SUMMARYA pseudodynamic testing procedure has been applied by which the seismic response of a base-isolated building is obtained by using as specimen the isolators, while the superstructure is numerically simulated. The procedure also takes advantage of the continuous pseudodynamic testing capabilities of the ELSA laboratory, which increase the accuracy of the results and reduce the strain-rate e ect of the rubber bearings. A simple proportional correction of the measured forces compensates the remaining strainrate e ect due to the unrealistic speed of the test. The correction factor is obtained by means of a characterizing test on the speciÿc rubber isolators.The developed method has been successfully applied to the prediction of the seismic response of a base-isolated four-storey building submitted to several speciÿed accelerograms. The results for those earthquakes as well as the e ects of some changes of the parameters of the system are discussed.
SUMMARYThe seismic response of elasto-plastic structures to both recorded and generated accelerograms is characterized by a large scattering of the results, even for accelerograms with similar peak ground acceleration values and frequency content. According to current code recommendations a design value of the seismic response of an elasto-plastic structure can be computed as the mean of the responses to a certain number of spectrum-ÿtting generated accelerograms. A more e ective probabilistic approach is presented herein. It allows the analyst to calculate a design value of the seismic response characterized by a predeÿned non-exceedance probability using a limited number of generated accelerograms. The results of the performed analyses are presented in diagrams that can be used for structural design applications. The applicability of the proposed method is demonstrated in the case of an elasto-plastic structural system and the results are compared with those obtained applying current code recommendations.
A great number of Italian highway bridges have been provided with seismic isolating devices. As a typical example of the criteria for the design of such structures the bridges of a new highway are illustrated. They are composed of various continuous multi-span sections. The seismic isolating systems have been designed on the basis of the dissipating behaviour of elastic-plastic restrainers. With reference to the cases studied, general considerations concerning the design of optimum structural configuration suggested by the use of seismic isolation, are also discussed.
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