Several analytical and empirical methods have been developed and adopted in Europe for the determination of shear and bending properties of Cross-laminated Timber (CLT) elements loaded out-of-plane and in-plane. However, proposed evaluation methods for determining in-plane shear strength in CLT elements acting as deep beam or lintels need to be verified on Canadian CLT products. This paper presents results from recent testing program following established ASTM standard methods for evaluating the in-plane shear strength of CLT elements for beam applications. Results indicate that the existing test method applicable to Structural Composite Lumber (SCL) may be suitable for the evaluation of in-plane shear strength of CLT elements.
International Council for Research and Innovation in Building and Construction, Working Commission W18 - Timber Structures
Research Status
Complete
Summary
Cross laminated timber (CLT) has become a well-known and widely applied two-dimensional, engineered timber product worldwide. It constitutes a rigid composite of an odd number of orthogonal and glued layers. Focusing on a single glued node loaded in plane in shear and composed of two crossed board segments and the adhesive layer in-between, in principle three types of shear mechanisms can be distinguished: mechanism I "net-shear" (shearing perpendicular to grain), mechanism II "torsion" and mechanism III "gross-shear" (shearing parallel to grain). In fact, while having generally accepted values for the resistance against mechanism II and good estimates for mechanism III the resistance against "net-shear" (mechanism I) is still in discussion. In spite of numerous investigations on nodes and on whole CLT elements in the past, a common sense concerning the test procedure, the consideration and handling of distinct influencing parameters and the quantification of the shear strength are open. We focus on the in plane shear resistance of single nodes according to mechanism I. We (i) propose a test configuration for reliable determination of the shear strength, (ii) determine the shear resistance in case of shear loads perpendicular to grain, (iii) discuss influences of some parameters on the shear strength of single nodes, and (iv) give a brief outlook concerning the resistance of CLT elements against shear loads in plane.
The scope of this study is to evaluate the existing test methods for deciding the in-plane shear strength and stiffness of cross laminated timber (CLT) panels, and suggest a new test method. The evaluation of the existing methods point out that none of the methods isolate the pure membrane shear stress. This means that the results have to be interpreted and modified analytically in the process to define the in-plane shear properties. A new Direct shear test method is suggested to apply pure membrane shear force on the test specimen. In the suggested method the force is applied to a hinged steel frame, which is continuously bonded to the edges of the CLT panel. As the steel frame and the panel are deformed as parallelograms, the applied force are translated to pure membrane shear in the tested panel.
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