For the vertically mixed structures, the dissipated energy mechanism varies from one substructure to another, which turns the damping matrix non-proportional. Based on the complex damping theory, the equivalent modal damping ratio of vertically mixed structures was deduced. Then the feasibility of this method was testified by comparing with experimental result of 12-story S/RC frame. Moreover, with different damping ratios, the elastic response history analysis on finite element model was carried out. The results show that this method is simple and highly efficiency. Finally, the paper studies how the substructures affected equivalent modal damping ratio via modal strain energy method and this method.
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