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

1:24 Slender Skyscraper - 111 West 57th Street

1:24 Slender Skyscraper - 111 West 57th Street

(OP)
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.

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

I saw this online a number of months ago and thought it was a photoshopped pie in the sky architect’s dream.. I can’t believe its actually being built - it looks totally wrong.

I wonder what happens when you’ve built up to the 80th storey and the TMD doesn’t go in until the 82nd? Do they use temporary TMD’s?

Its an incredible feat of engineering design!

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

WSP has considerable experience designing slender buildings, but this is their most slender to date. A difficult part of the design of any slender building is determining the long-term stiffness and damping of the reinforced concrete shear walls, outriggers/columns and foundation under service wind load. This is an area where experience is very important. There may be no need for temporary TMD during construction because the workers are less sensitive to small accelerations due to wind gusts and vortex shedding than the apartment occupants will be.

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

3

Quote (kissymouse)

How in the world is this possible?

Mostly by way of insanely high property values.

I have a friend in NYC who participates in high-rise design there, albeit not quite at that scale these days. He's graciously allowed me to participate in his work around the margins which has afforded me a fascinating glimpse into that market. I make the following observations:

1) Buildings this tall use their full width structurally as opposed to more conventional buildings where the structural width is really the width of the elevator shaft or the braced frames etc. Here, I believe that it's full width, perforated shear walls in one direction, as you mentioned, and those same walls used as outriggers in the other direction.

2) At the end of the day, a building like this is just a cantilever beam not exposed to all that much load (wind on it's own surfaces). Using the full width structurally, and throwing in some damping tech for occupant comfort, 1:24 isn't that much of a stretch when you think about it.

3) I've seen some of the unit floor plans for the building. The square footage of any one floor is disproportionately made up of monstrously thick shear walls. It almost looks oppressive in a way. On some visceral level, I'd have to think that you'd notice that the door jamb separating your kitchen from your stair shaft is 3' thick. Although, as you can see below, they clearly employ some clever architectural tricks to mitigate this. Losing this much floor space to walls is obviously only palatable in a market where insanely high property values can justify it.

4) A critical consideration for such a slender building is being able to successfully staple the damn thing to the ground convincingly. They seem to use a lot of very high capacity tension piles embedded into the bedrock that underlies the area. Very high capacity piles using central, high strength "rebar" to the tune of 4" in diameter. At that size, the bars are pretty much columns in their on right rather than reinforcing. These piles may cost upwards of $50K a piece. So, again, this is only palatable in a market where insanely high property values can justify that. I shudder to think that my own home, taken in its entirety, is probably only worth half a dozen of the piles under a skyscraper.

5) The engineering is sophisticated but probably not nearly so much so as you'd anticipate. A lot of it seems to just amount to being super aggressive with respect to design assumptions etc. The part of this that worries me a bit is that there seems to be very little standardization or code guidance to govern the lateral design of these types of buildings. You've got a gaggle of highly competitive envelope pushers all competing vigorously for these jobs and constantly feeling one another out to ascertain where the bar design of acceptability is located this month as opposed to last. It makes NYC a difficult market in which to practice and, ethically, it's hard to imagine how such a setup doesn't ultimately culminate in some problems. Thankfully, NYC does seem to have a fairly robust peer review system in place for major buildings.



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

Short promo video about some WSP's current slender towers - interesting watch. WSP - Engineering Super Slender Towers

East-West, you've got an I section with the perimeter walls being the flanges and the services core as the web.

North-South, you've got a healthy lever arm on your side. Probably some outriggers to those mega columns in combination with the perimeter shear walls.






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

Quote (KootK)

Mostly by way of insanely high property values.

Just how high are the values of these properties, 300 ksi steel, 20 ksi concrete?









I'm joking.

Although your sentence is probably true in both meanings :)

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

Well.. both I suppose. 120 ksi rebar, 10 ksi column concrete. Bedrock. They not messing around in NYC.

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

Of course not, they have to design for Avengers fight scenes. A 250 year recurrence-level Hulk punch is nothing to joke about.

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

Quote:

Bedrock. They not messing around in NYC.

After that fiasco in San Francisco.....can't say I blame them.

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

It's surely wider at the bottom isn't it? Otherwise I think a 50k pile is very good value for the amount you can get in there.

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

don't call me "Shirley".

what happens when the TMDs fail ? redundant power supply ?? Or is the structure ok without them, with the large displacements, only the occupants aren't (ie sea-sick) ?
What's the natural frequency ? can this get excited by a reasonable wind speed 9maybe if the TMDs fail) ?

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

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

432 Park was a similar proportion and was finished recently. I have heard on the grapevine that there have been some resident complaints about sway, but its hard to know how much stock to put in that.

432 Park has both TMD's and big holes in the building to interrupt vortex shedding. They did a lot of wind tunnel testing to prove out the aerodynamics.

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

(OP)
Thanks KootK and Trenno! That's exactly what I was looking for. I would love a glimpse into NYC engineering, seems very interesting. or Chinese high rise engineering.

Quote (SteelPE)

I'm not sure if this is the same building, but I did see this the other day.
That's the one.

Quote (glass99)

432 Park was a similar proportion and was finished recently.
432 Park, also done by WSP, was actually a 1:15 ratio and this is 1:24. Don't get me wrong, still very slender, but 111 W 57th took things up a notch.

Looks like units are going between 20-60 million each. I don't think they've sold out, but with making something no one's seen before, in the perfect location, and hyped up with videos like SteelPE posted, you can end up paying for unreasonable structures. I get asked frequently, and I'm sure most of us do, if something is possible. "Can I put a beam here?", "Can I tear out this wall?", "Can we move this over 5ft?" I usually say anything is possible, it just depends on how badly you want something, how much money and time you're willing to put into it. In this case, it looks like they made something crazy work because the money is there, people find it valuable enough. I like those clients, the ones who are passionate about making something happen and work with you to get it done. You get to rack your brain a bit, spend a lot of time on it, and get paid for all of it. It's a lot better compared to the more common disgruntled client who's mad about having to hire an engineer in the first place.

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

Quote (glass99)

They did a lot of wind tunnel testing to prove out the aerodynamics.

That is an excellent point that should not be overlooked. High end wind tunnel testing is also doing a great deal to facilitate these projects.

Quote (OP)

It's a lot better compared to the more common disgruntled client who's mad about having to hire an engineer in the first place.

Unfortunately, another of my observations is that this work is much more fee competitive than one might think. Rumors that I can't 100% confirm:

- The big dogs are basing their fees on being able to off shore much of the routine stuff such as two way slab design.

- Sometimes these things are treated as practically loss leaders in order to secure the associated, more lucrative special inspection work.

If all I had to do was cut off a thumb and bankrupt my family to work on one of these things, would I? Hell yes. Are the guys that do these things spending their days rolling around in gold doubloons while pleasuring themselves to sexy ETABS animations? Meh... I wouldn't count on it.

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

Quote (SteelPe)

Youtube videos

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

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

If those floor plans are accurate, how do they get away with one stairwell.

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

A lot of the taller buildings are able to use occupant evacuation elevators in lieu of of a second stair. There have been a few high rises completed in this manner.
This is in compliance with the exception in IBC 403.5.2 and in accordance with IBC Section 3008. I think 181 Fremont in SFO was the first building to utilize this.

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

Here’s a link to a very interesting article on why we might be seeing a lot more of these..

https://www.theguardian.com/cities/2019/feb/05/sup...

So essentially in NYC you can buy someone else’s unused air space and add it to your own plot! Developers with big pockets and even bigger egos will drive this.

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

Quote (KootK)

- The big dogs are basing their fees on being able to off shore much of the routine stuff such as two way slab design.

- Sometimes these things are treated as practically loss leaders in order to secure the associated, more lucrative special inspection work.

If all I had to do was cut off a thumb and bankrupt my family to work on one of these things, would I? Hell yes. Are the guys that do these things spending their days rolling around in gold doubloons while pleasuring themselves to sexy ETABS animations? Meh... I wouldn't count on it.


Ahhh, the scarcity makes me cringe.
Yes, these guys should be making millions of dollars designing these amazing structures (and pleasuring themselves to ETABS animations). How sad that the developers don’t see it that way. And yes, Kootk, if you want to work on one of these buildings, you should go for it.. You are more than qualified.

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

Quote (Trenno)

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

Ryan Ser-haaaaaant

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

Quote (XR250)

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.

Quote (XR250)

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...

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

Quote (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.

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

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

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

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.

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

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 ?

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

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.

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

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 www.432parkavenue.com .



edited to note that glass99 posted this first!

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

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!!

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

Quote:

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.

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

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

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

@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.

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

Quote (milkshakelake)

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.

Quote (milkshakelake)

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.

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

@Kootk - you should try Visicon.

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

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.

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

Quote (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.
Something like Opal tower?

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

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.

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

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!

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

Quote (Slickdeals)

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!

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

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

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

$130m?! I’m guessing the buyer wasn’t a structural engineer...

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

(OP)

Quote (milkshakelake)

They're not geniuses; they're just regular engineers...it looks like they're using outriggers on those gigantic columns

Quote (MIStructE_IRE)

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!
Well at the end of this thread, the structural stability of this stick seems a lot less daunting, so I'm thankful for the insight and discussion. It's an interesting feeling of switching tasks between making sure the building can stand up and not freaking people out with their bathwater sloshing around during a wind storm. It's a little relieving to have to design something beyond stability, but structural engineering would be a lot more interesting and technical if serviceability wasn't a thing.

Quote (milkshakelake)

they do have the best spreadsheets in the business.
I'm a sucker for a good spreadsheet. But developing automation in design can be such a time suck and just doesn't make sense for variety in project types. Just trying to figure out different aspects of Revit isn't worth the time, and someone else already made it.

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