Earthquakes can severely damage bridge structures, disrupt people's normal lives, and even threaten their lives. During the design process of highway bridges, seismic design schemes need to be adopted to effectively prevent serious bridge collapses during earthquakes. The following will conduct an in-depth study on the seismic design of bridges to promote the improvement of bridge construction technology.

1. The Purpose of Seismic Design for Highway Bridges

Improving the seismic capacity of highway bridges can effectively prevent the phenomenon of bridge beam falling. In the design stage, it is usually necessary to fully consider the seismic fortification intensity parameters of the construction area. At the joint position, the length of the beam slab placement is increased to install the seismic limit structure. Since the earthquake load is very uncertain, the method of connecting the bridge beam slabs should be selected to avoid the occurrence of beam falling accidents. In the event of a strong earthquake, the bridge connection and limit device can effectively prevent the bridge from experiencing severe displacement and deformation.

2. The Main Seismic Damage Forms of Bridges

2.1 Seismic Damage to the Superstructure

According to the causes of seismic damage to the bridge superstructure, it can usually be divided into two types: structural seismic damage and displacement seismic damage. Displacement seismic damage is a common seismic damage phenomenon, which mainly manifests as transverse and longitudinal hazards in the bridge superstructure. Generally speaking, displacement seismic damage occurs mostly at the expansion joint. If the displacement of the superstructure is greater than the support force of the abutment and pier column, it will cause severe damage to the structure, thereby triggering accidents such as beam falling.

2.2 Seismic Damage to Pier Columns

Shear failure and plastic hinge failure are common forms of seismic damage to pier columns. Under the action of an earthquake, the top and bottom of the bridge pier column are prone to shrinkage when connected to the tie beam, and the supporting force may be lost during repeated earthquakes. In addition, when shear failure occurs during repeated earthquakes, the bearing capacity strength will be reduced.

2.3 Seismic Damage to the Foundation

When the foundation is damaged to a certain extent, the foundation structure will be seriously affected, mainly manifested as subsidence, horizontal slippage, and fracture.

3. The Causes of Seismic Damage to Highway Bridges

After a highway bridge is subjected to an earthquake, the abutment, pier, bearing, beam body structure, and foundation part will be directly damaged. During the use of the abutment and subgrade, they will gradually move towards the center of the river, resulting in different degrees of settlement in the gravity structure part, and even cracking and breaking. Once the bridge settles, it will cause the wing wall to crack, which in turn will cause the entire abutment to undergo severe deformation and settlement. Under the influence of an earthquake, the entire pier part will be damaged. In addition to objective reasons, the subjective reason for the seismic damage is that in the design process of the bridge, the serious impact caused by the earthquake is not fully evaluated, resulting in serious deformation and offset of the bridge. After the earthquake, the main beam of the bridge will crack, deform, and even fall. Under the continuous action of the earthquake, the sand in the foundation will continue to liquefy, resulting in the foundation subsiding and the entire bridge collapsing due to deformation. This situation is often impossible to repair in the later stage.

4. Key Points of Seismic Design for Highway Bridges

In the design stage, structural design is extremely critical, and it is necessary to ensure coordination and unity. Whether it is a three-dimensional or planar design, a strong overall structural form should be ensured to prevent the structural components from falling after an earthquake. Under the action of an earthquake, the basic components of the bridge structure will undergo repeated deformation. The seismic design should comprehensively consider the seismic performance of the structure; at the same time, the ductility design should also be considered. In the design process, the vibration force transmitted from the foundation part to the bridge structure should be minimized to prevent serious damage to the bridge caused by the earthquake. The strength of the highway bridge should remain relatively stable, and it is necessary to ensure that after a strong seismic response, the bridge structure will have a ductile response. In the design of the contact structure of the bridge, multiple defense lines should be arranged. After the first defense line is severely damaged by the earthquake, the second defense line should be able to play a seismic role. In the seismic design of highway bridges, the basic principles of earthquakes and structural design should be taken as the consideration basis to adopt a more perfect structural design scheme and improve the safety of the bridge.

5. Seismic Reinforcement Measures for Highway Bridges

5.1 Reasonable Selection of Bridge Location

The selection of the bridge construction location is particularly important. The construction should try to select an area with a hard geological structure, as the soft area is prone to geological stability failure under the influence of an earthquake. Usually, bridge construction is mostly selected in hard clay foundation, bedrock, and hard gravel areas, and geological conditions such as artificial fill, saturated loose fine sand, etc. should be avoided as much as possible.

5.2 Reasonable Selection of Bridge Type

The selection of the bridge type is extremely important for the improvement of the seismic performance of the bridge. In the design process, it is necessary to combine the local construction environment and geological conditions, and determine the bridge type, pier and abutment, and foundation structure form based on engineering practice experience. On the premise of ensuring that the economy meets the requirements, a more advanced bridge structure should be used to ensure that the bridge body has a strong seismic capacity. For example, the use of steel-reinforced concrete structures can reduce the impact of earthquakes.

5.3 Reinforcement of the Main Beam

First, the cast-in-place transverse cantilevered corbel structure can be designed in the middle of the two-hole beam ends at the pier top position; then, the precast slightly curved slab is installed; finally, the pedestrian sidewalk beam structure needs to be designed at the cantilever position of the corbel. The bridge holes on both sides should be consistent with the length of the pedestrian sidewalk beam. The support structure is designed on the pier, and the other side is mainly to support the corbel structure, so there is no need to widen the entire abutment. The inner flange of the pedestrian sidewalk beam is set on the unreinforced bridge deck structure, and the widened part should be poured according to the actual situation, and a reinforcement mesh is laid in the widened structure area to improve the overall performance of the bridge. The bridge deck expansion joint at the center of the top of the corbel directly extends to the pedestrian sidewalk to ensure the effective lap of the bridge. The upper part of the corbel is paved with an asphalt felt cushion structure to prevent shrinkage and deformation due to the influence of temperature. At the same time, polyurethane material is injected into the expansion joint to ensure its performance.

5.4 Reinforcement of the Expansion Joint

After an earthquake, the frame structure between the bridges has different displacements, resulting in a severe collision inside the structure and a separation from the hinge. The bridge frame will be damaged to varying degrees due to the collision at this position, and the hinge part will also have the phenomenon of beam falling. Generally speaking, the cable restraint device can be used to reinforce the entire simply supported beam structure. In the design, the design of the cable should avoid occupying too much vertical space. If a larger longitudinal movement width is required, it is recommended to adopt a cable plus simply supported beam structure or an appropriately widened pier cap bearing structure. In an earthquake, the structural form of the simply supported beam will move more than the adjacent span. At this time, the multi-span continuous bridge cannot choose to use the cable reinforcement construction method, and it is more reasonable to choose to use the multi-span simply supported beam structure. At the same time, the web can also be made more stable by using a connecting plate to achieve the reinforcement effect. In addition, the adjacent connection limiters are also very critical, and the connection support is required to prevent serious displacement.

6. Conclusion

Many large-scale earthquakes have seriously threatened people's lives and property. Therefore, in the process of bridge design and construction, effective measures need to be taken to improve their seismic performance. This paper analyzes the purpose of bridge seismic design and the hazards caused by earthquakes, and summarizes a design plan to effectively improve the seismic performance, so as to comprehensively improve the seismic performance of highway bridges in China. Under the premise of ensuring the effective operation of transportation, it guarantees people's normal lives and promotes the improvement of bridge construction technology.