Opal Tower - Sydney Australia 28

[CivilEngAus]

https://www.news.com.au/national/ns...s/news-story/dad28af4aad5ff11cf968102635824f9

https://www.smh.com.au/national/nsw...ns-building-may-collapse-20181224-p50o4b.html

This could be an interesting and developing story in Sydney Australia. A 34 storey near new residential apartment tower in Sydney has been evacuated this afternoon over fears it is in structural distress with cracking noises heard during the day and one or more cracks developing; emergency services are treating it as a major incident.

Given we already have some of the toughest building codes in the world (although little to no registration requirements for engineers) it will be interesting to see how this plays out and what the crack(s) looks like to cause such a major emergency response.

 

[Tomfh]

What do you think the panels were sitting on? What sort of transfer members?

How would you design the interaction between discrete panels, transfer beams, and columns/walls under? What software would they have used?

 

[Agent666]

Opal Tower certifier previously disciplined by building watchdog

Not sure how it is in Australia, but in NZ walls cannot carry gravity load greater than 0.3f'cAg. This is due to poor performance under higher loads (lack of confinement). For higher levels of axial load I believe you can design using column provisions (much higher degree of confinement). I'm guessing we have a much higher confinement requirement anyway due to seismic issues, my previous experience with AS3600 is 10+ years ago and at that time it seemed miles behind our NZS3101 code in some aspects.

 

[SAIL3]

does not bode well longterm for the bldg if it is already showing signs of distress under gravity loads alone....
how does the "certifyer" system work or not work in Australia and who has overall responsibility for the design?...

 

[human909]

how does the "certifyer" system work or not work

Many have argued and are arguing more that it doesn't work. Of course the powerful and influential construction industry is arguing the opposite and largely opposing increase independent oversight.

My uninformed opinion. These sort of buildings get built, and sold (usually apartments are sold before they are even built) and hopefully no problems arise before the short term warranty is up. For many smaller builds this warranty might not mean much if the company conveniently no longer exists.

Opal Tower is seen by many as simply another in a whole line of problems that have been facing the residential building industry for a while. What makes this one a bit different is the severity of the failure (evacuated high rise buildings get plenty of media coverage).

https://www.news.com.au/finance/bus...g/news-story/8252377b84e0a4cd076874565dcbee73

https://www.weeklytimesnow.com.au/h...y/news-story/cdae0552b5b148c50d8cea367388f738

https://www.sbs.com.au/news/some-residents-of-cracked-opal-tower-are-refusing-to-move-out

The flammable cladding issue is a big one. The most prominent one took 4 years to resolve the dispute, remediation hasn't occured yet. And this is just one in the line of many.

https://www.theage.com.au/national/...ruling-protects-builders-20171222-h092gn.html

https://www.afr.com/real-estate/fou...place-cladding-for-56-million-20181205-h18qoo

https://www.theguardian.com/austral...ensland-buildings-may-have-flammable-cladding

https://www.abc.net.au/news/2018-04-11/flammable-cladding-class-action/9636126

I would say there are many in Australia who would like to see a major review of the entire industry.


On the structural side of things there are a few articles reporting that there is now concern of the 15 other identical panel connections in the building. Why this didn't concern the engineers from the very beginning is certainly puzzling but probably a reflection of the lack of responsibility taken by te building industry. The entire approach has been and continue to be more about protecting reputations that ethical engineering.

https://www.news.com.au/finance/bus.../news-story/f20c44e178f689b9a8d2a6c266045c78-

Another photo. Presumably the same level, same location but above a different column from the previously seen photo.

 

[Tomfh]

I suspect designers didn’t twig to the localised stresses. Maybe they assumed the transfer slab would carry it as UDL?

Presumably they’re now working out how it’s the precasters fault for inducing high localised stresses.

 

[rapt]

I think everyone is making up stories and we all need need to wait until we actually have some information to base our discussions on!

 

[hokie66]

That's the most sensible comment I have seen in this thread, rapt. Based on what I know, I know nothing.

 

[Tomfh]

There’s enough information available to at least discuss the topic.

We know it’s load bearing panels, sitting on transfer floor, and they are locally yielding, particularly where there is columns/walls under.

 

[degenn]

It’s impossible to say much based on available information.
That said, there is a lot of difficultly modeling building of this size with such an unclear load path. Precast wall are extremely stiff compared with the transfer beams and tend to attract loads that they have difficulty carrying. The drawings show a major load path shift at level 10. The load path is very dependent on construction sequence and differential creep and shrinkage in the vertical elements of such differing proportions. The fact that the failure occurred several months after completion with no high wind loads suggests to me that creep or shrinkage is a factor.
My guess is that basic strength is there but it is really poor detailing that has crack due to local excessive stress.
The previous discussion highlights the problem with using simple wall design in complex structures. Although addressed in As3600-2018 there is still a lot of lack of clarity. The rule to design a wall as a column allows no confinement ties for concrete below 50MPa and no need for having sufficient steel to match concrete cracking stress. The current code, As3600-2009 allows this for all strengths. This is exactly the sort of failure you would expect in a lightly reinforced wall without ties with a complex stress state.
As3600-2018 remains vague as to how a wall is to be designed as a column. A column should should have minimum steel and confinement ties yet the various exemptions allow this to be ignored. It is not clear if minimum moment is applicable in the in plane direction and if biaxial checks are required.

 

[rapt]

Aside from the wall design questions most of which I will dispute as to whether they are actually problems in the 2018 code, as being told to design something as a column in accordance with the column design chapter means to use the column design rules with any specific variations that are defined in the walls chapter (if a variation from the column design rules is not defined, then it is not allowed), the biggest problem with precast walls is the detailing at the ends. There is some very bad detailing out there which basically means that the walls are essentially unreinforced at the ends, resulting in a plain concrete compression member. But no one knows if that is the problem in this case.

1 - 2 mm movement will not cause doors to jam. That is just about all of the information we have, so we have no information. We have no structural design or detailing information.

 

[civeng80]

Agreed there is a lot of nonsence misinformation from reporters. But the topic is still interesting. Obviously there are serious problems with the building since it cannot safely withstand DL + partial LL.

From what I have been reading in this thread the walls were designed as walls and not columns ? I doubt that this would be the problem, just doesn't seem right to me.

What about workmanship issues and sloppy building practices (and also self certification doesn't help either) ?

 

[waross]

I suspect that a first responder saw a crack that he estimated to be 2 mm and commented on it.
The number stuck.
There are most likely other cracks that are much wider but no ones talking about them.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[human909]

Agreed there is a lot of nonsence misinformation from reporters. But the topic is still interesting. Obviously there are serious problems with the building since it cannot safely withstand DL + partial LL.

Agreed. So there is IMO a still room for a discussion. Is there any room to determine the exact cause(s)? No, but there rarely is in this forum. The reality is we are always going to be dealing with a small subset of information.

From what I have been reading in this thread the walls were designed as walls and not columns ? I doubt that this would be the problem, just doesn't seem right to me.

What about workmanship issues and sloppy building practices (and also self certification doesn't help either) ?

We don't this at all, we have no windows into how theses connections were designed nor about workmanship issue.

All indication do point to:
-partial failure of precast panel on the base of level 10, grid line 20
-this failure seems to have occured above the two supporting columns underneath with visible damage above these areas
-this failure seems to have resulted in the significant floor movement during which louds noises were heard over a period of hours

The speculation for the failure is simply that. But I think some pretty good points have been raised both about potential issues in the application of AS36000 and general concerns and risks when detailing such transitions.

 

[epoxybot]

I think the news reporting on this tower suffers from Christmas Holiday Reporting Syndrome. All the reliable reporting staff are enjoying time off. AAC is precast and that is what is seen cracking in the interior. Obviously not the problem but rather a symptom.

This is the only photo I have seen of real concrete damage, though the diagonal nature of the crack is not good. I don't think these are precast walls. It is hard to tell from construction photos. The "garden" walls rise after the core but in advance of the columns before the flat slab is finally poured.

 

[human909]

I believe it has been reliably established that these are precast walls.

Professor Mark Hoffman and John Carter, the two engineers tasked with figuring out why the building began to fail, will investigate the precast concrete construction method used for part of the Opal Tower.

Despite engineers narrowing in on the precast concrete, Professor Hoffman said the building method was extremely common worldwide. “If our investigation uncovers an issue relating to precast concrete, that information will be shared with our report to government,” the two engineers said in a joint statement.


These are official statements from engineers tasked with and independent examination. I wouldn't expect them to get it that wrong. In other reports the actual precast panel manufacturer has been named.



I think it needs to be emphasised. This incident is one building, one failure and might well not have any link systemic failings in the industry. However due to the media and politics it cannot be considered inconsequential to the wider construction industry. Sure this isn't engineering, but engineering is influenced by the systems and politics that surround it. There is plenty of indication that this may become the catalyst for a wider look into the industry. We already have politicians jumping onto the issue. With an election coming up this only stokes such fires.

https://www.abc.net.au/news/2018-12-30/opal-tower-damage-sparks-nsw-government-crackdown/10673968

https://www.news.com.au/national/ns...r/news-story/2326a65696330c04ac03747b82e83187

(Personally I think reform is absolutely necessary. Somewhere, sometime there might be an engineering conclusion on this building. But it will almost certainly be minor compared to the other reviews this has already triggered.)

 

[hokie66]

Most of us commenting here are in Australia. But to attempt to answer SAIL3's question above, the certifier system in most Australian states has essentially replaced the local government building inspector system, and is not working well, at least in my opinion. Part of that is because the certifiers are appointed by the builders or developers. They are paper pushers, with most of their paper about things like energy efficiency. I doubt many self respecting structural engineers have decided to become certifiers. Part of that problem may be our historic reluctance to "certify" anything, and especially not the work of others. Many of us don't even like to "inspect", and that is mostly to do with insurance requirements.

 

[Agent666]

So in Australia as an engineer are you not undertaking (or required to undertake) your own inspections of the thing you designed?

Are inspections only undertaken by this (not) independent certifier?

 

[rscassar]

I'm going to start speculating again from what I have.

The crushed hebel panels are at the entry to 1005, somewhere concealed within that party wall should be a column of some sort on grid 20 and from what I've seen on the Architectural DA drawings 2015, it is probably located about where the glazing line is for the skygarden.

The second photo which looks more damning with the large segments of precast walls crumbling looks like its the level 10 skygarden looking down onto Brushbox Street where it turns onto Bennelong Hwy which is on Gridline 6 and adjacent to apartment 1009. So if the as-built scheme is similar to the DA scheme, there should be circular RC column sitting behind those walls and those panels might have been detailed as non-loadbearing (but became load bearing with whatever happen, also the RC column may have been VE'd out of the design). Also the chunks of concrete that have popped of seem largely unreinforced so the panels may only have a single layer of reinforcement.

 

[human909]

My interpretation of is a bit different rscassar. But we are dealing with old architectural plans and limited photos...

The crushed hebel panels are at the entry to 1005, somewhere concealed within that party wall should be a column of some sort on grid 20 and from what I've seen on the Architectural DA drawings 2015, it is probably located about where the glazing line is for the skygarden.

I see no column on the architectural drawings nor in any construction photos. So I have presumed this wall is load bearing and the column beneath it seems to be position at the glazing line. (See floor plan for level 9 and overlay it with level 10)
Apartment 1005 Floorplan

So if the as-built scheme is similar to the DA scheme, there should be circular RC column sitting behind those walls and those panels might have been detailed as non-loadbearing

This column does appear clearing in the floor plans. However From what I can observe I cannot spot this column during construction. Thus I have presumed that the entire precast wall is load bearing with two columns underneath on level 9 and on top at level 16.

<EDIT> An additional sales floor plan for APT2204 has been found. You can see here that the third column in the corner is not included in the floor plan but the other two are. The missing column is where adjacent to the precast panels.

That has been my interpretation. But I'm open to alternatives. We pretty much only have photos and old architectural plans to go off. I might try trailing some old real estate advertisement for additional photos.

Most of my construction photos I've observed have been taken from here:

https://www.skyscrapercity.com/showthread.php?t=1738333&page=6

 

[Tomfh]

Human909, I view it similar to you. A wall bearing down on a transfer slab, supported primarily on the the L9 columns.

I wonder if the transfer slab and precast walls form a very deep beam (as opposed to precast walls *supported on* transfer beam), and the wall failure at the columns is effectively a web bearing failure, which the wall panels may not have been designed for.