Curved Stair Stringers
Curved Stair Stringers
(OP)
Hello, thank you for sharing your knowledge and experience!
I'm looking at stair stringer design for a curved stair, centerline radius 14'.
Q1 - What are the design parameters, allowable bending, slenderness ratios, torsional properties, for a using a plate stringer rather than an MC12. (I have the NAAMM Steel Stairs Manual already.)
Q2 - Lateral bracing. I agree that the risers stiffen the system to provide lateral bracing for regular bending, even though the compression flange (MC12x10.6) is still 'flying' in the breeze. For torsion, it looks like the loading eccentricity is relative to the stringer supports (10 to 15 feet) and the torsional supports are the riser attachments (1.5'). So I get torsion based on 1.5' eccentricity between 10' stair supports and apply that torque value over the 18" distance between riser connections.
The owner doesn't want to use a closed section (add 3/16" plate, go to TS12x2x3/16).
I'm looking at stair stringer design for a curved stair, centerline radius 14'.
Q1 - What are the design parameters, allowable bending, slenderness ratios, torsional properties, for a using a plate stringer rather than an MC12. (I have the NAAMM Steel Stairs Manual already.)
Q2 - Lateral bracing. I agree that the risers stiffen the system to provide lateral bracing for regular bending, even though the compression flange (MC12x10.6) is still 'flying' in the breeze. For torsion, it looks like the loading eccentricity is relative to the stringer supports (10 to 15 feet) and the torsional supports are the riser attachments (1.5'). So I get torsion based on 1.5' eccentricity between 10' stair supports and apply that torque value over the 18" distance between riser connections.
The owner doesn't want to use a closed section (add 3/16" plate, go to TS12x2x3/16).






RE: Curved Stair Stringers
Off the top, I would suggext that a MC 12 is light for the intended use and if it will support the loads, you may end up with the biggest helical spring I've ever seen. For thee geometry, I'd be expecting an HSS 4x12 type of secion.
Dik
RE: Curved Stair Stringers
As far as using a rectangular bar for the member, it should simplify the calcs. Not to say it will be adequate, but calcs will be simplified. Look for torsional properties in Roark or other engineering references. The 4x12 tube sounds like a promising member from that standpoint as well.
RE: Curved Stair Stringers
Dik
RE: Curved Stair Stringers
I think I'm going for a 3/16" cover plate on an MC12x10.6.
I downloaded the RISA3D demo and am working on the model.
Thanks for your comments.
RE: Curved Stair Stringers
As for the model, you can do one in AutoCAD and export a *.dxf file... kinda klunky but it sometines works...
Dik
RE: Curved Stair Stringers
RE: Curved Stair Stringers
Dik
RE: Curved Stair Stringers
RE: Curved Stair Stringers
In any event, rolling the HSS tube will distort it somewhat. You do, however, have a fairly large radius...
dik
RE: Curved Stair Stringers
The shop said that rolling a tube was not an option. From your comments I can see that the channel may also be a challenge.
I guess I was headed in the right direction with the plate stringer. I'll have a look at that.