Theoretic And Experimental Study Of Combined Base Isolation And Threediminsional Seismic And Vibration Isolation

The 1994 Northridge earthquake in the United States, the 1995 Kobe(Hyogo-Ken Nanbu) earthquake in Japan, the 1999 Izmit earthquake in Turkey, the 1999 Chi-Chi earthquake in Taiwan, China and 2008 Wenchuan earthquake in China, all caused significant loss of lives and damage to civil engineering structures. Seismic isolation, as a typical means of response control technology, has been widely used in both new and existing buildings to protect from the devastating effects of earthquakes. The concept of isolation is to prolong natural period and provide higher damping level to traditional structure to avoid resonance with the relatively short period components dominant in earthquake ground motions. Recently, seismic isolation has been utilized in more flexible structures to reduce acceleration or displacement response.Today, many buildings have been constructed near subways or other traffic facilities in inner city areas of the world. Transportation systems generate noise and vibration by the wheel-rail contact of the trains, which is transmitted through the ground and the foundations into the neighboring structures and reduce the quality of life of the people living in. Although seismic isolation systems are effective in reduce the responses of horizontal vibrations such as earthquakes, the systems are typically not effective in control of the vertical vibrations resulted from traffic operations. To reduce building responses towards seism and transportation vibration, a special 3D isolation system is necessary to investigate.Number of studies in the fields of response control and seismic isolation have been conducted in China. Many papers and dissertations have shed light on the theory research and development of seismic isolation, however, with less emphasis on the problems of design and application of the technologies in the daily practice of structural engineering. This dissertation represents comprehensive experimental and analytical study of base isolation technology for practical application in civil engineering, including following aspects: (1) Inferring the isolation responses under the sinusoidal wave by closed-analysis method and studying on the influences of system parameters and the entire response process. (2) Designing an innovative 3D isolator, and conducting the verifying tests of the 3D isolator and the routine and dependence tests of elastic sliding bearing. (3) Completing of the shaking table tests of a five-storey steel structure model, including vibration isolation comparison tests, pure sliding isolation tests and combined base isolation tests. (4) Proposing a simplified numerical model and comparing the simulation results and tests results. (5) Studying seismic isolation response under near-fault earthquake and discussing the means of seismic isolation design. (6) Revising the seismic isolation design response spectrum and the site characteristic period and establishing the equivalent linear forecast method. (7) Introducing the engineering application of the combined base isolation and the three-dimensional seismic and vibration isolation techniques and presenting the site test of vibration isolation.For seismic isolation building, it's more important to master the law of the maximum responses than to understand the process of seismic reactions. For the purpose, in Chapter 2, the steady-state response of single-degree-of-freedom system with isolation devices are derived. Considering the free vibration and steady-state response of rectangular hysteretic model, the entire response process are discussed. Draw the conclusion that the maximum response of isolation building are correlated with the maximum velocity of input wave and the period of isolation layer and the frequency ration of input to isolated building.In Chapter 3, seismic isolation and vibration isolation devices are introduced and tested. The 3D isolator is composed of the connecting plate, vertical rubber pad and horizontal rubber bearing. The vertical rubber pad and horizontal rubber bearing have very low stiffness, and both vertical and horizontal natural frequencies of the isolated building can be designed far from metro train and earthquake main frequency to insulate both environment vibration and seism. The verifying tests of the 3D isolator were carried out. Additionally, the elastic sliding bearing is a key isolator to combined base isolation technique. In this Chapter, compression test, compressive-shear test, compressive force dependence of horizontal properties and frequency dependence of horizontal properties test of elastic sliding bearings were conducted. The polyurethane rubber isolator applied in seismic and vibration isolation was discussed herein.In China, some buildings were isolated by pure sliding isolation technique, thus the large residual displacements, super-structure rotation response and large isolation deformation are the shortcomings of the isolation system. In Chapter 4, one, two and three-dimensional shaking table tests are carried out to investigate the performance of the pure sliding isolation system. A 5-story steel frame model with aspect ratios of 2.5 and 5 had a length scale of 1/4. The isolation layer contents four 100mm-diameter elastic sliding bearings. Dynamic response analysis was conducted to simulate the test results. Test and analysis results proved the shortcomings of the system. Although the single isolator vertical load change large and the horizontal properties is lack of physical stability, the isolation layer axial loads were change small, and the hysteresis loop of isolation system is stable. Therefore, the combined system of elastic sliding bearings uplifting super-structure and rubber bearings without vertical load is considered one of the measures to develop the pure sliding isolation technique. This gives a chance to build the most economical isolated building.Tri-axial earthquake simulator testing of a five-storey steel structure model with combined base isolation system was conducted in Chapter 5. The system includes 4 lower hardness lead rubber bearings and 2 elastic sliding bearings, and the merits of different seismic isolation devices can be applied to reduce seismic reaction of superstructure. Both the shaking table test results and time history analysis results show that the combined base isolation system can effectively reduce the superstructure reaction and the deformation of isolation layer and greatly improve the safety of the structure.In Chapter 6, seismic analysis of base-isolated structures subjected to near-fault ground motions was analytically and experimentally studied. The velocity pulse motions were simulated by one cycle sinusoidal wave, and the response spectra of the pulse model were calculated by analysis method, which studied in Chapter 2. it is illustrated that the large velocity pulse caused very large deformation of isolation layer. The sliding bearing with two sliding plate and Sliding bearing with polyurethane elastomer were presented for seismic isolation design in near-fault region.As for Chinese seismic design code, there are two aspects different from foreign design code for seismic isolation design, such as IBC2003 code. First, the design response spectrum curve in long period portion is defined by straight line and results the spectrum velocity additionally increased. Secondly, at the similar site class, the site characteristic period is much shorter than foreign code. According to periods are identical at the bedrock and the fact that real earthquake spectrum with a uniform velocity portion in the longer-period range, the site characteristic periods have been revised by a coefficient 1.6, as shown in Chapter 7. For seismic isolation design, this dissertation suggested that calculating the 1st mode response by uniform velocity spectrum and the rest mode mass response by uniform acceleration spectrum.In addition, Chapter 8 introduces the application of the combined base isolation technology and 3D isolator. An apartment building employing the isolation technology on a platform of subway is also presented. The in-situ tests of isolated building and non-isolated building were carried out. The comparative test results show that the vibration isolation system is effective in reducing building responses in high frequency domain.