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Collapse of the World Trade Center

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In the immediate aftermath of 9/11, numerous articles were published in newspapers, with the journalists consulting structural engineers and other experts for their opinions on what caused the towers to collapse. The experts also included engineers who worked on the design and construction of the towers. Numerous engineers consulted were not surprised that the buildings ended up collapsing, "given the extraordinary circumstances."[1]

Most experts mentioned explained that the tremendous heat of the fire heated steel structural elements, with the heat causing the structural steel to loose much of its strength. Upon heating, the steel deformed (creep) at first, and eventually reached a point where it fractures. A number of experts describing how the collapse occurred, mentioned that the steel "melted", though the temperatures of the fire did not get that hot and did not need to be that hot in order to substantially reduce the strength of steel. An added factor mentioned was the damage to many of the steel columns due to the aircraft impact, causing load to be shifted to the remaining columns which became overloaded. Many also noted that the fireproofing was likely damaged or dislodged, allowing the steel structural elements to heat up more rapidly, and that the sprinkler systems probably were not functioning.

Initial opinions and analysis

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The impact of the plane itself was not enough to cause the collapse, but the tremendous heat from the fire was the key factor.

  1. Cermak (Cermak Peterka Peterson; did wind tunnel testing for WTC)[2]
  2. Frischmann (Pell Frischmann Group and the City University, London)[1]
  3. Krauthammer (Penn State)[3][4][5]
  4. McIntyre (Skilling Ward Magnusson Barkshire)[6]
  5. Scott (HNTB Architects Engineers Planners)[7]
  6. Hooper (Skilling, Ward, Magnusson, Barkshire)[8][9]
  7. Elnimeiri (Illinois Institute of Technology)[10]
  8. Sanayei[11]
  9. Griffis (Polytechnic University in Brooklyn)[12]
  10. Cuoco (Thornton Tomasetti)[12]
  11. Schindler[13]

No building is designed to withstand "that kind of assault".

  1. Kielar (Tishman Realty and Construction Company)[2][14]
  2. Soane[15]
  3. Ast (Jablonsky, Ast and Partners in Toronto)[16]
  4. Pelli[17]
  5. Elnimeiri[10]
  6. Little (National Academy of Sciences)[18]
  7. Schindler (National Council of Structural Engineers Associations)[19]
  8. Ghorbanpoor (University of Wisconsin-Milwaukee)[20]

Buildings are not designed to withstand the extreme levels of heat that would be found in the situation with the amount of jet fuel and the explosion that occurred

  1. Brazil (Thornton-Tomasetti Engineers)[2]
  2. Magnusson (Skilling Ward Magnusson Barkshire)[2][4][21]
  3. Ast[16]
  4. Miller (University of Cincinnati)[6]

Fires were unlike any fire that a building would normally be subjected to.

  1. Normile (Keast & Hood)[19]
  2. Rittenhouse - There was fire on 15 or 20 different floors[22]

The structure itself performed very well, and would have survived, had there been no fire.

  1. Sanayei[11]

The structural damage from the aircraft impact, combined with tremendous heat from the fire which weakened the remaining columns, reached a point where the columns lost their strength and buckled.

  1. Donnelly (Washington University)[23]
  2. Krauthammer[24][4][5]
  3. Wilkinson

Load was shifted to adjacent members, which got overloaded, and eventually collapsed.

  1. Krauthammer[3][4][5]
  2. Mosher (U.S. Army Engineering Research and Development Center)[5]

Heating of the steel structural members cause them to loose much of their structural strength, deforming at first, and then eventually to the point where they could not hold up the above structure, with steel fracturing.

  1. Astaneh[25]
  2. Cermak[2]
  3. Gustafson (Demtech Inc.)[26]
  4. Kielar (Tishman)[2]
  5. Lebduska (New Jersey Institute of Technology) - thought the failure occurred with the floor trusses[27]
  6. Magnusson[2][4][21]
  7. Zucchi
  8. Donnelly[23]
  9. Krauthammer[3][4][5]
  10. Loizeaux (Controlled Demolitions Inc.)[28]
  11. Sanayei (Tufts University)[29]
  12. Colaco (CBM Engineers) - suggested the floor trusses failed[29][30]
  13. Scott[7]
  14. Snedegar (University of Missouri-Kansas City)[7]
  15. Hooper[8][9]
  16. Mosher[5]
  17. Destefano (U.S. National Council of Structural Engineers)[5]
  18. McGee (Ohio State University) - suggested the connections failed and the floor structure failed, "Then the upper floors begin to collapse, because connections fail, One floor collapses on another. It's not designed to carry two floors, so it collapses on another one, and there's a domino effect."[31]
  19. Mojekwu (Matrix Engineering)[10]
  20. Garrett (Exponent Failure Analysis Associates)[32]
  21. Liew (National University of Singapore)[33]
  22. Normile[19]
  23. Clark (Skilling Ward Magnusson Barkshire)[34]
  24. Cuoco[12]
  25. Nagata (Yokohama National University)[35]
  26. Burns (Thornton-Thomasetti)[22]
  27. Rittenhouse (blast engineer in New York City)[22]
  28. Nair (Chicago structural engineer, and former chairman of the Council on Tall Buildings and Urban Habitat)[36]
  29. Rahimzadeh (John Portman & Associates, structural engineer in Atlanta)[37]

The heating due to the fire caused the steel to melt.

  1. Brown (University of Colorado)[38]
  2. Zollo (University of Miami)[38]

Fireproofing was damaged or dislodged, allowing the steel structural elements to heat up more rapidly.

  1. Astaneh[25]
  2. Magnusson[2][4][21]
  3. Parfitt (Penn State)[17]
  4. Frischmann[1]

Office furnishings, computers, and other office contents were also a factor in fueling the fire and extreme heat.

  1. Lebduska[27]

The height of the fire within the building made the fires even more of a challenge.

  1. Lebduska[39]

The sprinkler system might not have functioned, allowing the fires to burn uncontrolled.

  1. Magnusson[2][4][40]
  2. Liew[41]
  3. Normile[19]

The sprinklers should have maintained the buildings internal strength for several hours.

  1. Frischmann [note: the sprinklers did not function][1]

Once some columns (or other structural elements) failed and the collapse initiated, progressive collapse was inevitable.

  1. Astaneh[25]
  2. Klemencic (Skilling Ward Magnusson Barkshire) - "The technical term is progressive collapse--the slang term is pancaking."[26]
  3. Lebduska[27]
  4. Magnusson[2][4][21]
  5. Zucchi
  6. Donnelly[23]
  7. Krauthammer[3][4][5]
  8. Sanayei[29]
  9. Scott[7]
  10. Garrett[32]
  11. Faschan (Leslie E. Robertson Associates)[42]
  12. Liew[33]
  13. Normile[19]
  14. Schindler[13]
  15. Nair[36]
  16. Rahimzadeh[37]

The planes weakened the buildings' structures at key points. Any higher, and the plane impact would have damaged just the tops, much lower and the base of the buildings were much stronger and could have withstood the damage.

  1. Fenves (University of California at Berkeley)[43][4]

Discounted the notion that controlled demolition or additional explosives were involved.

  1. Hamburger[26]
  2. Loizeaux[44]

It will take structural engineers a long time to figure out exactly how the towers collapsed.

  1. Pelli[17]
  2. Halvorson[1]

The Twin Towers should not have collapsed so quickly.

  1. Frischmann[1]
  2. Fenves - The collapse happened too quickly to be caused by the fire. The fireproofing on the steel structure probably has a rating of three hours" before failing, and the buildings came down sooner than that, about an hour after being struck. [note: if the fire proofing remained intact][43][4]

The towers should have withstood the fires, which reached up to 1,000 C., which is within the design limits for the towers.

  1. Frischmann[1]

The collapse of the World Trade Center came as a surprise to engineers.

  1. Hamburger[45]

There will be debate on whether or not the World Trade Center Towers should have collapsed in the way that they did.

  1. Halvorson (Halvorson and Kaye)[1]

The collapses well beyond realistic experience.

  1. Halvorson[1]

The buildings performed well, not collapsing immediately from the impact and allowing an hour for evacuation.

  1. Ghorbanpoor[20]

Even among designers of skyscrapers, not many of us can honestly say that we would have anticipated this particular chain of events leading to complete structural collapse from an airplane strike near the top of a tall building.

  1. Nair[36]

I don't think anyone imagined that the building would collapse that quickly.

  1. Burns[22]

Thought/anticipated that the towers would collapse.

  1. Rahimzadeh[37]

References

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  1. ^ a b c d e f g h i "WTC collapse forces skyscraper rethink". BBC News. 2001-10-04.
  2. ^ a b c d e f g h i j Glanz, James (September 12, 2001). "Towers Believed to Be Safe Proved Vulnerable to an Intense Jet Fuel Fire, Experts Say". The New York Times.
  3. ^ a b c d LaFee, Scott (2001-09-12). "What Made Towers Crumble - Experts differ on relative import of fire and jet impact". San Diego Union-Tribune.
  4. ^ a b c d e f g h i j k l Cooke, Robert (2001-09-12). "Towers Not Made For Jetliner Impact;Experts say design couldn't handle crash". Newsday (New York).
  5. ^ a b c d e f g h Oziewicz, Estanislao (2001-09-12). "Flames melted steel supports, toppling towers, experts say". The Globe and Mail.
  6. ^ a b Mangels, John (2001-09-12). "Fires fed by jet fuel forced towers down". Plain Dealer (Cleveland).
  7. ^ a b c d Collison, Kevin (2001-09-12). "Towers succumbed to stress, intense heat". Kansas City Star.
  8. ^ a b Feeney, Mary K. (2001-09-12). "A Strategic Strike; Fire, More than Planes' Impact, Caused Collapse of Twin Towers". Hartford Courant.
  9. ^ a b Gunts, Edward (2001-09-13). "Engineers blame collapses on fires". Baltimore Sun.
  10. ^ a b c Grossman, Kate (2001-09-12). "Jet fuel fed fire so hot it softened tower steel". Chicago Sun-Times.
  11. ^ a b Spears, Tom (2001-09-13). "Towering infernos: World Trade Centre designed to handle plane crashes, but not fire, expert says". Ottawa Citizen.
  12. ^ a b c Shifrel, Scott and Eric Herman (2001-09-13). "It Was the Heat, Not the Impact, That Felled WTC Experts Say No Bldg. Could Survive Such Damage". Daily News (New York ).
  13. ^ a b Smith, Stephen (2001-09-16). "The Mighty Icon". Miami Herald.
  14. ^ Post, Nadine M. and Sherie Winston (2001-09-17). "Massive Assault Doomed Towers". Engineering News-Record.
  15. ^ "The terrible transformation of the world's most celebrated skyline stands as a tragic testament to an act of unimaginable violence from which America may never recover". Western Daily Press. 2001-09-12.
  16. ^ a b Simmie, Scott (2001-09-12). "No building could have survived, experts say". Toronto Star.
  17. ^ a b c Gugliotta, Guy (2001-09-12). "'Magnitude Beyond Anything We'd Seen Before'; Towers Built to Last But Unprepared For Such an Attack". The Washington Post.
  18. ^ Smith, Deborah (2001-09-13). "Jet fuel behind collapse". Sydney Morning Herald.
  19. ^ a b c d e Saffron, Inga (2001-09-13). "Towers couldn't take heat of burning jet fuel". Philadelphia Inquirer.
  20. ^ a b Gould, Whitney (2001-09-17). "We cannot allow fear to dictate commercial architecture". Milwaukee Journal Sentinel.
  21. ^ a b c d "30 Questions, Sorting it Out, Looking Ahead". St. Petersburg Times. September 12, 2001.
  22. ^ a b c d Rodriguez, Rebeca (2001-09-16). "Towers survived crashes but not the fires". Fort Worth Star-Telegram.
  23. ^ a b c Duffy, Robert W. (2001-09-12). "Twin Towers that Withistood Bomb Couldn't Withstand Jetliner Attacks". St. Louis Post-Dispatch.
  24. ^ LaFee, Scott (2001-09-12). "What Made Towers Crumble - Experts differ on relative import of fire and jet impact". San Diego Union-Tribune.
  25. ^ a b c Perlman, David (2001-09-12). "Jets hit towers in most vulnerable spots;Killers appear to have known where to strike". San Francisco Chronicle.
  26. ^ a b c McFarling, Usha Lee (2001-09-12). "Structural engineers say the terrorists apparently knew they had to strike the World Trade Center as low as possible to cause the most damage". Los Angeles Times.
  27. ^ a b c "World Trade Center Symbolized America's Economic Might". Newhouse News Service. 2001-09-11.
  28. ^ Moran, Edward (2001-09-12). "Expert: It Wasn't the Blast, It was the Heat". Philadelphia Daily News.
  29. ^ a b c Berger, Eric (2001-09-12). "Towers' great strength saved lives, experts say". Houston Chronicle.
  30. ^ Greenberg, Mike (2001-09-13). "Structures' steel became 'spaghetti'". San Antonio Express-News.
  31. ^ Johnston, John (2001-09-12). "Towers turned into fatal targets". Cincinnati Enquirer.
  32. ^ a b Kamin, Blair (2001-09-12). "Engineers seek answers after mighty towers fall". Chicago Tribune.
  33. ^ a b Sim, Arthur (2001-09-13). "Twin towers not just ordinary skyscrapers". The Straits Times (Singapore).
  34. ^ Lynch, Jim (2001-09-13). "Seattle Engineers Have Tie to Tragedy". The Oregonian.
  35. ^ Yomiuri, Yasushi Yukinari (2001-09-13). "Towers were well designed, but not for this". The Daily Yomiuri.
  36. ^ a b c Nair, R. Shankar (2001-09-19). "A humbling experience for skyscraper professionals". Chicago Tribune.
  37. ^ a b c Galloway, Jim (2001-09-19). "High hopes abundant among skyscraper builders since attack". Atlanta Journal-Constitution.
  38. ^ a b Stepp, Holly (2001-09-12). "Collapse Linked to Fires". Miami Herald.
  39. ^ "World Trade Center Symbolized America's Economic Might". Newhouse News Service. 2001-09-11.
  40. ^ "30 Questions, Sorting it Out, Looking Ahead". St. Petersburg Times. September 12, 2001.
  41. ^ Sim, Arthur (2001-09-13). "Twin towers not just ordinary skyscrapers". The Straits Times (Singapore).
  42. ^ Lieberman, David (2001-09-13). "Extreme heat, 'pancaking' doom towers into rubble". USA Today.
  43. ^ a b Wyman, Bill (2001-09-11). "Why the towers collapsed". Salon.com.
  44. ^ Moran, Edward (2001-09-12). "Expert: It Wasn't the Blast, It was the Heat". Philadelphia Daily News.
  45. ^ Hallinan, Joseph T. (2001-09-19). "Top Structural Engineers to Do Autopsy On Twin Towers to Assess Why They Fell" (PDF). The Wall Street Journal.
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