LRB Lead Rubber Bearing

Main Components of Lead Rubber Bearing:

Rubber Layer: Typically made of natural or synthetic rubber, providing elastic resilience, absorbing seismic energy, and allowing horizontal deformation.

Stiffening Steel Plate: Multiple layers of steel plates are alternately stacked with the rubber layer to enhance the overall stability of the bearing, prevent excessive lateral deformation of the rubber, and bear the weight of the building.

Lead Core: Vertically pressed or vulcanized and embedded in the center of the bearing, it dissipates energy through plastic deformation under seismic loads and is the main damping element. The diameter or cross-sectional area of the lead core can be adjusted according to design requirements to control damping performance.

Installation :

1. Embedded Plate Installation (Applicable to Foundation Stage): Place the embedded plate in the designed position, and adjust its levelness (error ≤ 5‰) and elevation (error ≤ 5mm) using adjusting screws or wedge-shaped wooden blocks; After verifying with a level and spirit level, weld and fix the embedded steel bars to the main foundation reinforcement; Pour concrete, and after initial setting, loosen the bolts to prevent mortar from hardening, and remove surface cement after final setting.

2. Support Lifting and Positioning: Use special lifting tools when lifting the supports to avoid directly lifting the bolts; Align the support with the center of the embedded plate, with a plane position deviation ≤ 5mm and an elevation deviation ≤ 5mm; If the levelness is not up to standard, adjusting shims can be added between the support and the embedded plate.

3. Connection and Fixing: Tighten the connecting bolts symmetrically in stages to prevent the connecting plate from warping; When using high-strength bolts, tighten to the designed torque.

4. Grouting Construction (if required): Use high-performance bearing grout (flowability ≥300mm, micro-expansion, early strength); employ gravity or pressure grouting to ensure full filling without voids; cover with geotextile for curing after grouting.

5. Protective Measures: Apply anti-rust paint or grease to exposed metal parts and wrap with tar paper for dust protection; protect the bearings with wooden frames during upper construction to avoid mechanical damage.

Working Principle

When an earthquake occurs, the horizontal displacement of the superstructure causes deformation of the bearing. The rubber layers absorb seismic energy like a spring and provide a horizontal restoring force to return the structure to its original position. Simultaneously, the lead core undergoes plastic yielding during shear deformation, dissipating a significant amount of seismic energy through hysteretic damping. This synergistic mechanism of "rubber providing elastic restoring force and lead core providing damping energy dissipation" significantly reduces the seismic forces transmitted to the superstructure. Following an earthquake, the lead core, through dynamic recovery and recrystallization processes, combined with the restoring force of the rubber, helps the building automatically reset.

Characteristics:

1. Excellent Damping Performance: The plastic deformation of the lead core effectively absorbs seismic energy, improving the damping performance of pure rubber bearings. Its hysteretic performance is stable, exhibiting stable bilinear hysteretic characteristics even under large shear deformation.

3.2. Extended Structural Period: The yielding of the lead core reduces the bearing stiffness, thereby extending the natural period of the building structure to approximately 1.5 to 3.0 seconds, effectively reducing seismic response.

3. High Bearing Capacity and Durability: The bearing has sufficient vertical bearing capacity to stably support the building, with a service life of 60 to 80 years, exhibiting good fatigue resistance and aging resistance.

4. Design Flexibility: By adjusting the diameter, number, or cross-sectional area of the lead core, the damping performance and energy dissipation capacity of the bearing can be adjusted to meet different engineering requirements. Scope of Application: Primarily applicable to various buildings and bridges in areas with seismic fortification intensity of 8 degrees and below.

Main Application Areas:

Lead-core rubber bearings are suitable for areas with seismic fortification intensity of 8 degrees and below, and are widely used in following areas:

1. Various highway and municipal bridges.

2. Buildings with high seismic performance requirements, such as high-rise buildings, hospitals, and schools.

3. Isolation of important engineering structures and equipment foundations, and seismic reinforcement of existing buildings.

4. Domestic and international engineering examples include the Miyagawa Ohashi Bridge in Japan, and the Ishizu Canal Bridge, Jinjiang Bridge, and Xiamen-Zhangzhou Bridge in China. 

Selection Basis and Maintenance Points

The selection should be based on parameters such as building height, seismic intensity, and span, calculated and chosen by a professional team according to the "Code for Seismic Design of Buildings".

Quality Control :

Levelness Requirements: The levelness error of the top surface of the bearing after installation ≤8‰47;

Axis Alignment: The deviation between the bearing center and the design axis ≤5mm4;

Eccentric Compression Prohibition: Ensure the bearing is evenly stressed, without voids or local suspension.

Subsequent Maintenance: 

Regularly inspect the bearings for cracks, aging, and corrosion; after a strong earthquake, conduct a special inspection of the lead core deformation and recovery.