Structural Health Monitoring

plantcitybusinessUrban and Civil

Nov 26, 2013 (3 years and 4 months ago)


Use of Fiber Optic Sensors in
Structural Health Monitoring

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Structural Health Monitoring (SHM)

Monitoring qualities of structures to assess overall structure health

Common qualities inspected:


Deflection (bridges)

Vibrations/movement of a structure

Corrosion of metal elements

Classical methods of monitoring:

Visual inspection

Outdated technology

Engineers/civil workers

The Problem

‘Classical’ technology is becoming outdated

Visual inspection can be inaccurate

Only surface abnormalities can be found

Accuracy depends on human element

can vary greatly

Issues not found can lead to catastrophic failure of structures

Time and money spent to rebuild structures

Hinder efficiency of transportation/business

More prevalent in second/third
world countries

Fiber Optic Technology

First demonstrated during 1840s

Broad applications




Immune to electrical & magnetic interference

Typically manufactured using silica

Fluorides and crystalline materials also used

Different elements can change heat

Applying Fiber Optic Sensors to SHM

Crack detection within bridges/structures

Monitoring bridge deflection

Vibration sensing

Monitoring steel rebar corrosion

Crack Discovery in Structures

Concrete can not flex, so

can form

Caused by temperature changes, traffic, among others

Surface or internal

Current SHM methods are not
efficient or reliable

Visual inspection by workers

Inspection quality varies on the inspector

Very time

Visual inspections detect surface cracking only

Leaves internal cracks to increase in size

May lead to serious structural issues

Crack Discovery in Structures

Fiber optic sensing technology: SMARTape

Thin (.20mm) strip of thermoplastic tape

Embedded fiber optic cable

Stretches (strains) when a crack is present

Straining alters optic beam send through fiber

Used with the DITEST system

Signal pumped through length of cable

Output monitored to determine location of


mounted (concrete or steel)

Embedded within concrete during construction

Crack Discovery in Structures

Integration within structure allows for early detection of cracks

Allows for repair before problem becomes too serious

Solves problems of visual inspection

Able to be applied to existing structures

surface only

Can help increase the lifespan of a structure

Removes human element

More accurate & efficient

Readings can be given in as little as 5 minutes

Monitoring Bridge Deflection


Relative vertical displacement by a span

Determines load capacity and overall well
being of the structure

Current methods of measuring deflection

Direct connection of bridge span and ground

Surveying crews measure spans over time

GPS to measure coordinates (Z+ and Z

for displacement)

Monitoring Bridge Deflection

Fiber optic sensing technology: Liquid
leveling transducers

containing vessels (usually water)

Connected via pipe system

liquid flows freely between vessels

Archimedes’ principle of buoyancy applied

Force = Displacement

Uses fiber optic load sensors to measure height of float

Vessels mounted along bridge spans

Can be installed on existing structures

System output examined by inspectors

Can be accessed at any time, in real
time via fiber optic network

Deflections compared to reference measurement

located on ground

Monitoring Bridge Deflection

Transducers are self

No outside anchoring (direct connection)

Minimal human interaction (surveying)

No reliance on satellites (GPS)

Simple design

Utilizes centuries
old principle of buoyancy

Easy integration into existing structures and new constructions

Sensing Vibrations Within Structures

Accelerometers made using network of fiber optic cables

A mass
spring system is used to allow a reading of acceleration

The mass
spring system is fitted with a discontinuous fiber optic cable system

The ends of the fiber optic cable have lines of transparent and opaque material (grating A and B) that are
used to transmit or block light transfer between the cables

The net intensity of light is measured and is used to calculate

the acceleration of the building

The correlation between acceleration and vibration

The acceleration determines the rate at which

the speed of an object changes

In this context, the speed is used to determine

the oscillation of the building

Sensing Vibrations Within Structures

Structural effects from vibrations

Blatantly speaking, building vibrations are to be mitigated

Every structure has a ‘normal frequency’ at which it vibrates most sporadically

Sensors that are used to measure this oscillation can be used to determine if a structure is close to
naturally vibrating near its normal frequency, that is very detrimental to its integrity.

in Structures

Corrosion, in particular steel, is one of the leading causes to structural disasters

Corrosion greatly lowers the strength and endurance of structures. Therefore, it is sought to be
eliminated by any means possible

This also raises the cost of maintaining structures immensely, if not detected early

Monitoring Steel Corrosion

Monitoring Structures’ Corrosion

Structures will be outfitted with sensors that include a series of fiber optic cables through which light is

The change in intensity of light is used to interpret the impurities that are in the cable itself

This raw data is used to calculate the amount of corrosion INSIDE the structure, not just the exterior

coated film

Most light is reflected

Small fraction of light

s reflected

Light escapes core

of fiber

Monitoring Steel Corrosion

How to use this system

The fiber optic cables are implanted with small amounts of iron and other various materials

The iron is in an environment identical to the interior of the structure (
what is being monitored)

The iron inevitably reacts with surrounding oxygen, forming iron oxide

what we consider to be

This level of iron oxide is measured from the corresponding change in light intensity from the raw data

Benefits from contemporary and Existing Systems

Compared to competing sensor technology, this system can be measured to be on the order of
centimeters, thus severely diminishing the cost of implanting into structures, as well as maintaining the
integrity of the structures to a higher degree thanks to a smaller size factor

Availability of fiber optic technology due to its use in telecommunications and electronics.

Earlier detection of corrosion, saving an uncertainly vast amount of money for a myriad of projects

Ethical Impacts

Benefits over contemporary systems

As previously stated, fiber optic technology is implemented in other forms of technologies,
telecommunications, electronics, and illumination

Concrete success is implied by widespread use of fiber optics.

The use of these cables are not affected by electromagnetic and magnetic fields due to the complete
absence of an electric current in fiber optic cables

Less interference is proceeded by more accurate results

The new technology can accurately detect structural defects more quickly by its easy retrofitting into
older buildings

This vastly reduces the labor needed to maintain structures if a problem is detected sooner and when it
is not as augmented

Sustainability Factors


iber optic sensors in SHM aids in detecting problems before they become serious

The sooner a problem is found, the sooner it can be repaired

Minor repairs cost less than replacing an entire structure

Sensors and associated technology are inexpensive


Immune to electrical and magnetic interference

Major bridge repairs/failures are detrimental to traffic flow

Durable sensors can outlive their host structures