Implenia AG in Rümlang is expanding the timber construction capacity in Switzerland by 3200 m². For its timber construction department, the company chose of course a supporting structure made in timber. Rather than opting for solid web girders made from glulam, the designers came up with an exceptionally elegant lattice girder construction in screwed BauBuche Board Q, combining extremely narrow lattice elements with straight forward node connections.
Made with self-drilling fully threaded screws to connect multipiece cross-sections, these connections contain no slotted plates or metal fasteners. As the use of self-drilling screws is not yet generally approved for connections between BauBuche elements, the engineering firm Walt+Galmarini carried out comprehensive tests that showed that fully threaded screws with a diameter of 8.2 mm and a length of 190 mm, properly screwed in without predrilling, meet the required structural strength requirements. Although it would even have been possible to use thinner screws and predrill the holes, the chosen method proved cheaper, as the connections could be made much quicker without predrilling.
The lattice girders were assembled by the builder under a portable tent that provided adequate protection against the elements. As the girders could be assembled easily and quickly and there was no need for subsequent machining, they were screwed together on site and installed by crane.
The advantages of lattice girders made from BauBuche Board Q are obvious: on the one hand, BauBuche is a modern and innovative material and the slim boards give the construction a particularly elegant look. On the other, the girders can be assembled on site without the need for special tools.
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