This thesis explores how slender plates can be reinforced with stiffeners to improve their stability, and how new manufacturing methods can lead to more efficient designs. Traditional stiffeners are often simple in geometry, which limits their structural efficiency. With Wire Arc Additive Manufacturing (WAAM), however, it becomes possible to produce complex shapes that may perform better. The research combines experiments, numerical simulations, and optimization studies. Plates with WAAM stiffeners were manufactured and tested alongside plates with conventional rectangular stiffeners. Numerical models were developed and validated against the experimental results, including the influence of imperfections and residual stresses. Different initial stiffener shape models were then used in a topology optimization process to design further improved stiffener geometries. The results indicate that the numerical models of the WAAM stiffeners can replicate the experimental performance, considering the restricted number of specimens utilized in the tests. However, the models of the plates employing prismatic rectangular stiffeners demonstrated reduced compliance with the experimental results. New initial stiffener geometries underwent topological optimization and showed performance comparable to that of conventional prismatic stiffeners of equivalent volume, thus lacking any advantages. The study highlights both the opportunities and challenges of using WAAM in structural applications and provides recommendations for future research. ... Read more

This thesis presents the optimization of chord-bracing connections (tubular joints) in lattice boom structures using Wire Arc Additive Manufacturing (WAAM). The research aims to enhance the static and fatigue performance of critical joints, with a focus on the 1600mt LEC crane boom, which is used for offshore wind turbine installation. Through the integration of topology optimization and WAAM, the study seeks to improve structural efficiency by optimizing weld geometry and material distribution.
Finite Element Analysis (FEA) was employed to identify high-stress regions within the tubular joints, followed by topology optimization to refine their design. The study also investigates the impact of WAAM on material efficiency, fabrication flexibility, and the overall mechanical properties of the joints. The results demonstrate that the optimized tubular joints exhibit significant improvements in fatigue life and static strength compared to traditional designs, providing a more robust and cost-effective solution for lattice boom applications.
The findings of this research contribute to advancing the use of additive manufacturing in structural engineering, particularly in enhancing the performance and sustainability of offshore crane systems. The proposed optimization framework and design methodologies offer valuable insights for future applications of WAAM in heavy-duty structural components. ... Read more

Wire and Arc Additive Manufacturing (WAAM) enables large-scale steel fabrication but often produces rough surfaces that are detrimental under cyclic loading. This thesis investigates how surface finish affects the fatigue performance of WAAM AM70, a high-strength steel comparable to S690, through strain-controlled low-cycle fatigue (LCF) and stress-controlled high-cycle fatigue (HCF) tests. As-built and machined specimens were compared, revealing surface finish as the dominant fatigue driver. Machining increased fatigue strength by factors of 3–9 and reduced scatter. The study provides EN 1990:2023-compliant design curves and mechanistic insight, showing that machined WAAM AM70 achieves fatigue performance approaching conventional S690. ... Read more

The aim of this project is to benchmark the outcomes of a detailed performance based analysis using CFD and LS-DYNA software against codified methods used more generally on projects, and in particular to demonstrate whether this leads to an increase in the predicted capacity of the bridge under fire loading. The effect and influence of different parameters on the fire resistivity have been investigated. These are the location of the fire, the influence of different live loads, the influence of imperfections, the effect of wind fire interplay, and the effect of internal radiation between surfaces within a structural section. This research shows that doing a detailed thermal structural analysis of fire on a steel bridge can indeed lead to material savings. Performance based analyses show that the bridge does not fail for the considered fire scenarios for at least 30 minutes. When applying temperatures based on Eurocode, failure is reached after 15 minutes. Using a detailed FEM model to determine critical temperature results in four times less protection necessary than when the conservative Eurocode limit of 350 °C limit is used, a critical temperature of approximately 600 °C is found for the case study. ... Read more

Due to the transition towards a circular economy, sustainable design strategies are growing in importance. An example of such a strategy is IFD: Industrial, Flexible and Demountable design. This design strategy has been developed recently and focuses on modular designs that can be changed in shape and whose components can be demounted and reused. This thesis aims to investigate how the principles of IFD can be applied in the design of a sustainable superstructure for an overpass. The goal is to assess which structural system is best for use in a sustainable IFD overpass and to determine how the overpass can be converted into a modular overpass by focusing on connections and module dimensions. To demonstrate the potential of the IFD design, the sustainability benefits of the overpass are evaluated.

Through a review of literature on IFD and similar design strategies, guidelines were formulated that are relevant for overpasses. Based on the guidelines, designs for three structural systems were developed using a preliminary design approach. These designs were assessed on their environmental impact and compliance with IFD principles, using an Environmental Cost Indicator and Multi-Criteria Assessment respectively. Due to its good behaviour on both aspects, the Composite alternative was found to be the best.
Then, a literature study on the connections was performed to investigate the different options. The number of relevant shear connectors was reduced to four by considering the tolerances for assembly and the protrusion of connectors from the main elements of the structure. A finite-element model was made to evaluate the effects of the four different shear connectors on the structural behaviour. To be able to use the connectors in the model, an elastic limit was imposed to ensure demountability and reusability; small adjustments were made on the reported behaviour of the connectors using a parametric study. From the four remaining connectors, the Embedded Coupler Device connection without injected resin was found to be the most favourable, due to it requiring the lowest number of connectors in the serviceability limit state. For the steel girder connection, a shear-loaded bolted connection was proposed; shear keys were found to be a good solution for the deck connection. Moreover, module dimensions were determined based on sustainability considerations and IFD principles, leading to the final design.

The proposed design shows that IFD principles can successfully be applied to come to a design for an overpass. The use of a small selection of modular elements and demountable connections creates a flexible design, which complies with all the IFD principles. By application of a structural system with a low environmental impact, sustainability of the design is also accounted for.

The IFD design is competitive in situations where the overpass is extended or when it is disassembled and reassembled, since for these scenarios it ends up with the lowest overall environmental impact. This leads to the recommendation to use IFD design in situations where flexibility and reusability are advantageous.
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In the report the plate buckling verification for stiffened plates subjected to combinations of biaxial in-plane normal stress, in-plane shear stress and out-of-plane loads is performed based on Eurocodes and relevant literature. A normative panel is selected from the structure to go through the calculations step-by-step. As not much literature or information is available for the combination of in-plane stress and out-of-plane load, the main objective is to develop a reliable verification analysis for this load combination.

It was found that by combining the reduced stress method as given in EN-1993-1-5 and the simplified design method as given in EN-1993-1-7 (section 5.2.3.4) for the combination of in-plane stress and out-of-plane load, a verification is possible.

The obtained results were compared to the unity checks given by another design code (DNV-RP-C201) that has a validated design approach for this load combination for stiffened plates. The results showed large similarities in unity checks found for plates subjected to longitudinal in-plane normal stress and out-of-plane loads. In cases with high values of shear stress and for large plate thicknesses, the results for the unity check for out-of-plane loads showed less similarity.

It was recommended to perform the verification of panels subjected a combination of in-plane longitudinal normal stress, in-plane shear stress and out-of-plane loads according to the standard verification analysis given in EN-1993-1-5 (reduced stress method) and EN-1993-1-7 (simplified design method, section 5.2.3.4). For plates subjected to combinations of biaxial in-plane normal stress, in-plane shear stress and out of plane loads, it is recommended to verify the stiffeners according to EN-1993-1-5 section 9, and to check the local buckling according to the reduced stress method, as the local buckling should be normative in case the stiffeners comply with section EN-1993-1-5 section 9. ... Read more

An investigation into the application of additive manufacturing to the production of structural joints was conducted for this thesis. The main goal was to determine all necessary aspects that someone needs to consider when designing a structural part that is intended to be printed with additive manufacturing. As an example, the branched column connection was selected due to its inherent limitations, which can be effectively addressed through the integration of additive manufacturing techniques.
Within the construction realm, wire arc additive manufacturing (WAAM) stands out as particularly advantageous due to its ability to yield high mechanical properties comparable to conventionally manufactured materials, coupled with a high deposition rate. As with any manufacturing process, WAAM operates within certain constraints dictating the types of objects feasible for production.
To ensure compatibility with WAAM while achieving desired structural and aesthetic benchmarks, three laboratory tests were conducted. These tests scrutinized the impact of input process parameters, overhang, and overlapping on the quality of the build. Factors such as travel speed, wire feed speed, voltage, and current were examined for their influence on welding bead dimensions and quality. Additionally, an investigation into how the percentage of overlap affected print quality was done. Among the constraints, the most pivotal one was the overhang limitation, determining the minimum allowed overhang angle in perpendicular and parallel directions depending on the direction of the print.
The primary objective in designing the connection was to reduce the necessary material for the branched column connection’s manufacture. Topology optimization (TO) played a crucial role in achieving this goal. Various models were constructed, each differing in TO input parameters to find the model with the lowest required mass while maintaining adequate structural performance. These models varied based on TO objectives (equivalent von Mises stress, compliance, mass, and volume) and TO constraints (either mass retain percentage or maximum stress), while also integrating manufacturing constraints obtained from lab tests. Ultimately, the model that offered the lowest mass and satisfactory structural performance focused on compliance as its objective, while retaining 15% of its initial mass.
Based on the above explained research a design guideline could be proposed and includes all necessary steps and considerations that someone needs to take into account when designing a connection manufactured with WAAM. The steps of the guideline include: 1. Selection of additive manufacturing process; 2. Material selection; 3. Determination of additive manufacturing process manufacturing limitations; 4. Design phase including TO with the proposed input parameters.
In illustrating the advantages and limitations of WAAM in the construction industry and proposed design guideline, a case study involving a comparative analysis between a steel plate and a WAAM branch column connection was done. This study centered on the real life project, 6 Bevis Marks in London. The findings showcased a notable reduction in the required material. However, the limitations of this approach were apparent in the increased manufacturing time and costs. ... Read more

Plated girders have been extensively used in steel bridge construction since the 19th century. Over the past century, the effective width method was developed to take the nonlinearities resulting from shear lag and plate buckling into account. This method leads to having a cross-section with a reduced area in which the stress can linear be considered. The section properties of the reduced cross-section can be used for determining the resistance and the longitudinal stress in the plated girder. The reduction of the cross-section area takes place in two steps. First, the section area is reduced in local scale for subpanels that have class 4, and local effective section properties will be determined. Second, the local effective cross-section is reduced to consider the overall buckling, which can be plate-like buckling, column-like buckling, or their interaction.
The longitudinal compressive stress that can be determined from effective section properties in a box girder with pure bending moment will be higher since the effective section includes a reduced second moment of inertia and an increased distance between the neutral line and the compression flange. This master thesis aims to assess whether effective section properties accurately determine the compression stress magnitude in box sections with pure bending moment that remain unaffected by local buckling and experience overall buckling in the form of pure column-like buckling in the compression flange.
The findings indicate that if the subpanels of the isolated compression plate are stocky, and the overall buckling failure has the form of pure column-like buckling, the stress, and behavior remain within the elastic region up to column-like buckling failure. There does not exist any sudden increase in compression stress magnitude in the plate. The analytical method that can address the maximum magnitude of the compression stress in the plate has contribution of the gross section area of the plate.
If such a stiffened plate with pure column-like buckling failure and stocky subpanels serves as the compression flange of a box girder, the same conclusion was reached regarding determining the first moment of inertia. However, in the presence of the slender web in the cross-section, the effective area of the web, in combination with the gross section area of compression flange should be considered for determining the section properties with which the maximum longitudinal stress can be determined. ... Read more