Precast concrete panels stiffened by small, integral steel trusses can be used as stay-in-place forms for floor and roof slabs either solid flat plates and slabs or deeper slabs with voids. As an integral floor component, the reinforced concrete panels act as both the soffit of the floor and as the forms for a cast-in-place topping. Since they contain all or most of the bottom reinforcing steel, field work for bar setters is reduced.
The 2 1/4-inch-thick, 8-foot-wide panels are formed in polished steel casting beds to produce a dense, smooth undersurface. The 4000-psi concrete panels are reinforced with either conventional Grade 60 reinforcing steel or, for better control of deflections, with 270,000-psi prestressing strand. From 4 to 25 strands can be cast within each 8-foot-wide panel. Whether prestressed or conventionally reinforced, though, the factory-precast panels ensure the accurate placement of the slab's bottom steel. Four small trusses resembling open-web steel joists are also cast into each panel to facilitate handling and to ensure the interconnection of the precast and cast-in-place deck components so that the finished slab performs as one unit. Available in 2 to 6 1/4-inch heights, these trusses also serve as chairs for the slab's top reinforcing steel.
Immediately after placement, the panels, complete with prefabricated floor penetrations, provide a strong, stable platform for the installation of conduit, pipe, wire chases and other utilities to be encased in the concrete overlay. After the utilities are positioned, the top reinforcing steel is laid over the projecting panel trusses, and the concrete is placed. Flush joints and a factory-made undersurface produce a ceiling ready for finishing, with reportedly no need for grinding and patching.