RU2194978C2 - Procedure testing technical state of framework of bridge - Google Patents

Abstract

FIELD: non-destructive testing of frameworks. SUBSTANCE: procedure testing technical state of framework of bridge consists in action of dynamic load with wide spectrum of frequencies on framework, in measurement of parameters of mechanical vibration with the aid of accelerometers in check points of framework, in obtainment of parameter of diagnostic sign and in determination of zone of anomalous tension by change of this parameter on basis of criterion. Check points are selected on framework in pair symmetry relative to longitudinal and lateral symmetry axes of framework. Three angular accelerometers which sensitive axes lie on three mutually perpendicular directions are anchored in each check point. Framework is subjected to dynamic load symmetric with reference to axes of framework, root-mean-square value of output electric signal of each accelerometer is measured in this case in frequency range from 0.1-800.0 Hz. Ratios of RMS values per each pair of accelerometers with same orientation of sensitive axes in each pair of check points symmetric relative to longitudinal and lateral axes of framework are computed as parameter of diagnostic sign. These ratios are compared with the help of criterion by formula |1-r|>γ, where r is above-mentioned ratios of RMS values; γ is conventional numerical value specified in accord with technical standards for particular type of structure of framework and corresponding to anomalous deviation of mechanical stresses in framework from symmetry axis. Line connecting pair of check points symmetric with reference to longitudinal or lateral axes of framework for which value r satisfies given criterion indicates direction to position of zone of anomalous mechanical stress and crossing of these lines determines location of this zone. EFFECT: raised accuracy of location of zone of anomalous mechanical stress in framework. 2 dwg

Description

 The present invention relates to methods for non-destructive testing of the technical condition of spans and can be used to control and diagnose other engineering structures and structures, such as building frames, pipelines, factory pipes, television towers, ships, aircraft, etc.

 There are various methods of non-destructive instrumental control of the technical condition and diagnosis of damage (defects) of PSs, among which dynamic methods are widely used, in which PSs are subjected to various kinds of dynamic loads - single, periodically repeated shocks, sinusoidal or broadband vibration (1-3). In this case, forced and natural oscillations are excited in the PS, the parameters of which (frequency, amplitude, phase) are measured at fixed control points using primary measuring transducers of any mechanical value (displacement, speed, acceleration) into electrical (charge, current, voltage) ) Processing the information thus obtained, one obtains the so-called “dynamic portrait” of the substation (2), analyzing which, based on some diagnostic sign and criterion, it is possible to identify zones of abnormal behavior of the structural elements of the substation — mechanical overvoltages or, on the contrary, attenuation, open or hidden defects (cracks, breaks in the reinforcement, subsidence of supports, etc.), as well as monitor their development over time.

 In recent years, among the dynamic methods for monitoring and diagnosing PSs, spectral analysis methods have been developed (1), in which the information obtained using primary converters is presented in the form of frequency spectra. In this case, a shift in the frequency of the maxima in the spectrum of the output electrical signal of the converter corresponding to the natural frequencies of the structural elements of the substation in the case of zones of abnormal mechanical stress (defect) is used as a diagnostic feature.

 Closest to the proposed one is the method (5), in which during the dynamic impact on the PS, the parameters of torsional and bending vibrational vibrations of the supporting structural elements of the PS are measured using linear accelerometers installed at the PS control points, and the peak frequency shift is used as a diagnostic feature PS natural oscillations, by the nature of which, using a specially developed table of shear values, they judge the position and nature of the defect.

 The authors of method (5) acknowledge its limitations, due to the inability to take into account the diversity of their designs and the specifics of defects in the proposed mathematical model of PS. The disadvantages of this method, along with the aforementioned, include, firstly, the use as a diagnostic sign of a frequency shift of the maxima (peaks) of natural frequencies of PS oscillations, which limits the use of the method to objects that have spectral peaks (high in comparison with the general background) quality factor of oscillations), while for most real substations, for example, for reinforced concrete road bridges, the frequency spectrum of oscillations is, in fact, continuous spectra with blurry overlap peaks that make it difficult to judge the peak shift, especially if they are adjacent. This can lead to incorrect interpretation of the results and reduce the accuracy of determining the position of the anomalous zones (defects). Secondly, the use of linear accelerometers for measuring angular vibration parameters (torsional and bending vibrations) is methodologically impractical, since measuring transducers of another (linear acceleration) are used to measure one physical quantity (angular acceleration). It also complicates the interpretation of the results, reduces the accuracy of measurements and, as a result, the accuracy of localization in the PS of zones of abnormal mechanical stress, especially at an early stage of development of defects.

 At the same time, the use of integral characteristics (in contrast to the spectral ones, i.e., the shift of the maxima in frequency) obtained using angular accelerometers having high sensitivity in the entire frequency range characteristic of PS vibration would help to overcome these drawbacks.

 The aim of the proposed method is to increase the accuracy of determining the location of the zones of abnormal mechanical stress in the PS.

 This goal is achieved in that the control points on the PS are selected pairwise symmetric from the relatively longitudinal and transverse axes of symmetry of the PS, three angular accelerometers are fixed at each control point, the measuring axis of one of them being oriented parallel to the longitudinal axis of the PS, and the other parallel to the transverse axis of the PS , the third - perpendicular to the measuring axes of the first and second, the PS is subjected to a dynamic load symmetrical with respect to the PS axes, while the rms value (rms) is measured in Khodnev electric signal of each accelerometer in a frequency range 0,1-800 Hz, calculating a ratio s.k.z. for each pair of accelerometers with the same orientation of the measuring axes in each pair of control points symmetrical with respect to the longitudinal and transverse axes of the PS, and compare these relations with their maximum permissible values using the criterion according to the formula | 1-r |> γ, where r are the above relations r.p.c.s. relative to the longitudinal or transverse axis of the PS of the control points for which the value of r satisfies this criterion, indicates the direction of the position of the zone of abnormal mechanical stress, and the intersection of two such lines determines the position of this zone.

 The basis of the proposed method is the property of symmetry of the design of the investigated object (PS). The vast majority of PS has a rectangular (in plan) shape, and load-bearing structural elements (beams, supports) are located symmetrically with respect to the longitudinal and transverse axes of symmetry of the PS. Physically, this means that additional mechanical stresses arising in the PS due to the action of a symmetric dynamic load on it must also be symmetrical with respect to its axis (center) of symmetry when the PS is in perfect technical condition or close to symmetry for a real technically sound PS.

 In the presence of defects (rupture of reinforcement, cracks in beams and diaphragms, etc.) or zones of increased (reduced) mechanical stress (for example, raising or sagging of supports), the pattern of mechanical stresses, as a rule, ceases to be symmetrical, at least with respect to one of axes of symmetry (exception - the location of the defect is exactly in the geometric center of the PS, which is unlikely). Abnormal stresses lead to a change in vibration parameters (angular acceleration) at the points of control and symmetry of the dynamic portrait of the PS as a whole.

 The distortion of the symmetrical picture of stresses is a very sensitive diagnostic feature, which is used in the present invention, in particular, when measuring the signals of accelerometers to search for the location of defects.

 As a symmetrical dynamic action, for example, one can take a series of single, periodically repeating strokes in the geometric center of the PS, or the same series of strokes near each control point, etc. Moreover, the measurement results should be statistically averaged (over time and the number of strokes) . During shock exposure in PS almost all types of natural vibrations are excited.

 The movement of transport itself can also be used as a dynamic effect on the PS, while the spectrum of excited vibrations of the PS will also be very wide. To ensure a symmetrical effect in this case, a relatively long period of time and intensive movement along the PS in both directions are required so that the accumulated and averaged values of the measured parameter (ccc) correspond to the dynamic action statistically symmetric with respect to the longitudinal axis of the PS.

 Another feature of the proposed method is the use of angular accelerometers as primary information converters. The use of linear accelerometers in analogues and prototype can be explained by the lack of the authors of the known methods of highly sensitive angular accelerometers with a working frequency range that covers the frequency spectrum of the vibration PS. Indeed, to measure the angular acceleration of vibration of PS, angular accelerometers with an operating frequency range of at least 0.1 to 800 Hz are required, which until recently were not produced anywhere in the world. However, to date, FSUE "NPP Kvant" has developed and used specifically for diagnostic purposes molecular-electronic angle accelerometers of the IUU-M type that meet the necessary metrological and operational requirements. Their use can significantly improve the accuracy of determining zones of abnormal mechanical stress (defects).

 As an example of one of the options for the implementation of the proposed method, we can give a measurement scheme to determine the location of the defect in the substation, which was tested in practice on one of the spans of a real bridge during the development of design work on the creation of a mobile diagnostic laboratory "Volna" in FSUE "NPP" Quantum " -1 ". The placement of measuring equipment for express diagnostics PS is shown in figure 1, where A is a mobile laboratory (1 - control panel, 2 - information storage device, 3 - 2-channel spectrum analyzer, 4 - oscilloscope, 5 - source nick the hammer power, 6, 7 - the source equipment power) and B - installing accelerometers at the substation (1 - cubic bracket 2 - angular accelerometers type UIA-M, 3 - adhesive connection with the PS surface (tar) B - a striking mechanism.

The sequence of actions is as follows:
- choose the position of the control points on the surface of the PS, symmetrically with respect to its longitudinal and transverse axes of symmetry; in this case - the intersection of beams and diaphragms on the perimeter of the PS;
- in each pair of control points symmetrical with respect to one of the PS axes, three angular accelerometers with mutually perpendicular measuring axes are rigidly fixed (after measurements in one pair of control points, measurements are made in the following); for this, angular accelerometers are rigidly (on screws) fixed with base planes on the faces of the cubic bracket (while their measuring axes will be mutually perpendicular); the surface of the PS at the point of the control point is cleaned of dirt, a thin layer of hot tar is applied to it, on which the bracket is mounted so that the measuring axis of one of the accelerometers is oriented parallel to one of the PS axes (for example, longitudinal);
- in the center of the PS, the base of the percussion mechanism is fixed (on the tar);
- connect the communication line to the accelerometers and percussion mechanism (according to the scheme of Fig. 1); turn on all devices and check the operation of the circuit;
- produce a series of 50 strokes with a duty cycle of 2 s; at the same time, the output signals of the accelerometers are recorded on a multichannel magnetic storage device (type FC-4) when monitoring signals using an electronic oscilloscope (for example, type C-101). General control of the circuit (power supply, setting the number and duty cycle of strokes, monitoring signals from accelerometers, etc.) is carried out using a special control panel;
- after registering the signals in one pair of control points, the operations are repeated for the next pair of symmetric control points, etc .;
- after the registration is completed, the RMS of the output signals of pairs of accelerometers with the same orientation of the measuring axes (for example, parallel to the longitudinal axis of symmetry of the PS) is measured for each pair of control points symmetric with respect to the longitudinal axis of the PS; for this purpose, use a two-channel spectrum analyzer (for example, type 2034 "VK"); measurements are carried out in the range of 0.1-800 Hz;
- calculate the relationship S.K.Z. the output signals of the indicated pairs of accelerometers (r value), the results are entered in the table;
- similar measurements and calculations are carried out for pairs of accelerometers with a different orientation of the measuring axes, as well as calculations for pairs of control points symmetrical about the transverse axis of the PS;
- on the PS plan, vector diagrams of these relations (r values) are built for each orientation of the measuring axes of the accelerometers (each type of angular vibration: torsional and two types of bending) and for each of the symmetry axes of the PS; at the same time, the beginnings of the vectors are placed on the symmetry axis of the PS at the point of its intersection with the line connecting the pair of symmetric control points, the ends of the vectors are directed to the control points, and the lengths of the vectors on the corresponding scale are equal to the ccc accelerometer signal at the control point to s. c. the signal of a symmetrically located accelerometer, i.e. corresponding r value;
- on the diagram, lines are drawn parallel to the axis of symmetry and 1 + γ, 1,1-γ (on both sides of the axis) remote from it, where γ is the level (number) established in accordance with the technical standards of the maximum tolerance for asymmetry of mechanical voltages for PS of this design (in this case, it corresponded to 0.3); if the ends of the vectors are located outside the band 1 ± γ, then the line connecting such a pair of control points indicates the direction of the abnormal mechanical stress;
- compare vector diagrams constructed relative to both axes of symmetry of the PS; the intersection of the anomalous voltage lines on the PS plan indicates the position of the anomalous zone (defect).

 In FIG. 2 shows the vector diagrams of relations (r) pairs of accelerometers with the same orientation of the measuring axes parallel to the longitudinal axis of the PS (torsional vibrations), constructed relative to the longitudinal (X) and, accordingly, transverse (Y) axes of symmetry of the PS. From figa it follows that the direction of the zone of abnormal mechanical stress is on the line connecting the points located between the diaphragm "g" and the support beam "d" (δ is the relative measurement error of r, δ = 0.07); from Fig.2b shows that the direction of the zone of abnormal mechanical stress along the beam "b". The position of the zone of abnormal mechanical stress is determined by the intersection point of these two directions and is located on the beam "b" between the diaphragm "g" and the support beam "d".

 Evaluation of the economic efficiency of the proposed method from implementation into practice was carried out under the assumption that due to the objectivity and reliability of assessing the technical condition of the substation, it is possible to draw a timely conclusion about the need for ongoing repair, thereby prolonging the life of the substation. For example, with a total cost of planned bridge overhaul of $ 150,000, extending the life of the bridge to overhaul at 10% of the bridges will save 15,000. e. With the cost of laboratory equipment 15,000 cu it will pay off in 1 year.

Literature
1. UK patent 2137347 (National Research Development Corporation). "Impact tests of structures."

 2. Kyska. R. -Vech. L.: Automatizacia dynamickych skusok mostov. Inzenyrske stavby, l, 1982, str. 30-33 (P. Kishka, L. Vekh, Research Institute of Civil Engineering, Bratislava. Automation of dynamic testing of bridge structures).

 3. Bauman, K., Drescher J Hochschule fuer Verkehrswesen Friedrich List. Wissenshaftliche Zeitschrift. 1985. Vol. 32, 5, p. 846-853 (Research on technical diagnosis of bridges).

 4. Broch J.T .: Mechanical Vibration and Shock Measurements. (Bruel and Kjaer, NAERUM, Denmark, 1984).

 5. Nishimura A., Fudjii M, Migamoto A .: Sensitivity of mecanical of behavior of bridges for their damage assessment, "Doboku Gakkai rhombunsu, Proc. Jap. Soc. Civ. Eng. ", 1987, 380, p. 355-364.

Claims (1)

A method of monitoring the technical condition of the span (PS), including the impact on the PS of a dynamic load with a wide range of frequencies, the measurement of mechanical vibration parameters using accelerometers at the control points of the PS, obtaining a diagnostic parameter parameter and determining the position of the anomalous mechanical stress zone by changing this parameter based on the criterion, characterized in that the control points are selected on the PS pairwise symmetric with respect to the longitudinal and transverse axes of symmetry C, at each control point three angular accelerometers are fixed, the measuring axis of one of them being oriented parallel to the longitudinal axis of the PS, the other parallel to the transverse axis of the PS, and the third perpendicular to the measuring axes of the first and second, the PS is subjected to a dynamic load symmetrical with respect to the PS axes , the root mean square value (rms) of the output electric signal of each accelerometer is measured in the frequency range 0.1-800 Hz, calculated as a parameter of the diagnostic sign relationship with. c. for each pair of accelerometers with the same orientation of the measuring axes in each pair of control points that are symmetrical with respect to the longitudinal and transverse axes of the FS, and compare these ratios using the criterion by the formula
| 1-r |> γ,
where r is the above relationship with. c. ;
γ is a conditional numerical value specified in accordance with technical standards for a particular type of PS construction and corresponding to an anomalous deviation from the symmetry of mechanical stresses in the PS,
moreover, a line connecting a pair of control points symmetric with respect to the longitudinal or transverse axis of the PS, for which a value of r satisfies this criterion, indicates the direction of the position of the zone of abnormal mechanical stress, and the intersection of two such lines determines the location of this zone.

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