RU2317534C1 - Method of monitoring automotive bridge - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: method comprises measuring movements of the elements of the construction of the bridge under the action of loadings and determining remaining service life of the bridge. The positions of dangerous sites of the bridge are determined from the formulae presented.

EFFECT: enhanced precision.

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Description

The invention relates to construction and can be used to monitor the technical condition of building structures, namely, an automobile bridge.

The closest technical solution to the proposed one is a method for monitoring an automobile bridge during its operation, which includes measuring the displacements of structural elements of the bridge under the influence of loads and determining the remaining resource of the bridge (see RF Patent No. 2250444, publ. 10.01.2001).

Its disadvantage is the large complexity, lack of accuracy, since the process of changing the characteristics of the bridge over time is non-linear, and this is not taken into account in the known technical solution.

The invention solves the problem of reducing the complexity and increasing the accuracy of determining the resource.

To achieve this technical result, the displacements of the bridge structural elements under the influence of loads are measured and the remaining resource of the bridge is determined, namely, at equal intervals of at least 3 times a year, measurements of displacements at the corner points of the span of the bridge crossbars under the influence of the load from a moving vehicle during hours peak load, wavelet transforms are carried out over the measured values, the amplitude-frequency characteristics are obtained, the spectral concentration zones are determined and the dominant frequency power and remaining life of the bridge is given by:

t _rest = t _ave. -t ₃

Where:

t _ave. = af ² _ave. + bf _ave. + c

where f _ave - the limiting dominant oscillation frequency,

a, b, c - coefficients determined from a system of linear equations:

t ₁ = af ² ₁ + bf ₁ + s;

t ₂ = af ² ₂ + bf ₂ + c;

t ₃ = af ² ₃ + bf ₃ + c;

where: t ₁ , t ₂ , t ₃ - time of the last three tests, counted from the start of operation of the bridge;

f ₁ , f ₂ , f ₃ dominant frequencies in these trials. The distinguishing features of the proposed method for monitoring an automobile bridge from the above known, closest to it are the following features: at regular intervals at least 3 times a year, they measure movements at the corner points of the span of the bridge crossbars under the influence of the load from a moving vehicle during peak hours , wavelet transforms are carried out over the measured values, the amplitude-frequency characteristics are obtained, the concentration spectrum concentration zones are determined up to INIR frequencies and remaining life of the bridge is given by:

t _rest = t _ave. -t ₃

Where:

t _ave. = af ² _ave. + bf _ave. + c

where f _ave - the limiting dominant oscillation frequency,

a, b, c - coefficients determined from a system of linear equations:

t ₁ = af ² ₁ + bf ₁ + c;

t ₂ = af ² ₂ + bf ₂ + c;

t ₃ = af ² ₃ + bf ₃ + s;

where: t ₁ , t ₂ , t ₃ - time of the last three tests, counted from the start of operation of the bridge;

f ₁ , f ₂ , f ₃ dominant frequencies in these trials.

The proposed method is illustrated by drawings, where Fig. 1 shows a general diagram of a measuring complex, Fig. 2 shows a diagram of the placement of sensors on a crossbar of an automobile bridge, Fig. 3 is a spectrogram of movements of a crossbar of a bridge, in Fig. 4 a curve of the dependence of the dominant frequency on the test time .

The proposed method is implemented as follows.

The residual resource of the automobile bridge is estimated by the parameters of the experimental amplitude-frequency characteristics under the influence of the load. The measurements are carried out using the measuring complex (figure 1) at regular intervals at least 3 times a year. In this case, determine the current value of speeds or accelerations at the extreme corner points 1, 2, 3, 4 of the upper plate of each crossbar of the bridge (see figure 2) under the influence of moving vehicles during peak hours. With the obtained values, numerical integration is carried out, the wavelet transform is carried out (Vorobev V.I., Gribunin V.G. Theory and practice of wavelet transform. St. Petersburg: VUS Publishing House, 1999, 208 pp.), Spectrograms of displacements are obtained (see Fig. 3), determine the frequency of the zone of maximum amplitudes under the influence of the load from a moving vehicle during peak hours, determine the concentration zone of the power spectrum of the dominant frequencies and the remaining bridge resource is determined by the formula:

t _rest = t _ave. -t ₃

Where:

t _ave. = af ² _ave. + bf _ave. + c

where f _ave - the limiting dominant oscillation frequency,

a, b, c - coefficients determined from a system of linear equations:

t ₁ = af ² ₁ + bf ₁ + s;

t ₂ = af ² ₂ + bf ₂ + c;

t ₃ = af ² ₃ + bf ₃ + c;

where: t ₁ , t ₂ , t ₃ - time of the last three tests, counted from the start of operation of the bridge;

f ₁ , f ₂ , f ₃ dominant frequencies in these trials.

Using the proposed interval between experiments provides a sufficiently high accuracy of determining the resource and allows you to take measures in time to avoid a major accident.

The use for excitation of vibrations of the effects of automobile traffic during peak loads allows us to bring the test conditions closer to operational and to obtain maximum amplitudes of vibration displacements. In addition, this method reduces the material costs of monitoring. The implementation of wavelet transforms improves the accuracy of determining the dominant frequency of the oscillation of the bridge. The proposed monitoring method allows to take into account the non-linearity of the processes of changing the bridge parameters (its rigidity) that appear during the last most critical period of its operation and thereby increase the accuracy in determining the remaining resource and avoid an emergency.

An example of the proposed method.

Experiments and resource determination were carried out for the crossbar block of the Kama automobile bridge construction.

The precast concrete bridge over the Kama River was commissioned in 1967.

As primary elements for recording oscillations, seismic sensors were used:

- SM-4B - vibration acceleration sensor (accelerometer) with a working range of measured frequencies of 0.6-40 Hz;

- KVE-3B - vibration velocity sensor (cycle meter) with an operating range of 0.01-10 Hz.

Sensors were installed in the end zones inside the boxes of crossbar blocks on special horizontal metal platforms.

During three experiments (November 2002, May and October 2003), temporary signals (in volts) were recorded, which are the voltage of the sensor and characterize the vertical components of vibration acceleration (for the SM-4B accelerometer) or vibration velocities (for the KVE-3B bicycle meter) location. By numerically integrating the vibration acceleration or vibration velocity are converted into vibration displacement. For vibration displacement, wavelet transforms were performed and spectral characteristics were obtained (Fig. 3).

An analysis of the spectral characteristics of the crossbar for all sensors obtained in 2002 showed that a frequency of 0.74 Hz dominates in the power spectrum. Repeated testing in 2003 showed a decrease in the dominant frequency in May to 0.71 Hz, and in October to 0.67 Hz. The limiting frequency of the loss of elasticity of the structure f _pr = 0.48 Hz. This value of the limiting frequency corresponds to a 4-fold loss in the stiffness of the reinforced concrete structure of the bridge, relative to the stiffness at the time of acceptance tests. The residual resource is 5.5 years. Tests have shown that the proposed monitoring method improves the accuracy of determining the residual life of the bridge, and is especially necessary after half of the planned life, when the rigidity of its structural elements begins to change nonlinearly.

Claims (1)

A method for monitoring an automobile bridge during its operation, including measuring the displacements of structural elements of the bridge under the influence of loads and determining the remaining resource of the bridge, characterized in that, at equal intervals of at least 3 times a year, they measure movements at the corner points of the span of the bridge crossbars under the influence loads from a moving vehicle during peak hours, wavelet transforms are carried out over the measured values, and the amplitude-frequency characteristics are obtained ki, determine the concentration zone of the power spectrum of the dominant frequencies and the remaining bridge resource is determined by the formula t _rest = t _ave. -t ₃ , where t _ave. = af ² _ave. + bf _ave. + c, where f _ave - the limiting dominant oscillation frequency, a, b, c - coefficients determined from a system of linear equations t ₁ = af ² ₁ + bf ₁ + s; t ₂ = af ² ₂ + bf ₂ + c; t ₃ = af ² ₃ + bf ₃ + c, where t ₁ , t ₂ , t ₃ - the time of the last three tests, counted from the start of operation of the bridge; f ₁ , f ₂ , f ₃ are the dominant frequencies in these tests.

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