folded stair in timber 5

[lesgiu]

Good Morning,

Does anyone have experience designing a folded stair in timber? Is it doable?

See attached picture for reference

http://st.houzz.com/simgs/6361cf11015f06ab_4-2130/modern-staircase.jpg

Thanks in advance

 

[JAE]

My guess would be that is a steel frame covered with a wood finish.

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[Brad805]

Looks like a render, but could be built as JAE mentioned.

 

[lesgiu]

Yes, the stair in the picture is a timber cladding. Just wondering if anybody has done it in timber itself.

 

[KootK]

To my eye, it looks like the stair is cantilevered from the adjacent wall. That could be accomplished in all wood. How they're getting the glass fastened adequately is another story.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[bigmig]

You hide a piece of tube steel in the wall (the stringer). Then cantilever HSS shapes out for your treads. Then attached a column on each end of your stringer (hidden in wall).
I've done 3 of these.

 

[jayrod12]

Definitely steel clad in wood. I just finished one of these. How would you make a moment connection in wood that wasn't bouncy as all hell?

 

[lesgiu]

I think the railing is connected to the side of the stair and then use a render over so it appears it's slotted in.

 

[KootK]

How would you make a moment connection in wood that wasn't bouncy as all hell?

I was seeing a concrete or CLT wall and some sexy European connectors the exact nature of which I am currently uncertain.

I think the railing is connected to the side of the stair and then use a render over so it appears it's slotted in.

That's my guess too. Maybe some vertical plates welded to the horizontal ones and providing locations for button-ish support.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

sexy European connectors the exact nature of which I am currently uncertain

If you come across said sexy European connectors available for North American use, let me know. Those damn Europeans always have the coolest things.

 

[JAE]

A similar steel option - this one didn't use wood but glass treads infilled within the steel frame of each step....with a sloping tube stringer hidden in the wall.

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[JAE]

The finished product:

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[HouseBoy]

I did this with steel plates (see pics).
Doesn't seem possible for long span condition in wood alone unless you can provide some intermediate supports.

 

[SwinnyGG]

I'm getting practical in my old age.

I look at that lovely modern staircase and my first thought is 'my.... that's a lot of glass to keep clean'

 

[Ingenuity]

I did this with steel plates (see pics).

That is a sweet bit of steel fab. Having recently personally fabricated a welded steel stair to a mezzanine I appreciate what that welder had to do to control any distortion.

 

[jdgengineer]

You all have done some pretty great stairs. How did you analyze them? Vibration considerations?

 

[HouseBoy]

To clarify - I only did the analysis and design. A very skilled craftsman did the fabrication. And he did a fantastic job.
Yes, the fabrication was sweet. They used the cut-outs to control it some, and the treads and risers were just a couple of bent plates, folded to follow the layout of the cut-out pieces. Basically we ended up with two flanges and four webs, zig zagging their way up.
Here are some pics of that (attached).

I had some fun with the analysis. I use Visual Analysis for all my work. It's produced by a company in Bozeman MT called IES. I would encourage anyone to check it out. Incredibly intuitive and very versatile. (I have no connection to the company. I just like the product A LOT).

Anyway, I started with simple deflection limit of L/720. After fabrication, deflection was fine (very close to the analysis numbers) but vibration was very bad. Analysis indicated Natural Frequency to be in the "very perceptible" range and sure enough, it was! The program allowed me to try several different strategies to "muddy up the stiffness" and in the end we anchored the bottom better and added a small prop near the base, essentially creating some fixity at the bottom two treads.

 

[JAE]

Our stair was a simple sloping tube inside the wall with a custom made "L" shaped frame for each tread that cantilevered off the tube.
The analysis was with RISA 3d and simply looked at the deflection at the end of the tread cantilever with a 300 lb. load - tried to keep it very small.
The tread frames were ultimately infilled with a glass tread surface with LED lights at the root of the cantilever.

After it was completed I stood on the treads and walked up the stairs - a bit of "bounce" or flex as you walked if you were going up near the end of the cantilever.
Probably more than I would have liked but not too bad. If you walked up the center there was no significant bounce.

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[Ingenuity]

To clarify - I only did the analysis and design. A very skilled craftsman did the fabrication. And he did a fantastic job.

Put that fabricator's phone number in your speed dial list.

It is a great thing when engineer and fabricator work closely to jointly create a great end result.