This is one of the most eye-catching skyscraper designs of recent years,
and, at first glance, you may not be entirely sure what you’re seeing.
The renders show a pair of towers that seem to be
wrapped together in gold like the world’s biggest birthday present.
You’d be forgiven for thinking the architects were just having fun, but what looks like
a bit of decoration is actually a key part of the overall structural design.
Head down to central Melbourne, where these towers are now rising,
and you’ll see there was no trick. That strip of gold is going to be a skybridge.
But building something like this 40-storeys above the ground is far from easy and the team
trying to make it happen are grappling with extreme height, complex structural forces,
an ambitious architectural design and the eyes of the world looking on.
This is how engineers in Australia are building the world’s most impressive skybridge.
It’s no secret that skyscraper developers have been going to
ever-more-extreme lengths to get their buildings in the spotlight.
We’ve seen them get taller, thinner and just plain weirder, but there’s another
category of construction which is helping new structures get noticed — skybridges.
They link two or more buildings together above ground, creating a connected structure.
Yes, they’ve been around for a while — some believe as far
back as the 1600s — and they’ve become a common sight in many towns and cities.
But recently there’s been a big leap forward in what’s possible
at the higher — and taller — end of the scale.
2019 saw the completion of Raffles City Chongqing, which has an almost
300-metre-long skybridge called The Crystal balanced across four towers.
In 2020, Jumeirah Gate in Dubai followed up with the world’s highest occupiable skybridge floor.
Then, in 2021, we saw the world’s longest cantilever,
also in Dubai, lifted into place at One Za’abeel.
Now, while it might not be the biggest, longest, heaviest or highest skybridge we’ve seen,
this new effort in Australia will become a serious horizontal highlight when it completes in 2022.
It’s part of a project at 308 Exhibition Street, which began construction in late 2018.
The site will host two skyscrapers designed by Cox Architecture and Fender Katsalidis,
each rising over 200 metres.
Tower One, called Sapphire by the Gardens, is set to house apartments
while Tower Two will boast a luxury Shangri-La Hotel.
As well as being a way to get from one tower to the next, the skybridge will boast private
dining rooms, lounges and a glass floor offering some pretty scary views down to the city below.
It’ll wrap around one whole level of the apartment building before
stepping up to envelope two floors of the hotel.
There’s a structural element here as well — both towers need the skybridge to create a
rigid link between them, and that will allow them to share wind loads and seismic forces.
As you might have guessed, building such a unique connection between two
skyscrapers over 40 floors above the ground is a serious challenge.
To form the skybridge, steel beams and metal formwork are being used to
make the concrete slab - a structure which will also support the cladding underneath.
Inside the slab, steel tendons will stretch from one tower to the next,
holding them together and creating that fixed link.
Steel beams will also be used for the bridge’s roof, with
a movement joint on one side allowing for any minor differential movement.
But before any of this can happen, a plywood deck has to be installed.
This offers protection and a platform for adding the slab steelwork — which
is divided into seven pre-assembled modules — and the lower cladding.
The concrete will then be poured in two phases.
Once it’s strong enough, the steel tendons can be stressed in a process known as post-tensioning,
and the towers will then be locked together with steel ties.
At this point, work can continue on the upper levels of the towers themselves.
After post-tensioning is complete, the temporary steel ties are removed, and the facades and
cladding can be installed. The wooden deck is then taken out and the gaps left behind are filled in.
As these pictures show, work on the skybridge had already
started in early 2022 and it’s due to complete later this year.
Yes, the skybridge is pretty epic, but it isn’t the only interesting part of this project.
When construction began, the excavation and piling
were followed by one of the largest concrete pours in Melbourne’s history.
The stuff was spread three metres deep over a 1,000-square-metre
area and that took 469 truck loads of concrete.
On top of that there are railway tunnels running beneath the site to think about.
All this engineering work looks set to deliver quite a pay off:
Multiplex, the main construction firm building
Sapphire by the Gardens has described it as “Melbourne’s most exclusive address.”
That’s quite a statement. The city — now the fastest growing
in Australia — is already home to several other luxury skyscrapers.
There are more tall buildings here than in any other city on the continent –
over 60 skyscrapers are complete and at least ten more are being built right now.
With more people choosing to live here than ever before — and many wanting to
be as close as possible to the centre — there’s new demand for high-rise developments like this.
The towers aren’t your average apartment block or hotel.
They overlook the historic Royal Exhibition Building and Carlton Gardens — a UNESCO World
Heritage Site — giving panoramic views of the grounds and Melbourne’s central business district.
Sapphire’s jewel in the crown will be its 1,200-square-metre Super Penthouse.
Developer SP Setia says it’s the largest on the market in Australia,
and it currently has an asking price of AUD $39 million.
As well as the skybridge, the two skyscrapers will be linked at the base too,
through a ten-storey combined podium.
When the whole thing finishes, the project will
become the latest member of Melbourne’s increasingly crowded skyscraper club.
But the newcomer won’t have to work hard to stand out.
With its prominent location and clear visual impact, it’ll likely be impossible to miss.
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