Sydney Apartments Cracking

[SteynvW]

https://www.abc.net.au/news/2021-06...sidents-blocked-castle-hill-skyview/100223462

Any idea what those plates would help for?
Sliding Joint with the plates bending helping with differential movement across expansion joint?

 

[Ingenuity]

When I looked at this when it was in the press a few weeks back they had these whistle-blower photo from mid-May 2021:

I assume the shored slab was intended to be supported by slab on the other side of the joint. There are cast-in plates visible on the shored-slab side soffit (see mill-scale etc).

Appears to be a permanent joint (in what is probably a post-tensioned, long-distance slab framing system), so either the design engineer intended for a dapped-joint (where each slab/beam is half-notched so one receives the other BUT this only works if the slabs/beams are of significant thickness to tolerate the half-thickness) OR the spans of the two slabs/beams in the direction parallel to the joint are dis-similar such that is significant resulting differential vertical displacement.


The plates are an attempt to either structurally support the shored slab/beam to the side that is not shored OR a feeble attempt to preserve compatibility of vertical deflections across the joint whilst maintaining free movement (??) in the plan of the slab (hence why bolted connection on one side only). May work in theory - but not promising.

Those plates are bolted back some distance - possibly due to PT anchors close to the joint.

==> EDIT: Those post-installed bolts on the LHS are tiny compared to the plate thickness and the active lever-arm.

More questions than answers.

Guaranteed that the lawyers will win!

 

[Tomfh]

The plates sure look like a makeshift seat/corbel, presumably to bolster the shear capacity of the failing joint.

 

[SteynvW]

Also thought in the line vertical displacement compatibility. Just curious, how does inspections work with consultants in Australia?
Do the designers themselves inspect prior to casting? Or is sub contracted to a 3rd party?

 

[human909]

I'm a local, though I'm not necessarily the best person to ask as I'm in a niche area in industrial construction. But I'll try to answer some questions, most are just observations as a local rather than direct experience.

The checks and balances within the construction industry and even within structural design does seem to be less comprehensive than other comparable countries. Third party checks aren't generally required and if they are done they are paid for and chosen by those with a vested interest in having it pass. This applies to design checks and to construction inspections. So the entire system is open to cheating or outright corruption. In many cases we are just left with ethics and potential liability to keep things from falling over.

That said outside of residential construction things don't seem too bad. In general our infrastructure/commercial and industrial construction is generally reasonably well built and maintained. My observations are that we spend more money and time in construction and maintenance of public infrastructure than the US. Though we do probably overspend, but talk to the unions and politicians about that.

Residential is where many of the problems lie. There has been a race to the bottom in terms of construction costs, though this has mostly affected non structural aspects. Our stand alone dwellings are often cheaply and poorly built compared to say the EU though probably better than some parts of the US where everything seems to be a glue on façade. Fittings in our medium to large residential builds often suffer too from cost cutting.

On the structural side; For stand alone residential there have been a litany of issues in some areas regarding cheap foundations on reactive clay. For medium to high rise constructions there have been a few high profile cases of serious structural defects particularly in the state of NSW. One of the worst is this one where owners have lost almost everything.


Due to a rising number of these incidents the state government of NSW is probably going to get more involved and put more scrutiny on things, but that will all take time. For the reported case at the top of the thread occupation would likely have gone ahead but for a whistle blower going to the media which prompted the government to act.

 

[dik]

Has anyone considered a real engineering report? Might be the first step.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Tomfh]

They’d have multiple reports.

 

[human909]

Has anyone considered a real engineering report? Might be the first step.

Well that is the problem isn't it? The first step was a 'real' report(s) that wasn't been worth the paper they are written on. The building certifiers are paid to certify by the builder and funnily enough they did so. So it would seem that their inspections and reports did deem the building as safe to occupy.

Somebody whether it be a tradesman or a middle rank engineer thought the issues were sufficiently problematic to go to the media and state lawmakers. So we can thank this person. Given that the state government intervened it is likely they sought advice from a structural engineer and did obtain a "real engineering report".

Of course it would be more helpful for the discussion if we had all the details for discussion here. But lack of details in these discussions is the norm.

 

[FacEngrPE]

There is a structural problem with this process that has resulted in too many bad outcomes.

Australia has at least one leading expert that can advise on the structural problems in the building certifying process. Brady Haywood Experts in complex systems thinking - We help decision-makers understand and influence system behavior, embracing a unique combination of forensic engineering, data intelligence and high reliability organizational practice.

His blog and podcasts examine some fascinating engineering failures.

What liability do the certifiers have when they issue a defective "safe to occupy" certificate?