Professional Introduction to Laminated Elastomeric Bridge Bearings
- Definition and Core Functions
Laminated elastomeric bridge bearings are key load-transmitting and deformation-coordinating components between the superstructure and substructure of bridges. Fabricated by alternating lamination of rubber layers and stiffening steel plates, bonded via high-temperature vulcanization, they integrate three core functions: load transmission, displacement adaptation, and vibration buffering. Widely applied in highway, railway, municipal, and other bridge projects, they are one of the mainstream products in modern bridge bearing systems. Their design and performance directly affect the safety, serviceability, and durability of bridge structures.
- Structural Composition and Material Properties
(I) Structural Composition
Elastomeric Rubber Layers: The core elastic component of the bearing, responsible for deformation coordination and vibration absorption. Natural Rubber (NR) or Chloroprene Rubber (CR) is typically used; Nitrile Butadiene Rubber (NBR) or Ethylene Propylene Diene Monomer (EPDM) may be adopted for special environments.
Stiffening Steel Plates: Load-bearing skeletons embedded in rubber layers, primarily functioning to restrict lateral expansion of rubber under vertical loads, enhance the vertical load-bearing capacity of the bearing, and improve overall stiffness to prevent excessive deformation. The plates are usually made of Q235 steel, with surfaces treated by rust removal, galvanization, or anti-corrosion coating.
Protective Layers: Rubber layers (2-5mm thick) on the top, bottom, and sides of the bearing, designed to isolate moisture, ultraviolet radiation, and corrosive media in the environment, delay rubber aging, and extend the bearing’s service life.
Connection Structures: Pre-embedded steel plates or bolt holes are sometimes provided on the top and bottom surfaces of bearings to facilitate reliable connection with bridge girders and pier/abutment tops, ensuring effective load transmission.
(II) Key Material Indicators
Rubber layers: Shore hardness of 60±5 Shore A, tensile strength ≥15MPa, elongation at break ≥400%, post-aging performance retention rate ≥80% (under 70℃×168h conditions).
Stiffening steel plates: Thickness 3-10mm, yield strength ≥235MPa, adhesion strength with rubber ≥7MPa (per peel strength test).
III. Working Principle
(I) Load Transmission Mechanism
Under vertical loads, rubber layers undergo elastic deformation. Stiffening steel plates restrict the lateral expansion of rubber, enabling the bearing to achieve high vertical load-bearing capacity (ranging from tens of kN to thousands of kN per bearing) and uniformly transmit the superstructure load to the substructure piers and abutments.
(II) Deformation Adaptation Mechanism
Displacement Adaptation: Horizontal displacements of bridges caused by temperature changes, concrete shrinkage and creep, and live loads are accommodated through the shear deformation of rubber layers, which typically reaches 50%-100% of the total thickness of rubber layers.
Rotation Adaptation: End rotations of girders under loads are coordinated via local compression and tension of rubber layers, eliminating the need for additional rotating components and ensuring a simple and reliable structure.
(III) Vibration Buffering Mechanism
Vibration energy generated by dynamic loads such as vehicle impacts and seismic waves is absorbed and dissipated through the viscoelastic damping effect of rubber layers, reducing vibration transmission to the main bridge structure and lowering the risk of structural fatigue damage.
- Technical Classification and Selection Basis
(I) Main Classifications
By Rubber Type
Natural Rubber Laminated Bearings (NR Bearings): Excellent elasticity and low-temperature resistance (suitable for -40℃~60℃ environments), applicable to bridges in temperate and frigid regions.
Chloroprene Rubber Laminated Bearings (CR Bearings): Superior aging, ozone, and oil resistance (suitable for -30℃~60℃ environments), ideal for bridges in humid, coastal, and industrial pollution areas.
By Presence of Limit Devices
Ordinary Laminated Bearings: Only provide basic load transmission and deformation adaptation functions without additional limit structures, suitable for medium and short-span bridges with small displacements.
Laminated Bearings with Limits: Equipped with lateral stoppers, bolts, or other limit components to restrict excessive horizontal displacement, applicable to bridges in seismic zones or high-intensity vibration environments.
By Shape: Rectangular laminated bearings (for bridges with narrow girder ends) and circular laminated bearings (more uniform force distribution, suitable for long-span bridges).
(II) Core Selection Criteria
Load Parameters: Dead load, live load, and impact coefficient of the superstructure, determining the vertical load-bearing capacity of the bearing.
Deformation Parameters: Temperature displacement, shrinkage and creep displacement, and girder end rotation, defining the shear deformation and rotation capacity of the bearing.
Environmental Conditions: Temperature range, humidity, and corrosive media, guiding the selection of rubber material type and anti-corrosion measures.
Bridge Type: Differences in load characteristics between highway, railway, and municipal bridges influence the stiffness design of bearings.
- Design and Acceptance Standards
(I) Domestic Standards
Rubber Bearings for Highway Bridges (GB/T 20688.1~4-2007): Specifies material requirements, performance indices, test methods, and inspection rules for bearings.
Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts (JTG 3362-2018): Clarifies design and calculation requirements for bearings.
Rubber Bearings for Railway Bridges (TB/T 1893-2016): Specialized standard for railway bridge bearings.
(II) International Standards
European Standard: Rubber bearings for bridges (EN 1337-3:2005)
American Standard: Standard Specification for Elastomeric Bearings for Bridges (AASHTO M251-19)
- Installation and Maintenance Key Points
(I) Installation Requirements
Bearing pads on pier/abutment tops and girder bottoms must be flat, with elevation error ≤±2mm and plane flatness error ≤1mm/m.
Bearings shall be installed with their centers aligned with pad centers, with deviation ≤10mm. Upper and lower surfaces must be tightly attached to girders and pads without hollowing.
Installation temperature should be close to the design reference temperature to avoid pre-shear deformation of bearings due to temperature deviation.
(II) Maintenance Key Points
Regular Inspection: Conduct inspections every 6 months to 1 year, focusing on cracks, bulges, or aging of rubber layers, corrosion of steel plates, and loosening of connections.
Cleaning and Maintenance: Timely remove dust, debris, and standing water from bearing surfaces to prevent accumulation of corrosive media.
Replacement Criteria: Replace bearings if rubber layer cracks are ≥3mm deep or cover ≥20% of the area, or if vertical compression deformation exceeds 15% of the design value.
VII. Technical Development Trends
In recent years, the technical development of laminated elastomeric bridge bearings has focused on three directions: First, application of high-performance materials (e.g., modified rubber and nano-composite rubber) to enhance aging resistance and load-bearing performance. Second, intelligent upgrading (integrating sensors to realize real-time monitoring of bearing displacement, stress, and temperature, providing data support for bridge health monitoring). Third, eco-friendly design (developing recyclable rubber materials to reduce environmental impact of waste bearings, aligning with green engineering concepts).
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