The Adjustable Hear Restraint (AHR) is designed to provide lateral restraint at the top of an internal block wall or the inner leaf of a cavity wall. The ‘outer’ section of the AHR is fabricated from a rectangular hollow tube to create and maintain a void in the vertical mortar joint, allowing the ‘inner section’ to move freely. A movement joint of up to 25mm between the soffit/bottom of steel and the top of the inner section accommodates normal movement due to live loading, thermal expansion/contraction, and post-construction shrinkage.
The design shear resistance of shear ties that conform to BS EN 845‑1 should be considered as the declared shear load capacity relevant for the type of mortar and masonry units. This is divided by the γM value for use with ancillary components given in NA to BS EN 1996-1-1:2005, Table NA.1. For sites in the UK, this value is 3.5.
The horizontal leg of the outer section should be built into the bed joint, ensuring the unit’s centerline is no closer than 50mm from the edge of the block. The vertical section must be built into the perpendicular joints, with mortar filling the remaining voids on either side. The inner sliding section can be crafted with a hole or slot to accommodate an M6 fixing, or it can be supplied with a specially notched end to fit 28/15, 38/17, or 31/21 cast-in channels. The standard system is designed for a 215mm high block and resists a load of 1.5kN in a 7N block per unit. However, customized systems can be crafted to fit particular requirements. Depending on the load requirements and edge reactions of the specific panel, AHRs should be installed at 450mm, 675mm, or 900mm centres.