Prefabrication experiments - 346 - Concrete - timber composites

Ecological imperatives are challenging the building industry's habits. Timber platform frame for houses, steel for tall buildings, reinforced concrete for fireproofed multi-unit dwellings were the accepted methods of construction since these materials and systems were normalized at the beginning of the twentieth century. Recognized as both durable and regulated, steel and reinforced concrete were generalized while timber’s use was relegated to lightweight stick building or specialized laminations for large spanning roofs for arenas or stadiums. The last few decades have changed these entrenched perceptions of steel and concrete with the rediscovery of mass timber systems specifically with CLT technology (Cross laminated timber). Timber’s low carbon footprint when compared to the high-embodied energy of steel and concrete has opened a window of opportunity for its use in any building type. Tall timber building research is profiting from both industry and policy agendas. While this seems to promulgate the same type of material silos that have hindered true innovation within the construction industry, some are looking toward hybrid systems that unite material properties to elevate quality while mitigating challenges. 

 

A western Canada based architectural firm recently proposed a hybrid solution for an «Office building of the future». The CEI architects design of a 40-floor structure combines the advantages of CLT with those of reinforced concrete. A central concrete core braces the tall structure, and a timber / concrete composite is used for floor slabs. Taking advantage of concrete’s compression strength and wood’s tensile strength floor slabs use these characteristics to optimize beam effect (concrete above neutral axis; timber below neutral axis) for spans without significantly increasing weight or sag as would be the case with concrete or timber alone. Mayr Melnhof Holz is a European company based in Austria that has brought this type of composite to market. XC is their prefabricated concrete-timber laminated slab offered in multiple modular sizes. The combination of timber and concrete increases fire protection and offers the advantage of increasing mass to simplify foundations specifically in comparison to all-timber buildings which often require tensile anchors to compensate for their relative low mass. 

prefabricated concrete / CLT slabs