Handrail Posts 3

[Stenbrook]

I feel like I am missing something. I have run the calculations on a 3'-6" tall handrail post several times in this delusional hope that the calculations will come out differently but sure enough, they don't. The calcs point to needing a 1-1/2" STD handrail post (which has an O.D. of 1.9") to sustain the required load (50 lb/ft or a 200 lb concentrated load). But time and time again I check stair shop drawings where they call out a 1-1/4 STD pipe. Which, I have checked and absolutely does not work. I assume they do this so they can get away with a smaller stringer size (a MC12x10.6 as opposed to the C12x20.7 which has a larger flange width to accommodate the larger pipe), But I really don't know. Does anyone have any insight into this as to any other reasons why stair manufacturers use these smaller handrail posts ALL the time??

 

[hokie66]

oldgverden,

Your question is a good one, similar to mine above, which went unanswered. But your detail is even more problematic with the bolted connection. I think most of the others have been talking about welding the post to the channel. Surely two bolts centred on the post gives a connection which is the weak link.

 

[racookpe1978]

But as a standard detail, does that also have to reflect a standard installation: CH6 channels running at an angle, tied in at top of bottom of the two short 5 foot standard rises between 10 foot floors, each end of the stairs at a landing or floor, each sloped handrail secured at both ends, and tied at both ends to the next handrail set?

there are 3x verticals in the typical rise, a platform, then another 3x risers. The start of the second riser is tied to the stop of the first - sometimes with a curved or looping handrail, sometimes -as in my hotel here - with additional straight mitered segments. Thus, even a 200 lbf force at the top of the center of 3x verticals on a riser is opposed by a network of 5 verticals: 2 at the ends of the riser, and two more at the intersecting risers. Those final two are offset in plan view, and offer substantial stiffening resistance.

 

[Archie264]

Teguci,

In your calcs I think you used I = .104 instead of .108. It gets factored out so it doesn't affect the final outcome but I just thought I'd mention it in case you plan on submitting that calculation to a building official for review.

 

[BSVBD]

Archie & Teguci, my AISC book says that 1-1/4 Std has I= 0.184 in4

Teguci, did the top portion of the 8 get erased or not written in your calc?

 

[Archie264]

Yep. But the calc used .104. But since the three posts are the same and strain compatibility is being used it all factors out in the end. In other words, any value could have been used; it's independent of member size. It's correct, but independent of member size. Run the same calculation with anything else (W8x10, W16x26, Wxhatever...) and it yields the same result...which is the only part of it relevant to whether a 1 1/4" pipe is adequate: whether it can resist 5.56"k.

 

[Teguci]

Wow! My eyesight is really starting to go. Actually the whole exercise is pointless since, as Jayrod pointed out, the distributed loading condition would never work for the 1 1/4" STD Pipe (and my mind is going too). I'll forward that the only NAAMM standard cited by the International Building Code is for flagpoles and ASCE 7 identifies the handrail load as a live load, which, in my mind, is subject to the same factors and handling as other live loads. So, to completely reverse myself, the 1 1/4" STD pipe should not be used for guard posts (42" above surface) without checking for special circumstances (stringer is 8" high or there are posts at an average spacing of 3' or less).

 

[Archie264]

It's wasn't a pointless exercise; it was a beautiful and elegant calculation and a good way to approach the problem. I learned a lot by working through it and I tried to sear it in my mind in case I need to perform a quick finite element analysis on a cocktail napkin at some point, which is essentially what it was. But, I also saved a copy of it for when I forget the procedure. 'Hope you don't mind.

 

[Archie264]

To resurrect this dead horse and give it another whack, I noticed that since the 200# is all live load, if this calculation is run using LRFD a 2" standard pipe is actually required, though just barely. And indeed, I've noticed a lot of 2" (2.38" OD) guard rails lately.

 

[NWEng1]

You can generally spec 1-1/2"x0.12 round tube, grade A513 Type 5 DOM (Fy=70 ksi)

The 1-1/2" OD will allow you to weld on top of a standard MC12x10.6 stair stringer flange

 

[ellas1]

You can probably increase the 1 1/4" pipe section modulus (S) by inserting a solid round bar for the first few inches (6-12)above the base where the moment is max.

 

[MillR]

We've been hired multiple times to try and justify existing handrails by calculation and can't do it. The end result is they test the assembly and it passes. Like wood houses and masonry basement walls, they just don't behave exactly as calculations say they should.

 

[spats]

SeattleEng,

You can't properly weld a 1 1/2" OD tube to the 1 1/2" wide flange on a MC12x10.6 unless you groove weld. An MC12x10.6 isn't really wide enough to weld any kind of a proper steel guardrail post to it. I usually specify an MC12x14.3. See attached. These are generally readily available, have a 2 1/8" wide flange, and are intended specifically to be used as stair stringers. It save you from having to go to a C12x20.7, which is usually more than you need.

 

[BUGGAR]

I like Ellas's idea. Make the solid round bar like a huge Nelson stud and just zap it in.

 

[EdStainless]

I am not in the structural business, but this does explain something.
We made a run of stainless steel tubing for a shop, 1.75" OD x 0.095"(I think) wall at 75ksi min yield - 105ksi min UTS (this happens to be a standard strength level).
Afterward he told me that it was for hand rails.
We put a beautiful surface finish on it.

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P.E. Metallurgy, Plymouth Tube