Ronan Point

Last updated on 16 October 2017

Ronan Point was a 21-storey tower block in Canning Town in Newham, East London, which partly collapsed on 16 May 1968, only two months after it had opened. A gas explosion blew out some load-bearing walls, causing the collapse of one entire corner of the building, which killed four people and injured 17. Although casualties were relatively few, the spectacular nature of the failure, caused by both poor design and poor construction, led to a loss of public confidence in high-rise residential buildings, and major changes in UK building regulations resulted.

Ronan Point
Ronan Point - Daily Telegraph.jpg
Ronan Point, following the gas explosion
General information
Status Demolished
Type Tower block
Location Canning Town
Town or city London
Construction started 1966
Completed 1968
Demolished 1986
Owner Newham Council
Technical details
Structural system Large Panel System
Material Prefabricated pre-cast concrete
Floor count 22
Design and construction
Main contractor Taylor Woodrow Anglian
Known for Partial collapse following gas explosion

Construction

Ronan Point, named after Deputy Mayor Harry Ronan (a former Chairman of the Housing Committee of the London Borough of Newham), was part of the wave of tower blocks built in the 1960s as cheap, affordable prefabricated housing for inhabitants of West Ham and other areas of London. The tower was built by Taylor Woodrow Anglian[1] using a technique known as Large Panel System building (LPS), which involves casting large concrete prefabricated sections off-site and bolting them together to construct the building. The precast system used was the Danish Larsen & Nielsen system.[2][3]

Construction started in 1966 and was completed on 11 March 1968.

Collapse

Ronan Point collapse closeup.jpg
The explosion on the 18th floor brought down four flats above it, leading to a progressive collapse of one corner of the block

At approximately 5:45 am on 16 May 1968, resident Ivy Hodge went into her kitchen in flat 90, a corner flat on the 18th floor of the building, and lit a match to light the gas stove for a cup of tea. The match sparked a gas explosion that blew out the load-bearing flank walls, which had been supporting the four flats above. It is believed that the weaknesses were in the joints connecting the vertical walls to the floor slabs. The flank walls fell away, leaving the floors above unsupported and causing the progressive collapse of the south-east corner of the building.

The building had just opened, and three of the four flats immediately above Hodge's were unoccupied. Four of the 260 residents were killed immediately and seventeen were injured, including a young mother who was stranded on a narrow ledge when the rest of her living room disappeared. Hodge survived, despite being blown across the room by the explosion—as did her gas stove, which she took to her new address.

Griffiths inquiry

In the immediate aftermath of the collapse, the government commissioned an inquiry, led by Hugh Griffiths, QC. It reported on dangers caused by pressure on the walls from explosion, wind, or fire, finding that although the design had complied with the current regulations,

  • it was not adequate for even small explosions, as proved by the actual collapse, where lack of injury to the person who lit the match demonstrated the pressure had been low
  • it was not adequate for expected wind loading, since the wind speeds which the regulations required to be considered were much too low for a tall building—in a high wind, an upper wall panel could be sucked out, leading to collapse similar to the actual collapse
  • it was not adequate in a fire, a significant fire could lead to bowing of the structure, followed by collapse as above.[4]

Ronan Point was partly rebuilt after the explosion, using strengthened joints designed to deal with those issues, and the Building Regulations were altered to ensure that similar designs would not be permitted in the future. However, public confidence in the safety of residential tower blocks was irreparably shaken,[5] and the public scepticism was later found to be appropriate.[4]

Some people, including Sam Webb, an architect who had given evidence to the Griffiths inquiry, were not satisfied that every issue had been properly investigated. It was later shown that:

  • the assumptions made in determining the revised wind loading were inadequate, in that they assumed all windows were closed. However, if the glass in a window had broken, or somebody had gone out leaving a window open, a wall panel could suffer pressure on one side and suction on the other, to an extent that the panels on the upper levels of the building might still be sucked out
  • construction defects (failure to build as designed) had left unfilled gaps between floors and walls throughout, hidden only by skirting boards and ceiling paper, which left the building without fire separation (or acoustic separation) between flats. Tall blocks of flats in the UK are permitted relatively narrow staircases because the requirement for full fire separation between floors means that in theory, it is safer for people above the fire to stay in their flats rather than walk down the stairs. (This theory does not hold where the fire separation fails, as happened in the Grenfell Tower fire). Without fire separation it would be necessary for all people above a fire to escape, which would not be possible using the existing narrow staircases.
  • further construction defects had led to the whole weight supported by each wall panel being supported by the panel beneath by two steel rods, instead of being spread evenly along the panel, leading to extremely high stresses that the concrete was not designed to withstand
  • the strengthening brackets which had been fitted during the rebuilding were in many cases not properly attached, since they were fastened to hollow-core slabs, and in many cases they had been bolted only to the thin concrete surrounding the cores, which was inadequate to take the stress.[4]

The concern, most particularly about the fire separation issue, eventually led the council to evacuate the building, and then to demolish it in 1986 in a forensic manner (rather than, for example, using explosives). When this was done, the extent of the defects found shocked even some of the activists, such as the architect Sam Webb, who had been lobbying for years that the building was unsafe. On the lower floors, cracks were found in the concrete where it had been point loaded, and it was alleged that the extra pressure on those points during a high wind (such as during the Great Storm of 1987, barely a year after the demolition) would soon have led to building collapse.[4]

Effect on legislation

The partial collapse of Ronan Point led to major changes in building regulations. The first of these came with the 5th Amendment to the Building Regulations in 1970. These are now embodied in Part A of the Building Regulations and cover “Disproportionate Collapse”. They require that “the building shall be constructed so that in the event of an accident the building will not suffer collapse to an extent disproportionate to the cause”. They specifically cover pressures which may be caused for example by wind forces, explosions (either internal or external), or vehicle incursions, and note that seismic design may occasionally be required.[6]

Immediately after the publication of the report the Government brought out interim measures to ensure the safety and integrity of buildings in the event of an explosion. All new buildings of over five storeys constructed after November 1968 were required to be able to resist an explosive force of 34 kPa (4.9 psi)—the value still used as of 2014. Existing buildings were allowed to resist an explosive force of 17 kPa (2.5 psi), provided that the gas supply was removed and flats were refitted for electric cooking and heating. The gas supply was removed from Ronan Point and the other eight blocks on the estate.

It has been said that the location of the explosion, on the fifth floor from the top of the building, was critical to the collapse. If it had been much higher, the lesser momentum of the debris falling onto the floor of the explosion flat would not have caused its collapse, even though it might have sustained some damage, and the progressive collapse of the floors beneath would therefore not have occurred. If it had been much lower, the friction of the joints, under the great weight of the building above, would have prevented the wall panels from blowing out, and there would have been no structural damage at all.

This may be why no other such collapse had occurred worldwide at the time. Nonetheless, it demonstrated an area of design which had not previously been considered. Many other jurisdictions, including for example the US, have since amended their building codes to require that buildings subject to explosions or other accidents will not collapse to an extent disproportionate to the cause.[4]

Two days after the Grenfell Tower fire in 2017, John Knapton, emeritus professor of structural engineering at Newcastle University, claimed that regulations which came into force in 1971, following lessons learned from Ronan Point, had improved building structural strength in such a way as to prevent the collapse of the Grenfell Tower, which was built in 1974.[7]

Effect on housing

Newham Council voted in 1984 to demolish Ronan Point. All nine blocks on the Freemason Estate, comprising 990 flats, were demolished in 1986 and the area was redeveloped with two-storey houses with gardens.[5] Many other similar LPS buildings have since been demolished.

The Building Research Establishment published a series of reports in the 1980s to advise local councils and building owners on checking the structural stability of their LPS blocks. The contents of two of the reports relied on local authorities sending returns in to the Ministry of Housing and Local Government during 1968 and 1969. This was not exhaustive, with many authorities failing to do so and thus not having their blocks assessed after the issue of interim structural methods by the Ministry in 1968–69. Among these authorities were Lambeth and Southwark in London, and Birmingham. Birmingham owned over 300 LPS blocks, and when these were assessed in 1998 it was found that a number which did not meet 5 psi (34 kN/m²) still had a piped gas supply. A number of those blocks were demolished. The London Borough of Southwark owns the largest LPS estate in the UK, the Aylesbury Estate, which has a piped gas supply; it has been questioned whether the structure is strong enough to resist a 5 psi explosion. Southwark Council admitted in 2017 that strengthening work ordered after Ronan Point may not have been carried out on the Ledbury Estate, after structural weaknesses were found that led to the evacuation of four tower blocks.[8]

Within a couple of decades of the collapse of Ronan Point, the public's lack of confidence in the LPS construction technique, together with the social problems within such developments, led to the demolition of many tower blocks.[5]

Further reading

See also

References

  1. ^ "1968: Three die as tower block collapses". BBC. Retrieved 16 June 2016.
  2. ^ Practical Building Conservation: Concrete. English Heritage. 2013. p. 320. ISBN 978-0-7546-4565-8.
  3. ^ "Failure of a High-Rise System". Retrieved 23 January 2015.
  4. ^ a b c d e Beyond Failure: Forensic Case Studies for Civil Engineers. Reston, Virginia, USA: American Society of Civil Engineers Publications. 2009. p. 418. ISBN 978-0-7844-0973-2.
  5. ^ a b c "Ronan Point". Retrieved 31 October 2014.
  6. ^ "Approved Document A - Structure (2004 Edition incorporating 2010 and 2013 amendments)" (PDF). The Building Regulations 2010 (reprint ed.). HM Government. September 2013. Retrieved 3 March 2014.
  7. ^ "Grenfell Tower would have collapsed if built four years earlier, says expert". Daily Telegraph. 14 June 2017. Retrieved 16 June 2017.
  8. ^ "South London estate to be evacuated over safety fears - BBC News". BBC Online. Retrieved 10 August 2017.

Bibliography

A number of books have covered the collapse of Ronan Point, including Collapse: Why Buildings Fall Down by Phil Wearne ISBN 0-7522-1817-4. This was written to accompany the television series of the same name shown on Channel 4 in early 2000.

Building Research Establishment reports:

  • The Structure of Ronan Point and other Taylor Woodrow-Anglian Buildings 1985 ISBN 0-85125-342-3
  • Large panel system dwellings: preliminary information on ownership and condition 1986 ISBN 0-85125-186-2
  • The structural adequacy and durability of large panel system dwellings 1987 ISBN 0-85125-250-8

External links

Coordinates: 51°30′49″N 0°01′21″E / 51.5136°N 0.0226°E

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