Сomparison of maximal integral forces under the base with maximal rigid base accelerations as a tool for verification of seismic analysis

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Rubric:     Theoretical and experimental studies   
Annotation:
Development of verification tools for seismic SSI analysis is discussed in the paper. Combined asymptotic method (CAM) enables verification in different stages of analysis. Particular example of localization of an error is presented in the paper, using the comparison of maximal force under the base and maximal rigid base accelerations calculated by CAM. Two factors spoil the simple link between forces and acceleration based on the second Newton’s law. The first factor is the flexibility of the upper structure. The second factor is the rotational components of the response (without rotational components in seismic excitation). The author suggests the calculation of simple dimensionless ratios between forces, accelerations and masses after CAM calculations. For 1D rigid body motions these ratios are unit. For real structure these ratios are different due to the two abovementioned factors. However, this difference should stay reasonable. If there are any doubts, the author suggests additional CAM calculations without flexibility and rotations. Time-consuming modal analysis of fixed-base structure and calculation of impedances are not repeated, so the additional calculations are very fast and simple. If after excluding flexibility and rotations the ratios do not come to unit, the analyst should look for a mistake. The additional verification tool is a comparison of response spectra for all the variants with excitation spectra. Translational spectra for low frequencies must be almost similar. "