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Status Updated
on Recovered World Trade Center Steel at NIST
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.
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