Commercially available form ties have safe tension load ratings of 1,000 to 50,000 pounds or more. They are usually made of steel--in the form of wires, rods, bands, channels, or angles. On the outside of the form, various wedges, clamps, nut washers, or other devices hold the tie ends in place. There are several ways to classify form ties: light-duty and heavy-duty; removable or stay-in-place; single use or reusable; one-piece or internally disconnecting. One tie may fit into several categories.
ONE-PIECE TIES WITH BREAKBACK
Common prefabricated one-piece form ties are the snap, loop, and flat ties. These ties usually have a weakened cross section to facilitate breakback (or snapping) at a predetermined distance from the wall face, anywhere from 1/4 to 2 inches. These are typically light-duty ties, with safe tension loads ranging from 2,000 to 3,000 pounds.
REMOVABLE ONE-PIECE TIES
Both the pull-out tie and the taper tie are removed from the wall after use. Coating these ties with form release agent or grease helps in pulling them out. Reusable taper ties are manufactured in a wide range of strengths. Some are for light duty as low as 3,000 pounds load while others range up to 40,000 pounds or more. The prefabricated pull-out tie is for lighter duty, with load capacity in the 2,000- to 3,000-pound range.
INTERNALLY DISCONNECTING TIES
Two common types of internally disconnecting form ties are the coil tie and the she-bolt tie. Both have reusable end bolts that unscrew from the inner tie rod member, which stays in the concrete. The she-bolt tie system is commonly used with large crane-handled gang form panels, with tension load capacities from 6,000 up to about 40,000 pounds. Coil ties are also suitable for use with large crane-handled panels.