Abstract:
Seismic isolation is a widely employed technique on a global scale, aimed at prolonging the natural frequency of a structure and effectively isolating it from seismic disturbances. The proposed methodology entails the implementation of a flexible layer underneath a designed structure with the aim of mitigating the impact of seismic forces and minimizing structural displacements. The susceptibility of a base isolator to several seismic events mostly stems from its increased base drift. Large stiffness has the potential to mitigate base drift. However, it is important to note that this adjustment may result in the earthquake being shifted to a fixed system, so compromising certain fundamental benefits associated with the base isolator. This necessitates the utilization of an isolator that possesses the capability to adjust its stiffness. The implementation of such a base isolator would offer the requisite level of stiffness to mitigate the displacement of the base, while simultaneously preserving the effectiveness of response reduction measures. The objective of this work is to fabricate a laminated base isolator that has a significant capacity for carrying vertical loads. Nano and micro particles were integrated at a concentration of 40 percent. FEMM analysis yields the optimum dimensions of the isolator in order to determine the maximum flux. Subsequently, shake table testing was conducted to validate the observed correlation between the rise in magnetic flux of the base isolator and the corresponding increase in stiffness. The time period, frequency, and mode shapes of fixed and isolated systems were determined using MATLAB. The numerical analysis proved the effectiveness of the isolator in reducing lateral movement and minimizing story drift. Subsequently, dynamic testing was conducted at frequencies of 0.5Hz, 1Hz, and 1.5Hz, with amplitudes of 5mm, 10mm, and 15mm. Linear Variable Differential Transformers (LVDTs) were employed to measure the displacement of individual stories and isolators. This was done at different combinations of frequency and amplitude, while varying the current levels within the range of 0 to 4 amperes. The attainment of sufficient response reduction was observed while employing optimal current levels across various combinations of frequencies and amplitudes. The study additionally emphasizes the influence of amplitude and frequency of lateral loading on the dynamic response of a system equipped with a base isolator that possesses varying stiffness properties.
