Structural Monitoring
Bridge
DFOS • DISTRIBUTED FIBER OPTIC SENSING
Continuous structural response monitoring
BRIDGE CLASSIFICATION

Select Bridge Architecture

Bridge Anatomy

Girder Bridge

Girder Bridge System

Structural Health Monitoring

A bridge where the primary load-carrying system consists of longitudinal girders supporting the deck.

01

Typical Materials

Reinforced concrete
Prestressed concrete
Steel
Composite steel-concrete
02

Primary Components

Deck slab
Main girders
Cross girders
Bearings
Expansion joints
Piers
Abutments
Foundation
Failure Mechanisms

What Can Go Wrong?

Typical deterioration and failure mechanisms that should be considered while designing an SHM system.

!
Flexural fatigue
!
Shear cracking
!
Girder corrosion
!
Bearing deterioration
!
Deck cracking
!
Excessive deflection
!
Differential settlement
Distributed Fibre Optic Sensing

DFOS Monitoring Strategy

A distributed sensing architecture can provide continuous spatial information instead of relying only on measurements at predefined discrete points.

Recommended

Distributed Fibre Optic Monitoring

Continuous Spatial Sensing

DFOS cables can be routed along critical structural members and across crack-prone or high-gradient regions to capture distributed changes in strain and deformation.

01

Recommended Fibre Layouts

1

Longitudinal fiber along girder flanges

2

Transverse fiber across deck

3

Fiber around critical connections

4

Zig-zag routing across crack-prone regions

02

Primary Measurements

1

Distributed strain

2

Temperature

3

Crack localization

4

Deformation profile

03

Conventional Sensors Supplemented

1

Strain gauges

2

Temperature sensors

3

Selected displacement sensors

Structural Risk

Critical Monitoring Zones

Locations where structural behaviour, stress concentration or deterioration requires increased attention.

01

Mid-span

02

Near-support regions

03

Girder web and flange connections

04

Bearing zones

05

Expansion joints

06

Diaphragm connections

07

Pier caps

STRUCTURAL RESPONSE

What Should Be Monitored?

Strain

με

Indicates

+Load redistribution
+Flexural response
+Stress concentration
+Fatigue accumulation
+Crack development
+Abnormal structural response

Temperature

°C

Indicates

+Thermal expansion
+Thermal gradients
+Temperature compensation
+Environmental loading

Vibration / Dynamic Response

Hz / m/s²

Indicates

+Dynamic loading
+Traffic-induced vibration
+Wind response
+Structural frequency changes
+Damage-related dynamic behavior

Displacement / Deflection

mm

Indicates

+Global deformation
+Differential movement
+Bearing movement
+Excessive sag
+Settlement

Tilt / Rotation

degrees / mrad

Indicates

+Pier rotation
+Foundation movement
+Tower inclination
+Bearing behavior

Crack Development

mm

Indicates

Cable Force

kN

Indicates

Foundation / Pier Settlement

mm

Indicates

Corrosion / Section Loss

engineering-specific

Indicates

STRUCTURAL HEALTH MONITORING

Monitoring Parameters

Bridges are monitored through a combination of mechanical, environmental and dynamic parameters. Conventional monitoring typically relies on discrete sensors installed at selected locations, while Distributed Fiber Optic Sensing can extend measurement across the structure.

9
Parameters
7
Critical
2
High Importance
3
DFOS Suitable
4
Indirect DFOS
Monitoring Parametercritical

Strain

Unit: με
DFOS Suitable
Sensing ArchitectureDISTRIBUTED
Conventional sensor
DFOS fiber
◉What it Indicates
  • Load redistribution
  • Flexural response
  • Stress concentration
  • Fatigue accumulation
  • Crack development
  • Abnormal structural response
◇Conventional Sensors
01
Electrical resistance strain gauge
02
Vibrating wire strain gauge
03
Point fiber Bragg grating sensor
△Conventional Limitations
  • —Point measurement
  • —Limited spatial coverage
  • —Large sensor count for distributed monitoring
  • —Wiring complexity
DFOS

Distributed
Sensing

Applicability
Suitable
Sensing Modes
BrillouinRayleighOFDR
DFOS Advantage

Provides a continuous strain profile along the sensing fiber rather than a single point measurement.

Monitoring Parametercritical

Temperature

Unit: °C
DFOS Suitable
Sensing ArchitectureDISTRIBUTED
Conventional sensor
DFOS fiber
◉What it Indicates
  • Thermal expansion
  • Thermal gradients
  • Temperature compensation
  • Environmental loading
◇Conventional Sensors
01
PT100
02
Thermocouple
03
Thermistor
△Conventional Limitations

No specific limitations provided.

DFOS

Distributed
Sensing

Applicability
Suitable
Sensing Modes
RamanBrillouin
DFOS Advantage

Temperature can be measured continuously along the fiber and can also support compensation of strain measurements.

Monitoring Parametercritical

Vibration / Dynamic Response

Unit: Hz / m/s²
Technology Dependent
Sensing ArchitecturePOINT / HYBRID
Conventional sensor
DFOS fiber
◉What it Indicates
  • Dynamic loading
  • Traffic-induced vibration
  • Wind response
  • Structural frequency changes
  • Damage-related dynamic behavior
◇Conventional Sensors
01
MEMS accelerometer
02
Piezoelectric accelerometer
03
Geophone
△Conventional Limitations
  • —Point measurement
  • —Requires distributed instrumentation for spatial mode-shape mapping
DFOS

Distributed
Sensing

Applicability
Technology Dependent
Sensing Modes
Phase-sensitive OTDRRayleigh-based dynamic sensing
Technical Note

Dynamic DFOS capabilities depend strongly on interrogator architecture, sensing range, spatial resolution and required frequency bandwidth.

Monitoring Parametercritical

Displacement / Deflection

Unit: mm
Indirect Application
Sensing ArchitecturePOINT / HYBRID
Conventional sensor
DFOS fiber
◉What it Indicates
  • Global deformation
  • Differential movement
  • Bearing movement
  • Excessive sag
  • Settlement
◇Conventional Sensors
01
LVDT
02
Laser displacement sensor
03
GNSS
04
Total station
05
String potentiometer
△Conventional Limitations

No specific limitations provided.

DFOS

Distributed
Sensing

Applicability
Indirect
DFOS Approach

DFOS can derive deformation or displacement profiles from distributed strain measurements when the installation geometry and boundary conditions support the required reconstruction.

Monitoring Parameterhigh

Tilt / Rotation

Unit: degrees / mrad
Indirect Application
Sensing ArchitecturePOINT / HYBRID
Conventional sensor
DFOS fiber
◉What it Indicates
  • Pier rotation
  • Foundation movement
  • Tower inclination
  • Bearing behavior
◇Conventional Sensors
01
Tiltmeter
02
Inclinometer
△Conventional Limitations

No specific limitations provided.

DFOS

Distributed
Sensing

Applicability
Indirect
DFOS Approach

Distributed strain measurements can contribute to deformation reconstruction, but dedicated tilt sensors may remain preferable where direct angular measurement is required.

Monitoring Parametercritical

Crack Development

Unit: mm
DFOS Suitable
Sensing ArchitectureDISTRIBUTED
Conventional sensor
DFOS fiber
◉What it Indicates
    ◇Conventional Sensors
    01
    Crack gauge
    02
    Linear variable displacement transducer
    03
    Digital image correlation
    04
    Visual inspection
    △Conventional Limitations

    No specific limitations provided.

    DFOS

    Distributed
    Sensing

    Applicability
    Suitable
    DFOS Approach

    A properly installed distributed fiber can identify localized strain concentrations and changes associated with crack initiation or propagation.

    Monitoring Parametercritical

    Cable Force

    Unit: kN
    Supplementary
    Sensing ArchitecturePOINT / HYBRID
    Conventional sensor
    DFOS fiber
    ◉What it Indicates
      ◇Conventional Sensors
      01
      Load cell
      02
      Vibration-based cable force estimation
      03
      Magnetic induction sensor
      △Conventional Limitations

      No specific limitations provided.

      DFOS

      Distributed
      Sensing

      Applicability
      Supplementary
      DFOS Approach

      DFOS can monitor strain and vibration characteristics of cable systems, but direct force estimation requires appropriate calibration and structural mechanics.

      Monitoring Parametercritical

      Foundation / Pier Settlement

      Unit: mm
      Indirect Application
      Sensing ArchitecturePOINT / HYBRID
      Conventional sensor
      DFOS fiber
      ◉What it Indicates
        ◇Conventional Sensors
        01
        Precise leveling
        02
        Hydrostatic leveling system
        03
        GNSS
        04
        LVDT
        05
        Total station
        △Conventional Limitations

        No specific limitations provided.

        DFOS

        Distributed
        Sensing

        Applicability
        Indirect
        DFOS Approach

        Distributed strain sensing can identify structural response associated with support movement, but absolute settlement should generally be verified using suitable displacement/geodetic instrumentation.

        Monitoring Parameterhigh

        Corrosion / Section Loss

        Unit: engineering-specific
        Indirect Application
        Sensing ArchitecturePOINT / HYBRID
        Conventional sensor
        DFOS fiber
        ◉What it Indicates
          ◇Conventional Sensors
          01
          Half-cell potential
          02
          Corrosion rate sensors
          03
          Electrical resistance probes
          04
          Visual inspection
          △Conventional Limitations

          No specific limitations provided.

          DFOS

          Distributed
          Sensing

          Applicability
          Indirect
          DFOS Approach

          DFOS can identify strain and deformation consequences of deterioration but is not inherently a direct corrosion sensor.

          SENSOR TRANSFORMATION

          From Point Sensors to Distributed Intelligence

          Strain

          Conventional
          Electrical strain gaugeVibrating wire strain gaugeFBG
          DFOS
          Distributed strain fiberBrillouin sensingRayleigh / OFDR
          POTENTIAL
          High

          Temperature

          Conventional
          PT100Thermocouple
          DFOS
          Distributed temperature sensing
          POTENTIAL
          High

          Vibration

          Conventional
          Accelerometer
          DFOS
          Dynamic distributed fiber sensing
          POTENTIAL
          Medium

          Deflection

          Conventional
          LVDTLaser displacement sensorGNSS
          DFOS
          Strain-based deformation reconstruction
          POTENTIAL
          Low / Medium

          Tilt

          Conventional
          TiltmeterInclinometer
          DFOS
          Strain-based deformation reconstruction
          POTENTIAL
          Low

          Crack

          Conventional
          Crack gaugeLVDTVisual inspection
          DFOS
          Distributed strain concentration monitoring
          POTENTIAL
          Medium / High

          Cable Force

          Conventional
          Load cellVibration-based force estimation
          DFOS
          Distributed strainDistributed dynamic sensing
          POTENTIAL
          Medium

          Settlement

          Conventional
          GNSSPrecise levelingLVDT
          DFOS
          Structural strain response
          POTENTIAL
          Low
          FIBER DEPLOYMENT

          DFOS Deployment Methods

          Different fiber routing configurations can be used to monitor structural behavior across different directions, surfaces and structural elements.

          01
          Deployment Method

          Longitudinal Layout

          Fiber follows the primary load path of the structural member.

          FIBER ROUTING
          ✓Best For
          Girder strainDeck strainArch strainTower strain
          02
          Deployment Method

          Transverse Layout

          Fiber crosses the structural member perpendicular to the primary axis.

          FIBER ROUTING
          ✓Best For
          Transverse strainCross-sectional responseDeck behavior
          03
          Deployment Method

          Zig-Zag Layout

          Fiber is routed repeatedly across an area to increase spatial coverage and sensitivity to localized deformation.

          FIBER ROUTING
          ✓Best For
          Crack-prone areasConnectionsConcrete surfacesLocalized damage
          04
          Deployment Method

          Grid Layout

          Two-dimensional fiber network providing distributed coverage in longitudinal and transverse directions.

          FIBER ROUTING
          ✓Best For
          Deck slabsLarge concrete surfacesDamage localization
          05
          Deployment Method

          Circumferential Layout

          Fiber follows the perimeter of a structural element.

          FIBER ROUTING
          ✓Best For
          PiersColumnsTowersPipelines
          06
          Deployment Method

          Helical Layout

          Fiber follows a helical path around a structural member.

          FIBER ROUTING
          ✓Best For
          CablesPipesColumnsSpecialized deformation measurements
          STRUCTURAL ANALYTICS

          From Fiber Data to Structural Insight

          Distributed sensing data can be processed through a sequence of analytical stages, transforming raw structural measurements into localized anomalies, trends and performance information.

          STEP
          01

          Baseline establishment

          STEP
          02

          Temperature compensation

          STEP
          03

          Strain anomaly detection

          STEP
          04

          Spatial anomaly localization

          STEP
          05

          Trend analysis

          STEP
          06

          Fatigue cycle analysis

          STEP
          07

          Modal response analysis

          STEP
          08

          Threshold monitoring

          STEP
          09

          Event correlation

          STEP
          10

          Damage localization

          STEP
          11

          Remaining performance assessment