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Arup鈥檚 report into the structure of tower blocks on the Ledbury Estate in south London has concluded that the buildings would not withstand a gas explosion 鈥渨ithout incurring disproportionate collapse鈥� and that there are connection details in the buildings that need strengthening to reduce the risk of collapse.

Residents, who have been clamouring for Arup鈥檚 report to be released, had complained about cracks in floors and adjoining walls in their flats at the estate, prompting Southwark to appoint Arup to conduct a survey of the buildings, which it based on 鈥渧isual and intrusive鈥� investigations into two vacant flats.

A number of residents moved out of their homes following the council鈥檚 decision to switch off gas supplies to the towers in the wake of concerns around the structural integrity of the buildings, not least in the event of a gas explosion.

Arup鈥檚 report (see pdf for the full report below) said that while the gas supply to the towers had been turned off, 鈥渂ased on the findings of the investigations undertaken, it would be impractical to strengthen the building to accommodate piped gas鈥�.

The report also argued that wall panels 鈥渨ould fail under blast pressures defined by BRE for non-piped gas. It is therefore recommended that gas is not re-introduced in any form. It is further recommended that the gas pipes be removed, to ensure there will be no future use of piped gas.鈥�

The consultants were commissioned by Southwark council, which owns the towers on the estate, in July after residents complained about gaps and cracks appearing in walls and floors of flats.

Arup鈥檚 26-page report has now detailed how its investigations showed that flank walls and vertical ties between floors and walls were 鈥渘ot robust enough for buildings with piped gas鈥�, using BRE assessment criterion.

The report went on: 鈥淥ur investigations indicate that the flank and cross-walls are unreinforced concrete.

鈥淎s such the walls do not have sufficient capacity to resist 34kPa (accidental load requirement for a block with piped gas) or 17kPa (accidental load requirement for a block with bottled gas) and as such the wall surrounding the explosion will fail. This has consequences to the floor immediately above which relies on the walls for support.鈥�

It said: 鈥淭here is a possibility that such a failure would propagate to the failure of additional elements, causing progressive collapse such as was the case at Ronan Point, but without a fuller understanding of the structural details it is not possible at this time to conclusively conclude the full extent of damage.鈥�

The report also said that although this is not a full assessment it has 鈥漣dentified connection details that would require strengthening in order to enhance the margin of safety to where it needs to be for this type of building for future use, to bring within required limits the extent of damage that would be caused in the event of accidental damage to the structure鈥�.

Arup has been asked by Southwark council to continue with its investigations, including other empty flats across the four blocks, and has been requested to report back on 20 November.

The 14-storey high Ledbury towers were built for the GLC by Taylor Woodrow Anglian between 1968 and 1970 and are similar in construction to Ronan Point, also built by Taylor Woodrow Anglian and part of which collapsed following a gas explosion in 1968, leading to the deaths of four people.

In a statement Stephanie Cryan, deputy leader and cabinet member for housing at Southwark council, said: 鈥淲e are grateful to Arup for their detailed report, which will help us develop plans for the major works we have promised residents of the Ledbury towers. We know this is a worrying time, but this report expands on what we already knew and have communicated to residents 鈥� that the blocks should not have had a gas heating and hot water system installed in the 1960s without adequate strengthening work.

鈥淥f course, as soon as we found this out on 11 August, we turned off the gas, so the risk has been removed, and we are continuing our investigations. The wider question remains why the blocks may not have been sufficiently strengthened when they were built in the late 1960s before the council took ownership in the 1980s, and whether other blocks elsewhere in the country are affected.

鈥漌ith that in mind we met with the department for communities and local government this week, and have also now shared the Arup report with them.

鈥淎t a public meeting last week I apologised to our residents for the distress and inconvenience these issues have caused, and the council continues to offer every support we can while we resolve the issues on the Ledbury.鈥�