Abdelhamid Bouchaïr

Numerical simulation of embedding strength of glued laminated timber for dowel-type fasteners

A non-linear material model is proposed to describe the timber behavior. Anisotropic elasto-plastic constitutive law with hardening according to Hill yield criterion was used for the compressive behavior. Brittle behavior in tension and shear was modeled using the modified Hill failure criterion. The material model was implemented in a finite element code to simulate embedding strength of glued laminated timber for dowel-type fasteners. Reasonable agreement is found between numerical simulations and experimental measurements.

Mechanical Behavior and Modeling of Dowelled Steel-to-Timber Moment-Resisting Connections

AbstractThis paper investigates the mechanical behavior of dowelled steel-to-timber moment-resisting connections. Two configurations of joints were tested, and the experimental results were used to validate a three-dimensional (3D) nonlinear finite element method (FEM) model. The model uses the Hill criterion to manage the plastic yielding of timber. The brittle character of timber in shear and tension perpendicular to grain is managed through the damage evolution based on the Hoffman failure criterion. The numerical model represents with good accuracy the behavior observed during experiments. The analytical model based on the theory of plastic limit analysis was evaluated through the application to the tested connections.

Numerical 3D finite element modelling and experimental tests of rounded dovetail connection

The mechanical behaviour of the rounded dovetail connection subjected to shear load is analysed experimentally and numerically. The brittle failure of the joist member is observed in the experimental investigation. The experimental results are used to validate a three-dimensional (3D) non-linear finite element model. The non-linear models use the Hill criterion to manage the plastic yielding of the wood material. The modified Hill failure criteria, managing the damage evolution in wood, are used to take into account the brittle failure in shear and tension. Besides, the models also incorporate the contact and the geometric non-linearity. The comparison with experimental results shows that the numerical models are in good agreement with real behaviour. The validated models can be used to predict the strength and failure position of the rounded dovetail connection for parametric studies. Le comportement mécanique des assemblages par queue d’aronde sollicités en effort tranchant est analysé expérimentalement et numériquement. La rupture fragile du membre solive est observée dans l’étude expérimentale. Les résultats expérimentaux sont utilisés pour valider un modèle numérique tridimensionnel (3D) non-linéaire par éléments finis. Les modèles non-linéaires utilisent le critère de Hill pour gérer le comportement plastique du matériau bois. Les critères de Hill modifiés, qui gèrent l’évolution des dommages dans le bois, sont utilisés pour tenir compte de la rupture fragile en cisaillement et en traction. Par ailleurs, les modèles intègrent également le contact et la non-linéarité géométrique. La comparaison avec les résultats expérimentaux montre que les modèles numériques sont en bon accord avec le comportement mécanique réel. Les modèles validés peuvent être utilisés pour prédire la force et la position de rupture d’assemblage par queue d’aronde pour des études paramétriques.

Appropriate Wood Constitutive Law for Simulation of Nonlinear Behavior of Timber Joints

AbstractIn structural analysis, because of its anisotropic behavior, wood requires an appropriate constitutive law covering different behavior modes, such as ductile compressive behavior and brittle character in shear and tension. In this study, nonlinear material models were proposed to describe the behavior of timber in a finite-element method (FEM) model. An anisotropic elastoplastic constitutive law with hardening according to Hill yield criterion was used to describe the compressive behavior. Brittle behavior in tension and shear were modeled by using the progressive failure analysis approach, which is based on a failure criterion representing the evolution of damage in timber by a reduction of the elastic modulus. The wood material model was implemented in a three-dimensional FEM model to simulate the nonlinear behavior of timber joints with various types of loadings. The numerical model reliably predicted the stiffness and failure load of the joints. Furthermore, the failure index provided by the n...

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.

Travelling Fire in Full-Scale Experimental Building

In order to follow modern trends in contemporary building architecture design fire models travelling fire is investigated. The paper describes travelling fire test in experimental building performed in September 2011 in Czech Republic. As flames were spreading across the compartment considerable temperature gradients appeared. In this paper, the numerical simulation of the travelling fire test completed by using FDS (Fire Dynamics Simulator) is compared with simulation of compartment fire with uniform temperature conditions to highlight the potential impact of the gas temperature heterogeneity on structural behaviour. The temperature measurements from the fire test are used to validate the simulation of travelling fire in FDS. The fire test in middle large compartment which has provided important data for design model of travelling fire and its impact on structural behaviour, proves that there are clear needs and benefits in using a travelling design fire as the basis for structural design.

Modelling and analysis of bolted stainless steel cover plate joints

ABSTRACT Stainless steels are to be increasingly used in structural applications. Indeed, they exhibit high resistance and ductility. These characteristics are particularly useful in cover-plate connections, in which the main deformations arise in net section and bearing. However these deformations that require to be controlled remain difficult to estimate analytically. In this paper, a global model of cover-plate joint is presented. It combines elementary components characterized each by non-linear models using volume finite elements and contact. The model, validated on some experimental results, allows identifying the most influent factors on the behaviour of each component. One of the purposes is to contribute to the design approach based on analytical models for stainless steel connections.

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.

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.