The Yugoslav development known as the Zezelj system has been broad described in article F:730025. A square or rectangular module, about 10 to 10 feet up to 20 by 20 feet, forms the basic element. The module is composed of four columns and the floor between them. The slabs and columns are linked together by post-tensioning. The full set of components includes: columns, normal or cantilevered floor slabs and stairway-supporting staircase girders and steps, edge girders, shear walls, exterior wall panels, and partition walls. A building constructed according to this system is a three-dimensional prestressed concrete space frame stiffened with vertical diaphragms. Normally the design of the structure accounts for: vertical and gravity loads of 120 pounds per square foot, wind, and seismic forces. The floor slabs are designed as a grid of girders elastically fixed in the columns. This is conservative since the monolithic slab considerably increases the strength of the girders. Test performed at the Belgrade Institute for Testing Materials have shown that the 14 by 14 foot standard floor slab will fail at a total load of 515 pounds per square foot, which is more than four times the design loading. The relatively light weight of the construction makes this system particularly suitable for the erection of structures on terrain with low bearing capacity in that the foundation problem is easier than for other types of construction. The following types of foundations have so far been utilized: isolated footings, reinforced slabs and grade beams on column lines, grillage of prestressed concrete, and piles.