Cross-laminated timber, also known as X-Lam or CLT, is well established in
Europe as a construction material. Recently, implementation of X-Lam products and
systems has begun in countries such as Canada, United States, Australia and New
Zealand. So far, no relevant design codes for X-Lam construction were published in
Europe, therefore an extensive research on the field of cross-laminated timber is being
performed by research groups in Europe and overseas. Experimental test results are
required for development of design methods and for verification of design models
This thesis is part of a large research project on the development of a software
for the modelling of CLT structures, including analysis, calculation, design and
verification of connections and panels. It was born as collaboration between Padua
University and Barcelona"s CIMNE (International Centre for Numerical Methods in
Engineering). The research project started with the thesis “Una procedura numerica per
il progetto di edifici in Xlam” by Massimiliano Zecchetto, which develops a software,
using MATLAB interface, only for 2D linear elastic analysis. Follows the phase started
in March 2015, consisting in extending the 2D software to a 3D one, with the severity
caused by modelling in three dimensions. This phase is developed as a common project
and described in this thesis and in “Pre-process for numerical analysis of Cross
Laminated Timber Structures” by Alessandra Ferrandino.
The final aim of the software is to enable the modelling of an X-Lam structure in
the most efficient and reliable way, taking into account its peculiarities. Modelling of
CLT buildings lies into properly model the connections between panels. Through the
connections modelling, the final aim is to enable the check of preliminarily designed
connections or to find them iteratively, starting from hypothetical or random
This common project develops the pre-process and analysis phases of the 3D
software that allows the automatic modelling of connections between X-Lam panels. To achieve the goal, a new problem type for GiD interface and a new application for
KRATOS framework have been performed. The problem type enables the user to model
a CLT structure, starting from the creation of the geometry and the assignation of
numeric entities (beam, shell, etc.) to geometric ones, having defined the material, and
assigning loads and boundary conditions. The user does not need to create manually the
connections, as conversely needs for all commercial FEM software currently available;
he just set the connection properties to the different sides of the panels. The creation of
the connections is made automatically, keeping into account different typologies of
connections and assembling of Cross-Lam panels. The problem type is special for XLam structures, meaning that all features are intentionally studied for this kind of
structures and the software architecture is planned for future developments of the postprocess phase.
It can be concluded that sound bases for the pre-process and analysis phases of
the software have been laid. However, future research is required to develop the postprocess and verification phases of the research project.
Cross-laminated timber (CLT) is an innovative engineering wood product made by gluing layers of solid-sawn lumber at perpendicular angles. The commonly used wood species for CLT manufacturing include spruce-pine-fir (SPF), douglas fir-larch, and southern pine lumber. With the hope of broadening the wood species for CLT manufacturing, the purposes of this study include evaluating the mechanical properties of black spruce CLT and analyzing the influence of CLT thickness on its bending or shear properties. In this paper, bending, shear, and compressive tests were conducted respectively on 3-layer CLT panels with a thickness of 105 mm and on 5-layer CLT panels with a thickness of 155 mm, both of which were fabricated with No. 2-grade Canadian black spruce. Their bending or shear resisting properties as well as the failure modes were analyzed. Furthermore, comparison of mechanical properties was conducted between the black spruce CLT panels and the CLT panels fabricated with some other common wood species. Finally, for both the CLT bending panels and the CLT shear panels, their numerical models were developed and calibrated with the experimental results. For the CLT bending panels, results show that increasing the CLT thickness whilst maintaining identical span-to-thickness ratios can even slightly reduce the characteristic bending strength of the black spruce CLT. For the CLT shear panels, results show that increasing the CLT thickness whilst maintaining identical span-to-thickness ratios has little enhancement on their characteristic shear strength. For the CLT bending panels, their effective bending stiffness based on the Shear Analogy theory can be used as a more accurate prediction on their experiment-based global bending stiffness. The model of the CLT bending specimens is capable of predicting their bending properties; whereas, the model of the CLT shear specimens would underestimate their ultimate shear resisting capacity due to the absence of the rolling shear mechanism in the model, although the elastic stiffness can be predicted accurately. Overall, it is attested that the black spruce CLT can provide ideal bending or shear properties, which can be comparable to those of the CLT fabricated with other commonly used wood species. Besides, further efforts should focus on developing a numerical model that can consider the influence of the rolling shear mechanism.
A study was conducted with the primary objective of gathering information for the development of a protocol for evaluating the surface quality of cross-laminated timber (CLT) products. The secondary objectives were to examine the effect of moisture content (MC) reduction on the development of surface checks and gaps, and find ways of minimizing the checking problems in CLT panels. The wood materials used for the CLT samples were rough-sawn Select grade Hem-Fir boards 25 x 152 mm (1 x 6 inches). Polyurethane was the adhesive used. The development of checks and gaps were evaluated after drying at two temperature levels at ambient relative humidity (RH).
The checks and gaps, as a result of drying to 6% to 10% MC from an initial MC of 13%, occurred randomly depending upon the characteristics of the wood and the manner in which the outer laminas were laid up in the panel. Suggestions are made for minimizing checking and gap problems in CLT panels. The checks and gaps close when the panels are exposed to higher humidity.
Guidelines were proposed for the development of a protocol for classifying CLT panels into appearance grades in terms of the severity of checks and gaps. The grades can be based on the estimated dimensions of the checks and gaps, their frequency, and the number of laminas in which they appear.