Producers have always touted pre-cast concrete as a contractor-friendly building system. Often its design can eliminate extra work at the jobsite and boost safety and speed.
So it's not surprising that the use of the Supranos Systems' patented precast concrete structural floor and roof system has grown steadily in Florida over the past 12 years. But support for the system has come from a surprising source: Mason contractors who work on the flooring system report substantial gains in their productivity and margins.
“Masons love us because we offer the least disruptive approach,” says John Ambrose, Supranos' co-owner and CEO. “Our installation crews are in and out quickly and let the masons move up rapidly.” About 80% of the company's projects involved masonry structural systems.
But its not just mason contractors who can benefit. The precast floor system also has been installed on other structural systems, including insulating concrete forms, tilt-up, plant-manufactured precast, structural steel, and even wood.
Now with a proven construction record, the producer hopes to expand into new markets and is considering licensing the system to other producers.
“The challenges are to get people to understand the system and learn how to work with it efficiently,” says Jean-Pierre Ghazal, co-owner and director of operations for the South Bay, Fla.-based company. “It works beautifully when the design engineer understands its full capabilities and allows the contractor to use it to its best advantage.”
The system is very flexible, allowing architects to design buildings of practically any shape. “There's really nothing standard about most of the projects,” says Ambrose. “We can accommodate many shapes and loading conditions.”
The system consists of precast concrete panels, typically 8 feet wide and 3 inches thick, that utilize steel joists as the main load-carrying component. The slabs are cast with camber, increasing their load-carrying capabilities. They typically are fabricated up to 40 feet in length with the standard thickness, but can span longer via custom designs. Other widths can be provided, although joists typically are placed 8 feet on-center.
The 15½-inch joists are cast into the concrete, which is reinforced with welded wire mesh. Additional lifting points and other stress areas also are strengthened. The web and bottom chord feature 50-ksi steel, while the top chords have 60-ksi weldable rebar. A double top chord is fabricated for all joists longer than 25 feet. The webs are generally continuous for each specific diameter, and they are bent to a sinusoidal shape.
Getting the mix right
The concrete mix provides 1200 psi compressive strength within 18 hours. The slabs are cast at the company's 10-acre plant and stacked and delivered to the site in loads up to 1250 square feet per load. There, a crane (typically 70 tons, although 40- to 200-ton cranes can be used) lifts them into position. They are set with their joist shoes sitting on embeds installed by the shell contractor.