Stair Stringers
Stair Stringers
(OP)
I am designing an aluminum stair stringer that extends from landing to landing. The tread for the stairs is typical aluminum bar grating. The bar grating is attached to angle which have been welded to the channel stringers. The stringers are 3' apart and are oriented as such ] [.
My question is: What should I assume for the unbraced length when designing the channel for flexure. It seems as though the angles and bar grating would help tie this thing together and reduce the unbraced length. Using the entire length of the stringer seems very conservative. If I do this, I end up with allowable stresses under 1 ksi.
Does anyone out there have any advice from what you have done in the past? Any codes (NAAMM, etc.) that could help me with this?
My question is: What should I assume for the unbraced length when designing the channel for flexure. It seems as though the angles and bar grating would help tie this thing together and reduce the unbraced length. Using the entire length of the stringer seems very conservative. If I do this, I end up with allowable stresses under 1 ksi.
Does anyone out there have any advice from what you have done in the past? Any codes (NAAMM, etc.) that could help me with this?






RE: Stair Stringers
Thread507-86850
RE: Stair Stringers
RE: Stair Stringers
Strength is not everything! Human comfort is a serious consideration.
Good luck
RE: Stair Stringers
RE: Stair Stringers
I use the entire length of stringers for my unbraced length. But, I design steel stringers so this is seldom a problem.
When considering deflection in a stair, I use a minimum of l/480. But to allow this in a long stringer would result in excessive deflection, bounce, and nervous people. I like to limit stringer deflection to 1/2".
Why aluminum? Corrosive environment?
RE: Stair Stringers
RE: Stair Stringers
If a structural shape is to fail due to compressive loading member will fail by bowing laterally, then I want the bracing to keep the channel from bowing. In this case, I don't think you need intimate contact with the top flange.
If you are analyzing the top flange in compression and determine that as an outstanding leg it will itself buckle, leading to a more global failure of the beam, then I think intimate contact is needed.
RE: Stair Stringers