Lightweight and slender timber-concrete composite floors made of CLT-HPC and CLT-UHPC with ductile notch connectors

Cross-Laminated Timber (CLT) structures have been emerging worldwide for residential floors in multi-storey buildings thanks to their lightness, fast construction and low ecological footprint. This work aims at fostering this application, which is often limited by vibrational and deflection limits, by investigating composite slab floors made of CLT and High-Performance Concrete (HPC) slab as well as CLT and Ultra High-Performance Fiber Reinforced Concrete (UHPFRC). Firstly, the composite floors CLT-HPC and CLT-UHPFRC with a span of 8 m were designed by considering a multicriteria analysis. To assure a certain structural ductility, previously developed ductile notch connectors were employed. As an economic choice, no shear reinforcement in the concrete slab was employed. Then, fullscale composite beams were fabricated in order to verify the predicted flexural behaviour and natural frequency. A numerical analysis was carried out to verify the connectors could effectively yield before the timber collapse. The comparison between the numerical simulation and the slip measurements confirmed that about 50% of the notch connections fully yielded and underwent inelastic deformation which favors the structural ductility. In the case of the CLT-HPC floor, a reduction of the notch contact surface due to the use of plastic sheet waterproofing as well as shear cracks developing in the concrete close to the notch corner both reduced the expected structural stiffness. Finally, the CLT-UHPFRC floor is endowed with outstanding values of slenderness ratio (~35) and lightness (~2 kPa), while eliminating the use of shear reinforcement and sheet waterproofing

Impact of a reinforcement treatment with acrylate impregnation on the mechanical behavior of black spruce as connector member.

As a previous study has shown, it is possible to increase by 50% the dowel bearing strength of black spruce with an acrylate formulation applied by impregnation. Three diameters of bolts and two orientations of loading were included in this study. The effect of treatment on the dowel-bearing strength appeared to increase while the diameter of bolt decreased. The orientation of loading was significant as the treatment had a major impact in the parallel to grain direction and no impact in the perpendicular direction. With the digital image correlation analysis, an expanded strain field perpendicular to the load direction was observed. The superior embedding capacity would help to reduce the dimensions of the timbers as well as the number of connections required in the building design. With an increase of ductility, wood connections show a safer yielding behavior

Performance of Notched Connectors for CLT-Concrete Composite Floors

CLT-concrete composite floor systems are a solution for timber buildings with a long-span floor. It yields a reduction of carbon footprint and even eco-friendly structure at the end of its service life. This study will evaluate the structural performance of notched connectors in the CLT-concrete composite floor, comprised of the serviceability sti ness, maximum load, and behavior at failure. The parameters of the test plan are the loaded edge length, the notch depth, the concrete thickness, and the screw length. Other secondary variables are also assessed, such as di erent loading sequences, speed of test, and timber moisture content. Experimental results prove that the performance of the connector depends significantly but not linearly on the notch depth and the length of the loaded edge. The connector with a deeper notch and a shorter heel will be sti er and more robust, but it also tends to have a brittle rupture. The test results also help validate a solution for deconstructable connector systems. A nonlinear finite element model of the connector is built and validated versus the experimental results. It yields reasonably good predictions in terms of resistance and can capture the load-slip relationship

Analyse et modélisation du processus de rupture des assemblages bois par goujons collés

La technique d’assemblage par goujons collés est souvent utilisée en réhabilitation des structures bois et présente un avantage esthétique certain, dans la mesure où ce type d’assemblages est quasi-invisible. Dans le but de définir des règles de dimensionnement de ce type d’assemblages, une large campagne expérimentale est menée pour évaluer la résistance mécanique de 70 éprouvettes, confectionnées avec des tiges filetées en acier insérées au centre de cubes en épicéa. Le collage est réalisé avec un adhésif époxyde structural. La configuration et l’instrumentation permettent d’évaluer avec précision la résistance et la rigidité de l’assemblage, selon la longueur de scellement de la tige dans le bois. Sur la base de ces essais, une modélisation par éléments finis (Castem 2009) est réalisée afin de reproduire en détail la configuration expérimentale. La première étape consiste en une calibration du modèle élastique, de sorte que les rigidités numériques correspondent aux rigidités expérimentales. La distribution des contraintes à l’interface bois/colle (lieu de rupture des assemblages) révèle des contraintes de traction transverse 5 à 7 fois plus élevées que les contraintes de cisaillement en tête de collage. Cette tendance s’inverse à partir d’une profondeur de collage de 2 millimètres, quelque soit la longueur de scellement étudiée. La modélisation met en évidence une présence importante du mode d’ouverture (mode I) en début de fissuration et la nécessité d’utiliser un critère de mode mixte (mode I + mode II) afin de décrire précisément le processus complet de rupture de ces assemblages. L’approche utilisée est basée sur la Mécanique Linéaire Elastique de la Rupture équivalente. Ainsi, à partir des données expérimentales (courbes force-déplacement), il est possible d’estimer la résistance à la propagation de fissure des assemblages, ainsi que les parts respectives du mode I et du mode II dans cette résistance. Sur la base de ces résistances expérimentales, un critère de rupture en mode mixte est proposé. Il conduit à l’expression d’une formulation analytique, permettant l’estimation de la résistance effective à la propagation, ainsi que la longueur de fissure et la force au pic de charge de ces assemblages

BORASSUS AETHIOPUM MART OF BENIN USED AS REINFORCEMENT IN CONCRETE: ADHESION CARACTERISATION

Researches carried out in Benin allowed the use of Borassus aethiopum mart as reinforcement in concrete. The aim of this study is to examine the bond of the two materials. The results of pull out tests have shown that the bonding strength is around 1 MPa. This adhesion rate decreases slightly when the bond length increases; on the other hand, the adhesion rate increases slightly when the concrete strength increases. The behaviour of Borassus / concrete interface shows a first phase of perfect adhesion followed by a second phase of progressive loss of adhesion and a final friction phase which continues until the complete output of the reinforcement from the concrete

Optimisation multi-objectif de planchers intermédiaires bois tenant compte d'objectifs mécaniques et environnementaux

Afin d’optimiser simultanément l’épaisseur des planchers intermédiaires bois, leur niveau de confort vibratoire et leur impact sur l’environnement, un processus d’optimisation multi-objectif par essaim particulaire a été mis en œuvre. Dans un premiers temps les objectifs à optimiser, le cas d’étude et la méthodologie employée sont décrits. La modélisation des fonctions-objectif est ensuite réalisée. Les résultats sont alors présentés et discutés.A multi-objective particle swarm optimization process is implemented in order to simultaneously optimise thickness, vibration comfort level, and environmental impact of intermediate timber floors. First, the objective to optimise, the case study and the methodology are described. Secondly, the modelling of objective-functions is performed. Finally, results are presented and discussed

Engineering ductile notch connections for composite floors made of laminated timber and high or ultra-high performance fiber reinforced concrete

Different kinds of ductile connectors have been lately developed for enhancing the structural ductility of TimberConcrete Composite (TCC) structures. In particular, ductile notch connections can be designed by favoring the local compression failure of wood fibers. This work aims at further developing economic and ductile notch connector by considering different floor systems made of Glulam Laminated Timber (GLT) beam or Cross Laminated Timber (GLT or CLT) slab connected with a High Performance Concrete (HPC) slab or a Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) slab. Firstly, the geometry of the notch connector was suitably designed for favoring a ductile hierarchy of collapse modes. Then, a wide campaign of push-out tests was carried out to characterize the shear behaviour of 14 connection configurations by varying the notch geometry, the concrete type and the possible presence of acoustic insulation. Finally, based on the experimentally identified connection shear law, an example of design is presented for a TCC slab of 9 m span. The insulation layer was found to reduce the connection stiffness, but to increases the structural stiffness thanks to the enhanced lever arm of the composite action. For plastically designed TCC structures, the connection ductility allows increasing the structural ductility for both GLT-(U)HPC and for CLT-(U)UPC floor systems

The Effects of Acrylate Impregnation of Black Spruce Timber as Connectors Strength

Chemical impregnation of black spruce was conducted to enhance the wood embedment capacity. The formulation was made of 1,6 hexanediol diacrylate, trimethylpropane triacrylate, and a polyester acrylate oligomer. A second formulation, same as the first but with 1% wt of SiO2 nanoparticles, was selected to investigate the potential of nanoparticles and to improve the efficiency of the treatment. The wood embedment capacity was carried out by a dowel-bearing test, which was performed for the two treatments and for an untreated wood group. Both treatments showed an increase of strength of nearly 50% when compared to untreated samples. Micrograph views revealed that the impregnation solution penetrated into the wood only up to 100 μm. Hence, with low chemical consumption, the structural bearing capacity can be significantly increased

Effect of temperature on the mechanical performance of glued-in rods in timber structures

Structural bonding technology has proven to be an economically and attractive connection process in timber engineering. Within old or historical wooden buildings, local reinforcement of weak zones is often performed with glued-in rods. This kind of connection typically allows the transfer of loads within wooden elements by means of threaded steel rods glued with a structural adhesive. This paper relates to experimental and numerical investigations on small sized specimens, with the aim of providing a better knowledge about the elastic behavior according to temperature. Experimental results reveal that stiffness of bonded-in rods significantly decrease once the glass transition temperature of the adhesive is reached. However, the ultimate shear strength is constant and sudden failures occur in the wood close to the adhesive, whatever the temperature is. Then, an elastic finite element model allows the evolution of the Young modulus of the adhesive with temperature changes and also reveals the stress distribution along the glued-in depth during the elastic regime

Optimisation multi-objectif de planchers intermédiaires bois tenant compte d'objectifs mécaniques et environnementaux

Afin d'optimiser simultanément l'épaisseur des planchers intermédiaires bois, leur niveau de confort vibratoire et leur impact sur l'environnement, un processus d'optimisation multi-objectif par essaim particulaire a été mis en œuvre. Dans un premiers temps les objectifs à optimiser, le cas d'étude et la méthodologie employée sont décrits. La modélisation des fonctions-objectif est ensuite réalisée. Les résultats sont alors présentés et discutés