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Re: Commercial Sign structure

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     Alex,
     
     With a 2D analysis program you will be very limited in what you can do 
      here.  You could try to approximate the torsional forces on the 
     structure by hand and apply that to 2D frames representing the sides 
     of the tower.  If you have bracing on 4 sides that will be very rough 
     (probably conservative)
     
     You really have a 3D problem.
     
     Ed Haninger
     Fluor Daniel
     Irvine, CA


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Subject: Commercial Sign structure
Author:  anacio@skyinet.net_at_-FDInternet at FDINET
Date:    4/3/98 9:57 AM


I am designing a  commercial sign where  a steel open frame tower 
10'x10' with four legs and 90' tall supports a 30' high x 50'wide 
billboard  like a cantilever beam.  The billboard  is framed with 
several horizontal trusses connected to the four legs
of the tower. The wind load on the  billboard  produces  a large 
torsional force on the tower.
     
     
     
                                    50'
                      nnnnnnnnnnnnnnnn
               30'     n
n                                                  50'
                      nnnnnnnnnnnnnnnn
xxxxOxxOxxxxxxxxxxxxxx
                         n
n                                            10'   x      x     x 
x      x     x
                         n
n
xxxxOxxOxxxxxxxxxxxxxx
                         n    n 60'
                         n
n                                                                 Plan
                     __n__n __
     
                        Elevation
     
     
I am using RISA 2D only.  How do you create a 2D model for the open 
frame tower taking into account the torsional forces from the billboard? 
Is it possible to do this or do you need 3D analysis?
     
Thanks in advance.
     
     
Alex Nacionales, CE
anacio(--nospam--at)skyinet.net