Low-Rise Steel Structures Under Directional Winds: Mean Recurrence Interval of Failure.
Low-Rise Steel Structures Under Directional Winds: Mean
Recurrence Interval of Failure.
(533 K)
Duthinh, D.; Main, J. A.; Wright, A. P.; Simiu, E.
Journal of Structural Engineering, Vol. 134, No. 8,
1383-1388, August 2008.
Keywords:
steel structures; wind direction; failure; wind
velocity; methodology; wind load; wind tunnels;
simulation; structural behavior; aerodynamics
Abstract:
The Commentary to the American Society of Civil
Engineers (ASCE) Standard 7-05 states that the nominal
mean recurrence interval (MRI) of the wind speed
inducing the design strength is about 500 years if the
specified load factor is 1.5, as in early versions of
ASCE 7, and "somewhat higher than 500 years" if the
specified load factor is 1.6, as in ASCE 7-05. However,
the Commentary also states, "it is not likely that the
500-year event is the actual speed at which engineered
structures are expected to fail, due to resistance
factors in
materials, due to conservative design procedures that do
not always analyze all load capacity, and due to a lack
of a precise definition of 'failure'." In this paper, we
propose a working definition of "failure" for steel
structures using nonlinear finite-element analysis, and
we present a methodology for estimating the MRI of
failure under wind loads that accounts in a detailed and
rigorous manner for nonlinear structural behavior and
for the directionality of the wind speeds and the
aerodynamic effects. The methodology uses databases of
wind tunnel pressure (database-assisted design),
nonlinear finite-element analysis, and directional wind
speeds from the National Institute of
Standards and Technology (NIST) hurricane database
augmented by statistical techniques. As a case study to
illustrate the methodology, we consider a single frame
of a steel industrial building. Under the assumption
that uncertainties with respect to the parameters that
determine the wind loading and to the material behavior
are negligible, the minimum MRI of failure for the steel
frame being investigated was found to be of the order of
100,000 years, which corresponds to a probability of
1/2,000 that the frame will fail during a 50-year
lifetime.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899