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Timber concrete composite floors – a go-to guide for designers


Timber concrete composite floors
– a go-to guide for designers


When it comes to flooring systems, building designers need to consider much more than just finding a structural solution that works. There’s weight, acoustics, vibration and fire resistance to think about, to name a few aspects. Cutting-edge timber-concrete composite (TCC) flooring systems tick all these boxes, and more. And designers will soon be able to specify them with confidence, thanks to new design guidelines out later this year.


Designed by The Structural Timber Innovation Company (STIC) as part of its EXPAN building system, the TCC floor system combines a concrete topping with underlying timber joists. The timber works in tension, and the concrete in compression, optimising the use of each material. The concrete acts not only as a mass to assist vibration control and acoustic attenuation requirements, but also as a structural member.


The TCC system brings a myriad of benefits, firstly being lighter in weight than reinforced concrete. The floors also offer a high load bearing capacity, low noise transfer (particularly impact noise), and a favourable range of vibration performance. They are more fire resistant than traditional timber floors, and the concrete slab provides added thermal mass.


And to help facilitate their use in New Zealand, the upcoming design guidelines will address both the strength and serviceability design criteria for the flooring system. The document is the result of extensive laboratory testing, undertaken by a team of STIC researchers from The University of Technology Sydney, headed up by Professor Keith Crews.


This testing included an analysis of the shear connectors between the timber joist and concrete slab. Strength and stiffness of the TCC floor system depends upon all three of these components, with the shear connector particularly critical. As such, the design guidelines are prescriptive in terms of the types of shear connectors that can be used. Designers have the choice of different grades of concrete and a variety of commercially available engineered timber products.

In terms of serviceability, the design guidelines address short-term and long-term deflection checks, vibration checks, acoustic performance and fire performance.

The document offers industry best practices on acoustic performances, and will be updated based on further tests to be completed in the near future.


And when it comes to fire design, the guidelines provide detailed calculation methods, based on full scale fire performance testing carried out at the BRANZ laboratories.


Holes/penetrations are also covered as part of manufacturing details for the floors included in the guidelines. This section provides guidance on the maximum sizes of holes, minimum spacing between adjacent holes and edge distances.


Research leader Professor Keith Crews says the guidelines will provide designers with an effective and proven tool to address their design needs.

“It addresses the ultimate design, and considers all aspects of serviceability. Crucially, given that the systems prescribed in the guidelines are based on comprehensive lab testing, designers can use the information with confidence.”

“Our brief was for a natural looking, environmentally sound building – and that’s certainly been achieved, the space has a lot of mana with people here. We often see locals showing people around the centre proudly telling them all about its features.”


Please join us at the WCTE conference in Auckland, at the EXPAN Cafe to have a coffee and find out why people are getting so excited about this proven but innovative timber solution.



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