, averaged strain energy density factor, and fracture mechanics methods are employed to study the sensitivity of the weld toe and root cracks for different (geometrical) variations, such as the lack of weld penetration. Among them, the fracture mechanics method agrees best with the experimental data. With the increase of weld penetration ratios from 75% to 100%, the fracture mechanics predicted fatigue resistances remain approximately equal for the weld toe cracks and increase for the weld root cracks.

This study derives the fatigue resistance of welded details in orthotropic decks using structural stress (hot-spot stress where possible) based on tests described in literature and tests by the authors. The data are supported with linear elastic fracture mechanics simulations. Details covered are the rib to deck weld, the crossbeam to deck weld and the deck butt weld. High fatigue resistances are found, caused by favourable loading modes (bending and compression) and reduced driving force with the growth of cracks. The technical specification TS 1993-1-901, part of the new generation of Eurocodes, is based on the results of this study.

The failure assessment line (FAL) describes the interaction between plastic failure and fracture of flawed steel components subjected to tension or bending. This paper quantifies the model uncertainty of the FAL as provided in the internationally used British Standard BS 7910:2019 by comparing the assessment with the actual failure load of 82 wide plate and 4 tubular joint tests. In line with findings of others, it is demonstrated that the accuracy of the assessment is significantly improved if the crack tip constraint is considered in the assessment. Irrespective of this crack tip constraint consideration, a non-negligible number of wide plate tests has a lower failure load than the one predicted by the FAL in BS 7910:2019, if based on three fracture toughness tests. A penalty or safety margin on the FAL is advocated to compensate for this. It appears advantageous to base the assessment on the average instead of the minimum of three equivalent fracture mechanics tests together with an associated (quantified) safety margin.

A numerical model for corrosion pit propagation under mechanical loading is presented. The level set method is used for corrosion front tracking and also enables the domain to be split into a solid and a pit domain. In the pit the diffusion of atoms originating from the dissolution process occurring at the pit front is simulated. The model is capable of automatically capturing lacy cover formation due to the inclusion of activation control, diffusion control, and passivation. In the solid static equilibrium is solved to obtain strains and stresses. A parameter, dependent on the signs of the plastic strain increment and the back stress, is introduced to define the influence of plasticity on the corrosion rate. The model is used to study pit growth under electrochemical and mechanical loading. Under activation control combined with an elastic material response, pits propagate faster under constant loading than under cyclic loading. When plastic deformation occurs, cyclic loading can significantly increase the pit growth rate. Increasing the cyclic load frequency results in faster propagation due to kinematic hardening. Under diffusion control, mechanical loading does not influence the pit growth rate, given that the salt layer leading to diffusion control remains intact.

This study presents calibration and validation of a cohesive extended finite element model for fatigue crack propagation in ductile materials. The approach relies on a separation between plasticity around the crack tip and fatigue crack growth at the crack tip such that the influence of plasticity on fatigue driving forces is predicted. This implies that characterization of crack growth requires effective Paris parameters. It is shown that the calibrated model can capture fatigue crack growth behaviour in ductile materials for in-phase and out-of-phase biaxial fatigue loading as well as in-phase biaxial loading with an overload.

A probabilistic model is developed to investigate the crack growth development in welded details of orthotropic bridge decks. Bridge decks may contain many of these vulnerable details and bridge reliability cannot always be guaranteed upon the attainment of a critical crack. Therefore, insight into the crack growth development is crucial in guaranteeing bridge reliability and scheduling efficient maintenance schemes. The probabilistic nature of the crack growth development model and the dependence of this model on many interdependent random variables result in significant uncertainties regarding model outcome. To reduce some of these uncertainties, the probabilistic model is combined with a monitoring system installed on a part of the bridge. In addition, a Bayesian network is used to determine the dependence structure between the different details (monitored and non-monitored) of the bridge. This dependence structure enables us to make more accurate crack growth predictions for all details of the bridge while monitoring only a limited number of those details and updating the remaining uncertainties.