1 beam bridge
There are many common methods for strengthening the superstructure of beam bridges, which can be subdivided into the following specific methods.
1. The methods of increasing or increasing the section of members can be divided into the following methods according to the actual situation.
1) Bridge deck reinforcement method
Bridge deck reinforcement layer reinforcement method is a method of adding a layer of concrete or reinforced concrete reinforcement layer to the old concrete or reinforced concrete bridge deck for reinforcement. The implementation methods are: steel mesh and concrete, steel mesh and expansive concrete, steel fiber concrete, among which reinforced concrete reinforcement layer is the most widely used.
The reinforcement method of bridge deck reinforcement layer can not only repair the damaged bridge deck with cracks and peeling, but also increase the effective height of plateau beam slab, improve the bending capacity of beam slab and improve the lateral load distribution of hinged beam slab, thus improving the bearing capacity of bridge.
The advantage of this method is that it is convenient to construct, and it can be carried out like ordinary bridge deck concrete pavement construction: for two-lane or bridge deck widened slab bridges, it can be semi-open to traffic and semi-constructed, with little impact on traffic, and it can also be carried out together with pavement maintenance. The disadvantage is that the bridge deck must be maintained after reinforcement and traffic is restricted.
2) Increase beam section and reinforcement method
When the strength, stiffness, stability and crack resistance of beams are insufficient, reinforcement methods such as increasing the section of members and increasing reinforcement are usually adopted. The strengthening method of increasing the section and reinforcement of members to improve the bearing capacity of main girder is generally used to strengthen beam slab bridges and arch ribs. For the beam-slab bridge, the main consideration is to increase the main reinforcement and section at the bottom of the plate beam, such as the reinforcement method of T-beam bridge.
When strengthening a simply supported beam bridge with insufficient tensile strength, the main reinforcement of steel bars can be added at the bottom (tensile area) or side of the beam, or steel bars can be added at the web, and then concrete is sprayed or poured to increase the bending section of the beam and improve the bearing capacity of the beam.
The advantage of this method is that it can be constructed under the bridge without affecting the traffic, and the reinforcement workload is not large, and the reinforcement effect is also remarkable, so it is a widely used method. The disadvantage is that the old beam needs to be chiseled away during reinforcement, which is troublesome to operate and has a large workload, and scaffolding is often needed.
3) Bonding steel plate reinforcement method
Bonding steel plate reinforcement method is to use epoxy resin series adhesive to bond steel plate to the tensile edge or weak part of reinforced concrete structure, so that it can form a whole with the structure to replace the steel bars that need to be added, thus improving the bearing capacity of the beam and achieving the reinforcement effect. The principle is shown in Figure 3. Suitable for flexural, shear and tensile members, with relative humidity not more than 70% and no chemical corrosion.
Bonding steel plates to strengthen bridges does not need to destroy the original reinforcement structure, and the reinforcement project hardly increases the size of the original structure, and the construction period is short, the operation is simple, and the engineering quality is easy to control. The disadvantage is that the joint surface needs to be treated, bolt holes need to be drilled and buried, and the original structure is easy to be destroyed. The steel plate needs anti-corrosion treatment, which increases the future maintenance work.
4) Strengthening method by sticking carbon fiber cloth.
Carbon fiber cloth has the characteristics of light weight, high strength, simple operation, easy adhesion and no corrosion, and can be used for various forms of reinforcement such as bending, shearing and earthquake resistance.
The strengthening method of sticking carbon fiber sheets is suitable for flexural and shear strengthening of beam bridges and slab bridges, as well as shear and compressive strengthening of concrete piers. The reinforcement effect is particularly obvious for old bridges with low reinforcement ratio or serious corrosion of steel bars. However, it should be pointed out that the applicable environment (such as temperature, humidity, etc. When strengthening bridges in this way, the materials must be strictly observed. Due to the poor ductility of carbon fiber cloth, for beams and plates with high reinforcement ratio, the expected reinforcement effect can not be achieved only by sticking carbon fiber.
2. Change the structural system method
Changing the structural system method is a reinforcement method to improve the bearing capacity by changing the bridge structural system. There are many ways to change the structural system, and it is often necessary to operate or set up permanent facilities under the bridge, which will affect the clearance under the bridge. Therefore, the method of changing the structural system is generally adopted without affecting the navigation and flood discharge capacity of the bridge.
This method has a good reinforcement effect, especially for solving the temporary reinforcement problem of overweight vehicles. After heavy vehicles pass, the temporary piers can be removed at any time, which has little influence on navigation and flood discharge. The specific approach is:
1) simply supported continuous method
Add temporary piers under simply supported beams or connect adjacent simply supported beams to change the stress system of the original structure, or connect the beam ends of multi-span simply supported beams into multi-span continuous beams, so as to improve the stress condition of the structure and improve the bearing capacity of the bridge. The specific methods are: adding auxiliary pier method, changing simple supported beam into continuous beam reinforcement method, and splayed support method.
2) Strengthening method of changing bridge into culvert
For bridges with small spans, the method of replacing bridges with culverts can be used for reinforcement without affecting navigation and flood discharge capacity.
3. Prestressed reinforcement method:
Prestressed reinforcement method refers to a kind of reinforcement method which applies prestress to additional members or original members (such as main beams) by using prestress principle. For reinforced concrete or prestressed concrete beams and slabs, applying pre-pressure in the tension zone can offset part of the dead weight stress and play a role in unloading, thus greatly improving the bearing capacity.
Prestressed reinforcement method is suitable for cases where the flexural bearing capacity of the normal section is insufficient, the steel bars in the tensile area of the normal section are corroded, the deflection of the beam exceeds the specified value due to insufficient flexural stiffness, or the crack width in the tensile area of the beam exceeds the specified value because it is just too small, and the shear strength of the inclined section of the beam is insufficient.
The advantages of prestressed reinforcement method are simple construction technology, less traffic interference, simple equipment, less manpower input, short construction period and obvious economic benefits, which can greatly improve or restore the bearing capacity of the bridge, with little damage to the original structure and no influence on the clearance under the bridge. It is easy to give priority in the process of selecting reinforcement methods.
4. Method of adding longitudinal beam
When the pier foundation is in good technical condition and has sufficient bearing capacity, new longitudinal beams with high bearing capacity and high rigidity can be added. These new longitudinal beams are connected with the old longitudinal beams and bear the same force.
The principle of this method is: after strengthening, the load is redistributed in the bridge structure after adding the main beam, so that the load in the original beam is reduced, thus improving the bearing capacity and stiffness of the strengthened bridge. When the added longitudinal beam is located on one side or both sides of the main beam, it also has the function of widening.
When a longitudinal beam is added in the middle of the main beam of the old bridge, the wing plate between individual main beams or two adjacent main beams can be removed to form a vacancy, and then a new longitudinal beam with greater bearing capacity and stiffness than the original main beam can be installed on the vacancy. In order to ensure that the old and new main beams can work together, we must pay attention to the transverse connection between the old and new beams so that the old and new beams can be connected. The transverse connection methods include tongue-and-groove hinge, keyway connection, welding and steel plate hinge.
2 reinforced concrete arch bridge
The reinforcement of reinforced concrete arch bridge mainly refers to the reinforcement of arch ribs, the reinforcement of arch transverse beams and the adjustment of superstructure fillers. Now, various methods are described as follows:
1) Sticking steel plate and reinforcement method
The concrete method of strengthening arch rib by sticking steel plate is: after cleaning the surface of arch rib neatly, stick steel plate on the appropriate position of arch rib with epoxy mortar. The position where the steel plate is pasted is mainly below the cross section of the arch rib, and it can be pasted into a whole plate (or welded in blocks) at intervals within the arc range of the arch ring, and the thickness of the steel plate should be 4 ~10 mm. When the arch ring is cracked or the bearing capacity is insufficient, the reinforcement effect by sticking steel plate method is obvious.
In view of the problems of steel plate processing, forming and sometimes weak bonding, according to the needs of actual reinforcement work, the reinforcement method of sticking steel bars can also be adopted.
The construction method of sticking steel bars is basically the same as that of sticking steel plates to strengthen arch ribs, except that steel bars are used. From the actual situation, compared with the method of sticking steel plates, this method has the characteristics of good adhesion to structures, easy reinforcement molding and more obvious reinforcement effect.
2) Expansion and reinforcement methods of arch rib section
The bending stiffness of arch ribs can be improved by wrapping the original arch ribs with steel bars and concrete, increasing the cross-section size of arch ribs, increasing the reinforcement ratio of arch ribs or changing the unreinforced arch ribs into reinforced arch ribs. This reinforcement method of enlarging arch rib section has obvious reinforcement effect, remarkable effect and wide application.
3) Reinforcement method of cross beam between arch ribs
When the transverse connection is weak, the torsional rigidity and transverse integrity of the arch ribs can be strengthened by increasing the cross section of the transverse tie beam between the original arch ribs or adding another transverse tie beam beside the original transverse tie beam. This method can generally be considered together with the above-mentioned arch rib enlarging section method, and can achieve better reinforcement effect.
4) Adjust the dead weight on the arch and change the reinforcement mode of the structural system.
Adjusting the dead weight on the arch and changing the reinforcement method of the structural system are suitable for the horizontal displacement or rotation of the arch foot and the deformation of the arch axis due to the dead weight or insufficient bearing capacity of the foundation. If conditions permit, adjust the arrangement of self-weight on the arch, change the structural system of the arch bridge, improve the stress state of the structure, and achieve the purpose of reinforcement.
It must be noted that when the arch structure of the old bridge is demolished in the reinforcement construction, special attention should be paid to balancing the stress on the arch to prevent the bridge from collapsing.
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