Bridge expansion joint refers to the expansion device set on the bridge deck between two beam ends and between the beam ends and the back wall of abutment to ensure the free deformation of the bridge span structure under the influence of temperature change, live load and concrete shrinkage and creep. It not only ensures the free deformation of the beam, but also enables vehicles to pass through the joints smoothly, preventing rainwater leakage and garbage and soil blockage. Besides having sufficient strength, its members should also be firmly connected with the bridge deck pavement.
Take some bridges on a national highway as an example. Most of these bridges were built in the 1980s, and they were damaged to varying degrees after opening to traffic. The end edges of reinforced concrete members are falling off day by day, and the joint width is increasing year by year, which seriously affects the service effect and service life of the bridge. To this end, the author has conducted a special study on this in recent two years and gained preliminary experience.
1. Analyze the cause of damage and choose the treatment scheme.
1. 1 expansion joint damage reason
Although there are four kinds of expansion joints of these bridges, there are only two kinds, namely expansion joints without expansion devices and expansion joints with expansion devices. There are three reasons for the damage of rubber expansion joints: (1) The expansion joints are unreasonable in design, and now the U-shaped iron expansion joints have been eliminated, and the expansion joints separated by wooden boards can only be used for small bridges; (2) The bolts fixing the rubber plate are easy to be damaged. There are two kinds of damage. One is that the bolt is loose because the screw is not firmly embedded, and the other is that the rubber plate bounces when the load passes, which leads to the loosening of the nut over time, which seriously leads to the bolt slipping and losing the fixing effect on the rubber plate. (3) The concrete in the anchorage zone on both sides of the expansion joint is damaged due to insufficient strength, thus causing damage to the whole expansion joint.
1.2 treatment scheme selection
Rubber plate expansion joints are made of aging-resistant high-quality rubber inlaid with high-strength steel plates, which combines rigidity with flexibility. The embedded steel plate has considerable vertical stiffness and can bear various vehicle loads. Using the high elasticity and incompressibility of rubber to absorb the bridge deformation caused by shear tension and compression, fully meet the adaptability of driving to the road surface and reduce the impact damage of driving to the bridge. Good durability, can avoid falling into the joint, convenient construction and maintenance, waterproof.
1.3 expansion joint design
The type of rubber plate expansion joint is mainly determined by the bridge expansion caused by temperature change. The expansion and contraction of rubber plate depends on the shearing, tension and compression of rubber and steel plate. In order to complete this deformation, the rubber plate will be subjected to two opposite horizontal forces, which are applied to the rubber plate through the anchor bolts. According to the data, when the rubber plate reaches the expansion and contraction limit, the linear tensile (compressive) force generated by it is about 16KN/m, and such a large horizontal force is easy to damage the anchor bolts. In order to reduce the damage degree of bolts, it is necessary to avoid the rubber plate from generating excessive tensile (compressive) force, so when selecting the rubber plate model, it should be large rather than small, leaving enough room. The expansion and contraction of rubber sheet are mainly composed of two parts: one is the expansion and contraction caused by temperature change; One is shrinkage caused by solidification and creep of concrete. When rubber expansion joints are added to old bridges, the latter can be ignored, and only the expansion caused by temperature changes is considered to determine the model of rubber plates.
Considering that the concrete in the anchorage zone and transition zone is thin, it is not easy to form a whole with the old concrete, and the anchor bolt is not easy to "take root" and be damaged, electric hammer is used to drill holes and epoxy resin is injected for embedding. Considering that the edge concrete adjacent to the rubber plate and transition section is easy to be bitten, 10 channel steel is added.
2. Construction of expansion joints
There are two key problems in the construction of expansion joints of old bridges with rubber plates: first, the thickness of concrete for bridge deck pavement can not meet the minimum requirements for anchor bolt reinforcement, especially the thinnest part of arch bridge pavement is 8cm, and the buried depth below steel bars is only 2.5cm. If slabs are installed, it will be even less than the elevation. If the new and old concrete cannot be firmly bonded to form a whole during construction, the strength of the new concrete is only a hard skin, and it will be crushed when it is carried on the vehicle. Second, the embedded channel steel and anchor bolts are "rootless and soilless", which are easy to be loosened by the gravity of the vehicle and cause damage. In order to solve these two problems, the following two measures were taken in the construction: first, if the thickness of new concrete under the rubber plate is less than 6cm, epoxy resin concrete should be poured instead; The second is to use "N"16 steel bar to anchor and fix the steel bar, and use electric hammer to drill holes for epoxy tree limb inlay. In order to bury the anchor bar to the depth of the old concrete, if the rigid arch bridge is in the middle of the micro-bending plate, it is necessary to measure the total depth, so that the anchor bar is buried in the micro-bending plate 3cm-4cm (the design thickness of the micro-bending plate is 6cm). This part is the most difficult to drill. If you are not careful, you will punch through the microbend plate, so you should seal it with epoxy mortar first.
It is more realistic to use semi-closed and semi-closed construction scheme to erect expansion joints of old bridges. If it is opened to traffic one day earlier, its economic and social benefits will be very considerable. Therefore, the setting time of concrete can be shortened by adding 16%JK-24 quick repair agent and curing with plastic film. The indoor test results show that the curing time for concrete to reach the design strength (design mark C40) at different temperatures is 48h at average temperature 10℃, 36h at 20℃ and 24h at 25℃.
3. Treatment of expansion joints with connecting holes
The expansion joint of connecting hole is the expansion joint of hinged simply supported superstructure hole, where the bridge deck should be flexible enough to adapt to the vehicle load and hard enough to withstand the longitudinal force caused by temperature change and braking.
The stone bridge is a 9-hole 13m hollow slab bridge. It is impossible to connect all or part of the end edges of the hollow slab along the height (there are connecting steel bars inside) and separate them with thin rubber pads. In this way, only the bridge deck is treated, and the design scheme of three-hole connection is adopted. When the temperature difference reaches 65℃, its expansion and contraction amount is about 25.35mm, and the expansion and contraction amount caused by temperature difference can be met by using 45-type rubber plate expansion joint. Because there is no hinge at the connecting hole under load, reinforced concrete can't complete the task of hinge, so after use, regular cracks will inevitably appear at the connecting hole. However, this kind of crack will not expand into a disease and destroy the bridge cotton pavement at the connecting hole. In order to prevent water seepage from corroding steel bars, road sealant can be poured. The connecting hole is very simple, just arrange a few more steel bars in this area.
4. Conclusion
4. 1 In the past, the concrete in the transition area of expansion joint was designed to be 30cm wide, while the width of the wheel on the ground was 20cm. The impact force of the automobile passing through the expansion joint just acts on the edge of the transition zone, which accelerates the destruction of concrete in the transition zone. Now, we will widen the concrete in the transition area to not less than 40 cm, which can prolong the service life of the concrete in the transition area.
4.2 The bolts for anchoring rubber plates are difficult to fix due to geographical restrictions, but the damage of rubber plates is mostly caused by anchor bolts, so the two steel bars embedded with bolts should also be carefully constructed. When the concrete thickness of embedded bolts is less than 6cm, it must be poured with epoxy resin fine stone concrete, and the tamping should be paid attention to.
4.3 The usage of "n" for side buried 10 channel steel is ideal, and the thickness of concrete should not be less than 12cm, so special attention should be paid when vibrating, because the air in the internal area of the channel steel is not easy to be exhausted, which often leads to unconsolidated concrete or excessive laitance. If the thickness of concrete is less than 10cm, angle steel of 5cm×5cm can be used instead. Whether it is channel steel or angle steel, it is very important to fix their reinforcement. We use l6 steel bar to bury the bottom in the slab to a depth of not less than 15cm, inject epoxy resin for embedding, and weld "U"-shaped 16 steel bar on the side. The welding length is 20cm, and the anchoring length is not less than 25cm. The effect is quite good.
4.4 Rubber plate expansion joints have good elasticity. After a long time, the anchor nut often loosens, and some even cause the screw to slip. If it is not repaired in time, the whole rubber sheet will be damaged. Therefore, the maintenance of rubber expansion joints is very important. Highway bridge construction reinforcement technology is very important. Reasonable use of reinforcement technology to achieve the desired results, every construction detail is very critical. Zhong Da Consulting will explain the strengthening technology of highway bridge construction for you.
First, some diseases that often occur in highway bridges
Some main diseases of highway bridges are as follows: First, there are various cracks in the main arch ring, arch rib, joint between arch wave and arch rib, cross beam and so on. Second, the steel bars are rusted and corroded. When the rebar rusts, its volume will expand, thus squeezing the concrete around the rebar, cracking the concrete and reducing the bearing capacity of the bridge. At the same time, the bridge surface is not beautiful after the rust flows out. Thirdly, the pier and its abutment bear most of the weight of the bridge and are subjected to various forces, such as wind load and buoyancy of water. , resulting in different degrees of damage to piers and abutments. Fourthly, cracks will appear when the main beam is deformed, and most of the cracks in the main beam occur at the lower edge of the middle beam or the upper edge of the beam arm. This kind of crack is basically because the overload operation of the bridge makes the stress area of the bridge open, which is generally within the normal range, but this kind of crack is on it, so rain can easily flow into the beam from these cracks, which makes the steel bars in the beam rust and corrode, and reduces the structural strength of the bridge.
Second, the importance of bridge reinforcement
The bridge bears the overweight load every day, and after years of operation, some safety hazards will inevitably appear. After strengthening the bridge, these potential safety hazards can be effectively eliminated and the passing capacity of the bridge can be improved. In addition, the maintenance and reinforcement of bridges can promote the sustainable development of bridges, improve the effective utilization of resources and coordinate the development of economy, society and environment.
Bridge reinforcement technology can save a lot of reconstruction costs, and the maintenance and reinforcement of the bridge will not affect the bearing capacity of the bridge, prolong the service life of the bridge and receive good economic and social benefits.
Because the bridge is built in the natural environment, it is bound to be affected by some natural environment. Under the influence of these environments, any bridge will become an old bridge and some inevitable diseases will appear. According to the construction level at that time, there were some technical limitations in the deployment and use of materials, which led to some technical problems such as unstable bridge structure. Therefore, it is very important to maintain and strengthen these bridges.
Three. Technical measures for strengthening highway bridges
1, new reinforcement technology
In this respect, the new reinforcement technologies mainly include external prestressing reinforcement and high-strength composite fiber prestressing reinforcement technology.
External prestress reinforcement technology: This reinforcement technology is to install prestressed materials on the lower edge of the bridge, and generate eccentric prestress on the bridge by pulling up the prestressed materials, thus reducing the deformation and crack width of the bridge due to its own weight and some external forces, and improving the structural bearing capacity of the bridge. This reinforcement technology is widely used in long-span prestressed concrete. The characteristics of this reinforcement technology are as follows: firstly, steel bars can be designed to be irreplaceable or irreplaceable. Replaceable steel bars are more convenient for maintenance. Secondly, this kind of reinforcement technology is simple to operate, which saves the engineering quantity for ordinary reinforcement technology and is of great significance. Thirdly, the utilization rate of external prestressed steel bars is relatively high, and the system layout is flexible, which can not only strengthen the joints of the bridge, but also strengthen the arch frame of the bridge, which not only strengthens the integrity of the bridge but also optimizes the shear performance of the components. Therefore, this new reinforcement technology has a good application prospect. However, when this new technology is used to strengthen the bridge, reasonable calculation should be made first, and some corresponding measures should be taken in the construction process to minimize the loss of prestress.
Prestressed reinforcement technology of high-strength composite fiber: the high-strength composite fiber material is mainly carbon fiber material, and this reinforcement technology is relatively mature. Its principle is to use high-performance adhesive to stick carbon fiber on the surface of bridge structure, and the two work together to strengthen the bridge and improve its bearing capacity. The performance of adhesive and carbon fiber is the key to strengthening bridges. Therefore, in order to achieve the effect of strengthening bridges, it is necessary to apply prestress to carbon fiber materials. The characteristics of this reinforcement technology are as follows: First, high-performance composite fiber materials have the characteristics of high strength and high elasticity, which can effectively improve the bearing capacity of concrete structures. Secondly, when the temperature changes, the high-performance carbon fiber material can cooperate with concrete, and because the thickness of the high-performance composite fiber material is very thin, it will not increase the weight and volume of the bridge components after repair, and will not destroy the original structure of the bridge, so it has good corrosion resistance, durability and fatigue resistance. However, due to the material, when the temperature is higher than 60 degrees Celsius, the material will soften. Considering that the existing bridge is exposed to the air and the sunlight is direct, it is easy to be higher than 60 degrees Celsius, which is not conducive to the use of resin glue as adhesive.
2. Traditional reinforcement technology
(1) Bridge deck pavement reinforcement technology: 1. Bridge deck reinforcement. The principle of this method is to lay a layer of concrete on the basis of the original bridge deck. This method can not only effectively repair the cracks on the bridge deck, but also increase the effective height of the bridge deck and improve the bending moment resistance of the bridge deck under the action of gravity, thus improving the bearing capacity of the bridge. Secondly, the original bridge deck is demolished and the concrete bridge deck is re-paved. This method is suitable for bridges with serious bridge deck damage and poor concrete pouring quality or construction quality. Thirdly, a certain amount of excavation is carried out on the bridge deck to expose some reinforced aggregates, and then the bridge deck is wetted, and a layer of cement concrete is laid on this basis.
(2) Strengthening technology by increasing the cross-section of the bridge: This technology is to strengthen the bridge by increasing the cross-section area of the bridge. To increase the cross-sectional area of a bridge, two methods are generally adopted: thickening the bridge deck and increasing the height and width of the main girder ribs. This reinforcement technology has the characteristics of strong adaptability and simple construction, and the design of this reinforcement technology is mature and the construction experience is more. The bridge reinforced by this method can receive better results. However, this method takes a long time to construct.
(3) Bridge substructure reinforcement technology: For some high abutments, on the one hand, it is affected by vehicle load, on the other hand, it is affected by the natural environment, and there are usually some diseases such as cracking and dislocation. For some stone arch bridges with small span and small water flow, reinforced concrete frames can be used to strengthen them.
(4) Crack grouting technology: When there is a big crack in the highway bridge, it will cause serious harm to the bearing capacity and structure of the bridge. This kind of crack should be observed and recorded, and the causes of the crack should be analyzed so as to formulate some methods accordingly. For the treatment of cracks, grouting glue is generally used for treatment.
(5) Other reinforcement methods: such as paving a layer of asphalt concrete, repairing with steel fiber concrete and paving with polymer concrete.
Fourth, summary.
Strengthening highway bridges and ensuring the safe operation of highway traffic have attracted the attention of relevant departments. As a permanent subject, technicians should fully learn knowledge, further improve the reinforcement technology of highway bridges, and formulate a reasonable treatment plan for each bridge. The expansion will bring greater social and economic benefits to the bridge. Make the construction of highway bridges in China embark on the road of sustainable development.
The detailed information of "Highway Bridge Construction Reinforcement Technology" can be found in Zhong Da Consulting and Design Link, and all the relevant building construction information you want is available. Yes In addition to finding faults and maintaining them in time, it is best to repair the rubber plate expansion joints once every six months.
The detailed information of "Treatment of Expansion Joint Diseases in He Liang" was consulted and constructed in Zhong Da, and all relevant construction information you want is available.
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