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.

 

[human909]

Can anyone confirm that the column configuration was definitely changed between the issuance of the architectural drawings and the actual construction?

Compare the photo with the drawing for Levels 5-9. There is a marked column that very much doesn't appear in the photo.

http://majorprojects.planning.nsw.gov.au/index.pl?action=view_job&job_id=6603

The emphasis was added to show where I thought the problem was! You wrote it!
To suggest that they are being thorough NOW is to suggest that they were not previously, and that is still not known.

The emphasis changed the meaning. The statement was never meant to be interpret the way you did, and to my mind most people wouldn't interpret it that way. The word 'now' simply means at presently or currently which is exactly what they are doing. They are doing the inspections later they are doing them now. Your emphasis changes can change the perceived meaning but the literal mean is still the same.

 

[degenn]

I know that we are all talking about something were we don’t know all the facts. What we do know is something serious failed under normal service. That is at about a third of what should be its actual capacity. There are twenty similar details in the structure. Although they may not have failed it is important to question whether they have an acceptable factor of safety.

My experience with forensic review of failures has always shown that these failed exactly as they should have once all the facts are known. Such reviews give you a great deal of faith in the design methods we use and the safety factors built into our codes.

It does lead you to question why in NSW we don’t have a formal process of external design review for structures where failure can have such serious consequences.

 

[rscassar]

It's a good point. When working in the UK it was a requirement to submit a calculations package to the Authorities for review and I believe there is something similar in the UAE. From what I understand and I may be wrong as I have never worked in SA, but I believe that South Australia is the only Australian state that requires the certifying structural engineer to submit a calc's package or require the 'For Construction' drawings to undergo a complete Independent engineering review.

It might be a good time now to implement that throughout the country.

 

[QSIIN]

@degenn

Not just NSW, but the whole of Australia. Does anywhere do external design reviews? As you said, the structure is arguably the most important part of any project (concerning safety of life), yet we have tiny fees, and are constantly being pressured to deliver faster and more for less.

And having CPeng or RPEQ or any other form of qualification also doesn't mean much, anyone willing to pay the fee to be registered can sign off another Opal Tower...

 

[Tomfh]

I agree. Having to submit calculation packages and having designs reviewed would help to raise the bar far more than everyone sticking “CPEng NPER” on their business cards.

 

[Agent666]

Tomfh guess what came out of NZ experience 20 years ago... Exactly that.

Another photo of damage to walls and floor that hasn't been posted yet (sourced from local news site). Appears to be some good punching shear / shear type of failure in the floor.

 

[rapt]

That was my thought when I first saw it. And the wall crack seems to line up with it.

Would be nice to know what the structure below it looks like.

Hopefully we will find out eventually.

 

[rscassar]

I just got some engineering details:
- The precast wall adjacent to the skygarden above Level 10 is 200thk precast, don't have any details about the wall itself (eg. concrete grade or reinforcement).
- Level 10 slab is 200thk PT slab with 90mm setdown from internal to external. 40MPa generally with 65MPa puddle pours around the supporting columns below.
- L09 columns. Column closest to the slab edge is 700mm dia. Column closest to the entry of 1005 is 900x750 rectangular.

 

[QSIIN]

Wow. If there are punching shear issues then this is far more serious than anything reported.
And 200thk precast panels with 20 floors on top is pretty thin - and slender.

Similar to wall/columns, punching shear in 3600 is pretty vague, and again I've personally seen engineers outright ignore it because they don't "believe" in punching.

 

[degenn]

A quick calc...


30m2 x 10kPa x 23 floors = 6900kN
The area and load generous I think.

(0.7 + 2 x 0.2) x 0.2 = 0.22m2
Assuming a 45 degree dispersion

6900 / 0.22 = 31MPa.

Seems maybe a bit high for a wall but unlikely to cause an actual failure since the service load would only be about 70% of the design load.

I think something else is going on.

 

[rapt]

QSIIN,

Punching shear is a guess from the shape of the crack and what looks like significant vertical separation. We simply do not know enough. Another suggestion was prestress anchorage failure, but I doubt that it would damage the wall like that or that it would happen 6 months or more + construction time after stressing.

I did not realize that AS3600 or any other national code operated on a "belief" logic. We normally leave that to politics, religion and football! AS3600 is a minimum set of design requirements!

There is nothing vague about the AS3600 punching rules. Too prescriptive maybe, but any engineer who has read the development work it was based on should understand it sufficiently to apply it.

 

[QSIIN]

RAPT,you're exactly right, a minimum set of requirements. Meaning there's a lot more that might need to be considered that is not covered by the code. I wish more engineers understood that.

Regarding punching, I guess 3600 gives clear enough minimum requirements for an ideal situation, but these days, with all sorts of transfer, transitions, precast/insitu interaction, using the code method might not be most appropriate - again, just the minimum requirements. Most buildings aren't square columns, equal spans in all directions anymore- some require a little more thought.

 

[Agent666]

That's the problem rapt, engineers have to think to apply..... Scary how many times in doing peer reviews of small and simple or large and complex projects that I've seen someone unfamiliar with certain provisions completely misunderstood the requirements. When you set them right they are generally missing some basic understanding of the principles on which the provisions are based, sometimes having never even read the associated commentary clauses.

It would scare me if anyone believed punching shear didn't occur. Brittle failure modes with little or no warning warrant some additional attention if nothing else in my opinion.

 

[rapt]

Agent666/QSIIN,

You are preaching to the converted. That is why they are engineers and have all of that training. Or it used to be!

And it is not just that they have not read the commentary. Many have not read the code. Apparently software does it all for them!! Means they do not have to think. Just press the go button and then the print button and the code is satisfied. And the more complex the software gets, the less they have to think.

 

[Tomfh]

Punching failure. good grief, that would be scary.

 

[rscassar]

May have been initiated by the wall panel failure first.

- A 200thk panel bearing over a 1040mm length (700mm column + 2*0.85*200mm for dispersion thru the slab) = 4,050kN @ 80MPa.
- Working load at the time of failure 30sq.m x 7.5kPa x 23 floors = 5,175kN

If the wall underwent cracking to widen the bearing area then instead of going direct to the column it went thru the slab and cause the punching failure.

I'm not really happy that the company responsible for the engineering certification and an engineer appointed by the builder are heading the investigation. I think it would be more ethically if a reputable and independent consulting engineer was heading the forensics.

 

[degenn]

rscassar

You give the capacity of the wall over the column as 4050kN. This presumably includes a phi of 0.6. This is a safety factor and shouldn’t be considered in assessing an actual failure. Similarly the 5% eccentricity is a contingency but probably doesn’t actually exist with a symmetric floor load and high axial load from above.

The wall may be overloaded from a code point of view but failure shouldn’t be expected.

 

[Tomfh]

Degenn,

Agree. When assessing actual failure we need to look at actual expected capacity and actual loads, not code reduced capacities and code loading.

 

[Settingsun]

Scary how many times in doing peer reviews of small and simple or large and complex projects that I've seen someone unfamiliar with certain provisions completely misunderstood the requirements. When you set them right they are generally missing some basic understanding of the principles on which the provisions are based, sometimes having never even read the associated commentary clauses.

What experience/seniority have the people making these mistakes?

As for reading the commentary, the 2001 code didn't get one; the 2009 code didn't get one until 2014; the 2018 code doesn't have one. We probably can't learn much from the ACI code but their practice of publishing the commentary in the same document as the code itself is streets ahead of the Standards Australia shambles. (Can I coin 'Shambles Australia' or is that unfair?)

FWIW I didn't read the supposed slander in Human909's use of the word 'now'. If anything, it was a defence of WSP's professionalism when read in context.

 

[IRstuff]

There's a reason why a System Requirements Review (SRR) precedes Preliminary Design Review (PDR); it's a chance for the customer (or peers) to interact with the designer to ensure that everyone understands the meaning and intent of the requirements.

Finding out that someone misinterpreted a requirement, even at PDR, wastes time and money.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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