Stair Design
Stair Design
(OP)
I'm reviewing an exterior stair design. The rise of the stairs is 16', the run is 25', and the stair width is 3'. There is no intermediate landing, so the stringers are continuous. This is an industrial stair, so the live load is 100psf x 5 per OSHA. The fabricator wants to use C12x20.7 stringers and put an MC8x8.5 channel across the midpoint of the stringers and support the stairs at midpoint with one column.
If you load the stairs uniformly, then I don't have a problem with the single column at midpoint. However, is it reasonable to load the stairs with an unbalanced condition of one side of the stairs? This would create a moment condition between the MC channel and the column.
If you load the stairs uniformly, then I don't have a problem with the single column at midpoint. However, is it reasonable to load the stairs with an unbalanced condition of one side of the stairs? This would create a moment condition between the MC channel and the column.






RE: Stair Design
I agree with your reasoning here.
Can you point me to a reference clause for the 100 psf x 5 requirement? That's a new one for me.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Stair Design
RE: Stair Design
RE: Stair Design
RE: Stair Design
RE: Stair Design
To your original question, I would definitely consider all load cases, including one span unloaded. Don't forget the axial load in the stair stringers as well.
Maine EIT, Civil/Structural.
RE: Stair Design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Stair Design
RE: Stair Design
RE: Stair Design
Maine EIT, Civil/Structural.
RE: Stair Design
RE: Stair Design
RE: Stair Design
RE: Stair Design
Also: you could pin the top of the column rather than welding it. A single large diameter bolt would transfer no moment.
canwesteng: I think the unbalanced moment is along the length of the stringer not across the width of the tread, and 500psf not 100psf. Meaning the moment is approx wL^2/10 = 25ft^2 * 1.5ft * 500psf / 10 = 46.9k-ft.
RE: Stair Design
Make the load as eccentric as you see fit, it shouldn't matter.
The OP should get some helpl with this beyond what he can find on the internet.
RE: Stair Design
RE: Stair Design
1) The stringers forming an up/down couple in bending similar to warping torsion in wide flange beams.
2) Flexure in the channel/column assembly.
The degree to which flexure in the column will resist stair rotation will depend on the degree of fixity at the column/channel connection. Most common connections would transmit substantial moment, even if unintended. For that reason, I believe that virat's concern is warranted. The connection and column should both be designed for some moment.
If I understand correctly, this is the situation:
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Stair Design
RE: Stair Design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.