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

Stéphane Nicolas Roche
EPFL, 2017
Thèse EPFL

Résumé

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. ...

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https://infoscience.epfl.ch/record/233607?ln=fr

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Stéphane Nicolas Roche
EPFL, 2017
Thèse EPFL

Résumé

Official source

https://infoscience.epfl.ch/record/233607?ln=fr

À propos de ce résultat

Concepts associés (19)

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Publications associées (6)

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A Structural Design Methodology for Freeform Timber Plate Structures Using Wood-Wood Connections

Anh Chi Nguyen

Over the past decades, timber has gained popularity as a sustainable building material because of the rising environmental awareness. Furthermore, the resurgence of timber has also been encouraged by the advent of the digital age during the 21st century. The development of computer-aided design programming and digital fabrication tools has stimulated significant advances in both architecture and engineering. Within this context, researchers have shown a growing interest in wood-wood connections, inspired by traditional woodworking joints. Geometrically complex timber structures assembled with joints integrated in their plates have been developed using algorithmic geometry processing. However, although their design and fabrication have been automated, research focused on automated numerical tools for their structural analysis has been very limited. This thesis is providing a design methodology for the structural analysis of timber plate structures composed of a large number of discrete planar elements and wood-wood connections. A finite element model, in which the semi-rigid behaviour of the connections is implemented using springs, is proposed. It is applied to a specific case study, namely the Annen Plus SA head office project in Manternach, Luxembourg, which consists of a series of double-layered double-curved timber plate shells. A design framework is introduced to automate the generation of the model and integrate structural analysis into the existing design and fabrication workflow. The numerical model was built for both small- and large-scale structures through custom scripts and subsequently assessed through experimental investigations: first, laboratory tests were performed on small assemblies with simplified geometry; secondly, a displacement study was carried out onsite on a 24 m span structure. Results obtained with the semi-rigid spring model were found to be in good agreement with experimental tests. The proposed model was therefore validated for the serviceability limit state. Furthermore, the semi-rigidity of the connections in translation as well as in rotation was shown to highly influence the model and is therefore crucial for the accuracy of the model. Based on experimental tests observations, an alternative structural system was proposed and compared to the initial one through numerical investigations within the proposed design framework. A significant influence on the structureâs performance was found, demonstrating the possibilities for structural optimisation. Finally, a three-dimensional finite element model for wood-wood connections was investigated. It aimed to predict their semi-rigid behaviour, generally characterised through experimental tests, necessary for their implementation in global models. The material model was evaluated based on shear load tests performed on different engineered wood products. Stiffness and load-carrying capacity of the connections were approximated with numerical simulations. However, experimental tests remain necessary to precisely predict the behaviour of the joints. This thesis highlights the importance of adopting an integrated design strategy encompassing engineering and fabrication aspects for geometrically complex timber structures, as well as establishing a link between local behaviour of the connections and global behaviour of the structure. The gained knowledge can facilitate the design and realisation of large-scale freeform timber structures with wood-wood connections.

EPFL2020

Chargement

Timber folded plate Structures combine the advantages of timber as a construction material, such as its carbon-dioxide storage, low energy production and favorable weight-to-strength ratio, with the structural efficiency and elegance of folded surface structures. The construction of such surface-active structure systems with timber is a relatively new development, driven by an increasing awareness for sustainable building constructions, and enabled by new engineered wood products. However, these constructions require a large amount of edgewise joints between the thin timber plates, which are difficult to address with state-of-the-art connection techniques. Instead of using mass-produced mechanical fasteners for these connections, this thesis investigates the use of customized Integral Mechanical Attachment techniques, which use geometrical features of the parts to establish connections, rather than additional fasteners. Integral joints were common in traditional woodworking, but their manual crafting became infeasible during the industrialization. However, new computer-controlled fabrication technology, which is already available in the timber prefabrication industry, allows for an efficient, automatic production of integral joints. The advantages of such joints have already been demonstrated in framing constructions, where timber beams are used as the primary structural components. The proliferation of automatic joinery machines has repatriated customizable single-degree-of-freedom (1DOF) joints, which allow for the fast and precise assembly of prefabricated components. The objective of this thesis is to transfer these advantages to the construction of timber folded plate structures. Inspiration is taken from traditional cabinetmaking joints from Europe and Asia, as well as other industry sectors, where mass-produced integral joints are commonly used. The thesis will demonstrate several adaptations which have been made for the application of the joints on cross-laminated wood panels, for their automatic fabrication and for the customized purposes in the jointing timber folded plate structures. The geometry, fabrication and assembly of these new joints is being implemented and tested through the development of algorithmic tools. This is followed up by a verification of the proposed methods through large- and small scale physical prototypes. In its three peer-reviewed core chapters, the thesis presents investigations ranging from an initial hybrid approach, where integral joints are combined with adhesive bonding, towards a completely integral mechanical attachment solution. After a first application of the joints on a surface which is folded in one direction, the integral attachment of bidirectionally folded surfaces will be demonstrated. This is achieved through a new technique, which allows for the simultaneous jointing of multiple non-parallel edges, with single-degree-of-freedom joints. Algorithms will be presented, which allow for the automatic processing and the automatic fabrication of the joints. The automation of these processes will then be used for the construction of a doubly-curved, bidirectionally-folded surface, which obtains its structurally beneficial double-curvature through incremental changes in the geometry of the plates. [...]

EPFL2015

Chargement

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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.

World Conference on Timber Engineering2016

Chargement

A Structural Design Methodology for Freeform Timber Plate Structures Using Wood-Wood Connections

Anh Chi Nguyen

EPFL2020

EPFL2015