Many regions are located in seismic zones. To ensure that the performance of bridge projects is not affected, the seismic resistance characteristics should be carefully considered during the design stage, and the seismic design work should be actively carried out. 

 1. The Destructiveness of Earthquakes to Bridges 

 As is well known, the influence of earthquakes is very large. Once a disaster occurs, the first to be damaged is the foundation, especially for those bridges whose foundations are on steeper slopes. When facing earthquake disasters, the damage is more severe. Therefore, when selecting the foundation, we must conduct comprehensive analysis, full discussion, and multiple comparisons before reaching a conclusion. After an earthquake occurs, the damage forms of the project are not exactly the same. Specifically, there are the following differences. The pier body of the bridge pier is displaced, the anchor bolts of the support are cut off, and sometimes the beam body will also break and fall; cracks appear in the pier body, resulting in the possibility of bridge collapse; due to the scouring of the river water, the sand and soil is liquefied at this time, resulting in the settlement of the bridge pier. The so-called support damage specifically refers to the force generated by the upper structure being transmitted downward to the lower structure through the components of the support itself. If the intensity of the transmitted force is higher than the original strength of the component, the support will be damaged. For the lower structure of the bridge, due to the damage of the support, the vast majority of the force is dispersed, so that the force generated by the earthquake can be prevented from being transmitted to the pier and abutment, and the lower structure will not be further damaged at this time, but there is the possibility of the beam body falling. 

 2. Principles of Bridge Seismic Design 

 2.1 Correct Site SelectionWhen selecting the site of a bridge, its seismic resistance must be taken into account. Therefore, it is necessary to ensure that the seismic performance of the area where it is located is good, and at the same time, it is necessary to ensure that the ground is hard. If its foundation is not very firm, it cannot be guaranteed to be unaffected when an earthquake disaster occurs. However, in the work, it must be realized that when choosing the site, not only soft soil should not be selected, but also areas that may be affected should be resolutely abandoned. Because any possibility has a certain chance of becoming a reality, and once it becomes a reality, the negative impact it brings will be very serious. 

 2.2 Pay Attention to Structural SymmetryIn terms of seismic resistance, symmetrical structural stiffness has more advantages compared to unequal-span bridges and can better deal with earthquake problems. For example, if there is a large difference in the height of the bridge piers, the low piers are more vulnerable to earthquakes. Therefore, when carrying out the design work, it is necessary to try to ensure that the structure presents a symmetrical pattern, and it is best not to use those types with relatively large spans. 

 2.3 Focus on the Integrity of the BridgeFor bridges, its totality is of very crucial significance. If the integrity feature is lost, it will lead to the structure being unable to play its due role, and when an earthquake occurs, it will cause the components to not have sufficient bearing capacity, and then the phenomenon of seismic fall occurs. Therefore, it is necessary to ensure that the upper structure is uninterrupted, and reasonable measures should also be taken to effectively improve its integrity. Good vibration damping work should be done in all connection areas. The purpose of this is to effectively improve the stability of the project. At the same time, in order to prevent some sudden problems, when laying out the structure, try to ensure that its mass and stiffness are uniform. 

 2.4 Set Multiple Seismic Defense LinesTo truly deal with the earthquake problem well, many defense lines should be arranged during the design. Only in this way can it be ensured that the bridge can cope with the force generated by the earthquake from multiple angles. If a high-level earthquake occurs, after the previous defense line is damaged, there are others that can play a role. This measure can significantly improve the safety of the project and maximize the avoidance of the project's collapse. 

 3. Several Methods of Bridge Seismic Design 

 3.1 Conceptual Design of Bridge Seismic Resistance 

 The seismic conceptual design refers to the basic seismic design principles and design ideas obtained based on previous earthquake disasters and engineering seismic experience, etc., to propose the correct overall scheme of the bridge structure, material selection, and detailed structure, etc., so as to achieve the design purpose of reasonable seismic resistance. The main task of the conceptual design of bridge seismic resistance is to select the appropriate seismic structural system. 

 3.2 Changes in Earthquake Response Analysis MethodsWith the continuous understanding of earthquake dynamics and structural dynamics by people, various methods of seismic design theory and earthquake response analysis and design methods have also developed. From the three elements of earthquake ground motion amplitude, spectrum, and duration, the dynamic theory of seismic design not only considers the duration of earthquake ground motion, but also considers other characteristics that the response spectrum in earthquake ground motion cannot summarize. 

 3.3 Multi-Stage Design MethodWith the continuous deepening of research on the mechanism of earthquake generation and the different performance goals of different structures under different probabilities of earthquake action expectations, the design work is constantly evolving. The seismic design of bridge engineering has also been improved from the original single seismic fortification level and one-stage design to the two-level or three-level two-stage and three-stage design methods.

This article mainly discusses the importance of considering seismic resistance in bridge design. It begins by highlighting the destructiveness of earthquakes to bridges, including damage to foundations, pier displacements, support and beam failures, and settlement. Then, it presents the principles of bridge seismic design: correct site selection considering seismic performance and avoiding potentially unstable areas; attention to structural symmetry to better handle earthquakes; focus on the integrity of the bridge to ensure its functionality and stability; and setting multiple seismic defense lines to enhance safety and prevent collapse. Further, it elaborates on several methods of bridge seismic design, such as the conceptual design for selecting the right seismic structural system, changes in earthquake response analysis methods considering more factors of earthquake ground motion, and the multi-stage design method evolving with research and different performance goals.