How to Ensure the Installation Quality of Laminated Rubber Bearings

How to Ensure the Installation Quality of Laminated Rubber Bearings

The installation quality of laminated rubber bearings directly determines their functional performance and the long-term safety of bridge structures. A full-process control system must be established covering four core links: pre-installation preparation, construction control, quality inspection, and post-installation maintenance. The specific points are as follows:

1. Pre-installation Preparation: Laying the Foundation for Quality
2. Acceptance of Bearings and Supporting Components Upon Delivery

Strict inspection of delivered bearings is mandatory before installation to prevent unqualified products from entering the construction process:

Appearance Inspection: The bearing surface shall be flat without cracks, bulges, or rubber defects, and there shall be no detachment between rubber and steel plates. The side protective layers (e.g., polytetrafluoroethylene (PTFE) sheets, stainless steel plates) shall be firmly bonded without scratches or deformation.

Parameter Verification: Compare with design drawings to check key parameters such as bearing model, dimensions (length, width, thickness), rubber hardness (Shore A 60±5), and load-bearing grade. Meanwhile, verify product qualification certificates and factory inspection reports (e.g., compressive strength, shear deformation test data).

Sampling Test: For batch-delivered bearings, randomly sample and send them to a third-party laboratory for testing in accordance with specifications. Test their mechanical properties (e.g., compressive elastic modulus, ultimate compressive strength) and material properties (e.g., rubber aging resistance, steel-rubber adhesion strength) to ensure compliance with GB/T 20688 (highway bridges) or TB/T 1893 (railway bridges) standards.

2. Treatment of Installation Substrates

The upper (beam bottom) and lower (pier/abutment top) installation surfaces of bearings must meet the requirements of “flatness, cleanliness, and firmness” to avoid uneven stress on bearings due to substrate defects:

Flatness Control: Use a 2m straightedge to check the flatness of the installation surface, with an allowable deviation ≤2mm/m. If exceeding the limit, repair with epoxy mortar or high-strength leveling layer; random leveling with cement mortar (prone to cracking and insufficient strength) is strictly prohibited.

Cleaning and Drying: Remove laitance, oil, and debris from the installation surface; if necessary, sand to expose the concrete substrate or steel plate. The substrate surface must be dry to avoid affecting the bonding between the bearing and the substrate (for adhesive installation).

Embedded Part Inspection: For bearings fixed with embedded parts (e.g., anchor bolts, steel plates), check the position deviation (planar position ≤5mm, elevation ≤3mm), anchoring depth, and firmness. Offset embedded parts must be corrected in advance or supplemented.

3. Construction Plan and Personnel Preparation

Special Plan Compilation: Prepare a special construction plan based on the bridge type (e.g., simply supported beam, continuous beam) and bearing installation method (e.g., cast-in-place beam embedding, prefabricated beam hoisting), specifying the installation process, precision control standards, and emergency measures (e.g., bearing deviation adjustment plan).

Personnel Training and Technical Disclosure: Conduct technical disclosure for construction personnel, emphasizing operational points of key processes such as bearing positioning, leveling, and fixing. Special operation personnel (e.g., crane operators, welders) must hold certificates to ensure compliance in hoisting, welding, and other links.

1. Core Control During Installation: Precise Execution of Key Processes

The installation precision of laminated rubber bearings directly affects their stress state. Four core processes—positioning, leveling, fixing, and gap adjustment—require focused control.

1. Bearing Positioning: Ensuring “Zero Deviation in Coordinates”

Use a total station or level to accurately stake out based on the bearing centerline coordinates in the design drawings:

Planar Positioning: Mark the longitudinal and transverse centerlines of the bearing on the pier/abutment top and beam bottom respectively. During installation, ensure the bearing centerline coincides with the stakeout line, with an allowable deviation ≤3mm. For skewed or curved bridges, special attention must be paid to matching the bearing deflection angle with the bridge axis.

Elevation Control: Measure the elevation of the pier/abutment top installation surface with a level, and calculate the designed elevation of the bearing top surface based on the bearing thickness. Ensure the beam elevation meets design requirements after installation (allowable deviation ≤2mm). For wedge-shaped bearings used to adjust slopes, verify that the wedge angle matches the bridge longitudinal slope.

2. Bearing Leveling: Avoiding “Uneven Stress”

The bearing installation surface must be horizontal (or match the bridge slope) to prevent premature aging or damage of the rubber layer due to local compression:

Levelness Detection: Use a level to check the levelness of the installed bearing, with an allowable deviation ≤1‰. For circular bearings, test at multiple points along the circumference; for rectangular bearings, check the elevation difference at four corners.

Leveling Method Selection:

For slightly uneven substrates, use a thin epoxy mortar cushion (5~10mm thick) for leveling; excessively thick cushions (prone to compressive deformation) are prohibited.

For prefabricated beam installation, lay stainless steel sliding plates + PTFE sheets (for sliding bearings) on the bearing top surface. Ensure the sliding plates are clean and free of debris, and the grooves of PTFE sheets align with the bosses of stainless steel plates.

3. Bearing Fixing: Ensuring “Firm Connection”

Select appropriate fixing methods based on bearing types to prevent sliding or falling off during operation:

Anchor Bolt Fixing: For bearings fixed with anchor bolts, the bolt hole diameter should be 2~3mm larger than the bolt diameter (for easy adjustment). Tighten bolts with a torque wrench to control pre-tightening force (usually 60%~70% of the bolt yield strength). After tightening, spot-weld nuts to prevent loosening, and grout anchor bolt holes with non-shrink grout for sealing.

Adhesive Fixing: For small bearings, epoxy resin adhesive can be used for fixing. Ensure the adhesive layer is uniform (2~3mm thick) and allow it to set for more than 24 hours before applying loads.

Temporary Fixing: When hoisting prefabricated beams, set temporary stoppers on both sides of the bearing to prevent deviation during beam placement. Remove temporary stoppers only after beam installation and confirmation of correct bearing position.

4. Gap and Sealing Treatment: Enhancing Durability

Sliding Gap Control: For sliding laminated rubber bearings (with PTFE sheets), check that the gap between the bearing and limit devices meets design requirements (usually 5~10mm) to ensure free sliding without jamming during temperature-induced beam deformation.

Side Sealing: Repair damaged rubber protective layers on bearing sides with special sealants. For open-air installed bearings, install rain shields (e.g., stainless steel covers) on the top to prevent rainwater and dust from accelerating rubber aging.

III. Post-installation Quality Inspection: Closing the Quality Loop

1. Appearance and Dimension Recheck

Re-inspect the bearing surface for damage, rubber defects, or steel plate deformation caused by installation.

Recheck the planar position and elevation deviation of bearings with a tape measure and caliper to ensure compliance with specifications (see the table below for specific deviation standards).

2. On-site Mechanical Performance Testing

Compression Test: For installed bearings, use a small jack for local compression testing. Check for obvious compressive deformation (allowable compression ≤10% of the design value) and elastic recovery (recovery rate ≥90%) after unloading.

Shear Test: For sliding bearings, apply horizontal thrust (simulating temperature deformation) to check for free sliding without jamming. For fixed bearings, verify that horizontal stiffness meets design requirements.

3. Concealed Works Acceptance

For bearings fixed by grouting (e.g., anchor bolt hole grouting, bearing bottom cushion grouting), conduct concealed works acceptance after the grout strength reaches the design value (usually C40 or higher). Check that the grout is full and free of voids (using ultrasonic testing if necessary).

1. Post-installation Maintenance: Extending Bearing Service Life

Installation completion is not the end; regular maintenance is key to ensuring long-term bearing stability:

Regular Inspection: Conduct monthly visual inspections of bearings, focusing on rubber cracks/bulges, PTFE sheet wear, anchor bolt looseness, and drainage smoothness (to avoid long-term immersion of bearings in water).

Cleaning and Lubrication: Clean stainless steel sliding plates of sliding bearings with alcohol annually and apply special silicone grease lubricant to ensure smooth sliding.

Defect Repair: Repair minor rubber cracks (width <1mm) with special rubber repair agents. Replace bearings immediately if cracks exceed 1mm, or if steel plate rust or detachment occurs.

Long-term Monitoring: For long-span or seismic-zone bridges, install displacement and pressure sensors to monitor bearing displacement and stress in real time, and take timely measures for abnormalities.

Summary

The installation quality control of laminated rubber bearings must follow the principle of “strict pre-acceptance, precise in-process control, rigorous post-inspection, and intensive post-maintenance”. The core is to ensure coordinated stress between bearings and bridge structures through “accurate positioning, strict leveling, and firm fixing”. Meanwhile, full-process standardized operations prevent premature bearing failure due to installation defects, ultimately ensuring the safe operation and service life of the bridge.

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