Pan joist construction refers to a one-way structural system using a ribbed slab formed with pans. The system achieves economy through the re-use of standard forming pans. Special design provisions for pan joists have been established through many years of construction experience. Standard pan forms produce dimensions of 20 to 30 inches and depths range from 6 to 20 inches, although other sizes are available. Spans normally range from 15 to 50 feet, but may be extended by post-tensioning. Waffle plates are coffered flat plates that result in a two-way structural system. Forming domes are available in standard sizes or may be custom-made to suit specific job requirements. Repetition of form use permits overall economy. Waffle plates provide convenient two-way cantilevering. With standard dome sizes, waffles can provide an attractive patterned ceiling. Special finishes can be obtained through the use of precast concrete or plastic domes. Recesses formed by the domes provide convenient space for lighting fixtures and other mechanical services. Holes may be provided to accommodate mechanical functions within the depth of the slab. A flat plate is a two way reinforced concrete framing system utilizing the simplest for structural shapes- a slab of uniform thickness. The flat ceiling is economical to form and may be used for the finished surface without additional treatment. The simple forming and two-way structural action permit economical cantilevers and other architectural projections. A flat slab is a two-way reinforced structural system that includes either drop panels or column capitals at columns. It is essentially a flat-plate roof with additional depth near the columns to resist heavier loads, thus permitting longer spans.