Application of seismic strengthening technology for highway bridges?

The application of seismic strengthening technology for highway bridges is very important. Only by understanding the technology and application can we play a role in the actual construction, and the treatment of every detail is very important. Zhong Da Consulting will explain the application of seismic strengthening technology for highway bridges.

The geographical location of China makes some areas between the Pacific Rim seismic belt and the Eurasian seismic belt, and the probability of earthquakes in some areas is high. As the lifeline of economy, traffic trunk line is also the lifeline of disaster relief when an earthquake occurs. As an important part of traffic, bridge is the most vulnerable link when earthquake disaster occurs, and it has become a key part that restricts the function of highway traffic. In recent years, there have been many major earthquakes in China, which have caused serious damage to bridges and indirectly caused great loss of life and property. Therefore, it is of great significance to strengthen the seismic reinforcement of highway bridges in China.

First, the current situation of seismic strengthening technology of highway bridges in China

In recent years, countries all over the world have increased their research on seismic strengthening technology of highway bridges, and the seismic strengthening technology in China has been established on the basis of drawing lessons from advanced technologies in other countries. Earthquake evaluation in China mainly includes two stages: priority research and structural analysis. The first stage mainly determines the structures that need seismic strengthening, and the second stage analyzes the corresponding seismic strengthening structures. In the first stage of seismic evaluation, the function, characteristics, vulnerability, structural foundation and soil properties of the structure are mainly analyzed. In the second stage, the seismic performance of the structure should be evaluated, and its performance and state under earthquake action should be clarified as much as possible, so as to select appropriate seismic strengthening technologies and measures.

Second, the reasons for the destruction of highway bridges under earthquake conditions

1. When the earthquake occurred, the ground geology changed greatly, resulting in the damage of bridges, such as the Wei Long Bridge in Beichuan County, which was damaged by ground fissures and faults.

The earthquake liquefied the sand and damaged the foundation of the bridge.

3. During the earthquake, the bridge structure was damaged to varying degrees due to the force generated by the earthquake.

4. The structural characteristics of curved bridge make it easy to be damaged or even collapsed due to the deviation of the upper center during the earthquake.

5. The impact of landslides, landslides and other disasters on highway bridges during the earthquake causes the damage of highway bridges.

6. The construction quality of the highway bridge itself is not up to standard, which makes the bridge damaged in the earthquake.

Three, the highway bridge seismic suggestions

1. When choosing a bridge, we should clearly understand the seismic intensity, topography and other geological conditions in this area, avoid areas that may cause serious collapse, landslide and sand liquefaction, and areas such as caves and underground rivers that may collapse and sink during an earthquake, and fully consider their possible impact on the bridge.

2. When building highway bridges in earthquake-prone areas, we should choose the bridge form with simple structure and good stability as far as possible, and mainly strengthen the bridge connection parts.

Fourthly, the application of seismic strengthening technology for highway bridges.

Seismic strengthening of highway bridges is firstly to prevent the bridge from collapsing, and secondly to control the degree of damage as much as possible. The superstructure of bridge elastic design is an important link of seismic reinforcement, and the substructure providing stable support is the basis of seismic reinforcement.

Seismic strengthening of bridge superstructure

The damage of superstructure during earthquake is mainly caused by the instability of substructure and the collision between bridge segments, and the reinforcement is to avoid the damage of falling beam caused by superstructure.

1. Expansion joint reinforcement technology

In the (1) earthquake, the frames between bridges are prone to collision or hinge separation due to different phase movements. The former generally causes less damage, while the latter may cause the beam to fall. The commonly used method is to strengthen the simply supported steel beam with cable restraint device, and the cable design should consider reducing the vertical gap between the lower pavement and the beam. When the longitudinal displacement is greater than the width of the effective support, the simply supported steel beam can be strengthened by widening the pier cap support and cable. Because the relative displacement of adjacent spans in the earthquake will not be as large as that of simply supported beam bridges, the method of cable reinforcement is not suitable for multi-span continuous bridges, but for multi-span simply supported beam bridges. Another way to strengthen the steel beam is to connect the webs with splicing plates to keep the steel beam continuous. In addition, internationally, stops are often used to install adjacent spans in all directions to connect supports and limit relative displacement. More advanced is the use of memory alloy block, which has strong elasticity and can withstand greater deformation, which may effectively limit relative displacement.

(2) When there is a hinge point in the middle of the steel beam, it is necessary to increase the hinge point restraint device, and widening the hinge point support or connecting frame can well avoid the damage of the support during the earthquake.

2. Lateral support reinforcement technology

Diaphragm beams or other lateral supports provide lateral stiffness between beams. Because the lateral support has to resist the centrifugal force caused by various loads, it is difficult to bear such forces as shear key and bearing capacity. The general reinforcement measures are to add additional supports or diaphragm beams close to the supports.

3. Reinforcement technology of concrete side beam

Side beams can be connected with adjacent bent frames to improve the longitudinal seismic capacity of concrete bridges. Single-layer bridge structure can strengthen the overhanging pier cap, keep the bent and fixed connection and torsion of the column top, or hinge the column top to avoid the torsion of the overhanging beam; The double-deck bridge structure should strengthen the strength and stiffness of the side beams to avoid damage.

Seismic strengthening of bridge substructure

The damage of bridge substructure generally refers to the damage of bridge foundation such as pier. During the earthquake, abutment and pier can not bear seismic force and their own inertia force, which will cause cracking and fracture. The technology to increase the seismic capacity of piers is mainly to increase the cross section, fiber and steel plate, and also to design the ductility of piers to avoid excessive damage to piers. Bridges with concrete structure can be strengthened by various methods such as fiber reinforcement and composite material reinforcement, and bridges with masonry structure can be strengthened by steel plates and concrete bushings.

1. column cap technology

Column cap technology can effectively improve the seismic capacity of pier. The first is the steel cover. Steel plate welded sleeve can improve the bending and shearing capacity of columns. For circular or square piers, a circular steel cover can be used, and for rectangular piers, an oval cover can be used. In addition, in order to prevent the steel cover from bearing the reaction force, a gap of not less than 50mm is left at the top of the pier. Secondly, the concrete protective layer can be used to strengthen the pier without changing the shape of the pier. First, steel bars are wound on the surface of the pier and drilled into the column, and then concrete is poured. The third is the advanced composite protective layer, which has a high level of science and technology, not only greatly improves the seismic capacity of the pier, but also maintains the original shape of the pier. Usually, CFRP and FRP are used to strengthen pier columns, which can enhance the lateral deformation and ductility of pier columns. CFRP has a particularly good reinforcement effect on columns with cracks, and FRP can significantly improve the performance of flexible piers.

2. Filled wall technology

Filled wall can improve the lateral bearing capacity of multi-column bridge pier, which not only has low cost, but also limits the lateral displacement of pier.

3. Bearing reinforcement technology

Try not to use rigid roller bearings, but use lead rubber pad bearings or isolation bearings to ensure the seismic capacity of the bearings, which is not easy to be damaged.

4. The capping beam reinforcement technology

Cushioning and prestressing can effectively strengthen the capping beam and avoid its bending and shearing.

5. Abutment reinforcement technology

Filling the gap between the diaphragm beam and the back wall and increasing the support extension device can effectively strengthen the abutment.

6. Foundation reinforcement technology

Widening the foundation evenly or adding foundation protective layer, connecting foundation, pile cap and pile, or fixing foundation anchor rod can effectively strengthen the foundation. Because the foundation is not easy to be damaged and the cost of reinforcement is high, seismic reinforcement measures are generally less adopted.

Summary:

The application of bridge seismic strengthening technology in the world has made great progress. In recent years, frequent earthquake disasters in China have made highway bridge builders pay enough attention to the application of bridge seismic reinforcement technology. The seismic strengthening of highway bridges in China needs to fully learn from foreign advanced experience and technology, and vigorously carry out the research and application of related technologies to ensure that China's highway traffic becomes a safe and reliable lifeline for economic development and earthquake relief.

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