SF tower settlement 25

[lilliput1]

Another concern is that earthquake can cause liquefaction of the soil which would be catastrophic because the piles do not go all the way to bedrock.

 

[epoxybot]

Correction: In my post on 25 Aug 17 01:44, I alluded to GFRP rebar in photos for the Millennium Tower reinforcement but after more searching it now seems that Baugrid is produced using smooth steel bar. The smoothness of the bar & the color of the surface corrosion on the bars led me to believe I was seeing GFRP.

Attached is a copy of the July 2017, City of San Francisco Safety Review of the Millennium Tower Link

The report is the City of San Francisco's interpretation of the 2016 Structural Review with requested follow up analysis performed by Simpson Gumpertz & Heger on behalf of Millennium Partners and is seen by some as a walk back from SGH's 2014 review that concluded 8 of the Outrigger Columns (upper floors) would be over stressed during an earthquake. The 2014 report was seen by some engineers as a sign the building could be "Red Tagged" after a major quake. Link In the City's July 2017 review the focus is on the Outrigger Coupling Beams.

The City of San Francisco vis-a-vis the SF Dept. of Building Inspection, SFDBI has two strikes against it in this affair.
Firstly, the City had previously halted work on a project of almost identical design, 50+ story, concrete building with friction piles (geo-tech by Treadwell & Rollo) at 80 Natoma, citing 'new information' that it was too heavy and sink too much. 80 Natoma was a property directly over the favored path of the CalTrain underground extension to the planned Transbay Center transportation hub. If the tower was built it would be impossible to come back later and tunnel under such a heavy building resting on friction piles. The developer refused to sink piles to bedrock citing delays would compromise project funding. The site was eventually purchased via Eminent Domain for between $58 & $90 million. More than a little speculation circulated that the whole project was always a shakedown.
Secondly, the City's failure to look into the accelerated sinking of Millennium Tower, AFTER they had initiated inquiry & subsequently approved the structure for occupation (sale of condos).

The City of San Francisco & Millennium Partners have a common interest in dissociating themselves from blame. Both Millenium Partners & SFDBI claim there was no requirement for the developer or the Peer Review panel to consider the Transbay Project next door. Link That seems to be in conflict with the Mission Street Development LLC (Millennium Partners) 301 Mission Street - Environmental Impact Report that cited the adjacent proposed Transbay Center project Link and SFDBI's actions at 80 Natoma.

 

[dik]

All is well... at this time. From the report, "To an extent consistent with the scope of our review, our professional opinion is that the foundation settlement experienced by the Tower has not appreciatively affected the safety of the building at this time."

Sounds great, and at an inch per year, who knows... settled 18" so far.

Dik

 

[stevenal]

Further, the review is
limited to evaluation of the current condition of the Tower and does not address the effects of
future settlement or other changes that may occur to the Tower in the future.

All was well July 28th; July 29th is out of scope. Does the report contain any useful information?

 

[dik]

stevenal... nothing of substance... nothing to give you a warm fuzzy feeling...

Dik

 

[JedClampett]

That ought to increase the value of those condos.

 

[epoxybot]

Description of the shoring work for the Millennium Tower & adjacent 5 level parking structure basement. Webcor Builders: The garage is an internally braced soil cement slurry wall system with soldier piles 5’ OC and the High Rise foundation is a soil cement slurry wall system with soldier piles 5’ OC with a few rakers and the balance of the hole supported with a single row of tiebacks. Both of these perimeter wall systems are augured 3’ diameter overlapping holes creating a continuous wall.

Early into the pile driving - Photo (A): Link
Looks like pile driving started in the Northwest corner of the lot: Photo (B): Link
Pile driving complete Photo (C): Link
ARUP's illustration of the relationship of the Transbay Center excavation & Millennium Tower Photo (D): Link
Photo of full excavation next to Millennium Tower - Link

In photo (B) note the high concentration of soldier piles on the left side of the photo. In photo (C) the soldier pile are capped with a steel beam & rakers tie to a stepped perimeter wall. What is different about this section of the shoring?

In this Old Tranbay Terminal demolition phase photo you can see that ground water is somewhere around 7 to 12 feet below grade. Millennium Tower is to the right in the photo. The area was used for staging for most of the Transbay Center project. Soil stabilizing fabric was laid & a waste slab poured.

 

[Ingenuity]

On Tuesday, October 3rd, 2017, UC Berkeley professor, Abolhassan ASTANEH-ASL, gave an Ethics Seminar: "Did the Unethical Conduct of Engineers and Academics Contribute to the Tilting and Sinking of the Millennium Tower?"

The seminar was a live webcast, however it was recorded and is available for public viewing here:

https://drive.google.com/file/d/0B6Cv_TTKSlYiMWdZSVdBcnJvSjQ/view?usp=sharing

I have yet to view the presentation.

 

[dik]

Really good article... I don't envy the position Abolhassan has taken... but, I think he's correct. At Harvard, he'd have been turfed.

Dik

 

[hokie66]

Maybe there is some validity in some of his opinions, but he is a blowhard. Although he promised to limit his discussion of the WTC, he spent more than half the time talking about it. Then his only conclusion about the Millennium Tower was that the piles are too short. We all know that already. Ethics? He stated he doesn't know about geotechnical issues, but then proceeds to comment on the piling.

Maybe it is just his accent, but some of his terminology is not that of a structural engineer.

He speaks about conflict of interest. I think at this point, anybody from UC Berkeley is conflicted.

 

[dik]

Blowhard or diehard or whatever, he raises some very good points for both the WTC and Millenium... call him Don Quixote... He likely feels 'slighted' and the presentation was his vindication. I've never seen a 'flat plate' with an 11" slab... contributes to the mass and rate of settlement...

With the WTC, there was an excellent thread on Eng-tips that disappeared... don't know if the webmeister was asked to remove it and 'turn it over' or what... it was just gone. A lot of what was discussed on the presentation was there... I didn't realise that a permit was not required and that stuff was 'approved on the fly' by those with a vested interest.

I'm not a geotekkie, and unlike Moehle, I would not have signed off on the foundations... The foundations would have been my first concern. My first posting on this thread ended with, "I don't know if the sand is saturated, but, there could also be problems during a seismic event..." and, is still a concern, and very likely the mode of failure, and, maybe after the first floor is at grade. I'm surprised that the SEAOC has not done a study... if a potential life safety issue, then they are 'obligated' to look into it...

Dik

 

[hokie66]

11", and thicker, flat plates are common in my environment. That's what our builders and developers want. Simple, it is. He called it a flat slab, one example of my reference to terminology.

He said more than once that there was "no structure" in the WTC, and no columns. Rubbish. And I would take the "no permit" thing with a grain of salt.

Anyone with that many pictures of "my projects", bridges and buildings, is a horn blower.

 

[dik]

A flat slab in these environs is one with drop panels or slab bands or a mix...

As to codes... I don't know, except, that I have never heard a prior reference to design requirements, and never considered that there were no permits if that's the case.

Whatever the issues, there are/were serious oversights made with both structures... not common, in these environs, to design for 747 767 loading... I thought and still do that using trusses from a core to an outside 'tube' structure was a neat way to do tall buildings... Light weight and using the outside 'skin', about as stiff as you could make it.

Dik

 

[hokie66]

Yes, that is my definition as well. I think the floors of Millennium are flat plates, but he called them flat slabs. I saw a report this morning about the Mexico City earthquake, where some California engineer reckons that flat slabs should be outlawed in seismic areas. I would agree, if there are not cores or shear walls, but the statement was misleading.

Disagree about the trusses, if you mean bar joists. They didn't adequately connect the exterior tube to the core, and that is a big reason for the collapse.

 

[dik]

They can be adequately connected... bar joists may be the correct term (more likely) depending on how they are fabbed... My only reservation about bar joists is that they have a large surface area for fire resistance protection... on impact (like a plane), the fire proofing can be 'knocked off' leaving little or no protection. Prior to the 'attack' I thought the approach was real 'neat'. I still think it can be workable... my tallest building is less than 1/4 the number of storeys of the WTC... and, not what I would call a tall building...

Dik

 

[Toby43]

Hell hath no fury like a woman professor scorned

 

[dik]

Hokie66:
"where some California engineer reckons that flat slabs should be outlawed in seismic areas. I would agree" Can you elaborate? I would think that the reduction in mass would be beneficial.

Diiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiik

 

[hokie66]

I think the issue is the use of flat plates supported only by columns, with no other lateral system. But just to say flat slabs should be outlawed is ridiculoua. The old flat slab has a place in our tool kit.

 

[SwinnyGG]

This is diverging the discussion a bit.. but this dude's assertion is that WTC building failures were due to unethical or, at best, ethically ambiguous behavior by its engineers? Really?

 

[dik]

jgKRI: The part I got from his presentation was that there were some questionable decisions made with any peer review... and, if his information is correct, then I concur with some of his criticisms.

Dik