Damage analysis and reinforcement method of bridge structure?

In the popular road construction in China, only concrete stones or asphalt are laid on the road. This kind of engineering does not consider the bearing capacity, strength and stability of the pavement, and has no systematic design parameters and principles, which makes the pavement engineering collapse in a short time and causes economic losses to the government and even the country. Bridge structure is the main carrier to bear the load and gravity, and it is also an important pillar to ensure the safety of the bridge. With the increase of service time, some damages have appeared in the bridge structure, which leads to functional defects in the bridge deck structure and threatens the safety of the bridge.

Causes of damage of bridge structure With the passage of time, the bridge structure will be damaged to varying degrees. The main reasons for these damages are: the performance of building materials is reduced, the load of bridge structure is too large, environmental impact, natural disasters, man-made accidents, unreasonable design, unfavorable factors in the construction process and so on. The performance of building materials is reduced. The longer the bridge structure is used, the more the building materials used to build these bridge structures will be worn, and its performance will be reduced, thus causing different degrees of damage to the bridge structure and affecting the use of the bridge structure. The bridge structure is overloaded by gravity. At present, many bridge structures in China are designed and built according to the design standards around the 1980s. At that time, the road traffic volume was low, so the bearing capacity of the bridge structure was low. In recent years, with the development of economy, the number of motor vehicles in China has increased sharply, and the road traffic volume has been increasing, especially the frequent appearance of heavy trucks for engineering, which has increased the load gravity of bridge structures and led to the overload of bridge structures, thus causing the roads and bridge structures along the line to be damaged to varying degrees.

Environmental impact. Environmental impact mainly refers to the influence of temperature and humidity. The change of temperature and humidity will bring different degrees of damage to the bridge structure. Natural disasters. Natural disasters mainly refer to wind, rain, flood erosion, lightning attacks, earthquakes and landslides. Natural disasters will lead to the destruction and deformation of bridge structures. Man-made destruction Man-made damage mainly refers to vehicle-ship collision. Man-made accidents will bring direct damage to the bridge structure. The design is unreasonable. Unreasonable design mainly includes unreasonable design of bridge structure, endless design assumptions and lack of reasonable monitoring during design demonstration. These unreasonable designs may become the defects of the bridge structure itself. Unfavorable factors in the construction process. The influence of unfavorable factors in the construction process mainly includes unfavorable factors that are difficult to control in the construction process and unfavorable factors caused by unreasonable construction. These unfavorable factors will cause damage to the bridge. The former is difficult to control, but the latter can be avoided.

Three. Strengthening principle of bridge structure

1. Overall effect principle. In structural reinforcement, we should consider what will happen to the whole structural system after reinforcement. When designing the reinforcement scheme of the bridge structure, the overall structure of the bridge should be comprehensively analyzed to ensure that the overall performance of the bridge structure will not be damaged.

2. Optimization principle of design case. Before the reinforcement scheme is determined, it should be judged by the optimization principle. Among them, we should try our best to meet the comprehensive economic indicators of the project, consider the characteristics and technical level of reinforcement construction, and take appropriate measures in the design and construction organization of reinforcement cases to reduce the impact on the external environment and local components and shorten the construction period as much as possible. Before determining the reinforcement design scheme of bridge structure, the existing structure should be comprehensively tested and analyzed. While mastering the performance, structure and defects of the existing structure, it is also necessary to analyze the stress and bearing level of the structure, laying the foundation for determining the reinforcement design case in the later stage.

3. The principle of maximum utilization. When strengthening the bridge structure, the damage to the original bridge structure should be reduced as much as possible to ensure that the service performance of the original structure will not be damaged; For those existing structures or members, after structural inspection and reliability appraisal analysis, on the basis of comprehensive understanding of their structural structure and bearing capacity, they should be preserved and used as much as possible [1].

Four. Bridge reinforcement method

1. Surface paving reinforcement method. Bridge deck pavement reinforcement methods mainly include local repair chisel method, re-pouring concrete slab reinforcement method and bridge deck reinforcement layer reinforcement method. The local patching chisel patching method is a local patching method for cracks, falls off and caves. The sidewalk. What needs attention here is: before repairing, the hair should be cut and the aggregate should be exposed, and then the soaked holes should be repaired with cement concrete, and the bonding materials should be painted to strengthen the bonding between the new and old concrete; The re-pouring concrete slab reinforcement method is suitable for the bridge deck that cannot be repaired. The method is to completely remove the original pavement of the roadway and re-pour concrete slabs for reinforcement. The reinforcement method of bridge deck can not only achieve the effect of repair, but also enhance the bending capacity of beam and slab and improve its bearing capacity. The concrete method is to resurface a layer of concrete or reinforced concrete on the old bridge deck.

2. Enlarged section method. The strengthening method of enlarging section, also known as external concrete strengthening method, is to add a layer of cast-in-place concrete in the compression area of reinforced concrete flexural members to increase the cross-sectional area of the original concrete members, thus enhancing the flexural capacity of the normal section of the members and achieving the purpose of strengthening. We can achieve this by thickening the bridge deck or increasing the height and width of the main girder ribs. Its construction technology is simple, adaptable and mature, which can significantly improve the stiffness of the bridge and achieve better reinforcement effect, and can widely reinforce concrete structures such as beams, slabs, columns and walls of general buildings. However, this method also has some shortcomings, such as long wet working time, reduced building clearance after reinforcement, corrosion of embedded steel bars and high risk of concrete deterioration.

3. Carbon fiber reinforcement method. Carbon fiber reinforcement method, also known as sticking fiber reinforced plastics method, is to use special resin to stick carbon fiber on the Lamian Noodles of concrete structure, so that carbon fiber and the original structure form a new stress whole, which makes it stretch together with the reinforced section, thus achieving the reinforcement effect of the structure. The technical performance index of carbon fiber sheet should meet the requirements.

This method will hardly increase the weight and section size of the structure, and will not change the clearance height. The construction is convenient, and it will hardly cause new damage to the original road and bridge structure. It has good corrosion resistance, durability and fatigue resistance. According to the stress analysis, multi-layer bonding can be used for reinforcement, and its direction can be flexibly grasped. For example, it can greatly improve the ductility and bearing capacity of concrete structures, so its application range is very wide [2].

4. Bonding steel reinforcement method. The so-called steel-bonded reinforcement method is to stick a certain number of steel plates on the cross-sectional surface of reinforced concrete structural members with insufficient bearing capacity. This method is suitable for all kinds of large, medium and small bridges, and can protect the original concrete members well. It is also very simple in case design and structural calculation. However, in the process of implementation, it is difficult to ensure the durability of bonding because the steel plate is overweight, the operation is complicated and the curing agent is fragile after hardening. In addition, there are some potential corrosion on the interface between steel plate and colloid.

5. Bolting and shotcreting technology. With the development of shotcrete machinery and the use of accelerator, modern technology promotes the cooperation of shotcrete alkali with steel mesh and anchor rod, and gradually improves the bolting and shotcreting technology. It can avoid using side formwork as much as possible, and its transportation, pouring and tamping are integrated into one, with small floor space, simple equipment, high degree of construction mechanization, high efficiency, labor saving and uninterrupted traffic during implementation.

6. External prestressing reinforcement method. This method is also called the reverse bending moment method, which is mainly a reinforcement method with the help of "prestress". By stretching prestressed reinforcement outside the member, not only the main reinforcement can be increased, but also the section strength of the member can be improved, and the settlement at the bottom of the pier can be reduced. It can be said that it is a very active reinforcement method, which can offset part of self-weight stress, unload and prevent cracks, and prolong the service life of bridge structure.

A Case Study of verb (abbreviation of verb)

Maintenance and reinforcement measures for enlarged foundation and pile foundation of bridge substructure 3].

1. Project overview.

The total length of the bridge is 583m, and the superstructure adopts 30m standard span prestressed T-beam and 16m reinforced concrete hollow slab. The superstructure is simply supported and the bridge deck is continuous. The bridge within pier 0 -7 is the main bridge, crossing the main river, with a span of (330+430)m T-beam, and the rest spans are 16m reinforced concrete hollow slab approach bridge. The No.0 main pier adopts the ribbed slab pier with enlarged foundation, No.65438 +0-2 pier adopts the double-column pier with enlarged foundation, and the other main piers adopt the double-column pier with rock-socketed piles, with the main pier column diameter of 1.5m, the approach bridge adopts the three-column pier with the diameter of1.2m.. ..

2.0 -6 Bridge pier foundation diseases.

The bridge was completed and opened to traffic on 1997. Due to a large amount of sand mining in the river, the riverbed has fallen seriously. Pier 0-6 spans the main river bed. At present, the riverbed ground at the bridge site is about 3m lower than when the bridge was built, and the deepest part is 4m. Among them, 1 pier and pier 2' s enlarged foundation were seriously damaged. The following describes and analyzes the foundation diseases of pier 0 -6 one by one.

(1)0 abutment foundation disease. Abutment No.0 is a ribbed slab bridge abutment. It is found that the abutment has no slope protection abutment, and the abutment covering soil has been washed away a lot, which enlarges the foundation exposure, partially hollows out the foundation, and basically exposes the stratum bedrock surface. There are two reasons for the failure of slope protection: one is the failure of slope protection caused by years of floods; Second, the rainwater discharged from the highway drainage ditch at the abutment washes the pier and abutment slope protection all the year round, causing the inclined rock foundation to be exposed. The damage of slope protection reduces the stability of abutment and accelerates the stability and strength of rock foundation at the bottom of foundation.

(2) 1 -2 pier foundation disease. The substructure of pier 1-2 is a double-column pier with enlarged foundation. It is found that there is an open caisson left by the construction on the column side, and the elevation of the bottom of the open caisson is slightly higher than that of the enlarged foundation. 1 The bottom of pier expansion foundation is suspended, and the bearing layer at the bottom is inverted trapezoid. The lower part of pier/kloc-0 near the shore is on the bedrock, but the lower part of the foundation near the river center does not completely fall on the bedrock, and the lower part of the foundation is sandy locally. The foundation of Pier 2 is in the river, but the open caisson on the water side of the river center is obviously inclined, and there are wide cracks in the concrete on the side wall there. At present, the columns of pier 1 and pier 2 do not appear obvious inclination.

The causes of foundation erosion are: first, the serious sand mining in the river channel leads to the decline of riverbed erosion; Another reason is that the running water of the highway drainage ditch directly impacts the soil layer near the pier foundation, which causes the bottom of the pier foundation of 1 to be particularly scoured.

The reason why the bottom of the enlarged foundation is inverted trapezoid: during construction, when the open caisson sinks, the bank side touches the bedrock first, while the bedrock line of the other open caisson is deeper. At this time, the side of the open caisson has not reached the bedrock, but it is only in the sandy soil layer, but the bank of the open caisson can't sink because of the obstruction of the bedrock, so the construction unit poured an expanded foundation in the open caisson, resulting in some foundations not falling on the bedrock. Because the size of the upper part of the enlarged foundation is larger than that of the lower part, the soil at the lower part of the foundation is washed away, and the bottom of the foundation looks like an inverted trapezoid from the site.

Possible causes of inclined cracking of open caisson: under flood scouring, the riverbed is continuously lowered, which leads to hollowing out of supporting soil at the lower part of open caisson, resulting in open caisson rollover, uneven settlement, local cracking and continuous inclination.

From the analysis of the results of open caisson inclination, foundation void and geological drilling, it is found that the enlarged foundation and the bottom of open caisson are not in complete contact with the inclined bedrock surface. After soil erosion, the open caisson inclines, and the enlarged foundation is suspended, which reduces the effective force transfer area and stability of the enlarged foundation.

(3) The foundation disease of pier 3-6. Pier 3 -6 is a pile pier, and the site inspection found that the foundation of pier 3 -6 was seriously eroded. The average depth of ground erosion there is 4 meters. The original design pile foundation is buried in the rock for 2 meters. After calculation, the safety factor of various mechanical indexes of pile foundation is small, especially the earth pressure on the side of pile has exceeded the standard.

3. Implement maintenance and reinforcement methods

According to the structure, disease and drilling data of pier 0 -6, combined with the opinions of the expert group, different methods are used to repair and strengthen the pier abutment. The foundation of platform 0 is mainly protected by rectangular retaining wall, and drainage ditch is set for drainage. The foundation of pier 1-2 is mainly protected by closed box-shaped rock-socketed retaining wall, and the soil in the wall is grouted. In order to reduce the disturbance of construction to the foundation, keep the original open caisson and dismantle the upper part of the inclined open caisson foundation of Pier 2. There are two methods for the pile foundation of pier 3-6: one is to protect the pile foundation from erosion by using the rock-embedded wall of oval closed box, and the other is to add new pile caps and bored pile foundations to share the original foundation load.

(1).0 Maintenance and reinforcement measures for abutment foundation. Platform 0 mainly adopts slope protection, and the drainage ditch space is reserved, considering the cost. C30 concrete retaining wall is at the outer edge of exposed abutment foundation with a horizontal distance of1.5m.. The section of retaining wall is rectangular (mainly considering the uneven bedrock surface, which is convenient for construction), and the plane is arranged in a rectangular shape around the abutment. The rock-socketed depth of slope protection foundation shall not be less than 2m. After that, do concrete slope protection on the retaining wall, and the slope is 1: 1. At the same time, the highway drainage ditch should be rectified to prevent the running water from scouring the slope protection, and a drainage ditch should be made on one side of the slope protection.

(2). 1 -2 pier foundation reinforcement measures. 1 pier -2 pier mainly adopts the method of protection and reinforcement, and uses the newly embedded bedrock retaining wall to protect and expand the foundation. The steps are as follows: there is a gap at the bottom of the enlarged foundation. Before construction, use flaky concrete to tamp the gap of the foundation, and use steel sheet pile cofferdam to temporarily support and expand the foundation during construction. Then the foundation and sand around the sheet pile cofferdam are grouted with double liquid slurry, and the soil at the lower edge of the foundation is filled. After foundation construction and support, sand bag cofferdam will be carried out in the outer area of retaining wall. After the bedrock surface of the retaining wall is cleaned, 2m bedrock is drilled at the designated position with a geological drilling rig with a diameter of 12.7cm, and embedded in concrete filled steel tubular piles, and at the same time, 0.2m rock is embedded in the root of the retaining wall. After the reinforcement of retaining wall is bound with formwork and concrete is poured, concrete is poured, so that the retaining wall and concrete-filled steel tubular pile become a whole. After backfilling and covering the soil around the foundation, complete the maintenance of the enlarged foundation.

(3) The reinforcement measures for pier No.3-6 foundation, the designed rock-socketed depth of the original bridge pile foundation is 2m, and the bearing capacity of the foundation meets the specification requirements. However, due to serious erosion, the safety factor is low. In order to ensure the continuous normal use of the bridge, there are two reinforcement measures for the maintenance and reinforcement of the pile foundation:

A. reinforce with new pile foundation. Add a 2.4m-high cap down the upper edge of the tie beam of pier No.3-6, and plant steel bars on the contact surface between the new cap and the pile foundation and tie beam. In order to increase the path of load transfer from the column to the cap, a column with a height of 1.5m was added along the circumference of the original column on the upper edge of the cap, and steel bars were planted at the interface. Because the newly added high pile caps have a great influence on the flood discharge capacity of the river, the size of the caps should be as small as possible and the lines should be smooth. Four new pile caps are designed under the pile cap, and the newly added pile foundation is embedded in rock with a diameter of1.2m. The distance between the newly added pile foundation and the original pile foundation is not less than 2 times the pile diameter.

This method can greatly improve the bearing capacity of the lower foundation, but it needs to plant a large number of steel bars on the original pile, which has certain damage to the original structure, high cost, large operating space for pile foundation construction and inconvenient construction.

B. Add a new retaining wall to prevent erosion. Because the bearing capacity of pile foundation has a certain degree of safety, sand bag cofferdam can be directly used for construction around pile. At the designated position, drill 2m into the bedrock with a geological drilling rig of 12.7cm, and bury the concrete filled steel tubular pile. At the same time, ensure that the root of the retaining wall is embedded with 0.2m rock, bind the reinforcement of the concrete retaining wall with formwork, and pour concrete, so that the retaining wall and the concrete-filled steel tubular pile become a whole. After the retaining wall is backfilled and covered with soil inside and outside, the pile foundation protection treatment is completed.

This method can permanently protect the pile foundation from scouring, with little damage and disturbance to the original structure, but the improvement of foundation bearing capacity is limited. During the construction, after the maintenance of pier 3 -6 foundation, the second maintenance and reinforcement method is adopted.

Ending of intransitive verbs

The damage of bridge structure is the result of many factors. In order to ensure the safety of the bridge, appropriate reinforcement methods should be selected according to the damage characteristics, causes and degrees.

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