AS/NZS 4671 Reinforcement

Purpose Minimum dimensions of the standard hooks and cogs of AS 3600:2018 (incorporating Amendments 1 and 2) Clause 13.1.2.7, for D500N bars to AS/NZS 4671:2019, for detailing and scheduling bar ends anchored by a hook or cog. Basis Pin diameter d_i to Clause 17.2.3.3: 4d_b for D500N bars used as fitments (Item (a)(iii)) and 5d_b for other reinforcement (Item (b)). A 180° hook has a straight extension e of 4d_b or 70 mm, whichever is greater (Clause 13.1.2.7(a)); a 135° hook has the same pin and the same length of bar, so its straight leg is longer by the 45° of bend it does not use (Item (b)); a cog has a pin not greater than 8d_b and the same total length of bar as the 180° hook (Item (c)). How a, b and c are measured is shown on the drawing and in the table note; they are rounded up to 5 mm. Using hooks and cogs A deformed bar ending in a standard hook or cog develops 0.5L_sy.t (or 0.5L_st), measured from the outside of the hook or cog (Clause 13.1.2.6; see the Development and Lap Lengths calculator). Where the bar stress exceeds 400 MPa, the hook or cog must enclose, and be in contact with, a transverse bar of diameter not less than d_b extending at least 4d_b on each side. These bends are too tight for tensile stress to be developed around the curve itself, which needs an internal diameter of 10d_b or more (Clause 13.1.2.5). Fitment bends enclose a longitudinal bar not smaller than the fitment bar; fitment cogs are not used where the anchorage is solely in the outer layer of reinforcement (use hooks) or where the cog is within 50 mm of a concrete surface (Clause 8.3.2.4). Working values Below the table: pin diameter, extension, the straight leg of the 135° hook, a, b and c before rounding, the length of bar in each hook and cog, the cog pin check and the Clause 13.1.2.6 transverse bar. Not covered 500L and R250N fitments (3d_b); bends to be straightened or rebent (Clause 17.2.3.3(c)); epoxy-coated or galvanised bars (Item (d)); hooks and cogs on bundled bars; headed bars; bending tolerances. Revision v2 (October 2026): N50 and D500N fitments N28 to N40 added; tables generated from the clause formulas (every v1 value unchanged); dimensioned drawing, labelled with every value, in place of the image and the result cards; working values, notes and tooltips added; inputs renamed.