Modeling inherent damping in nonlinear dynamic analysis.

Abstract

Modeling of inherent damping in nonlinear dynamic analysis has generated significant interest over the past 35 years, and there is little agreement as to the approach that should be used. In most cases, it is assumed that the damping is linear, viscous, and classical, which is almost univerisally recognized as unrealistic. Additionally, a host of problems have been identified wherein unrealistic damping forces and other detrimental effects can arise. Methodologies have been forwarded for minimizing or potentially eliminating the problems, but no classical viscous damping model has been developed that is reliable in all circumstances.In this paper, issues related to modeling damping as linear and viscous are reviewed and explained through the analysis of a simple 4-story moment resisting frame. Approaches evaluated include Rayleigh damping (using full initial stiffness, partial initial stiffness, full tangent stiffness, and partial tangent stiffness), and Modal damping. With regard to tangent stiffness damping, issues related to imparted energy due to negative tangent stiffness, damping force – velocity hysteresis, and implementation with the P-Delta or corotational geometric transformations are discussed. The paper concludes with a recommendation to move away from the use of linear viscous damping, and instead to model inherent energy dissipation as nonlinear, amplitude dependent, frequency independent, and evolutionary.