Four things you need to know about how bridge bearings are maintained

August 12, 2024
By Enerpac, for the Blue Print

Bridge bearings play a crucial role in ensuring the safety and longevity of bridges, yet they are often overlooked and taken for granted as they are hidden from view. Without them, bridges would be vulnerable to significant damage and eventual failure. Here are the different types of bridge bearings and how they are maintained.
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Bridge bearings

The primary purpose of bridge bearings is to provide flexibility and support to bridges, allowing them to adjust to various external factors such as temperature changes, traffic loads, and seismic activity. They transfer the load from the superstructure (deck) to the substructure or piers, while also allowing for the movement and rotation of the bridge deck.
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Types of bridge bearings

Bridge bearings are typically made of steel, elastomeric materials, or a combination of both. They allow bridge parts to move freely, while helping to reduce the stresses that can build up within the structure.
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Common types

• Elastomeric 
• Pot
• Spherical 
• Rocker
• Roller
• Sliding

The type of bridge bearing used will depend on several factors, including the expected load weights, the span length, and the available space for accessing the bearing. 
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Aspects of bridge bearing maintenance 

To ensure longevity and performance, bridge bearings need regular maintenance. There are four key steps to maintain bridge bearings.

1. Monitor: Bearing performance should be monitored regularly to detect changes or problems. This can be done using various methods, such as measuring displacement or strain, or observing any unusual movements or vibrations. 
   
2. Clean: Bearing pads should be cleaned to remove any dirt, debris, or other contaminants that may cause damage or reduce their effectiveness. 
   
3. Lubricate: Proper lubrication is crucial to ensure smooth movement of the bearing pads. This should be performed using a suitable lubricant, such as silicone or mineral oil, and usually with the deck raised by a very small amount. Raising the deck is done using hydraulic cylinders which allows lubricant to be pumped into the aperture. 
   
4. Replace: Over time, bridge bearing pads wear out or become damaged, and they will therefore need to be replaced. Reasons for this include: 
   
   1. ​Leaking bridge deck joints - allowing corrosive water and debris to reach the bearings 
      
   2. Inadequate visibility that prevents inspection
      
   3. Extreme environmental conditions caused by cold, we, or industrial pollution 
      
   4. Improper bearing specification and orientation 
      
   5. Inadequate multidirectional movement 
      
   6. Bearing defects caused in production 
      
   7. Wear and fatigue due to overload 
      

Replacement of bearings should be done according to the manufacturer's specifications, and by a qualified engineer or contractor.
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How to maintain bridge bearings

Replacement of bearings is often done using hydraulic equipment such as cylinders (jacks or rams) connected to hydraulic pumps, these raise the deck beams by a small amount – just enough to free the bearings for replacement or resetting. Precise control of the jacks is needed to avoid damage to the structure. This can be achieved using split flow or a more advanced synchronous lifting pump.

Depending on the type of bridge, structure, and the nature of the project, the bearings may be replaced individually or as a group. The effect of traffic closures can be significant, so a quick turnaround is essential.

When using hydraulic jacks, these typically support the bridge beams next to the bearing being replaced. The hydraulic flow is activated, extending the cylinder plungers by a very small amount. The load is then secured mechanically using the locknut mechanism on each cylinder.

Next, the bearing is removed, which sometimes can require the top of the supporting pedestal or mortar pad to be partially demolished. The area is then reconstructed or cleaned, before the new bearings are installed. Finally, the locknuts are deactivated and the is cylinder retracted until the new bearing takes the load.
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Equipment for bearing replacements 

Any hydraulic equipment used to temporarily raise and support a bridge deck needs to be robust and reliable and made by a reputable brand with a long history of success. The risks involved are far too high to rely on equipment that’s low quality or damaged.

Safety can be enhanced by using the right hydraulic system to suit the project. For example, if you intend to lift multiple points simultaneously, consider using a split flow pump such as the EVO from Enerpac. This can be specified to control up to 12 points and deliver accuracy of up to 0.040 in (1 mm) between leading and lagging cylinders. Built-in warning and stop alarms also help to ensure safe operation.

Each project will have its own unique requirements. Typical examples of hydraulic equipment used include:

• High tonnage locknut hydraulic cylinders (can be either load return or double-acting) 
• Pancake (low-height) locknut hydraulic cylinders 
  
• Hydraulic pumps, either individual or controlled synchronous lifting pumps 
  
• Components and accessories such as couplers, valves, gauges, manifolds, and hoses 

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​Content originally from Enerpac. Reused here with permission.

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