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Re: commercial sign structure

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Michael Valley wrote:

> On 04 Apr 1998 20:50:11 +0800 Alex Nacionales  wrote:
> > 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.
>
> You should exercise some caution.  Even if the billboard is centered
> on the tower, (in reality) torsional response still results when the
> wind blows at an angle to the face.  If your structure is very
> sensitive to such torsion (for instance due to its flexibility), you
> should still consider some torsional response.
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> - -
> Michael Valley                                   E-mail:
> mtv(--nospam--at)skilling.com
> Skilling Ward Magnusson Barkshire Inc.
> Tel:(206)292-1200
> 1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:
> -1201
>
>

 The torsional force  in this case should be much smaller and but I will
take your advice and check it.

  I have a follow up question. The billboard has two faces facing both
directions on the road. If  the space between the billboards is open on
top, bottom and sides.  What would be the wind loads on the billboard
behind  assuming wind direction is perpendicular to the billboard in
front? Using the same wind  pressures as the front billboard would be
conservative.
My reference is based on UBC 1988 and the nearest provision that  i can
find  is that no reduction in wind pressure shall be taken for the
shielding effect of adjacent structure. My other reference is based on
the ASCE report of sub-committe 31 which is entirely different. The UBC
1988 provisions are more conservative.


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