Safety alert issued after precast concrete element fails during erection

WorkSafe Victoria recently issued a safety alert about the risks associated with the design, manufacture and erection of precast concrete elements following a recent incident.

Two workers narrowly avoided being seriously injured or killed when a nearly 10-tonne precast concrete element snapped in two during rotation whilst suspended from two cranes.

The alert said project structural engineers (PSE) typically only design precast concrete elements for their final permanent position in the building or structure, however, these elements are exposed to many forces during manufacture, storage, transport, lifting, rotation and erection.

If an element is not designed and manufactured to be robust enough to resist these forces, it may fail during rotation, lifting or erection. Workers and others near the failed element may be struck by falling sections of concrete and steel, and these sections could weigh several tonnes each.

Several factors that have the potential to cause a precast concrete element failure during rotation include:

• poor design of element shapes and element ‘break-up’
• insufficient concrete strength at the time of lift
• inadequate, incorrect or missing reinforcement in the element and lifting inserts
• inadequate specification of the strong-backs and associated fixings
• using strong-backs and associated fixings that don’t align to the engineer’s specification
• incorrectly rigging the element

The alert recommended a number of ways to control risk and said the builder or principal contractor should ensure that precast concrete elements are appropriately designed to resist all forces they will likely be exposed to.

A suitably qualified person, such as a structural engineer experienced in erection design, should be engaged to develop a safe system of work for the handling, transport, lifting, rotation and erection of precast concrete elements. This person is referred to as the erection design engineer.

The erection design engineer should review the precast concrete element designs and specify any additional reinforcing or strong-backs required to ensure the element is safe for transport, lifting, rotation and erection into its final position.

The erection design engineer may not always be directly engaged by the builder or principal contractor. However, both the builder or principal contractor and precast erector should ensure that a suitably qualified person has been engaged and has undertaken the functions of the erection design engineer before erection works begin.

Furthermore, the alert said the PSE and builder should consult with the erection design engineer and precast element manufacturer to ensure that the precast element ‘break up’ design achieves element shapes that are robust and can be handled safely, where possible without the need for strong-backs and additional reinforcement.

The erection design engineer should carefully consider all forces that the element will be exposed to during lifting, rotation and placement and:

• review the design of the element to determine whether additional reinforcement or strong-backs are required to ensure that it can be handled safely, especially where the element has cut-outs or penetrations
• provide the precast manufacturer with marked-up structural or shop drawings that accurately and clearly show the necessary lifting and bracing insert locations and any additional reinforcement or strong-backs required
• where strong-backs are required, the strong-back type and associated fixings should be accurately and clearly specified
• produce rigging designs for the various lifting stages required (demoulding, pre-transport, rotation, installation)
• review and approve the updated shop drawings (prior to them being issued for construction), to ensure that the lifting and brace inserts and any additional reinforcement and strong-backs are correctly detailed on the drawings
• following completion of the above steps, issue the erection design engineer’s certificate of compliance

During element manufacture, the precast manufacturer should ensure:

• the shop drawing for the element has been reviewed and approved by the project design engineer and erection design engineer prior to commencing the manufacture
• a suitably competent person, who was not involved in the original set-up, has ensured all reinforcement and components comply with the approved shop drawings before casting
• minimum specified concrete strength is achieved before the initial lift of the casting bed
• all strong-backs are installed as per the erection design engineer’s specification prior to lifting or transport
• non-specified and non-structural strong-back components and fixings are not used
• minimum specified concrete strength has been achieved prior to transporting the element to the site
• they have completed and issued the manufacturer’s certificate of compliance (birth certificate) to the builder or principal contractor
• any variations to the original design (including changes to strong-back or component specifications) are approved in writing by the erection design engineer

When the precast concrete element arrives at the site, but prior to lifting, an appropriately licenced rigger should:

• inspect the element to ensure it aligns with the shop drawing (dimensions, cast-in plates, inserts and ferrule locations all match the drawing) and that the element and components are free from damage
• confirm the lifting inserts match the shop drawing specification and are free from damage
• confirm the concrete adjacent to the lifting inserts is in good condition and free from significant cracking, honeycombing or damage (if in doubt seek advice from the erection design engineer)
• ensure strong-backs are all in place and as per the shop drawing specification (type, size, location, orientation, fixings)
• review the birth certificate for the element to confirm the casting date
• confirm the lifting clutches are compatible with the lifting inserts, and inspect all rigging gear prior to use
• ensure the element is rigged in accordance with the relevant rigging design, being sure to use the correct lifting inserts where there are multiple inserts present
• stop the lift and seek advice from the erection design engineer if any of the above safety critical information is missing or if there are any issues identified during inspection of the element.

‍