Modular floating structures suitable for supporting offshore oil drilling and production platforms may be fabricated utilizing a Y-shaped joint interconnecting plural legs of a space frame. The space frame may be made up of plural frame members where each corner of the frame includes a Y-shaped joint. Stable offshore floating structures for drilling and production platforms may utilize the integral space frames in a truncated dodecahedral, inverted pyramid or tetrahedral configuration. The Y-shaped joint may be formed of three channel members each having opposed legs which may be secured to the opposed legs of the other channel members in a back-to-back or face-to-face configuration to form the Y-shaped joint. The channel members may be fabricated of flat plate folded and cut along predetermined lines to form the channel members. If the channel members are secured to each other face-to-face, they may form hollow flotation chambers suitable for use with the floating structures. Cylindrical tanks can be used as modular components. The Y-shaped joints may be easily fabricated on site or prefabricated and nested for ease of storage and transport. The Y-shaped joints may be formed as flexible inflatable members interconnected by coupling members to form a rigid floating structure. The Y-shaped joints and connecting leg portions may also be used to temporarily store fluids, such as crude oil, produced from subsea wells connected to the floating structures. The Y-shaped joints may be deflated for transportation of the structure on the sea.