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# Re: commercial sign structure

• To: seaoc(--nospam--at)seaoc.org, Fernando.Nacionales(--nospam--at)health.state.mn.us, anacio(--nospam--at)skyinet.net
• Subject: Re: commercial sign structure
• From: Ed.Haninger(--nospam--at)fluordaniel.com
• Date: Mon, 6 Apr 1998 11:39:00 -0400

```     ASCE 7 is available from ASCE at 1-800-548-2723 or www.asce.org

On the analysis part of your question, torsion in a 4 sided truss
tower can be approximated by resolving the moment portion into
reactions on the 4 sides rotating about the center of stiffness,
probably the tower center.  Considering the global torsion action in
this case will probably result in lower forces than the simple 2D
frame type analysis (simple reactions on 2 sides).  You roughly have
the 4 sides of the tower resisting the torsion vs the 2 sides you are
looking at.  It is difficult to assess your situation accurately over
email, but in this case it sounds like you need to consider the 3D
effects.

Ed Haninger
Fluor Daniel

_________________________________
Subject: commercial sign structure
Author:  anacio@skyinet.net_at_-FDInternet at FDINET
Date:    4/4/98 7:47 AM
The tower has bracings on four sides.
I made a similar computation. First a made a plane truss model for the
horizontal truss
with  its 4 hinged supports representing the 4 legs of the tower. I then
applied the reactions to the plane tower  model frame neglecting the
bracing on the two sides.
The forces on this frame is more than twice in magnitude than the forces
for the wind load alone without the torsion.  The resulting members are
quite big so I  advised my client
to place the tower at the center of the billboard to avoid the torsion.
Actually a similar structure is already being constructed here with the
tower at the center. The second structure is for another city where the
site has an  existing small shed that will be affected by the foundation
if the tower is in the center. It will be cheaper to demolish the shed
and rebuild it at about 500 US dollars.

A 3D analysis will be probably give a more economical design but I only
know 2D analysis and do not have a 3D software. I can't afford it yet .

Thanks to all who replied to my post.

Ed Haninger, Harold Sprague, Bruce Bates and Jim Warne.

Harold,

How do I get a copy of ASCE 7-95. Thanks again.

Alex Nacionales
A.C. Nacionales Construction
Iloilo City, Philippines

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