SHM of Steel Bridges
-
Upload
muhammed-nouman-mohsin-ramzi -
Category
Documents
-
view
13 -
download
0
description
Transcript of SHM of Steel Bridges
Structural Health Structural Health Monitoring ofMonitoring of Steel Steel
BridgesBridgesPradipta BanerjiPradipta BanerjiProfessor of Civil Professor of Civil
Engineering, IIT BombayEngineering, IIT Bombay
CE 152 LECTURECE 152 LECTURE
OverviewOverview
Why Structural Health Monitoring?Why Structural Health Monitoring?
How Structural Health Monitoring?How Structural Health Monitoring?
Investigation for an Example Steel Investigation for an Example Steel
BridgeBridge
Outcomes from the InvestigationOutcomes from the Investigation
Why SHM?Why SHM?
Health Assessment for Increased Service Health Assessment for Increased Service
LoadsLoads
Condition Assessment for Aged StructuresCondition Assessment for Aged Structures
Life Extension Beyond Design LifeLife Extension Beyond Design Life
Experimental Verification of Design Experimental Verification of Design
ProcedureProcedure
How SHM?How SHM?
Measure Sensitive Structural Responses to Measure Sensitive Structural Responses to
LoadsLoads
Use Mathematical Model of StructureUse Mathematical Model of Structure
Optimize Information and Sensor Optimize Information and Sensor
RequirementsRequirements
Determine Critical Sensor LocationsDetermine Critical Sensor Locations
Determine Sensor and DAQ RequirementsDetermine Sensor and DAQ Requirements
Material PropertiesMaterial Properties
UTS (MPa)UTS (MPa) 413413
YS (MPa)YS (MPa) 235235
Elongation (%)Elongation (%) 2929
Poisson`s RatioPoisson`s Ratio 0.280.28
E (MPa)E (MPa)2.09x102.09x1055
ElementElement Content (Wt. Content (Wt. %)%)
CarbonCarbon 0.1600.160
SulphurSulphur 0.0200.020
PhosphorousPhosphorous 0.0500.050
SiliconSilicon 0.0860.086
ManganeseManganese 0.6200.620
ChromiumChromium 0.0420.042
NickelNickel 0.0520.052
TitaniumTitanium 0.0200.020
AluminiumAluminium TracesTraces
CopperCopper 0.0920.092
Iron Iron (Remainder)(Remainder)
98.85898.858
Instrumentation SchemeInstrumentation SchemeL'1L'7 L'2L'6 L'3L'5 L'4
L1
U7 U6 U5 U4 U3 U2 U1
U7U1
L1L7 L2L6 L3L5 L4 L7L1
Electronic Tilt Sensors Gauges on
both bearings
Vibrating Wire Strain Gauge(Location to be determined after site visit
Gages on L6U7
Gages on L6L5
L1L7L2L6 L3L5 L4
Fixed
Gauges on L7L8
L'7L'8
Gages on L7U7
L'7U'7
Free
Gauges on Stringers
Gauges on Cross Girders
InstrumentationInstrumentation
Instrumentation mainly Instrumentation mainly includes equipments includes equipments and accessories for and accessories for 20-channel strain 20-channel strain
measurement;measurement; 8-channel vibration 8-channel vibration
measurement and; measurement and; 8-channel LVDT display 8-channel LVDT display
for deflection for deflection measurementmeasurement
2-channel thermocouple2-channel thermocouple
Sensors(Strain Gages, Accelerometers, Thermocouples)
Signal Conditioning
Data Acquisition
Raw Data File
Data Processing
Data Packaging
Data Analysis
Raw Data File
DATA ACQUISITION AT SITE
DATA ANALYSIS OFFSITE
Data Acquisition & Data Acquisition & AnalysisAnalysis
Centre Span DeflectionCentre Span Deflection
Average Max. Deflection in mm at the Average Max. Deflection in mm at the center of the spans under controlled static center of the spans under controlled static
loadingloadingOuter Outer Girder (Up Girder (Up line)line)
Central Central GirderGirder
Outer Outer Girder (Dn Girder (Dn line)line)
ExperimentExperimental Valuesal Values
17.217.2 19.219.2 16.816.8
Numerical Numerical ValuesValues
17.6*17.6* 17.617.6** 17.6*17.6*
*Difference due to problems of site measurement and inability to numerically simulate actual joint conditions. Pinned connections – 19.8 mm
Strain MeasurementStrain Measurement InstrumentationInstrumentation
20-channel System 6000, Vishay, USA20-channel System 6000, Vishay, USA Uniaxial strain gages, Korean makeUniaxial strain gages, Korean make Triple coated strain gage wires etc.Triple coated strain gage wires etc.
Location of Strain Gages..?Location of Strain Gages..? To measure axial strains in critical membersTo measure axial strains in critical members To measure presence of bending strainsTo measure presence of bending strains
Axial Strains in Critical Axial Strains in Critical MembersMembers
NumericNumerical Valuesal Values
ExperimenExperimental Valuestal Values
%age %age differendifferen
cece
Location of strain Location of strain gagegage
-136-136 -138-138 -1.5-1.5 Post-support (OG)Post-support (OG)
-136-136 -137-137 -0.7-0.7 Post-support (CG)Post-support (CG)
169169 180180 -6.1-6.1 Diagonal-support Diagonal-support (CG)(CG)
170170 175175 -2.9-2.9 BC-support (OG)BC-support (OG)
170170 179179 -5.0-5.0 BC-support( CG)BC-support( CG)
180180 188188 -4.2-4.2 BC-center (OG)BC-center (OG)
180180 184184 -2.1-2.1 BC-center (CG)BC-center (CG)
182182 179179 +1.6+1.6 BC-center (OG)BC-center (OG)
-131-131 -105-105 +25.0+25.0 TC-center (OG)TC-center (OG)
Vibration MeasurementVibration Measurement InstrumentationInstrumentation
Six-channel Pulse System, B & K, NetherlandsSix-channel Pulse System, B & K, Netherlands Six DeltaTron Accelerometers, B & K makeSix DeltaTron Accelerometers, B & K make Miniature cables, dot connectors etc.Miniature cables, dot connectors etc.
Location of AccelerometersLocation of Accelerometers A1V-At the center of outer girder (Dn line) on bottom chord A1V-At the center of outer girder (Dn line) on bottom chord
(Dir-Vertical)(Dir-Vertical) A2H- At the center of outer girder (Dn line) on bottom chord A2H- At the center of outer girder (Dn line) on bottom chord
(Dir-Horizontal)(Dir-Horizontal) A3V- At the center of central girder on bottom chord (Dir-A3V- At the center of central girder on bottom chord (Dir-
Vertical)Vertical) A4H-At the center of outer girder (Dn line) on top chord (Dir-A4H-At the center of outer girder (Dn line) on top chord (Dir-
Horizontal)Horizontal) A5H-Near support of outer girder (Dn line) on bottom chord A5H-Near support of outer girder (Dn line) on bottom chord
(Dir-Horizontal)(Dir-Horizontal)
Autospectrum(Signal 1) - InputWorking : Input : Input : FFT Analyzer
0 4 8 12 16 20 24 28 32
0
0.2
0.4
0.6
[Hz]
[m/s²]OVERLOAD
Autospectrum(Signal 1) - InputWorking : Input : Input : FFT Analyzer
0 4 8 12 16 20 24 28 32
0
0.2
0.4
0.6
[Hz]
[m/s²]Fig: FFT of a typical time history recorded by vertical accelerometer at the center of the span (A1V, A3V)
Autospectrum(Signal 5) - InputWorking : Input : Input : FFT Analyzer
4 8 12 16 20 24 28 32
0
0.2
0.4
0.6
0.8
[Hz]
[m/s²]OVERLOAD
Autospectrum(Signal 5) - InputWorking : Input : Input : FFT Analyzer
4 8 12 16 20 24 28 32
0
0.2
0.4
0.6
0.8
[Hz]
[m/s²]Fig: FFT of a typical time history recorded by horizontal accelerometer near the support of the span (A5H)
1st mode (plan)
lateral vibration2nd mode (plan)lateral vibration
3rd mode (elevation)vertical vibration
4th mode (plan)torsional vibration
Natural Vibration FrequenciesNatural Vibration Frequencies
Observations:Observations: *Structure is weak in lateral *Structure is weak in lateral
direction (as first two mode direction (as first two mode shapes are in lateral direction)shapes are in lateral direction)
More accelerometers required More accelerometers required for mode shape comparisonfor mode shape comparison
Movement in lateral direction Movement in lateral direction is predominant when train is predominant when train passes over the bridge with a passes over the bridge with a speed of 10-20 kmph speed of 10-20 kmph (resonance). (resonance).
ExperimenExperimental Valuestal Values
Numerical Numerical Values Values
*2.7*2.7
*5.8*5.8
6.76.7
7.47.4
*2.5*2.5
*6.0*6.0
6.26.2
6.76.7
Fatigue TestsFatigue Tests
10 samples at 3 stress levels (R = 0)10 samples at 3 stress levels (R = 0)
StressStress 100 MPa100 MPa 200 MPa200 MPa 300 300
MPaMPa
Min.Min. >10 million>10 million3.5 million3.5 million 1.8 million1.8 million
Avg.Avg. >10 million>10 million4.2 million4.2 million 2.1 million2.1 million
In log stress terms, very little variation In log stress terms, very little variation
from average valuesfrom average values
100 MPa below the endurance limit for 100 MPa below the endurance limit for
steelsteel
Ductile crack propagationDuctile crack propagation
Remaining Life Remaining Life AssessmentAssessment
Use Miner’s Rule for estimating remaining lifeUse Miner’s Rule for estimating remaining life
Use rainfall counting procedures to estimate Use rainfall counting procedures to estimate
stress histogramsstress histograms
Maximum dynamic stress (incl. DL)Maximum dynamic stress (incl. DL)
ChordsChords 150 MPa150 MPa (5 million cycles)(5 million cycles)
BracingsBracings 80 MPa (below endurance limit)80 MPa (below endurance limit)
Estimate of traffic over last 95 years = 900,000Estimate of traffic over last 95 years = 900,000
Remaining life at current traffic - 45 yearsRemaining life at current traffic - 45 years
ConclusionsConclusions Objective of SHM has to be clearObjective of SHM has to be clear Comprehensive procedure for condition Comprehensive procedure for condition
and remaining life assessment is and remaining life assessment is illustratedillustrated
Metallurgy, physical and fatigue test Metallurgy, physical and fatigue test show the ductile crack propagation show the ductile crack propagation phenomenonphenomenon
Experimentally validated numerical Experimentally validated numerical model used to determine current model used to determine current condition and estimate remaining life condition and estimate remaining life based on current traffic conditionsbased on current traffic conditions