More Weird NYC Engineering

[kissymoose]

Check out this connection WSP came up with for a 66 story Manhattan skyscraper. They've got outriggers transferring vertical load into the core and horizontal trusses at the same location (they said some of the outrigger members are designed for 11,000 kips), coming in at varying angles to one point, so they decided the most economical thing would be to forge big ole cubes of steel to weld the members to. Some of those bad boys are probably around 3 tons by themselves.

 

[structuralCADspecialist]

I'm more of a concrete guy but I'm no stranger to seeing engineers use massive amounts of materials.

American jurisdictions would do well to keep a very close eye on any Canadian Engineering firms performing work on their turf. I know of at least a couple engineers who've gotten in trouble in Canada yet continue to perform work in the U.S. unabated. I should mention however that this company is pretty global (meaning they hire local talent) and doesn't have any strikes against them as far as I know.

 

[bones206]

Another recent project with solid forged nodes:

https://lsc-pagepro.mydigitalpublic...icle_id=3901119&view=articleBrowser&ver=html5

 

[kissymoose]

Another recent project with solid forged nodes:

https://lsc-pagepro.mydigitalpublication.com/publi...

That sounds very familiar to this Hudson Blvd building, with the exception that they started off with the EOR doing a lot of the connection design and using BIM to coordinate design with fabrication. They even used a steel core for erection before embedding it in concrete. However, your article gave a number. The largest node was 3' x 3' x 10' and weighed 22 tons!

structuralCADspecialist, I'll be honest, I didn't even know WSP was Canadian. They've been doing crazy buildings in NYC for quite a while now, and with how cutthroat that area is, I'm confident this node design is in the best financial interest of the developer. The article does mention how comparable designs would require extensive fabrication (like welding) which I expect ended up more expensive.

Maybe I'll through in a 2' x 2' x 2' hunk of steel in my next portal just for kicks.

 

[structuralCADspecialist]

...and with how cutthroat that area is, I'm confident this node design is in the best financial interest of the developer.

It came as a huge surprise to myself when I first learned of it but there is little incentive on the typical Structural Engineers part to make the structure as economical as possible, especially with real estate being as crazy as it is right now. Developers want it built and there hands clean of it ASAP. Profit margins are high enough that they can get away with economically inefficient designs. And the consultants aren't really rewarded if their designs result in a project that costs much less. Keep in mind these comments are coming from someone who's much more knowledgeable about concrete than tall steel buildings. These nodes may in fact be the best solution. But never think that a developer actually has someone in-house that knows enough about structural design to say whether or not their design is efficient. If they make their 20% return their design was efficient from their perspective. And even if the consultants could have made it 25%, exactly 0% of that would find it's way back to the consultants.

I've seen projects where a value-engineering consultant was used. After their review there were still huge hunks of concrete where it didn't need to be, as well as poor rebar detailing practices. But I think this was the result of someone deciding to pay the lowest possible fee to their main consultant, followed by a trip to the bargain bin for their 'value' consultant. Since many value engineering consultations are done by the same firms that (kind of) chase the same work and compete against one another, they are often too chicken to really critique another firm due to fear of reciprocation when the roles are reversed (or are simply not good enough to design things better).

I think there is a lot of money in good designs. Or even just designs as good as they were 10 years ago. I've been pondering ways to convince ownership groups (and design build contractors) of this. I'll mention again that I'm only involved in concrete construction. Those tall steel buildings look like they are design by people who are at a much higher level than the one's I'm likely to encounter.

 

[kissymoose]

I would imagine the most economical design in this area is the one that gets the job done faster.

I've seen projects where a value-engineering consultant was used. After their review there were still huge hunks of concrete where it didn't need to be, as well as poor rebar detailing practices

Value engineering can be such a complicated thing, and it seems many clients can be penny wise, pound foolish with it. You have to juggle engineering cost, amount of materials used, amount of labor in the form of fabrication, shoring, forms, etc.., collaboration with the rest of the design team (risking making your design easy, their design harder), simple ease of construction and complexity of the design, among others. Meanwhile you could have value engineering save you some steel tonnage and as a result, completely miss having fabrication and erection time increase, higher chance of construction errors, other consultants having to find different loads paths, etc.

 

[hokie66]

I wouldn't say that WSP has an unblemished reputation. They do tend to stretch resources far and wide.

https://www.planning.nsw.gov.au/-/m...wer-investigation-final-report-2018-02-22.pdf

 

[sauce_man]

You realize the Australian office of WSP is not the same as NYC's building structures group right?

 

[hokie66]

Yes, of course the offices are different. But my comment was in relation to structuralCADspecialist's statement above that WSP Global "doesn't have any strikes against them" as far as he knows.

 

[sauce_man]

ahh fair enough

 

[human909]

In my experience on the projects I work on it is rare for me to see much value engineering going on regarding structural engineering designs. I've seen massive overspends simply because the structural consultants are lazy and have no incentive to minimise cost.

I've seen massive truss structure build to span tiny distances with low loads simply because in an early, early concept design some process designer drew a stick truss in instead of a stick beam. On a current project I see columns used that are about twice the weight that are needed and massive tubular bracing members going to a dead end load path point. (AKA they are not needed because they won't take any load whatsoever.)

Honestly it boggles the mind how much money is wasted on projects that I see just by incompetent structural design. It might be because many big firms in Australia deal more with concrete than steel. I still haven't figured it out.

 

[bookowski]

These massive nodes are becoming somewhat common in nyc for highrise with complex connections. I've only had some limited peeks behind the scenes but from what i've heard the analysis/design is not as high tech as you'd imagine. Often the non-elegant solution is best. A lot less brainpower at every step to have a massive blob of steel. Check out the nodes on the moma tower which are used to join rebar nodes in a concrete frame:

https://www.structuremag.org/?p=11647

 

[Tomfh]

big ole cubes of steel

When I was a junior engineer I was faffing around with some truss detail. My non engineer friend told me all that nonsense was a waste of time and I should just make it a solid block. How right he was…

 

[bones206]

Seems like these connections are driven by high brace forces, which are a result of having fewer, concentrated lateral elements doing the work rather than a more widely distributed system. I can see how that’s driven by the value of a square foot in NYC, but not a good idea from a resiliency and redundancy standpoint IMO.

 

[kissymoose]

not a good idea from a resiliency and redundancy standpoint IMO

Just a guess, is this due to a movement towards larger, open spaces in the floor plan?

 

[bones206]

I’m sure that plays a role as well.

Personally I’m looking forward to the AISC Design Guide for Volkswagen-Sized Solid Steel Block Connections

 

[JLNJ]

What are the issues around welding to such a beast? I'd hate to find out in 20 years that these welds were not well understood and fail prematurely (see: Northridge moment connection failures).

 

[bones206]

I had the same concerns. Hard to detect defects, could be unforeseen failure modes with those big forgings like delamination or local tear out that haven’t been vetted out through rigorous testing. I’m sure the connection engineers did their due diligence to address these kinds of concerns, but it does seem like a novel design typology that should be scrutinized and tested.

 

[Tomfh]

Would they do cyclic testing on these sort of novel joints?

 

[bones206]

Just noticed that Cast Connex offers these solid steel blocks as an engineered product:

https://www.castconnex.com/products/high-integrity-blocks

They claim to have done a lot of R&D.