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Re: SAP, RISA3D, STAAD

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Greg,

To elaborate further on torsional warping, you're right that a typical moment
connection will not fully develop warping restraint, but a moment connection
where the flanges are restrained will develop SOME warping restraint, so to
assume that no warping restraint is present is also incorrect. So, in reality,
we would have partial warping restraint.

So the next question is "How MUCH warp restraint is present?", and the answer
is "It depends". The degree of warp restraint depends on the type and quality
of the connection, the size and properties of the wide flange and also the
length of the wide flange. I've fooled around a bit using finite element
models to model warp restraint for I shaped cross sections and I've found that
varying any of the previously listed parameters can make a significant
difference in the amount of warp restraint. So, really, it's up to the RISA-3D
user to decide whether he (or she) wishes to include warping restraint, with
the resulting warping stresses, in the analysis. If you are of the opinion
that warping restraint at your connections should not be modeled, simply turn
that feature off in RISA-3D. If DO want to include torsional warping, turn the
option on.

Maybe some grad student out there looking for a thesis or dissertation topic
might consider "The Modeling of Partial Torsional Warping Restraint".

Regarding master/slave and rigid diaphragms, let me address this in a more
general sense (rather than in a "program specific" sense). Classically, a
"master/slave" relationship involves two or more joints sharing one or more
degrees of freedom (DOF). A typical application for this is in modeling X
bracing where the braces are pinned at their crossing point. They would share
the same translational DOF at that point, but be released from each other for
rotation. To model this, two nodes representing the midpoints of the two
braces would be slaved to each other for translations, but not for rotations. 

Rigid diaphragms must be modeled using rigid links rather than master/slaves
in order to maintain translation consistency. Granted all the nodes on the
diaphragm should, in a strict sense, have the same inplane rotation, their
global translations will not be numerically equal. This a brief and incomplete
answer to your question, I know, but for more on this, I recommend you review
the section "Diaphgrams" in the RISA-3D user's guide (anyone else who is
interested and doesn't have access to the RISA-3D manual can email me
PRIVATELY and I will fax this to you).

Regarding STAAD specifically, the last time I used that program they modeled
master/slave in the classical sense. 


Bruce Bates
RISA Technologies