Progressive collapse is the process where a primary structural element fails, resulting in the failure of adjoining structural elements, which in turn causes further structural failure.
Progressive collapses may be accidental, as the result of design deficiencies, fire, unintentional overload, material failure or natural phenomenon (e.g. erosion, wind or earthquakes). They can also be induced deliberately as a demolition method, specifically that of building implosion, or caused by acts of terrorism or war.
Notable examples On July 14, 1902, the 98 m (323-foot) St Mark's Campanile in Venice, Italy, collapsed after its northern load-bearing wall began to separate from the main structure. The cause of the separation was attributed to more than 700 years of wear on the structure, including fires, earthquakes, and stress redistribution, primarily from drying-induced shrinkage on the wooden support beams, the bells swaying back and forth, and creep. No one was injured except for a cat belonging to a caretaker. The tower was a stonemasonry design.A study on St. Mark's Campanile can be found in Northwestern Universities civil engineering archive and a study about the effects of aging on ancient medieval bell towers was released by the University of Pisa in 2001. On November 1, 1966, the seven-story University of Aberdeen Zoology Department building in Aberdeen, Scotland, suffered a total collapse while under construction. The collapse was attributed to poor girder welds that were weakened by metal fatigue. The metal fatigue was induced by oscillating lateral forces on the structure (primarily wind). Five people were killed and three others were injured. The building was a steel-frame design, and the collapse was the first known example of the total progressive collapse of a steel-framed building.An engineering overview on the collapse with articles from The Scotsman is available. An article on the collapse can also be found in The St. Petersburg Times as well as in the Hansard Archives HERE and HERE
On May 16, 1968, the 22-story Ronan Point apartment tower in West Ham, London, suffered a fatal collapse of one of its corners because of a natural-gas explosion, which destroyed a load-bearing wall. Four people were killed and 17 others were injured. The building was a large-panel system building. On March 2, 1973, the 26-story Skyline Towers Building in Fairfax County, Virginia, collapsed as a result of wooden shoring being removed too soon from an upper-story floor during construction. Fourteen people were killed and 34 others were injured. The tower was a steel-reinforced concrete design. On December 19, 1985, the 22-storyAlthough certain articles claim the building was a 21-story building and others claim it to be a 22-story building, the ultimate height of the building was attained by looking up renter addresses for "1000 Wilshire Blvd 22nd Floor" There are renter addresses listed up to the 22nd floor but not higher commercial office building at 1000 Wilshire Blvd, Los Angeles, currently known as the Wedbush Building,1000 Wilshire Blvd. Los Angeles, CA 90017 was named the Wedbush Building in January 2002 experienced a partial collapse of the structure. Construction crews were offloading steel girders from a flatbed truck onto the deck of the newly completed fifth floor via crane when a girder broke loose from the crane and fell down on to the current stockpile below, which was already loaded to twice the maximum designed load capacity of the floor. This initiated a progressive collapse of the overloaded floor, causing the floor section and girders to crash through the bottom four floors, finally coming to rest in the parking garage. Three people were killed. The building was a steel-frame design.The location of the office building was at 1000 Wilshire Blvd. in Los Angeles and consisted of a 5 floor collapse On March 15, 1986, the six-story Hotel New World in Little India, Singapore, collapsed because the structural engineer had forgotten to add the building's dead load (the weight of the building itself) to his calculations when determining the required strength of the building's support pillars when the hotel was constructed in 1971.A documentary about the Hotel New World collapse is available on YouTube Thirty-three people were killed and 17 others were injured. The building was a steel-reinforced concrete design. On April 23, 1987, the 16-story L'Ambiance Plaza in Bridgeport, Connecticut, collapsed during its construction phase as a result of various instances of inadequate shoring that were in use throughout the construction site.The L'Ambiance Plaza case can be found on Engineering.com Twenty-eight people were killed. The building was a lift-slab design. On March 17, 1989, the 78 m (255-foot) Pavia Civic Tower in Pavia, Italy, collapsed after 800 years of stress redistribution on the structure, primarily from drying-induced shrinkage on the wooden support beams, the bells swaying back and forth, and creep.A study on Pavia Civic Tower can be found in Northwestern Universities civil engineering archive and a study about the effects of aging on ancient medieval bell towers was released by the University of Pisa in 2001. Four people were killed and 15 others were injured. The tower was a stonemasonry design. On May 10, 1993, the four-story Kader Toy Factory in Nakhon Pathom, Thailand, collapsed after fire broke out on the first floor and spread throughout the complex. The factory was in full production at the time and all fire exits were locked. The collapse killed 188 people and injured more than 500 others. The building was a steel-frame design.A case study on the Kader Toy Factory fire is available. On May 24, 1993,From a brief history of the organs at St. Maria Magdalena upon the dedication of the new organ in 2015. the ancient bell tower at the medieval church of St. Maria Magdalena in Goch, Germany, collapsed. The cause was attributed to hundreds of years of stress redistribution on the structure, primarily from drying-induced shrinkage on the wooden support beams, the bells swaying back and forth in the centuries prior, creep, and weathering on the exposed and unmaintained masonry, including crack enlargement from water freezing and expanding between stones in the winter months, causing further expansion of cracks. No one was injured. The tower was a stonemasonry design.Reference to the church of St Maria Magdalena can be found in a study about the effects of aging on ancient medieval bell towers, which was released by the University of Pisa in 2001. On April 19, 1995, the nine-story Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma, collapsed after a truck bomb was detonated outside of the northern façade. The bomb's compression wave caused the fourth and fifth floors to shear up and off their columns and collapse onto the third floor. Floor 3 was connected to the main transfer beam, and pulled it inwards when Floors 4 and 5 fell on it. This caused all of the vertical columns on the northern perimeter that were connected to the transfer beam to collapse as well, along with any floor sections that depended on those columns for vertical support. The Oklahoma City bombing was the first-known example of a terrorist-initiated progressive collapse of a building on American soil. The attack killed 168 people and injured 680 others. The building was a steel-reinforced concrete design.A documentary about the Murrah Federal Building collapse is available on YouTube. Note that the building floors in this documentary are referred to by British Convention and will thus be one floor less than the American name for each floor.The NIST has released a summary and a report on the bombing of the Alfred P. Murrah Federal Building and its collapse. On June 29, 1995, the five-story Sampoong Department Store in Seoul, South Korea, collapsed as the result of the removal of several support columns on the lower floors in order to make room for escalators. This lack of structural support was worsened years later by the addition of several heavy air conditioners on the roof above the area where support columns had been removed. This caused the support column that was closest to the air conditioners to fail and pass its load onto nearby columns, which led to complete failure and collapse within 24 hours of major cracks appearing around the failed column.A documentary about the Sampoong Department Store collapse is available on YouTube The collapse killed 502 people and injured 937 others. The complex was a steel-reinforced concrete design. On September 11, 2001, World Trade Center Buildings 1, 2 and 7 in New York City collapsed as a result of terrorist attacks and the resulting fires. After a three-year investigation by the National Institute of Standards and Technology, it was concluded that fire weakened the steel structure until the long bridge-like floor sections (called trusses) began to progressively sag. This sagging converted the downward pull of the trusses into an inward pull. This intensifying inward pull on the walls eventually caused the outer columns of Tower 2, and later the inner columns of Tower 1, to buckle and fold, thus initiating the collapses.NIST has published a final report on the causes of the World Trade Center collapse. A total of 2,752 people died in the buildings, including 157 passengers and crew members who were aboard two hijacked airplanes that struck Buildings 1 and 2, initiating fires in both, with debris initiating fires in Building 7 upon the collapse of Buildings 1 and 2. The buildings were a steel-frame design. Progressive failure of the floor systems, or so-called "pancake theory," was ruled out as the initiating factor of the structural failure, but was found by both FEMA and NIST scientists to be the primary mode of failure after collapse initiation. On February 12, 2005, the 28-story Windsor Tower in Madrid, Spain, suffered the collapse of the upper 11 floors of the building. The tower had a reinforced concrete inner core surrounded by a traditional webbed steel-frame outer perimeter. Between Floors 16 and 17 was a seven-foot thick reinforced concrete transfer floor, designed to act as a bulkhead and to support the steel framework of the upper 11 stories. An office fire began on the 21st floor and after five hours, the concrete inner core could no longer support the buckling steel outer framework. The upper 11 stories collapsed down to street level with remnants of the upper three floors collapsing down on to the transfer floor. No one was killed. The building was a composite steel-frame and steel-reinforced concrete design.An engineering case study on the Windsor Tower Fire is available. On August 1, 2007, the I-35W Mississippi River Bridge in Minneapolis, Minnesota, collapsed during afternoon rush hour, resulting in the deaths of 13 people. The collapse was attributed to the failure of a gusset plate connecting two members within one of the main arch ribs. Failure of this fracture-critical joint resulted in total collapse of the structure.