What Factors Need to Be Considered in the Selection of Laminated Elastomeric Bridge Bearings?
The selection of laminated elastomeric bridge bearings is a critical link to ensure the safety and performance of bridge structures. It requires comprehensive consideration of various factors, including the bridge’s own characteristics, load conditions, environmental factors, and functional requirements. The details are as follows:
- Bridge Structure and Force Characteristics
- Bridge Type and Span
Medium and Small-span Bridges (e.g., municipal bridges, rural highway bridges): With small loads and limited displacement, ordinary laminated rubber bearings (without special limit devices) can be selected.
Long-span Bridges (e.g., cable-stayed bridges, continuous beam bridges): Featuring large loads, significant temperature deformation, and obvious girder end rotation, high-load-bearing circular laminated bearings are required. Additionally, the total thickness of the rubber layer must be checked to meet the shear deformation requirements.
Railway Bridges: Due to high vibration frequency and large impact loads, bearings with higher stiffness and excellent fatigue resistance are needed. Chloroprene Rubber (CR) bearings are usually adopted to enhance durability.
- Superstructure Form
Simply Supported Beam Bridges: Bearings mainly bear vertical loads and small horizontal displacements, so the selection focuses on vertical load-bearing capacity and basic shear deformation capacity.
Continuous Beam Bridges/Rigid Frame Bridges: With negative moment zones, bearings may bear uplifting forces. It is necessary to combine limit devices or select laminated bearings with tensile structures.
Curved Bridges/Skewed Bridges: Bearings need to adapt to lateral displacement and torsion effects. Circular bearings (with more uniform force distribution) or specially designed bearings with multi-directional limits are preferred.
- Load Parameters
- Vertical Load
Based on the sum of the dead load (girder weight, deck pavement, etc.) and live load (vehicles, crowds, etc.) of the superstructure, the design vertical load-bearing capacity of the bearing is determined to ensure that the compressive strength of the bearing meets the requirements (the safety factor is usually 1.5~2.0). For example, for highway bridges with dense heavy trucks, the load-bearing capacity of a single bearing may need to reach several thousand kN.
- Horizontal Load and Displacement
Temperature Displacement: Calculated based on the maximum temperature difference in the area where the bridge is located (e.g., the temperature difference in northern China can reach more than 60℃). It is necessary to ensure that the shear deformation of the bearing (usually 50%~100% of the total thickness of the rubber layer) can cover the expansion and contraction caused by temperature.
Braking Load/Centrifugal Force: For railway bridges or curved bridges, horizontal forces generated by train braking or vehicle centrifugation must be considered, and bearings must have corresponding horizontal load-bearing capacity.
Seismic Action: For bridges in seismic zones, bearings with limit devices or high-damping rubber should be selected according to the seismic intensity to limit excessive displacement during earthquakes (e.g., setting lateral stoppers to control displacement ≤100mm).
III. Environmental Conditions
- Temperature Range
Frigid/Extremely Frigid Regions (-40℃ and below): Natural Rubber (NR) bearings are preferred due to their good low-temperature elasticity retention, avoiding hardening and cracking of chloroprene rubber at low temperatures.
High-Temperature Regions (summer temperature ≥40℃): The high-temperature resistance of rubber must be verified. If necessary, heat-resistant modified rubber should be selected to prevent accelerated aging of bearings due to long-term high temperatures.
- Corrosive Environment
Coastal Areas (high humidity, high salt spray): Chloroprene Rubber (CR) bearings are selected for their superior ozone resistance and salt corrosion resistance compared to natural rubber. Meanwhile, stiffening steel plates should adopt hot-dip galvanizing or epoxy coating for enhanced corrosion protection.
Industrial Areas (with sulfides, dust): The thickness of the bearing’s protective layer should be increased (≥5mm), and rubber formulations resistant to chemical corrosion (e.g., Nitrile Butadiene Rubber (NBR)) should be used.
- Humidity and Ultraviolet Radiation
In rainy or high-ultraviolet areas (e.g., plateaus, tropical regions), the anti-aging design of the side protective layer of the bearing must be strengthened to prevent rubber cracking due to long-term exposure.
- Rubber Material Performance
- Rubber Type Selection
Natural Rubber (NR): Good elasticity and low cost, suitable for temperate and dry areas, with a service life of about 20~30 years.
Chloroprene Rubber (CR): Excellent aging resistance and weather resistance, suitable for humid, coastal, and moderately corrosive environments, with a service life 5~10 years longer than NR.
Special Requirements: Nitrile Butadiene Rubber (NBR) for oily environments; Ethylene Propylene Diene Monomer (EPDM) for high-temperature environments.
- Key Material Indicators
It is necessary to verify the rubber’s Shore hardness (60±5 Shore A), tensile strength (≥15MPa), post-aging performance retention rate (≥80%), and steel-rubber adhesion strength (≥7MPa) to ensure compliance with standards such as GB/T 20688.
- Functional Requirements and Additional Structures
- Limit Requirements
No Limit: Suitable for bridges with small displacement in non-seismic zones, featuring simple structure and low cost.
Unidirectional/Bidirectional Limit: Restricting displacement in specific directions (e.g., longitudinal or lateral of the bridge) through stoppers or bolts to prevent excessive girder offset.
Seismic Energy Dissipation: For seismic zones, laminated bearings with built-in lead cores (LRB) can be selected, which use lead core yielding to dissipate seismic energy.
- Installation and Leveling Requirements
Bridges with Large Slopes: Bearings need leveling functions (e.g., setting wedge-shaped steel plates) to ensure horizontal force bearing on the bearing top surface.
Rapid Construction Scenarios: Prefabricated bearings are selected to reduce on-site installation time and improve efficiency.
- Adaptation to Standards and Specifications
The selection must comply with the design standards of the region where the project is located:
Domestic Projects: Follow Rubber Bearings for Highway Bridges (GB/T 20688), Rubber Bearings for Railway Bridges (TB/T 1893), etc.
International Projects: Must meet standards such as European EN 1337-3 and American AASHTO M251. For example, European standards have stricter requirements for rubber aging tests (100℃×90 days).
Summary
The selection of laminated elastomeric bridge bearings needs to achieve “load matching, environmental adaptation, and functional compliance”. The core logic is: determine basic parameters based on the bridge’s structural characteristics → screen load-bearing capacity and deformation capacity according to load and displacement requirements → select rubber materials based on environmental conditions → supplement functional structures to meet special needs → finally comply with relevant standards and specifications. Only through multi-dimensional comprehensive evaluation can an economical, reasonable, safe, and reliable bearing scheme be selected.
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