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.

 

[MIStructE_IRE]

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!

 

[bob33]

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.

 

[KootK]

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.

 

[Trenno]

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.

 

[cal91]

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

 

[KootK]

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

 

[cal91]

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

 

[WARose]

Bedrock. They not messing around in NYC.

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

 

[canwesteng]

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.

 

[rb1957]

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 ?

 

[glass99]

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.

 

[SteelPE]

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

https://www.youtube.com/watch?v=aekZX4Banmk

Insane property values is an understatement. Who buys these things anyways?

Edit:

And another video

https://www.youtube.com/watch?v=rcAgDU-ESnI

It appears to be that building.

 

[kissymoose]

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.

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

That's the one.

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.

 

[KootK]

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.

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.

 

[Trenno]

Youtube videos

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

 

[SteelPE]

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

 

[slickdeals]

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.

 

[MIStructE_IRE]

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/...ive-the-pencil-towers-of-new-yorks-super-rich

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.

 

[XR250]

- 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.