LNR and LRB Seismic Isolation Rubber Bearing Product Introduction

▶ I. Basic Definition and Core Principle

LNR: Laminated Natural Rubber Bearing, made of multiple layers of natural rubber sheets and thin steel plates bonded and vulcanized alternately. It relies on the elastic deformation of the rubber to achieve horizontal seismic isolation and recovery.

LRB: Lead-Rubber Bearing, with a lead core embedded in the center of the LNR bearing. Combining the elastic restoring force of the rubber with the energy dissipation capacity of the lead core's plastic deformation, it has both seismic isolation and damping functions.

Core Principle: Through the characteristics of "horizontal flexibility + vertical stiffness," the bearing undergoes shear deformation during an earthquake, prolonging the structure's natural period, avoiding the dominant period of the seismic motion, and reducing the seismic response of the superstructure (by 60%-80%).

▶ II. Structural Composition and Classification

1. Structural Comparison

2. Common Classifications

Shape: Round (LNR300/LRB500, etc., numbers refer to diameter in mm), rectangular.

Load Capacity: Small (≤500kN), Medium (500-5000kN), Large (≥5000kN).

Reinforcement Methods: Pure rubber reinforcement, fiber reinforcement, steel plate reinforcement (mainstream).

▶ III. Core Performance Characteristics

1. Common Advantages

High Vertical Load Capacity: Can withstand loads of 500kN~10000kN, suitable for various buildings and bridges.

Excellent Durability: Natural rubber is resistant to aging and fatigue, with a service life of 80-100 years.

Good Temperature Adaptability: Applicable temperature range **-30℃~60℃**, adaptable to different climatic conditions.

Easy Installation: Lightweight and accurately positioned, can be prefabricated in the factory and installed on-site.

2. Performance Difference Comparison

▶ IV. Specifications and Key Technical Parameters (National Standard GB 20688.3-2006)

▶ V. Applicable Engineering Scenarios

1. LNR Applicable Scenarios

General buildings in low-to-medium seismic intensity zones (≤7 degrees): residential buildings, office buildings, and commercial buildings.

Bridges and municipal facilities with low damping requirements.

Seismic reinforcement and retrofitting projects (lower loads, moderate deformation).

2. LRB Applicable Scenarios

Important public buildings in high-seismic intensity zones (≥7 degrees): hospitals, schools, stadiums, and command centers.

Long-span bridges, viaducts, and rail transit hubs.

Facilities with extremely high safety requirements, such as nuclear power plants, hydroelectric power plants, and large industrial plants.

High-rise buildings on soft soil foundations (requiring stronger energy dissipation capacity).

▶ VI. Installation Key Points and Precautions

Installation Process

1. Foundation Preparation: The concrete base should be level and clean, and the embedded steel plate should be accurately positioned (horizontal error ≤ 2mm).

2. Support Positioning: Place according to the design axis. The center deviation of circular supports should be ≤ 5mm, and the edge alignment error of rectangular supports should be ≤ 3mm.

3. Fixed Connection: Use bolts or welding for fixing to ensure reliable connection with the upper and lower structures.

4. Protective Measures: Install dust covers, avoid damage from sharp objects, and keep away from heat sources (≥ 1m).

Key Contraindications:

✖ Eccentric installation of the bearings leads to uneven stress and localized shear failure.

✖ Exposed lead core (LRB) requires proper corrosion protection (lead core wrapped with a rubber layer).

✖ Unauthorized repositioning after installation affects the seismic isolation effect.

✖ Using the bearings with other seismic isolation components without proper compatibility design.

▶ VII. LNR vs LRB Core Comparison Table

▶ I. General Basic Processes (LNR and LRB share the same preliminary steps)

1. Raw Material Preparation

Rubber: Natural rubber (NR) is used. Mooney viscosity (40-60 MU), tensile strength (≥28 MPa), and elongation (≥600%) must be tested to ensure elasticity and durability.

Steel Plate: Q235 galvanized steel plate is used, with a thickness of 2-6 mm and a zinc coating thickness ≥8 μm to ensure rust prevention and adhesion.

Lead Core (LRB only): Electrolytic lead with a purity ≥99.994%, processed into a cylindrical shape, with a diameter error ≤0.5 mm and a length accuracy ±1 mm.

2. Rubber Compounding

Natural rubber is mixed with vulcanizing agent (sulfur), accelerator (CZ), antioxidant (RD), and reinforcing agent (carbon black N330) according to the formula (e.g., 100 parts rubber, 2.5 parts sulfur, 40 parts carbon black). The mixture is then added to an internal mixer and mixed at 80-110℃ for 5-8 minutes to obtain a homogeneous rubber compound.

After mixing, the compound needs to be left to stand for 24 hours to allow internal stress release and performance stabilization.

3. Pretreatment of Rubber Sheets and Steel Plates

Rubber Sheets: The compounded rubber is calendered on an open mill into sheets of uniform thickness (error ≤ 0.2mm), with a width matching the steel plate.

Steel Plates: The surface of the galvanized steel plate is ground and cleaned to remove oil and oxide layers. A special adhesive (such as epoxy-rubber composite adhesive) is applied to ensure a bond strength ≥ 3MPa with the rubber.

▶ II. Core Processes of LNR (Natural Rubber Seismic Isolation Bearing)

1. Lamination Assembly

According to the designed number of layers (e.g., 10 layers of rubber + 11 layers of steel plate), pre-treated rubber sheets and steel plates are alternately placed. The thickness of each rubber layer is designed according to the bearing height (e.g., 5mm thick for a single rubber layer).

During assembly, positioning fixtures are used to ensure the steel plates are aligned, with a deviation ≤1mm, to prevent uneven stress later.

2. Overall Vulcanization

The laminated assembly is placed in a vulcanization mold and vulcanized at 150-160℃ and 15-20MPa pressure for 30-60 minutes (time adjusted according to bearing dimensions).

Vulcanization causes the rubber molecules to cross-link, forming a stable elastomer. Simultaneously, the rubber and steel plate are firmly bonded through adhesives and high temperature and pressure.

3. Trimming and Inspection

After vulcanization, the burrs are removed, and the bearing surface is polished to ensure flatness (flatness ≤0.5mm).

Key testing indicators: vertical compression deformation (≤5% of design height), horizontal shear modulus (0.8 - 1.2MPa), and bond strength (≥3MPa). After passing the test, the product is marked and put into storage.

▶ III. Core Process of LRB (Lead-Core Rubber Isolation Bearing) (Adding a Lead-Core Process to LNR)

1. Lead-Core Insertion (Key Differentiating Step)

A circular hole matching the diameter of the lead core is drilled in the center of the laminated assembly before vulcanization (error ≤ 0.2mm).

The pre-treated lead core is slowly pressed into the circular hole, ensuring the lead core is centered and the gap between it and the surrounding rubber is uniform (≤ 0.5mm), avoiding premature yielding due to misalignment.

2. Overall Vulcanization (Similar to LNR but requiring more precise control)

The vulcanization temperature and pressure are the same as LNR, but the temperature distribution within the mold must be strictly monitored to prevent the lead core from melting due to localized high temperatures (lead melting point 327℃, vulcanization temperature is much lower than this, excessive temperature fluctuations must be avoided).

During vulcanization, the lead core and surrounding rubber vulcanize and bond synchronously, forming a unified whole.

3. Post-processing and Inspection

After vulcanization, the edges are trimmed and polished, with a focus on checking the lead core position (X/Y direction offset ≤ 1mm).

Additional testing parameters: lead core yield strength (50 - 500kN, as designed) and damping ratio (20% - 30%) to ensure energy dissipation performance meets standards.