PRESENTATION:STRUCTURAL HEALTH MONITORING SYSTEM(VIBRATING WIRE STRAIN GAUGE)

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Introduction SHM Components Dawn of SHM Techniques of SHM Significance of SHM

CONTENTS:

INTRIDUCTION:

SHM

Process of implementing a damage detection .Process involves the observation of a system using periodically sampled dynamic response measurements from an array of sensors.The extraction of damage-sensitive features from measurements .

The statistical analysis of these features to determine the current state of system health.

Used for rapid condition screening. Provides reliable information regarding the integrity of the structure.

SHM COMPOMENTS

Data Acquisition system StructureDiagonosisData InterpreterData ManagementSHM

Qualitative and non continuous methods were used in the beginning. Railroad wheel-tappers have used the sound of a hammer striking the train wheel to evaluate if damage was present.DAWN OF SHM:

PRINCIPLES OF SHM

DetectionLocalizationClassification

TextAssessmentPrediction

TECHNIQUES OF SHMLocal Strain: Local strain analysis, compare to finite element methods (FEM), vibration strain Average Strain: Macro-strain analysis, compare to FEM, vibration deformationsDisplacement: Joint openings, existing crack openingSettlement: Differential settlement between columns or foundations Tilt: Global or local tilt3D Movement: Differential settlement, roof deflectionVibration: Modal analysis, wind / seismic induced vibrationLoad: Cable / Stay forces, reaction forcesTemperature: Steel / Concrete temperatureRebar Corrosion: Concrete corrosion & humidityEnvironment: Wind, air temperature, precipitationImages: Building images, construction progress

TECHNIQUES OF SHMEstimate that how long the structure can surviveTo incorporate some additional loads on the existing structureEstimate the loads and their effectsEstimate the state of fatigueForecast the probable evolution of the bridgemodifications to an existing structure,monitoring of structures affected by external works,monitoring during demolition,structures subject to long-term movement or degradation of materialsfeedback loop to improve future design based on experience,fatigue assessment,

VIBRATING WIRE STRAIN GAUGEOPERATIONAL PRINCIPLEWORKING PRINCIPLESTEPS OF WORKINGINSTALLATIONTEST RESULTSAPPLICATIONSADVANTAGESDISADVANTAGES

OPERATIONAL PRINCIPALMeasure the strain at a point by monitoring the changes in vibration properties of a tensioned wire attached to the area.A coil is used to bring the wire in movement as well as to measure the frequency of vibration of the wire.Strain in the wire is proportional to frequency of vibration of wire. Loading of the concrete structure changes the distance between the two flanges and results in a change in the tension of the wire.By comparing the new frequency measurement to the wires vibrating frequency at installation, the strain can be calculated. Change in square of frequency of oscillations is directly proportional to the change in strain in the structural element.

OPERATIONAL PRINCIPALBased on the strain-resistance relationship of electrical conductors.Electrical conductor changes its resistance with mechanical stress, e.g. through tension or compression forces.Electrical resistance is proportional to the instantaneous average strain over its surface.relationship between resistance change and strain in the foil or wire used in strain-gage construction can be expressed asDL/L= 1/K * DR/RK=(DR/R)/(DL/L)

STEPS OF WORKING

Conversion converts the mechanical strain into a change in the electrical resistance.Wheat stone bridge / measuring circuit Produces output voltage signal due to change of strain gage's resistance which changes due to a strainAmplifier amplifies the bridge output voltage to a level suitable for indicating instruments.Display converts the amplifier's output signal into a meaning full parameter of observation.

INSTALLATION

Embedded installation:Embedment Strain Gauges in Beams & ColumnsEmbedment Strain Gauges in Wall and SlabsEmbedment Strain Gauges in Bored Cast In-Situ PilesSurface Mounted installation:

TEST RESULTS

Measurement setupa VWSG data logger was used to measure the VWSG frequency readings using the measurement software.Data collected from the digital strain gauge collectors are then evaluated in the form of graphs and from that graphs, we analyse the structure strength , deformation and its sustainability for the future.

APPLICATION

The primary uses for Strain Gauges are the measurement of Load and Bending in steel, concrete and composite structural members, with applications such as, but not limited to:

Piled foundations(concrete and/or steel) Retaining Walls Floor Slabs Columns and Beams Mass concrete dams Formwork Strutting and Temporary Works Bridgeworks

It has applications in the measurement of positive or negative strain in soil, concrete mass or steel structures including:Measurement of strain in mass concreteMeasurement of strain in concrete and rock construction.Determining and monitoring of stress distribution in concrete &masonry dams.Study of stress distribution in the supporting ribs of underground cavities and tunnels.Long term analysis of stress distribution in pressure shaft, enclosing concrete and the rock over burden.Measurement and monitoring of strain and consequently stress in steel structures.

ADVANTAGESReliabilityAccuracySensor outputTransmission of output signalEnvironmental, chemical & corrosion resistance

DISADVANTAGESNon uniformities in strain reading due to dynamic load applicationproblems with the measuring grid and the connectionsFatigue in measuring gridincrease in electrical resistancecracks occur on the grain boundaries