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Modeling truss or space frame with STAAD-Pro (was RE: Greetings!)

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John is right. My experience has been that it is more hate than love
relationship. I too have used staad since a long time ago. I could never get
its graphic user interface to work properly without having to go back and do
lots of other things to make it work. But that was before the Pro edition.
This version may be more friendly, however, I have been using SAP2k for the
past two years and have stated really liking structural modeling again! I
use it exclusively in graphic mode and it works great.

Ghassem

-----Original Message-----
From: Connor, John A NWK [mailto:John.A.Connor(--nospam--at)nwk02.usace.army.mil]
Sent: Thursday, October 05, 2000 8:05 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Greetings!


Staad:  I've been using this program since version 14.  Its a love-hate
relationship.  If you are not familiar with Staad, you are in for a wild
ride.  My advice is don't take the graphical interface for granted.  Learn
the commands and the structure of the text input file.  The graphical
interface is a just a tool to help create the input file.  The graphical
interface is not perfect, so you really need to check the input file.  As
you check your input file, you should understand the assumptions and
limitations for each command you are using.  Look up every command you are
using in the reference manual until you become more familiar with the
command.

Another way to model the members which only take axial load is to use the
"truss" command (not related to space/truss file classifications).  This
command will automatically release the supports for these members so that
they only transfer axial loads.  You won't have to assign moment releases
when doing it this way.  Using the graphical interface, the command can be
found under Commands:Member Specifications:Truss.

I believe the correct way to model your tower is to use the "space"
classification.  If you were to use "truss" classification, I think this
will release all moment forces, and every joint would be a pinned joint.
You probably have some members in your tower that have continuous spans
(columns), so "space" classification is most appropriate to get the moment
action in these members.  Also, I think "truss" is for 2D modeling, not
sure. 

I suggest next time that you change your subject description to something
more useful than "Greetings".  (like Staad Pro- Modeling).  I almost deleted
your message until I skimmed over the mention of Staad.

John Connor, PE
Kansas City, MO



-----Original Message-----
From: arman s rivera [mailto:asrivera(--nospam--at)edsamail.com.ph]
Sent: Friday, October 06, 2000 12:49 AM
To: seaint(--nospam--at)seaint.org
Subject: Greetings!


Dear fellow engineers!

Greetings!

I am Arman Rivera, a practicing structural engineer in the Philippines.  Our
firm recently purchased the software Staad Pro 2000 and from the limited
hands-on I have had on it, this software is remarkable.  However, as I've
been reading the manual that came with the software, I have many questions
regarding it.  Is anybody familiar with Staad Pro 2000 that won't mind
answering questions from a novice user?

I've been using Staad Pro 2000 to design communication towers.  My first
question is, should the tower be classified as SPACE or TRUSS?  What I've
done is to treat it is a space and then assign the moment releases at the
end of the diagonals and verticals only (not the main posts), so that these
members would carry only axial forces.  Is this correct?

My next question is on the support conditions.  I have modeled the mat
foundation using finite elements in Staad Pro 2000.  I have defined the
joint supports as ELASTIC MAT by specifying the modulus of subgrade
reactions (kv).  Given the allowable soil bearing capacity, how is the
modulus of subgrade reaction computed?

I have many more questions regarding this software, any help you could give
me would be greatly appreciated.

Thank you very much.


Regards,
Arman S. Rivera

_