From skyscraper to 'plyscraper': The towering potential of timber

In the inner Brisbane suburb of Bowen Hills, the finishing touches are being put on a giant jigsaw puzzle — a nine-storey office block built almost entirely of wood.
Tens of thousands of prefabricated panels and beams have been bolted and screwed into place.
At first glance the building looks indistinguishable from its steel and concrete contemporaries.

But glimpse through the large glass panels that skin its frame and you can see the chunky timber skeleton.
Known simply as 25 King Street, the wooden high-rise is cutting-edge, but it also gives a nod to the past.
Wood once dominated the building industry. It was used as the structural support for everything from cabins to cathedrals.
That all changed in 1885 when the 10-storey Home Insurance Building — the world's first steel-framed office tower — officially opened in Chicago. The modern 'skyscraper' was born.
Over the next century, steel gradually replaced timber as the main load-bearing material for all but single or double-storey dwellings.
But wood is making a comeback.
Tall timber buildings have been going up across Europe and North America for more than a decade, and there are currently around 50 commercial or residential towers either completed or under construction in Australia, including International House in Sydney and Library at the Dock in Melbourne.

Engineered for strength and portability

This new approach to construction involves what's called "mass engineered timber": wooden beams and sheeting designed and manufactured for maximum strength by using a process of lamination or layering.

As a result, only the first two stories of the King Street building need to be constructed with concrete.
That firm footing is necessary, says engineer John McGuire, to establish a "construction barrier" against termites and rising damp.
Two forms of mass engineered timber are used: cross-laminated timber (CLT) and glue-laminated timber (glulam).

Glulam is used to make the large columns, beams and diagonal braces that give the building its final form, as well as providing for lateral stability; while CLT — essentially, a form of high-tech plywood — is used for the flooring and wall sheeting.
Mr McGuire says it's the combination of both that makes wooden framing a feasible alternative to steel and cement.
He says recent changes to the composition of cross-laminated timber has also made it safer.
"They used to use formaldehyde adhesives, which were toxic. Now new technologies are using polyurethane adhesives," he says.
"So, they're environmentally friendly, they're non-toxic and they give great strength."
And there are logistical benefits, because the engineered timber is prefabricated and precision-cut.
"In this particular building, the columns are set out on an 8-by-6-metre grid such that everything can fit into a 40-foot container. All the elements come out of that container and are bolted together on site," Mr McGuire says.
"That is a huge saving on the amount of [building] time on site, the number of on-site staff required, and therefore safety as well. And a minimisation of waste."
In addition, the Lego-like construction process allows for the building to be easily and cleanly disposed of at the end of its anticipated 50-year lifespan.
It's simply unbolted and shipped away, without the noise, dust and danger of traditional high-rise demolition.

Plyscrapers in the sky

How high timber-framed buildings can go is an open question.
25 King Street has been billed as the world's tallest and largest "engineered timber office building".
It rises vertically almost 45 metres. But a newly completed residential "plyscraper" in Vancouver, Canada, stretches skyward some 53 metres.
"As you go higher the wind loading on a building becomes a much more dominant force," Mr McGuire says.
"So, as you get higher you might look at hybrid designs using some reinforced concrete, maybe for the core or other elements of the building, to take the lateral stability.
"But I can definitely see that the benefits to time, safety and cost will make timber buildings a much more viable alternative for contractors, architects and structural engineers going forward."
Lendlease, the construction giant responsible for the King Street project, has now established a final-stage fabrication facility in Sydney; and late last year the University of Queensland opened its own independent Australian Research Council-funded Future Timber Hub.
"Our role is to develop not only engineering tools, but also the manufacturing tools that will allow industry to deliver better products," the Hub's Dr Cristian Maluk says.
"All developments that we're carrying out within the Hub are undertaken with industry partners and government, in order to enable safer, better timber buildings.

Dr Maluk is quick to dispel the notion that timber-framed buildings are more susceptible to fire.
"Engineered timber products have been demonstrated to be fire-safe and viable," he says.
"Timber is a combustible material, there's no question about it. And there's a public perception that a timber building is inherently less safe than a concrete or a steel building. But mass engineered timber is actually hard to burn."
'Better in every sense' — including for the environment
Underpinning the future of mass engineered timber are its environmental benefits.
Mr McGuire says all timber used in the construction of 25 King Street has been responsibly sourced.
And unlike concrete, which adds to global carbon emissions, engineered wood acts as a carbon sink.
For Planet Ark's David Rowlinson, that's a considerable plus.

"Trees absorb CO2 and one of the benefits of that is that 50 per cent of the dry weight of timber is carbon. And in the building sector that can be stored for a very long time," he says.

Mr Rowlinson runs the organisation's Make it Wood campaign.

"The oldest timber building in the world is the Horyuji temple in Japan, which was first built in 710AD, and which has been storing carbon for over 1,300 years," he says.
Mass engineered timber, he adds, also has a lower "embodied energy" cost than carbon-intensive materials, meaning far less CO2 is emitted during the total process of making and transporting the product.

And it's a renewable resource.
Mr Rowlinson estimates the 2,233 cubic metres of timber used to create Vancouver's new 53 metre "plyscraper" would have been regrown by US and Canadian forests in just six minutes.

But the environmental credentials only stack up if the supply of wood comes from a genuinely sustainable source.
"The wood can and should be certified, which guarantees that the wood comes from responsibly managed forests and plantations, and that guarantees that when a tree is harvested, another one, or more than one, is planted in its place," Mr Rowlinson says.

"The potential is to enable an industry that is sustainable, safe, and cost-effective," adds Dr Maluk, "and that will provide for a built-environment that is better in every sense of the word".

Original link - abc.net

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