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Re: QUERY: Use of "Beta" and "Theta" in VisualAnalysis

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When in doubt, check the rendered picture window to see the member
orientation. Sometimes is hard to remember the meaning of some parameters,
and this is a good resouce to avoid modeling errors.

Javier Encinas
----- Original Message -----
From: Brian K. Smith <smithegr(--nospam--at)bellsouth.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, August 03, 2000 6:28 PM
Subject: RE: QUERY: Use of "Beta" and "Theta" in VisualAnalysis


> Bill,
>
> I am sure that the guys from VA can give you a better description, but I
> will give it a shot.  When you draw a member, you are defining the local x
> axis of the member.  The y and z axis are of course perpendicular to the
x.
> If for some reason you need to rotate the member about the primary axis,
you
> would use the theta angle.  I typically do this if I am doing a rigid
frame
> analysis, and I need my columns to align in the strong direction of the
> beams (girders).  This is theta.
>
> Now remember when you apply a load, you can choose to apply the load along
> the global or local direction.  The local direction is defined by the beta
> angle.  If you set up a 3D model, draw a beam, and put a point load on it,
> through the local direction.  Look at it, then change the beta angle to
like
> 22 degrees.  You will see the load rotate 22 degrees, because it is still
> through the "local" section.  Now from here you can change theta all you
> want, hence rotating the beam about the x direction, but the load still is
> applied through the local (beta) direction.  Now set beta back to 0, and
> play with theta again.  You will see that the load never moves.
>
> One reason that the beta angle never showed up on your tubes is because
you
> were in a 2D mode instead of 3D.
>
> Oh and by the way, I thought I was in the IES group, but I have never
> received any email.
>
> Brian K. Smith, P.E.
>
> > -----Original Message-----
> > From: Bill Polhemus [mailto:bpolhem(--nospam--at)swbell.net]
> > Sent: Thursday, August 03, 2000 10:01 AM
> > To: iesug(--nospam--at)polhemus.cc; seaint(--nospam--at)seaint.org; structx(--nospam--at)polhemus.cc
> > Subject: QUERY: Use of "Beta" and "Theta" in VisualAnalysis
> >
> >
> > Sorry to cross-post, but I realize there may be users of VA who
> > are not on the
> > IESUG mailing list, and I want to understand this.
> >
> > I note that VA uses botha "Beta" angle and a "Theta" angle to describe
the
> > orientation of the local coordinate system axes with respect to
> > the global.
> >
> > I am a little puzzled by this, as the description in the dialogue
> > box doesn't
> > really help me understand the distinction between Theta and Beta. To
make
> > matters more unclear, I note that the input field for Theta is
> > "grayed out"
> > disallowing input, at least when the member is an HSS section.
> >
> > Can anyone shed some light on this for me?
> >
> > Thanks.
> >
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