Workplace Health & Safety Queensland recently issued a health and safety alert to inform workers, employers, builders and designers about the risk of failure of lifting clutches associated with tilt-up and pre-cast concrete erection.
The alert was issued following an incident last month, in which a lifting clutch link on a 5-tonne lifting clutch failed when a 100-tonne crawler crane was lifting a 16-tonne concrete wall panel.
The panel was rigged with four face lifting inserts (lifters) at the time with equalising sheaves each fitted between two inserts.
When the lifting clutch link broke, it caused two of the lifting points to become ineffective and the panel dropped onto the casting stack below.
Although no workers were injured, the incident caused extensive damage to the panel and had the potential to cause serious injuries.
It appears the primary cause of the lifting clutch link failure was that it had a substantial, undetected crack through its cross-section.
Rust on the failure surface indicates that the crack may have been present for some time.
The crack was close to a weld and started on the inside of the lifting clutch link, so it may have been difficult to notice the crack by visual inspection.
The lifting clutch link was inspected and proof tested by a third-party lifting gear organisation six months prior to the incident.
The alert recommended a number of required actions, and said this incident highlights the serious consequences of lifting gear element failure.
Although it occurred on a tilt-up site, the same type of lifting clutches are commonly used for pre-cast element erection.
The lifting clutches had been supplied by a company that specialises in gear associated with the erection of concrete elements and has a quality assurance program.
The lifting gear was not owned by the company employing the crane and rigging crew.
A rigorous inspection and testing program is needed on lifting clutches, possibly beyond the current minimum industry benchmarks.
Australian Standard AS3850.1:2015 Prefabricated concrete elements: Part 1 General requirements specifies non-destructive testing (NDT) of lifting clutches at manufacture, but does not specify any NDT during the 12-monthly inspection.
Therefore, to help prevent unexpected failures, the alert said to consider carrying out NDT to inspect for cracks at the 12-monthly inspection.
The inspection should include dimensional checking to determine that tolerances remain within the manufacturer’s specifications.