Although many factors affecting the expansion amount are fully considered in the design and calculation, bridge expansion joints are mainly located in weak structural parts such as beam ends, which not only bear the repeated impact of wheel loads directly, but also are exposed to nature for a long time, and the use environment is relatively harsh, which easily leads to the damage of expansion joints and bridge deck and beam slab. Moreover, this position is often the most difficult part of the bridge structure to repair. Generally speaking, the bridge joint is a discontinuous line on the bridge deck, and its stiffness is much lower than that of the concrete beams on both sides. In the process of driving, it will be severely impacted, which is directly proportional to the product of vehicle mass and driving speed. Therefore, when heavy vehicles are driving at high speed, the damage to bridge deck joints is particularly serious. Shock is accompanied by vibration. Due to construction and other reasons, bridge deck joints are often uneven. Under the repeated action of vehicle load, vehicle impact force and beam-slab vibration are very serious, which accelerates the further damage of joints. The end of beam and slab produces vertical displacement under the action of vehicle load, so the bridge deck joint device needs to bear repeated vertical shear force; In addition, under the action of live load, the beam end will also produce angular displacement due to the bending of the beam body, which will make the joint bear repeated bending action and often lead to the failure of the joint because it can not stand the test of fatigue. In addition, bridge deck water seepage is also a major cause of bridge joints and components damage, especially in the northern region, because of the use of snow remover, bridge deck water is corrosive to some extent, and bridge deck water mainly penetrates through joints, thus causing corrosion and damage of steel guide beams, continuous bridge deck reinforcement, expansion joint beam ends, bearings and pier caps. Due to the damage of the bridge deck joints, not only will the car jump when it meets the joints when driving on the bridge, but also the driving comfort will be greatly reduced. At the same time, it will also lead to the damage of expansion joints, bearings and beams, and the durability of the structure will be reduced. Therefore, we have to invest a lot of manpower and financial resources for maintenance in the later period, which will also bring great interference and harm to the normal traffic on the road.
2. Improvement and preventive measures
(1) Improve and develop all kinds of high-efficiency expansion joints and bearing products. At present, the expansion joints on highway bridges generally cancel or improve the previous rubber plate expansion joints (some bridges on highways are still in use) and replace them with hairy joints with better performance, combined W or V expansion joints and comb expansion joints. TST expansion joints widely used in recent years are also reasonable in design, but their performance is unstable in cold areas in the north. In addition, the improved plate expansion joint has been tested in some provinces and cities, and the effect is also ideal. Paper test.
(2) Reduce the number of bridge deck joints as much as possible, increase the continuous length of bridge deck, use flexible piers to increase the continuity of bridge deck at pier top, and minimize the number of expansion joints, so that all intermediate fulcrums are completely continuous, and only expansion joints are set between beam end and abutment. Due to the influence of temperature horizontal force, the pier far away from the displacement zero point is more displaced than the pier near the displacement zero point, which often leads to cracking at the bottom of the pier. Therefore, the rubber bearing on the pier top far from the center line of the bridge can be changed into a skateboard bearing. The advantages of continuous bridge deck are that the number of expansion joints on bridge deck is reduced, the cost is economical, the maintenance cost of expansion joints is low, and the driving bridge deck is smooth.
(3) Adopt high-strength and corrosion-resistant concrete bridge superstructure, including high-grade concrete or steel fiber concrete for deck pavement, so as to improve its impact resistance and crack resistance. For bridge structures prone to salt water corrosion, a certain amount of active additives are added to concrete to improve and improve its corrosion resistance, thus improving the durability of the structure.
3. Strictly control the building installation process.
(1) Before kerfing, the smoothness of asphalt pavement must be tested. According to the actual flatness, consider whether to appropriately expand the width of the cutting surface (one side is required to be widened by at most 30cm). If the smoothness of the pavement still cannot meet the installation requirements of expansion joints after increasing the cutting width, it is required to rework the pavement here. After being qualified, determine the groove width according to the requirements of construction drawings, pay off accurately, cut the seam online with a cutting machine, saw the asphalt concrete pavement except the seam, and stick adhesive tape. Sawing seam should be neat and straight, and pay attention to cut through asphalt concrete pavement to avoid loosening asphalt concrete outside the seam when slotting.
(2) When slotting with a pneumatic pick, the depth should not be less than 12cm. After grooving, the concrete in the groove should be chiseled and all sundries should be removed to ensure the effective combination of new and old concrete. If it is found that the gap between beams does not meet the requirements (greater than or less than the specified range), measures should be taken to deal with it, and the embedded steel bars and anchor steel bars in the groove should be straightened and derusted. At the same time, for the original beam slab or abutment with insufficient embedded reinforcement, a sufficient number of expansion bolts should be added in time to ensure the installation quality of reinforcement. After grooving, vehicles are prohibited from passing, and construction workers and other personnel are prohibited from stepping on the edges on both sides of the groove, which will affect the quality of concrete construction.
(3) Before the telescopic device is installed, when the air temperature at the time of installation is quite different from that at the factory, the clearance value of assembly and positioning must be adjusted. The allowable error of telescopic positioning width is 2mm, and the error is required to be a unified symbol. It is forbidden for a seam to have both positive and negative errors at different positions.
(4) When installing, the telescopic device should coincide with the center line of the bridge and be placed symmetrically on the telescopic gap, so that the height of its top surface coincides with the deck pavement elevation (longitudinal slope and transverse slope), and then leveling. After the anchor bar on the telescopic device is positioned correctly, it should be welded firmly with the embedded steel bar on the beam, plate and abutment. Pay attention to the welding position and method when welding to prevent the deformation of the side beam and middle beam of the telescopic device. After the steel is positioned, the steel is reinforced by segmental spot welding to avoid overheating and deformation of the steel. It is suggested to weld the top surface first, then the side surface, and finally the bottom surface. Paper test.
(5) Before concrete pouring, the positioning anchor reinforcement and the surface reinforcement of the bridge deck must be installed up to standard, and the garbage in the tank should be washed clean with water for the second time. Paper test. In order to prevent the gap from blocking during pouring, the expansion gap should be filled with foam plastic. Install the necessary formwork, and pour concrete symmetrically in the reserved groove to prevent concrete from infiltrating into the displacement box, and it is not allowed to splash in the seam and surface of the sealing rubber belt. If this happens, it should be cleaned immediately. When pouring concrete, the slump should be controlled within 30mm, and it should be vibrated and compacted, so that it is flat and honeycomb-free, especially in some dead corners, and more attention should be paid to the vibrating compactness of concrete. After that, the concrete surface shall be leveled with a scraper, and the flatness shall be generally controlled within 2mm (not more than 2mm) below the road elevation, that is, between-2 and 0mm.
4. Strengthen the maintenance of expansion joints
Normal maintenance is an essential and important link to ensure the normal operation of expansion device, reduce damage, prolong service life and prevent bridge expansion joints from bumping. Therefore, the following work should be done during maintenance:
(1) Health preservation during construction. Before the initial setting of concrete, brush should be used to brush the hair. After the initial setting of concrete, it should be covered with sacks or geotextiles for water conservation in time, and the time should be more than 7d. At the same time, special personnel should be assigned to implement traffic control during the maintenance period. When the strength reaches 70%, the rubber sealing belt should be installed with special tools.
(2) Regularly clean up the road garbage such as silt and gravel accumulated in the sealing rubber belt to prevent the expansion device from being blocked, and regularly check whether the sealing rubber belt is damaged. If it is damaged, contact the manufacturer for replacement in time.
(3) Always check whether there is any damage or crack in the concrete at the joint between the beam end and the bridge deck pavement and in the groove area, and repair it in time once found, so as not to affect the anchorage strength between the telescopic device and the beam slab.
(4) The unevenness and flatness damage near the expansion joint shall be repaired in time.
In short, strictly controlling the construction and installation process of bridge expansion joints, strengthening the maintenance of expansion joints, focusing on prevention and taking effective preventive measures to ensure the quality of bridge expansion joints can prolong the service life of expansion joints and greatly improve the service quality of bridges.