Why is it said that the seismic performance of spherical bearings on railway rail transit bridges is
The excellent seismic performance of spherical bearings on railway rail transit bridges is determined by their structural design, working principle, and material properties. Especially when dealing with horizontal displacement, rotation, and vibration loads caused by earthquakes, they can reduce damage to bridge structures through multiple mechanisms. The specific reasons are as follows:
1. Flexi
The excellent seismic performance of spherical bearings on railway rail transit bridges is determined by their structural design, working principle, and material properties. Especially when dealing with horizontal displacement, rotation, and vibration loads caused by earthquakes, they can reduce damage to bridge structures through multiple mechanisms. The specific reasons are as follows:
1. Flexible multi angle displacement capability to adapt to complex movements during earthquakes
The core structure of a spherical support consists of an upper support plate, a lower support plate, and a spherical steel liner (or PTFE sliding plate) in the middle. Its spherical contact surface design enables it to have the following displacement characteristics:
Horizontal free sliding: When an earthquake occurs, the upper structure of the bridge will experience horizontal reciprocating displacement (including longitudinal, transverse, and diagonal) due to seismic waves. The spherical contact surface of the spherical bearing, combined with the low friction coefficient of the polytetrafluoroethylene (PTFE) sliding plate, can achieve free sliding in multiple directions, effectively releasing horizontal seismic forces and avoiding excessive stress between the bearing and the beam or pier due to forced constraints.
Multi angle corner adaptation: During earthquakes, bridge beams may produce small corners due to uneven vibration (such as settlement differences or flexural deformation at both ends of the beam). The spherical structure of spherical bearings allows the beam to rotate flexibly within a certain range (usually up to 0.02~0.05 rad), avoiding local cracking or damage caused by "rigid constraints" on the bearings.
2. Hierarchical energy dissipation and force transmission mechanism, buffering seismic loads
Spherical bearings disperse or cushion seismic loads through a combination of flexible constraints and directional guidance
Load dispersion transmission: The spherical structure of the support can evenly transmit the vertical load (self weight+live load) of the upper beam to the lower pier, even during earthquake shaking, and maintain the stability of load transmission through spherical contact, avoiding local stress concentration.
Controllable displacement limit: Some seismic ball bearings will be designed with displacement limit devices (such as stoppers, elastic limit members):
During a small earthquake, the limit device does not intervene and the support slides freely to release displacement;
During moderate to strong earthquakes, the limiting device gradually comes into play, absorbing some seismic energy through elastic deformation or friction, limiting excessive displacement (preventing beam detachment), and achieving a graded seismic effect of "buffering first, limiting later".
3. Material and structural reinforcement to enhance impact resistance and wear resistance
High strength material support: The core components of the support (such as spherical steel pads, upper and lower support plates) are often made of high-quality carbon structural steel or low-alloy steel (such as Q355, 45 steel), which has high compressive strength (usually ≥ 300MPa) and toughness after quenching and tempering treatment, and can withstand instantaneous impact loads during earthquakes without brittle fracture.
Wear resistant and friction reducing design: Polytetrafluoroethylene sliding plates or stainless steel plates are usually installed between the spherical contact surfaces, with a low friction coefficient (about 0.03-0.05 at room temperature). Even under high-frequency seismic vibrations, they can maintain smooth sliding and reduce the phenomenon of "jamming" caused by excessive frictional resistance (jamming can concentrate seismic forces on the beam or pier, causing damage).
4. Adapt to the seismic requirements of bridge structures and reduce secondary disasters
Railway bridges (especially high-speed railway bridges) have high safety requirements for bearings. If the bearings fail during an earthquake, it may cause the beam to fall, the track to be misaligned, and lead to major accidents such as train derailment. The seismic design of spherical bearings has addressed this issue in a targeted manner:
Preventing beam collision or detachment: By controlling the displacement (such as setting limit plates), it is ensured that there is no rigid collision between beams and between beams and piers during earthquakes, while avoiding the "pulling out" or "flipping" of supports.
Compatible with the expansion and vibration of bridges: Railway bridges themselves will experience certain expansion and vibration during train operation. The normalized displacement capacity of spherical bearings (such as temperature expansion and live load deflection) seamlessly connects with seismic displacement capacity, and can quickly respond to sudden loads without additional adjustments during earthquakes.
5. Collaborate with the seismic system to form a comprehensive protection system
Spherical bearings do not work in isolation, but work in synergy with the overall seismic system of the bridge, such as the ductility design of piers and abutments, energy dissipation devices, seismic blocks, etc
The support reduces the horizontal force transmitted to the pier and abutment by releasing some seismic energy, thereby lowering the seismic design load of the pier and abutment;
For complex structures such as continuous beams and rigid frame bridges, the multi-directional displacement capability of spherical supports can coordinate the uneven vibration of each span beam body, avoiding chain failure of the structure due to "force imbalance".
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