Due to the limitations of existing stiffness devices and systems, Dyck et al. (2006), as preliminary work for this proposal, have focused on the development of an adjustable passive stiffness and damping (ASD) fluid-based device. The device is integrated within a single unit as shown schematically in Figure 1 and has been studied in a framed structure with a scissor-jack brace for amplification of device motion (Dyck et al. 2006). The experimental force-displacement behavior with variable damping and stiffness is shown in Figure 2. Such a device offers the advantages of an adjustable fluid damper with an added variable spring. The capability of the ASD with adjustable stiffness and damping is evident in loop shaping, shown in Figure 2, wherein, both stiffness and damping variation is evident, which offers a new level of capability in such devices. In Figure 2b the stiffness is varied in compression only [the force is always compressive], and in Figure 2c the stiffness is varied only during the compression half of the cycle. This allows for a range of possibilities to modify the structural stiffness and damping properties by placing the ASD at selected locations within the structure.

Figure 1. Schematic of adjustable Passive Stiffness and Damping Device (ASD).

Figure 2. Force-displacement loops of ASD: (a) with variable damping (b) with variable damping and stiffness and (c) with variable stiffness (only in compression stroke) and variable damping.