Applications of Spherical Bearings in Bridge Supports

1. Large-Span Bridges: Managing Complex Deformations

1.1 Cable-Stayed & Suspension Bridges

• Bridge Characteristics:

  The main girder (often steel box girders or composite girders) undergoes substantial rotational deformation at support points (near towers or piers) due to uneven load distribution (e.g., unbalanced vehicle loads) or wind-induced lateral movement. Additionally, thermal expansion/contraction can cause large longitudinal displacements.

• Rationale for Spherical Bearings:

• Multi-axial rotation: Can tolerate rotational angles up to 0.08 rad (≈ 4.58°), surpassing the 0.05 rad limit of pot bearings, thus preventing stress concentration in the girder.

• Large displacement capacity: Supports horizontal displacements of ±200 mm to ±500 mm (bidirectional), adapting to both thermal changes and wind-induced lateral shifts (critical for sea-crossing cable-stayed bridges).

• Typical Application:

  The main tower supports of the Hong Kong-Zhuhai-Macao Bridge (main span 488 m) utilize high-load spherical bearings (vertical load capacity ≥ 30,000 kN) to accommodate the steel box girder’s rotation and tidal-induced displacements.

1.2 Continuous Rigid Frame Bridges

• Bridge Characteristics:

  The girder and piers are rigidly connected; under load, pier-top supports experience coupled rotation and displacement (e.g., downward mid-span girder rotation causes horizontal tension at the pier top).

• Rationale for Spherical Bearings:

• Integrates "rotation + displacement" in a single component: Eliminates the need for separate rotation and sliding devices (e.g., combining pot bearings with sliding plates), simplifying the support system.

• High load stability: Constructed from high-strength steel (Q355B/Q460) and spherical PTFE (polytetrafluoroethylene) sliding pairs, it withstands vertical loads up to 50,000 kN without permanent deformation.

• Typical Application:

  The pier-top supports of the Sidu River Bridge (main span 900 m, a continuous rigid frame bridge in China) employ spherical bearings to handle the girder’s large rotation and temperature-driven displacements.

2. Special-Shaped Bridges: Adapting to Non-Standard Displacements

2.1 Curved Bridges (Urban Interchanges, Mountainous Bridges)

• Bridge Characteristics:

  Vehicles generate centrifugal force on curved girders, causing transverse displacement (perpendicular to the bridge axis). Uneven thermal deformation along the curved alignment further demands multi-directional adjustment.

• Rationale for Spherical Bearings:

• Bidirectional horizontal displacement: Allows both longitudinal (tangential to the curve) and transverse (radial) movement, avoiding "jamming"—a common issue with guided pot bearings.

• Uniform load transmission: The spherical contact surface ensures even load distribution between the girder and pier, even when the girder shifts transversely.

• Typical Application:

  Urban interchange curved bridges (e.g., a 150 m-radius cloverleaf interchange in Shanghai) use spherical bearings to adapt to ±150 mm transverse displacement and 0.06 rad rotation.

2.2 Skew Bridges (Crossing Rivers/Railways at Angles)

• Bridge Characteristics:

  The girder is skew to the pier (angle 30°–60°), so loads (e.g., vehicle weight) are transmitted obliquely, leading to combined longitudinal-transverse displacement at supports.

• Rationale for Spherical Bearings:

• No fixed displacement direction: Unlike guided bearings (limited to one-way movement), spherical bearings slide freely along any axis, matching the skew girder’s displacement path.

• Reduced shear stress: The spherical sliding pair minimizes friction during oblique displacement, preventing shear damage to the pier top.

3. Heavy-Load & Harsh-Environment Bridges: Ensuring Durability

3.1 Heavy-Haul Railway Bridges (Axle Load ≥ 30 t)

• Bridge Characteristics:

  Sustains repeated heavy loads (freight trains) and large vertical impact forces; supports must exhibit high fatigue resistance and load capacity.

• Rationale for Spherical Bearings:

• High load density: The spherical steel core and thickened connecting plates (thickness ≥ 40 mm) withstand vertical loads up to 80,000 kN—exceeding the capacity of rubber bearings (max 20,000 kN).

• Fatigue resilience: The sliding surface uses wear-resistant PTFE composites (backed by stainless steel), ensuring no failure after 2 million load cycles (compliant with GB/T 17955-2019).

• Typical Application:

  China’s Daqin Railway (a heavy-haul coal transport line) uses spherical bearings for bridge supports, adapting to 30 t axle loads and frequent impact.

3.2 Coastal/High-Corrosion Bridges

• Bridge Characteristics:

  Exposed to salt spray (coastal) or industrial fumes (chemical zones), which cause steel corrosion and rubber aging—ordinary bearings require frequent maintenance.

• Rationale for Spherical Bearings:

• Corrosion-resistant materials: All steel components (spherical core, connecting plates) use 316L stainless steel or hot-dip galvanizing + epoxy coating (thickness ≥ 200 μm); the PTFE plate is coated with an anti-aging fluorine film.

• Sealed structure: A rubber dust cover with a stainless steel frame prevents saltwater or dust from entering the sliding pair, extending service life to ≥ 50 years.

• Typical Application:

  Coastal sea-crossing bridges (e.g., the Xiamen-Zhangzhou Bay Bridge) utilize corrosion-resistant spherical bearings to resist salt spray erosion.

3.3 High-Altitude/Frigid Bridges (Temperature ≤ -30℃)

• Bridge Characteristics:

  Extreme low temperatures cause rubber materials (in rubber bearings) to become brittle and lose elasticity; supports must remain functional in freezing conditions.

• Rationale for Spherical Bearings:

• No rubber components: Relies on metal (steel) and PTFE sliding pairs, which operate stably at -40℃ (PTFE’s low-temperature friction coefficient remains 0.02–0.05).

• Anti-freezing design: The sliding surface is lubricated with low-temperature grease (lithium-based, -50℃ to 120℃) to prevent ice formation and ensure smooth displacement.

• Typical Application:

  Bridges in the Qinghai-Tibet Plateau (average temperature -10℃) use frigid-resistant spherical bearings to avoid winter support failure.

4. Seismic-Prone Areas: Enhancing Disaster Resilience

• Seismic Modifications:

  Embed a lead core (within the spherical core) or add a friction damping ring (between the spherical surface and connecting plate) to dissipate seismic energy via plastic deformation or friction.

• Application Advantage:

  During earthquakes, the bearing allows controlled rotation/displacement while absorbing energy, reducing seismic force transmission to piers by 40–60% (equivalent damping ratio ≥ 18%).

• Typical Application:

  Bridges in Sichuan and Yunnan (high-seismic zones in China) use seismic spherical bearings to improve structural resilience against earthquakes.

5. Key Selection Principles for Spherical Bearings

1. Bridge Load & Deformation: Calculate vertical load (girder weight + live load) and required rotation/displacement (e.g., large-span bridges need ≥ 0.06 rad rotation).

2. Environmental Conditions: Choose corrosion-resistant variants for coastal/industrial areas, and low-temperature-resistant models for frigid regions.

3. Seismic Requirements: Opt for seismic-integrated spherical bearings in high-seismic zones, aligning with local fortification intensity.