| Energy dissipation technique can effectively reduce seismic damages and dynamic responses of engineering structures under strong earthquakes,and seismic performance of structures can be significantly improved.Compared with traditional aseismic methods,the energy dissipation technique is more reliable and economically practical.Therefore,it has been extensively applied in the rehabilitation of existing and newly built structures in China to render them a larger safety margin.At present,most design methods for energy dissipation structures depend on nonlinear time history analyses,engineering experience and trial and error procedures.There is still a lack of practical design methods in accordance with the current seismic design codes and procedures.This paper proposed a model-based design method for energy dissipative frame structures,which was further applied on a four-story RC frame with 8-degree seismic fortification intensity.Both nonlinear time history analyses and shaking table tests were conducted for the RC frame and the passive controlled RC frames.The numerical results and experimental findings demonstrated the effectiveness of the proposed design method.The main findings are listed as follows:1.A design method of energy dissipation based on mechanical models of dampers and the main structure is proposed,which is applicable for the application of metallic dampers and viscous dampers.The transformation between the multi-degree-of-freedom system and the equivalent single-degree-of-freedom system,which is usually employed by traditional design methods,is not necessary,so that the uncertainty and complexity in this transformation can be avoided.The main structure,the dampers,and the connections are all included in the proposed procedure,making it well adapted to the existing seismic design method of China.2.A four-story RC frame structure was first designed considering the seismic fortification intensity of 8.Then the proposed method was applied twice to improve the seismic performance of the structure,one using metallic wall dampers,and the other using viscous wall dampers.Nonlinear time history analyses were carried out using OpenSEES,and the results demonstrated the effectiveness of the model-based design method.3.According to the similitude law,two 1/4 scaled RC frame structure models with and without metallic dampers were designed and built.Metallic wall dampers and viscous wall dampers were also designed and fabricated.Tests of the dampers were conducted,and the results show that the mechanical properties of the dampers well matched with the models used in the proposed design procedure.4.Shaking table tests on RC frames with and without metallic dampers were conducted.Both models were test from initiation of damages until the state near collapse.The local responses of dampers and connecting components were also investigated.The effectiveness of the model-based design method was thus validated.The main conclusions from the shaking table tests are listed as follows:(1)Metallic wall dampers provided both additional stiffness and additional damping to the structures.The natural vibration frequency of the damped RC frame increased by about 20% compared with the pure RC frame.The additional damping ratio increases with the increase of ground motion amplitude.(2)Compared with the pure RC frame structure,the displacement response of the damped RC frame decreased significantly under various excitation intensities,specifically,40%-60% dropping in the X-direction,and 50%-70% in the Y-direction.The control effect on the displacement response agrees well with the design expectation.(3)The connecting components of dampers have sufficient stiffness and strength.The connection pattern is reliable,and the associated design method is effective. |
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