wood stair stringer design
wood stair stringer design
(OP)
I have a interior stair design in a public building. Client wants all wood construction for ease of fabrication. Residential live load in Canada for stairs is 40 psf, but for a public stairway live load is 100 psf. The stringer is 18 ft long between landings. A 2x12 stringer with a 12" run and 7" rise results in only 5.5" of actual cross sectional depth, so for load carry capacity the stringer is really a 2x6. No resonable number of 2x6 wood members can span 18 ft and support 100 psf. Any ideas as how to support the stair treads for this load besides stringers spanning bewteen landings? (In wood framing)






RE: wood stair stringer design
Try a microlam or parallam, or 4X12 or 6X12 stringers? I see 6X12's used a lot ads exterior stringers with no cuts for treads in apartment buildings. Treads are bolted to inside of stringers.
Mike McCann
McCann Engineering
RE: wood stair stringer design
One thing you can do is use a full depth stringer (i.e. don't cut it for the treads) and then add triangular steps on top of it to support the treads. That way you have the advantage of a full section to span the distance.
First choice though is to add an intermediate post to cut the span.
RE: wood stair stringer design
If there are walls on each side of the stairs, you can nail the stringers directly to each stud.
RE: wood stair stringer design
To make the 2x12 members work I specified two intermediate support walls or posts located at the third points of the span. If the contractor can not locate 2x12's that long he will have to use an LVL to get the extra length.
RE: wood stair stringer design
If your 5.5" depth only just works then any overcut of the triangle for the stringers will reduce the capacity significantly.
Have you considered a fletch beam with a 5" deep plate?
Or provide a timber beam with triangular spacers over (less cutting than cutting it out of the stringer).
csd
RE: wood stair stringer design
RE: wood stair stringer design
RE: wood stair stringer design
Thanks again