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In the early morning hours of May 16, 1968, the occupant of apartment 90 on the 18th floor of the Ronan Point apartment tower lit a match for

her stove to brew her morning cup of tea. The resulting gas explosion, due to a leak, knocked her unconscious.

Design and Construction

The Ronan Point Apartment Tower was constructed using the Larsen-Neilsen system. This system was developed in Denmark in 1948. The Larsen-Nielson system was “…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 bearing (System, 1968).” This building technique encompassed the patterns for the panels and joints, the method of panel assembly, and the methods of production of the panels.

CASE V

RONAN POINT

LONDON, 1968

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Collapse

The collapse was initiated by a gas-stove leak on the eighteenth floor in apartment ninety. The resident struck a match to light the stove to make a cup of tea, and was knocked unconscious by the resulting explosion. The force of the explosion knocked out the opposite corner walls of the apartment. These walls were the sole support for the walls directly above. This created a chain reaction in which floor nineteen collapsed, then floor twenty and so on, propagating upward.

Causes of Failure

A substandard brass nut had been used to connect the hose to the stove. The nut had a thinner flange than the standard, and also had an unusual degree of chamfer. A replicate of this nut was made and tested to determine how much force was required to break it in tension.

It was concluded that a force of 15.6 kN (3,500 pounds) would break the connection. It was also concluded that the hose connecting the stove to the gas would have failed before the nut at a force of 1.6 kN (360 pounds). The nut was assumed to have been previously fractured by over-tightening during installation, causing it to break, allowing gas to leak into the apartment (Griffiths et al., 1968).

The Building Research Station and Imperial College of London performed an extensive battery of tests to discover how much internal force Ronan Point could withstand. The results indicated that the walls could have been displaced by a pressure of only 19.3 kPa (2.8 psi) (Levy 1992). It was estimated that the kitchen and living room walls were moved at a pressure of only 1.7 kPa (0.25 psi), while the exterior wall was moved at a gas pressure of 21 kPa (3 psi) (Griffiths et al., 1968).

Ultimately, the collapse of Ronan Point was due to its lack of structural redundancy. It had no fail-safe mechanisms, and no alternative load paths for the upper floors should a lower level give way.

Without any type of structural frame, the upper floors had no support, and fell onto floor seventeen. The panels forming floor seventeen could not support the sudden loading caused by the upper five floors that fell on it. Consequently, they gave way, and the process continued until it reached the ground level.

Ethical Aspects

Substandard workmanship had been detected in the initial inquiry of the collapse. Even though it was determined to be a negligible factor in the corner collapsing, this information was hidden from the public. Was it a question of ethics or politics? By the time the inquiry’s findings were published in 1968, many large panel concrete buildings had been completed. This was the

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government’s method of keeping its promise of housing the numbers of people living in slums, after the war had demolished a quarter of the homes in England. The government did not want to consider demolishing these buildings. At least six Larsen-Nielson system buildings had been completed by this time. There was not enough money to strengthen them. So the question is, ‘did the government endanger the lives of the residents of these facilities by taking only minimal action to strengthen the buildings?’

Webb was very active in taking measures to inform the public of the possible hazards associated with these types of buildings. He made officials aware of possible dangers that could lead to another progressive collapse such as high winds, or a building fire. He was a strong advocate of demolishing these “death traps.”

References Bignell, Victor; Peters, Jeoff; Pym, Christopher. (1977). Catastrophic Failures.

Open University Press, Milton Keynes, New York.

Britain. (1970). “Britain tightens building standards, moves to stern ‘progressive collapse.’”

Engineering News-Record. April 16, 1970, 12.

Feld, Jacob and Carper, Kenneth (1997). Construction Failure. John Wiley and Sons, Inc., USA.

Fuller, Robert (1975). “Industrialized concrete Construction for HUD.” Industrialization in Concrete Building Construction. American Concrete Institute, Detroit, Michigan USA.

Griffiths, Hugh; Pugsley, A. G.; Saunders, Owen, (1968). Report of the Inquiry into the Collapse of Flats at Ronan Point, Canning Town. Her Majesty’s Stationery Office, London.

Hendry, Arnold, W. (1979). “Summary of Research and Design Philosophy for Bearing Wall Structures.”

Journal of the American Concrete Institute. 76(33), 723-737.

Levy, Matthys and Salvadori, Mario, (1992). Why Buildings Fall Down.

W.W. Norton and Company, New York, New York.

Ross, Steven (1984). Construction Disasters: Design Failures, Causes, and Prevention.

An Engineering News-Record Book. McGraw-Hill Book Company, USA.

Shepherd, Robin and Frost, J. David (1995). Failures in Civil Engineering, Structural, Foundation and Geoenvironmental Case Studies. American Society of Civil Engineers, New York, New York.

Systems. (1968). “Systems Built Apartments Collapse.” Engineering News-Record. May 23, 1968, 23.

Wearne, Phillip (2000). Collapse: When Buildings Fall Down. TV Books, L.L.C., USA.

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Photograph from MontrealGazette.com

The de la Concorde Overpass over Autoroute 19 in Laval, Quebec, collapsed on September 30, 2006, killing five and injuring six. The Government of Quebec convened a commission to investigate.

Design and Construction

The bridge was an unusual side-by-side prestressed box girder configuration designed and built between 1968 and 1971. The ends of the girders rested on cast-in-place concrete cantilevers extending out from the abutments. The bridge was an unusual structure, difficult to inspect, and no more bridges of this type were built in Canada after 1972.

The cantilever supports also doubled as expansion joints, and had very complex load transfer mechanisms. The joints were difficult to seal and maintain, and allowed water and de-icing

CASE VI

AUTOROUTE 19 DELA CONCORDE OVERPASS

CANADA, 2006

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chemicals to collect at the cantilever supports. Substantial repair work undertaken in 1992 might have caused some damage that later led to the bridge collapse.

The cantilever supports relied on a complex reinforcement detail to transfer bearing forces into the top bars through stirrups. However, the tops stirrups were placed slightly below the top reinforcement, leaving a horizontal plane of weakness.

Causes of Collapse

The investigating commission cited as primary physical causes the improper detailing of reinforcement (the top bars were not anchored), improper installation of reinforcement, and low quality concrete. The concrete specification was confusing and appeared to allow the use of weaker and less durable concrete. At the time of the collapse, the concrete strength was a bit higher than the specified 27.6 MPa (4,000 psi), but a higher strength would have been expected after 36 years. The air content and de-icer scaling resistance of the concrete were also poor. The commission also cited the contributing physical causes of lack of shear reinforcement in the thick cantilever slabs, lack of waterproofing of the cantilever concrete, and possible damage caused during the 1992 repair work.

Just prior to the collapse, puddles of water and chunks of falling concrete were observed. Some drivers also noticed bumps at the expansion joints when crossing the overpass. The concrete cantilever peeled off just below the top layer of reinforcement, and the prestressed box girders fell onto Autoroute 19 and two passing cars. Three cars and a motorcycle fell with the overpass.

References Commission of Inquiry (2007). Report of the Commision of Inquiry into the Collapse of a Portion of the de la Concorde Overpass, Transcontinental Metrolitho.

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Photograph from DailyWireless.org

On August 1, 2007, an eight-lane, three-span section of the I-35W