Effectiveness of the genetic approach for the optimal insertion of viscous dampers into torsionally coupled structures considering nonlinear behaviour

In a companion paper, the authors have proposed a procedure based upon the use of genetic algorithms to numerically identify the system of added viscous dampers which minimises simultaneously the variance of both the longitudinal and the rotational responses to a stochastic white noise input of asymmetric one-storey structures. The goal of this paper is twofold. The first one is to perform an extensive parametric study (with respect to characteristics of the eccentric structures here analysed) in order to provide support to the effectiveness of the proposed procedure for optimal damper arrangement (for both linear dampers and structures). The second goal is to verify how the proposed procedure still leads to acceptable results also when more accurate non-linear modeling of the dampers is taken into account. The parametric studies here illustrated have been performed with reference to one-storey stiffness eccentric structures subjected to a series of historical records of earthquake ground motions. The genetic algorithm approach here tested is capable of leading, in both cases of linear and non linear modeling of the dampers, to the identification of damping systems which lead to a reduced dynamic response when subjected to earthquake excitation only when in the optimisation search are used as objective functions performance indexes based upon the lateral (longitudinal + transversal) response of the system. Minimisation of the torsional response of the system only is capable of reducing substantially the torsional response of the system but may lead (in both cases of linear and non linear modeling of the dampers) to large deformations at the center of mass of the system. The investigations carried out also indicate that, in general, structures equipped with Newtonian dampers exhibit dissipative performances similar to those exhibited by structures equipped with corresponding (as obtained following the procedure here proposed) pseudoplastic dampers.