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Re: Master/Slave (Was STAAD or RISA?)

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Daryl,

In a "true" master/slave relationship you are correct...you are locking a
certain number of the degrees of freedom of the slave joints to the master
joint.  Note that I believe in some/most programs that include this
feature, that you can set it to only lock certain degrees of freedom.  For
example, if I recall correctly, when using STAAD (older versions) you
could lock the X and Z translation by leave the Y translation and
rotations unlocked.  This would force the slave nodes to translate
identically to the master node in the X and Z directions, but could move
differently in rotation (that is the node itself could rotate but the
"diaphram" could not) and in the Y direction translation.  I have to admit
that I am not sure to what use this would be put...but then I have not
really thought to hard about it.

Now, some programs (which might include STAAD now a days) don't really do
a true master/slave function but rather force the "slave" nodes to
maintain a constant relative distance (which directions can be set...i.e.
is it in the X dir only or X and Z, etc) from the "master" node.  This to
me is no longer a master/slave function, but a rigid diaphram function.
Just my own symantics.  <grin>

HTH,

Scott
Ypsilanti, MI


On Fri, 6 Sep 2002, Daryl Richardson wrote:

> Scott,
>
>         Thanks for bringing this Master/Slave thing up.  I have never properly understood it.
>
>         As I see it making a group of nodes slave to one other node makes ALL of the degrees of freedom for the group the same.  This means that the group can move "en mass" but can not rotate since rotation would some nodes to move more than others (ie. rotate about some axis).  I can't visualize any practical use for this feature.  If anyone can clarify the real use of this Master/Slave thing I would appreciate it.
>
>         Thanks for any clarification that can be provided.
>
> Best regards,
>
> H. Daryl Richardson
>
> Scott Maxwell wrote:
>
> > Dave,
> >
> > I am curious...what do you use the master/slave funciton for?  Is it
> > per chance to "model" the diaphram action in a 3-D model?  If so, you may
> > want to be a little careful with STAAD.  While they may have updated the
> > function, I do know that in older versions (not too old) the master/slave
> > could not be used to get a true rigid diaphram effect.  The master/slave
> > function makes ALL the slave joints translate the same as the master joint
> > in plane of interest.  The result is that using the master/slave method
> > will not allow for torsional rotaion of floor plane due to relative
> > stiffness of lateral frames/walls.  In otherwords, your model (if using
> > the master/slave function to model the diaphram) will be ignoring the
> > torsional effects of the lateral loads.
> >
> > RISA does have a diaphram option that at least appeared (it has been a
> > while and I don't have RISA to use at this time) to include the torsional
> > effects.
> >
> > HTH,
> >
> > Scott
> > Ypsilanti, MI
> >
> > On Fri, 6 Sep 2002, Dave Langhone wrote:
> >
> > >
> > > I had to sign-up once James told me about this discussion. STAAD, baby! The flexibility you have in that program is amazing. It has the power of the free-form command file (unlike SAP or Strudl) and batch processing with great interface. You can do unlimited project sizes, multiple structures, vibrational analysis - can't in RISA. RISA is a nice program - but STAAD has the power and the user-interface. It is like a hybrid of the Incrdible Hulk and Wonder Woman (hee, hee!). We do a lot of multi-story parking structures - so I need the concrete design, master/slave and advanced plate elements - plate releases, pre-stressed loadings. The great thing is that I can make a change in so many ways - command file, Excel-like spreadsheets, graphically. We used to maintain a few packages but now have consolidated to STAAD.
> > >
> > > Go Mariners!
> > >
> > > Dave
> > >
> > > PRCE
> > >
> > >
> > >
> > > ---------------------------------
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> > > Yahoo! Finance - Get real-time stock quotes
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