This article describes an analysis of the structural collapse that occurred in World Trade Center (WTC) building 5 due to fire exposure on 11 September 2001. It is hypothesized that the steel column-tree assembly failed during the heating phase of the fire. A failure analysis is performed to determine the response of the portion of the building frame that collapsed during the fire ignited by falling debris from the WTC towers. Results from a finite element, thermal-stress model confirm the column-tree failure hypothesis. Based on this model, the authors conclude that the catastrophic, progressive structural collapse occurred $2 hours into the fire exposure.

Summary For furnace testing of fire‐resistant floor and roof assemblies in the United States, the ASTM E 119 standard (and similarly the UL 263 standard) permits two classifications for boundary conditions: “restrained” and “unrestrained.” When incorporating tested assemblies into an actual structural system, the designer, oftentimes a fire protection or structural engineer, must judge whether a “restrained” or “unrestrained” classification is appropriate for the application. It is critical that this assumption be carefully considered and understood, as many qualified listings permit a lesser thickness of applied fire protection for steel structures (or less concrete cover for concrete structures) to achieve a certain fire resistance rating if a “restrained” classification is confirmed, as compared with an “unrestrained” classification. The emerging standardization of structural fire engineering practice in the United States will disrupt century‐long norms in the manner to which structural behavior in fire is addressed. For instance, the current edition of the ASCE/SEI 7 standard will greatly impact how designers consider restraint. Accordingly, this paper serves as an exposé of the “restrained vs unrestrained” paradigm in terms of its paradoxical nature and its controversial impact on the industry. More importantly, potential solutions toward industry rectification are provided for the first time in a contemporary study of this paradigm.

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<p>Advancements put forth by the Structural Engineering Institute (SEI) of ASCE are paving the way for a regulated engineered alternative to the long‐standing archaic requirements for structural fire design. For the past century, project stakeholders have tolerated a strikingly inefficient and amorphous system for protecting structures from uncontrolled fire. Traditionally, fire protection is prescribed for structures after they have been optimized for ambient design loads (i.e., gravity, wind, seismic, and others), with no explicit consideration of structural fire performance. Accordingly, the vulnerability of buildings to structural failure from uncontrolled fire is presumably variable across different jurisdictions, which have varying structural design requirements for ambient loads. Also, structural engineers are often absent from the structural fire protection design process entirely.</p><p>In conjunction with new provisions in Appendix E of Minimum Design Loads and Associated Criterial for Buildings and Other Structures (ASCE/SEI 7‐16), a first‐of‐its‐kind ASCE/SEI Manual of Practice 138: Structural Fire Engineering, has been developed to provide structural engineers a baseline level of guidance to practice structural fire engineering. Also, ASCE/SEI has partnered with the Charles Pankow Foundation to conduct an ambitious project meant to showcase this new technology to the industry. Advancing the adoption of performance‐based structural fire engineering within the AEC industry will benefit public safety while delivering more efficient and economic building designs.</p>