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Re: welded truss design assumptions

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> I am reviewing someone elses truss design and question one of his 
> assumptions.  When we do trusses, we typically assume that the web members 
> are pinned and that these members only carry axial load 

You might want to give some thought to the connections. Assuming pin 
ended members is worst case (usually) for the members but it produces 
non-conservative connection loads. Where the connections loads are partly 
redundant they'll be relieved somewhat by yielding, but only if the joint 
is sufficiently ductile. And even statically redundant loading is 
susecptible to fatigue failure if the loading is cyclic. 

I have a tough time imagining that most structural joints aren't 
substantially continuous anyway, without some specific provisions for 
relative motion, like actual pins. Relative motion isn't possible across 
welds and relative motion between bolted parts tends to loosen bolts. 
Maybe not a problem for joints where the load isn't cyclic, but I don't 
imagine there are really all that many of those.

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw


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