Engineered wood | EPFL Graph Search

Engineered wood, also called mass timber, composite wood, man-made wood, or manufactured board, includes a range of derivative wood products which are manufactured by binding or fixing the strands, particles, fibres, or veneers or boards of wood, together with adhesives, or other methods of fixation to form composite material. The panels vary in size but can range upwards of and in the case of cross-laminated timber (CLT) can be of any thickness from a few inches to or more. These products are engineered to precise design specifications, which are tested to meet national or international standards and provide uniformity and predictability in their structural performance. Engineered wood products are used in a variety of applications, from home construction to commercial buildings to industrial products. The products can be used for joists and beams that replace steel in many building projects. The term mass timber describes a group of building materials that can replace concrete as

Semi-Rigid Moment-Resisting Behavior of Multiple Tab-and-Slot Joint for Freeform Timber Plate Structures

Stéphane Nicolas Roche

Historically based on the transfer of ancestral know-how, the art of carpentry changed considerably at the beginning of the 21st century with the arrival on the market of engineered wood products (EWP) and computer numerically controlled machines (CNC). The development of these wood products was initially started for the needs of aeronautics : lightweight panels but with high structural capacity. It is also in this field that automated multi-axis milling machines and the accompanying computing tool, computer-aided design and manufacturing (CAD / CAM), have begun to be developed to produce more complex mechanical parts. It was also in the early 2000s that several teams of researchers in the field of computer graphics but also in architecture were interested in complex free forms. One of the many challenges is still the discretization with planar elements of doubly curved surfaces oriented freely in space. The encounter of these `` algorithms '' with the high-performant wood panels was ineluctable. However, the assembly of polygonal panels in space to form a structure is not trivial. Optimization efforts are made so that the topology in itself favors the distribution of forces to tend towards a behavior of shells. But the problem is sometimes insoluble for very irregular shapes alternating negative, zero and positive Gaussian curvatures. To ensure the transmission of the axial, shear and bending internal forces induced by vertical or horizontal external loads, whether symmetrical or not, the performance of the assemblies used to connect these panels by their edges becomes paramount. In wood construction, this is a topic currently being studied by a few research laboratories including EPFL for innovative wood-to-wood joints with multiple tab and slots (MTSJ). The main difficulty lies in how to connect thin wood panels with the best stiffness and strength. In the recent past, the assembly of wood parts between them, often with metal fasteners to provide a certain ductility, was assimilated to a hinge. With the new standards like the Eurocodes, the notion of semi-rigidity is now essential to obtain a realistic response of structures to both ultimate and service limit states. The solution proposed at IBOIS enters into this new context. It allows, without glue or metallic connectors, to interconnect thin engineered wood panels, ensuring both locator and connector features and the transfer of multidirectional forces. This thesis focuses on the semi-rigid moment resisting behavior of the through tenon variant (TT) with closed slots. The numerous experiments conducted during this study demonstrated the ability of this variant to compete with screws to resist a moment around the angularly connected edges. The joint is directly generated during the multiaxial cutting of laminated veneer lumber(LVL) panels which include a certain percentage of cross-layers. From a structural point of view, the local mechanical study under a bending moment was inspired by a wood-to-wood joint in service in the ancestral Japanese shrines, the "Nuki" joint. Analyzed by Japanese researchers as it historically participates in the resilience of their ancestral constructions to typhoons and earthquakes, it activates embedment mechanisms of wood in rotational partial compression (RPC) to resist the moment resulting from the external loads. It is these mechanisms that are taken into account for through tenon variant. ...

EPFL2017

Geodesic Lines on Free-Form Surfaces - Optimized Grids for Timber Rib Shells

Claudio Pirazzi, Yves Weinand

In addition to glue-laminated timber, screw-laminated timber has increasingly been applied to rib shells. The ribs are made from laminated timber boards, which are joined together with the aid of pin-like fasteners such as screws or nails. The current research is meant to optimize these grids on free-form surfaces with regard to the bending stress due to initial curvature of the boards. This can be done by arranging the ribs according to geodesic lines which allows the application of straight boards, subjected only to bending about their week axis and to torsion. The determination of such geodesic grids on free-form surfaces, currently enjoying great popularity in contemporary architecture, is quite complex. In order to satisfy this demand and to improve automation of the production process, the software GEOS has been developed in close collaboration with the Laboratory of Timber Construction (EPFL/IBOIS) and the chair of Geometry (EPFL/GEOM). This software calculates grids of geodesic lines on free-form surfaces and provides all geometrical data necessary for computer-controlled sawing. Free-form surfaces are treated as Bézier surfaces. In order to proved the reliability of the assumptions the program is based upon, a timber rib shell prototype (length/width/height: 8000 mm x 3000 mm x 2060 mm) was build. Thin timber laths (12/60 mm) were used. All laths were sawn and predrilled by means of computer-controlled sawing. The prototype could thus be built in relatively short time. In general, it can be stated that even after assembly of the fourth layer the predrilled holes at the intersections fitted precisely about 85% of the time. This confirms the reliability of the calculation and shows that the demanded precision is kept even for significant curvatures. For a better understanding of the load-bearing behavior of the structure load tests were carried out. The comparison of the measured deformations with the calculated deformations enabled us to evaluate the calculation model, based on a framed load-bearing system. For small charges, good accordance between calculation and reality could be noticed. The software GEOS provides an important tool for the design and the realization of timber rib shells. It contributes to clarifying current uncertainties in the design planning process and will highly improve the confidence of engineers and architects in conceiving and realizing this type of challenging lightweight spatial structures.

2006

Multiple Tab-and-Slot Joint : Improvement of the Rotational Stiffness for the Connection of Thin Structural Wood Panels

Julien Gamerro, Stéphane Nicolas Roche, Yves Weinand

Researchers in Asia have focused on analyzing the rotational performance of traditional connections based on embedment. The Nuki through-joint has inspired work at the laboratory of wood construction (IBOIS), Ecole Polytechnique Fédérale de Lausanne, to improve the rotational behavior of the multiple tab and slot joint (MTSJ). In this work, through tenon (TT) and closed slot joints were added to initial dovetail and Nejiri arigata joints used for foldedplate structures. The bending performance of the improved MTSJ-TT joint was higher than that of screwed angular connections. Numerical monitoring of the embedded volumes under partial compression on the contact surfaces was used to characterize the directly and indirectly loaded areas. The decay coefficients for the exponential form, which defined the additional length in the indirectly loaded area, were quantified for both single (SC) and double contact (DC). The evolution of these coefficients was also monitored along the angular deformation. Finally, an analytical formulation of the embedded volumes was provided to prepare an analytical model for the MTSJ-TT joint subjected to bending.