Analysis and strengthening of carpentry joints

Joints play a major role in the structural behaviour of old timber frames [1]. Current standards mainly focus on modern dowel-type joints and usually provide little guidance (with the exception of German and Swiss NAs) to designers regarding traditional joints. With few exceptions, see e.g. [2], [3], [4], most of the research undertaken today is mainly focused on the reinforcement of dowel-type connections. When considering old carpentry joints, it is neither realistic nor useful to try to describe the behaviour of each and every type of joint. The discussion here is not an extra attempt to classify or compare joint configurations [5], [6], [7]. Despite the existence of some classification rules which define different types of carpentry joints, their applicability becomes difficult. This is due to the differences in the way joints are fashioned depending, on the geographical location and their age. In view of this, it is mandatory to check the relevance of the calculations as a first step. This first step, to, is mandatory. A limited number of carpentry joints, along with some calculation rules and possible strengthening techniques are presented here

Design of three step joint typologies: review of european standardized approaches

When assessing timber roof structures on-site for any restoration project, engineers can be faced with elements that, over time, were poorly preserved, especially damaged joints in contact with moist masonry walls. Before dealing with any intervention technique, the mechanical behaviour of such carpentry connections must be properly understood. Therefore, it has to be determined how the joints fail, which parameters (i.e. geometrical configurations and mechanical properties of the joint) influence the appearance conditions of failure modes, and the way how the internal forces are distributed within the connection. Therefore, the present paper aims at overviewing three different typologies of Step Joints (SJ) which can often be encountered within traditional timber carpentries between the rafter and the tie beam: the Single Step Joint, the Double Step Joint, and the Single Step Joint with Tenon-Mortise. Regarding each SJ typology, some design rules and geometrical recommendations can be gathered from European Standards and from authors of works on the subject, but no design equation is conventionally defined. Hence, new design models have been determined through the Analytical Campaign for the investigated Step Joints according to their geometrical parameters and to both failure modes: the shear crack in the tie beam and the crushing at the front-notch surface. In order to check the reliability of new design models and the emergence conditions of both failure modes, future experiments and numerical analysis on the three SJ typologies are going to be performed.This work was partly financed in the framework of the Portuguese Public Procurement Code, LOTE 3ES2 – Escola Secundária de Loulé e Olhão. This work was financed by FEDER funds through the Competitively Factors Operational Programme – COMPETE and by national funds through FCT – Foundation for Science and Technology within the scope of the project PTDC/EPH-PAT/2401/2014 and PhD Scholarships SFRH/BD/128580/2017.info:eu-repo/semantics/publishedVersio

Assessment, reinforcement and monitoring of timber structures: FPS Cost Action FP1101

Interest in extending the life of existing and historic timber structures has increased steadily in the last decade, owing to a shift in emphasis forward sustainability and low carbon emission of the construction industry. This increased interest and the growing number of researchers and institutions active in this field are the motivation for the setting of COST ACTION FP1101 on assessment, reinforcement and monitoring of timber structures, now nearing completion of its second year of activity. The paper explains what a COST Action is and presents the aims and objectives of this European Research network initiative. It discussed the state of the art in these three fields of research activities as outlined by the work developed jointly by the network. It discusses avenues for further international collaboration beyond Europe by using some of the implementation instruments available within the COST framework. The paper concludes with a discussion on the current research gaps identified through the network workshop, and a view as to how the major outcomes of the network activities can be further disseminated and find institutional outputs through collaboration with RILEM and European Standardisation Technical Committees.Cost Action FP110

Contribution à l'étude de plaques perforées en régime élastoplastique

Il est avantageux de procéder au dimensionnement mécanique des plaques tubulaires des échangeurs de chaleur dans le domaine plastique. En effet, ces plaques ont tout intérêt à être d'épaisseur la plus faible possible, d'une part afin de réduire les gradients internes de température et les risques liés à la fatigue thermique et, d'autre part afin de réduire les coûts de réalisation liés au matériau et au perçage. Dans la pratique, les plaques sont forées selon un réseau de perforation périodique suivant un pas carré ou triangulaire équilatéral. Ces réseaux sont caractérisés géométriquement par le facteur de ligament dépendant du diamètre de perforation et du pas de la maille. L'objectif de l'article est de proposer une méthode de dimensionnement des plaques tubulaires basée sur l'emploi de plaques pleines équivalentes. Dans un premier temps, les résultats de l'analyse élastoplastique de plaques perforées par voie numérique sont commentés. Une plaque pleine équivalente à la plaque perforée peut servir au dimensionnement à l'état limite de la plaque tubulaire. Dans ce cas, une loi d'écoulement plastique est reformulée pour tenir compte des perforations

Développement d'un élément fini semi-rigide pour l'étude des structures planes en bois

Bien souvent, les calculs de dimensionnement des structures en bois suppose que les nœuds d'assemblages se comportent comme des rotules parfaites ou comme des encastrements parfaits. A l'exception de certains assemblages collés, les assemblages utilisés dans la pratique présentent un comportement semi-rigide bien marqué. Pour de tels assemblages, des déformations relatives apparaissent entre les membrures connectées. Le travail entrepris a pour finalité de développer un élément fini semi-rigide (EFSR) connectant les degrés de liberté en translation et en rotation des nœuds assemblés et dédicacé à la modélisation des assemblages par gousset en bois. La matrice de raideur locale de cet élément est alors définie à partir de résultats expérimentaux caractérisant les rigidités parallèle et perpendiculaire aux fibres. Un des intérêts de cette approche est la prise en compte au niveau même de la matrice de raideur le l'EFSR du comportement orthotrope et éventuellement plastique du bois

Experimentations on the retrofitting of damaged Single Step Joints with Self-Tapping Screws

When assessing the roof of existing buildings, engineers may be confronted with structural joints badly preserved, for instance the damaged Single Step Joint (SSJ) located at the foot of timber trusses. Since the early appearance of failure modes in this traditional carpentry connection may lead to the collapse of the whole timber truss, the retrofitting of damaged SSJ is then required as an economically-viable intervention to stabilize the roof structure. In consequence, the retrofitting of damaged SSJ with Self-Tapping Screws (STS) has been conducted through the Experimental Campaign in order to explore further different possibilities offered by this recent intervention technique (Sobra et al. (2016)). To this end, two strategies, noted R1 and R2, have been proposed to retrofit the SSJ specimens with STS, which had been previously damaged due to both failure modes, namely the crushing at the front-notch surface and the shear crack in the tie beam (Verbist et al. (2017)). Afterwards, the SSJ specimens retrofitted with STS have been tested under monotonic compression in the rafter in order to pull out their mechanical behaviour encompassing the failure modes, the force-displacement response, the stiffness of the connection, and the ultimate normal force in the rafter. By comparing the mechanical behaviour of retrofitted SSJ specimens with the initial ones from Verbist et al. (2017), the performances of both retrofitting strategies with STS have been discussed. Furthermore, the impact of the shear row splitting on the mechanical behaviour of retrofitted SSJ has been evaluated, by providing some warnings to engineers when intervening in existing timber trusses featuring natural damage such as the shrinkage splitting.This work was financed by FEDER funds through the Competitively Factors Operational Programme - COMPETE and by national funds through FCT – Foundation for Science and Technology within the scope of the research projects INVISIBLE WOODS PTDC/EPH-PAT/2401/2014, PROTIMBER PTDC/ECM-EST/1072/2014, and the PhD Scholarships SFRH/BD/128580/2017.info:eu-repo/semantics/publishedVersio

Single step joint: overview of European standardized approaches and experimentations

In the field of the built heritage restoration, engineers have to work with old structures made of badly preserved timber elements. The assessment of timber elements and connections is a major issue for engineers involved in a restoration project. Before thinking about any intervention technics, engineers have to properly understand how the carpentry connections fail, which parameters influence the failure modes (geometry of the joint, mechanical properties of the wood,…) and how the internal forces are distributed into the joint to finally figure out how to design the traditional carpentry connections. The present paper aims to raise those questions focusing on the Single Step Joint design. Even if this common joint between the rafter and the tie beam is geometrically simple, one may pick up three geometrical configurations of Simple Notched Joints from the past till today: the geometrical configuration ideal (GCID), the geometrical configuration perpendicular to the tie beam (GCPTB) and the geometrical configuration perpendicular to the rafter (GCPR). The first one is more recent because it requires a highest accuracy production, and so the use of the new technologies (e.g., CNC). For each one, some general design rules about the geometrical parameters of the Single Step Joint are defined by some European standards (Siem and Jorissen, 2015), but no one details how to design this connection to prevent shear cracks at the heel depth or the compressive crushing at the joint contact surfaces. Hence the design rules and the emergence of failure modes according to the geometrical parameters of the Simple Notched Joint must be defined. In order to check the design equations and the failure modes, lab tests about the three geometrical configurations of the Single Step Joint have been carried out, varying the heel depth, the shear length and the inclination of the rafter

Study of mechanical compatibility at the mortar-block interface in a heritage building

ce travail a pour objectif de modéliser l'ensemble mortier/bloc et d'analyser la résistance mécanique à l'interface. l'étude prend comme support d'étude une batisse historique au Maroc. Nous choisissons un mur de la construction et nous procédons à une simulation numérique. Nous étudierons la répartition des contraintes dans le mur. Deux cas seront considérés : un mur sollicité non restauré et un mur sollicité non restauré. Le but de ces simulations étant de comparer les répartitions des contraintes dans chacun des deux cas afin de justifier ou non l’intérêt de l’utilisation d’un mortier de restauration de faible résistance. Les caractéristiques mécaniques obtenues lors des essais non-conventionnels, en l’occurrence le module d’élasticité statique et le coefficient de Poisson seront utilisés dans cette analyse. le comportement du système est considéré comme élastoplastique

Climate change in the Arctic: Testing the poleward expansion of ticks and tick‐borne diseases

Climate change is most strongly felt in the polar regions of the world, with significant impacts on the species that live there. The arrival of parasites and pathogens from more temperate areas may become a significant problem for these populations, but current observations of parasite presence often lack a historical reference of prior absence. Observations in the high Arctic of the seabird tick Ixodes uriae suggested that this species expanded poleward in the last two decades in relation to climate change. As this tick can have a direct impact on the breeding success of its seabird hosts and vectors several pathogens, including Lyme disease spirochaetes, understanding its invasion dynamics is essential for predicting its impact on polar seabird populations. Here, we use population genetic data and host serology to test the hypothesis that I. uriae recently expanded into Svalbard. Both black-legged kittiwakes (Rissa tridactyla) and thick-billed murres (Uria lomvia) were sampled for ticks and blood in Kongsfjorden, Spitsbergen. Ticks were genotyped using microsatellite markers and population genetic analyses were performed using data from 14 reference populations from across the tick's northern distribution. In contrast to predictions, the Spitsbergen population showed high genetic diversity and significant differentiation from reference populations, suggesting long-term isolation. Host serology also demonstrated a high exposure rate to Lyme disease spirochaetes (Bbsl). Targeted PCR and sequencing confirmed the presence of Borrelia garinii in a Spitsbergen tick, demonstrating the presence of Lyme disease bacteria in the high Arctic for the first time. Taken together, results contradict the notion that I. uriae has recently expanded into the high Arctic. Rather, this tick has likely been present for some time, maintaining relatively high population sizes and an endemic transmission cycle of Bbsl. Close future observations of population infestation/infection rates will now be necessary to relate epidemiological changes to ongoing climate modifications