Stair Design Live Load Exemptions 5

[dik]

I have a recent project that has an exterior six storey exterior stair. It is an industrial facility and there will be limited access. The stair is normal with about 10' floor to floor. It consists of landings at the top and bottom of each stair with metal grating stairs connecting them. the stairs are exposed to wind and the elements. This includes snow loading. The wind load is not an issue and I will design them for wind exposure and provide lateral bracing. Other than being outside of the building footprint, it looks like a normal stair, but in steel with grating.

I would normally design these and the landings for 100 psf live load and about 25 psf dead load (actual weight).

With ladders and ship ladders, the load can be considered as point loads at discreet locations. Is anyone aware if any of the safety codes have a design criteria that allows a lesser load than 100 psf for the entire six floors? Are there any exceptions? The reduction in loading is mostly for the foundation design; it will have little impact on the design of the stair elements.

Thanks, Dik

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

dik - I've always approached these as I would a catwalk/walkway. Biggest question: is it in the egress path for a normally occupied space? If so, then I design it for 100psf. If not, and it's only accessing an area that is occupied for maintenance or similar operations, then I design it for 40psf or 60psf with 300lbf point loads depending on the application and governing code.

 

[Lomarandil]

I'm with Pham (there's a niche t-shirt opportunity in here somewhere)

 

[dik]

Thanks gentlemen... The foundation design loading is the concern... maybe 2 or 3 300lb point loads per floor and a 50 psf live load overall.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JLNJ]

I don't see in ASCE 7 where stairs are not eligible for live load reduction. The Live Load is not in excess of 100 psf. Table 4-1 does not exclude it.

It seems reasonable to me, even if it's a code-required accessible means of egress stair. You might have other non-structural issues to address (uncovered exterior stair, open risers, non-solid treads, etc.).

 

[dik]

Live load reduction, because of the limited area is not very helpful. The stairs will be sufficiently strong. It's matter of deciding on the foundation loading. At most there might be a few people on the stair.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[jayrod12]

I think if you were to do 50 psf on all horizontal surfaces, you could likely bypass including additional point loads when it comes to foundation loads.

 

[dik]

Thanks jay... I was thinking of using 50psf. For lateral loading, with 1/50 wind load and gust and wind pressure coef the wind load will be just a little under 30 psf. I'll assume exposed elements account for 40% of the total area. I'll plug the numbers into my SMath load combination to determine max and min loads.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[HTURKAK]

Mr. DIK,

I will suggest you to look PIP STC01015 (Process Industry Practices Structural Design Criteria ). The min,mum LL for stairs and exit ways , 100 psf (Uniform) or 1000 lb ( concentrated ) which ever more stringent ( uniform and concentrated loads will not be applied simultaneously.) I have copy and pasted the relevant excerpt from PIP STC01015.

Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[dik]

Thanks HTURKAK... I'm trying to avoid the high live loads for the foundation design. Individual elements will be to regular stair and platform and platform loading. It just the foundations that I want to reduce the loading for. Thanks for the load data... filed away, it's good data to have. I should have added... it's just Dik.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik