Curved Stair Stringers
Curved Stair Stringers
(OP)
I have a client that would like a curved set of stairs between the main and upper floor of their custom home. The layout of the house does not allow for any intermediate support of the stringers. The concept has the stairs curving a total of 90 degrees with open treads. The stair contractor is proposing multi-laminations of plywood be used for the stringers. I have not used plywood in edgewise bending before.
Using a design live load of 40 psf and assuming edgewise bending of the plywood, I have calculated the minimum number of laminations of 3/8" plywood based on bending, shear and deflection of an idealized stringer without the curve.
I believe the loading on the curved staircase will produce a significant amount of torque top and bottom of the stringers. Does anyone have any information/suggestions on how to calculate how much resistance a multi laminated plywood stringer would have to torque??? None of my wood reference manuals seems to contain any information specific to this type of application.
The connection top and bottom is another question .... I am thinking of bolting the stringers to 3/8" thick steel knife edge plates inserted into the end laminations that are then welded to a backer plate that is lagged to the stair opening. Any suggestions???
Thank you!
Skiis and Bikes






RE: Curved Stair Stringers
Again, I'm sure others will comment, but I think you are supposed to avoid torsion in wood.
Can you talk him into a small piece of tube steel? It would be much smaller and would look nice (my idea of nice in this instance means very small compared to what most people might expect, this would usually get people thinking right away).
Don't forget to check vibrations.
RE: Curved Stair Stringers
Call a manufacturer and he might be able to give you some guidance.
http://www.arcways.com/
RE: Curved Stair Stringers
RE: Curved Stair Stringers
Jike - Thank you for your comments. The request came from the stair contractor, they have never built unsupported curved stringers and requested engineering. This is the first request I have had for calculations related to a staircase, therefore the questions.
OCI - Glad to hear you have similar experience. At this point I have 10" depth below the treads and am in the ballpark with 10 laminations of 3/8". Do you have any information on how your stringers were connected top and bottom?
SkiisAndBikes
RE: Curved Stair Stringers
RE: Curved Stair Stringers
RE: Curved Stair Stringers