Combined asymptotic method in seismic analysis of high-rise building: results

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Rubric:     Theoretical and experimental studies   
Annotation:
Combined Asymptotic Method (CAM) has been developed and used for SSI analysis of stiff and heavy NPP structures. However, some of civil structures nowadays are comparable with NPP
structures in terms of size and mass. The question is whether SSI is significant for such structures and whether it should be accounted for in the design process. The authors apply CAM to the
seismic analysis of the high-rise structure resting on a sample homogeneous half-space modeling soil. The main peculiarity of this structure as compared to the conventional NPP structures 
are very low first natural frequencies of the fixed-base model for the horizontally-rocking modes, and very intensive accumulation of the modal masses (especially rocking ones) in the frequency range far below dominant excitation frequency. As a result, at the dominant excitation frequency the effective horizontal and rocking masses are far less than the conventional masses, and the overall impact of SSI is surprisingly small. In the vertical direction the first natural frequency is greater (about 1.5 Hz) which makes vertical seismic response look like conventional seismic response of the NPP structures – and SSI effects are more pronounced here. Due to the wide scope of results only main results are presented here. 6D response spectra for rigid base calculated for three variants of soil parameters are compared to 3D spectra of excitation. Maximal integral forces under the base are presented in comparison with those obtained for the fixed-base analysis and with maximal accelerations of the base. The authors are going to provide detailed comments in the nearest future.