Why is it said that the bearing capacity of special bearings for highway bridges is high
The high bearing capacity of special bearings for highway bridges is the result of the combined effects of their material properties, structural design, manufacturing processes, and functional characteristics. The following provides a detailed analysis from the perspectives of technical principles and engineering applications:
The high bearing capacity of special bearings for highway bridges is the result of the combined effects of their material properties, structural design, manufacturing processes, and functional characteristics. The following provides a detailed analysis from the perspectives of technical principles and engineering applications:
1、 Material selection: Mainly high-strength and high durability materials
Main structural materials
steel products:
The main body of the support is usually made of high-strength low-alloy steel such as Q345 and Q370, whose yield strength is more than 30% higher than ordinary carbon steel (such as Q345 yield strength ≥ 345MPa), and can withstand greater axial pressure and horizontal force.
Alloy element strengthening:
Adding alloying elements such as manganese, silicon, and vanadium to steel can enhance its tensile strength, impact resistance, and fatigue resistance. For example, the fatigue limit of vanadium containing steel can be increased by 20% to 30%.
Casting or forging steel process:
Key components such as support base plates and pressure plates are made of cast steel or forged, resulting in a denser internal structure and avoiding casting defects. Their load-bearing capacity is 15% to 20% higher than that of ordinary rolled steel.
Functional materials
Rubber components:
High purity natural rubber or ethylene propylene diene monomer (EPDM) is used, with a tensile strength of ≥ 18MPa (ordinary rubber is only 10-15 MPa), and the addition of vulcanizing agents and reinforcing agents (such as carbon black) improves the elastic modulus and compressive performance, which can withstand compressive stress of 20-30 MPa (ordinary rubber bearings are about 10-15 MPa).
Polytetrafluoroethylene (PTFE) skateboard:
The friction coefficient is low (≤ 0.03) and the compressive strength is high (≥ 30MPa), which can still ensure the horizontal sliding performance of the support under high bearing capacity.
2、 Structural Design: Multi directional Force Optimization and Force Transmission Path Enhancement
Three dimensional force system
Special bearings (such as spherical bearings and seismic isolation bearings) adopt a combination structure of spherical crown lining plate and flat sliding plate:
The spherical crown liner plate transmits vertical loads through spherical contact, with a large contact area and uniform stress distribution, which can avoid local stress concentration (the stress concentration factor of traditional supports is reduced by more than 50%).
The flat skateboard allows for horizontal displacement, and through the combination of stainless steel plate and PTFE skateboard, the horizontal shear force is converted into frictional force, improving the overall shear resistance of the support.
Composite force transmission path
Taking the bowl shaped support as an example:
The rubber block is sealed inside the steel pelvic cavity, and the vertical load is transmitted through the sidewall of the pelvic ring. The rubber is in a triaxial compression state, and the compressive strength is 5-8 times higher than the free state (up to 40-50 MPa).
The horizontal force is transmitted through the contact surface between the support top plate and the stainless steel plate, combined with the elastic deformation of the rubber, to achieve the dual function of "vertical bearing+horizontal energy dissipation".
Anti void and limit design
Set limit blocks or elastic restraint devices at the edge of the support to prevent detachment during loading (detachment rate ≤ 5%), ensure uniform force distribution across the entire section, and enhance the ultimate bearing capacity.
3、 Manufacturing process: high-precision machining and quality control
Precision machining technology
Key components (such as steel balls for spherical supports and pelvic supports) are machined using CNC lathes or grinders, with dimensional tolerances controlled within ± 0.02mm and surface roughness Ra ≤ 1.6 μ m, ensuring tight contact after assembly and stress transmission efficiency ≥ 95%.
The vulcanization bonding process between rubber and steel plate:
By vulcanization at high temperature (140~160 ℃) and high pressure (10~15MPa), the rubber is chemically bonded to the steel plate, with a peel strength of ≥ 8kN/m (ordinary bonding process only 3~5kN/m), avoiding the detachment of the rubber layer during load-bearing.
Strict mechanical performance testing
Each support must undergo vertical compressive tests (loaded to 1.5 times the design bearing capacity, with deformation ≤ 10% of the theoretical value), horizontal shear tests (displacement ≤ 1mm when the shear stress reaches the design value), and fatigue tests (performance degradation ≤ 5% after millions of cycles of loading) to ensure that the actual bearing capacity far exceeds the design value.
4、 Functional feature: Enhanced design that adapts to complex working conditions
Compatible with high bearing capacity and large displacement
The vertical bearing capacity of special bearings (such as pot bearings for high-speed railway bridges) can reach 5000~20000kN, while allowing horizontal displacement of ± 200mm or more. By optimizing the size of the sliding plate and the thickness of the rubber layer, a balance of "strong bearing+large deformation" can be achieved.
Corrosion resistance and weather resistance
The surface of the steel is treated with hot-dip galvanizing (coating thickness ≥ 85 μ m) or fluorocarbon spraying, with a salt spray test life of ≥ 1000 hours (ordinary anti rust treatment only 200 hours), to avoid section weakening due to corrosion and indirectly ensure long-term stability of the bearing capacity.
Overlay of seismic isolation function
Some special bearings, such as lead rubber bearings and friction pendulum bearings, integrate energy dissipation elements on the bearing foundation. Under earthquake action, energy is dissipated through plastic deformation or friction. Although the bearing capacity may temporarily decrease, it can avoid structural collapse and reflect the design concept of "ductile bearing".
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