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January 10, 2019

Concrete Failure – Opal Tower Sydney

Opal Tower

One group of people that would’ve had the “worst Christmas ever” would be the structural guys at WSP. Discovering on Christmas Eve a significant structural issue with their recently completed Opal Tower in Sydney.

And of course, the developer and builder, and the residents who were forced to spend Christmas in their cars, and a whole lot of other people affected by this issue.

According to published news, residents reported hearing a screeching noise and loud bang along with seeing cracks in the precast wall panels. Police have said an internal support wall failed.

The photo below shows plaster strewn across the ground on level 10 of the apartment tower and the large crack that caused the building to move 1-2 mm. Wait – did I just type 1-2 mm!

Plaster strewn off the wall

I’m not going to speculate on the cause of the cracks – I don’t think it has been established in any case, and there’s plenty of “expert” commentary on the subject if you care to look.

What “got my goat” was the instant news surrounding issues with approvers and certifiers. Apparently dodgy builders get to self-certify their work and hence take shortcuts that aren’t picked up by independent certifiers. So it’s the government’s fault and policy needs to change.

Why does this annoy me? Well, each of us are responsible for the things we do, the decisions we make, and the care with which we do them. Policies protect people but that is not the issue. Does a super-competent builder/engineer/grano-worker/etc need a policy? Nope. Does a competently prepared documentation for a building need approval to ensure it won’t fall down? No.

I’m not saying approval is unnecessary. I’m just saying, lack of independent approval is not the reason this building is in this mess. A design or construction error is the reason. And the responsibility for that lies with the person(s) responsible for making the error, not the person(s) allegedly responsible for catching it.

The more exciting story that isn’t getting published is that concrete is meant to crack under excessive load and it doesn’t mean the whole building will come crumbling down. It would help to relieve those residents that are too scared to return to their apartments.

As Yenem’s design engineer David Pote puts it:

When structural engineers design concrete, we not only size up concrete and reinforcements to take the loads imposed on them. We check that concrete elements can move enough to give occupants warning that there is something wrong. This is called ductility.

concrete test

Concrete is a brittle material. This means that if it is overloaded, it will break in a snap without warning. Reinforcing steel on the other hand is a ductile material which means that it stretches before it breaks like a rubber band. When the right amount of steel is placed in concrete, you get a piece of concrete that can move enough to warn you to take off loads or get out of the building.

If you’re curious for how reinforced concrete works, here’s a youtube video for you. Warning – this video contains destruction of concrete specimens!

Structural engineers think about your safety so next time you see one, give them a hug, or if it feels awkward, just give them a beer to show your appreciation.

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