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Survey of Steel Moment-Resisting Frame Buildings Affected by the 1994 Northridge Earthquake.

pdf icon Survey of Steel Moment-Resisting Frame Buildings Affected by the 1994 Northridge Earthquake. (9210 K)
Youssef, N. F. G.; Bonowitz, D.; Gross, J. L.

NISTIR 5625; 174 p. April 1995.

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National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
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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.