Short answer
Fiber optic structural health monitoring (SHM) uses Fiber Bragg Grating (FBG) sensors and Distributed Acoustic Sensing (DAS) installed on buildings, bridges, tunnels and dams to continuously measure strain, temperature, tilt and vibration. One fiber carries many measurement points, needs no power at the sensor and is immune to electromagnetic interference. DuyuSense develops FBG and DAS sensing systems for this purpose.
What is structural health monitoring (SHM)?
Structural health monitoring is the continuous measurement of a structure's behaviour with sensors to detect damage, fatigue and unexpected deformation early. It replaces or supplements periodic visual inspection with measurable, time-stamped data.
The core outputs of an SHM system are strain, temperature, tilt, crack opening, settlement and dynamic response (natural frequencies and amplitudes). Together they show how the structure performs against its design assumptions, so maintenance decisions rest on measurement rather than observation alone.
Which structures use fiber optic monitoring?
Fiber optic monitoring is used on high-rise buildings, bridges and viaducts, tunnels, dams, stadiums and historic structures. What they share is a long service life, high consequence of failure and limited access for visual inspection.
- Buildings: column and shear wall strain, inter-storey drift, foundation settlement
- Bridges and viaducts: deck strain, bearing movement, traffic and wind-induced vibration
- Tunnels: lining deformation, convergence and crack monitoring
- Dams: body temperature, joint opening, long-term deformation
- Stadiums and long-span roofs: dynamic response under crowd loading
- Historic structures: crack and tilt tracking with minimal intervention
What do FBG sensors measure on a structure?
Fiber Bragg Grating (FBG) sensors measure strain, temperature, tilt and crack opening at discrete points. Each FBG reflects a specific wavelength that shifts with strain and temperature: near 1550 nm, typically about 1.2 pm per microstrain and about 10 pm per °C.
Strain resolution is typically in the 1 microstrain class. Temperature effects are separated using a strain-free reference FBG. Combining the same principle with a mechanical fixture yields tiltmeters, crack meters and displacement sensors, all read by the same interrogator.
What does DAS and distributed sensing add to structural monitoring?
Distributed Acoustic Sensing (DAS) turns the entire fiber into thousands of virtual vibration sensors, measuring a structure's dynamic response continuously along its length. Spatial resolution is typically a few metres, which makes it practical to monitor the response of bridges, tunnels and other long structures to traffic, wind and seismic excitation with a single cable.
For quantities other than vibration, distributed strain and temperature techniques such as Brillouin-based sensing also exist. In practice the strongest design is usually hybrid: high-precision FBGs at critical points and DAS for global coverage.
How does fiber optics support rapid post-earthquake damage assessment?
Fiber optic monitoring delivers inter-storey drift, residual strain and changes in dynamic properties within minutes of an earthquake, giving engineers data on a building's condition before a field team enters. This supports triage when many buildings must be assessed at once.
In Turkey, with its high seismic risk, this capability is especially relevant. The Turkish Building Earthquake Code (TBDY 2018) treats inter-storey drift as one of its key performance criteria, and continuous monitoring makes the actual value of that quantity visible in the real structure. A permanent drop in natural frequencies is also a strong indicator of stiffness loss.
- Inter-storey drift: derived from tilt and strain data
- Residual strain: comparison of readings before and after the event
- Modal analysis: stiffness loss estimated from shifts in natural frequency and damping
Should sensors be embedded in concrete or surface mounted?
In new construction, embedding sensors in concrete is preferred because it measures internal strain, creep and shrinkage directly. On existing structures, bonded or anchored surface mounting allows installation with minimal intervention.
Embedded sensors need mechanical protection during casting and cannot be replaced later, so sensor selection and cable routing must be planned up front. Surface mounting is more flexible for maintenance and expansion but needs more careful compensation for temperature and external effects. For slow processes such as settlement and creep, stable measurement over many years is essential with either method.
How does monitoring data turn into maintenance decisions?
Data becomes condition-based maintenance decisions by comparing it against alarm thresholds, long-term trends and a digital twin. Threshold exceedances trigger immediate alerts, while long-term trends reveal fatigue and deterioration before failure.
DuyuSense works on SHM projects from concept to field-tested prototype through custom sensor design, prototyping, system integration and consultancy. Its patented FBG interrogation system targets real-time, high-speed readout, and its patented DAS signal-processing approach targets noise reduction and more accurate event detection.
- Multi-level alarm thresholds (warning, alarm, emergency)
- Comparison of measurements with a finite element model or digital twin
- Condition-based rather than calendar-based maintenance planning
| Feature | Fiber optic (FBG / DAS) | Electrical strain gauge / vibrating wire |
|---|---|---|
| Electromagnetic interference | Immune; suited to railway, power line and lightning-prone sites | Exposed to electrical noise and lightning-induced surges |
| Multiplexing | Many FBGs on a single fiber; DAS measures along the whole length | Usually a separate cable or channel per sensor |
| Power at the sensor | None required; fully passive | Requires excitation current or voltage |
| Long-term stability | Wavelength-encoded, independent of signal amplitude | Vibrating wire is stable long term; electrical gauges can drift |
| Cable distance | Remote readout over kilometres of cable | Signal loss and noise grow with long cables |
| Dynamic measurement | High sampling rate with FBG, distributed vibration with DAS | Vibrating wire suits static and slow measurements |
Frequently asked questions
Why use fiber optic sensors instead of electrical sensors for structural health monitoring?
Fiber optic sensors are immune to electromagnetic interference, need no power at the sensor and can carry many measurement points on a single fiber. Wavelength-encoded measurement gives good long-term stability. These properties reduce cabling and maintenance effort, especially on large, long-lived or electrically noisy structures.
Can fiber optic monitoring tell whether a building is safe after an earthquake?
Fiber optic monitoring provides damage-related indicators such as inter-storey drift, residual strain and natural frequency shifts within minutes. This helps engineers prioritise buildings and speed up damage assessment. The final safety decision is still made by qualified engineers who evaluate the measured data.
How long does an FBG sensor last?
Properly packaged and installed FBG sensors are designed to measure for many years, thanks to the chemical stability of glass fiber and their passive operating principle. Actual lifetime depends on the packaging material, adhesive, installation quality and environmental conditions, so sensor selection should be specific to each project.
Can a fiber optic monitoring system be retrofitted to an existing building?
Yes. On existing structures, FBG sensors are bonded or anchored to columns, beams, shear walls and joints. Tiltmeters and crack meters can be added to the same fiber line. Installation requires minimal intervention, which also makes the method suitable for historic buildings.
What is the difference between DAS and FBG, and which should I choose for structural monitoring?
FBG measures strain, temperature and tilt with high precision at specific points. DAS measures vibration continuously along the whole fiber, with spatial resolution typically of a few metres. Structural projects usually combine them: FBG on critical members and DAS for the global dynamic response of long structures such as bridges or tunnels.
Can fiber optic sensors be embedded in concrete?
Yes. With suitable protective packaging, FBG sensors and sensing cables can be fixed to the reinforcement and embedded before casting. This measures internal strain, hydration temperature and long-term creep and shrinkage directly. Because embedded sensors cannot be replaced later, redundant cable routing is recommended.
What does DuyuSense offer for structural health monitoring projects?
DuyuSense develops FBG and DAS sensing systems and offers custom sensor design, prototyping, system integration, consultancy and training support. The company is open to B2B collaboration, pilots and project partnerships. You can reach the team at contact@duyusense.com or +90 212 285 6987.