Discussion: View Thread

Structural drawings and specifications often note that one half (or 0.67) of the maximum uniform load table value should be used for connection design when no reaction is given.  This is widely accepted as a conservative and useful approach by most engineers.  This approach is problematic for short beams when the value derived can be too high for practical connection design or for sections not listed in the table.

Does using the uniform load table conform with the AISC Code of Standard Practice which requires design loads be given?  Is there a source available that addresses the issue in a way that resolves disputes that arise from its application?

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Chad Morrison P.E., M.ASCE
Professional Engineer
Greenville RI
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Larry Muir is presenting an AISC Night School course on connections this summer. The course is titled "Developing an Eye for Connection Design". In the second class Larry presented the arguments for and against this exact subject.  I suggest reaching out to AISC or Larry to review that video and slide presentation.  It is extremely insightful.

Steven C. Govoni, P.E., M. ASCE
Skowhegan, ME

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Steven Govoni P.E., M.ASCE
Wentworth Partners and Associates, Inc.
Skowhegan ME
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Original Message:
Sent: 07-22-2021 12:46 PM
From: Chad Morrison
Subject: Using the maximum total uniform load table to derive design loads

Structural drawings and specifications often note that one half (or 0.67) of the maximum uniform load table value should be used for connection design when no reaction is given.  This is widely accepted as a conservative and useful approach by most engineers.  This approach is problematic for short beams when the value derived can be too high for practical connection design or for sections not listed in the table.

Does using the uniform load table conform with the AISC Code of Standard Practice which requires design loads be given?  Is there a source available that addresses the issue in a way that resolves disputes that arise from its application?

------------------------------
Chad Morrison P.E., M.ASCE
Professional Engineer
Greenville RI
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Not sure about COSP, but I suspect an engineer is within their rights to put the requirement in the contract documents, and a contractor is within their rights to ask for a change if that engineer later realizes the loads are unconservative at some locations.  Regardless, it's not practical, and AISC has repeatedly made the plea for designers to show actual loads instead.  Here is an article (co-authored by Muir and probably similar to the webinar Steven mentions) from the Nov. 2019 issue of Modern Steel Construction which discusses the issue:

https://lsc-pagepro.mydigitalpublication.com/publication/?m=7946&i=626249&view=articleBrowser&article_id=3503098&pre=1

Chad, I'm curious as to what sort of disputes you see coming up?  Have you seen fabricators underbid a job relative to max. uniform load when it is required on the bid documents?

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Christian Parker EIT, A.M.ASCE
Structural Project Engineer
Washington DC
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Original Message:
Sent: 07-22-2021 12:46 PM
From: Chad Morrison
Subject: Using the maximum total uniform load table to derive design loads

Structural drawings and specifications often note that one half (or 0.67) of the maximum uniform load table value should be used for connection design when no reaction is given.  This is widely accepted as a conservative and useful approach by most engineers.  This approach is problematic for short beams when the value derived can be too high for practical connection design or for sections not listed in the table.

Does using the uniform load table conform with the AISC Code of Standard Practice which requires design loads be given?  Is there a source available that addresses the issue in a way that resolves disputes that arise from its application?

------------------------------
Chad Morrison P.E., M.ASCE
Professional Engineer
Greenville RI
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Assuming you are not the Engineer of Record (EOR), and are tasked with designing the connection, then the EOR must provide the reaction, or the means for determining the reaction (loads on the beam). If you are to use the uniform load table, the EOR must state that in writing or on the design drawings. See AISC Code of Standard Practice Section 3.1.1.

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Jeffrey Walkley P.E., S.E., M.ASCE
Vice President
Michael J Walkley, PA
Towson MD
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Original Message:
Sent: 07-22-2021 12:46 PM
From: Chad Morrison
Subject: Using the maximum total uniform load table to derive design loads

Structural drawings and specifications often note that one half (or 0.67) of the maximum uniform load table value should be used for connection design when no reaction is given.  This is widely accepted as a conservative and useful approach by most engineers.  This approach is problematic for short beams when the value derived can be too high for practical connection design or for sections not listed in the table.

Does using the uniform load table conform with the AISC Code of Standard Practice which requires design loads be given?  Is there a source available that addresses the issue in a way that resolves disputes that arise from its application?

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