What is the main purpose of special bearings for highway bridges to solve
Special bearings for highway bridges are specialized bearings designed for complex working conditions or special functional requirements that conventional bearings cannot meet. Their core function is to solve the problems of bridge structural deformation, force transmission, environmental adaptation, and functional expansion that conventional bearings cannot cope with, ensuring the safety, stabili
Special bearings for highway bridges are specialized bearings designed for complex working conditions or special functional requirements that conventional bearings cannot meet. Their core function is to solve the problems of bridge structural deformation, force transmission, environmental adaptation, and functional expansion that conventional bearings cannot cope with, ensuring the safety, stability, and durability of bridges under complex service conditions. Specifically, it mainly addresses the following key issues:
1、 Solving the problem of "special deformation coordination": dealing with unconventional displacement and rotation of bridges
Conventional bearings (such as ordinary plate rubber bearings) can only adapt to the "small amplitude, one-way/two-way" displacement of bridges caused by temperature changes and load effects (such as horizontal expansion and a small amount of turning). However, when bridges have excessive displacement, multi-directional deformation, and complex turning angles, special bearings are needed to achieve coordination and avoid cracking or damage to the structure due to limited deformation:
Solving the problem of excessive displacement: For some large-span bridges (such as cable-stayed bridges and continuous rigid frame bridges) or bridges located in areas with severe temperature differences (such as northern cold regions), temperature changes can cause the main beam to experience horizontal expansion and contraction exceeding 100mm or even larger. At this time, "special supports with large displacement" (such as large displacement bowl type supports and multi-directional sliding supports) are needed. By increasing the sliding stroke of the supports (the sliding amount of conventional supports is mostly ≤ 50mm, while special supports can reach 200mm or more), the large expansion and contraction requirements of the main beam can be met, avoiding the support or beam body from being "pulled apart/damaged".
Solving multi-directional deformation problems: For curved bridges, skew bridges, or bridges affected by earthquakes or vehicle braking forces, in addition to horizontal expansion and contraction, the main beam will also experience "lateral displacement and torsional deformation" (such as centrifugal force causing lateral displacement of curved bridges). Conventional bearings cannot adapt to multi-directional displacement simultaneously, and require "multi-directional active special bearings" (such as spherical multi-directional bearings and seismic universal bearings). Through spherical or multiple sets of sliding structures, the main beam can be flexibly deformed in horizontal, transverse, and even torsional directions to avoid local stress concentration.
Solving the problem of large turning angles: Under the action of loads (such as vehicles and self weight), the main beam of large-span bridges may have a turning angle at the support that exceeds the allowable turning angle of conventional supports (ordinary rubber supports allow a turning angle of about 0.005rad), resulting in support detachment or local crushing. At this time, "special supports with large turning angles" (such as large turning basin supports and hinge shaft supports) are needed. By optimizing the support structure (such as increasing the spherical curvature radius and using hinge shaft connections), the allowable turning angle can be raised to above 0.01 rad to ensure that the support is always in contact with the beam and pier, and the load is evenly transmitted.
2、 Solving the problem of "extreme load adaptation": resisting unconventional external forces such as earthquakes and impacts
The design load of conventional bearings mainly considers "conventional static/dynamic loads" such as bridge weight, vehicle live load, temperature force, etc. However, when the bridge faces extreme loads such as earthquakes, strong winds, vehicle impacts, and ship impacts, conventional bearings are prone to damage, leading to bridge collapse. Special supports solve structural safety issues under extreme loads through designs such as energy dissipation, pull-out resistance, and limiting
Seismic load resistance: Earthquakes can cause severe horizontal vibrations and vertical impacts on bridges, and conventional bearings may derail due to excessive displacement or crack piers and abutments due to rigid connections. Anti seismic special bearings "(such as lead core isolation rubber bearings and friction pendulum isolation bearings) are solved through two core methods: one is" energy dissipation "(such as lead core yielding to absorb seismic energy), and the other is" isolation "(such as friction pendulum extending the natural vibration period of the structure through spherical sliding, reducing seismic force transmission), greatly reducing the damage of earthquakes to bridges.
Anti pull and limit: During earthquakes, strong winds, or ship impacts, bridges may experience "upward pull forces" (such as beam warping) or "lateral displacement beyond the design range". Conventional supports lack anti pull capabilities and are prone to being pulled up and dislodged. Special anti pull bearings (such as anti pull pot bearings and anchor pull bearings) limit the upward and excessive lateral displacement of the beam by setting anti pull anchor rods or limit devices, avoiding the bearings from detaching from the pier and ensuring the overall stability of the structure.
Impact load adaptation: Bridges crossing highways, railways, or near waterways may face sudden loads such as vehicle loss of control and ship collisions. Special impact resistant bearings (such as pot type bearings with buffer layers and elastic limit bearings) absorb impact energy by setting up elastic buffer structures (such as rubber buffer pads and spring devices), avoiding direct transmission of loads to piers and abutments, and protecting bearings and bridge bodies.
3、 Solving the problem of "adaptation to complex environments": dealing with harsh conditions such as high temperature, corrosion, freeze-thaw, etc
The materials of conventional bearings (such as ordinary rubber and carbon steel) are prone to aging, rusting, or damage in harsh environments such as high temperature, high humidity corrosion, severe cold freeze-thaw, and strong ultraviolet radiation, which shortens their service life. Special supports solve environmental adaptability problems through "material optimization and structural protection":
High temperature environment adaptation: Bridges crossing metallurgical plants and volcanic activity areas may experience temperatures exceeding 60 ℃, and ordinary rubber bearings may soften and age due to high temperatures. High temperature resistant special bearings "(such as silicone rubber isolation bearings and metal friction bearings) use high-temperature resistant materials (such as silicone rubber and high-temperature alloys), or replace rubber with metal structures to ensure stable bearing and deformation capacity at high temperatures of 80-200 ℃.
Corrosion environment adaptation: Coastal bridges (corroded by seawater salt), chemical park bridges (corroded by acidic and alkaline gases), conventional carbon steel bearings are prone to corrosion, and rubber bearings are easily corroded and degraded. Special corrosion-resistant bearings (such as stainless steel bowl bearings and fluororubber isolation bearings) are protected in two ways: first, the bearing body is made of stainless steel and corrosion-resistant alloys; Secondly, the rubber material is made of acid and alkali resistant fluororubber, and anti-corrosion coating (such as polytetrafluoroethylene coating) is applied to the connecting components to resist corrosion.
Adaptation to freeze-thaw environment: In cold northern regions, winter temperatures can drop below -30 ℃, and there is a "freeze-thaw cycle" (rain and snow entering the gaps between supports, causing structural cracking due to ice expansion). Anti freezing special bearings "(such as low-temperature modified rubber bearings and sealed metal bearings) adapt to freeze-thaw cycles by using modified rubber (to enhance low-temperature elasticity and avoid brittle cracking) or all metal sealing structures (to prevent moisture from entering), avoiding damage to the bearings due to ice expansion.
4、 Solving the problem of "functional expansion and special needs": meeting the personalized design goals of bridges
Due to the "special structural form" or "personalized functional requirements" of some bridges, conventional bearings cannot achieve specific functions. Special bearings can solve these unconventional needs through customized design:
Weight reduction and lightweighting requirements: Urban elevated bridges, pedestrian overpasses, and other structures are sensitive to their own weight, and conventional bearings (such as heavy-duty bowl bearings) have a large self weight, increasing the load on piers and abutments. Lightweight special bearings "(such as composite material bearings and thin-walled metal bearings) use high-strength lightweight materials (such as carbon fiber composite materials and aluminum alloys) to reduce the weight of the bearings by 30% -50% while ensuring bearing capacity, thereby reducing the burden on piers and abutments.
Displacement monitoring and warning requirements: Long bridges require real-time monitoring of support displacement to determine the structural health status. Conventional supports do not have monitoring functions. Intelligent special supports "(such as monitoring supports with sensors) are equipped with displacement sensors and pressure sensors, which can collect real-time displacement and force values of the supports and transmit them to the backend system. When the data exceeds the threshold, it will automatically warn and facilitate bridge operation and maintenance.
Special structural adaptation: such as opening bridges (requiring temporary opening for navigation) and rotating bridges (requiring rotation and closure during construction), conventional supports cannot meet the requirements of "dynamic opening and closing" or "rotation". Special function supports "(such as hinge supports for opening bridges and ball joint supports for rotating bridges) achieve the rotation and opening and closing functions of bridges through hinge shafts, ball joints, and other structures, ensuring the smooth implementation of special construction or usage scenarios.
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