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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., Bio-based Structures & Materials

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., Bio-based Structures & Materials

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., Bio-based Structures & Materials, Structural Integrity & Composites, Adhesion Institute

This contribution aims for an enhanced numerical representation for strength prediction of timber. This implies a validated elasto-plastic continuum damage model which considers orthotropy and heterogeneity of the material, and represents the ductile behavior under compression and the brittle material behavior under tension dependent on the three-dimensional orthogonal fiber directions. The behavior under compression is captured by Hill (1948) plasticity and an exponential hardening law enhanced by the loading direction dependency. The same model covers also the brittle damaging behavior by means of continuum damage mechanics (CDM). In this study, a separated damage mode (SDM) criterion with simultaneously evolving damage variables is investigated. After the experimental validation of the model for axially loaded clear wood samples, the developed numerical model is implemented to a sawn timber with fiber deviation, where homogenization of the material and simplification to transverse isotropy is not anymore possible. The 3D orthotropic material behavior is experimentally validated for this application example with bi-axial loading and aims for further numerical investigation of wood with heterogeneities as occurring in sawn (hard)wood for its efficient use in engineered wood products such as glued laminated timber., Bio-based Structures & Materials

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., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Bio-based Structures & Materials

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., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Bio-based Structures & Materials

When curved glulam beams are subjected to bending, tension perpendicular to grain is introduced. In this work, Monte-Carlo analysis is conducted to study the influence of the annual-ring orientation of individual board on stress concentration in the radial direction. A virtual cutting program is developed which simulates the sawing processes of boards and yields a database of sawn boards, each with a characterized material direction with respect to the pith location. Lamellas are randomly selected from the database to construct curved glulam beams in FE models for Monte-Carlo simulation. Parameters including lumber diameter distribution, taper function, orthotropic elastic properties are considered for four common wood genera in Europe: spruce, pine, larch, and beech. Statistical analysis shows that when the annual-ring effect is considered, the average radial stress in the middle height area of the glulam beams can reach up 1.56 times (even higher on the middle width and height area) compared to the common practice, where wood is usually simplified as transverse isotropic material. Such stress concentration, which can trigger early damage of the structure, indicates an underestimation of stress perpendicular to grain in common practice. Moreover, parameter studies show that the stress redistribution depends not only on the mechanical properties of wood species but also on the width of the board layer., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Bio-based Structures & Materials

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., Bio-based Structures & Materials

This work investigated the influence of knots on the compression strength of wooden foundation piles. The study involved 110 pile segments sawn from 18 spruce and 9 pine piles with a mean diameter of approximately 200 mm, and moisture contents above fiber saturation. The mechanical properties were determined performing both full-scale compression tests on pile segments, and small-scale experiments on discs sawn from selected segments, considering samples with and without knots. A knot ratio (KR) was defined analysing the knots layout of each wooden pile, and evaluating how the compressive strength was influenced by size, number and layout of knots. As final step, a prediction model was implemented based on the dry density and KR of wooden piles, to estimate the influence of knots on their compressive strength., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Bio-based Structures & Materials

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., Bio-based Structures & Materials, Structural Integrity & Composites

Mechanical properties of wood such as stiffness and strength vary locally especially due to heterogeneities and anisotropy. Analytical models and numerical simulations of wooden boards are able to represent varying material orientation e.g. with local fiber directions from laser scanning as input for the prediction of strength. Current Finite Element Models reconstructed the grain orientation by means of computationally demanding fluid analysis around obstacles like knots; whereas the available fiber pattern, captured by means of laser scanning, was passed solely into the detection of knots, but not directly processed for the inclusion of material fiber orientation. Therefore, the goal of this paper was the development of a numerical approach to directly include locally varying measured fiber orientation with orthotropic material properties and to predict the tensile strength of boards with reduced computational effort. Therefore, the stiffness was transformed element-wise according to the measured fiber deviations and the local fiber stress components were computed for the specific tensile load case. For the virtual strength prediction, numerical maximum stress values were compared to experimental tensile strength. Good agreements were observed with reduced computational effort compared to existing approaches between numerical and experimental results., Bio-based Structures & Materials

This work presents the application of timber-based retrofitting techniques to a case-study stone masonry church featuring a wooden roof from 18th century. From the static point of view, the original roof structure presented a number of undersized structural elements, and its members were poorly or not connected among each other and to the masonry, making the church vulnerable to seismic loads as well. Thus, the roof was retrofitted with wood-based techniques, including an overlay of plywood panels, against seismic actions. These affordable, rapid, easily realizable interventions enabled both the conservation and seismic retrofitting of the roof, providing an adequate load-carrying capacity for static loads, and an effective diaphragm action against seismic loads. The conducted numerical analyses showed that the realized interventions greatly improve the seismic behaviour of the building. Besides, when the additional energy dissipation provided by the plywood panels overlay is taken into account in the numerical model, the church would even potentially be able to fully withstand the expected seismic action of the site., Bio-based Structures & Materials

Timber is one of the most widely applied engineering materials due to its favorable physical and mechanical characteristics. Nevertheless, over the service life, the combination of mechanical load and varying environmental conditions can have a critical influence on the mechanical response of timber structures, considering especially the mechano-sorptive characteristics. In this work, the performance analysis of the existing time- and moisture-dependent models identifies the need of a more comprehensive 3D constitutive rheological model, which can take into account orthotropic, elastic-plastic, viscoelastic and mechano-sorptive aspects, including the complex mechano-sorptive recovery phases that may occur over the lifetime. Therefore, a comprehensive algorithm of such a model is developed here. An improvement is made for the mechano-sorptive component by introducing an ordinary and a transcending mechano-sorptive part, which are governed by the absolute change of moisture content and the change exceeding the historical highest moisture content at each loading phase, respectively. Simulations are run under cases with mechanical loading of tension and compression perpendicular and parallel to the direction of the fibers. Both medium-term (up to 2500 h) as well as short-term (up to 350 h) mechanical behavior of the material under constant temperature is analyzed and good agreements are achieved with literature results. Comparison with existing models indicates that the proposed model gives an improved prediction of the mechano-sorptive creep and recovery, which has a non-linear dependence on the moisture history. Furthermore, sensitivity analyses are performed and the applicability of the model to different species under different combinations of load and moisture variation is studied here., Bio-based Structures & Materials

The conversion to climate-stable, resilient and productive forests has resulted in an increasing share of mixed stands. Different growth conditions and silvicultural treatments lead to an increased scatter in strength compared to what is expected from monoculture experience. The study (i) quantified the magnitude of variation in strength of European beech timber from stands of different composition and (ii) showed the impact of grading on the characteristic strength value of timber coming from those stands. Strength grading models and machine settings for hardwood tensile classes on over 900 European beech (Fagus sylvatica L.) boards were derived. One model used only the dynamic modulus of elasticity (Edyn), and a more complex model used a knot value in addition. Afterwards, 407 boards from pure beech stands as well as mixed stands of beech with Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), Norway spruce (Picea abies (L.) Karst.), sessile oak (Quercus petraea (Matt.) Liebl.), and Scots pine (Pinus sylvestris L.) were graded and analyzed for their material properties from tension tests parallel to grain. Although a variance components analysis attributed only 4.2% of the variation to mixture, the ungraded timber showed significant strength differences between the pure and the beech-pine stands (65.2 versus 46.6 MPa). The yield of the material graded to the highest class in a class combination was higher in pure beech stands. The required characteristic strength values were mostly met for boards from the pure stands; while boards from the beech-pine mixed stands hardly ever reached the required values. To reduce strength variation and guarantee reliable timber products, strength grading should consider the various growth situations in forests when sampling material for the derivation of settings., Bio-based Structures & Materials

The market share of European beech (Fagus sylvatica L.) wood in the construction sector is low despite an increase in beech stock in Central European Forests in recent years. More efficient sawing techniques, higher lamella grading yields and solving of adhesion challenges may increase the competitiveness of beech glulam and promote its use. The aim of this paper is to revise the lamella grading system in the current German technical approval for beech glulam Z-9.1-679:2019 (DIBt (2019). BS-Holz aus Buche und BS-Holz Buche Hybridträger und zugehörige Bauarten. Allgemeine bauaufsichtliche Zulassung Z-9.1-679:2019. Deutsches Institut für Bautechnik) and to suggest modifications in the lamella grading rules for glulam production allowing higher yields and reliable tensile strength values at the same time. The unique dataset in this study combined different origins of lamellas and covered a wide range of visual, physical and mechanical wood characteristics including a high amount of low quality material. Indicating properties (IPs) for tensile strength, such as knot parameters and dynamic modulus of elasticity, were contrasted with tensile strength and static modulus of elasticity. Beech lamellas, graded by means of Z-9.1-679:2019 (DIBt (2019). BS-Holz aus Buche und BS-Holz Buche Hybridträger und zugehörige Bauarten. Allgemeine bauaufsichtliche Zulassung Z-9.1-679:2019. Deutsches Institut für Bautechnik), did not achieve the tensile strengths required for glulam production in many grading classes and the yield was low. A machine grading approach with dynamic modulus of elasticity as a single grading criterion gave higher yields than the current grading procedure and high reliability for tensile strength prediction with a prediction accuracy of R2 = 0.67., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Bio-based Structures & Materials

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., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Bio-based Structures & Materials, Adhesion Institute

The conversion to climate-stable, resilient and productive forests has resulted in an increasing share of mixed stands. Different growth conditions and silvicultural treatments lead to an increased scatter in strength compared to what is expected from monoculture experience. The study (i) quantified the magnitude of variation in strength of European beech timber from stands of different composition and (ii) showed the impact of grading on the characteristic strength value of timber coming from those stands. Strength grading models and machine settings for hardwood tensile classes on over 900 European beech (Fagus sylvatica L.) boards were derived. One model used only the dynamic modulus of elasticity (Edyn), and a more complex model used a knot value in addition. Afterwards, 407 boards from pure beech stands as well as mixed stands of beech with Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), Norway spruce (Picea abies (L.) Karst.), sessile oak (Quercus petraea (Matt.) Liebl.), and Scots pine (Pinus sylvestris L.) were graded and analyzed for their material properties from tension tests parallel to grain. Although a variance components analysis attributed only 4.2% of the variation to mixture, the ungraded timber showed significant strength differences between the pure and the beech-pine stands (65.2 versus 46.6 MPa). The yield of the material graded to the highest class in a class combination was higher in pure beech stands. The required characteristic strength values were mostly met for boards from the pure stands; while boards from the beech-pine mixed stands hardly ever reached the required values. To reduce strength variation and guarantee reliable timber products, strength grading should consider the various growth situations in forests when sampling material for the derivation of settings., Bio-based Structures & Materials

Timber is one of the most widely applied engineering materials due to its favorable physical and mechanical characteristics. Nevertheless, over the service life, the combination of mechanical load and varying environmental conditions can have a critical influence on the mechanical response of timber structures, considering especially the mechano-sorptive characteristics. In this work, the performance analysis of the existing time- and moisture-dependent models identifies the need of a more comprehensive 3D constitutive rheological model, which can take into account orthotropic, elastic-plastic, viscoelastic and mechano-sorptive aspects, including the complex mechano-sorptive recovery phases that may occur over the lifetime. Therefore, a comprehensive algorithm of such a model is developed here. An improvement is made for the mechano-sorptive component by introducing an ordinary and a transcending mechano-sorptive part, which are governed by the absolute change of moisture content and the change exceeding the historical highest moisture content at each loading phase, respectively. Simulations are run under cases with mechanical loading of tension and compression perpendicular and parallel to the direction of the fibers. Both medium-term (up to 2500 h) as well as short-term (up to 350 h) mechanical behavior of the material under constant temperature is analyzed and good agreements are achieved with literature results. Comparison with existing models indicates that the proposed model gives an improved prediction of the mechano-sorptive creep and recovery, which has a non-linear dependence on the moisture history. Furthermore, sensitivity analyses are performed and the applicability of the model to different species under different combinations of load and moisture variation is studied here., Bio-based Structures & Materials

Before timber boards can be used for engineering applications, they need to be strength graded. This step is currently done based on visual or machine grading methods. Each approach may face problems such as frequent measurement (human) errors or problems in dynamic measurements due to missing density values, respectively. To increase accuracy of the predictions, an advanced numerical method has been developed based on FE-analysis to predict tensile strength of the boards. By simulating the tensile test procedure virtually, stress developments around wood heterogeneities have been analysed, and identifying parameters (IPs) have been provided, representing the stress concentrations in 3D anisotropic space. Virtual dynamic-MoE has been derived after performing the stress-wave analysis, to be used as another IP for strength predictions. These parameters have been used in a non-linear multiple regression analysis with the tensile strength for the predictions. Similar approach has been performed, using the parameters of the visual and machine grading methods. The quality of strength prediction based on virtual method was in the same level/slightly higher than recently available methods, depending on the wood species. The model has been developed by considering a scatter for the quality range of 450 spruce, Douglas fir and beech boards. For the model verification, the approach has been used for strength prediction of a group of ash and maple boards, which provided satisfactory results., Accepted Author Manuscript, Bio-based Structures & Materials

In the field of seismic retrofitting, a common intervention to improve box-like behaviour in an existing building is the strengthening and stiffening of existing timber floors and roofs. However, these retrofitting methods should be carefully applied, because they change the static scheme and the buildings' response to earthquakes. Strengthening solutions with high reversibility and light weight have therefore to be preferred, and in this context the overlay of plywood panels on existing floors can improve their characteristics in terms of strength and stiffness, but also enhance their energy dissipation, already at a very limited deflection. This strengthening technique was adopted and tested within an experimental campaign aimed at assessing the seismic response of timber diaphragms with typical characteristics from the Groningen area, located in the northern part of the Netherlands. In that region, human-induced earthquakes take place due to gas extraction and the existing buildings are not suitable to safely withstand these seismic events. This paper presents a summary of the results of the experimental campaign on as-built and retrofitted timber diaphragms, and evaluates the beneficial damping properties of floors strengthened with plywood panels, connected only to the underlying planks and not directly to the joists. The results are compared with the data available in literature and provide new reference values for the coming version of the Dutch seismic standard., Accepted Author Manuscript, Bio-based Structures & Materials

Wood is one of the most widely applied engineering materials due to its favourable physical and mechanical characteristics. As an inhomogeneous biomaterial, wood exhibits complicated mechanical properties including anisotropy, elasto-plasticity, viscoelasticity, and hygroscopic characters. To analyse the time- and moisture-dependent behaviour of timber structures, both mechanical loading and moisture evolution has to be taken into account. This study analyzes the capability and limitations of different rheological models. A 3D-orthotropic viscoelastic, mechano-sorptive model for wood is presented here, which covers the timber behavior under varying moisture condition during loading and unloading phases., Accepted Author Manuscript, Bio-based Structures & Materials

Tall timber buildings are of growing interest worldwide and also in the Netherlands. With the introduction of CLT, higher timber buildings are possible compared to traditional timber frame housing. Tall timber buildings can be made as modular buildings or as buildings with a CLT or concrete core and a timber wall/column-floor system that can contribute to the overall stability. In this paper, master student thesis projects dealing with various aspects of timber highrise buildings are presented. These include the possibilities of using 3D-modules in high-rise buildings, design aspects of differential vertical shortening, parametric design, as well as wind-induced behaviour. For tall timber buildings specific aspects as the influence of the connections on the stability and comfort (accelerations), and the necessity of performing a phased analysis to account for the different creep behaviour of timber and concrete. When this is done properly, tall timber buildings can be designed with various structural appearances, fulfilling the requirements and the wishes of architects and users. The raised technical questions have been incorporated in the teaching program of Delft University of Technology and formed the basis for the master thesis projects presented in this paper., Accepted Author Manuscript, Bio-based Structures & Materials

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., Accepted Author Manuscript, Bio-based Structures & Materials

In-plane behavior of timber diaphragms is usually characterized by means of an equivalent shear stiffness. However, this value depends on how the stiffness of the floors is evaluated from the experimental tests. Although an increasing number of research studies have provided a deeper insight into the seismic characterization of as-built and retrofitted timber diaphragms, the use of different standards or assumptions have led to inhomogeneous and not comparable results. With a focus on light, reversible, wood-based strengthening techniques applied to existing diaphragms, this study proposes a uniform and simple method based on the calculation of the secant stiffness of the floors at reference drifts. By means of this procedure, relevant research studies from the literature were compared, and homogeneous, indicative values of equivalent shear stiffness were proposed for each considered strengthening technique. These results can contribute to a more aware and reliable use, design, and linear modeling of wood-based retrofitting solutions for existing timber diaphragms., Bio-based Structures & Materials

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., Optical and Laser Remote Sensing, Bio-based Structures & Materials

In this work, the relationship for a socket-type connection in wooden foundation piles is investigated, and a trilinear moment-rotation diagram was determined by means of experiment. Numerical and analytical models confirmed that the material properties for compression perpendicular to the grain are governing for the connections’ strength and stiffness properties. This was similar to the response found in the experiment, where ductile behaviour was observed, which can be explained from the plasticization after the compression strength perpendicular was reached. Although because of the specific configuration (confined in a circular tube) the found strength perpendicular to the grain cannot be assigned to other configurations, a good estimation of the stiffness of the connection can be made with FEM models, assuming an MOE90 of 70 N/mm2 for a fully saturated pile. With a conservative assumption for the strength perpendicular to the grain the influence of the connection in a pile-soil model can be investigated also for other configurations than the tested one. A procedure to study the influence of tangential (usually horizontal) soil displacements on timber piles with concrete extensions piles on top is proposed. The outcome of a specific situation from practice with high horizontal loads showed that the bending capacity of the timber pile will in most cases be governing and not the investigated socket connection., Bio-based Structures & Materials, Geo-engineering

Timber diaphragms in existing buildings are often too flexible in their plane, and can thus potentially cause out-of-plane collapses of walls during earthquakes. A very efficient retrofitting method to increase their in-plane stiffness and energy dissipation is the overlay of plywood panels. However, the usual characterization of the floors by means of a general equivalent shear stiffness cannot account for their nonlinearity and dissipative properties. Therefore, in this work, an analytical model is formulated to describe the in-plane response of timber diaphragms strengthened with plywood panels screwed along their perimeter to the existing sheathing. The proposed formulation starts from the definition of the load-slip equation for a single screw connecting a plank and a plywood panel. The whole floor’s response is then derived, with the prediction of both backbone curve and pinching cycles. From the comparison between the response of tested full-scale diaphragms and the analytically calculated one, it can be concluded that the proposed model accurately predicts the in-plane behaviour and dissipative properties of timber floors retrofitted with plywood panels., Bio-based Structures & Materials, Steel & Composite Structures

Historical or existing buildings are often composed of brick or stone masonry walls, and timber floors and roofs. When these buildings are subjected to earthquakes, the interaction among such structural components is essential to avoid collapse or excessive damage to the constructions. In this framework, a crucial role is played by the connections between horizontal and vertical structural elements: this is especially true when considering existing buildings not designed or realized taking into account seismic actions, because no measures against these events are present. An example of such a situation is noticeable in the province of Groningen, in the northern part of the Netherlands, where human-induced earthquakes take place due to gas extraction. Given the absence of seismic events until recently, a characterization of the existing buildings is necessary, and strengthening measures have to be analysed, in order to make them earthquake-safe. This work describes the experimental campaign conducted at Delft University of Technology to assess the seismic behaviour of as-built and strengthened timber-masonry connections. Results show that existing joints are not suitable to withstand earthquakes, while the proposed strengthened configurations can increase not only strength and stiffness, but also energy dissipation of the connections., Bio-based Structures & Materials

Tall timber buildings are of growing interest worldwide and also in the Netherlands. With the introduction of CLT, higher timber buildings are possible compared to traditional timber frame housing. Tall timber buildings can be made as modular buildings or as buildings with a CLT or concrete core and a timber wall/column-floor system that can contribute to the overall stability. In this paper, master student thesis projects dealing with various aspects of timber highrise buildings are presented. These include the possibilities of using 3D-modules in high-rise buildings, design aspects of differential vertical shortening, parametric design, as well as wind-induced behaviour. For tall timber buildings specific aspects as the influence of the connections on the stability and comfort (accelerations), and the necessity of performing a phased analysis to account for the different creep behaviour of timber and concrete. When this is done properly, tall timber buildings can be designed with various structural appearances, fulfilling the requirements and the wishes of architects and users. The raised technical questions have been incorporated in the teaching program of Delft University of Technology and formed the basis for the master thesis projects presented in this paper., Accepted Author Manuscript, Bio-based Structures & Materials

Wood is one of the most widely applied engineering materials due to its favourable physical and mechanical characteristics. As an inhomogeneous biomaterial, wood exhibits complicated mechanical properties including anisotropy, elasto-plasticity, viscoelasticity, and hygroscopic characters. To analyse the time- and moisture-dependent behaviour of timber structures, both mechanical loading and moisture evolution has to be taken into account. This study analyzes the capability and limitations of different rheological models. A 3D-orthotropic viscoelastic, mechano-sorptive model for wood is presented here, which covers the timber behavior under varying moisture condition during loading and unloading phases., Accepted Author Manuscript, Bio-based Structures & Materials

In the field of seismic retrofitting, a common intervention to improve box-like behaviour in an existing building is the strengthening and stiffening of existing timber floors and roofs. However, these retrofitting methods should be carefully applied, because they change the static scheme and the buildings' response to earthquakes. Strengthening solutions with high reversibility and light weight have therefore to be preferred, and in this context the overlay of plywood panels on existing floors can improve their characteristics in terms of strength and stiffness, but also enhance their energy dissipation, already at a very limited deflection. This strengthening technique was adopted and tested within an experimental campaign aimed at assessing the seismic response of timber diaphragms with typical characteristics from the Groningen area, located in the northern part of the Netherlands. In that region, human-induced earthquakes take place due to gas extraction and the existing buildings are not suitable to safely withstand these seismic events. This paper presents a summary of the results of the experimental campaign on as-built and retrofitted timber diaphragms, and evaluates the beneficial damping properties of floors strengthened with plywood panels, connected only to the underlying planks and not directly to the joists. The results are compared with the data available in literature and provide new reference values for the coming version of the Dutch seismic standard., Accepted Author Manuscript, Bio-based Structures & Materials

Before timber boards can be used for engineering applications, they need to be strength graded. This step is currently done based on visual or machine grading methods. Each approach may face problems such as frequent measurement (human) errors or problems in dynamic measurements due to missing density values, respectively. To increase accuracy of the predictions, an advanced numerical method has been developed based on FE-analysis to predict tensile strength of the boards. By simulating the tensile test procedure virtually, stress developments around wood heterogeneities have been analysed, and identifying parameters (IPs) have been provided, representing the stress concentrations in 3D anisotropic space. Virtual dynamic-MoE has been derived after performing the stress-wave analysis, to be used as another IP for strength predictions. These parameters have been used in a non-linear multiple regression analysis with the tensile strength for the predictions. Similar approach has been performed, using the parameters of the visual and machine grading methods. The quality of strength prediction based on virtual method was in the same level/slightly higher than recently available methods, depending on the wood species. The model has been developed by considering a scatter for the quality range of 450 spruce, Douglas fir and beech boards. For the model verification, the approach has been used for strength prediction of a group of ash and maple boards, which provided satisfactory results., Accepted Author Manuscript, Bio-based Structures & Materials

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., Accepted Author Manuscript, Bio-based Structures & Materials

In this work, the relationship for a socket-type connection in wooden foundation piles is investigated, and a trilinear moment-rotation diagram was determined by means of experiment. Numerical and analytical models confirmed that the material properties for compression perpendicular to the grain are governing for the connections’ strength and stiffness properties. This was similar to the response found in the experiment, where ductile behaviour was observed, which can be explained from the plasticization after the compression strength perpendicular was reached. Although because of the specific configuration (confined in a circular tube) the found strength perpendicular to the grain cannot be assigned to other configurations, a good estimation of the stiffness of the connection can be made with FEM models, assuming an MOE90 of 70 N/mm2 for a fully saturated pile. With a conservative assumption for the strength perpendicular to the grain the influence of the connection in a pile-soil model can be investigated also for other configurations than the tested one. A procedure to study the influence of tangential (usually horizontal) soil displacements on timber piles with concrete extensions piles on top is proposed. The outcome of a specific situation from practice with high horizontal loads showed that the bending capacity of the timber pile will in most cases be governing and not the investigated socket connection., Bio-based Structures & Materials, Geo-engineering

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., Optical and Laser Remote Sensing, Bio-based Structures & Materials

In-plane behavior of timber diaphragms is usually characterized by means of an equivalent shear stiffness. However, this value depends on how the stiffness of the floors is evaluated from the experimental tests. Although an increasing number of research studies have provided a deeper insight into the seismic characterization of as-built and retrofitted timber diaphragms, the use of different standards or assumptions have led to inhomogeneous and not comparable results. With a focus on light, reversible, wood-based strengthening techniques applied to existing diaphragms, this study proposes a uniform and simple method based on the calculation of the secant stiffness of the floors at reference drifts. By means of this procedure, relevant research studies from the literature were compared, and homogeneous, indicative values of equivalent shear stiffness were proposed for each considered strengthening technique. These results can contribute to a more aware and reliable use, design, and linear modeling of wood-based retrofitting solutions for existing timber diaphragms., Bio-based Structures & Materials

Timber diaphragms in existing buildings are often too flexible in their plane, and can thus potentially cause out-of-plane collapses of walls during earthquakes. A very efficient retrofitting method to increase their in-plane stiffness and energy dissipation is the overlay of plywood panels. However, the usual characterization of the floors by means of a general equivalent shear stiffness cannot account for their nonlinearity and dissipative properties. Therefore, in this work, an analytical model is formulated to describe the in-plane response of timber diaphragms strengthened with plywood panels screwed along their perimeter to the existing sheathing. The proposed formulation starts from the definition of the load-slip equation for a single screw connecting a plank and a plywood panel. The whole floor’s response is then derived, with the prediction of both backbone curve and pinching cycles. From the comparison between the response of tested full-scale diaphragms and the analytically calculated one, it can be concluded that the proposed model accurately predicts the in-plane behaviour and dissipative properties of timber floors retrofitted with plywood panels., Bio-based Structures & Materials, Steel & Composite Structures

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., Accepted Author Manuscript, Bio-based Structures & Materials

The geotechnical construction industry is a major component of the overall construction sector and is strategically important in infrastructure development (transportation, flood and landslide protection, building foundations, waste disposal). Although industry and research in the overall construction sector have been investing significantly in recent years to produce innovative low-carbon technologies, little innovation has been created in geotechnical construction industry, which is lagging behind other construction industry sectors. This paper discusses the interplay between low-carbon geotechnical engineering and unsaturated soil mechanics based on the research carried out within the project TERRE (Marie Skłodowska-Curie Innovative Training Networks funded by the European Commission, 2015-2019,H2020-MSCA-ITN-2015-675762)., Bio-based Structures & Materials

Timber sheet pile walls are widely used for the protection of stream banks in different parts of the world. However, there is a tendency to create more sustainable types of stream banks not only because exploitable wood is more difficult to obtain, but also because of disturbance to the natural habitat of plants and animals due to hard embankments. In the Netherlands alone, about 2500 km of engineered timber sheet pile wall embankments exist, primarily made with tropical hardwood, besides an even much larger amount of ‘non-engineered’ small-size timber-based embankments. As an alternative, the authors propose to use a mixed timber sheet pile-vegetation system, where locally available timber can be applied in combination with natural vegetation. Unlike the usual bioengineering scheme, vegetation is not seen as an element, which could replace the timber sheet piles. Instead, a new perspective is tested, where the vegetation is included as a ‘structural’ element which can even counteract the consequences of time-dependent biological degradation of the timber sheet pile. By doing so, both long-term durability as well as reliability of the stream bank is improved. A comprehensive design strategy was developed based on well-established sub-models from the literature on plant growth, root reinforcement as well as timber damage accumulation. The timber sheet pile wall-vegetation system is illustrated in an example case study. Preliminary analysis including only the mechanical reinforcement of vegetation shows that there is a decrease in moment and shear acting on the timber sheet pile with growth of the vegetation. Consequently, the damage accumulation due to load duration effects on the timber decreases and the service life of the system increases. Thus, using vegetation in combination with highly degradable timber could possibly negate the need for using hardwood timber, or more generally, save resources that are currently used for these structures., Bio-based Structures & Materials

Strength grading is an important step for the production of homogenous and high-quality solid wood material. In particular, for hardwoods, the use of non-visible characteristics is indispensable. Dynamic MOE (Edyn) is an important parameter widely used for grading of softwoods and applicable to hardwoods as well. There are two common ways to measure Edyn—ultrasound (US) wave propagation and longitudinal vibration (LV) method. Both methods are used in practice, however, due to the different inherent measurement techniques, the results differ. The current paper analyses the stiffness and strength coefficients of determination for several temperate European hardwood species and emphasizes the differences between the two measurement systems. The performance was analysed with regard to grading techniques, testing modes for the mechanical properties (tension and bending) and wood qualities. For more than 2861 pieces of European ash (Fraxinus excelsior), European beech (Fagus sylvatica), European oak (Quercus spp.) and maple (Acer spp.), the Edyn was measured using both techniques, and destructive tests (tension and edgewise bending) were applied. The results show that LV has higher coefficient of determination compared to the US Edyn. The coefficient of determination for both methods and tensile application can be increased by calculating Edyn with average density. Furthermore, the results support species-independent strength grading of hardwoods. Further research on the effect of different wood qualities and sawing patterns is required., Bio-based Structures & Materials

The main parameter that influences the bending strength of timber from tropical hardwood is the slope of grain. Although, in the grading rules, a specific threshold value is given, in these hardwoods, the global slope of grain is very difficult to quantify by visual assessment. The slope of grain measured after testing gives a better indication, but still it can only poorly describe the Hankinson relations. By rewriting the Hankinson relations, the slope of grain can be determined from the bending strength test values and from the MOE test value, both in combination with the density values and constants derived by non-linear regression analysis. These two values correlate very well, and the average value is designated as the theoretical slope of grain. With the theoretical slope of grain, five test samples of the tropical wood species okan were evaluated, and slope of grain values of 0.3 were observed, where 0.1 is the limit value. Because all pieces passed the visual grading method as applied in practice, slope of grain values should be incorporated in the strength class assignment test program, when these qualities cannot be ruled out for coming on the market. The (dynamic) modulus of elasticity can be used to evaluate the occurrence of the desired range of slope of grain values in the test samples., Bio-based Structures & Materials

Detection of local wood inhomogeneities is important for accurate strength and stiffness prediction. In hardwood specimens, visual characteristics (e.g. knots or fibre deviation) are difficult to detect, either with a visual surface inspection or by the machine. Transversal ultrasound scan (TUS) is a non-destructive evaluation method with high potential for hardwoods. The method relies on differences in ultrasound wave propagation in perpendicular to the grain direction. The aim of this study is to estimate and analyse the capabilities of TUS for defect detection in hardwoods and prediction of mechanical property values. In the current paper, the TUS was applied to the hardwood species European ash (Fraxinus excelsior L.), Norway maple (Acer platanoides L.) and sycamore maple (Acer pseudoplatanus L.). In total, 16 boards of both specimens were completely scanned perpendicular to the grain using a laboratory scanner with dry-coupled transducers. The measurements were processed to 2D scan images of the boards, and image processing routines were applied to further feature extraction, defect detection and grading criteria calculation. In addition, as a reference for each board, all relevant visual characteristics and mechanical properties from the tensile test were measured. Using the TUS global fibre deviation, the size and the position of the knots can be detected. Knottiness correlates to the strength properties similarly or even better compared to the manual knottiness measurement. Between the global fibre angle measured using TUS and measured on the failure pattern, no correlation could be found. The ultrasound modulus of elasticity perpendicular to the grain does not show any meaningful correlation to the elastic properties parallel to the grain. In overall, TUS shows high potential for the strength grading of hardwoods., Bio-based Structures & Materials

The integration of buildings into vegetation has become a necessity in many metropolitan areas of the world today. It expands the potential of vertical and horizontal, exterior and interior, exposed and enclosed spaces in a building that can be used to accommodate plants. Green infrastructures have benefits both on urban and building scales. They can be categorized into green roofs and vertical greenery systems that can be divided further into green façade, green wall, green terraces, elevated forest and vertical forest. There are many design and planting considerations for architects, structural engineers and botanists when using living architectures to mimic natural systems, such as plant characteristics and environmental conditions. Plants used for vertical greenery are more likely to be hardwood species to adjust solar radiation during cooling and heating periods, as well as for aesthetic pleasure. Take Bosco Verticale, which is located in Milan, as an example to look into engineering methods when trees grow on balconies of high-rise buildings. It can be concluded that planting restraint safety systems and regular maintenance are necessary for the tree growth in the sky. However, the change in growing conditions causes various problems such as stability and irregular growth of trees. Instead of using steel cables and cages to prevent trees from falling off in the sky, the concept of self-growing connections is proposed to act as natural bracings and provide the stability for vertical forests. This paper is meant to generate awareness of the possibilities of the vertical integration of trees into buildings, show application considerations, and inspire future developments., Bio-based Structures & Materials, BT/Botanical Garden Delft

Samples of European beech (Fagus sylvatica) were used for this study. Logs of these samples covered a scatter of mild-to-strong curvatures and the boards of these samples covered strong fiber deviations. This study consists of two separate parts: (1) log reconstruction and optimization of the cutting pattern, and (2) board reconstruction and strength prediction. Information about the internal quality of the logs is missing in this study, as laser scanning has been used for surface reconstruction of logs. Therefore, two separate steps were implemented here. (1) Influence of cutting pattern and board-dimensions on yield were analyzed. For this step, 50 logs were checked. (2) A more advanced numerical method based on the finite element (FE) analysis was developed to improve the accuracy of tensile strength predictions. This step was performed, because visual grading parameters were relatively weak predictors for tensile strength of these samples. In total, 200 beech boards were analyzed in this step. However, due to the geometrical configuration of some knots, the reconstruction and numerical strength prediction of 194 boards out of 200 boards were possible. By performing tensile tests numerically, stress concentration factors (SCFs) were derived, considering the average and maximum stresses around the imperfections. SCFs in combination with the longitudinal stress wave velocity were the numerical identifying parameters (IPs), used in the nonlinear regression model for tensile strength prediction. The influence of the combination of different numerical parameters in the developed non-linear model on improving the quality of the strength prediction was analyzed. For this reason, improvement of coefficient of determination (R2) after adding each parameter to the multiple regression analysis was checked. Performance of the developed numerical method was compared to the typical grading approaches [using knottiness and the dynamic MoE (MoEdyn)], and, Bio-based Structures & Materials

Controlling the long-term effect of management on the quantity and properties of individual boards is a fundamental challenge for silviculture. Within this basic study on Douglas-fir, we have investigated the sensitivity of the net present value (NPV) to three most common planting densities and a prominent pruning strategy. We therefore have applied an individual tree growth model, which represents intrinsic stem structure as a result of crown competition. The model extrapolated board strength development to the rotational age of 70 years, starting from real and comprehensive data recorded from experimental Douglas-fir plots at the age of 20 years. Total volume production increased from about 1600 m3 ha−1 for 1000 and 2000 trees ha−1 to 1800 m3 ha−1 for 4000 trees ha−1. The economic superiority of the lowest density stands increased considering the NPV at inflation-adjusted interest rates of 0%, 2% and 4%: Given an interest rate of 2% and no pruning, the NPV at 2000 was at about 50% of the one at 1000 trees ha−1. The NPV at 4000 trees ha−1 was even negative. Generally, artificial pruning was not effective. The revealed financial trade-off between growth and timber quality in young stands underlines the importance of silvicultural guidelines, which quantify the effect of management on yield per strength class and financial outcome., Bio-based Structures & Materials

Traditional timber floors cannot normally withstand horizontal seismic loads without large deformations. This may lead to a corresponding out-of-plane collapse of masonry walls in existing buildings. This situation is even more critical in the Netherlands, around the city of Groningen, where human-induced earthquakes started to take place. Since no seismic events have been experienced until recently, none of the existing buildings was designed with seismic events in mind, with no exception for the timber floors: therefore, it was necessary to characterize their in-plane response. To obtain representative results, firstly floor and roof samples were extracted from existing buildings. The relevant material properties were determined, together with the plank-joist connections behaviour. Replicas were then built with new material and tested to confirm the similarity in response compared to extracted samples. Based on these results, full-scale replicated diaphragms were constructed, and tested quasi-static reversed-cyclic in their plane, either parallel or perpendicular to the joists. Besides characterizing as-built diaphragms, a simple strengthening technique with plywood panels was applied as well, improving their in-plane response in terms of strength, stiffness and energy dissipation, as test results confirm. This study is concluded with an analytical characterization of the diaphragms’ in-plane response, for as-built and strengthened configurations., Bio-based Structures & Materials

The main parameter that influences the bending strength of timber from tropical hardwood is the slope of grain. Although, in the grading rules, a specific threshold value is given, in these hardwoods, the global slope of grain is very difficult to quantify by visual assessment. The slope of grain measured after testing gives a better indication, but still it can only poorly describe the Hankinson relations. By rewriting the Hankinson relations, the slope of grain can be determined from the bending strength test values and from the MOE test value, both in combination with the density values and constants derived by non-linear regression analysis. These two values correlate very well, and the average value is designated as the theoretical slope of grain. With the theoretical slope of grain, five test samples of the tropical wood species okan were evaluated, and slope of grain values of 0.3 were observed, where 0.1 is the limit value. Because all pieces passed the visual grading method as applied in practice, slope of grain values should be incorporated in the strength class assignment test program, when these qualities cannot be ruled out for coming on the market. The (dynamic) modulus of elasticity can be used to evaluate the occurrence of the desired range of slope of grain values in the test samples., Bio-based Structures & Materials

The geotechnical construction industry is a major component of the overall construction sector and is strategically important in infrastructure development (transportation, flood and landslide protection, building foundations, waste disposal). Although industry and research in the overall construction sector have been investing significantly in recent years to produce innovative low-carbon technologies, little innovation has been created in geotechnical construction industry, which is lagging behind other construction industry sectors. This paper discusses the interplay between low-carbon geotechnical engineering and unsaturated soil mechanics based on the research carried out within the project TERRE (Marie Skłodowska-Curie Innovative Training Networks funded by the European Commission, 2015-2019,H2020-MSCA-ITN-2015-675762)., Bio-based Structures & Materials

Strength grading is an important step for the production of homogenous and high-quality solid wood material. In particular, for hardwoods, the use of non-visible characteristics is indispensable. Dynamic MOE (Edyn) is an important parameter widely used for grading of softwoods and applicable to hardwoods as well. There are two common ways to measure Edyn—ultrasound (US) wave propagation and longitudinal vibration (LV) method. Both methods are used in practice, however, due to the different inherent measurement techniques, the results differ. The current paper analyses the stiffness and strength coefficients of determination for several temperate European hardwood species and emphasizes the differences between the two measurement systems. The performance was analysed with regard to grading techniques, testing modes for the mechanical properties (tension and bending) and wood qualities. For more than 2861 pieces of European ash (Fraxinus excelsior), European beech (Fagus sylvatica), European oak (Quercus spp.) and maple (Acer spp.), the Edyn was measured using both techniques, and destructive tests (tension and edgewise bending) were applied. The results show that LV has higher coefficient of determination compared to the US Edyn. The coefficient of determination for both methods and tensile application can be increased by calculating Edyn with average density. Furthermore, the results support species-independent strength grading of hardwoods. Further research on the effect of different wood qualities and sawing patterns is required., Bio-based Structures & Materials