Essential Guide to Bearing Selection: Common Types, Principles, and Key Considerations

Essential Guide to Bearing Selection: Common Types, Principles, and Key Considerations

In bridge and building structures, bearings are critical components connecting the superstructure and substructure. Their primary functions are to transfer loads and accommodate structural deformations. Correct bearing selection is vital to ensure structural safety, durability, and conformity with the intended design force diagram. This article details seven common types of bearings—including laminated rubber bearings for bridges, pot bearings for bridges, spherical bearings, spherical steel bearings, seismic isolation rubber bearings, space frame bearings, and rubber pads—explaining their working principles and key selection points.

I. Common Bearing Types and Working Principles

1.Laminated Rubber Bearings for Bridges: This is a widely used bearing type, manufactured by vulcanizing and bonding multiple layers of thin steel plates and rubber sheets. Its working principle relies on the elasticity of rubber: rotation is achieved through uneven elastic compression, and horizontal displacement is achieved through shear deformation. These bearings typically do not have fixed or movable distinctions, have a simple structure, and are suitable for small to medium span bridges with moderate reaction forces and small displacement requirements.

2.Pot Bearings for Bridges: Designed for large reaction forces and large displacement demands. The principle involves sealing a rubber block within a steel pot, subjecting the rubber to a triaxial stress state, thereby significantly enhancing load capacity. Horizontal displacement is achieved through the sliding of the upper bearing plate against a polytetrafluoroethylene (PTFE) (or stainless steel) sheet, and rotation is achieved through the compressive deformation of the rubber. Pot bearings offer high load capacity and flexible rotation. They are available in fixed, unidirectional movable, and multi-directional movable types and are widely used in medium and large span bridges.

3.Spherical Bearings: Rotation is achieved through sliding between the spherical crown liner and a concave spherical PTFE sheet, while displacement is achieved through sliding between the lower bearing plate and a PTFE sheet. They are characterized by consistent rotational performance in all directions, large rotation angles, and uniform force distribution. They are particularly suitable for curved bridges, wide bridges, and structures with high rotational requirements.

4.Spherical Steel Bearings: Essentially a steel version of spherical bearings, typically offering higher load capacity and better durability. Their core principle is consistent with spherical bearings, utilizing spherical sliding to accommodate rotation and planar sliding to accommodate displacement. They are suitable for large bridges, railway bridges, and heavy-load structures.

5.Seismic Isolation Rubber Bearings: A special type of bearing with seismic isolation function, commonly divided into lead rubber bearings (LRB) and high damping rubber bearings (HDR). The principle involves adding a lead core or using high-damping rubber material on the basis of ordinary laminated rubber bearings, providing greater damping and energy dissipation capacity, lengthening the natural vibration period of the structure, thereby effectively reducing seismic forces. Primarily used in bridge and building seismic isolation design in high-intensity earthquake zones.

6.Space Frame Bearings: Bearing types specifically designed for space frame structures and large-span spatial structures. They typically include various forms such as plate-type pressure bearings, single curved surface pressure bearings, and spherical hinge pressure bearings. Their working principle must accommodate the mechanical characteristics of the space frame, bearing axial forces and shear forces while also accommodating specific rotations. Commonly used in large-span spatial structures like stadiums, exhibition centers, and airport terminals.

7.Rubber Pads: The simplest form of bearing, usually made of plain rubber or rubber with minimal reinforcement. Their working principle utilizes the compressive and shear deformation of rubber to accommodate structural displacement and rotation. Primarily used for secondary components or temporary supports with low load capacity and minimal displacement requirements, or for auxiliary functions such as leveling adjustments and vibration/noise damping.

II. Key Considerations for Bearing Selection

When selecting bearing types, the following critical factors must be comprehensively considered:

Structural Load Requirements: Determine the bearing capacity based on the span, dead load, and live load reactions at the support point. Simultaneously, clarify the required displacement (longitudinal, transverse) and rotation angle for the structure to decide if movable or fixed bearings are needed.

Structural System and Layout: Simply supported beam bridges typically require a fixed bearing at one end and a movable bearing at the other. For continuous beam bridges, only one fixed bearing is generally set per continuous unit. For curved bridges, sloped bridges, wide bridges, and space frame structures, bearing layout must consider special needs like transverse displacement, torsion resistance, and uplift resistance.

Special Condition Requirements: Seismic zones require consideration of seismic isolators (elastomeric seismic isolators); cold regions require low-temperature-resistant bearings; coastal and cross-sea bridges require corrosion-resistant bearings. For structures with potential uplift forces, tension-resistant bearings are necessary.

Economy and Maintainability: While meeting technical performance requirements, the principles of economy, practicality, and ease of maintenance should be followed. The design should consider the feasibility of future bearing replacement, reserving necessary jacking space and structural provisions.

In summary, scientifically sound bearing selection requires comprehensive evaluation of structural load characteristics, deformation demands, environmental conditions, and long-term maintenance requirements to ensure project safety and durability.