Abstract: A high-rigidity structure is formed using vertical column members comprising hollow right cylinders with four integral, radially-projecting, equally-spaced flanges. The flanges have a plurality of holes for mounting structural elements along the length of the columns. A set of platforms may be supported by structure that resides in the space immediately below the platforms, thus access to the platforms is unobstructed by support structure for the platforms above. This arrangement allows the platform to be serviced by hoists from more than one side, and for access from the hoists to be unobstructed.