RU2808099C1 - Method for quick determination of possibility of passing excessive load across span structure - Google Patents

Abstract

FIELD: non-destructive testing.

SUBSTANCE: invention relates to methods for non-destructive testing of the load-bearing capacity of building structures, in particular to methods for promptly determining the load-bearing capacity of road bridge spans when carrying excess loads through them. When implementing the method, initially a sensor for measuring angular displacements measures angular deviations in the supporting section of the span structure under the influence of a test load on it, located on the span structure in a position corresponding to the maximum bending moment from it. Then the deflection from the test load in the middle of the span, the permissible deflection and the maximum stresses at the lower and upper edges are calculated. In this case, a load with a mass corresponding to the standard one is used as a test load; the deflection from the test load is calculated taking into account the rotation angle coefficient, which takes into account the influence of the span system on angular deviations. The deflection from the excess load is determined by calculation by multiplying the deflection from the test load by the ratio of bending moments from the excess load to the test load, and the maximum stresses in the lower and upper edges are calculated from the excess load with their subsequent comparison with the calculated values of the materials of the lower and upper edges, while the deflection from excess load is compared with the permissible deflection.

EFFECT: providing the possibility of creating a method for quick determination of the possibility of passing an excess load on a span, increasing the reliability of its determination.

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Description

The invention relates to methods for non-destructive testing of the load-bearing capacity of building structures, in particular to methods for promptly determining the load-bearing capacity of road bridge spans when carrying excess loads through them.

The relevance of the proposed method is due to the increasing need to make a decision on the possibility of passing excess load on the span of various static systems, taking into account its actual operational condition in a short time. The main disadvantages of the known methods are the high complexity of their implementation.

There is a known method for determining the load-bearing capacity of a span using the finite element method [1], adopted as an analogue. The method involves the following sequence: taking measurements of the beams of the superstructure, determining the thickness and materials of each layer of road pavement, drawing up a finite element model of the superstructure, loading the model with a constant and moving load, obtaining deformations and stresses in the elements of the superstructure. To implement the calculations, the MIDAS and Soflstic software packages have been created, which contain blocks specifically focused on bridge structures.

The disadvantages of this method are the high labor intensity and complexity of constructing a finite element model of the span.

There is a known method of non-destructive testing of the strength of building structures [RU 2161788 C2, published on January 10, 2001], adopted as an analogue, by which the locations of possible maximum linear or angular movements are determined, in these places the structure is loaded with a test mechanical load not exceeding its maximum strength value and structural rigidity, and determine the values of maximum displacements. In this case, the structure is loaded in the same place 5-10 times with a constant mechanical load and carried out at least at three different load levels. Based on the results of three average displacement values and the corresponding loads, a direct dependence of the load on the displacement is constructed, at least three confidence intervals for displacement measurements are determined, at the points of which the confidence limits of the measured displacements are constructed. The strength of the structure is determined taking into account the average displacement values with a linear relationship between load and displacement.

The disadvantages of this method are the high labor intensity of its implementation; in addition, the load-bearing capacity is assessed only by the criterion of maximum displacement for materials with a linear relationship between load and displacement.

The closest in its technical essence is the method for determining the bearing capacity of a span [RU 2771598, publ. 05/06/2022], accepted as a prototype. When implementing this method, the test load is initially placed behind the bridge span, after which the frequency of natural vibrations is measured using seismic vibration sensors in the middle part of the span, after which measurement cycles begin, each of which includes moving the test load along the span in the direction of the opposite support at a speed , excluding dynamic vibrations of the span structure, at the same time, the angular movements of the span structure are continuously measured and at the end of the measurement cycle they are recorded, then the indicated cycles are repeated with a set step until the center of gravity of the test load reaches the middle of the span structure, while the actual linear weight is calculated from the frequency of natural vibrations q _ce and the bending moment from the own weight of the span M _sv, taking into account the coefficient β taking into account the continuity of the span, and from the fixed angular displacements, the deflection f in the middle of the span, the stresses in the lower and upper edges of the span from the test load, taking into account the coefficient α, depending on the position of the neutral axis of the cross section of the span, and then calculate the flexural stiffness EI in the middle of the span, taking into account the actual operational condition, moments of inertia I and resistance W at the upper and lower edges of the span , stress from own weight then the total stresses σ ⁿ , σ ⁱⁿ are compared with the calculated values of the materials of the upper and lower edges R ⁿ , R ⁱⁿ , and the deflection f with the permissible deflection [f _add ].

The main problem of the prototype is the unreliable assessment of the bearing capacity of a continuous type span structure, since the influence of the continuous span structure system on the angle of rotation of the supporting section, measured using sensors for measuring angular displacements, is not taken into account, and there is also a safety threat to both the span structure itself and the trial load with a driver in cases where the mass of the test load will be higher than the current bearing capacity of the span.

The objective of the invention is to eliminate the shortcomings of the prototype.

The technical result of the proposed invention is to provide the possibility of creating a method for quickly determining the possibility of passing an excess load on a span structure, which increases the reliability of its determination and the safety of the span structure, the excess load and its driver.

The essence of the proposed method for quickly determining the possibility of passing excess load on a span is as follows.

Initially, using a sensor for measuring angular displacements, the angular deviations θ of the supporting section of the span are measured under the influence of a test load on it, located on the span in a position corresponding to the maximum bending moment from it, the deflection from the test load in the middle of the span, the permissible deflection and the maximum stresses in the lower and upper edges, while a load with a mass corresponding to the standard one is used as a test load, the deflection from the test load f _npo6 is calculated taking into account the rotation angle coefficient δ, which takes into account the influence of the span system on the angular deviations θ, the deflection from the excess load is determined by calculation using the product of the deflection from the test load by the ratio of bending moments from the excess load to the test load, and the maximum stresses in the lower and upper edges are calculated from the excess load, followed by their comparison with the calculated values of the materials of the lower and upper edges, and the deflection from the excess load is compared with the permissible deflection.

In a particular case, the deflection from the test load is calculated according to the dependence:

l - span length.

In a particular case, the rotation angle coefficient δ is taken depending on the static system of the span and the position of the sensor for measuring angular displacements on it: for split spans - 1.0; for the left edge of continuous spans on one support (first and last span) - 0.77; for the right edge of continuous spans on one support (first and last span) - 0.54; for continuous spans on two supports - 0.36. Implementation of the invention.

Initially, a sensor for measuring angular displacements, for example, an inclinometer 2, is installed on the tested span 1 (see Fig. 1) from one of its edges, and its position is aligned relative to the earth's horizon, while the test load 3, with a mass corresponding to the normative one for its passage on the test span 1 and the excess load 4, the possibility of passing which is to be determined, is located outside the span 1. After that, the position of the test load 3 on the span 1 is determined, at which there will be a maximum bending moment M _{of tests} from it on the span 1 s using, for example, the construction of the line of influence 5 (see Fig. 2) with the calculation of the ordinates Y _i 6 of the axes of the test load 3 and the bending moment M _{of tests} from it along the entire length of the span 1 with a given calculation step, for example, every 10 cm, followed by selecting its maximum value according to the dependencies:

M _samples =P _i ^⋅ Y _i ^⋅ β,

where: Y _i - ordinate 5 of the line of influence of the 4 i-th load axis;

S _i - distance from the original support to the i-th axis of the load;

- length of the span;

P _i - load on the i-th axis;

β is the coefficient of continuity of the span.

Then, similarly to the calculation of the maximum bending moment from a test load of 3 M _samples , the maximum bending moment from an excess load of 4 M _st is calculated.

After which the test load 3 (see Fig. 3) is placed on the span of the structure 1 in a position corresponding to the maximum bending moment from it M _tests , the angular deviations 7 of the reference section of the span 1 are measured using an inclinometer 2, recording their average value and determined by the calculated by deflection f _npo6 in the middle of the span 1, taking into account the rotation angle coefficient δ, taking into account the influence of the span system 1 on the angular deviations 7, according to the dependence:

θ - angular deviations 7.

In this case, the rotation angle coefficient d is taken depending on the static system of the span 1 and the position of the angular displacement measuring sensor 2 on it:

for split spans - 1;

for the left edge of continuous spans on one support (first and last span) - 0.77;

for the right edge of continuous spans on one support (first and last span) - 0.54;

for continuous spans on two supports - 0.36.

Then, by calculation, the deflection f _St in the middle of the span 1 from the excess load is determined according to the dependence:

After this, the stresses from the excess load 4 are determined by calculation for the lower and upper edges in the center of the span 1 according to the dependencies [2]:

where: α is a coefficient depending on the position of the neutral axis of the span;

ρ-coefficient depending on its loading pattern (test load is reduced to an equivalent uniformly distributed load ρ=48/5=9.6);

h is the height of the beams of the bridge superstructure;

E ⁿ , E ⁱⁿ - elastic moduli of the material of the lower and upper edges, respectively, kgf/cm ² .

Next, the flexural stiffness EI in the middle of span 1 is calculated taking into account the actual operational state according to the dependence:

The moment of inertia for the lower and upper edges in the center of the span of any structural materials is determined by the dependencies:

The moment of resistance for the lower and upper edges in the center of the span is calculated according to the dependencies:

Next, the stress from its own weight is determined for the lower and upper edges in the center of the span 1 using the formulas:

The field of this is determined by the total voltage according to the formula:

The total stresses are compared with the calculated resistance of the materials of the lower and upper edges, and the deflection is compared with the permissible:

where: R ⁿ , R ⁱⁿ - design resistance of the material of the lower and upper edges, respectively, kgf/cm ² ;

[f _add ] - permissible deflection determined by calculation according to the dependence:

If all inequalities are met, the passage of excess load 4 along the span 1 is allowed at a speed that ensures the elimination of dynamic vibrations of the span 1 during its passage. If the stress or deflection in the center of the span 1 is exceeded compared to the calculated resistances and permissible deflection, the passage of the excess load 4 through the span 1 is prohibited.

The technical result of the proposed invention, which consists in providing the possibility of creating a method for quickly determining the possibility of passing an excess load on a span structure, which increases the reliability of its determination and the safety of the span structure, the excess load and its driver, is achieved due to the fact that by taking into account the influence of the static system of the span structure on the angle of rotation supporting section, measured using an angular displacement sensor, as well as the absence of the need to impose an excess load on the span in order to assess the possibility of its passage.

Examples of achieving a technical result are tests carried out by the authors in 2022:

1) with reinforced concrete beams of the span of a split-type road bridge on the river. Volkovitsa in the Kirov region, as a result of the operational implementation of which the passage of excess load was prohibited due to the excess of the deflection in the middle of the span from the excess load, determined by calculation using measurements of the angular deviations of the supporting section of the span from the test load, the permissible deflection, thereby the safety of both the span itself and the excess load with its driver is preserved;

2) with metal beams of the span structure of a continuous-type overpass across the railway on the bypass of Kaluga on the Annenki-Zherelo section, as a result of the operational implementation of which the reliability of determining the possibility of passing excess load was increased by 40-50% due to taking into account the influence of the static system of a continuous span on angular deviations of the reference section measured using an inclinometer.

Thus, the claimed method provides the possibility of creating a method for quickly determining the possibility of passing an excess load on a span, which increases the reliability of its determination and the safety of the span, the excess load and its driver.

Literature:

1. Sekulovich M. Finite element method. - Moscow: Stroyizdat, 1993, 661 p.

2. Design of bridges and building structures: textbook / Salamakhin P.M. - Moscow: KNORUS, 2010, 402 p.

Claims (5)

1. A method for quickly determining the possibility of passing an excess load on a span structure, characterized by the fact that initially, with a sensor for measuring angular displacements, the angular deviations θ of the supporting section of the span structure are measured under the influence of a test load on it, located on the span structure in a position corresponding to its maximum bending moment on the span structure, the deflection from the test load in the middle of the span, the permissible deflection and maximum stresses at the lower and upper edges are calculated, characterized in that a load with a mass corresponding to the standard is used as a test load, the deflection from the test load f _{of the samples} is calculated taking into account rotation angle coefficient δ, which takes into account the influence of the span structure system on the angular deviations θ, the deflection from the excess load is calculated by multiplying the deflection from the test load by the ratio of bending moments from the excess load to the test load, and the maximum stresses in the lower and upper edges are calculated from the excess load followed by by comparing them with the calculated values of the materials of the lower and upper edges, while the deflection from excess load is compared with the permissible deflection. 2. The method according to claim 1, characterized in that the deflection from the test load is calculated according to the dependence: where l is the span length. 3. The method according to claim 2, characterized in that the rotation angle coefficient δ is taken depending on the static system of the span and the position of the sensor for measuring angular displacements on it: for split spans - 1.0; for the left edge of continuous spans on one support, the first and last spans are 0.77; for the right edge of continuous spans on one support, the first and last span is 0.54; for continuous spans on two supports - 0.36.