Stair handrail loading

[enginerding]

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?

 

[Lion06]

1.) I don't see why it wouldn't be required together. After all, you're more likely to have the full handrail load when you have full LL on the stair. Don't forget about the 200# point load on the railing (this often controls)

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.

 

[Ron]

Yes, you apply the loads simultaneously. You can do the calcs on "uplift" of the handrail, but it won't mean much except for the connection, and even then the moment due to the lateral load will prevail. The uplift will "net out" on the stringer, so no big deal...after all, you'll have to consider the worst case condition.

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.

 

[enginerding]

Thanks for your quick responses! I agree that there does not seem to be justification to not consider them simultaneously, but I have been told my sizes are too big and I wanted to make sure that your typical engineer would make the same assumption.

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!

 

[CTW]

"...I have been told my sizes are too big..."

What were the sizes?

 

[enginerding]

MC12x10.6

 

[BAretired]

I would be more concerned about lateral loads on a suspended catwalk than uplift. Tension hangers do not provide much lateral resistance.

Best regards,

BA

 

[Ron]

MC 12x10.6 is sometimes used for stringers, but MC 10x8.4 is more common.

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)

 

[nutte]

Ron, that's funny, because for the stairs we do, MC12x10.6 is extremely common. I don't think I've ever seen an MC10x8.4 used.

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.

 

[SteelPE]

Not to hijack the thread but.

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?

 

[slickdeals]

@SteelPE,
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.

 

[Ron]

nutte..you're right...the overstress is only for ASD.

I have done analysis for 2 different manufacturers and the more common section for both has been the MC10x8.4.

 

[WillisV]

The stress increase is not recommended even for ASD (yes I know its in the IBC - but not for long...

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/

 

[kslee1000]

Here is the page of this article.

http://www.modernsteel.com/steelinterchange_details.php?id=707

 

[WillisV]

kslee1000-umm..no thats not it. It is actually this one:

http://www.modernsteel.com/Uploads/Issues/February_2009/022009_Feb09_Handrails_web.pdf

 

[kslee1000]

Thanks, WillisV

 

[rcd445]

I would argue that the 50 plf downward or upward load on the rail is already accounted for by the live load of the person(s) on the stair tread. What other force is likely to be creating the handrail load?

 

[w16x26]

I agree with rcd445. I have never designed the stringers for a combination of live load plus downward handrail load. Just imagine a person pushing down on a handrail. Would it not produce an uplift at their feet?

 

[Ron]

One combined load would be the lateral handrail load producing a moment on the top flange of the stringer and the live load of the treads.

 

[SteelPE]

That was a great article in Modern Steel Construction.

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?