Bridge bearings play a crucial role in the structural integrity and functionality of bridges. These devices, installed between the bridge’s substructure and superstructure, are designed to transfer applied loads—including seismic, wind, traffic, and self-weight loads—while accommodating movements such as rotation and translation. Bridge bearings are categorized into expansion bearings, which allow both translational and rotational movements, and fixed bearings, which permit rotational and limited translational movements. This article explores the various types of bridge bearings used in construction and their specific characteristics.

Understanding Bridge Bearings

What Are Bridge Bearings?

Bridge bearings are structural devices placed between the substructure and superstructure of a bridge. They facilitate the transfer of loads while allowing for necessary movements, ensuring the bridge’s stability and durability. These bearings accommodate different types of loads, such as seismic, wind, traffic, and the bridge’s own weight, while also allowing for movements like rotation and translation.

Types of Bridge Bearings

Bridge bearings are broadly classified into two categories: expansion bearings and fixed bearings. Expansion bearings permit both translational and rotational movements, while fixed bearings allow for rotational and limited translational movements. The primary types of bridge bearings include sliding bearings, rocker and pin bearings, roller bearings, elastomeric bearings, curved bearings, pot bearings, and disk bearings.

Sliding Bearings for Bridges

Overview of Sliding Bearings

Sliding bearings consist of two metal plates, typically stainless steel, that slide relative to each other, facilitating translational movement. To minimize friction, lubricating materials such as polytetrafluoroethylene (PTFE) are used between the plates.

Application and Limitations

Sliding bearings generate frictional forces that impact the substructure, superstructure, and the bearings themselves. According to ASSHTO guidelines, sliding bearings are not suitable for bridge spans exceeding 15 meters, as they do not accommodate rotational movements. However, this limitation can be overcome by combining sliding bearings with other bearing types.

Rocker and Pin Bearings for Bridges

Structure and Function

Rocker bearings feature a curved bottom surface for translational movement and a pin at the top for rotational movement. Pin bearings, on the other hand, are fixed bearings that accommodate rotational movement via a steel pin. Both types are primarily used in steel bridge structures.

Considerations and Maintenance

Rocker and pin bearings should be used when bridge movements are well-understood and described, as they accommodate movements in one direction only. Regular inspection and maintenance are crucial due to their susceptibility to corrosion and deterioration.

Roller Bearings for Bridges

Types of Roller Bearings

Roller bearings can be used in reinforced concrete and steel bridge structures. They come in two main configurations: single roller bearings, which consist of one roller between two plates, and multiple roller bearings, which include several rollers between two plates.

Benefits and Drawbacks

Single roller bearings are economical and can accommodate both rotation and translational movements, but they have limited vertical load capacity. Multiple roller bearings can support large vertical loads and accommodate translational movements, but they are more expensive. Both types require regular maintenance to prevent corrosion and damage.

Curved Bearings for Bridges

Design and Functionality

Curved bearings consist of two matching curved plates. Cylindrical curved bearings accommodate rotational movements, while spherical curved bearings allow for both rotational and translational movements. The geometry and gravity loads provide lateral resistance, which is mitigated by adding PTFE sliders to accommodate lateral movements.

Usage and Advantages

Curved bearings are effective in managing rotational and translational movements, especially in spherical configurations. The use of PTFE sliders enhances their ability to handle lateral movements, making them versatile for various bridge designs.

Pot Bearings for Bridges

Composition and Mechanism

Pot bearings comprise an elastomeric disk confined in a pot, a steel piston tailored to the pot wall, and flat sealing rings that keep the elastomer inside the pot. These bearings can support significant vertical loads, transferred through the steel piston to the elastomeric disk.

Movement and Load Transfer

Pot bearings primarily accommodate rotational movements, with limited translational movement. To enhance translational capability, PTFE sliders are introduced to the sliding surface. This design makes pot bearings suitable for handling substantial vertical and lateral loads.

Disk Bearings for Bridges

Components and Function

Disk bearings include an elastomeric disk and a metal ring in the center. Rotational movement is accommodated through elastomer deformation, while translational movement is managed by PTFE sliders. The elastomer must be hard enough to support vertical loads without excessive deformation and flexible enough to allow for rotational movements.

Applications and Maintenance

Disk bearings are effective in supporting both vertical and lateral loads. Regular maintenance is essential to ensure the elastomer retains its properties and the bearing functions correctly over time.

Conclusion

Bridge bearings are indispensable in modern bridge construction, providing the necessary support and movement accommodation to ensure structural integrity and longevity. Each type of bearing has specific applications, advantages, and limitations, making it essential to choose the right bearing type based on the bridge’s design and load requirements. Regular inspection and maintenance are crucial to the performance and durability of these bearings.

Summary

Bridge bearings are crucial components in bridge construction, enabling load transfer and movement accommodation between the bridge’s substructure and superstructure. The main types include sliding, rocker and pin, roller, curved, pot, and disk bearings, each with unique features and applications. Proper selection, installation, and maintenance of these bearings are vital for the bridge’s functionality and longevity.

FAQs

What are bridge bearings?

Bridge bearings are devices installed between a bridge’s substructure and superstructure to transfer loads and allow for necessary movements like rotation and translation.

What are the main types of bridge bearings?

The main types of bridge bearings include sliding bearings, rocker and pin bearings, roller bearings, elastomeric bearings, curved bearings, pot bearings, and disk bearings.

What is the difference between expansion and fixed bearings?

Expansion bearings allow for both translational and rotational movements, while fixed bearings permit rotational and limited translational movements.

Why is regular maintenance of bridge bearings important?

Regular maintenance is crucial to prevent corrosion, deterioration, and damage, ensuring the bearings function correctly and extend the bridge’s lifespan.

How do sliding bearings reduce friction?

Sliding bearings reduce friction using lubricating materials like polytetrafluoroethylene (PTFE) between the sliding metal plates.

When are pot bearings used in bridge construction?

Pot bearings are used when substantial vertical loads need to be supported, as they can accommodate significant rotational movements and, with PTFE sliders, limited translational movements.