Title: Advances in Precast Floor Systems
Author(s): F. N. Menefee
Publication: Journal Proceedings
Appears on pages(s): 113-124
Keywords: no keywords
Reinforced concrete floors and roofs for office and school buildings, apart-ments, and similarly loaded structures are being made of precast blocks assembled to form a "plank" or "slab," precast joists with a precast filler placed between, and 4-ft wide precast slabs supported by two integrally pre-cast T-joists. The high cost of carpentry has brought about a successful attempt to eliminate most of the previously required formwork. The trend is toward units made of high strength, lightweight aggregate under closely controlled factory conditions. In one of the plank or slab types herein reported the steel is given a stress of approximately 18,000 psi, but it is believed that most of this prestress is lost through shrinkage and plastic flow by the time actual working loads are imposed. Special shape block forming and grinding equipment produces blocks to be assembled into floor plank or slabs held in compressed relationship by threaded steel reinforcing rods. Precast inverted T-joist forming machinery makes joists to be used with a special shaped hollow filler block to make a floor which may be laid without form work. Tests show that for the most part standard reinforced concrete theory is applicable to these new floor systems. Where there is doubt as to the theory covering the new types, tests are being made under Sec. 103 (a) ACI Building Code (318-51) and Minimum Standard Requirements for Precast Floor Units ACI 711-46, resulting in widespread approval.