The project has successfully developed and validated a method for designing steel beams acting compositely with plain CLT floor panels, a first in UK construction. Key outcomes include:

• Enhanced Structural Efficiency: The hybrid system leverages the strengths of both CLT and steel, creating a more efficient floor system.
• Codified Design Method: The research provides a basis for establishing a codified value for the shear connector capacity, addressing a critical gap in UK and European standards.
• Environmental Impact: The use of CLT floor panels reduces the carbon footprint of buildings, supporting broader sustainability goals within the construction industry.
• Industry Adoption: With the system based on the inventive use of existing construction techniques which do not require any specialist site labour, this should encourage wide acceptance and implementation of this innovative method in future building projects.

With steel-framed buildings currently dominating the multi-storey office market in the UK, the replacement of the metal deck or precast concrete floor slabs with a CSCF system aims to reduce embodied carbon and increase carbon sequestration within the structure. Additionally, the use of sustainably grown British softwood for CLT production aligns with environmental sustainability goals.

An enhancement of around 40% of the plain steel section is achieved through composite action and the embodied carbon of a CLT/Steel composite floor system has around 60% of the carbon of a traditional steel/composite slab floor and only 40% of the mass. In addition, the CLT panels also sequester over 135% of the total embodied carbon of the floor system.

Bringing the system to market

WSP and the University of Warwick are jointly funding a PhD student to advance the existing testing and research. Additionally, we are collaborating with the Steel Construction Institute to create a design guide that will offer a codified method for designing composite steel and CLT floor systems. The system uses recognised construction methods, without the need of specialised workmanship, reducing potential barriers to implementation. This approach ensures that the CSCF system is practical and can be easily adopted within the construction industry.

The project will have nationwide application as the reduction in embodied carbon and dead load makes this system appealing to both new build projects and vertical extensions to existing buildings where the maximum benefit of its lower dead load can be realised. It could serve as a model for sustainable building practices, not only in the UK but also globally, contributing to the broader goals of mitigating climate change through innovative and environmentally conscious construction methods, changing cityscapes and reusing existing buildings.

Partners

Prof. Stephen J. Hicks, University of Warwick has led the laboratory testing. Stephen is well known internationally as an expert on composite steel and concrete construction, with a particular specialism in developing design rules for shear connectors. He is the Chair of the European Committee for Standardization Sub-committee (CEN/TC250/SC4), which is responsible for the design standard for composite steel and concrete structures, Eurocode 4. 

The laboratory testing has been funded by the Woods into Management Forestry Innovation Fund administered by the Forestry Commission. 

CLT panels have been supplied by B&K Hybrid Solutions and steelwork from Severfield UK and ArcelorMittal.