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Mechanical and Metallurgical Analysis of Structural Steel. Federal Building and Fire Safety Investigation of the World Trade Center Disaster (NIST NCSTAR 1-3) ***DRAFT for Public Comments***



Frank W. Gayle, Richard J. Fields, William E. Luecke, Stephen W. Banovic, Timothy J. Foecke, Christopher N. McCowan, Joseph D. McColskey, Thomas A. Siewert


This report is an overview of the results of the mechanical and metallurgical analysis of structural steel from the World Trade Center (WTC), part of the National institute of Standards and Technology Investigation of the WTC disaster of September 11, 2001. The goal of the study was threefold: (1) Determine mechanical propetties of WTC stnctural steel, (2) Determine the quality of the steel and if design requirements were met, and (3) Analyze the recovered steel to provide insight into failure mechanisms to guide and/or validate models of building performance. Structural steel recovered from the WTC site was analyzed for composition, microstructure, and mechanical properties, including room temperature properties (for modeling baseline building performance), high temperature properties (for modeling structural response of the building to fire), and behavior at high strain rates (for modeling airplane impact). Failure analysis of the recovered steel, complemented by pre-collapse photographs of the damaged building, was used to establish failure modes and temperature excursions experienced by the steel. In addition, documents from the construction era covering issues ranging from steel specifications to engineering design drawings were used to help interpret the results and supplement models of mechanical properties used in the models of building performance. The analysis focused on the WTC 1 and WTC 2. Although no steel was recovered from WTC 7, a 47-story building that also collapsed on September 11, properties for steel used in its construction were estimated based on literature and contemporaneous documents.
National Construction Safety Team Act Reports (NIST NCSTAR) - 1-3
Report Number


World Trade Center, high rise buildings, building collapse, disasters, fire safety, fire investigations, terrorists, terrorism, steel structures, mechanical properties, failure analysis, specifications, steels, construction, damage, physical properties, structural steel
Created September 1, 2005, Updated February 19, 2017