Guide to Determining the Need for Bridge Elastomeric Bearing Replacement: From Inspection Indicators to Decision-Making Criteria
I. Visual and Structural Damage Inspection: Intuitive Assessment of Aging and Failure
1. Aging Characteristics of Rubber Materials
Surface Cracks
Longitudinal or circumferential cracks exceeding 0.5mm in width and 1/3 of the bearing edge length may indicate loss of elasticity (e.g., surface crazing in plain plate bearings).
Case Study: A 20-year-old concrete simply supported beam bridge exhibited mesh cracks on bearing rubber layers due to UV aging, with measured elastic modulus decreasing by 40%.
Deformation and Bulging
Local swelling or bulging of rubber layers (bulge height >1/10 of bearing thickness) or overall compression deformation exceeding 20% of the design value (e.g., plate bearing thickness reduced from 40mm to <32mm).
Hardening and Brittleness
Rubber feels hard and loses elasticity, producing a crisp sound when struck (normal rubber should emit a dull, elastic sound). Shore hardness tests exceeding 15% of the design value indicate degradation.
2. Internal and Connection Component Damage
Exposed and Corroded Steel Plates
Wear of rubber protective layers on multi-layer bearings exposes steel plate edges, or rust appears on steel surfaces (e.g., corrosion of stainless steel plates in PTFE sliding bearings).
Failure of Sliding Components
Wear of PTFE plates exceeding 2mm (for original thickness of 5mm) or surface scratches deeper than 1mm cause a significant increase in friction coefficient (normal ≤0.03, failed >0.1).
II. Mechanical Performance Testing: Quantifying Functional Degradation
| Test Item | Normal State 指标 | Replacement Threshold | Testing Method |
| Vertical Compression Stiffness | Within ±10% of design value | Stiffness reduction >25% (significant load capacity decrease) | Jack loading test, measure load-deformation curve |
| Horizontal Displacement Capacity | Within ±15% of design displacement | Measured displacement <50% of design value (e.g., 100mm displacement bearing moves only 40mm) | Displacement sensor monitoring during temperature changes |
| Rotational Capacity | Within ±0.005 rad of design rotation | Rotation <30% of design value (e.g., 0.02 rad bearing measures only 0.006 rad) | Inclinometer measurement of angle difference between beam and bearing |
| Damping Performance | Energy dissipation efficiency ≥80% of design under seismic loads | Efficiency <50% (damping function 失效) | Shaking table test or ambient vibration spectral analysis |
III. Abnormal Bridge Response: Indirect Signs of Bearing Failure
1. Additional Stress in Beams and Piers
Crack Propagation at Beam Ends
Diagonal cracks (45°–60°) at beam ends may indicate stress concentration due to restricted bearing rotation (e.g., 0.3mm-wide cracks in web plates of a continuous beam bridge after bearing aging).
Abnormal Pier Displacement
Horizontal displacement at pier tops exceeding code limits (≤5mm for highway bridges, ≤2mm for railway bridges) unrelated to temperature changes may signal excessive pier loading due to bearing constraint failure.
2. Ride Comfort and Abnormal Noises
Vehicle Bouncing
Noticeable vehicle 颠簸 during passage, with 桥面 roughness index (IRI) exceeding 3.0m/km (normal ≤2.5m/km), may result from bearing settlement or uneven stiffness.
Abnormal Noises and Vibrations
Metallic friction sounds during traffic (e.g., direct steel-to-steel contact after PTFE wear) or increased low-frequency bridge vibrations (e.g., resonance caused by failed damping function).
IV. Environmental and Load Factors: External Conditions Accelerating Failure
Exceeding Design Loads
Prolonged heavy truck traffic (e.g., single-axle loads >25 tons) causes excessive compression deformation and plastic flow in rubber layers (e.g., a freight corridor bearing failed 5 years prematurely due to overloading).
Harsh Environmental Erosion
Coastal bearings may swell due to salt spray corrosion (volume change >10%), or those near chemical plants may experience surface carbonization from acid rain (10+ years in pH<4 environments).
Earthquakes and Extreme Temperatures
Shear failure (rubber-steel delamination) may occur after strong earthquakes (exceeding design seismic intensity). High temperatures (>60°C) accelerate thermo-oxidative aging, reducing service life to <10 years.
V. Inspection Intervals and Decision-Making Process
Regular Inspection Frequencies
New Bridges: Inspect at 1 year and 3 years post-construction, then every 5 years.
Aged Bridges (>15 years): Inspect every 2–3 years, focusing on UV-exposed areas and poor drainage locations.
Replacement Decision Matrix
| Damage Level | Functional Degradation | Repair Cost Ratio | Recommended Action |
| Minor Cracks/Hardening | Stiffness reduction <15% | <30% of new bearing cost | Surface protection (anti-aging coating) |
| Moderate Cracks/Displacement Deficiency | Stiffness reduction 15%–25% | 30%–50% of new bearing cost | Partial replacement or repair of sliding components |
| Severe Damage/Functional Failure | Stiffness reduction >25% or rotation <50% of design | >50% of new bearing cost | Complete bearing replacement |
VI. Engineering Case Studies: Typical Failure Modes and Solutions
Case 1: Aging of Plain Plate Bearings
A 1998-built urban overpass showed 普遍 cracking (0.8mm width) and 25% over-design compression in 2015. The entire bridge was retrofitted with PTFE sliding bearings due to reduced deck smoothness.
Case 2: Leakage and Corrosion of Pot Bearings
Pot bearings on a river-crossing bridge leaked due to seal aging, causing internal rubber swelling and 30% load capacity reduction from steel corrosion. Remediation involved full replacement with stainless steel protective covers.
VII. Preventive Maintenance Recommendations
Regular Cleaning and Protection: Annually remove dust, oil, and debris from bearing surfaces; apply anti-aging coatings (e.g., silicone-based protective layers) to rubber bearings.
Intelligent Monitoring: Install displacement-stress sensors on critical bridges to trigger alerts when thresholds are exceeded (e.g., sudden displacement >5mm/day).
Overload Control: Deploy weigh-in-motion systems at bridge entrances to restrict overweight vehicles, extending bearing service life.
Through multi-dimensional assessments combining visual inspections, mechanical testing, and bridge response analysis, the failure degree of elastomeric bearings can be accurately determined. Timely replacement is critical when damage threatens structural safety or operational functionality to prevent cascading failures in beams or piers. Future integration of digital twin technology for lifecycle management will further enhance the scientific rigor and cost-effectiveness of replacement decisions.
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