Each time you drive across a bridge, it’s unlikely that you consider the complicated engineering components working beneath your wheels. Still, buried between the bridge deck and its supporting piers are important devices called bridge bearings: unsung heroes that make structural integrity and longevity possible.
What Are Bridge Bearings?
Bridge bearings are specialty structural elements placed at the interface between a bridge’s superstructure-the deck-and its substructure-the piers and abutments. They have two primary functions: transferring loads from the deck to the supporting structure while allowing controlled movement of the bridge.
Think of them as the joints in a bridge-they allow for necessary movement while maintaining structural stability.
How Bridge Bearings Work
Bridge bearings function through a carefully engineered balance of load transfer and movement accommodation. Here’s how they operate:
Load Transfer Mechanism
Bearings act as the critical connection point, distributing vertical loads (dead loads from the structure’s weight and live loads from traffic) from the bridge deck down to the piers and abutments. They’re designed to handle millions of pounds of force while maintaining precise positioning.
Movement Accommodation
Through various mechanical designs—whether elastic deformation in rubber compounds, sliding surfaces with low-friction materials like PTFE (polytetrafluoroethylene), or spherical articulation—bearings permit controlled displacement. This allows the bridge to expand and contract with temperature changes, rotate slightly under uneven loading, and shift horizontally during seismic events without transmitting damaging stresses to the substructure.
Force Distribution
Quality bearings ensure that forces are evenly distributed across the support surface, preventing stress concentrations that could lead to localized damage in concrete piers or steel supports. This uniform distribution is essential for the long-term durability of both the superstructure and substructure.
Why Bridges Need to Move
Bridges are not static structures. Constantly, they undergo forces from a multitude of sources: temperature fluctuations, causing expansion or contraction; traffic loads, creating dynamic stress; wind forces; seismic activity; and even the natural settlement of foundations over time.
Without bearings to allow for these movements, bridges would be prone to cracking, excessive stress concentration, and premature structural failure. In essence, bridge bearings serve to safeguard the structure by absorbing and controlling these inevitable movements and resultant forces.
Common Types of Bridge Bearings
1.Elastomeric Bearings
Elastomeric bearings are the most economical option to carry moderate loads, manufactured from reinforced rubber compounds. They allow for displacements through their elastic deformation. They require very little maintenance and are, therefore, particularly suited for smaller and medium-span bridges. These bearings conform to international standards including AASHTO and EN 1337 specifications.
2.Pot Bearings
Pot bearings are used in applications where structures have heavy vertical loads: They consist of an elastomeric disc confined within a steel pot. These bearings offer very good load-carrying capacity with controlled rotation, and can be combined with sliding surfaces for translational movement.
3.Spherical Bearings
Spherical bearings account for high vertical loads with considerable horizontal forces that require rotation in most, if not all, directions. The design of curved plates allows them to support higher loads and movement; hence, they are ideal for complicated geometries of bridges and the most challenging environments. Foster International has extensive experience in supplying and supervising spherical bearing installations for major infrastructure projects.
4.Specialized Bearings
Modern infrastructure requires specialized solutions such as lead rubber bearings for seismic isolation, incremental launching method (ILM) bearings for particular construction techniques, and guide bearings for constraining movement in certain directions.
Bridge Bearings and Expansion Joints: A Critical Partnership
While bridge bearings and expansion joints are distinct components, they work in tandem to manage bridge movement and maintain structural integrity.
Bridge bearings accommodate movement at the support points where the deck meets the piers, while expansion joints handle movement at the deck surface—typically at bridge ends or between sections. The movement capacity of both systems must be coordinated: if bearings allow for 100mm of thermal expansion, expansion joints must accommodate that same displacement. Mismatched capacities can lead to system failure.
Common expansion joint types include strip seals for moderate movements, modular joints for large displacements, finger joints for medium-range applications, and sliding plate joints for smaller movements.
Both systems require coordinated maintenance and inspection programs. Failed expansion joints can allow water infiltration that damages bearings, while malfunctioning bearings can cause excessive movement that damages joints. During construction, both must be installed at similar ambient temperatures to ensure the structure is in its neutral position.
Key Considerations for Bridge Bearing Selection
Proper selection of the bearing system requires careful consideration of a number of factors:
- Load Requirements: The vertical loads from the weight of the structure, as well as horizontal forces from traffic, wind, and seismic activity, must be correctly determined.
- Movement Capacity: The range of translational and rotational movements the structure will experience during its service life should be determined by engineers using industry-standard design methodologies.
- The environmental conditions include climate, temperature fluctuation, and exposure to corrosive agents that impact material selection and design specifications.
- Maintenance Accessibility: Some bearing types require more frequent inspection and maintenance than others, affecting long-term operational costs.
- Construction method: Some bridge construction methods, such as incremental launching and others, may be the sole reason for adopting specific bearing requirements.
The Importance of Quality and Expertise
Bridge bearings are precision-engineered components that require exacting standards of manufacture and installation. Poor-quality bearings or inadequately installed bearings will compromise the safety and durability of the entire structure.
At Foster International, we recognize that successful infrastructure projects are about more than the supply of components—they are about expertise, quality assurance, and comprehensive support throughout the project lifecycle. Our experience with major projects throughout the Middle East, including recent awards for the Al Shindagha Corridor and DEWA Metro Link Bridge projects, illustrates our commitment to providing reliable bearing solutions with full technical supervision.
We partner with established manufacturers like TechStar Inc, specialists in bridge-related products with over 100 years of combined engineering experience, to ensure our clients receive world-class bearing systems designed and manufactured to the highest standards.
Looking Forward
Bridge bearing technology continues to evolve and improve as infrastructure evolves with longer spans, heavier loads, and increased seismic requirements. These modern bearings incorporate sophisticated materials, integrated monitoring systems, and enhancements for durability that will meet the challenges of tomorrow.
Whether it’s a new bridge project or the maintenance of existing infrastructure, understanding bridge bearings and choosing the right partner for the supply and installation is critical for long-term success.
Foster International LLC specializes in providing comprehensive civil engineering solutions, including the supply and supervision of bridge bearings for infrastructure projects across the Middle East. Contact our expert team to discuss your project requirements.
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