Based on experience from the design of 20 concrete ductile core wall buildings using performance-based design concepts and a sample design for a high-rise concrete core wall building performed for the Los Angeles Tall Buildings Structural Design Council, several important issues to be considered before embarking on a detailed analysis have been identifi ed. Nonlinear response history analysis for large, complicated structures can consume many hours of engineering effort. It is always advisable to understand as much as possible about the anticipated building behaviour before beginning this analysis. Performance objectives should be clearly identifi ed for both frequent and maximum considered earthquakes. In particular, acceptable performance at serviceability levels should be understood, as current building codes do not provide much guidance. Factors such as anticipated demand on the lateral system, building height, soil type and seismic hazard should all be considered before running computer models, so appropriate cracking assumptions can be made. Even the design spectra themselves can be indicators of anticipated higher mode effects that may govern design.

SUMMARYA 64-story, performance-based design building with reinforced concrete core shear walls and unique dynamic response modification features (tuned liquid sloshing dampers and buckling-restrained braces) has been instrumented with a monitoring array of 72 channels of accelerometers. The responses of the building to ambient motions from ground or wind were recorded and analyzed to identify modes and associated frequencies and damping. Not unexpectedly, the low-amplitude dynamic characteristics are considerably different than those computed from design analyses. Nonetheless, these computed values serve as a baseline against which to compare future strong shaking responses. Such studies help to improve our understanding of the effectiveness of the response modification features at various levels of shaking, to evaluate the predictive capabilities of the design analysis tools and to improve similar designs in the future.

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