The KERTO-Q cross-ply panel (lamibois): the essential solution for this project
Kerto-Q meets two essential requirements for such projects: the dimensional stability of the elements to achieve large spans and the high resistance to the structural constraints of the project. Indeed, the use of Lamibois for this framework covering the entire sports complex is explained in particular by the interest of large dimension of Kerto panels (up to 21m span on this project) which are cut out on a custom numerically controlled waist gantry. Here, the shape of the beams made it possible to optimize the material as well as possible and therefore limit the loss of material thanks to precise cutting.
“The choice of Kerto was justified in particular by the mechanical efficiency of the product, in particular in its resistance to bending in X and Y, less effective in non-cross glued laminate. In addition, thanks to the use of hollow boxes, the framework is lighter by placing the material where it is needed to support the structure, ” specifies Gontran Dufour, co-managing associate director of the VS-A design office.
This solution is also justified because of the ability of Kerto-Q to adapt to different radii of curvature, sometimes very tight at the level of continuity between the crossbowmen and the posts.
“Kerto is a very interesting material which will have made it possible to respond to the technical specificities of this project. This will have required a wide range of technical knowledge, ” highlights Antoine Roux, Framing Concept. “For example, the wooden frame rests on a metal mesh. We therefore had to skillfully make the expansion of the metal coincide with the Kerto, which precisely does not expand. "
Box beams, an original use of the Kerto-Q
The beams are cut from Kerto-Q cross-ply laminate panels 2.50m wide and up to 69mm thick: when the geometry changes from one beam to another, just change the layout cutting. (see box beam diagram)
The frame formed of 3m by 3m is thus obtained by large beams and spacers in Kerto with the particularity of being box beams.
Box beams are hollow beams made up of 2 Kerto-Q flanges (panels) assembled by high and low interior furring and sometimes intermediate Kerto-S glued-screwed. This rigidity bonding of the furring strips enables the desired inertia of the beam to be recreated.
To meet the large volume of assembly to be carried out, production was spread over two sites: in the Poulingue workshops in Beuzeville and on the Cosylva site in Bourganeuf.
An aesthetic solution, both in the general appearance and in the finishes
“The use of Kerto particularly appealed to us because of its visual advantages, in particular an interesting grain finish that can be seen on the face of the beams and thus giving an impression of solid wood, which would not have had this result with glued laminated timber » specifies Gaétan Morales, in charge of project for the Gaëtan Le Penhuel Architects agency.
“The expectations regarding the hanging system and their final rendering were also very specific, which is why we designed the fastening system to make it discreet and keep the appearance of a wooden frame and avoid making visible important metal fittings, » recalls Gontran Dufour.
« The work carried out for the fasteners was particularly substantial since more than 100 tons of steel were needed just for the realization of the fittings.s ", details Humphrey Delahaye, technical director of the carpenter Poulingue.
Indeed, one of the great interests of rendering this frame was also to find a aesthetic solution for hanging systems (connection detail, relatively long construction phase, etc.), hence the importance in particular of the continuity joints to visually recreate beams up to 30.4m span between supports. However, thanks to the very high mechanical values of Kerto-Q for shear absorption for metal connectors (fittings, bolts, pins), the hollow cavity of the beam makes it possible to integrate fittings with a concealed core.
"In order to go even further in this overall impression of unity, 40m long beams being inconceivable, the company suggested that we install a covering in Kerto plates which thus perfectly masks the assembly when necessary," » details Gaétan Morales, project manager for the Gaëtan Le Penhuel Architects agency.
Thus, this attention to detail already suggested in the detail books of the call for tenders (BET VS-A) and then confirmed in the EXE phase (Poulingue and Charpente Concept), ultimately made it possible to create a Very light and homogeneous looking frame with discreet brocaded assemblies.
Meticulous execution carried out by the Poulingue company
In parallel with the execution study, a mobilization of the studies and methods office of the Poulingue company will have made it possible to rigorously fix the prefabrication of the large beams and box spacers as well as the supply of metal connection parts. Due to the complexity and scope of the project, real project management was thus put in place until delivery to the site.
“With an average of 8 to 10 people on the site, 6 days a week for almost 4 months, we had to show increased vigilance, particularly in terms of lifting, because of the superior precautions to be taken for construction sites. this guy, " points out Humphrey Delahaye, technical director of carpenter Poulingue. “In addition, we also had to be particularly attentive in monitoring the execution plan since no axis is identical.e, ”he adds.
In addition, a colorless stain was applied during the construction phase by the Poulingue company to protect the wood and keep its naturalness until the building was completely covered.
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