## 1 Introduction
In addition to the above-mentioned lever amplification devices, toggle-style amplification devices are also widely applied in engineering. [PERSON] et al. [32; 33] proposed a toggle damping system utilizing crank connecting rod technology. The theoretical analysis results indicated that the toggle significantly increased the damper's displacement. Moreover, the stronger the amplification capability of the toggle device is, the more sensitive it is to changes in the length of the connecting rod. Subsequently, [PERSON] [34; 35; 36] and [PERSON] [37] proposed the improved toggle brace devices and scissor-style devices, respectively. On this basis, inorder to reduce the impact on building functionality, [PERSON] [38] proposed an open damping amplification device, and [PERSON] [39] proposed a local toggle brace damper. Meanwhile, [PERSON] et al. [40,41] proposed a seesaw amplification mechanism composed with a bracket, a seesaw, and a viscous damper. Through a dynamic analysis of the 6-floor framework attached to the mechanism, it was found that the seesaw mechanism had strong energy dissipation capacity. Meanwhile, it was pointed out that the focus of the mechanism design was to balance the damping coefficient and brace stiffness. However, the above-mentioned amplification devices either have an enormous impact on building function or are susceptible to small changes in the connecting rod's length of the toggle or need a high stiffness of the brace component. As a result, these problems increase the difficulties of their extensive applications. To significantly enhance the damper's energy dissipation, the brace components or amplification devices connected to the damper themselves need to have a high stiffness. However, [PERSON] [42] found that when the support is flexible, the negative stiffness device will aggravate the damper's displacement. Currently, various forms of negative stiffness devices have been proposed successively. [PERSON] et al. [43, 44, 45] proposed realizing negative stiffness through preloading springs or gap springs. Meanwhile, [PERSON] et al. [46, 47] applied a preloading spring to the inclined surface to realize negative stiffness. [PERSON] [48] launched a negative stiffness damper on the basis of turbine damping and permanent magnets. [PERSON] [49] put forward a double triangular damper and applied it to replace traditional lead rubber isolation bearings in the foundation isolation system. Numerical simulations show that the damping system has a significant vibration isolation effect. [PERSON] [50] analyzed the multimodal seismic control effect of the negative stiffness damping system on cables, and the results indicated that a small negative stiffness damper equipped with flexible braces can achieve high damping effects. [PERSON] [51] analyzed the negative stiffness damper's impact on the dynamic responses of the structures under pulse excitation, random excitation, and earthquake excitation. The results revealed the following: adding the negative stiffness device to the flexible brace damper significantly increased the damper's energy dissipation while effectively reducing the structure's displacement and acceleration responses. The energy dissipation capacity of the damper was improved by 5 times to 16 times, even if the ratio of the damper's damping to the structure's damping was lowered to 2.8%.The above studies indicate the following: negative stiffness devices are capable of improving the performance of dampers significantly while decreasing the stiffness demands on the damper's connecting components. However, there is currently limited research on the combination of amplification devices and negative stiffness damping systems, which will be a new and effective passive control technology. Aimed at improving the damper's displacement, decreasing the stiffness requirements on the damper connecting components, and minimizing the obstruction to building space, this paper introduces the intermediate column-lever negative stiffness viscous damper (CLNVD).