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Basic Principles of Bridge Isolation Design

Nov. 06, 2023

Basic Principles of Bridge Isolation Design

Bridge isolation design can enhance the seismic performance of bridges, but the following basic principles should be followed when conducting isolation design. Only by carefully adhering to these principles 

can the seismic performance of bridges be effectively and effectively improved.


1Basic Principles of Bridge Isolation Design


1). Firstly, it is necessary to examine whether the bridge is suitable for seismic isolation design, and whether the system can effectively improve energy absorption during earthquakes after its cycle growth should be taken as the criterion for judgment. For bridge sections that are not suitable for seismic structures, construction cannot be carried out blindly.


2). If isolation devices are used in bridge design, their upper structures will experience relative displacement after an earthquake, which will have an impact on the later use and function of the bridge. Therefore, after an earthquake, it is necessary to strengthen the repair and improvement of the isolation devices.


3). If relevant seismic isolation measures are adopted in bridge design, it should be ensured that the seismic performance of the bridge is not lower than that achieved by ordinary seismic design.


4). Scientific research and survey should be conducted on the geological environment and bridge foundation near the bridge using isolation measures, and there should be relatively solid geological conditions near the isolation bridge.


5). When using isolation devices, it is necessary to choose and use devices with simple structures that meet the required isolation performance as much as possible, and to ensure that they are scientifically used within their mechanical performance range.


2Design of isolation devices

The two main aspects of bridge isolation design are the design of isolation devices and the design of other structural components. The design of isolation devices is the center of isolation design. At present, the most commonly used method in bridge isolation design is the elastic response spectrum method. This method is adopted by most countries, but there are different specifications, mainly from the United States, Japan, and Europe. The difference between them is not significant, mainly due to the difference in calculation formulas. These calculation formulas refer to the calculation of the equivalent stiffness of the isolation device and the calculation of the equivalent damping, and are compared with them, The commonly used method for bridges with strong complexity or relatively irregular shapes is the time history method.


The reason why the elastic response spectrum method is widely adopted is not only because the calculation during construction is relatively simple, but also because it is very close to existing standard calculation methods, making it easy to accept. It should be noted that the calculation of equivalent stiffness and equivalent damping of isolation devices is well-known to be related to the large deformation degree of isolation devices in earthquakes, Subsequently, the deformation of the isolation device is related to the seismic response of the entire bridge, so objectively, it is required that the isolation design using the elastic response spectrum method should be a constantly improving and changing process. Bridge guardrail bracket


Due to the lack of direct formulas for achieving and achieving goals in specific calculations, it requires designers to have a good grasp and estimation of the seismic response of bridge structures. After an earthquake occurs, more skilled engineers can develop a preliminary design plan based on their long-term work experience. After the plan is completed, a series of time histories are used to analyze and verify whether the design is reasonable. Bridge guardrail bracket


3Design of detailed structure

The auxiliary structures of bridges also play a huge role in the isolation design of bridges. These auxiliary structures and components mainly include limiting devices, expansion joints, anti falling beam devices, etc. Through the analysis of many earthquake damage investigations and dynamic time history analysis, we have found that these detailed structures are important aspects that affect the dynamic response and isolation effect of bridge structures. However, the current common problem is that most designers overlook the design of detailed structures and place them in a secondary position. On the other hand, this is also due to the complexity of the calculation methods for auxiliary structures in earthquake response calculations. The design of detailed components should have good continuity.