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.

 

[Agent666]

It does surprise/concern me that the chaps looking independently into it are not themselves structural engineers by trade. Judging them by the cover I would imagine the average geotech professor potentially doesn't know the first thing about structural design, structural codes, current best practice, etc. A materials professor would be in the same camp to a lesser/same degree. I await their initial report, and I hope they are drawing on the experience of the structural forensics community where required.

Something I picked up from the inspection and propping letter is that they are obviously looking at levels 15/16 & 25/26 as well and apartments all over the floor plate, presumably where there are similar details to that which has allegedly failed. I'd imagine any proposed fix/repairs would be to all similar locations unless the failed location had something else going on. Even if not strictly required the owners might demand it, hopefully those responsible do a good job to reassure the public that its safe again (typically if in cover your arse mode I'd imagine you are trying to do the least possible to bring it back to standard so you can say after some investigation that there was never an issue, no one was ever in danger, etc).

It's interesting sometimes the opposing views from different sides of the fence. Some will want the world while others are trying to get by on the minimum.

 

[david256]

What I'd like to know is why there are no columns on L1-L3 and L10-L15 at grid line 20, above the point of failure. Why would the builder/designer unnecessarily load the slabs on L1 and L10. What's different/special.

Every other garden location where you have prefab panels installed at grid lines 1-2,5-6,8-9,12-13,15-16,19 from L1-L35 there are columns, you can clearly see them in photos of the building.

I know the panels are/should be okay to carry the load as stated earlier in the thread.

I apologise in advance for my lack of understanding. Cheers David

 

[human909]

It does surprise/concern me that the chaps looking independently into it are not themselves structural engineers by trade.Judging them by the cover I would imagine the average geotech professor potentially doesn't know the first thing about structural design, structural codes, current best practice, etc. A materials professor would be in the same camp to a lesser/same degree.

Politicians wanting to be SEEN to be doing something.

The conversation probably went something like this:
"The media is having a field day and fingers are being pointed! Which department is in charge of investigating this stuff?"
"Nobody Mam. The private sector does it. We also privatised the building certification system decades ago."
"Well, we need an independent review! Who do we have who knows about this stuff but isn't in the private sector."
"Um.. Maybe try a University.

I await their initial report, and I hope they are drawing on the experience of the structural forensics community where required.

Exactly. I will give these guys the benefit of the doubt. They should be able to impartially analyse the situation and engage appropriate resources.

(typically if in cover your arse mode I'd imagine you are trying to do the least possible to bring it back to standard so you can say after some investigation that there was never an issue, no one was ever in danger, etc).

Which seems to have been the reactions from the developer and the builder from the very beginning. Sure the builder (Icon) did rapidly accept responsibility, however the public statements have always been on the optimistic end of the spectrum giving residents and the public much more hope for a quick resolution than was likely.

 

[CivilEngAus]

Judging them by the cover I would imagine the average geotech professor potentially doesn't know the first thing about structural design, structural codes, current best practice, etc. A materials professor would be in the same camp to a lesser/same degree. I await their initial report, and I hope they are drawing on the experience of the structural forensics community where required.

In one of the media videos of the engineers leaving Opal Tower there was a very well respected concrete structural engineering professor amongst the group and who is presumably helping with the investigation.

 

[StructEng23]

CivilEngAus

Can you name the professor, or what university or forward a link to the video for us to see who you are talking of.

Interested to find out who is involved.

 

[human909]

As per media reports the majority of residents have been advised by the builder that they can move back in this weekend. Not that I see that this is much of a development. It is just an indication that they do not anticipate any further risk or deterioration. Given the building is paying accommodation and other expenses for around 392 apartments residents it is obviously in their interest to give the all clear ASAP.

Meanwhile, there is conflicting commentary about the independent report that was reported to be made available today (an unrealistic expectation). Unsurprisingly it is not finalised, the state government has also said it needs time to digest the report.

For those wanting to read about some of the broader issues facing the industry here is a decent media summary:

https://www.theguardian.com/austral...vernment-for-failure-to-reform-building-rules

 

[rapt]

I thought this website was about engineering, something normally based on facts and science.

Not conspiracy theories based on press reports by people who have no idea what they are talking about, guesses as to how a building is behaving without any knowledge of the structure or the design and complaints about reports and timelines for presentation of reports and those reporting even before the reports are finalised.

 

[Agent666]

I don't know any engineer or company that would say any structure is 100% safe, especially one that's undergone a previous failure and with the reported doubt over what seems to have been designed/constructed. Those types of broad statements can easily be turned against you, by others or by nature taking its course and working its wonders. It complies with code, or it doesn't, that's all I'd be reporting on as this is the minimum benchmark that needs to be achieved.

David256, the architectural drawing that have been posted are not representative of the final structure based on what a lot of people have observed, guessing they are quite preliminary and lack coordination with the final structural scheme. So basically cannot be relied on for delving into the structural behaviour.

 

[CivilEngAus]

CivilEngAus

Can you name the professor, or what university or forward a link to the video for us to see who you are talking of.

Interested to find out who is involved.

I intentionally did not name them given that the media could potentially see them as another person to hassle for comment

Seven News 31/12/18

There is a copy of the video here; around 10 to 15 seconds in:

https://www.instagram.com/p/BsDAo-qFoBs/?utm_source=ig_web_button_share_sheet

 

[mangotree]

The news reports mentioned “remediation” and “stabilisation” works that were scheduled to be completed last Friday.
This suggests works to the structure, which is why they have all the heavy duty props, while those are carried out.

This is speculation- but perhaps they need the 4-6 weeks for the any new structural concrete elements to cure before removing the props and then start the fit out works.

If they were otherwise giving the all clear without structural works, and the props were truly redundant as purported in the press releases, shouldn’t they first monitor the building’s performance prop-less? Eg To see if there is further movement prior to fitout works commencing.

 

[georgeverghese]

The Olympic Park underground line linking Lidcombe to the nearby Olympic Park station seems to pass very close or right underneath this Opal Tower - could this have something to do with this engineering /construction disaster?

 

[human909]

Based on my vaguely informed opinion:

The news reports mentioned “remediation” and “stabilisation” works that were scheduled to be completed last Friday.
This suggests works to the structure, which is why they have all the heavy duty props, while those are carried out.

This is speculation- but perhaps they need the 4-6 weeks for the any new structural concrete elements to cure before removing the props and then start the fit out works.

It is very unlikely that proper remediation has even begun. At this stage works have likely been about stabilisation and investigation. It is quite unlikely that there have been any "new concrete elements"

If they were otherwise giving the all clear without structural works, and the props were truly redundant as purported in the press releases, shouldn’t they first monitor the building’s performance prop-less? Eg To see if there is further movement prior to fitout works commencing.

You don't install props if you think they are completely unnecessary. Statements made to that effect are about PR rather than engineering. Forget the PR. The building has had structural failure. Floors have sagged. This hasn't changed and this still needs to be addressed.

The Olympic Park underground line linking Lidcombe to the nearby Olympic Park station seems to pass very close or right underneath this Opal Tower - could this have something to do with this engineering /construction disaster?

Quite unlikely. And I would call it a 'disaster' a bit extreme.

 

[Agent666]

The Olympic Park underground line linking Lidcombe to the nearby Olympic Park station seems to pass very close or right underneath this Opal Tower - could this have something to do with this engineering /construction disaster?

Yeah some of the workers might have arrived on site via the train, perhaps even the designer took the train to the site... maybe the report will cover this aspect.

The experts have already publicly noted that they didn't find any issues with the foundations about a week or so ago. Presumably based on this fact the designers accounted for the presence of the train station appropriately. Issues appear to be concentrated in the superstructure based on where the failure occurred and where the destructive investigations were noted as being undertaken in the letter posted above.

 

[mangotree]

SBS World News managed to obtain Cardno’s letter to the owners, explaining their current professional opinion.

https://www.sbs.com.au/news/opal-to...return-amid-calls-for-building-industry-audit

The text was a bit blurry from the video, so I’ve typed out what I could make out.

11th January 2019
Dear Owners,

RE: OPAL TOWER

Before residents can return to the Opal Tower, the structural adequacy of the building should be confirmed in a totally unqualified manner by WSP that acknowledges the damage that has occurred to the structure, the temporary propping that has been installed to help prevent further damage, and the stabilisation works currently underway to reduce stresses in critical regions.

Before Cardno is in a position to even recommend that the building can be reoccupied in part, the Stage A stabilisation works must be fully completed and the investigations to:
a) Confirm concrete strengths in the damaged regions must be completed.

b) The investigation works to confirm finding of the non-compliant reinforcing in the precast on Level 10 and that suffered significant spalling is a one-off occurrence as opposed to a systemic problem must be completed.
Because of the considerable disruption that the completion of the major remedial works will cause to residents who may choose to return, Cardno is reluctant to recommend that residents return at an early stage.

Regards,
D. R. McMillan
Cardno

 

[tornear]

Thanks mangotree, an interesting and reserved letter from Cardno.

Having thought a lot about this failure, I would like to pose a question to the thread: what was different on 24 December from 23 December or earlier?

The building was completed in August, the elements in question at Level 10 were installed months before this, and the majority of the load they carry was in place when the structural works topped out, which would have been long before August. Some live load was added as residents moved in after August. Inadequate structural elements are likely to exhibit some form of distress during the construction phase when the concrete strength is lowest. Internal to the unit this would have been concealed by finishes, but the external face of the panel was always exposed.

It is unclear from the available information whether the failed element contributed to the lateral load resisting system. The wall appears stiff enough to pick up some lateral load, whether it was intended to do so or not, but the 24 December was not a 'windy' day and Sydney had experienced a significant storm on 20 December. So what changed on 24/12 to initiate failure?

Perhaps ongoing creep, shrinkage or deflection growth contributed, but for that to be a factor the element must have been particularly sensitive to such effects.

Cardno's letter mentions 'non-compliant reinforcing in the precast'. It seems unclear whether the precast panel was acting as a simple vertical load-bearing element, with a bearing failure mode per Human909's analysis, or a deep beam performing a transfer, in which case it looks more like a failure at the nodes anchoring a tension tie.

While we wait for formal comment from those conducting the investigation, I would welcome any thoughts on what changed on 24/12 to make the failure occur in seemingly benign circumstances.

 

[human909]

The investigation works to confirm finding of the non-compliant reinforcing in the precast on Level 10 and that suffered significant spalling is a one-off occurrence as opposed to a systemic problem must be completed.

Well that is the first indication of a primary cause of this failure.

Cardno's letter mentions 'non-compliant reinforcing in the precast'. It seems unclear whether the precast panel was acting as a simple vertical load-bearing element, with a bearing failure mode per Human909's analysis, or a deep beam performing a transfer, in which case it looks more like a failure at the nodes anchoring a tension tie.

Considering it as a vertical load bearing element or a deep beam is just modelling simplifications. Regardless it doesn't change the bearing stress concentrations. Those stress concentrations are pretty unavoidable. But that doesn't mean it is bad or they are the issue. As far as a tension tie in a beam model goes, the beam is so deep the tension in the bottom flange is quite low. (the same rough and dirty FEA shows this) Compressive stress at the supports and shear stress next to them are both very high as you would expect. Both would need appropriate reinforcement detailing.

 

[Tomfh]

Tornear, what was different on december 24 was the stresses reached the failure point!

I suspect it was shriankge/creep/temperature/deflection etc. those cracks often take a while to appear.

 

[human909]

A couple of snippets from the report being circulated:

https://www.news.com.au/finance/bus...h/news-story/87bacda9b12460926a01b4f181c9a1cc

https://www.theaustralian.com.au/na...s/news-story/02720b016719259891036d3c1e92c021

"As an interim report into the cracking of concrete panels that triggered two evacuations of the building is expected to be released, investigators disagree as to whether the grade of reinforced concrete used in the support beams was strong enough to withstand the pressure of precast concrete panels installed on top of them.

Several sources close to the ­investigation have told The Australian that one theory is that the beams lacked sufficient strength, causing pressure on the concrete panels, which cracked and sparked the evacuations."

"But another theory is that grouting between the precast panels and the beams contributed to the cracking in the panels."

"Investigators’ reports handed to Planning Minister Anthony Roberts last week appear to have found the builder, Icon Co, ­appeared to have built Opal Tower according to the specifications it was provided with."

The last comment if accurate seems to point towards design issues. There might be reliable information available later today if the report is publicly released.

 

[rapt]

Another one

https://www.abc.net.au/news/2019-01...cant-rectifiaction-work-report-finds/10713054

"We can confirm that, while the building is structurally sound, significant rectification works are required to repair and strengthen damaged hob beams and in some cases the panels that rest on them," they said in a statement.

The trio said while the "probable cause" was narrowed down to "localised structural design and construction issues", more information was needed to make a conclusion.

 

[Tomfh]

The report:

https://www.planning.nsw.gov.au/-/m...stigation-Draft-Interim-Report-2019-01-15.pdf