SAC Phase 1 Analytical Studies of Building Performance


Project Title:
Drift Demand Spectra for Selected Northridge Sites
Wilfred D. Iwan, California Institute of Technology
Project Summary:
The objectives of this project were to: 1) provide uniformly processed data of ground motion at selected near-field (near-field source) sites where high peak ground velocities were observed during the Northridge earthquake, 2)produce drift demand spectra for selected near-field sites, 3) produce drift demand spectra for artificially generated Northridge ground motions provided by Paul Somerville, and 4) compare the results of teh drift demand spectra to results of more extensive numerical analyses of prototype buildings subjected to the same ground motion.

The funding provided by SAC was, in itself, insufficient to achieve the above objectives. Therefore, the SAC funding was used to supplement funding received from NSF and other sources. The results of this project cannot be attributed to nor wholly owned by any sole sponsor.

Based on the results of this limited study, it is concluded that the drift demand spectrum has promise as a simple means of describing drift demand for real structures subjected to damaging earthquakes. For buildings in the elastic range, good agreement is obtained between the simple drift demand spectrum and detailed numerical computations. For buildings that are strongly nonlinear, some adjustment needs to be made to the drift demand spectrum just as in the case of the response spectrum. A simple period adjustment seems to work well for the limited number of cases considered in this study. Further efforts to develop ductility-based drift demand spectra are currently uderway.

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