Optimized retrofit of multi-storey buildings using seismic isolation at various elevations: assessment for several earthquake excitations

This work is concerned with the seismic retrofit of multi-storey buildings by installing isolation devices at various levels along their height. The design of an effective retrofit solution of this type requires the selection of the appropriate number of isolation levels to introduce in a building, the elevations at which to place these isolation levels and the properties of each of the isolators to install. The task of identifying configurations of isolators vertically distributed over the height of a building that yield favourable structural behaviour is handled in the present paper with a specially developed optimization procedure, which can automatically and effectively explore the huge set of potential retrofit solutions formed by all possible combinations of isolator numbers, locations and properties. Specifically, a genetic algorithm is implemented to detect the isolation configuration that minimizes the maximum floor acceleration of the building under retrofit, subject to constraints ensuring that maximum allowable values for interstorey drifts, base displacements and overall isolation cost are not exceeded. A 6-storey building is used to test the presented optimization procedure, while several recorded strong earthquake motions are considered, which are applied either individually or in sets to the building in the framework of time-history analyses. The numerical results obtained demonstrate the validity and effectiveness of the optimization procedure, which manages to identify feasible isolation configurations for all test cases examined. Of particular importance is the ability of the optimization procedure to provide valid retrofit solutions for buildings with narrow seismic gaps subjected to very strong earthquakes, in which configurations employing only base isolation usually prove to be ineffective.