Damping in buildings and estimation techniques

Abstract

This chapter first discusses physical causes of damping in buildings and dynamic properties of buildings, especially amplitude dependency of damping. It is emphasized that there is no evidence of increasing damping ratio in the very high amplitude range within the elastic range of main frames, unless there is damage to secondary members or cladding. Then, damping predictors are introduced based on the Japanese Damping Database, and design values for damping ratio are recommended. Next, damping estimation techniques are introduced and some points to note in damping estimation are discussed. The feasibility and efficiency of two simple and user-friendly but accurate damping estimation techniques are discussed. One is the Frequency Domain Decomposition technique, which uses Singular Value Decomposition of the Power Spectral Density matrix of multiple outputs, and the other is the Multi-mode Random Decrement technique. Both can be applied to ambient excitations such as micro-tremors, enabling easy handling of closely-spaced and even repeated modes. Some full-scale examples demonstrating the damping estimation efficiency of both techniques are also shown.