The role of road bridge expansion joints and classification
- 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 Taiwan, 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 type), modulus bearing, butt joint and seamless expansion joints.
Construction technology of road bridge expansion joints
- Construction preparation
Before the construction, familiar with the relevant construction drawings and expansion joint installation operation procedures, check the flatness, straightness and seam clearance of the shaped side beams; according to the actual situation of the project must be equipped with sufficient mechanical equipment, small machines, and the gangplank must be of solid quality so that the passing construction vehicles can pass smoothly, and at the same time, complete and sufficient canvas, plastic sheet, plastic film and straw thatch for maintenance to prevent pollution of the road, to ensure the smooth construction.
- Cutting joints
According to the construction design drawings before the proofing, use 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 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 the supervisor to jointly check and accept to ensure the quality of the expansion joint.
(1). Before installing the expansion joint, check the anchorage width of the pre-embedded tendons of the expansion joint. Generally set at 50cm, the bridge is easy to adopt the width of the back wall, which strengthens the stability of the expansion joint device and facilitates the construction of the bridge deck; use a high-pressure water gun to clear the 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 the installation process, with the flatness controlled within 2mm and the straightness controlled within 3mm. The height difference between the top surface and the pavement is controlled within 2mm.
(2). The gantry hangers and 10*10 angles are used as positioning angles, the center line of the expansion joint coincides with the center line of the beam end, and the top surface of the expansion joint is lower than the elevation of asphalt concrete pavement (1~2mm). Before the temporary fixing and spacer welding is carried out, the elevation and straightness should be adjusted to meet the design requirements, and the welded joint should be welded every 2-3 anchorages from one side of the bridge width to the other according to the anchorages of the side beam and the reserved slot.
(3). After fixing, remeasure the elevation of the expansion joint to make sure there is no deformation and deviation, then weld the anchor bar and embedded bar on both sides at the same time, weld them all at once. When one side of the welding workload is large and long time, and the influence of temperature changes, can be in one side after welding, and then weld 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 jumping, according to the specifications of the steel flatness should be controlled within 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.
(4). Template installation, the template is generally foam board, fiber board, thin iron, etc., and the installation must be firm and tight, to ensure that no movement during 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 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, so that it is flush with the top surface of the expansion joint device.
Before the cement concrete first set, brush hair, covered with plastic sheeting, sacks, etc., sprinkled with water to keep the concrete surface moist, the maintenance period of not less than 7 days, the intervening period is strictly prohibited vehicle traffic, the strength of more than 50% of the design strength before the installation of rubber sealing strip.
the bridge expansion joints of diseases and control measures
Expansion joints are susceptible to damage under vehicle loads and various factors, such as cracking and breaking of the anchor concrete, jamming of expansion joints, deterioration of materials, damage to anchorages and rubber strip breakage.
The causes are
- Inadequate design, inadequate design quantities, improper selection and lack of clear provisions for filler such as post-cast concrete and pavement layer materials on both sides.
The expansion joint device itself is not sufficiently rigid and the anchors are not strong enough, resulting in varying degrees of damage under repeated loading.
- Improper construction methods, improper selection of materials, spacing not set according to design requirements, incorrect location of positioning angles, anchor steel welding is not firm. Or the location of the embedded reinforcement is not accurate, the strength of the filling concrete, curing time, adhesion and flatness fail to meet the design standards, and the prefabrication and installation of the beam plate does not meet the design requirements.
- High traffic flow, high speed, many heavy vehicles, and the impact of the wheels cause the expansion joint members to break, fall off, loosen, or even cause damage, seriously affecting traffic safety.
- Improper routine cleaning and maintenance in expansion joints.
Prevention and control measures
Reasonable choice of expansion joint device, to ensure the rigidity of the expansion joint and the strength quality of the anchor; the anchor of the expansion joint should be able to resist the influence of machinery, friction and collision, firm, reliable and durable, according to the specification to make the vehicle running smoothly, strengthen maintenance and regular inspection.
- Strengthen the quality control of raw materials
The length of expansion joints, shaped steel and rubber strips shall be in accordance with the design; the length of expansion joints shall be measured on site by the factory personnel and processed according to the actual length to eliminate the error between the design and the actual length and to facilitate the installation; the shaped steel shall be lightly loaded and lightly discharged during transportation and shall not be damaged or deformed; the pile shall be elevated with sleepers to avoid wind and rain. The steel can be used only after passing the inspection; the field ratio and the test results of raw materials and reinforcement can be used only after meeting the requirements.
- Strengthen the construction quality control of expansion joint
(1). Expansion joint device must be reported to the supervising engineer for inspection and acceptance before pouring concrete, the entire pouring of concrete should have a supervisory side station to see whether the pre-buried tendons and the main beam reinforcement connection is firm, and the beam and the two sides of the road elevation is smooth, the template is firm and tight, the template is clean, the slot is clean, in order to prevent concrete from entering the inner groove of the profile steel, the top of the profile steel sealed with tape, when all the processes after passing the inspection, and then concrete construction.
(2). If paving the road first and then install expansion joints, before paving the road, the gap must be cleared and filled with foam board, and then sand bags and grade sand bags to fill the slot. The elevation of filling is appropriate to control the asphalt will not contaminate the embedded steel reinforcement.
(3). Bridge expansion joints cut joints, clear the groove according to the width of the reserved groove with a cut joint machine to cut joints. When cutting the joints, pay attention to the intact notch, no gnawing edge image, and timely removal of asphalt concrete and filler in the slot, chiseled inner surface of the notch. During installation, check whether the embedded steel bar in the groove is cracked or broken, otherwise take remedial measures, ensure that the embedded steel bar and the anchor ring of the expansion gap are firmly welded, and repair the steel beam if deformation or inconsistent spacing is found. During installation, the center line of the expansion joint should coincide with the center line of the actual reserved joint, and slowly put into the groove, the deviation should not exceed the allowable design range, and adjusted according to the vertical and horizontal slope and elevation, the top surface of the steel beam should be 1-2mm lower than the adjacent asphalt concrete pavement, and should not exceed the elevation of the pavement.
(4). Attention should be paid to the standing mold, pouring concrete template seal, pay special attention to the expansion joints after pouring concrete maintenance.
Bridge expansion joint is an important part of the bridge project, the expansion joint installation quality is directly involved in the bridge life, as long as the above methods and requirements, to prevent, take effective preventive measures to ensure the quality of the bridge expansion joint, so that the vehicle comfortable and safe exercise.