Dynamics of a Multiple Building Base Isolated System

Abstract eng:
In multiple-building real state complexes, where seismic protection needs to be delivered to all structures, individual isolation may bring a series of construction difficulties. An alternative, is to create a large isolated concrete slab, on which all structures are built, delivering seismic protection to all of them, including common areas and connections. This concept has already been implemented and delivers diverse construction benefits; however, the behavior of each structure differs greatly from its response with individual isolation and this aspect has not been studied in proper depth. The objective is to characterize the dynamic behavior of a multiple-building base-isolated system subject to spatial motion by identifying its equivalent modal properties and analyzing its non-linear response. To do this, a simplified case of two structures was adopted and several configurations were simulated through a 3D numerical model, which considered the non-linear hysteresis of isolators and the possibility of structures undergoing non-linear incursions in addition. All simulations were complemented with a modal analysis of the system. Results indicate that there is a significant interaction between the two structures, caused mainly by the influence of higher modes, in which each structure has an effect on the kinematic of the isolation system. That is to say, the modal response of one structure depends on the parameters of adjacent buildings. As a consequence, common isolation of two dissimilar structures could lead to a significant increase in their displacements or interstory drift. The magnitude of this interaction depends principally on building distribution, structure properties (mainly their period and mass difference) and analysis direction.

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