Ronan Point

Ronan Point was a 22-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. 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.
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 using a technique known as large panel system building, 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.
Collapse.
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, having been blown across the room and clear of the collapsing walls 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,
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 inquiry, were not satisfied that every issue had been properly investigated. It was later shown that:
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.
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 of over five storeys constructed after November 1968 were required to be able to resist an explosive force of —that value still being relevant in 2014. Existing buildings were allowed to resist an explosive force of , 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. The reason that an explosion lower down the block would not have affected the load walls is that the combined mass of all the load above it creates force downwards due to gravity that would have required far greater lateral forces to create catastrophic structural failure and there are specific equilibrium equations used by civil engineers to calculate such forces. The principal non-layman explanation is this: the lateral force required to blow out the upper floor walls is in linear proportion to the vertical load above multiplied by the lateral frictional resistance, and Mohr's circle calculations bear this out. 
This may also 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 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.
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.
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. Many other similar 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 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 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 similar 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.
Within a couple of decades of the collapse of Ronan Point, the public's lack of confidence in the construction technique, together with the social problems within such developments, led to the demolition of many tower blocks. Despite this, many buildings like Ronan Point are still standing; there are at least 1,585 of them and 200 towers with 20 storeys or higher. There are concerns that problems might emerge as the buildings weaken with age. Wind, heat and rain affect buildings. Metal bolts expand when they rust and crack the concrete round them. In 2018, it was reported that two tower blocks on the Broadwater Farm estate in Tottenham, Tangmere House and Northholt House, are structurally unsound and could collapse catastrophically if there is a gas explosion or if a vehicle collides with the base. Both are to be evacuated urgently. Other buildings in Broadwater Farm also have less serious problems.
Legacy.
In May 2018, 50 years after the partial collapse, Ronan Point was the subject of an experimental documentary film, And then we heard shouts and cries by artist Ricky Chambers. Chambers' grandparents and mother had lived in flat 87 on the 18th floor of the tower block at the time of the gas explosion.
Bibliography.
A number of books have covered the collapse of Ronan Point, including "Collapse: Why Buildings Fall Down" by Phil Wearne . This was written to accompany the television series of the same name shown on Channel 4 in early 2000.
Building Research Establishment reports: