In recent years, the building industry is experiencing a shift towards timber buildings driven by the need for a sustainable building industry. A popular building typology consists of Cross-Laminated Timber (CLT) panels. There is an ongoing trend for leaving CLT panels exposed, meaning without protective fire-resistant cladding. This enhances the aesthetical appeal of the building but raises questions regarding fire safety.

This thesis attempts to model the fire dynamics within a CLT compartment with Fire Dynamics Simulator (FDS), which is a CFD software. Hereby, special attention is given to modelling the pyrolysis and combustion reaction for the fire exposed CLT panels. The ability to model the burning behaviour of wood in FDS is a big step forward to be able to move from large-scale experiments to computational models.

This thesis validates the FDS model by comparing the simulated results with the experimental series by Olivier (2019). This series assessed small-scale cubical compartments with 0,5 m sides and a varying amount and orientation of CLT.

Extensive analyses of the simulated results show that the energy release due to the burning CLT is overestimated by approximately 50%. The simulated burning rates range from 1,15 – 1,33 mm/min, while experimentally measured burning rates are approximately 0,60 mm/min which is more commonly assumed in practice. The fire growth phase is approximated well, however validation of the decay phase is poor.

The simulated gas temperatures vary significantly more locally compared to the experimental data. Simulated gas temperatures in the middle of the compartment are underestimated by approximately 30%. On the other hand, gas temperatures near the burning CLT surfaces are approximated well. It is therefore concluded that the radiation from the burning CLT is poorly approximated and has a further reach in real-life experiments.

Extensive sensitivity analyses have shown that the simulated results in the FDS model are highly sensitive to the mesh cell size and the heat of combustion of wood. It is concluded that the three-dimensional mesh should consist of 20 mm cubical cells positioned within a proximity of 10 – 20 cm from the CLT surfaces. In the remainder of the computational domain 100 mm cubical cells should be used to minimise the number of cells in the simulation while maintaining simulation accuracy.

Conclusively, this thesis provides significant added value by enhancing the knowledge within the CFD modelling research field for FSE. The presented FDS model has potential for serving as a tool to roughly predict the fire dynamics within a CLT compartment. However, further optimisation of the model is required before practical applications in daily engineering can be justified.

The presented research aims to design and optimize a timber observation tower, with a primary focus being the influence of topological and curvature parameters on its stability and lateral stiffness in resistance to non-uniform wind load profiles.

Having recognised the environmental benefits and urgency to find other alternatives, there's a clear necessity to incorporate wood as the main construction material into the infrastructure projects, like observational towers. By conducting a study on hyperboloid towers implemented in the last 100 years, this project questions the necessity of in plane stiff platforms, flexurally stiff rings and continuous vertical members as being pivotal to the stability and lateral stiffness of the global structure when subjected to non-uniform wind loads. In addition, the study intends to investigate how the narrowness of the hyperboloid might affect the lateral stiffness of the structure. Thus, by utilizing parametric tools (Grasshopper, Karamba3D and Beaver plug-in), the study aims to design a timber tower structure comprised of fully segmented members as well as incorporation of circular (flexurally stiff) rings, aiming to address the questions raised. In terms of structural member arrangement, the study will investigate two topologies: one featuring a diagrid pattern that emulates a geometrical shape of an antiprism, and a custom pattern inspired by the post and beam approach, which resembles a regular prism shape. The study emphasizes the tower's multi-functionality and adaptability throughout its lifespan. Tower's main structural framework is a pivotal element in providing required stiffness and strength by excluding the need for in-plane reinforcement provided by arbitrarily placed platforms.

The key realisation of this research was the kinematic behaviour exhibited by the segmented, triangular tower, adversely impacting its stability characteristics. The study used a combination of analytical and graphic kinematics techniques, along with a physical mock-up model, to confirm the kinematic behavior of the tower given that even sided polygons for rings are incorporated. This revelation would have an impact on how a structure like that would perform as well the way it would be built. Further research unveils the strong influence of ring type on structural stiffness showing that segmented rings render tower structures less stiff than ones employing curved ring members, regardless of the pattern. In terms of the direct comparison between tower patterns, custom one demonstrated a more consistent and stable performance in general, particularly achieving higher stiffness levels when employing segmented rings. As regards the triangular pattern, the stiffest response against wind loads has been exhibited through the use of curved rings. In addition, the study validates that adopting a hyperboloid shape along with smaller shape factors for the global tower geometry yields more favorable lateral stiffness characteristics. Finally, the study navigates through the exploration of the most optimal connection design, illustrating how considerations related to detailing have necessitated a re-evaluation of the most optimal tower configuration, which initially was chosen to be a triangular one equipped with curved rings. A qualitative assessment of a potential joint within this specific tower variant has confirmed that designing such a connection is significantly more complex. This is due to the necessity of ensuring the continuous flow of the curved ring, emergence of a kink within the insertion of the plate and how that is needed to be addressed.

Alternatively, these considerations have motivated the design process to converge into a new hybrid design, integrating segmented rings with a curved top ring defined by the custom pattern. This choice has been made by conducting a separate parametric study of the new tower design and ensuring that the new connection design fulfills elastic slipping modulus and ultimate strength requirements. The final topology that showed higher stiffness metrics was the custom one. It's also highlighted that maintaining the top of the tower constrained leads to favorable effects on stability and stiffness, irrespective of the chosen topology. The resulting structure is optimized for mass by strategically reducing member cross-sections in accordance with connection scheming while adhering to both SLS and ULS criteria.

To address the increasing housing demand in Europe and simultaneously tackle the challenge of creating a more sustainable construction industry, timber modular buildings present an innovative solution. However, before multi-storey modular buildings become a widespread practice, various engineering challenges need to be addressed. Ensuring robustness is one such challenge. This study focuses on the robustness of post-and-beam timber modular buildings, particularly through catenary action. The challenge with ensuring robust catenary action lies in designing connections with sufficient resistance and deformation capacity. This study proposes an optimisation process to determine the required mechanical properties of inter-module connections to enable robustness through catenary action.

The principle of a catenary relies on the equilibrium between a vertical point load and the vertical component of the tie force in the deflected floor elements. Larger deflections result in a lower required tension resistance but demand a larger deformation capacity in the components. This study introduces a catenary equation to determine the required tensile resistance in a catenary at a specified elongation, creating a catenary requirement boundary. For a timber modular building to form robust catenary action, the axial force-elongation response in a catenary must meet this boundary. The catenary equation and the force-elongation response of the catenary form the basis of the connection optimisation, as the inter-module connection governs the response.

To determine the optimised mechanical properties of an inter-module connection in a timber modular building, a case study was performed on a building consisting of twelve post-and-beam modules in width and five modules in height. To determine the effect of a change in the inter-module connection design on the force-elongation response of the buildings, quasi-static numerical analyses were conducted on 2D models, focussing on the frontal view frame of the building, and the floor plane. The load distribution through the floor system and corresponding deformation were added to the frame model by use of spring boundary constraints, after which the catenary could be examined.

As a catenary can be formed by increasing the axial resistance, or its ductility, two optimisation methods were formulated, resulting in a high-strength inter-module connection and a ductile inter-module connection with a fuse. The optimisation process is based on iterations of the inter-module connection design. The resulting high-strength connection required a 143% increase in tension resistance, while the ductile connection relied on a 55% increase in resistance and a 550 mm fuse.

This study underscores the complexity and critical importance of correct connection design to ensure structural robustness, emphasising the need for sufficient strength and deformation capacity. While the proposed methodology serves as a valuable tool for optimising connections in timber modular buildings, further research is recommended by including dynamic analyses in the optimisation process and experimental testing of inter-module connections to enhance the accuracy of the models.

The transverse stability of timber terraced houses can be provided by CLT stability walls where decoupled timber terraced houses are preferred to meet acoustic requirements leading to rather large thicknesses for the CLT stability walls and many large connections for anchorage to the foundation. The main goal of this research was to investigate the transverse stability behaviour of timber terraced houses, using a case study provided by WSP.

Models to assess the transverse stability of timber terraced houses are simple schematizations with hand calculations of the decoupled and coupled timber terraced houses and FE models of decoupled timber terraced houses with and without T-section and coupled timber terraced houses with and without T-section. The coupling of the houses can be achieved by 4 Straviwood Modulink 6.0 kN connections per floor level. The T-section can be realised with double screws with diameter Q = 12 ZZ with a spacing of ` = 100 ZZ.

Simple schematizations with hand calculations of the decoupled and coupled timber terraced houses result in overdimensioning of the connections since bending of the floors due to deformation of the stability wall, providing resistance to the deformation of the stability wall, is not considered. This resulted in 6 hold downs per CLT stability wall.

Compared to the FE model of decoupled timber terraced houses without T-section, all FE models have a positive influence on the design of connections in terms of reduction of number of hold downs and improvement of the total tension support reaction. Coupling of the houses is better compared to application of a T-section for decoupled houses. An improvement of the total tension support reaction of 83% and 67% for respectively the house on the left and the house on the right, compared to the decoupled timber terraced houses without T-section, can be achieved by coupled timber terraced houses with T-section. This also resulted in a reduction of 5 hold downs per CLT stability wall and the possibility to reduce the thickness of the CLT stability wall.

Currently, the building industry contributes to up to 50% of climate change. A way to reduce the impact is by replacing current building materials with more environmentally friendly materials, such as timber. Engineered wood products, such as cross-laminated timber (CLT) panels, have increased strength, stiffness, and stability which enables building higher buildings and floors with bigger spans. However, due to the low weight of timber, CLT floors are susceptible to unwanted high floor vibrations and therefore need to be verified on their footfall-induced vibration performance. Predicting the vibration performance is a complex problem as the load-bearing structure and architectural finishing have distinct structural behavior under small vibrations. Due to the novelty of the problem, the distinct behavior is not captured well in the current design codes. As a result, the Eurocode 5 guidelines on vibrations are currently being updated and extended. In support, this thesis addresses the critical issue of predicting the vibration performance of CLT floors, with a specific focus on the impact of architectural finishing.

To achieve this goal, a literature review was conducted to identify structural components that are often overlooked, but may lead to inaccuracies in vibration predictions. These factors include the connections between CLT panels and different types of floor finishing. A case study was then carried out using the building HOUTlab, which features CLT floors with a concrete floating screed. On-site measurements were performed at key locations, including at the inter-panel connection line and in the middle of the panel. This was done before and after architectural finishing was placed. Subsequently, analytical and numerical calculations were used to gain insight into the structural behavior of the system subject to footfall-loading by investigating the accuracy of common engineering practices and other assumptions regarding their structural behavior.

Onsite measurements, where the floor was loaded and the response was measured at the same location, showed that the root mean square velocity (vrms) values were much higher at the inter-panel connection line compared to in the middle of the panel. The vrms is a measure of the amplitude of the vibration. The initial finite element analysis (FEA), assuming a rigid inter-panel connection, inaccurately located the highest vrms values. When assuming a hinge, the FEA correctly allocated the critical vrms values but compromised the accuracy of frequency estimates. The experimental results revealed that adding architectural finishing increased the damping, reduced the vrms, and maintained a similar frequency, ultimately improving the vibration performance from level 3 to level 1 according to the preliminary Eurocode 5 (prEC5) standards. The prEC5 and FEA following common engineering practices accurately estimated the frequency before architectural finishing was placed but underestimated it by 39% after it was placed, indicating a higher increase in the bending stiffness of the floor than initially assumed. While prior calculations assumed slip between the floor layers due to the presence of the insulation layer, assuming full cooperation between the layers resulted in an overestimation of the frequency by 9%, suggesting that there is some cooperation, but the floors are not fully bonded...

An analytical study of an energy-based approach to damping of a clamped timber column in free vibration under axial, lateral and torsional loading conditions was conducted. Backed by experiments it was confirmed that an energy-based approach, as proposed by Sánchez Gómez (2018), could describe the energy dissipation in a laterally vibrating timber column. With the help of an energy balance equation, the energy flow in a timber column was formulated including any energy dissipated during vibration. It was found that the energy in the system could be approximated by an exponential function for which a new dissipation constant E_D (s-1) was introduced. For lateral vibrating columns of Norway spruce, typical values of E_D were 0.4 - 0.6 s-1. Furthermore, a case study on a timber high-rise building demonstrated
that damping has a significant influence on reducing peak accelerations which, in turn, could potentially lead to lowered costs. This largely untapped design lever warrants significant research and design improvement for these timber high-rise structures and, hence, several recommendations for follow-up research are offered.

The construction industry contributes significantly to global emissions. In response to the growing concern about climate change, new methods are being developed to reduce these emissions. Building with timber is one such approach, as it can be CO2 neutral if reforestation is practiced. Timber is a lightweight and flexible material compared to traditional construction materials like steel and concrete, which can result in high accelerations and deflections, negatively affecting user comfort. Engineered wood products such as CLT and GLT make it possible to construct larger panel sizes and spans, which can lead to more efficient building design. Many buildings utilize core systems to provide lateral stability and facilitate vertical transportation of goods and people. Therefore, replacing a conventional concrete core with a CLT core could be a viable solution to reduce the building’s environmental impact. Timber, being a flexible material, often lacks the necessary stability to meet user requirements for deflection and acceleration in high-rise buildings. An outrigger, similar to those used in concrete and steel structures, can provide the solution to enhance user comfort. The outrigger transfers bending moments from the core to the columns, reducing forces in the core and increasing overall stiffness. However it is unclear what the influence of the addition of a timber outrigger on a CLT core building is and how such a system can be improved. Therefore the purpose of this thesis is to evaluate the impact of a timber outrigger on a CLT core building, and provide guidance for structural engineers on how to improve the structural behaviour of such a system. The impact of adding an outrigger is evaluated through the comparison of different numerical case studies with and without timber outriggers. Additionally a sensitivity analysis is performed in which the influence of core joint design and the impact of outrigger design parameters is evaluated. By introducing a timber outrigger to a CLT core building bending moments are transferred from the core to the column, partially restricting rotation of the core. This will have the following effects on the behaviour of the structure. Firstly, the deflections due to lateral wind loading are reduced due to the increased global stiffness. Secondly, the increased stiffness of the structure will result in a reduction of peak lateral acceleration. Thirdly, by transferring loads from the core to the columns the strength requirements on the connections of the core are reduced. Finally, by introducing a timber outrigger system to a CLT core building horizontal forces are generated in the core at outrigger level, which should be accounted for in the design phase of the vertical core joints. Increasing the stiffness of the outrigger will further reduce deflections, peak lateral acceleration and strength requirements on the core joint, however strength requirements on the vertical core joints at outrigger level will further increase. An exponential relationship has been derived between the lateral deflections and the ratio between the effective bending stiffness of the outrigger and the effective bending stiffness of the core, a similar exponential relationship has been derived for the peak lateral accelerations Additionally it was investigated what the critical design parameters are and how the performance of a CLT core building with timber outriggers can be improved. For the design of a CLT core the connection between the core and foundation showed to be critical, having large effects on the lateral deformation. While increasing the stiffness of the vertical connections showed to have little influence on the interaction between core walls due to their respective high interaction factors. In the design of the outrigger it was shown that a two storey outrigger is able to more than double the reduction in deflections compared to a single storey outrigger, further increasing the overall effectiveness of the system. Finally the effectiveness of the system was found to be significantly influenced by the configuration of the outrigger truss, demonstrating a greater impact than increasing member size or connection stiffness.

Summary

Numerous ancient historical constructions worldwide depend primarily on an extensive array of wooden foundation piles, as they are subject to loading conditions governed by the superstructure above. Wooden foundations transfer loads through a combination of compression and lateral resistance. The inherent strength of wood handles compressive forces, while stiffness and soil friction counteract lateral loads. Proper arrangement and maintenance ensure even load distribution. Careful design, wood quality, depth, and protective treatments are essential for longevity and load-bearing efficiency.

Amsterdam, the Netherlands' capital city, renowned for its rich artistic heritage, intricate canal infrastructure, and slender architectural dwellings, originated as a modest fishing hamlet that underwent remarkable development into a prominent global European city. During this urban transformation, less visible engineering elements, such as wooden foundation piles, were overlooked, despite their critical significance. In Amsterdam's historical core, the majority of structures including buildings, bridges, and quay walls, rely on these wooden supports. Noteworthy, the city estimates that 12 million such piles are still active. These structural components have consistently demonstrated economic efficiency and reliability. Nonetheless, the aging process affecting these foundations, with some dating back up to 500 years, introduces complexities when assessing their current load-bearing capacities and the ensuing reliability of the structures they support.

The lack of knowledge and inspection techniques of the mechanical and physical properties of these timber piles hinders a proper evaluation of the remaining life span of the foundations which could lead to possible irreplaceable structural damage to these structures. This body of research evaluates the physical and mechanical properties such as the actual moisture content, density distribution, compressive strength, and modulus of elasticity through the cross section of Spruce (Picea abies) foundation piles. Therefore, the overarching research question has arisen:

“How do the variations of mechanical and physical attributes manifest across the cross-sectional profile of both degraded and non-degraded spruce foundation piles and how can micro-drilling techniques be utilized to assess these characteristics?“

This will be achieved by means of small-scale compressive experimental testing of five prisms extracted from each cross-section (3 separate locations along the length of the pile) of foundation piles never driven into the soil and piles that were retrieved under bridges in the historical centre of Amsterdam that were planned to be demolished. These aforementioned retrieved piles had a service life between 100 years and 300 years, always under the water table, presenting mechanical degradation due to loading over time and in addition possible bacterial degradation of the cross-section peripheral regions.

Initially, micro-drilling techniques were employed to ascertain the drilling amplitude. This step served to assess the initial quality of the wood under examination. Additionally, it aided in identifying specific points of interest for specimen extraction, including degraded wood in the peripheral regions, sound wood in the internal section, and the pith. Subsequently, the acquired data underwent thorough analysis. This analysis, combined with the micro-drilling measurements, enabled an assessment of the potential applicability of drilling amplitude in predicting the mechanical and physical properties of the pile. This sequential approach ensured a systematic and scientifically rigorous evaluation of the wood's characteristics and its implications for pile performance. The investigation was conducted to enhance the understanding of the structural performance and material characteristics of spruce foundation piles, while also evaluating the applicability of micro-drilling methods as a predictive tool in engineering assessments...

Masonry structures occupy a significant share of the current building stock due to widespread material availability and cost-effectiveness. Regions with high seismicity, like the Himalayas, have typically developed local seismic culture over the centuries. This has led to improved construction techniques providing an enhanced seismic performance, as evident from post-earthquake surveys. Bhatar is a building typology found in the Himalayas, featuring embedded horizontal timber bands in masonry walls, enhancing the box-behaviour and in turn avoiding their premature out-of-plane failure.
This work aims to quantify the improvement of the out-of-plane performance of masonry walls due to the presence of horizontal timber bands. Numerical analyses were conducted in DIANA FEA software starting from the few experimental results available in literature on this typology. These were used to calibrate the properties of masonry, which was represented as a homogeneous isotropic continuum, with nonlinearities considered by means of a total strain rotating crack model.
Firstly, a U-shaped masonry wall having the same geometry and boundary conditions as the experimental tests was simulated using 3D modelling approach. Non-linear static analyses were performed exploring two different strategies, with minor variations in analysis parameters. Very good agreement was obtained with the results from literature for both strategies with one able to simulate local cracks better, while the other was able to simulate global failure mechanism better. The calibrated numerical model was then employed to conduct sensitivity analyses for precompression load and aspect ratio.
Further refinements to the calibrated model were done. The influence of the frictional behaviour between timber and masonry was explored through discretely modelled interface elements. The timber-to-timber connection was modelled as a hinge. The improvement in the behaviour of the wall due to timber bands connected throughout the frontal wall was also evaluated.
Finally, the calibrated numerical model was employed for the pushover analysis of a full-scale structure representing the geometry of a typical Bhatar house. The results from the numerical analysis were used for seismic assessment using Capacity Spectrum Method. The assessment demonstrated the capability of a Bhatar structure to resist ground acceleration specified for the highest earthquake category defined by Indian Standard Criteria for Earthquake Resistant Design of Structures. Contrarily, an unreinforced masonry structure did not possess the required ductility to resist such an earthquake.
Inclusion of timber bands at corners of a U-shaped masonry wall resulted in an increase of lateral resistance by 40%. Walls with timber bands connected throughout the front wall presented a further increase of 35% in the force capacity. The corresponding improvement in force capacity for a full-scale Bhatar house was even more remarkable at 109% compared to an identical unreinforced house. There was also a noticeable increase in the ductility.
This work constitutes a further step towards a better understanding of the behaviour of Himalayan masonry structures under earthquakes, promoting better seismic risk reduction strategies. This improved understanding into the role of timber in greater seismic resilience of masonry structures also informs better maintenance, conservation and preservation of heritage and historical masonry structures in the Himalayas.

The demand for timber buildings is rising because of the need to make the construction industry more sustainable. Eurocode 5 provides guidance in the design process of timber structures. Numerical modelling is generally used for complex structures like multi-storey timber buildings. Currently, there is limited understanding of the serviceability behaviour of multi-storey timber buildings that are stabilized by glulam trusses. This is partly because the load-slip behaviour of large timber connections is not well understood.

The aim of this thesis is to develop a better understanding of the influence of the connections on the serviceability behaviour of timber buildings with glulam stability trusses. In the first part of this thesis, the state-of-the-art of timber connection design is discussed. The second part is dedicated to the development of a finite element model. A modelling approach is developed that allows for the specification of the load-slip behaviour of the truss connections in the end nodes of the modelled members. A sensitivity study focused on the serviceability stiffness of the truss connections is performed using the FE model. Next, variants on the base design are modelled and studied for comparison, which provides insight into the effect that changing geometry has on serviceability behaviour.

This thesis shows that the load-slip behaviour of the truss connections has a significant influence on the serviceability behaviour of a timber building. It is also found that the current design rules are not suitable for predicting the serviceability stiffness of these connections. For timber connections with slotted-in steel plates and dowels, their load-slip behaviour can be idealized by an initial slip followed by its elastic stiffness. The initial slip is caused by the hole clearance in the steel plates in combination with various non-linear effects like densification of the timber. The hole clearance in the steel plates is also responsible for the sequential activation of the dowels, which is considered to be the primary cause for the reduction in elastic stiffness per dowel per shear plane as the number of dowels increases. This so-called ’group effect’ results in a much lower stiffness of the truss connections than the current design formula suggests.

The results from the numerical modelling show that the load-slip behaviour of the connections between the diagonals and columns has a large influence on the serviceability behaviour of the truss. A distinction is made between diagonal connections and vertical components. The initial slip in the connections causes an increase in the maximum displacement of the structure. The elastic stiffness of the truss connections decreases the global stiffness of the structure. This resulted in an increase in maximum displacement, a decrease in the natural frequency, and an increase in peak accelerations.

The serviceability behaviour of large timber connections should be explored further. Current design codes are not suitable for predicting their serviceability behaviour, which can have consequences for the design of complex structures like multi-storey timber buildings with glulam stability trusses. To ensure the proper design of these buildings, our understanding of their serviceability behaviour is critical. This thesis is anticipated to be a valuable contribution to bridging the knowledge gap. It shows the shortcomings of the current design rules and provides practical information about how to predict the serviceability behaviour of a timber building that is stabilized using glulam trusses.

Given the desire to construct more structures using sustainable building materials, demand for wood and other bio-based building materials has risen dramatically over the decade. While timber itself is a carbon-neutral material and can sometimes even be carbon-negative, reusing wooden structural members made that have been in service for several years can widen the approach to structural design using wood. In the extensive network of rivers and canal systems that the Netherlands has, the banks are often covered with sheet-pile walls and a majority of these are made of timber. Tropical hardwood, especially Azobé (Lophira alata), due to its high biological resistance to decay, is used to make these sheet-piles. However, when exposed to the groundwater table for a long period of time, the wood undergoes decay due to bacteria destroying the cellulose slowly, while the lignin remains constant, and over decades the large cellulose molecules are replaced by water making the walls weaker.

In this study, the characteristic mechanical properties of Azobé sheet-piles that have been in service for 57 years have been found, so that they can be assigned with an appropriate strength class and reused. Destructive, quasi-destructive and non-destructive tests have been performed on the sheet-pile boards to understand the correlation between them and to also ascertain to what level tests on timber specimens that do not affect their usability can be reliable. Since the knowledge of how visual grading can be performed on used, decayed structural timber, especially hardwood specimens is limited, a methodology has been developed in line with NEN-EN 14081-1:2019 along with the definition of a visual decay score. The results from the RPD tests are quantified in terms of the resistographic measure value to identify whether, in tropical hardwood, is there any effect in the drilling direction and whether this value can qualitatively or quantitatively describe the actual mechanical strength of the sheet-pile boards. The stress-wave tests and the four-point bending test are used to calculate the strength and stiffness of the boards, which determine the characteristic values, that are also based on their wet density (at which the tests are conducted). The results obtained are also analyzed for occurring patterns in terms of the location of the board in the sheet-pile wall (top or bottom), testing configuration (E-side or W-side-up) and variation in thickness within the boards due to decay.

The bending test performed on the boards is modelled numerically in multiple iterations with curved-shell, layered-shell and 3D brick elements also varying the respective material models to find which one of them is best suitable to model bending of timber. The load-sharing mechanism observed when grouping multiple timber specimens has been simulated numerically to predict the characteristic load-sharing factor of the sheet-pile wall system.

This thesis comprises of vertical deformation differences in high-rise structures where a concrete stability core is combined with a timber frame. The timber frame consists out of prefab timber modules which derive all lateral stability from the concrete core. Due to contrasting elastic, hygroexpansion and viscoelastic properties there is a notable difference in the vertical deformation of the concrete core and the timber units. The impact of these deformations have been outlined and possibilities to minimize the impact have been explored in this thesis.

The climate emergency calls for a global shift towards a low-carbon economy, to preserve natural resources and biodiversity, while limiting global warming and its consequences. This project focuses on the impact of distribution centres, intended for the storage of commercial goods. Warehouses are characterised by large flexible spaces and simple structural systems, most often with steel or concrete frames aiming at efficiency and low costs. The aim of this research is to create a sustainable single-storey warehouse with a significantly lower environmental impact compared to reference designs with steel and concrete frames. Considering a new-build project with no reuse of existing elements, a meaningful target for embodied carbon reduction is set to 50% of the environmental impact score of reference steel and concrete warehouse designs.
A selection of sustainable design strategies are investigated, giving insight into which actions designers shall take in priority to effectively reduce the embodied carbon of a warehouse. Reducing upfront emissions (LCA modules A1-A3) requires looking into short-term sustainability measures like reducing material use or using low carbon alternatives wherever possible. Replacing fossil-based products by renewable carbon sequestering materials like timber or other biobased alternatives contributes to lowering the impact of a building, by storing biogenic carbon for the lifespan of these elements. A sustainable use of wood presumes that its design lifespan is at least equal to forest rotation periods to maintain or increase the forest timber stock, combined with sustainable forest management practices. Biogenic carbon storage may be extended by designing for long-term reuse or recycling. Greening the envelope of a building takes advantage of ecosystem services provided by vegetation, like improving air quality, enhancing thermal performance or supporting biodiversity. Many systems can be applied on facades and roofs, depending on project-specific requirements (plant species, layout, load-bearing capacity), to effectively introduce vegetation in the built environment.
The first design step investigates the embodied carbon reduction potential of substituting steel or concrete by timber in the load-bearing frame of a warehouse. Reference steel and concrete structures are selected, and baseline timber designs are created with similar geometrical characteristics and stability systems, to compare their environmental impact on a fair basis. The second design step of the research aims at further reducing the impact of not only the frame, but also other parts of the timber warehouse (foundation pads, floor slab, envelope). Big ticket items responsible for the most impact are identified and tackled in priority: in both timber designs, the floor slab and envelope are responsible for the largest share of embodied carbon. Based on the results of design steps 1 and 2, the 50% embodied carbon reduction target can be achieved by substituting steel or concrete in the frame by timber (-31%), replacing sandwich panels on steel supports by biobased materials in the envelope (-13%), and reducing the floor slab thickness by 50mm (-7%), when considering only fossil emissions. If biogenic carbon storage is accounted for, using biobased materials in the frame (-65%) and in the envelope (-58%), without modifying the floor slab, results in a carbon positive warehouse design. These results are only valid assuming long-term carbon storage in biobased materials, supported by circular design measures. Greening the envelope also contributes to making warehouses more sustainable, provided that benefits from ecosystem services outweigh environmental costs from additional materials.

A large share of the buildings today is still masonry buildings, both reinforced and unreinforced. Post-earthquake reconnaissance studies have shown a remarkable difference between the performance of reinforced and unreinforced masonry buildings. While the unreinforced masonry buildings tend to suffer severe damage, even collapse, resulting in loss of innumerable and invaluable life; reinforced masonry buildings have often been reported to perform remarkably well under seismic events. Sometimes, this performance has exceeded performance of engineered buildings as well.

Himalayas are a highly seismic region in South Asia with multiple major earthquakes recorded across the past two centuries. The remoteness of the region and abundant availability of local materials along with frequent earthquakes has resulted in the development of a seismic culture of earthquake-resistant, timber-reinforced masonry buildings. Though these buildings have shown superior performance under seismic actions, little scientific research has been done to understand and analyse the reason behind this superior performance.

Across the different regions of Himalayas, timber has been used in different structural configurations to increase the seismic resistance of the masonry structures. These traditional building systems remain popular in the Himalayan region for their cheap and easy availability locally. This additional graduation project is a step towards understanding the behaviour of these masonry structures, and the role of timber in preventing catastrophic failure in the former.

In this study, different building typologies in the Himalayas that use timber as a structural element are identified and described. Failure mechanisms of masonry structures are widely studied and a brief overview is presented. In-plane, out-of-plane, combined in-plane and out-of-plane and local failure mechanisms of unreinforced masonry are discussed in detail. Furthermore, a literature review of post-earthquake reconnaissance surveys is conducted to understand different mechanisms through which masonry structures fail.

A review of state-of-the-art on experimental, analytical and numerical studies conducted on resistance of some of the building typologies of Himalayan region (for example, Bhatar, Dhajji Dewari, Ikra, Kath Kuni) is done in this study to understand work done previously. Finally, an analytical analysis is conducted on single room, one-storeyed Bhatar building to investigate the response of an in-plane wall to a lateral load exerted by earthquake excitation.

Timber high-rise buildings have been gaining in popularity. However, due to the low material stiffness of timber the stability systems of these buildings are often made with steel or concrete. To avoid this the material efficiency of the timber stability systems must be improved. The most material efficient stability systems for timber high-rise are the externally braced systems according to literature. The externally braced systems are the diagrid and external braced frame stability systems. In literature the diagrid is concluded to be more material efficient than the external braced frame. Nonetheless, in practice only external braced frame systems are used for timber high-rise buildings. This disconnect could be caused by the steel connections which are often simplified or overlooked in literature studies but have a large influence on the material usage of a timber stability system. The connections can increase the timber element size because the required connection does not fit, and the connections will decrease the global stiffness of the stability system. For this reason, the connections must be regarded when comparing stability systems.
One diagrid and two external braced frame designs will be compared with a parametric model. In this model other parameters will be studied as well. These parameters are: plot sizes of 27.2 x 27.2 m & 27.2 x 40.8 m, floor spans of 3.4 m & 6.8 m, permanent floor loads of 3.5 kN/m^2 & 5.3 kN/m^2 & 6.7 kN/m^2 and element widths ranging from 400 mm to 650 mm. The parametric model will first size the elements individually for the ULS checks and afterwards the elements will be sized per group for the SLS checks. The ULS checks start with a regular ULS member check, then a member check in the fire situation is performed and lastly the connection design component used. This connection design component will create slotted-in steel plate connections where the amount of steel per connection is calculated, and the timber element sizes are increased if needed. In the SLS checks the global lateral displacement is checked and the along-wind acceleration. The along-wind acceleration is often normative for the sizing of the elements in timber high-rise. With a higher global stiffness or higher building mass the acceleration decreases. To make a fair comparison in the results the amount of timber and steel of the internal structure is also added to the material required in the stability system in the façade.
From the results it is seen that all buildings are sized on the connection design or on the along-wind acceleration. The diagrid designs have a higher global stiffness so they are sized more often on the connection design whereas the braced frame designs are sized more often on the along-wind acceleration. The diagrid designs use 3x more steel than the braced designs. The results for the other parameters are:
Plot size: A smaller plot size requires a higher floor load to meet the acceleration requirement, therefore the large plot size is more material efficient.
Floor span: The floor span in the external braced frame has a large influence on the designs with a small plot size. That is because the facade with the smaller span becomes normative for the global displacement. When this happens a smaller floor span decreases the material efficiency significantly. In the larger plot size the influence of the floor span on the braced frame designs is insignificant. For the diagrid designs the larger floor span causes higher normal forces in the diagonals. This increases the material usage in the facade. However, considering the internal structure of the building the large floor span is still more efficient.
Floor weight: A higher floor weight is more timber efficient for a small plot size, and the lowest floor weight is the most material efficient for a large plot size. With a higher floor weight, the steel usage always increases since the connection designs are sized on the ULS checks only.
Element width: The steel efficiency increases when the element width increases. This is a result of the chosen connection design. The timber usage is similar for all the element widths.
Some of the designs with a small plot size and low floor weight are unfeasible since the elements in the facade are too large. This is a result of the choice to only increase the timber element heights and not the connection stiffness to improve the global stiffness. Therefore, it is recommended to study how the global stiffness can be improved more material efficiently. Other recommendations for further research are on the stability system design and the connection design. Since in this thesis many designs are fixed in simplified exploratory studies to decrease the design space of the parametric model.

The importance of joints in timber structures is strongly emphasized in the existing literature (e.g., Blaß & Sandhaas, 2017; McLain, 1998). The aim of this project is to provide insight into whether the cross-sectional sizes of the member are dictated by the dimensional sizes of the laterally loaded dowel-type connection or the strength and stiffness requirements of the member itself in timber frame structures.

In this research project, a parametric study is performed. The parameters in this study represent the global frame structure and the laterally loaded dowel-type connections. Together, these parameters form a parametric model that lays the foundation for the tool that is constructed in this study. This tool is built in order to generate a number of unique configurations that fulfill the design verifications. Using the tool, two analyses are performed. In analysis 1, the effect of different distances between the secondary beams is examined. In analysis 2, the effect of different grid sizes of the column in the frame structure is studied. In both analyses, two member sizes are first selected based on the criteria 'lowest cross-sectional area' (LCA) and 'lowest height beam' (LHB). These two member sizes form the starting point for generating different configurations of laterally loaded dowel-type connections.

In this research project, three factors are found to contribute to the largest reduction in the number of unique configurations for all constructed cases examined in analysis 1 and 2. These three factors are small column widths combined with high shear forces, the effect of a 'compact' member, and the effect of 'brittle' failure mechanisms on the LCA-members, which was selected as a design constraint in this study. These factors may be relevant for engineers to take into account when designing the structural members.

However, in this study, no constructed case is found in which the member needs to be redesigned in order to fit the connection. This means that one can conclude that the dimensional size of the structural member is dictated by the strength and stiffness requirements of the member itself. Important to note is that, although a large number of parameters was incorporated into this study, not all potentially relevant parameters were taken into account. When incorporating factors such as the horizontal forces in the connection, the effect of shrinkage and swelling, the level of difficultly in terms of assembling the joints on site, and adjustments to guarantee a certain level of fire resistance, certain turning points in the dimensional interaction between joints and members may be found.

Finally, beyond allowing for the dimensional interaction between joints and members to be studied, the tool constructed in this study is also valuable to practical engineering. The large amount of data that is generated by the tool allows the engineer to explore the different possible configurations in the process of designing joints. By connecting the output of the tool to the Design Explorer interface, the engineer has the opportunity to search through all the individual characteristics or a specific range and examine different possible connections in an efficient manner. One of the main contributions of this research project, therefore, lies in the tool itself.

Self-tapping screws are popular tools used in timber engineering. The axial withdrawal strength of self-tapping screws could be used in timber structures as an active or passive application. An example of an active application is the use as a fastener in wall to wall connections. An example of a passive application is the use as reinforcement perpendicular to the grain, to prevent cracking along the grain. Existing methods to calculate the withdrawal strength of self-tapping screws are mainly based on tests done on softwood. Some screw manufacturers offer calculation methods for the use of their screws in hardwood from temperate regions in so called European Technical Assessments (ETAs). But the Eurocode and the ETAs offer no calculation methods for high density tropical hardwood species. Tropical hardwood species are generally used in The Netherlands for hydraulic and outside structures such as lock-doors, bridges, weirs and jetties. Tropical hardwood species are used because of their strength and durability in outside conditions. There are no well-established methods to calculate the withdrawal strength of self-tapping screws in tropical hardwood perpendicular to the grain and the purpose of this thesis is to gain more knowledge on this topic. The central question of this thesis is: What is the withdrawal strength of self-tapping screws in tropical hardwood species perpendicular to the grain and is it possible to develop a verification model for engineering purposes?
To find answers to the main question first a literature review has been conducted. Literature on timber anatomy, self-tapping screw properties and available calculation methods have been reviewed. This is followed by a literature review on possibilities to drive self-tapping screws into high density woods. This is problematic because screws could fail already during insertion or cause splitting of the timber. Screw modifications such as cutter tips could be used to reduce the insertion moment, but also pre-drilling of the timber could be done to avoid torque failure of screws or the splitting of timber. The literature study is finalized with an investigation to the influence of material properties on the withdrawal strength. Tropical hardwood species are often used in outside or wet structures so literature on the influence of moisture content has been investigated. In research done by Ringhofer et al. [22] it was found that if the moisture content increases above 12 % the withdrawal capacity significantly decreases. Pre-drilling of the timber helps to insert self-tapping screws more easily into timber, but this also removes material and could therefore reduce the withdrawal strength. Research done by Brandner, Ringhofer, and Reichinger [5] found that if the pre-drilling diameter is smaller or equal to 80 % of the nominal screw diameter pre-drilling had no influence on the withdrawal strength. The mentioned research however has been done on temperate hardwood and the question is whether this is the case for tropical hardwood as well. According to EN 1995-1-1:2011 pre-drilling is necessary if the characteristic density of the timber is larger than 500 kg/m³. With increasing timber density the withdrawal strength also increases (Hubner, Rasser, and Schickhofer [13]). Regarding the screw diameter, with increasing diameter the withdrawal strength (f_ax, MPa) decreases as was found by for example Hubner, Rasser, and Schickhofer [13]. With increasing diameter the withdrawal capacity (F_ax, kN) also increases. With increasing effective length of self-tapping screws inserted in wood the withdrawal strength (f_ax, MPa) does not increase or decrease (Xu et al. [30]). The withdrawal capacity (F_ax, kN) however increases, a linear relationship between the effective length withdrawal capacity can be observed in research done by Xu et al. [30].
Findings in the literature study were the basis of how the test series were designed. EN1382:2016 describes how to test and determine the withdrawal strength of screws in timber. This standard also gives rules on the dimensions of the test piece. The width of the available tropical hardwood pieces was to small according to EN1382:2016 which states that a minimal edge distance of 5d has to be used. Methods from the EN 1995-1-1:2011 and ETA-11/0030:2020 from Rotho Blaas have been used to make a selection of screws that will be used in testing. The goal is to have withdrawal as main failure mode. The following screw diameters have been selected: 6, 8 and 11 mm. The diameter 11 mm screw has been tested in a pre-testing series with pre-drilling diameters: 0,7d and 0,8d; with insertion depth 90 mm; Also three tropical hardwood species with the highest density were selected to test the limits of the materials. It was found that the smaller edge distances did not cause any problems. Further because of pre-drilling no damages occurred on the timber or screw, and there were no problems during screw insertion. No significant difference in withdrawal capacity was found between pre-drilling 0,7d and 0,8d so this was changed to pre-drilling 0,8d and 0,9d in the main test series. Also screw failure was observed for insertion depth 90 mm, this was changed to a maximum of 70 mm in the main test series to make sure screw withdrawal is the main failure mode.
For the main test series 6 tropical hardwood species were used (Kanda, Lati, Longhi, Tali, Limbali and Mukulungu), and also the softwood Spruce as a reference material. The diameter 6 mm, 8 mm and 11 mm screws were used with pre-drilling diameter 0,8d and 0,9d. Conditioning of the wet test pieces has been done by putting the timber blocks underwater. On every test piece or timber block four tests were done: two withdrawal strength tests (according to EN 1382:2016) and two stiffness tests (according to EN 26891:1991). Also the insertion moment was measured. After testing the density of every test piece was determined together with the moiture content.
The main test series provided a broad range of data. The following was measured: the density, the moisture content, the withdrawal capacity, the insertion moment and slip modulus. All results can be found in annex A. The test piece geometry was not according to EN 1382:2016, in general larger edge distances were required. Nevertheless did this not lead to any problems, no cracks or screw failure occurred during the insertion of the self-tapping screws nor was it any problem to insert the screws at all. This had all to do with the pre-drilling diameters of 0,8d and 0,9d what was used. Because of this very low insertion moments were measured. Also during and after withdrawal tests no significant damage was observed. Even in extreme situations that were tested during pre-testing there was no evidence that a larger edge distance was needed. In the analysis it was found that with increasing density the withdrawal strength also increases, this is in line with literature. It was also found that the species does influence the withdrawal strength, as was found by calculating the withdrawal strength to density ratio per species. With increasing screw diameter the withdrawal strength decreases as was found in this analysis, and also in line with literature. Only in the case of pre-drilling 0,9d for the diameter 8 mm screw this was not the case when comparing it to the diameter 6 mm screw, this probably was a result of pre-drilling accuracy. Regarding the influence of pre-drilling it was found that on average the withdrawal strength is reduced by a factor of 0,68 when the pre-drilled hole is 0,9d instead of 0,8d. In literature it was found that the effective screw length does not influence the withdrawal strength. No clear influence of effective length has been found, except for screw diameter 6 mm and 8 mm when pre-drilled 0,9d. The diameter 6 mm and 8 mm screws are HSBH screws with a larger inner diameter and it might be that the withdrawal strength is not optimal for these types of screw when inserted in 0,9d pre-drilled holes. During testing wet and dry pieces were tested. It was found that the moisture uptake rate is very different for the various tropical hardwood species that were tested. It was also found that as expected the withdrawal strength is negatively influenced by an increased moisture content. First of all it has to be mentioned that the scatter in data is larger when compared to the test data from withdrawal tests, this has to be taken into account. In the analysis it was found that with increasing density the slip modulus also increases. Also the timber species influences the slip modulus just like in the case of the withdrawal strength. No clear influence of screw diameter was found on the withdrawal strength. Just like for the withdrawal strength is the slip modulus influenced negatively when pre-drilling 0,9d has been used instead of 0,8d. This negative influence increases with increasing diameter. With increasing effective screw length also the slip modulus increases, this would be expected and was also found in the test results. Also a higher moisture content has a negative influence on the slip modulus, this was also as expected. A larger influence was observed in the case of timber species with the highest densities measured (Tali and Mukulungu), while for these species the lowest moisture content was measured in wet conditions compared to other species.
Finally two models have been proposed to better predict the withdrawal strength of self-tapping screws perpendicular to the grain in tropical hardwood. For the first model withdrawal strength $f_{ax}$ parameters are determined per species, per timber condition and per pre-drilling diameter. The second model is one formula based on the density, screw diameter and effective screw length for all tested tropical hardwood species. Both proposed models show a good fit to the test data. 

To mitigate climate change and to reach Dutch targets to reduce greenhouse gas emissions with 49% by 2030, emissions by the construction industry must be lowered. Developments regarding mass timber construction have increased the potential to do so. This thesis addresses the problem that the opportunity of reducing CO2 emissions by constructing in timber is not utilised to its full potential. Timber can contribute because the production of structural timber elements is less carbon intensive compared to concrete, the most used structural building material in the Netherlands. Additionally, timber has the capacity to capture and store carbon. From a literature study it is concluded that one of the main reasons for the reluctance towards timber structures is the perception of higher cost.

The goal of this thesis is to qualify and quantify the conditions under which timber structures can be competitive with concrete structures in the Netherlands. For two designs to compete at the same level they must have the same potential profit and serve the same function. Nine interdependent variables are investigated in this research: |1| building use, |2| vertical bearing system, |3| stability system, |4| structural floor system, |5| floor span, |6| building height, |7| CO2 emission costs, |8| additional revenue for timber structures, and |9| the calculation method regarding biogenic carbon.

It is found that considering both the costs and the (non-financial and financial) benefits is important when choosing a structural building material. The competitiveness of timber structures increases if CLT is efficiently used with a limited building height and reduced floor span. Imposing a CO2 tax will give the industry an incentive to reduce CO2 emissions and therefore use timber more frequently, which is essential to mitigate climate change.

The goal of the thesis is to investigate two main questions for the purpose of modelling fractures in timber with a finite element method. The first question is to evaluate the use of digital image correlation during a three point bending test to obtain mean values for tensile strength and fracture energy, and the follow up question is if it is possible to replicate the tests with these mean values. The final result should be a guide to help modelling fractures in timber and how to obtain the necessary data.

The demand to build with wood and other bio-based materials has increased rapidly the last decade, due to the ambition to build more with sustainable building materials. One of the major challenges in building with wood, is to account for the lower strength and stiffness perpendicular to the grain. Wood is an anisotropic material, meaning the material has different properties in different directions. Loading in the perpendicular to the grain direction is sometimes unavoidable and fracture often occurs in a brittle manner. Unfortunately, our understanding and knowledge of the perpendicular to the grain fracture is limited. This is especially the case for hardwoods, for which the material properties and the parameters important for the fracture process are often unknown.

The goal of this thesis is to reduce this knowledge gap on the material properties and the relevant parameters in mode-I (pure tension) fracture process of (tropical) hardwood. The knowledge gained in this research provides the answer to the main research question of this thesis: Which parameters should be considered when describing the constitutive model of a (tropical) hardwood in mode-I tension?

A single-end notch three-point bending (SEN-TPB) test demonstrated a strong influence of the orientation of the growth rings on the perpendicular to the grain fracture process of azobé. The value for the peak load and post-peak behaviour change significantly depending on the orientation in which the sample is placed. Furthermore, visual observations and results from a profilometer revealed that there is an inconsistency in the roughness of the cracked surface area between the different series. From the microscopic analysis is concluded that this inconsistency in general mechanical behaviour and the roughness of the cracked surface area is linked to the composition of ray and parenchyma cells. Moreover, the direction of the ray and parenchyma cells with respect to the fracture plane is different depending on the orientation of the sample. When the ray cells are orientated perpendicular to the crack plane, a higher strength is obtained. The thin-walled parenchyma cells significantly reduce the post-elastic stiffness if these cells are orientated perpendicular to the crack plane. The influence of the composition and orientation of both cells is reflected in the numerical value for the modulus of elasticity, the tensile strength and the fracture energy. This research showed that the composition of the cells in a wood specie and the orientation in which the growth rings are placed significantly influence the mode-I fracture process of a hardwood. This influence is reflected in the modulus of elasticity, the tensile strength, the fracture energy and the shape of the tension softening curve perpendicular to the grain. The results of this research provide new insight into the fracture modelling of hardwood. Both in numerical modelling and design considerations the variation in the material properties because of the orientation of the growth rings, should not be neglected.