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CROSS Safety Report

Lack of masonry wall ties causes failure

Report ID: 665 Published: 1 April 2018 Region: CROSS-UK

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Overview

A reporter states that they have come across the presence of serious defects in masonry construction in the past and have no doubt that many other engineers have had similar experiences.

Key Learning Outcomes

For construction professionals:

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

  • Consider introducing a quality control procedure for the inspection of safety critical elements such wall ties and head restraints

Full Report

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A reporter was not surprised whatsoever when they read the Standing Committee on Structural Safety (SCOSS) alert on the Inquiry into the Construction of Edinburgh Schools. They state that they have come across the presence of serious defects in masonry construction in the past and have no doubt that many other engineers have had similar experiences. In one particular instance, they recall a concern on a large concrete framed structure constructed in the 1970s having extensive amounts of plain cavity brick cladding up to 15m high.

Around 2010, they were asked to look at a general problem with this brickwork where, at horizontal intermediate masonry supports, there was spalling off of slip bricks and slight, local, outward movement of the panel above. The supports proved to have been very badly designed and poorly executed such that remediation work was needed.

Further concerns discovered

During the remediation works, the reporter was asked to look at a panel of the blockwork inner leaf. The panel was framed by columns and beams and, when pushed, swayed alarmingly. An initial investigation confirmed it had no functioning peripheral ties and almost certainly there were no functioning cavity ties.

The reporter agreed with the client that a panel of the external masonry they were working on should be investigated further. This investigation proved to be disturbing, revealing very poor workmanship, limited numbers of ties overall, large areas with no ties, ties which had little or no embedment, loose ties and few ties restraining the panels back to the frame.

Falsification of mortar test results

The reporter came across another startling instance on a very large, masonry clad, new build project in the mid-1990s, where they encountered the falsification of all the mortar test results. This was only discovered when the mortar began disintegrating before final completion due to lack of cement. Why this was done is a mystery to the reporter, but they wonder how many other similar projects lie undiscovered?

The reporter emphasises that these two instances were remediated, the first at considerable cost to the client and the second at great cost to the contractor. In the reporter’s view, the basic problem is that masonry has too many variables, it is hard laborious work and human nature is to take shortcuts when no one is looking.

Are ‘As Constructed’ drawings representative of what has been built?

The reporter also comments on the Edinburgh Schools Independent Inquiry's gripe about the lack of ‘As Constructed’ drawing. They believe that no engineer or consultant could issue such drawings as they carry out only occasional visits and would have no full idea what the contractor has actually built. The best that can be done is ‘Last Drawings Issued for Construction’ which should include any major variations agreed with the contractor but cannot under any circumstances be representative of what has been built. In the reporter's view, if there is a necessity for such drawings, then there needs to be either a Resident Engineer or Clerk of Works to ensure the engineer’s requirements are met.

They believe that no engineer or consultant could issue such drawings as they carry out only occasional visits and would have no full idea what the contractor has actually built

Expert Panel Comments

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Whilst this report contains many valid observations and highlights a problem with masonry, it is more beneficial to draw wider lessons. Any building is only as good as its detailing and innumerable examples can be given whereby structures as a whole have become unsafe because of lack of attention or because buildings can’t be constructed to design assumptions. Although ‘less glamorous’ than mathematics, it must remain vital for all designers to have a sound grounding in basic principles of good building. Regarding ties, modern designers have probably forgotten severe problems on older structures due to galvanised ties corroding with age.

Lack of site supervision in recent years

The use of Resident Architects, Resident Engineers and Clerks of Works has dramatically reduced over recent years. CROSS has previously said that this deficiency must be recognised and addressed. Furthermore, public sector clients (and others) should require that tenders contain a full description of the proposed scope of design team services, including any proposed role in the inspection of the works on site.

The use of Resident Architects, Resident Engineers and Clerks of Works has dramatically reduced over recent years. CROSS has previously said that this deficiency must be recognised and addressed

To ensure masonry is correctly erected with ties, reinforcement, windposts, flashings and DPCs requires clear instructions to the bricklayers and their supervisor and also to the independent (principal contractor) supervisor. Builders should be encouraged to engage competent, experienced skilled and semi-skilled site operatives. Those who have the power to do so must not be afraid to say; ‘take it down and start again’.

Are ‘As Built’ drawings not practical for masonry construction?

This is especially important in the early stages, to reinforce the message that walls must be built correctly. It is not practical to produce an ‘As Built’ drawing to include location of all ties as they get built in very quickly and are then hidden. Radar scans can be done but are very time consuming, equally borescope surveys are possible if the cavity does not have full fill insulation.

Industry would welcome an innovation that either removes the need for brick ties, which as hidden but critical fixings are hard to manage, or provides a sure-fire, quick and easy way to assure that they have been installed correctly. A thought for researchers.

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