Recent studies have shown that base-isolated objects with long fundamental natural periods are highly influenced by long-period earthquakes. These long-period waves result in large displacements for isolators, possibly leading to exceedance of the allowable displacement limits. Conventional isolation systems, in general, fail to resist such large displacements. This has prompted the need to modify conventional base isolation systems. The current work focuses on the development of an external device, comprising a unit of negative and positive springs, for improving the performance of conventional base isolation systems. This unit accelerates the change in the stiffness of the isolation system where the stiffness of the positive spring varies linearly in terms of the displacement response of the isolated objects. The target objects of the present study are small structures such as computer servers, sensitive instruments and machinery. Numerical studies show that the increase in the damping of the system and the slope of the linear function is effective in reducing the displacement response. An optimal range of damping values and slope, satisfying the stability condition and the allowable limits of both displacement and acceleration responses when the system is subjected to near-fault and long-period ground motions simultaneously, is proposed.

最近的研究表明，具有基本自然周期长的基础隔离物体受长期地震的强烈影响。这些长周期的波导致隔离器的大位移，可能导致超出允许的位移极限。通常，传统的隔离系统无法抵抗如此大的位移。这促使需要修改常规的基本隔离系统。当前的工作集中在开发一种外部设备，该设备包括一个负向弹簧和正向弹簧，以改善常规基础隔离系统的性能。该单元可加速隔离系统的刚度变化，其中，正向弹簧的刚度会根据隔离对象的位移响应线性变化。本研究的目标对象是小型结构，例如计算机服务器，敏感仪器和机械。数值研究表明，增加系统的阻尼和线性函数的斜率可以有效地减小位移响应。提出了当系统同时遭受近断层和长周期地面运动时，满足稳定性条件以及位移和加速度响应的允许极限的阻尼值和斜率的最佳范围。