Rubber bearing refers to the supporting parts used to support the weight of vessels or equipment and fix them in a certain position, and also to bear the vibration and seismic load during operation.
Laminated rubber bearingBy multiple layersNatural rubberIt is embedded, bonded and vulcanized with at least two layers of thin steel plates of the same thickness to form a bridge bearing product.
Chinese name
Rubber bearing
Foreign name
Rubber bearing
Introduction
Withstand vibration and seismic load during operation
This type of rubber bearing has sufficient vertical stiffness to bear vertical load, and can reliably transfer the pressure of superstructure to the pier and abutment;Have good flexibility to adaptBeam endEarth rotation;There is a relatively large shear deformation to meet the horizontal displacement of the superstructure;
Plate bearings are divided into rectangular and circular products according to their shapes.
According to whether it can provide horizontal displacement, it can be divided into: polytetrafluoroethylene sliding plate bearing and ordinary rubber bearing.
Rectangular (round) plate
(1) Performance: This product is made by inlaying multilayer rubber sheets and thin steel plates, bonding them to a certain pressure, temperature and time, and vulcanizing and pressing them.There is sufficient vertical stiffness to bear the vertical load, which can reliably transfer the reaction force of the beam slab superstructure to the pier and abutment, and has good elasticity to adapt to the rotation of the beam end;There is also a large shear deformation to meet the horizontal displacement of the upper beam structure.
(2) Features: This product has been widely used in bridge construction, hydropower engineering, and building seismic facilities. Compared with the original steel bearing, it has simple structure and convenient installation;Steel saving and low price;It has the advantages of simple maintenance, easy replacement, and low building height, which is beneficial to bridge design and cost reduction;It has good isolation effect and can reduce the impact of live load and seismic force on buildings.
PTFE sliding plate type
It is called tetrafluoro sliding plate bridge bearing for short. This product is bonded to ordinary plate rubber bearing with a layer of 2-3mm thickPTFE boardAnd become.In addition to the vertical stiffness and elastic deformation of ordinary plate rubber bearings, which can withstand vertical loads and adapt to the rotation of beam ends, the low friction coefficient (μ ≤ 0.03) between tetrafluoroethylene and the stainless steel plate at the bottom of the beam can make the horizontal displacement of the bridge superstructure unrestricted, and long-span bridges with a span>30 meters, simple supported beam continuous slab bridges and multi span continuous beam bridges can be used as movable bearings;Continuous beam pushing, T-beam transverse moving and large equipment sliding can be used as sliding blocks.
a: Check the installation of plate rubber bearingConstruction drawingsThe main technical parameters of the plate rubber bearing, such as specification, thickness, design bearing capacity, etc.Attention should also be paid to the rubber bearing of the PTFE sliding plateEmbeddedSize, installation position and direction of steel plate;
b: When the plate rubber bearing is selected, the maximum bearing capacity of the bearing shall be consistent with the reaction force of the bridge fulcrum, and the allowable deviation range should be ± 10%;
c: For curved, sloping, inclined and wide bridgesCircular plate rubber bearing。Rubber bearing with spherical crown or slope shape should not be used in highway bridge engineering;
d: When the longitudinal slope gradient of the bridge is not more than 1%, the plate rubber bearing can be directly set on the pier and abutment, but the thickness required by the longitudinal slope shall be considered.When the longitudinal slope gradient is greater than 1%, the beam bottom shall be leveled with embedded steel plates (with wedge-shaped steel plates), concrete cushion blocks (with gradient cushion stones) or other measures to ensure that the supports are flat.The plate rubber bearing shall be checked according to the relevant provisions of JTG D62 and can be used only after the checking meets the specified requirements.
e: GJZF4 and GYZF4 PTFE sliding plate rubber bearings shall be installed horizontally.The upper and lower steel plates shall be set. 5201-2 silicone grease lubricating oil shall be applied between the PTFE sliding plate and the stainless steel plate. After installation, the dust cover must be set;The PTFE sliding plate of the bearing shall not be set at the bottom of the bearing, and the stainless steel plate in contact with the PTFE sliding plate shall not be directly set on the bridge pier and abutment pad stone.
2. Installation
a: Installation preparation
a. 1 Bearing pad stone should be set at the installation place of plate rubber bearing. The plane size of the bearing pad stone should be determined according to the local pressure calculation. The length and width of the pad stone should be at least 50 mm more than the corresponding size of the bearing, and its height should be more than 100 mm, and it should be considered to facilitate the replacement of the bearing.
a. 2 Reinforcement mesh shall be arranged in the bearing pad stone. When the diameter of reinforcement is 8mm, the spacing should be 50mm × 50mm. There should be vertical reinforcement extending into the bearing pad stone in the bridge pier and abutmentConcrete strength gradeIt shall not be lower than C50.
a. 3 The surface of bearing pad stone shall be flat, clean, dry and free of floating sand.The elevation of the top surface of the bearing pad stone is required to be accurate.Under the condition of flat slope, the bearing pad stone at both ends of the same beam and the bearing pad stone on the same pier and abutment shall be in the same design elevation plane, and the relative height difference shall not exceed ± 1.5 mm, and the height difference of the same bearing pad stone shall be less than 0.5 mm.
b: Support installation
b. 1 After entering the site, check whether there is manufacturer's trademark or permanent mark on the bearing.During installation, the center line of the bearing position shall be marked on the bearing pad stone and the bearing according to the requirements of the design drawing to ensure the accurate positioning of the bearing.
b. 2 When installing the bearing, it is necessary to prevent the bearing from bias pressure or excessive initial shear deformation.After installation, it must be ensured that the bearing is in close contact with the upper and lower structures and there is no void.For beam and slab structures that do not form a whole, heavy vehicles shall be avoided.
b. 3 The design of bridge piers and abutments shall consider the needs of bearing maintenance and replacement.In any case, two or more supports are not allowed to be installed side by side at the same bearing point along the longitudinal centerline of the beam;On the same beam (slab), more than two supports should not be set horizontally;Supports of different specifications shall not be installed side by side.
b. 4 After the installation of the support, it is necessary to comprehensively check whether there is any omission of the support, whether there is any error in the direction and position of the support installation (contact with the embedded steel plate, the position of the support centerline), the specification and model of the support, whether the temporary fixed facilities are removed, and whether the tetrafluoroslide support is injected with silicone grease (it is strictly prohibited to use lubricating oil instead of silicone grease). Once found, it should be adjusted and handled in a timely manner,Ensure the normal operation of the support after installation, and record all deviations and abnormalities after installation of the support.
b. 5 Average compressive stress σ c=10MPa in the use stage of bearing.The volume of rubber elastomer of support Eb=2000MPa.
When the bearing contacts the concrete, the friction coefficient μ=0.3;When contacting with steel plate, the friction coefficient μ=0.2;The friction coefficient μ of the contact between the polytetrafluoroethylene plate and the stainless steel plate (when silicone grease is added) is less than or equal to 0.03. When the temperature is lower than - 25 ℃, the μ f value increases by 30%. When the sliding plate support must be installed, silicone grease is added to the surface of the PTFE plate.
b. 6 The rectangular bearing shall be installed along the bridge with the short side size.
(1) . Plate rubber bearings shall be maintained and repaired regularly. Once problems are found, they shall be repaired or replaced in a timely manner.
(2) The following contents shall be checked for plate rubber bearing and PTFE sliding plate rubber bearing:
a: Whether the bearing slips or is disengaged;
b: Whether the shear displacement of the bearing is too large (the shear angle shall not be greater than 35 °);
c: Whether the bearing has excessive compression deformation;(The maximum compression deformation shall not exceed 0.07te, and te is the total thickness of the rubber layer of the bearing)
d: Whether the rubber protective layer of the bearing has cracking, hardening and other aging phenomena, and record the crack location, crack width and length;
e: Whether the rubber plate protrusion between each layer of stiffening steel plate of the bearing is uniform and normal;
f: For the rubber bearing of the PTFE sliding plate, check whether the layer of PTFE sliding plate above the bearing is intact, whether there is peeling, whether the bearing slides out of the stainless steel plate on the top of the bearing, and whether 5201-2 silicone grease is coated and filled with the oil storage pit of the rubber bearing of the PTFE sliding plate.
(3) All parts of the support shall be kept intact and clean.The garbage and sundries around the bearing shall be removed in time, and the snow and ice shall be removed in winter to ensure the normal operation of the bearing.At the same time, the sewage shall be cleaned frequently to drain the accumulated water on the pier, abutment and abutment cap. The rubber bearing shall be prevented from contacting grease. The residual oil on the beam bottom, pier and abutment cap shall be cleaned.Prevent rubber from aging and deterioration.
2.4.4 Adjustment shall be made when the bearing of beam fulcrum is uneven, and the support is empty or has excessive compression deformation.
2.4.5 The plate rubber bearing shall be replaced in time in case of excessive shear deformation, aging, cracking, etc
2.4.6 For the rubber bearing of the tetrafluoro sliding plate, if it is found to enter sediment or silicone grease dries up between the contact surface of the tetrafluoro sliding plate and the stainless steel plate, it shall be cleaned in time and new silicone grease shall be injected.
Pot bearing
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Structural features
Pot type rubber bearing
The structural principle of pot type rubber bearing is that the rubber block placed in the sealed steel pot can bear the vertical load of the bridge with the reaction force generated under the three-way stress. At the same time, the elasticity of the rubber can meet the rotation of the beam end, and the horizontal displacement of the bridge superstructure can be completed through the free sliding of the stainless steel plate welded on the upper seat plate and the polytetrafluoroethylene.This series of products has reasonable structure, large bearing capacity, small deformation, large horizontal displacement, flexible rotation, and good buffer performance. It is the best support for building continuous bridges, and has the advantages of light weight, compact structure, simple structure, low building height, convenient processing and manufacturing, steel saving, and cost reduction,It is an ideal bearing suitable for large span bridges.GPZ, GPZ (Ⅱ) and GPZ (KZ) are commonly used.The bearing capacity of GPZ (II) series bearings is 31 levels, with a bearing capacity of 0.8MN-60MN, which can meet the needs of large bridge construction.
In the GPZ (II) standard series, the horizontal bearing capacity of fixed bearings in all directions and the non slip direction of one-way movable bearings is not less than 10% of the rigid bearing capacity of bearings.The horizontal bearing capacity of seismic bearing shall not be less than 20% of the vertical bearing capacity of bearing.The rotation angle of support is not less than 0.02 rad
After 5201 silicone grease is added for lubrication, the minimum design friction coefficient of normal temperature movable bearing is 0.03;After lubricating with 5201 silicone grease, the minimum design friction coefficient of cold resistant movable bearing is 0.06.
Bearing classification
Pot rubber bearings can be divided into three categories according to the scope of application: pot rubber bearings for highway bridgesPot type rubber bearing for railway bridgeAnd derivatives of pot rubber bearings.Commonly used highway pot rubber bearings include GPZ pot rubber bearings, GPZ (Ⅱ) pot rubber bearings (according to GT391-1999), GPZ (KZ) pot rubber bearings and other series.Commonly used railway pot rubber bearings include TPZ-I railway pot rubber bearings, TPZ standard railway pot rubber bearings, and special bridge 8156 railway bridge bearings.There are many derivatives of pot rubber bearings, such as QPZ pot rubber bearings, KPZ series pot rubber bearings, elastic shock absorption spherical steel bearings, self elevating pot rubber bearings, etc.
Each type can be divided into fixed (GD), one-way (DX) and two-way (SX) activities according to the displacement form.
3. Installation
1. Install the anchor column at the four corners of the support base plate.
2. Pour the bearing buttress, and reserve a height at the top, which is larger than the anchor column of the bearing;
3. Lift the support above the pad stone and correct the plane position and height;
4. Placing pad stone concrete;
5. Install 4 anchor columns on the upper part of the support;
6. Install the cast-in-place beam formwork and bind the cast-in-place beam reinforcement;
7. Pouring beam concrete;
8. Remove the temporary connections on both sides of the support.
spherical bearing
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Structural characteristics
QZ series spherical bearings are composed of upper bearing plate, lower bearing plate, spherical platePTFE sliding plate(F4, spherical PTFE plate) and rubber retaining ring.It changes the rubber plate in the pot bearing to spherical PTFE plate, so it is named. Because the middle steel plate and bottom basin of QZ spherical bearing are also changed to spherical surface, the friction coefficient is reduced.The displacement is realized by the sliding between the upper support plate and the plane tetrafluoro plate.A guide groove or a guide ring is arranged on the upper support plate to restrict the one-way or multi-directional displacement of the support, and spherical one-way movable support and fixed support can be made.The sliding between the spherical plate and the spherical PTFE plate can meet the needs of the bearing angle.
advantage
QZ spherical bearing is characterized by reliable force transmission and flexible rotation. It not only has the characteristics of GPZ pot rubber bearing with large bearing capacity and large seat displacement, but also can better meet the needs of large corners. Compared with ordinary pot bearings, it has the following advantages:
1. The spherical rubber bearing transmits force through the spherical surface, so there is no force necking phenomenon, and the reaction force acting on the concrete is relatively uniform;
2. The spherical bearing realizes the rotation process of the bearing by sliding the spherical polytetrafluoroethylene plate. The dynamic moment is small, and the rotation moment is only related to the spherical radius of the bearing and the friction coefficient of the polytetrafluoroethylene plate, and has nothing to do with the size of the bearing angle. It is especially suitable for the requirements of large angle. The design angle can reach 0.05 rad
3. The QZ spherical bearing has the same rotational performance in all directions and is suitable for wide and curved bridges;
4. This kind of bearing product does not need rubber to bear pressure, and there is no influence of rubber aging on bearing rotation performance. It is especially suitable for low temperature areas.
Installation details
(1) : When using this series of bearings, the concrete grade of the bridge beam body, pier and abutment supporting parts shall not be lower than 300.Special circumstances shall be approved by the design unit.
(2) : The support is connected with the beam body, pier and abutment by embedded bolts, or welded with embedded steel plates if necessary. However, when welding the support with the beam body, pier and abutment embedded steel plates, the steel body of the support should be prevented from overheating to avoid burning silicone grease and polytetrafluoroethylene plates.
(3) : The installation elevation of the bearing shall meet the design requirements, and the bearing surface of the bearing shall be horizontal and flat. The height difference of the four corners of the bearing surface of the bearing shall not be greater than 2mm.
(4) After the bearings enter the site, the packing list shall be checked, including the list of accessories, the bearing product certificate, and the detailed rules for the installation and maintenance of bearings.
(5) : Pay attention to the following items when installing the support:
A: The center line of the support shall be parallel to the center line of the main beam.
B: The center lines of the upper and lower bearing plates of the movable bearing along the bridge direction shall coincide, and the intersection angle shall not be greater than 5 °;rad。
C: The connecting plates of the upper and lower bearings shall not be loosened during the installation of the bearing to prevent the bearing from overturning due to excessive corner.The connecting plate shall be removed after the installation of the beam body to prevent the normal rotation of the constraint beam body.
D: After the upper and lower bearing connecting plates are removed, the rubber dust covers of SX and DX movable bearings shall be installed in time.
E：cast-in-place concreteAfter the beam is cast into a whole, the connecting plate shall be removed before the construction of beam prestress.
F: Before installing the coaming, the stainless steel sliding surface of the support shall be carefully wiped with cotton wire to prevent dust from invading the surface of the PTFE board.
G: One coat of paint shall be added to the part of the steel parts of the support where the paint is knocked off.
(6) : The bearing shall be inspected and maintained regularly every year during its use, including:
A: Check whether the anchor bolt of the support is sheared, and whether the rubber seal ring of the support is cracked or aged.
B: Check whether the relative displacement value of the support is even, and record the displacement value of the support one by one.
C: Remove the sundries and dust near the support, and carefully wipe the dust on the stainless steel surface with cotton wool.
D: Loosen the anchor bolt nut, clean and oil it at one time to prevent the nut from rusting, and then tighten it.
E: Check and fixed-point check the height change of the support, so as to check the friction of the PTFE plate in the support.When the support changes by more than 3mm, the rubber seal ring shall be removed and the condition of PTFE plate shall be checked.
F: The support steel parts shall be painted regularly for rust prevention (except for stainless steel sliding surface).
Manufacturing steps
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First, it is very necessary to provide drawings, because the drawings are the most accurate embodiment of the manufacturing steps. If there is no common type of plate bearing, please pay attention to the conversion of units when calculating the length, width and height or radius and height, pay attention to whether the displacement of basin bearing is fixed or movable, and remember not to drop the weight of anchor bolts when calculating.
Second, pay attention to the customer's needs, whether the customer wants the national standard or the general standard.The production process varies with different demands and quotations.
Whether the third party needs to be tested or not, many times there will be uncertainties as long as there is a third party involved in the test. If the customer wants to pass the test, he or she must pass the test through the relationship. Of course, we produce these bearings that are qualified in the factory test.
Fourth, try to provide the customer with some installation suggestions. If the customer is a long-term bridge builder, don't go overboard. If you don't understand what data you must tell the customer to consult to ensure the correctness of the installation, it must be rubber products. If the installation is incorrect, there will be a problem of bearing floating or extrusion affecting the normal load of the bearing,Then the quality and service life of the whole bridge are also worrying.
computing method
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Laminated rubber bearingIt is the most commonly used support, and of course the simplest one.Plate type rubber bearings are divided into rectangular and circular shapes, and of course there are other shapes, which are the most common.
The price of bearings is calculated according to the volume. For rectangular bearings, the price of the product is the length multiplied by the width multiplied by the height multiplied by the unit price. However, in the calculation process, we must pay attention to the conversion of units. Generally, customers tell us that all bearings are millimeters, which should be converted into centimeters. Of course, the price of bearings is also calculated in cubic centimeters. Let's take an example.
The price of 200 * 300 * 42 is 20 * 30 * 4.2 * unit price, which is the price of the product.
For the calculation of the price of circular bearings, the formula of the area of the circle multiplied by the height is π r ² * h. There is no example.
Of course, there are also plates with PTFE skateboards in the plate rubber. This calculation is the bottom area multiplied by (the height minus the thickness of the PTFE skateboard is generally 2~3mm, of course, there are special cases, here we will make a detailed calculation according to the construction requirements) multiplied by the unit price plus the price of the PTFE skateboard (the bottom area multiplied by the unit price).
The common code of plate rubber bearing is GYZ GJZ GYZF4 GJZF4.
Pot type rubber bearing is relatively simple. It is charged by weight. Of course, we have detailed specifications and weight introduction, which can be similar to that in the dictionary. Of course, don't forget to add the weight of bolts.
Support layout
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The layout of bridge bearings is mainly related to the structural form of the bridge.In general, the following basic principles need to be considered when arranging bearings:
(1) When the superstructure is a spatial structure, the bearing shall be able to adapt to the deformation of the bridge along the bridge direction (X direction) and across the bridge direction (Y direction) at the same time;
(2) The bearing must be able to reliably transmit vertical and horizontal reaction forces;
(3) The support shall make the longitudinal displacement, transverse displacement and longitudinal and constant rotation angle caused by the deformation of the beam as unconstrained as possible;
(4) The railway bridge must usually be equipped with a fixed support on each joint beam;
(5) When the bridge is located on the ramp, the fixed support shall be generally located on the abutment in the downhill direction;
(6) When the bridge is located on a flat slope, the fixed support should be set on the front abutment in the main driving direction;
(7) The fixed bearing should be set at the place with large bearing reaction force;
(8) Several bearings on the same pier shall have similar rotational stiffness;
(9) When the support of continuous beam may sink, the possibility of support height adjustment shall be considered.
In a word, the layout principle of bridge bearings is not only to facilitate the transfer of bearing reaction, but also to make the bearings fully adapt to the free deformation of the beam.
Usage rules
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The following is a brief introduction to the different use rules of rubber bearings for highway bridges:
(1) Plate rubber bearing
The working principle of the plate rubber bearing is to realize the vertical rotation of the beam with the elastic compression of the rubber, and to ensure the horizontal displacement of the beam with the shear deformation of the rubber block.Therefore, there is no difference between fixed bearing and movable bearing.Because its horizontal displacement is realized by the shear deformation of rubber, the allowable horizontal displacement is small, so it is suitable for highway, urban bridge and railway bridge with small and medium spans.Generally, plate rubber bearings can be used for bridges with standard spans less than 20m.Plate type rubber bearings can be divided into rectangular and circular ones. Circular plate type rubber bearings are mainly used for bridges with circular piers.The model and height of plate rubber bearing shall be determined according to the actual displacement and bearing reaction force.The plate rubber bearing shall be installed horizontally as far as possible. When it is necessary to install it obliquely, the maximum longitudinal slope shall be ≤ 2%.
(2) Teflon sliding plate support
Teflon sliding plate bearing is to stick a layer of polytetrafluoroethylene plate with the same plane size on the top surface of the plate rubber bearing, and set a stainless steel plate on the bottom surface of the beam for relative sliding movement.This is the use of PTFE and stainless steel relative motion between the friction coefficient is very small, so that it becomes a movable support.In addition to the advantages of plate rubber bearing, it can also meet the requirements of large horizontal displacement.Therefore, it is suitable for simple supported beams with large span, continuous beams and bridges with continuous deck.There are two types of PTFE sliding plate bearings: closed type and simple type.For urban bridges and areas with serious ultraviolet radiation, air pollution and dust, closed type shall be used, and simple type can be used for the rest.The model and height of PTFE sliding plate bearing shall be determined according to the actual displacement and bearing reaction force.The tetrafluororubber sliding plate support shall be installed horizontally as far as possible. When it is necessary to install it obliquely, the maximum longitudinal slope shall be ≤ 2%.
(3) Pot type rubber bearing
Pot type rubber bearing is to place a rubber block in a pot shaped base, use the characteristics of the rubber's fluid nature under three-phase stress to achieve a large corner, and realize the horizontal displacement of the beam through the low friction coefficient of the relative movement between the polytetrafluoroethylene plate and the stainless steel plate placed on the middle support steel plate.Pot type rubber bearings can meet the requirements of large bearing reaction, large horizontal displacement and large corner, and are suitable for bridges with large span and bearing reaction.
Quality factors
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1、Colloid of rubber usedThis is the main factor affecting the quality of plate type rubber bearings. Due to fierce market competition and severe price pressure from customers, many rubber bearing manufacturers have reduced their costs and used inferior rubber. From the appearance, we can see that good rubber has a shiny and dark surface. You can feel a little elasticity when pressing with your fingers. The rubber with poor quality has a black surface,No gloss.However, the real quality of the glue needs to be tested, and the quality problem cannot be found by simply judging from the compressive elastic modulus and shear elastic modulus. Generally, the problem can be found only by testing the intermediate adhesive film.
2、Internal steel plate: The steel plate is the guarantee of the bearing capacity of the plate rubber bearing, so the thickness of the steel plate must meet the standard, the material must be finished plate, no bending plate, etc., and the rust removal and sand blasting must be done in the treatment to ensure the bonding of rubber and steel plate.(Some defective manufacturers replace scrap iron sheet or replace thick steel plate with thin thickness, which leads to insufficient storage of product strength and easy to cause serious problems. In some places, it is required to detect the ultimate compressive strength in order to find the quality defect.)
3、Production process: The automatic production of the plate rubber bearing has not been completely realized yet. The steps before vulcanization are basically manual operations. The quality of the processes such as unloading, cutting and stacking is greatly related to the proficiency of workers.The curing time and temperature control on the curing press are also very important. The curing time of rubber bearings of different specifications is different. If the corresponding curing time is not reached, the sandwiches will be formed, and the rubber inside is not fully vulcanized, affecting the product quality.
Test items
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1. Compressive elastic modulus: test the designed elasticity of the product.
2. Shear modulus of elasticity: measure the horizontal deformation stress of the product (key item)
4. Shear bonding performance: detect whether there are defects in the bonding of steel plate and rubber inside the product (key item)
5. Shear aging resistance: to test the aging resistance of the product, this standard is of little significance because of the low test standard.
6. Allowable rotation angle performance: check the maximum allowable rotation of the beam body without void during rotation.
7. Friction coefficient: check the maximum friction force of PTFE sliding plate and stainless steel plate under the condition of silicone grease lubrication.
Development history
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Plate typeRubber bearingIt is a new type of bridge bearing.The utility model has the advantages of simple structure, easy processing and manufacturing, low sodium consumption, low cost, convenient installation, etc.It has been widely used in bridge engineering at home and abroad.
In China, plate rubber bearings have been developed and tested by Shanghai Rubber Products Research Institute, Shanghai Municipal Engineering Research Institute and Shanghai Municipal Design Institute since 1965, and have been successively used on some highway bridges in Guangdong, Shanghai, Shandong, Guangxi, Fujian, Jiangsu, Zhejiang and Anhui.The road bridge in Zhaoqing, Guangdong, was the first to use the plate rubber bearing in China, which has been used for 25 years.The plate rubber bearing has become a widely used and popular bearing form for highway and urban bridges in China.In 1988, the Technical Conditions for Plate Rubber Bearings of Highway Bridges (JT3132.288) was formulated, followed by the Ministry of Transport standards such as the Specification Series for Plate Rubber Bearings of Highway Bridges (JT3132.1-88) and the Inspection Rules for Mechanical Properties of Plate Rubber Bearings of Highway Bridges (JT3I32.3-90). In 1994, the Standard for Plate Rubber Bearings of Highway Bridges (JT/T4 -- 93) was revised and promulgatedLater, it was revised to (JT/T4-2004), which laid the foundation for the correct use of large area of plate rubber bearings.
On our railway bridge, the first trial of plate rubber bearing was on a 12m prestressed concrete pretensioned beam at the side span of Anhui Guzhen Bridge in 1969.Subsequently, due to the need to replace old beams and new projects, Taiyuan, Shanghai, Jinan, Shenyang and other railway bureaus have also adopted plate rubber bearings.In order to systematically study the mechanical properties of plate rubber bearings such as compression, shear, rotation, etc., from 1979 to 1981, the Academy of Sciences of the Ministry of Railways conducted a systematic experimental study on 160 rubber bearings with different specifications, different shape coefficients, and different rubber layer thicknesses, and passed the technical appraisal of the Ministry of Railways in September 1982.Various research parameters were included in the Code for Design of Railway Bridge Oil (TN2-85), and the Technical Conditions for Plate Rubber Bearings of Railway Bridges (TBl893-87) was formulated in 1987.The plate rubber bearing is mainly used on reinforced concrete, prestressed concrete and steel railway bridges with medium and small spans of 6-20m, and the maximum bearing reaction is about 2.2MN.
Plate type rubber bearings are widely used all over the world.As early as 1936, rubber bearings were used on a railway bridge in the suburb of Paris, France. After the Second World War, many countries, such as Britain, Germany, the United States, Japan, etc., successively used plate rubber bearings, but it was not until 1958 that they really accumulated extensive experience in use.In particular, French Frenchner put forward the method of setting reinforcement grids or steel plates in the rubber to restrict the lateral expansion of rubber, thus making the plate rubber bearing develop rapidly.
Replacement scheme
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1、 Analysis on the quality causes of rubber bearings
(1) The material of the bearing itself is uneven, and some bearings use recycled rubber.
(2) Some sliding bearings were not coated with silicone grease during installation, resulting in shear failure of sliding plate bearings.
(3) During the installation, the elevation of the support pad stone was not well controlled, the force on the four load-bearing bearings of the single beam was uneven, and some rubber bearings were disengaged, resulting in the deformation of the bearing with large force exceeding the specified value.
(4) The expansion joint of the structure is not completed, the traffic is not completely closed, and the brake of some heavy social vehicles causes large shear force on the bearing, resulting in damage.
2、 Replacement scheme
(1) Support foundation large tonnage jack is used to jack up the bridge span at one time
In order to facilitate the installation of the support and provide sufficient bearing capacity, a reinforced concrete foundation shall be set under the support.Since the support foundation is located in the river, the foundation is relatively weak, with low and uneven bearing capacity.The foundation placed on it will produce large uneven settlement.In order to reduce the settlement, the size of reinforced concrete foundation must be increased and the support must be preloaded.This scheme has large quantities, longer construction period, low safety and high cost.
(2) The super thin one-way jack pier top and dial indicator are used to support and jack up the bridge span to make full use of the space between the beam body and pier top. The super thin one-way jack pier top is used to support and jack up the bridge span with a height of 70mm,The Φ=300mm round flat oil jack (the maximum lifting weight is 250t, the maximum stroke is 15mm) is equipped with an electric oil pump to lift the bridge span synchronously, and the rising speed of the beam body is observed with a dial indicator to ensure that the force on each beam body of the bridge span is uniform
In addition, there are high damping isolation rubber bearings, see the entry for details
