stresses in framed structures

[chthulu]

Hi,
In the picture that follows, is fig 9 correct?
Using the scale in pounds shown there, the 70LBS line seems to be correct, where line a seems to be more or less 110 lbs and line b seems to be more or less 130 lbs, but using trigonometry I got something else for a and b.
So, is it possible to get a and b through trigonometry?
If you draw the line for the 70lbs according to the scale in pounds, how do you know where to stop when drawing a? or b? if you start from b.
I mean line a could be any length and fig 8 does not indicate how long line a should be.
What would be the best way to add the sketch of fig 8 together?
I really do not understand even how the 180 and 230 lbs are get.

 

[WKTaylor]

Where did this figure come from? Bruhn?

 

[chthulu]

no, how-to-build-ultralights-amp-plans-by-herbert-beaujon

 

[WKTaylor]

More info is likely available at www.homebuiltairplanes.com/forums/...

How to Build Ultralights by Herbert Beaujon Technical Manual

Technical manual on How to Build Ultralights by Herbert Beaujon

www.homebuiltairplanes.com

Your 'worked/partially intact figure' came from pg. 24... this left me scratching my head.



There is a 'CAUTION' about using Beaujon's manual for design, posted in the following thread on the Hombuiltairplane.com/forums...

Herbert Beaujon- My all time hero !

Home or this specific page Tubing Connections I was bouncing around the internet and was happy to find a website that is sharing his work. He wasnt the most accomplished engineer ( was a real estate agent ) but he had the best imagination and was willing to put ideas on paper far...

www.homebuiltairplanes.com

 

[GregLocock]

I'd be very wary of using a reference that labels a force diagram as a stress diagram.

Anyway he's constructed a Cremona/Maxwell diagram . This is good. I'm not crazy about his notation, should have used Bow's.

The key to determining the forces in a and b is shown in the little triangle at the top right. The vertical component of 70 lbf can only be provided by b, which then generates a tension in a to react the horizontal component of b.

The force in each member is purely axial, hence must be aligned with the geometry of that member.