Fire Technology

, Volume 49, Issue 3, pp 741–765 | Cite as

The World Trade Center 9/11 Disaster and Progressive Collapse of Tall Buildings

  • Panagiotis Kotsovinos
  • Asif UsmaniEmail author


The collapse of the World Trade Center buildings on September 11, 2001 posed questions on the stability of tall buildings in fire. Understanding the collapse of the WTC Towers offers the opportunity to learn useful engineering lessons in order to improve the design of future tall buildings against fire induced collapse. This paper extends previous research on the modelling of the collapse of the WTC Towers on September 11, 2001 using a newly developed “structures in fire” simulation capability in the open source software framework OpenSees. The simulations carried out are validated by comparisons with previous work and against the findings from the NIST investigation, albeit not in the forensic sense. The column “pull in” that triggers the instability of the structure and leads to collapse is explained. The collapse mechanisms of generic composite tall buildings are also examined. This is achieved through carrying out a detailed parametric study varying the relative stiffness of the column and the floors. The two main mechanisms identified in previous research (weak and strong floor) are reproduced and criteria are established on their occurrence. The analyses performed revealed that the collapse mechanism type depended on the bending stiffness ratio and the number of floors subjected to fire and that the most probable type of failure is the strong floor collapse. The knowledge of these mechanisms is of practical use if stakeholders wish to extend the tenability of a tall building structure in a major fire.


Structures in fire Progressive collapse Tall building collapse mechanisms WTC collapses Nonlinear dynamic thermo-mechanical analysis of structural frames OpenSees 



Authors are grateful to Professor Jose Torero for helpful comments and advice on the draft of this paper and also acknowledge the assistance provided by the OpenSees team at PEER, UC Berkeley.


  1. 1.
    Torero JL (2011) Challenging attitudes on codes and safety. CTBUH J 2011(3,Special edn):36–37Google Scholar
  2. 2.
    Lamster M (2011) Castles in the air. Sci Am (special issue) doi: 10.1038/scientificamerican0911-76.
  3. 3.
    FEMA (2002) World Trade Center Building performance study: data collection, preliminary observations and recommendations. Technical Report 403. Washington, DC.Google Scholar
  4. 4.
    Sunder SS, Gann RG, Grosshandler WL et al (2006) Federal building and fire safety investigation of the World Trade Center disaster: final report of the national construction safety team on the collapses of the World Trade Center towers. NIST, Gaithersburg 1Google Scholar
  5. 5.
    (2012) Summary of the structural design of the WTC buildings. Fire Technol (WTC special issue, in press).Google Scholar
  6. 6.
    (2012) Summary NIST findings on aircraft damage. Fire Technol (WTC special issue, in press).Google Scholar
  7. 7.
    Summary of NIST findings on fire dynamics in WTC 1&2 “Fire Technology 2012, WTC special issue (in press).Google Scholar
  8. 8.
    (2012) Summary of NIST findings on fire damage on WTC 1,2 &7″) plus. Fire Technol (WTC special issue, in press).Google Scholar
  9. 9.
    Quintiere JG, diMarzo M, Becker R (2002) A suggested cause of the fire-induced collapse of the World Trade Towers. Fire Saf J 37(7):707–716. doi: 10.1016/S0379-7112(02)00034-6 CrossRefGoogle Scholar
  10. 10.
    Usmani AS, Chung YC, Torero JL (2003) How did the WTC towers collapse? A new theory. Fire Saf J 38(6):501–591. doi: 10.1016/S0379-7112(03)00069-9 CrossRefGoogle Scholar
  11. 11.
    Kodur (2003) Role of fire resistance issues in the collapse of the Twin Towers. In: Proceedings of the CIB-CTBUH conference on tall buildings, 20–23 October, Kuala Lumpur, MalaysiaGoogle Scholar
  12. 12.
    Usmani AS (2005) Stability of the World Trade Center Twin Towers structural frame in multiple floor fires. J Eng Mech 131(6):654–657. doi: 10.1061/(ASCE)0733-9399(2005)131:6(654) CrossRefGoogle Scholar
  13. 13.
    Flint G, Usmani A, Lamont S, Lane B, Torero J (2007) Structural response of tall buildings to multiple floor fires. J Struct Eng 133(12):1719–1732. doi: 10.1061/(ASCE)0733-9445(2007)133:12(1719) CrossRefGoogle Scholar
  14. 14.
    Baum HR (2005) Simulating fire effects on complex building structures. Fire Saf Sci 8:3–18. doi: 10.3801/IAFSS.FSS.8-3 CrossRefGoogle Scholar
  15. 15.
    Ali F, O’Connor D (2001) Structural performance of rotationally restrained steel columns in fire. Fire Saf J 36(7):679–691. doi: 10.1016/S0379-7112(01)00017-0 CrossRefGoogle Scholar
  16. 16.
    Franssen JM (2000) Failure temperature of a system comprising a restrained column submitted to fire. Fire Saf J 34:191–207. doi: 10.1016/S0379-7112(99)00047-8 CrossRefGoogle Scholar
  17. 17.
    Huang ZF, Tan KH, Ting SK (2006) Heating rate and boundary restraint effects on fire resistance of steel columns with creep. Eng Struct 28(6):805–817. doi: 10.1016/j.engstruct.2005.10.009 CrossRefGoogle Scholar
  18. 18.
    Shepherd PG, Burgess IW (2011) On the buckling of axially restrained steel columns in fire. Eng Struct 33(10):2832–2838. doi: 10.1016/j.engstruct.2011.06.007 CrossRefGoogle Scholar
  19. 19.
    Quiel ES, Garlock MEM (2010) Parameters for modeling a high-rise steel building frame subject to fire. J Struct Fire Eng 1(2):115–134. doi: 10.1260/2040-2317.1.2.115 CrossRefGoogle Scholar
  20. 20.
    Torero JL (2011) Forensic analysis of fire induced structural failure: the world trade centre, New York. ICE J Forensic Eng 164(2):69–77CrossRefGoogle Scholar
  21. 21.
    Usmani A, Roben C, Al-Remal A (2009) A very simple method for assessing tall building safety in major fires. Int J Steel Struct 9(1):1–15CrossRefGoogle Scholar
  22. 22.
    Weingardt R (2005) Engineering legends. Am Soc Civil Eng. doi: 10.1061/(ASCE)1532-6748(2001)1:1(58) Google Scholar
  23. 23.
    (2011) Opensees Software, University of California, Berkeley, 11 September 2011.
  24. 24.
    McKenna FT (1997) Object-oriented finite element programming: frameworks for analysis. Algorithms and parallel computing. Dissertation, University of California, BerkeleyGoogle Scholar
  25. 25.
    Usmani A, Zhang J, Jiang J, Jiang Y, Kotsovinos P, May I, Zhang J (2010) Using OpenSees for structures in fire. In: Proceedings of international conference on structures in fire, 2–4 June, Michigan, USAGoogle Scholar
  26. 26.
    Neuenhofer A, Filippou FC (1998) Geometrically nonlinear flexibility-based frame finite element. J Struct Eng ASCE 124:704–711. doi: 10.1061/(ASCE)0733-9445(1998)124:6(704) CrossRefGoogle Scholar
  27. 27.
    M de Souza R (2000) Force-based finite element for large displacement inelastic analysis of frames. Dissertation, University of California, BerkeleyGoogle Scholar
  28. 28.
    Spacone E, Ciampi V, Filippou FC (1996) Mixed formulation of nonlinear beam finite element. Comput Struct 58:71–83. doi: 10.1016/0045-7949(95)00103-N zbMATHCrossRefGoogle Scholar
  29. 29.
    Spacone E, El-Tawil S (2004) Nonlinear analysis of steel concrete composite structures: state of the art. J Struct Eng 130(2):159–168. doi: 10.1061/(ASCE)0733-9445(2004)130:2(159) CrossRefGoogle Scholar
  30. 30.
    Hilber HM, Hughes TJR, Taylor RL (1977) Improved numerical dissipation for time integration algorithms in structural dynamics. Earthq Eng Struct Dyn 5:283–292. doi: 10.1002/eqe.4290050306 CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.School of EngineeringThe University of EdinburghEdinburghUK

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