Patent ID: 7618217

Claim:
A post-tensioned concrete foundation for supporting on its upper surface a tower or other structure subject to high upset forces which comprises: a cementious foundation cap for supporting a tower or other structure from an upper surface and having a lower surface; a plurality of cementious pile anchors spaced from one another and extending downwardly from said foundation cap lower surface into surrounding soil underneath said foundation cap; a plurality of tensioning elements each having a lower end adjacent and bonded to a bottom portion of a respective one of said pile anchors, and extending upwardly within an elongated sleeve through each said pile anchor and said foundation cap, and terminating at an upper end above said foundation cap upper surface; and a void forming element for creating a void space or highly compressible region between a top of each of said pile anchors and an adjacent portion of said foundation cap lower surface which, upon tensioning of said tensioning elements, allows said foundation cap to move downwardly against soil adjacent said foundation cap lower surface and said pile anchors to move upwardly into said void space or compressible region to at least partly reduce a size of said void forming element.