Survey of Steel Moment-Resisting Frame Buildings Affected by the 1994 Northridge Earthquake.
Survey of Steel Moment-Resisting Frame Buildings
Affected by the 1994 Northridge Earthquake.
Youssef, N. F. G.; Bonowitz, D.; Gross, J. L.
NISTIR 5625; 174 p. April 1995.
Available from: National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900; Rush
Service (Telephone Orders Only) 800-553-6847;
Order number: PB95-211918
earthquakes; steel structures; building technology;
connections; cracking (fracturing); damage; earthquake
engineering; facture; frame structures; steels; surveys
The January 1994 Northridge earthquake damaged a variety
of building types throughout greater Los Angeles.
Perhaps the most alarming pattern of structural damage
involved brittle failures at beam-to-column connections
in steel moment-resisting frames (MRF's). This damage
has called into question the predictability of the
behavior of steel MRF's and the reliability of
conventional connections used in California buildings
over the last two decades. In response to this damage,
emergency changes to the Uniform Building Code now
require specific test results in lieu of reliance on a
prescribed detail. This report presents results of a
survey of MRF's inspected for connection damage since
the earthquake. As a catalogue of inspected MRF's, both
damaged and undamaged, the survey is intended to provide
an overall view of the greater Los Angeles steel frame
population, as well as a single-source building-specific
record of observed conditions. Tabulated survey
responses can help form a quantitative context for
future research, hazard assessment, and policy making.
A computerized database was developed to track
submittals, compile basic survey data, and generate the
summary tables show in the report. Principal
conclusions from the survey data support the observation
that MRF connection damage is not well correlated to any
single structural characteristic. On the contrary, the
survey data show that connection performance may be best
understood in probabilistic, not deterministic, terms,
with emphasis on construction and inspection quality.
In other words, when the connection works, it works
extremely well. But it might not work, if any link in
the chain of design assumptions and construction
procedures is weak. It is essential to note, however,
that current survey data does not include analysis
results or estimates of actural seismic demands from the
Northridge earthquake. Without these, any reading of
survey results must remain open to the possibility that
conventional MRF connections are flawed by their basic
configuration and are simply incapable of ductile
behavior at high strain rates. This alternate theory,
which would fundamentally change the way engineers think
about steel MRF behavior, can only be discarded if
analysis with recorded ground motions can show that
damage did not correlate with demand. Survey results
reported here show only that damage did not correlate
well with design.