Discussion: View Thread

Guardrail, Handrail Concentrated Load

  • 1.  Guardrail, Handrail Concentrated Load

    Posted 05-10-2023 02:17 PM

    Background:
    In ASCE 7-16, paragraph 4.5, a concentrated load of 200 lbs. applied in any direction is specified. Further, for anything other than one- and two-family dwellings, factory, industrial and storage occupancies, a 50 PLF is also specified, not concurrent with the 200 lbs. concentrated load. Obviously, this case will govern when the guardrail/handrail posts are spaced greater than 4 feet on center. This has been in the ASCE 7 as well as the IBC/UBC for a long time. In the past, rightly or wrongly, I, like many other engineers would apply a 1.33 factor to the resistance side of the equation back in the old days when we would apply this to transient loads such as wind or seismic. More recently, this load was clarified to be a live load with no increase in allowable resistance (although wind loads got a boost to 1.6 and seismic loads got a boost to 1.4).

    For many years, too many to count, I've taken this load at face value. This load is particularly onerous especially when attaching to wood framing members. I'm quite aware of the need to design these railings for life safety. Here in California, we have Senate Bills 721 and 326 which are requiring apartment building owners and condominium HOAs to have their exterior elevated elements inspected. Most of the focus is on dry rot and corrosion. Little, if any, mention is made to the design practice back in the 70s and 80s.

    Question:
    What is the basis of this (200 lbs/50 PLF) criteria? Is it scientific or arbitrary?

    Thank you,


    #ASCE7-16
    #LiveLoads

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    Bill Allen P.E., S.E., M.ASCE
    Principal
    Allen Designs
    Mission Viejo CA
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  • 2.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-10-2023 10:31 PM

    Bill, Cole Graveen, chair of the ASCE 7 Live Loads task committee provides the following insights:

    The ASCE 7-22 commentary states that the single concentrated load represents load from one person or object, or a small number of people, and the uniform load represents distributed loads such as from a group of people. A specific basis for the values of the concentrated and uniform loads, such as test data, engineering judgement, calculations, or a combination thereof, is not indicated.

    A review of historical standards and codes indicates that design load values for guards have varied over the years, and prior to the International Building Code, varied between the various model building codes. The requirement for guards to resist a uniform load appears to pre-date the requirement to resist a concentrated load. For example, the 1945 edition of ANSI A58.1, the predecessor to ASCE 7, required stairway and balcony railings to resist a horizontal thrust of 50 pounds per linear foot, no concentrated load was specified.

    While not specifically referenced in the ASCE 7-22 commentary, guardrail performance research was conducted in the 1970's under the direction of the U.S. Department of Commerce and the National Bureau of Standards. This research is described in three publications, NBSIR76-1131, NBSIR76-1132, and NBSIR76-1139, which can be found on the NIST publications website.



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    Ronald Hamburger, SE
    Consulting Principal
    Simpson Gumpertz & Heger
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  • 3.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-11-2023 01:47 PM

    Ron,

    Thanks for your response. I did read the first reference you provided. At least now I believe this load is not just some fictious invention. However, it appears to me that the criteria were established based on industrial occupancies. This makes sense. However, I see it as extreme to apply these criteria to residential occupancies. Sure, maybe three frat brothers from Cal Berkeley can come close to this if provided the right environment, but it is still a pretty extreme condition in my eyes. 

    Regards,



    ------------------------------
    Bill Allen P.E., S.E., M.ASCE
    Principal
    Allen Designs
    Mission Viejo CA
    ------------------------------



  • 4.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-13-2023 03:51 PM
      |   view attached

    Hi, Ron.

    I read through quite a bit and found this in NBSIR 56-1139. This research is clearly directed towards industrial workplace safety as it was conducted for OSHA. The attached figure demonstrates the criteria. The worst case in the figure shows three rows of workers pushing on a guardrail resulting in a 94 pound force. Not sure how this becomes 200 pounds and particularly for residential occupancies. 

    Thank you,



    ------------------------------
    Bill Allen P.E., S.E., M.ASCE
    Principal
    Allen Designs
    Mission Viejo CA
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    Attachment(s)

    pdf
    nbsir76-1139.pdf   5.30 MB 1 version


  • 5.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-16-2023 08:07 PM
      |   view attached

    Hi, Ron.
    I would be most appreciative if you would run the attached figure by Cole Graveen and ask him if this is a reasonable application of loading of guardrails for residential occupancy.

    Regards,



    ------------------------------
    Bill Allen P.E., S.E., M.ASCE
    Principal
    Allen Designs
    Mission Viejo CA
    ------------------------------



  • 6.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-17-2023 11:05 AM

    The code being the design minimum, there is nothing to prevent the designer from applying a load that exceeds 50 plf or 200 lbf.  The issue arises when the architect has a specific look in mind for the railing.  Increased loads require reduced post spacing, thicker material, and substantial anchorage.  This adds to cost as well... the architect and owner have to be on board to accept the additional performance requirements.  In Massachusetts there is a code 780 CMR 1607.7 requirement for stadiums and grandstands that is 100 plf and 300 lbf.  I would cite this code for such an application regardless of jurisdiction.



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    Chad Morrison P.E., F.ASCE
    Professional Engineer
    Greenville RI
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  • 7.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-17-2023 11:45 AM

    I believe you missed my point. It appears to me that the 200 lbs concentrated force is quite excessive for residential occupancies. ASCE 7 excludes the 50 PLF force. IMO, the concentrated load should be reduced to 100 lbs or 200/1.6 = 125 lbs.



    ------------------------------
    Bill Allen P.E., S.E., M.ASCE
    Principal
    Allen Designs
    Mission Viejo CA
    ------------------------------



  • 8.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-17-2023 12:53 PM
    Edited by Tirza Austin 05-17-2023 02:03 PM

    The loads in the chart appear to be uniform, given as lbf/ft.  Excessive to the point where the design becomes offensive to the architect or owner?  Often it is the base material or superstructure that is insufficient.  Deck/Rail collapses are common during parties.  I do not see a benefit for designing for less in the residential setting.  We accept many existing conditions in houses, but new construction should be robust.  When I questioned my nationally known insurance company about the issue, they directed me to the town building official.  Rules in a municipality vary greatly if they even have any.



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    Chad Morrison P.E., F.ASCE
    Professional Engineer
    Greenville RI
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  • 9.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-17-2023 09:45 PM

    Chart? What chart? Guardrail loads are found in section 4.5. Most residential guardrails are wood framed. Design-wise, the most critical connection is the guardrail post to the supporting structure. Detailing is the most difficult part of wood design. Most failures in wood framed guardrails are due to dry rot and termites. This is what has prompted SB 721 and 326 here in California. These senate bills require inspections of apartments and condominiums respectively predominately looking for deterioration. Sure, there are several designs out there that are deficient. Before the increased scrutiny of the design, many would merely attach the post to blocking and call it a day. Now, particularly with the failure of the deck in Berkeley in 2015, most building officials are looking for the load to be completely dissipated into the supporting structure, which is a good thing. But 200 pounds at the top rail? That would be me hitting the guardrail at greater than 1g. This is also much greater (double) than the recommended loads in the documents referenced by Ron Hamberger. Sometimes, the hardware required to transfer this load is embarrassing.



    ------------------------------
    Bill Allen P.E., S.E., M.ASCE
    Principal
    Allen Designs
    Mission Viejo CA
    ------------------------------



  • 10.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-18-2023 09:30 PM

    Chad,

    I see the 100/300 stadium loading in 780 CMR seventh edition (circa 2008) but I don't see it in the more recent editions.  As best I can tell, it was dropped by the eighth edition (2013).  It appears to me that the CMR currently agrees with ASCE/IBC loading of 50/200.  Do you know if the 100/300 is current? 

    Many thanks,

    Keith



    ------------------------------
    Keith MacBain Ph.D., P.E., M.ASCE
    Associate & Chief Analyst
    Geiger Engineers, Campus 2
    Suffern NY
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  • 11.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-19-2023 10:42 AM

    100 plf and 300 lbf for grandstands appears in the Massachusetts 7th edition, but not the current 9th edition.  It can still appear in current job specifications.  

    The figure below looks like the condition described by 100 lbf per foot grandstand loading.
    3 fans acting at one point along a rail would be odd behavior to say the least.  I see this figure as having the depth of a grandstand section with multiple groups pushing at once, resulting in a uniform load of 94 lbf per foot.

    As far as residential loads are concerned, there are reductions based on occupancies that can be applied.  Check that local code recognizes them.

    Should 50plf and 200lbf result in an unsightly or perceived overkill design, there are other considerations that should be taken into account before applying any reduced loads that may be applicable in commercial or residential cases.

    -  have corner conditions been considered?
    - does the owner/architect understand the trade-off between a sleek look and safety (and potential for serviceability issues)?
    - has the carpenter or the contractor been engaged to offer design solutions?
    - should suppliers be furnishing IRC/IBC compliant products as the default rather than the premium option?
    - should insurance carriers play a bigger role in advising owners incentivizing safety? 
    - does any resulting overkill offer redundancy should components rot in the future?

    In situ testing is also a good option when calculations and modeling involve too many assumptions that may be conservative.




    ------------------------------
    Chad Morrison P.E., F.ASCE
    Professional Engineer
    Greenville RI
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  • 12.  RE: Guardrail, Handrail Concentrated Load

    Posted 05-22-2023 10:03 AM

    The images brought back so many memories but may not be keeping up with the times given parkour ("The practice of traversing obstacles in a man-made ..." ) and freerunning. 

    Are there any images of the big guy stepping on or standing on the rail to access a part of the roof?

    I have placed and/or accidentally dropped a variety of heavy objects on a top rail moving it off a deck or into the house. I have seen folks with home gyms lean bars or attach bans to rails.

    One can witness top rails being used for diving platforms and backyard wrestling rings on Social Media.

    The platform or extra seating for residential parties that exceed the desired occupancy.

    In fact, the game of tag we played as kids has become a professional sport for adults.  

    Could never truly design for the unrecommended nor the unconventional usage of rails.

    Is it time to start posting plates noting what decks and rails are designed for?



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    James Williams P.E., M.ASCE
    Principal/Owner
    POA&M Structural Engineering, PLC
    Yorktown, VA
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