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CROSS Safety Report

Fabrication different from design drawings

Report ID: 513 Published: 1 July 2015 Region: CROSS-UK

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Overview

A reporter shares their experience of how a propping design they had undertaken was fabricated and installed but not in accordance with the design drawings.

Key Learning Outcomes

For construction professionals:

  • Any alternations to structural elements must first be approved by the design engineer

  • Quality control and competent supervision on site can help to ensure that the structure is built in accordance with the design

For civil and structural design engineers:

  • Consider attending site and inspecting the installation of critical structural elements

  • If you are unable to attend site, consider asking the contractor for site photos of the installation of critical structural elements

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An Australian reporter created a design for propping required to carry out partial demolition and re-construction of a small tower on a mine.

Later while on a site visit for another project, the reporter noticed that the propping design had been fabricated and installed but a number of connection details did not match the design drawings. The structure as fabricated effectively had no stability in one plane and there were other non-conformities.

Unauthorised modifications made

Investigation revealed that the mine had submitted the design drawings to a fabrication company, which had then sub-contracted the fabrication out to a second fabricator who had then sub-contracted out the creation of shop detail drawings to yet another drafting company. Somewhere in this chain of responsibility the decision was made to standardise the end details of each member without getting approval from the design engineer. This had simplified the fabricator's task but completely voided the design intent.

Somewhere in this chain of responsibility the decision was made to standardise the end details of each member without getting approval from the design engineer

Lack of engineering oversight

More important, however, was the lack of engineering oversight of the fabrication and construction stages of the build. In the reporter's experience in the local mining industry, small projects such as this one are often done in three stages - design, fabrication and installation.

Typically, all of these are done by different companies. They rarely interact except through the project manager from the mine site who is usually not a qualified structural engineer and often has no engineering background at all. This means that there is a lack of engineering oversight that could identify potentially dangerous modifications or construction defects.

Expert Panel Comments

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Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

It is always important to have engineering oversight to all areas of design and construction. The disconnect between each stage is becoming increasingly common and is leading to serious risks.

This example illustrates a lack of oversight and control, with the potential for dangerous consequences.

It should not happen in the UK if the CDM Regulations 2015 are applied correctly. It is a reminder of the Hyatt Regency catastrophe in 1981 (Investigation of the Kansas City Hyatt Regency Walkways Collapse) when 113 people were killed and 186 injured because of a difference between design and detailing.

To quote from the NIST report ‘…a change in hanger rod arrangement during construction that essentially doubled the load on the box beam-hanger rod connections at the fourth-floor walkway’.

A general safety principle is for designers always to assure themselves that what they meant to be built was actually built.

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