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,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,Structural Health Monitoring of,Steel Bridges,Pradipta Banerji,Professor of Civil Engineering,IIT Bombay,CE 152 LECTURE,Overview,Why Structural Health Monitoring?,How Structural Health Monitoring?,Investigation for an Example Steel Bridge,Outcomes from the Investigation,Why SHM?,Health Assessment for Increased Service Loads,Condition Assessment for Aged Structures,Life Extension Beyond Design Life,Experimental Verification of Design Procedure,How SHM?,Measure Sensitive Structural Responses to Loads,Use Mathematical Model of Structure,Optimize Information and Sensor Requirements,Determine Critical Sensor Locations,Determine Sensor and DAQ Requirements,Example Old Railway Bridge,Material Properties,UTS(MPa)413,YS(MPa)235,Elongation(%)29,Poissons Ratio0.28,E(MPa)2.09x10,5,Element,Content(Wt.%),Carbon,0.160,Sulphur,0.020,Phosphorous,0.050,Silicon,0.086,Manganese,0.620,Chromium,0.042,Nickel,0.052,Titanium,0.020,Aluminium,Traces,Copper,0.092,Iron(Remainder),98.858,Numerical Modelling,Fig:3-D Model of Bridge Span,Instrumentation Scheme,L,1,L,7,L,2,L,6,L,3,L,5,L,4,L,1,U,7,U,6,U,5,U,4,U,3,U,2,U,1,U,7,U,1,L,1,L,7,L,2,L,6,L,3,L,5,L,4,L,7,L,1,Electronic Tilt Sensors,Gauges on both bearings,Vibrating Wire Strain Gauge,(Location to be determined after site visit,Gages on L,6,U,7,Gages on L,6,L,5,L,1,L,7,L,2,L,6,L,3,L,5,L,4,Fixed,Gauges on L,7,L,8,L,7,L,8,Gages on L,7,U,7,L,7,U,7,Free,Gauges on Stringers,Gauges on Cross Girders,Instrumentation,Instrumentation mainly includes equipments and accessories for,20-channel strain measurement;,8-channel vibration measurement and;,8-channel LVDT display for deflection measurement,2-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&Analysis,Centre Span Deflection,Average Max.Deflection in mm at the center of the spans under controlled static loading,Outer Girder(Up line),Central Girder,Outer Girder(Dn line),Experimental Values,17.2,19.2,16.8,Numerical Values,17.6*,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 Measurement,Instrumentation,20-channel System 6000,Vishay,USA,Uniaxial strain gages,Korean make,Triple coated strain gage wires etc.,Location of Strain Gages.?,To measure axial strains in critical members,To measure presence of bending strains,Fig:Goods train (uniform strain),Fig:Passenger up train,(higher strain level while engine on span),Fig:Data Processing and Analysis,Axial Strains in Critical Members,Numerical Values,Experimental Values,%age difference,Location of strain gage,-136,-138,-1.5,Post-support(OG),-136,-137,-0.7,Post-support(CG),169,180,-6.1,Diagonal-support(CG),170,175,-2.9,BC-support(OG),170,179,-5.0,BC-support(CG),180,188,-4.2,BC-center(OG),180,184,-2.1,BC-center(CG),182,179,+1.6,BC-center(OG),-131,-105,+25.0,TC-center(OG),Vibration Measurement,Instrumentation,Six-channel Pulse System,B&K,Netherlands,Six DeltaTron Accelerometers,B&K make,Miniature cables,dot connectors etc.,Location of Accelerometers,A1V-At the center of outer girder(,Dn,line)on bottom chord(Dir-Vertical),A2H-At the center of outer girder(,Dn,line)on bottom chord(Dir-Horizontal),A3V-At the center of central girder on bottom chord(Dir-Vertical),A4H-At the center of outer girder(,Dn,line)on top chord(Dir-Horizontal),A5H-Near support of outer girder(,Dn,line)on bottom chord(Dir-Horizontal),Fig:FFT of a typical time history recorded by vertical accelerometer at the center of the span(A1V,A3V),Fig:FFT of a typical time history recorded by horizontal accelerometer near the support of the span(A5H),1,st,mode(plan),lateral vibration,2,nd,mode(plan),lateral vibration,3,rd,mode(elevation),vertical vibration,4,th,mode(plan),torsional vibration,Natural Vibration Frequencies,Observations:,*Structure is weak in lateral direction(as first two mode shapes are in lateral direction),More accelerometers required for mode shape comparison,Movement in lateral direction is predominant when train passes over the bridge with a speed of 10-20 kmph(resonance).,Experimental Values,Numerical Values,*2.7,*5.8,6.7,7.4,*2.5,*6.0,6.2,6.7,Fatigue Tests,10 samples at 3 stress levels(R=0),Stress100 MPa200 MPa300 MPa,Min.10 million3.5 million1.8 million,Avg.10 million4.2 million2.1 million,In log stress terms,very little variation from average values,100,MPa,below the endurance limit for steel,Ductile crack propagation,Remaining Life Assessment,Use Miners Rule for estimating remaining life,Use rainfall counting procedures to estimate stress histograms,Maximum dynamic stress(incl.DL),Chords150 MPa(5 million cycles),Bracings80 MPa (below endurance limit),Estimate of traffic over last 95 years=900,000,Remainin
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