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 Specifications Ambient 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 min Warm-up time, warm start 5 min Largest beam diameter 4 mm Interferometer distance resolution 0.32 μm ( ”) Interferometer distance accuracy ± 0.5 μm/m (± ”/ft) Typical lock-on working range 1.0 – 80.0 m (3.3 – 262 ft) Measuring and Tracking Performance Measuring rate 3 kHz Measuring rate output 1 kHZ Tracking speed lateral > 4 m/s (13 ft/s) Tracking speed radial > 6 m/s (19 ft/s)

Laser Tracker - Accessories 0.5" Reflector acceptance angle   " Red-Ring Reflector acceptance angle of   30 0 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 Access Mounting 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 L2 Distance, ft (m) % Error 32.5 (19. 2) (28.7) (36.6)7.7 Oct , 2010 Field Implementation - Bridge Deflection Measurements

Bridge vibration under transient loads Maximum deflection at the reflector = = 0.18 in. OR 4.6 mm 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 ” 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 settingsSummary/Conclusions

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