35314 Viscous Fluid Dampers
Damping devices based on the operating principle of high-velocity fluid flow through orifices have found numerous applications in shock and vibration isolation of aerospace and defense systems. In the past decade, research and development of viscous fluid dampers for seismic applications to civil
engineering structures have been performed to accomplish three major objectives. The first was to demonstrate by analysis and experiment that viscous fluid dampers can improve seismic capacity of a structure by reducing damage and displacements and without increasing stresses. The second was to develop mathematical models for these devices and demonstrate how these models can be incorporated into existing structural engineering software codes. Finally, the third was to evaluate reliability and environmental stability of the dampers for structural engineering applications.
As a result, viscous fluid (VF) dampers have in recent years been incorporated into many civil engineering structures. For example, early applications of VF dampers include the Pacific Bell North Area Operations Center and the Woodland Hotel in California and a 35-story building in downtown Boston (Constantinou et al. 1998).
As with most of the passive systems considered above, the VF dampers are incorporated into the structural system through the use of either diagonal or chevron bracing. With this configuration, the magnitude of the displacement across the passive device is at most equal to the interstory drift. Consequently, large dampers may be required, particularly for stiff structures.
One remedy is to introduce a damping amplification, such as in the toggle-brace damper system (Constantinou et al. 2001). Furthermore, in order to reduce the impact of bracing on the architectural aspects of design, alternative configurations can be utilized. An example is the scissor-jack-damper energy dissipation system (Sigaher and Constantinou 2003), which can provide relatively open bays and damping magnification factors between two and five.
In several other applications, VF dampers were used in combination with seismic isolation systems. For example, VF dampers were incorporated into base isolation systems for five buildings of the new San Bernardino County Medical Center, located close to two major fault lines, in 1995. The five buildings required a total of 233 dampers, each having an output force of 320,000 lbs and generating an energy dissipation level of 3,000 horsepower at a speed of 60 in./s. A layout of the damper-isolation system assembly is shown in Figure 35.18 and Figure 35.19 gives the dimensions ofthe viscous dampers employed.
- FIGURE 35.18 San Bernardino County Medical Center damper-base isolation system assembly.
FIGURE 35.19 Dimensions of viscous fluid damper for San Bernardino County Medical Center.
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