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Handrail Posts
2

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 how the smaller diameter 1-1/4 pipe vertical is mounted?
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 believe that some of the relevant design guides give you factors for including system behavior as opposed to single, isolated post behavior. And that, I think, is what makes the 1.25" diameter fly.

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

(OP)
1-1/4" pipe - OD=1.66 in, ID=1.38in
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

(OP)
KootK, Do you happen to know which Design Guide that might be in?

RE: Handrail Posts

Just dug it up for you: Link. You are now indebted to the tune of 0.25 KootK Billable Hours. Not to worry though, it's in Canadian currency so, like, a slurpee or something.

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

(OP)
I appreciate it! I will look into that. What flavor slurpee do you want?

RE: Handrail Posts

I've wondered this myself. I've seen handrails built both ways, for what it's worth. I assumed the 1 1/4" systems were built prior to the 200#, 50#/' criteria being instituted but it sounds like they are still being built.

This place is great for being force-fed humble pie so thanks for asking the question.

RE: Handrail Posts

One way the 1-1/4" pipes work is until the 2009 IBC, the IBC allowed guardrails to have a 1/3 stress increase provided you followed the loads described for guardrails and handrails. I also have design guardrails using the bigger pipe only to get questioned by the architect and steel shop who have always used the smaller size before because "that is what we have always used".

RE: Handrail Posts

Quote (Stenbrook)

What flavor slurpee do you want?

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

I am under the impression that the 200# OSHA load is to be compared to the yield strength of the material, not the allowable (see quote below). In Ontario, we compare 150# to the allowable. What code are you getting your design loads?

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

(OP)
I am using the loads described in the IBC. And since my project is being designed using the 2012 IBC, the 1/3 stress increase is not allowed. I believe that the allowable capacity of the handrail should be compared to the full 200 lb load. I don't see any way to justify using anything less. Maybe there are specifications in the code in Canada that are different than here in Texas.

RE: Handrail Posts

Stenbrook....AISC does not recognize stairs and rails as "structural steel" in the sense of building design. I asked of them several questions about serviceability because I was concerned about lateral deflection of rails near the end of a stair section that does not switch back to another floor. Here is the text of the email response I got......

Quote (AISC Solutions Center)

Stairs are not generally considered structural steel per Section 2.2 of the Code of Standard Practice; therefore, AISC does not have very much information on stairs and their applicable material specifications. The National Association of Architectural Metals Manufacturers web site (www.naamm.org) may be one place to start. You may be interested in 2 documents in NAAMM’s AMP technical literature section (http://naamm.org/amp/amp_technical_literature.aspx). Although they do not specifically address your question, both the pipe railing manual and the metal stairs manual discuss structural considerations for the design of stairs and handrails.

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

Interesting stuff,

on our offshore oil platforms, we use 1-1/2" STD

RE: Handrail Posts

How do I archive this thread? Thank you!

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

Done. Thank you. I was asked several months ago by a senior engineer to prove to him how the 1-1/4" posts work on paper.

EIT

RE: Handrail Posts

While we are on topic, has anyone seen or specified an MC12x14.3 with wider flanges? They were mentioned in a modern steel article http://msc.aisc.org/globalassets/modern-steel/stee....

Quote (Modern Steel)

A Channel Especially for Stair Stringers: The MC12×14.3 that recently was added to ASTM A6 was conceived as a stair stringer. It has a 21∕8in. flange width, which is wide enough to accept the common handrail pipe size and fillet weld around it. No more crimping the pipe or goobering the weld!

RE: Handrail Posts

An Engineering Journal paper (second quarter, 2002) by Thomas Sputo addresses guardrail post design and compares the results from five different methods: NAAMM, AISC ASD, AISC LRFD, AISI ASD, and AISI LRFD. The NAAMM method distributes the 200 lb concentrated load between adjacent posts. The paper is available on the AISC website (www.aisc.org) and is free of charge to members.

I also suspect that some engineers may still use the 1/3 stress increase that is no longer permitted by IBC.

RE: Handrail Posts

The size of handrail posts has been a point of contention for years. But I have always thought the weak link was the connection to the channel, and the distortion of the channel itself. I don't know if this connection has been subject to testing.

RE: Handrail Posts

The NAAMM document uses the 200# load, calculates a moment, and compares it to an allowable moment on the pipe. Not a yield moment, but an allowable moment. (They use an old cold-formed value 0.72*Fy for an allowable bending stress.)

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

All of my guys use 1 1/4" such 80 posts here with MC12x14.3 stringers which allow for proper welding. I know it's tight, but theses item rest on top of a stinger so you can deduct around two inches from the overall height.

You guys need to push your clients in the right direction or suffer the consequences.

RE: Handrail Posts

But go back to the "words" ... 200 lbs force at the rail (top of post) must not "fail" .. So even IF it bends (yields plastically some how so the rail is bent by a guy running full speed into the rail perpendicular from a room) it has not failed to protect the public from falling.

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

Racookpe1978, one could go by your interpretation, or one could go by the NAAMM's interpretation. I prefer the consensus industry authority.

RE: Handrail Posts

Time for an AISC Appendix D?

RE: Handrail Posts

Why not? Take something that should be just about the simplest thing we deal with on a regular basis and do this to it.

RE: Handrail Posts

(OP)
As far as I am concerned, we are talking about such a minor increase in steel from a 1-1/4" pipe to a 1-1/2" pipe with respect to a project, and I know that all day long I can justify that a 1-1/2" pipe will work per every code out there. Due to that reason I will continue to specify 1-1/2" Diameter STD pipes and will mark up shop drawings I get that it should be 1-1/2. If they want to use 1-1/4 that is on them, but at least it is on record that I told them to use the 1-1/2"

RE: Handrail Posts

Stenbrook, you need to create typical details for your company showing handrail. In the detail, show 1 1/2 inch pipe. If it goes out with the project, there should be no argument. Well, there still will be an argument ("...we've done it that way for 50 years"... "I've never heared something so stupid"), but it will be in black and white.
We have a detail and we never have a problem.
Now for aluminum handrail and anchorage to concrete, that's a whole different story.

RE: Handrail Posts

Don't forget the human factor. 1.9" OD is pushing the ADA allowed dimensions.

Quote (Access Board)

505.7.1 Circular Cross Section. Handrail gripping surfaces with a circular cross section shall have an outside diameter of 1¼ inches (32 mm) minimum and 2 inches (51 mm) maximum.

ADA Standards

RE: Handrail Posts

(OP)
I have said details on my drawings. That doesn't stop over 50% of the fabricators from putting whatever the heck they want on their shop drawings.

RE: Handrail Posts

PS: BUGGER, if it wasn't clear the first time around, my post was intended to show agreement with you. That is, to express amazement that something that should be so simple could have this degree of complexity and ambiguity.

RE: Handrail Posts

The 1 1/4" Pipe will work if flanked by posts to both sides. Have a look -



Final deflection is a little over 1"

RE: Handrail Posts

Ok but what happens when you have the 50 plf load acting along the top rail and your posts are at 4' centres. Then the load sharing argument goes out the window.

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

Hokie93 - thanks for the AISC article reference.

RE: Handrail Posts

A couple of ideas I've used:

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

We could design these dynamically like traffic bollards. This would probably be a more realistic approach. Energy methods make it easy.

RE: Handrail Posts

The AISC Specification for Structural Steel Buildings (ANSI/AISC 360) does not apply to the design of guardrails. The industry standards NAAMM AMP 510-92 and NAAMM AMP 521-01.

RE: Handrail Posts

I'm right in the middle of similar calcs so thank you, Stenbrook, for reading my mind. And thank you to all who have contributed well-thought-out responses. My case has 1.5inch square tubes for posts so those are fine, but the connection to the channel flange below has been a thinker. Any suggestions on an approach to make that connection work without adding a stiffener as shown in the attached?

RE: Handrail Posts

I think deflection vs failure is where this all breaks down. OBC, which is what I work to, is vague on railing deflections; other codes may be more stringent. I've physically tried to load a residential wood railing with the 1 kN/250lb concentrated horizontal load and it's a lot harder than you might think, and I achieved some pretty good deflection (L/20) without the slightest sign of failure. That leads me to believe that 1 1/4" HSS welded to a channel stringer is going to outperform anything that is contemplated in the code that I have to follow.

RE: Handrail Posts

I did new company standards on this a while back. I wasn't willing to use the assumption of load sharing, because on occasion the hand or guardrails will terminate without some sort of return around a corner. In that case the final post doesn't have an adjacent post on one side to share with.

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

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.

RE: Handrail Posts

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.

RE: Handrail Posts

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.

RE: Handrail Posts

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?

RE: Handrail Posts

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.

RE: Handrail Posts

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).

RE: Handrail Posts

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.smile

RE: Handrail Posts

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.

RE: Handrail Posts

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

RE: Handrail Posts

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.

RE: Handrail Posts

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.

RE: Handrail Posts

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.

RE: Handrail Posts

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

RE: Handrail Posts

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.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

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