In the Netherlands there are many waterways where bridges or locks are situated within the navigation way of inland waterway vessels. To protect these civil structures from potential collision risks, protection structures are placed around them. In this research, a commonly used protection structure, the steel piled fender structure, is analyzed under impact events, followed by a comparison with the design methodology prescribed in the Dutch codes. In the Netherlands, design guidance is provided by the "Richtlijnen Ontwerp Kunstwerken", abbreviated as ROK. The ROK adopts a design formula for the required energy absorption capacity of fender structures from the EAU 2012. By applying the principle of work, the required energy absorption capacity can be converted into an equivalent static load that incorporates dynamic effects. This allows the soil-fender structure system to be designed using static analysis.

In this research, a triangular-shaped fender structure with fixed geometrical properties is examined. Additionally, the bow structure of a CEMT class IV ship is included to capture the interaction between the ship and the fender structure during impact events. The aim of this study is to obtain a transient response of the system, investigate the interaction between the ship, soil, and fender structure during dynamic impact events, and evaluate this against the design methodology prescribed in the Dutch codes.

To determine the transient response, two different models are developed. A simplified dynamic model based on linear beam theory is constructed. In this model, the problem is reduced to two-dimensional space, where the fender structure is modeled as a 2D frame partially supported by linear elastic foundations representing the surrounding soil. The ship's bow structure is simplified as a mass-spring system attached to the frame structure. Furthermore, a non-linear finite element model (NLFE) is developed in three-dimensional space. The NLFE model includes the full geometry of the fender structure of interest, with the ship's bow structure modeled up to the most frontal bulkhead, and the soil is represented by a series of non-linear discrete springs.

Before performing NLFE impact simulations that account for the full interaction between the ship, soil, and fender structure, an extensive sensitivity study was conducted on the individual models, showing expected behavior. Impact simulations performed during the sensitivity study were used to set up the impact configuration for the final head-on and oblique impact simulations, in which the ship, soil, and fender structure behave flexible simultaneously, allowing full interaction.

A comparison between the simplified model and the head-on impact simulation from the NLFE model revealed different peak responses. The response of the NLFE model was dominated by significant plastic deformations, resulting in larger peak displacements compared to the simplified model. However, during the initial stage of impact loading, dominated by elastic deformations, both models showed good agreement.

Finally, NLFE simulation results are compared to the design methodology prescribed in the Dutch codes. The energy absorption observed in the fender-soil system from the NLFE simulations is compared to the required energy absorption capacity according to the codes. For the head-on impact scenario, significant crushing of the ship's bow led to reduced energy absorption by the fender-soil system. In the oblique impact simulation, the NLFE model predicted higher energy absorption by the fender-soil system compared to the code requirements. There are numerous differences in modelling assumptions between the NLFE model and the method prescribed in the codes. Moreover, the NLFE model includes simplifications of the real-world problem that may lead to an overestimation of the absorbed energy by the fender-soil system. Therefore, extending the NLFE model by removing simplifying assumptions remains highly recommended.

Welded details in orthotropic steel decks (OSD) are susceptible to fatigue cracks which are caused by local weld defects, geometric stress concentrations and residual tensile stresses. Residual tensile stresses are formed during the welding process and the distribution depends on many factors. Knowledge about the residual stress distribution is required for accurate fatigue assessment. The rib-to-crossbeam detail in the design of the new Schipholbridge does not meet the fatigue requirements according to Eurocode 3 when using a reasonable geometry. Therefore, high frequency mechanical impact (HFMI) post weld treatment will be used to improve fatigue resistance. Incorporating the residual stress distribution in fatigue life prediction models will improve their accuracy, which can lead to more favorable results which can avoid the use of HFMI. The main objective of this master thesis is to determine the accuracy of a subsequently coupled thermo-mechanical finite-element model which predicts welding induced residual stresses in a segment of an OSD. The fatigue life prediction is not included in the scope of this thesis. The accuracy of the model was determined by comparing temperature
and distortions with experimental data from three specimens consisting of a 900x400mm deck plate, a 350mm deep trapezoidal stiffener and a 600x15mm crossbeam web with a Haibach cope hole. During the welding, temperatures were recorded by a FLIR© E96 thermal camera. Welding distortions were obtained by subtracting the geometry before welding from the geometry after welding. The 3D
geometry was obtained by the Artec© LEO scanner. The scans were post processed in Artec© studio software and data was extracted by the NumPy-stl package in Python. The predicted temperature distribution and deformations corresponded well to experimental results. The maximum deviation in the
temperature distribution 1.8s after welding was 67 °C and occurred at the last position of the welding torch. The maximum deviation between predicted and measured upward displacements of the deck plate 10mm from the edge was 0.2mm, with smaller deviations on average. Due to the good correspondence
of experimental and numerical results, residual stresses were presented. On the deck plate in longitudinal direction, tensile stresses of yield strength magnitude were obtained after unclamping. At the rib-to-crossbeam connection, the stress in the direction perpendicular to the weld toe at the location of the weld toe was equal to the yield strength after unclamping. The stresses quasi-linearly go to zero through the thickness of the rib.

In the course of this thesis, a research has been conducted to the application of fracture mechanics on an othotropic steel deck (OSD). Obtaining accurate predictions of crack path and fatigue life assessment were the main objectives for this thesis. As 3D crack propagation modelling in orthotropic steel decks is an arduous task, simpler studies were examined first in order to obtain confidence for the task at hand. These studies are comprised of a through thickness crack in an asymmetrical four point bending specimen and a semi-elliptical crack in a centre cracked plate. Furthermore, studies on computational fracture mechanics and the integration of Python scripting language with Abaqus were conducted for numerical analysis of crack propagation in complex structures. The extended finite element method was used for evaluation of contour integrals of a crack with a constant mesh throughout the propagation analysis. Post-treatment of the results was applied by smoothing stress intensity factors and the shape of the crack front. Moreover, inaccurate contour integral results were excluded from analysis through extrapolation. A Python code was developed for updating the crack front for a given number of loading cycles integrated in Paris' law. The investigated crack was located at the rib-to-crossbeam joint of an OSD. Here, crack propagation occurs along the lower weld toe and in the longitudinal direction of the rib. Validation of results was obtained through experimental studies conducted at the TU Delft laboratory. The weld geometry was incorporated in the model from measurements in order to identify local stresses. Finally, results of strain gauges were used to validate the model. Measurements of the experimental crack growth were obtained at the surface of the crack only. Consequently, assumptions were made of both the depth and shape of the crack in the thickness direction of the rib. A semi-elliptical crack shape was selected with an initial crack depth of 1 mm. Initially, Paris law parameters C and m were selected as recommended by BS7910. The numerical results of crack path complied with those of experimental results, with deviations of no more than 1 mm. Both data sets show that the propagation rate remained somewhat constant. On the other hand, fatigue life assessment results showed stronger deviation. A parametric study was performed to investigate the effect of the initial crack depth. Three different cases were examined for which the initial crack depths were selected as 1, 2 and 3 mm. Varying the initial crack depth did not lead to a significant change in crack path at the surface of the rib, while the depth in the thickness direction was affected. Regarding the fatigue life assessment, the results with respect to an initial crack depth of 1 mm, complied best with experimental results. Given the strong correlation between experimental and numerical results, the methodology followed in this thesis has proven valuable regarding fatigue crack modelling. As the methodology is based on fracture mechanics, an initial crack is required prior to evaluation. Consequently, the application in engineering practices lies in re-evaluation of structures. Moreover, as the parameters in crack propagation relations have a significant influence on the fatigue life assessment, these should be carefully chosen. Therefore, more insights must be obtained regarding the selection of such parameters.