The Netherlands is currently facing a severe housing shortage. As the supply of new homes cannot keep up with demand, housing prices have increased significantly. At the same time, the construction sector must comply with strict climate requirements to reduce CO2 emissions. Timber is a construction material with low carbon emissions, but building higher than 6 stories traditionally requires a concrete core or CLT, which significantly increase CO2 emissions and construction costs. To fill this gap, the WoodCore consortium was founded to develop a low-emission and affordable building concept. This thesis aims to study the lateral stability and stiffness system of this concept, which consists of a timber exoskeleton, a braced timber core, and timber frame shear walls. The main objective is to investigate, through a parametric study, how these various stability systems influence the horizontal deflection of the building and how they can be optimized.

To achieve this objective, a parametric workflow was developed using the finite element software SCIA Engineer. Models of the timber building concept were created and exported to XML files. By modifying these files with a Python script and running them using SCIA OpenAPI modules, many different parameter configurations could be studied. To reduce the total computational time for thousands of configurations, the workflow was expanded with a surrogate model. This mathematical model mimics the finite element analysis results, allowing for a significant expansion of the studied parameter configurations.

With this approach, the influence of seven parameters on the horizontal displacement was investigated across variants with a varying number of stories and diagonal layouts. Parameters for both the exoskeleton and the braced core included the dimensions of the timber diagonals and columns, and the axial stiffness of the diagonal connections. Additionally, the stiffness of the timber frame shear walls was studied. To evaluate these parameters, a local sensitivity analysis (One-At-a-Time method) and a global sensitivity analysis (Variance-based Sobol method) were performed. Furthermore, the economic and environmental influence was studied using a material and shadow costs comparison.

The analyses show that the exoskeleton has a significantly larger influence on the horizontal deflection than the braced core and timber frame shear walls. Furthermore, the dimensions of the diagonals and the axial stiffness of the connections have a greater influence than the column dimensions. The global sensitivity analysis also reveals that parallel linked parameters interact with each other, meaning their influence is interdependent. Although the influence of each parameter is highly dependent on the chosen parameter ranges and baseline geometry, the number of stories does not necessarily influence the results.

Finally, the cost-effectiveness analysis indicates that changing the diagonals and connection stiffness is highly effective regarding material and shadow costs. Although the braced core has a lower influence on the lateral stiffness than the exoskeleton, the cost-effectiveness of these parameters is comparable in both systems. Based on these results, it can be concluded that optimal parameter configurations for material costs are characterized by minimal column dimensions and low stiffness of the shear walls, and that the design should focus on the diagonals and axial connection stiffness for the global lateral stiffness of the building.
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The increasing demand for sustainable and easily constructible housing has led to the exploration of alternative foundation systems for lightweight modular structures. This research investigates the feasibility of using short helical piles to support a lightweight wooden building, assessing its settlement behaviour and structural integrity over time. Unlike traditional deep pile foundations, short helical piles are designed to be easily installed, removed, and reused, offering both environmental and economic advantages. However, their application in soft soils raises concerns regarding excessive and differential settlement.

The main research question for this thesis is:
”What is the structural feasibility of a lightweight, modular wooden building design on short, screwed foundation piles that is expected to have large amount of settlement?”
To answer this question, a literature study was done in combination with a case study. The literature established the boundary conditions for the use of helical foundation piles and explores the expected capacity and settlement behaviour in soft soil. Afterwards, it focusses on aspects such as decay and modular systems of timber construction elements.
With the knowledge obtained from the literature, a case study was developed. To investigate the behaviour of a lightweight structure that is expected to settle, a numerical modelling approach is used, combining PLAXIS 2D and SCIA Engineer. PLAXIS 2D was used for simulating the settlement behaviour of the structure at multiple stages in time, while the effect of these settlements on the superstructure was analysed in SCIA Engineer. Different wall systems were investigated, focusing on the influence of the wall stiffness, varying pile capacities, and the impact of uneven loading. Time-dependent settlement effects were evaluated at time stages just after the completion of the construction and at three additional points further in time. This provides insight on the short-term and long-term behaviour of the structure. To prove that a structure of this typology is sufficient for housing, it is tested on total settlement (𝑈), differential rotations (𝛽), tilt (𝜔), and element capacity (𝜎).

The results of the calculations indicate that for a lightweight, timber structure placed on short helical piles large amount of settlement can be expected when positioned in soft soil. However, the settlements will not lead to a significant stress increase that causes failure of structural elements. A stiffer wall system has the ability to redistribute more force to the foundation piles at the most outer position. This reduces the differential settlement between piles, but also reduces the maximum total settlement of the wall. The resistance to deformations of the outer foundation piles is therefore more impactful with a stiffer superstructure. In general, the findings suggest that with careful consideration of settlement behaviour, short helical piles can be a viable foundation solution for supporting lightweight houses. ... Read more

The main motive for this research was to study the behaviour of quay walls when there is an uneven pile foundation present. This means that the number of piles varies in the thickness of the quay wall along the length. The inspiration came from the failure of the Grimburgwal (Amsterdam, the Netherlands) that collapsed in 2020, which had a length of 65 meters, according to Korff et al. (2021). Korff et al. (2021) reported that the main failure mechanisms that are considered in the case of the Grimburgwal, is the deformation of the piles due to horizontal bending, in the section where there were only two instead of three rows of piles present in the thickness of the wall.

A 2D model with a length of 22.5 meters in the longitudinal direction (along the length of the quay) wall is used in this research, to study the influence of the uneven pile foundation in the thickness of the wall. The quay wall’s out-of-plane behaviour is not considered. The masonry and timber floor are modelled with linear plane stress elements. An interface condition is used to model the interaction between masonry and the timber floor. The longitudinal support beams and kespen are modelled as one element. The piles are modelled as equivalent translational springs that are evenly distributed in the longitudinal direction. In the central area, one spring represents two piles in the cross-section, while the rest of the springs represent three piles. After the application of the deadweight of masonry and timber, a uniform distributed load was used on top of the model to cause settlement of the piles and wall. The dilatation joint was modelled with a nonlinear interface with a high dummy stiffness and no tension, and with a gap of one millimeter.

If the length of the section with two rows of piles is increased, the capacity of the wall reduces. The cracks at the bottom of the masonry, still do not increase significantly if the length of the length of the section with two rows of piles is increased, but it does take less load to generate the same cracks. The boundary conditions also play a large role in the distribution of forces, since it is seen that the piles near the dilatation joint are less critical than the piles near the constrained edge. In the end, this model does give information on how the forces in the piles distribute and how the piles settle, before both brittle and ductile failure of the piles occurs and cracking within the model. However, it should be kept in mind that the model that is considered is a 2D model, whereas the problem of a quay wall is a 3D problem, so the results are not expected to be accurate.
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