North American cross laminated timber is currently made of softwood lumber following the guidelines of the ANSI/APA PRG-320 manufacturing standard. In this study, the potential of manufacturing CLT panels using various hardwood species and engineered wood products (EWP) was investigated for their compatibility and the impact on the dimensional stability and aesthetics of the end products. Yellow birch, trembling aspen, sugar maple, laminated strand lumber (LSL) and laminated veneer lumber (LVL) were compared to 100% spruce-pine-fir group species (SPF) lumber made CLT panel. The bond line performance of the assemblies was tested as well as the dimensional stability and appearance of the panels when subjected to conditions with equilibrium moisture contents (EMC) of 4.5%, 12% and 16%. Results showed that higher density hardwood species were prone to delamination. LSL, LVL and trembling aspen yielded promising delamination results. Best overall dimensional stability results were achieved with EWP inclusive configurations. Aesthetic integrity assessment showed that the use of hardwood for the core layer and edge gluing of softwood outer layers had a negative impact. Overall, the study showed a great potential for manufacturing future composite CLT (CCLT) products using EWP and low density hardwood species. The cost premium of using these alternative materials would need to be offset by valuable sets of properties or by a reduction of the manufacturing cost.
Is a wood processing company with about 1,000 employees andplants in Austria, Slovenia and Russia. In the forest around their Russian sawmill “HasslacherLes” the wood species birch (Betula pendula) is growing in large quantities and cut-able qualities. The company has also very modern equipment for the production of glued laminated and cross laminated timber. Consequently the idea was born to develop a project to produce load-carrying members to check the possibility of production of glued laminated timber and cross laminated timber without large modification of the existing production process. The goal of the project was to set up a complete profile of the mechanical properties needed for the design according to EN 1995-1-1. In addition by the means of a pilot project (detached house) erected with birch Cross Laminated Timber the effectiveness of this product for structural purposes with slender wooden components could be shown. The second pilot project was an industrial hall made of Glued Laminated Timber with birch.
Cross laminated timber (CLT) has gained popularity and relevance in the construction industry during the past decade. Its versatile applicability, economic competitiveness as well as an increasing social consciousness for sustainable constructions have been main reasons for this positive development. Its laminar composition enables CLT to withstand in- and out-of-plane loads. Due to its structure featuring orthogonally oriented adjacent layers, in CLT loaded out-of-plane, shear and more specific rolling shear has to be considered in ultimate (ULS) as well as serviceability limit state (SLS) design. This is because rolling shear constitutes a potential failure mechanism and contributes a noticeable amount to the overall deflection. Comprehensive knowledge on rolling shear modulus (GR) and strength (fR) is therefore of utmost importance for an adequate design of CLT structures. Previous investigations on rolling shear properties and their influential parameters have primarily been performed numerically and using Norway spruce (Picea abies). The main goal of our contribution, based on investigations detailed in Ehrhart (2014), was to identify the most important parameters for rolling shear characteristics and to quantify their influence. Furthermore, information about the rolling shear performance of several timber species was analysed to investigate their potential for use in CLT-products. In view of upcoming new timber species increasingly pushed into the market, investigations on rolling shear comprised also some hardwood and other softwood species with a potential to be used for (cross) laminated timber products.