Status quo

The combination of the positive properties of different building materials in a new composite construction or in a mixed construction method has contributed significantly to numerous innovations in the building industry. A typical example is the steel-concrete composite construction that has been established for decades. In order to achieve climate policy aims, the consideration of resource-efficient and low-emission buildings is becoming increasingly important. In this context, steel is not only the building material with the highest recycling rate and the only building material for which upcycling is possible, but also enables large spans without intermediate supports and thus flexible building use. At the same time, the use of bio-based materials such as wood for storing and avoiding CO₂ is becoming increasingly relevant. The hybrid steel-timber construction therfore can combine these aspects.

For corresponding multi-storey buildings, building codes set high requirements for fire safety. However, a consistent and broad practical implementation of this construction method is currently failing due to gaps in knowledge regarding the behaviour under fire load and the verification of such constructions. Due to its high thermal conductivity, unprotected steel heats up quickly in case of fire and loses part of its strength. It must therefore be protected in many cases, e.g. by fire protection coverings or by reactive fire protection systems, although unprotected hot-dip galvanised steel constructions in particular can certainly achieve a fire resistance of R30. Wooden components, on the other hand, can burn and thus lose part of their load-bearing cross-section. At the same time, the resulting charcoal layer and the low thermal conductivity of wood can protect the interior of the building components. By combining the two building materials, steel components can thus be fully or partially protected against the effects of fire.

However, there are still no reliable verification methods for hybrid steel-timber sonstructions that allow a regulated assessment of the fire resistance of this construction method.