The attractiveness of the Candlebark School Library lies greatly in its earth-laden form and beautiful exposed timbers. While credit is due to the architect, the project’s structural engineers, Keith Long & Associates, also played a central role in making the original designs come to live.
Engineer in charge Steve Lee says they had to work in tandem with the architect, Paul Haar, to realise and build the library according to Haar’s visions and plans.
This process began with Haar sending his plans to Keith Long & Associates. From there, the Melbourne-based structural engineering firm designed all the columns, beams, retaining walls, footings, slabs and bracing walls, taking into account the soil that would be sitting on the building, as well as Haar's vision of featuring exposed timbers on the main structure and part of the library roof.
From the outset, the biggest issue faced by the team was finding the right sized beams. Haar wanted the main beams to span continuously from one side of the building to the other, but sourcing for timber that was big enough to be cut and used as one single piece without any visible joints was challenging.
“And then it became an issue of getting the strength timber that we originally wanted to use. We had to come down a grade, which made it slightly deeper and wider than the initial design. This changed the size and design because the timber that was available, was only available in a certain grade,” says Lee.
In the end, Haar was able to get sustainable, 14 grade timber from Western Australia – the only place where he could find it.
The timber was originally 1200 deep by the length of the building, and the beams and two columns were cut out from that one piece of timber. The rafters were also made from the off-cuts of the beam, thereby eliminating the problem of wasting the big timber slabs.
However, Lee is quick to point out that the timber only takes vertical, and no actual horizontal loads.
“If you think of the building as a horse shoe, the curved part – the steel part – is actually made of concrete masonry reinforced walls, so they brace all the earth loads to stop it pushing out.”
A following issue the structural engineers faced was the overall depth of soil, which Lee notes had to be slightly compromised due to the available timbers.
“If we kept to the original amount of soil at the top, the timbers would have been too large, and that would mean losing the architectural intent of what Paul wanted the structure to look like on the inside.”
As a result, they came up with a depth of 500 for the soil above – deep enough to maintain the cooling effects and grow grass, while balancing out the lower-grade timber that was available.
Despite these initial problems, Lee says that the entire project ran relatively smoothly. This is mainly attributed to Haar’s role as both the architect and the project manager, which allowed him to work closely with the builders and the school to finalise the project quickly and without major changes.
“Usually the problems come when the builders have already started building and someone decides, ‘oh, I want to put a window in here,’ which changes the load. So you can get things changed all the way through because someone wants to change something,” he says, although he adds that all structural engineers understand that these changes are a part of the job.
“You don’t very often get a project like this where you actually only do it once. It was only a couple of minor revisions in there, so this was a very straightforward, well-set up project.”