Jerry Hey wrote:

Paul,  on the longer Schertz beams could I weld plates inside the beam
in the form of a  W truss to stiffen the beam instead of a strut

brace?

    Jerry

That would not help. Just make it 1/4 or 1/2 inch deeper.
The strrength goes up with the square of the depth. A 1 inch deep
beam is 1. A 1.25 inch deep beam is 50% stronger. a 1.5 inch deep
beam is 125% stronger.

Paul Lamar

"Decker, Michael" wrote:

It's more acurate to say that stiffness, not strength, increases as the

cube

of thickness.

Correct. Stress is inversely proportional to I/c = 1/6 bd^2 I had the

right

formula the first time. Square law. Thanks for catching that.

Paul Lamar

OK! I cannot stand this any longer - since we are building airplanes,
I doubt that we are using solid bars for this mount - for a rectangular
tube, or a hat section, the major working areas are the top and bottom
"flanges" so for a given wall thickness strength only goes up slightly
faster than linear with increased depth. dig out your old copies of
Rourke, and compute some I over C's for the real sections you are proposing.
Vance

I did Vance. A hat section with wide flanges is equivalent in "I" to a rectangular
tube with the lower wall split in half and the parts bent outwards.

For a  one inch high hat section with .0625 wall:

I = (bd^3-b1d1^3)/12

I1 = (2 X 1)^3 = 8    I2 = (2 X 0.875) ^3 = 5.359

I  = 8 - 5.358 = 2.641

Height of beam doubled to two inches high wall .0625:

I1 = (2 X 2)^3 = 64  I2 = (2 X 1.875)^3 = 52.73  

Therefor I now equals 64 - 52.73 or 11.27 which is a whole bunch higher
than 2.641!!!!!!

Max Stress = MaxMoment/(I/c) where c is half the height of the flange.


BTW you computer clock is off :) 

Paul Lamar
 
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