# Homework Help: Tough Civil Eng. Problem

1. Oct 6, 2009

### will3330

1. The problem statement, all variables and given/known data

When building a tall support, often the self weight of the support must be considered. For an optimal support, the volume of material, and hence the cost, will be a minimum. If the maximum allowable stress in concrete is 12 MPa, determine the optimal geometry of the column 100m tall made of concrete to support a mass of 1000 tonnes at its top (like the CN tower).

2. Relevant equations

Weight concrete: 24Kn/m^3
Stiffness: 30000MPa
Cost: \$0.05/kg

3. The attempt at a solution

well I guess I can find the total force = 1000(#tonnes) x 9.81.

Also Stress = Force/Area and from that I can find the radius/diameter of the cylinder.

But the cylinder is suppose to be sort of "cone" shaped I think for optimal geometry (like the CN Tower)

Also, would there have to be a function to find the minimum cost and volume of building this structure?

Thanks

2. Oct 6, 2009

### niteman555

I can't say much, but as for the minimum cost, you might want to try some linear programming given your constraints