Summary Direct displacement‐based design (DDBD) approach is one of the most effective performance‐based design methods. In this paper, a modified version of DDBD is proposed for the design of structures equipped with fluid viscous damper (FVD) that the effect of higher modes and difference between spectral velocity and pseudo‐spectral velocity are applied in the design process. Different steel moment frames equipped with FVD have been designed using the proposed method, and the achievement of desirable performance level has been evaluated under different earthquake records. For comparison objectives, the performance of the modified method has been compared with the previously proposed DDBD. Although the structures designed using the previously proposed DDBD have achieved the desirable performance level, the peak story drift is significantly less than the target drift and this design approach leads to an expensive overdesign, whereas in the structures designed using the modified DDBD, the peak story drift is close to the target drift and the achievement of desirable performance level has been effectively satisfied. Therefore, the drawback of overdesign has been solved, and the modified version of DDBD can be considered as an effective design approach for structures equipped with FVD.
In this paper, the performance of a semi-active base isolation system, including a magneto-rheological (MR) damper and base isolation system for different combinations of response-related weighting matrices, has been studied. To consider all possible sets of response-related matrices, seven H2/linear quadratic Gaussian (LQG) control designs have been considered. For a numerical simulation, a six-story shear frame has been subjected to different earthquakes, and the performance of the control system has been evaluated. The results show that the optimal force-related weighting parameter is identical for different sets of response-related weighting matrices and is also independent of earthquake records when minimizing the maximum base drift is considered as the design objective. Also, the results of different sets of response-related weighting matrices show that the optimal sets for the design objective of minimizing the maximum base drift are the velocity and displacement/velocity-related weighting matrices.
In this article, the effect of various factors, such as earthquake characteristics, base isolation system properties, and dynamic model of isolated structure, on the design of control algorithm of the semi-active base isolation systems composed of a magneto-rheological damper and a base isolation system is studied. The weighting parameters defined in the control algorithm are the design variables that are determined for various design objectives. For numerical simulation, a six-story base isolated shear frame has been subjected to different earthquakes while different values have been considered for the dynamic parameters of both base isolation system and isolated structure. The results show that to design the control algorithm proportionally with each design objective, an appropriate range to select the weighting parameter can be determined instead of a specific value, which these ranges are almost similar under different earthquake records. Hence, when the control algorithm is designed under an earthquake, the designed control algorithm satisfies the considered design objective under other earthquake records. Also, because the appropriate ranges to select the weighting parameter are independent of the dynamic properties of both the base isolation system and the isolated structure, the company that produces the magneto-rheological damper can propose the appropriate range for designing the weighting parameters of control algorithm which is compatible with both different structures and earthquakes.
Direct displacement-based design (DDBD) method is one of the most effective methods for performance-base design of structures that has been also employed to design structures controlled by fluid viscous damper (FVD). In previous studies, a modified DDBD has been developed to apply the higher mode effects as well as difference between spectral velocity and pseudo-spectral velocity on the design velocity of FVD. To this end, two constants were defined to correct the damping coefficient of FVD that these correction constants had been determined in a non-classical and iterative manner. In this study, a new classical method is proposed for determining these constant such that no iteration is required in DDBD. In order to be able to introduce this design approach as a reliable framework, its performance is validated under different sets of earthquake records and this design approach is also developed for structures controlled by nonlinear FVD. Steel moment-resisting frames with different numbers of stories have been designed using this method. For comparison, structures have been also designed based on DDBD proposed in previous researches. The results show that DDBD approach improved in this study is capable to achieve the design performance level under different sets of earthquake records and this design approach has more effective performance than previous design methods. Performance of steel moment-resisting frames equipped with nonlinear FVD also shows excellent performance of this design approach in achievement of desirable performance level. Therefore, DDBD approach proposed in this study can be introduced as a new classical and reliable framework because of its simplicity and excellent performance under different sets of earthquakes.
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