Architecturally exposed structural steelwork (AESS)

When Section 10 applies

AS/NZS 5131 defines architecturally exposed structural steelwork as steel that is visible and forms part of the architectural intent of the building (Clause 3.1.1). Section 10 is not triggered by the construction category: it applies only where the construction specification expressly designates members as AESS, and its requirements sit on top of everything else in the Standard. A CC2 shopping centre can contain AESS 4 feature columns, while a CC3 industrial frame may contain none.

For an assessor, the first question is therefore simple: which members are AESS, and in which category? Without that designation the fabricator works to normal structural workmanship, as described in preparation and fabrication and welding. Each step up the AESS scale adds grinding, filling, handling care and inspection time, so designers are well advised to designate only the surfaces that are actually seen.

The five AESS categories

Clause 10.2 and the AESS matrix in Table 10.2 describe each category by a set of characteristics. The matrix is cumulative: a higher category inherits the characteristics of the lower ones and adds its own. The summary below is written in our words; refer to Table 10.2 for the full matrix.

The 6 m viewing distance is the practical boundary between AESS 2 and AESS 3. It is a useful prompt for the designer: a roof truss 9 m overhead seldom justifies AESS 3 finishing.

What the construction specification must state

Clause 10.3 places the obligation on the designer to set out AESS requirements in the construction specification (see Appendix B). Machined or locally abraded surfaces must also be identified on the shop and erection drawings. In addition the specification should identify:

• where one surface treatment changes to another on a member – the transition line or plane;
• tack welds, temporary braces and fabrication fixtures, and how they are treated;
• any fabrication or erection tolerances tighter than those in Appendix F;
• every architecturally sensitive connection detail;
• the specific requirements of any AESS C element;
• whether a visual sample or first-off component is required for acceptance before production.

For an offshore fabricator these points must be settled during detailing, before material is cut. Missing information should be raised as a formal request for information and the answer recorded on the shop drawings, so that the factory, the client's inspector and the erector all work to the same standard of finish. See also specification and documentation.

Additional fabrication requirements

Clause 10.4 lists the extra shop controls. The most significant, in summary:

• Handling: special care to avoid marks and distortion; nylon slings, or chains or wire rope with softeners; soft tie-downs on loads; minimal damage to coatings.
• Temporary work: tack welds ground smooth; blemishes left by removed braces or fixtures repaired.
• Geometry: for AESS 2, 3 and 4 the straightness tolerance is half the Appendix F value (Clause 10.4(g)); AESS 3 and 4 require matched abutting cross-sections and uniform gaps or uniform contact at copes, mitres and butt cuts.
• Welds: spatter, slivers and surface discontinuities removed in every category, with weld preparation grade P3 (Clause 9.8.4); in corrosive environments all joints seal welded.
• Surfaces: sharp edges from flame cutting, shearing or grinding softened; blast cleaning to at least Sa 2 to AS 1627.4 unless specified otherwise.

Coating requirements follow the normal provisions of Section 9, described in corrosion protection; for AESS the surface preparation and any filler must be compatible with the specified paint or galvanized system.

Visual samples and first-off approval

Table 10.2 treats visual samples as optional in every category; when used, the construction specification chooses the form: a 3D rendering, a physical sample, a first-off inspection, or a scaled or full-scale mock-up. For a project fabricated overseas, an agreed first-off piece is the most reliable way to turn words such as "smooth" and "blended" into an objective acceptance standard. The approved piece – or detailed photographs and measurements of it – then becomes the reference for the rest of the production run and for the pre-shipment inspection.

A first-off approval works best as a hold point in the inspection and test plan, with the client's representative attending in person or by live video, and the outcome recorded in English in the project quality records.

Additional erection requirements

Clause 10.5 – and Clause 11.5.9 in the erection section – carry AESS through to site. The erection must be planned so the architectural appearance survives unloading, handling and lifting. The main points:

• slings of nylon strap, or chains with softeners; care to limit coating damage;
• marks from temporary braces or fixtures repaired, and tack welds ground smooth;
• unwanted holes ground and filled, then finished to the same standard as the shop work;
• backing bars for site welds removed, the area ground smooth and the coating repaired in accordance with Clause 9.12;
• bolt heads on the same side within a connection and consistent from one connection to the next;
• Appendix F erection tolerances, unless the specification sets tighter values.

Because erection is normally carried out by the client's erector, the fabricator's contribution is protective packing, clear piece marks that do not remain visible on finished faces, and erection drawings that flag AESS members. See erection and site work.