1:24 Slender Skyscraper - 111 West 57th Street 8

[kissymoose]

This isn't a very technical question, but more coming from strong curiosity and amazement at what we're building nowadays.
There's this new residential skyscraper going up in New York City with a slenderness ratio of 1:24. It's more than 1400ft tall.

I don't know much about or have any experience of this "pinnacle of engineering" type of work. How in the world is this possible? They mention two of the four walls are shear walls, I guess without any openings, and there's a tuned mass damper on top. Is the majority of the lateral load countered by the tuned mass damper or the shear walls?
Kind of a short question, but I also wanted to see others' opinions on the building.

 

[XL83NL]

You could probably use that real estate agent's head as a TMD...

Ryan Ser-haaaaaant

 

[KootK]

How sad that the developers don’t see it that way.

Part of what is interesting is that the developers for these projects are often very savvy about structural costs and, in some cases, will be former structural folks themselves. So you'll go to a meeting to show off your wares and find them received to the tune of "this is 4% higher shear wall rebar density than a building like this should have". And back to your cubby hole you go to keep up/down with the Joneses. It's a double edged sword I think. One the one hand, it's a great learning experience working with such sophisticated development teams. On the other hand, it's surely frustrating and/or stifling at times having your client be so savvy structurally.

And yes, Kootk, if you want to work on one of these buildings, you should go for it.. You are more than qualified.

Thanks for that. I've actually explored this kind of thing on a few occasions with little success. Two factors always come into play:

- Need to move family to an expensive market for paltry pay and;
- On balance these firms have little respect for the "kind of engineering" that my resume reflects. Not even the institutional stuff.

Funny story. WSP is one of these big aggregator firms fueled by pension fund investments etc. Canadian headquartered no less. A while back, they bought a firm at which I was working. I was miffed at the time but decided to view it as an opportunity. So I contacted their NY office which used to be Cantor Seniuk, deities of skyscraper design. They were advertising a bunch of positions and I thought I might be able to finagle some kind of "internal" transfer into the world of mega-projects since we were all basically the same company now. So we had a Skype interview...

1) They administered a couple of test quiz questions. Moment diagrams etc... ridiculous to the point of being offensive for a ten year guy.

2) They liked me and offered me a position in their Manhattan office for $65K. I actually looked into the viability of that, I wanted it so badly. I would have either had to live on the street in Manhattan or commute in from South Dakota somehow.

3) When I pointed out that I was already making $115K working for WSP, it became clear that they weren't actually aware that I was a current employee of WSP. And, of course, why would they? The NYC WSP guys neither know nor care what a bunch of hillbillies in one of their Canadian offices are up to. Maybe Toronto...

As you can imagine, the whole thing was pretty awkward and a little disheartening.

I will say though, every-time that I come back to check on this thread, I see the photo a the top and am blown away by the proportions of that building. It is definitely bold and amazing. I wish that I had access to their ETABS model. I'd be curious to know how far you could shift the upper floors to one side before P-delta would kick and she'd wet noodle into the neighboring buildings. Or maybe something that is full width structural like this really isn't ever heavy enough relative to lateral stiffness for P-delta to doom it...

 

[KootK]

I'd be curious to know how far you could shift the upper floors to one side before P-delta would kick and she'd wet noodle into the neighboring buildings. Or maybe something that is full width structural like this really isn't ever heavy enough relative to lateral stiffness for P-delta to doom it...

You know your focus is drifting when you start responding to yourself on anonymous web forums...

In my mind's eye, I see the building much like this.

 

[SteelPE]

You just wonder with them "pushing" the limits, how long before the limits push back and we, as a profession, end up going backwards?

 

[glass99]

What's interesting about these buildings is that the structural engineering has enabled a new business model. They can build a large amount of high end space on small lots and sell them for high prices. Its quite different from the structural engineering being treated as a secondary service as it is frequently.

Technically, its all about the dynamic performance. Tall buildings have very low natural frequencies, so aeroelastic performance is important. Also allowable accelerations can be hard to pin down. I think the wind engineers RWDI deserve as much credit for the structure as WSP.

 

[rb1957]

if TVDs are added late in the build, how to they stabilise these things during build ?

how about glass cleaning these guys !?

another day in paradise, or is paradise one day closer ?

 

[glass99]

These structures do not need damping for strength, only for user comfort, so no TMD's are required during construction.

The amount of sway they can sustain strength wise can be quite gigantic - we worked on a 70 story building in LA which swayed +/-30ft in a seismic event.

 

[JLNJ]

I think there is another one right down the street on Park Avenue. When we were in the City up in the Empire State Building last year it was really striking to look north and see the Park Avenue 432 building so tall and skinny. Honestly, it didn't look right. My son (the artist) thought it was pretty cool looking. To my eye it seems like a cartoon somebody drew in on the skyline.

Check out

http://www.432parkavenue.com

.

edited to note that glass99 posted this first!

 

[MIStructE_IRE]

I’d really wonder about the long term fatigue effects of something drifting 30ft!

432 Pk Av is impressive. However its L/d is in the order of 15, this new one is L/d = 24! I’d love to stand on top of it during a storm! Somehow however, working as an engineer I don’t think I’ll ever have $60m to spend on an apartment!!

 

[XL83NL]

I’d really wonder about the long term fatigue effects of something drifting 30ft!

If you consider wheel bolts and their fatigue loading vs slenderness, it wouldn’t be the first to succeed, albeit the (end) constraints are different.

 

[bob33]

Regarding the number of stair exits, these appear to be scissor stairs which would count as two separate exit stairs.

 

[milkshakelake]

@KootK I'm based in NYC and I know 3 people who worked at WSP, including one principal. They're not geniuses; they're just regular engineers. I think the really good engineers at that company are the ones with PhDs. A lot of their work is based on spreadsheets and regular ETABS models with typical assumptions, no extra magic. I'd love to see their ETABS model though, to see how they deal with cracked and uncracked shear walls. But they don't even do wind tunnel testing for most of their buildings. I have problems with one of their typical practices: how they calculate column loads (which we had a discussion about earlier, but I just didn't mention WSP).

That being said, they do have the best spreadsheets in the business. Not going to say how I got them. But they do real magic, like making CAD column schedules.

@kissymoose I don't have insight into this specific project, but a lot of these supertalls are done with 2 floor high outriggers at the mechanical floors, plus the damper as you mentioned. Based on Trenno's layout, it looks like they're using outriggers on those gigantic columns.

 

[KootK]

But they don't even do wind tunnel testing for most of their buildings.

Where do you see the cutoff being for when wind tunnel testing is performed? Certainly, I've been seeing it for even "modest" building in the 40 story range.

That being said, they do have the best spreadsheets in the business.

Agreed. And this may be the part that makes me the most envious. I have some of those spreadsheets and would love to generate my own versions. Unfortunately, you really need projects with a simple, highly regularized, gravity load path for those tools to be useful. WSP and the like obviously have that in their phallic monsters. I don't have it at all in my typical, shorter, vastly choppier projects. Anyone who's knows me well knows that my biggest annoyance with structural engineering is load take down. I'd happily trade an incurable case of syphilis for the ability to always know my loads effortlessly. No doubt doubt my wife would have something to say about that. Let's make it an incommunicable, incurable case of syphilis.

 

[slickdeals]

@Kootk - you should try Visicon.

 

[canwesteng]

I can't imagine signing off on something like this where engineering is done on spreadsheets. Even a small mistake that isn't catastrophic would cost tens of millions of dollars.

 

[jayrod12]

I can't imagine signing off on something like this where engineering is done on spreadsheets. Even a small mistake that isn't catastrophic would cost tens of millions of dollars.

Something like Opal tower?

 

[canwesteng]

Something like that, or if someone doesn't properly understand the scope of the spreadsheet and you end up with unsightly concrete deflections. If it's 50 million a unit you can get sued out of your fees pretty fast.

 

[MIStructE_IRE]

Well they didn’t have ETABS or spreadsheets when they built the empire state!

I believe if you can’t explain a fancy computer model using a couple of quick calcs and some free body diagrams - then either there’s something wrong or the engineer hasn’t a clue what they’re doing!

 

[Trenno]

Visicon

Wow... this is seriously impressive. Can CSI please just buy the rights to this software and integrate it into ETABS... It's what the graphics capability SHOULD be in ETABS.

Visicon & ETABS video

RE: Column load run downs - the true column load lies somewhere between MAX (trib area analysis - hand calcs/spreadsheets, elastic distribution of single floor plate - RAM Concept, staged construction analysis - ETABS). Find a way to combine the results of all 3 methods in a simple yet robust data management system mapping shared parameters back to the Revit model and then bob's your uncle!

 

[bridgebuster]

I read a blurb in one of the papers some time back that the penthouse was sold for $130 Million.