http://fiatech.org/images/stories/techprojects/SC_wireless_microstrain

Wireless Sensor Solutions for Civil Engineering MicroStrain Inc Mike Robinson FIATECH Smart Chips Workshop January 20, 2005

1

Civil Engineering Applications   



Construction monitoring Structural health monitoring Long-term monitoring Periodic load testing

2

Construction Monitoring Determine stability of structure during construction:  Short-term ~ 2 to 5 years  Static analysis: Low sample rates ~ min/hrs  Moderate number of sensors

3

Structural Health Monitoring Determine long-term stability and provide feedback to maximize/extend working life of structure:  Long-term ~ 20 to 50 years  Static/dynamic analysis: Low sample rates ~ min/hrs, switching to higher rates when event occurs ~50 to 200Hz  Large number of sensors

4

Periodic Load Testing Determine condition of structure at given intervals:  Short-term ~ hours to days  Dynamic: High sample rates ~ 50 to 200 hz  Small number of sensors

5

What is a Wireless Sensor Node Sensor Inputs Lithium thionyl chloride battery Radio Frequency (RF) transceiver

Sensor signal conditioning

8-bit , low power, microcontroller Flash EEPROM for sensor logging

multiplexer, PG instrumentation amplifier

A/D converter (12 or 16 bit resolution)

6

MicroStrain’s Wireless Sensor Node 

 



7

Networking Topologies

8

Hybrid Star-Mesh Network

9

Wireless Sensor Networks Remote System Management Local Access

Wireless repeater •USA: 32 km @ 1000 mW) •Europe: 5 km @ 200 mW

Worldwide Access

10

Carnegie Mellon University Field Testing 



Study feasibility of using wireless sensors in concrete production facility to monitor curing and handling Wireless nodes were used to measure temperature and strain during 12 hour curing cycle

11

Hardwired System Vs Wireless



Hardwired system was difficult to protect from the environment (cable breakage, moisture, dust) Wireless nodes were quickly installed and non-intrusive during production Wireless data transmitted to office location © MicroStrain, Inc. 2004 all rights reserved

12

Comparison of Wireless Vs Hard-Wired Embedded Strain Gauges Strain (microstrain)

200 180 160 140

Series1

120

Series2

100

Series3

80

Series4

60

Series5

40 20 0 0

1

2

3

4

5

6

7

8

9

10

Concrete Curing Time (Hours)

13

Field Testing Results Temperature with Curing Time, Sensor 84, 8 24 01

150 125 100 75 50 25 0 -25 0

Temperature, degree F

Strain, microstrains

S train with Curing Time, S pandrel Beam 8 24 01

5

10

150 125 100 Concrete

75

Ambient

50 25 0 0

Time from Placement, hours

5

10

Time, hours

Wireless strain and temperature were successfully recorded over 12 hour cure cycle 

Wireless nodes can monitor structure during removal from mold and transportation to site 

14

Ben Franklin Bridge – Philadelphia, PA to Camden, NJ

15

Ben Franklin Bridge - Requirements 



Monitoring system to determine structural integrity of certain elements Background data obtained every second, presence of train triggers sampling at 32 Hz

16

Ben Franklin Bridge - System 



4 wireless nodes 3 strain gauges per node (12 total) 1 temperature sensor per node (4 total)

17

Ben Franklin Bridge – System (cont)



2 base stations Cellular access to base stations

18

Preliminary Data from Ben Franklin Bridge

19

LaPlatte River Composite Bridge Load Test – Shelburne, VT

20

LaPlatte River Bridge - Requirements  

Dynamic monitoring system Quick and easy to deploy • Magnetically mounted strain gauges • Wireless data acquisition system

21

Magnetic Mount DVRT vs Conventional Bonded Foil Strain Gauge

22

Magnetic Mount DVRT Strain Gauge vs Conventional Bonded Strain Gauge  

4 trials, magnetic mount reapplied Slope: 0.91 +/- .01, R^2=.998 Offset: 14 trials repeat plucking, +/- 0.16 microstrain Measured Strain of Surface Mounted strain gauge -vs- magnetic mounted strain gauge. Magnetic mount reapplied 4 times test #1: y = 0.9157x + 14.767 test #2: y = 0.9164x + 13.929 200

test #3: y = 0.913x + 13.409 test #4: y = 0.9032x + 12.688

150

100

Strain gauge (microstrain)



test #1

50

test #2 test #3 test #4

0 -200

-150

-100

-50

0

50

100

150

200

Linear (test #1) Linear (test #2)

-50

Linear (test #3) Linear (test #4)

-100

-150

-200 DVRT (microstrain)

23

Temperature Testing DVRT span test with magnetic mounting with 100mm gauge length , 316 SS core, steel substrate and electronics out of chamber 48.5 deg C y = x - 24.236 R2 = 0.9994

150

22.7 deg C y = 0.9994x - 4.6105 R2 = 0.9994

100

0 deg C y = 1.0105x + 21.523 R2 = 0.9991

DVRT output (microstrain)

50

0 -150

-100

-50

0

50

100

-50

150

48.5 deg C 22.7 deg C 0 deg C Linear (0 deg C) Linear (22.7 deg C) Linear (48.5 deg C)

-100

-150

-200 Strain gauge (microstrain)

24

Field testing on composite deck bridge in Shelburne, VT Continuous sensor output with truck driving over bridge 25

20 Large truck crossing bridge 15

Output (microstrain)

10

medium truck from opposite direction

5 CH1 CH2 0 105

110

115

120

125

130

-5

-10

-15

25

Acknowledgements 

  

FIATECH Carnegie Mellon University Delaware River Port Authority University of Vermont

26

Turn static files into dynamic content formats.

Create a flipbook