To: atm{at}shore.net, tkrajci{at}san.osd.mil
From: tkrajci{at}san.osd.mil
Reply-To: tkrajci{at}san.osd.mil


>From: "Roy Diffrient" 

>...I didn't see the standard truss listed in the results table, but the
>deflection for that design can be easily calculated, and that could be a
>good check on the FEA software, setup, etc.  The deflection is calculated
>by the formula W L^3 / (c^2 A E), where W = load (plus half the truss
>weight, as above), L = truss member length, c = base spacing between
>members, A = cross sectional area of the material in a member, and E =
>elasticity modulus (for steel, 30 million psi).

I ran numbers tonight to compare your equation to my GRAPE software
results.  I used the following:

W = 40 lbs (ignoring truss weight) and 91.8 lbs (considering truss elements)

L = 74 inches

c = 18 inches

A = 0.494 square inches (for the 1 inch pipe I was using)

E = 29 million PSI (GRAPE uses 29 vice 30 million PSI for steel)

...and the results?....

Agreement within 2 percent or better in both cases (ignoring, and including
truss weight)!

That's very promising.  I'm gaining more confidence that I am using the
software correctly and that it is a good analytical tool.

Tom Krajci
Tashkent, Uzbekistan

--- BBBS/NT v4.00 MP