Double tees are used primarily as deck floor and roof components for any type of structure, including parking structures, office buildings and industrial buildings. They are made either pretopped or field topped.
Pretopped tees have a flange thickness of 4 inches, which creates the wearing surface in parking structures. Field-topped tees have a 2-inch flange, on which a cast-in-place concrete composite topping of 2 to 4 inches is added in the field. For roof construction, there is typically no need to add topping on the 2-inch flange.
Tees typically are made in four widths (8, 10, 12 and 15 feet) and six depths (24, 26, 28, 30, 32 and 34 inches). Typical span-to-depth ratios for floors range between 25 and 35, while roofs typically are 35 to 40.
Double tees typically are cast in 300- to 500-foot-long prestressing facilities that are sub-divided into specific lengths for a particular project.
The general production method consists of a 10-step process:
- laying out forms
- stressing the strand
- installing other embedded material and flange reinforcing
- making a pre-pour quality control check
- pouring and finishing the concrete
- allowing about 12-16 hours of curing
- detensioning (cutting) the strands at the ends of each piece
- stripping from the form
- making a post-pour quality control check
- moving the tee to the storage area awaiting shipment to the site.
The form side will generally be “as cast,” resulting in a smooth, hard finish. This usually remains as is and is not painted, although it can be if desired. The top-of-flange side will be smoothed for roof construction, left rough if it will receive a field topping or broomed (either transversally or longitudinally) or circular swirl-finished if it will be used as the wearing surface in a parking structure.
For more information, contact a PCI Certified Manufacturer.