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Industry fears over fixings

A recent New Civil Engineer survey revealed 21% of respondents have expressed doubts that concrete fixings are being properly installed on site.

An alarming number of engineers and contractors have a lack of confidence that chemical anchors are being properly installed on construction projects.

Over 7% of the 1,309 engineers, contractors and sub-contractors who completed a survey in NCE said they were ‘not at all’ confident while a further 14% said they were “slightly confident” that chemical fixings are being correctly installed on site.

 Fixing image

The purpose of the NCE survey, posted in June, was to establish the levels of knowledge about the selection and installation of fixings.

Correct chemical anchor installation is particularly pertinent in light of recent anchor failures which have resulted in fatalities, including lining failures in the Boston Big Dig Tunnel (2006) and Japan’s Sasago Tunnel in 2012.

Eighty two per cent of those who responded to the survey described themselves as either a contractor, subcontractor, consultant or designer. In total, 86% described themselves as influencing the design and selection of fixings to varying degrees.

Alastair Soane, director of Structural Safety, an organisation which collects confidential data on the concerns of structural and civil engineers, welcomed the survey as an important step in recognising the safety critical aspects of chemical anchor systems. He said it gave the impression that fixture failures have been experienced by those who responded to the survey.

“Most respondents very often or often consider fixings to be safety critical [84%] but most are not confident that they are properly installed on site [55%],” he said.

 

Hilti survey results

Breakdown of survey respondents by company

Levels of awareness about BS8539:2012, the code of practice for the selection and installation of post-installed anchors in concrete and masonry, were also surprisingly low. This seemed to be the case across the data set. 38% of those surveyed said they had not heard of the standard while 28% said they were “not sure” if they were aware of the standard.

Soane said that best practice is to work to BS8539 and select fixings with a European Technical Approval (ETA).

“The British Standard is becoming increasingly well-known and its influence is valuable in helping to reduce failures,” he said. He added that another vital aspect was to follow manufacturers’ recommendations for installation.

There was more agreement when it came to a question about the most critical step in the installation of chemical fixings. 80% of those surveyed said that properly cleaning the hole before attaching the fixing was paramount.

This was corroborated by a selection of comments provided by those surveyed.

Hilti survey results

Breakdown of survey question about fixings confidence

Capita structural engineer Carl Bebbington said: “I think it would be a very good idea to educate engineers on how critical the installation is [by] showing the difference in capacity if say the hole was not adequately cleaned prior to chemical anchor installation.”

“The biggest cause of failure I have experienced with chemical anchors has been due to insufficient depth of drilling and poor hole cleanliness,” said Costain square works manager Andy Parkin.

Laing O’Rourke temporary works manager Robert Garford-Tull suggested: “New technology to address issues with cleaning holes. Hollow drill bits and tapered anchors help”.

Hilti survey results

Breakdown of survey response about most critical steps for fixings installation

Other engineers said there was a danger that main contractors were not taking chemical fixing installation seriously enough. “[It is] critical to ensure that ‘as designed’ fixings are installed, as often contractors will utilise cheaper alternatives without necessarily requesting designer approval,” said Ramboll senior structural engineer James Drew.

Kier site manager Ed Dwight explained that anchor design, selection and installation “is often an interface item that becomes [the] subcontractor’s designed portion.”

He argued that principal contractors “have to ensure it is designed and managed correctly”.

  • To download the complete survey results or a copy of the original survey questions go to the related files tab at the top right-hand side of this story.

The industry speaks

“The confidence in the selection, design and installation as a designer is influenced by the confidence in the contractor to carry out the manufacturer’s instructions correctly”

Rob Paul associate, WSP Parsons Brinckerhoff

“When using subcontractors to perform the works it is essential that they are supervised correctly by a competent individual”

Paul Hutton section engineer, Costain  

“It is critical to ensure that ‘as designed’ fixings are installed, as often contractors will utilise cheaper alternatives without necessarily requesting designer approval”  

James Drew senior structural engineer, Ramboll

“Contractors often wish to use other fixings than those specified which may be inferior for the planned use although they consider them ‘similar’. Often without designer knowledge, installation quality is a concern”

Ross Hampton project engineer, Skanska

“Not all subcontractors have sufficient design experience capability in preparing calculations and preparing relevant shop drawings to consulting engineers or building control authorities for approval”

Paul Perry associate director, Sir William Halcrow and Partners

“Interim advice notes and specification appendices need to be written to better suit site construction”

Gordon Wright senior principal engineer, Jacobs

“My general experience is that main contractors, subcontractors and their operatives do not fully appreciate the safety critical function of the fixings and the importance of strictly adhering to the manufacturer’s instructions”

Barry McAuliffe senior engineer, Consibee

“Most of my projects the contractors self-certify, so I have no control over site works. I know that if not applied correctly or if the design is changed onsite they are likely to fail and this has been a concern to me”

Neil Gwynne principal engineer, Jacobs

 

Produced in association with

 

Hilti logo

Readers' comments (2)

  • Pull out tests on a representative sample is a prudent measure, especially if tensile forces are involved in service.

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  • I would concur with the comments made in this article but one important aspect that must be considered by the client is on site quality assurance i.e. Employment of a clerk of works or the Supervisor (NEC). Fixings may be in place but how many attempts did it take to drill the hole and avoid the reinforcement; is the bolt perpendicular to the concrete and the plate; does the nut sit flat against the plate.
    Having asked these questions of contractors I've seen the blank look on their faces but have the confidence to know that these defects have been rectified.

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