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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?.

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structural health monitoring of steel bridges

Structural Health Monitoring of Steel Bridges

Pradipta BanerjiProfessor of Civil Engineering, IIT Bombay

CE 152 LECTURE

overview
Overview
  • Why Structural Health Monitoring?
  • How Structural Health Monitoring?
  • Investigation for an Example Steel Bridge
  • Outcomes from the Investigation
why shm
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
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
material properties
Material Properties

UTS (MPa) 413

YS (MPa) 235

Elongation (%) 29

Poisson`s Ratio 0.28

E (MPa) 2.09x105

numerical modelling
Numerical Modelling

Fig: 3-D Model of Bridge Span

instrumentation scheme
Instrumentation Scheme

L'7

L'6

L'5

L'4

L'3

L'2

L'1

Gauges on Stringers

L7

L6

L5

L4

L3

L2

L1

Gages on L7U7 L'7U'7

Gauges on Cross Girders

U7

U1

U7

U6

U5

U4

U3

U2

U1

L1

L1

L7

L6

L5

L4

L3

L2

L1

L7

Fixed

Gages on L6L5

Free

Gages on L6U7

Electronic Tilt Sensors

Gauges on both bearings

Gauges on L7L8 L'7L'8

Vibrating Wire Strain Gauge

(Location to be determined after site visit

instrumentation
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
data acquisition analysis

Sensors

(Strain Gages, Accelerometers, Thermocouples)

Raw Data File

Signal Conditioning

Data Processing

Data Acquisition

Data Packaging

Raw Data File

Data Analysis

DATA ACQUISITION AT SITE

DATA ANALYSIS OFFSITE

Data Acquisition & Analysis
centre span deflection
Centre Span Deflection

*Difference due to problems of site measurement and inability to numerically simulate actual joint conditions. Pinned connections – 19.8 mm

strain measurement
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
vibration measurement
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)
slide18

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)

slide19

1st mode (plan)

lateral vibration

2nd mode (plan)

lateral vibration

3rd mode (elevation)

vertical vibration

4th 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).

Natural Vibration Frequencies
fatigue tests

Fatigue Tests

10 samples at 3 stress levels (R = 0)

Stress 100 MPa 200 MPa 300 MPa

Min. >10 million 3.5 million 1.8 million

Avg. >10 million 4.2 million 2.1 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
Remaining Life Assessment
  • Use Miner’s Rule for estimating remaining life
  • Use rainfall counting procedures to estimate stress histograms
  • Maximum dynamic stress (incl. DL)

Chords 150 MPa (5 million cycles)

Bracings 80 MPa (below endurance limit)

  • Estimate of traffic over last 95 years = 900,000
  • Remaining life at current traffic - 45 years
conclusions
Conclusions
  • Objective of SHM has to be clear
  • Comprehensive procedure for condition and remaining life assessment is illustrated
  • Metallurgy, physical and fatigue test show the ductile crack propagation phenomenon
  • Experimentally validated numerical model used to determine current condition and estimate remaining life based on current traffic conditions