The National Institute of Standards and Technology has completed a 4 year investigation of the World Trade Center disaster. The investigation addressed many aspects of the catastrophe, from occupant egress to factors affecting how long the Twin Towers stood after being hit by the airplanes, with the goal of gaining valuable information for the future. A major part of the investigation is the metallurgical analysis of structural steel from the Twin Towers. The analysis includes characterization of mechanical properties, failure modes, and temperature excursions seen by the steel. This talk on the metallurgical investigation will describe the structure of the towers, recovered steel, and special issues faced in the analysis of the steel. In addition, major results and conclusions of the NIST Investigation will be presented.Speaker Bio:Frank W. Gayle is Chief of the Metallurgy Division in the NIST Materials Science and Engineering Laboratory (MSEL). His work at NIST involves materials characterization and structure-property relationships, and has covered a wide range of materials, including quasicrystals, high temperature superconductors, lead-free solder, and aerospace materials ranging from the Wright Flyer to the Space Shuttle. Most recently he led the team of experts addressing the steel forensics aspects of NIST's investigation of the World Trade Center collapses, evaluating steel recovered from the WTC site to determine its quality, mechanical properties, and behavior under impact and high temperature conditions. Dr. Gayle holds a Doctor of Science degree in Metallurgy from the Massachusetts Institute of Technology (1985). He also earned a BS in Civil Engineering and a MS in Materials Science from Duke University. Prior to coming to NIST, Dr. Gayle spent 11 years in industry in the field of alloy development for aerospace applications. Major accomplishments and awards include two Gold Medals (the highest award from the Department of Commerce), winner of the Duke University Paper Airplane Contest, and being the only metallurgist in the world over six feet tall who can walk on his hands.