Pierre Quenneville

In-Plane Orthotropic Behavior of Timber Floor Diaphragms in Unreinforced Masonry Buildings

AbstractA full-scale experimental program consisting of testing four as-built diaphragms and four retrofitted diaphragms in both principal loading directions is presented. As-built configurations were typical of those found in historic unreinforced masonry buildings in North America and Australasia, whereas retrofitted diaphragms consisted of plywood panel overlays with stapled sheet metal blocking systems (SMBS). Test results were characterized using bilinear representations to establish recognizable performance parameters such as shear strength, shear stiffness, and ductility capacity, which were then used for comparative analysis. The nonlinear and low stiffness behavior of as-built diaphragms was confirmed in each principal loading direction. The plywood overlay and SMBS dramatically improved as-built diaphragm shear strength and shear stiffness and were shown to perform satisfactorily from a serviceability perspective. The orthotropic nature of as-built diaphragms was proven, with perpendicular-to-jo...

Numerical Modeling of the Failure Behavior of Dowel Connections in Wood

Finite-element (FE) analysis makes it possible to investigate different parameters and their effect on the carrying capacity or failure behavior of a component in an easy and cost-effective way. But to do this, the numerical model needs to reproduce the material behavior as close to reality as possible. This paper presents a numerical model developed to simulate the complex failure behavior of dowel connections in wood loaded perpendicular to grain. This includes both the ductile behavior, such as the embedding or bearing failure under the dowel or supports, and the brittle failure, such as cracking of the wood near the dowels. Using contact elements, the crack growing under tension perpendicular to grain and/or shear stresses can be modeled explicitly. The linear elastic-plastic stress-strain behavior of the wood allows one to simulate the plastic deformations of the ductile behavior. The comparison of the numerical results with the load capacity of different experimental test series confirms that the numerical model is accurate and useful to extend existing experimental test series.

Wood Block Tear-Out Resistance and Failure Modes of Timber Rivet Connections: A Stiffness-Based Approach

AbstractExisting prediction models for parallel to grain wood failure in timber connections using dowel-type fasteners consider the minimum, maximum, or summation of the tensile and shear capacities of the failed wood block planes. This results in disagreements between the experimental values and the predictions because the stiffness of the tensile and shear planes differs, which leads to uneven load distribution among the resisting planes. The present study focuses on timber rivet connections. A closed-form analytical method is proposed to determine the load-carrying capacity of wood under longitudinal loading in rivet connections in timber products. For the wood strength, the stiffness and strength of the planes subjected to nonuniform shear and tension stresses are taken into account. Furthermore, an algorithm is presented that allows the designer to predict the possible brittle, ductile, and mixed failure modes. The results of tests on New Zealand Radiata Pine Laminated Veneer Lumber (LVL) and glulam,...

Natural Period and Seismic Idealization of Flexible Timber Diaphragms

The current equations for diaphragm fundamental period determination and for diaphragm deformation determination published in commonly used seismic assessment documents are firstly reviewed to establish their origin. Using a validated analytical model that captures diaphragm deformation mechanics, three beam idealizations (a fixed-ended flexure beam, a pin-ended flexure beam, and a shear beam) are compared against true diaphragm behavior to determine which idealization is most suitable for the seismic assessment of diaphragm performance. Wherever necessary, recommendations have been made to update and to harmonize the current seismic assessment procedures for timber diaphragms in unreinforced masonry buildings. The presented analysis is specifically focused on straight-sheathed timber diaphragm configurations that are typically found in historic unreinforced masonry buildings.

Rocking Timber Structure with Slip-Friction Connectors Conceptualized As a Plastically Deformable Hinge within a Multistory Shear Wall

AbstractRecent experiments on a 2.44×2.44  m rigid timber wall panel with slip-friction connectors have demonstrated the feasibility of enabling elastoplastic behavior in structures that would otherwise be essentially rigid. The slip-friction connectors are adopted as the hold-downs that anchor the ends of the wall to the foundation. These replace the traditionally used steel bracket hold-downs, which relied on inelastic damage to the screw or nail connections for energy dissipation. Overturning resistance of the wall directly relates to the slip-force in the slip-friction connectors. On the slip-force being reached, the intention is that the wall rocks in a controlled manner. A numerical study demonstrates the energy dissipation advantages of this approach. A direct-displacement-based design procedure is proposed for a multistory wall with slip-friction connectors. The wall is numerically modeled, and its response to earthquake time-history loadings compared with that of an idealized structure with a sin...

A simple unified model for withdrawal of lag screws and glued-in rods

A mean stress failure criterion is applied to the Volkersen-model used for analysis of lag screws and glued-in rods subjected to withdrawal. Expressions are derived for pull-pull as well as pull-push loading conditions. The solutions for glued-in rods appear as special cases of the theory for lag screws, and the usual solutions for a maximum stress failure criterion appear as special cases of the solutions for a mean stress failure criterion. The theoretical solutions for lag screws are compared with test results, and a suggestion is made for taking into account initial shear stresses caused by the thread of the screw when driving the screw into the wood. The main advantage of considering initial shear stresses is that the number of necessary fitting parameters is limited to one, and that the usual values of shear strength and mode II fracture energy of wood can be applied.ZusammenfassungEin Versagenskriterium auf Basis der mittleren Spannung wird auf das Volkersen-Modell angewandt, um das Ausziehverhalten von Schrauben und eingeklebten Gewindestangen zu untersuchen. Gleichungen wurden sowohl für Zug-Zug-Beanspruchung als auch für Zug-Druck-Beanspruchung hergeleitet. Die Lösungen für eingeklebte Gewindestangen ergeben sich als Sonderfälle der Theorie für Schrauben, und die üblichen Lösungen für ein Versagenskriterium auf Basis der Maximalspannung ergeben sich als Sonderfälle des Versagenskriteriums auf Basis der mittleren Spannung. Die theoretischen Lösungen für Schrauben werden mit den Versuchsergebnissen verglichen und es wird vorgeschlagen, die Schubspannungen, die durch das Schraubengewinde beim Eindrehen der Schraube im Holz entstehen, zu berücksichtigen. Der wesentliche Vorteil bei der Berücksichtung dieser Spannungen liegt darin, dass nur ein Anpassungsparameter benötigt wird und dass die üblichen Werte für die Scherfestigkeit und die Bruchenergie im Modus II angewandt werden können.

Fracture mechanics analysis of row shear failure in dowelled timber connections

A quasi-nonlinear fracture mechanics model is presented for the analysis of row shear failure in timber connections with multiple fasteners in a row. A prerequisite for use of the model is a known distribution on the fasteners of the total applied load. It is shown that the ideal plastic and linear elastic fracture mechanics solutions appear as special cases of the quasi-nonlinear model. The model offers strength predictions that include the effect of among others the number of fasteners in a row, fastener spacing, row spacing, end-distance, edge-distance, fastener diameter, and material properties, such as shear strength, fracture energy, and modulus of elasticity. Simple explicit expressions are obtained from the analysis for any known fastener load distribution. For bolted connections, where bolt-hole gaps cause high loads on certain bolts at random, the model may be used in simulation procedures or in probabilistic models.

Group Tear-Out in Small-Dowel-Type Timber Connections: Brittle and Mixed Failure Modes of Multinail Joints

AbstractIn existing wood strength prediction models for parallel to grain failure in timber connections using dowel-type fasteners, different methods consider the minimum, maximum, or summation of the tensile and shear capacities of the failed wood block planes. It is postulated that these methods are not appropriate since the stiffness of the adjacent wood loading the tensile and shear planes differs, and this leads to uneven load distribution among the resisting planes. A closed-form analytical method to determine the load-carrying capacity of wood under parallel-to-grain loading in small-dowel-type connections in timber products is thus proposed. For the wood strength, the stiffness of the adjacent loading volumes and strength of the failure planes subjected to nonuniform shear and tension stresses are considered. The effective wood thickness for the brittle failure mode is derived and related to the elastic deformation of the fastener. A mixed failure mode is also defined (a mixture of brittle and duc...

Splitting Strength of Small Dowel-Type Timber Connections: Rivet Joint Loaded Perpendicular to Grain

AbstractThe existing models for the prediction of the splitting failure of dowel-type connections loaded perpendicular to grain are determined generally based on crack growth of the entire member cross-section. These models can be appropriate for stocky or rigid fasteners installed through the full thickness of the wood member. However, for slender dowel-type fasteners such as timber rivets, particularly when the penetration depth of the fastener does not cover the whole member thickness, the crack formation is different. Observations from current tests in thick members show that the crack growth across the grain occurs to a depth corresponding to the effective embedment depth of the fastener and propagates along the grain until it reaches its unstable condition. The design method presented in this paper to predict the connection splitting capacity takes into account the observed two possible failure modes of wood: either partial or full width splitting. In the proposed method, the effect of geometry para...

Nonlinear In-Plane Deformation Mechanics of Timber Floor Diaphragms in Unreinforced Masonry Buildings

AbstractAn analytical model was developed to describe the nonlinear in-plane deformations of timber floor diaphragms in historic unreinforced masonry buildings. Diaphragm deformation mechanics are detailed for both principal-loading directions (parallel to joists and perpendicular to joists) and are shown to produce differential equations of identical form. The model is formulated based on the assumption of pinned-end conditions, symmetrical configurations, and a uniformly distributed applied lateral load. The model is validated against full-scale diaphragm experimental data and is shown to predict response in both principal-loading directions with good accuracy. It is recommended that further research be undertaken to establish representative parameter values for the governing nail connection load-slip function.