Shear modulus analysis of cross-laminated timber using picture frame tests and finite element simulations
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ORIGINAL ARTICLE
Shear modulus analysis of cross-laminated timber using picture frame tests and finite element simulations Jonas Turesson
. Sven Berg . Anders Bjo¨rnfot . Mats Ekevad
Received: 5 March 2020 / Accepted: 29 July 2020 / Published online: 5 August 2020 Ó The Author(s) 2020
Abstract Determining the mechanical properties of cross-laminated timber (CLT) panels is an important issue. A property that is particularly important for CLT used as shear walls in buildings is the in-plane shear modulus. In this study, a method to determine the in-plane shear modulus of 3- and 5-layer CLT panels was developed based on picture frame tests and a correction factor evaluated from finite element simulations. The picture frame test is a biaxial test where a panel is simultaneously compressed and tensioned. Two different testing methods are simulated by finite elements: theoretical pure shear models as a reference cases and picture frame models to simulate the picture frame test setup. An equation for calculating the shear modulus from the measured shear stiffnesses in the picture frame tests is developed by comparisons between tests and finite element simulations of the CLT panels. The results show that pure shear conditions are achieved in the central region of the panels. No influence from the size of the
J. Turesson (&) S. Berg M. Ekevad Department of Engineering Sciences and Mathematics, Division of Wood Science and Engineering, Skelleftea˚ Campus, Lulea˚ University of Technology, Forskargatan 1, SE-931 77 Skelleftea˚, Sweden e-mail: [email protected] A. Bjo¨rnfot Section for Building and Civil Engineering, Centre for Bachelor of Engineering Studies, Lautrupvang 15, 2750 Ballerup, Denmark
tested panels is observed in the finite element simulations. Keywords In-plane shear stiffness Picture frame method CLT Shear modulus Finite elements
1 Introduction Cross laminated timber (CLT) panels are normally used in the building industry [1] for walls and flooring. The popularity of CLT has increased due to its prefabrication potential, relatively high strength to weight ratio and reputation as an environmentally friendly building material. CLT is a plate-like material built up from boards in a crosswise arrangement in a number of layers. The number of layers is odd or even and at least three. The board material, the number and arrangement of layers and the layer thicknesses define the properties of CLT panels [2]. Since CLT is being a relatively new construction material, many of its properties are currently under investigation [3]. The in-plane shear properties of CLT panels may limit the possibility of constructing tall wooden buildings [4], rendering the investigation of the in-plane shear properties of CLT panels highly important. The picture frame test (sometimes denoted as the direct shear test) is a biaxial test commonly used for determining the shear properties of textiles [5] but is
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used here for CLT panels. Earlier tests [6, 7] o
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