Mechanical Splices

Mechanical splices to reinforcing bars are usually achieved using any one of the
wide-range of coupling systems available on the Australian market. The most
common types of couplers are Ancon Bartec, Erico Lenton and Reidbar.

AS3600-2009 does not have any rules governing the adequacy of mechanical
splices. Factors that should be considered when selecting a coupler are:

Slip – Most international codes limit the slip in the coupler to 0.1mm at 70%
of the yield load. This is to restrict the width of cracking at the coupler
location. Typically cracks in concrete are limited to 0.3mm width. If the
coupler slips 0.1mm under load, then the crack at the surface of the
concrete will be greater than 0.1mm. Shrinkage, creep and flexural cracking
will add to the crack width that has resulted from slip within the coupler.
Uniform Elongation – To maintain the ductility of the structure, the coupling
system must also be ductile. Although a uniform elongation greater than
5% would be desirable very few coupling systems can achieve this. The ISO
standard is a minimum uniform elongation of 3.5% for mechanical splices.
Care should be taken when locating couplers to ensure the ductility of the
structure is not reduced below the design requirements.
Minimum Yield Stress – The coupler system should be strong enough to
develop the characteristic yield stress of the reinforcement, typically 500
MPa. Be aware that actual yield stresses for D500N reinforcement can
range from 500 MPa to 650 MPa.
Tensile Strength / Yield Stress Ratio – To maintain the ductility of the
structure, the Tensile Strength / Yield Stress Ratio of the coupler system
should not be less than 1.08, measured for actual stresses across the full
range of yield stresses (500 MPa to 650 MPa for a D500N bar).
Dynamic Capacity – In areas subjected to dynamic loads, a coupler system
that has been tested for cyclic loading and fatigue should be used. The ISO
and ICBO codes have good cyclic and fatigue testing programs.

When selecting the grade of reinforcement, whether it is L or N, assumptions
are made about the design method and the structure’s performance. It is
important that the designer ensures the coupler system selected is able to
perform in a manner that is consistent with the reinforcement design.

Bartec thread