Why is it said that the horizontal displacement capacity of spherical bearings on railway rail trans
The reason why the spherical bearings of railway rail transit bridges are considered to have strong horizontal displacement capacity is mainly related to their unique structural design, material properties, and mechanical principles. The following provides a detailed analysis from the aspects of technical principles, structural composition, and performance advantages:
The reason why the spherical bearings of railway rail transit bridges are considered to have strong horizontal displacement capacity is mainly related to their unique structural design, material properties, and mechanical principles. The following provides a detailed analysis from the aspects of technical principles, structural composition, and performance advantages:
1、 The core structure and displacement mechanism of spherical bearings
The core structure of a spherical support includes upper support plate, spherical PTFE sliding plate, middle ball core, lower support plate and other components, and its horizontal displacement capability is derived from the following design:
1. Universal rotation characteristics of spherical contact pairs
Structural features: The upper surface of the middle core is a convex spherical surface, forming a spherical contact pair with the concave spherical surface of the upper support plate (similar to a "ball and socket" structure).
Displacement principle: When a bridge experiences horizontal displacement due to temperature changes, concrete shrinkage and creep, train loads, and other factors, the ball core can rotate in multiple directions (such as longitudinal, transverse, or any angle) within the ball socket, thereby releasing horizontal displacement stress.
Advantages: Traditional bearings (such as plate rubber bearings) can only achieve limited displacement through rubber shear deformation, while spherical bearings have almost no directional restrictions on spherical rotation, which can adapt to the multi-dimensional horizontal displacement requirements of bridges (such as complex displacements of curved bridges and inclined bridges).
2. Low friction characteristics of PTFE skateboard
Material application: A polytetrafluoroethylene (PTFE) sliding plate is attached to the concave spherical surface of the ball core or upper support plate, forming a sliding pair with the stainless steel plate (embedded in the corresponding contact surface).
Friction coefficient: The friction coefficient between PTFE skateboard and stainless steel plate is relatively low (usually ≤ 0.03), much lower than the friction coefficient between rubber and concrete (about 0.3-0.5).
Function: The low friction characteristic allows the support to overcome only small resistance during horizontal displacement, greatly improving displacement efficiency, especially suitable for large-span bridges or areas with significant temperature differences (such as areas with annual temperature differences exceeding 50 ℃).
2、 Key factors affecting horizontal displacement capability
1. Core curvature radius and support height
Curvature radius: The larger the curvature radius of the core, the longer the arc length during rotation, and the greater the horizontal displacement that can be released (such as a core with a curvature radius of 1m, rotating 1 ° corresponds to a horizontal displacement of about 17mm).
Support height: Higher supports can provide longer sliding travel, avoiding component collision and interference during displacement.
2. Material strength and durability
Core material: Made of high-strength cast steel (such as ZG270-500) or forged steel, with a yield strength of ≥ 270MPa, capable of withstanding huge horizontal thrust (such as tens of thousands of tons) without plastic deformation.
Durability of PTFE skateboard: PTFE material is resistant to aging and wear, with a service life of over 50 years, ensuring stable long-term displacement performance.
3. Installation and adjustment accuracy
Pre embedded steel plate flatness: During installation, it is necessary to ensure that the flatness of the upper and lower support plates is ≤ 1mm/m to avoid displacement obstruction caused by installation deviation.
Displacement pre offset setting: During construction, the installation position of the support can be adjusted in advance based on the expected displacement direction of the bridge (such as offsetting 50mm to one side), to reserve space for future displacement.
3、 Typical application scenarios and advantages
1. Large span bridges (such as cable-stayed bridges, suspension bridges)
Requirement: When the temperature changes, the main beam can expand and contract by several hundred millimeters, causing lateral vibration displacement during train operation.
Advantages of spherical bearings: Adapt to multi-directional displacement through spherical rotation, reduce friction resistance with PTFE sliding plates, and avoid structural cracking caused by limited displacement in traditional bearings.
2. High speed railway bridges
Characteristics: The train speed is high (≥ 250km/h), and the wheel rail force causes high-frequency horizontal vibration of the bridge.
Function: The low friction characteristics of the spherical support can quickly absorb vibration energy, reduce the impact of displacement lag on track smoothness, and ensure driving safety.
3. Bridges in earthquake prone areas
Performance: During earthquakes, the support can release horizontal seismic forces through spherical sliding, avoiding stress concentration caused by displacement obstruction of the structure. Coupled with damping devices, it can further enhance seismic resistance (such as lead core ball bearings).
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