This thesis investigates the optimization of steel weight and the Environmental Cost Indicator (ECI) in steel structures, addressing the significant contribution of materials and construction to global carbon emissions. Focusing on European office structures, which face high vacancy rates and substantial environmental impact, a parametric study is conducted on a 5-story, 30x30m steel office building. The study evaluates design choices, including column, beam, and composite beam spacings, cross-section selection, connection design, and stability systems.
A preliminary building is designed under consistent load conditions, followed by over 50 variants incorporating different stability systems, frame designs, and composite beam spacings. Analysis indicates that smaller column and beam spacings, along with larger composite beam spacings, optimize steel use and ECI costs. HEA sections for columns, IPE sections for beams, and CHS sections for diagrid braces and angled columns are identified as the most efficient.
The study also highlights that material use does not always correlate with ECI costs. Designs incorporating demountability initially increase steel use due to elastic design requirements but result in lower ECI costs over multiple lifecycles by enabling reuse of materials. Several diagrid designs, benefiting from lower ECI costs per kilogram of CHS sections, perform better than conventional and braced structures despite higher initial material use.
Demountability was a key focus, with bolted connections identified as essential for achieving demountability standards. The reuse potential of stability members varies significantly; unlike conventional designs, diagrid structures are tailor-made, making their reuse challenging for subsequent applications.
The findings are consolidated into a final design framework to guide engineers in optimizing steel use and ECI costs, providing a practical tool that reduces the need for extensive modelling. This research fills gaps in the literature by focusing on short structures and offering insights into efficient structural design practices.

In heavy lifting a paradoxical problem has arisen: A gantry is brought to life to omit the use of a large crane, because of spatial, durational, and monetary reasons. But, in order to assemble and disassemble the gantry, a large crane is needed. This thesis presents a solution to this paradoxical problem. The solution is a novel design that is able to (dis)assemble a gantry without a large crane.

The design is established via a set of requirements based on a case study, crane capacities, and ways of working in Mammoet. Best practice solutions were developed for the five stages from assembly to disassembly of a gantry. A selection of best practice solutions, based on the requirements, was put in a morphological chart. This chart generated seven concepts that were evaluated using a qualitative multi criteria analysis. The top three concepts had similar scores, therefore a second round of assessment was performed to decide on a final concept.

The final concept is a climbing frame. This frame consists of two climbing cages that are connected via two gantry beams. Each climbing frame is equipped with a hoisting system that is used to lift and roll the new MLS mast sections in place. The two towers that form the gantry will be erected simultaneously, with the total upper structure on top. Climbing will happen via the vertical moving frame. This frame is equipped with retractable pins that grab on to jack-up blocks that are present on the mast sections. The vertical moving frame can translate in vertical direction by means of winches that are connected to the climbing frame. It was required that the disassembly procedure happened using the same system as the assembly procedure. Disassembly would be impossible if the upper structure is still over the vessel. Therefore, after the gantry lifted the vessel, the gantry beams must split. To split the gantry beams, two cantilevering guidance beams are present. The climbing frame is designed such, that when the gantry is in its final position, the case study gantry design is established. The only difference is that the self-weight of the climbing frame is acting on the gantry. Meaning that solely the original top frame beams and the added self-weight are decisive in the validity of the gantry’s main purpose; lifting the vessel. This also means that the climbing frames are solely meant for climbing.

The validation of the final design follows from hand calculations and a finite element model made in SCIA Engineer. Fundamental design features, such as the climbing system, the MLS hoisting system, and skidding of the upper structure are designed and validated too.

Debatable elements of this research are the scope limitations like other duties of the assist crane or being a tailored solution for a Mammoet gantry. However, this design offers freedom in projects and the route to arrive at the design can be applied more broadly. The subjective nature of the qualitative multi criteria analysis, the assumptions made, and the preliminary design stage are debatable too. Therefore, it is recommended to investigate other solutions to the problem. Promising solutions according to this thesis are; a climbing crane, a climbing frame that climbs from the bottom, and a skidding system that translates the whole gantry. Also, all assumptions need to be investigated to be able to fabricate and use this design.

Nevertheless, a proof of concept can be concluded from this research. This self-erecting gantry system is able to (dis)assemble a gantry. Compared to the crawler crane that was needed to perform the critical lift for the case study gantry, this design saves roughly 2100 m2 of space. That is a reduction of 65%. Approximately €6,000,000.- is needed for the realization of this design. Meaning that during the ninth project the costs for the crawler crane are earned back. It is estimated that the erection of the gantry and the assembly of the climbing frame is comparable to the assembly of the crawler crane and the erection of the gantry. All in all, the design is a future proof solution that can conquer the never-ending need for cheaper and faster heavy lifting projects on dense locations.

Orthotropic steel decks (OSDs) are commonly used in bridge construction due to their material efficiency and strength. However, fatigue issues in welded joints remain a concern. Fatigue cracks often occur due to high stress concentrations, especially under heavy traffic loads. Current approaches of determining damage in a bridge are limited by the computational demands of Finite Element (FE) models to calculate stresses and the complexity of the fatigue verification. Consequently, there has been limited exploration of parametric optimization for OSDs. This research seeks to address this gap by developing a parametric model to assess the fatigue performance of OSDs according to the ROK version 2.0, the new Dutch Guideline, additionally focusing on identifying the influence of key design parameters through a parameter sensitivity analysis (PSA). This study aims to provide insights for optimizing OSDs to enhance fatigue resistance and design. Thereby aiming to increase material efficiency about OSDs and creating a parametric framework to determine damage in an OSD.

This resulted in the following research question: How can a parametric model be developed to assess the fatigue performance of Orthotropic Steel Deck bridges and what insights can be gained from analyzing the influence of key design parameters?

To answer this question, in part 1 a literature study is performed. This began by reviewing the theory of the OSD’s and fatigue, identifying the critical fatigue parameters which were expected to influence the incorporated directly ridden details. Furthermore, the Dutch regulations and state-of-the-art about automatizing of fatigue verifications were explored, after which a parametric model is developed.

Part 2 began by developing this model. Simplifications in the mesh and loading scheme are tested and applied to ensure the model is fast and sufficiently accurate. Utilizing various mesh sizes in different regions helps to reduce computation time by almost 300% while maintaining accuracy. Additionally incorporating symmetry in the loading scheme further reduces the computational time by about 127%. With this model, the first part of the main research question is answered. The model is used to find the governing details in the bridge within the design domain of the ROK [2]. The governing details are: the crack initiating at the weld toe located at the intersection of the trough and the deckplate, and the crack initiating at the weld root located at the intersection between the deckplate, trough and crossbeam. Which are respectively detail 1A and 1C of the ROK[2]. After this, a benchmark model is found to start the PSA and a sensitivity analysis is conducted for these previously mentioned details by systematically altering one parameter at a time (OAT).

Results of the PSA are distinguished for the two aforementioned details. For detail 1C, the deckplate thickness and trough top width influence the damage of the detail primarily, represented by respectively an exponential function and second order polynomial. The crossbeam thickness influences the damage by maximally 30% of the damage number of the benchmark, while this parameter is not included in the analytical solution. Other included parameters show small or negligible influence on the damage of detail 1C. The governing load position within the design domain is the transversal load distribution exactly above the middle of a trough. Furthermore, a difference in stiffness exists between two trough legs of the same
trough for detail 1C, significantly influencing the damage. The governing transversal location of detail 1C is at the trough leg closest to the main girder.

For detail 1A, by far the most influential parameter on the damage of this detail is the deckplate thickness, having a exponential influence. The trough center-to-center distance has the second greatest influence on the damage, this can be represented by a second order polynomial. The top trough width and crossbeam center-to-center account for a maximum influence of the damage number of 20% of the benchmark damage number. The influence of the other included parameters were small or negligible. The governing transversal location of detail 1A is, similarly to 1C, at the trough leg closest to the main girder.

The validation of the model shows a great difference in the difference in damage numbers obtained from version 2.0 of the ROK in comparison with version 1.4. Validation of the Goereese bridges therefore show damage numbers greater than 1 for the 2 aforementioned details. It is suggested to show extra attention to bridges designed with ROK version 1.4, or earlier versions, and to repair occurring cracks in a way that the local damage complies with the verification of ROK version 2.0. The parametric tool can play a useful part in this when expanded. Another future use case can be to support the goal of the Rijkswaterstaat of replacing the current labor-intensive fatigue calculation method with a table that outlines the dimensions of OSDs, by generating a large amount of data.

The increase in demand for renewable energy has resulted in higher demand for wind energy. To meet this requirement, the wind turbine sizes are increasing rapidly, and this results in increasing load on the connections between MP-TP and the segments of the tower.
This research focuses on traditional L-flange connection and novel C1 wedge connection, former the most widely used in the offshore industry and other being new to the offshore industry. The objective of this thesis is to evaluate the limits of the L-flange and C1 wedge connection. The design of the L-flange connection carried out on the basis of Petersen’s theory[1]. It is designed to have higher ULS resistance with steel mass as low as possible. This analytical designed is then compared to finite element analysis (FEA). Previous study of Cheng[2] is used to validate the setup and methodology for FEM in Ansys.
For the same overturning moment, C1 wedge connection is designed using the design tool provided by C1 Connections. The design check for flanges is carried out. The design is then compared to finite element analysis (FEA). Fatigue limit state was verified for both the connections.
Based on the study, the following conclusions are made. Firstly, L-flange connection has around 30% higher ULS resistance compared to design overturning moment of 609MNm whereas C1 wedge connection has 55% higher ULS resistance. Secondly, L-flange connection has higher meridional deformation at the same elevation in the shell as compared to C1 wedge connection. The gap opening at the interface of the flanges is studied and it is observed that C1 wedge connection opens after the loss of contact force at the interface which is generated more efficiently through the pretension of stud whereas L-flange connection being an eccentric connection starts opening without full loss of contact force at the interface and the secondary path of load transfer is activated. This results in the lower meridional rigidity provided by the L-flange connection as compared to the C1 wedge connection. Lastly, C1 wedge connection provided an opportunity for several optimizations to have the same ULS resistance as that of L-flange connection. The mass of steel reduced for these optimizations. The L-flange connection weighed 53.72 tonnes for both ULS and FLS criterion whereas C1 wedge connection weights 20.8 tonnes for ULS criterion and 28.8 tonnes for FLS criterion.