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

## 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.

### 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

(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)

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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