Ronan Point was a 22-storey tower block in Newham, East London, which partly collapsed on 16 May 1968 when a gas explosion demolished a load-bearing wall, causing the collapse of one entire corner of the building. Four people were killed in the incident, and 17 were injured. Although casualties were relatively light, the spectacular nature of the failure -caused by both poor design and poor construction- led to complete loss of public confidence in high rise residential buildings and major changes in UK building regulations.
Ronan Point, named after Harry Louis 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 the West Ham region of London. The tower was built by Taylor Woodrow Anglian 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.
Construction started in 1966 and was completed on 11 March 1968.
There are three main methods of constructing tall buildings:
- Steel building. Here a set of steel members are fixed together to make the frame of the building. Skyscrapers in New York City like the Empire State Building are examples of this type of building.
- In situ concrete. Here a mould or formwork is made using wood or another similar material. Steel reinforcement is placed in the formwork, then concrete is poured into the mould and allowed to set. The mould is removed, and may be reused to make identical castings in other areas of the building. The resulting building is a solid block of concrete made from multiple castings poured on top of one another. The Bank of America Tower in New York is an example of this.
- Large panel systems (LPS). Here a set of prefabricated concrete parts are transported to the site, where they are lifted into place with a crane and joined together. This is the type of structure that Ronan Point used. It is thought that a failure to join the panels correctly contributed to the Ronan Point collapse. The structure of Ronan Point and other LPS buildings of the time relied on gravity holding everything together.
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 stove for a cup of tea. The match sparked a gas explosion that blew out the load-bearing flank walls, removing the structural supports to the four flats above. It is believed that the weakness was 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.
In the immediate aftermath of the collapse, the government commissioned an enquiry, led by Mr. Hugh Griffiths, Q.C. 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.
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, and the public scepticism was later found to be appropriate.
Some people, including Sam Webb, an architect who had given evidence to the Griffiths enquiry, 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
- that 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 it is actually safer for people above the fire to stay in their flats rather than walk down the stairs. Without fire separation, all people above would need to escape, which would not be possible in the existing narrow staircases.
- that further construction defects had led to the whole weight supported by each wall panel being supported off 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
- that 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.
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 about the building being 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 would soon have led to building collapse.
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.
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 constructed after November 1968 and over 5 storeys were required to be able to resist an explosive force of 3.4×104 Pa (34 kilopascals) which is equivalent to 5 psi, which is the value still used as of 2014. Existing buildings were allowed to resist an explosive force of 1.7×104 Pa (17 kilopascals) which is equivalent to 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 preventing 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 USA, 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.
Effect on housing
In 1984 Newham Council voted to demolish Ronan Point. All nine blocks on the estate, comprising 990 flats, were demolished in 1986 and the area was redeveloped with 20 two-storey houses with gardens. 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 over the years 1968–69. 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.
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.
- Template:Cite book title = Practical Building Conservation: Concrete
- "Failure of a High-Rise System". Retrieved 23 January 2015.
- "Ronan Point". Retrieved 31 October 2014.
- 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.
- "Approved Document A - Structure (2004 Edition incorporating 2010 and 2013 amendments)". The Building Regulations 2010 (reprint ed.). HM Government. September 2013. Retrieved 3 March 2014.
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 TV 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