15.2 Common bridge defects and deterioration mechanisms

Bridges face a variety of defects and deterioration mechanisms that can compromise their safety and performance. From corrosion and fatigue in steel to freeze-thaw damage in concrete, these issues require careful monitoring and maintenance to prevent failure.

Understanding the causes and effects of bridge deterioration is crucial for developing effective repair strategies. By assessing defects through visual inspection, non-destructive testing, and advanced techniques, engineers can prioritize interventions and extend the service life of these critical infrastructure assets.

Bridge Defects and Deterioration

Types of Bridge Defects

Top images from around the web for Types of Bridge Defects

• 

  Frontiers | Modeling Steel Corrosion Failure in Reinforced Concrete by Cover Crack Width 3D FEM ... View original

  Is this image relevant?

• 

  Bridge failure - All this View original

  Is this image relevant?

• 

  File:Nandu River Iron Bridge corrosion - 03.jpg - Wikimedia Commons View original

  Is this image relevant?

• 

  Frontiers | Modeling Steel Corrosion Failure in Reinforced Concrete by Cover Crack Width 3D FEM ... View original

  Is this image relevant?

• 

  Bridge failure - All this View original

  Is this image relevant?

1 of 3

Top images from around the web for Types of Bridge Defects

• 

  Frontiers | Modeling Steel Corrosion Failure in Reinforced Concrete by Cover Crack Width 3D FEM ... View original

  Is this image relevant?

• 

  Bridge failure - All this View original

  Is this image relevant?

• 

  File:Nandu River Iron Bridge corrosion - 03.jpg - Wikimedia Commons View original

  Is this image relevant?

• 

  Frontiers | Modeling Steel Corrosion Failure in Reinforced Concrete by Cover Crack Width 3D FEM ... View original

  Is this image relevant?

• 

  Bridge failure - All this View original

  Is this image relevant?

1 of 3

• Bridge defects categorized into structural, material, and functional deficiencies impact bridge performance differently
  • Structural deficiencies compromise load-bearing capacity (cracked girders)
  • Material deficiencies degrade component quality (corroded steel)
  • Functional deficiencies impair intended use (damaged deck surface)
• Corrosion of steel elements prevalent in reinforced concrete and steel bridges exposed to harsh environments
  • Chloride-induced corrosion common in coastal areas and regions using deicing salts
  • Atmospheric corrosion affects exposed steel members in humid climates
• Fatigue cracking occurs in steel bridge components due to repetitive loading
  • Initiates at stress concentration points (welded connections, sudden changes in geometry)
  • Poor fabrication quality exacerbates fatigue crack formation (improper weld profiles, misalignments)
• Concrete deterioration manifests through various mechanisms
  • Freeze-thaw damage causes surface scaling and internal cracking in cold climates
  • Alkali-silica reaction (ASR) leads to expansive cracking in concrete with reactive aggregates
  • Carbonation reduces concrete alkalinity, potentially leading to reinforcement corrosion

Environmental and Structural Factors

• Scour critical for bridge foundations, particularly in waterway crossings
  • Undermines piers and abutments by eroding supporting soil
  • Can lead to sudden collapse if severe (1987 Schoharie Creek Bridge failure)
• Bearing deterioration and joint failure common defects affecting load distribution
  • Seized bearings restrict intended movement, inducing additional stresses
  • Failed joints allow water and de-icing chemicals to penetrate, accelerating deterioration
• Environmental factors contribute to bridge material and component degradation
  • Temperature fluctuations cause expansion and contraction, stressing materials
  • Chemical exposure (acid rain, marine environments) accelerates corrosion and material breakdown
  • Moisture ingress leads to freeze-thaw damage and reinforcement corrosion in concrete

Causes and Effects of Bridge Deterioration

Corrosion and Fatigue Mechanisms

• Corrosion in steel reinforcement primarily caused by chloride ion penetration and concrete carbonation
  • Chlorides break down protective passive layer on steel surface
  • Carbonation reduces concrete alkalinity, depassivating steel
  • Results in section loss, reduced load-carrying capacity, and potential structural failure
• Fatigue cracking in steel bridges initiated by cyclic loading and stress concentrations
  • Repeated stress cycles cause microscopic damage accumulation
  • Cracks propagate over time, potentially leading to sudden fracture if unaddressed
  • Critical in elements subject to tension or reversal of stresses (girder flanges, connection plates)

Concrete Deterioration Processes

• Freeze-thaw damage in concrete occurs due to water expansion during freezing cycles
  • Water in pores expands ~9% when freezing, creating internal stresses
  • Repeated cycles cause progressive damage, leading to cracking, scaling, and spalling
  • Air-entrained concrete more resistant due to expansion space provided by air bubbles
• Alkali-silica reaction (ASR) caused by interaction between cement alkalis and reactive silica in aggregates
  • Forms expansive gel that absorbs water and increases in volume
  • Results in concrete cracking, reduced strength, and accelerated deterioration
  • Can take years to manifest, making early detection challenging

Structural and Functional Deterioration

• Scour caused by erosive action of water flow around bridge foundations
  • Faster water velocities increase scour potential
  • Can lead to foundation settlement, misalignment, or collapse if severe
  • Particularly problematic during flood events (1987 Schoharie Creek Bridge collapse)
• Bearing deterioration often caused by improper maintenance, corrosion, or overloading
  • Restricted movement increases stresses in superstructure elements
  • Can damage other bridge components (girder ends, diaphragms)
  • Elastomeric bearings prone to deterioration from ozone exposure and material aging
• Joint failure attributed to thermal expansion, traffic loading, and debris accumulation
  • Allows water infiltration, accelerating deterioration of adjacent elements
  • Reduces ride quality and can damage vehicles
  • Failed expansion joints can induce unintended stresses in bridge superstructure

Assessing Bridge Defects

Visual Inspection Techniques

• Visual inspection involves systematic examination of bridge components to identify surface defects
  • Requires knowledge of common defect patterns and their significance
  • Utilizes tools like crack gauges, pachometers, and high-resolution cameras
  • Limitations include inability to detect internal defects or quantify material properties
• Concrete crack mapping and measurement techniques document extent and progression of deterioration
  • Grid systems used to record crack locations and widths
  • Crack comparator cards help classify crack widths (hairline, medium, severe)
  • Time-lapse photography can track crack growth over inspection intervals

Non-Destructive Testing Methods

• Non-destructive testing (NDT) provides insights into internal defects and material properties
  • Ultrasonic testing detects internal flaws in steel members (cracks, delaminations)
  • Ground-penetrating radar assesses concrete deck condition and rebar placement
  • Infrared thermography identifies delaminations and moisture ingress in concrete
• Corrosion assessment tools quantify extent and severity of reinforcement corrosion
  • Half-cell potential measurements indicate likelihood of active corrosion
  • Corrosion rate monitoring estimates steel section loss over time
  • Concrete resistivity measurements assess corrosion risk in reinforced concrete

Advanced Assessment Techniques

• Load testing and structural health monitoring evaluate overall bridge performance
  • Static load tests assess load distribution and identify potential overloads
  • Dynamic load tests measure vibration characteristics and detect changes in stiffness
  • Long-term monitoring systems track structural behavior under various conditions
• Scour evaluation techniques crucial for assessing bridge foundation condition
  • Sonar surveys map riverbed topography around piers and abutments
  • Underwater inspections identify scour holes and foundation damage
  • Scour monitoring devices provide real-time alerts during flood events
• Interpretation of inspection and testing results requires understanding of bridge design
  • Knowledge of load-carrying mechanisms essential for accurate defect impact assessment
  • Material properties and deterioration mechanisms influence interpretation of test data
  • Historical inspection data helps track progression of defects over time

Impact of Defects on Bridge Performance

Structural Analysis and Modeling

• Structural analysis techniques assess impact of defects on load-carrying capacity
  • Finite element modeling simulates effects of deterioration on stress distribution
  • Load rating calculations determine safe load-carrying capacity of defective bridges
  • Fracture mechanics analysis predicts fatigue crack growth and remaining fatigue life
• Deterioration modeling and service life prediction estimate long-term defect progression
  • Corrosion rate models predict reinforcement section loss over time
  • Concrete deterioration models account for mechanisms like carbonation and chloride ingress
  • Fatigue damage accumulation models estimate remaining cycles to failure for steel components

Risk Assessment and Failure Modes

• Risk assessment frameworks prioritize maintenance and rehabilitation interventions
  • Incorporate factors such as defect severity, structural redundancy, and traffic volume
  • Probability of failure and consequences of failure considered in risk calculations
  • Help allocate limited resources to bridges with highest risk profiles
• Potential for sudden failure modes carefully evaluated when assessing critical defects
  • Brittle fracture in steel bridges can occur with little warning (2007 I-35W bridge collapse)
  • Shear failure in concrete elements can be catastrophic (1967 Silver Bridge collapse)
  • Scour-induced foundation failure can lead to rapid bridge collapse (1987 Schoharie Creek Bridge)

Cumulative Effects and Environmental Factors

• Load redistribution and stress concentration from localized defects accelerate deterioration
  • Corroded reinforcement transfers load to adjacent bars, increasing their stress
  • Cracked concrete allows faster ingress of deleterious substances, accelerating deterioration
  • Failed joints concentrate impact loads, damaging adjacent deck and superstructure elements
• Cumulative impact of multiple defects considered when predicting bridge performance
  • Interaction between different deterioration mechanisms can accelerate overall degradation
  • Redundancy loss from multiple defective components increases vulnerability to failure
  • Synergistic effects (corrosion-induced cracking leading to faster chloride ingress) assessed
• Environmental factors and loading conditions influence defect progression rate
  • Coastal environments accelerate corrosion due to chloride exposure
  • Freeze-thaw cycles in cold climates exacerbate concrete deterioration
  • Heavy truck traffic increases fatigue damage accumulation in steel bridges