A novel framework to assess stability of slender structures with base flexibility under bidirectional shaking

The investigation explores the dynamic response of three-dimensional slender structures, focusing on the influence of base flexibility under both unidirectional and bidirectional seismic excitations. A previously developed physical model is extended to incorporate flexible base conditions and has been validated for both free and forced vibration. A dimensionless framework is formulated to generalize the findings across varying soil conditions and system properties. Key response parameters, namely overturning acceleration and maximum rotation, are analyzed to assess dynamic stability. The study introduces the novel stability coefficient spectra, which in conjunction with the rocking spectra can provide quantitative measures of acceleration intensity for a selected performance state. Results reveal that base flexibility can significantly enhance stability by reducing overturning zones and limiting peak rotations suggesting the deficiencies of conventional unidirectional analysis and rigid base assumptions. The proposed framework of rocking spectra triad for bidirectional loading appears promising in reducing dispersion when applied to an ensemble of seismic records. This approach may be examined further as a viable strategy for improved seismic design accounting for the effects of base flexibility and ground motion directionality.