Stair Anchor To Main Structure

[surjaan]

I am designing steel stairs. What code equation will be the right to anchor the stair to main resisting system.Is there is a minimum lateral force that can be used to anchor the stairs?

 

[Ron]

Since you are in the US, you can use the loading in the International Building Code, unless your jurisdiction requires otherwise. For the IBC, the stair loading is 100 psf, applied to the treads. Resolve the forces from this loading.

For a typical 34 to 35 degree stair section, the lateral load is usually small. Apply the vertical shear at the top fasteners and horizontal shear at the lower fasteners.

Depending on the bearing conditions at the intermediate landings, they will be applied similarly or vertical shear will be applied at both upper and lower connections (unusual, but have seen it necessary).

 

[surjaan]

Thanks Ron,
I was told by the plan checker to use chapter 13 or chapter 15 equations to calculate horizontal force and then apply to the anchors. I think it is over killed.

 

[Ron]

surjan...the forces are what they are...Chapters 13 and 15 do not apply. Chapter 16 applies.

If you are a licensed engineer, you can evaluate as your judgment dictates, complying with the minimum provisions of the code.

 

[surjaan]

I was referring to chapter 13 or 15 of ASCE 7-05
Thanks

 

[Ron]

Sorry...I was assuming IBC. Chapter 15 certainly applies in your area; however, Chapter 13 is not likely to be critical in any case (except for slip and fall considerations!). Ice accumulation will not exceed the required live load.

Combining live load and seismic could be an issue. It is possible that those can occur simultaneously (evacuation of a building during/after a seismic event), so consider that in accordance with the load cases required in ASCE 7.