How to Select Elastomeric Bridge Bearings Suitable for Specific Bridge Structures

How to Select Elastomeric Bridge Bearings Suitable for Specific Bridge Structures

1. Core Selection Process: From Requirement Analysis to Final Verification
2. Clarify the Bridge’s Core Parameters and Service Conditions (Basic Input)

Before selecting bearings, key information about the bridge must be obtained, as these serve as the basis for determining the bearing type, size, and performance:

Structural parameters: Bridge type (beam bridge/arch bridge/cable-stayed bridge, etc.), span length, superstructure dead load and live load (e.g., vehicle load class: Urban-A, Highway-I), and beam deformation (vertical compression, horizontal displacement, rotation angle).

Environmental parameters: Temperature range (low-temperature performance below -40°C must be considered in frigid regions, and UV aging in high-temperature areas), corrosive environment (chloride ions in coastal areas, chemical waste gas in industrial zones), and seismic intensity (additional shear resistance and shock absorption requirements are needed in high-intensity seismic zones).

Functional requirements: Whether shock absorption is required, whether adaptation to large rotation angles or displacements of the beam is needed, and whether ease of later replacement and maintenance is necessary.

2. Determine the Basic Type of Elastomeric Bearings (Classified by Structure and Function)

Based on the bridge’s parameters and requirements, the appropriate bearing type is first selected from major categories. Common classifications are as follows:

3. Calculate Key Performance Parameters of Bearings (Quantitative Design)

Based on the bridge’s load and deformation requirements, structural mechanics calculations are used to determine the performance indicators that bearings must meet. Core indicators include:

Vertical load-bearing capacity: The design reaction of the bearing must be greater than or equal to the maximum vertical load transmitted by the bridge superstructure (dead load + live load + additional loads such as thermal stress), with a safety factor of 1.2~1.5 reserved (in accordance with JT/T 4-2019 or EN 1337).

Horizontal displacement capacity: Divided into fixed bearings (restricting horizontal displacement, only allowing rotation) and expansion bearings (allowing both horizontal displacement and rotation). The displacement capacity of expansion bearings must cover the total horizontal displacement caused by thermal deformation, concrete shrinkage, and creep of the bridge.

Rotation capacity: Bearings must accommodate the end rotation of the beam under load (usually determined by the beam’s span and deflection; rotation angles for medium and small-span beam bridges are generally 0.005~0.01 rad). The thickness of the rubber layer directly affects rotation capacity (greater thickness improves adaptability to rotation).

Horizontal shear performance: Under seismic or braking loads, the horizontal shear capacity of bearings must exceed the maximum horizontal force (usually 0.1~0.3 times the vertical load-bearing capacity, adjusted according to seismic codes for seismic zones) to prevent shear failure or uplift of bearings.

4. Select Rubber Material Formulations (Matching Environmental and Performance Requirements)

Rubber materials are the core of bearings, and their formulations directly determine durability and mechanical properties. Selections should be based on the service environment:

Rubber matrix:

Ordinary environments: Natural Rubber (NR) is used for its cost-effectiveness and good elasticity, but its low-temperature performance and aging resistance are moderate.

Frigid environments (below -30°C): Ethylene Propylene Diene Monomer (EPDM) is preferred for its excellent low-temperature elasticity and low glass transition temperature (below -60°C).

Corrosive/aging environments (coastal, industrial areas): Chloroprene Rubber (CR) or EPDM is used for their superior weather resistance and corrosion resistance.

Reinforcement and modification: Adjust vulcanization systems (e.g., sulfur vulcanization vs. peroxide vulcanization) to improve strength; add fillers such as carbon black and silica to enhance stiffness; incorporate nanoparticles (e.g., nano-SiO₂) to improve wear resistance and aging resistance.

5. Verify Bearing Compliance and Reliability (Testing per Codes)

Selected bearings must pass mandatory testing in accordance with national or industry codes to ensure performance compliance. Core testing items include:

Mechanical properties: Compressive elastic modulus, shear elastic modulus, ultimate compressive strength, and ultimate shear strength (meeting requirements of JT/T 4-2019 or EN 1337-3).

Durability: After aging tests (high-low temperature cycling, UV irradiation, salt spray corrosion), the attenuation rate of mechanical properties must be ≤ 20%; no cracking, bulging, or other damage after fatigue tests (1 million cycles of reciprocating load).

Seismic performance: Bearings for seismic zones must pass horizontal cyclic loading tests to verify their hysteresis curves and energy dissipation capacity under seismic action, ensuring they meet shock absorption requirements.

6. Consider Construction and Maintenance Feasibility (Implementability Assessment)

The final selection must balance “design rationality” and “engineering implementability”:

Installation difficulty: The size of bearings must match the space between the beam bottom and pier top. For sliding bearings, the installation flatness of stainless steel plates and PTFE plates must be ensured (error ≤ 0.5mm/m).

Maintenance cost: Maintenance-free bearings (e.g., with stainless steel protective covers) are preferred for corrosive environments; replaceable bearings (e.g., designs with reserved holes for temporary supports) are recommended for long-span bridges.

Economy: On the premise of meeting performance requirements, cost-effective solutions are prioritized (e.g., plain elastomeric bearings instead of pot bearings for medium and small-span bridges).

1. Core Decision-Making Dimensions: 4 Key Trade-Offs
2. Balance Between Stiffness and Deformation

Excessively high bearing stiffness: Restricts free deformation of the beam, leading to additional internal forces (e.g., thermal stress concentration) in the beam or pier columns.

Excessively low bearing stiffness: Causes excessive beam displacement, even leading to bearing uplift or damage to bridge deck joints.

Decision logic: Precisely match the bridge’s deformation requirements by adjusting the rubber layer thickness (greater thickness reduces stiffness) and the number of stiffening steel plates (more layers increase stiffness).

2. Coordination of Load-Bearing and Shock Absorption

Ordinary bridges: Only basic load-bearing is required; plain or sliding elastomeric bearings are sufficient.

Bridges in seismic zones: Shock absorption functions must be integrated with load-bearing. Lead-rubber or high-damping rubber bearings are preferred, as they absorb seismic energy through the hysteretic energy dissipation of rubber and plastic deformation of lead cores.

3. Trade-Off Between Durability and Economy

Severe environments (coastal, frigid): Increased material costs (e.g., EPDM + stainless steel protective covers) are justified to extend bearing service life (from 15 to 30 years) and reduce later replacement costs.

Ordinary environments: Natural rubber bearings are used to meet design life requirements at lower costs.

4. Code Compliance

Performance requirements for bearings vary across national/regional codes, so project-specific codes must be prioritized:

Chinese code (JT/T 4-2019): Provides detailed requirements for compressive and shear moduli of bearings, emphasizing compatibility with domestic bridge load systems.

European code (EN 1337): Focuses on quantitative indicators for durability testing and seismic performance, applicable to European and overseas projects.

III. Typical Application Examples

Rural highway medium-small span beam bridge (10m span, Highway-II load, ordinary environment)
Selection: Plain natural rubber bearings (GJZ series), no sliding plates required, cost-effective, meeting basic load-bearing and small-displacement needs.

Urban expressway continuous beam bridge (40m span, Urban-A load, high-temperature and rainy environment)
Selection: EPDM sliding elastomeric bearings (GYZF4 series), with EPDM for aging resistance and sliding structure adapting to large horizontal displacement caused by temperature changes.

High-speed railway bridge in high-intensity seismic zone (9 degrees, 32m span, large load, shock absorption required)
Selection: Lead-rubber bearings (LRB series), providing both high load-bearing capacity and seismic energy dissipation to prevent collision between beams and piers.

Coastal long-span cable-stayed bridge (10,000kN bearing reaction, chloride corrosion environment)
Selection: Pot EPDM rubber bearings with stainless steel outer covers, where the steel pot bears large loads, EPDM resists corrosion, and the outer cover prevents chloride ion intrusion.

1. Summary

The core logic for selecting elastomeric bridge bearings is “demand-driven, quantitative design, code-based verification, and implementable”:

First clarify the bridge’s three basic parameters: structure, load, and environment;

Select bearing types based on functional requirements, and calculate key indicators such as load-bearing capacity, displacement, and rotation angle;

Match rubber formulations to the environment and verify performance through code-compliant testing;

Finally determine the optimal solution considering construction difficulty, maintenance costs, and economy.

Reinforce bridge resilience with our premium elastomeric bridge bearing – high-grade rubber solutions. Engineered for load distribution, seismic damping, all-weather durability. Quick install, ISO-certified. Trusted for global bridge infrastructure.