WO2000043768A1 - Surveillance de structures - Google Patents

Surveillance de structures Download PDF

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Publication number
WO2000043768A1
WO2000043768A1 PCT/CA2000/000048 CA0000048W WO0043768A1 WO 2000043768 A1 WO2000043768 A1 WO 2000043768A1 CA 0000048 W CA0000048 W CA 0000048W WO 0043768 A1 WO0043768 A1 WO 0043768A1
Authority
WO
WIPO (PCT)
Prior art keywords
emissions
acoustic
triggering event
monitoring
predetermined period
Prior art date
Application number
PCT/CA2000/000048
Other languages
English (en)
Inventor
John Elliott
Peter O. Paulson
Original Assignee
Pure Technologies Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from CA 2259717 external-priority patent/CA2259717A1/fr
Application filed by Pure Technologies Ltd. filed Critical Pure Technologies Ltd.
Priority to AU20880/00A priority Critical patent/AU2088000A/en
Publication of WO2000043768A1 publication Critical patent/WO2000043768A1/fr

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/08—Testing mechanical properties
    • G01M11/083—Testing mechanical properties by using an optical fiber in contact with the device under test [DUT]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/08—Testing mechanical properties
    • G01M11/081—Testing mechanical properties by using a contact-less detection method, i.e. with a camera
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
    • G01M5/0008—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings of bridges
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
    • G01M5/0033—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by determining damage, crack or wear
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
    • G01M5/0066—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by exciting or detecting vibration or acceleration
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
    • G01M5/0075—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by means of external apparatus, e.g. test benches or portable test systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M5/00—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings
    • G01M5/0091—Investigating the elasticity of structures, e.g. deflection of bridges or air-craft wings by using electromagnetic excitation or detection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/14—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object using acoustic emission techniques

Definitions

  • This invention relates to a method and apparatus for surveillance of structures.
  • Bridges can also be damaged by vandalism, for example by persons attempting to cut the suspender ropes which attach the roadway to the main suspension cable of a suspension bridge.
  • light standards can be damaged by collisions with a vehicle, or the lights in them can be smashed.
  • Decorative structures, such as statues, can be damaged by collision with a vehicle, or by persons trying to cut them loose and remove them.
  • the owner of the structure will only find out about the damage when the next scheduled inspection of it takes place. In the case of load bearing structures, the owner may find out when the structure fails because of the damage.
  • Damage to a structure can also occur because of natural events. For example a flash flood can wash away a portion of the foundation, causing the structure to shift, or earth tremors such as an earthquake can cause structural damage. If the structure is unsupervised by humans, and at a distance from supervised structures, the damage may go unnoticed.
  • steps can be taken to identify or apprehend the perpetrator if the damage was caused by a perpetrator.
  • the owner of the structure may be able to take steps which will minimize further damage. For example, damaged portions of the structure can be strengthened or repaired before they fall off. If the structure is a load-bearing structure, such as a bridge, it can be closed to traffic, so that the added weight of vehicles crossing it will not cause it to collapse.
  • the invention provides a method and apparatus for continuous recording of one or more chosen parameters which indicate the state of a structure.
  • parameters include but are not limited to acoustic emissions (as measured by an acoustic monitoring system), and displacement of a portion of the structure.
  • Displacement can be measured by strain (as measured by strain gauges on the structure), acceleration of different parts of the structure (as measured by accelerometers), rotation rate of elements of the structure (as determined by rotation rate sensors) or the like.
  • one recorded parameter includes data which can provide a human viewable record of events on the structure or in the surroundings of the structure, as recorded by video, infrared or like means.
  • the recording of the chosen parameters is continuous.
  • the output records are retained for a first predetermined period, and are then discarded unless a triggering event as discussed below is identified.
  • the first predetermined period can be different for different parameters.
  • acoustic or displacement monitoring are done continuously.
  • Acoustic monitoring monitors sound waves recorded by sensors on, in or close to the structure.
  • Displacement monitoring monitors events which involve movement of a structural element. Criteria are established which define acoustic or displacement events with pre-defined characteristics as triggering events, and any event which meet these criteria is declared to be a triggering event. A triggering event is considered as indicating a likelihood that something has occurred which has caused damage to the structure. After a triggering event, the system changes its mode of data acquisition and retention.
  • a recording of the chose parameters (signals of a chosen instrument or chosen instruments which sensed such parameters) for the first predetermined period before the event is either saved or forwarded to a guard station for evaluation, and the recording of the signals from such chosen instrument or instruments occurring after the event, either for a second predetermined period or until manually terminated, is either saved or forwarded to the guard station.
  • additional method steps are carried out for verifying whether the triggering event was caused by a collision or an act of vandalism.
  • additional method steps are carried out to determine whether structural damage was caused by the events which gave rise to the triggering event.
  • Acoustic monitoring is done by having acoustic sensors placed on or about the structure, which sensors give an output signals representing acoustic emissions which impinge on them.
  • the acoustic emissions may reach the sensors through the air or as vibrations caused by sound waves in the structure.
  • Typical acoustic monitoring systems are described in U.S. P. 5,798,457 and PCT published application W098/57166, both of Pure Technologies Ltd.
  • the acoustic monitoring equipment used for the present invention can also be used for other acoustic monitoring on the structure. For example, it can be used for the purposes set out in U.S. P. 5,798,457 and PCT application W098/57166. Such other monitoring is not part of this invention.
  • the use of the acoustic signals received for the purpose of the present invention involves first creating a profile of the acoustic emissions expected from the particular structure.
  • Any structure will have particular characteristic sounds which occur merely because of normal activities in or around that structure.
  • the characteristic sounds can include the tire noise of vehicles, the noise of vehicle tires hitting expansion joints of the road crossing the bridge, wind vibration and the like.
  • Vandalism may involve an impact or may involve cutting, both of which can be recognized acoustically.
  • the particular frequency ranges which are monitored will depend on the nature of the structure, and on whether acoustic monitoring is already being done for other purposes. The higher the frequency, the greater the attenuation with distance of propagation of acoustic waves in structures.
  • frequencies above 10 kHz for acoustic monitoring, so that sounds having their origin at a distance from the monitor are attenuated and not heard.
  • this requires sensors spaced more closely together than would be the case if lower frequencies were sensed. If sensors are present for some other purpose, therefore, such as the sensing of wire breaks in suspension or reinforcing cables, and are closely spaced, it is advantageous to monitor frequencies in ranges above 10 kHz, because the increased attenuation in such ranges will mean that fewer irrelevant emissions will be detected .
  • lower frequencies e.g. narrow ranges within the 2000-10000 Hz range.
  • the particular range or ranges of frequencies chosen for monitoring are chosen having regard to a profile which is prepared from the structure to be monitored.
  • the structure is monitored for a suitable period of time (for example, one week) and the acoustic emissions are monitored for frequency and amplitude.
  • One or more than one small sampling interval is selected where there are few or no emissions which typically occur during the normal activities in or around the structure, but where rending metal, or sawed metal, or an unusual impact will create an acoustic event.
  • the particular frequency band or bands selected will vary, depending on the background noises of the structure, and two or more bands can be selected if desired.
  • the bands can be very small, for example a bandwidth of about 20-50 Hz. Where small bandwidths are used, it is preferable to select several bandwidths, in case there is an event of interest which does not cause an unusual signal in one of the bandwidths selected, but does in the other. For example, on a typical suspension bridge which already has sensors in place for other purposes, monitoring can occur in the band 12,500 - 12,520 Hz and in the band 14,200 - 14,220 Hz, if these bands do not have much usual bridge noise in them.
  • the entire spectrum can be monitored. For, example, it is found that many bridges do not have much acoustic activity in the range of 2000-7000 Hz. With such a bridge, the band monitored can be the entire range of 2000-7000 Hz , or one or more smaller bands within such range.
  • the particular bands chosen are examined in detail. If there are normal noises which occur in these bands, they are examined to see whether they provide waveforms having a typical shape. If so, a suitable analyser can be programmed to ignore waveforms having this shape. Also, noises having less than an arbitrarily chosen duration can also be ignored, as not likely to have arisen from one of the conditions which the system seeks to detect. For example, it can arbitrarily be decided that any burst of noise with a duration of less than 0.5 second will be ignored, as sounds from vandalism or collision are likely to have a longer duration.
  • Each possible triggering event which is detected can be declared to be a triggering event if desired. Alternately, further analysis can be carried out to see whether possible triggering events occur in at least a specified number more than one of the selected bands. With this analysis, a triggering event is declared only when there are possible triggering events detected in more than the specified number of bands, i For example, if there are three selected bands, a triggering event can if desired be declared when possible triggering events occur in two of the three bands, or if desired, only when possible triggering events occur in all three bands.
  • While further analysis of this sort reduces the number of false alarms among the triggering events declared, it may also increase the risk of not declaring a triggering event when there is a collision of vandalism of an unanticipated type. For example, if one band is chosen because tearing metal is likely to produce sound in that band, it may not give a potential triggering event if there is a collision between a glass-fibre-reinforced plastic boat hull and a bridge being monitored. However, if several bands are being monitored, the other bands may record other sounds from the collision.
  • a method of determining that the structure has been in a collision, or has been subject to types of vandalism which involve removal or movement of a part of the structure is to equip the structure with instrumentation to monitor displacement.
  • instrumentation There are several types of suitable instrumentation. For example, accelerometers which are sensitive to very low frequency vibrations (in the 0 - 4 Hz range) will register acceleration when there is a displacement of the members on which they are placed.
  • the strain on the member will change as it is deformed, and this can be measured by a strain gauge attached to it.
  • a fiber optic cable which has been modified to act as a strain gauge, as is known in the art, can be used.
  • Another suitable instrument is a rotation rate sensor, which will show an angular displacement between parts of a structure. Suitable rotation rate sensors are fiber optic gyros or fiber optic Sagnac loop interferometers. Other suitable displacement monitoring instruments will be obvious to persons skilled in the art, having regard to the structure to be monitored.
  • a triggering event can then be defined as an event which displaces a chosen portion of the structure by an arbitrary pre-set amount, or in an arbitrary pre- set direction, or for an arbitrary pre-set time.
  • the condition for declaring a triggering event should be set with regard to the desirability of reducing false alarms, and to take into account normal flexing of components which occurs in many structures.
  • the condition and its value will be defined using common sense and with regard to the nature of the structure. In many structures, a time condition is suitable, because the normal flexing of components seldom results in sustained movement in any direction. Thus for example any acceleration lasting longer than 0.5 seconds can be considered as a triggering event for some structures.
  • the triggering event can be re-defined as being a longer period of acceleration, for example anything greater than 1.5 seconds.
  • rotations measured by a rotation rate sensor must be corrected for signals caused by the rotation of the earth, and for rotations which are found by a test period of observation to be characteristic of the structure.
  • suitable instrumentation for acoustic monitoring, or displacement monitoring, or both.
  • Suitable triggering conditions are defined having regard to the structure.
  • Monitoring is preferably carried out automatically at the location of the structure, by having a computer examine the signals received from the monitoring system, and by having it declare the existence of a triggering event when the criteria which have been set for a triggering event with respect to that structure are observed.
  • the monitoring can be done at a site remote from the structure, but this entails transferring large amounts of data to the remote site, which is generally not preferred for reasons of cost. Verification Process When a Triggering Event Occurs
  • the recognition by the computer of a triggering event will preferably start a verification process.
  • a video, infrared or radar verification system is also useful, but primarily to identify or apprehend the perpetrator of the act that has been identified.
  • the triggering event causes the video or infrared record for the first predetermined period to be saved permanently.
  • the video or infrared record of events occurring after the triggering event is saved permanently and is preferably simultaneously (in real time) forwarded to a guard center, where it can be evaluated in real time to determine whether some sort of emergency has occurred and whether it is ongoing.
  • the evaluation can either be done by a human (with or without computer enhancement of the video image) or by automated video image processing.
  • the review of the real time video or other record permits the guard center to determine immediately whether there is a situation requiring intervention.
  • the record of the period leading up to the incident has been saved, and is available if later needed to help identify the perpetrator of the incident or as evidence of what happened.
  • the video cameras are preferably located in places in which they will collect information useful to identify the perpetrator. For example, where the structure is associated with a highway, video cameras may be located where they are likely to record the license numbers of vehicles involved in a collision with the structure.
  • the predetermined first period can be selected based on the nature of the structure, the nature of the expected damage and the number of cameras for which storage must be provided. Typical predetermined periods are from 0.1 second to 1 hour. In many cases, 0.5 seconds to 1 minute is found to be a suitable period. In situations where vehicles are passing at high speeds (as for example with a structure associated with a highway), a first predetermined period of 0.5-1.0 seconds before the triggering event is usually sufficient to identify any vehicle which may have been involved in the event. The video, infrared or record of events after the triggering event can be saved until the guard manually resets the system. However, in most cases, it is advisable to have a second predetermined period, which starts on the determination by the monitoring computer that there is a the triggering event.
  • the second predetermined period can be, for example, from about 0.5 second to one hour.
  • the video for the second predetermined period will be saved permanently, unless the guard manually resets to retain either less than the entire video from the second predetermined period, or else to retain a period extending beyond the second predetermined period.
  • the storage of video or infrared signals takes a large amount of data storage, so the cost of storage is often significant.
  • the first and second predetermined periods are generally chosen to be as short as possible, consistent with keeping a record of the unusual events being observed. It will be noted that the data being acquired in the first predetermined period is only viewed if there is subsequently a triggering event, and a subsequent requirement to view it. Otherwise, it not kept after the period expires. Therefore, it is preferred in some cases not to do full image processing of the data acquired unless it is required to view it. For example, a video camera first coverts light falling on its imaging device into an analogue signal, which is subsequently digitized.
  • analogue signal only for the first predetermined period, and not to digitize it unless there is a triggering event which causes it to be saved, and a subsequent requirement to view it.
  • Data for the second predetermined period can be submitted to the guard station in its analogue form, and be digitized there for viewing if desired.
  • video cameras are preferred over infrared cameras in locations where there is considerable ambient heat, such as a structure that is exposed to strong sunlight and/or warm weather.
  • Infrared cameras are preferred where collisions are likely to take place in weather conditions which are not good conditions for video recording, such as in darkness, or in fog or precipitation.
  • the structure can be equipped with a radar transmitter and receiver (transceiver), which is turned on by the triggering event.
  • the radar transceiver can determine the presence or absence of an object which may have caused the triggering event. For example, when the structure is a bridge or a buoy or the like in a location where a ship might collide with it, the radar can determine that there is either a ship in the proximity or that there is no ship. If there is no ship, the event can be disregarded.
  • Radar is a preferred verification means, either as the primary verification means or as an additional one, in cases where ship collisions with bridges or buoys are anticipated. This is because many ships are equipped with radar transponders, which provide an identification of the ship when it is illuminated by a radar beam. This permits later identification of the ship.
  • the records from at least one of the instruments such as the acoustic monitoring devices, strain gauges, low frequency accelerometers or rotation sensing devices, for at least the first predetermined period, are saved.
  • the first predetermined period can be different, if desired, for the different devices.
  • the amount of data storage required to keep the signals from the different types of instruments will be taken into account in deciding what the first predetermined period should be. For example, it may be desired to save the information from acoustic monitoring for a period of (for example) 0.01 second to 1 minute before the triggering event.
  • Data from a low frequency accelerometer may be kept for a first predetermined period of (for example) 1 minute -2 days, because its storage requirements are modest.
  • a verification process is carried out to determine that the triggering event is something such as a collision or a vandalism which may have caused damage to the structure, before a damage assessment process is carried out.
  • the verification process may be omitted, for example in cases where weather conditions or possible damage to the verification equipment makes verification impossible, or where instrument readings after the triggering event make it seem likely that damage may have occurred, or where other information makes it likely that damage has occurred from reasons which are already apparent (such as earthquake tremors experienced directly by guards in the guard station.). In such cases, it may be decided to proceed directly with damage assessment.
  • Damage assessment is an optional but preferred part of the preferred embodiment of the invention. It involves comparison of the signals from before and after the triggering event for at least one of an acoustic sensing system, strain gauge, low frequency accelerometer, or rotation rate sensor. Preferably, signals from each such instrument which is present on or about the structure are compared with the signals from the same instrument before the triggering event.
  • the video or infrared or like records from before and after the triggering event are compared, if video, infrared or like systems are present, to see if any visible damage has occurred.
  • the acoustic information which is received from the bridge in response to normal events such as wind or traffic noise will often be different, before and after the snapping of the cable
  • the bridge is instrumented to recover acoustic information for more than the specific band or bands being used to identify a triggering event
  • all of the acoustic information available (both for the band or bands which had been monitored for triggering events and for other bands which may have been monitored for other purposes) is compared with corresponding information from before the triggering event. If the patterns recorded appear to be different, and the difference has no obvious explanation (such as a difference in the presence or absence of traffic on or around the structure) then the structure is noted as having probable serious damage. Suitable action can then be taken, such as closing off access to the structure or having it examined by a human.
  • differences in the signals received from a strain gauge before and after the triggering event can indicate that the structure has a bent or broken component.
  • Signals from a rotation rate sensor from before and from after the triggering event may indicate that the structure has a piece which has either been moved by the triggering event, or which has become loosened or is swinging as a result of the triggering event.
  • Signals from low- frequency accelerometers can indicate that the structure is moving in an abnormal way, for example swaying.
  • signals occurring during a first predetermined period before the triggering event are saved, and are compared with signals occurring in a second predetermined period after the triggering event. This is done for at least one instrument, and preferably for all instruments, which have been recording information with respect to the structure. This comparison can give information which is strongly indicative of whether or not serious structural damage has been sustained by the structure.
  • This information can be very valuable, as it can cause the owners of the structure to decide whether the triggering event was sufficiently important so that the structure should be taken out of service (as for example, by the closing of a bridge to traffic) until it can be inspected for damage and repaired if necessary.
  • radar In general, radar is not turned on before the triggering event, but only after the triggering event. This is because, in many areas of the world, radar transceivers are not allowed to be used except for necessary purposes. Generally, therefore, radar in association with this invention is used after a triggering event, to determine the presence or absence of an object which could have caused the triggering event, such as a vehicle or ship which could have collided with the structure.
  • Figure 1 is a perspective representation of an apparatus according to the present invention installed on a bridge.
  • Figure 2 is a perspective representation of a system according to the invention installed to protect a statue.
  • FIG. 3 is a diagrammatic representation of apparatus useful in the process of the present invention.
  • Figure 4 is a diagrammatic representation of the logical steps taken when an acoustic trigger event occurs.
  • bridge 1 passes over river 2 between banks 3 and 4.
  • Bridge 1 has two piers 5, each of which is sunk into the bed of river 2.
  • the piers are protected, as known in the art, by fenders 6, which are intended to shield the piers from collision with a ship.
  • the bridge has two suspension cables 10 (only one of which is shown) which run from cable housing 11 over the two piers 5 to cable housing 12.
  • the suspension cables support suspender ropes 15, which support roadway 18.
  • the bridge is provided with roadway lighting as is known in the art. Examples of such lighting are lamps 20.
  • the piers are also illuminated as by floodlights 21 , so that they can readily be seen by ships passing in the river.
  • Video cameras, generally indicated by the numeral 30 are ranged to capture video pictures of parts of the bridge structure which may be damaged by collision or vandalism or which may aid in the identification of a perpetrator. Some or all of the video cameras can be replaced by infrared cameras, if it is considered that the location is more likely to give better infrared recordings than video recordings.
  • two cameras 31 are shown attached to a main suspension cables 10 of the bridge, so as to have a view of the roadway 18.
  • Cameras 32 are positioned on piers 5, so as to survey the roadway 18.
  • the bridge may also have a scale (as shown at 19) painted at one or more locations surveyed by the video cameras to give an indication of the height or size of objects seen by the video camera. This will aid in identifying the perpetrator of an event registered by the video camera. Further, some of the video cameras are located at an angle which makes it likely that they will be able to record the license plates of vehicles passing along the bridge, again for the purpose of identification.
  • Further cameras 33 are positioned on piers 5 to survey the river so as to take images of approaching ships.
  • Other cameras can be positioned on the opposite side of the bridge and piers to point in the other direction along the river, in a fashion similar to cameras 32 and 33.
  • Cameras 34 are positioned under the roadway 18 and are directed at the piers.
  • Cameras 35 are positioned on buildings and trees on the shore, and are directed at the bridge. All of the cameras are preferably ones which will give clear images in the applicable lighting conditions of the part of the bridge at which they are directed. When these cameras and the data they record are discussed generally, the reference numeral 30 will be used.
  • a radar transceiver 70 is placed on a portion of the bridge which will give an image of ships both upriver and downriver when the transceiver is activated.
  • Strain gauges 80, 81 are placed on the rigid metal supports of fenders 6.
  • Low frequency accelerometers, having a range extending upwardly from 0 Hz to at least 4 Hz (preferably 0 - 20 Hz) 90, 91 and 92 are placed at intervals along the bridge in locations which are likely to be deflected if there is a collision.
  • the accelerometers are of the type which are conventionally used for earthquake detection. Suitable accelerometers are those made by the Analog Company and sold under model ADXL 202.
  • Rate of rotation sensors 95 and 96 are positioned to measure the rate of rotation of pier 5 relative to fenders 6.
  • An equipment housing 40 is located at a convenient place near the bridge.
  • the equipment housing 40 is concealed or otherwise inaccessible to unauthorized personnel.
  • the equipment housing 40 is shown as being located near the top of one of the piers 5, but it could instead be located in an inaccessible or concealed location on the one or other of the riverbanks 3 or 4.
  • each river bank has a cable house 11 or 12 in which the cables are anchored, and this forms a convenient place for the instrument housing 40 provided that it is suitably protected from trespass.
  • Computer 42 ( Figure 3) is located in the equipment housing 40. It is connected to a remote guard station 206 by suitable communications means, such as a communications cable 205 or a satellite or radio link. Signal storage means 41 is also located in equipment housing 40.
  • Cables run from each of the video or infrared cameras 31 , 32, 33 34 and 35, strain gauge 80 and 81 , low frequency accelerometers 90, 91 and 92 and rotation rate sensors 95 and 96 to computer 42, and thence to signal storage means 41.
  • a single cable 201 which runs from a camera 30 to a video signal storage medium 41 a within storage means 41 , and a single data transfer means 204 between computer 42 and data storage means 41.
  • Signals from each of the cameras, strain gauges, accelerometers and rotation sensing devices (which, generically will be called “instruments") are brought by their respective cables to storage means 41.
  • the storage means 41 are designed to record the signal from each instrument continuously, and to delete any recordings which are older than the first predetermined period. As discussed above, the first predetermined period can be different for different ones of the instruments.
  • a recording means 41a which can record for a first predetermined period (for example 1 second). As recording continues, all signals older than 1 second are discarded and replaced with new signals. Instead of discarding, it is of course possible to further store these signals, if there is some other reason to do so. It is also possible to store the signals at the instrument where they are generated, or at some intermediate location, instead of at storage medium 41 , if this is desired, and if the particular signals so stored are not being monitored for triggering events.
  • the radar transceiver 70 also has a cable 220 connecting it to computer 42.
  • the radar is not normally in operation, and is only turned on when a triggering event is detected by the computer 42.. When it is turned on, signals received from it can be forwarded by the cable to equipment housing 40 and thence to a guard station 206, or they can be forwarded directly to the guard station, for example by a radio link, as indicated schematically by antenna 221 associated with the radar transceiver and antenna 222 associated with the guard station.
  • Acoustic sensors, generally described by the numeral 50 are located at various places on the bridge, with the numbers 51-53 representing sensors 50 in particular places. By way of example, acoustic sensors 51 are located at intervals along the suspension cable of the bridge, preferably where it intersects with suspender ropes 15. Other sensors 52 are located on the fenders 6 and others numbered 53 are located on or near the roadway 18.
  • the acoustic sensors can be either dumb sensors, which transmit signals representing the sounds which they have sensed to a central computer 42 without analysis or they can be "smart" sensors, that do some analysis before sending the signals. The selection will be dependent on the relative cost of having more processing capacity of the computer 42 to deal with the wide range of signals sent by dumb sensors, as against the additional cost per sensor of having smart sensors instead of dumb ones.
  • the acoustic sensors are connected to the computer 42 by suitable cabling, or by suitable other links (for example infrared links). For simplicity, only one cable 203 is shown, connecting a sensor 50 to computer 42.
  • the preferred acoustic sensors are accelerometers.
  • the preferred accelerometers are piezoelectric accelerometers responsive to frequencies between 50 Hz and 50 kHz made by Pure Technologies Ltd. and identified by model no. UA-1.
  • FIG. 2 shows an analogous system for protection of a statue.
  • statue 100 is located on pedestal 101.
  • Surrounding the statue is an open area 102, beyond which are trees 103.
  • trees 103 are located floodlights 20', which illuminate the statue, and video cameras 30'.
  • An equipment housing 40' is located in the base of the statue, and can be accessed through a suitable locked door (not shown).
  • video storage 41a' In the equipment housing 40' is located video storage 41a', where the signals from the video cameras are stored for the predetermined period.
  • the statue is provided with acoustic sensors 51 ' and the base of the statue is provided with acoustic sensors 52'.
  • the base of the statue is also supplied with low frequency accelerometers 90' and 91 '.
  • the output of the acoustic sensors goes to computer 42' located in equipment housing 40'.
  • Strain gauges, and rotation rate sensors as shown in Figure 1 can also be used in the embodiments of Figure 2. However, they are not shown in order to illustrate the fact that not all types of instrumentation disclosed herein need be used in every installation. The particular instrumentation in each installation will be chosen to ensure that there will be monitoring of data from which a trigger event can be determined and also monitoring of something which indicates the state of the structure being monitored. In many cases, the two types of monitoring can be the same. For example, in the embodiment of Figure 2, acoustic monitoring is used for both purposes but, for the purpose of example, the low frequency accelerometers are not used to determine triggering events (although they could be used in this way within the scope of the invention). Instead, for the purpose of illustration, they only collect data for use in damage assessment.
  • the triggering event there is a saving of the monitored data from the first predetermined period, and preferably the saving of data for a second predetermined period.
  • the data from the first predetermined period can then be used either to determine the events that lead up to the triggering event (eg. identifying the perpetrator of a collision or vandalism) or to compare the state of the structure before and after the triggering event, (the damage assessment process), or both. Note that it is not absolutely necessary to save data from the second predetermined period for damage assessment, as the data from the first predetermined period can be compared with unsaved real-time data from the structure's instrumentation.
  • signals from video or infrared cameras 30 are transmitted through cable 201 to storage 41a in housing 40. Only a predetermined length of video or infrared record is maintained, and any signal older than the predetermined period is deleted. This is indicated schematically by arrow 202.
  • Storage 41a can suitably be a tape loop or a digital register.
  • Sensors 50 are connected by cable 203 to computer 42, where they are analyzed. Alternately, part or all of the analysis can take place at the sensors, if the sensors are "smart" sensors, and only the results of the whole or partial analysis can be forwarded to the computer. The analysis takes place as is described below with reference to Figure 4. If the analysis indicates that a likely event of accident or vandalism has occurred, the computer 42 causes the video or infrared signals stored at 41a to be transmitted to a guard station or to further storage, as may be desired in the particular installation. It also transmits in real time the video signals after the triggering event to the guard station, either for a second predetermined time, or until it receives a command to stop transmitting. This is indicated by cable 205 going to guard station 206.
  • a signal 303 is received, and is analysed to see whether there is a signal in one or more of the bands which has been selected as being of particular relevance.
  • the bands be in a frequency range where common acoustical events on the structure being monitored do not occur.
  • a first step of analysis be done by verifying that a signal occurs in at least a preselected number of such bands.
  • a second preferred step of analysis is the step of comparing those signals with known noises from the structure which occur within that band.
  • This step will only occur if there are known noises which can readily be identified from some feature such as the shape of their waveform, the fact that they reoccur in a periodic way, or with a fixed duration, or are predictable in some other feature. Assuming that any such comparison does not identify the noises as being a common noise from the structure, a signal is then sent as shown at 306 to video storage 41a. This signal causes further video or infrared output of the camera 30 ( Figure 3) to be transmitted along line 205 to guard station 206 ( Figure 3), as is represented by logic arrow 307 ( Figure 4).
  • Signal 306 also saves the video or infrared recording for the predetermined period immediately preceding signal 306 in a separate video or infrared storage 47 so that nothing will be recorded over it, and so that it can be retrieved when desired. This is represented by logic arrow 308 ( Figure 4).
  • the acoustic emissions for the first predetermined period, which were found by the computer to have included a triggering event are saved permanently, as at storage 48. If there are triggering events reported to the guard station which turn out not to be caused by emergency situations, these can then be examined as to their frequency and amplitude, and the results of such analysis can be used to change the frequency band or bands selected in the future, or to modify the analysis done on emissions sensed in the future.
  • the signals from strain gauge 80 or low frequency accelerometers 90, 91 and 92 and the rotation rate sensor 95 are transmitted to the equipment housing 40.
  • Those which are being used for displacement monitoring go first to computer 42 for analysis, then are stored. The others go direct to storage and are retained for the predetermined period defined for their instrument, for eventual possible use in damage assessment.
  • the signals which are being used for displacement monitoring, if such monitoring is being done, will be the signals received from one or more of the strain gauges, low frequency accelerometers or rotation rate sensors. They are examined by computer 42 to identify a possible trigger event. It is not necessary that all of the signals of all of the instruments be examined. Indeed, it would be possible to examine only the output of one instrument for a triggering event. However, it is preferred to examine the output of three or more instruments, preferably including two different types of instrument (such as a strain gauge and a low frequency accelerometer) and to declare a triggering event only when at least two of these exhibit signals similar to a trigger event.
  • a signal 306 is sent, just as in the case of a triggering event detected by acoustic monitoring.
  • some other means of ascertaining the cause of the event is preferably used. For example, this can be done by triggering the radar transceiver 70, which sends signals directly to the guard post, so that the guard can determine whether there is a vehicle or ship nearby which could have collided with the structure.
  • the guard at the guard station can then decide whether an emergency has occurred and can take appropriate action.
  • the guard can also retrieve the events for the predetermined period before the triggering event from video storage 41a or permanent storage 49 , and review these to see the historical record of what led up to the conditions being observed.
  • the signals 303 from the acoustic monitoring system (together will any other signals from the acoustic monitoring system which may have been collected for other purposes, such as listening for wire breakage in cables) and the signals from strain gauges and from the low frequency accelerometers are all saved, when a triggering event occurs, for a predetermined period before the triggering event (the "first predetermined period") and a predetermined period after the triggering event, (the second predetermined period).
  • the first predetermined period a predetermined period before the triggering event
  • the second predetermined period a predetermined period after the triggering event
  • the signals for the first predetermined period which occurs immediately before the triggering event are saved (that is, the signals are not discarded and replaced with new signals).
  • Signals for the second predetermined period (which may the same length as, or a different length from, the first predetermined period) after the triggering event are also saved.
  • the acoustic signals which occurred before the event and after the event can be compared, to see if there is any change in the typical background acoustic noise recorded. If there is, this may indicate that a structural member has been broken or damaged.
  • strains indicated by strain gauges may indicate that the structure has buckled or been dented.
  • a change in the rotation rate analysis between two parts of the structure may indicate that two parts which were joined are no longer joined, or are joined incompletely.
  • Comparison of low frequency accelerometer readings before and after the triggering event can show that the structure is moving (eg. oscillating or swaying) more than it did before the event. All of these data can be evaluated, either by a human or a suitable computer program. A determination is made, depending on the evaluation of the data, as to whether the structure has probably been damaged seriously or not.
  • the guards at guard station 206 may take further action, such as causing the vehicle which participated in the collision to the intercepted, or determining the license number of the vehicle from the video record of its license plate, or determining the identity of a ship from the radar record sent back from its transponder.
  • the information in the case of a ship, it is also possible to use the information as to the time of the collision, and the image of the ship, as a basis for later retrieval of satellite images, which will permit the ship to be tracked to its destination.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Acoustics & Sound (AREA)
  • Electromagnetism (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Alarm Systems (AREA)
  • Emergency Alarm Devices (AREA)

Abstract

L'invention concerne une structure, notamment une structure, telle qu'un pont, sujette aux collisions ou au vandalisme, qui est surveillée au moyen d'instruments, tels qu'un système de détection acoustique, des jauges de contraintes, des accéléromètres et des capteurs de rotation. On réalise un enregistrement vidéo, infrarouge ou analogue, de la structure, qu'on garde pendant une période de temps prédéterminée. Des critères sont établis afin de déterminer des résultats des instruments, qui indiquent un état d'endommagement possible, appelé événement déclencheur. Lorsqu'un événement déclencheur est enregistré, l'enregistrement vidéo du moment précédant immédiatement l'événement est conservé, contribuant ainsi à identifier les faits et l'auteur des faits, le cas échéant. Dans des modes de réalisation préférés, une vérification de la présence ou non de dommages est effectuée, et l'étendue de ces derniers est évaluée.
PCT/CA2000/000048 1999-01-20 2000-01-19 Surveillance de structures WO2000043768A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU20880/00A AU2088000A (en) 1999-01-20 2000-01-19 Surveillance of structures

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
CA 2259717 CA2259717A1 (fr) 1999-01-20 1999-01-20 Methode et appareil pour la surveillance video de structures
CA2,259,717 1999-01-20
CA2,281,332 1999-09-03
CA 2281332 CA2281332A1 (fr) 1999-01-20 1999-09-03 Surveillance de structures

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Cited By (4)

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WO2007088042A1 (fr) * 2006-02-02 2007-08-09 Northrop Grumman Litef Gmbh PROCEDE DE detection DE SOLLICITATIONS SUR ET/OU DE DOMMAGES À UNE STRUCTURE MECANIQUE
EP3096925A4 (fr) * 2014-01-24 2018-05-16 The Trustees Of The University Of Pennsylvania Dispositif de mouvement lineaire a tube d'extension pour son positionnement
CN112419686A (zh) * 2020-12-14 2021-02-26 中科蓝卓(北京)信息科技有限公司 一种桥梁撞击探测的多级判断报警与事件记录系统
DE102022103042B3 (de) 2022-02-09 2023-05-25 Dekra E.V. Vorrichtung und Verfahren zur Überprüfung der Standsicherheit von Masten

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FR2514047A1 (fr) * 1981-10-01 1983-04-08 Coussineux Henri Procede et dispositif de detection automatique d'accidents routiers
EP0371631A2 (fr) * 1988-11-30 1990-06-06 GP TAURIO, INC. a wholly-owned subsidiary of GENERAL PHYSICS CORPORATION Méthode et appareil de surveillance de pièces structurelles, exposées à des charges transitoires
US5798457A (en) * 1993-06-25 1998-08-25 Pure Technologies Inc. Continuous monitoring of reinforcements in structures
JPH0851491A (ja) * 1994-08-08 1996-02-20 Mitsubishi Denki Bill Techno Service Kk ビル設備監視装置
WO1997041686A1 (fr) * 1996-05-01 1997-11-06 Tvx, Inc. Systeme de securite pour plate-forme mobile se deplaçant sur le sol
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WO2007088042A1 (fr) * 2006-02-02 2007-08-09 Northrop Grumman Litef Gmbh PROCEDE DE detection DE SOLLICITATIONS SUR ET/OU DE DOMMAGES À UNE STRUCTURE MECANIQUE
JP2009525418A (ja) * 2006-02-02 2009-07-09 ノースロップ グルマン リテフ ゲーエムベーハー 機械的構造物における負荷／損傷を特定する方法
US20100231919A1 (en) * 2006-02-02 2010-09-16 Ulrich Schreiber Method for determining loads on a mechanical structure and the resultant damage
JP4707746B2 (ja) * 2006-02-02 2011-06-22 ノースロップ グルマン リテフ ゲーエムベーハー 機械的構造物における負荷／損傷を特定する方法
US8830477B2 (en) * 2006-02-02 2014-09-09 Northrop Grumman Litef Gmbh Method for determining loads on a mechanical structure and the resultant damage
EP3096925A4 (fr) * 2014-01-24 2018-05-16 The Trustees Of The University Of Pennsylvania Dispositif de mouvement lineaire a tube d'extension pour son positionnement
US10183404B2 (en) 2014-01-24 2019-01-22 The Trustees Of The University Of Pennsylvania Linear motion device with extending tube for positioning
CN112419686A (zh) * 2020-12-14 2021-02-26 中科蓝卓(北京)信息科技有限公司 一种桥梁撞击探测的多级判断报警与事件记录系统
DE102022103042B3 (de) 2022-02-09 2023-05-25 Dekra E.V. Vorrichtung und Verfahren zur Überprüfung der Standsicherheit von Masten
WO2023152106A1 (fr) 2022-02-09 2023-08-17 Dekra E.V. Dispositif et procédé pour vérifier la stabilité de mâts

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AU2088000A (en) 2000-08-07

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