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handrail bracket calculations

  • 1.  handrail bracket calculations

    Posted 03-16-2018 10:32 AM
    Edited by Chad Morrison 03-16-2018 10:51 AM
    Does anyone have sources available for useful approaches for handrail bracket design?  I have 10 years experience in producing calculations for various bracket types and base materials and continue to encounter the obstacles that I have from the onset of my career.  Without testing of the bracket (and becoming the "approved authority") calculations are needed to justify the anchorage. Historical performance of handrail installations indicate that under most cases they are safe.  One cannot prevent abuse and some maintenance during the rail's lifetime should be expected.  

    Producing calculations for handrail brackets fastened to concrete is fairly straightforward.  Calculations for fastening to hollow CMU and stud walls prove more problematic.  Before I share my methods, I am interested in how others approach the problem.  What anchors do you use in hollow CMU?  What safety factor do you apply to them?  Do you specify wood blocking or metal sheets within the stud wall to fasten to?  What allowable bearing strength do you use for GWB?

    Please feel free share any questions or comments you have on the topic, as it does cover much more ground than expected.  Thanks!

    ------------------------------
    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
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  • 2.  RE: handrail bracket calculations

    Posted 03-17-2018 11:02 AM
    Hi Chad,

    Following are two documents that I've found helpful for handrail design.  Even though you may not find answers specific to your application, they both discuss the design philosophy and hopefully provide some guidance to those who stumble into this discussion topic.
    1)  Pipe Railing Systems Manual (ANSI/NAAMM AMP 521-01)
    2)  Technical Note: Comparison of Design Specifications for Design of Pipe and Round HSS Pedestrian Guardrail Systems (by AISC).

    Very curious to see other contributions to this topic.

    Cheers,
    Tadas

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    Tadas Saudargas P.E., M.ASCE
    Ambitech Engineering Corporation
    Downers Grove IL
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  • 3.  RE: handrail bracket calculations

    Posted 03-19-2018 10:30 AM
    Edited by Tirza Austin 03-19-2018 10:30 AM
    ​You might find this section on handrails specified for the International Space Station useful:

    1.02 PERFORMANCE REQUIREMENTS:

    1. General: In engineering railings to withstand structural loads indicated, determine allowable design working stresses of railing materials based on the following:
    2. Steel: 72 percent of minimum yield strength.
    3. Structural Performance of Railings: Provide railings capable of withstanding the effects of gravity loads and the following loads and stresses within limits and under conditions indicated:
    4. Handrails:
    5. Uniform load of 50 lbf/ ft. applied in any direction.
    6. Concentrated load of 200 lbf applied in any direction.
    7. Uniform and concentrated loads need not be assumed to act concurrently.
    8. Top Rails of Guards:
    9. Uniform load of 50 lbf/ft. applied in any direction.
    10. Concentrated load of 200 lbf applied in any direction.
    11. Uniform and concentrated loads need not be assumed to act concurrently.
    12. Infill of Guards:
    13. Concentrated load of 50 lbf. applied horizontally on an area of 1 sq. ft..
    14. Uniform load of 25 lbf/sq. ft. applied horizontally.
    15. Infill load and other loads need not be assumed to act concurrently.
         C. Thermal Movements: Provide exterior railings that allow for thermal movements resulting from the following maximum change (range) in ambient and surface temperatures by preventing buckling, opening of joints, overstressing of components, failure of connections, and other detrimental effects. Base engineering calculation on surface temperatures of materials due to both solar heat gain and nighttime-sky heat loss.


    Keep in mind the requirements that the ADA Guidelines make for the handrail diameter (1 3/4" is typically used) and that there be no obstructions within 3" above the rail and within 3/4" of either side. Essentially, that requires that the brackets supporting the handrails extend from below the rails. Although the IBC allows the brackets to be spaced up to 6'-0" apart, 4"-0" pacing (or less) makes for easier attachments and deflection control.

    ------------------------------
    Robert Crossno P.E., M.ASCE
    Civil Engineer Supervisor
    Albuquerque NM
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  • 4.  RE: handrail bracket calculations

    Posted 03-23-2018 10:33 AM
    I agree with Tadas with making reference to the NAAMM especially in the worst case application of attaching a bracket to wood blocking behind sheetrock. There simply is no engineering method to justify that unless walls are going to be built differently. Hollow block,metal stud, etc are all similar.

    It may be worth noting that many of the commercially handrail brackets themselves don't meet any engineering design attempt.Take a look at one major bracket manufacturer with their Style B type brackets. I'll just put a disclaimer in the calc package that certain items like this have performed successfully based on the historical sample (or manufacturer's testing) and are installed similar to the NAAMM recommended figures with no further statements or claims about it.

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    James Wilson P.E.
    Wilson Engineering
    Stroudsburg PA
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  • 5.  RE: handrail bracket calculations

    Posted 03-18-2018 09:41 AM

    With respect to design/installation of anchors in a CMU wall for handrail bracket attachment or any other purpose you may wish to review the anchor manufacturer's literature/catalogue(s). I know that Hilit has provided the specified information/guidance in their past literature/catalogues and possibly in their current literature/catalogues.

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    Murray Moser P.E., M.ASCE
    RETIRED
    Maumelle AR
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  • 6.  RE: handrail bracket calculations

    Posted 03-19-2018 10:33 AM
    Thank you for the responses.  I am familiar with the NAAMM, AISC, and anchor manufacturer publications.  NAAMM provides typical details for handrail bracket mounting the walls, but no design calculation guidelines/examples.  AISC discusses guardrails, but avoids the handrail bracket attachment to the wall condition.  Selecting the proper anchor bolt is trickier than it appears.  Applying a safety factor of 5 is overkill for the application and using a hardware store anchor is not prudent even if it passes analysis.  The attachment of the bracket to the wall is a unique base plate design and the allowable bearing capacity of concrete, CMU, or GWB is not addressed in any source that I can find.  Bracket manufactures typically provide testing data to demonstrate that it can resist 200 pounds, but do not provide any guidance on anchorage to the wall (nor should they).

    ------------------------------
    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
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  • 7.  RE: handrail bracket calculations

    Posted 03-19-2018 10:32 AM
    Edited by Tirza Austin 03-19-2018 10:31 AM
    I've had a relationship with a local railing manufacturer/installer who provided load test data for all of their components and we designed the attachments to various substrates. Over time, we built up a library of calcs for the most common construction types in their territory, and it was easy.

    In the beginning, we did have to make them enlarge the base plates for their posts in order to get anchors to work with real-world edge distances. 

    For post bases to concrete, we found that the large diameter concrete screws from Hilti or Simpson seemed to work best for short edge distances and close spacings. For attachment of rail brackets to masonry, we usually relied on tapcons. For wood structures, we always specified that blocking should be located at attachments and often even provided reactions for the attachments on the shop drawings.

    Dan Vines, PE

    ------------------------------
    Sherman Vines P.E., M.ASCE
    Forensic Engineer
    Unified Investigations and Sciences
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  • 8.  RE: handrail bracket calculations

    Posted 03-20-2018 10:19 AM
    This spring AISC will be releasing a Design Guide on Steel Framed Stairways which addresses the design of handrail wall brackets as well as complete steel stair, guardrail, and handrail design.   There will also be a presentation by the author at NASCC: The Steel Conference held in Baltimore April 11th through 13th.

    ------------------------------
    Lawrence F. Kruth P.E., M.ASCE
    Vice President Engineering & Research
    American Institute of Steel Construction
    Chicago IL
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  • 9.  RE: handrail bracket calculations

    Posted 03-21-2018 10:10 AM
    This is wonderful news!  I hope that it takes the next step beyond the NAAMM manual.  We will have to revisit this topic after it is released.  Thanks!

    ------------------------------
    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
    ------------------------------



  • 10.  RE: handrail bracket calculations

    Posted 03-22-2018 08:00 AM
    I've been designing and testing rails for many years. The IBC/ASCE 7 addresses the MINIMUM loading requirements for handrails and guardrails.  The requirement is 50  applied in any direction along the rail or a 200 point load applied in any direction along the rail. The prevailing test standard is ICC-ES AC273 and ASTM D7032, which provide factors of safety and deflection limits.

    The limiting factor is generally the attachment to the substrate, such as wood and concrete.  The anchorage capacity will typically limit the spacing of the brackets and/or posts to 48" on-center.  If you see anything greater than 48" on-center it most likely wasn't designed or only considers the one- and two-family dwelling loading requirements. For handrails, the connecting bracket seldom works by design and must be tested. For guardrails, nearly any attachment using 3/8 lags or smaller into wood does not work.  If you rely on manufacturer's ICC-ES ESR report, ask for the actual test data, most testing has not been performed correctly--yet it is accepted by ICC-ES--or the limits of use are misrepresented in the ESR report.

    For example, most reports will indicate a guardrail span of 8-ft--this is for the handrail only and does not include the post supplied by the manufacturer.  The fine print in the ESR reports require the rail to be supported by a rigid supporting structure and NOT the cantilevered post supplied by the manufacturer.  In some reports, the posts are shown as part of the report, but they do not meet any the loading requirements--most posts on the market only have been optimized for 200-. Also, many reports DO NOT include the attachment to the substrate even though connection hardware is shown in the report.

    ------------------------------
    Eric Tompos P.E., M.ASCE
    Executive Vice President
    NTA, Inc.
    Nappanee IN
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  • 11.  RE: handrail bracket calculations

    Posted 03-22-2018 01:22 PM
    Agreed!  The request by the design team and GC to produce calculations is problematic.  We can produce calculations to satisfy ourselves, but they are based on judgment and open to criticism.  Testing is costly, time consuming, and presents a question of whether we are an "approved authority."

    ------------------------------
    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
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  • 12.  RE: handrail bracket calculations

    Posted 12-18-2018 09:48 AM
    Edited by Tirza Austin 12-18-2018 09:48 AM
    AISC Design Guide 34 - Stairs is now available.  There is 1 paragraph regarding handrail bracket design.  It refers to bracket/anchor manufacturers data to ensure the design can support load required by code.  It explicitly states that bearing directly on GWB rarely meets loading requirements.  In the past, I have run afoul in proving a filler between the bracket and blocking due to penetrating the fire rated partition.  My current design case for a handrail bracket remains unresolved, but I hope to be able to offer further insight on my solutions when it is completed.  In the mean time, any additional thoughts on handrail bracket design are appreciated!

    ------------------------------
    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
    (401)231-4870 EXT 2207
    ------------------------------