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The development of variable friction base isolation systems (VFSs) is the object of an ongoing international research project that involves extensive numerical and experimental activities. This article presents some of the recent numerical developments carried out as part of this project. More specifically, a three-dimensional (3D) variable friction (VF) element is formulated and implemented into OpenSees, providing the foundation for studying structural response in the context of nonlinear time history (NLTH) analysis. The element implementation captures the bearing bidirectional horizontal response along with horizontal–vertical coupling effects. Response predictions obtained using this newly implemented element are compared with the experimental results obtained from testing a full-scale VFS prototype, showing promising results. Finally, a demonstrative numerical study is carried out in which a steel moment resisting frame (MRF) structure, isolated using VFSs, is analyzed via NLTH analyses.

The serious problem exists in the electro-hydraulic force servo system, that there is flexible load link as the natural link in the system, and there is a second-order differential section whose oscillation frequency is low in the numerator of the transfer function. So, the frequency range of the system may be low and the system may oscillate easily even is instability since the above factors. Aiming at this characteristic of electro-hydraulic force servo system, neural network and fussy intelligent control strategy were combined and applied to the force servo system to improve the whole system performance. The mathematic models of the electro-hydraulic force system with and without the neural network and the fussy intelligent control strategy were built. Comparing the control result of the controller from the above intelligent control theory to the control result of the controller built by the traditional classical control strategy, and from the results of simulation and experiment, we can find that the controller with the above intelligent control theory can increase the frequency range and improve the precision of the system, and the controller can quicken the response ability of the system obviously, and we can know also that the mathematic model of the electro-hydraulic force servo system controlled by the above intelligent control strategy is correct.

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