Second, the common diseases of highway bridges and their causes
1. The design load of the original bridge is low.
A large number of bridges have low requirements for vehicle load during construction. In order to save money, they seldom predict the demand of future traffic development and make long-term plans. Therefore, their load standards are not high in design, and lower standards are adopted in practical application, which makes most existing bridges have lower load standards and cannot meet the requirements of rapid development of automobile transportation.
2. Improper construction reduces the bearing capacity of the original bridge.
Construction is a process of actual design, the correctness of design will be tested in construction, and the quality of construction will also affect the overall performance of the bridge. In production practice, sometimes even though the design is correct. However, due to improper construction methods, lax construction quality control and some unforeseen disasters, such as floods, earthquakes, etc., the bearing capacity of the bridge will often be reduced and the expected purpose of the design will not be achieved.
3. The bridge has been in disrepair for a long time and is seriously damaged. Due to the lack of maintenance and repair work, many bridges are in disrepair and seriously damaged. Especially the arch bridge built on soft soil foundation, due to the settlement and passage of the foundation, the bridge is deformed and cracked, which makes the damage more serious.
4. Other reasons
Bridge is a kind of structure in nature, and it often encounters all kinds of unexpected disasters, such as earthquake, fire and collision. The bridge structure is damaged and the bearing capacity is reduced.
Third, highway bridge detection technology
General detection (routine detection), basic detection (routine detection) and special detection (special detection) can also be regarded as three different stages of detection.
1. Routine detection
That is, responsible for the regular inspection of road and bridge maintenance personnel, aiming at timely maintenance of roads and bridges and making corresponding reports on some sudden major problems. In case of damage to roads and bridges caused by major natural disasters such as earthquakes and mudslides, road and bridge inspectors should report accurate information to their superiors in time.
2. Basic detection
In other words, professionals regularly track the quality of roads and bridges, especially some newly built bridges and some bridges that have passed the general inspection. Professional engineers are needed to form a tracking team. Professional inspection is carried out by visual inspection, camera and other measuring instruments, and the inspection scheme is formulated to ensure the service life of roads and bridges and eliminate potential safety hazards. When necessary, traffic suggestions can be put forward for the corresponding problematic roads or bridges according to specific conditions.
3. Special detection
When the detected roads or bridges are determined to have serious problems, road and bridge experts shall promptly put forward the requirements for special inspection. After approval, an expert group will be formed to carry out nondestructive testing of roads and bridges by physical or chemical means, and it is forbidden to carry out all-round inspection of road sections or bridges to find out the root causes of the problems, so as to formulate corresponding measures. Under normal circumstances, roads or bridges that need special inspection should be prohibited from being used until the problem is solved.
Four, the common methods of highway bridge maintenance
1. Maintenance of bridge structure surface layer
Common surface repair methods are: concrete repair method, cement mortar repair method, concrete binder repair method and epoxy resin repair method, and each repair method has its own applicable conditions, construction procedures and matters needing attention.
2. Bridge structure reinforcement and maintenance
The maintenance methods and steps of structural reinforcement are as follows: ① Chisel off some damaged concrete such as looseness and peeling; (2) derusting the steel bar to remove the dust on the surface of the old concrete, and carrying out antirust treatment on the derusting steel bar; (3) coating adhesive such as epoxy glue; (4) formwork erection, batching and pouring, guniting and daubing; ⑤ Surface treatment of newly sprayed or poured concrete surface.
3. Maintenance of surface damage of masonry bridge structure
Maintenance methods include: jointing repair; Plastering or shotcreting to treat the weathering of masonry surface; Partial surface repair; Repair of decorative stone.
Five, the common methods of highway bridge reinforcement
The technical methods for strengthening bridges with defects and diseases usually include reducing load, strengthening critical stress members or changing geometric characteristics, providing new supplementary members, improving the stress system and state of remote structures, and increasing their ability to bear or exist. In addition; It is of great significance to reasonably replace or change the geometric shapes of the bearings and expansion joints of the structure and improve the safety factor, so as to improve the use function and prolong the service life.
1. Bridge deck reinforcement method: overlay a layer of reinforced concrete on the top of the beam. First, the overlay on the old bridge deck is chiseled to form the same force as the original main beam, so as to improve the compressive section strength and moment of inertia, improve the lateral distribution ability of the bridge, and thus achieve the purpose of improving the bearing capacity of the bridge.
2. Reinforcement method of increasing section reinforcement: When the strength, stiffness, stability and crack resistance of the beam are insufficient, the effective height and bending strength of the beam are improved by increasing the section of the member and the gold content of the main reinforcement, thus improving the bearing capacity of the bridge. This method is widely used in the reinforcement of beam bridges or arch bridges and arch ribs.
3. Shotcrete reinforcement method: With the help of professional concrete spraying equipment, the newly designed concrete is continuously sprayed on the surface of anchoring reinforcement, and new concrete is formed by condensation and hardening with the original components, which increases the stress section of the bridge, and at the same time, the added reinforcement strengthens the integrity of the structure and makes it bear greater external load.
4. Sticking steel plate method: When the traffic volume and load increase and the bearing capacity of the bridge slab is insufficient, or when the longitudinal main reinforcement is seriously corroded, serious transverse cracks will appear in the bridge slab. In the tensile area or weak part of concrete structure, the steel plate is bonded and anchored with adhesive and anchor bolt, so that it forms an integral stress state with the original structure, and the steel plate is used to replace the added steel bar to improve the bearing capacity. This method has simple construction technology and easy control of construction quality.
5. Method of changing the stress system of the structure: This method is a technical means and purpose to improve the bearing capacity of the bridge through the stress system of the bridge structure. For example, adding a bracket or pier under a simply supported beam can reduce the span and stress bending moment or vertically connect the simply supported beam with adjacent openings to replace the continuous beam; Or after adding a steel analysis frame under the simply supported beam to form a composite beam, the internal force state of the beam is reduced to improve the bearing capacity. The way to change the structural system is to set up permanent facilities under the bridge, but at the same time reduce the clearance under the bridge, which affects the navigation capacity and flood control capacity, but we must pay attention to the timely turnover and demolition of temporary facilities.
6. External prestress reinforcement method: For prestressed beam bridges or slab bridges, external prestress is applied in the tension area to reinforce the bridge, which can offset the expected unloading effect of part of self-weight stress, thus greatly improving the bearing capacity of the bridge. Its characteristics are: it can greatly improve and adjust the stress state of the original structure under the condition of little increase in self-weight, improve the rigidity and crack resistance of the load-bearing structure, and have little influence on the stress state of the pier or foundation due to the small weight of the white weight structure (which can reduce the workload of reinforcement for the next project).
7. External prestress method: it can be used as a temporary reinforcement method for passing through heavy-duty bridges, and also as a technical measure to permanently improve the load level of bridges. In application, the longitudinal beam slab can be widened and strengthened, and a longitudinal beam slab with high rigidity and bearing capacity can be added under the condition that the substructure has enough bearing capacity, so that the new beam slab and the old beam slab can bear the same force through transverse hinge joints, and the load of the original beam or slab can be reduced. When the added beam and slab are on one side or both sides of the main beam, it will be widened and strengthened.
8. Enlarged foundation reinforcement method: it is suitable for the reinforcement conditions with insufficient foundation bearing capacity or shallow buried depth. The enlarged area of the bottom surface of the foundation is determined by the strength checking calculation of the foundation. When the low-strength reinforced concrete meets the requirements and the existing defects are only excessive uneven settlement and deformation, the geometric form of this reinforcement method can be selected through foundation deformation calculation.
9. Pile foundation reinforcement method: When the pier with soft cushion under the foundation sinks or the foundation inclines due to hydrological reasons, the reinforcement method is to add bored piles or drive prestressed reinforced concrete piles around the pier or pile foundation to improve the stability and bearing capacity of the foundation.
Ending of intransitive verbs
Many highway bridges in China have been built for some time, so the maintenance and reinforcement of highway bridges is also of great significance to improve the service life of highway bridges and increase the utilization value of resources.
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