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# Re: Bow String Truss

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Bow String Truss
• From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
• Date: Wed, 17 May 2006 16:29:19 -0400 (EDT)

```Seeing as I was never a Boy Scout, I am going to offer up what you likely
intented, but just not in "Boy Scout" language...why not just use trig
stuff.  If you go a measured perpendicular distance to the
truss span horizontally on the ground from the truss location and then
sight up to the top and bottom of the truss and measure the angle of those
sight lines, you then will have one leg of the triangle and the
angle...you can then use trig to get the other leg (at least close enough
likely for what you need).  This would get you the height to the bottom of
the truss and the top of the truss.

We did this back in high school to measure heights of trees and buidlings
and signs.  And in reality, if you took a surveying class you did it with
more "accurate" equipment.

Regards,

Scott

On Wed, 17 May 2006, John Riley wrote:

> Can you use an approximation method found in any Boy Scout manual?  Seems like a visual approximation would be far better than a rule-of-thumb approximation.  JPRiley
>
>
> Rich Lewis <seaint03(--nospam--at)lewisengineering.com> wrote:              Is there a standard rise to run ratio that most bow string trusses would use?  I canâ€™t find anything regarding this in my text books.  I have a hanger with a 120 ft. clear span.  I eyeball the truss height at 15-16 feet.  It would take rental of a lift to verify it.  I want to check the wind load on the building and would like to find a good approximation of the height.  The truss is fabricated from pipe.
>
>   Thanks for any insight you may be able to give.
>
>   Rich
>
>
>
>
>
> ---------------------------------
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