AS/NZS 3678:2016

AS/NZS 3678 is decision-controlling for TRSC engagements involving plated steel structures — typically welded-girder bridges, column-base plates, gusset-plate connections, and post-1960 plate-girder buildings. Three application points matter for existing-asset practice. First, the standard's distinction between standard-grade and weldable-grade plate is decision-controlling for any continuing-life assessment that includes welded retrofit. Pre-1980 plate steel was frequently produced without restricted chemical composition for improved weldability, and field welding to such plate in retrofit scenarios produces unpredictable weld quality and elevated brittle-fracture risk in the heat-affected zone. TRSC's protocol for retrofit welding to existing plate is to first establish the as-installed plate's chemical composition (typically through extracted-sample analysis per AS 1391.1, focusing on carbon equivalent and sulphur and phosphorus content), then specify the welding procedure (per AS/NZS 1554 series) appropriate to the established plate weldability. Where the as-installed plate is non-weldable, retrofit is achieved through bolted connections rather than field welding, with AS 4100 connection-capacity verification. Second, AS/NZS 3678 plate thickness drives the mechanical-property acceptance criteria — thicker plate has reduced characteristic yield strength because of through-thickness anisotropy and rolling effects. For thick-plate connection details (typical of high-rise transfer-truss connections, bridge-girder webs, and heavy industrial structures), the as-installed plate's characteristic yield strength may be lower than the AS/NZS 3678 standard-thickness value, and the AS 4100 capacity calculation must reflect the thickness-corrected value. TRSC's transfer-truss and bridge-girder assessments include explicit thickness-correction in the capacity calculation, with the engineering basis documented in the Form 15 file. Third, AS/NZS 3678 plate-condition provisions (lamination defects, rolling-induced stress, surface inclusions) are decision-controlling for fatigue-loaded plated structures. Pre-1980 plate frequently has lamination defects (delamination through-thickness defects from mill-rolling) that AS/NZS 3678:2016 quality acceptance would identify and reject, but which were accepted under earlier supply standards. For existing fatigue-loaded plated structures (typically bridges, crane runway girders, offshore-related structures), the assessment includes ultrasonic-testing of plate sections per AS 2207 to identify lamination defects, with the resulting fatigue-life calculation reflecting the as-installed defect population. Where lamination defects exceed the AS/NZS 3678:2016 acceptance criteria, the assessment quantifies the impact on fatigue capacity and prescribes either weld-through-defect repair, bolted-overlay reinforcement, or section replacement depending on the criticality.