Couplers for reinforcement
When long lengths of bar are required, or when joining additional reinforcement to existing bars, bars are generally ‘lapped’ i.e. tied next to each over (with an overlap equal in length to, say, 50 bar diameters). An alternative approach is to use couplers, that provide a direct connection between the ends of the bars. This is particularly economic for large bar diameters.
Various types of coupler are available, some carrying both compression and tension while others are designed to work in compression only. The most common type are described briefly below, though other types are available:
Couplers with parallel threads: Threads are rolled or forged on the bars, so that the threaded portion has a diameter equal to or greater than the main bar. With cut threads the diameter will be smaller and the load capacity reduced. The threaded ends are screwed into the coupler.
Couplers with shear bolts. This type of coupler, which does not require the bars to be threaded, consists of a cylindrical steel coupler with a line of ´lockshear´ bolts running along its length. The two bars to be joined are placed in the coupler. The bolts are tightened, forcing the bars against hardened steel locking strips, until a specified torque is reached.
Metal sleeves swaged onto bars. A seamless malleable steel sleeve is slipped over the abutting ends of two reinforcing bars. The sleeve is then swaged (deformed) onto the ends of the bars using a hydraulic press, which compresses the sleeve laterally over the bar, gripping the ribs.
Wedge locking sleeves. This system can be used for connecting bars in compression only. The bars to be joined are held in concentric bearing by the lateral clamping action of a sleeve and wedge. Driving in the wedge compresses the sleeve laterally clamping the bars together. It is important that the bar faces are cut accurately and are aligned before assembly.
Several types of coupler are covered by CARES Technical Approval assessment. Further information may be found in Ancillary products for reinforced concrete construction, Part 8 of The CARES Guide to Reinforcing Steels series, which is available from UK CARES (www.ukcares.com)