Thousands were evacuated after hearing loud cracking sounds in their building. What happened?

On Christmas Eve, three thousand residents were forced to leave their apartments in the 38-storey Opal Tower in Olympic Park.

Residents had reported hearing a loud ‘cracking’ noise throughout the day, which led to a mass evacuation.

A huge crack had been found in a wall, and it was feared the building would collapse.

Engineers estimated that the crack on the 10th floor caused parts of the building to shift up to 2mm.

But this building was not decades old or weathered. It was completed in August this year.

So how does a newly built tower result in an evacuation?

It could be symptomatic of a wider systematic pressure on tradesmen to quickly complete jobs, sacrificing quality over quantity.

A structural engineer who has worked for large developers in the Sydney building boom between 2015 and 2016 has explained the culture on Reddit, breaking down how the problem may have emerged.

“Quite frankly I’m not surprised. I regularly saw poor planning, poor execution, poor workmanship during my limited site inspections, and that’s only the parts I was looking at. Several of the projects I’ve worked on required remedial action during construction due to poor planning and workmanship,” he wrote in the post.

He explained that he was a main engineer for a large building company in the same area, and that the building concepts do not make him confident.

Here is how he explains what might have resulted in Opal Tower.

Firstly, he explains that new connections in the buildings are made without engineer consultation.

“Slab to column and slab to shear wall connections were regularly missed as frequent changes in architectural layouts (to squeeze more apartments in after the initial DA). New connections had to be doweled in – decisions often made by site personnel with no engineering training. Even if an engineer signs off on it there’s rarely checks – they only follow what they’ve been instructed to do in the past,” he wrote.

He added that these floor layout changes cause important reinforcement to be missed, and that to save time designs are copied from one floor to the next.

“Some floors have small changes which have significant structural impacts,” he wrote.

“[These] may not be picked up because by this time the junior engineers are doing the design now and they lack the experience. Senior engineers are typically swamped with work so they lack the time to review everything critically,” he added.

He continued to explain that temporary site loading forces engineers to organise temp connections under pressure.

“Temporary site loading is not taken into account. The drawings I received only generally showed the finished arrangement and loading. It’s all about rushing through the application process. Engineers might need to “guess” where the temp connections for the crane will need to go. I’ve had numerous requests by subcontractors for penetrations through floors to get hoist penetrations, all with less than a couple of day’s notice. This leads to design checks not being done and senior engineers using “standard” details – which doesn’t always work,” he wrote.

“I’ve seen dowels [pegs that hold up a structure] installed the wrong way round and be ineffective. It’s a nightmare,” he added.

Perhaps most problematically, the engineer explained that the structural success of a building can rely on a key few people.

“I’ve found that large projects often depend on several key personnel who are “switched on” so to speak. If you don’t have those on your team, you’re stuffed,” he finished the post.

The 300 residents were informed the building would need to be emptied for at least 10 days.