Eric Fournely

On Numerical Evaluation of Mixed Mode Crack Propagation Coupling Mechanical and Thermal Loads in Wood Material

The mixed-mode crack growth coupling mechanical and thermal loads in wood material is investigated in this numerical work. The analytical formulation the crack driving force, namely the energy release rate, is introduced by T-integral that takes into account mixed mode fracture, thermal process in orthotropic material and pressure applied on the crack lips. This new formulation is based on Nother’s theorem and the definition of the strain energy density according to Lagrangian’s and Eulerian’s configurations. Moreover, this analytical formulation is implemented in finite element software Cast3m. First of all, several numerical examples, dealing with isotropic material, are provided to illustrate the accuracy of the FEM model. Then, the crack resistance of a timber CTS (Compact Tension Specimen) is investigated to show the efficiency of the proposed approach in the case of orthotropic material.

Experimental study of the in-plan stiffness of timber floor diaphragms

The mechanical behaviour of horizontal diaphragms is an important parameter in the performance of a building undergoing seismic actions. The behaviour of a timber diaphragm is quite complex due to the local effects of its several components including the nailed connections and the unilateral contact. This study focuses on the experimental results of two timber floors with or without struts tested as diaphragms (blocked or unblocked diaphragm). Experimental set-up, instrumentation, material characteristics and the composition of the specimens are presented. Furthermore, the strength, the failure modes and the diaphragm stiffness behaviour while loading and the kinematic of the various components are also reported. The comparison with an analytical approach used to predict the in-plane displacement is performed and discussed. Elementary tests on components are also presented in order to provide the main information on mechanical parameters to be used in further numerical modelling.

Experimental Analysis of Semi-rigidity Joint in the Standardized Timber Beam

Truss timber beams, with glued joints and various types of thick glue layers, can exhibit a semi-rigid behaviour in translation and in rotation. The global behaviour of truss beams depends on the local behaviours of joints. In this study, the results are obtained from tests on standardized timber beams used in wooden houses. Classical measurement devices, such as LVDT and load cells, are used in combination with 3D images analysis. A comparison is done between the measurements given by different experimental techniques. The image analysis results are in good agreement with those of classical equipments. Thus, global deflexion, axial displacements and relative rotations in joint zones are obtained from two different techniques. The geometrical configurations of the beams allow reaching the local failure before lateral buckling. The experimental results are discussed considering load-deflexion curves, and local behaviour of the joints. The behaviour of the joints is analysed regarding the resistance, the ductility, the failure modes, the cracks evolutions, the rotation and the axial slip. Physical and mechanical characteristics of used softwood are measured. The mechanical characteristics of the joints obtained from tests are introduced in a simple beam modelling. The obtained numerical results are discussed and compared with experimental results.

Experimental Results of Green Wood Slice Under Natural Drying

The natural or artificial shrinkage due to drying is commonly responsible of crack appears in wood pieces. These defects are even more marked on the logs pieces cut up and stored in the open air during a long time. In this fact, it is essential to understand the different processes that lead to these phenomena in the green woods. In this work, the radial and tangential strains due to the natural drying of a green wood slice are studied by analytical and experimental methods. The analytical method applied is based on a mathematical model coming from cylindrical strain calculations integrating the orthotropy and mechano-sorptive effects. The experimental device is based on the mark tracking method composed of an acquisition system recording the displacement of target posted on the wood slice during the drying process. The sample weight is measured with an electronic balance during test. As results, the moisture content evolution during drying tests and the determination of the fibre point saturation are obtained. Also according to the used analytical method, the radial and tangential strain components are posted versus the distance to the center of slide. Finally, the crack initiation region is indentified.

Evaluating the Behaviour Factor of Concentric X-Braced Steel Structures

The behaviour factor (q-factor) is a factor introduced in Eurocode-8 (EC8) to reduce the seismic elastic forces of structures obtained from an elastic analysis accounting for their ductility and overstrength. Seismic codes, especially the EC8, gives a constant value for q-factor, since change in structural characteristics of building change in behaviour of braced steel structures and that affects on q-factor. In this paper, the q-factor is evaluated for X-braced steel structures using pushover analysis. The effects of brace slenderness ratio and stories number are investigated. The results of this study indicate that the most important parameter that affects the q-factor is the brace slenderness ratio. Furthermore, the EC8 recommends a higher than actual value of q-factor, which is potentially unsafe.

Influence of Interlayer in Timber-Concrete Composite Structures with Threaded Rebar as Shear Connector-Experimental Study

The influence of interlayer on mechanical properties of timber-concrete composite structures using threaded rebar as shear connector is studied. Push-out tests are performed with two configurations of connection between timber and concrete with and without plywood interlayer: one threaded rebar and two cross-threaded rebars. The experimental study consists of push-out tests to characterize the failure modes, the load carrying capacity, and the stiffness for serviceability and ultimate limit states of the connections. The responses of the configurations with interlayer are compared with those without interlayer. The comparisons show that the presence of interlayer reduces the shear strength and the stiffness of the timber-concrete connection with threaded reinforcing bar as connector. Furthermore, based on the experimental results and using nonlinear regression, a mathematical model of each one of configurations of connection is derived which can be easily used with nonlinear FE analyses of Timber-Concrete Connection (TCC) beams.

Exterior Wood-Concrete Slabs, Experimentation and Modeling of Mechanical Behavior. Part 1.

Structural elements of composite materials are widely used as them allow conceiving stronger as well as economic structures. In the case of wood-concrete composite slabs, the high compressive strength of concrete, together with the great performance and behavior of wood under traction, allows to obtain a resistance, weight and stiffness effective structure; features widely proven in indoor environments. The objective of this research is to analyze wood-concrete slabs behavior under outdoor environmental conditions in order to study its usage in walkways. Experimental tests were performed in two composite slabs, which were subjected to diverse loading configurations for 1250 days in outdoor environment. According to the results, was determined that the real moisture is greater than the theoretical one, which promotes the decay of wood, nevertheless, this variation did not produce a significant change in the overall mechanical characteristics of composite slabs

Impact of Semi-rigidity of Joint on Timber Composite Truss Beam

The DOREAN design system is based on a wood structure made with girder trusses. This paper quantifies the contribution of the OSB panels on the load carrying capacity of the trusses in the DOREAN house structure. On the one hand, by experimental tests carried out on double shear specimens, and on the other hand by modelling a T-beam including the stiffness of the assembly between the panel and the truss beam. The connexion between the OSB panel and the upper chord of the lattice beam is realized by staples. Shear tests are performed varying the number of fasteners with three thicknesses of panel and three different orientations of the staples. This last parameter is of high importance because of the short loaded edge distance in the narrow wood element of the chords. Strength and stiffness of the stapled joint are obtained from tests and the interaction between fasteners is analysed. The T-beam obtained by the connexion between the OSB panels and the DOREAN lattice beam is modelled using beam elements. The semi-rigid behaviour is taken into account for all the connexions between the lattice beam elements and the OSB panels. Conditions of serviceability and ultimate strength are analysed with the influence of the variability of the T-beam parameters.

Simplified Calculation Method of the Torsion Effect on the Seismic Behaviour of Timber Building

An analytical approach is developed to take into account the vertical axis torsion phenomenon which is more difficult to evaluate than bending modes for seismic situations. A typological analysis of current buildings is done and an original classification, based on the distribution of the bracing implantations and the degree of symmetry is proposed. A parametric study is conducted with the method of multi-2D combination to analyze the influence of different bracing configurations on the sensitivity of the analyzed structure to the torsion phenomena. The simplified method is checked using more sophisticated methods according to the approaches proposed in Eurocode 8. The results showed that the proposed approach gives simple, accurate and safe calculation method to take account of the torsion effect on timber buildings. All these results lead to the creation of a database that can serve as reference for the analysis of the semi-rigidity diaphragm influence or the real non-linearity bracings on the load distributions under seismic event.

Mechanical behavior of timber-concrete slabs under real environmental conditions by experimental and numerical approaches

ABSTRACT Experimentations on composite slabs have been carried out during 1 250 days in order to exhibit the behavior of timber-concrete structures in outdoor climatic conditions leading to high moisture content. Successive bending loadings are applied during this test; deflection and slip modulus of joints are studied. Real climatic conditions and moisture contents are recorded. Numerical modeling using FEM (Cast3m) is performed; results show the mechanical influence of the semi-rigidity of connections and the evolution of wood physical and mechanical characteristics during the experimentation. Numerical and experimental results are compared and present a good accuracy.