Why is it said that the multi-directional displacement adaptability of spherical bearings in railway
The reason why the spherical bearings of railway rail transit bridges are considered to have good adaptability to multi-directional displacement lies in their unique structural design, force transmission mechanism, and material properties. They can correctly match the rigid requirements of railway bridges for "multi-dimensional displacement compensation" under complex working conditions (such as t
The reason why the spherical bearings of railway rail transit bridges are considered to have good adaptability to multi-directional displacement lies in their unique structural design, force transmission mechanism, and material properties. They can correctly match the rigid requirements of railway bridges for "multi-dimensional displacement compensation" under complex working conditions (such as temperature changes, load effects, foundation settlement, etc.), while ensuring driving safety and structural stability. The following provides a detailed analysis from three aspects: structural principles, displacement adaptation dimensions, and core advantages:
1、 Core structure: "Spherical+Sliding Pair" design, laying the foundation for multi-directional displacement
The core structure of a spherical bearing consists of four parts: an upper bearing plate, a lower bearing plate, a spherical sliding plate (PTFE sliding plate+stainless steel plate), and a spherical crown liner plate. Its "multi-directional displacement capability" is essentially achieved through the combination of "spherical rotation" and "planar sliding". This composite structure of "spherical rotation+planar sliding" breaks the displacement limitations of traditional bearings (such as plate rubber bearings that can only slide unidirectionally and pot type bearings with limited rotation angles), and has the potential for "multi-directional adaptation" from the structural root.
2、 Specific manifestation of multi-directional displacement adaptability: covering the core displacement requirements of railway bridges
During the operation of railway bridges, there will be three types of displacement: vertical, horizontal, and angular, due to factors such as temperature changes, train loads, concrete shrinkage and creep, and foundation settlement. Horizontal displacement often involves two directions: longitudinal (along the railway line) and transverse (perpendicular to the railway line). Spherical bearings can fully cover these displacement requirements. The specific adaptation scenarios are as follows:
1. Horizontal displacement: bi-directional free sliding, adapted to temperature and load deformation
The horizontal displacement of railway bridges mainly originates from two major scenarios:
Temperature deformation: In summer, the beam undergoes thermal elongation, and in winter, it undergoes cold shrinkage and shortening, resulting in a "longitudinal horizontal displacement" along the railway line (the larger the span, the greater the displacement, such as a 32m simply supported beam with a longitudinal displacement of ± 20mm or more);
Lateral load effect: The train passing through bends and lateral wind loads will cause the beam to experience "lateral horizontal displacement" (which needs to be controlled at the millimeter level to avoid track deviation).
The "spherical sliding plate" design of the spherical bearing allows the spherical crown liner to slide in any horizontal direction (longitudinal, transverse): due to the low friction coefficient between PTFE sliding plate and stainless steel plate, even under vertical loads (such as the self weight of a thousand ton beam), it can still achieve "small resistance, no jamming" horizontal displacement compensation, and the sliding amount can be adjusted through design (conventional can reach ± 50mm, special requirements can customize larger displacement), fully adapting to the horizontal deformation requirements of railway bridges.
2. Angular displacement: Rotate in any direction to solve the angular displacement at the end of the beam
Under the action of loads (such as local loads during train passage and self weight distribution of the beam), the beam body of railway bridges will experience "corner displacement" at the end (such as when a simply supported beam is bent at the mid span, the beam end will rotate downward, and the corner is usually between 0.005 and 0.01 rad); In addition, uneven settlement of bridge piers and abutments can also cause additional turning angles in the beam body.
The rotation of traditional bearings (such as plate rubber bearings) relies on the elastic deformation of the rubber, and their turning ability is limited (which can easily lead to rubber cracking due to excessive rotation); The "ball crown lining plate" of the spherical support can rotate 360 ° in any direction around the center of the ball, with a rotation angle of up to 0.05 rad (about 2.86 °), far exceeding the actual turning angle requirements of railway bridges. At the same time, the "spherical contact" during the rotation process can ensure that the load is always transmitted through the center of the sphere, avoid local stress concentration, and ensure the safety of the connection between the support and the beam, pier and abutment.
3. Vertical displacement: limited compensation, adapted to foundation settlement
The vertical displacement of railway bridges is mainly caused by uneven settlement of pier and abutment foundations (such as compression of soft soil foundations and slight settlement of foundations after earthquakes). Although the core of spherical bearings is "horizontal+angular displacement compensation", they can achieve vertical displacement compensation of ± 2-5mm through the "vertical compression of spherical sliding plates" (PTFE material has a certain degree of elasticity, can withstand vertical pressure and produce slight deformation), which can effectively buffer the impact of foundation settlement on the beam body and avoid the detachment of the beam body from the bearing or excessive local compression.
3、 Spherical bearings: the core advantage of multi-directional displacement adaptability
The "multi-directional displacement adaptability" of spherical bearings is not only reflected in the "full coverage dimension" (horizontal and bidirectional+arbitrary turning angle+vertical trace), but also in the "no preset direction limitation" - especially suitable for complex bridges such as railway curved bridges and cable-stayed bridges (the displacement of such bridges often involves composite deformation of "longitudinal+transverse+turning angle"), while traditional bearings are difficult to meet the correct compensation needs of such scenarios.
4、 Engineering value: Ensuring railway operation safety and structural durability
Railway rail transit has high requirements for "track smoothness" and "structural stability" (even millimeter level displacement deviation may lead to train bumps and increased wheel rail wear). The "multi-directional displacement adaptability" of spherical bearings essentially achieves two core engineering values through "correct compensation of deformation":
Avoiding the accumulation of internal forces in the structure: By freely sliding and rotating, the additional internal forces generated by temperature and load in the bridge (such as temperature stress and bending stress) are released to prevent beam cracking and pier displacement;
Ensure track smoothness: displacement compensation without jamming or sudden changes, ensuring stable relative position between the beam and the track, avoiding track height differences and directional deviations caused by insufficient support displacement, and thus ensuring safe and smooth train operation.
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