A report into structural failures in Belfast’s Victoria Square has stated that one column was “constructed with concrete that had a strength of less than 75%”, the BBC has revealed.

Tentative findings suggest that a dozen other columns also have low strength, although to a lesser degree.

Need for more testing

The authors said the failures posed “a serious health and safety issue” but emphasised the need for more testing.

The companies involved in the construction and fitting out of the apartments deny all responsibility.

The owners of the city centre apartments commissioned a report from engineering and architectural firm William J Marshall and Partners in collaboration with testing and consulting firm Sandberg LLP.

BBC News NI reported that it has seen the authors’ provisional views.

The owners hoped the document would help them make a legal case against the construction and architectural firms involved in the development and would be followed by a formal expert report analysing a broader set of evidence.

The 91 properties were evacuated five years ago for safety reasons, after cracks began to appear in the walls and what is described as “a serious and substantial structural failure” of a column.

It decided the case could not proceed because, under the law, such claims must be made within six years of completion of construction.

As a result, the provisional findings will now not be tested in court.

The north's Stormont ministers are considering amending the law in Northern Ireland to allow defect claims up to 30 years after completion, to bring it in line with other parts of the UK.

Joint venture between construction companies Farrans and Gilbert Ash

The development was a joint venture between construction companies Farrans and Gilbert Ash, with Farrans responsible for the “construction obligations” and Gilbert Ash in charge of fitting out the apartments.

In response to specific questions about the concrete used in the construction, Farrans said: “We will not comment.” In a statement, Gilbert Ash said it “only carried out internal fit-out work” at the development. “This included internal finishing, carpentry, bathroom and kitchen supply and installation, as well as electrical and mechanical work for the apartments,” it said.

“It did not include any structural work, including the construction of structural columns or the provision of concrete for those columns.”

The report’s authors said too much water and too little cement was used in the mix for some of the concrete on the site.

Faulty repair

The report also found that the column that splintered in Victoria Square had been further weakened due to a faulty repair.

They believe adhesive plaster rather than concrete was used to secure that column, which they suggest was a “key factor” in its “failure”.

Farrans and Gilbert Ash said they did not carry out the faulty repair and the report concluded that it was not possible to say when the work was carried out or who was responsible for it.

Only a limited number of columns were examined and the authors recommended that concrete strength testing be extended to all “columns, slabs and beams in the building”.

They noted that if low-strength concrete was used on site, it is likely that one truck load would have provided enough for between 17 and 25 columns.

A combination of on-site testing was used, including ‘coring’, which involves drilling and removing concrete cylinders.

However, although that method is considered reliable, it causes vibrations and, for safety reasons, some less precise “rebound hammer tests” were also carried out.

The report said that of the 30 columns examined “more than 50%… are affected by low-strength concrete and are therefore defective”.

The residential block sits above the shops in the centre of Victoria Square and part of its underground car park.

Steel struts have been put in place to try to stabilise the building, at a cost of £1m paid by the owners, although it was always intended to be a temporary measure.

'Serious structural failure'

The report said “the serious structural failure is an alarming situation with significant implications for the health and safety of the building”.

DUP MP Gavin Robinson has been working with residents and said a judge should consider the provisional findings. “I think it’s vitally important,” he told BBC News NI.

“Unless these issues are tested in court, and unless there is a decision from the High Court in Belfast, there will be no resolution for all the homeowners who have been terribly affected and impacted.”

Concerns are also being raised about the design of the building, although it is said to have been “not the main factor” in the failure of a key concrete column.

However, the author of the report stated: “At this time I cannot rule out deficiencies in [the] structural design as a significant and/or contributing factor.”

The project’s architects, the Building Design Partnership (BDP), did not comment when asked about the interim report.