Linear Natural Rubber Seismic Isolation Bearing(LNR)

The Linear Natural Rubber isolation bearing(LNR/NRB) is a professional building isolation device, mainly composed of multiple layers of natural rubber sheets and thin steel plates alternately laminated and bonded through high-temperature vulcanization. According to different manufacturing processes of the laminated structure and formulation designs, the upper connecting cover plate connects the seismic isolation device to the upper structure of the building; the lower connecting plate connects the seismic isolation device to the foundation of the building to transfer the horizontal shear force. Through its unique structural design, this rubber bearing can effectively isolate the transmission of seismic energy to the upper structure, significantly enhancing the safety and stability of the building structure during an earthquake.

This laminated rubber bearing complies with the international standard ISO 22762 and is suitable for high-intensity earthquake regions and important facilities that are sensitive to vibrations. It is widely applied in bridges, buildings, steel structure and important infrastructure.

1), Rubber Shim: High-quality natural rubber is used. Its molecular structure endows it with excellent elasticity, flexibility, and good energy dissipation characteristics. The thickness of the rubber sheets is precisely controlled within the range of 4 - 12mm, and the number of layers varies according to different design requirements, usually ranging from 10 to 30 layers. These rubber layers undertake the core functions of horizontal deformation and seismic energy dissipation. Under the action of an earthquake, they can generate large horizontal displacements. At the same time, the mechanical energy is converted into heat energy through the internal friction between molecular chains and conformational changes.

2), Steel Plate Layer: Thin steel plates are made of low-alloy high-strength structural steels such as Q345, with a thickness range of 2 - 8mm. After surface treatment, the steel plates are vulcanized and bonded with rubber. Their main function is to significantly enhance the vertical bearing capacity and horizontal stiffness of the bearing. Under the action of vertical loads, the steel plates evenly distribute the pressure transmitted from the upper structure to the rubber layer to prevent excessive local compression of the rubber. In the horizontal direction, the steel plates limit the excessive deformation of the rubber to ensure the overall stability of the bearing.

3), Connecting Steel Plates: Connecting steel plates are installed at both the upper and lower ends of the bearing. The material is similar to the internal thin steel plates, and the thickness is generally between 10 - 20mm. The connecting steel plates are closely connected to the upper and lower components of the building structure through welding or high-strength bolts to ensure the efficient transmission of seismic forces. Their dimensions and shapes are customized according to the specific installation requirements of the project to achieve a good fit with different structures.

Under normal service conditions, the Linear natural rubber isolation bearing mainly bears the vertical dead load and live load of the building. Relying on the combined structure of multiple layers of internal steel plates and rubber, it provides strong vertical stiffness and controls the vertical deformation within a very small range (generally less than 5mm) to maintain the structural stability.

When an earthquake strikes, the seismic waves trigger a strong horizontal movement of the ground. At this time, the characteristic of low horizontal shear stiffness of natural rubber comes into play. The bearing allows the building structure to generate a large displacement in the horizontal direction. Generally, the horizontal displacement capacity can reach 200% - 350% of the diameter of the bearing.

During the process of horizontal shear deformation of the rubber, the mechanical energy input by the earthquake is converted into heat energy and dissipated, thus reducing the seismic energy transmitted to the upper structure. At the same time, the elastic nature of natural rubber endows the bearing with the characteristic of restoring force. After the earthquake action ends, it can pull the upper structure back to the vicinity of the initial position, reducing the residual deformation and ensuring that the building structure still has a certain service function after the earthquake.

1), Excellent Vertical Load-Bearing Capacity: It has a relatively large vertical stiffness, usually ranging from 1000 to 5000 KN/mm, it can bear a large vertical loading, and meet the vertical load-bearing requirements of various building structures. Under the long-term action of vertical loads, the creep deformation is extremely small. Within a 10-year service period, the increment of creep deformation is less than 0.5 mm, ensuring the long-term vertical stability of the structure.

2), Outstanding Horizontal Deformation and Energy Dissipation Capacity: The horizontal stiffness is relatively small, generally between 0.1 and 1.0 KN/mm. It can effectively extend the natural vibration period of the building structure, from the conventional 0.5 - 1.0 s to 1.5 - 3.0 s, avoiding the dominant period of seismic waves and reducing the risk of resonance. The horizontal equivalent damping ratio is between 5% and 15%. The deformation of rubber effectively consumes seismic energy and reduces the structural vibration response.

3), Exceptional Durability: Natural rubber has good weather resistance, and its aging rate is slow under the action of environmental factors such as ultraviolet rays and ozone. In a normal service environment, the designed service life of bearing can reach 60 to 80 years.

After more than one million simulated seismic cyclic loading tests, the mechanical properties of the bearing degrade very little, and it can withstand multiple seismic effects.

4,) Stable Elastic Reset Function: After the earthquake action ends, it can quickly pull the upper structure back to the vicinity of the initial position relying on the elasticity of natural rubber, reducing the residual deformation. This is beneficial for the rapid restoration of the building's functions after the earthquake and reduces the repairing cost and time.

5), Convenient Installation and Maintenance: The standardized design and manufacturing process make the dimensions and interface forms of the bearing universal, facilitating the connection with different types of building structures. The installation process is simple. Construction workers can operate with conventional tools according to detailed drawings and instructions, greatly shortening the construction period. Daily maintenance and regular inspections are convenient. Staff can easily inspect and evaluate the appearance, deformation, and connection parts, etc. When problems occur, it is convenient to repair or replace, reducing the use cost and maintenance difficulty.

In the design of the isolated structure, it is necessary to reasonably set the overall characteristics of the structure, structural layout, and the distribution of structural stiffness to control the response performance of the structure during an earthquake and achieve the goal of reducing the seismic response. Generally, the following principles need to be followed:

1), The seismic fortification target of isolated buildings should generally be higher than that of traditional buildings. Reasonably designed isolated buildings can all achieve the seismic fortification target of "no damage under minor earthquakes, no damage or slight damage under moderate earthquakes, and no loss of service functions under major earthquakes".

Basic rules for the finalization of the structure of isolated buildings. The layout of isolation bearings and the stiffness of the structure should be controlled to make their distribution uniform. Try to make the offset between the stiffness center of the structure and the mass center of the upper structure as small as possible. This can ensure that the structure will not be accidentally damaged due to excessive torsional effects.

2), The base isolation technology is most suitable for low-rise and multi-story buildings. The height and number of floors of isolated buildings should comply with the corresponding provisions in relevant design technical specifications.
Due to the characteristics of building isolation technology, isolated buildings are generally more suitable for building sites of types I, II, and III. In addition, a foundation type with better rigidity should be selected in the structural design to ensure the stability of the isolation layer and the consistency of its movement during an earthquake.
Generally speaking, the tensile capacity of the isolation layer of isolated buildings is relatively weak. According to the characteristics of the shear structure, in order to ensure the stability of the isolated structure, the anti-overturning ability of the isolated structure, and effectively prevent the separation between the upper structure and the isolation layer during an earthquake, the aspect ratio of the isolated structure should be controlled. The aspect ratio of the isolated structure should meet the requirements in the following table. When the aspect ratio does not meet the requirements, the anti-overturning check calculation under rare earthquakes should be carried out.

At the same time, the horizontal loads under non-seismic actions (such as wind loads) should also be restricted. Generally speaking, the horizontal loads under non-seismic actions should be controlled not to exceed 10% of the total gravity of the structure. This can also effectively ensure the comfort of isolated buildings.

4), Reasonably set the basic period of the isolated structure to avoid the site period and the period of the upper structure, and effectively give play to the effectiveness of the isolation technology.
The base isolation layer should generally be set below the structural layer. The isolation layer should remain stable under rare earthquakes and there should be no unrecoverable deformation. Controlling the joint construction of the isolated structure to ensure that the isolation layer can effectively play its role during an earthquake. For the equipment piping passing through the isolation layer and the wiring of the electrical and communication systems, measures such as flexible connections with flexibility should be adopted to adapt to the horizontal displacement of the isolation layer under rare earthquakes; for lightning protection equipment grounded with steel bars or steel frames, grounding wiring spanning the isolation layer should be provided.

5), Isolated buildings should have measures to prevent serious damage when the isolation bearings accidentally lose their stability during an earthquake. Generally, measures that make the isolation bearings easy to inspect and replace should also be considered.
6), The building isolation rubber bearings and other components of the isolation layer should also adopt corresponding fire prevention measures according to the fire resistance rating of the location where the isolation layer is located.

For structures with complex shapes or special requirements that adopt isolation technology, model experiments should be carried out.

(only recommendation, it could be OEM on the request of Client or manufactured to drawing of Clients)

Note: For more specification parameters and customized requirements, please contact with us.

1), Inspecting facilities

2), Testing reports.

3), Type testing reports.

1), Certification Standards: The products are under the EU CE certification (EN 15129/EN 1337) and applied these codes according to request of Clients.

2), Quality Assurance Commitment: Provide lifetime technical services and respond to on-site problems within 98hours.

3), Technical Documents: Type inspection reports, third-party type inspection reports and product ex-factory reports can be provided.

It can meet the standards of EU EN15129/EN1337, the US ASCE 7 and other countries for OEM production and manufacturing, or process and manufacture according to provided drawings and samples.

1), Precisely assemble the upper and lower connection plates, and the upper embedded parts on the ground.

2), After the concrete of the lower structure reaches 75% of the designed strength, cleaning the threaded holes of the embedded parts, applying butter, and making a layer of isolation layer using butter and asphalt felt to prepare for the subsequent replacement of the rubber isolation bearing.

3), According to the numbering on the layout plan of the rubber isolation bearing, accurately hoisting the isolation bearing into place.

4), Use high-strength bolts to firmly fix the lower connection plate to the lower embedded parts.

5), Strictly checking whether the installation quality meets the requirements of relevant regulations and standards.

6), After passing the inspection, first taking anti-rust measures for the connection plates of the isolation bearing and the exposed connection bolts, and then properly protecting the isolation bearing with a wooden frame to prevent damage during the upper construction process.

7), Binding the reinforcement of the part above the isolation bearing and carrying out the construction of the upper structure.

8), During the installation process of the isolation bearing, make detailed construction records of the installation process. During the construction of the upper structure, conduct a vertical deformation observation of the rubber isolation layer once for each completed floor.

9), After the isolation building is completed, carefully checking the separation distance between the upper structure and the obstacles in the horizontal and vertical directions.

10), Precautions​

• Strictly Prohibiting Overloading: Using it strictly in accordance with the vertical and horizontal loads required by the design. It is strictly prohibited to exceed the bearing capacity range of the bearing to avoid damage to the bearing, which may affect the isolation effect and structural safety. ​
• Preventing the influence of High Temperature: Avoiding keeping the bearing in a high-temperature environment (exceeding 60°C) for a long time. High temperature may cause the deterioration of the rubber performance and reduce the isolation performance of the bearing. If it is impossible to avoid a high-temperature environment, effective heat insulation and cooling measures should be taken. ​
• Avoiding External Impact: During the construction and using of the building, paying attention to protecting the bearing and prevent it from being impacted by heavy objects or external forces, so as not to cause local damage to the bearing and affect its overall performance. ​
• Following the installation Specifications: The installation process must be carried out strictly in accordance with the product installation guide and relevant specifications to ensure the installation quality. If the installation is improper, it may lead to uneven force on the bearing, affecting the isolation effect and even causing safety accidents. ​
• Paying Attention to the Scope of Application: This product is suitable for building sites of Category I, II, and III. When selecting, it is necessary to reasonably design and select the type according to the category of the building site and the actual situation of the project to ensure that the product can effectively play the role of isolation.

1. Regular Appearance Inspection: Inspect the appearance of the bearing every six months to check for any signs of rubber aging, cracking, steel plate rusting, deformation, or looseness of the connection parts. If obvious cracks appear on the rubber surface, the steel plate is severely rusted, or the connection bolts are loose, record it in a timely manner and take corresponding maintenance measures.
2. Deformation Monitoring: Conduct vertical and horizontal deformation monitoring of the bearing once a year. Compare with the initial installation data. If the vertical deformation exceeds 5mm or the horizontal deformation exceeds the allowable value (generally 10% of the bearing diameter), analyze the causes and conduct an evaluation. Replace the bearing if necessary.
3. Environmental Inspection: Pay attention to the environment around the bearing to avoid the bearing being in harsh environments such as long-term water accumulation and chemical corrosion. If factors that may damage the bearing are found in the surrounding environment, take protective or isolation measures in a timely manner.
4. Inspection after Earthquake: After experiencing an earthquake, regardless of the magnitude, conduct a comprehensive inspection of the bearing, including its appearance, deformation, internal structure, etc. If the bearing is severely damaged and affects the structural safety, immediately organize professional personnel to replace it.

1)In the Field of Building Structures

• Residential Buildings: It is widely applied in newly constructed residential buildings in earthquake-prone areas, significantly enhancing the safety of residences during earthquakes and protecting the lives and property of residents. In earthquake-prone countries such as Myanmar, Japan, and Chile, a large number of low-rise and medium-high-rise residential buildings use LNR bearings. After an earthquake, the degree of damage to the building structure is significantly reduced, and most of them can still be used.

• Public Buildings: For public buildings with dense personnel, such as schools, hospitals, libraries, or those with special requirements for post-earthquake functional restoration, the use of LNR natural rubber isolation bearings can ensure the safe evacuation of people during an earthquake and the rapid restoration of the building's functions after the earthquake. Some schools in Wenchuan, China, used these bearings during seismic reinforcement, which enhanced the stability of school buildings during earthquakes.

2),In the Field of Bridge Engineering

• Medium and Small Span Bridges: For medium and small span bridges with a span of 20 - 80m, this bearing can effectively reduce the damage of earthquakes to the superstructure and substructure of the bridge, and prevent serious seismic hazards such as bridge girder falling. In the construction of numerous mountain bridges in the southwest region of China, this bearing has been widely used, improving the seismic performance of bridges in complex geological and seismic environments.
• Urban Viaducts: The surrounding environment of urban viaducts is complex, and the traffic flow is large. The LNR natural rubber isolation bearing can reduce the vibration response of the viaduct during an earthquake, reduce the impact on surrounding buildings and traffic facilities, and ensure the rapid restoration of urban traffic after the earthquake. This bearing has played an important role in the seismic retrofit projects of viaducts in some large cities.

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