Application of Guard Rail Load on Stairs 1

[phamENG]

Working on some shop drawing calcs for a fabricator client, and I've run into an issue that I want to take a closer look at. IBC 2015.

Everything I've done with this fabricator to date has been steel, but this is an aluminum project and includes guard rails - both for elevated platforms and stair rail systems (combined 42" guard with hand rail set at 36" above treads and connected to verticals on the guard). Unfortunately, it was bid and detailed like a steel system with 1-1/2 pipe at 4' on center...not even close to working. Before I go back and tell him he has to double his material, I need to sharpen my pencil a little. The architect classified this building as U, so I don't get to take advantage of the 20plf allowed for I-3, F, H, and S. 50plf and 200lbf point load.

When we apply live loads to a sloped surface (roof, ramp, stair, etc.), we apply it to the projected surface. So if you have a 100psf stair live load and a 3' wide stair with a 8' rise and 12'10" run, total live load would be 3'x12.8333'x100psf=3850lbf even though the actual sloped surface is about 15'2". The idea being that people or material occupy the vertical space above the surface and not the space perpendicular to it. Has anyone applied this concept to stair rails? So on that same stair, your rail has a run of 15'2", but the equivalent occupancy is only 12'10". In other words, you can't have enough people on the stair to apply the 50plf contemplated by a horizontal rail. So the rail would be designed for a load of about 42plf rather than the full 50.

Best bet is probably to just stick to the 50plf along the rake, but I'm curious to see if people are doing something different elsewhere.

 

[phamENG]

Pretty sure we're confusing everyone.

When I say concurrent loading, I mean:

Apply either the point load OR the UDL to the guardrail while concurrently applying the occupancy live load to the treads of the stair or joists on the platform supporting the rail. See Ron's post above.

Mike Mike - IBC doesn't say anything about not applying it with the occupancy load either, and it says it should be applied in accordance with ASCE 7. (Don't mean to be overly argumentative...just curious about where you're interpretation comes from.)

 

[jayrod12]

I would agree that when analyzing the stringers you would account for both the vertical gravity loads on the stairs, plus the effects of the handrail/guard loads. Can't have the guard loads without people on the stairs.

 

[Mike Mike]

phamENG, jayrod, Ron, I agree that in the real world you can't have a rail load without an occupant, but as I quoted above from the IBC, rail loads "are permitted to be applied independent of other loads". Maybe the code committee decided the chance of each load being simultaneously at their maximum value is small? Whatever their reasoning, it seems pretty clear to me the occupancy load would be considered an "other" load, and would not be required to be applied concurrently, but maybe I'm missing something?

 

[phamENG]

Mike Mike - thanks...I guess I missed the 'commentary' statement in the previous post, which is why I was so confused.

It says it's permitted, but it doesn't say it's required. So, since you need an occupant to have a load (unless it's a rail in a skate park - they frequently have rail loads without somebody on the stair), I'll keep applying it that way. But clearly there's nothing wrong with the way you're doing it, either. Sounds like everybody wins.

I'm not sure that this is a case where you would be unlikely to have simultaneous peak loading, though. Seems like the most likely time to have somebody fall hard against a rail would be when everyone in the building is crammed into the stair well and freaking out in a fire. Just thinking anecdotally. Anyone aware of a loading survey for stairs and rail like the summary ASCE 7 has for live loads in the commentary for chapter 4?

 

[dik]

I never include the guardrail or handrail load with the stair loading, and never have.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik