The FWPA (Forest Wood Products Australia) contacted us to design a relocatable, pre-fabricated timber structure that could be used to promote the recent changes to the National Construction Code (NCC), which now allows structural timber buildings as a Deemed to Satisfy (DTS) solution for structures up to 25m in effective height, which equates to 8 storeys. These changes to the NCC represent a great opportunity for midrise timber construction to go mainstream, which will be great for both the environment, the construction industry and building occupants.
The brief for the FWPA was to design a building using structural timber that was 8 storeys in height, included a potential café and events space, and offered an opportunity to showcase the ways that timber can be used to deliver solutions now allowed by the revisions to the NCC. Our initial concept coalesced around the need to deliver a central circulation core which would allow for safe paths of egress, and would be continuous vertically both from an ease of navigation standpoint, but also to allow a fixed datum for the individual floors to be built from.
The central stair is a scissor stair comprising two interlocking flights that create a clear up and down direction, with breakout floors at levels 2, 4 and 5 for those who want to change sides and head down before reaching the lookout at the top. Each floor’s size is limited by constraints imposed on road transportation, and so can’t exceed 3.5m W x 3m H x 12m L. We were conscious in developing the design that the project had to demonstrate the construction capabilities of timber without being an exercise in modularity and prefabrication, and so we had to develop a way of avoiding the stacked shipping container look.
The lowest floor is rotated 90 degrees to the main tower for structural stability and the walls of this floor act as buttresses for the tower proper. Each level is rotated by 10 degrees around the core centrepoint to aid the façade articulation, and then groups of floors are designed with co-planar faces to disguise the series of transportable elements and associated floor by floor stacking required for construction. Select Australian hardwood battens clad the tower and act as both façade, internal balustrade and allow for wind to pass through the structure which reduces the sail effect on the building and thus the required wind loading required to be engineered around.
The anticipated construction sequence is
• Installation is expected to be complete in
• Day 1 will comprise site works, foundations
an preparation of services.
• Day 2 will see 10 trucks deliver fully prefabricated levels that will be craned into place and connected.
• Services (power, water) would then be connected to between levels and commissioned prior to a public opening.
• Prefabricated levels will have lighting, elec and all services pre-installed and will only require fitting off on site.
Aecom provided structural engineering services, and the need for prefabrication and quick erection on site meant that this central core would be designed in Cross Laminated Timber (CLT) and would use Rothoblass connectors, with each of the individual floors hung off this central core in a variety of timber products.
Our understanding of the possibilities of CLT has evolved from work we have undertaken for the CLT Development Association in Australia on a prototypical greenfield apartment building, and our Punt Rd project designed in CLT and due to commence construction in mid 2016.