In order to meet the requirements of the bridge deck deformation, expansion joints are usually installed between the two beam ends, between the beam end and the bridge abutment or the articulated position of the bridge. The expansion joints are required in parallel and perpendicular to the bridge axis in both directions, free expansion and expansion, strong and reliable, and should be smooth and no sudden jump and noise when the vehicle is running through; to prevent the infiltration of rainwater and garbage and soil blocking; easy and convenient installation, inspection, maintenance and elimination of dirt. In the installation of expansion joints, the railings and bridge deck pavement should be disconnected.
Bridge expansion joints
The role of the bridge expansion joint: Is to adjust the vehicle load and bridge construction materials caused by the displacement of the superstructure between the connection. If the expansion joint of an inclined bridge is damaged, it will seriously affect the speed, comfort and safety of the traffic, and even cause traffic safety accidents.
Expansion joints function:
Ensure free expansion and contraction of the beam
Settle
Good water tightness and drainage
Easy to remove trench dirt
Bridge expansion joints are exposed to the atmosphere for a long time, the use of the environment is harsh, is the most vulnerable and difficult to repair the bridge structure. Damage to the bridge expansion joints may cause a large vehicle impact load, worsening traffic conditions, which will lead to jumping, noise, water leakage, affecting traffic safety and drastically reduce the service life of the bridge.
Hazards of missing or damaged expansion joint function:
Expansion and contraction is impeded, or the top of the pier is bad, or there is increased force in the beam.
Vehicle travels jumpy and unstable
Increased impact action, causing damage to bridges, especially at the end.
Water seepage endangers durability
Expansion joint type
The bridge expansion joints are gqf-c, gqf-z, gqf-e, gqf-f and gqf-mzl, all of which are hot-rolled shaped steel bridge expansion joints.
The gqf-c, gqf-z, gqf-l and gqf-f bridge expansion joints are suitable for bridges with expansion capacity below 80mm.
Gqf-mzl bridge expansion joint is a modulo bridge expansion joint composed of side beam, middle beam, cross beam and linkage, which is suitable for large and medium span bridges with expansion capacity of 80mm-1200mm.
The code representation is consistent with the prc traffic industry standard representation.
, gqf-c60, gqf-f80, gqf-mzl480, gqf-c60(nr), gqf-f80(cr) for example.
Gqf is the code of expansion joint device specified in the traffic industry standard.
Model code:-mzl indicates modulus type and straight beam linkage chain type:
(c, z, f, l,) denotes the shape of shaped steel.
The number indicates the movement of the expansion joint: 0-1200mm.
Nr and cr indicate rubber types: Nr indicates natural rubber, cr indicates neoprene rubber.
Types of expansion joints:
Seamless type: Concealed type (bridge deck continuous, tst)
Butt type: Plug and socket type (moller-like)
Steel support: (comb plate)
Combination type: Rubber plate type
Modulo: Maurerian
Seamless
Seamless expansion joint, when the joint structure does not extend out of the bridge deck, the expansion gap at the end of the bridge is filled with elastic material and paved with waterproof material, and then paved with visco-elastic composite material in the bridge deck pavement layer, so that the expansion joint at the bridge deck pavement and the road surface to form a continuum, with the deformation of asphalt concrete, elastic plastic and other materials at the joint to absorb the expansion of the beam, while providing support for the wheels of the structure. The common forms are mainly bridge deck continuous, tst gravel elastomer expansion joints.
The main features of this kind of expansion joint are: ① it can adapt to the expansion deformation of the upper structure of the bridge and a small amount of rotational deformation; ② the bridge deck pavement to form a continuum, driving without impact, vibration, driving comfort; ③ the expansion joint itself to form multiple waterproof structure, good waterproof; ④ in cold areas, easy to mechanized snow removal maintenance, not to damage the joints; ⑤ simple construction, easy to repair and replace . This type of expansion joint is usually constructed by cutting the pavement with a cutter after construction of the pavement (bridge deck) and injecting joint material into the groove, and is only suitable for small expansion areas (generally <40mm).
Seamless expansion joint bonding material installed in strict accordance with workmanship requirements has a lifespan of about twice that of a typical modified asphalt pavement.
Continuous expansion joints for bridge deck
Tst gravel and plastic expansion joint
Tst bonding material usually does not become brittle at -40°c and does not flow in the summer when the temperature reaches 80°c. It can be used throughout the country. It can be used normally throughout the country. Tst is a special high viscosity elastomeric plastic material, which is elastomeric at room temperature, and can be hot-filled with gravel after melting at high temperature, and can be shaped like asphalt concrete after shaping, which can bear vehicle load and has elasticity, and can replace the function of small expansion joints. The construction is convenient and can be opened to traffic after the pavement is cooled down. When the expansion joint needs to be replaced, it can be constructed halfway. No interruption of traffic in busy traffic sections.
Tst seamless expansion joints construction process
- Grooving: According to the width of the notch determined by the design requirements, sample, cut slit, remove the removed pavement material and clean the notch.
- Reinforcement planting: In the distance of 5cm from the edge of the notch, every 25cm interval across the bridge is typed into an expansion bolt, the height is up to 1/2 depth of the notch, and a 12 steel bar is welded on the inner nut of the bolt in the direction of the seam.
- Fill the sponge: Clean the notch with high-pressure water, then bake the surface with flame and dry the notch. Fill the sponge tape in the gap between the adjacent beam ends as much as possible, leaving no gaps.
- Brush the tst adhesive evenly on the exposed surface of the notch, wait for 15 min, pour the melted tst, and smear it evenly on the bottom and side of the notch with a scraper with a thickness of 1~2 mnl. Then place the span joint steel plate, fix it with locating nails, and pay attention to the alignment.
- Start from one end of the slot, put in a large stone that has been fired (130-150℃), the thickness of which should be such that the bottom layer of tst can be seen. Then pour in the tst and flood the stone. Lay the layer by layer according to this.
- Pave the small fried stone, 10mm above the bridge deck, with a plate vibrator vibration, and then leveled with a scraper. Generally, to prevent sinking, it should be 1~2mm higher than the bridge deck, then it can be trimmed and leveled with a shovel.
- Pour enough tst, flooded stones, then to prevent the tst flow to both sides of the bridge deck. Wooden boards can be used on both sides of the slot to keep the edges neat.
- Trim the edges, remove the baffles on both sides, cool for 1 to 2h and open to traffic.
Docking
The stuffed butted expansion joint is an expansion joint that uses the elasticity of the expansion body to bear the wheel load. The expansion body is made of sand, gravel, rubber products of various shapes, or foam board or synthetic resin material, and the expansion body is always in compression. The u-shaped galvanized iron expansion joint is widely used in the 1970s and 1980s as a kind of plug and joint expansion joint.
The main features of this type of expansion joint are: ① low cost; ② the required materials are easy to process; ③ simple construction; this type is generally suitable for the expansion capacity of 40mm bridge, due to poor durability, waterproof, short service life, has been rarely used.
The structure principle is that the rubber products with different shapes are embedded with different shapes of steel components, and then the anchoring system anchors them to the beam or bridge back wall at the joints, and the support for the wheels is provided by the profiled steel, and the rubber strip and rubber belt are used to absorb the deformation of the beam end. It can also be in the tensile state. This is a widely used expansion joint in the domestic highway and bridge construction, the common ones are w type, sw type, m type, pg type and so on.
This kind of expansion joint is suitable for the bridge structure whose expansion capacity is less than 80mm, i.e. The joint width is 20mm and 80mm.
The main features of this type of expansion joint are: ① simple structure, clear force and low cost; ② the main components of the expansion joint are processed by the manufacturer and installed at the construction site, the connection with the beam end is usually welded by steel, so the structure is reliable and the construction quality is easy to ensure; ③ good durability; ④ good anti-drainage performance; ⑤ good driving comfort.
The two design principles of maurer expansion joint are “Rigid anchorage” And “Sealing and waterproofing”.
- The anchoring of the rigid anchor expansion joint directly affects the life of the expansion joint. The anchoring metal plate mainly plays the role of force transmission. After fatigue test, the anchoring device is welded directly to the side beam. At the same time, the side beams are rigidly connected to the bridge superstructure to ensure that the expansion joints carry the maximum traffic load. In the case of long-term dynamic traffic loads, other methods of connecting the expansion joints with screws or bolts to the bridge superstructure are not feasible. Maurer expansion joints are designed one step ahead in this respect by separating the load-bearing and waterproofing functions, which is more conducive to the strengthening and improvement of both functions.
(2). Complete waterproofing
One of the features of the maurer expansion joints is that the neoprene seals are effectively embedded in the grooves of the side beams, ensuring complete waterproofing. At the same time, they can be replaced on the bridge deck with a simple tool or repaired by vulcanization. Protected by the side girders, the seal is not subjected to direct rolling by the wheels, and its “V” Structure removes sediment on its own. The seal is both tensile and capable of lateral and vertical movement. In contrast, a leaky expansion joint will cause some damage to the bridge structure.
Steel bearing type
The steel-bearing expansion joint is a structure made of steel assembled to directly support the wheel load. This expansion joint was previously used for steel bridges, but now concrete bridges are also used. The steel bearing expansion joint types, status, size, the more widely used is mainly steel comb type. The construction of the steel comb type bridge expansion joint is composed of comb plate, joints and anchoring system, some steel comb type bridge expansion joint, filled with synthetic rubber between the comb teeth for waterproofing, there are also special drainage tank to solve the drainage problem. The steel comb type bridge expansion joint, also known as steel plate finger joint, is divided into bearing and cantilever type according to the supporting condition of the comb.
The main features of this type of expansion joint are.
- All components are made of steel with high structural strength.
- It can provide continuous support for the wheels and good driving comfort.
- The connection with the beam is made of pre-buried steel members, which is reliable.
- High impact and vibration resistance, good durability.
- Can be adapted to large horizontal deflections and can be used for large bridges.
Such expansion joints are suitable for bridges with expansion capacity greater than 40mm, but the application range is not very wide due to its high cost.
Comb tooth plate expansion joint
Rubber sheet
The rubber plate expansion joint takes full advantage of the low shear modulus of the rubber material, with load-bearing and anchoring steel plates and bolt holes in the rubber body, and is connected to the beam end by bolts. This structure relies on the shear deformation of the rubber body between the upper and lower grooves to absorb the expansion and displacement of the beam, and the steel plate embedded in the rubber body spans the gap between the beam ends to bear the wheel load. This device is used earlier in china, and there are more manufacturers in the country, with different names, mainly used in the 80s and 90s of the last century. The rubber plate expansion joint has the advantages of simple structure, easy installation and economic application. It is mainly suitable for highway bridges with the expansion capacity of 30mm and 60mm, which is more widely used in china.
This kind of expansion joint has the following performance characteristics: ① it relies on the shear deformation of the rubber body between the upper and lower two steel plates to meet the deformation of the structure, after the deformation of the device, there is a certain deformation energy in the rubber body, there will be a certain constraint on the structure; ② the load-bearing span steel plate is buried in the rubber body, compared with the steel expansion joint, it has a certain buffering effect on the impact of the wheels. It effectively protects the expansion device and the beam and improves the driving conditions; (3) the angle steel of the expansion device effectively strengthens the end strength of the beam. The horizontal deformation of the rubber plate expansion joint has a large internal force, generally about 30-35nk per linear meter, the larger the deformation, the larger the horizontal force, the greater the possibility of the overall destruction of the device.
Therefore, when selecting the rubber plate expansion joint, the deformation affluence should not be less than 30mm to ensure the normal use of the joint.
Rubber plate expansion joint
Modulo
Modular bridge expansion joint is composed of longitudinal beam (profiled steel), cross beam, displacement control box, rubber sealing belt and other components of the expansion joint. The rubber sealing strip (belt) with v section or other cross-sectional shape is embedded in the side beam and middle beam to form a retractable sealing body, the profiled steel directly bears the wheel load and transmits the load to the cross beam, which transmits the load to the beam body and bridge abutment; the displacement control box ensures the clearance between the profiled steel remains even when the deformation of the beam end is absorbed by the expansion device; the rubber sealing belt prevents the entry of debris and waterproofs. The modulus expansion joint can be used to increase the number of middle beam steel and sealing body according to the actual expansion requirement, which can form the expansion joint to meet the large movement. From 8omm single seam to 12oomm multi-seam, there are 15 levels.
The main features of this kind of expansion joint are: ① the whole expansion joint is composed of shaped steel longitudinal beam, steel crossbeam, control transmission mechanism, displacement box, sealing rubber strip and other components, with a complex structure; ② good sealing performance, good anti-drainage performance; ③ applicable to bridges with large expansion requirements; ④ higher overall structural rigidity and durability; ⑤ better driving comfort.
However, due to the complex structure of the expansion joint, maintenance and replacement require professional technicians, and the high cost, it is generally only used for large bridges with high grade.
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