What are the types of pot bearings for bridge supports?

Types of Pot Bearings for Bridge Supports

1. Classification by Displacement & Rotation Capabilities

1.1 Fixed Pot Bearings (FPB)

• Structural Features:

• No horizontal displacement allowed; only supports vertical loads and enables multi-directional rotation (around X, Y axes).

• Key components: A fixed "pot" (steel shell), a spherical PTFE (polytetrafluoroethylene) sliding plate (for rotation), and an upper connecting plate restricted by anti-displacement ribs (prevents horizontal movement).

• Functional Scope:

• Vertical load capacity: Typically 1,000–50,000 kN (customizable for large-span bridges).

• Rotation angle: ≤ 0.05 rad (≈ 2.86°), meeting the rotational needs of beam ends under load.

• Application Scenarios:

• Fixed supports of simply supported beams, continuous beams, or arch bridges (e.g., the fixed pier of a 30m-span highway simply supported T-beam bridge).

• Positions where the bridge superstructure requires no horizontal movement (e.g., piers near bridge abutments).

1.2 Guided Pot Bearings (GPB)

• Structural Features:

• Allows one-way horizontal displacement (usually longitudinal, along the bridge axis) and multi-directional rotation; restricts transverse displacement (perpendicular to the bridge axis).

• Added "guide ribs" or "guide plates" on the upper connecting plate, which slide along matching grooves in the pot shell to limit displacement direction.

• Functional Scope:

• Horizontal displacement capacity: ±50 mm to ±300 mm (adjustable via PTFE plate size).

• Vertical load and rotation angle: Same as fixed pot bearings.

• Application Scenarios:

• Expansion supports of continuous beams, cable-stayed bridges, or rigid frame bridges (e.g., the middle piers of a 50m-span continuous box girder bridge).

• Bridges requiring adaptation to longitudinal thermal expansion/contraction but no transverse movement (e.g., straight highway bridges).

1.3 Free Pot Bearings (Free PB)

• Structural Features:

• Allows two-way horizontal displacement (longitudinal + transverse) and multi-directional rotation, with no displacement direction restrictions.

• Omits guide ribs; the upper connecting plate slides freely on the spherical PTFE plate within the pot shell.

• Functional Scope:

• Horizontal displacement capacity: ±50 mm to ±400 mm (two-way).

• Suitable for bridges with complex horizontal movements (e.g., curved bridges, bridges on soft soil foundations with uneven settlement).

• Application Scenarios:

• Supports of curved bridges (e.g., a 200m-radius urban interchange curved beam bridge) to adapt to transverse displacement caused by centrifugal force.

• Bridges with potential horizontal settlement (e.g., bridges over soft soil areas) or multi-directional thermal deformation (e.g., large-span steel truss bridges).

2. Specialized Pot Bearings for Specific Demands

2.1 Seismic Pot Bearings (SPB)

• Structural Modifications:

• Lead-core inserts: Similar to seismic rubber bearings, a lead cylinder is added to the pot to dissipate seismic energy via plastic deformation.

• Friction damping layers: A high-friction material (e.g., brass-PTFE composite) is added between the upper plate and pot shell to enhance energy dissipation during earthquakes.

• Integrates seismic damping components into standard pot bearings, such as:

• May include "displacement limiters" to prevent excessive horizontal movement (e.g., shear pins that break at preset force to control displacement).

• Functional Advantage:

• Reduces seismic force transmission to piers by 30–50% (equivalent damping ratio ≥ 15%).

• Maintains normal load-bearing/rotation functions under small earthquakes; activates damping under strong earthquakes.

• Application Scenarios:

• Bridges in high-seismic-intensity areas (seismic fortification intensity ≥ 8 degrees), such as bridges in Sichuan, Yunnan, or coastal earthquake zones in China.

• Critical infrastructure (e.g., highway overpasses, railway bridges) requiring enhanced seismic safety.

2.2 High-Load Pot Bearings (HLPB)

• Structural Modifications:

• Uses thicker steel plates (Q355B or Q460) for the pot shell and upper/lower connecting plates (thickness ≥ 30 mm) to withstand ultra-high vertical loads.

• Reinforces the spherical PTFE plate with a metal backup layer (e.g., stainless steel) to prevent extrusion damage under high pressure.

• Optimizes the pot’s internal geometry (e.g., larger spherical radius) to distribute stress evenly.

• Functional Scope:

• Vertical load capacity: 50,000–200,000 kN (far exceeding standard pot bearings).

• Suitable for super-heavy bridges with large dead weights.

• Application Scenarios:

• Large-span cable-stayed bridges or suspension bridges (e.g., the main tower supports of a 1,000m-span sea-crossing bridge).

• Heavy-haul railway bridges (e.g., bridges for 30t-axis-load freight trains) or bridges with oversized superstructures (e.g., steel box girders with large cross-sections).

2.3 Corrosion-Resistant Pot Bearings (CRPB)

• Structural Modifications:

• Stainless steel (304 or 316 grade) for coastal areas with salt spray.

• Hot-dip galvanizing + epoxy coating (thickness ≥ 150 μm) for industrial areas with acid/alkali pollution.

• All steel components (pot shell, connecting plates) use corrosion-resistant materials:

• The PTFE plate is coated with a anti-aging film (e.g., fluorinated ethylene propylene) to resist UV radiation and chemical erosion.

• Application Scenarios:

• Coastal bridges (e.g., sea-crossing bridges, estuary bridges) exposed to saltwater.

• Bridges in chemical industrial zones or areas with high air pollution.

3. Key Parameter Comparison of Main Types

4. Standards & Selection Principles

• Core Standards:

• China: GB/T 17955-2019 Bridge Bearings (specifies material, performance, and testing requirements).

• International: EN 1337-5 (European standard for pot bearings) and AASHTO LRFD Bridge Design Specifications (American standard).

• Selection Tips:

1. Determine displacement direction/amount based on bridge type (straight/curved, simply supported/continuous).

2. Calculate vertical load based on superstructure weight + live load (e.g., vehicle, wind load).

3. Consider environmental factors (seismic intensity, corrosion, temperature) to select specialized types.