I obtained a volume of 260400 cubic feet. This may be off by a percent or two because of the crude method I used.]]>

Let's center our circle at the origin and draw two vertical lines at x=40 and x=-40 (so the distance between them is 80). We know that our circle intersects both lines, and that the "top" of the circle (where it intersects the y axis) is 24' higher than that point of intersection. Connect the points of intersection, and you have your secant line.

Now:

r = (c² + 4h²) / (8h)

Source: The Math Forum

c = 80

h = 24

r = (80² + 4*24²) / (8 * 24) = 45 1/3

Now, you need to find the area (K) of the segment, but first, you need to find the central angle (theta). The formulas from MathForum:

theta = 2 arcsin( c / [2r] )

K = r²[ theta - sin(theta) ] / 2

You can then "extrude" your segment area by multiplying by the length of your quonset.

]]>Also, it would probably make more sense if the hut's cross-section was a segment rather than a semi-circle, because then the height and width could both take the given values. Unfortunately working out the volume of a segmentular prism (?) involves more complex maths than before. Whatever the calculated value is, you should probably round it down a bit if you are thinking of using the information practically, because some of the volume will be impractical as storage space, unless you're filling it with gas or something.]]>

The volume would be pi*r²*h/2 = (3.141592 x 648.4556 x 205)/2

= 208,811.285 cubic feet]]>

I need to know how many cubic feet it will take to fill it completly.

here is a link so you can see what I am talking about.

http://en.wikipedia.org/wiki/Quonset_hut

Thanks for your help