torsional section properties

[3dboy]

This may be an obscure question but any help would be wonderful. I am reviewing some calc's from another engineer and he has used a formula for "torsional section property: hollow rectangle" try as I might I can not locate any reference which includes the formula it is: k=[2t*t1*(a-t)^2(b-t1)^2]/{at+bt1-t^2-t1^2} I've checked roark's, salmon and Johnson, my advanced mechanics of materials book, my Beer and Johnson book, and I'm kind of lost thanks for the help.

 

[desertfox]

Hi 3dboy

The formula is correct I have the same formula in the book
"Machine Design theory and practice" authors are Deutschman,
Michels and Wilson publishers are Collier Macmillan.
The formula is the "Polar Moment Of Inertia".
To help you visualise where the letters fit draw yourself
a hollow rectangle and mark the following letters on the drawing:-

a = horizontal overall width of rectangle

b = vertical overall height of rectangle

a1 = horizontal inside width of rectangle

b1 = vertical inside width of rectangle

t1 = vertical wall thickness of the horizontal
dimension a1

t2 = horizontal wall thickness of the vertical
dimension b1

and the formula looks like this:-

k= 2*t1*t2(a-t2)^2*(b-t1)^2
------------------------
a*t2+b*t1-t2^2-t1^2



hope this helps

regards desertfox

 

[jec67]

Hello. The formula is in Roark's. It is in the It is Table 20, case 16 in the 6th edition.

 

[3dboy]

Awesome!

Thanks guys I appreciate the help.