A general seismic event can be considered as the superposition of two individual time histories of ground acceleration, acting simultaneously at the base of a structural system, along the main directions of a given reference system. Response spectra can be computed either for each component, or for the global seismic event, by considering a Single Degree of Freedom with different values of self-period, subjected to both the x and y accelerograms. Such a bi-directional response spectrum has higher spectral coordinates with respect to the individual ones, because of the instantaneous contributions of both directions of ground motion in the structural response. Nonetheless, an earthquake is expected to release most of the total energy of the event along an actual radial direction, mainly due to the propagation direction of seismic waves from the hypocenter toward the ground surface, even though the ground motion develops according to a random trajectory. A recent research work proposed an analytical procedure for the computation of an “equivalent uniaxial accelerogram” for a bidirectional earthquake: the proposed theory allows to compute a single ground acceleration time-history, related to a proper direction angle, able to reproduce the same effects of a two-components seismic event on a base-isolated structural system: results showed a good agreement between the equivalent radial and the bidirectional structural responses, even if non-negligible differences were observed. In this work a more refined procedure is proposed for the definition of the equivalent unidirectional accelerogram for a base-isolated structure. A wide validation study is reported, by analyzing 100 bidirectional seismic events: two different ranges for vibration period have been assumed, in order to evaluate the accuracy of the overall procedure, by considering a large rather than a small portion of the reference response spectrum. Finally, a case study structure has been modeled, to underline effects of theequivalent radial response, in comparison to the reference bidirectional case.
EFFECTS OF EQUIVALENT RADIAL ACCELEROGRAMS FOR BIDIRECTIONAL SEISMIC EVENTS ON BASE-ISOLATED STRUCTURES
Marco Furinghetti;Alberto Pavese;
2017-01-01
Abstract
A general seismic event can be considered as the superposition of two individual time histories of ground acceleration, acting simultaneously at the base of a structural system, along the main directions of a given reference system. Response spectra can be computed either for each component, or for the global seismic event, by considering a Single Degree of Freedom with different values of self-period, subjected to both the x and y accelerograms. Such a bi-directional response spectrum has higher spectral coordinates with respect to the individual ones, because of the instantaneous contributions of both directions of ground motion in the structural response. Nonetheless, an earthquake is expected to release most of the total energy of the event along an actual radial direction, mainly due to the propagation direction of seismic waves from the hypocenter toward the ground surface, even though the ground motion develops according to a random trajectory. A recent research work proposed an analytical procedure for the computation of an “equivalent uniaxial accelerogram” for a bidirectional earthquake: the proposed theory allows to compute a single ground acceleration time-history, related to a proper direction angle, able to reproduce the same effects of a two-components seismic event on a base-isolated structural system: results showed a good agreement between the equivalent radial and the bidirectional structural responses, even if non-negligible differences were observed. In this work a more refined procedure is proposed for the definition of the equivalent unidirectional accelerogram for a base-isolated structure. A wide validation study is reported, by analyzing 100 bidirectional seismic events: two different ranges for vibration period have been assumed, in order to evaluate the accuracy of the overall procedure, by considering a large rather than a small portion of the reference response spectrum. Finally, a case study structure has been modeled, to underline effects of theequivalent radial response, in comparison to the reference bidirectional case.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
