Application of Seismic Isolation Technology in Bridge Structure Design

With the continuous advancement of China's traffic infrastructure, all kinds of highways, railways and bridges construction become an important part of local traffic construction. In order to improve the quality and increase service life of bridge, technical personnel adopt professional technical measures and methods and carry out the professional research and innovation. In this study, the application of seismic isolation not only improves seismic performance, but ensures that the overall structure of bridge in the serious disasters is still good. This technology has been recognized by the designer and widely used in practice. Therefore, combining the characteristics of isolation, we carry out special researches to provide effective theoretical support.

1. Type and principle of seismic isolation and reduction
The main types are included in bridge design and practice. This technology can be divided into two principles of seismic isolation and reduction.
1.1 The main types are included in bridge design and practice. This technology can be divided into two principles of seismic isolation and reduction.
(1) The principle of seismic reduction. Seismic isolation is to change structural dynamics making use of damping and energy consuming components to enhance the seismic performance. At the same time, the researchers also found that energy-consuming components in the seismic process can also use their own structural characteristics to absorb the destructive energy caused by strong vibration so as that the components can provide buffering for the bridge to ensure its overall stability and integrity.
(2) The principle of seismic isolation. Isolation technology improves the seismic performance of bridge through special structural design, which use vibrational periodic structure so that the bridge could adapt to inputting seismic energy ensuring that the overall structure is not severely damaged.
1.2 Principle analysis of the isolation and reduction in use
Seismic performance is achieved by its device studied as the research focuses by technical personnel in practical use. It is found in the experiment that the main technical principle of the isolation device is to disperse the seismic force to reduce its damage to the bridge. The main design includes the following two points
(1) Ductility design of seismic equipment device. It is designed as plastic hinge structure in the important position of the bridge and is detailed to design the bridge structure.
(2) Structural control technology of bridge design. Structural control technology is an important component of bridge design. Based on the actual situation of the bridge and other factors, projectors would take different technical measures to design.

2. Using conditions of seismic reduction and isolation
Although the isolation technology has a good effect on improving the seismic performance of the shell, the practical application of this technology is also subject to certain conditions. Therefore, the technology must conduct a comprehensive technical analysis based on the actual situation and other factors before design. In accordance with our many years of experience in the design analysis, the application of isolation technology in bridge should meet the following conditions.
(1) Short-period bridge engineering. It is difficult to adapt to the long-period bridge construction due to the defects. Therefore, the technical personnel need to effectively assess the scale of the project to ensure that the scale is in line with the isolation technology.
(2) Seismic area with high frequency wave. The researchers found that seismic reduction and isolation technology is the most effective and obvious way for resisting high frequency wave earthquakes and destroying energy. So it is necessary for the technical personnel to communicate with the geological survey personnel and determine whether to use it on the basis of earthquake situation in construction area.
(3) Bridge structure standardization. Whether the bridge structure is standardized or not is an important factor in the design of isolation technology. Therefore, projectors should study the initial design of the bridge to ensure that the structural standardization is in accordance with the technology. At the same time the technical personnel also required to analyze the height of the pier to avoid the height is too high or too low, which affects the use of isolation technology.
(4) The angle and direction of the bridge are in accordance with the technical requirements. Before studying the bridge design and construction, the technical personnel need to carry out experimental research on the design and actual situation. The research carries out detailed observation and technical data analysis including the angle of the bridge, the law of the ground movement and movement characteristics etc. Only the experiment meet the technical and design requirements, can the technology be put into use.

3. Current Application of Earthquake Isolation Technology in China
Seismic isolation technology has been widely used in international bridge construction, but the technology is not perfect because China has a short introduction history.
(1) Technical standards are still to be improved. This field has not yet formed a perfect technical standard due to the shortage of research and practical experience in China, especially in the details and structure of seismic isolation. The emergence of this technical standard problem has a strong impact on the practical effect of the isolation technology.
(2) Matching technology research is still lagging behind. The use of isolation technology is not only a separate building technology, but also the coordination of material technology and geological prospecting technology. However, in China its matching technology is still relatively backward, affecting the promotion of the use of this technology. For example, it needed high-quality rubber products, however, the quality of most of current rubber products in China are not very high. It is difficult to achieve the device requirements of seismic reduction and isolation. Therefore, the projectors must base on the design and process plan to make a choice of the quality of rubber products.
(3) Technical personnel’s level is still to be improved. Because of the late application of this technology in China, the technical personnel lack the relevant technical information and practical work experience. For example, most of the technical personnel often appear judgment errors in the selection of equipment and the process of installation, resulting in the decline of using effect of isolation technology.

4.Practical application analysis of seismic reduction and isolation
The seismic isolation device plays an important role both in application and research. Therefore, we combine with the current practical application of various types of isolation devices to carry out professional and technical research.
(1) Lead rubber bearing device. This device is mainly using one or more than one lead with high purity of more than 98%, and placed in high-quality rubber. The isolation damping is completed by the main working principle that is through the cross-sectional area of technical device and diameter configuration of lead. This device is featured with the flexibility and strong durability in the application.
(2) Viscous damping isolation device. It utilizes a piston device to create a pressure difference in the forward and backward movement, pushing the viscous fluid in the device into the orifice. In this process, the isolation device will produce damping force and energy consumption to reduce the damage to the bridge. This device has the following characteristics. Firstly, the pier bears little because the viscous damping device has a strong bearing capacity. Thus, the viscous damper is less destructive to the pier during the earthquake. Secondly, the devise does not affect the normal use of the bridge as the viscous damping device stress is small. This is also the main reason why this device is welcomed by technical projectors.
(3) High damping rubber bearing device. High damping rubber refers to the graphite, plastic fibers and other additive. This device has advantage of high energy consumption, but there is also a problem of heat generation during damping.
(4) Sliding friction damping bearing. This device makes use of small friction coefficient of PTFE(Poly tetra fluoroethylene) material and stainless steel. During the earthquake, the bridge body is protected by the slip motion of the bridge formed by the frictional force and inertia difference. This device is often used in medium-sized seismic device in practical application.
(5) Metal damping device. Such devices utilize damping devices made of metal materials with low yield or low elasticity. This type of device in China is less used in bridge design.