Steel spiral stair on wood floor framing 6

[SleeplessEngineer]

Hi everyone!
I am very new to wood building design. I was asked to support this pre-engineered steel stair (shown below) on LVL beams. To me, it sound like a dump idea I would rathe run steel WF beams below the stair post to support it; but I was told this has been on many projects and this is norm. The detailing involves in steel bent plate on top of LVL and bolt through side ways. The stair post is welded to the bent plate.

[highlight #FCE94F][/highlight]I feel mostly the LVL (sized accordingly) can be sufficient to support load, but I'm just uncomfortable supporting this way. Perhaps because, I feel wood is not ductile, different flexural stiffness and so not compatible. Is this really common and I 'm just being irrational?

Thank you for reading my post! I appreciate your time.

 

[XR250]

You are being irrational..
Actually, LVL's are very ductile
There is no reason a properly sized PT LVL should not be able to support this.

 

[SleeplessEngineer]

Thanks for the quick slap in face lol! Always good to hear from others when I'm uncomfortable with somethings.

Thank you for reading my post! I appreciate your time.

 

[jayrod12]

In case you missed the one minor thing in XR's post, a treated LVL would need to be used. Not sure whether that is available in your locale. I know we can't get it where I practice.

 

[phamENG]

Check on availability of PT LVLs. They're spreading, but not everywhere yet. You may need to go with a treated PSL or treated Glulam depending on your local lumber market.

 

[SleeplessEngineer]

Thanks jayrod12 and phameng, yes I know about the treated requirement. but thanks anyway for your concerns that I might have missed it.
We typically call out PT LVL or PSL Plus for exterior beams. Mostly contactors here complain about PT LVL; I think it is not available readily and there is lead time to procure for special orders.

Thank you for reading my post! I appreciate your time.

 

[NorthCivil]

hope you live in a dry climate. I always prefer to never layer anything significant with high durability over something less durable.

Gonna be a real task to remediate those decks in the future when there is enormous steel staircases running through them. Ive always lived in wet climates though, where decks can only be counted on for ten-fifteen years max. this may be OK in a desert climate I suppose

 

[STrctPono]

I don't think you're being irrational. I also agree with NorthCivil, this would never fly in my climate. It's crazy to me that someone would design something like this and support it off a metal cladded LVL (regardless if it's pressure treated or not). This is outdoors. There is no way that you can stop weather from getting to that supporting beam. This staircase is vertically supported completely from the first floor, correct? Not at each floor level. To me, it's not a strength issue, it's a durability issue.

On a side note, I have a personal love interest with spiral staircases and even went so far as to build my own a few years back in my own home. Albeit, only one story... but I digress...

 

[SleeplessEngineer]

Thanks Northcivil and StrctPono
Yes exactly, it is only supported on the first floor wood framing. BTW, the deck is not gonna be metal cladded; the call out out is wrong and needs to be revised.
Also I'm not sure how this gonna be braced at each level with all wood floor framing. I was told, as the main structural engineer we only design the support for base. It doesn't not make sense to me. It would not fly past anyone in my previous company. Is this also reasonable???
I never thought residential design approach is so much different from other buildings design approach

Thank you for reading my post! I appreciate your time.

 

[phamENG]

For something like this, don't let the architect get away with not spec'ing flashing for all horizontal members. You need flashing on your beams, and at least flashing tape on all joists. In damp climates with decent maintenance, it can take a 10 year deck and stretch it closer to 30. I live in a very damp coastal climate; when I dismantled my in-law's 30 year old deck a few years back it took me 3 days to pry apart and I was able to salvage about 80% of the substructure for re-use on odd jobs. Ground contact and most of the decking material was gone, but joists and beams were in great shape. But they also maintained it annually with near religious devotion.

When materials are properly specified, details properly prepared and executed in the field, and the structure is maintained correctly even this kind of structure can last a long time. I understand this is a tall order and rarely happens, but it's not impossible.

As the EOR, you're responsible for making sure everything fits together. The stair can be delegated, but you have to make sure everything works around it. If they say they need bracing of X strength and Y stiffness at each level, it's your job to provide it. Things do happen a little differently in the residential world, but not that differently.

 

[NorthCivil]

When materials are properly specified, details properly prepared and executed in the field, and the structure is maintained correctly even this kind of structure can last a long time. I understand this is a tall order and rarely happens, but it's not impossible.

Designing for the worst case scenario allows you to make a lot of accomodation in the field, everyone loves an engineer who can be flexible and accomodate. Designing for the best case scenario leads to a very strict engineer on site, giving a lot of extra requests for additional work, generally being painful to the contractor, leading to change orders, extra site visits by the engineer, sleepless nights by the engineer, and anxiety for everyone involved (and usually less money for the engineer)

maybe what you can do, is at minimum get the lowest portion of the staircase supported on something decent. steelwork or concrete work. that way, collapse of the lowest and dampest deck does not lead to progressive collapse of the 3 decks above.

If you are a junior, I would look for somewhere else to work where you will get decent training. If someone was asking me to stamp this, I wouldnt. I would never buy a house built like this either.

The market is busy enough these days to not risk your neck on these idiotic architectural ideas. "We've done it many times before", yeah, how many times have i heard that...

One of the jurisdictions i practice in, there has been a huge push from AHJ's to have structural engineers include a clause on considerations for durability in their designs. explicitely to put the brakes on bad ideas like this.

 

[phamENG]

NorthCivil - I agree with you 100%. Mostly playing devil's advocate here. There's a flip side to it, too - nobody likes an engineer who always designs for the worst possible case, and they'll rarely get hired twice.

I do like your idea of compromising and putting some minimal steel below the stair and framing out around it with wood.

 

[XR250]

I did not realize it was only supported at the lowest level. It does seem like a bad idea due to the lack of redundancy.

 

[SleeplessEngineer]

Thanks everyone for jumping back in and clarifying further! I am glad I asked this here instead of worrying by myself!!
The problem I face in these residential projects (not all but most) is that things don't get coordinated and somehow project gets completed at contractor's own choice.
I am going add some notes to submit stair shop drawing ( I doubt we actually receive this, but I 'm just gonna cover myself) and to coordinate on bracing as required by the stair designer.
Agree with northcivil, there is always someone who cuts corners and accommodates clients. So we can't be too restrictive, need to look out for our business as well.

Thank you for reading my post! I appreciate your time.