Ronan Point Disaster 16th May 1968 Group 1: Michael Day Jean Giblin Chris Maguire James Wilkinson QuickTime™ and a decompressor are needed to see this picture. 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. This involved the casting of concrete floor, wall and staircase sections off-site before transporting them to site where they were bolted together. Construction began in 1966 and was completed in March 1968. Two months after construction had finished, the south-east 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 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 was adopted for the construction of the Ronan Point Apartment Tower. This is an example of 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 QuickTime™ and a decompressor are needed to see this picture. 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 and 17 injured. 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. QuickTime™ and a decompressor are needed to see this picture. Conclusions 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, although higher winds than outlined in the 1952 code 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. Although triggered by the gas explosion in apartment 90 “On investigation, the apartment tower was found to be deeply flawed in both design and constructionv.” The LarsonNielsen structural system, was only intended to be used for buildings up to six stories tall, but in this case used for a building of 22 stories. As all units are load bearing, the floorwall 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 QuickTime™ and a decompressor are needed to see this picture. methods could have otherwise led to future problems with the building’s structure. “Unfortunately, quality control…was almost completely absentvi” 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. These codes included the possibility of internal explosion and progressive collapse, and highlighted the need for ductility and redundancy in the structural design. The subsequent inspection and demolition of Ronan Point 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 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. vi http://www.open2.net/modernity/3_13.htm ii