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Reports of the Federal Building and Fire
Investigation of the World Trade Center Disaster
NIST NCSTAR 1-3: Mechanical and Metallurgical Analysis of Structural Steel
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: Determine mechanical properties of WTC structural steel, Determine the quality of the steel and if design requirements were met, and 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.
- NIST NCSTAR 1-3: Mechanical and Metallurgical Analysis of Structural Steel
- NIST NCSTAR 1-3A: Contemporaneous Structural Steel Specifications
- NIST NCSTAR 1-3B: Steel Inventory and Identification
- NIST NCSTAR 1-3C: Damage and Failure Modes of Structural Steel Components
- NIST NCSTAR 1-3D: Mechanical Properties of Structural Steels
- NIST NCSTAR 1-3E: Physical Properties of Structural Steels
For additional information: WTC Contacts | Building and Fire Research Laboratory | NIST
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Last updated: November 2008
