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Crazy cantilevered steel deck 7

DoubleStud

DoubleStud

Structural
Joined
Jul 6, 2022
Messages
512
Location
US
I found this video on youtube. What do you think of this deck? The guy went to the end of the deck and jumped a little bit, you can clearly see the deck moves up and down. At minute 3:55 he shows the structural detail.


 
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Wait, did he say he was 150 lbs? Not a chance!
Flotsam7018 said:
I’d prefer the joists to simple span to the front edge beam and cantilever an edge beam off the HSS post at each end. That may prove tricky to meet the arch’s minimal depth at the front edge though.
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That would be my choice as well. Looks like the 12x4 tube steel is in torsion. Seem a bit spindly for this situation.
 
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That balcony is a little bouncy under the load of one person. What happens during a gathering when they "show off the slick new deck".
 
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EngDM said:
That balcony is a little bouncy under the load of one person. What happens during a gathering when they "show of the slick new deck".
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My guess is no engineer involved in this design. I don't see how the numbers work out. The HSS12x4x1/4 is doing all the work. Of course it is bouncy AF.
 
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For something that small, I could see a 12x4 "working". Or, at least, it wasn't red on the RISA model. I doubt anyone considered twist in the deflection checks, though, and I seriously doubt they checked vibration.
 
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Not liking the look of this design.
Balconies can attract sizeable gatherings/parties etc. and there's many cases of collapse in recent years.
 
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XR250 said:
My guess is no engineer involved in this design. I don't see how the numbers work out. The HSS12x4x1/4 is doing all the work. Of course it is bouncy AF.
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That is my consensus. Since the HSS attaches to the two 3/8" plates with no flanges, I wonder how much it serves to make the joists act more simple span than cantilever. The edge angle is only intermittently welded to the plate. It would take a 3-D model that is accounting for the tapers to better understand the force distribution. The guy in the video is more of a salesman than an engineer. If they somewhat designed this with a bunch of 2D logic, there could be several problems.

From what I see, the HSS 2.5x4 cannot be fix-fix, the 3/8" plate has no real torsion resistance. That makes it SS. The deflection of the 3/8" edge plates makes load distribution a little dicey.

The designer hopefully explained how the final product will function, and they are fully aware of the magnitudes. Not "there may be some minor movement", but you will Wobble Like Weebles during brunch (another old reference).

Also, this guy cost me a good bathroom scale. Being slightly larger than what he appears to be, I weighed myself expecting 160 to 170 with a 180 absolute max. When the scales indicated much more than 180 lbs, I tore it up and threw it out in frustration. I am sure my wife will understand (or at least take pity on me).
 
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I'm with the others here, the anchors look like the weak point. I would have at least had heavy hex headed anchors for anything with reasonable tension or moment. J-bolts aren't that great in tension. A single 3/4" dia. J bolt with 12" embed with tension only is going to give you about 3700 lbs ultimate tension, IMO these are under designed for this use.

The vibrations are expected, however I bet it wasn't even a concern and IMO should have been checked and should have been a design consideration in member size selections.

Overall I'm not impressed by the design and have my issues/concerns with it without running any real numbers. Not saying it can't be made to work, but I definitly see some weak spots which leads me to believe it probably wasn't engineered properly if at all.
 
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Not a fan at all.

The anchor bolts detail and the bearing on the RHS tube in particular. I’d be surprised if the numbers work.

10mm bounce is a lot for a “150 lb” guy.

Backspan cantilever is vastly superior.
 
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This is impressive architecture. The steel fabrication and overall construction appears top notch. And I really like how it's not connected to the building in terms of a clean waterproofing detail.

With that said, even if it works on paper, I wouldn't be brave enough to design something like this. It's asking a lot of 4 anchor bolts with no other redundancy. Maybe if the railings were structural and tied back into the building to provide some extra redundancy I'd feel a bit better about this. The thought of a 4th of July party on it in 20 or 30 years scares me, after the anchor bolts could have potentially corroded and the concrete spalled. I doubt anybody will be inspecting this critical connection in the future, especially if it's a residence.
 
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Eng16080 said:
Maybe if the railings were structural and tied back into the building to provide some extra redundancy I'd feel a bit better about this.
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This is a good idea. As an example, an 8tall x 4wide x thick-as-hell tube for the upper rail welded to the 8x8. Post struts you to the floor.
 
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Eng16080 said:
This is impressive architecture. The steel fabrication and overall construction appears top notch.
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I agree, the fabrication is clean, good looking welds and great fit of materials. I was in the fab business for a brief while; it is hard to do that quality of work on a consistent basis.

I need to stop watching the video, I see something every time I did not see before. At 8:45 into the video, you see under the angles. The angles look like 3/16" thick or 1/4" max to me. The gap between angles is supposed to be 3/8" like the angle thickness. Look at the gap where the 2x4 diagonal wood brace is on the middle set of angles in the picture. That gap looks a lot wider than the angle thickness.

I do not see any stirrups around the pier stem where the house loads are at. Would like to see one or two at least since the deck is trying to rotate part of the stem away from the other part this is somewhat stabilized by the house floor framing.

The lack of redundancy gets amplified by the lack of water protection at the base plate. With a grouted gap, water can seep in but may not get out so easily. Increases the chance of rust-out.

I am not saying it does not work from a stress perspective, but I am concerned with serviceability and longevity.
 
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Aesur said:
I'm with the others here, the anchors look like the weak point. I would have at least had heavy hex headed anchors for anything with reasonable tension or moment. J-bolts aren't that great in tension. A single 3/4" dia. J bolt with 12" embed with tension only is going to give you about 3700 lbs ultimate tension, IMO these are under designed for this use.

The vibrations are expected, however I bet it wasn't even a concern and IMO should have been checked and should have been a design consideration in member size selections.

Overall I'm not impressed by the design and have my issues/concerns with it without running any real numbers. Not saying it can't be made to work, but I definitly see some weak spots which leads me to believe it probably wasn't engineered properly if at all.
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Well it works, until it doesnt. Hopefully nothing bad happens.

A good case and point on why its hard for a common person to judge what is engineered well and what is not, just because it looks 'nice' and 'well built' doesnt mean it was constructed with good engineering.

Hope this message reaches the designer of this deck. Wish he would do the right thing and engage an engineer to make sure everything checks out before the deck is used. He can always add post at the cantilever ends, its not aesthetically pleasing but its safe.
 
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Unlike other here I'm not excited by this. Personally I'd considered it too bouncy based on the visuals.

And the like others have said the footing and the anchors don't inspire complete confidence. Sure I'd expect it to mostly work. But it is a deck which are well known for congregated crowds. If the crown moves together to music this would be a trampoline!

The ductile and flexible steel members will at least give plenty of warning. The anchor bolts or footing rotation not so much.
 
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I would at least use all thread with nut and peened thread embedded pass (plus maybe 6") pass the development length of vertical rebar.
 
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Enhineyero said:
Crunching some numbers based on his drawings:

Width = Joist at 600mm cts x 8 = 4.8m
Length = 2.5m

assume DL = 0.5kPa, LL = 2kPa
Design UDL = 1.2 x 0.5 + 2 x 1.5 = 3.6kPa
Max Moment per column = 3.6 x 4.8/2 x 2.5^2/2 = 27kN.m

Column: 200SHS

Tension on each anchor bolt = 27/0.2 x 0.5 = 67.5kN

The anchor bolt tension is decent but nothing concerning.

I'm more concerned if the footing supporting the post is a shallow isolated footing, he might need to get it checked such that it wont rotate due to the pure bending moment being applied by the post.
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The weight of the L178x102x9.5 (SW=0.198kN/m) spaced at 610mm is 0.65kPa alone, add to it the weight of wood deck, and railing system distributed over the whole deck(just to simplify) you'll get significantly more then DL=0.5kPa and I am pretty sure balconies are LL=4.8kPa
So no, it doesn't check out. but like others have said there was no engineer involved.
 
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Struct123ure said:
So no, it doesn't check out. but like others have said there was no engineer involved.
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Hmmm. So as licensed engineers who are aware of a design that is being constructed that doesn't meet code and poses a risk to public safety and welfare - is there an obligation to speak up?

Some years ago I attended an all day structural seminar in Austin, TX, and one of the professor speakers noted that a three story steel framed office building was being constructed next to their test facility and they watched it frame up each morning as they drove in to work. They noticed a flaw in the design from a distance (lack of vertical stiffeners in the beams running over columns) and finally decided they needed to act and contacted the engineer of record to inquire. Stiffeners were then added.
 
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JAE said:
is there an obligation to speak up?
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I'd say yes. Though, of course, if I did it somebody would surely file a complaint with the board that I was practicing engineering without a license.

Anyone here with a Missouri license that can send a note to the building official and/or reach out directly to the guy who posted the video?
 
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though it shouldn't be an accusatory message - more of a 'hey, I noticed these things that didn't look right to me. I want to make sure there was a competent engineer involved the design of this structure that so clearly goes beyond the limits of the IRC."
 
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