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Re: 125' long steel truss, connection question

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David Guerrero wrote:

>If you model your chords as pin at the connection node then doesn't one of
the web members needs to be fixed to provide some rotational rigidity.  If
all the members (chords and webs) framing into a node are pinned (no
rotational rigidity) the analysis program should give you a warning or
error. >

On RISA3D the truss was modeled with all the members pinned and I got an
error. I had to "fix" the node at one end of the top horizontal web members
(member that runs perpendicular to the top chords). The node was "fix" in
the "y" direction (y direction is perpendicular to the chord members). I
assumed this was O.K. since the top chord will be attached to the rood
diaphragm. The top and bottom chord forces I got were what I was expecting.

On CSTRAAD, I could model the truss with all the members pinned, and I got
the same results as RISA3D.

I'm still "playing" with the computer models, I always try to visualise what
the structure is going to do and come up with estimated forces before I run
a computer model so I can somehow verify what is being "inputed" and
"outputed" makes sense.