How Fixed Bearings and Slide Bearings Work in Bridge Construction
An integral piece of modern infrastructure, bridges connect us to parts of the world that were previously unattainable for modern travel. Some of the most notable engineering feats in humanity come in the form of bridges. Whether it be the Golden Gate Bridge on the west coast, or the historic Brooklyn Bridge on the east coast, bridges make up an impressive array of construction accomplishments.
Just like any other project, bridge construction requires careful consideration down to the finest detail. From the location of the project to the usage of the bridge, to the basic materials, there is much to factor into bridge engineering. Two types of bearings structural engineers may take into consideration are slide bearings and fixed bearings.
While similar in name, both types of bearings serve an important purpose when it comes to bridge construction. The type of project and the specific application may require one or both solutions, each with its own properties that make them essentials for bridge engineering.
In this article, we discuss slide bearings and fixed bearings, while also highlighting the importance of high-quality bearings in bridge construction. Read on to learn more.
What are Slide Bearings?
Also known as expansion bearings, slide bearings are a fundamental feature of bridge construction. Despite their size in comparison to the rest of the structure, they serve an essential purpose that allows bridges to fulfill their purpose without major issues.
In general, bearings allow for controlled movement and reduce the amount of stress placed on the structure. Some causes of movement in bridges are thermal expansion and contraction, fatigue in the structure and natural forces. The slide bearings accommodate for these forces to allow for a reliable, safe bridge structure.
“Slide bearings consist of two metal plates, commonly stainless-steel plates, that slide relative to each other and hence makes room for translational movement and lubricating material,” says The Constructor. Slide bearings are usually coated in other materials, like PTFE, to reduce generated friction and accommodate for other conditions.
What are Fixed Bearings?
As we mentioned, different types of bearings serve different purposes when it comes to bridge construction and bridge engineering. Fixed bearings are usually made of rubber or other resilient materials. They do not have any moving parts but allow for other types of movement in the structure. While they are similar in name, slide bearings and fixed bearings serve different purposes.
According to the Ohio Department of Transportation, fixed bearings “anchor the superstructure to the substructure (only allowing rotation), while others allow for expansion and contraction.” Bearings can be fixed in both longitudinal and transverse directions, transferring lateral forces from the superstructure to the substructure units.
In situations where the substructure is under excessive force, the fixed bearings are used to withstand the load. As you might imagine, the material of the fixed bearings usually differs from slide bearings given their different applications. For example, The Wisconsin Department of Transportation highlights that “it is best to use a fixed bearing utilizing an unreinforced elastomeric bearing pad.”
Improving Bridge Construction with Fabreeka Slide Bearings and Fixed Bearings
Although both slide bearings and fixed bearings differ in their usage, they are parts of a whole solution that allow for appropriate rotation and movement on bridges. With their range of applications in mind, what exactly does this mean for bridge construction?
Even though we highlighted the major differences between slide bearings and fixed bearings in bridge construction, they are both essential pieces in bridge engineering. Despite their differences, slide bearings and fixed bearings work together as part of a larger system that allows the bridge to expand, contract, rotate and safely shift loads.
Bridge engineering and bridge construction requires careful attention to detail, and that is especially true for the materials bridge engineers must consider. When designing a complete system, every type of bearing, whether fixed or slide bearings, must meet the specifications the project requires.
At Fabreeka, our portfolio of expansion bearings and solutions for fixed bearings meet any standard your project requires. Our array of slide bearings suits several applications and conditions, ensuring you have the right materials in place for expansion, contraction and rotation. Conversely, our resilient materials for fixed bearings protect the integrity of the structure.
Fabreeka Expansion Bearings
Designed to accommodate expansion and structural rotation in bridges and other construction applications, Fabreeka structural expansion bearings come available in several types to support your application. For example, our bridge bearings include Teflon® to accommodate for specific conditions.
With the Fabreeka-PTFE pad as part of the lower unit, the Fabreeka SBX type slide bearings are used where rotation is present with loads up to 1,500 psi. The SBX type slide bearing is the most resilient in our line of expansion bearings.
For applications with loads up to 2,000 psi, expansion and no rotation, the STX and TTX slide bearings are exceptional solutions. With a higher coefficient of friction than the STX slide bearing, the TTX slide bearing is better suited for applications with a limited expansion criterion.
Our line of slide bearings can also be made with holes and slots if your project requires them. This way, the slide bearings allow for mechanical attachment of expansion units to steel structures or anchoring for concrete structures.
For fixed bearings, our flagship elastomeric pad, the Fabreeka Pad, is our best solution for bridge construction and engineering. Effective, flexible and tough, the Fabreeka pad is commonly used as a bridge bearing pad. It accommodates for surface irregularity and rotations between load bearing faces.
As we mentioned before, the Fabreeka bearing pads come equipped with a PTFE surface that works in tandem with our line of slide bearings. The Fabreeka pad can withstand loads up to 10,000 psi depending on the size and thickness. Impervious to most oils, steam, water, mildew and brine, its remarkable resiliency makes the Fabreeka pad the premier solution for your bridge construction.
Moreover, the Fabreeka Pad meets AASHTO 22.214.171.124 Div. II specifications and most State DOT guidelines. The next time you need a reliable bearing pad to meet your specifications, turn to the Fabreeka Pad.
SA-47 Random Oriented Fiber Pad
Economic and effective, the SA-47 random oriented fiber pad withstands loads up to 7,000 psi and is made from masticated rubber using a blend of recycled rubber compounds and synthetic fiber reinforcement. The SA-47’s enhanced compressive strength, stiffness and tensile strength makes it a standout among other bearing pads.
Fabreeka’s SA-47 bearing pads provide compensation for surface irregularities and non-parallel load bearing surfaces in precast concrete structures or bridges. Widely used in bridge construction, the SA-47 pad is cost-effective and resilient, making it a great solution for your applications to meet many State DOT guidelines.
Considering their different functions, the importance of slide bearings and fixed bearings in bridge construction is vital. Both types of bearings work as part of a larger, carefully designed system in bridge engineering.
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Fabreeka’s line of slide bearings and fixed bearing solutions provide your next project with guaranteed quality and results. Our resilient, tested and trusted solutions help your project meet standards and certifications. The next time you need industry-leading solutions for bridge construction, turn to Fabreeka and our dedicate team of engineers to develop a solution with you.
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