Concrete and Steel are the materials with the largest market share in the construction industry and have been for a long time. With environmental awareness increasing, timber is regaining popularity due to the potential for carbon neutral and even carbon negative construction. Use of structural wood elements in bridges, however, is often limited to foot- and cycle bridges. In this thesis, key aspects with regards to the design of heavy traffic bridges incorporating timber members are identified. A fully steel bridge and an equivalent bridge, combining timber members with steel are designed within boundaries set by a case study. These designs are developed to a level sufficient for an adequate comparison of the bridges. The basis on which the bridges are compared are laid out, followed by the conditions the bridges are subjected to. These are based on typical conditions found in an urban Dutch environment. Analytic equations are automated, by way of python scripts, for the analysis and optimization of the steel bridge longitudinal dimensions under simplified ULS loading. After the optimization is complete, these initial bridge dimensions are verified with a 2D plate element model in SCIA engineer. The full loading for the bridge during utilization, save for accidental loading, is then modelled and the bridge dimensions are adapted in order to meet ULS, SLS, and fatigue conditions. Several potential versions of a bridge with timber members are considered. Following this, a bridge with a mostly timber superstructure, supported by a self-anchored cable system is further worked out. For this, a SCIA model, with 1D elements and subjected to the same loads as its steel counterpart, is produced. The incompatible combination of 1D elements, thick cross sections, and surface loads is addressed by the use of connector elements (“dummy members”) and individual load panels per member. After the global optimization of the bridge dimensions with regards to ULS and SLS, the connections are designed with a combination of detail 2D element FE models and analytic equations. The forces and support conditions of the connections follow from the global bridge design. A fatigue check is then run on the timber members of the bridge. Subsequently, the durability and eco- costs of the bridges are computed. The data for the durability estimation of the steel bridge is based on experience within IV- Infra and the durability of the timber bridge is estimated using the RISE factor method. The eco- costs of the bridges are computed using the IDEMAT database. The results from the analyses are discussed based on this. Finally, aspects of relevance in the design of timber bridges are synthesized and recommendations for the application of bridges and further research are given.

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.

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.