A new method for nonlinear dynamic analysis of base isolated structures

Base isolation has been one of the most effective approaches to structural control in the last few decades. Because of nonlinear behavior of base isolators, analysis of such structures requires efficient nonlinear analysis software that has both characteristics of speed and accuracy. Many classical approaches have been proposed for efficient nonlinear dynamic analyses, however this subject still needs more attention. In this paper a novel nonlinear dynamic analysis is proposed that not only increases the analysis speed significantly, but also gives more accurate results compared to those in the literature. The method is formulated based on release of extra internal forces that are mistakenly stored in linear analysis of nonlinear structures. To explain the method, one should remind that in linear analysis of structures, it is intuitively assumed that structural members have infinite capacities and the internal forces of members are proportional to the external loads. Application of the proposed method to nonlinear analysis of several base isolated structures show that the proposed method results in much less computation time compared to classical methods. To illustrate the power and speed of the proposed method two examples have been included in the paper. It is shown that the proposed method can reach to a certain level of accuracy using larger time intervals compared to traditional classical methods.