What are the applications of spherical bearings for railway rail transit bridges on ramp bridges
The application of spherical bearings in railway rail transit bridges on ramp bridges mainly relies on their unique structural characteristics (which can achieve multi-directional rotation, adapt to vertical and horizontal forces), and solve the special stress, displacement, and stability problems caused by the slope of ramp bridges. The specific applications are reflected in the following aspects
The application of spherical bearings in railway rail transit bridges on ramp bridges mainly relies on their unique structural characteristics (which can achieve multi-directional rotation, adapt to vertical and horizontal forces), and solve the special stress, displacement, and stability problems caused by the slope of ramp bridges. The specific applications are reflected in the following aspects:
1、 Adapt to the vertical force inclined transmission of ramp bridges
Correctly transmitting vertical loads: The beam of a ramp bridge has a tilt angle due to the slope (usually ≤ 3%, and can reach 5% in special sections). The spherical structure of the spherical support can adjust its own angle by rotating it, so that the top surface of the support is closely attached to the bottom surface of the beam, ensuring that the vertical forces such as the self weight of the beam and train loads are transmitted vertically to the bridge pier (platform), avoiding damage to the support due to excessive local stress caused by load deflection.
Distributed inclined load stress: The spherical contact form of the spherical support (the upper and lower seat plates are in contact through spherical PTFE sliding plates or steel steel contact) can evenly disperse the vertical force under inclined state, reduce the local compressive stress on the top of the bridge pier (abutment), and protect the durability of the lower structure.
2、 Meet the displacement requirements of the beam along the slope
Adapting to longitudinal slope displacement: During train operation, the beam may experience longitudinal displacement along the slope direction (uphill or downhill direction) due to temperature changes, concrete shrinkage and creep. The horizontal sliding function of the spherical support (through low friction contact between the PTFE sliding plate and the stainless steel plate) can smoothly release this displacement, avoiding additional stress on the beam due to excessive constraints.
Compatible with lateral and angular displacement: In addition to longitudinal displacement, ramp bridges will also experience lateral displacement under the action of train centrifugal force, wind force, etc. At the same time, the end of the beam will produce angular displacement due to deflection. The spherical rotation (angle of rotation can reach 0.02~0.05 rad) and multi-directional sliding ability of the spherical support can simultaneously adapt to these displacements, ensuring the free deformation of the beam.
3、 To withstand the unique horizontal and additional forces of a slope
The longitudinal force component that resists the braking/traction force of the train: On a slope, the longitudinal force generated when the train starts or brakes will be decomposed into force components along the slope direction. The spherical support can effectively transmit or restrain this force component by setting a horizontal bearing capacity limit device (such as a fixed support or a one-way movable support baffle), preventing the beam from sliding along the slope.
Balancing centrifugal force and lateral force: In curved ramp bridges, the centrifugal force generated by train travel can cause lateral displacement of the beam. The lateral bearing capacity and limiting function of spherical supports can limit excessive displacement and ensure the relative stability of the beam and bridge piers.
4、 Ensure the stability and safety of bridge structures
Reduce additional stress on the beam: If ordinary bearings (such as plate rubber bearings) are used, they may not be able to adapt to the tilt angle and multi-directional displacement on a slope, resulting in "separation" or local compression between the beam and the bearings, generating additional bending moments and shear forces. The multi angle adaptability of spherical bearings can avoid such problems and protect the beam structure.
Enhancing earthquake resistance and disaster reduction capabilities: Under dynamic loads such as earthquakes, the stress on ramp bridges is more complex. Ball bearings (especially seismic ball bearings) can buffer seismic force transmission and reduce structural damage through reasonable sliding friction coefficient design and energy dissipation devices.
Easy to maintain and replace: Ball bearings usually adopt modular design, and components such as upper and lower seat plates, spherical pads, etc. can be separately inspected or replaced. In the limited maintenance space of ramp bridges, it can reduce maintenance difficulty and cost.
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