IBOIS at Compwood 2019

© 2019 CompWood, Växjö, Sweden

© 2019 CompWood, Växjö, Sweden

Three PhD students from the IBOIS Laboratory for Timber Constructions are in Sweden to present their research at the International Conference on Computational Methods in Wood Mechanics in Växjö, Sweden (June 17th to 19th).

A New Macro Modeling Approach in Structural Analysis of Integrally-Attached Timber Plate Structures
Speaker: Aryan Rezaei Rad, on Monday 17th June, 03:00 pm

Abstract : The recent advancements in the robotic fabrication of engineered timber products are used to re-consider the oldest known method of wood-wood joinery, apply it in modern architecture, and provide an integrated design framework in free-form spatial timber plate structures. The structures are adaptable to a wide range of large-scaled 3D forms; nevertheless, there have been few systematic investigations of their mechanical characteristics.
Providing an efficient and practical-oriented mechanical models seems inevitable. In light of this, through avoiding plasticity governed shell and solid meshes, a novel modeling approach is proposed, where series of beam-column elements are used. This approach, which is referred to as the “macro models”, remarkably enhances the efficiency of structural computations.

Simplified calculation model for interconnected timber elements using wood-wood connections
Speaker: Julien Gamerro, Wednesday 19th June, 11:20 am
Abstract: Metal fasteners and adhesive bonding are the main assembly methods in modern timber constructions. However, traditional wood-wood connections can be used effectively as well, thanks to increasing automation of the construction industry (CNC, robotics, etc.). The feasibility of this type of construction technique has been proven for buildings with complex geometry such as the wooden pavilion of the Vidy theatre. As a result, this research is focused on the development of a simplified calculation model for standard construction elements using wood-wood connections called Through Tenon (TT). The goal is to obtain a dimensioning tool which is easy to use in practice for roof, slab and wall elements.
The newly proposed calculation model is inspired by previous research done on interconnected timber elements using both metal fasteners and wood-wood connections. The numerical model is composed of beam elements with eccentricities represented by rigid fictive beams. Associated geometrical and material properties are assigned to each beam element. For TT joints, the tenon part of the connection is also represented by beams, while the contact zone between the tenon and the mortise is defined by springs to simulate the contact stiffness of the joint. The effective bending stiffness (EIef) of this type of structural element was analyzed to understand the corresponding mechanical behaviour and to assess the calculation model. Therefore, experiments were carried out on TT joints to determine the contact stiffness of the joint, and four points bending tests were performed on large specimens of eight meters made out of oriented strand board and laminated lumber veneer panels.
The EIef of the model was 12% lower compared to the test specimens, while a fully rigid model was 42% higher. The results show the importance of the semi-rigidity of TT joints. However, friction is not considered within the model which might explain the difference between model and tests. Concerning the tensile failure mode in the bottom flange, a shear lag coefficient should be applied due to the non-uniform stress distribution.

followed at 12:00 by Anh Chi Nguyen's presentation:
3D Finite Element Model for Shear Stiffness of Wood-Wood Connections for Engineered Timber Panels
Abstract : With the development of automated design and fabrication tools, researchers have shown a growing interest for traditional timber joining techniques. Innovative wood-wood connections, referred to as integral mechanical attachments, have been developed and successfully applied to full-scale building structures. However, it has been shown that these connections highly influence the mechanical behavior of structures. The mechanical behavior of the connections themselves therefore needs to be investigated. Numerical modelling is largely used for complex structural analysis problems when analytical solutions are either cumbersome or non-existent. Furthermore, it has the potential to replace expensive and time-consuming experimental tests, for which a limited number of parameter combinations can be tested. For the numerical modelling of timber connections in particular, various studies have been carried out because of the difficulty to achieve analytical models. However, numerical modelling of timber remains arduous due to the anisotropy and inhomogeneity of timber, with largely different mechanical properties parallel and perpendicular-tograin.
In this paper, a 3D finite element model predicting the shear stiffness of wood-wood connections is presented. It is based on models developed by Sandhaas for timber joints and Roche et al. for the study of the rotational stiffness of multiple tab-and-slot joints. In this paper, instead of modelling each layer of engineered timber panels with its orientation (longitudinal layers at 0° and crosswise layers at 90°), a single material with the thickness of the timber panel
was used, allowing to extend the model for a larger range of engineered timber panels. The model was compared to experimental tests performed on a shear testing setup. Promising results were obtained when comparing experimental tests to the numerical model. However, the model showed limitations for some configurations of joints.