Trees exhibit adaptability in response to external loads, which allows them to form an inosculated connection (self-growing connection) with a neighboring tree. Such connections have the mechanical potential to build living tree structures. Although qualitative studies have studied this phenomenon, quantitative analysis of its growth features remains limited. Self-growing connections fused by weeping figs (Ficus benjamina L.) are utilized to study growth features. X-ray scanning and optical microscopy techniques are employed to investigate parameters including density, geometry, fiber structures, and material compositions. Key findings demonstrate that the fused region of a connection has a larger volume and a higher density on the intersected surface. Microscopic analysis identifies that the enlarged wood in the fused area is tension wood characterized by G-layers. The key component that connects trees is referred to as merged fibers, and the pattern of their distribution is found to be mainly in the outer layer of the larger cross-angle of a connection. At the cellular level, crystals within cells are identified in the fused region, implying possible mechanical stresses the interface has experienced. The findings in self-growing connections can serve as inspiration for structural design in living structures, biomimicry, bioinspired structures, and advancements in bioeconomics.

Trees can adapt to external loads and form inosculations (self-growing connections), where stems or branches naturally fuse together. However, a limited understanding of biomechanical features of connections hinders their practical applications. This study used connections formed by Ficus benjamina L. to investigate their mechanical properties at different growth levels. Two parameters (fusion degree and interface curvature) were identified to describe growth levels. Customized tensile tests were designed to measure mechanical properties perpendicular to the interconnected surface. Growth levels of studied connections ranged from initial formation to almost fusion of piths, which provided a range of tensile strength of 0.23 to 1.38 MPa. Two primary failure modes (failure at the interface and failure across the stems) were found to be linked to growth levels. The fusion degree, at approximately 15%, contributed to distinguishing failure modes. The average diameter of a connection had the most significant effect on its tensile strength and stiffness. Moreover, the interface curvature correlated negatively with mechanical properties. Average diameter, interface curvature, and fusion degree were effective predictors of connections’ tensile strength. Regarding Ficus connections, dry connections were stronger than wet connections. These findings provide evidence for nature-based design using self-growing connections under different moisture conditions and growth levels.

The lack of strength values for wooden foundation piles in the design standards for timber (Eurocode 5) hinders their proper engineering design and assessment. In order to fill this gap, an extensive experimental campaign was conducted to characterize the mechanical properties of large-scale, water-submerged spruce (Picea abies L.) and pine (Pinus sylvestris L.) piles. This was achieved through the execution of axial compression tests on 253 full-scale pile segments. Wet compressive strength and stiffness values were derived for both spruce and pine piles, applicable to the whole pile and/or its parts: head, middle-part, and tip. The quality variables that most influenced the wet compressive strength of the piles were density, knot ratio (KR), number of annual rings (age), and growth rate. Based on this, characteristic strength values were derived for piles with the following grading limits: KR < 0.5, age between 20 and 100 years, and a growth rate <5 mm/year. These variables were used as key parameters to develop prediction models for the wet compressive strength of spruce and pine piles. The saturated compressive strength values and grading boundaries presented in this study contribute to the engineering design of timber piles and support the integration of reliable design values into future versions of Eurocode 5.

Wooden piles are the most common foundation system in the historic city of Amsterdam (NL). The piles are fully submerged below water table and subject to bacterial decay. This study investigated sapwood and heartwood proportions in spruce, pine, and fir piles from different construction periods, in relation to their degradation. X-ray computed tomography scans on 49 wet discs were performed to measure the piles’ sapwood width, which was then validated against an empirical model based on annual rings and growth rate. Degraded areas, identified with micro-drilling measurements, were found to affect sapwood only. These outcomes were further validated on 201 pile segments, with the predicted sapwood widths being greater than or equal to the decayed portions, even in 300-year-old piles. Therefore, estimating sapwood width can contribute to determine the remaining sound cross section of the piles, providing useful input for service life models for planning timely maintenance interventions.

Similar to wood, adhesives may exhibit duration of load effects. When loaded for longer periods of time, damage processes in the material may develop, eventually leading to failure. From wood research it is known that load level, temperature and relative humidity have an important influence on this behaviour. In general, higher stress levels, temperatures, and moisture content will lead to shorter times to failure and these effects may be more pronounced in loading directions such as shear or tension perpendicular to the grain. It is shown that the reaction kinetics based approach for damage accumulation effects in polyurethane based adhesives can be described using the same non-linear damage accumulation expression as used for wood. The relationship between the time to failure and load-level as influenced by for instance temperature is determined for lap joints, immersed in hot water with temperature of 60oC and 90oC, and at load levels varying between 30 and 90% of the mean short term shear strength.

It is shown that a non-linear damage accumulation expression as used for wood, can also be used for damage accumulation effects in melamine-urea-formaldehyde adhesives. The relationship between the time to failure and load-level as influenced by temperature is determined for beech lap joints loaded in tensile shear. The specimens have been immersed in hot water with temperatures of 60oC and 90oC respectively, and at load levels varying between 30 and 90% of the mean short term shear strength.

The majority of bridges and quay walls in the centre of Amsterdam are supported by 100–300 years-old wooden foundation piles subjected to bacterial decay. Bacterial degradation proceeds at a slow rate, allowing the piles to perform their function for many years, although causing a reduction of their load-carrying capacity over time. In this study, micro-drilling measurements were employed to capture the amount of decay and remaining short-term compressive strength of the historic wooden piles. The applicability of micro-drilling was studied on 60 wooden piles with various decay levels, retrieved after 100–295 years of service life. An algorithm was developed for analysing the micro-drilling signals, aimed at determining the decayed outer layer of the piles’ cross section, and validated with the results of mechanical testing on the piles. The micro-drilling technique is now used on a large scale in Amsterdam, supporting the assessment of the wooden foundation piles in the city.

In the historic city centre of Amsterdam (NL), the predominant foundation system is comprised of wooden piles. Due to their placement below the water table, these foundations are susceptible to bacterial decay. This study aims to investigate and compare various methods for characterizing decay patterns within the cross sections of piles retrieved from two bridges in Amsterdam. The examined piles span different construction years: three originate from 1727, four from 1886, and two from 1922. Following extraction, the piles were transported to TU Delft Stevin II Laboratory, where they underwent further subdivision into three segments, each representing the head, middle, and tip, resulting in a total of 27 segments. The effects of bacterial decay were characterised by performing micro-drilling measurements, small-scale material and compressive tests on prismatic samples extracted from the segments' cross sections, computed tomography scans, and light microscopy observations. Microscopic examination revealed severe degradation in all segments dating back to 1727, extending 20–50 mm from their surface. This outcome was also confirmed by the other adopted methods: the corresponding prisms had large moisture contents and poor mechanical properties, while low basic densities and drilling amplitudes were obtained from CT scans and micro-drilling measurements, respectively. On the contrary, the internal sections of the 1727 segments exhibited no evidence of decay and demonstrated properties consistent with those observed in sound segments from 1886 and 1922. Finally, the observed gradients of density, strength, and stiffness were well correlated with micro-drilling measurements, which can therefore be reliably used as on-site assessment method to reconstruct the properties of the piles.

Wooden pile foundations are present in many historic towns in Europe and beyond. The technology of making such foundations was developed primarily in southern Europe, but rapidly spread to other countries. The foundations themselves are made with wooden piles of up to 15m, on top of which horizontal wood members are placed acting as interface between structure and piles. Assessment of the state of wood and its mechanical properties is fundamental for a thorough structural analysis, whether for an existing structure or for re-use. In both cases, the type and amount of degradation needs to be addressed. For wooden structural elements, a fundamental analysis is required regarding the mechanical degradation because of long term loading (duration of load effect), in combination with an assessment of the size and severity of biological or physical decay. These effects are responsible for the remaining load carrying capacity and consequently, also for the decision-making process whether the foundation can be re-used. The assessment of this remaining load carrying capacity is done using an integral damage accumulation model, taking into account the severity and type of degradation, combined with the mechanical load components causing the duration of load effect in wood. As such, the structural analysis approach is different from current design standards for new timber structures, and in-line with the principles laid out in ISO standard 13822 for the assessment of existing structures.

The majority of the bridges in the historic city centre of Amsterdam are supported by wooden foundation piles. Most of these were constructed 100–300 years ago, currently raising concerns about potential safety issues. The wooden piles under the bridges remain entirely under the water table, potentially subjected to bacterial decay in anaerobic conditions. Bacterial degradation proceeds at a slow rate, allowing the piles to perform their function for many years, although causing a reduction of their load-carrying capacity over time. To this end, a large experimental campaign was conducted to characterize the material and mechanical properties in relation to biological decay of 60 spruce and fir piles, dated back to 1727, 1886 and 1922, retrieved from two bridges in Amsterdam. Large-scale compression tests were carried out on 201 pile-segments extracted from head, middle-part and tip of the piles to determine their remaining short-term compressive strength. Micro-drilling measurements were conducted on each pile and analysed with a TU-Delft-developed algorithm, aimed at determining the soft shell – the width of the decayed outer layer of the piles’ cross section. Micro-drilling allowed to accurately assess the remaining sound cross section of the pile, which resulted to be well correlated to its mechanical properties. The extent of decay throughout the cross-section of the piles was assessed within sapwood and heartwood through experimental models from literature and validated with Computed Tomography (CT) scanning. This allowed to identify that bacterial decay was only present in the non-durable sapwood, even in very degraded piles. Moreover, the soft shell resulted to be rather uniform along the piles’ length. The analysis of decay, supported by micro-drilling and CT scans, allowed to develop experimental equations to predict the remaining short-term compressive strength along the pile length. The micro-drilling technique is now used on a large scale in Amsterdam, supporting the assessment of the remaining load carrying-capacity of wooden foundation piles in the city, aiding in the planning of conservation, maintenance and preservation strategies.

The majority of bridges and quay walls in the inner city of Amsterdam rely on wooden foundation piles. Most of these were constructed 100–300 years ago, implying several challenges for the assessment of the current residual load-carrying capacity and their reliability. In Amsterdam, the wooden piles supporting bridges and quay walls remain entirely under the water table, which means that only bacterial decay can occur. Bacterial degradation proceeds at a slow rate, allowing the piles to perform their function for many years, although causing a reduction of the load-carrying capacity over time. To this end, the municipality of Amsterdam started a large project where non-destructive micro-drilling measurements were employed, with the goal of capturing the in-situ level of decay and the remaining strength of wooden foundation piles. The applicability of micro-drilling was studied on 60 wooden piles with various decay levels, driven between 1727 and 1922, and retrieved from two bridges in Amsterdam. An algorithm was developed for analysing the micro-drilling signals, aimed at determining the decayed outer layer of the pile (soft shell). The micro-drilling approach was validated with the results of mechanical testing on the piles. This study contributes to reliably assessing the decay and remaining load carrying-capacity of wooden foundation piles utilizing in-situ micro-drilling measurements.

Gelatine adhesives, also known as animal glues, are collagen-based water-soluble biopolymers derived from vertebrate connective tissues. One of the various fields in which gelatine adhesives are widely used is the conservation of cultural heritage such as decorated furniture and panel paintings. It is observed that, with time, the failure in these objects often occurs along the adhesive bondlines. Given the moisture and temperature sensitivity of these adhesives, obtaining knowledge of their long-term behaviour, when exposed to climate variations, is pivotal. Here, the influence of hygrothermal ageing (exposure to a combination of elevated temperature and relative humidity (RH) cycling) on the microstructure and macroscopic properties of four different types of gelatine adhesives is investigated. These adhesives were selected from different animal origins namely bovine, rabbit, and fish with different Bloom strengths. It was observed that ageing cycles interfere with the most critical structural feature of protein chains namely triple helices. A clear decay in triple helix content at the micro-scale, determined by Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) techniques, was observed which had implications on the macroscopic properties of these adhesives such as reduction of strain to failure and toughness (strain energy density to failure). The rate of decay in properties was revealed to be the highest in the adhesives with the lowest triple helix content. This study provides a scientific view of microstructure-property relationships in gelatinous adhesives as a function of environmental ageing, and stipulates the underlying mechanism of the degradation of mechanical properties as the loss of structural triple helices, regardless of the animal origin.

Gelatine adhesives aka ‘animal glues’ are water-soluble biopolymers used in historic objects such as wooden cabinets and panel paintings since ancient times. This paper investigates the correlations between microstructural features, namely triple helices, and macroscopic properties of four different types of gelatine adhesives, prevalently used in conservation practices, irrespective of the animal origin. These adhesives include bovine bone, bovine skin, rabbit skin, and fish glues. Thin adhesive films were produced via solution casting methods in controlled climate conditions and their thermal and mechanical properties, and moisture sensitivity were investigated. XRD as a non-destructive characterisation method demonstrated good agreement with DSC in the quantification of gelatine adhesive (animal glue) triple helix content irrespective of the animal origin. Linear correlations between triple helices and gel (Bloom) strength and tensile strain energy to failure (toughness) were found for all adhesive types. Dynamic vapour sorption experiments demonstrated that lower triple helix content is correlated with higher moisture sensitivity of the adhesives. Moreover, the effect of environmental RH on the thermal behaviour of adhesives was investigated by DSC. The results demonstrated that the increase in environmental RH causes a reduction in the adhesives' glass transition and denaturation temperatures whilst triple helix content did not alter. Bovine bone glue with the lowest triple helix content showed the least toughness and highest moisture sensitivity, whilst fish glue with the highest triple helix content was identified as the most flexible glue.

Timber pile foundations are widespread in many areas around Europe and North-America. Especially in areas with weak soils, timber pile foundations have been a very good and economic solution. That foundations can be up to 500 years in service in cities like Venice, Amsterdam, Boston and many others. Degradation of the piles may occur over time which may influence considerably the residual service life. Residual service life is depending both on the time-to-failure behavior of wood, as well as the dead and live loads on the piles below buildings, quay walls and bridges. A good assessment method is required, as closing down infrastructure (bridges, quays) or buildings because of failing foundations causes considerable economical damage. In recent years in the cities of Rotterdam and Amsterdam failures occurs on such foundations. A comprehensive research program has been set up, that includes the development of underwater microdrilling equipment, so that an indication of the wood quality can be done in situ, without the need of bringing samples to the laboratory. The development of this microdrilling has been paired with a large scale campaign to determine the strength of new and recovered piles. In a next step, by applying a non-linear damage accumulation model, the remaining service life is estimated as a function of the decay level and decay rate, as well as the expected mechanical loads.

In the historic city centre of Amsterdam (NL), the most widespread foundation system consists of wooden piles. With the aim of modelling and predicting remaining service life of these foundations and the piles in particular, one of the possible methods for collecting data and monitoring their condition consists of micro-drilling (MD) measurements. This work evaluates the reliability of MD measurements in identifying decayed portions and specific features of wooden foundation piles, considering different moisture content (MC) values. To this end, 24 segments were selected, sawn from wooden piles extracted from site, and having time in service (TS) of 2 to 294 years (with reference to 2021, the year of extraction). 240 MD measurements were conducted at varying MC values of 7% to 212%. The obtained MD profiles showed for all TS a slight decrease in drilling resistance when increasing MC. However, from the MD signals it is possible to reliably detect the areas affected by biodegradation phenomena (e.g. bacterial decay) along the drilling depth, regardless the MC of the segment or its gradient along the drilling depth. The present study contributes to research aiming at utilizing (in-situ) MD techniques for reliably assessing and quantifying decay and to be used in remaining service life planning of wooden foundation piles.

The paper deals with the specific approach to teach the subject of assessment and retrofitting of historical timber structures to students of various colleges in an integrated and multidisciplinary course. Timber structures belong to the oldest structures in the world and because of their specific susceptibility to ageing, often require a profound analysis with respect to their current state and functionality. Especially in Europe, city centres are full of historical buildings that present an important cultural heritage, and as a consequence have a protected status. This status entails that these structures need to be assessed, maintained and monitored carefully, to keep the state of these structures at a level that they can perform. These tasks are often complicated and require interdisciplinary work. In education, this interdisciplinarity is often difficult to incorporate in the curriculum, as various expertises needed for cultural heritage assessment are separately and often fragmentary present at various colleges or faculties of universities, if present at all. Also, different teaching approaches may hinder course development. This paper deals with educational activities that have been developed and experienced at TU Munich and TU Delft, along with the cooperation with the University of Zagreb, dealing with the most important aspects of the assessment and analysis of historical timber structures.

Collagen-based bioadhesives, also known as animal glues, are derived from animal parts (e.g. skin, bone, and cartilage). They have been widely used in the production of decorative wood working, paintings, bookbinding, and other historical objects for centuries as well as for their restoration and preservation [1]. Collagen, in which the term (kólla) is derived from the Greek word for glue, is a fibrous structural protein with a hierarchical microstructure at different length scales. Collagen is water insoluble and can be turned into water-soluble gelatine through the denaturation process. Upon denaturation, the triple helix structure in collagen unwinds and turns into random coils giving gelatinous animal glue. Gelatinous animal glue can be dissolved in water and during gelling and subsequent drying, the random protein coils undergo partial renaturation back into triple helices. These triple helices in the adhesive act as physical cross-links leading to a continuous three-dimensional network structure [2]. These microstructural features affect the physical and mechanical performance of the glue at micro and macro scales. In this study four different adhesives from different animal species both mammalian and fish are investigated. These adhesives are bovine bone, bovine skin, rabbit skin, and fish. For this study, thin films of these adhesives were manufactured using the solution casting method. Physical and mechanical behaviour of the adhesives were characterized using Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), Bloom strength evaluation, and uniaxial tensile tests.

Tropical hardwood or treated wooden sheet piles have been used historically to protect stream banks in countries like the Netherlands. However, there is an imminent need for alternative as exploitable tropical hardwood forests available in the country is limited. Locally available softwoods are less resistant to decay and in extreme conditions like in a stream bank with high moisture content, softwoods show minimal durability. The section of the sheet pile at air-water-soil interface is the most prone to decay. Hence twin-wood sheet piles have been developed in industrial scale, which is a combination of hardwood and softwood. Hardwoods which have high resistance to decay is used above the water table while softwood is used in the section which is always below water. An alternative stream bank protection system using vegetation and softwood sheet pile was proposed recently. In such a system the effect of vegetation can be included as an increase in cohesion of the soil or an increase in internal friction angle. In this article two different approaches (System approach (SA) and Discrete approach (DA)) for the design of wooden sheet pile-vegetation system are examined. The SA shows that the presence of vegetation increased the time for complete damage of the wooden sheet pile-vegetation system to occur. In DA approach a change in slope of the face of the stream bank is required if the effect of vegetation is considered as an increase in friction angle of the soil.

Churches are part of heritage structures that take an important role in Europe ́s cultural identity. As such, these structures must be protected to prevent catastrophic collapse and any damage must be reported timely to establish planning to maintenance and restoration. This can be achievable when the churches are monitored periodically with regular intervals. However, this monitoring strategy has not been available in most of the Europe’s churches for a number of reasons, complexity of the structures and limited budget are just two of them. Laser scanning has been widely used in capturing rich three-dimensional (3D) topographic data of visible surfaces of a structure with high accuracy. This paper presents a methodology to determine the shape and possible deviation from verticality of the church’s tower for monitoring deformation using a terrestrial laser scanner. The 500-year old wooden tower of St. Bavo Church in Haarlem, Netherlands is selected as a case study. First, point clouds of the tower captured from different views are registered into the same coordinate system. Second, a RANSAC method is employed to extract point clouds of a whole façades of the tower. Next, a point and surface-based method is proposed to compute the deformation of the surface from its data points. The results indicate that there is slightly different deformation between the tower facades in the same story and in neighbour stories. Moreover, the maximum total relative deformation at Story 7 of the tower by 0.63m.

Timber pile foundations are widespread in many areas around Europe and North-America. Especially in areas with weak soils, timber pile foundations have been a very good and economic solution. However, aging of the foundations can become a problem, as physical, biological and/or chemical degradation may occur over time. Now, that foundations can be up to 500 years in cities like Venice, Amsterdam, Hamburg, Boston and many others, questions arise about the reliability and which assessment methods can be used in order to estimate the current load carrying capacity and their residual service life. Residual service life is depending both on the time-to-failure behaviour of wood, as well as, the dead and live loads on the piles below buildings, quay walls and bridges. The approach taken integrates degradation models with a reaction kinetics based damage model. For wood that remains consistently below the waterline, the combination of bacterial degradation and long term loading is considered the most important, but degradation by fungi also may occur depending on soil and groundwater conditions. The integral assessment model will function as a tool for repair and maintenance strategies for asset managers and structural engineers.

Lignin, one of the most abundant natural polymers, has been extensively studied as liquid or solid additive in bituminous binders. Despite the fact the organosolv lignin in bitumen improves the overall resistance against oxidative aging, lignin could lead to binders of high thermal cracking sensitivity. In this study, a bio-based oil is implemented in a lignin modified bitumen to ameliorate characteristics, such as fatigue and thermal cracking resistance. Pressure aging vessel conditioning was applied to new binders formulated by different proportions of bio-oil to simulate the long-term aging. A series of rheological tests were performed. Based on the linear amplitude sweep test results, fatigue damage of lignin-bitumen could be reduced by increasing the oil content. According to relaxation test results, the addition of oil significantly decreased the ratio of residual stress and relaxation time. This study has shown preliminary conclusions on the use of bio-oil to improve the low-intermediate temperature performance of lignin-bitumen binders.