Bridge monitoring system

• US 6,240,783 B1
• Filed: 05/02/1998
• Issued: 06/05/2001
• Est. Priority Date: 05/02/1998
• Status: Active Grant

• Current Assignee: USBI Co.
• Original Assignee: USBI Co.
• Inventors: Wiggs, George Ashley, McGugin, Terry Curtis, Bishop, Stephen Keith
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US09/071,993
• Time in Patent Office: 1,130 Days
• Field of Search: 735/94, 735/79, 735/80, 736/55, 736/56, 736/57, 340/540, 340/669, 340/670, 340/683, 250/559.3, 250/559.32
• US Class Current: 73/594
• CPC Class Codes: G01H 9/00 Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
• CPC Class Codes: G01M 11/081 by using a contact-less detection method, i.e. with a camera
• CPC Class Codes: G01M 5/0008 of bridges
• CPC Class Codes: G01M 5/0041 by determining deflection or stress
• CPC Class Codes: G01M 5/0066 by exciting or detecting vibration or acceleration vibration testing of structures G01M7/00
• CPC Class Codes: G01M 7/00 Vibration-testing of structures; Shock-testing of structures G01M9/00 takes precedence

Abstract

A bridge monitoring system uses laser light reflected from structural members of a bridge to create velocity and displacement time signals of the bridge'"'"'s vibratory response to quiescent conditions, and converts the sensed velocity and displacement time data to frequency domain data to provide a “signature” waveform for the bridge indicative of its structural characteristics.

Claims

1. Apparatus for monitoring a vibratory state of structural members of a bridge in response to quiescent bridge conditions, comprising

a laser light source producing a single laser light beam;

a 1;

N splitter forming a plurality of individual laser light beams from said single laser light beam, wherein each individual laser light beam in said plurality thereof is directed to illuminate a target area within a plurality of target areas on the surface of each of one or more individual bridge structural elements for a period of time;

detector means, for receiving a reflection of said individual laser light beam from each said target area to provide individual velocity time signals indicative of surface deflections of said individual target areas in said period of time; and

signal processing means, connected for response to said detector means for converting each said velocity time signal into a corresponding frequency domain signal, to identify quiescent frequency response characteristics of an associated structural element.

2. The apparatus of claim 1, wherein

said signal processing means multiplexes said individual velocity time signals from each said target area to provide a composite velocity time signal indicative of the overall response of the bridge to the surface deflections of the aggregate of said individual target areas in said period of time.

3. The apparatus of claim 1, wherein

said signal processing means multiplexes said individual velocity time signals from each said target area to provide a composite velocity time signal indicative of the overall response of the bridge to the surface deflections of the aggregate of said individual target areas in said period of time;

and wherein

said signal processing means converts said composite velocity time signal into a corresponding composite frequency domain signal to provide a signature indicative of the overall frequency response of the bridge to the surface deflections of the aggregate of said individual target areas in said period of time.

4. The apparatus of claim 1, wherein said laser light source includes:

an Er-doped solid state continuous wave laser, and

an Er-doped fiber amplifier, wherein a laser output beam is directed to said fiber amplifier from said continuous-wave laser, and wherein said single laser light beam is directed to said splitter from said fiber amplifier.

5. The apparatus of claim 4, wherein said continuous wave laser generates said laser output beam having a single frequency of approximately 1.55 μ

m.

6. The apparatus of claim 4, wherein said continuous wave laser generates said laser output beam at a power of approximately 15 mW.

7. The apparatus of claim 1, wherein each individual laser light beam in said plurality thereof is directed into an individual laser sensor including:

said detector means

a first individual beam splitter directing an output signal portion of said individual laser light beam toward a target area in said plurality of target areas and a reference signal portion of said individual laser light beam toward said detector means.

8. The apparatus of claim 7, wherein

said individual laser sensor additionally includes an optical circulator,

said output signal portion is directed toward said target area through said optical circulator,

said individual laser sensor is aligned with said target area so that a reflection of said output signal portion is returned from said target area to said optical circulator,

said optical circulator directs said reflection of said output signal portion toward said detector means, and

said reference signal portion and said reflection of said output signal portion are combined in said detector means.

9. The apparatus of claim 8, wherein

said first individual beam splitter is a first fiber-optic splitter;

said detector means includes a second fiber-optic splitter; and

said reference signal portion and said reflection of said output signal are combined in said second fiber-optic splitter.

10. The apparatus of claim 8, wherein an output of said detector means includes a signal representing a difference in frequency between said reference beam portion and said reflection of said output signal portion.

11. The apparatus of claim 10, wherein said detector means additionally includes a fringe counter measuring a number of wavelengths of said individual laser beam through which said target area moves.

12. The apparatus of claim 11, wherein

said detector means additionally includes a digital to analog convertor, and

an output of said fringe counter is passed through said digital to analog convertor to generate an analog signal representing displacement of said target area.

13. Apparatus for monitoring movement of a target area on a structural member of a bridge, in response to quiescent conditions, comprising:

means for generating a laser light beam; and

an individual light sensor including a detector, a first beam splitter directing an output signal portion of said laser light beam toward said target area and a reference signal portion of said laser light beam toward said detector, and an optical circulator, wherein said output signal portion is directed toward said target area through said optical circulator, said individual laser sensor is aligned with said target area so that a reflection of said output signal portion is returned from said target area to said optical circulator, said optical circulator directs said reflection of said output signal portion toward said detector, and said reference signal portion and said reflection of said output signal portion are combined in said detector.

14. The apparatus of claim 13, wherein

said first individual beam splitter is a first fiber-optic splitter;

said detector includes a second fiber-optic splitter; and

said reference signal portion and said reflection of said output signal are combined in said second fiber-optic splitter.

15. The apparatus of claim 13, wherein an output of said detector includes a signal representing a difference in frequency between said reference signal portion and said reflection of said output signal portion.

16. The apparatus of claim 15, wherein said detector additionally includes a fringe counter measuring a number of wavelengths of said output signal portion of said laser light beam through which said target area moves.

17. The apparatus of claim 16, wherein

said detector additionally includes a digital to analog convertor, and

an output of said fringe counter is passed through said digital to analog convertor to generate an analog signal representing displacement of said target area.

18. Apparatus for monitoring a vibratory state of structural members of a bridge in response to quiescent bridge conditions, comprising:

a plurality of reflective targets in a plurality of positions on said structural members;

laser means generating a plurality of individual laser light beams;

a plurality of sensors arranged so that each individual laser light beam enters a sensor within said plurality of sensors, wherein an output portion of each individual laser light beam is directed from said sensor to a target within said plurality of reflective targets, wherein a reflection of said output portion returns to said sensor, and wherein said sensor includes a detector forming a motion detection signal in response to movement of said target;

a local data processing system receiving said motion detection signal from each sensor within said plurality of sensors;

a remote data processing system wherein said remote data processing system includes storage holding data from previous measurements of said vibratory state of structural members of said bridge, and wherein data received from current measurements of said vibratory state of structural members of said bridge is compared to said data from previous measurements of said vibratory state of structural members of said bridge; and

a transmission link between said local data processing system and said remote data processing system for transmitting data and instructions, wherein said local data processing system calculates data indicating said vibratory state of structural members of said bridge and transmits said data over said transmission link to said remote data processing system.

19. The apparatus of claim 18, wherein said laser means includes:

a laser light source producing a single laser light beam; and

a 1;

N splitter forming said plurality of individual laser light beams from said single laser light beam.

20. The apparatus of claim 19, wherein said laser light source includes:

an Er-doped solid state continuous wave laser, and

an Er-doped fiber amplifier, wherein a laser output beam is directed to said fiber amplifier from said continuous-wave laser, and wherein said single laser light beam is directed to said splitter from said fiber amplifier.

21. The apparatus of claim 18, wherein each sensor within said plurality of sensors includes a first individual beam splitter directing an output signal portion of said individual laser light beam toward a target within said plurality reflective targets and a reference signal portion of said individual laser light beam toward said detector.

22. The apparatus of claim 21, wherein

each sensor within said plurality of sensors additionally includes an optical circulator,

said output signal portion is directed toward said target through said optical circulator,

said individual laser sensor is aligned with said target area so that a reflection of said output signal portion is returned from said target area to said optical circulator,

said optical circulator directs said reflection of said output signal portion toward said detector, and

said reference signal portion and said reflection of said output signal portion are combined in said detector.

23. The apparatus of claim 18, wherein an output of said detector includes a signal representing a difference in frequency between said reference beam portion and said reflection of said output signal portion.

24. The apparatus of claim 23, wherein said detector additionally includes a fringe counter measuring a number of wavelengths of said individual laser beam through which said target area moves.

25. The apparatus of claim 18, wherein

said remote data processing system calculates and stores a cosine Fourier transform of an auto-correlated time history signal of movement of said structural members of said bridge;

and

said cosine Fourier transform of current measurements of movement of said structural members of said bridge is compared to a cosine Fourier transform calculated from previous measurements of movement of said structural members of said bridge.

26. The apparatus of claim 25, wherein said auto-correlated time history signal is an average of the product of the value of the signal of movement of said structural members of said bridge at a particular time, multiplied by the product of the value of the signal of movement of said structural members of said bridge at an incremental time after said particular time.