Handrail Posts
Handrail Posts
(OP)
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??






RE: Handrail Posts
What are your assumptions about wall thickness and strength points?
Where is the failure point, and how is it failing? (Buckling at the lowest place where it hits a ring or mounting hardware around the vertical to the floor?
The 1-1/2 rail diameter "feels" much better to most people's hands - 1-1/2 is too big to grasp easily. But verticals? Have not heard before about 1-1/4 failing a theoretical 200 lb sideways force at 42 inch off the floor.
RE: Handrail Posts
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Handrail Posts
1-1/2" pipe - OD=1.9 in, ID=1.61 in
All of these values are listed in Table 1-14 in the AISC Steel Manual
it is a quite simple calculation:
1-1/4" STD diameter handrail post with a 200 lb point load at the top and "Fixed" at the base.
M= 200*3.5*12=8400 lb-in
V=200 lb
Design using Section F8 in the AISC Steel Manual
Yielding - Mn=Mp=FyZ
Z=0.305 in^3
Fy=35 ksi
Safety factor = 1.67
Mn=35*.305/1.67=6392 lb-in < 8400 lb-in
The pipe clearly does not work due to the loads required by the IBC, yet everyone seems to think it does.
The 1-1/2" diameter pipe in comparison has a Z=0.421
Mn=35*.421/1.67=8823 lb-in > 8400 lb-in so the design is ok for yielding.
The rails are typically 1-1/4 and I have no issue with that.
RE: Handrail Posts
RE: Handrail Posts
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Handrail Posts
RE: Handrail Posts
This place is great for being force-fed humble pie so thanks for asking the question.
RE: Handrail Posts
RE: Handrail Posts
Due to some unfortunate features of my genetic heritage, sugary beverages are no longer on the docket for me. However, if you could convince somebody to invent a Diet Coke Slurpee, I would be forever in your debt. We put a man on the moon damn it! Surely a sugar free Slurpee can't be beyond our reach. And I'll digi-slap anyone who tries to sell me on those Crystal Light Slurpee abominations. Not the same.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Handrail Posts
1926.502(b)(3)
Guardrail systems shall be capable of withstanding, without failure, a force of at least 200 pounds (890 N) applied within 2 inches (5.1 cm) of the top edge, in any outward or downward direction, at any point along the top edge.
RE: Handrail Posts
RE: Handrail Posts
I already had checked the NAAMM document and go no help from that!
It is likely that the design was done by the prescriptive method in the NAAMM document. Another explanation is that some engineers use the height of the grip rail (34"), not the top rail height (42") as this is actually the line of action of the force.
I analyze stairs and rails for a local fabricator and we often run into issues such as this. We use heavier wall (3/16"-1/4"), 1-1/2" square tubing for the posts. The material has a yield of 45 ksi.
Check out the NAAMM document.
RE: Handrail Posts
on our offshore oil platforms, we use 1-1/2" STD
RE: Handrail Posts
EIT
RE: Handrail Posts
Look near the scroll bar on the right.
I already archived this, as you can see, but, you will find it in the same area.
RE: Handrail Posts
EIT
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RE: Handrail Posts
I also suspect that some engineers may still use the 1/3 stress increase that is no longer permitted by IBC.
RE: Handrail Posts
RE: Handrail Posts
How do 1.25 standard pipe posts work? On paper they don't. We call out 1.25 extra strong pipe for posts, where that OD is required.
Why don't they fail? They probably never see the 200# load. And the material yield stress is surely higher than 35 ksi. I've seen mill certification reports on "pipe" material that was triple certified (A53 Gr B, A500 Gr B, and A500 Gr C) and had an actual yield stress of 65 ksi. That's nearly double the design yield stress.
RE: Handrail Posts
You guys need to push your clients in the right direction or suffer the consequences.
RE: Handrail Posts
Handrails are an odd-ball "structure" and are out in the open. They have to be safe, but let's face it. Even that 200 lbsf is an written number in the Code and OSHA that you'd very hard-pressed to justify physically and with measurements of 1000 different people of different weights and ages trying different ways to "fall" through a railing, run into a railing, jump over a railing, etc.
Compared to the tens of thousands of "unknowns" and assumptions affecting the real structural steel of a building and its walls, roofs and floors, surely somebody has tested to destruction 42 inch high vertical posts mounted in various ways to steel channels, steel beams, wood floors, concrete slabs, walls, floors, and sidewalks.
RE: Handrail Posts
RE: Handrail Posts
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We have a detail and we never have a problem.
Now for aluminum handrail and anchorage to concrete, that's a whole different story.
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ADA Standards
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Final deflection is a little over 1"
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I don't believe it is realistic to have that 50 plf load along the entire thing but there are code officials out there who may try to enforce it.
Guardrail design around here is typically a delegated item anyway.
RE: Handrail Posts
RE: Handrail Posts
You can specify 1 1/2" tubing. You can get it exactly 1/5" OD (which the architects like) and it comes in a wide variety of wall thicknesses.
We have a client who put an end to the question by requiring 1.5 x 2.5 rectangular posts with 1.5 square rails. Strong in the posts and easy to fab, alter in the field, grip, and paint.
RE: Handrail Posts
RE: Handrail Posts
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I also ran into problems with direct mounting on the top of the flange without a stiffener on all possible channel sizes and with some types of clips direct welded to the web of members with all types of web thicknesses. As a result there's a stiffener on the standard detail with a note that it's UNO on the drawings. If someone wants to show that they work without stiffeners for some cases, they're free to do it, and I did it on our standard stair detail, but a standard detail needs to work in all cases.
RE: Handrail Posts
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.
RE: Handrail Posts
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.
RE: Handrail Posts
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.
RE: Handrail Posts
Teguci, did the top portion of the 8 get erased or not written in your calc?
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RE: Handrail Posts
The 1-1/2" OD will allow you to weld on top of a standard MC12x10.6 stair stringer flange
RE: Handrail Posts
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RE: Handrail Posts
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.
RE: Handrail Posts
RE: Handrail Posts
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