K0 Structural Bolt Installation to AS/NZS 5131: Snug Tight, Part Turn and DTI

Key things to remember

The essentials from this document in plain words. Check the full document before you rely on a figure.

• ✓Snug tight means a few impacts of an impact wrench or the full effort of a person on a standard podger spanner, with the plies brought into firm contact.
• ✓After snug tightening the gap between plies must be 2mm or less, or 1mm or less if the joint is to be tensioned.
• ✓If the fabrication specification gives no tightening pattern, tighten from the stiffest part of the connection out to the free edges, completing each step on every bolt before the next.
• ✓Minimum bolt tension for class 8.8 (AS 4100 Table 15.2.2.2): M16 95kN, M20 145kN, M24 210kN, M30 335kN, M36 490kN.
• ✓Tension K0 structural bolts only by part turn of nut or with DTI washers. Never use torque or hydraulic or pneumatic pressure to measure the tension.
• ✓Part turn of nut from snug tight, with both faces square to the bolt: 1/3 turn for bolt lengths up to 4 diameters, 1/2 turn up to 8 diameters, 2/3 turn up to 12 diameters. Sloped faces need more, per the table.
• ✓DTI (DuraSquirt) washers: orange squirt material faces the steel, best placed on the nut side, and the bolts are tightened until orange shows at every bump (4 bumps on M12 and M16, 5 on M20 and M24, 7 on M30, 8 on M36).

Who it helps: Steel erectors and fabricators installing tensioned structural bolts.