Stair handrail loading
Stair handrail loading
(OP)
The 2000 IBC requires 100 psf for stair loading. It also requires 50 plf for handrail loading and states that it shall be "applied in any direction at the top and to transfer this load through the supports to the structure."
When designing the stair stringer, does the 50 plf handrail load need to be applied simultaneously with the 100 psf live loading on the stair tread?
Related (less important) question: The dead load of my stairs is less than 50 plf per stringer, does the stringer need to be designed for an uplift load (handrail load applied "in any direction") with the compression flange (bottom flange) unbraced because the stringers are connected at a distance from this flange?
When designing the stair stringer, does the 50 plf handrail load need to be applied simultaneously with the 100 psf live loading on the stair tread?
Related (less important) question: The dead load of my stairs is less than 50 plf per stringer, does the stringer need to be designed for an uplift load (handrail load applied "in any direction") with the compression flange (bottom flange) unbraced because the stringers are connected at a distance from this flange?






RE: Stair handrail loading
2.) My initial thought would be to say no because you wouldn't have the handrail load unless there is at least some LL on the stair, but I am interested in hearing what others have to say.
RE: Stair handrail loading
If your handrail post spacing is greater than 48 inches, then the 50 plf and 200 lbf need to be checked. At 48 inches, they are the same laterally...greater spacing allows the 50plf to prevail. For spacing less than 48 inches, the 200 lbf will prevail.
In most cases, I would consider the bottom flange to be braced because the tread attachment is so close; however, the "uplift" is small compared to the section of a typical stringer.
RE: Stair handrail loading
I agree with StructuralEIT for #2. But I have been asked one by a [crazy] building official to revise support details for a suspended catwalk system. There were supports (tension only) that were not designed for the net uplift. I had to revise everything to single angles for the compressive load due to handrail uplift applied without catwalk live load!
RE: Stair handrail loading
What were the sizes?
RE: Stair handrail loading
RE: Stair handrail loading
Best regards,
BA
RE: Stair handrail loading
One thing you might consider is that the rails and attachment are allowed an overstress factor of 1.33 (See Section 1607.7.1.3, International Building Code)
RE: Stair handrail loading
Another shape that is good for stair stringers is the MC12x14.3. It's fairly new, and it is not in the 13th edition manual. The sheet I have on it says it fills the gap between the MC12x10.6 and the C12x20.7.
Also, the 1.33 overstress is specifically for ASD. It is not applicable for LRFD.
RE: Stair handrail loading
Most of our clients locate the posts on top of the stringer. Depending on our location we end up with 1-1/2" dia or 1-1/4" dia posts. How do you justify welding a post with a 1-5/8" outside diameter to a stringer flange that is 1-1/2" wide?
RE: Stair handrail loading
I always have the problem you mentioned. Most often a 1-1/2 pipe or square tube does not work in flexure without an insert. Even if it does, you can never weld all around as is always detailed in the shop drawings. The amount of weld needed is almost close to a CJP.
I would like to hear other people's opinions as well.
RE: Stair handrail loading
I have done analysis for 2 different manufacturers and the more common section for both has been the MC10x8.4.
RE: Stair handrail loading
See p44 of the latest Modern Steel for additional info on handrail design including a discussion (and strong recommendation against) the use of the stress increase:
http://www.modernsteel.com/
RE: Stair handrail loading
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RE: Stair handrail loading
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RE: Stair handrail loading
However, I am still having a hard time with the attachment of the post to the top flange of the stringer. They show a partial joint penetration weld on the sides of the post that are flush with the stringer flange. The question I have is how do you get enough effective weld on material that is 1/4" thick or less? It appears that you would have to have a double bevel in order to gain the proper amount of weld. This means a bevel would have to be created in the field once the final location of the post was known. I'm not sure I trust the stair erector to properly prepare this bevel.
What do other people think of this?
RE: Stair handrail loading
We specify C12x20.7 for our stringers where handrails will be attached and MC12x10.6 where the handrails are attached to the wall.
For exposed stairs we like to use HSS12x2 stringers.
Actually it is unlikely that the 50 plf horizontal load would be applied to the full length of the handrail. If there are three or more posts supporting the hand rail, I have no problem using the 1/3 stress increase.
What I find surprising is that a lot of fabricators in Ohio use pipe 1 1/4 STD as their generic size when the Architect doesn't specify a size.
RE: Stair handrail loading
RE: Stair handrail loading
RE: Stair handrail loading
RE: Stair handrail loading
I use C12x20.7 channels for stringers to facilitate welding of handrail posts to the top flange of the stringers. The 12" depth helps reduce bouncing stairs more than the 10" stringer depths.