Using timber concrete composite (TCC) floors in multi-storey buildings is a viable, lightweight alternative to other flooring systems that offers potential cost savings and environmental benefits. That is the conclusion of an innovative trans-Tasman study funded by FWPA. Researchers at universities in Sydney and Canterbury designed a virtual multi- storey timber building and found there was potential for timber-based systems to be used more widely in commercial construction. A multi-storey virtual timber building has been created to examine the feasibility of using engineered wood products for frames and floors in buildings up to eight storeys high. Researchers from universities in Sydney and Canterbury, New Zealand, collaborated on the innovative FWPA-funded project, demonstrating that the use of timber concrete composite (TCC) floors was a viable and effective alternative to other flooring systems - and offered the potential for cost savings.
The two-year study also highlighted the environmental benefits of timber-based building systems for commercial applications.
How the virtual building worked
The virtual building was based on an actual six- storey building being constructed in concrete at the University of Canterbury. Three other virtual buildings were designed for comparison in concrete, steel, and TimberPlus.
The virtual timber building was designed using the new hybrid laminated veneer lumber (LVL) system. Timber framing columns were 600mm x 378mm solid laminate, while the hollow, laminated timber beams were tensioned using steel tendons, which reduced the weight and cost of the beams. The design also featured a semi-prefabricated TCC floor system of 65mm of reinforced concrete poured onto 17mm ply sheets supported by LVL joists.
Lead researcher Professor Keith Crews said: "In comparison to traditional floor systems, it was found that TCC floors provide an excellent balance between increased stiffness, reduced weight, better acoustic separation and good thermal mass. Testing was very successful and has shown the LVL system to be a viable option for multi-storey timber buildings."
Cost analysis
A cost analysis of the virtual buildings found that the timber building would cost approximately 6% more than the concrete and steel structures due to the expense of the timber framing elements. However, the post-tensioned timber structure needed far fewer columns than the concrete building. Removing these from the design would have led to a significant 33% cost reduction.
Life Cycle Analysis (LCA)
A LCA was undertaken which considered the embodied energy of the materials and maintenance, materials transport, operational energy and two end-of-life scenarios, where deconstructed materials were either land filled or reused. The timber design was found to have a lower environmental impact than concrete or steel.
Commercial flooring systems review
The various flooring systems currently used for commercial buildings in Australia were reviewed to identify the issues that need to be addressed by timber alternative systems. Traditional, cast in-situ flooring systems and precast systems were studied. Researchers concluded that the selection of a flooring system is influenced by numerous factors, including:
- functional requirements structural design requirements
- type of structural frame
- the shape in plan
- the span between columns.
They also found that designers often resist adopting new flooring systems and when asked which method is "easiest" would identify their own area of expertise or the product they knew best.
Professor Crews said: "The lack of a clear industry standard, coupled with the multiple and varied advantages and disadvantages of each flooring system, makes it impossible to identify a single 'best' commercial flooring system."
Conclusion
The project confirmed TCC floors are a viable and effective alternative to other flooring systems for commercial applications in terms of short-term structural performance. They are about half the weight of reinforced concrete construction, which creates potential for cost reduction in terms of foundations and other load bearing structural elements. Further research will determine both long term and dynamic performance.
The LCA also highlighted the environmental benefits of timber-based building systems. Furthermore, a total cost comparison of commercial flooring systems with TCC flooring options has confirmed the viability and potential of the "timber based" structural systems for this market.
However, the review also revealed a need for more detailed cost investigations into LVL and TCC construction, particularly fabrication and erection costs