How can special bearings for highway bridges withstand vehicle loads
The core mechanism of special bearings for highway bridges (pot type, spherical, seismic isolation, anti pull, etc.) to bear vehicle loads is: vertical rigid bearing+horizontal flexible adaptation+dynamic buffering energy dissipation, which smoothly, uniformly, and controllably transmits the vertical pressure, braking/centrifugal horizontal force, and impact vibration of the vehicle to the pier.
The core mechanism of special bearings for highway bridges (pot type, spherical, seismic isolation, anti pull, etc.) to bear vehicle loads is: vertical rigid bearing+horizontal flexible adaptation+dynamic buffering energy dissipation, which smoothly, uniformly, and controllably transmits the vertical pressure, braking/centrifugal horizontal force, and impact vibration of the vehicle to the pier.
1、 Three forms of action of vehicle load
The vehicle will exert three types of forces on the support on the bridge:
Vertical pressure: the vertical pressure of self weight+load (including impact coefficient, about 1.1-1.4)
Horizontal force:
Longitudinal: braking force/traction force
Lateral: centrifugal force (curved bridge), wind force, lateral thrust under unbalanced load
Dynamic loads and vibrations: wheel bumps, instantaneous impacts of acceleration and deceleration, reciprocating vibrations
2、 The load-bearing principle of common special supports
1. Basin type rubber bearing (large load, medium span mainstream)
Vertical bearing capacity
Vehicle pressure → Upper seat plate → Rubber block inside steel basin (three-way constraint, significantly increased compressive modulus) → Bottom basin → Pier and abutment.
Rubber is restrained by a steel basin and cannot bulge laterally, with a bearing capacity of thousands to tens of thousands of tons.
Horizontal force processing
Fixed support (GD): Steel components+anchor bolts directly resist horizontal forces
Active support (DX/SX): stainless steel plate+polytetrafluoroethylene (PTFE) low friction sliding (μ ≈ 0.06), releasing displacement without additional amplification of horizontal force
Rotation adaptation
Uneven compression of rubber+spherical crown lining plate, adapted to the deflection angle of the beam, always transmitting force vertically without bias
2. Spherical steel bearings (large-span, curved bridges, cable-stayed bridges)
Vertical+Rotation
Vehicle load → spherical secondary point → uniform force transmission on the surface, capable of multi-directional free rotation (no stress concentration on curved and wide bridges).
horizontal force
Fixed type: spherical surface+limit to resist horizontal force; Sliding type: spherical+PTFE sliding, suitable for large displacement.
Spherical steel support
3. Seismic isolation bearings (lead rubber, friction pendulum, seismic+vibration control)
vertical
Same plate/bowl type: rubber pressure bearing, stable force transmission.
Horizontal+vibration reduction (key)
Lead core rubber bearings: horizontal force → rubber shear deformation+lead core plastic yielding, absorbing vehicle braking/impact energy, reducing the force and vibration transmitted to the pier and abutment
Friction pendulum support: spherical sliding prolongs the period, consumes energy, and significantly reduces dynamic load effects
Lead rubber bearings
4. Anti pull bearings (steep slopes, strong winds, earthquake zones)
Vehicle unbalanced load/braking/wind load may cause the beam end to tilt upwards and generate tensile force:
Install anti pull anchor bolts, inverted hooks, and limit steel blocks that can both press and pull to prevent support detachment and beam displacement.
3、 Complete load transfer path (taking heavy-duty vehicles as an example)
Bridge deck → paving → beams and slabs → pedestal plates on supports
Vertical: → (steel basin/spherical/rubber bearing) → lower seat plate → cushion stone → bridge pier → foundation
Level:
Fixed support: → Steel parts/anchor bolts → Directly transmitted to the pier and abutment
Active support: → sliding surface sliding → releasing displacement, only transmitting frictional resistance
Shock/vibration: → Rubber damping/Lead core energy dissipation/Spherical friction → Attenuation before transmission to pier and abutment
4、 Key design points (ensuring safety)
Bearing capacity: Vertical ≥ dead load+live load (including impact) × 1.2~1.5 safety factor
Horizontal force matching:
Fixed support horizontal bearing capacity ≥ braking force+centrifugal force
Sliding resistance of movable support ≤ allowable horizontal force (without top cracking pier) Shaanxi Provincial Department of Transportation
Dynamic adaptation:
Moderate vertical stiffness: stable compression, minimal deformation, and good buffering
Controllable horizontal stiffness: if it slides, it slides; if it resists, it resists
Damping: absorbing impact and reducing resonance
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