Crazy cantilevered steel deck

[DoubleStud]

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.

 

[KootK]

I love it. Sure, some vibration. But it's a clean and simple load path to design and trust. And the building envelope angle is slick. Even drainage slope on the top of the HSS.

Plus he gives us his details. I don't love the j-bolts in tension and feel that the footings are a little small for the OT but, whatever, if it works it works.

 

[Greenalleycat]

That looks pretty sick, I like it a lot
The flex looked reasonable for what it is, and I expect it'll stiffen up quite a bit once the decking goes on

The hold down bolt detail looks weak though - look how much reo is in the foundation relative to the shallow bolts
I would have cast in 500mm long bolts for that - not like the rods are expensive but would help me sleep at night

I find it funny that there is the thermal break consideration
I can only expect that the minor energy savings of the non-thermal bridge over the lifetime will pale in comparison to the energy required for the footing and steel framing that could have been avoided by a simpler detail using posts continuous to the roof framing etc
That said, I love the huge separation from a waterproofing perspective

 

[Enhineyero]

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.

 

[Greenalleycat]

Actual bolt lever arm is probably 250-300mm as they're outside the SHS, but it's a decent estimate
Not gonna lie, 67.5kN (or even 40-50kN) PER BOLT is quite concerning in my eyes
They're really shallowly embedded

Even if it calcs out, it seems to me that the weakest element in the design is the hold down bolts which isn't a great philosophy

Also, 67.5kN is a decent tension demand - what size are the bolts, I can't read the detail as it's blurry
Could the bolts yield in tension?

 

[DoubleStud]

Actual bolt lever arm is probably 250-300mm as they're outside the SHS, but it's a decent estimate
Not gonna lie, 67.5kN (or even 40-50kN) PER BOLT is quite concerning in my eyes
They're really shallowly embedded

Even if it calcs out, it seems to me that the weakest element in the design is the hold down bolts which isn't a great philosophy

Also, 67.5kN is a decent tension demand - what size are the bolts, I can't read the detail as it's blurry
Could the bolts yield in tension?

I zoomed in, it looks like 3/4" dia.

 

[Enhineyero]

Actual bolt lever arm is probably 250-300mm as they're outside the SHS, but it's a decent estimate
Not gonna lie, 67.5kN (or even 40-50kN) PER BOLT is quite concerning in my eyes
They're really shallowly embedded

Even if it calcs out, it seems to me that the weakest element in the design is the hold down bolts which isn't a great philosophy

Also, 67.5kN is a decent tension demand - what size are the bolts, I can't read the detail as it's blurry
Could the bolts yield in tension?

I couldnt read the details on the bolt. Hopefully they are 20mm dia, those usually work around 60kN if edge distance is at least 100mm.

Wish they could record a load test on it. install a spa/tub fill it 200mm with water, see if it works. He could title it "pushing the bounds of engineering for thermal efficiency"

 

[Nick6781]

Looks good

 

[LittleInch]

You wonder why he didn't make the plate on the base of the sport a bit larger to bring down the holding loads.

Just needs the fat guy test now....

 

[GeorgeTheCivilEngineer]

What about when they add a hot tub??

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.

I did think that but then the house is sat on the rest of that pad.

 

[Flotsam7018]

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.

Hopefully there’s some blocking or something for the center handrail post at the edges behind the 3/8 PL.

 

[DoubleStud]

I dont know, it feels scary to me that the whole heavy deck is literally being supported by only 4 bolts in tension. They should make the decking glass .

 

[duckhawk]

Nah. I'd prefer the cantilever to come from a long beam connected to the framing of the house, not a couple of 4-bolt baseplate connections.

 

[DrZoidberWoop]

Anything lacking structural redundancy between performance/serviceability and collapse makes me uncomfortable.

 

[Flotsam7018]

Nah. I'd prefer the cantilever to come from a long beam connected to the framing of the house, not a couple of 4-bolt baseplate connections.

Moments are resolved through baseplate connections all the time with much larger loads, if properly designed and detailed - no problem. Plus, you can make the arch happy with the drainage/thermal break detailing aspects which would be obliterated with a backspan beam into the floor framing.

 

[JAE]

In it's initial constructed state perhaps the numbers work out.

But this is outdoors and over time there will be concrete weathering and degradation.
It's in Columbia, Missouri, so freeze-thaw deterioration is a possibility - especially on a flat surface of concrete around the bolts.
Once the concrete cracks things will get worse very fast.

"J" bolts don't look right - agree with above that a deeper embedment would make me feel better.

Lack of redundancy always reveals a poor design. Where you can't get redundancy then additional safety factors should be considered.

 

[Ron247]

The appearance is extremely "clean and pleasant", but beyond that, I would have to know more structurally to be impressed. He walks out, lies about his weight, and does a little bounce. You easily see the deck move from the little bounce but there was already some deflection from him walking out slowly to the corner. Hard to tell how much existing deflection was temporarily corrected by his light bounce. While as engineers, we understand the deflection is to be expected, living with that deflection can suck. You never fill a cup of coffee too much and feel the bouncing anytime someone walks around on the deck. It is a lot easier if only 1 person is on the deck, but not so easy with multiple people. Get that cup of hot coffee tipped to your lips when some hefty person walks up behind you on the same joist you are on, and you wind up wearing the coffee. Having the decking will increase how fast someone walks on the deck, changes direction etc. as compared to his slow walk out and bounce while partially holding onto the railing.

Most of the deflection is probably from the joists, not the 2 columns. None of the compression faces have a flange, and the edge plates have no flanges. Back to Back Channels would have been a better choice. Tapers also affect deflection calcs whereas they do not affect internal loads. While adding the decking will help distribute the load, it also causes you to feel load at times due to the distribution. Distribution means loads in an isolated location partially route to another area.

I think the design load is 60 psf for a balcony such as this. That would be well over 7,000 lbs where he claimed to be 150. From what I saw, his profile matches the old Alfred Hitchcock profile from his show (only us old geezers know what I am talking about). He also said it was sturdy as can be while easily being seen bouncing some.

But, it is "Purdy".

 

[azcats]

Wonder if the center has more or less flex than the ends? IE, how torsionally stiff is that 12 x 4 HSS? Maybe the small HSS at the end mitigates some of that.

I share others' concerns about the AB size/embed. Also curious about the welding of the angle to the HSS.

 

[Brad805]

An 8'-0" cantilever does not seem that notable. Finding someone to pay for this on your typical residential project seems the hurdle. That anchor detail is terrible.

 

[Ron247]

Watched the presentation a 2nd time. Noticed the edge joist is a single angle, not a back to back. Bothers me a little due to torsion.

How many readers think the handrails reduced the vertical deflection to some degree when he was bouncing his petite body on it. I think they did reduce it some since the upper railing is tied back to the 8x8s.