Seismic Isolation of Buildings Subjected to Typical Subduction Earthquake Motions for the Mexican Pacific Coast

An analytical study on the application of different base isolation systems for original design or retrofit of typical building structures of the Mexican Pacific Coast is presented. The subject hypothetical buildings are located on hard soil conditions at Acapulco. Typical accelerograms for the Mexican subduction zone recorded during recent earthquakes were used for 3-D time-history analyses. Bidirectional input was used for the time-history analyses. The studied base isolation systems reported in this study are lead-rubber bearings (LRB) and steel-hysteretic dampers (SHD). For the original design case studies, the superstructures were designed: a) according to the seismic provisions of the building code of Guerrero state (RCGS-90) for the fixed-base condition and, b) according to an elastic design based upon a 3-D lateral force distribution consistent with dominant mode shapes for the isolated structure to yield the peak dynamic base shear transmitted by the isolation system. Material volumes for the superstructure were estimated for both the fixed-base code designs and the base-isolation designs. Important savings on the volume of concrete and steel reinforcement can be attained for the base isolated designs with respect to their counterpart fixed-base designs. Dynamic responses for the isolated structures compare favorably with those for the fixed-base structures. The study confirms many findings published in the literature regarding the effectiveness of base isolation and the effect of torsional responses. However, the study also shows that the dynamic stability of isolators is not always achieved using rational design procedures. The dynamic stability and design of the studied base isolators can be controlled by acceleration records associated to moderate earthquakes when these records are near the fault plane and by torsional responses.