Damping reduction factors and code-based design equation for structures using semi-active viscous dampers

This study uses a semi-active viscous damper with three different control laws to reshape the structural hysteresis loop and mitigate structural response, referred to as 1-4, 1-3 and 2-4 devices, respectively. The 1-4 control law provides damping in all four quadrants of the force-displacement graph (it behaves like a standard viscous damper), the 1-3 control law provides resisting forces only in the first and third quadrants, and the 2-4 control law provides damping in the second and fourth quadrants. This paper first outlines the linear single degree of freedom structural performance when the three types of semi-active viscous dampers are applied. The results show that simultaneous reduction in both displacement and base-shear demand is only available with the semi-active 2-4 device. To enable guidelines for adding a 2-4 device into the design procedure, damping reduction factors (RFs) are developed, as they play an important role and provide a means of linking devices to design procedures. Three methods are presented to obtain RF and equivalent viscous damping of a structure with a 2-4 semi-active viscous damper. In the first method, the relationship between RF and the damping of a semi-active structure can be obtained by calculating the area under the force-deformation diagram. The second and third method modified the Eurocode8 formula of RF and smoothed results from analysis, respectively. Finally, a simple method is proposed to incorporate the design or retrofit of structures with simple, robust and reliable 2-4 semi-active viscous dampers using standard design approaches. Copyright (c) 2016 John Wiley & Sons, Ltd.