OPTIMIZED USE OF VISCOUS DAMPERS FOR REDUCTION OF SEISMIC RISK IN CONCRETE BUILDINGS USING GENETIC ALGORITHM

Existing concrete buildings designed according to old building codes present a major earthquake risk because they do not possess the ductility required to survive the displacements induced by large earthquakes. Consequently, the seismic retrofit of these buildings typically involves the addition of new, stiff structural elements to reduce earthquake-induced displacements. This approach often requires significant strengthening of the structure and typically involves extensive and expensive foundation work that intrudes on building operations. This paper explores the use of viscous dampers as an alternative method for the seismic rehabilitation of non-duc tile concrete buildings. The methodology is based on nonlinear static analyses in which the effect of external dampers is included by an iterative procedure that modifies the overall building damping to match the expected response in the dampers. Once the equivalent damping has been obtained, the design response spectrum is modified to account for the increase in damping. Since changes to the damper properties only affect the loading used in the analysis, the pushover curve is calculated only once for the unretrofitted building and used throughout the optimization procedure. The paper utilizes Genetic Algorithm as an optimization technique for selecting damper properties. This algorithm is capable of finding near optimal solutions for non-linear problems and is applicable to problems with large number of variables. The optimization ensures that the dampers are highly effective, even at relatively small displacements. An existing Building is used as an illustration, and the properties of dampers are optimized to assure minimum cost.