NONLINEAR INERTIAL COUPLING IN ASYMMETRIC BASE-ISOLATED STRUCTURES

It has been well proved that seismic base isolation systems, as passive tools of structural control, mitigate the intensity of damage caused by earthquakes. On the other hand, structures are often built in irregular plans, which lead to much more damage under earthquake motions. So, the present research dealt with the dynamic interaction of asymmetric base-isolated structures in a new point of view. The motion equations were presented in two coordinates: one fixed on the building base (inertial or global coordinate) and the other at the torsional isolation level (local coordinate), which led to linear and nonlinear forms of equations, respectively. Two types of structures were defined with different natural frequencies. Responses of both linear and nonlinear models for the two types of structures under harmonic effects were compared while analyzing time history and frequency. Some non-linear phenomena such as saturation and energy transfer between the modes in such structures were observed. Historical response peaks of linear and nonlinear models under real earthquake were compared in terms of various base torsional natural frequencies of the base isolation system in different directions. It can be inferred from the results of the analysis that nonlinear responses can be more critical than linear ones and design prescriptions should be adapted regarding nonlinear effects.