Pot Bearing For Bridges Applications Under Structure Bearing

Bridge pot bearings are critical structural components that facilitate load transfer between a bridge's superstructure and substructure while accommodating horizontal displacements and rotations induced by thermal effects, traffic loads, seismic activity, and creep. Engineered for durability and precision, our pot bearings integrate advanced materials and manufacturing processes to meet global standards, ensuring long-term performance in diverse environmental and loading conditions.
The pot rubber bearing is a type of bridge bearing product that adopts an elastic rubber block enclosed in a semi-sealed steel pot. This rubber block exhibits fluid-like properties when subjected to three-dimensional forces.

This product enables the rotation of the bridge superstructure. Meanwhile, it relies on the low friction coefficient between the F4 plate (polytetrafluoroethylene plate) on the middle steel plate and the stainless steel plate of the upper seat plate to achieve the horizontal displacement of the superstructure. As a result, the shear force borne by the rubber bearing is no longer fully carried by the rubber; instead, it acts indirectly on the steel base pot and the sliding between the F4 plate and the stainless steel plate.

When the rubber inside the pot bearing is in a three-dimensionally constrained state, its compressive elastic modulus is 50,000 kg/cm², which is nearly 20 times higher than the compressive elastic modulus without lateral constraints. Therefore, the load-bearing capacity of the bearing is significantly improved, overcoming the drawback of the relatively low load-bearing capacity of plate rubber bearings. It can meet the requirements of large support reaction forces, large horizontal displacements, and large rotation angles.

2.1 Key Advantages
● Multi-Standard Compliance: Designed to meet EN 1337-5, JTT391, and AASHTO LRFD specifications, ensuring adaptability to global projects.
● High Load Capacity: Capable of withstanding vertical loads from 2,500 kN to 50,000 kN (customizable for higher demands), suitable for heavy-duty highway and railway bridges.
● Robust Rotation & Displacement Control: Accommodates rotations up to 0.02 rad and horizontal displacements up to ±250 mm, ensuring structural flexibility under dynamic loads.
● Durable Materials: Utilizes high-grade alloy steel, vulcanized elastomers, and low-friction PTFE, resistant to corrosion, aging, and extreme temperatures (-40°C to +60°C).
● Low Maintenance: Sealed design and lubricated sliding surfaces minimize wear, reducing lifecycle costs.
2.2 Limitations
● Weight & Handling: Steel-intensive construction increases weight, requiring specialized lifting equipment during installation.
● Precision Installation: Demands strict alignment tolerances (±1 mm) to avoid uneven load distribution, necessitating skilled labor.
● Cost: High-performance materials and compliance with multiple standards result in higher upfront costs compared to simpler bearing types.
● Temperature Sensitivity: Standard neoprene models may degrade in extreme cold; cold-resistant EPDM variants are required for sub-zero climates.

3.1 EN 1337-5 (European Norms)
Adheres to requirements for static and dynamic load testing, material durability, and displacement capacity. Specifically, EN 1337-5 mandates:
● Minimum compressive strength of 30 MPa for steel components.
● Elastomer shear modulus ≥0.8 MPa at 23°C.
● Sliding surface friction coefficient ≤0.03 under standard conditions.
3.2 JTT391 (Chinese Highway Standards)
Complies with dimensional tolerances (e.g., pot diameter ±0.5 mm) and corrosion protection protocols, including:
● Hot-dip galvanization (minimum 85 μm thickness) for steel parts.
● Rubber hardness 60±5 Shore A, with elongation at break ≥300%.
3.3 AASHTO LRFD (U.S. Specifications)
Aligns with HLMR (High Load Multi-Rotational) bearing requirements, including:
● Load factors for dead and live loads (1.25 and 1.75, respectively).
● Seismic design provisions (horizontal force coefficients based on peak ground acceleration).

4.1 Main Structure
● Steel Pot: Rigid housing (S355JR steel) distributing vertical loads to the substructure.
● Elastomeric Disc: Vulcanized rubber (neoprene or EPDM) absorbing shocks and enabling rotation.
● Piston: High-strength steel (42CrMo) component transferring loads from the superstructure to the rubber disc.
● Sliding Interface: Stainless steel (304 grade) plate with PTFE sheet, reducing friction during horizontal movement.
4.2 Material Specifications
Component Material Key Properties (per Standards)
Steel Pot/Piston S355JR/42CrMo Yield strength ≥355 MPa; tensile strength ≥510 MPa
Elastomer Neoprene/EPDM Hardness 60±5 Shore A; compression set ≤25%
Sliding Plate 304 Stainless Steel Mirror finish (Ra ≤0.8 μm); thickness ≥4 mm
PTFE Sheet Virgin PTFE Density ≥2.15 g/cm³; friction coefficient ≤0.03

4.3, Working Principle
The working principle of the pot rubber bearing is to utilize the rubber block enclosed in a steel pot. This rubber block, when subjected to three-dimensional forces, exhibits the characteristic of incompressible volume similar to a fluid. By leveraging this property, the bearing reliably transmits the reaction force of the bridge superstructure to the pier, while enabling the rotation of the bridge beam ends. Meanwhile, it relies on the free sliding between the polytetrafluoroethylene (PTFE) plate and the stainless steel plate to accommodate the horizontal displacement of the bridge superstructure caused by factors such as temperature changes and creep shrinkage of concrete. This ensures the safe operation of the bridge.
This product is suitable for high-grade highway bridges and other large and medium-sized bridges.

4.4, Product Types
4.4.1, Classified by Service Performance:

• Bidirectional Movable Bearing: Features vertical load-bearing, vertical rotation, and bidirectional sliding performance, with the code SX.
• Unidirectional Movable Bearing: Features vertical load-bearing, vertical rotation, and unidirectional sliding performance, with the code DX.
• Fixed Bearing: Features vertical load-bearing and vertical rotation performance, with the code GD.

4.4.2, Classified by Applicable Temperature Range:

•  Normal-Temperature Bearing: Suitable for use in the temperature range of -25℃ ~ +60℃.
• Cold-Resistant Bearing: Suitable for use in the temperature range of -40℃ ~ +60℃, with the code F.

4.4.3, Classified by Application Scope:
It can be divided into three major categories: pot rubber bearings for highway bridges, pot rubber bearings for railway bridges, and derivatives of pot rubber bearings.
4.4.3.1, Common Models of Pot Rubber Bearings for Highways:
GPZ series pot rubber bearings
GPZ (Ⅱ) series pot rubber bearings (in accordance with JTT391-1999)
GPZ (III) series pot rubber bearings (in accordance with JTT391-2009)
GPZ (KZ) series anti-seismic pot rubber bearings
GPZ (2019) series pot rubber bearing (in accordance with JTT391-2019)
4.4.3.2, Common Models of Pot Rubber Bearings for Railways:
TPZ-I railway pot rubber bearings
TPZ standard railway pot rubber bearings
Special Bridges 8156 Series railway bridge bearings
4.4.3.3, Derivatives of Pot Rubber Bearings:
There are many types of derivatives, such as:
QPZ series pot rubber bearings
KPZ series pot rubber bearings
Elastic shock-absorbing spherical steel bearings
Self-height-adjusting pot rubber bearings.

5.1, Technical Performance Parameters
● Vertical Load Capacity: 2,500–50,000 kN (customizable).
● Rotation Capacity: ≥0.02 rad (3.43°) under full design load.
● Horizontal Displacement: ±50 mm to ±250 mm (longitudinal/transverse).
● Horizontal Force Resistance: - Fixed bearings: 15–40% of vertical load (based on seismic zone). - Movable bearings: 5% of vertical load.
● Friction Coefficient: ≤0.03 (normal temperature); ≤0.05 (cold-resistant).
● Service Life: ≥50 years under standard maintenance.
5.2, Specification List (According to standard JTT391 of China Highway Bridges Standard).
▲ GPZ(III) Specifications of pot bearing under structure bearing;
▲ GPZ(KZ) Specifications of pot bearing under structure bearing;
▲ GPZ(2019) Specifications of pot bearing under structure bearing;

6.1, Testing equipment;

6.2, Type testing &Testing reports by Third Party;

7.1 Highway Bridge, Yangtze River Delta, China
● Project: 6-span continuous beam bridge (total length 380 m).
● Bearing Type: 4000 kN capacity, bidirectional movable pot bearings (JTT391 compliant).
● Performance: Withstood seasonal temperature variations (-10°C to +35°C) and heavy truck loads (up to 550 kN) for 12 years with minimal wear.
7.2 Railway Bridge, Bavaria, Germany
● Project: High-speed rail bridge (design speed 300 km/h).
● Bearing Type: 12,000 kN fixed pot bearings (EN 1337-5 compliant).
● Performance: Accommodated dynamic train loads and thermal displacements (±120 mm) with rotation accuracy ≤0.015 rad.
7.3 Interstate Bridge, Texas, USA
● Project: Cable-stayed bridge with 200 m main span.
● Bearing Type: 25,000 kN HLMR pot bearings (AASHTO LRFD compliant).
● Performance: Survived 2021 seismic events (peak acceleration 0.2g) with no structural damage, validated by post-event inspections.

8.1 Installation Steps
● Site Preparation: - Clean the bearing seat (concrete or steel) to remove debris; ensure flatness (tolerance ≤2 mm/m). - Verify anchor bolt positions match design drawings (±5 mm tolerance).
● Bearing Placement: - Use a crane with a spreader beam to lift the bearing (avoid direct hooks on sliding surfaces). - Lower the bearing onto the seat, aligning centerlines with bridge longitudinal/transverse axes (±1 mm).
● Anchoring: - Tighten anchor bolts in a crisscross pattern to 80% of torque (per JTT391: 350 N·m for M24 bolts). - Recheck alignment after tightening; adjust if necessary.
● Superstructure Placement: - Lower the superstructure onto the bearing slowly (≤50 mm/min) to avoid impact loads. - Measure initial rotation and displacement using dial gauges; record for future reference.
● Final Inspection: - Confirm no gaps between bearing and seat; seal perimeter with polyurethane sealant. - Document installation parameters (alignment, torque values) for as-built records.
8.2 Key Precautions
● Environmental Conditions: Avoid installation in rain/snow; protect PTFE surfaces from dust with temporary covers.
● Load Distribution: Ensure uniform contact between bearing and superstructure/substructure (use shims if gaps >0.5 mm).
● Safety: Use fall protection for elevated installations; follow OSHA/AWS safety protocols for steelwork.

9.1 Routine Inspection (Annually)
● Visual Checks: Inspect steel components for corrosion, rubber for cracks/aging, and sliding surfaces for wear.
● Functional Tests: Measure horizontal displacement under thermal cycles; check rotation using inclinometers.
● Lubrication: Reapply silicone grease (NLGI Grade 2) to PTFE surfaces; remove old grease before application.
9.2 Periodic Maintenance (Every 2 Years)
● Cleaning: Power-wash steel surfaces; remove debris from sliding interfaces.
● Corrosion Protection: Touch up galvanized areas with zinc-rich paint (dry film thickness ≥60 μm).
● Component Replacement: Replace PTFE sheets if wear exceeds 30% of original thickness; replace rubber discs if hardness deviates by >10 Shore A.
9.3 Post-Event Inspections
● After earthquakes, floods, or extreme temperature events: - Check for bolt loosening (retorque if needed). - Verify no permanent deformation of steel components. - Test sliding functionality to ensure no seizing.

● Packaging: Bearings are crated in weatherproof wooden boxes with foam insulation. Sliding surfaces are covered with protective film; anchor bolts are packed separately.
● Transportation: Secure crates to trucks with steel straps (minimum 4 points); avoid stacking >2 crates. Temperature-controlled transport is required for cold-resistant bearings (-40°C models).

● Material Innovation: Integration of carbon fiber-reinforced polymers (CFRP) to reduce weight while maintaining strength.
● Smart Monitoring: Embedded sensors (strain gauges, accelerometers) for real-time load/displacement tracking, enabling predictive maintenance.
● Sustainability: Use of recycled rubber in elastomers and water-based coatings to reduce environmental impact.
● Modular Design: Standardized components for faster on-site assembly, reducing installation time by 30%.

● Warranty: 10-year warranty against manufacturing defects; covers replacement of faulty components (excludes damage from improper installation/maintenance).
● Support: 24*7 technical hotline; on-site inspection teams available within 48 hours for critical issues. Training programs for installers and maintenance crews upon request.

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