We've discussed many causes of bridge collapse, but there are collapses that weren't caused by any of the usual factors -- rather, they were caused by events that can only be described as unusual.
In 1958, Cuba held the second Cuban Grand Prix. Legendary racer Juan Fangio was actually kidnapped by socialist revolutionaries before the race, but that wasn't the worst thing about the event. The course was lined not with guard rails or safety fences, but with spectators standing right at the edge of the track. During the race, driver Armando Garcia Cifuentes lost control of his Ferrari and plowed into the crowd, destroying a temporary pedestrian bridge in the process. Seven people were killed [source: Edmondson].
The Lacey V. Murrow Memorial Bridge in Seattle crosses Lake Washington. It's a floating bridge, suspended on pontoons. In 1990, a bizarre series of construction errors filled the pontoons with water used in resurfacing the bridge along with rain and lake water from a storm. Over the course of several hours, the bridge sank to the bottom of the lake.
The Winkley Bridge was a pedestrian suspension bridge in Arkansas. It was known for swaying significantly under load. In 1989, a group crossing the bridge started intentionally swinging it. They caused the bridge to sway so fiercely that the support structures failed and the bridge collapsed, killing five [source: Bridgehunter].
- ABC News. "Granville victims remembered." Jan. 18, 2007. Accessed Sept. 16, 2011. http://www.abc.net.au/news/2007-01-18/granville-victims-remembered/2174440
- Associated Press. "Lives forever changed by skywalk collapse." Lawrence Journal-World, July 15, 2001. Accessed Sept. 15, 2011. http://www2.ljworld.com/news/2001/jul/15/lives_forever_changed/
- Bridgehunter. "Winkley Bridge: Cleburne County, Arkansas." Accessed Sept. 16, 2011. http://www.bridgehunter.com/ar/cleburne/winkley/
- Edmondson, Laurence. "Kidnapped in Cuba." ESPN, July 20, 2010. Accessed Sept. 19, 2011. http://en.espnf1.com/f1/motorsport/story/23608.html
- Guthrie, Doug. "Tanker fire shuts down I-75, collapses Nine Mile Bridge." The Detroit News, July 16, 2009. Accessed Sept. 15, 2011. http://detnews.com/article/20090716/METRO/907160424/Tanker-fire-shuts-down-I-75--collapses-Nine-Mile-bridge
- Korea National Emergency Management Agency. "Seongsu Bridge Collapse." Accessed Sept. 15, 2011. http://eng.nema.go.kr/sub/cms3/3_9.asp
- LeRose, Chris. "The Collapse of the Silver Bridge." West Virginia Historical Society Quarterly, Oct. 2001. Accessed Sept. 15, 2011. http://www.wvculture.org/history/wvhs1504.html
- Letchworth, William Pryor. "Portage Bridge. Its destruction as Described by an Eye-witness. A Brilliant Conflagration and a realistic Account of it." Buffalo Courier, May 7, 1875. Accessed Sept. 15, 2011. http://www.letchworthparkhistory.com/burningbridge.html
- Martin, Rachel. "Hyatt Regency Walkway Collapse." University of Alabama at Birmingham. Accessed Sept. 15, 2011. http://www.eng.uab.edu/cee/faculty/ndelatte/case_studies_project/Hyatt%20Regency/hyatt.htm#Causes
- National Park Service. "Run for Your Lives! The Johnstown Flood of 1889." Accessed Sept. 15, 2011. http://www.nps.gov/history/NR/twhp/wwwlps/lessons/5johnstown/5johnstown.htm
- NYCRoads. "Connecticut Turnpike." Accessed Sept. 19, 2011. http://www.nycroads.com/roads/ct-turnpike/
- Oestern, HJ. "Facts about the disaster at Eschede." Journal of Orthopedic Trauma, May, 2000. Accessed Sept. 15, 2011. http://www.ncbi.nlm.nih.gov/pubmed/10898202
- Storey & Delatte. "The Collapse of the Schoharie Creek Bridge." Proceedings of the 3rd ASCE Forensics Congress, October 19 - 21, 2003. Accessed Sept. 16, 2011. http://www.eng.uab.edu/cee/faculty/ndelatte/case_studies_project/Schoharie.htm
- Structurae. "Quebec Bridge." Accessed Sept. 15, 2011. http://en.structurae.de/structures/data/index.cfm?ID=s0000479
- United States Geological Survey. "The October 17, 1989, Loma Prieta, California, Earthquakeâ€”Selected Photographs." 1999. Accessed Sept. 16, 2011. http://pubs.usgs.gov/dds/dds-29/
- Wardhana, Kumalasari & Hadipriono, Fabian C. "Analysis of Recent Bridge Failures in the United States." Journal of Performance of Constructed Facilities, 17, 144 (2003).
- Wilber, Del Quentin. "A Crash's Improbable Impact." Washington Post, Jan. 12, 2007. Accessed Sept. 19, 2011. http://www.washingtonpost.com/wp-dyn/content/article/2007/01/11/AR2007011102220.html
The Hong Kong-Zhuhai-Macao Bridge is an engineering marvel. HowStuffWorks looks at this amazing structure.