Fastener

Résumé

A fastener (US English) or fastening (UK English) is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or dismantled without damaging the joining components. Steel fasteners are usually made of stainless steel, carbon steel, or alloy steel. Other methods of joining materials, some of which may create permanent joints, include: crimping, welding, soldering, brazing, taping, gluing, cement, or the use of other adhesives. Force may also be used, such as with magnets, vacuum (like suction cups), or even friction (like sticky pads). Some types of woodworking joints make use of separate internal reinforcements, such as dowels or biscuits, which in a sense can be considered fasteners within the scope of the joint system, although on their own they are not general purpose fasteners. Furniture supplied in flat-pack form often uses cam dowels locked by cam locks

Source officielle

https://en.wikipedia.org/wiki/Fastener

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Zur Berechnung von Holzschalen in Brettrippenbauweise mit elastischem Verbundquerschnitt

Claudio Pirazzi

The design of timber rip shells confronts the engineer with major uncertainties during the planning process. The consideration of the elastic compound cross section during structural analysis of curved members by means of conventional calculation methods is possible only in a restricted manner. The shear-analogy provides a seemingly useful method for calculating these structures. However it is only an approximation, particularly with regard to cross sections with high flexibility in terms of shear stress. This thesis treats the limitations of applying of the shearanalogy with regard to the calculation of straight and curved members with elastic compound cross section. The bending of timber lamellas generates initial bending stress. Due to the rheological behaviour of wood and the associated process of plastification within the microstructure of wood, the stress becomes partially reduced as a function of time (stress relaxation). Prior work provides contradictory information about the duration and intensity of this reduction. To shed light on these uncertainties, appropriate experiments have been conducted. To join timber lamellas to a multi-layered cross section, mechanical fasteners like screws, nails and bolts are used. The knowledge of the physical properties, like rigidity and resistance, are of significant importance for the verification of the ultimate limit states. Tests conducted in the past in order to evaluate theoretical models and to determine empirical values refer generally to connections, which differ clearly from the multi-layered connection treated here concerning the deformation and failure mechanisms. Experiments carried out provide estimation in how far the existing values can be applied to structural analysis of the present case. The theoretical model according to Johansen was adapted in an appropriate manner. The aim of the work presented here is to contribute to the clarification of several problems related to the design of spatial timber structures with elastic compound cross section. The results provide further confidence to engineers for planning and realising these challenging lightweight structures.

EPFL2005

Chargement

Simplified calculation model for interconnected timber elements using wood-wood connections

Julien Gamerro

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 [1]. 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.

2019

Chargement

Traditional wood-wood connections, widely used in the past, have been progressively replaced by steel fasteners and bonding processes in modern timber constructions. However, the emergence of digital fabrication and innovative engineered timber products have offered new design possibilities for wood-wood connections. The design-to-production workflow has evolved considerably over the last few decades, such that a large number of connections with various geometries can now be easily produced. These connections have become a cost-competitive alternative for the edgewise connection of thin timber panels. Several challenges remain in order to broaden the use of this specific joining technique into common timber construction practice: (1) prove the applicability at the building scale, (2) propose a standardized construction system, (3) develop a convenient calculation model for practice, and (4) investigate the mechanical behavior of wood-wood connections. The first building implementation of digitally produced through-tenon connections for a folded-plate structure is presented in this work. Specific computational tools for the design and manufacture of more than 300 different plates were efficiently applied in a multi-stakeholder project environment. Cross-laminated timber panels were investigated for the first time, and the potential of such connections was demonstrated for different engineered timber products. Moreover, this work demonstrated the feasibility of this construction system at the building scale. For a more resilient and locally distributed construction process, a standardized system using through-tenon connections and commonly available small panels was developed to reconstitute basic housing components. Based on a case-study with industry partners, the fabrication and assembly processes were validated with prototypes made of oriented strand board. Their structural performance was investigated by means of a numerical model and a comparison with glued and nailed assemblies. The results showed that through-tenon connections are a viable alternative to commonly used mechanical fasteners. So far, the structural analysis of such construction systems has been mainly achieved with complex finite element models, not in line with the simplicity of basic housing elements. A convenient calculation model for practice, which can capture the semi-rigid behavior of the connections and predict the effective bending stiffness, was thus introduced and subjected to large-scale bending tests. The proposed model was in good agreement with the experimental results, highlighting the importance of the connection behavior. The in-plane behavior of through-tenon connections for several timber panel materials was characterized through an experimental campaign to determine the load-carrying capacity and slip modulus required for calculation models. Based on the test results, existing guidelines were evaluated to safely apply these connections in structural elements while a finite element model was developed to approximate their performance. This work constitutes a firm basis for the optimization of design guidelines and the creation of an extensive database on digitally produced wood-wood connections. Finally, this thesis provides a convenient design framework for the newly developed standardized timber construction system and a solid foundation for research into digitally produced wood-wood connections.

EPFL2020

Chargement

Zur Berechnung von Holzschalen in Brettrippenbauweise mit elastischem Verbundquerschnitt

Claudio Pirazzi

EPFL2005

EPFL2020