Jupit’air : an upgraded timber connectorSandoz J. L.1, Oth J.B.2

SUMMARY

The use of timber for outdoor applications is mostly affected by the connection system. For terraces, facades or floors,horizontal timber planks in contact with soil are strongly exposed to weathering and a chemical treatment is generallyrequired.

Therefore, in order to have a non-exposed connection, screws have to be connected to the internal surface of the plank. Inrespect of this constructive rule, natural durability can be reached. Furthermore, it will be improved if the naturalventilation can be activated.

The Jupit’Air connection is based on the finger joint technology and an ingenious clips system obtained by usingpolyamide-injected material. This small connector can be screwed directly on the plank. After set up on the soil or on thefacade, the timber external surface is not affected by the connection and is ventilated by natural air movement. Severalpilot constructions have shown both architectural and technical interests.

This technology is opening new possibilities for timber in urban expressions and can be erected by using local species,like pine, Douglas fir or larch. With this method usual timber has a natural durability of several decades without anychemical treatment.

INTRODUCTION

For outdoor timber constructions, related in Eurocode 5 “Timber Structures” as service classes [1] :

� Class 3 : Exposed to weathering� Class 4 : In contact with the soil� Class 5 : In the soil or in the water

The use of timber is challenged by the durability of the construction. This durability is a function of the timber materialweathering behaviour in a general sense and in function of bad conditions of water penetration, especially around exposedconnectors.

DURABILITY FUNCTIONS

The timber construction durability is quite complex to modelize, because the long-term physical behaviour of the materialis affected by a lot of parameters.

Timber has a reduced durability when it is exposed to weathering, but it is not the only one. Steel and concrete also sufferof weathering conditions and damages may be much more radical than for timber.

Back to timber, the prediction models have to include parameters like geographical conditions, timber natural durability,general and local design and also other parameters. [2]

But the durability functions which affect strongly the long-term behaviour of timber constructions are of three levels :

1 Director CBT (Concept Bois Technologie), start-up new technology, CH-1025 Saint-Sulpice2 Scientific assistant, Chair of timber construction, Swiss Federal Institute of Technology, CH-1015 Lausanne

• the chemical treatments :

In order to increase the durability of timber constructions of service classes 4 or 5 (sometimes 3), a chemical treatmentcan be applied. During the last decades salt products including heavy metallic components like boron, copper or arsenichave been developed.

They perform quite well for products like wooden poles, but are a bit too much aggressive to promote timber in urbanconstructions.

• the specie :

Because wood cells into the tree can be modified during the stage from sapwood to heartwood ; some species reach a veryefficient natural durability. It is especially the case for ipe, teak or iroko [3]. Most of the durable woods are tropical ones.This geographical distribution affects the use of such wood materials, because of the doubt of the ecological forestmanagement or because of the ecological transport costs.For European countries, local species like larch, oak or chestnut could be used for class 3 or 4 constructions withouttreatment, but here a special design is required : the protective construction design.

• the protective construction design :

The protective construction design is a way to design exposed timber constructions by taking into account basic physicalrules related to water penetration in the wood elements. Basically there are two main ideas to practise:

� when it is possible the protection of wood elements by clothing, in order to bring the construction in class 2 instead ofclass 3.

� when it is not possible to protect wood the conception allows to the construction system a natural and activeventilation. It is the case for wood terraces or wood plank facades.

But in a general sense, this kind of construction has to solve the connector technologies, because the connector is veryoften an opened door for water penetration in wood through capillarity (figure 1).

Figure 1 - Water penetration in wood through capillarity. Figure 2 – Jupit’air fixing adapted for wood terraces.

TECHNOLOGIES CONNECTOR

Because the connecting systems are very often the weak point for the durability function, new technologies are needed tohelp timber to join more constructions classes 3 or 4.

For a couple of years a new connecting system called Jupit’air has been developed [4] in order to reach a special point :the invisible connecting system.

After many tests related to both form and construction material, Jupit’air has been developed for the market and is nowavailable on it (figure 2).

Several timber constructions have been erected in France, Belgium, Switzerland and Germany with this new system.

PILOT PROJECTS

A first pilot project, figures 3 and 4, is a wall façade made of larch planks in the French Jura Mountains (altitude 800m).This construction is very interesting, because the wall is following a curve making the wood façade more architectural.Jupit’air connection works in tension owing to the curved planks. But the tension limit of the connector is not reached. Itsultimate limit strength is about 500 N.A second project is an urban mixed wood and concrete place near a train station in Geneva, Switzerland.

Wood plank squares have been designed with Brazilian Ipe planks, length: five meters. Then seven connection knots havebeen accurately located on the same line in order to be able to receive the plank, figures 5 and 6.To help the feasibility of the set up, jigs have been developed.

Figures 3 & 4 – Application of Jupit’air for outside façade.

Figures 5 & 6 – Application of Jupit’air for terrace.

CONCLUSION

For timber constructions of service classes 3 and 4, a new connecting system has been developed in order to help this kindof constructions to be durable. This connecting system is called Jupit’air, figure 7. The connecting set is not at all visibleand so is not exposed to weathering. Furthermore, the system thickness allows very efficient natural ventilation. Severalpilot projects have already been erected successfully by using this new technology.

Figure 7 – Jupit’air : an upgraded timber connector for outdoors applications.

REFERENCES

[1] Eurocode 5: Timber structures

[2] Leicester R.H., Cole I.S., Foliente G.C., Mackenzie C., 1998 : Prediction models for durability of timberconstruction, WCTE’98. Proceed. August 17-20, Montreux, Switzerland.

[3] Centre Technique du Bois, Guide pour l’utilisation pratique de la durabilité naturelle des bois. Paris, CTB, 1972

[4] Sandoz J.L., Kratzeisen S., 1998 : New connection for outdoor Timber Construction. WCTE’98. Proceed. August17-20, Montreux, Switzerland.