Study of a novel adaptive passive stiffness device and its application for seismic protection

The present paper proposes a novel adaptive passive stiffness (APS) device which can produce variable stiffness in an adaptive fashion. This APS device consists of four springs arranged in a rhombus configuration and a guidance template. The stiffness of the device is controlled through varying the angle of the rhombus configuration. The function of the guidance template is to relate the angle of the rhombus to the targeted system response such that the stiffness can be varied in an adaptive manner, without the need for feedback or external energy. Two analytical models are developed to capture the behavior of the APS device which shows good agreement with the experimental data. Experimental result indicates that the proposed APS device can produce adaptive stiffness as expected. A cubic nonlinearity is produced and deployed in a single-degree-of-freedom (SDOF) system to form a hardening Duffing oscillator. Dynamic tests show that the experimental characteristics of the Duffing system agrees well with the numerical results, thereby demonstrating that the APS device is effective in producing smoothly and continuously adaptive stiffness in an adaptive fashion. In addition, a fourth order even function is used as the guidance template to produce a softening-hardening adaptive stiffness. The performance of this adaptive stiffness is numerically evaluated for seismic protection. It is found that the structural responses can be reduced effectively when using this softening-hardening adaptive stiffness. The key value of this APS device is that the guidance template can be easily changed to any desired continuous function such that the targeted adaptive stiffness can be obtained. This provides possibility for controlling the vibrations of structures in a passively adaptive manner. (C) 2018 Elsevier Ltd. All rights reserved.