Summary

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

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

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

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

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

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

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

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

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

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

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