In light of the growing impact of the production of construction materials, the imperative for sustainable design is considered a necessity. Newly developed design strategies and design for deconstruction offer great potential and perspective to achieve the sustainability goals that are set in the European Commission’s ”Green Deal” towards net zero greenhouse gas emissions by 2050. Demountable and reusable steel-concrete composite structures allow for the opportunity to contribute to these sustainability goals. Demountability in steel-concrete composites is generally offered through the application of demountable shear connectors. Multiple studies have investigated the performance of various shear bolt connectors. Shear connectors generally showed inferior structural performance compared to that of conventional welded shear studs. Throughout the years, there has been significant advancement in the practice of reusing structural steel elements in the construction industry. Conversely, the exploration of re-purposing concrete from existing structures for structural use has not been extensively investigated. In response to this growing emphasis, reusing concrete slabs appears to be a sophisticated and innovative strategy. To enable deconstruction and reuse practices in such steel-concrete composite structures, bolted connections are considered a key characteristic in establishing the incentive. To maintain the strength characteristics of conventional shear studs in composite beams, demountability of a steel-concrete floor system can be offered through a concrete deck-to-deck connection between the composite beam and concrete slab. However, there exists a scarcity of solutions for connecting concrete slabs through demountable shear connectors, limiting comprehension on the structural behaviour and performance on true floor level. This thesis presents two numerical finite element models, the first of which is a simplified deck-to-deck connection subjected to tensile loading conditions to determine basic characteristics and behaviour. The knowledge gained from the first model is implemented in the secondary finite element model, comprising a demountable floor system which is compared with a traditional conventional floor system. A subsequent parametric study focused on altering bolt spacing, edge distance and span width to allow for a broader perspective on the performance of the proposed demountable floor system. The numerical results showed that the demountable beam model is able to replicate the behaviour of the conventional beam system, where local plastic deformation of the connecting elements was hardly observed. The numerical results demonstrated that the serviceability loading capacity of the demountable floor system was 3% lower, and the discrepancy in ultimate loading resistance was magnified further. The parametric study indicated that modifications to the distance of the bolts from the edge of the slab and bolt spacing did not show a shift in the ultimate loading resistance and ductility. Increasing the span width of the demountable slab model indicated a gradual reduction of approximately 24% in load carrying capacity, where the ductility was not affected. While future research into the reliability and validity of the numerical results is considered necessary, the proposed solution for connecting concrete slabs has shown significant potential in terms of replicating the structural behaviour of conventional floor systems, without compromising the structural integrity. The solution demonstrated the ability to develop a demountable and reusable floor system, thus contributing to an enhanced sustainable and circular built environment.

Multiple methods exist for simulating crack propagation in the finite element method (FEM). Among these, the extended finite element method (XFEM) shows great potential as it allows for the use of larger elements while maintaining accuracy and practicality. Within XFEM, the employment of traction separation laws (TSLs) is a promising approach to capture post-necking effects, which are typically predicted poorly with larger elements. These TSLs are often assumed to be constant along the crack length and are determined by fitting to experimental data.

However, it has been proven that necking and fracture both depend on the state of stress, expressed as stress triaxiality. It is also known that the stress triaxiality within the crack region varies as the crack progresses through a plate due to changing boundary conditions and crack blunting. Consequently, the necking behaviour ahead of the crack tip changes, necessitating multiple stress state-dependent TSLs along the crack length to capture this effect accurately.

In this thesis, a subroutine is developed to enable the use of multiple TSLs along an extending crack in Abaqus based on the stress triaxiality of each element. Additionally, the relationship between TSL parameters and stress triaxiality was determined by minimizing the difference between simulations and experimental data of a large-scale CCT experiment. With this relationship known, it is possible to account for the effect of the changing stress state when determining the TSLs.

The study finds that stress triaxiality-dependent TSLs produce a significantly better match with experimental results compared to a stress triaxiality invariant TSL. This underscores the importance of addressing stress-state dependency in TSL determination. The study also highlights that mesh size and material dependency on TSLs must be addressed so that these TSLs can be applied universally across different conditions.

This thesis introduces the Discontinuity-Enriched Finite Element Method (DE-FEM) for the modeling of dynamic multiple crack growth problems including branching and merging, as an alternative to eXtended/Generalized Finite Element Method (X/GFEM). DE-FEM differs from X/GFEM by placing the enriched degrees of freedom (DOFs) directly along the discontinuities, and the enrichment functions vanish at standard mesh nodes. This approach allows DE-FEM to preserve the physical meaning of standard mesh nodes and avoid the issues associated with blending elements. Moreover, by adding enrichment directly along the discontinuities, DE-FEM is more straightforward in computer implementation. These properties of DE-FEM facilitate its modeling of complex crack configurations such as the dynamic crack propagation problems with multiple cracks. Here we propose a scheme for dynamic multiple crack propagation using DE-FEM, which covers crack initiation, propagation, and interaction. Numerical examples are provided to validate the effectiveness of DE-FEM in capturing crack patterns that are similar to those observed in other studies. Meanwhile, the reasons for the numerical instabilities observed during crack propagation and methods to mitigate them are also discussed.

The first part of the thesis explores the process of homogenization, particularly for the permeability properties of rock samples. The Hill-Mandel postulate of energy consistency throughout the transitioning of scales is revisited since traditional homogenization methods rely on applying specific boundary conditions to enforce energy consistency. However, it is shown that the applied boundary conditions influence the effective physical parameter and provide upper or lower bound estimations. Recently, it is shown that these boundary conditions influence a layer near the boundary of the sample and that homogenization applied on the subsample away from this boundary layer is not affected by the boundary conditions.

The research focuses on energy consistency by studying the evolution of the energy within the intrinsic subsample, away from the boundaries. With the help of Finite Element simulations of Stokes-flow through idealized structures, the energy of the fluid is traced without the influences of grain properties on the energy dissipation. By plotting the ratio of the energy dissipation of the macro- and micro-scale, it is shown that the energy consistency is not found within small subsamples. Yet, with a growing subsample, energy consistency is achieved naturally, without the enforcement of boundary conditions. As a result, it is concluded that the energy consistency is found at the Representative Elementary Volume (REV), which is a similar requirement as for traditional homogenization methods. The study of the natural energy consistency in idealized microstructures is extended to real microstructures, which include more natural heterogeneities, such as grain properties. It is shown that energy consistency is also found with the natural heterogeneities included, albeit with a slower convergence.

For the homogenization of the permeability of a sample, the energy ratio is now known to be unitary, which can be used as an accurate indicator to determine the size of the REV.

The second part of the thesis explores the process of determining the size of the REV, which is a common, yet essential practice in Digital Rock Physics. Currently, this is an extensive exercise, involving many and large-size simulations to trace the convergence of the physical property and requires a lot of computational resources and time. Numerical-statistical studies have shown that the convergence of the REV visualizes in a cone-like shape. By plotting the convergence for both the permeability and the energy dissipation ratio for idealized microstructures, this study analyses the shape and evolution of the cone of convergence. From this, the generic evolution law of the convergence is determined.

It is shown that the asymmetrical convergence cone is described with a log-normal distribution, with a stable mean throughout the evolution of the cone and a variance for each sample size. The evolution of the variance is described with the law of large numbers, taking into account a reference value. This makes it possible to determine the size of the REV. Since the statistical method applies, information about the error of the fit, the error of the determined homogenized property, and the error of the size of the REV is provided.

The study is extended to real microstructures to validate whether the determined evolution law applies when natural heterogeneities are included. It is shown that the evolution law still accurately describes the REV's convergence. Therefore, the REV's size of real rock samples can also be determined. Even when the REV is not included within the sample, the evolution law can provide an estimate of the size of the REV or the homogenized property.

By using the cone of convergence, it is not necessary to run simulations on the full sample to find the REV, which is computationally expensive, instead running a number of simulations on small subsamples is sufficient, which saves both time and computational resources. It also unlocks the possibility to find the REV for high-resolution samples, as splitting the sample into subsamples allows for smaller simulations.

The aim of this thesis is to investigate and quantify the efficiency of high capacity self-stabilising modules in mid-rise residential buildings. These modules have a higher stabilising capacity than modules that are currently being used in the Netherlands and other countries and can therefore be used for more storeys without requiring an additional stabilising structure such as a concrete core.
In the first part, reference projects and case studies are looked at to get a good understanding of the current applications in The Netherlands and the United Kingdom. After analysing four case studies, an assessment is done on the functional efficiency, structural capacity and environmental impact of these modules. By doing so, the load-bearing structure of self-stabilising modules that can be used at a greater height can be identified. Design variants can now be drafted with different bracing configurations, which are later verified on strength and stability requirements. To effectively design a suitable braced frame, it has been researched what the displacement components for braced frames are. This has been done for simple frames without eccentricity as well as frames including eccentricity. Apart from single-cross frames with a relatively large span, double-cross frames are also looked into due to their increased stiffness.
As part of the total structure of the building, a design for the foundation as well as the inter-module joint, which is required to be demountable, has been made. These parts of the design are required to calculate the horizontal displacement during lateral loads.
A structural assessment is done on the stabilising capacity of each variant at 8 storeys. The design adjustments that are required to further increase the number of storeys up to 10 are looked into as to see whether or not an efficient structure can be maintained. It turns out that each design variant requires adjustments that reduces the efficiency. These changes are the result of a large increase of braced span, resulting in either inefficient use of beam profiles or a too large length when there is more than one braced span along the length.
Apart from a structural assessment, the functionality and environmental impact of the design variants has been analysed as part of the overall efficiency of the modules. The functional assessment includes several criteria such as wall-to-floor area and space efficiency factor. Using the required material use in partition structures and load bearing elements, the environmental impact is calculated, resulting in values for the embodied energy and embodied carbon per square meter in each design variant. Since the differences between the design variants are relatively small, they are also compared to four case studies that were done before.
On the basis of the results of this research, it can be concluded that self-stabilising modules can be constructed with different possible bracing layouts and an efficient load-bearing structure up to 8 storeys.

Cardiovascular disease has caused 3.9 million deaths in Europe and over 1.8 million deaths in the European Union, which accounts for 45\% of all deaths in Europe and 37\% of all death in the European Union in 2017. Cardiovascular disease is mainly caused by atherosclerosis. Atherosclerosis is a kind of disease where the inside of the artery gets narrow due to the build-up of plaque. Plaque is an abnormal accumulation of material in the inner layer of the arterial wall. A swelling can be formed by the accumulated material. The swelling may intrude into the channel of the artery wall, which will make the channel get narrower and restrict blood flow. Based on current medical technology, images of the plaques can be taken. However, there are no efficient simulation tools for plaque rupture. In order to set up sufficient simulation tools, a good representation of the material behaviour and the progression of the failure is needed. There are material models for the arterial wall accounting for large deformations (hyperelasticity) and anisotropy in the material response. And, there are also failure models. However, the material models and the failure models have not been combined. In this thesis, three material models and one failure model are included. The three material models are Neo-Hookean material model and two anisotropic models developed for arterial wall tissue developed by Holzapfel and Gasser. They are combined with anisotropic damage model to obtain three new constitutive models for failure of hyperelastic material. After the three constitutive models are set up, a parameter study is performed to explore the material properties of the new constitutive models. Verification of the material models is also included. Finally, the performance of the model is demonstrated with failure analyses on different geometries: a simple plane, a bar, a plane with an imperfection and a plane with a rectangular hole in the middle.

The aim of this thesis is to propose a simple technique to estimate the maximum impact forces acting on bridge piers in the event of ship collisions. This technique is determined for Dutch commercial inland waterway ships (CEMT classes) and set up to be applied by bridge engineers to determine the required bridge pier strength. Many collision events on bridge piers have occurred in history where some led to a major failure of the bridge deck due to insufficient strength of the bridge pier. The accuracy of the Dutch guideline on calculating these impact forces (ROK 1.4) is questioned, mainly regarding the generalisation of the guideline to different ship types. Therefore, an investigation on this topic has been initiated to provide more accuracy in the estimations on bridge pier impact forces in the event of ship collisions. A dynamic nonlinear finite element model has been created using ABAQUS/Explicit to simulate the ship-bridge pier collision event. The bridge pier is assumed to be rigid and fixed, while the ship structure is assumed to dissipate all initial kinetic energy through plastic deformation (crushing of the structure). Material properties have been obtained from a test database and include rate effects. It has been concluded that the numerical calculation model is verified as stable, and results are in agreement with existing calculation methods. Numerical simulations have been performed on one class IV and two class V ship's bow structures. A relationship between initial kinetic energy levels and maximum impact force has been developed based on the results of the numerical calculations. With the established expression, the estimated impact force can be calculated for the event of a ship collision, given an initial kinetic energy level involved in the collision event. Maximum impact force values have been presented for different ship classes using this expression. For ships smaller than a medium-sized ship (CEMT IV), the impact force values are higher than is found in the current Dutch guideline. However, lower impact forces are estimated for ships larger than this medium-sized ship. This difference mainly originate from the relatively stiff response of the frontal part of the analysed ship's bows, compared to the ship's bow structure that led to the current Dutch guideline. With the proposed impact force expression, the maximum impact force on bridge piers in the event of ship collisions could be estimated with increased accuracy.

The use of the Classical Laminate Theory (CLT) is limited to laminates where all the fibres in a ply are oriented in the plane of the laminate. In some applications, it is possible that the plies will start at the bottom of a laminate and end at the top of the laminate. This means an inclination is added to the plies, which creates an extra rotation in the fibre direction with respect to the plane of the laminate. Such a laminate with inclined plies is found for example in the skin of InfraCore panels. In the regular CLT, this extra rotation cannot be taken into account, thus the elastic behaviour of a laminate with inclined plies cannot be described properly. The extra rotation that occurs in a laminate with inclined plies has analytically been implemented in the regular CLT to obtain a modified CLT, which has been verified using Finite Element analyses. Using the modified CLT, a reduction in equivalent stiffness can be observed for a single unidirectional ply with an inclination in the fibre direction. The exact value of stiffness reduction strongly depends on the material properties and the lay-up of the laminate. For InfraCore skins, the stiffness reduction is very small (0.15%). Due to the inclination in the plies, the lay-up of the laminate differs along the length of the plate. As a result, the output of the modified CLT is only applicable to one location along the plate. Due to the lay-up differences, the equivalent stiffness will also differ along the inclination direction. The in-plane equivalent stiffnesses will be the highest for symmetric laminates, where the flexural equivalent stiffness will be the highest when the plies with the stiffest fibre direction are located on the outside of a laminate.

The design of steel structures consisting mostly of Circular Hollow Sections (CHS) such as jacket structures and bridges is governed by fatigue loading due to the low fatigue resistance of the welded regions. A solution has been proposed where welding is completely avoided, thus eliminating the weakest factor of these structures. In this solution, joints are wrapped in FRP, which is bonded to the steel. Simple Finite Element (FE) models of these joints already exist. In this thesis, these models will be further developed in Abaqus for more accurate prediction of the behaviour of such FRP wrapped joints. A set of model and solver parameters will be established as a starting point formore detailed modelling of FRP wrapped joints with different geometry and static load conditions.

Because of large complexity of the models, and inclusion of many contact interactions, Abaqus/Explicit should be used to model such joints. The anisotropic nature of the FRP requires elements that are robust and able to handle this anisotropy. Also the complex, curved and layered geometry of the wrap requires elements that discretize a 3D volume. Without the use of user subroutines, continuum shell elements are the only elements that meet this requirement.

Prediction of the behaviour of axial joints was very accurate, although no unique set of input parameters for the Cohesive ZoneModel were found. This is because multiple failure modes occur at the same time, which makes the system very sensitive to some parameters and completely insensitive to other parameters. Prediction of more complex X-joints was not very accurate. This is mostly due to differences between the geometry of the model and the real life joint. The models did suffer from hourglass modes. Different methods of hourglass control had limited effect. It was found that as irregularity of the mesh increases, the effects of hourglass modes decreases. However, the effect of hourglass modes needs to be decreased further. A solution to do this is proposed at the end of this thesis.

An increase in apparent mode II fracture toughness in Fiber Reinforced Polymers has been found from modified Transverse Crack Tension (mTCT) tests with compressive stresses added orthogonal to the delamination plane. Numerical reproduction of these results has not yet led to a good understanding of the reasons for this behavior. Currently, an analytical approach is used for determining the mode II fracture toughness from an mTCT test. In this research, the validity of the analytical relation is investigated for the case of an added compressive stress. The behavior of the material in the
test is therefore numerically investigated in a qualitative manner. A mesh, using a material model for plasticity and a cohesive law for interface elements to form the crack, which have been proven to give good results, has been build. A refinement on mesh and geometrical dimensions, focused on the pressure zone of the specimen, ensures the degree of detail required to investigate the local behavior. A parameter study on the inlfuence of geometrical and material parameters is performed and linked to results from previous conducted experiments. A standard mTCT test without compressive stress shows a linear load displacement relation until crack initiation and then a constant load at which the crack grows through the specimen. This crack growth load is used for the analytical approach. The results from this research show a change from a constant crack growth load to a linear crack growth load range in the zone of the applied compressive stress. After crack initiation, the crack growth load through the compressed zone has an increasing, nearly linear relation, based on the compressive stress and length of the pressure zone. The analytical approach, in
which the highest reached load on the specimen before failure is used as input, no longer applies for this case. The failure load is now dependent on the length of the pressure zone and pressure magnitude.

Marine structures are mostly exposed to mild and moderate sea-states, where the structural response is elastic. Characteristics of environmental loading are highly stochastic in nature, resulting in stress-states that might be multiaxial. This thesis attempts to identify the source and effect of these multiaxial stress-states on fatigue damage in frigate type structures.
A stress invariant based method called the Projection-by-Projection approach was adopted to estimate damage in the presence of multiaxial stress-states. This method was tested for its applicability and modified, where necessary, to better cope with the encountered stress-states. The design rules by the International Institute of Welding (IIW) were also used to be able to distinguish physical phenomena from methodological properties.
The available data consisted of strain measurements from the United States Coast Guard (USCG) Cutters Bertholf and Stratton. The Bertholf was equipped with the WaMoS wave radar. Measured wave data was reinforced with simulated waves to make the research independent of encountered sea-states.
It was concluded that multiaxiality is most relevant at low damage estimates (i.e.: low wave). The governing influence factor is the incoming wave direction. It was also shown that multiaxial stress-states may significantly contribute to fatigue damage (up to a factor 2, depending on the structural detail and location in the vessel) at an estimated life time of 2 · 10^{6} cycles.