What Are the Application Key Points of Laminated Elastomeric Bridge Bearings?
The application effect of laminated elastomeric bridge bearings directly affects the safety, stability, and durability of bridge structures. Their core application key points can be summarized into three dimensions: appropriate selection, standardized installation, and effective operation & maintenance, as detailed below:
- Preliminary Selection: Accurate Matching with Bridge Working Conditions
Selection is the foundation of application, which needs to combine core parameters such as the bridge’s structural form, load characteristics, and environmental conditions to ensure the bearing is “functionally suitable and performance-compliant”.
- Selection Based on Bridge Type and Load Parameters
Load Matching: Determine the vertical load-bearing capacity of the bearing (ranging from tens of kN to thousands of kN per bearing) according to the dead load, live load (e.g., vehicle, train load) and impact coefficient of the bridge superstructure. This avoids rubber layer crushing due to “overloading” or material waste due to “underloading”.
Example: Railway bridges require bearings with higher stiffness and better fatigue resistance due to high live load impact and frequent vibration; highway bridges can be reasonably matched according to the number of lanes and design load level.
Deformation Adaptation: Determine the horizontal shear deformation capacity of the bearing (usually required to meet 50%-100% shear of the total rubber layer thickness) based on the bridge’s temperature deformation (beam expansion/contraction caused by temperature difference) and concrete shrinkage/creep displacement. Meanwhile, combined with the girder end rotation (beam rotation under load), ensure the rubber layer can coordinate rotation through local compression/tension to avoid “hard contact” between the beam and the bearing.
- Rubber Material Selection Based on Environmental Conditions
Rubber is the core elastomer of the bearing, and its weather resistance directly affects service life. It needs to be selected according to the service environment:
Temperate/Frigid Regions: Prioritize Natural Rubber (NR) bearings due to their excellent elasticity and low-temperature performance (suitable for -40℃~60℃), preventing rubber embrittlement and cracking at low temperatures.
Coastal/Humid/Industrial Pollution Areas: Select Chloroprene Rubber (CR) bearings for their superior ozone resistance, aging resistance, and corrosion resistance (suitable for -30℃~60℃), which can resist erosion of rubber by seawater and industrial waste gas. Nitrile Butadiene Rubber (NBR) can be considered for special oil-polluted environments.
- Additional Function Selection Based on Structural Safety Requirements
Ordinary Bridges (Non-seismic Zones, Small Displacements): Use ordinary laminated bearings without limits, which only meet basic load transmission and deformation coordination.
Seismic Zones/High-vibration Bridges: Adopt laminated bearings with limit devices (e.g., lateral stoppers, limit bolts) to restrict excessive horizontal displacement during earthquakes or strong vibrations and prevent beam slipping. If necessary, lead cores or high-damping rubber can be combined to enhance seismic energy dissipation capacity.
Girder End Size Adaptation: Choose rectangular bearings for narrow girder ends (space-saving) and circular bearings for long-span bridges (more uniform force distribution, avoiding local stress concentration).
- Mid-term Installation: Strict Control of Construction Quality Details
Installation is a key link to ensure the bearing’s function is realized. It must follow the principles of “accurate positioning, flat fitting, and stress-free installation” to avoid early damage caused by construction deviations.
- Pre-installation Preparation: Foundation Surface Treatment and Bearing Inspection
Foundation Surface Flatness: Bearing pads (or pre-embedded steel plates) on pier/abutment tops and beam bottoms must be flat, with elevation error ≤±2mm and plane flatness error ≤1mm/m. The surface must be cleaned of laitance and debris to prevent uneven force on the bearing.
Bearing Incoming Inspection: Verify parameters such as the bearing’s model, specification, load-bearing capacity, rubber hardness (60±5 Shore A), and steel-rubber adhesion strength (≥7MPa), which must comply with standards such as Rubber Bearings for Highway Bridges (GB/T 20688). Check for no cracks, bulges on the rubber layer, no rust on steel plates, and intact protective layers.
- Installation Process: Positioning, Fitting, and Temperature Control
Accurate Positioning: The bearing center must be aligned with the pad center and beam center, with deviation ≤10mm. The upper and lower surfaces of the bearing must be tightly fitted to the beam bottom and pad (or pre-embedded steel plate) without hollowing or gaps (inspectable with feeler gauges) to ensure uniform load transmission.
Stress-free Installation: The installation temperature should be as close as possible to the bridge’s designed “reference temperature” (usually the local annual average temperature) to avoid pre-shear deformation of the bearing due to excessive temperature deviation (e.g., high-temperature installation in summer may cause bearing tension during winter contraction, while low-temperature installation in winter may cause compression during summer expansion).
Secure Connection: For bearings fixed with bolts, bolts must be tightened in place (torque meets design requirements) to prevent slipping due to loosening. Welding between pre-embedded steel plates and bearings must be full without cold welding or missing welding.
- Post-installation Recheck: Performance and Position Verification
Check if the bearing is horizontal (inclination ≤1°) without eccentricity or distortion;
Simulate small-displacement working conditions (e.g., temporary loading) to observe whether the bearing’s shear deformation is smooth without jamming.
III. Later Operation & Maintenance: Regular Monitoring and Timely Disposal
The service life of laminated elastomeric bridge bearings is usually 20-30 years. Scientific operation and maintenance can extend their service life and avoid bridge structural diseases caused by bearing failure.
- Regular Inspections: Establishing a Normalized Inspection Mechanism
A comprehensive inspection is recommended every 6 months to 1 year, focusing on the following indicators:
Rubber Layer Condition: Check for cracks (alert if depth ≥3mm), bulges, aging (sticky or hard surface), and peeling. Replace promptly if damaged area ≥20%.
Steel Plates and Connections: Inspect for rust and exposure of stiffening steel plates (caused by damaged protective layers), loose or broken bolts, and desoldering of pre-embedded steel plates.
Displacement and Deformation: Check if the bearing’s horizontal displacement exceeds the design allowable value and if vertical compression deformation exceeds 15% of the design value (excessive compression may cause rubber layer failure).
Environmental Impact: Clear dust, debris, and standing water from the bearing surface in time to prevent long-term accumulation of corrosive media.
- Daily Maintenance: Targeted Protection Measures
Cleaning and Protection: Regularly rinse the bearing surface with clean water to remove sediment and oil; apply anti-corrosion coatings to steel components in coastal areas.
Drainage Treatment: Ensure smooth drainage around the bearing to avoid long-term immersion of the bearing in rainwater and bridge deck seepage (which accelerates rubber aging and steel plate rusting).
Abnormal Disposal: Timely adjust and fasten if slight bearing deviation or bolt loosening is found; repair the protective layer for local aging (small-scale damage).
- Replacement Standards: Clear Disposal Principles After Failure
Replace the bearing with a special plan if:
The rubber layer is severely aged, cracked, or bulged, losing elasticity;
Vertical compression deformation exceeds the standard (>15% of design value) or horizontal displacement is jammed;
Steel plates are severely rusted and structurally damaged, unable to transmit loads;
Bearing load-bearing capacity decreases by ≥20% (verified by testing).
- Compliance Requirements: Adhering to Standards and Specifications
The entire application process must strictly comply with national and industry standards to ensure compliance in design, production, installation, operation, and maintenance:
Domestic Standards: Rubber Bearings for Highway Bridges (GB/T 20688.1~4), Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts (JTG 3362), Rubber Bearings for Railway Bridges (TB/T 1893), etc.;
International Standards: Such as European EN 1337-3 and American AASHTO M251 (for foreign-related projects).
Summary
The application of laminated elastomeric bridge bearings is a “systematic project”—preliminary accurate selection to match bridge needs, mid-term standardized installation to ensure function realization, and later scientific operation & maintenance to extend service life. Only by controlling the entire process of “selection-installation-operation & maintenance” can their core functions of “load transmission, deformation coordination, and vibration buffering” be fully exerted, providing reliable support for bridge structural safety.
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