Amsterdam and many other cities consist of a network of old quay walls, which sometimes have been constructed over a century ago. A large uncertainty exists concerning the current safety of these quay walls and their remaining service lifetime. In the current framework for the assessment of old urban quay walls, the influence of timber creep in the structure is being omitted. It had been expected that a part of the excessive deformations occurred are part of this timber creep as opposed to progressive failure. Hence, this research studied the influence of wood creep on the structural behaviour of old urban quay walls, using a case study based on the Herengracht. For the modelling of the quay walls, use has been made of the Embedded Beam Row (EBR) elements in Plaxis 2D. As this element type has no material model which takes into account creep, use has been made of pseudo-elasticity. The behaviour over time had been modelled by reducing the elastic stiffness of the EBR elements with increasing creep factors. To force Plaxis to perform calculations, this stiffness reduction has been introduced as a reduced strength in the form of a custom moment-curvature diagram. At the time of writing, the Embedded Beam Row had not yet been validated for cohesive soils. Hence, a verification has been executed of the EBR using a full-scale load test performed on a pile group in Salt Lake City. In this case, a 3x5 pile group driven in multi-layered cohesive and non-cohesive soils had been laterally loaded. The results included deformations, total horizontal load and bending moment distributions over depth. It has been found that the EBR provides reasonable results when modelling laterally loaded pile groups. The force-displacement curve from the field test was only slightly stiffer compared to those obtained using Plaxis 2D. Maximum bending moments obtained using the EBR had been found to be 20 to 30% compared to the experimental data. The group efficiency of the pile group was initially lower for small displacements, which was likely caused by the lack of installation effects of driven piles in the Plaxis model. It has been observed that the Interface Stiffness Factors (ISF) that are used to calibrate the EBR behaviour have a limited range. Increasing the ISF values beyond a certain limit will no longer affect results, as the interface connecting the EBR to the soil will have become practically rigid at this point. Nevertheless, it has been concluded the EBR can be used in this case to model laterally loaded pile groups. The influence of the timber creep on the structural behaviour of quay walls has been studied using a model based on the Herengracht in Amsterdam. A maximum creep factor has been applied of Φ=1.6. Two methods have been used to apply the final creep factor. With the "Direct" method, the maximum creep factor was applied in the same phase as the load. With the "Indirect" method, the creep factor has been applied incrementally in steps of 0.1. It has been observed that the results from these methods deviate significantly. With the Indirect method, larger creep displacements have been calculated, as well as lower maximum compressive stresses in the piles. The creep behaviour has been studied in more depth using the Indirect method. In this case study, creep displacements of 2.22 times the initial displacement have been calculated. When plotted against the increasing creep factors, it has been observed a power function could be fitted to the data. In addition, a stress reduction of 0.590 times the initial maximum compressive stress has been observed in the front two pile rows. This stress reduction was achieved at φ=0.4. In the most landinwards pile row, stresses continued to decrease, with a reduced rate beyond φ=0.4. A sensitivity analysis has been performed to study which parameters have significant influence on the creep behaviour. Conclusions were drawn based on the relative change in horizontal displacement and maximum compressive stress in the front pile row. It has been concluded that the shear strength parameters of the top layer, the elastic modulus of the timber, surface load and the geometry have the largest influence on the creep behaviour. Furthermore, it has been discovered that the size of the creep factor steps influences the final stress and displacement. With decreasing stepsize, convergence occurred in the results. From the results it has been concluded that the structural behaviour of old urban quay walls is significantly influenced by timber creep. The inclusion of timber creep resulted in large displacement increases, but also in stress reduction. The results suggest that excessive deformations of quay walls does not mean that an ultimate limit state has been reached. It is recommended to include the timber creep in the modelling and assessment of existing quay walls.

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.

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...

The increased loading and decreasing strength of historical quay walls calls for remedyand has drawn the attention of many Dutch municipalities, Rotterdam being oneof those. In order to set up proper assessment methods that result in an economicaland ecological policy for renovation or replacement of these structures the Port of Rotterdamhas asked Delft University of Technology to assist them. This thesis focusses onthe elements perhaps most prone to decay and hardest to inspect: the timber foundationsimplemented in quay walls with relieving platforms from the late 19th and early20th century. The main research question of this thesis is What is the (remaining) capacityof the timber foundation of a quay wall with relieving platform? and focusses onthe Maaskade case. The aim is the provision of a structural analysis and appointmentof weakspots on a representative quay section build-up using measured material characteristics.This quay has partially collapsed and has been replaced as of May 2020. 45Timber piles from the site have been investigated in the Rotterdam harbour to derivedensity and (dynamic) Young’s modulus measured by a Timber Grader MTG. A selectionof these piles was then further tested in pieces (21) at the TU Delft structural laboratory(Stevin II) to derive the Young’s modulus and compressive strength. Using the correlationfound between the compressive strength parallel to the fibre ( fc,0) and the dynamicYoung’s modulus parallel to the fibre (E0) the compressive strength values of the entire45 pile group have been derived. This results in fc,0,k = 12.64 MPa and E0,mean = 11.3GPa under 50% moisture content, the saturated state the wood is expected to be in inthe quay. The resulting design strength fc,0,d = 10.7MPa is very much in line with the advisedstrength of 10.8 MPa in NEN 8707 . Missing characteristics necessary for structuralassessment are used from bending class C22 (sawn timber) from EN 338 . A FEMmodel of section 4-1 of theMaaskade under different historical build ups has been set upin Plaxis 2D, and an Ultimate Limit State computation has been carried out on the finalbuild-up before replacement under four load cases. The found normative location thatcan be seen as the weakspot is the joint between the raking pile and the adjacent cappingbeam. A structural assessment based on sectional forces results in a negative outcome ofthe structure even on the self weight governed loadcase as unity checks > 3 are given for thecapping beam. These results do have the shortcomings due to simplifications from 3D to2D and a modelling with linear elements with no volume in the model and no allowancefor further load distribution beyond elasticity. A definite answer on the capacity in termsof additional external loads cannot be given and the need for a model that incorporatesthe exact lay out and positioning of the loads is stressed. Further recommendations forpractice are to find out if the capping beam- pile connections are expected to be able totake tension and to name their state after an inspection.

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.

Cross-Laminated timber (CLT), and other engineered timber products, are under high demand due to their prefabricated nature and environmental benefits. A key concern surrounding the application of CLT in buildings is its combustible nature and subsequent contribution to a compartment fire. Previous research has shown that exposed CLT, under certain circumstances, can achieve self-extinguishment. This research aims to further experimentally investigate the fire performance of small-scale compartments containing exposed CLT. The focus of this study is threefold, namely to investigate: i) the influence of (commercially available) adhesives used in CLT panels on fire behaviour; ii) the influence of CLT panel configuration on fire behaviour and iii) the ability of design guidelines to predict experimentally obtained fire behaviour. By investigating these aspects, a detailed investigation into fire behaviour of compartments with exposed CLT is presented to characterise the influence of CLT on enclosure fire behaviour and assess the ability of CLT to reliably self-extinguish. In general, it was found that reliable self-extinguishment is promoted when small-scale compartment fire tests reveal the avoidance of burn-through behaviour (and a second flashover), due to the combined effect of CLT adhesive type and CLT panel configuration. The particular observations recorded in this research project (relating to adhesive type and CLT panel configuration) serve as a base on which to conduct further research (especially by conducting experiments at real compartment scales). In addition, the investigation into the ability of a design guideline to predict fire behaviour, namely a Parametric Fire Curve (PFC) calculation method that includes the contribution of exposed CLT to the fuel load, provided mixed results. Further refinement is required to improve the model’s ability to predict compartment behaviour.

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...

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.

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.

Concrete and Steel are the materials with the largest market share in the construction industry and have been for a long time. With environmental awareness increasing, timber is regaining popularity due to the potential for carbon neutral and even carbon negative construction. Use of structural wood elements in bridges, however, is often limited to foot- and cycle bridges. In this thesis, key aspects with regards to the design of heavy traffic bridges incorporating timber members are identified. A fully steel bridge and an equivalent bridge, combining timber members with steel are designed within boundaries set by a case study. These designs are developed to a level sufficient for an adequate comparison of the bridges. The basis on which the bridges are compared are laid out, followed by the conditions the bridges are subjected to. These are based on typical conditions found in an urban Dutch environment. Analytic equations are automated, by way of python scripts, for the analysis and optimization of the steel bridge longitudinal dimensions under simplified ULS loading. After the optimization is complete, these initial bridge dimensions are verified with a 2D plate element model in SCIA engineer. The full loading for the bridge during utilization, save for accidental loading, is then modelled and the bridge dimensions are adapted in order to meet ULS, SLS, and fatigue conditions. Several potential versions of a bridge with timber members are considered. Following this, a bridge with a mostly timber superstructure, supported by a self-anchored cable system is further worked out. For this, a SCIA model, with 1D elements and subjected to the same loads as its steel counterpart, is produced. The incompatible combination of 1D elements, thick cross sections, and surface loads is addressed by the use of connector elements (“dummy members”) and individual load panels per member. After the global optimization of the bridge dimensions with regards to ULS and SLS, the connections are designed with a combination of detail 2D element FE models and analytic equations. The forces and support conditions of the connections follow from the global bridge design. A fatigue check is then run on the timber members of the bridge. Subsequently, the durability and eco- costs of the bridges are computed. The data for the durability estimation of the steel bridge is based on experience within IV- Infra and the durability of the timber bridge is estimated using the RISE factor method. The eco- costs of the bridges are computed using the IDEMAT database. The results from the analyses are discussed based on this. Finally, aspects of relevance in the design of timber bridges are synthesized and recommendations for the application of bridges and further research are given.

The structural reliability of the wooden tower of the Grote of St. BavoChurch in Haarlem has been assessed with the regular methods. In addition to the regular methods, some modern technologies have been used in the structural analysis. The mechanical properties of the timber have been determined with longitudinal vibration tests and visual grading. The inclination of the tower has been determined with a terrestrial laser scanner and the entire has been modeled and verified with a Finite Element Model. Conclusions are based on the results of the Finite Element Model, which takes the determined mechanical properties and inclination in consideration.

Wood is an important building material that has been used for thousands of years throughout the world. It is the most widely used building material and due to its characteristics suitable for a wide range of applications. Still, for the last century steel and concrete have been the materials of choice for large buildings. Part of the reason for this is the lack of knowledge in the industry regarding timber construction. Now that the environmental problems such as climate change get more and more attention, there is an opportunity for timber as a building material and the manufacturers of timber products to increase its popularity. Cross-Laminated Timber, or CLT, is a relatively new product. First introduced in the early 1990’s in Austria and Germany, now gaining popularity in residential and non-residential applications in several countries around the world. The panels normally have 3 or more layers of side-by-side placed boards, that are stacked crosswise at a 90 degree angle. The boards are glued on their wide faces and may or may not be glued together on their narrow faces. The Derix Group, a company with a vast experience in the timber industry, specializes in laminated timber constructions and are interested in developing a new panel configuration. The idea is that by relocating boards from the middle layer of a CLT element, to a more favourable position, material usage can be optimized. A problem definition is formulated and used to derive the research questions that form the direction of the thesis. The research questions are related to the possible advantages and the consequences of the Hollow Core Cross-Laminated Timber (HCCLT) configuration. The first thing that is done in order to investigate the possibilities, is research into the manufacturing process and the structural design of CLT. As a relatively flexible building material with a low dead weight, the design of CLT is often determined by serviceability criteria, such as deformation and vibration. However, the rolling shear properties of the cross-layers can control the design, it influences the effective bending stiffness and stress distribution. It also causes a larger deformation due to shear than for other wood based products. Since there is not one specific design method, the most common methods are researched and described.  The composite theory  The mechanically jointed beams theory  The shear analogy To determine how the existing methods perform and to investigate the structural behaviour of a HCCLT element compared to a CLT element, the methods are used to calculate different configurations in order to compare the results. The knowledge obtained during the research and calculations is then used to model a HCCLT element. Different models are made in order to investigate the behaviour during manufacturing and for when the element is in use.

The Netherlands has an extensive network of rivers and canals systems serving purposes like irrigation, transportation and water removal. The banks along the canals are either protected by earth retaining structures such as sheet pile walls or left unprotected. A bulk of the engineered sheet piles used to protect the canal banks in the Netherlands are made of timber. Tropical hardwoods such as Azobé (Lophira alata) are used to make these timber sheet piles durable, owing to its high biological resistance to decay. Pine from North-west Europe is also used, but need to be treated chemically for sufficient durability. Even though roots of vegetation are known to increase the shear strength of soil, the positive effects of vegetation are not quantified in depth. Vegetation roots in a root-soil composite primarily act in tension when subjected to load, thus acting similar to steel in reinforced concrete. This thesis summarizes the efforts to study a bio-engineered earth retaining structure made of non-durable locally available wood species and vegetation to protect the canal banks as an alternative to the currently used bank protection structures. Such a retaining structure would not only reduce the need for durable hardwoods, but are also more environmentally friendly than the ‘hard’ retaining structures currently in use. Two vegetation types, Humulus lupulus L. and Salix fragilis L. were chosen for investigation based on their potential to reinforce canal banks, nativity, root characteristics and growth conditions such as presence of high ground water table. An extensive laboratory campaign was planned and conducted to characterize the strength of roots, root-soil composite and to study the behavior of the timber sheet pile-vegetation combination as a system. The experimental results were further extended to develop approaches in the design of timber sheet pile-vegetation system. To study the root-soil composite behavior in shear, a large scale direct shear apparatus was built. The apparatus was built in the view of conducting tests in dual loading modes, displacement controlled and load controlled shear. In order to simulate the canal bank conditions as closely as possible, the samples were tested in saturated conditions at low confining pressure. Bare soil, rooted samples of Humulus lupulus L. and Salix fragilis L. were tested in both displacement controlled and load controlled conditions. The roots were excavated after the test and analysis of root orientation, diameter and root biomass was conducted. Rooted samples showed a higher friction angle when compared to bare soil. Contractive behavior was shown by rooted samples and the peak stress ratio vs displacement trend of rooted samples were seen to diverge from the trend for bare soil. Burger model was seen to be able to capture the time dependent behavior under loading mode, when simulated over the experimental results. A tensile testing program was devised to test roots in tension in a displacement controlled and load controlled tests. Roots of Humulus lupulus L. and Salix fragilis L. were tested in both wet and dry conditions in displacement controlled tests. Load controlled tensile testing was conducted on samples of Humulus lupulus L. of two diameters. Power law was observed to estimate volume-effect and fit all the tensile strength-diameter variations. Comparison of tensile strength in dry and wet conditions revealed that significant difference in tensile strength was observed for Salix fragilis L. while no significant difference in tensile strength was observed for Humulus lupulus L. Further, time to failure of roots were studied using a power law model. A physical modelling approach was attempted to study the behavior of the timber sheet pile-vegetation system. A root system similar to Humulus lupulus L. was 3D printed using PLA material to be used in physical model. A comparison of unreinforced bank and bank reinforced with root analogues revealed that the presence of roots increase the volume of soil that needs to be mobilized for failure to occur. It was also observed that when root analogues were placed in the most efficient spatial pattern, among the conducted tests, are able to sustain twice the drawdown pressure. Subsequently, finite element modelling was conducted by including the effect of roots as an increased cohesion parameter. The results from modelling were seen to be able to capture the failure. Parametric analysis revealed that the influence of spatial distribution of the roots on forces acting on the sheet pile is higher, after a threshold value of additional cohesion is reached. That implies any additional cohesion after the threshold value might not provide any additional benefits to the stability. The results thus indicate that vegetation with more spatially distributed roots will be more suitable to be used in timber sheet pile-vegetation retaining system. Finally, two different perspectives in design approach of a timber sheet pile-vegetation system are investigated. The system approach is based on the concept that the mechanical reinforcement of the soil with growth of vegetation could result in a reduction of horizontal pressure against the sheet pile, bending moments and shear stresses acting on the sheet pile over time. This results in decreasing the duration of load effect in the timber and counteracting the effects of slow biological degradation of wood in air-water-soil conditions. Timber sheet pile components that are below the water level are less prone to decay. However, those components that are at the air water-soil interface are more susceptible to decay. In the discrete approach the vegetation is perceived as supporting the top parts of the stream bank (< 2meters) after timber decay has occurred. The effect of vegetation is analyzed as both increase in internal friction angle and increase in cohesion, on stream banks of retaining height of 2m and 3m. An increase in service life of nthe timber sheet pile-vegetation system is achieved in a system approach compared to when only timber sheet pile is present. In the discrete approach, it was observed that modification to the landscape by changing the slope angle of the bank might be necessary when the influence of vegetation is incorporated as an increase in friction angle of soil. In laboratory scale, as in this study, timber sheet pile-vegetation earth retaining systems show promises to be used for stream bank protection. Future studies need to focus on field scale system level studies and quantification of reinforcement of vegetation in presence of multiple species of vegetation.@en