The study of steel recovered from the site of the fallen World Trade Center towers and the WTC-7 building in New York City will be a critical component of the pending National Institute of Standards and Technology (NIST) building and fire safety investigation of the disaster. Since February, the Commerce Department's NIST has been storing steel at its Gaithersburg, Md., headquarters. A small portion of the steel has been transferred to NIST's Boulder, Colo., laboratories for future analysis.
Here are some current facts about the stored steel and what will be done with it once the NIST investigation is officially under way:
- As of July 11, 2002, NIST had in its possession in excess of 100 pieces of steel from the WTC site. These pieces include the following types: perimeter columns, wide-flanged beams and trusses. Identification and cataloging of the pieces are in progress.
- As of July 11, 2002, three sections cut from columns stored in Gaithersburg have been transferred to Boulder.
- Analysis of the steel to be conducted in both Gaithersburg and Boulder will be done to determine properties and quality of the metal, welds and connections, and to provide data for other investigation projects. This portion of the research will include:
- documenting failure mechanisms and damage based on visual observations of recovered steel, especially focused on available columns, connectors and floor trusses;
- determining the metallurgical and mechanical properties of the steel, welds and connections;
- correlating the properties of the recovered steel with the material properties specified for construction of the buildings; and
- analyzing the steel to estimate maximum temperatures reached. It is recognized that high temperature exposure before the collapse may be difficult to distinguish from exposure during post-collapse fires.
- The Boulder lab will conduct traditional tensile testing (where steel is pulled to measure strength and ductility), high strain-rate testing (using pull rates higher than those for traditional tests in order to approach the rapid deformation rates of an aircraft impact), and all analyses of welds. Boulder also will share the workload of the high-temperature property measurement with Gaithersburg.
- Extremely high strain-rate testing of steel will be conducted exclusively at Gaithersburg using technology under development by two of the agency's labs.