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Re: QUERY: Steel Connection Design Philosophy

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My understanding of steel connections has always been that you want the
member (typically the beam not the column) to "fail" not the connection.

This could be accomplished by either a reaction based upon rational
analysis or the capacity of the member.  One might suggest that if the
reaction based upon rational analysis is used then it would theoretically
"fail" the same time as the member.  However, I believe (someone correct
me if I am wrong) that connection design uses a high factor of safety.
Beside, when I use "actual" reactions, I artifically increase that
reaction slightly (usually about 10%).

I am used to specifying a reaction based upon analysis to be used i nthe
connection design.

I have certainly seen the "capacity" of the member used to size
connections.  Typically, I see this more for moment connections than
standard simply supported connections.  I have seen many people design
moment connections for "full capacity" of the section.

Hope this helps,

Scott Maxwell, PE, SE 

On Wed, 26 Jul 2000, Bill Polhemus wrote:

> Here's one to file under the "Things You Thought You Knew But Now Realize You
> Might Be Wrong" category.
> 
> I had engrained in me somehow the idea that when one is designing a connection
> of any kind for structural steel, one makes sure the connection is at LEAST as
> strong as the member(s) being connected. In other words, regardless of the
> design forces, make sure that if an overload were to occur, the connection would
> NOT fail before the member did.
> 
> However, reading the applicable passage from the AISC LRFD 2nd Edition, J1.1, I
> find this:
> 
> "[C]omponents shall be proportioned so that their design strength equals or
> exceeds the REQUIRED STRENGTH DETERMINED BY STRUCTURAL ANALYSIS FOR FACTORED
> LOADS ACTING ON THE STRUCTURE, or a specified proportion of the strength of the
> connected member, whichever is appropriate." [Emphasis is mine]
> 
> Now, the latter clause seems to give you wide latitude. For instance I could say
> that "I've determined to use a specified proportion of the strength of the
> connected member in this structure, that proportion being 100%". So I'd not
> really be WRONG. It becomes a question, then, of philosophy.
> 
> This comes up, of course, when for practical reasons you have members that are
> more than adequate to handle the required loading, and a connection sized
> according to that member's capacity would mean adding bolts or weld, etc., above
> that required to resist the loads from analysis.
> 
> I'd like to know what others have decided in their approach to steel connection
> design.
> 
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