×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Handrail 200 lb. concentrated load, is there a built-in safety factor?
2

Handrail 200 lb. concentrated load, is there a built-in safety factor?

Handrail 200 lb. concentrated load, is there a built-in safety factor?

(OP)
When designing handrails with the 200 lb. c.l., does the allowable stress need to be divided by 4?  Or, can the moment caused by the 200 lb. load be compared to the yield allowable of the material?(Florida, to conform to FBC.)  Thanks in advance.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

It's just like any other service load.  Design with it straight up with ASD methodology or factor it with LRFD.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

(OP)
Thanks for the response.  Can you give me an example using the building code load of 200 lbs. concentrated load?  (With 6063-T52 aluminum.)

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

Well, there are two components to the design the handrail and the post.

For the handrail, just see if the 200# controls over the 50 plf (it usually does).  

For the post, if the posts are spaced less than 4' use the 200#, if they are spaced greater than 4' then use the 50 plf.  If you need the help, you can reduce the load on a post through some loadsharing factors that you can find in the Julius Blum handrail catalog, but I don't typically use that unless I absolutely need to (not that it matters, I usually only checks other engineer's designs for this).

As far as the design goes, just track the load through.  

I use PL/4 (or (wl^2)/8)for the moment in the rail (I know it's not pinned-pinned).  Use that moment with the section properties of your section to compare to the allowables of your material.

Same goes for the post.  200# at the top of a cantileverd post (Pl).  Moment at the base with section properties to compare actual stress to allowable of material.
 

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

YES there is a built in safety factor if you only weigh 50lbs.  But, NO there is probably not if you weigh 400lbs. and push/lean real hard, or if you are three down linemen all showing off for a cheerleader at the same time.  Decks and handrails usually don't fail from normal use or 40lbs./sq.ft. LL's., They fail frequently from poor design, detailing and construction.  And, ledgers, guardrails and posts poorly designed, detailed and constructed, w.r.t. reasonably expected loadings caused by crazy partying (stupid) people are often the cause.  It says apply a 200lb. load, anyplace, any direction, and it should not fail.
 

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

Lion06 is correct.

When analyzing the components of a railing system (keep in mind that if it is attached to the stair section, it is a "handrail".  If it is not part of the stair section, it is a "guardrail".), isolating the components is a conservative approach.  For instance, to determine the moment at the bottom of the post, if you apply 200 lbf to the top of the post alone, you are not gettig the benefit of any load sharing.  In most cases, a typical 6063-T52 square post will fail under ASD.  Load sharing typically begins with the continuity of the top rail.  It is a pinned, continuous beam in most cases.  

To develop the weld at the baseplate for the post, you consider that the post-to-plate connection is fixed, yet the plate-to-concrete attachment is not really fixed, but the resulting couple from the base plate is the load on the anchors.

Further, many codes still allow a 1.33 overstress for stairs and rails.  Check your code.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

As wannabeEIT says, use the NAAMM pulication. There is load sharing betwwen posts for concentrated loads, and you can design for 65% for a two span rail, and 60% for a three span or greater rail.

I would use 6061-T6 aluminum. It's yield strength is 35 ksi, with an allowable stress of 24 ksi, as opposed to 16 ksi/11.5 ksi for 6063-T52. Also note Table 1 in the referenced publication, allowable stress for aluminum is greatly reduced within 1" of a weld. Unfortunately, that means a big reduction at the base of the guardrail posts where the stress is the highest.

The FBC allows a 33% increase when using allowable stress design.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

The NAAMM document is a good one; however, it is not a code-referenced document (either in the International Building Code (IBC) or the Florida Building Code (FBC)), so the provisions of the code, particularly the reference to the Aluminum Design Manual (ADM) will apply.

Heed spats' warning about the reduction in allowable stress near welds.  That's what usually kills an aluminum handrail calc.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

"It says apply a 200lb. load, anyplace, any direction, and it should not fail."

If I remember correctly, OSHA has similar wording for industrial handrails, and also specifies minimum member sizes.  But the way that is worded, I would take it to already include factors of safety associated with the loading.  If it fails at 201 lbs, that's okay, just as long as it holds 200 lbs.  "Should not fail" is not the same requirement as "Should not result in an overstress condition under Code XYZ".  
 

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

The NBC makes it quite clear that the load is a service load.   

BA

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

JStephen

The problem with OSHA, unless it has changed recently, is that the member sizes it specifies actually fail even if the 200lbs is taken as an ultimate loading.

Last I checked, OSHA called for 2x4 railings and posts at 8' on centre for guardrails used on construction sites. These fail when taking the 200lb horizontal loading as an ultimate load. As another side note, OSHA and WCB guidelines are usually meaningless as they provide no details on the anchorage of posts, which is where the failures are most likely to occur from my experience.

This is not meant to be a jab at you, so I hope it is not  taken that way. I was hoping to point out the failings of some safety codes. And I will refrain from commenting on the continued use of ASD as well.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

FBC permits increasing the allowable stress by one-third if allowable stress design is utilized. I am not sure are aware of FBC provision 1607.7.1.3

"1607.7.1.3 Stress increase. Where handrails and guards are designed in accordance with the provisions for allowable stress design (working stress design) exclusively for the loads specified in Section 1607.7.1, the allowable stress for the members and their attachments is permitted to be increased by one-third.?

Good Luck.
 

Regards,
Lutfi
 

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

@Lutfi,
I don't think that 1/3rd increase applies in the HVHZ zone though (aka South Florida)

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

slickdeals...yeah it does...not wind related.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

Ron, I may be mistaken, but I remember seeing a reference for no allowable stress increases in FBC. Not sure if it was in 2004 or 2007.
 

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

1618.9 Load combination.

The safety of structures shall be checked using the provisions of 2.3 and 2.4 of ASCE 7 with commentary.

Exception: Increases in allowable stress shall be permitted in accordance with ACI 530/ASCE 5/TMS 402 provided the load reduction factor of 0.75 of combinations 4 and 6 of ASCE 7 Section 2.4.1 shall not be applied

Doesn't this mean that 1/3rd stress increase is not permitted unless it is for the exception?

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

slickdeals....

1607.7.1.3 Stress increase. Where handrails and guards
are designed in accordance with the provisions for allowable
stress design (working stress design) exclusively for
the loads specified in Section 1607.7.1, the allowable
stress for the members and their attachments is permitted
to be increased by one-third.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

Right..........but isn't that in the non-HVHZ portion of the code?

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

(OP)
Lion06, dhengr, wannabeEIT, Ron, spats, JStephen, BAretired, gwynn, Lutfi, and slickdeals:

Thanks much... very helpful suggestions and discussion.  btw, this particular case is not HVHZ.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

I had a glass handrail manufacturer place a 200# horizontal load on his in-place guardrail and wanted to use that as demontrating compliance with the code-required load. This makes sense on its face, but there are additional safety/load factors which come into play. (I don't know of a Code provision for in-place testing.) He also didn't bother contacting us to ask where the load needed to be placed, and he placed it bewteen posts where there was convenient load sharing.

To me it is odd that the handrail provisions, so long a part of the code, are still open to so much interpretation. In my book OSHA is largely to blame because the CFR for this is poorly worded and confusing.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

slickdeals...HVHZ provisions only apply to wind loads.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

I meant to do some more research on this, and kind of let it get by.

In general, if the load is a specified load from a building code and just referred to as a "design load" or something of the sort, then I would agree it would be be designed just like other members of the building or whatever it's on, as noted in the other posts above.

In looking at the OSHA requirements, they say the handrail is to "withstand" a 200 lb load, and of course, don't specify any design code or method to be used for it, and that leaves it fairly unclear.  OSHA also specifies a 2"x2"x3/8" angle or member of equivalent bending strength, or a 1.5" "nominal" pipe, which they interpret elsewhere to mean 1.5" OD.  Anyway, using 2"x2"x3/8 posts, I think gives 24,000 psi if the load is on a single post.  Using 1-1/4" pipe gives 36,000 psi or so.  In both cases, that would seem to exceed allowable AISC-ASD stresses, but does not calculate as a failure, either.

I'm not sure where the "should not fail" wording comes from, if anywhere.

The NAAMM publication mentioned above addresses the question on pages 15 and 16, with the authors agreeeing with the other posts above.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

The 1/3 stress increase for ASD was removed in the IBC 2009.  I don't know if the FBC has caught up to this yet.  If not, it's just a matter of time before it does.  I'd suggest not relying on this stress increase.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

You've mentioned OSHA a few times, make sure the owner does not intend to use any part of this assembly for fall protection tie-off... That is 5000lb!

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

Actually OSHA also allows "twice the anticipated load" for tie-off or 5,000 lbs.  This helps when using yo-yo's or shock absorbing lanyards which really lowers the forces.

BTW - I have two pre-teen grandkids that could shred a handrail rated only for 200 lbs - and they are not even close to being over weight - just a bit active.  Come to think of it - my 4 year g-daughter could probably do it on her own!!.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

Sounds like a dangerous four year old.

BA

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

She is absolutely fearless!!  Jumped into the deep end of the pool last week.  At least she had enough brains to get to the side before everyone rushed over.  

I call her a SHE-DEVIL.  Terrorizes the 8 and 11 year old.  1 year old just cringes and screams when she comes near.

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

Mike...get her into engineering!  The profession could use a few like that!

RE: Handrail 200 lb. concentrated load, is there a built-in safety factor?

(OP)
Thanks, all, for the excellent information.  

Thanks for the heads-up re fall protection tie-off, a2mfk.  Not an issue here, thank goodness.  Now, MiketheEngineer's 4-year-old granddaughter sounds like a force of nature that no amount of engineering could protect against.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources