The role and classification of highway bridge expansion joints
The role of bridge expansion joints
As the bridge is outdoors, under the action of dynamic load, temperature, concrete shrinkage and creep, the girders will be displaced, and excessive displacement will affect the driving comfort and safety.
In order to adjust the displacement and connection between the superstructure of the bridge, expansion joints are needed. However, improper design, poor installation quality, and lack of scientific and timely maintenance, the expansion joints will jump, which is a common and increasingly prominent disease in china.
Bridge expansion joints appear at the damage, sinking, wrong table, when the two vehicles through the bridge to produce beating impact, resulting in additional load, affecting the driving comfort, and in serious cases, produce safety accidents.
In order to eliminate the steps, jumping and other phenomena, china has adopted many proven methods, including the installation of bridge expansion joints is an extremely important project, the construction defects can not be ignored.
Bridge expansion joints are divided into the following five categories: Steel bearing, combined shear (plate), modulus bearing, butt joint and seamless expansion joints.
Construction technology of highway bridge expansion joints
Before the construction, familiar with the relevant construction drawings and expansion joints operation procedures, check the flatness, straightness and joints gap of the shaped side beams; according to the actual situation of the project, enough mechanical equipment and small machines must be equipped, and the gangway must be of solid quality so that the passing construction vehicles can pass smoothly, as well as the canvas, plastic sheeting, plastic film and straw that prevent pollution of the road, to ensure that the construction goes smoothly.
Before construction, according to the construction design drawings of proofing, use the cutting machine according to the seam, pay attention to the protection of the road outside the seam line, to prevent pollution, and to ensure that the cutting seam incision intact.
Use a pneumatic pick to open the groove, the concrete and debris in the groove should be cleaned, especially the debris in the clearance of the beam end, and straighten and straighten the embedded tendons in the groove, if the number of embedded tendons is found to be insufficient, should hit the expansion bolt to make up for the embedded steel, and ask the owner’s representative and supervisors to jointly check and accept to ensure the quality of the expansion joint.
Before installation of the expansion joint, check the anchorage width of the expansion joint pre-installed tendons. Generally 50 cm is appropriate, and the bridge abutment can easily adopt the width of the back wall, which enhances the stability of the expansion joint device and facilitates the construction of the bridge deck.
Use a high-pressure water gun to remove debris in the expansion joint groove and check whether it is clean, and check the flatness of the section steel, and check the straightness and flatness of the expansion joint section steel during installation, with the flatness controlled within 2mm, the straightness controlled within 2mm, and the height difference between the top surface and the pavement controlled within 2mm.
When installing and fixing, the center line of the expansion joint and the center line of the beam end should coincide, and the top surface of the expansion joint should be lower than the elevation of asphalt concrete pavement (1~2mm).
The elevation and straightness should be adjusted to meet the design requirements before the temporary fixing and spacer welding, and the welded joint should be welded from one side to the other side every 2-3 anchorages according to the anchorages of the side beams and the reserved grooves.
After fixing, the elevation of the expansion joint is measured again to make sure there is no deformation and deviation, then the anchor bar and embedded bar are welded on both sides at the same time. More wechat search highway maintenance network public number
When the unilateral welding workload is large and long time, and the influence of temperature changes, can be welded on one side, and then welded on the other side of the left, middle and right parts of the anchor, and at the same time on the other side of the anchor to be welded, pay attention to the distance between the welding point and the section steel, to ensure that the section steel is not deformed.
In order to prevent the phenomenon of skipping, according to the specifications of the steel flatness should be controlled in the range of 0-2mm, expansion joints after welding solid, to remove the temporary fixed clamps, positioning angles, etc., to make it free to expand and contract.
Formwork installation, the formwork generally adopts foam board, fiber board, thin iron, etc., and the installation must be firm and tight to ensure that there is no movement in the concrete tamping, to prevent mortar flow into the seam, affecting the use of expansion joints. In two measurements below the pavement elevation of 3mm steel reinforcement mesh.
Pouring of concrete
Before pouring, the two joints should be covered with plastic sheeting to avoid concrete pollution of the road. The slump of concrete should be <2cm, in order to reduce the water-cement ratio and improve the early strength, admixtures can be mixed to reduce the surface shrinkage of concrete, and after the concrete is vibrated and compacted, the cement slurry should be rubbed out with a trowel plate and smooth out in 4 to 5 times. Strictly control the flatness of the concrete surface to make it flush with the top surface of the expansion joint device.
In the cement concrete before the first set, brush hair, covered with plastic sheeting, sacks, etc., sprinkling of water for health, to always keep the surface of the concrete wet, health period of not less than 7 days, the intervening period is strictly prohibited vehicle traffic, the strength of the design strength of more than 50% before the installation of rubber sealing strip.