First, the bridge deck pavement
1. Bridge deck pavement is also called roadway pavement, or bridge deck protective layer. It is the direct part of the wheel. Its function is to prevent the vehicle tires from directly wearing the carriageway plate as a part of the main beam, to prevent the main beam from being eroded by rain, and to some extent, to disperse the concentrated load of the wheel weight.
Therefore, bridge deck pavement requires rutting resistance, driving comfort, sliding resistance, wear resistance, low temperature crack resistance, impermeability and good rigidity. Deck pavement occupies a considerable proportion in bridge dead load, especially for small-span bridges, and the quality of pavement should be reduced as much as possible.
2. The bridge deck should be provided with longitudinal and transverse slopes, so as to facilitate the rapid removal of rainwater and prevent or reduce rainwater from infiltrating into the road surface, thus protecting the bridge deck and prolonging the service life of the bridge.
The cross slope of bridge deck is usually set in two directions, and the cross slope can be taken or increased by 5% according to the cross slope of road. For asphalt or cement concrete pavement, parabolic cross slope is generally used for pavement, while straight slope is used for sidewalk.
3. Bridge deck pavement often adopts various types such as gravel, asphalt surface treatment, cement concrete and asphalt concrete pavement. Cement concrete and asphalt concrete pavement can meet various requirements and are widely used. In particular, asphalt concrete should be used for deck pavement of extra-large bridges and bridges on expressway and Class I highways.
Cement concrete pavement has good wear resistance and is suitable for heavy traffic, but the maintenance period is long and it is troublesome in the future. The strength grade of pavement concrete is not less than C40, and the pavement thickness is not less than 80mm. Good compactness is required when laying to avoid secondary molding. In order to make the pavement have sufficient strength and good integrity, the pavement should also be provided with bidirectional steel wire mesh with a diameter of not less than 8mm and a spacing of not more than 100 mm, and the cross-sectional area of the steel wire mesh along the bridge direction and across the bridge direction should be not less than 500mm? .
Asphalt concrete bridge deck pavement should be composed of adhesive layer, waterproof layer and asphalt surface layer. The thickness of asphalt concrete pavement of expressway and first-class highway is 70 ~ 80 mm, which can be increased to100 mm; When necessary; Secondary and secondary roads are 50 ~ 80mm. The asphalt pavement shall be treated according to the relevant provisions of specifications for design of highway asphalt pavement (JTJ0 14-97). Asphalt concrete pavement is light in weight and easy to maintain. It can be opened to traffic in a few hours after paving, which is comfortable to drive, but it is easy to age and deform and is greatly affected by temperature.
Second, the bridge deck waterproof and drainage system
1, waterproof layer
Waterproofing of bridge deck is mainly accomplished by setting waterproof layer. The function of waterproof layer is to collect rainwater that has penetrated the pavement in the drainage system for drainage. The bridge deck waterproof layer is set under the bridge deck pavement. According to the Bridge Code (JTG D6), the waterproof layer should be set on the bridge deck pavement, but its method and form should depend on the local climate, rainfall and bridge structure.
Waterproof materials with convenient construction, durability and stable quality should be adopted for the waterproof layer. At present, the waterproof layer commonly used in bridges has the following three types:
(1) Asphalt gluing, that is, paving a thin layer of asphalt or modified asphalt first, then paving a layer of sand, and then rolling repeatedly.
(2) Brush polymer coatings, such as polyurethane cement, epoxy resin, cationic emulsified asphalt, neoprene latex, etc.
(3) Laying asphalt or modified asphalt waterproofing membrane, and non-woven geotextile impregnated with asphalt, etc.
2. Drainage system
In order to quickly eliminate the accumulated water on the bridge deck and ensure the driving safety, the bridge deck should be equipped with a drainage system. The drainage system is mainly composed of longitudinal and transverse slopes of the bridge deck and a certain number of drainage pipes.
The setting of drainage pipe should be determined according to the design runoff calculation. Usually, when the longitudinal slope of the bridge deck is more than 2% and the length of the bridge is less than 50m, rainwater can generally flow to the bridge head and be discharged from the approach road, so there is no need to set up special drainage pipes on the bridge. At this time, in order to avoid rain washing the approach road foundation, water tanks can be set on both sides of the bridge head. When the longitudinal slope of the bridge deck is more than 2%, but the length of the bridge deck is more than 50 m, in order to prevent rainwater accumulation, a drainage pipe should be set every 12 ~ 15 m on the bridge deck. When the longitudinal slope of the bridge deck is less than 2%, it is generally appropriate to set a drainage pipe every 6 ~ 8m m. In addition, drainage pipes should be added in the upstream direction of bridge expansion joints, and drainage pipes should be set at the lowest point of concave curve and 3 ~ 5 m before and after.
The internal diameter of the drainage pipe is generally 100 ~ 150㎜, and the drainage pipe with a diameter of 150㎜ is generally used in expressway and first-class highways, with a spacing of 4 ~ 5m. Drainage pipes can be symmetrically arranged on both sides of the roadway or staggered.
The drainage pipes commonly used in beam bridges are arranged at the edge of the roadway, with the distance from the kerb of 0. 10 ~ 0.50 m, and the bridge deck water flows into the drainage pipes and is directly discharged downwards. The drainage pipe can also be arranged under the sidewalk, and the bridge deck water flows into the drainage hole through the water inlet hole arranged on the side of the kerb or sidewalk component. The lower end of the drainage pipe should extend to at least 0. 15 ~ 0.20 m below the bottom of the carriageway slab to prevent it from infiltrating into the bridge deck. The pipeline is closely combined with the waterproof layer, and the seepage on the waterproof layer can be discharged to the outside of the bridge through the drainage pipeline.
For small bridges without sidewalks, horizontal holes can be reserved directly on the seat belts or kerbs on both sides of the sidewalk, and the water can be discharged from the bridge with iron pipes or bamboo tubes, and the nozzle should extend out of the bridge for 20 ~ 30 ㎜ so as to drip water, but this practice is easy to block because of the slow slope of the holes.
For bridges crossing roads, railways and navigable rivers, as well as urban bridges, in order to ensure the traffic safety under the bridge and the needs of highway sanitation, a closed drainage system should be set up to collect rainwater flowing into the drainage pipe to the longitudinal drainage pipe, and then flow into the ground drainage facilities or rivers through the longitudinal drainage pipe located at the pier.
Third, the bridge expansion joint
The bridge expansion device is directly exposed to the atmosphere and bears the repeated actions of vehicles and people. Tiny defects and deficiencies will cause undesirable phenomena such as vehicle bumping, which will bear a huge impact and even affect the safety of the bridge structure itself and peers. It is the most easily damaged and difficult to repair part of the bridge structure.
1, bridge expansion joints shall meet the following requirements
(1) can meet the requirements of free expansion and contraction of bridges and ensure sufficient expansion and contraction;
(2) The telescopic device is firm and reliable, integrated with the bridge structure, impact-resistant and durable;
(3) The bridge deck is flat, with good driving performance, and vehicles should pass smoothly without sudden jump and noise;
(4) It has a safe waterproof and drainage structure to effectively prevent rainwater from infiltrating;
(5) It can effectively prevent garbage from infiltrating and blocking.
(6) simple structure, convenient construction and installation, and convenient maintenance, repair and replacement; (7) Economical and cheap;
2. Type of expansion joint
(1) u-shaped zinc-iron expansion joint
Generally used for small and medium-span bridges, its adaptive deformation is within 20 ~ 40 ㎜. In this kind of expansion joint, U-shaped zinc plate is used as cross joint material, and the zinc plate is divided into upper and lower layers. The bent part of the upper layer is cut into plum blossom eyes, and asbestos fiber cushion rope is arranged on it, and then asphalt glue is poured. The expansion and contraction of the bridge deck will deform the zinc sheet. The lower zinc-iron sheet can discharge rainwater outside the bridge along the transverse direction of the bridge.
The expansion joint structure of sidewalk usually spans a layer of U-shaped zinc-iron sheet and then is filled with asphalt.
(2)TST crushed stone elastic expansion joint
TST crushed stone elastic expansion joint is suitable for small and medium-span bridges with expansion joints not more than 50㎜. The elastic-plastic composite TST is heated and melted on site, and then poured into the cleaned and heated gravel to form the elastic expansion joint of TST gravel. Gravel is used to support vehicle load, and TST elastic-plastic body can meet the requirements of expansion and contraction at -25 ~+60℃.
TST elastic expansion joint is simple in structure, convenient and fast in construction, easy to maintain and replace, and usually can be opened to traffic in 2-3 hours after construction is completed. Because the elastic-plastic body of TST macadam forms a continuum with the front and rear bridge decks and pavement, the bridge deck is smooth and seamless, and it will not produce impact and vibration when driving, and it is comfortable and waterproof. The elastic-plastic body of TST crushed stone can be deformed in all directions, so this elastic expansion joint can also meet the expansion deformation of curved bridge, inclined bridge and inclined bridge, and can also be used for sidewalk expansion joints.
3. Steel plate expansion joint
Steel plate expansion joint is a kind of structure which uses steel as cross joint material and can bear wheel load directly.
There are many kinds of steel plate expansion joints with complex structures, which can adapt to a wide range of beam end deformation. It is a steel plate with a thickness of about 10㎜. One side of the steel plate is welded on the angle steel anchored in the pavement concrete, and the other side can slide freely along the opposite angle steel. The deformation of this expansion energy-saving adaptation is above 40 ~ 60 ㎜. However, because one side is fixed, when vehicles pass by, the structure will often be damaged by slapping, which greatly affects the service life of expansion joints. Therefore, the sliding steel plate can be fixed by means of the spiral spring device to eliminate the adverse flapping effect and reduce the impact of vehicle load.
4. Rubber expansion joint
Rubber expansion joints use rubber belts with various cross-sectional shapes as caulking materials. Rubber is widely used in bridge engineering at home and abroad because of its elasticity, easy adhesion, meeting deformation requirements, waterproof function and convenient construction and maintenance.
Rubber expansion joints can be divided into embedded butt joints and shear joints according to the different force transmission and rubber mechanism of rubber belts.
The embedded butt joint absorbs the deformation of the beam through the tensile and compressive deformation of the rubber belt. The cross section of the adhesive tape has many forms, such as 3-segment, 2-hole strip, M-shape, W-shape and so on. Usually, after the erection of the beam is completed, the angle steel is welded at the beam end, and then the rubber strip is forcibly embedded.
5 combined telescopic device
The composite expansion joint is made of rubber and steel plate or section steel, which can adapt to large deformation. This expansion joint is applied to extra-large bridges and bridges. The composite expansion joint has various forms and complex structure. The similarity of this telescopic device is that rubber sealing strips with V-shaped section or other cross-sectional shapes are embedded in the special-shaped steel beam and the middle steel beam to form a telescopic sealing body. The special-shaped steel beam directly bears the vehicle load, and its height should be determined according to the calculation, but it should not be less than 70㎜, and it should have a solid anchoring system. According to the needs of expansion, the number of intermediate steel beams and rubber sealing strips can be arbitrarily increased and processed and assembled into various expansion series products.
Four, sidewalks, railings, guardrails and lamp posts
1, sidewalks and seat belts
The width of the sidewalk is determined by the traffic flow of pedestrians, which can be 0.75m or 1.0m. When the required width is greater than1.0m, it will be increased by a multiple of 0.5m. ..
Seat belts can be made into prefabricated express mail or cast-in-place together with bridge deck pavement. There are two kinds of prefabricated safety belts: rectangular section and ribbed section, and rectangular section is more commonly used. The safety belt should be broken every 2.5~3.0m to avoid damage due to the stress on the main beam.
There are various structural forms of sidewalks, which can be divided into cast-in-place, prefabricated assembly, partial assembly and partial cast-in-place mixing according to different construction methods.
2, railings and lamp posts
The railing is a kind of safety protection measure on the bridge, which requires both durability and economy and beauty. The height of the railing is generally 0.8 ~ 1.2m, and the standard design is1.0m.: The railing spacing is generally 1.6 ~ 2.7m, and the standard design is 2.5m..
The design of railings should first meet the stress requirements of the structure, but also consider economy, convenient construction and labor-saving maintenance. The beauty of railings should be considered in highway bridges, urban bridges and important bridges in the suburbs. In the process of design and construction, it should also be noted that all railings near the expansion joints of the bridge deck should be free to deform.
3, guardrail
Rails and safety belts can be installed in extra large, large and medium bridges on the second, third and fourth grade highways, and safety guardrails combining railings and safety belts can also be used. Expressway and the bridges on the first-class highways must be provided with guardrails. The main function of the guardrail is to close both sides along the line to prevent people, animals and non-motor vehicles from breaking into expressway; Induce sight; Play the role of some delimiters, let the vehicles drive within the width of the road as much as possible, and give the driver a sense of security; At the same time, it also has the function of absorbing collision energy, forcing out-of-control vehicles to change direction and restore their original driving direction, and preventing them from rushing off the road or falling under the bridge.
The form selection of bridge guardrail should first meet the requirements of its anti-collision grade, so as to avoid runaway vehicles jumping out under the corresponding design conditions. At the same time, factors such as highway grade, characteristics of dangerous objects outside the bridge guardrail, aesthetics, economy and maintenance should be considered.
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