Preparation, assembly and fabrication under AS/NZS 5131 Section 6

What Section 6 covers and why assessors start here

Section 6 of AS/NZS 5131 governs everything that happens to steel between receipt and welding or bolting: identification, handling, cutting, shaping, holing and assembly into fabricated items, and finally protection for transit. Clause 6.1.1 ties all of this to the fabrication tolerances of Appendix F and requires that the facility and equipment are maintained so that wear does not cause inconsistent output. In other words, the standard expects a controlled process, not just a good final dimension check.

Two procedural requirements apply regardless of construction category. Clause 6.1.2 requires the operations to run under a suitable quality management system (see quality management under AS/NZS 5131), and Clause 6.1.3 requires a documented work method statement for each operation and each stage of work before it starts, available to the people doing the work. Steel that will be painted or galvanized must also meet Clauses 9.3 and 9.8, and AESS must meet Section 10 (Clauses 6.1.4–6.1.5).

Identification, marking, handling and customer property

Clause 6.2 requires the fabricator to keep the manufacturer's test reports and certificates for every item of steel and to run a tracking system that supports the traceability rules of Clause 5.2.3 (covered in materials and traceability). For New Zealand work at CC3 and CC4, the tracking system must also trace welders and welding procedures to individual primary connection welds, by weld map or welder ID stamp.

Marking must not damage the steel. Unless the specification says otherwise, hard stamped, punched or drilled marks are limited to grades up to GR 350, are not used on coated cold-formed material, and are kept to areas where fatigue life is unaffected. Zones where marks are prohibited – typically fatigue-loaded details or potential plastic hinge regions – should be stated in the construction specification. Any piece that cannot be clearly identified becomes unidentified steel and is dealt with under Clause 13.3.7.

Clause 6.3 asks that members, components and fasteners are handled and stacked to avoid damage or permanent deformation, with painted and galvanized items following Clauses 9.9.19 and 9.10.10. Clause 6.4 treats customer supplied property – components, but also drawings, models and data – like purchased items: identified, verified, protected, and any loss or damage reported and recorded.

Cutting: methods, cut quality and re-entrant corners

Clause 6.5.1 allows sawing, shearing, cropping, machining, thermal cutting (oxy, plasma, laser) and water cutting unless the specification excludes a process. Two restrictions matter in practice: material over 16 mm thick should not be sheared where it will be galvanized and loaded in tension (unless stress relieved), and shearing is not permitted in designated seismic yielding regions – sheared material there is cut 3 mm oversize and machined back.

Cut surfaces not incorporated in a weld must meet the roughness limits of Table 6.5, measured by the CLA method of BS 1134. For statically loaded steel the limit is 25 µm; tighter values apply to higher fatigue detail categories and to New Zealand yielding regions. Oversize roughness is ground out, with grinding marks parallel to the cut. Clause 6.5.2 also sets limits on isolated notches and gouges and on when they must be ground or weld repaired under Clause 13.6.2.5. Re-entrant corners must be notch free with a radius of at least 10 mm, normally by drilling at the corner and cutting to the hole (Clause 6.5.3). Edge condition for coating – edge rounding and surface preparation of cut and rolled edges – is referred to Clauses 9.8.4 and 9.8.5; see corrosion protection.

Shaping: hot forming, flame straightening and cold bending

Clause 6.6 permits straightening, bending, pressing and cambering, hot or cold, provided material properties do not drop below those used in design. Where bending strain causes permanent deformation, the designer must confirm the effect has been allowed for under AS 4100 or AS 5100.6. Any cracking, tearing or coating damage from forming makes the piece nonconforming.

• Hot forming and flame straightening (Clauses 6.6.2–6.6.3): heated areas must not exceed 620 °C, with 580–620 °C the preferred range for AS/NZS 3678 plate and AS/NZS 3679.1/3679.2 sections; quenched and tempered steel has a lower cap. Working in the blue heat range (250–380 °C) is prohibited, and peak temperature and cooling must be controlled.
• Cold forming (Clause 6.6.4): minimum bend radii follow AS/NZS 3678 for plate and AS/NZS 3679.1 for sections; weld distortion is corrected mechanically, by limited local heat, or both.
• NZ fracture critical bridge members (Clause 6.6.5): no mechanical cold working and a 600 °C cap.

Holing: punching limits, hole sizes and slots

Clause 6.7.1 allows holes to be machine cut, drilled or punched full size, or subpunched 3 mm undersize and reamed. Hand flame cutting of bolt holes is not allowed, other than as a site fix for base plate holes. The construction category directly changes the rule: at CC1 and CC2 full-size punching is permitted only in thinner, lower-strength material, whereas at CC3 and CC4 punching is limited to subpunching and reaming. Holes must be free of burrs, and full-size punching is excluded in seismic yielding regions.

Slots are only made where the specification shows them; otherwise approval is needed. Cold-formed members to AS/NZS 4600 follow tighter hole clearances. Clause 6.7 also covers countersinking (drilled after holing, bolt flush), pin holes, and weld access holes, whose length and height scale with plate thickness and which need smooth cut surfaces and a minimum 10 mm radius (Clause 6.7.7). Hole details feed straight into mechanical fastening.

Bearing surfaces, assembly and the pre-dispatch fit check

Full contact bearing surfaces must be identified in the specification and produced by cold sawing or machining (Clause 6.8). With members aligned within Appendix F, the gap between abutting ends must not exceed 1 mm, and must be within 0.5 mm over at least two-thirds of the contact area.

Clause 6.9 requires assembly to achieve the Appendix F fabrication and erection tolerances, temporary fabrication attachments to comply with Sections 6–8, and camber or pre-set to be shown in the specification. Clause 6.10 then requires the fit at more complex connection interfaces to be checked and documented before dispatch, using templates, accurate measurement, trial assembly or the method the specification nominates. For an offshore supplier this is the main defence against site misfits that cannot be fixed quickly; see geometrical tolerances.

Transit, supervision and New Zealand yielding regions

Clause 6.11 requires items to be protected before they leave the shop: free ends stiffened, distortion prevented, bearing surfaces protected, coating damage minimised, and loose fasteners and small parts packed and identified in containers. Clause 6.12 requires cutting, holing, shaping and assembly to be supervised by a competent person at CC2, CC3 and CC4; the informative note suggests a trade qualification plus about ten years' experience. Clause 6.13 adds New Zealand rules for seismic yielding regions: subpunch-and-ream for punched holes, a 12 µm roughness limit, and controlled thickness transitions.

This is a summary for orientation only. Refer to the current edition of AS/NZS 5131 for the full requirements, and to the project's construction specification, which governs.