As sustainability becomes increasingly essential in construction practices, the incorporation of concepts such as circularity and material efficiency are more required than ever. The present research investigates how these concepts can be effectively applied to Steel-Cross Laminated Timber (CLT) composite floor systems in order to promote more sustainable construction methods, specifically reducing carbon footprint. The findings are intended to benefit practicing engineers and designers, as well as lay the groundwork for future academic research and innovation in sustainable construction.
WSP developed the baseline steel-CLT composite floor system, which bonds composite materials using shear studs and grout . However, this design restricts disassembly at the end of its lifecycle, posing challenges that limit its potential for reuse in subsequent applications. In addition to that limitation, while the system was validated via laboratory push-out tests, using a standardized CLT configuration across varying spans resulted in material inefficiencies, highlighting the need for additional optimization.
To address the aforementioned drawbacks, this study develops an "optimized design" for a Steel-CLT composite floor system that enhances both circularity and material efficiency. The optimized system, which includes demountable shear connectors, allows for easy disassembly and reuse, extending the life of its components. The study also investigates the optimal CLT configuration and lay-up to maximize material efficiency, demonstrating that adapting the CLT design to the unique characteristics of each composite floor structure (e.g., dimensions, spans, and load requirements) is crucial for optimal performance.
Finally, the baseline- and optimized designs were compared in terms of environmental impact, focusing on a Life Cycle Assessment (LCA) of embodied carbon. This evaluation highlights the environmental benefits of the optimized design, offering valuable insights into how circularity and material efficiency can significantly reduce the carbon footprint in constructions.
Overall, this research transforms the baseline steel-CLT composite floor system from a linear to a circular design, thereby highlighting the significant advantages of circular design principles within the construction industry. By advocating for the broader adoption of circular approaches, this research underscores the potential for creating a more environmentally sustainable future in building practices. In addition to achieving circularity, the study focuses on optimizing the CLT design to enhance material efficiency within the floor system. It also identifies key factors to consider when designing CLT for composite applications, ensuring that the material is used most effectively within this innovative context.
The present paper begins with a comprehensive literature review, which provides the foundational background necessary for the research. This is followed by a detailed explanation of the design rules employed in the structural analysis. Next, the application of demountable shear connectors is discussed, highlighting their role and implications for the steel-CLT composite system. A subsequent chapter delves into the design of CLT panels, emphasizing their dual function within composite floor systems. Both the baseline and optimized floor systems are then presented, with an outline of their structural characteristics and geometric configurations, followed by a rigorous structural analysis. The study proceeds with a comparative analysis, evaluating the structural and environmental performance of both designs. This analysis resulted in conclusions that highlight the substantial role of circular design principles and material efficiency in reducing the environmental impact of construction materials and systems, as well as the crucial role that structural designers can play in advancing the decarbonization of the built environment.

In the Netherlands, there is a significant housing demand. The Dutch government aims to construct 100,000 houses per year, which presents an enormous challenge. To address this demand and simultaneously tackle the challenge of creating a more sustainable construction industry, timber modular construction emerges as a potential solution. Compared to traditional construction methods, timber modular buildings offer several advantages: lower weight, more sustainable, faster construction, reduced waste, greater efficiency, and higher quality. Currently, most modular components can be prefabricated off-site, except for the stability system. Traditionally, this system involves a concrete core
or a steel frame. To eliminate their need, self-supporting modules can be applied, making the building purely modular and more sustainable. Within self-supporting modules, stability is a critical aspect. While incorporating stability elements along the longitudinal side of the module poses no issue, the main challenge lies in the limited available length for stability walls in the transverse direction. Also, the shear wall located in the module conflicts with the preferred open floor area. The design of the module, and in particular the shear wall, has a significant influence on the transverse deflection. Calculating the deflection is crucial to fulfil the requirements for maximum displacements. Therefore, the
main research question of this thesis is: Is it possible to predict the lateral deflection in the transverse direction of multi-storey timber modular buildings with a calculation method based on proposed equations?. The goal of this thesis is to propose a calculation method that can be used in the design phase, which will give insight in the effect of design choices on the lateral deflection of multi-storey modular buildings.

The approach to answer the main research question consists of several steps. The first step was a literature study that was conducted on modular construction, lateral stability and deformations of modular buildings. Knowledge on the structural design of timber modules and cross-laminated timber was obtained. Also, the deformation mechanisms of multi-storey modular buildings were investigated. The second step was analysing the deformation of individual modules. A general module design and four configurations were established and the numerical modelling method was investigated and validated.
Hereafter, the equations to calculate the deformation of individual modules in the transverse direction were proposed for the four module configurations. Based on the numerical model, the equations for the horizontal displacement and rotation were established. Additionally, the formulas were extended to incorporate various design options like connection design, shear wall thickness and shear wall position. The proposed equations were integrated in a calculation method that predicts the lateral deflection of multi-storey modular buildings in transverse direction. Hereby only the deformation of the modules was taken into account and not those from the inter-module connections. The cumulative effect due to rotation of lower modules is added to the individual module displacement to find the total deflection.

The results showed that the proposed equations accurately calculate the deformation of the individual modules. With differences below 10%, the formulas are able to calculate the horizontal displacement and rotation for various designs. The calculation method was validated with two examples. Example 1 was a four-storey, four-span building where at the top a maximum error of 8.7% was found. Example 2 was an eight-storey, eight-span building where the proposed calculation method resulted in a maximum error of 9.5%, which was on the lowest storey. At the top, a difference of 2.6% was found. Both
errors were lower than 10% and at the safe side, meaning that the calculation method provides accurate and safe results. A case study was performed to verify the practical applicability of the method. The lateral deflection results showed significant differences (45%), which can be assigned to limitations of the calculation method. These limitations ensure the method is not suited for detailed calculations that are necessary in later design phases. For these detailed calculations, a (parametric) finite element model
would be more suited. However, the calculation method offers a solution for early design stages, as it provides quick and easy insight into effects of certain design choices on the building’s lateral deflection.

With the building and construction sector accounting for a significant portion of final energy use and emissions, and society’s increasing focus on environmental awareness and improvements, the impor- tance of sustainable construction has never been greater. The utilisation of timber in construction offers clear sustainability benefits and has the potential to replace traditional functions of concrete. One notable replacement is the use of Cross-Laminated Timber (CLT) in composite structures with steel, enabling the potential creation of greatly performing floor systems which has seen a limited amount of research. The research explores the application of Steel-CLT Composite floor systems and assesses composite beam performance as well as predictive methods for analysing their behaviour in hopes of advancing the body of knowledge on this method of environmentally friendly construction. The literature study revealed the current knowledge on steel-CLT composite floor systems and connections. Two particular floor systems, with and without the use of grout, are highlighted as well the potential for future exploration. The steel-CLT composite connection utilised in the floor system significantly impacts performance and composite action as the use of grout is concluded to increase initial-, secondary stiffness and load carrying capacity of the connection. However, restricting the use of grout can promote circular con- struction practices. In this research the behaviour of steel-CLT composite beams is predicted by the use of a numerical finite element model with shell elements and an analytical approach based on the simplified analysis of Eurocode 5(EN1995-1-1): Mechanically jointed beams. The analytical method can predict the bending stiffness with a margin of error just slightly above 10%. However, it should be noted that the analytical method incorporates an incomplete representation of the composite connection used in the beam. On the other hand, the finite element model is able to accurately capture the pre-plasticity behaviour of the steel-CLT composite beam. This is achieved by incorporating the complete load-slip behaviour of the shear connection. A parametric study was conducted to assess the importance of closely spacing composite shear connections in a steel-CLT composite beam to achieve a higher level of composite action. The study also demonstrates that by utilising connections with higher initial stiffness, secondary stiffness, and ultimate capacity, this effect can be further strengthened. As a result, the force resisted at the service- ability limit state experiences a notable boost due to the implementation of both a stronger and stiffer connection, as well as their close spacing. Shear connection position optimisation by concentration of connectors near the supports showed to have a small positive effect on beam deflection. After evaluation of steel-CLT floor systems the research concludes that a steel-CLT composite floor system can be successfully constructed, offering environmental benefits and reduced structural weight while achieving the required structural performance for the set design conditions.

This research investigates the feasibility and potential of utilizing BFRP floors in modular buildings as a low environmental impact and cost-effective alternative to conventional floors. A modular building is introduced as a case study, the Natural Pavilion in Almere, to bring focus to the research and set a baseline for the requirements of the BFRP floor. A second case study, the bio-composite bridge in Ritsumasyl, is introduced to utilize its comprehensive dataset of material properties representing the state-of-the-art BFRP. Using the two case studies, two design solutions, a one-way and two-way floor, are developed.

Comparing the designed BFRP floor to conventional floors such as cross-laminated timber, concrete hollow core slab, and concrete flat slab, several conclusions can be drawn:

(1) The construction height of BFRP floors is similar to that of conventional floors. The weight of the floor is similar to a CLT floor, while a concrete floor is 6-8 times heavier. Design optimization is possible, and the amount of BFRP material utilized can be reduced by up to 21% for the one-way floor and 19% for the two-way floor. Additionally, the floor design proposed in this thesis is intended for buildings with a design life of 15 years and no specific fire resistance requirements. For structures with a design life of 50 years, it is imperative to increase the floor height to meet deflection criteria. Further research on fire resistance and additional measures is necessary to extend applicability beyond single-compartment buildings and terrace housing.

(2) The environmental impact of a BFRP floor, assessed in terms of Global Warming Potential through a Life Cycle Analysis encompassing stages A1-A5, is found to be twice that of a concrete floor. Through optimization of the floor design and reduction of BFRP material usage, it is possible to achieve a reduction in CO2 emissions of approximately 10%. Nevertheless, in the current state-of-the-art, BFRP floors exhibit a higher environmental impact than conventional flooring systems. The use of resin and the production process are the primary contributors to CO2 emissions. The contribution from the production process requires nuance, as results heavily depend on the data source. Factors such as manufacturing techniques and production scale significantly affect this impact. By reducing the impact of the resin and production techniques while also exploring end-of-life possibilities for 100% bio-based BFRP, the environmental impact of BFRP floors holds potential for the future.

(3) The floor cost is nearly twice as high as a comparable CLT floor. This can be attributed to introducing new design solutions with a sustainability focus, often resulting in increased costs due to lower demand, higher material and design expenses, and limited production scale. Even though current costs are much higher for BFRP floors than for conventional floors, there is potential for BFRP floors to become more cost-effective and competitive in the future, especially when the environmental impact is reduced. It is difficult to estimate how the price of BFRP floors would change over time, and therefore, it has not been taken into account in the results.

The recent developments in the building industry to build more sustainable should result in the use of light constructions with a low environmental impact. Timber is a suitable material for this purpose. To reduce the environmental impact of a building, an improvement in an often used structural element can have a significant impact on the sustainability. Floors are a large part of the material consumption of building. A challenge with lightweight timber floors is the vibrational performance of the floor due to walking humans. Conventional concrete floors are less sensitive to vibrations due to their large weight. The vibrations of the floor have influence on the comfort of the humans residing on the floor. Furthermore, concrete is generally seen as a less environmentally friendly material than timber. This raised the main research question of this thesis: How do vibrational performance levels influence the sustainability of several timber floor systems, considering multiple design configurations, compared to conventional concrete floor systems?

The floors used in this research are a CLT floor, LVL box floor, TCC floor, concrete cast in situ floor and concrete hollow core floor. For the research on the vibrational performance and sustainability of floors some methods for assessment are used. For the vibrational performance the assessment method from the renewed Eurocode 5: Timber structures is used. This assesses the resonant and transient vibration response of the floor and checks them with predetermined vibrational comfort criteria. For the assessment of the sustainability the environmental cost indication is used. This method assesses several environmental impact categories and weighs their impact onto the environment, separately the global warming potential is also assessed by the CO2eq emissions of a material.

The result gathered from the research show that timber floors are more sensitive to vibrational performance than concrete floors. Floors with a high vibrational performance need a significantly higher floor height than low performance floors. The influence of damping and floor configurations is important for the vibrational performance. The environmental impact of timber floors have an advantage when biogenic carbon is taken into account. Concrete floors can reach longer floor spans and for high performance floors have a lower increase of environmental impact than timber floors. For the environmental impact of a floor, reuse or recycling is important for the end-of-life scenario.

To draw a conclusion to the main research question; Vibrational performance of floors do effect the environmental impact of the floors. High performance floors have a significantly higher environmental impact than low performance floors. The environmental impact of concrete floors increases less for higher floor performances than timber floors. Timber floors are more sustainable within their technical feasibility. The floor configurations can mitigate vibrations and can thus reduce the environmental impact of the floors.

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.

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.

With the effects of climate change being more and more frequent, the European union, and other governments world-wide are looking for sustainable alternatives for processes and products that are part of the daily requirements of people. Among these requirements, the construction industry plays a vital role, as it accounts for the consumption of about 50% of the total raw materials. In
line with its targets of 100% recycling by 2050, the industry in Europe, and particularly in the Netherlands is shifting towards the use of circular and sustainable construction products. This thesis investigates into both these aspects: Circularity by addressing the requirements for demountable structural elements, thus providing scope for reusing, and Sustainability by addressing the impact of substituting concrete and steel with timber products.

Structural timber products obtained from sustainable forestry are considered as eco-friendly construction products. The benefits are two-fold: First of all, it is produced or grown naturally, and thus avoids the emission of harmful gases during production. Second, growing timber products helps in CO2 storage for the duration of the technical service life of the product. Thus, increasing the market share of timber products in the construction industry can play a huge and decisive role to achieve the targets of sustainability.

The focus of this thesis is on steel-timber floor systems i.e., a floor system with timber slabs supported by steel beams. There are many timber products available that can be used as slabs, as a substitute to hollow core slabs and steel-concrete composite slabs, which are the conventional solutions for floor systems in the Netherlands (the former more than the latter). Owing to the disadvantage of timber in stiffness, coupled with the effects of creep, steel beams are considered for traversing larger spans.

From the plethora of steel and timber products that can be coupled together to form a floor system, the best solution is obtained with the help of a Multi Criteria Analysis. This is done by scoring the different floor systems on the aspects of utility, circularity and sustainability. The obtained solution is a conventional non-integrated floor system with Lignatur surface elements as the slab, supported by steel I beams. Lignatur elements are box-shaped slabs that can span over large
distances typically required for office use. Being made of sawn timber, it boasts the advantage of being more sustainable than other timber products made of cross laminated timber and laminated veneer lumber. I beams were found to perform better than other steel beams, posing as more accessible for demounting, over the other beams.

With the help of a case study, the benefits of the chosen steel-timber floor system were evaluated and compared against the hollow core slabs and steel-concrete composite slabs. Owing to the lightweight nature of timber, the chosen floor system was approximately 45% lighter than hollow core slabs, and 25% lighter than composite slabs. They were comparable in terms of floor height,
to the composite slabs.

The main benefit was the fact that the use of concrete and/or steel could be substituted with the use of timber slabs, and the supporting steel frame could be lighter owing to the lightweight nature of timber. A life cycle analysis was done to compare the different floor systems. Due to the use of sustainably produced timber, the steel-timber floor system had the least environment impact. Considering the effects of carbon storage meant that the total environmental footprint of the floor system could be negative. On further analysis, by excluding the benefit of carbon storage, the steel-timber floor system was still found to have the least impact (39% lesser than hollow core slabs, 31% lesser than steel-concrete composite slabs).

Another aspect that was investigated in this thesis was whether the consideration of composite action (similar to that in steel-concrete) could lead to any benefits i.e., composite action between the timber slab and the supporting steel beam. Based on the calculations in the case study, it was concluded that there were no such benefits i.e., the reduction in size of the steel beams was not
enough to justify the use of added shear connectors.

Another limitation of timber was found to be its lack of reusability. Being a biomaterial, timber is associated with a large reduction in strength for each reuse (although this reduction cannot be quantified using the present state of the art). Other materials such as steel and concrete do not experience this strength loss, and thus assume to have better performance than timber regarding this aspect.

The main barrier for implementing a steel-timber floor system would be in terms of costs. Though not explicitly investigated into in this thesis, it is expected to be more than that for its conventional counterparts. Currently, hollow core slabs are the most widely used, in the Netherlands, which is mainly owed to its low costs. Thus, the circulation of a product is closely related to its costs in the
market. By showing light on the benefits of the steel-timber floor system, it is expected that the results of this thesis will help the industry shift to the more responsible choice, in the near future. Wider circulation of steel-timber floors can help in reducing its costs, thus making it more desirable.

The extraction of natural gas in the northern part of the Netherlands, from the region of Groningen, has been causing human-induced seismic activities for the past several decades. This is a problem since the existing building stock in this region, which consists of mainly unreinforced masonry buildings and historical structures, are not designed to withstand seismic events due to the lack of empirical earthquake-resistant design features. Further, the combination of a soft topsoil and the gas extraction, is responsible for ground settlements which may compromise the capacity of the existing buildings.

The bed-joint reinforcement technique is a strengthening method which consists of cutting a slot in the bed-joints and installing steel bars embedded in a high-strength repair mortar. Although this strengthening method is commonly applied in the Netherlands to counteract settlement damage, limited investigations on the performance against seismic loading are available in the literature. Therefore, an experimental campaign (Licciardello et al., 2021) was conducted at Delft University of Technology in which a quasi-static cyclic in-plane test on a full scale wall was performed to characterize the performance of the bed-joint reinforcement technique. The wall featured artificially introduced cracks (pre-damage), achieved by the inclusion of plastic sheets between bricks and mortar, to account for the settlement-induced damage. Compared to the un-strengthened walls, tested in a previous experimental campaign (Korswagen et al., 2019) under similar conditions, it is observed that the bed-joint reinforcement technique can provide a significant increment in terms of displacement capacity and ductility of the wall but not in terms of the force capacity.

In this thesis, numerical simulations of both un-strengthened and strengthened walls from the experiments were performed using 2D-models and the nonlinear static analyses (monotonic and cyclic) were carried out in the finite element software DIANA. The objective of this research was to compare different numerical modeling approaches and material models to find the best suited one for simulating the in-plane seismic response of both un-strengthened and strengthened masonry walls. Moreover, the objective was also to extrapolate the experimental results to other wall configurations, which are not experimentally tested, to investigate the combined effect of the bed-joint reinforcement technique and the change in size and location of the window opening on the in-plane response of the wall (parametric study).

In the scope of this thesis, three numerical modeling approaches were investigated (Figure i). The bricks and mortar joints are modeled as one homogeneous continuum in the macro-model. On the other hand, the bricks and mortar joints are modeled separately for the continuous and detailed micro-model where interface elements are included at the brick-mortar bonds for the latter one. The discrete (simplified) micro-model was not investigated because the reinforcement bars cannot be connected to the mortar joints since they are substituted by zero-thickness interface elements. Moreover, the Discrete modeling approach of the reinforcement was used in order to simulate the pull out behavior of the bars. Cracks were modeled using the discrete cracking approach and the smeared cracking approach where the former one was used at the brick-mortar interfaces and the latter one was used for cracking in the mortar joints (micro-models) and in the masonry composite (macro-model)…

For centuries timber has been the most commonly used material for constructions. All over the world examples of timber structures that date back from a few centuries are still standing today. The Netherlands feature about 60,000 national monuments with internally timber structures. These timber structures often need strengthening due to increasing loads that are applied. The strengthening techniques are narrowed down to a few options whenever historical ceiling designs, such as ceiling paintings, plaster works or timber beams need to remain intact.

Timber floors encounter two major challenges: low stiffness which leads to limited load-bearing capacity and low surface mass which leads to poor acoustic sound insulation. This research seeks to provide structural engineers to make a factual choice in an early design stage for using a reversible strengthening technique on a monumental timber floor preserving original appearance. This strengthening technique is verified for strength, stiffness and acoustics, both airborne and structure-borne sound transmission. To this end, the following research question was formulated: "What is the influence on the strength, stiffness and acoustic properties of monumental timber floors by strengthening them with multiple layers of plates fastened on top of the existing floor?"

To answer the research question, a case study was performed on two monumental floors of the Prinsenhof Museum in Delft. These floors were investigated for their current strength, stiffness and acoustic properties. Then, equations were derived which considered the separate timber plates in the reinforcement technique as an equivalent layer. This equivalent layer is used to determine the effective stiffness for mechanically connected girders by the gamma-method. These equations were validated using software for 2D frameworks. Subsequently, a parameter study was used to determine the influence of the parameters on the strength, stiffness and acoustic properties. Finally, by applying the reinforcement technique to the case study based on the results of the parameter study, the strengthening technique was assessed more in detail by taking into account the influence of the non-cooperating intermediate layer.

The results of the parameter study and the case study demonstrated that the strengthening technique increase the strength and stiffness of the floor considerably. However, by increasing the stiffness, the connections between the additional timber plates and the reinforced component becomes governing. Furthermore, the increase in stiffness does not significantly improve the acoustic sound insulation, as this is mainly governed by the surface mass of the timber floor.

It is therefore concluded that strengthening of monumental timber floors, by means of several layers of separate timber plates fastened on top of the floor, is an effective way to achieve the desired strength and stiffness. Thick plates, small spacing between fasteners and inclined fasteners are a requirement to achieve higher strength and stiffness. However, additional measures must be taken to meet the sound transmission requirements. For the original perseverance of the monumental timber floor and reversibility, these measures would be dry floating floors. A significant fact is that dry floating floors only add mass and do not increase stiffness, which lowers the maximum allowable load on the floor.

A major limitation of this thesis is the consideration of the non-cooperating intermediate layer between the additional timber layers and the reinforced component. This intermediate layer results in multiple shear planes between the reinforced component and the additional timber plates. This thesis suggested to use a factor, determined from Roensmaens et al. (2020) research, to convert the multiple shear planes into a single shear plane. It is therefore important that further research investigates the influence of these multiple shear planes that do not contribute to the bending stiffness of the reinforced component.

The building industry consumes a lot of material, which causes depletion of material stocks, toxic emissions, and waste. Circular building design can help to reduce this impact, by moving from a linear to a circular design approach.
To reach a circular build environment, all disciplines should be involved, including fire safety design. However, there is a contradiction between the objectives of circular and fire safety design, either affecting the aim of protection of material sources, or protection against fire risk.

Timber is a material that has high potential in contributing to a circular building industry, as it is renewable, recyclable and can store CO2. However, timber is combustible, which increases the risk of fire. Therefore, mass timber building design has traditionally been restricted by building regulations. To enhance mass timber building design research on timber buildings has increased, to allow understanding of the risks. However, yet general guidelines or understanding on the fire behaviour and risk in timber buildings is lacking. This is a problem for the fire safety design and the potentials of timber contributing to a circular building industry.

Until now, there was no specific method available that quantifies this relation between material use and fire risk in mass timber buildings. This limits the possibility of fire safety design and mass timber design to contribute to a more circular building industry. By creating a method that allows comparison between the economic and environmental impact of material use and fire risk, a well-founded choice of building materials is easier to make.

The design tool created in this research quantifies the impact on material use for fire safety measures relating to CLT, encapsulation and sprinkler availability and their effect on the fire risk in mass timber buildings. This way insight is provided between the balance of material use and fire risk. By the sum of the impact on material use and fire risk, the total “circular fire safety impact” value is calculated. This value represents the total economic and environmental impact of the design based on the choice of building materials. By changing the fire safety design, the most optimal design variant can be determined. This is the variant with the lowest total impact value.

This way, a circular design approach is used to steer fire safety design in mass timber buildings towards a design solution that does not only provide sufficient safety for people, but also provides maximum economic and environmental safety from a material point of view.

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.

This master thesis' main objective is to develop a parametric design tool which improves the design process and explores the building typologies of a hybrid modular timber construction based on global and local structural requirements. The hybrid modular timber construction is core-less and combines load-bearing and corner-supported modules. The parametric design tool, which is named Habitat21, consists of an automatic placement function (Grasshopper), a manual placement function (Rhinoceros) and a structural analysis program (Karamba). The hybrid modular timber construction concept is tested by comparing the displacements in the x- and y-direction of a replicate of Hotel Jakarta, generated in Habitat21, with the original displacements in the x- and y-direction of Hotel Jakarta, generated by the case study of Gijzen. It appears that the replicated hybrid modular timber construction of Hotel Jakarta in Habitat 21 is able to approximately reproduce the original displacement in the y-direction of Hotel Jakarta calculated by Gijzen (difference of 0.642 mm). However, the displacement in the x-direction could not be reproduced in the same order of magnitude as the original displacement in the x-direction (difference of 13.081 mm). This could be caused by the fact the assumed inter-module connections, connection 1 and 4, of the hybrid modular timber construction concept were modelled as line elements with two hinges (”pendelstaven”), this could have influenced the displacement behaviour of the CLT shear wall mechanism. To examine the usability of the manual placement of the modules by Rhinoceros within Habitat21 a workshop with 5 participants (2 architects and 3 engineers) and two cases is performed. In the first case each participant created 3 buildings, each building was generated within 8 minutes, resulting in a total of fifteen different building typologies of the hybrid modular timber construction concept. Ten out of the fifteen building typologies satisfied the global structural requirements, five did not satisfy the global structural requirements. Two buildings were not stable in one or more directions, two buildings did not satisfy the unit check for the displacement in the x-, y- or z-direction and for one building an error occurred. To explore the diversity of the typologies from the fifteen buildings a typology score was given for each building. The highest score was 102 points and the lowest score was 10. This indicates a relatively large diversity in typologies. In the second case each participant worked on two buildings that both did not satisfy the global and local structural requirements but the second building had 2 extra design restrictions. The participants had 5 minutes per building to fix this. For the building with extra design restrictions three participants (all engineers) were not able to meet the local structural requirements. This suggests that the feedback from Habitat21 provided to the user in this case was not adequate. To examine the automatic placement of the modules by Grasshopper within Habitat21 the calculation time of the automatic placement of one extra CLT shear wall is analysed for 6 different buildings by using an iterative process. These buildings were all stable in the y- and z-direction but unstable in the x-direction. The calculation time for the placement of the extra CLT shear wall at a building with 4 modules and 8 possible positions was 6 seconds and the calculation time for the placement of the extra CLT shear wall at a building with 24 modules and 48 possible positions was 360 seconds. Combining the calculation times of the 6 different buildings it appeared that the calculation time increased exponentially when the amount of modules increased linearly. In conclusion, it was possible to discretize a hybrid modular timber construction in a parametric design tool. Furthermore, both engineers and architects were able to work with the tool and to independently create diverse typologies of a hybrid modular timber construction. The boundaries of the hybrid modular timber construction concept in Habitat 21 were determined by the inter-module connections, as found in the comparison study with Hotel Jakarta. The applicability of the parametric design tool and the hybrid modular timber construction concept could be increased by more research into inter-module connections and point supported cross-laminated timber slabs. Also, feedback about how the structural systems works could be implemented in the parametric design tool, where the user gets necessary feedback to fulfill the global or local structural requirements instead of using a trial and error design method.

Masonry is one of the most common building materials globally due to its ease of construction, price, durability and fire resistance. Its heterogeneity and orthotropic nature make its mechanical behaviour rather complex, highlighting the importance of an appropriate constitutive model to describe such behaviour accurately. In literature, most of the existing constitutive models for masonry fall in one of the two following categories: macro-models or micro-models. The micro-models (also called block-based models), which explicitly describe masonry's geometrical and material heterogeneities, exhibit higher accuracy but require higher numerical efforts when simulating masonry's mechanical behaviour. The macro-models (also called continuum models), which model masonry as homogeneous material and smear out the damage over the continua, are less accurate but offer a good compromise between accuracy and numerical efficiency. They are therefore used more often to simulate masonry structures. However, most of the macro-models are not capturing well the damage localization occurring along the mortar joints and the energy dissipation in the bricks and mortars. To increase the applicability of continuum models, the components' damage localization and energy dissipation should be improved. This thesis presents a homogenized constitutive model for applications on masonry structures under in-plane loading. The developed homogenized material model for masonry includes the description of shearing, tensile cracking, crushing and splitting. Inspired by the micro-mechanical models of Zucchini and Lourenço, four models were developed in this thesis to describe the different types of in-plane failure of masonry, naming: tensile failure of bed joints, horizontal shear sliding of bed joints, tensile cracking of unit, diagonal tensile cracking failure, masonry crushing failure. The first model is derived for the masonry’s pure shear behaviour, where the shear sliding failure is introduced. The second one is derived for the horizontal tensile behaviour, where the vertical tensile cracking of brick units and the vertical joints is proposed. The third one is derived for the vertical compression behaviour, where masonry crushing failure is adopted. The fourth one is coupling the failure mechanisms described in the previous three models with a novel algorithm. Additionally, the diagonal tension cracking failure and the horizontal tensile cracking of horizontal joints are incorporated in the fourth and final material model. To derive these models, first, a representative volume element (RVE) was selected for running bond wall, where the bricks are staggered by half-length of brick from the adjoining courses above and below. Each RVE consists of two-quarters of bricks connected through a bed joint, and each one is connected to a head joint on one side. For each of the models, the active internal stresses of each component (brick, bed, head or cross joint) are calculated through the compatibility and equilibrium equations resulting from the assumed deformed mechanisms. Different damage state variables are introduced for every component in the damage model, where exponential softening is assumed for tension and shear. Additionally, a Ducker-Prager yield criterion with bi-parabolic hardening is used in combination with an explicit Euler-forward algorithm to describe the elastoplastic behaviour of the material in compression. As a result, the material model’s constitutive law is obtained with the homogenization procedures after coupling the damage and plastic model together by a specific algorithm originally introduced by Zucchini and Lourenço. The constitutive equations for model 1 (shear), model 2 (tension), model 3 (compression) and model 4 (coupled) were coded successfully in MATLAB. The components’ shearing, tensile cracking, crushing and splitting failures are correctly modelled analytically with an algorithm, which can be applied to simplify the micro-mechanical model. Besides, constitutive laws of models 1 and 2 were also implemented successfully in the finite element software DIANA version 10.4 (check). The ability of the model to capture the failure of the components in shear, tensile cracking or crushing was examined through simple analytical applications. Moreover, the model was compared against experimental results from tests performed on masonry wallets under compressive loading; the model was able to predict the strength of the specimens satisfactorily. Therefore, this alternative constitutive material model can adequately simulate masonry’s behaviours with a simpler algorithm than the previous model. Meanwhile, the component’s elastic and elastoplastic behaviours can be simulated in more detail in this model, as the case that the horizontal joint is first damaged in shear and compressive splitting effects are additionally included.

Fibre reinforced polymers (FRP) can be a solution for future bridge renovation when only the deck of the bridge needs replacement. In these cases the deck is replaced with an FRP sandwich panel deck. The main advantages are a high strength-to-weight ratio which is beneficial for the ever heavier lorries and the fast installation which prevents hindrance. To connect the FRP deck with the steel superstructure, bolted connectors are used. One of the aspects that needs to be investigated before the bolted connectors can be applied are the relevant loads on the bolted connectors. The focus of this thesis will be to investigate the relevant static and fatigue forces on the connectors.
55 existing girder and arch bridges have been selected from a database of Rijkswaterstaat. For each bridge an appropriate FRP deck has been designed with an analytical method. The bridges are modelled in SOFiSTiK to investigate the shear forces in the connectors. The layout of the bolted connectors is kept constant for all bridges, as well as the transverse stiffness of the connector. The shear forces are calculated with a linear analysis. Before the static and fatigue analyses, first the hybrid interaction of the model is investigated. The hybrid interaction is the amount of horizontal forces transferred between the FRP deck and the steel super-structure. Hybrid interaction is beneficial as it increases the strength of the structure. Two models of a generic bridge have been investigated, the first is the standard model which is supposed to use hybrid interaction. The second model is an adjusted version to create a non-hybrid model. Three parameters are investigated: the deflection, the slip and the longitudinal stress over the height of the beam. The results show that hybrid interaction is created with the bolted connectors in the standard model.
In the static analyses two loads are investigated: traffic loads and temperature loads. The shear forces in the longitudinal direction are investigated as this is the governing direction. Before the loads are applied on the existing bridges, first a generic bridge has been investigated to gain knowledge over three bridge parameters. First the facing laminate of the FRP deck is changed. Second the direction of the webs of the FRP deck, and this also changes the connector layout due to feasibility. Third the expansion coefficient of the resin is changed. For traffic loads mainly the direction of the webs influences the shear forces in the connectors. For temperature loading the shear forces are largely depending on the expansion coefficient of the laminate, the close the expansion coefficient to the expansion coefficient to the steel superstructure, the lower the shear forces. The existing bridges that have been investigated resulted in a large scatter in results. The layout of the superstructure of the bridge influences the facing laminate and the number of connectors, which influences the maximum shear forces in the connectors. For both traffic and temperature loads, the connectors close to the supports experience the highest shear forces.
Besides the static loading, also fatigue is investigated. The shear forces in the connectors are calculated for one bridge, namely the approach bridge Nieuw Vossemeer. This bridge is one of the heaviest loaded bridges in the static analyses and it is according to expect judgement facing deck problems. Two aspects are investigated in the fatigue analysis, first the magnitude and second the type of load cycles. The magnitude is important as this needs to be below the slip resistance of the bolted connectors. The type of load cycles is important as this is related to how damaging the load cycle is. Because there are no S-N curves for bolted connectors between an FRP deck with a steel superstructure, the damage cannot be calculated. The R-ratio is used to investigate the type of load cycles. To calculate the R-ratio of a load cycle, the minimum shear force is divided by the maximum shear force. The resulting number expresses the type of load cycle. For the results, distinction has been made between the connectors close to the supports and connectors in the lengthwise middle of the bridge span. Both the magnitude as the type of loading is different.
Finally, it is concluded that the shear forces in the connectors is one of the aspects to be considered when designing a bridge with hybrid interaction between the FRP deck and steel superstructure. A large scatter of shear forces can be expected, depending on the bridge layout. Incorrect deck design can result in unnecessary high shear forces. The connector layout can be optimised to make the design more cost efficient.

Buildings influence the environment due to the emission of greenhouse gases, energy use, water consumption, and waste generation. The load-bearing structures of buildings also have a significant share in these emissions. Currently, European and national regulations oblige to focus on sustainability in designs as well. In this research, it is therefore investigated how the environmental impact of a specific case study can be reduced (the Base design). This is a distribution centre’s load-bearing structure and is a sway steel structure with one mezzanine floor made from concrete and steel. In the first part of this research, the design choices to reduce the yearly environmental impact of a distribution centre’s load-bearing structure are investigated. This is done by following three circular economy strategies to improve the Base design. The first strategy focuses on the building’s initial material use, where it is aimed to reduce the current impact of these materials as much as possible. This strategy is applied in a non-sway steel structure and a non-sway timber structure. The second strategy focuses on the afterlife of a building. This led to a steel sway structure where Design for Deconstruction is applied, which means that extra attention is given to the connections to ensure reuse is possible at the end of life. The third strategy focuses on extending the use stage, meaning that the design is optimised for multiple functions. This is implemented in two designs where the principle of Design for Adaptability is applied. In the second part of the research, several environmental impact calculation methods to measure the environmental impact are investigated. It is decided to consider the current product impact (Stages A1-A3 of a Life Cycle Assessment) and the final stage (Stage D), where benefits and loads beyond the system boundary are calculated. As a result, the yearly environmental impact is calculated for the different design alternatives and is given in a shadow price (in euros) per year. This is done separately for the main load-bearing structure and the mezzanine floor load-bearing structure. From the environmental impact calculation of the design alternatives, it can be concluded that there are several ways to reduce the environmental impact of a distribution centre. Though, the following design aspects influence this most significantly. Firstly, it is concluded that environmentally friendly material should always be chosen over other materials to reduce the environmental impact of a building. More specifically, it is recommended to design a timber sway structure (Alternative B) if the reference service life of the building is unknown or if a long reference service life is expected. For a short reference service life, it is recommended to focus on the afterlife of a building. This strategy is most effective if this is combined with a reduction in initial material use. For the main load-bearing structure, Alternative A with an end of life scenario with a high chance of reuse results in the lowest yearly environmental impact. For the mezzanine floor, the demountable floor design with a high chance of reuse of Alternative C leads to the lowest yearly environmental impact. Besides, using the building for a longer time is also an effective measure to reduce the yearly environmental impact. The reference service life may extend if a building is designed for multiple functions. This can be assessed by asking the client about their expectations of the use of the building. By assessing this issue in the design phase, it can be decided to include some overcapacity to ensure a longer reference service life.

The implementation of timber as a load-bearing and stabilizing material for high-rise structures has significantly increased over the last decades due to its potential of reducing the environmental footprint of a structure. Timber structures present a reduced global stiffness and self-weight compared to structures incorporating traditional construction materials, making them prone to high accelerations caused by wind load which affects the structural integrity and user comfort. The acceleration of a structure is a highly complex parameter that must be determined using modal analysis computed by a full-scale finite element model, and is significantly influenced by the magnitude of the wind and vertical loads, as well as the global stiffness of the structure. During the preliminary design phase, it is the responsibility of structural engineers to determine the feasibility of the design and estimate the amount of material required and the distribution of the structural elements. However, this process must be done under a limited amount of time, forcing engineers to rely on rules of thumb and previous experience, which are not currently available for the design of timber high-rise structures. Therefore, the goal of this investigation is to perform a parametric study to determine the influence of various parameters on the design of timber high-rise structures and assist structural engineers in making well-argued decisions during the preliminary design phase. The preliminary design parameters to be studied in the parametric study are: stability system design, connection stiffness and building height. The ranges for the parameters were selected based on extreme values such that clear trends regarding their influence on design could be visualized. This decision limits the design feasibility of some configurations studied in this investigation. The selected stability systems to be studied are glulam frame, CLT core and glulam diagrid. The design verification for each design alternative is done using ULS and SLS criteria provided by Eurocode, as well as a simplified method to estimate the dynamic response of the structure. Finally, the sizing of the structural elements and data collection was done by the implementation of evolutionary algorithms. From the data collected it was determined that the most influential design parameter for the design of timber high-rise structures is the stability system selection given that it determines the global stiffness, which showed a significantly higher influence on the dynamic response of the structure than its self-weight. Moreover, the efficiency of the different stability systems was assessed based on the maximum slenderness they could achieve compared to the amount of material they required. Based on this definition, it was determined that the glulam diagrid is two times more efficient than the CLT core and three times more efficient than the glulam frame. The efficiency of the glulam diagrid is caused by its high global stiffness provided by the triangular configuration of the diagonal elements. These observations prove that the effect of timber’s low density can be mitigated by the implementation of efficient stability systems. The influence of connection stiffness was determined to be directly related to the ability of the stability system to provide lateral stability to the structure. The influence of this parameter on form stable structures such as the CLT core and the glulam diagrid, proved to be nearly negligible, while for non-form stable structures such as the glulam frame it proved to be highly influential. However, it was also determined that the addition of rotational stiffness in the connections causes an exponential increase of the costs and environmental footprint of the structure, which decreases their design feasibility. Finally, the influence of building height on the design is visualized by its effect on the dynamic response of the structure caused by the logarithmic increase of the wind speed as this parameter increases, as well as a decrease of the global stiffness proportional to the efficiency of the stability system.

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.

This master thesis is on post-tensioning cross-laminated timber stability cores for multiple story buildings. When designing a CLT core, significantly larger core sections will be needed than when designing a stabilizing core in concrete. This is for one part due to the limited stiffness of the CLT compared to concrete. For another part it is due to the limited stiffness of connectors in CLT. Sliding and uplift can occur in connections in CLT loaded in tension and shear respectively. The CLT panels behave like rigid bodies, with most of the displacement occurring at the connections. In addition, cooperation between flange and web may be limited, depending on the stiffness of the corner connection and the occurrence of shear lag. Post-tensioning is suggested as a solution to diminish uplift and sliding in the connectors. In this way, with the same core section, a taller building may be realized compared to the non-post-tensioned case. In the thesis also the long-term effects on the prestress level is assessed, as estimating these effects is important for the safety of the system.
This thesis adds to the body of knowledge on post-tensioned CLT structures. Firstly, previous studies on post-tensioned CLT focus on individual shear walls and on seismic design situations. This thesis explores how beneficial post-tensioning is from the perspective of serviceability limit state governed design. Furthermore, though post-tensioning as a prestressing method has been applied often in concrete structures, prestressing of CLT is a novel research subject. Especially the estimation of long-term force loss is a topic that still requires research. This thesis provides the designer with a straightforward calculation method (using python) for estimation of prestress force loss in the long-term.
The research was carried out with a literature study and a case-study. The literature research comprised of studies on structural design with CLT loaded in-plane; the effective flange of a CLT core; stiffness of connections in CLT; prestressing of CLT; a design approach for post-tensioning; time dependent losses in post-tensioned CLT. The case study was based on a fictitious floorplan including a “minimal core”, and at expressing the benefit of post-tensioning in terms of height gain.
The degree to which the flange and the web cooperate showed highly dependent on the connection between flange and web and the core height. In the case study, the effective flange width showed to depend highly on the height of the core and the stiffness of the connection between flange and web.
In the case-study, without post-tensioning, approximately half of the displacements could be attributed to the connections. With post-tensioning, the uplift and sliding displacements in the horizontal joints was eliminated. Consequently, the attainable height was significantly increased: from 5 storeys in the un-post-tensioned case, to 8 storeys in the post-tensioned case. Long-term effects on the prestress loss were considerable. In the case-study, approximately 40% loss of post-tension force in the lifetime of the building was predicted and included in the design. Largest causeof force loss was due to changes of moisture content during construction. The remaining lateral displacements after post-tensioning were due to bending and shear.
Post-tensioning of CLT cores is a powerful method for reducing lateral displacements in cases where uplift and sliding are dominant contributors to the lateral displacements. This is especially the case in light-weight buildings. Uplift and sliding displacements can be eliminated altogether with post-tensioning. The designer should realize that post-tensioning does not increase the bending and shear stiffness of the core. The thesis also concludes that with the post-tensioning of CLT walls, the compressive strength of the CLT in the so-called “compression-toe” might be exceeded. It is an important check in design. Furthermore, depending on the decision to re-tighten the rods at some point or not, the post-tension force loss should be calculated and included in finding the right prestress level. For this estimation of the moisture level of the CLT proved to be an important but difficult step. It is likely that the 40% force loss in the case-study is on the conservative side, since a large change in moisture content has been assumed. In practice, the moisture content can be measured on site. This can help verify the assumptions on the moisture content used in force loss calculations. This can help in assuring the structure is safe in the long-term.