Laminated Rubber Bearings (LRBs) Rubber Pads Laminated Elastomeric Bridge Bearings

Expanded Application Scenarios of Rubber Bearings (Plate-Type) and Pot Bearings1. Overview of Bridge Bearings: Core Functions and Classification Significance

Bridge bearings serve as the "connecting joints" between a bridge’s superstructure (e.g., girders, beams) and substructure (e.g., piers, abutments). Their core functions are threefold: first, to reliably transmit vertical loads (including the bridge’s dead weight, live loads from vehicles/pedestrians, and environmental loads like snow and wind) from the superstructure to the substructure; second, to accommodate horizontal displacements and rotational deformations of the superstructure caused by temperature variations (expansion in heat, contraction in cold), concrete creep/shrinkage, and load-induced bending; third, to buffer vibrations and shocks (e.g., from heavy vehicles or minor seismic activity) to protect the bridge structure from fatigue damage.

Among the various types of bridge bearings, plate-type rubber bearings (a representative category of rubber bearings) and pot bearings are the most widely used in civil engineering. Their application scenarios are strictly aligned with their structural characteristics, material properties, load-bearing capacities, and environmental adaptability. Understanding their detailed application scopes is critical for ensuring structural safety, reducing construction costs, and extending the bridge’s service life.

2. Deep Dive into Plate-Type Rubber Bearings: Application Scenarios, Influencing Factors, and Practical Cases

Plate-type rubber bearings (PTRBs) consist of multiple layers of rubber sheets and thin steel plates bonded together through vulcanization. The steel plates enhance the bearing’s vertical stiffness to resist compression, while the rubber layers provide flexibility for horizontal displacement and rotation. Their advantages—simple structure, low manufacturing cost, easy installation, and good shock absorption—make them ideal for specific engineering contexts, but they are limited by relatively low load-bearing capacity (typically 100–5000 kN) and small horizontal displacement ranges (usually ±50 mm or less), which defines their application boundaries.

2.1 Application Scenarios by Bridge Type and Span2.1.1 Medium and Small-Span Highway Simply Supported Beam Bridges

PTRBs are the dominant bearing type for highway simply supported beam bridges with spans less than 20 meters—a common structure in rural highways, suburban roads, and county-level transportation networks. In such bridges:

· Vertical load transmission: They bear the dead weight of precast concrete beams (e.g., T-beams, I-beams) and dynamic live loads from passenger cars, trucks (with axle loads generally ≤140 kN), and agricultural vehicles. The multi-layer rubber-steel composite structure ensures uniform load distribution, preventing local stress concentration on piers.

· Displacement adaptation: Temperature changes in most temperate regions (annual temperature differences of 30–50°C) cause the beam body to expand or contract by 5–20 mm. The rubber layers of PTRBs can deform elastically to absorb this displacement without generating excessive horizontal force on the substructure.

· Cost and construction alignment: Rural and suburban highway projects often have limited budgets and simple construction conditions. PTRBs require no complex installation equipment (e.g., hydraulic lifting systems) — they can be placed manually after leveling the pier top, reducing construction time by 30–50% compared to complex bearings.

Case Example: In the rural highway network renovation project of Hebei Province, China (2021–2023), over 800 simply supported beam bridges (spans 8–16 meters) adopted PTRBs with a design bearing capacity of 800–1500 kN. The use of PTRBs reduced the total bearing cost by approximately 40% compared to pot bearings, and the construction period per bridge was shortened to 2–3 days, minimizing disruption to rural traffic.

2.1.2 Urban Pedestrian Bridges and Small-Scale Municipal Bridges

Urban pedestrian bridges (e.g., overpasses across busy streets, footbridges in parks) and small municipal bridges (e.g., canal-crossing bridges with spans ≤15 meters) prioritize shock absorption, noise reduction, and landscape integration—all strengths of PTRBs:

· Vibration buffering: Pedestrian-induced vibrations (frequency 1–3 Hz) can cause discomfort if not attenuated. The rubber material of PTRBs has a damping ratio of 0.05–0.1, which absorbs 10–20% of vibration energy, reducing the maximum vibration amplitude of the bridge deck by 30–40%. This is particularly important for footbridges near residential areas, where noise from vibrations (≤50 dB) meets urban environmental standards.

· Space efficiency: PTRBs have a low profile (typical height 50–150 mm), which is critical for pedestrian bridges with limited vertical clearance (e.g., underpasses with overhead power lines). Their compact design avoids increasing the bridge’s overall height, ensuring compliance with urban planning height restrictions.

· Aesthetic flexibility: PTRBs can be customized with rubber covers in colors matching the bridge’s landscape (e.g., gray for concrete bridges, green for park footbridges), enhancing visual harmony. Unlike metal bearings, they do not require regular painting to prevent rust, maintaining a clean appearance long-term.

Case Example: The pedestrian footbridge network in Changzhou City, Jiangsu Province (2022), includes 12 bridges (spans 10–14 meters) using PTRBs with chloroprene rubber (CR) layers. The CR material’s excellent weather resistance ensures the bearings remain flexible in the city’s humid subtropical climate (annual rainfall 1000–1200 mm), and the low vibration transmission has received positive feedback from nearby residents.

2.1.3 Low-Traffic Rural and Mountainous Bridges

In rural areas with low traffic volumes (daily vehicle counts<500) and mountainous regions with difficult construction access, PTRBs are favored for their low maintenance needs and adaptability to simple construction conditions:

· Maintenance simplicity: Rural areas often lack professional maintenance teams. PTRBs have no moving parts (e.g., sliding plates, seals) that require regular lubrication or replacement. Routine inspections only involve checking for rubber cracks or steel plate exposure—tasks that can be completed by local road maintenance workers with basic training.

· Adaptation to uneven pier tops: Mountainous bridge piers may have minor surface irregularities (≤3 mm) due to difficult construction terrain. The rubber layers of PTRBs can elastically deform to fill small gaps, ensuring stable load transmission without the need for precise pier top leveling (which would require expensive equipment like laser levelers).

· Resistance to minor impacts: Mountainous roads often have narrow lanes, increasing the risk of vehicles scraping the bridge edges. PTRBs’ rubber outer layers are more impact-resistant than brittle materials (e.g., concrete) or rigid metal bearings—minor impacts (≤5 kN) will only cause temporary deformation, not permanent damage.

2.2 Application Scenarios by Environmental Conditions2.2.1 Temperate and Humid Regions (Non-Corrosive Environments)

In regions with mild climates (annual temperatures 0–35°C) and low corrosion risks (e.g., inland areas far from oceans or industrial zones), standard PTRBs (with natural rubber (NR) or chloroprene rubber (CR) layers) perform well:

· NR-based PTRBs: Natural rubber has excellent elasticity (elongation at break >500%) and low cost, making it suitable for highways in central China (e.g., Henan, Hubei provinces) where temperatures rarely drop below 0°C. They can maintain flexibility for 15–20 years under normal use.

· CR-based PTRBs: Chloroprene rubber offers better weather resistance than NR, making it ideal for humid regions (e.g., Sichuan Basin, where annual relative humidity >80%). CR resists mold growth and moisture absorption, preventing rubber degradation caused by long-term humidity.

2.2.2 Cold Regions (Temperatures ≤-20°C)

In cold regions (e.g., Northeast China, Mongolia, Siberian Russia), standard rubber materials become brittle at low temperatures, so PTRBs use ethylene-propylene-diene monomer (EPDM) rubber with excellent low-temperature resistance:

· Low-temperature performance: EPDM remains flexible at temperatures as low as -40°C, avoiding brittle cracking that would occur with NR (which becomes rigid below -10°C). This is critical for bridges in Heilongjiang Province, China, where winter temperatures often reach -30°C.

· Snow load adaptation: Cold regions experience heavy snowfall (annual snow load 0.3–0.8 kN/m2). PTRBs with enhanced vertical stiffness (steel plate thickness increased from 2 mm to 3 mm) can bear the additional snow load without excessive compression (compression deformation ≤10% of the bearing height).

2.2.3 Mild Corrosion Environments (e.g., Near Lakes or Light Industrial Areas)

For bridges near freshwater lakes or light industrial zones (with low concentrations of sulfur dioxide or chloride ions), PTRBs are modified with anti-corrosion measures:

· Galvanized steel plates: The internal steel plates are hot-dip galvanized (zinc coating thickness ≥85 μm) to prevent rust caused by occasional water splashes (e.g., from lake waves or rainwater runoff).

· Rubber surface coating: A thin layer of polyurethane (PU) coating (thickness 0.5–1 mm) is applied to the rubber surface to resist chemical erosion from light industrial emissions, extending the bearing’s service life from 15 years to 20 years.

3. Comprehensive Analysis of Pot Bearings: Application Scope, Engineering Adaptability, and Technical Advantages

Pot bearings consist of a steel pot, a rubber pad (elastic body), a steel piston, and a sliding friction pair (e.g., polytetrafluoroethylene (PTFE) and stainless steel). Their structural design enables high load-bearing capacity (500–50,000 kN), large horizontal displacement (±50–±300 mm), and stable rotation performance—making them suitable for large-span, heavy-load, and complex environmental conditions where PTRBs are insufficient.

3.1 Application Scenarios by Bridge Type and Load Requirements3.1.1 Long-Span Highway and Railway Continuous Beam Bridges (Spans 20–50 Meters)

Continuous beam bridges (common in expressways and high-speed railways) have large spans, heavy loads, and significant structural deformations—requirements that pot bearings meet perfectly:

· Heavy load bearing: High-speed railway bridges (e.g., China’s Fuxing EMU lines) bear dynamic loads from trains (axle loads up to 250 kN) and static loads from long-span concrete beams (dead weight per meter >150 kN). Pot bearings with a design capacity of 5000–15,000 kN can reliably transmit these loads to piers, with a safety factor of ≥2.5.

· Horizontal force resistance: Train braking generates large horizontal forces (up to 10% of the vertical load). The steel pot and piston structure of pot bearings provides high horizontal stiffness, preventing excessive horizontal displacement of the beam body (which could cause derailment). For example, on the Beijing-Shanghai High-Speed Railway, pot bearings with a horizontal bearing capacity of 2000 kN ensure stable train operation at speeds up to 350 km/h.

· Rotation adaptation: Continuous beam bridges experience significant rotational deformation at supports (rotation angle up to 0.005 rad) due to load-induced bending. The rubber pad in the pot bearing deforms elastically to accommodate this rotation, avoiding stress concentration at the beam-pier interface.

Case Example: The Wuhan-Yichang High-Speed Railway (2020) includes 36 continuous beam bridges (spans 24–48 meters) using pot bearings with PTFE-stainless steel sliding pairs. These bearings allow horizontal displacements of ±120 mm (to adapt to temperature changes of 40°C) and have a design service life of 30 years, matching the railway’s overall design life.

3.1.2 Cable-Stayed Bridges and Arch Bridges (Key Stress Components)

Cable-stayed bridges and arch bridges have complex force systems (e.g., cable tension, arch thrust) and require bearings that can accommodate large displacements while maintaining load stability—pot bearings are the optimal choice:

· Cable-stayed bridges: The main girder of a cable-stayed bridge is subject to horizontal pull from cables (tension up to 10,000 kN) and vertical loads. Pot bearings installed at the girder-pier interface must resist this horizontal pull and allow small rotations (0.002–0.004 rad) caused by cable tension changes. For example, the Sutong Yangtze River Bridge (China’s longest cable-stayed bridge) uses pot bearings with a vertical capacity of 30,000 kN and a horizontal capacity of 5000 kN to handle the bridge’s massive loads.

· Arch bridges: Arch bridges transmit loads through arch thrust (horizontal force up to 20,000 kN). Pot bearings with fixed or guided designs are used to resist this thrust: fixed pot bearings (no horizontal displacement) are installed at one end of the arch to anchor the structure, while guided pot bearings (allowing unidirectional displacement) are installed at the other end to accommodate temperature-induced expansion/contraction. The Lupu Bridge (Shanghai, China) uses guided pot bearings with a horizontal displacement range of ±200 mm to adapt to the arch’s thermal deformation.

3.1.3 Heavy-Duty Bridges (Highway Overpasses, Industrial Bridges)

Highway overpasses with frequent heavy vehicle traffic (e.g., trucks with gross weights >100 tons) and industrial bridges (e.g., bridges for transporting coal or steel) require bearings with high wear resistance and fatigue resistance—pot bearings excel in these scenarios:

· Wear resistance: The PTFE-stainless steel sliding pair in pot bearings has a low friction coefficient (0.02–0.05), reducing wear even under frequent displacement. For highway overpasses with 10,000 heavy vehicles per day, the PTFE layer (thickness 5–8 mm) can last 25–30 years before needing replacement.

· Fatigue resistance: Industrial bridges are subject to cyclic loads (e.g., hourly passage of heavy trains). The steel components of pot bearings (made of Q345 steel, yield strength 345 MPa) have high fatigue limits (150–200 MPa), ensuring they can withstand millions of load cycles without cracking.

Case Example: The Tianjin Binhai New Area Industrial Bridge (2021) — used for transporting steel coils (gross vehicle weight 150 tons) — uses pot bearings with a vertical capacity of 20,000 kN. The bearings’ PTFE layers are reinforced with glass fiber (to improve wear resistance), and the steel pot is coated with epoxy resin (for corrosion protection against industrial dust). After 2 years of operation, wear on the PTFE layer is less than 0.5 mm, well within the allowable range.

3.2 Application Scenarios by Environmental and Geological Conditions

3.2.1 Coastal Regions (High Chloride Ion Concentration)

Coastal bridges are exposed to salt spray (chloride ion concentration 50–100 mg/m3) and seawater splashes, which cause severe corrosion of metal components. Pot bearings for coastal use are modified with heavy anti-corrosion measures:

· Stainless steel components: All exposed steel parts (e.g., piston, sliding plate) are made of 316L stainless steel (chromium content ≥16%, nickel content ≥10%), which resists chloride corrosion. Unlike ordinary carbon steel (which rusts in 6 months in coastal areas), 316L stainless steel remains corrosion-free for 30 years.

· Sealed structure: The pot bearing’s internal cavity is filled with waterproof grease (e.g., lithium-based grease) and sealed with a rubber O-ring (EPDM material) to prevent saltwater from entering and corroding the rubber pad or steel pot.

· Cathodic protection: For large pot bearings (capacity >20,000 kN), sacrificial anodes (zinc blocks) are attached to the steel pot to provide cathodic protection, further slowing corrosion.

Case Example: The Hong Kong-Zhuhai-Macao Bridge (2018), a 55-kilometer cross-sea bridge, uses over 1000 pot bearings with 316L stainless steel components and EPDM seals. These bearings have withstood 5 years of salt spray exposure with no visible corrosion, meeting the bridge’s 120-year design life requirement.

3.2.2 Earthquake-Prone Regions (Seismic Intensity ≥Ⅷ)

In earthquake-prone regions (e.g., Sichuan, Yunnan provinces in China; Japan; California, USA), pot bearings are equipped with seismic isolation devices to reduce earthquake damage:

· Lead-core rubber pot bearings: A lead core is inserted into the rubber pad of the pot bearing. During an earthquake, the lead core yields and dissipates seismic energy (damping ratio 0.15–0.25), reducing the horizontal force transmitted to the substructure by 40–60%.

· Sliding seismic pot bearings: The PTFE-stainless steel sliding pair is designed with a "limit stop" — during a small earthquake, the bearing slides normally to accommodate displacement; during a major earthquake, the limit stop restricts excessive displacement (preventing the beam from falling off the pier).

Case Example: The Chengdu-Chongqing High-Speed Railway (2023) passes through a seismic zone (intensity Ⅸ). The bridges use lead-core pot bearings with a vertical capacity of 8000 kN and a horizontal seismic capacity of 3000 kN. Seismic tests show that these bearings can reduce the peak seismic force on piers by 55%, protecting the bridge from collapse during a magnitude 7 earthquake.

3.2.3 High-Altitude Regions (Elevation >3000 Meters)

High-altitude regions (e.g., Qinghai-Tibet Plateau) have low atmospheric pressure (60–70 kPa at 3000 meters), large temperature differences (day-night differences up to 25°C), and strong ultraviolet (UV) radiation—conditions that require special adaptations for pot bearings:

· UV-resistant rubber pads: The rubber pad is made of EPDM rubber with UV stabilizers (e.g., carbon black, hindered amine light stabilizers) to resist degradation from strong UV radiation (which can cause ordinary rubber to crack in 2–3 years).

· Pressure-adapted seals: The low atmospheric pressure increases the risk of grease leakage from the bearing’s sealed cavity. High-pressure seals (silicone rubber material with a Shore hardness of 70±5) are used to maintain grease pressure, preventing leakage.

· Cold-resistant lubricants: The grease in the bearing is replaced with synthetic lubricants (e.g., polyalphaolefin) that remain fluid at low temperatures (-30°C), ensuring smooth sliding of the PTFE-stainless steel pair.

Case Example: The Lhasa-Nyingchi Railway (2021), built on the Qinghai-Tibet Plateau (elevation 3000–4500 meters), uses pot bearings with UV-resistant EPDM rubber and synthetic lubricants. After 2 years of operation, the bearings’ sliding performance remains stable, with no rubber cracking or grease leakage.

4. Selection Criteria: Matching Bearings to Application Scenarios

The choice between plate-type rubber bearings and pot bearings depends on four key factors: bridge span, load magnitude, environmental conditions, and construction/maintenance resources. The following decision framework guides engineering practice:

4.1 Bridge Span and Displacement Requirements

· Spans<20 meters, horizontal displacement <±50 mm: Plate-type rubber bearings are preferred (cost-effective, simple installation). Examples: rural highway simply supported beams, urban pedestrian bridges.

· Spans 20–50 meters, horizontal displacement ±50–±200 mm: Pot bearings are required (to accommodate larger displacements). Examples: highway continuous beams, medium-span arch bridges.

· Spans >50 meters, horizontal displacement >±200 mm: Specialized pot bearings (e.g., multi-directional sliding pot bearings) are used. Examples: long-span cable-stayed bridges, suspension bridges.

4.2 Load Magnitude

· Vertical load<5000 kN, horizontal load <1000 kN: Plate-type rubber bearings (sufficient capacity, low cost). Examples: small municipal bridges, low-traffic rural bridges.

· Vertical load 5000–50,000 kN, horizontal load 1000–10,000 kN: Pot bearings (high load-bearing capacity). Examples: high-speed railway bridges, heavy-duty industrial bridges.

4.3 Environmental Conditions

4.4 Construction and Maintenance Resources

· Limited construction equipment/maintenance teams: Plate-type rubber bearings (easy to install, low maintenance). Examples: rural bridges, small municipal projects.

· Professional construction teams/long design life (≥30 years): Pot bearings (complex installation, but durable with proper maintenance). Examples: high-speed railways, cross-sea bridges.

5. Maintenance Strategies Aligned with Application Scenarios

Proper maintenance extends bearing service life and ensures bridge safety. Maintenance measures vary by bearing type and application environment:

5.1 Maintenance for Plate-Type Rubber Bearings5.1.1 Routine Inspection (Quarterly)

· Check rubber surface for cracks, bulging, or steel plate exposure (common in high-traffic bridges). Cracks >5 mm in length require immediate repair.

· Clean debris (e.g., sand, leaves) from the bearing surface to prevent abrasive wear.

· Verify that the bearing is not displaced horizontally beyond the allowable range (±50 mm for standard PTRBs).

5.1.2 Seasonal Maintenance

· Winter (cold regions): Apply silicone grease to the rubber surface to prevent low-temperature brittleness.

· Rainy season (humid regions): Drain water from the pier top to avoid long-term immersion of the bearing (which causes rubber swelling).

5.1.3 Repair and Replacement

· Minor cracks: Use rubber repair adhesive (e.g., CR-based adhesive) to fill cracks and seal the surface.

· Severe damage (steel plate exposure, rubber tearing): Replace the bearing entirely. For rural bridges, replacement can be completed in 1 day with a small crane.

5.2 Maintenance for Pot Bearings

5.2.1 Routine Inspection (Semi-Annually)

· Check the PTFE-stainless steel sliding pair for wear (wear >2 mm requires PTFE replacement).

· Inspect seals for leakage (grease stains indicate seal failure; replace O-rings immediately).

· Measure bearing displacement/rotation with a laser leveler to ensure it stays within design limits.

5.2.2 Annual Maintenance

· Refill waterproof grease in the pot cavity (use the same type of grease to avoid chemical incompatibility).

· Clean stainless steel sliding plates with acetone to remove dirt and maintain low friction.

· Test seismic components (e.g., lead cores) for deformation (permanent deformation >10% requires replacement).

5.2.3 Long-Term Maintenance (Every 10 Years)

· Conduct load tests to verify bearing capacity (reduce load to 80% of design capacity and check for abnormal deformation).

· Replace PTFE layers and seals (even if wear is minimal) to prevent sudden failure.

6. Case Studies: Practical Application Contrasts

6.1 Case 1: Rural Highway Bridge (Plate-Type Rubber Bearings)

· Project: County-level highway bridge in Shanxi Province, China (2022).

· Bridge Parameters: Span 16 meters (simply supported T-beams), daily traffic 300 vehicles (mostly passenger cars and small trucks).

· Bearing Selection: PTRBs with NR rubber, vertical capacity 1200 kN, horizontal displacement ±30 mm.

· Performance: After 2 years, no rubber cracks or displacement issues. Maintenance cost: ~$200/year (only routine cleaning and inspection).

6.2 Case 2: High-Speed Railway Bridge (Pot Bearings)

· Project: Beijing-Xiong’an High-Speed Railway Bridge (2021).

· Bridge Parameters: Span 40 meters (continuous beams), train speed 350 km/h, axle load 250 kN.

· Bearing Selection: Pot bearings with 316L stainless steel, vertical capacity 10,000 kN, horizontal displacement ±150 mm, lead-core seismic design.

· Performance: 3 years of operation, no wear on PTFE layers, seismic components function normally. Maintenance cost: ~$5000/year (grease refilling, seal inspection).

6.3 Case 3: Coastal Cross-Sea Bridge (Pot Bearings)

· Project: Xiamen-Jinmen Cross-Sea Bridge (2023).

· Bridge Parameters: Span 50 meters (arch bridge), salt spray exposure, design life 100 years.

· Bearing Selection: Pot bearings with 316L stainless steel, EPDM seals, cathodic protection, vertical capacity 15,000 kN.

· Performance: 1 year of operation, no corrosion or grease leakage. Annual maintenance includes salt spray cleaning and seal inspection.

7. Conclusion

Plate-type rubber bearings and pot bearings are indispensable components in modern bridge engineering, each with distinct application boundaries shaped by structural performance, environmental adaptability, and economic factors. Plate-type rubber bearings excel in medium-small-span, low-load, and low-maintenance scenarios (e.g., rural highways, urban footbridges), offering cost-effectiveness and simplicity. Pot bearings, by contrast, are the backbone of large-span, heavy-load, and harsh-environment bridges (e.g., high-speed railways, cross-sea bridges, seismic zones), providing high capacity, stability, and durability.

Understanding their expanded application scenarios—from temperate rural areas to coastal seismic zones—enables engineers to make optimal bearing selections, ensuring bridges are safe, durable, and cost-efficient. As bridge engineering advances (e.g., longer spans, harsher service environments), both bearing types will continue to evolve (e.g., smarter sensors for real-time monitoring, more durable materials), further expanding their application horizons in the future.