PROJECT DATA
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Client: Amabilis, Renens Architect: Yves Weinand Architectes sàrl, Lausanne Timber Engineering: Bureau d’Etudes Weinand, Liège (BE) Technology Transfer: Laboratory for Timber Construction, IBOIS, EPFL, Prof. Yves Weinand, Petras Vestartas, Martin Nakad, Loïc Pelletier Date: November 2018 |
PROJECT
In 2014, IBOIS laboratory presented at the Acadia 2014 Design Agency conference in Los Angeles a model of clipped wooden joint. By exploring the elastic properties of wood, the laboratory has developed a new male and female plug system, which once nested (or “clipped”) are able to hold two pieces of wood together without adding glue or metal. There is many opportunities and advantages for this system to be used in construction fields. If this principle started to be used, it could simplify the implementation, shorten the assembly time and reduce its cost.
The snap-fit joint consist of one male (hook) and one female part. The temporary bending of the cantilever hook allows the fit of two pieces, using the material’s elasticity property. After the joining operation, the pieces return to a stress-free state. During the joining operation, the hook will be bent. This implies bending moment at the base of the cantilever and a deflection force against the mating panel. For a given undercut, the length and height of the cantilever have been chosen to limit the strain at the base in its elastic range and to avoid the crushing of the fibers at the tip of the hook and the top layer of the mating part, due to the deflection force. The geometrical parameters of the parts define the force needed to assemble or disassemble it and the separable or inseparable characters of the joints
In Novembre 2018, the Lausanne Cathedral has hosted four (+ 2 additionnals) representations of Nabucco’s opéra. For that specific event, IBOIS has developped a new wooden scenography, showing a technology transfert of the snap-fit joints. The scenography include benches and bleachers for spectators. Those benches are all in wood panels, assembled together thanks to a combination of snap-fit joints and mortise and tenon joints, for about 740 spectactors at each representation.
While Snap-fit joints can resist a certain retention force, they do not provide any shear resistance. In order to use this joint as a load-bearing connection for building components, snap-fit joints are combined with prismatic tab-and-slot joints, which receive the majority of the forces.
The assemblage of the bench panels does not require specific tools nor any additional material such as glue or metal assemblie. This combination of integrated joints achieve a mechanical behavior equivalent to a screwed joint. Also the elements (pre-fabricated wood panels) can be transported to the construction site flat-packed and put together on site. This reduces the necessary transportation volume. Moreover, they can be quickly put together or disassembled if needed. Finally, the snap-fit connection is a mono-material connection, including advantages such as aesthetics, ease-of recycling or a homogenous thermal conductivity of the parts, which can reduce condensation and decay.
See also : Acadia 2014 Design Agency, USC School of Architecture, Los Angeles, edited by D. Gerber, A. Huang and J. Sanchez
Snap-fit joint research : C. Robeller, Y. Weinand, P. Mayencourt
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