Study on Energy-Based Damping Evaluation of Structural Systems

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The main objective of this study is to develop an energy-based method for evaluating damping characteristics of structures with special reference to sub-structural interaction. The main parts of the present study are summarized as follows.1. The coupled cable-vibration characteristics and its effect on the modal damping characteristics have been investigated for long-span cable-stayed bridges by conducting the experimental modal analysis based on ERA, the theoretical modal analysis based on FEM, and the damping analysis based on sub-structural synthesis for the Tatara Bridge.2. A explicit formula for modal damping of girder bridge has been derived by applying the energy-based evaluation method with an assumption of girder's internal damping and support's friction damping, and its validity has been checked with field vibration data as well as a model experiment data. The damping mechanism of girder bridges has been also clarified by evaluatin damping contributions of substructures such as concrete slab and steel main girder in 2-girders and 4-girders bridges.3. The energy-based damping analysis of a cable system model consisting of two identical cables with a secondary cable was conducted and the results were compared with the experimental ones. It is concluded that the modal damping of system can be made higher by means of internal resonance among substructures.4. Robust performance of hysteretic dampers, used in controlling mid-rise buildings, against change of earthquake characteristics is investigated by introducing an energy-based damper performance index. It is found out that, besides the effect of maximum energy input on damper efficiency, othertime dependant properties as energy-based effective duration and earthquake dominant period have great influence on the damper efficiency.5. A general method for evaluating a damping matrix of structure has been studied by considering an equivalent complex stiffness matrix but is still under investigation.