Classification of Seismic Isolation Rubber Bearings

In recent years, due to the impact of earthquakes, there has been a growing call for the use of seismic isolation rubber bearings in the construction of houses, bridges, and other structures in earthquake-prone areas. Hengshui Guoheng Rubber & Plastic Products Co., Ltd. has continuously carried out technological research and development and developed high-quality seismic isolation rubber bearings. According to the materials used in the bearings and the presence or absence of lead cores, seismic isolation rubber bearings are divided into three types: Natural Rubber Bearings (abbreviated as LNR), High-Damping Rubber Bearings (abbreviated as HDR), and Lead-Core Rubber Bearings (abbreviated as LRB).  

1. Natural Rubber Bearing (LNR)  

It uses natural rubber as the main raw material and is composed of multiple layers of rubber with steel plates sandwiched between them. This bearing features low horizontal stiffness and high vertical stiffness, and exhibits excellent performance in terms of resistance to low-cycle fatigue, hot air aging, ozone aging, acid resistance, and water resistance. However, its energy dissipation performance is relatively poor, so it usually needs to be used in conjunction with other products.  

2. Lead-Core Rubber Bearing (LRB)  

Based on the natural rubber bearing, a vertical lead core is embedded inside it, and it is composed of composite rubber layers, steel plates, and a lead core. It has high damping, strong horizontal displacement capacity, and a reset function, with stable vertical stiffness and good vertical load-bearing effect. When an earthquake occurs, the lead core absorbs energy through plastic deformation, helping the building quickly return to its original position after the earthquake.  

3. High-Damping Rubber Bearing (HDR)  

Carbon or other elements are added to the rubber base material to improve its damping performance, realizing the trinity of vertical load-bearing capacity, horizontal restoring force, and damping. It is formed by bonding composite rubber layers and steel plates, with a full hysteretic characteristic and significant energy dissipation. It is suitable for important projects such as high-rise buildings and long-span bridges.  

Analysis of Similarities and Differences Between Natural Rubber Bearings, High-Damping Rubber Bearings, and Lead-Core Rubber Bearings  

I. Similarities

1. Vertical Performance: All three types have the characteristics of high vertical stiffness and high vertical load-bearing capacity. They can effectively bear the vertical load of buildings and ensure the vertical stability of the structure under normal use and earthquake action.  

2. Horizontal Performance: All have the characteristics of low horizontal stiffness and strong horizontal deformation capacity. During an earthquake, they can absorb and dissipate seismic energy through horizontal deformation, extend the natural vibration period of the structure, and thereby reduce the impact of horizontal seismic action on the building structure.  

II. Differences  

1. Seismic Damping Mechanism  

  - Natural Rubber Bearing (LNR): It achieves seismic isolation only by relying on the elastic deformation of rubber. Its equivalent damping ratio is usually 2%-3%, and its energy dissipation capacity is limited.  

  - Lead-Core Rubber Bearing (LRB): It forms a dual seismic damping mechanism through the plastic deformation of the lead core and the elastic deformation of the rubber layer. Its equivalent damping ratio can reach 13.5%-22.7%.  

  - High-Damping Rubber Bearing (HDR): It improves damping performance by adding elements to the rubber base material, and absorbs energy through the elastic deformation of rubber and converts it into heat energy. Its damping ratio is more than 18%.  

2. Stiffness and Energy Dissipation  

  - Lead-Core Rubber Bearing (LRB): Its horizontal equivalent stiffness is significantly higher than that of the natural rubber bearing, and the stiffness can be flexibly adjusted by changing the diameter of the lead core. Its hysteresis curve shows a stable bilinear characteristic with an obvious energy dissipation inflection point.  

  - Natural Rubber Bearing (LNR): Its hysteresis curve is approximately linear, with no obvious energy dissipation inflection point, and its overall energy dissipation capacity is weak.  

  - High-Damping Rubber Bearing (HDR): Its hysteresis curve is full, and its energy dissipation capacity is strong, which is between that of the natural rubber bearing and the lead-core rubber bearing.  

3. Deformation Capacity  

  - Lead-Core Rubber Bearing (LRB): It can maintain stable performance under a shear strain of 250%, with excellent deformation capacity.  

  - Natural Rubber Bearing (LNR): When the shear strain reaches 150%, its horizontal stiffness may increase by 20%-25%, and its deformation capacity is relatively limited.  

  - High-Damping Rubber Bearing (HDR): It has strong deformation capacity and can meet the demand for large deformation of the structure under earthquake action.  

4. Temperature Sensitivity  

  - Natural Rubber Bearing (LNR): It is relatively sensitive to temperature, and its stiffness may decrease by 10%-15% in a high-temperature environment.  

  - Lead-Core Rubber Bearing (LRB): It has good temperature adaptability and maintains stable performance in the temperature range of -25℃ to +60℃.  

  - High-Damping Rubber Bearing (HDR): It also has good temperature adaptability and can maintain stable performance in a relatively wide temperature range.