Curved plywood stair stringer
Curved plywood stair stringer
(OP)
My client is removing the existing bearing walls below the sides of a curved staircase. See the attached pdf plan view with dimensions.
Although the loads are relatively light, DL = 80plf & LL = 120plf I opted to use curved steel stringers, but the Architect came back with, "I would rather use curved plywood stringers." Not sure why, probably trying to save the owner money.
I am a little apprehensive about having some yahoos constructing this in the field. I can just see these guys squirting Elmers glue on the plywood then trying to clamp it together...with something like duct tape.
Has anyone had any experience with specifying a curved plywood beam? Or any input would greatly be appreciated.
Although the loads are relatively light, DL = 80plf & LL = 120plf I opted to use curved steel stringers, but the Architect came back with, "I would rather use curved plywood stringers." Not sure why, probably trying to save the owner money.
I am a little apprehensive about having some yahoos constructing this in the field. I can just see these guys squirting Elmers glue on the plywood then trying to clamp it together...with something like duct tape.
Has anyone had any experience with specifying a curved plywood beam? Or any input would greatly be appreciated.






RE: Curved plywood stair stringer
BA
RE: Curved plywood stair stringer
I wouldn't trust field built plywood stringers.
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P.E. Metallurgy, Plymouth Tube
RE: Curved plywood stair stringer
RE: Curved plywood stair stringer
I would start by reading the various supplements related to Plywood Design Specifications produced by the APA. I started my design for simplicity sake assuming the stringer was straight, then added from there to account for the curve. I was very conservative, many thin plies bonded together. You need to stagger the joints, account for the joints in your analysis, etc... The plies were adhered together with structural wood adhesive (there are standards for the type of adhesives for wood)and lots of structural screw fasteners. Only the screws were accounted for in the design, not the glue. Everything was shop fabricated by a very good stair builder then brought to site and erected.
All the above being said, my preference would be for curved steel stringers clad in wood. Simpler and less time consuming to design and fabricate.
RE: Curved plywood stair stringer
I would specify a "shop fabricated" stairs and then list pre-qualified fabricators. I suggest that you contact a company like "Arcways" or others whose specific business has been to build and install curved stairs, curved handrails, "Juliet" balconies, etc. for many, many years. Do NOT use someone who is inexperienced in this type of construction. Request a list previous projects, photos and visit one of their nearby projects. Check CSI to see if they have a specific spec. for this specialty.
PS Indicate required radius on your drawing.
RE: Curved plywood stair stringer
I think that the Architects reason for using plywood is to cut cost for the homeowner, but the way I see it steel stringers may be comparably priced considering the labor intensive process of fabricating the plywood stringers.
Thanks guys, that helps.
RE: Curved plywood stair stringer
RE: Curved plywood stair stringer
The information that I previously provided is still applicable.
If your Architect wants you to design the structural details of the stairs, you can suggest that he use a "Performance" Spec where the fabricator can provide everything needed including the structural calculations. Sometimes it is better to engage an expert to do the specific design rather then to take on something that you are unsure of.
I hope this helps!
RE: Curved plywood stair stringer
Thanks for your help
RE: Curved plywood stair stringer
I love walking through their building as seeing the different stairs ready for shipment.