Optimization of nonlinear viscous damper characteristics to reduce the response of concrete structures with linear and nonlinear behaviours

Nowadays, controlling vibration of a structure in earthquakes and reducing the structural responses are of great importance. Dampers are a type of systems controlling the absorption of the earthquake energy and dissipating it in order to reduce the structural responses. The main objective of this paper is to find the optimal characteristics of the nonlinear viscose dampers placed at all storeys in a three-storey single bay concrete frame. It is assumed that the structure is subjected to the Elcentro and Gazli earthquakes; and both linear and nonlinear behaviors are considered for the structure during the earthquakes. OpenSees software is used to model the concrete frame and nonlinear viscous dampers. The structural responses are calculated at different time steps, using Newmark's numerical method. A series of constraints which are considered during the optimization process include the limits for parameters of nonlinear viscous damper (Viscous coefficient, axial stiffness and damper exponent) and the maximum absolute value for base shear. The objective is to find optimal values for these parameters in such a way that the maximum absolute value would be minimized for the roof displacement during the earthquake load. The results show that the nonlinear viscous damper is very suitable to control the structure responses when it has linear behavior. In fact, when the structure is subjected to the Elcentro earthquake, the maximum absolute value of the roof displacement and base shear decrease by 37.51% and 43.39%, respectively. The nonlinear behavior of the concrete frame does not improved considerably when the nonlinear viscous dampers are used to control the nonlinear response of the structure in the earthquake.