Single Stair Stringer

[jimtheengineer10]

Does anyone have an experience or references for designing stairs with a single stringer in the middle? The owner would like to use wood. I am looking for ideas for stinger size/material and how to fasten the treads to the stringer. Thanks.

 

[CANPRO]

The stringer would have to be fairly wide to make a decent connection with the treads. Maybe some braces from the bottom of the stringer to the underside of the treads?

The connection at the top and bottom will be tricky. Especially when you consider the potential of unbalanced load and the torsion at the ends. You might have better luck with 2 stringers spaced apart and centered under the treads so you still get some cantilever on the treads.

 

[boo1]

Houzz shows some see:

http://www.houzz.com/single-stringer

Looked like most are steel tubing or big gluelam w steel frames holding the treads and handrail.

 

[dhengr]

Those are certainly interesting architectural pictures. The problem is that hardly any of them show which building code they were designed to, or which AHJ blessed and permitted them. Architects (and homeowners) think they can do anything, if they think it is pretty. The rest of us have to deal with the laws of physics, statics, strength of materials, serviceability, etc. With enough money you can do damn near anything. Since you are talking about timber framing and the like, I’ve seen single stringers made out a large log, and more or less cut out with a chain saw. How you hold the cantilevered treads down to the stringer, and how you make the handrails comply with today’s codes will be the problems.

 

[BAretired]

Personally, I would favor an HSS because it has good torsional resistance, but if the client wants to do it all in wood, it will be a fairly bulky member.

BA

 

[msquared48]

Yea... Nothing like using an 8.75 X 9 glulam!

Mike McCann
MMC Engineering

 

[Ron]

Agree with BAretired; however, you could encase the HSS in wood to make it look like the owner wants. Otherwise, as Mike noted, a hefty glulam will likely be necessary, depending on the span. As for the tread to stringer connection, I would use upside-down steel saddles, through bolted through the stringer. If you use the HSS, you could provide a welded flat plate on top to hold a wood tread, but would have to be a beefy plate.

Watch out for torsional shear from tread-to-tread, oppositely loaded.

 

[jimtheengineer10]

thanks for all the replies. The homeowner would like to use a single stringer for the bottom 4 or five treads and then switch to conventional stair construction so the span will not be that much.

 

[ToadJones]

Go with a no stringer set of stairs.

We did that once with a structural railing that supported the stair treads.
Railing worked like a truss.