12 Jan Engineers certification of structural steelwork
With an increasing number of engineers being asked to certify structural steelwork from overseas sources, concern has been raised that RPEQs are taking on increased risk by approving structural steel that does not comply with Australian Standards through not meeting the Deemed to Satisfy (DTS) provisions of the National Construction Code (NCC). Some of the increased demands being placed on certifying engineers is being driven by product substitution where a cheaper product is being substituted for the originally specified product to save costs.
To address this concern, the Australian Steel Institute (ASI) has recently issued guidance for engineers to assist them to meet their duty of care under the NCC and Workplace Health and Safety. ASI Technical Note 015 Ascertaining Compliance of Structural Steel has been released after peer review by industry experts including engineering consultant Arcadis.
High Risk Factor – spot checks vs five percentile characteristic steel material properties
There have been cases where an importer has provided a local engineer with a single or small batch of test results of imported steelwork. These tests have shown a yield strength value equal to or above that of the specified Australian manufactured steel, so the engineer has approved the use of the imported steel (or even regraded the steel to a higher grade based on the test results).
Unfortunately, by basing approval on a single or small number of test results, the certifying engineer is taking on considerable risk, as the substituted steelwork may not meet the requirements of Australian Standards and the NCC.
‘…the certifying engineer is taking on considerable risk, as the substituted steelwork may not meet the requirements…’
It is important to understand that a single batch test of steel, as one gets from one or limited test results, only affords a snapshot of the manufacturer’s production at a point in time. A batch test does not give any indication of long-term quality levels. A statistical approach utilising test data collected over a period of time is required to determine this.
The limit state design basis for the Australian Steel Design Standard AS 4100 is predicated on and calibrated against five percentile characteristic material properties, as required under the NCC. Australian steel product standards define characteristic strength based on the five percentile (95 per cent passing), which is assessed from long term quality testing data.
A single test result provided on a manufacturer’s test certificate, or a single testing outcome, cannot be used to establish the five percentile characteristic strength used in AS 4100.
Structural steel that cannot be demonstrated to have been manufactured to the requirements of the string of Australian Standards called up in AS 4100 cannot be a DTS solution but must be treated as a performance solution and must be demonstrated to comply to all relevant performance requirements through an assessment method.
Implementing a performance solution is not a trivial task, and in most cases requires information to be assessed early in the process, rather than after a building or structure has been procured. The design, as typically defined in the design drawings and specifications, prescribes the required product compliance, usually by reference to Australian Standards. If a product that does not comply with the design requirements is proposed to be procured, authorisation for the change must be obtained from the design engineer prior to procurement. The design engineer may need to undertake verification according to the requirements of the NCC (and utilising ASI Technical Note 015) for a performance solution.
A specific example of the need to be cautious is where imported fabricated three plate beams are being substituted for the specified Australian standard hot rolled universal beams. The three plate beams cannot be approved as a direct replacement without thorough investigation. If the investigation reveals that the beams have not been manufactured to the requirements of Australian Standards called up in AS 4100, then the beams must be treated as a performance solution.
Free access to further information
To share further details on this topic with the engineering community, ASI joined with Engineers Australia to produce a webinar which was aired earlier this year. The webinar which was presented by Dr Peter Key, ASI National Technical Development Manager is now available to view free of charge and on-demand on the ASI eLearning platform at learn.steel. org.au/courses/ascertaining-the-compliance-of-structuralsteel-to-meet-australian-standards-and-the-ncc/
A free copy of the ASI Technical Note 015 Ascertaining Compliance of Structural Steel can be downloaded at ASI – Technical Notes (steel.org.au)