Noncontact Displacement Monitoring by Lasers

Upul Attanayake, Ph.D., P.E.Assistant Professor

CAIT Workshop on International Bridge Study (IBS)June 14 – 15, 2011

Outline

Laser tracker specifications Laser tracker - accessories Reflector mounting process Field implementation - bridge deflection measurements Summary/Conclusions

Laser Tracker SpecificationsAmbient Conditions

Working temperature 0°C to 40°C (32°F to 104°F)Storage temperature -10°C to 60°C (14°F to 140°F)Relative humidity 10% to 90%, non-condensing

Absolute Interferometer (AIFM) Wavelength 633 nm / 795 nm (visible / IR - HeNe)Warm-up time, cold start 8 minWarm-up time, warm start 5 minLargest beam diameter 4 mmInterferometer distance resolution 0.32 μm (0.000013”)Interferometer distance accuracy ± 0.5 μm/m (± 0.000006”/ft)Typical lock-on working range 1.0 – 80.0 m (3.3 – 262 ft)

Measuring and Tracking PerformanceMeasuring rate 3 kHzMeasuring rate output 1 kHZTracking speed lateral > 4 m/s (13 ft/s)Tracking speed radial > 6 m/s (19 ft/s)

Laser Tracker - Accessories

0.5" Reflectoracceptance angle 500

1.5" Red-Ring Reflectoracceptance angle of

300

Laser Tracker

AT MeteoStation(Temp., humidity,

and pressure) Control Unit and Laptop Power Supply

Reflector Mounting Process

A reflector with a magnetic base

Mounting a reflector on a girder A reflector is mounted next to a potentiometer

AccessMounting a reflector using hot glue

Field Implementation -Bridge Deflection Measurements

General view of the bridge Plan view of the bridge

Reflector location on southbound span 2

Girder 3 deflection under 6 LT-BB @ L2

Distance, ft (m) % Error32.5 (19. 2) 9.865.0 (28.7) 3.097.5 (36.6) 7.7

Oct. 10-11, 2010

Field Implementation - Bridge Deflection Measurements

Bridge vibration under transient loads

0 30 60 90 120216.90

217.00

217.10

Time (sec)

Brid

ge d

eflec

tion

(in.)

Maximum deflection at the reflector = 217.09 -216.91= 0.18 in. OR 4.6 mm

90 92 94 96 98 100216.90

216.95

217.00

217.05

217.10

Time (sec)

Brid

ge d

eflec

tion

(in.)

Field Implementation - Bridge Deflection Measurements

Operational Conclusions• Laser Tracker measures deflections and translations without contact. • The technology can acquire static displacements at multiple locations and/or

dynamic displacement at a single location at a maximum rate of 3kHz.• Technology can be used during daylight or night (night time is preferred to

minimize the interference of sunlight). • Entire operation can be completed in less than two hours on a typical single span

bridge including reflector mounting. • A single operator can execute the entire measurement operation if traffic control

is provided.

Summary/Conclusions

Measurement Related Conclusions• Highly accurate measurements• Resolution of 0.0001” can be achieved very easily under field conditions• Beam divergence requires using 1.5” RR reflectors beyond 160 ft (50 m) under

normal operating conditions• 1.5” RRR could read well beyond 260 ft (80 m) distance stated in specifications• Intensity of ambient light can interfere with initial auto measurement settings

Summary/Conclusions

Thanks You !

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