What is the expansion joint of a highway bridge? What does it do?

01expansion jointsSetting and function

The expansion joints of highway bridges are usually set in two positionsLiang Duanbetween the beam end and the abutment, or the hinge of the bridgeThe important function of this facility is to ensure the stable connection of the structure by adjusting the displacement of the superstructure caused by the vehicle load and the bridge building materials. However, once the telescopic device of a diagonal bridge is damaged, it will not only seriously affect the speed, comfort and safety of the vehicle, but may even cause serious traffic accidents, so its installation and maintenance are crucial.

02 Key points of abutment and beam end construction

In the construction of expansion joints at the end of the abutment and beam, the plane position and elevation of the steel bars need to be accurate, and the thickness of the protective layer of the outer steel bars must also be fully guaranteed. The embedded steel bars should be effectively connected with the structural steel bars of the beam body and the back wall to ensure the integrity of the structure. In addition, the size of the reserved groove at the beam end must also strictly meet the design requirements, especially when checking the design elevation of the back wall roof. Usually, the height of the top of the back wall in the design drawing of the abutment back wall will be set at the bottom of the pavement structure layer, so when constructing the back wall, sufficient expansion joint installation height should be reserved to ensure that the expansion joint can function normally.

During the construction of the abutment back wall, in order to ensure the smooth installation of expansion joints, we need to make appropriate adjustments to the design elevation of the back wall roof. Specifically, when the design height of the back wall roof to the pavement is 0.1 meters, we should reduce the construction elevation of the back wall roof by 0.1 meters to meet the installation height requirement of 0.2 meters. If this is not done, the super-high part of the back wall may need to be chiseled when installing expansion joints in the later stage, which will not only affect the construction progress, but also cause the expansion joint embedded steel bars to be damaged during the chiseling process, affecting the overall structural safety of the bridge.

03 Pavement treatment and grooving

inasphalt concrete After the construction of the bridge deck pavement is completed, the expansion joint construction is carried out. To ensure the smooth installation of expansion joints, sandbags are filled in the reserved grooves and paved with gravel and gravel mixture. After the construction of the pavement layer, it should be ensured that the height of the loose paving layer is slightly higher than that of the cement concrete bridge deck, about 2~3 cm higher, and then compacted.

After the asphalt concrete pavement is paved, the expansion joint grooving construction is carried out. In order to ensure construction safety, road traffic needs to be closed, and vehicles and pedestrians are strictly prohibited from entering the construction area. The slotting width should strictly follow the design requirements, and use the detection ruler to detect the subsidence of the asphalt pavement at the expansion joint after compaction or driving rolling, so as to accurately determine the slotting width and avoid being too wide. During the grooving process, use a cutting machine to cut the seam to ensure that the depth reaches the thickness of the asphalt concrete surface layer, and then use a small pneumatic hammer or electric pickaxe to chisel the asphalt concrete.

04 Expansion joint installation process

Before the installation of expansion joints, L-shaped, S-shaped, U-shaped and other connecting steel bars, reinforcement drilling equipment and reinforcement glue should be prepared. The position correction and reinforcement of the reserved steel bars are carried out. If the actual installation temperature of the expansion joint is very different from the factory when it is shipped, the assembly and positioning void value should be adjusted accordingly to ensure that the centerline of the expansion joint and the centerline of the beam seam coincide accurately. When installing, the height of the top surface of the expansion joint should be slightly lower than 2~3mm of the road surface, and a steel hanger should be used for positioning.

During the positioning process, use a 3m ruler and feeler gauge to detect and temporarily spot weld and fix at any time. Every 2~3 anchor bars, symmetrical welding of one welding point is carried out. The length of the connection and welding between the expansion joint steel bar and the embedded steel bar should not be less than 10cm, and spot welding, skipping welding or missing welding are strictly prohibited. After the welding is completed, the temporary fixing fixture and positioning section steel are cut off with an air cutting gun.

05 Concrete construction and maintenance

In the concrete construction process of expansion joints, we usuallySelectionC50 steel fiber concrete Before pouring, the debris in the joints must be thoroughly cleaned. If the gap between the sections is small, foam board can be used for blocking and isolation; if the gap is large, bamboo rubber board is used to seal the mold and isolate it to prevent slurry leakage and pollution of the road surface. During construction, attention should be paid to keeping the road surface clean and protective treatment with transparent tape and plastic film.

After the concrete construction is completed, it is necessary to plaster the surface several times before the initial setting to ensure that the top surface of the expansion joint concrete is not higher than the top surface of the asphalt concrete, and remove the cracks on the surface. After the initial setting, cover the geotextile and sprinkle water to moisten and cure for at least 7 days. The installation time of the sealing rubber belt is after the final setting of the expansion joint concrete, after the installation is completed, the construction site is cleaned and opened to traffic.