LVL structural elements made of beech wood

Clear wood has excellent mechanical and thermal properties. However, natural growth leads to weaknesses that negatively affect the load-bearing capacity of structural timber elements and reduce their reliability. The aim of this project was the development of efficient and reliable timber structures made of beech wood.

An increase in hardwood and a decline in softwood is expected over the long term. Because of its excellent mechanical properties, beech wood has an important role to play as a building material. Thus, there is a need for innovative ideas and novel applications for beech wood in the construction sector.

The primary goal of the project was the development of efficient and reliable timber structures made of beech laminated veneer lumber, with the focus on trusses and timber-concrete composite slabs. The researchers began by the characterisation of the mechanical properties of the material. Then they develop innovative, high-performance connections and design models to predict the structural behavior of the connections and the structural elements.

Beech wood has excellent mechanical properties, but until now has mainly been used for energetic purposes. This research project provides the basis for an increased application of the up to now insufficiently used beech wood in building construction and significantly improves the substitution potential of wood. The large availability of beech wood and the sustainability of the final products significantly increases the use of the resource wood for structural applications.

The developed timber-concrete composite slab consists of a 40- to 60-mm-thick beech laminated veneer lumber plate and a 120-mm-thick concrete layer. The beech plate acts as formwork during construction, then as reinforcement in combination with the concrete and finally as pleasant ceiling. The wood and concrete are connected by means of 15-mm-deep notches cut into the wood. The notches enable mechanical connection through compressive contact with the concrete. Analytical and experimental investigations showed that optimal design of the timber-concrete composite slab ensures reliable and ductile load-bearing capacity. The developed timber-concrete composite slab was used for the first time in the ETH House of Natural Resources (Zurich, Hönggerberg).

For the developed timber trusses , we investigated steel-to-timber dowelled connections with internal steel plates and bolted connections with external steel plates. Tests on the connections showed that the use of beech laminated veneer lumber with cross-layers prevents the wood from splitting, leading to ductile failure. In this way, the reliability, ductility and robustness of timber trusses made of beech laminated veneer lumber is significantly improved.

The results of the project demonstrate the great potential of timber-concrete composite slabs and timber trusses made of beech laminated veneer lumber. The models developed allow a safe and economic design of the structural timber elements made of beech wood.

Reliable timber and innovative wood products for structures – Structural elements of wood and wood products made of beech