Ronan Point Collapse - 16th May 1968
Group 1:
Martin Phelan
Michael Grimes
Matthew Arnold
Introduction
Ronan Point was one of a large number of tower blocks
built in West Ham region of London during the 1960’s.
The aim behind the tower blocks was to provide cheap,
affordable prefabricated houses for people of the
surrounding area. Ronan Point was named after Harry
Ronan, a former Chairman of the Housing Committee of
the London Borough of Newham.
The tower block was built by Taylor Woodrow Holdings
Limited, one of the largest based British house building and general construction
companies at the time. Taylor Woodrow used a technique known Larsen-Nielsen System
to construct Ronan Point. Construction began in 1966 and was completed in March 1968.
Two months after construction had finished, the southeast corner of the building
collapsed as a result of a small gas explosion in Flat 90 on 18th floor. The resulting
collapse caused the loss of 4 lives and injured 17 people. The building was later repaired,
but was demolished in 1986 due to a lack of public confidence in high-rise developments
and mounting social problems in the building.
Design and construction
Around the time of the construction of Ronan Point, a change in national policy “allowed
the density of occupancy to doublei” resulting in many high-density blocks being built to
replace parts of London destroyed in WWII. In fact in 1956 Housing Act introduced
subsidies to local councils for every floor built over five storeys. In addition, the lack of
skilled labourers in the construction sector led to huge advancements in prefabricated
construction techniques and technologies. As a
result, the construction of high-rise apartment
blocks became a lot more common; new
residential tower blocks could “accommodate large
numbers of people, save on land and labour, and
be constructed quicklyii”.
The Larsen-Nielsen system of construction is an
example of Plattenbau or Large Panel System
building technique (LPS), developed in Denmark in
1948. The Larsen-Nielsen system is “…composed
of factory-built, precast concrete components
designed to minimize on-site construction work.
Walls, floors and stairways are all precast. All
units, installed one-story high, are load bearingiii.”
This all-encompassing technique included the
patterns for the panels and joints, a method of
production and assembly.
In this type of structural system, each floor in supported by the load bearing walls directly
beneath it. Gravity load transfer occurred only through these load-bearing walls. The
wall and floor system fitted together in slots; these joints were then bolted together and
filled with dry pack mortar to secure the connection. Crucially, this joining process
requires precision and skill. Essentially, the structure of Ronan Point (and other LPS
buildings of the time) relied on gravity to hold everything together by developing friction at
the joints.
Collapse
The collapse of this 22-storey building was brought on by the simplest of tasks; at about
5.45am on 16th May 1968, Ivy Hodge went into the kitchen in her 18th floor apartment to
make her morning cup of tea. Ms. Hodge struck a match, intending to light her gas stove.
Instead this caused a relatively small gas explosion, though large enough to blow Ms.
Hodge across the kitchen floor, which had much more severe results on the structure
than would be expected.
The explosion blew out the load-bearing flank walls in the southeast corner of the 18th
floor, leaving the four floors above unsupported. Floors 19-22 came crashing down in turn
as the supporting walls on the floor below gave way. This began a domino effect as
successive lower floors failed due to the additional
loads from the collapsed floors above. The
collapse was a perfect example of progressive
failure, the same failure mode as the most
infamous collapse in history, the collapse of The
World Trade Centre in 2001.
Surprisingly for this scale of disaster, only 4 people
were killed at the time and 17 injured and a 5th
person died later in hospital. This was probably
due to the fact that Ronan Point had just opened
and some of the flats were still unoccupied. Also,
the time of day meant that the majority of residents
were in their bedrooms rather than their living
rooms. The 260 residents that escaped unharmed
had to climb down several flights of stairs and were
lucky to escape unharmed.
Report and Conclusion
After much pressure from the general public, the British Government formed a panel to
investigate the collapse. The Report of Inquiry into the Collapse of Flats at Ronan Point,
Canning Town was published in August 1968, concluding “a gas explosion had triggered
the collapse of a building that was structurally unsoundiv.”
The gas explosion was caused by a substandard connection between the hose and the
stove. After testing a replica of the brass nut and the supply hose it was found that the nut
had been over-tightened during construction, causing it to break and allowing gas to leak
into apartment 90 slowly rather than instantaneously. The magnitude of the gas explosion
was proved not to be significant in size, at 70kPa or less.
A number of tests, initiated by Imperial College London, concluded that the kitchen and
living room walls were only moved at a pressure of 1.7kPa, with the external wall being
moved at a pressure of 21kPa. The relatively low pressure resulting from the gas
explosion, could have caused localised damage, but should not have caused catastrophic
structural failure on the scale that was seen in May 1968.
The building code used to design Ronan Point was published in 1952, sixteen years
before the accident. Ronan Point was designed to withstand wind velocities of only
100km/h even though winds of much higher velocities than that were known to occur at
the site. According to the investigation, suction pressures caused by these winds would
have had a similar effect to the gas explosion. In addition, the report found that the
building was highly susceptible to fire loading and a relatively small fire could have
caused the sufficient movement in the wall and floor panels to displace the poorly
constructed H-2 flank joint (shown below), that was the sole connection between floor
slabs and flank walls, which could have resulted in a progressive collapse.
Although triggered by the gas explosion in apartment 90 “On investigation, the apartment
tower was found to be deeply flawed in both design and construction.” The LarsonNielsen structural system, was only intended to be used for buildings up to six stories tall,
but in this case it was used for a building of 22 stories. As all units are load bearing, the
floor-wall connections are crucial in this structural system. Once the flank-wall had been
removed, there was no secondary system of supporting the loads and the building
systematically collapsed. This
design gives no alternative load
path, and no redundant structural
members.
Although the design flaw was the
primary cause for the collapse of
Ronan Point, poor construction
methods could have otherwise led
to future problems with the
building’s structure.
“Unfortunately, quality
control…was almost completely
absentv” during construction, with
critical wall-floor connections
being filled with rubble and
newspaper rather than mortar.
Clearly, there were a number of lessons learnt from this disaster. The design of the
building was flawed: the tower consisted of prefabricated panels without a structural
frame; there was not sufficient redundancy to allow for load redistribution in the event of a
localized collapse; the design wind pressures did not account for the building’s height; the
existing building codes were inadequate; the Larsen-Nielsen system was extended past
the point of safety without testing. In addition the construction methods were also
responsible for the structural failure, in particular quality control of workmanship was
severely lacking.
The collapse of Ronan Point led to the development of new regulation codes.
Immediately following the original report the government agreed to a dual standard for
system-built flats, with all new structures being built to resist internal explosions of 35 kPa
pressure while existing ones had to be strengthened to resist 17.5 kPa. They also
highlighted the need for ductility and redundancy in the structural design. The subsequent
inspection and demolition of Ronan Point, more than 15 years later, highlighted the extent
of the poor workmanship in the building. It is imperative that quality of workmanship is
monitored onsite to prevent any abnormal structural loading or safety-issues throughout a
building’s design-life.
i
http://matdl.org/failurecases/Building%20Cases/Ronan%20Point.htm
Pearson, C. & Delatte, N. (2005) Ronan Point Apartment Tower Collapse and its Effect on Building Codes. Journal of
Performance of Constructed Facilities, 19(2) May, pp172-177.
iii
Systems. (1968). Systems Built Apartments Collapse. Engineering News-Record. May 23, 1968.
iv
http://news.bbc.co.uk/onthisday/hi/dates/stories/may/16/newsid_2514000/2514277.stm
v
http://www.open2.net/modernity/3_13.htm
ii