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CROSS Safety Report

Design and erection of prefabricated (precast) concrete

Report ID: 871 Published: 1 February 2020 Region: CROSS-AUS

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Overview

A correspondent considers that there should always be an experienced temporary works designer for prefabricated concrete structures as many structural engineers do not consider the erection methodology when designing such structures.

Danger from confusion about responsibility for design and execution of temporary works needed during erection of precast panels is highlighted, together with guidance currently available.

Key Learning Outcomes

For structural and civil engineers:

  • The sequence and requirements for successful safe erection of precast concrete elements must be considered early in the design stage

  • Erection procedures must be specified by an experienced structural engineer who understands both design and construction

For construction personnel:

  • Erection procedures for precast concrete panels must be provided by a competent and experienced civil or structural engineer and must be followed

  • Any changes to an erection procedure must be confirmed with the engineer responsible before the erection work begins

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A correspondent considers that many structural engineers do not consider the erection methodology when designing prefabricated concrete structures.

Erection sequence must be considered in design

Their view is that many structural engineers, known as the In-service designer in AS3850 (Prefabricated Concrete Elements), use sophisticated software to design structures but do not always consider how prefabricated concrete elements are detailed, specified, manufactured and erected; how these integrate with the final structure; and how to document those processes correctly. The Safety in Design requirements for prefabricated concrete are sometimes ignored or poorly understood. The correspondent believes that erection procedures must be specified by an experienced structural engineer who understands both design and construction.

Legal requirements during erection

The correspondent also considers that many contractors do not fully understand their statutory requirements regarding the erection of prefabricated concrete elements and may not be prepared to pay for the cost of the temporary works design. The erection of prefabricated concrete elements is a temporary works design in the same way as formwork or deep excavations and requires the same level of input.

Professional guidance

The correspondent makes reference to the Professional Guidance Note on Temporary Works by John Carpenter[i] where he states: Temporary works are a vital element of most projects. They demand careful attention by all duty-holders if economic loss and accidents are to be avoided.

Prefabricated concrete elements can weigh between 1-40 tonnes, and if not properly restrained in the temporary condition, significant failures and possible loss of life can occur. It is the correspondent’s experience that contractors will commonly split the prefabricated concrete works into a supply package and an erection package, with the award of each package commonly assigned to different organisations. Who then takes responsibility for the erection procedures?

Recent failures and fatalities

There have been some recent failures resulting in the loss of life associated with the erection of prefabricated concrete in Australia, and it is the correspondent’s opinion that these incidents could have been avoided if the correct erection procedures had been documented and carried out appropriately on site. They also believe that the various health and safety regulators in the States and Territories of Australia should demand to see the erection procedures, temporary works design and documentation for prefabricated concrete from an Erection Designer before any erection occurs on site.

The correspondent quotes the Director of Structural-Safety in the UK, Alastair Soane, who said “the reasons for failures can be generically attributed to the three Ps - people, process or product.” and “ultimately most are related to people. Causes include one or more of the following: incompetence; negligence; oversight and carelessness; greed; disorganisation; poor communication; misuse; or neglect.”  [ii]  

[i] Carpenter, J., Temporary works and the structural engineer, Institution of Structural Engineers, The Structural Engineer, December 2012

[ii] Soane, A., Temporary Works Toolkit, Part 5: “Temporary Works Failure - What Are the Common Causes”, Institution of Structural Engineers, The Structural Engineer, January 2017.

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The publication “Construction and Erection of Bridge Beams” (Worksafe Victoria, 2004) followed a fatality that occurred in 2000 during the erection of a precast concrete bridge beam. This comprehensive document could serve as a template for the requirements for safe design, manufacture, transportation and erection of large precast elements. To quote from the document:

“Prior to manufacture, the erector, in association with the design engineer and the principal contractor, should have planned the complete construction and erection sequences. The planning process should be documented as part of a Work Method Statement and take into account: …..” (the document then gives a comprehensive list that is relevant to all forms of prefabricated elements).

Standard covering erection of precast concrete elements

The installation of prefabricated concrete elements is broadly covered in AS3850.2 (Prefabricated concrete elements – Building construction) and as noted in the scope: “This Standard provides requirements for planning, construction, design, casting, transportation, erection and incorporation into the final structure of prefabricated concrete elements in building construction.”

Danger from confusion over responsibility

When several parties are involved, and especially with specialist sub-trades as in this case, the question of divided responsibilities is always a concern. Safe Work Australia’s Guide to managing risk in construction: Prefabricated Concrete (Sept. 2019) sets out the responsibilities of all parties and notes that:  “Everyone involved in construction work that uses prefabricated concrete elements has health and safety duties when carrying out the work.”

The Guide further notes that: “The in-service design engineer must think about the practical implications of their design, and how risks to health and safety can be eliminated or minimised during construction.”  And that: “A suitably competent person, such as an engineer with experience in such matters, should be engaged to develop a safe system of work for the erection of precast or tilt-up concrete or panels. This person is referred to as the erection design engineer.”

The use of a suitably competent person should be specified in the contract documents and their details should be requested and verified to ensure that they have the relevant experience to understand how the building will perform in both the temporary and final condition.

Further guidance

Reference should also be made to the relevant Codes of Practice and other guidance material that has been legislated under work health and safety (WHS) legislation in each state and territory, e.g. WHS Queensland’s Tilt-up and pre-cast construction.

The National Precast Concrete Association Australia (NPCAA) has a wide range of resources covering all aspects of precast concrete such as this fact sheet on the temporary bracing of precast elements.

The intent behind the obligations in the documents and guidance material referred to above is to ensure that there is an erection designer who is responsible for the overall installation planning, methodology and temporary stability of prefabricated concrete elements. In most cases this is not the permanent works designer. As contractors look to reduce costs and deliver projects in shorter timeframes than scheduled, these tasks are frequently fragmented and allocated to various parties. As a result, the temporary works engineer may be reduced to designing the bracing and propping only, with little, if any, input into other aspects. The process is further complicated if the permanent works designer does not fully consider the installation procedure and their connection details are impractical for the installation of the precast element. This situation clearly does not satisfy duties under WHS legislation and the project should include a sensible budget to allow an experienced temporary works designer to be engaged. There are a number of reports about precast concrete elements in the CROSS-AUS database.

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