Form ties (sometimes referred to as tie bolts) connect opposite faces of wall formwork to restrain the applied concrete pressures. They transmit loads in tension between stiff vertical and/or horizontal members associated with the main formwork.
The principal types of systems of tie rods that can be used are listed below. It should be noted that not all are available in the UK:
(a) High tensile through ties which are usually reusable ties sleeved in the concrete.
(b) High tensile ties with she-bolts where the tie is lost in the concrete.
(c) Taper ties are reusable through ties which do not require any sleeving in the concrete.
(d) Mild steel ties are generally lost ties.
(e) Coil ties are usually high tensile wires (2 or 4) welded to a wire coil at each end. They are lost ties with cones at each end acting as spacers.
(f) Snap ties are lost ties, and are wire or flat steel ties with a stress inducer allowing the end of the tie to be snapped off after concreting. They are used in building work for thin walls.
(g) Friction clamp ties are clamping devices which are attached to each end of a mild steel or high tensile bar.