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...

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

This research tries to answer the question which construction material, concrete or timber, is best to use during the construction of terraced housing in the Netherlands, based on the environmental performance. Existing studies often do not take all aspects of a design for the comparison into account, or have a bias toward one material. In order to investigate the main research question, a literature study has been executed together with a practical case study.

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.

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

Timber as a renewable source has been extensively applied among European countries in the construction field. Among more than 1000 available wood species which could be potentially applied as engineered wood, tropical hardwood takes up a significant portion and has advantages of high mechanical resistance and remarkable biological durability against micro-organisms compared to coniferous species and European grown hardwood. Okan has been part of this development, as a hardwood species mostly from the West African regions.The objective of this thesis is to investigate the strength influencing features, calculate corresponding characteristic values and establish the correlation between the influencing factors and the bending strength with the least deviation and create a representative Okan strength predicting model. Abstracted from literature and dataset, geographically speaking, climate, precipitation, soil quality, water sources are expected to have varying degrees of impacts on mechanical properties. From the material perspective, knot ratio, fiber orientation (slope of grain & ring angle), moisture content, density, Modulus of elasticity (dynamic, static) are important factors. Several experiments about hardwood bending strength have been conducted. However, none of those focus on the growth ring angle and the 3D effect of the fiber orientation. To dive deep into Okan, a series of laboratory tests are conducted, including non-destructive inspection, a four-point bending test on 20 beams (10 stored in the dry condition, 10 stored in the wet condition) with the assistance of digital image correlation technology [DIC]). Except for the regulated experimental procedure, two innovative visual inspection methods based on image processing via Matlab were conducted and verified, which turns out the automation method has preferable efficiency and precision. However, this method could hardly identify compression failure. To avoid the compression failure, beams with the dynamic modulus of elasticity less than 18500 N/mm^2 are supposed to be checked again by the inspector. All possible influencing factors are well determined by the above-mentioned testing.Influencing factors of the fracture section form could be concluded from the observation of damaged samples. The slope of grain and growth ring work together to determine the form of the governing crack section. From the experimental outcome, it is clear to observe the linear correlation between mechanical properties and moisture content grouped by the slope of grain. Constant k= 0.13 for bending strength is found, k = 0.05 is found for dynamic modulus of elasticity. The experimental results yield the following adjusted characteristic values: bending strength 63.56 N/mm^2, dynamic modulus of elasticity 21134.55 N/mm^2, density 866.58 kg/mm^3. Based on 20 beams, this batch of Okan could be graded to D55 which is higher than D30-D35 yielded from the dataset. Besides, Okan beams from Gabon could also be graded into D55. Current European standards advise that the reasonable slope of grain range for tropical hardwood is 0 to 0.1. Through the calculation of the theoretical slope of grain of the dataset and experimental samples, increasing the threshold of the slope of grain to 0.3 should be considered in the testing program. Further promotion to 0.2 doesn’t improve the grading outcome and even worsen it.The linear regression result of modulus of elasticity and bending strength is more preferable than density and bending strength in literature and experimental results, which proves the modulus of elasticity is a good indicator of bending strength. Large scatter happens in the regression of the Hankinson formula. In the combination of two basic models, the new proposed model has an optimized coefficient of determination (R^2 = 0.685). The distribution function of the bending strength of the dataset has preferrable overlapping with the theoretical bending strength calculated from the new strength model. To keep the model on the safe side, a safety factor y = 0.9 is applied.It is still unclear if the growth ring angle has a clear numerical relationship with mechanical properties. However, the growth ring angle does bring apparent influences on the form of the fracture section. The 3D effect of fiber orientation needs further investigation.

Today, society is becoming more and more aware of the environment and the (negative) influence we have on it. Especially the current workings of our economy have a detrimental effect on the environment. To reduce these effects, a transition is being made towards a circular economy. The construction sector plays a big role in the degradation: in the Netherlands the sector accounts for 50% of the raw material use, 40% of the energy consumption, 40% of the waste production and 35% of the CO2 emission. For the construction sector, one of the changes to establish a more circular economy, is the adoption of a circular design method. This method consists of the construction of buildings, building systems and building elements being designed for disassembly and reuse. This reduces raw material use and the expel of harmful emissions. While we see some developments being made in the construction sector regarding circularity, not many developments can be found in the field of reusable floor systems. For the sizable use of raw materials and expel of harmful emissions during the manufacturing process of floors, a more circular design for floor systems can (eventually) contribute to the sectors transition to circularity. Therefore, this research is focussed on developing demountable connections which can be used in such a circular floor system. The result is a system comprising a prefabricated timber-concrete composite (hereafter: TCC) floor slab connected to steel edge beams with toothed-plate connectors. An important aspect taken into account in the development of this design is the efficiency of erecting, disassembling and reassembling the floor. A multi-criteria analysis is conducted to determine floor slabs viable for use in a reusable floor system. A timber-concrete composite floor slab is chosen and designed. The slab is verified using analytical calculations. Design variants are made for demountable connections at the slab-beam positions at the head end and the side of the slab and for the slab-slab position. A choice between design variants is made by reviewing the fabrication and assembly tolerances and by assuring a non-destructive disassembly procedure. Analytical calculations are performed to verify the chosen connections. A case study building is used for the development of the floor system. The TCC floor slab spans 10.8m, has a total height of 510mm and a width of 1800mm. The used edge beam is an L-section. On the web a toothed-plate connector is adhesively bonded onto which the timber beams are placed to enable shear force transfer between the timber beams and the edge girder. At the top of the web a compression bolt is installed which is fastened after instalment of the floor slabs to ensure force transfer between the bolt and the concrete slab. Two angle sections are screwed to the outer sides of the outer timber beams and bolted to the edge girder to guide the slab to its intended position and to ensure structural soundness by vertically fixing the floor slab to the girder. Lastly the limits of the developed floor system are determined by performing a parameter study of the floor slab and the connection. The floor slab can be designed to span 12.6m. The connection still meets the structural requirements when the system is used in a building of maximally 70m high. This is applicable on many combinations of the building length (10m to 70m) and width (6m to 12.6m), if the right cross-sectional dimensions are used.