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The Collapse of World Trade Center 7: Revisited

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Abstract

The catastrophic events of September 11, 2001, stand out as a major motivation for research on improving the understanding of structural behaviour in fire. These events included the first complete collapse of a tall steel framed structure solely due to fire. World Trade Center 7 (WTC7) was a 47-storey office building within the WTC complex that collapsed due to a fire initiated by debris from the collapse of WTC1. In the following years, detailed investigations were carried out by expert teams to pinpoint the cause of the progressive failure of WTC7. Each of the expert teams analysed the fire and structure and made varying conclusions with regards to the mechanisms responsible for initiating and propagating the collapse of the building. This paper revisits the collapse of WTC7 and its investigation, and then explores the hypothesis that a potential hydrocarbon fire may have compromised the large transfer structure within the mechanical space of the building. This is done via two OpenSees finite element models. The first model explores the thermomechanical response of the mechanical floors to a potential diesel fire, and the second investigates the response of the structure to a failure caused by that fire. The outcome of the analyses shows that it is feasible that a mechanical room fire could lead to a failure in the transfer structure, which would then result in the loss of support to at least two columns within the building core. The failure of these columns may unbrace the eastern-most core columns and precipitate in the failure of the structure as observed on 9/11.

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Acknowledgements

The work described in this paper was supported by a grant from the Research Grants Council (RGC) of the Hong Kong Special Administrative Region, China, for the Project ‘OpenFIRE: An Open Computational Framework for Integrated Simulation of Structural Response to Fires’ (Project No. PolyU 15220618), and by the Hong Kong Polytechnic University start-up fund 'Computational modelling on modern buildings subjected to fires' (Project No. P0031564). The PhD studies of the second author are supported by the Hong Kong PhD Fellowship Scheme established and funded by the RGC.

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Authors and Affiliations

  1. Research Centre for Fire Safety Engineering, Department of Building Environment and Energy Engineering, Faculty of Building and Environment, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China

    Mhd Anwar Orabi, Liming Jiang & Asif Usmani

  2. Department of Civil, Environmental, and Geomatic Engineering, University College London, London, UK

    Jose Torero

Authors
  1. Mhd Anwar Orabi
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  2. Liming Jiang
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  3. Asif Usmani
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  4. Jose Torero
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Contributions

Mhd Anwar Orabi: Conceptualization, Investigation, Writing-original draft, Formal analysis. Liming Jiang: Supervision, Writing-review & editing, Funding acquisition. Asif Usmani: Conceptualization, Supervision, Formal analysis, Investigation, Resources. Jose Torero: Conceptualization, Supervision, Formal analysis, Investigation.

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Correspondence to Liming Jiang or Asif Usmani.

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Orabi, M.A., Jiang, L., Usmani, A. et al. The Collapse of World Trade Center 7: Revisited. Fire Technol (2022). https://doi.org/10.1007/s10694-022-01225-2

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