Timber and Adhesive

Automatic Google-Translation from the German Original:

“The architects’ requirements for roofs and ceilings are clear,” says Damien Gigandet, timber construction engineer (FH) and project manager at Walliser Dénériaz S.A. in Sion. “You want longer and longer elements that take up less space.” With traditional wooden ceilings with a maximum span of four meters, you quickly reach your limits. For multi-storey buildings one often has to resort to wood-concrete connections or solid wood panels for load-bearing components.

Advantages of glued wooden parts on the market

Compared to traditional wooden ceilings, box elements (adhesive bond of beam structure with wood-based panels on both sides) and ribbed ceilings (only one-sided wood-based panel) have the advantage of improved statics. Thanks to the adhesive connection, box elements can have over 50 percent more span or, alternatively, their thickness can be reduced by a third. In addition, the adhesive bond gives them improved vibration stiffness, which makes freely spanned elements up to seven or eight meters possible.

Compared to solid wood panels, box elements have the advantage of the cavities between the beams. These enable additional heat and sound insulation and also offer space for electrical installations. Thanks to the adhesive connection, wood can also be saved compared to solid wood panels and traditional wooden ceilings, which reduces costs. With new, efficient production methods, there is now a further possibility of reducing costs and thus becoming competitive with inexpensive concrete ceilings. New production methods make glued wooden parts competitive At Dénériaz, up to now, an adhesive has been used to glue box elements, which hardened without pressing and allows a glue joint of one to six millimeters. “This type of adhesive was very expensive,” explains Gigandet. “Because of the thick glue line, we needed a large amount and the adhesive was very hard and could not withstand the shrinking and swelling of the wood.” Other traditional production methods such as nailing or screwing are very time-consuming and costly and often do not provide convincing test results.

Together with customer companies, the Swiss machine manufacturer Woodtec Fankhauser GmbH has now developed a new, pneumatic system for the production of box elements. The pneumatic pressing device has the advantage that box elements can be glued and pressed with wood-based panels on both sides in a single operation, which was previously only possible in two steps. The fact that there is no need to screw not only saves time, it also saves costs for expensive special screws and the surfaces are not drilled through. As a result, the wood-based panels of the box element have a load-bearing function and can also be used as a visible surface.

Precisely defined pressing pressure ensures safety

The press device is an extension of the already widespread Woodtec element construction table. The beam structure can easily be prepared on this. Then the wooden panels are glued on and fixed to the press frame on both sides of the element in the perforated grid of the element construction table at intervals of 50 centimeters. These are connected to the compressed air and then press pneumatically on the component, with up to four tons per press frame. A precisely controllable and monitorable pressure is a decisive factor in the pneumatic production method. In this way, correct gluing can be guaranteed to architects, engineers and builders, which is essential for load-bearing components.