What are the factors affecting the service life of plate rubber bearings for highway bridges
The service life of plate rubber bearings for highway bridges is controlled by the coupling of six major factors: product manufacturing quality, design selection, construction and installation quality, service environmental conditions, operational load, and maintenance management. According to the relevant technical requirements of "Plate Rubber Bearings for Highway Bridges" (JT/T 4-2019), "Mainte
The service life of plate rubber bearings for highway bridges is controlled by the coupling of six major factors: product manufacturing quality, design selection, construction and installation quality, service environmental conditions, operational load, and maintenance management. According to the relevant technical requirements of "Plate Rubber Bearings for Highway Bridges" (JT/T 4-2019), "Maintenance Specification for Highway Bridges and Culverts" (JTG 5120), and "Technical Specification for Maintenance and Replacement of Highway Bridge Bearings and Expansion Devices" (JTG/T 5532-2023), each factor is explained as follows:
1、 Product manufacturing and material quality factors
The base material, formula, and manufacturing process of the support are the basic conditions that determine durability. The type of rubber matrix directly affects the anti-aging performance. Natural rubber has excellent mechanical properties at room temperature, but its ozone resistance and weather resistance are general; Neoprene rubber and EPDM have better aging resistance and salt corrosion resistance, which are suitable for corrosive environment. The quality of rubber raw materials, vulcanization process, reinforced steel plate material and surface anti-corrosion treatment, and rubber steel plate interface bonding process all play a key role in long-term service performance. If there are defects in the rubber formula during the production stage, the addition of recycled rubber, insufficient vulcanization, bubbles and inclusions at the bonding interface, or inadequate anti-corrosion treatment of the reinforced steel plate, rubber cracking, interlayer debonding, and steel plate corrosion will occur in the early stages of service, causing rapid deterioration of the mechanical properties of the support and shortening the effective service life. The mechanical indicators of the bearings at the factory (compressive elastic modulus, shear elastic modulus, ultimate compressive strength, and performance change rate after aging) do not meet the requirements of the specifications, which will also reduce the long-term fatigue bearing capacity.
2、 Design selection factors
Whether the selection of bearing specifications, stress control, and deformation verification match the actual working conditions of the bridge directly affects its long-term durability performance. During the design phase, if the vertical compressive stress value is too high and the support is in a high compression state for a long time, it will accelerate rubber plastic deformation and fatigue damage; Improper selection of support thickness can result in horizontal shear displacement caused by temperature expansion and concrete shrinkage and creep of the beam, which can easily lead to excessive shear deformation. Special bridge types such as slope bridges, inclined bridges, and curved bridges, if the effects of beam rotation and lateral displacement are not fully considered, will generate additional eccentric bending moments, causing local stress concentration in the supports. For areas with severe cold, coastal salt spray, and industrial corrosion, failure to select suitable rubber varieties according to environmental categories, and lack of targeted protective design, will significantly accelerate material aging and deterioration.
3、 Construction and installation quality factors
Installation quality is an important factor in the early occurrence of bearing diseases. The flatness and elevation control of the top surface of the bearing pad stone do not meet the specifications. The pad stone has local protrusions, depressions, and voids, which can cause uneven stress on the bearing and result in local stress concentration; Improper handling of eccentricity, inclination, and slope adjustment at the bottom of the beam will introduce additional shear and torsional deformation. During the installation of the support, it may be scratched by hard objects, contaminated by oil, damaged by direct sunlight, or the temporary limiting components may not be removed as required, resulting in the displacement constraint of the support being stuck and hindering the normal expansion and deformation of the beam. The sealing of mortar and debris around the support, which restricts the free shear and rotation of the support, will accelerate the development of rubber cracking, bulging, delamination and other diseases, reducing the service life.
4、 Service environment factors
The continuous effects of environmental media and temperature changes can cause aging of rubber materials and corrosion of steel components. Long term exposure to ultraviolet radiation and ozone can damage the polymer chains of rubber, causing surface hardening, cracking, and continuous expansion from the surface to the inside; The environment alternates between dry and wet conditions, with rain and snow infiltration. Moisture seeps into the interior of the support through rubber cracks or adhesive interfaces, causing corrosion of the reinforcing steel plate. The volume expansion of the corrosion products further expands the adhesive layer, forming a chain disease of detachment and peeling. Chloride ion salt spray in coastal areas and acidic and alkaline corrosive media in industrial areas can accelerate rubber aging and steel plate corrosion; Extreme high and low temperature cycling can generate alternating thermal stress inside the rubber, reducing the fatigue performance of the material; Long term contact of bearings with oil, diesel, and other oils can cause rubber swelling and irreversible degradation of mechanical properties.
5、 Operational load factors
Vehicle cyclic load, overload, and dynamic load impact result in compression shear coupled fatigue damage. Under normal driving conditions, the repeated action of vehicles generates cyclic compressive shear loads, and the rubber material generates hysteresis heating, resulting in fatigue performance degradation as the load cycles accumulate. Frequent passage of overloaded and over limit vehicles can cause the actual compressive and shear stresses on the bearings to exceed the design limits, increasing the risk of plastic deformation and cracking; Vehicle braking and impact can generate additional horizontal shear forces, exacerbating damage to the rubber layer and adhesive interface. Uneven settlement of the beam foundation and abnormal displacement of the upper structure can cause the bearings to withstand excessive shear deformation for a long time, accelerating the deterioration of bearing performance.
6、 Maintenance management factors
Normalized inspection and preventive maintenance directly determine the actual service life of bearings. Failure to conduct regular appearance and performance inspections in accordance with regulations has resulted in potential hazards such as early microcracks, slight voids, and accumulation of debris in the bearings that cannot be promptly addressed, leading to the continuous expansion of the disease; Dust, sand, and debris accumulate on the surface of the support for a long time, continuously squeezing and scratching the rubber surface, hindering the free deformation of the support; The waterproof protection measures of the support failed to be repaired in a timely manner, and the corrosive medium continued to invade. Failure to timely handle diseases, such as rubber cracking, steel plate corrosion, and excessive shear deformation, and failure to monitor or replace according to regulations, will continue to reduce the remaining service life of the bearings.
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