Papers by Keyword: Base-Isolation

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Authors: Jin Xia Kang
Abstract: In this paper, the models of traditional anti-seismic and base-isolated masonry and concrete frame composite structures were created by the three-dimensional finite element program and their time history responses were analyzed under the actions of different seismic waves. The results show that whether they were under the action of frequently occurred earthquake or rarely occurred earthquake, the story shears of base-isolated structure are far less than those of traditional anti-seismic structure; the lateral displacements of the former are nearly translational, while those of the latter are approximately parabolic; and the fundamental period of the former is much longer than the counterpart. In conclusion, the seismic fortification intensity of base-isolated structure is one or two degree less than that of traditional anti-seismic structure, and adopting the base-isolated structure will protect the life-safety and property of people and achieve good economic benefits as well.
Authors: Guo Wei Ni, Deng Ling Jiang, Jia Rui Qi, Juan Nong Chen
Abstract: In order to improve the effect of isolation structure, the principles and behaviours of the base-isolation system are studied, and the types and characteristics of the base-isolation are also discussed. Compared to the traditional aseismatic structures, the base isolation structures decrease the seismic response obviously: the total structural aseismatic value decrease 1/4-1/32, the seismic shear stress in the upper structure decrease 1/14-1/23. In the huge seism, the structure can have the obvious aseismatic effect.
Authors: He Len Wu
Abstract: The paper proposes an aseismic hybrid control system to control the response of structures subjected to large ground motions caused by large magnitude earthquakes. The proposed hybrid control system consists of a base isolation system (laminated rubber bearings) connected to an active control system (a tuned mass damper and an actuator). The base isolation system is used to decouple the horizontal ground motions from the structure, whereas the active control system is used to protect the safety and integrity of the base isolation system. A 5-story benchmark building model is developed to study the effectiveness of the hybrid control system against different ground motions. It was found from the numerical results that rubber bearing system alone shows good performance and resists ground motion due to Hachinohe 1968, Kobe 1995, and Northridge 1994 earthquakes, but is somewhat unable to protect the model against El-Centro 1940 earthquake. After the installation of an active control system onto the rubber-isolated model, further improvements to earthquake resistance against these four earthquakes were observed, especially against the El-Centro earthquake. The merit of the hybrid control system lies in its capability to protect against different ground motions, with varying intensity and frequency content.
Authors: Zi Shu Dai
Abstract: Conventional isolation systems may induce an excessive response in near-fault earthquakes. A new short time Fourier transformation (STFT) control algorithm for variable friction dampers (VFD) is developed to improve the performance of base isolation buildings in near-fault earthquakes. The STFT controller varies the clamping force in the VFD damper to achieve the response reduction. In addition, the STFT algorithm is implemented analytically on a multi degree of freedom system (MDOF) with laminated rubber bearings and variable friction dampers in Simulink environment. Three types of earthquakes representing a wide variety of ground motions are considered as the ground excitations in the simulation. The numerical show that, compared with conventional isolation systems, the semi-active isolation system controlled by the STFT algorithm can reduce the excessive response in near-fault earthquakes effectively.
Authors: Si Hong Liu, Yan Qiao Wang, Jiao Rong Gao, Yuan Zheng Jin
Abstract: Soilbags have been understood to have the effect of vibration reduction and can be used as a kind of base isolation in building foundations. In this paper, a series of cyclic simple shear tests were carried out on soilbags filled with three kinds of soils under different vertical stresses to investigate the damping and stiffness characters of the soilbags. The results show that soilbags have a relatively high damping ratio and variable horizontal stiffness so that they can be used as base isolation materials.
Authors: Tian Li Huang, Wei Xin Ren
Abstract: This paper presents a dynamic reliability-based optimization technique for the seismic design of base-isolated structures. Firstly, the governing equation of multi-degree-of-freedom base-isolated structures is established. Then, the superstructure is unfolded by the first mode. Considering that the damping is non-classical and the total base-isolation system is un-symmetric, the complex modal analysis is adopted to uncouple the governing equation and the analytical solutions of stochastic seismic response under the Kanai-Tajimi spectrum loading are obtained. Taking the ratio between the first-order modal displacement standard deviation of the superstructure with base- isolated system and the fixed-base structure as the optimal objective function, the dynamic reliability of the isolated system displacement as the constraint, the optimal design parameters of the isolated system are obtained through the penalty function method. A 3-story building with isolated system illustrates the proposed dynamic reliability-based optimization method. It is believed that such an optimization technique provides an effective tool for the seismic design of base-isolated structures.
Authors: Hai Qing Liu, Xiao Guo, Hao Wang
Abstract: This paper expounded the basic principle of the base-isolated structures. Established the equations of motion of single particle and multi-particle base isolation structural system. Adopted multi-layer and high-level framework groups, added laminated rubber bearings in the bottom respectively, input EL Centro seismic waves, and then the modal, time-history, base shear are compared and analyzed. By comparing the results obtained: base-isolated structure used in high-rise building can decrease a certain degree of the seismic response, in the multi-layer building the effect was more apparent. It also confirmed that the application of base isolation on multi-layer and high-level framework in the existing conditions still had some limitations.
Authors: Cong Zeng, Zhong Tao, Wen Pan
Abstract: Terminal No. A of Kunming International Airport (TA) is a complex steel-concrete hybrid structure. The airport is located in Kunming, China; the seismic fortification intensity is 8 degree. After multi-analysis, base-isolation technique is applied to the structure, and the terminal will be the biggest base-isolated monomer building in the world after its accomplishment. By using ANSYS, the structural FEM model, which is mainly composed of linear beams elements, linear shells elements and nonlinear isolator elements, was established. Demonstration of isolation schemes and influence of isolator’s layout to the isolation efficiency were firstly introduced. And the selection processes of earthquake waves were introduced. Finally, the elastic time history analysis was carried out to study the seismic performance and isolation efficiency of the structure under the frequently and rarely occurred earthquakes. The results showed that not only the expected shock-absorption goal of ‘reduce 1 degree’under frequently occurred earthquakes is achieved, but also the maximal shear displacement of isolation layer under rarely occurred earthquakes can meet the Chinese code requirements. It is concluded that the design of isolation layer is appropriate; the isolation efficiency of the structure after applying base-isolation technique can meet the challenge.
Authors: Shao Wei Duan, Xiao Wei Tao, Hai Kuan Liu
Abstract: Through establishing single material point model of base isolation system and two material points model of story isolation system in vertical earthquake, the isolation effect of base and story isolation system in vertical earthquake are studied. Results show that two kinds of isolation systems cannot effectively keep apart the vertical seismic action, and the effect is amplified on the contrary, especially the position of isolation layers in story structures affect the amplification effect. Compared with the base and story isolation structures, while using the same isolation device, the former is better than the latter in isolating vertical seismic action.
Authors: Giorgio Monti
Abstract: In this paper the new Italian seismic code issued in January 2008 is presented, with particular reference to the ample section devoted to constructions built with isolation and energy dissipation systems. Such attention is justified by the undisputed effectiveness of this design approach and by its increasing diffusion in the professional community. The code is based on Eurocode 8 [1], though resulting more synthetic and easier to use. During the last years of evolution, the code has significantly contributed to the development of new concepts in seismic isolation, such as the hybrid biaxial isolating/dissipating device here presented, obtained from parallel coupling of two different types of device: one mechanical, which realizes the necessary dissipation, and one elastomeric, which has the scope, beyond that of sustaining the vertical load, of reducing the deck residual displacement at the end of the seismic action. An application is shown of a seismically retrofitted highway bridge, in order to show the effectiveness of this device, both during, in terms of isolation, and at the end of the seismic event, in terms of residual displacements. For the sake of comparison, the same bridge is analyzed with different types of isolation techniques.
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