Simple scale model demonstrating the "bundled tube" principle developed by Fazlur Khan, first used in the construction of the Sears Tower.
Needs various lengths of 1/2" Schedule 40 PVC pipe: 2 @ 204mm, 2 @ 271mm, 3 @ 373mm, and 2 @ 457mm. These lengths were calculated on the Tower's base of 225 ft. square and a height of 1450 ft., without antennae. All these numbers could be wrong, but it looks okay to me. This was a very simple project to build.
Once the novelty value has faded, you can cut the tubes in half and make something useful, like a dandy holder for artist's brushes.
Yes, I know it's now called the Willis Tower, but old habits die hard. It's the Sears Tower. Period.