Timber pile foundations were historically adopted to improve the stability of buildings, bridges, and quay walls in delta cities in Europe such as Amsterdam (NL), typically characterized by soft soils with poor load-bearing capacity. Many historic buildings still rely on wooden piles, even though in current structures mostly concrete foundation piles are used. Presently, there is a growing interest in using timber foundation piles to support buildings, promoting a new circular construction ecosystem. However, the continued use of timber piles—whether in new constructions or maintaining older buildings—requires a thorough and accurate assessment of their current condition. Ensuring the structural reliability and safety of timber piles is essential, as their degradation over time could compromise the stability of the buildings they support.

The design and assessment of timber foundation piles are still open research topics, hindered by several knowledge gaps in understanding their material and mechanical properties. Timber piles have not been extensively studied in the literature, and the design standards offer minimal to no guidance on their utilization. To enable engineers to adequately design timber foundation piles, verification rules, reliable material properties, and grading specifications are required.....@en

In timber connections, screws have a benefit over dowels or nails, as due to their withdrawal capacity they can transfer loads both perpendicular and parallel to the screw axis. Screws display their largest stiffness and load-bearing capacity in the direction parallel to the screw axis. These properties can be taken advantage of in case timber elements are connected with screws inserted under an angle with respect to the shear plane. Although a calculation method for the translational stiffness of connections with inclined screws is currently not included in Eurocode 5, multiple methods are discussed in the literature. This work focuses on the rotational stiffness of connections with inclined screws, which remains
a considerable knowledge gap to date.

An extensive literature study is carried out, in which methods for the calculation of translational stiffness of inclined screws as well as methods for the calculation of rotational stiffness of dowel-type fasteners are studied. Combinations of these methods are used to put forward fourteen calculation methods for the rotational stiffness of inclined screw connections. Rotational stiffness tests of connections with inclined screws have been carried out prior to the start of this thesis project. The calculated rotational stiffness values of each of the fourteen methods are compared to the experimentally obtained values. Two prototypes of a novel truss concept developed at Karlsruhe Institute of Technology, in which inclined screws are implemented in the chord-diagonal connections, are modelled in Rhinoceros Grasshopper. The influence of the rotational stiffness of the chord-diagonal connections on the serviceability and ultimate limit state behaviour is studied.

A correction for friction occurring between the timber members as a result of the specific sequence of the application of the loads in a subset of the rotational stiffness experiments is proposed. After this correction, the best method shows good similarity with experimental results, yielding a coefficient of determination of 0.79 for a total of 91 tests. With regard to the truss model, it is concluded that the rotational stiffness has no influence on the deflections of the truss, however, the moments in the connections increase for higher rotational stiffness values. Individual screws in the connections are found to receive an additional load of 5-10 % in their main loading direction as a result of the moments in the connections in the large-scale truss prototype. The model can be used in the preliminary design of these trusses to quantify moments in the connections and the forces per screw as a result of these moments.

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...

Riparian ecosystems are crucial for maintaining ecological balance in riverine landscapes, offering diverse habitats, regulating water quality, and preventing soil erosion. However, these ecosystems are vulnerable to slope instability, leading to detrimental effects such as land loss, habitat destruction, and increased sedimentation in water bodies. In the Netherlands, the banks of waterways are typically protected using various materials, some of which emit significant carbon during production. To meet environmental goals such as the Paris Agreement (2022), there is a need for alternative bank protection structures that utilise natural materials.

Root reinforcement, which refers to the ability of plant roots to enhance soil strength and stability, plays a crucial role in assessing slope stability. The presence of roots influences soil strength through hydrological and mechanical effects. Existing methods for quantifying root reinforcement involve mechanical models or time-consuming in-situ measurements using large equipment. Therefore, the corkscrew extraction method has been developed as a quicker, lighter, and simpler approach to measure shear strength in root-reinforced soil. Previous studies have demonstrated the potential of this method for quantifying root reinforcement in field conditions, providing rapid data collection on shear strength at different depths and steep slopes. Throughout the thesis, a corkscrew set-up, inspired from Meijer et al. (2018) was used to assess root reinforcement in riparian environments. Also, it was determined whether this technique is applicable in riparian conditions.

The corkscrew device consists of a garden corkscrew weeder, a tripod with a ratchet winch, a steel cable, a load cell, and a draw wire sensor. The corkscrew is maunally rotated into the soil, and the load and displacement are measured during extraction. The force-displacement curves are analysed to determine rooted soil parameters.

The measurements were conducted at two locations in the Netherlands: the Botanical Garden of the TU Delft in Delft and a testing site in Middenmeer. The Delft location had fields with reed plants (Phragmites australis) and willow trees (Salix fragilis and Salix purpurea), while the Middenmeer site was planted with hawthorns (Crataegus laevigata). Corkscrew extractions produce force-displacement curves, which exhibit different patterns depending on the root content (root area ratio).

The study finds that the corkscrew method is a promising technique for measuring root reinforcement in challenging terrains like riparian areas. It offers advantages in terms of time efficiency, field applicability, and non-destructiveness compared to complex and destructive methods. However, challenges related to root recovery and the limited testing depth need to be addressed through further research.

The thesis also examined root and strength parameters related to root reinforcement. While root biomass provides information about the quantity of roots, it may not accurately quantify root reinforcement. The root area ratio was found to affect soil behaviour and showed correlations with strength parameters for certain selected species. However, other factors such as moisture content, the soil conditions and root diameter could also influence the relationship between root area ratio and shear strength. The force-displacement graphs obtained from corkscrew measurements highlight the significant influence of roots crossing the shear surface on soil behaviour by comparing the pattern of the curves. Also, root breakages are identified as sudden drops in force displacement graphs.

The presence of roots mobilising at higher displacements than the peak strength of bare soil is crucial for slope stability. The combination of species might provide the best reinforcement effect for stability owing to difference in root paterns spatially and with depth.

This thesis report provides an analysis of the structural behavior of façades made of CLT panels with openings. These openings will have a significant influence on the transfer of forces in the panels, as well as the stiffness of the façade. The connections required to transfer the forces between the panels are designed. Deformations of the connections introduce addition deformation of the façade itself. The components that influence the force transfer and deformation of the façade have been identified in this research. Their contributions have been investigated. The theoretical calculations have been compared to computer results. The resulting conclusions aid designers in an early design phase regarding the feasibility of a CLT façade structure.

The main focus of the research has been on the mechanical fastener connections that are required for the CLT façades. The research question is stated as:

“What is the influence of mechanical fastener connections on the strength and stiffness of CLT façades that function as the main stability system?”

The research started with the goal to find the limitations of CLT façades for multi-story timber buildings. In order to find these limitations, a complete understanding of the structural behavior of the façade was required. Since connections were found to be of great influence the research focused on this topic.

The structural behavior of the façade was defined as the top deformation of the structure and the force transfer and resulting stresses in the panels. The dynamic response of the structure has not been analyzed.
Seven components were identified that influence the stiffness and force transfer in the structure.

Bending of the façade
Shearing of the façade
Bending of lintels
Bending of piers
Sliding of connections
Rocking of connections
Additional bending deformations due to connections

Computer models were used to verify the overall behavior of the façade as found with the theory. The computer model did not verify each individual component.

Peak shear forces in the CLT panels near the corners of openings determine the required panel thickness.
When these shear forces are reduced (for example by applying a concrete core in the structure) the required panel thickness can be reduced.

Top deformations of a façade with a width of 20 meter limit the maximum height to 45 to 55 meter, depending on the connection stiffness.

The main contributor to the top deformation is the connection stiffness of the connections between the vertical edges of the CLT panels. These influence the collaboration between the panels, hence significantly affect the bending stiffness and corresponding bending forces in the panels.

The lintels of the façade panels highly influence the load distribution in the façade. There is no accurate method to calculate this influence on the load distribution.

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...

This Master Thesis research is carried out to investigate the most efficient re-mountable timber car park in terms of feasibility and structural performance. Applying the re-mountability principle with a sustainable material like timber is important to help the construction industry tackle environmental problems like global warming. Specifically, re-mountability is important because it ensures a second use of the car park without applying environmentally affecting processes, like redesigning or repairing the gained elements, and without creating waste.
In summary, the research question is: What is the most suitable design for a timber re-mountable car park, including global structure and details based on structural performance and feasibility?
The first part of this research is determining the most suitable floor system. This is important because of the large floor span in a timber car park and the reduced stiffness of timber compared to concrete and steel. Information is gathered by investigating car park and floor system references and the boundary conditions from regulations, material behaviour, transportation, etc. Next, a preliminary design is made for the four largest potential floor systems.
Based on this preliminary design combined with the earlier gained knowledge, the most suitable floor system is chosen in a multi-criteria analysis. A spruce CLT floor system of 140 mm thick combined with 360 mm x 1040 mm glulam beams becomes the most suitable alternative. A Triflex coating is necessary on top to ensure sufficient moisture resistance and re-mountability of the floor system. The fire resistance does not affect the floor system design because the serviceability limit state is governing.
Then, the second part of this research uses the known floor system to design the re-mountable connections in a final design phase. Using the knowledge gained from the references and boundary conditions, a bolted connection is the most suitable re-mountable connection type. However, a console is most suitable for the column-to-beam connection due to the positive effect on the necessary crane operation time.

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.

Low-frequency sound transmission in a cross-laminated timber apartment building can result in annoyance, even if the acoustic requirements of the building code are fulfilled. Cross-laminated timber is an upcoming material in the building industry. But there are also problems arising when building with this relatively new material. CLT is a lightweight building material, which means that the mass itself is insufficient for meeting the acoustical requirements. The total sound transmission depends on the amount of direct sound and flanking sound transmission. The ISO 12354 standard used to determine the amount of sound transmission between rooms does not include frequencies below 100 Hz. Even though these low-frequency sounds are the main cause of annoyance in lightweight construction buildings. The low-frequency sound transmission is hard to measure because of the long wavelength. In this research, a numerical model was developed and used to determine the low-frequency sound transmission in CLT apartment buildings.


The effect of the following sound-reducing measures are studied: the material properties of the material CLT, additional linings on the room separating elements, use of elastic interlayers between CLT panels and the type and number of connectors connecting the CLT panels. These are all common sound-reducing measures for lightweight constructions. The effect of the material properties of the CLT and the effect of additional linings are computed by a numerical direct sound transmission model. The effects of elastic interlayer and connectors between the CLT panels are computed with a numerical vibration reduction index model. The results of the numerical models are compared to measurements found in literature and the sound transmission according to the ISO standard.

The results showed the importance of Young’s modulus in the y and z-direction, these influence the location of the resonance induced dips in the sound insulation. The internal loss factor of the CLT panels influenced the height of the dips. A loss factor of 20 % resulted in results most similar to the measurements. The direct sound transmission through a bare CLT panel can be predicted within a range of 3 dB difference with measurements. The prediction of the ISO standard is within a range of 5 dB with the measured values.

The vibration reduction index between panels without interlayers is modelled with frictional contact regions between the panels. The numerical results showed similarities with the measurement results for the vibration reduction index of panels with screwed connectors. The ISO standard significantly overpredicts the vibration reduction index of CLT junctions. The effect of the elastic interlayer showed insignificant improvements in the frequency range 50-500 Hz, the additional reduction stays below 3 dB. The ISO standard does not include a method to determine the effect of elastic interlayers or connectors between CLT panels.


The numerical models prove that is possible to predict the low-frequency sound transmission in CLT apartments. Important notes are that the CLT lamellas need to be modelled separately. Only in this way the model is able to capture the sound that goes through a structure within a range of 3 dB. In order to test the effect of additional lining, the material properties need to be known.
The vibration transmission between panels in the junctions is more complex, as it depends on more design parameters. A frictionally bonded contact region between the panels results in vibration reduction indices that are in line with measurement results of panels with several connectors. The effect of the elastic interlayer is minimal in the low-frequency range, but the results are similar to measurement results. Both the direct sound transmission model and the vibration reduction model were influenced by the boundary conditions.

A study carried out to understand the effects on including vegetation as an additional reinforcement to improve streambank stability.

The isostatic slab was developed by Pier Nervi and his colleague Aldo Arcangeli to create an elegant and easy to produce floor system, with efficient use of material. These slabs are designed with ribs aligned to the principal bending stress lines that support a flat deck. Concrete isostatic slabs are no longer constructed due to their expensive formwork. However, this system could be advantageous when made from timber as the grain direction will be aligned to the optimal flow of forces. Additionally, isostatic slabs can be designed for any support conditions, so an isostatic timber slab may be more desirable than the typical one-way spanning timber systems. The isostatic timber slab is a new concept and has not been previously used. Therefore, before the system can be applied, there needs to be a greater understanding of the design process. This research achieves this goal by splitting the process into two parts. Firstly, the rib geometry is created by generating the principal bending stress lines. Secondly, the system is designed and analysed for a case study. The aim is achieved by creating a functional design and identifying the critical areas in the design process. An approach for measuring the accuracy of stress lines is developed and used to test different methods for improving the stress line generation process. The improved process uses a more advanced integration method and a holistic seeding method. Additionally, a novel method for interpolating the principal stress trajectories from finite element analysis (FEA) results is established by utilising the shape functions from the theory of FEA. An iterative approach used to select stress lines to create optimised truss geometries in in-plane-loaded plates is tested for its applicability to out-of-plane loaded plates (i.e. slabs). The rib geometry produced was measured by the approximation error and the deck elements' span lengths. This iterative approach does not apply to slabs as it creates clustered areas and excludes symmetries. Analysis of principal stresses under different load cases shows that the most considerable difference from the primary load case is when half of the slab is loaded with a maximum load and half with a minimum load. (The primary load case is the condition used to create the stress lines for the rib geometry). Using FEA to calculate the stresses under each load case shows that uneven loading of the slab does not produce higher stresses than the primary load case. A functional isostatic timber slab design is made for the case study using laminated veneer lumber (LVL) for the ribs and plywood for the deck. Linear elastic FE modelling of the structure shows that increasing the deck thickness and decreasing the rib depth, causes the deck to carry more load and the ribs to carry less and vice versa. Increasing the rib thickness has a small effect on the force distribution due to the available LVL thicknesses. The FE modelling also showed that the torsional load transfer mechanisms are reduced by increasing the rib slenderness. The design is made based on the ultimate limit state (ULS) stress requirements for the elements and three critical connections, and the deflection under the serviceability limit state (SLS). The rib-to-deck joint requirements determine the deck thickness, and the deck has a low utilisation for the stress conditions, meaning that the deck span lengths are not critical. The ribs' depth is heavily dependent on the rib-to-rib moment connection as a large lever is needed. The cross-sectional properties of the ribs are also dependant on the standard LVL sizes. This system is compared to several conventional one-way spanning alternatives based on the total material volume, the structural weight, and the structural depth. The isostatic timber slab has a reduced volume and weight compared to a flat cross-laminated timber (CLT) slab, a Kerto-Ripa slab, and a concrete hollow-core slab; however, the isostatic timber slab has a larger structural depth. A ‘T’-beam equivalent to the two-way spanning isostatic slab has less volume and weight while maintaining the same structural depth, but has a larger average deflection. Timber isostatic slabs are complex to design with a highly connected network of parameters. The system should be designed by minimising the peak moment forces at connections, curating the support conditions to reduce stress line clustering, and selecting stress lines for the rib geometry which ensure sufficient stiffness at the peak deflection location. It is advised to produce a parametric model of the slab that can quickly assess the design performances and efficiently complete design cycles.

Conventional building methods are still based on the reinforced concrete industry. In the last decades, timber has become more popular because it could be a more sustainable alternative. However, pure timber is not always an option, especially when slender design is required by the client. Because of its low elastic modulus, deflections often require an increased deck height. Therefore, this research focuses on the strengthening of timber bridge decks with reinforcement and prestress in order to increase their slenderness (= the ratio of the span to the height of the cross-section). This might make timber decks more competitive to reinforced concrete designs regarding slenderness. The problem is that prestressing timber decks will lead to creep deformations that induce losses of prestress force. This research is focused on modelling the creep deformations and the resulting resistance losses of prestressed timber decks.

First, a cross-sectional model is developed to be able to find the initial resistance of a reinforced- and prestressed timber deck. This model is based on an incrementally increasing curvature so that the deck behaviour can be quantified from zero load to the failure load. Second, a time dependent model is developed to find the displacements and resistance through time. The timber bridge deck is modelled with ODE systems. The ODE's are used to find the (1) displacements and (2) strains of the deck. To obtain the time dependent behaviour of the deck, a viscoelastic E-modulus is substituted into the displacement- and strain equations. This viscoelastic E-modulus decreases with time, which causes an increase in displacements (= creep displacement). In the same way, the strains are modelled over time. The time dependent creep stains are implemented in the cross-sectional model to find the reduced resistance of the timber deck.

The outcomes of the model suggest that large prestress forces lead to negative creep deflections (= creep in upwards direction). Meaning that for the right value of the prestress force, also zero creep deflections can be obtained. Besides creep, the instantaneous deflections are a large part of the total deflections. According to the results of the model, the instantaneous deflections can be decreased by up to 70%. Regarding the resistance, the final increase of bending moment resistance can reach up to 30% by incorporating prestress (at t = 50 years, including losses due to creep). Due to creep, prestress force is lost over time, resulting in a decreased deck resistance. This research shows that the creep losses result in a bending moment resistance decrease of up to 12%. Taking this into account, a bridge deck with a slenderness of 31 to 33 will be able fulfil its requirements after 50 years of service life. Depending on the client requirements, a slenderness of over 34 can be reached.

Using Eurocode, creep deformations are calculated with a simplistic and conservative method. The model that is built in this research gives a more advanced way of determining the creep deformations of a timber deck. This leads to more realistic quantification of creep behaviour. However, Several factors still cause uncertainty in the model. Therefore, experiments with timber decks should be done to obtain more accurate data for the creep behaviour. The model from this research can be calibrated according to data from experiments, which will increase the reliability of the results.

Highway traffic bridges have been subjected to increasing loads over the past decades. Some of the movable bridge leafs in these highway bridges were constructed in the 1960s and they are now close to the end of their intended life span. These bridge leafs were typically designed and executed with hardwood deck boards. In the initial design calculations, traffic loads were smaller, complex calculation by computer models did not yet exist. Therefore, some phenomena like for example fatigue and global hybrid interaction were never considered. Since some movable highway bridges are now due to be re-assessed, there is a growing need to gain knowledge on the way timber decks are functioning within the movable bridge leaf. These bridge decks have sustained all loads throughout the years without significant damage, but we don’t know whether these timber deck boards help the main load bearing steel structure as well. Or in other words; do the timber deck boards interact with the steel girders in the current situation? In this research, the degree of hybrid interaction was measured in terms of the magnitude of the main girder deflection for the reference case of the Bridge across the Beneden Merwede. The main girder deflection for bolted connections, having a certain free slip and embedding stiffness, was determined by running a linear sequential secant stiffness analysis. This analysis approximates a physically non-linear analysis. The maximum deflection of the main girder was compared to the maximum main girder deflections for no hybrid interaction versus full hybrid interaction. The resulting global deflections from the Secant Stiffness Analysis have shown that practically no hybrid interaction can be found between the current deck and the steel structure. For retrofitting options, the level of hybrid interaction can be significant. An increasing or decreasing degree of hybrid interaction did not only change the forces and moments in the steel girders, but also had a considerable effect on the deck and its connections. There is a gain and a loss for every retrofitting option considered. Decision-making for retrofitting timber bridge decks should take multiple contradicting criteria into account. An optimisation could be necessary in order to take a well-advised decision.

Practical combinations of floor configurations and support conditions are studied for the development of a lightweight timber building method that is suitable for multi-family residential buildings. Classical vibration theory forms the base for a methodology that is developed to assess transmittance of vibrations to adjoining floor fields. Especially when the source is out of sight, humans humans are tend to classify vibrations as annoying for low vibration levels. With the introduction of new engineered timber products made wood a more suitable and used material for residential buildings. Strength- and stiffness variation is reduced by homogenizing the material and regarding soundproofing innovative concepts have been improved, such as floating screeds and resilient materials. Based on these products and acoustic concepts, 32 design combinations are studied. A distinction between forced- and free vibrations is made and related to low- and high-frequency floors. Forced vibrations are in structural dynamics described by the particular solution, and free vibrations by the homogeneous solution of the equation of motion. This solution is found through the method of separation of variables, which multiplies the space- and time-related parts. Mode shapes are studied regarding transmittance and effective measures for prevention. Fundamental frequencies of floors supported either rigid and flexible are determined with one-dimensional undamped continuous systems where supported beams are represented by equivalent springs. All floors are transformed into Single Degree of Freedom systems to include damping. These systems are assessed making use of modal superposition, for steady-state- and transient response. The behaviour of floors under walking load harmonics provides the resonant response, and free vibration of the system due to initial conditions the transient response. Since the perception of vibrations by humans is frequency-dependent, vibrations are weighted accordingly. Eurocodes currently available are found to provide guidance regarding human-induced vibrations of lightweight structures marginally. Non-timber Eurocodes do not provide an assessment method, EN1990 only provides requirements when no assessment has to be done, and current code for timber structures prescribe criteria that are not sufficient as found in the literature. The future revision of Eurocode 5 holds several methods for assessment of vibrations but is generally focussed on rigidly supported floors. In extending to this code methods are developed to acquire fundamental frequencies of flexible, supported floors, and by transformation into SDOF systems an equation is developed for the appropriate determination of modal mass for two-span or beam supported floors using a simple formula. 32 combinations of floor configurations and support conditions are assessed at the excited field and at adjoining floor fields, where both steady-state and transient response are combined. Based on this assessment, transient responses are found to contribute significantly for low-frequency floors, where generally is assumed that the mass is sufficient to neglect this response.

Timber bridges are much applied structures in the Dutch landscape. In contrast to the other two most common building materials, concrete and steel, the use of timber is however almost exclusively limited to bridges for lighter traffic, e.g. pedestrians and bicycles. Examples of timber traffic bridges in Germany, Scandinavia and even in the Netherlands, show however that, at least structuraly, timber can be perfectly used in the construction of bridges for heavier traffic. Although structuraly feasible, there are still a number of doubts and uncertainties that go hand in hand with timber bridges. One of them is the maximum reachable service life. This research focusses on the ability to estimate this service life with the help of so called factor methods. The service life of a timber element in the Netherlands, with respect to biological decay, is in the basis determined by two main factors: the natural durability of the timber specie, and the moisture and temperature levels of the timber during its service life. In the case of timber bridges, where the timber elements are subjected to the weather, this can be broken down in three main influencing factors, namely:
1. Natural durability of the used timber specie 2. Local climate (Temperature, rainfall and humidity) 3. Detailing of the bridge (Protection against water accumulation) With these three main influencing factors in mind, factor methods can be used to estimate the service life of bridge elements. These factor methods estimate the service life based on reference situations, and use modification factors to modify these reference situations into the actual situation of the element. In this research two different factor methods have been reviewed in depth: the DuraTB method, developed in Sweden, and the TimberLife method, developed in Australia. The two factor methods have in this research been compared with each other and after that their usability and accuracy has been tested with the use of two reality checks on existing bridges in Amsterdam. For the reality checks, first an expected bridge condition was determined with the help of the two factor methods. After this the actual condition of the bridge was determined by an in-field visual inspection. Then the expected and the actual conditions were compared in order to obtain insight in the correctness of the service life estimation of the two factor methods. In addition, the role of factor methods in the processes of service life planning and especially during the calculation of the total costs of ownership (TCO) has been discussed. An example of a TCO calculation has been performed for two bridge designs, in which the focus was put on the incorporation of both the DuraTB and the TimberLife factor methods. Even though this TCO example is not representative from a total cost point of view (since the values of the different costs were guessed), it does show how factor methods can be used in the calculation of these total costs.

Sustainability is an important aspect in the construction industry nowadays and therefore timber is interesting to use as it is considered a sustainable building material. With the development of mass timber engineered products such as glued and cross laminated timber, there are more and more possibilities to use timber as a structural element, but this material is not yet widely used in high-rise buildings. Recent research has shown different aspects to take into account when using timber. Due to the lightweight, high flexibility and strength, attention must be paid to the dynamic behaviour and the high horizontal deflections of the top levels of the building due to wind. A parametric model is used to generate the structural model, which enables you to easily change certain parameters to gain a quick insight into the consequences of these changes on the behaviour of the structure. The model is developed in the program Autodesk Dynamo, where a plug-in developed by the company Arcadis is used to connect Dynamo to a FEA application called RFEM to be able to check the generated structure on relevant criteria. The parametric model is able to design a building which has certain dimensions and lateral stability systems which can be changed. It is chosen to implement lateral stability systems consisting of shear core(s), a diagrid and a tube, which can be used either independently or combined. The connections between the elements cannot be modelled with a finite stiffness using the Arcadis plug-in. Therefore, several assumptions had to be made to encounter for the characteristics of the connections. The Young’s modulus of the structural elements are modified to take into account the stiffness of the connections and openings in surfaces if present. To check if the parametric model gives satisfying results, a case study is performed on the BrockCommons Tallwood House. This showed that the parametric model gives satisfactory results. A parametric study is performed to check the possibilities of timber high-rise regarding maximum building height in The Netherlands. An office building with a width of 32.4 metres, a depth of 28.8 metres with a specific floor plan and connection characteristics is used. Optimal configurations regarding compressive and tensile resistance of connections between structural elements are resolved using MATLAB and the reduction of Young’s modulus of the elements is determined using the specific connection characteristics. The connections used in the parametric study are compared to commonly used connections regarding strength and stiffness. Furthermore, an insight is given on the influence of the stiffness of the connections on the structure. The maximum building heights are investigated for stability systems consisting of either a shear core, diagrid, tube or a combination of 2 stability systems. Results show that a 4-storey diagrid system with infinite stiff connections can reach the greatest height of 187.2metres. No additional measures had to be taken to ensure that each structure complied with the maximum acceleration limit for office buildings. Finally, a comparison
is made between the stability systems with regard to total timber volume and steel mass usage.

The application of vertical forests in the building industry is a popular development with promising advantages regarding sustainability. However, placing trees along a façade gives additional loads which often results in extra material use. This is undesired concerning building design, costs, and the environment. To mitigate these adverse effects, trees could be used as load-bearing structural elements. To increase the stability of such elements, it might be advantageous to connect the trees to each other. Such connections can naturally be created with inosculations: self-growing connections in which the bark and inner tissue of two trees merge. Applying living trees as structural elements requires a deeper understanding of both the botanical and structural behaviour of trees. Likewise, more must be known about the botanical and structural behaviour of self-growing connections. This research expands the knowledge on the topic of using living trees as structural elements, both as single tree elements and self-growing interconnected tree elements. This aim is reached by proposing a structural model of (interconnected) trees, which is verified by comparing the outcome of the model with the outcome of winching tests. Furthermore, a design is made in which living trees are used as structural elements in a vertical forest case study. This lays the groundwork on how to approach a living tree design, both from a structural and botanical point of view. The structural model is verified by carrying out winching tests on the Living Tree Pavilion, including one single tree, one pair of cross-connected trees and one pair of parallel-connected trees. Additionally, winching tests are performed on a tree in an airpot, in which boundaries constrain the root system. During the winching tests, a force is applied to the tree system, and the elongation is measured on several locations of the tree, providing insight into the strain distribution. Additionally, the displacement of the trees is measured at the height of the force application. Based on geometry measurements, the trees are modelled as solids in a finite element software. From the models of the interconnected trees, a compound solid is created which behaves like a single solid. The winching load is applied to the models to allow for a comparison between the results of the winching tests and the models. The geometry measurements show indications that leaning trees create an oval cross-section, which is influenced by the presence of inosculations. The winching tests show that an unconstrained root system is stiffer than a root system constrained by an airpot. Furthermore, the tests show that interconnected trees do not have favourable stiffness qualities compared to single trees. A comparison between the model and test results indicates that the finite element model is a plausible representation of reality for the single tree, the parallel-connected trees, and the out-of-plane results of the cross-connected trees. The finite element model fitted poorer with the in-plane winching test results of the cross-connected trees. More research is needed to determine whether diverging tree characteristics, in the direction that is rarely subjected to loads, could explain the discrepancy in measured and modelled behaviour. Two designs are created in which living trees of the Wonderwoods vertical forest carry the loads of a plant container. There are three reasons why cross-connected trees are not favourable over a design with single trees. First, the single trees can bear the plant containers at a younger age. Second, the risk of trees not creating suitable inosculations is high. Third, as interconnected trees share one container, the competition for space can become fierce. This research concludes that a system of interconnected trees as structural elements is not favourable over a system of single trees. This is mainly because no clear advantages in terms of strength and stability could be found in both the winching tests and the design for Wonderwoods.

Timber structures are experiencing a revelation in the build environment due to new technologies and production techniques. However, the longest spans created with timber structures still don't compete with the span widths of structures made of steel. This thesis provides a preliminary design for the long-span football stadium roof structure of The New Feyenoord stadium, which expends far beyond the existing maximum spans of timber structures. The aim is to provide insight in the feasibility of a long-span structure in timber. New Feyenoord stadium The city of Rotterdam is planning to built a new football stadium for the football club Feyenoord with a magnificent roof structure. This stadium is used to determine initial boundary conditions for the preliminary design in this thesis. A perfect bowl with an elegant flat, almost floating, roof that allows unobstructed viewing is desired. The playing field needs to be exposed to the weather conditions for the natural quality of the grass. The stadium will consist of three tiers with a total height of 40 metres, that need to be covered by a roof structure with a width of 205 metres, and length of 245 metres. Structural timber for a grand roof Timber has a high strength-to-weight ratio that is beneficial for long-span structures in which the self-weight of the structure is a significant part of the load. It has natural durability, a good performance in fire conditions, ease of workability, and a high ratio of prefabrication. The latter two result in an ease of construction and less human induced errors. Engineered wood products make it possible to create complex timber structures with more reliability than wood in its natural shape. The most promising are laminated veneer lumber (LVL) and glued laminated timber (Glulam), where LVL made of beech hardwood has the highest strength properties. Furthermore, new types of connections diminish the impact that connections traditionally have on the structural performance of timber structures. The enormous size of this stadium means that multiple connections are necessary due to dimensional restrictions for transport. Which reduces the amount of prefabrication. Structural systems for long-span stadium roofs Promising configurations for a long-span stadium roof structure are the single span, stress ribbon, shell roof system, and tension / compression ring. First, several existing stadium roof structures are presented to gain better insight on the possibilities of these systems. These stadiums are De Kuip, preliminary design of The New Feyenoord stadium by RHDHV, the Allianz Riviera stadium, the Wanda Metropolitano stadium, the Estadio Municipal, and the Tokyo National stadium. Initial designs are made for each structural system applicable to the case of the New Feyenoord stadium. These initial designs are explored on their structural behaviour and benefits for the case of the New Feyenoord stadium in combination with the material behaviour of timber. Structural forms for long-span timber structures Several structural forms are applied in long-span timber structures showing their applicability. These forms are the arch, box girder, truss, shell structure, space frame, and stress ribbon. This is explored by means of respective reference projects. These projects are the Multi-use Arena in Lisbon, Trade Fair Hall 11 in Frankfurt, the Anaklia-Ganmukhuri bridge in the Georgian Republic, the Maicasagi bridge in Nord-du-Quêbec, the geodesic domes in Brindisi, the Elephant House in Zurich, the Allianz-Riviera stadium in Nice, the Grandview Heights Aquatics Centre in Surrey, and the Essing bridge in Essing. These existing long-span timber structures mainly span only half of the required length of the New Feyenoord stadium. Possibility to create an efficient structural design for a long-span stadium timber roof structure After a rough assessment of the design concepts it is found that a combination between a tension / compression ring structure and a stress ribbon configuration shows the greatest potential for an efficient roof structure for the New Feyenoord stadium. Their are still many uncertainties for this type of structure for such a long span. There is no reference project and thus there can not be learned from mistakes. Also, the system is mathematically very complex because of its non-linear behaviour. Consequently, the structural system is modelled and verified in the parametric FEM environment of Grasshopper and Karamba3D. The found structural behaviour is verified by the strength verifications for timber structures. Tension / compression ring with radial stress ribbons The design consists of a triangular truss for the outer ring and a flat truss for the inner ring with radial stress ribbons in between. The structural design shows a feasible solution for the highest downward load, namely loads instigated by wind. The strength verification is performed on the maximum occurring force combination within a element group. Only the strength verification of shear stiffness in the bottom chord at the inside perimeter of the outer truss ring is not met. Which is a very localised effect and hence can be strengthened. Furthermore, the element groups of the rings show a undesirable utilisation distribution due to the non-circumferential perimeter of The New Feyenoord stadium. Large cross sections are required to provide stiffness to the entire structural system. The ribbons make use of their inherent bending stiffness to carry the loads in the long and short straight sides of the stadium. An elegant and stiff tensile force flow is found for the ribbons in the corners. At last, the designed connections for the ribbons which are attached to the timber fulfil the strength verifications. These connections consist of self-drilling dowels with slotted in steel plates, self-drilling screws, and glued in steel rods. Many steel fasteners are used to increase the efficiency factor of the joint. Suggested connections for the complex nodes in the ring trusses consist of slotted in steel plates with bolts and dowels, glued-in rods, and cast steel parts. The structural system is supported on roller bearings. The presented structural design only takes downward loading into account. Potential solutions for the severe upward loading are increasing the weight of the structural elements in the loaded area, tensile ties in the long and short side of the stadium, or tensile cables attached to the bottom side of the ribbons in the long and short side. An more in depth analysation of its stability against uplift forces and asymmetrical loading is needed to verify the proposed solutions. Recommendations are made to improve the design for The New Feyenoord stadium, for general possibilities for the chosen structural system, and for improvements and advice on the feasibility of special timber structures. It is concluded that a timber long-span stadium roof structure consisting of the chosen structural system shows potential to be a feasible solution for the New Feyenoord stadium. It will be a grand architectural statement that makes a stadium iconic, being the only timber tension / compression ring stress ribbon roof structure spanning with an exceptional distance.

As timber is being used for several millennia as construction material, glued laminated timber (glulam), a highly engineered timber product, exists for about hundred and fifty years. In Europe, it is nowadays common practise to make glulam from softwood species, though in the last few decades glulam made from different kinds of hardwoods emerged. Iroko glulam is part of this development, as iroko is a hardwood species from the African tropical regions. The aim of this thesis is to investigate the bending strength of iroko glulam, as well as strength influencing features. From literature it is expected that the following features are of influence: density, modulus of elasticity, tension strength of the lamellas, finger joint strength and size. Several researches conducted in the past experiments to determine these mechanical and physical properties, focusing mainly on iroko sawn timber. Only few investigated iroko glulam, and none of those focused on finger jointed iroko glulam. In this lies the originality of this work: determining bending strength values of finger jointed iroko glulam, as well as density, modulus of elasticity and investigating mechanical and physical properties of the base material: iroko sawn timber and iroko finger joints. The laboratory experiments included the following: tension tests on 38 unjointed and 38 finger jointed lamellas, and four point bending tests on 12 glulam beams. Also density, modulus of elasticity and moisture content were determined. The experimental results yield the following characteristic values: a lamella tension strength of 17 N/mm2, a finger joint tension strength of 29 N/mm2, and a glulam bending strength of 42 N/mm2 (including size effect according to NEN-EN 1995, 2011). The experimentally determined characteristic lamella tension strength is a little lower than values found in literature. This is due to a large scatter in the test results: a coefficient of variance equal to 0.37 was found. However, if the grain angle is equal or smaller than 5°, a higher lamella tension strength of 27 N/mm2 is feasible. Grain angle is as expected a significant strength influencing parameter for iroko sawn timber. And it would suggest that the strength class is as expected D40 if the lamella bending strength equals 0.6 divided by the lamella tension strength. The ratio of finger joint bending strength (30 N/mm2) and tension strength (29 N/mm2) on the characteristic level was found to be equal to 1.06. This is smaller than expected from theory: apparently the 1.4 ratio commonly assumed for softwood finger joint strength values does not hold for iroko finger joint strength values. The investigated iroko glulam beams with depth 108 mm yielded a mean bending strength of 66 N/mm2 and a characteristic bending strength of 42 N/mm2. Due to the size effect and quasi-brittle failure this figures lie lower for full scale glulam beams, however, strength class GL24h is indeed a safe assumption for iroko glulam beams. These aspects explain the higher mean glulam bending strength compared to the mean finger joint tension strength of 40 N/mm2. A strong mathematical relationship between characteristic glulam bending strength and both lamella tension strength and finger joint strength was not found; however lamella and finger joint tension strength do influence the glulam bending strength. Furthermore, density does not influence any strength or stiffness property for both iroko sawn timber, finger joints, and glulam beams. Although there is a slight positive correlation with both dynamic and local modulus of elasticity of lamellas and its tension strength.