Mechanical Properties of Structural Steels. Federal Building and Fire Safety Investigation of the World Trade Center Disaster.
Mechanical Properties of Structural Steels. Federal
Building and Fire Safety Investigation of the World
Trade Center Disaster.
Luecke, W. E.; McColskey, J. D.; McCowan, C. N.;
Banovic, S. W.; Fields, R. J.; Foecke, T.; Siewert, T.
A.; Gayle, F. W.
NIST NCSTAR 1-3D; 322 p. September 2005.
World Trade Center; high rise buildings; building
collapse; disasters; fire safety; fire investigations;
terrorists; terrorism; steel structures; mechanical
properties; high temperature; impact; creep; strain
rate; modulus; tensile strength; yield strength
This report provides five types of mechanical properties
for steels from the World Trade Center (WTC): elastic,
room-temperature tensile, room-temperature high strain
rate, impact, and elevated-temperature tensile.
Specimens of 29 different steels representing the 12
identified strength levels in the building as built were
characterized. Elastic properties include modulus, E,
and Poisson's ratio, v for temperatures up to 900 DGC.
The expression for E(T) for T < 723 DGC is based on
measurements of WTC perimeter column steels. Behavior
for T > 723 DGC is estimated from literature data. Room
temperature tensile properties include yield and tensile
strength and total elongation for samples of all grades
of steel used in the towers. The report provides model
stress-strain curves for each type of steel, estimated
from the measured stress- strain curves, surviving mill
test reports, and historically expected values. With a
few exceptions, the recovered steels, bolts, and welds
met the specifications they were supplied to. In a few
cases, the measured yield strengths of recovered steels
were slightly lower than specified, probably because of
a combination of mechanical damage, natural variability,
and differences in testing methodology. High-
strain-rate properties for selected perimeter and core
column steels include yield and tensile strength, total
elongation and strain rate sensitivity for rates up to
400 s-1. Measured properties were consistent with
literature reports on other structural steels. Impact
properties were evaluated with Charpy testing.
Properties for perimeter and core column steels were
consistent with other structural steels of the era. The
impact toughness at room temperature of nearly all WTC
steels tested exceeded 15 ft-lbf at room temperature.
Elevated-temperature stress-strain curves were collected
for selected perimeter and core column and truss steels.
The report presents a methodology for estimating
high-temperature stress-strain curves for the steels not
characterized based on room-temperature behavior and
behavior of other structural steels from the literature.
The measured elevated-temperature stress-strain behavior
of WTC steels is consistent with other structural steels
from that era. For the truss steels, the report presents
a complete constitutive law for creep deformation based
on experimental measurements. For the steels not
characterized, the report presents a methodology for
estimating the creep deformation law.