Lead rubber bearing,
Lead Rubber Bearing (LRB)
Introduction:
A lead rubber bearing is a type of seismic isolation bearing. Its core design principle is not to “rigidly resist” seismic forces but to “flexibly isolate and dissipate” seismic energy, thereby protecting the superstructure (such as bridges or buildings). Its working principle can be summarized as the perfect integration of “flexible support” and “energy dissipation.”
Decomposition of Core Structure
A standard LRB consists of three main components:
-
Alternating Layers of Rubber and Steel Plates:
-
Provides vertical stiffness to support the weight of the structure while offering substantial horizontal flexibility, allowing for slow, large displacements.
-
-
Central Lead Core:
-
Inserted or cast into a hole at the center of the bearing. This is the key component for energy dissipation.
-
-
Top and Bottom Connection Steel Plates:
-
Used to securely connect the bearing to the superstructure (e.g., bridge deck) and the substructure (e.g., bridge pier or building foundation).
-
Detailed Working Principle (Explained by Mechanism)
Mechanism 1: Rubber Provides Flexible Isolation (Elastic Restoring Force)
-
Function: The laminated structure of alternating rubber and steel layers allows the bearing to behave like a large spring in the horizontal direction, providing significant flexibility.
-
During an Earthquake: When the ground shakes violently, the bottom of the bearing moves with the ground, while the superstructure tends to remain stationary due to inertia. At this moment, the flexible rubber layers undergo large deformations, elongating the natural vibration period of the structure. This significantly reduces the seismic acceleration and forces transmitted to the superstructure. After the earthquake, the elasticity of the rubber helps the structure slowly return to its original position.
Mechanism 2: Lead Core Provides Damping and Energy Dissipation (Plastic Energy Dissipation)
-
Function: The lead core is the soul of the LRB. Lead is a metal capable of recrystallization at room temperature, offering excellent plastic deformation and energy dissipation capabilities.
-
During an Earthquake: When the bearing undergoes horizontal deformation due to seismic activity, the central lead core is forced to undergo shear plastic deformation. This process is similar to repeatedly bending a wire—it generates heat. As the lead core deforms, it converts a large amount of seismic kinetic energy (mechanical energy) into heat, which is then dissipated into the air.
-
Result: By dissipating energy, the lead core significantly reduces the amplitude of structural vibrations, preventing the structure from oscillating like a pendulum. This provides “supplementary damping” to Mechanism 1, enabling rapid attenuation of vibrations.
Mechanism 3: Vertical Load-Bearing and Stability
-
Function: The internal thin steel layers constrain the vertical expansion of the rubber, giving the bearing high vertical compressive stiffness. This allows it to stably support permanent loads weighing thousands of tons while maintaining horizontal flexibility.
