Cantilever stairs

[Joel Yzerman]

Hi, I recently installed these , design was submitted to my engineer. We are fighting small vibrations on the treads.

I'm wondering if I can use a vibration app on my phone to see if it's unacceptable.

I realized that I need more posts to weld my stringer to in order to stop vibrations, issue is I can't fit anymore in the wall , there is an seismic x brace in the way.

What can I add to make this work ?

Stringer is c12x25/ treads are c10x15.3

I'm new here. Can I add Multiple pictures?

 

[LittleInch]

The easiest way is to add multiple individual pictures is in the thread using the camera IMAGE button and doing one at a time.

You can see the results in preview thread.

You can only add one attachment at a time and many people don't bother or can't download the attachment....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

That looks to me horrible and unless there's something on the end someone is going to end up with a very nasty head / eye injury, especially small children or drunk adults.

Teach the people to walk up next to the handrail....

Oooops, sorry there is no handrail!
Is this legal?

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Also: If you get a response it's polite to respond to it.

 

[GeorgeTheCivilEngineer]

A 'structural handrail' to tie the cantilever ends together would *probably* damp vibrations.

 

[LittleInch]

George, you're a philistine - don't you realise that would drive the stair designer / architect berserk and RUIN the whole look of the place.

What's a bit of vibration and injury to people got to do with anything!

Could you make the stringer a box section and also weld in some rectangular cross plates before adding the cover to the outside?

won't be easy now it's in place.

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Also: If you get a response it's polite to respond to it.

 

[GeorgeTheCivilEngineer]

George, you're a philistine

You are not the first... unlikely to be the last.

Just realised the stringer is a channel.

Yeah that needs to be a box section for sure.

 

[XR250]

You might want to try to add a cover plate on the channel to box it. That will help a bunch - but, yeah, that should have been a beefy box section.
Your engineer is a dummy to think a channel was a good plan.

 

[dik]

Paint it Safety Yellow?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JLNJ]

I'd like to see the torsion calc on that stringer.

 

[dik]

It looks like a large rect HSS section and not a channel... should be easy.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Enable]

dik: he says the stringer is a channel in the OP. I also made that mistake looking at it but apparently it's a C12x25

I'm with XR250 and GeorgeTCE. Probably would look at adding a plate on backside of stringer to box the section and then ensure the handrails on the opposing side are rigid / welded moment connections (edit - of beefy proportions) to help stiffen the free end.

 

[BulbTheBuilder]

Everyone has the same idea. That concludes it....Plates are very good at resolving vibration related issues (due to the stiffness in plane) in stairs depending on the usage. Adding the handrails, all are solid and you're ready to run down this stair.

 

[dik]

Sorry... stand corrected. The flange looked too wide to be a channel section.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleInch]

I've no doubt you could use your phone or something similar, but defining what is and is not "acceptable" is actually very difficult and what's ok to one person isn't to another.

Plus the weight and heaviness of feet is a huge variable.

So ok for a 7 stone ballet dancer and not for a 20 stone football player....

There's a good reason why these are not more popular.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BulbTheBuilder]

Sorry... stand corrected. The flange looked too wide to be a channel section.

OP mentioned the stringer is C12x25 with C10x15.3 treads.

 

[Joel Yzerman]

You guys , it's at a raw stage in the build , of course it looks dangerous and doesn't have a handrail yet lol they haven't even put drywall up, haven't you ever been to site (little inch guy)

It's being wrapped in some Dupont polymer sort of product for a modern look. Walls being furred out to cover the stringer.

Handrail is on the wall (stringer side) nothing attached to the open side, they are Installing some sort of cable wall separate from the stairs.

I welded alot of flat bar stiffeners inside the C section of the stringer (2) per tread top to bottom.

I also welded a 2x3/4 flat bar on the top flange of the stringer. To stop torsion.

As seen it's very strong, we have very little vibrations at this point.my eng is done with it I think and I can't determine the natural frequency of these stairs on my own, or can I with my phone ?

Boxing the channel I should have done in the first place yes.

The box plate would have to be at least 3/8 thick ? So about 14" wide , and can it be sections of plate or does it have to be one full length plate ? (Sections would be easier at this point.

The treads I welded as partial penetration welds 6mm throat to the stringer CWB 7018 stick.

My engineer did suggest adding a plate the open end , clients want an open look.

In the future, would say a 3x12 X3/8 wall rec tube be a better stringer ? Or keep using the channel and box it off ?

I found the rec tube stringer wall wants to bend , and I have no access inside to add stiffeners so I like using an open member like c channel.

Thanks very much for the responses.

 

[KootK]

I imagine that the handrail will be point fixed glass. Sketchy as it will be to rely on that for vibration control, it will help some.

In my experience, there is a good chance that turning the channel into a box will not get the job done, despite that being a generally fine idea. If that comes to pass, it will likely be because the connections between the stringer and its supports are, themselves, unsuitable for resisting torsion. So there might be some work to be done there as well.

I'm wondering if I can use a vibration app on my phone to see if it's unacceptable.

The trouble with that lies in deciding what will be deemed "acceptable". That will, usually, come down owner perception of footfall vibration of one person traversing the stair in a residential structure. Concerns for group lockstep etc are the domain of institutional stairs.

I had one stair vibration issue that went on for a couple of years. We added landing bracing, concrete filled the HSS stringers, and a bunch of other stuff. It still resulted in a cantilevered landing swaying 2" laterally under one person's footfall. In the end, the owner decided that it made for an interesting conversation piece for his guests and just left it as is. This speaks to the fluid nature of "acceptable" when it comes to serviceability issues on the sexy stuff.

 

[KootK]

So about 14" wide , and can it be sections of plate or does it have to be one full length plate ?

It can be sections that get nominally connected together at the joints in the field. Even without the connections, the plates might be enough to stiffen things up acceptably, it's difficult to say.

 

[Joel Yzerman]

The clients are happy with it, builders are too. Eng won't sign off.

No there is no glass or railing on the open end. Cable wall completely separate from the stairs, client wants a true open cantilever.

I'm on my own, but I have good experience with structure, just these eccentric loads/ structure are new to me.

I find that the posts (floor to ceiling) that I installed (4x4x1/4wall) helped the most, I'm going to maybe :

Put (2) 2x2x1/4 wall tubes , weld them together and make another post that will fit in front of the x brace in that wall and weld it to the stringer.

The vertical post make the tread crazy stuff , I just wish I could get more in there and I would have been done with this a month ago lol

I want to learn from my mistakes

http://www.cdfdesign.ca

is my website, I'm all about the weird, wild and challenging haha.

I really appreciate the responses !

 

[LittleInch]

Of course I've been to site, but we only know what you tell us and you didn't mention any of that information until now.... It did look a bit open, but thought that was maybe the look they wanted. There's no point in paying $$$$ for a special set of stairs if they are not on display

"some sort of cable wall" will be better than nothing, but open ended channel looks a danger to the construction workers before that goes in - "clients want an open look". Yeah right.

At least the hand rail on the stringer side will encourage people to walk closer to the stringer.

A picture of the open side of the stringer channel would be good.

Image function is best.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.