Concrete foundations for supporting towers and other structures under heavy cyclical loads are described. Some or all of the major concrete components, such as the beams and the hubs, that form the foundation are fabricated off-site and then transported to the intended use site for the foundation. The concrete components can be fabricated as pre-cast segments, sections, or pieces, with the pre-cast segments then being assembled in the field at the use site to form each component, and the components then being assembled together to form the foundation. In one embodiment, the beams used in the foundation may have a box-girder construction.