STEINBAUER, Pavel (V Roninách 17, praha 4, 14000, CZ)
VALÁŠEK, Michael (Palmetová 2104/40, Praha 4, 14300, CZ)
STEINBAUER, Pavel (V Roninách 17, praha 4, 14000, CZ)
| Patent Claims 1. A method for determination of damage rate of a structure, in particular poles and towers, on the basis of determination of toughness change of a structure or a pole which is determined by specification of proportion of the amplitude of a harmonic force quasi-static loading with a frequency significantly lower than the first actual structure frequency and of the amplitude of the structure deformation harmonic course, characterized in that the structure toughness change is determined by specification of proportion of a harmonic force amplitude and a structure deformation amplitude which has been defined from the amplitude and frequency of the harmonic response created by a deflection, velocity or acceleration and; follow-up, damage rate of a structure is determined on the ground of this change. 2. A method for determination of damage rate of a structure according to the Claim 1 characterized in that the harmonic response of the structure is defined from a reconstruction of a time harmonic behaviour of a deflection, velocity or acceleration in the point of the response determination and that proportion of a harmonic force amplitude and a structure deformation amplitude is defined at least in two different points of the structure and this proportion corresponds with toughness change whereas the factual damage rate of a pole is obtained by comparison with toughness of an equivalent reference structure or with toughnesses of the inspected structure acquired from previous measurements. 3. A method for determination of damage rate of a structure, in particular a pole, according to some of the above mentioned Claims characterized in that a harmonic force loading of a structure is performed in the point of the structure which is within the same or a farther distance from at least one anchorage of the structure to the frame than the points of the structure response measuring are. 4. A method for determination of damage rate of a structure, in particular a pole, according to some of the above mentioned Claims characterized in that a harmonic force loading of a structure is performed in at least two points and the structure response measuring points are between the structure loading points. 5. A method for determination of damage rate of a structure, in particular a pole, according to some of the above mentioned Claims, consisting in a reconstruction of the measured time harmonic behaviour, characterized in that the amplitude of the harmonic force and of the harmonic deformation of the structure is defined from the time flow for at least two time periods of the loading harmonic force and the structure harmonic response by determination of a consonant harmonic function for the loading force and the response where parameters of this harmonic function are different in their amplitudes and phases. 6. A method for determination of damage rate of a structure, in particular a pole, according to some of the above mentioned Claims characterized in featured by the fact that the structure is loaded by a dynamic force of a mass performing a harmonic motion. 7. A method for determination of damage rate of a structure, in particular a pole, according to some of the above mentioned Claims characterized in that the structure is loaded by a harmonic force which is generated by a dynamic force of a mass performing a harmonic motion so that the mass-spring-structure loading mass has a resonance frequency near the required loading frequency. 8. A method for determination of damage rate of a structure, in particular a pole, according to some of the above mentioned Claims characterized in that the structure is loaded by a harmonic force which is generated by at least one unbalanced rotating mass which is connected to the structure by means of a force sensor. 8. Equipment for determination of damage rate of a structure according to the method mentioned above in the foregoing Claims, with an excitation force source and a sensor for its response measuring, where a harmonic force source bears on the structure through a force sensor, characterized in that there are at least two structure response sensors (3) arranged on a structure (1) between a harmonic force source (2) and a frame (5) of an anchored structure or the second harmonic force source (2), whereas in a case of an unanchored structure, the response sensors (3) are arranged on the structure (1) between the first and the second harmonic force source (2). 9. Equipment for determination of damage rate of a structure according to the Claim 8 characterized in that the structure (1) response sensors (3) are arranged in the direction of the harmonic force source (2) action. |
Technical Field
The invention concerns a method and equipment for determination of damage rate of a structure, in particular poles and towers, with a force excitation source and a sensor for measurement of its response.
State-of-the-art
Sizeable steel structures, particularly poles and towers, e.g. public lighting poles, power- transmission poles, aerial masts and other sizable constructions are damaged especially by corrosion or other material decrease. Assessment of their condition is nowadays, if at all, realized above all with the help of visual inspection and also endoscopy of the inside of the pole.
Other methods are mostly based on measuring a remaining thickness of a wall. Such methods can be destructive (e.g. drilling into a wall and detecting local material decrease) or nondestructive, e.g. simple ultrasonic or controlled ultrasonic waves, eddy-current method used for material decrease measurement, roentgen, relative comparison of electromagnetic characteristics of particular sections of a pole.
Methods based on determination of change rate of mechanical properties, which are toughness, modal characteristics (actual frequency), damping and acoustic emission, are the last big group. Either static or dynamic loading of a structure is used for it. At static loading, deformation is measured and the pole construction toughness is determined from it. At dynamic loading, time behaviour of a pole construction response to action of time variable loading on various spots is measured. Modal characteristics (e.g. frequency transmissions, actual frequency, actual wave shapes, damping et al.) are evaluated from the measurements. This is utilization of the Experimental Modal Analysis (EMA) methods. Measurement of acoustic emission of a structure to a consonant dynamic excitation and its comparison with the last measurement or signs of non-linear behaviour is a special case. Disadvantages of existing solutions are given either by damaging the construction of the pole which should continue to be in service, e.g. by drilling at each measurement of its damage rate, or by small efficiency of the used measurement method. The small efficiency is given either by small sensibility or inconclusiveness of damage rate or by high time, space, material or qualification demandingness of application of the method. Thus visual inspection is inconclusive, as damage can be hidden under paint coat or behind other part of the structure or under soil, and it is subjective. An example of disproportionate time demandingness is wall thickness measurement because, on principle, material thickness is assessed only in one point. Accordingly, measuring through the whole pole is very time demanding and there is a threat of local damage. Moreover, for example, measuring material decrease by eddy-current methods demands wide theoretical knowledge. Measuring mechanical properties by static loading requires a massive - rigid structure and a force source and a separate construction bearing a device for measuring a deformation. It is space-demanding then Furthermore^ a similar arrangement is time-demanding when performed in practice. Measurement of mechanical properties by dynamic loading is usually performed by the Experimental Modal Analysis methods which are demanding for the measurement boundary conditions guarantee. For example, measurement of change of actual frequencies or modal characteristics of poles, but also of acoustic emission, cannot be generally used for small conclusiveness of the measurement because quite a number of poles is embedded in gravel or sand ballast with high and above all very non-linear damping which makes the measurement with the help of the Experimental Modal Analysis distorted or impossible at all.
In order to measure toughness of beams in a laboratory or toughness of tool machines in a laboratory or in a workshop, methods of quasi-static loading by a harmonic force and measuring acceleration of a beam or a tool machine frame simultaneously only in one point were used. These measurements had both problems with an accurate determination of the amplitude of excitation and a response when being read only on the recording device, and there are problems with the use of these measurements for structures outside a laboratory or a workshop when meeting the assumption of ideal attachment (fixation) into a frame both of its own structure, and of a supporting construction for clamping of a force excitation source and a sensor for measurement of its response. The assumption of ideal attachment into a frame at sizable structures is often strongly infringed, e.g. a pole imbedded in sand, earth or rock features different properties. It is very difficult to build a supporting construction which features satisfactory toughness in order to clamp a force excitation source and a sensor for measurement of its response outside a laboratory. The aim of this invention is a method and equipment for determination of damage rate of public lighting poles, power-transmission poles, aerial masts and other sizable structures.
Subject Matter of an Invention
The body of this method for determination of damage rate of a structure according to this invention lies in the fact that a structure toughness change is determined by specification of proportion of a harmonic force amplitude and a structure deformation amplitude which has been defined from the amplitude and frequency of the harmonic response created by a deflection, velocity or acceleration and, follow-up, damage rate of a structure is determined on the ground of this change.
The harmonic response of a structure is defined from a reconstruction of time harmonic behaviour of a deflection, velocity or acceleration in a point of the response determination and the proportion of a harmonic force amplitude and a structure deformation amplitude is determined at least in two different points of the structure and this proportion corresponds to toughness change whereas the actual damage rate of a pole is obtained by comparison with toughness of equivalent reference structure or with toughness of an assessed structure acquired from previous measurements.
Harmonic force loading of a structure is performed in a point of the structure which is within the same or a farther distance from at least one anchorage of the structure to the frame than the structure response measurement points are or at least in two points and the structure response measurement points are between structure loading points. The amplitude of a harmonic force and of a structure harmonic deformation is defined from time behaviour for at least two time periods of harmonic force loading and of a structure harmonic response by determination of a consonant harmonic function for the loading force and the response where parameters of this harmonic function are different in their amplitudes and phases.
The structure is loaded by a dynamic force of a mass performing a harmonic motion or by a harmonic force generated by a dynamic force of a mass performing a harmonic motion so that the mass-spring-structure loading system has resonant frequency near the required loading frequency. The structure is eventually loaded by a harmonic force generated by at least one unbalanced rotating mass which is connected to the structure by means of a force sensor. The equipment for determination of damage rate of a structure according to this method lies in the fact that there are at least two structure response sensors arranged on a structure in a way one under another, respectively between a harmonic force source and a frame of an anchored structure or the second harmonic force source, whereas in a case of an unanchored structure, response sensors are arranged on a structure between the first and the second harmonic force source.
The structure response sensors are arranged in the direction of the harmonic force source action.
The advantage of the proposed solution is the fact that damaged poles feature less toughness at least in one direction, above all the relative toughness between two points of a pole, but also general toughness. Behavior even of damaged poles is linear within the elastic deformation scope. This method is suitable for assessing damage of a structure in a large scale, and that not only between the measured points, but also between a more distant measured point and the structure's anchor.
Another advantage of this method is possibility to use a connection of static and dynamic measurements of mechanical properties of a pole structure which enables to carry out a measuring equipment of a light construction with easy and fast installation. For deformation rate determination with this method, there is no need to ensure tough attachment of the measuring sensor, which is demanding, particularly in high altitudes on a measured structure.
At the same time, measurement error risk owing to ambient conditions, e.g. shaking of a structure, effect of wind etc., is reduced. Using a structure loading by a harmonic force, the structure characteristics are multiply recorded and eventual random errors are eliminated when processing the acquired data.
Review of the Pictures in the Drawings
An example of an embodiment of the equipment for measurement of damage rate of supporting poles is schematically plotted in the attached figures where 00109
Fig.1 shows the equipment arranged on a fixed structure,
Fig.2 shows an alternative embodiment arranged on a moving structure,
Fig.3 shows the equipment according to Fig.1 with a detailed illustration of a harmonic force source,
Fig.4 shows the equipment according to Fig.1 which is arranged on a fixedly attached pole, Fig.5 shows the equipment according to Fig.2 which is arranged on a moving pole,
Fig.6 shows utilization of the equipment according to Fig.4 for measurement in two
directions.
Example of Embodiment of the Invention
In Fig.1, there is a structure 1 shown in general which is fixedly attached to the frame 5 which is represented e.g. by earth in which the structure is fixedly imbedded. On one side of the structure 1, there is a source 2 of harmonic forces excitation positioned which is equipped with a force sensor 4. On the opposite side of the supporting component I, there are two sensors 3 arranged one under another, sensing responses from the source 2 of harmonic forces excitation. The higher positioned sensing element 3 is placed lower than the source 2 of harmonic forces excitation.
Arrangement according to Fig.2 shows an unanchored structure I where there is a lower source 2 of harmonic forces excitation positioned under the sensors 3.
In Fig.3, there is equipment with a detailed illustration of the source 2 of harmonic forces excitation arranged on a fixedly attached structure 1. The source 2 is arranged on an immovable or movable telescopic support 10 which allows setting the source 2 to the altitude needed. The source 2 of harmonic forces excitation is attached to the inspected structure through a force sensor 4 which senses the actual acting force.
The excitation force is generated by a harmonic motion of a battering ram 7 which is attached to the force sensor 4 via a resonance spring 6. The system consisting of the battering ram 7, the resonance spring 6 and the inspected bearing element I creates a resonance system tuned to the required excitation force harmonic frequency. This excitation frequency is chosen so that it is significantly lower than the first actual frequency of the bearing element 1. The battering ram 7 is put in harmonic motion by means of a linear motor 8 and its seismic mass
9. ■ *- ■ . .. ....
On the inspected structure 1, there are response sensing sensors 3 positioned in two places between points of action of the excitation force which is measured by the force sensors 4 and the frame 5.
Fig.4 and 5 show equipments similar to the equipments in Fig.l and 2 where the structure \ is represented by a pole upon which the excitation harmonic force acts in the direction perpendicularly to its axis. In Fig.4, the pole is anchored and there is one source 2 of harmonic forces excitation used between which and the frame 5 there are two sensors 3 arranged one under another on the opposite side while in Fig. 5, the pole is unanchored there, whereas there are two one-under-another-arrahged sources 2 of harmonic forces excitation used and, on the opposite side of the pole, there are two sensors 3 arranged one under another between them.
Then, in Fig.6, there is an anchored structure I showed upon which one source 2 of harmonic forces excitation acts in one direction and under it, there is at least one sensor 3 on the opposite side of the pole, whereas in another direction, advantageously perpendicular, another source 2 of harmonic forces excitation acts upon the pole between which and the frame 5 there is at least one other sensor 3 arranged on the opposite side of the pole.
In the above mentioned embodiments according to Fig.l - 6, sensors (3) for the structure (1) response are arranged in the direction of acting of the harmonic force source (2), however, generally they can be arranged on the perimeter of the structure (1) as well as out of the forward direction of the harmonic force source (2) acting.
A pole is loaded by a time variable force in one or more different directions. Time flow of the loading force corresponds to a harmonic function with suitably chosen frequency and amplitude. The loading force frequency is significantly lower than the first actual frequency of the inspected structure. Thus, excitation of resonance actions does not occur.
After a short transient performance, the structure loading with a harmonic force will cause a deformation with harmonic time flow. Process of this deformation is detected with the help of response sensors, i.e. a position or velocity or acceleration in a chosen point of the structure. Time flow of the loading force is recorded together with the deformation signal with the help of a data collection device. By computation with the help of regression algorithms, the acting harmonic force amplitude and the deformation amplitude in the point of sensor's position is determined afterwards. In a case of recording velocity or acceleration, the structure deformation amplitude determination is based on harmonic motion characteristics.
Based on these values, the structure toughness, eventually relative toughness related to one point of the structure, can be defined then. Comparison of results for poles of the same type will bring information on their condition. Other detailing information will be brought by evaluation of changes of the structure toughnesses detected by measurements repeated in time. The structure toughness change is subsequently defined by determination of proportion of a harmonic force amplitude and a structure deformation amplitude which has been defined from the amplitude and frequency of the harmonic response created by a deflection, velocity or acceleration
The structure damage rate is then determined from the difference of toughness change:
The harmonic response of a structure is defined from a reconstruction of time harmonic behaviour of a deflection, velocity or acceleration in a point of the response determination and the proportion of a harmonic force amplitude and a structure deformation amplitude is determined at least in two different points of the structure and this proportion corresponds to toughness change, whereas the actual damage rate of a pole is obtained by comparison with toughness of an equivalent reference structure or with toughnesses of an assessed structure acquired from previous measurements. The amplitude of a harmonic force and of a structure harmonic deformation is defined from time behaviour for at least two time periods of a loading harmonic force and of a structure harmonic response by determination of a consonant harmonic function for the loading force and the response where parameters of this harmonic function are different in their amplitudes and phases. The structure is loaded by a dynamic force of a mass performing a harmonic motion or by a harmonic force generated by a dynamic force of a mass performing a harmonic motion so that the mass-spring-structure loading system has resonant frequency near the required loading frequency, eventually it is loaded by a harmonic force generated by at least one unbalanced rotating mass which is connected to the structure by means of a force sensor.
The time variable harmonic excitation force can be advantageously generated by the system showed in Fig.3 consisting of a battering ram 7, a linear drive 8, a motor mass 9 and a resonance spring 6. This system's parameters are tuned so that its resonance frequency is as near as possible to the required harmonic excitation frequency. Tuning of the excitation system is performed by a change of weight of the battering ram 7 mass and a change of toughness of the resonance spring 6 which is designed as a variable. This enables to use a source of harmonic forces excitation, in our case the linear motor 8, with a significantly lower maximal force. This force source is controlled with the help of methods of optimal control so that harmonic course of the force on the pole in the point of force 4 is reached.
Another possibility for generating the time variable harmonic excitation force is to use dynamic forces of an unbalanced rotating mass, respectively two coupled rotating masses.
The pole deformation is measured in two points at minimum (advantageously as lowly as possible and in the point of loading or under it). The deformation rate results from a response measurement, i.e. position and/or velocity and/or acceleration of a point of a pole in dependence on time. Other data can be determined by calculation. When loading a pole harmonically, this dependence is harmonic as well and the measured dependence can be, knowing the signal frequency, approximated by a method of least squares with the help of one of the following relations
where A is a searched deformation in the measured point, a - acceleration of a point of a pole, v - velocity of a point of a pole, x - position of a point of a pole, ω - circular frequency of a moving point of a pole, t - time and φ - eventual phase shift of a motion of a point of a pole. Frequency of harmonic excitation and of the subsequent harmonic response can be defined from the excitation source setting or by the Fourier Analysis of the measured signal; this knowledge of frequency can be always verified and specified in terms of the method of least squares. Then, toughness is defined from the response at least in two points from the following relations
χ, - χι ¾„ =/( „) =* 9 / r « where k; is toughness of a pole, Fi is an acting force, x is a deflection value in points ; - X|. In the first formula mentioned above, there is relative toughness between points of a pole 1 and i; the second formula is for determination of absolute toughness. P T/CZ2010/000109
The proposed principle of measuring a response - a position change with the help of measurements of velocity and acceleration does not need an outer fixed point for attachement of the response sensing sensor 3. Similarly, the source 2 of harmonic forces excitation does not need a fixed point to generate the harmonic excitation force.
In order to generate the loading harmonic force, the loading equipment can make use of the dynamic force of the battering ram mass 7 - the resonance spring 6 system which has been tuned so that its resonance frequency corresponds to the required excitation frequency. This enables to use a source of harmonic forces excitation, in our case the linear motor 8, with a significantly lower maximal force. This force source is controlled with the help of methods of optimal control so that harmonic course of the force on the pole in the point of the force sensor 4 is reached.
The acquired relative as well as absolute toughnesses are compared to toughnesses of the reference (undamaged) pole (with the same dimensional and material properties as the measured pole has) or with toughness values of the same pole acquired from previous measurements which were performed with the same parameters.
Another possibility is that the structure is loaded by an excitation harmonic force at least in two points and the points of measurements of the structure response are arranged between the structure loading points so that deformation occurs in them by the operation of loading.
When assessing the pole toughness in comparison with a reference pole, it is necessary to keep the frequency of the excitation harmonic force significantly lower than the first actual frequency of the pole. This is not a must for tracking changes of the same pole after a certain time, when using the same frequency as with the previous measurement needs to be kept.
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