RU2161788C2 - Method of nondestructive test of load-carrying capacity of building constructions - Google Patents

Abstract

FIELD: civil engineering. SUBSTANCE: method is intended for building constructions such as beams, girders, frames, etc made of materials and systems characterized by linear dependence. Places of maximum linear or angular displacements are determined in construction. Constructions is loaded by mechanical load which does not exceed limiting value. Loading is performed at one and the place in not less than three different steps of loading by 5-10 times. Construction strength is determined with due regard for average values of displacements at linear dependence between load and displacement. EFFECT: enhanced accuracy of determination. 3 dwg

Description

 The invention relates to non-destructive testing of the bearing capacity of building structures.

 This invention is applicable to building structures and cranes, for example beams, trusses, frames and so on, from materials and systems with a linear relationship between the load and the movement of the structure.

 The purpose of the invention is to increase the accuracy of determining the bearing capacity of a structure, the measure of which is the value of the ultimate load, which causes the ultimate angular or linear displacements.

 A known method of non-destructive testing of the strength of the product (see A.S. USSR N 606124, class MPK G 01 N 3/00, 1976), which consists in the fact that the products are loaded with a variable load not exceeding its limit value, determine the location of the maximum deformations, excite elastic vibrations in these places and determine the deformations in them, and by the formulas establish the strength of the structure.

 The disadvantage of this method is the high complexity, applicability only for products made of polymeric material, the method is not applicable for structures in operation.

 To obtain a more accurate result, the maximum possible load is required, the operational load must be removed from the structure.

 Closest to the invention is a method of non-destructive testing of the bearing capacity of structures of a patent (see N 2006814, class MKI 5 G 01 N 3/00, 1991), which consists in the fact that places with possible maximum deformations (angular or linear displacements), in these places the structure is loaded with a mechanical load that does not exceed the limit value calculated theoretically, a constant load is applied in the same place 5-10 times, the deformation values are determined and a trust is found interval of these values. Then, a graph is plotted between the load and the displacement at two points (at the origin and at the coordinates of the experimental load, the displacement from this load). Then, through the points of the confidence interval, direct - confidence boundaries are drawn, parallel to the direct dependence of the load on displacement. According to the schedule, the maximum load is found.

The disadvantage of this method is the low accuracy and unreliability of the results, due to the fact that the confidence limits are drawn along one point of the confidence interval parallel to the direct dependence of the load on the movement
The aim of the invention is to improve the accuracy of determining the bearing capacity of building structures. This is achieved by the fact that the design determines the location of the maximum possible linear or angular displacements, in these places the structure is loaded with a test mechanical load that does not exceed its limiting value in terms of strength and rigidity of the structure and the maximum displacements are determined, while the structure is loaded in the same place 5-10 times, loading is carried out not less than at three different load levels, according to the results of three average values of displacements and corresponding loads, they build a straight line dependence of the load on the displacement, determine at least three confidence intervals for measuring displacements, at the points of which build the confidence boundaries of the measured displacements, and the structural strength is determined taking into account the average values of displacements with a linear relationship between load and displacement.

 In FIG. 1 shows a graph of the dependence of the load on displacement, 00 'with confidence limits 1-2-3-4 and 1'-2'-3'-4', in FIG. 2 is a graph of load versus displacement for a floor beam, in FIG. 3 is a design diagram of a floor beam. The ordinate value O 'corresponds to an abscissa equal to the limiting standard value of displacement.

 The method is as follows. The places of greatest possible displacements are determined, for example, in the middle of the beam span, displacement meters are installed in these places. If it is not possible to install devices in these places, then they can be installed in another place, with the subsequent transfer of measurements (theoretically) to the value of the movements of the places of greatest displacements. Apply the first stage of the load (unloading) and determine the movement, repeating the operation 5-10 times.

 The number of loads was chosen n = 5-10 times, since for n <5 the displacement value noticeably statistically changes, and for n> 10 there are practically no statistical changes in displacement value (P. Okulov. Determination of the design resistance of steel in operated structures. Construction and architecture. 1990, N 3, p. 112, 113).

и доверительные интервалы по формуле,

где S_i, - среднее квадратическое отклонение, t - коэффициент Стьюдента, n - число измерений, i = 1, 2, 3.Then calculate the average value

and confidence intervals according to the formula,

where S _i , is the standard deviation, t is the student coefficient, n is the number of measurements, i = 1, 2, 3.

 The resulting points are laid in the coordinate axes (F-Δ). Such an operation is carried out at least two more times with other values of the load.

 If the load cannot be applied at the place of greatest displacements, then it can be applied at another place, followed by recalculation of its value (theoretically) for the case of application at the place of greatest displacements. Based on the obtained points of the average displacement values, the F-Δ graph is plotted, and the confidence boundaries are plotted at the points of confidence intervals (1, 2, 3 and 1 ', 2', 3 ').

На пересечении доверительных границ с прямой, параллельной оси абсцисс Δ и проходящей через точку 0', находят доверительный интервал 4-4'. Из точки 4 опускают вертикаль (см. фиг. 1) до пересечения с нижней доверительной границей 1'-2'-3' и из точки пересечения проводят горизонталь до пересечения с осью нагрузки F. По точке пересечения находят предельную нагрузку F_пр, при необходимости любую другую ей эквивалентную по воздействию (теоретически).Find the point 0 'at the intersection of the straight line of the average displacement values and the values of the loading steps with the ordinate drawn through the value of the maximum maximum normative displacement. For example, for a beam

At the intersection of confidence boundaries with a straight line parallel to the abscissa axis Δ and passing through point 0 ', a confidence interval of 4-4' is found. From point 4, lower the vertical (see Fig. 1) to the intersection with the lower confidence boundary 1'-2'-3 'and from the intersection point draw a horizontal line to the intersection with the load axis F. At the intersection point, find the ultimate load F _CR , if necessary any other equivalent effect (theoretically).

 Example. Determine the load capacity of the beam from the I-beam N 20, with a span of l = 6 m, under a load q - uniformly distributed along the entire length. The theoretical ultimate load is 32 kN.

Прикладываем нагрузку F_i в середине балки и измеряем перемещение - прогиб f_i в середине пролета индикаторами часового типа. По результатам испытаний получены следующие значения средних прогибов f_i, и их доверительных интервалов Δf_i.
F₁ = 3,2 кН; f₁ = 4,0 мм; Δf₁ = 0,10 мм;
F₂ = 6,4 кН; f₂ = 8,6 мм; Δf₂ = 0,22 мм;
F₃ = 9,6 кН; f₃ = 11,4 мм; f₃ = 0,40 мм.

We apply the load F _i in the middle of the beam and measure the displacement - deflection f _i in the middle of the span with dial gauges. According to the test results obtained the following values of the average deflections f _i , and their confidence intervals Δf _i .
F ₁ = 3.2 kN; f ₁ = 4.0 mm; Δf ₁ = 0.10 mm;
F ₂ = 6.4 kN; f ₂ = 8.6 mm; Δf ₂ = 0.22 mm;
F ₃ = 9.6 kN; f ₃ = 11.4 mm; f ₃ = 0.40 mm.

The graphic part is shown in FIG. 2. From it we find F _CR = 15.3 kN. From the equality of bending moments:
F l _pr / _pr 4 = q l ^2/8 we find q = 2F _{pr pr} / l = 2 · 15.3 / 6 = 5.1 kN / m.

 Thus, loading is carried out several times. The first load by value takes (10-20)% of the ultimate load, determined theoretically, the second (20-30)% of the maximum, the third (30-40)% of the maximum load. Such loads are carried out for at least three different load levels. If the structure cannot be loaded due to the safety or because of the operational load, then it can be unloaded by applying the load in the opposite direction compared to the operational one, while the maximum value of the unloading stage should not exceed the value of the operational load.

 According to the results of each stage of loading, the average displacement value and confidence intervals of measurements are found. At least three points of average values and values of confidence intervals conduct direct graphs of the dependence of the load on displacement and confidence limits.

Claims (1)

 The method of non-destructive testing of the strength of building structures, which determines the places of possible maximum linear or angular displacements, in these places the structure is loaded with a test mechanical load that does not exceed its limit value in terms of strength and rigidity of the structure and the values of maximum displacements are determined, while the structure is loaded in one at the same place 5-10 times constant in value by mechanical load, characterized in that the loading is carried out not less than when at different load levels, based on the results of three average displacements and the corresponding loads, a direct dependence of the load on displacement is constructed, at least three confidence intervals of displacement measurements are determined, at the points of which the confidence limits of the measured displacements are built, and the structural strength is determined taking into account the average displacements with linear dependencies between load and displacement.

Images