Seismic Reliability of Special Moment Steel Frames with Welded Connections: I

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Abstract
The Northridge earthquake of 1994 led to numerous weld fractures in beam-to-column connections in welded special moment-resisting frames. To address building performance issues raised by these failures and to support improvements in probability-based load resistance factor design for steel building structures, four welded special moment-resisting frames of different sizes and configurations that suffered connection damage during the earthquake are evaluated using both deterministic and stochastic approaches. The results of this investigation are presented in two companion papers. This paper focuses on deterministic dynamic modeling issues, using a new hysteretic model that incorporates the effects of connection weld fractures on building response and ground motions believed to be representative of the Northridge earthquake. The degraded connection model results in somewhat larger frame deformations, but its impact only becomes significant at spectral accelerations larger than those believed to have occurred. The agreement of predicted and surveyed damage was quite good for two of the frames, but not as good for the other two. Inherent randomness and modeling uncertainties limit the quality of the agreement that is possible from a single deterministic analysis. Thus, in the companion paper, the role of uncertainties in making such comparisons is investigated. Randomizing the strength and ground motion yields a probabilistic description of building performance that places such comparisons of predicted and observed damage in better perspective.

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