Purpose - The objective is to study the optimal damper placement of a given number of passive viscoelastic dampers, when the structure (nuclear plant) is subjected to motions from earthquake, in order to reduce the acceleration responses at a particular location, for example, a vibration-sensitive room (nuclear reactor).

Design/methodology/approach - The IDESIGN software including genetic algorithms for the optimisation task has been interfaced with a finite element program, ABAQUS, to create a structural optimisation tool. The tool has been tested on a 3D building structure.

Findings - Optimisation results for different constraints on number of dampers shows that eight optimally located dampers results in an overall maximum reduction of 59 per cent of the cost function for the uncontrolled structure. It is also found that six optimally placed dampers are more effective than the fully damped case with 12 dampers.

Research limitations/implications - More powerful computers are needed in order to reduce the computational time for many engineering models. Especially parallel processing would make more efficient use of the genetic algorithm. It is also necessary to perform stochastic finite element analysis to investigate the impact on the cost function due to different earthquakes. Practical implications - The study of vibration reduction by an optimal number and location of viscoelastic dampers indicate that structures subjected to dynamic forces can be designed both safely and economically.

Originality/value - The tool developed is quite general and is believed to be applicable to many types of structural optimisation analyses.