Mageba modulus bridge expansion joint
Modular bridge expansion joint
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 beam steel and sealing body according to the actual expansion capacity, which can be formed to meet the large displacement.
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 drive 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 the overall structural rigidity, good durability; ⑤ driving comfort.
However, due to the complicated structure of the expansion joint, repair and replacement require professional technicians from a wide range of manufacturers, and the high cost, it is generally only used for large bridges with high grade.
Comparison of types
Bridge expansion joint setting basis
The beam expansion is the most important basis for the selection of expansion joints.
Basic factors affecting expansion joint expansion capacity
- Temperature changes
Temperature variation is the main factor affecting the bridge expansion, which is divided into linear temperature variation and nonlinear temperature variation, with linear temperature variation playing a dominant role in the bridge expansion. The bridge structure is subjected to a specific external temperature environment, the internal temperature distribution of the beam is not uniform, and the angular dislocation of the beam end is caused by the change of thermal properties of the material. For small span bridges (l ≤ 8m), the coefficient of linear expansion is small and can be disregarded; for large span bridges, the design must be paid sufficient attention. The general design of the coefficient of linear expansion can be as follows
Temperature range and coefficient of linear expansion
- Shrinkage and creep of concrete
The shrinkage and creep of concrete is an inherent property of the concrete element itself, and also a random phenomenon. The concrete ratio, water-cement ratio, slump, cement variety, temperature, relative humidity, concrete loading age, load-bearing time and strength have great influence on the concrete shrinkage and creep. Both reinforced concrete bridges and prestressed concrete bridges need to consider their shrinkage and creep. Xu variant is obtained by multiplying the elastic deformation of the beam under prestressing by the creep factor ф=2; shrinkage is converted by the temperature drop of 20℃. In the installation of expansion joints, the shrinkage and creep have developed to a certain degree, the calculation should be based on the moment of installation, the concrete shrinkage and creep are discounted. The discount factor β can be selected from the following table.
- Longitudinal slope of bridge
Longitudinal slope bridge movable bearing is usually made horizontal, when the bearing displacement, expansion joints not only horizontal dislocation, but also vertical dislocation (δd), the value of which is equal to the horizontal displacement multiplied by the longitudinal slope tgθ.
- Dislocation of inclined and curved bridges
In the case of inclined and curved bridges, when the deflection in the direction of bearing displacement (δl) occurs, the deflection also occurs along and perpendicular to the bridge end line, i.e.: Δd = δl-sinα δs = δl-cosα where α —- inclination angle, δl —- expansion
- Various loads caused by the bridge forgiveness
Under the action of live load and constant load, the bridge undergoes angular dislocation at the end, causing vertical, horizontal and angular dislocation of the expansion joint, and if the beam is taller, vibration will also occur.
The effect of the earthquake on the dislocation of the expansion joint is complicated and difficult to grasp, which is usually not taken into account in the design, but when reliable data are available to calculate the sinking, slewing, horizontal movement and tilt of the bridge piers, the design should be taken into account.
Beam expansion calculation
A prestressed concrete girder bridge, girder length 40m, temperature range -4.c ~42.c, linear expansion coefficient α=10×10-6, shrinkage strain ε=20×10-5, creep factor φ=2.0, shrinkage and creep depreciation coefficient β=0.6, average axial stress of prestressed concrete σp=80kg/cm2, elastic modulus of concrete ec=3.4×105kg/cm2, installation temperature 20οc. 105kg/cm2; installation temperature 20οc.
Expansion joint diseases and maintenance
Forms of damage and analysis of causes
In the absence of overload, the recommended fatigue life of the expansion joint is 10~15 years.
- For the stuffed butted expansion joint, the service life can be judged as the end if the angle steel falls off, the concrete on both sides is broken, the concrete on the bridge abutment side is completely broken, the rubber belt is broken and the pit is deep.
- For the seamless expansion joint, the service life can be judged to be at an end if the jumping is obvious, the two sides of the concrete partly broken, broken severely, wrinkles.
- The service life of the embedded butted expansion joint can be judged as the end of service if the jumping is obvious and the bridge deck pavement is seriously damaged.
- For the plate rubber expansion joint, if the anchor bolt falls off, the rubber deforms and the concrete cracks, the service life of the joint can be judged as the end of service.
The main forms of damage of seamless expansion joints are: Obvious rutting and cracks on the surface of the elastic plastic body, the surface of the elastic plastic body to produce rubbing plate or local off, the local off or large pieces of aggregate spalling; or the bridge deck cracks at the joints with the bridge deck pavement and gradually crumbling, falling off; or the expansion device within the bridge deck pavement damage.
Analysis of the causes: The material performance of the elastomer filler itself, such as insufficient ability of the elastomer to absorb the deformation of the beam end, insufficient strength of the material, the quality of the binder does not meet the actual use requirements, the construction is not in accordance with the requirements of the manufacturer; the displacement of the bridge caused by the external temperature, load and other factors, the corner of the elastomer cracking and damage; the structure of the expansion joint itself, such as the span plate strength is insufficient.
The main forms of damage are: Rubber bulging hot days, winter off, local perforation leakage; anchoring area concrete cracks, fracture; bridge deck pavement broken, off.
Analysis of the cause of damage: It is difficult to achieve the ideal rubber strip installation; the main anchor, and the beam of the weak connection of embedded parts, combined with the pavement concrete thin, after pouring concrete surface layer more lack of tamping, density and strength have certain problems, resulting in both sides of the concrete is easy to break; anchor concrete and bridge deck pavement connection strength is insufficient, by the development of small cracks to local fracture, fall off.
Steel support type
The main forms of damage of this type of expansion joint are: Weld, due to the process problems of individual weld is not easy to weld, the whole steel plate falls off, the anchor is weak caused by the loosening; individual steel tooth plate fatigue fracture.
Analysis of the causes of damage: This type of expansion joint is easy to deformation in the process of processing, it is difficult to ensure that the tooth plate and the pad fit, once a gap occurs, the force is unfavorable to the connection parts, resulting in noise, tripping, and day and night operation, the tooth plate under repeated load, causing premature fatigue, fastening bolts loosening, and the card board rotation is exposed.
The main damage forms of this type of expansion joint are: Rubber plate stripping, embedded steel plate exposure, falling off, fracture, anchor bolts cut off the hole fly out, the two sides of the concrete cracking and breaking, the appearance of pits and grooves and other destructive phenomena.
Analysis of the causes of damage: The first is the structure itself (design reasons), such expansion devices, the principle is to use the shear deformation of the rubber between the upper and lower grooves to meet the expansion of the beam body. There is a steel plate embedded in the expansion body, which can bear the load across the gap of the beam end, and there are anchored steel plates on both sides, which are connected to the beam end by bolts, and installed in pieces per meter, so the integrity is poor. The horizontal friction resistance of the expansion joint is very high, which makes the anchoring system very demanding. Secondly, the quality of the product is poor, such as the rubber material, the material and reasonable arrangement of the stiffening steel plate, the bond strength between the steel plate and rubber, the temperature and humidity control during production and so on are all very strict, if there is a slight quality problem, the whole plate often breaks, delaminating, rubber layer wear, exposed steel plate, the anchor bolt shears the rubber plate flying out and so on. There is a direct relationship between the large differences in stiffness, etc.
The main damage of this type of expansion joint includes: Welded main beam members, shaking and noise; poor expansion uniformity; aging, falling off or jumping out of the sealing rubber belt, serious water leakage; cracks and grooves in the concrete on both sides of the device, partial breakage of the bridge deck pavement layer, poor anchoring system, partial or overall damage.
Firstly, the side beams and middle beams of this kind of expansion joint are mostly welded together with steel plates or beams, which makes it difficult to guarantee the welding quality; and the sealing rubber belt is fastened by the crimp (or clip) and screws, which makes the fasteners easy to rust and fracture, resulting in poor structural integrity, large welding workload, and poor welding technology, which makes it difficult to guarantee the welding quality and causes weld or failure. The rubber band falls off or even jumps out; secondly, there are both anchor boxes and more anchor bars in the notch of the installation of the expansion joint, including the main steel and the embedded anchor bars in the beam, which makes it difficult to pour concrete, and is prone to cavities, density is not easy to ensure, insufficient strength and other problems, which will lead to gaps, cracks, local pits and grooves in use, and if not treated in time, the anchor will appear. A serious problem with total destruction of parts.
- The expansion joint is too narrow disease analysis: Expansion joint construction and installation of the width is not appropriate. As a result of the insufficient compression amount reserved, the expansion joint is crushed, the internal stress increases, and the expansion joint body concrete is crushed, causing pavement damage such as potholes.
The width of the expansion joint has abnormal changes compared with the normal width reserved in the design.
- Expansion joint height difference disease analysis: Due to the bridge subsidence, installation errors, bearing bedding stone cracking and other reasons leading to one side of the bridge is lower than the road side, the formation of the bridge head to jump the car. The inspection of the bridge subsidence did not cause serious damage to the substructure. At the same time, the bridge head jumper and expansion joint damage of the two types of diseases are interrelated, the bridge head jumper causes a large impact load directly on the expansion joint near the expansion joint, resulting in expansion joint damage.
- Expansion joint blockage disease analysis: Due to the aggregation of debris such as sand and gravel, expansion joints are prone to lose the ability to free expansion and contraction, in the summer when the temperature rises, the main beam is not free to elongate, it is easy to produce thrust in the adjacent main beam or between the main beam and the bridge abutment, serious or even the top of the main beam or bridge deck back wall cracking.
- Expansion joint rubber strip damage disease analysis: In addition to aging, due to the above three expansion joint diseases, is likely to cause the expansion joint rubber strip cracking damage warping.
- Anchoring area damage disease analysis: Construction of the anchoring area after pouring concrete with insufficient strength, or maintenance is not in place. Or height difference with the bridge deck, resulting in jumping, coupled with the frequent role of overloaded vehicles resulting in damage. Easily cause the expansion joint steel structure part of the damage.
- Expansion joint water seepage: This is the rubber strip damage or anchorage area damage caused by associated diseases. Water seepage causes water erosion hazard is very large.
Direct hazards: Water seepage to the following parts cause the corresponding hazards.
(1). Pier (platform) bearing rubber aging cracking, corrosion of steel plate.
(2). Pier (platform) concrete, solid slab beam body erosion pitting, steel rust swelling.
(3). Water accumulation in the hollow slab beam cavity.
(4). Corrosion of beam ends of steel structure
Indirect hazards: Water erosion can spread to girders, joints, and damage upper load-bearing components. If the bridge deck pavement is permeable to water, it will aggravate the following diseases.
(5). Water leaking from hinge joints, severe hinge loss.
(6) hollow slab web cracks.
(7). Bridge veneer stress (small and medium hollow slab girder bridge more serious such damage).
Bridge expansion joint installation
Measuring→drawing line→cutting joints→breaking concrete and debris→plugging foam board between beam joints→maole expansion joint hanging in place→adjusting the plane position of maurer expansion joint→adjusting the height of maurer expansion joint→anchoring→unlocking→protecting→pouring concrete→wiping up the surface→opening traffic.
Example of maurer expansion joint:
- Cutting and grooving: The installation of expansion joint device should be carried out as far as possible after the pavement is installed, and the size of the notch meets the requirements of the installation of expansion joint device.
- Clean the notch: All dirt, dust and other unwanted things must be removed.
- Check whether the gap between the beams of the expansion joint device meets the requirements of the installation temperature, if not must be adjusted under the guidance of the factory engineers and technicians, so that the gap between the beams of the expansion joint device meets the design requirements, and then press the clamps, ready for installation.
- Take the two sides of the asphalt pavement as the elevation, place the expansion joint device in the slot, adjust the expansion joint device so that its top surface is the same as the pavement elevation, and its longitudinal and transverse slopes should be in accordance with the bridge pavement.
- Check the position of the expansion joint device, so that the expansion joint device in the direction of the vertical joints and along the direction of the location of the joints in line with the design requirements if the individual embedded rebar on the expansion joint device in the correct direction to prevent, can be cut with gas.
- Connect and weld the anchor reinforcement on one side of the expansion joint with the buried reinforcement in the reserved groove, one at a time, and then weld the anchor reinforcement on the other side according to the above steps. When the expansion joint device is confirmed fixed, the clamps can be removed, and then the remaining unwelded anchor reinforcement is completely welded to the embedded reinforcement, so that the expansion joint device is anchored reliably.
- If the expansion joint is installed in sections, the joints must be welded. The welded joints of the beams are already available in the manufacturing factory, and can be installed when the two adjacent joints are correct.
- Install the template at the beam end, and the template should be made according to the size of the expansion joint and the notch of the reserved slot, and the template should be made tight to prevent the mortar from flowing into the displacement control box or into the gap at the beam end.
- After checking that the installed formwork is tight and seamless, the reserved groove should be cleaned before pouring concrete (using steel fiber concrete) and tamping it down. The concrete should be at least of the same strength as the structural concrete, and the top surface of the expansion joint device should be kept clean when pouring concrete.
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