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Re: Bow String Truss

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Scott,

You're on the right track, Scott. We used to do just that back when I was a new graduate. We even took it to the next step and drew vector force drawings (to scale, of course) and could thereby solve for all of the member forces in a truss. Generally this was faster than many people today could enter the co-ordinates and member connectivities in a computer program. The downside, of course, was that the procedure had to be repeated from the beginning for each load case.

You may be interested in knowing (in case you didn't already know) that the resulting vector diagram was called a Maxwell Diagram.

Regards,

H. Daryl Richardson

----- Original Message ----- From: "Scott Maxwell" <smaxwell(--nospam--at)engin.umich.edu>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, May 17, 2006 2:29 PM
Subject: Re: Bow String Truss


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
Adrian, MI


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?Tt 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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