RU2578662C1 - Method of testing building structures for bending with torsion at static and dynamic short-term action - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention can be used during testing of structures and separate elements of buildings and structures operated at bending with torsion at static and dynamic short-term action with determination of accurate deformation of, for example beams or slabs. First test specimen is installed on rigid supports. In specified places on the tested sample is fixed arm with oppositely directed lengths, on the overhangs of pull head distribution traverses ends are placed. Via distribution crossbar test specimen is loaded and its strain state is studied which is caused by simultaneous bending and twisting under load, fixing movement in sections of the tested sample. Strain state of the tested sample is assessed by absolute value of vertical deflections of the tested sample and absolute angle of twisting of the tested sample, that simultaneously on both sides from longitudinal axis of the tested sample near each of pull head and symmetrically relative to longitudinal axis of the tested sample is set deflection indicators, by means of which the vertical displacement of opposite sides of the tested sample under preset load, wherein each deflection indicator is installed with possibility of providing strictly vertical position of movable stock and the absolute vertical deflection f_PR in the considered section of the tested sample is determined by formula.

EFFECT: technical result is possibility of determining absolute values of angle of twist and vertical deflection structure operated at bending with torsion, which enable to determine the exact circuit deformation element under complex VAT.

4 cl, 1 tbl, 9 dwg

Description

The invention relates to the field of construction and can be used in testing structures and individual elements of buildings and structures working on bending with torsion under static and short-term dynamic effects, with the determination of the exact deformation model of the structure, for example beams or plates.

A known method of testing the structure for impact according to the patent of the Russian Federation on utility model No. 61881. According to the method, the reinforced concrete element is mounted on supports, one end of the element is tightly put on a headband with a lever for accepting shock load and a bearing, and the second end of the reinforced concrete element is rigidly fixed in a metal shoe. An integral acceleration sensor is attached to the end of the reinforced concrete specimen from the head end, connected to a measuring and computing complex. Torque is created by dropping a load of a certain mass from a given height onto a lever attached to the headband. Information about the angle of rotation of the element simultaneously with its rotation and without interference is recorded using an integrated acceleration sensor fixed to the end of the reinforced concrete element.

This test method allows you to judge the angle of rotation of the structure under the action of torques on it. However, the information obtained using the integrated acceleration sensor does not accurately determine the value of the angle of rotation of the reinforced concrete element due to the fact that the acceleration vector of the point lying on the surface of the sample contains both horizontal and vertical components. The use of an integral sensor when testing a reinforced concrete element, which simultaneously perceives bending and torques, is unacceptable due to the inability to distinguish torsion-induced deformations from this sensor from bending deformations, which have a significant effect on the final deformation model of the element.

The prototype of the claimed invention is a method of testing concrete elements for bending with torsion under static pressure using a hydraulic jack (Vishnu N. Jariwala, Paresh V. Patel, Sharadkumar P. Purohit. Strengthening of RC Beams fully to Combined Torsion and Bending with GFRP Composites. Procedia Engineering, 2013, No. 51, 282-289), namely, that the reinforced concrete element is tested for bending moment due to the application of two vertical forces perpendicular to its longitudinal axis and for the influence of two multidirectional torques arising from the presence of eccentricities of the application of vertical forces. To ensure such a test scheme, a reinforced concrete element is mounted on rigid supports. In predetermined places on the reinforced concrete element fix the headband. On the departures of the head-ends, directed in opposite directions, a distribution beam is installed, through which the reinforced concrete element is loaded. Moreover, the method involves the installation of indicators with wire connection, designed to measure the movements of departures of the head-end, to which the load is applied through the distribution beam during testing. According to these movements, one can judge the intensity of twisting of reinforced concrete elements.

The application of the method allows you to recreate in reinforced concrete elements stress-strain state (VAT), close to the VAT of reinforced concrete structures operating in bending with torsion. The disadvantage of this method is that the method cannot be applied when testing the design for short-term dynamic effects. From the measured displacements of the cantilever beams, it is impossible to judge the absolute value of the bend and the absolute value of the twist angles of the structure due to the presence of both vertical and horizontal components of the displacements that are not taken into account in the prototype. In this regard, the reliability of the results and the accuracy of determining the VAT of a reinforced concrete element when exposed to a load are reduced. In addition, the use of indicators with wire connection when testing for exposure to short-term dynamic load is not possible due to the transience of the processes, which narrows the scope of research.

The objective of the invention is to test structures for bending with torsion with the determination of reliable absolute values of torsional and bending strains when exposed to static and short-term dynamic loads.

The technical result consists in determining the absolute values of the angle of twist and vertical deflections of the structure, working on bending with torsion, which allow us to determine the exact scheme of deformation of the element, which is in conditions of complex VAT.

The method of testing building structures for bending with torsion under static and short-term dynamic effects has in common with the prototype that first the test specimen is mounted on rigid supports and in the specified places on the test specimen are mounted goggles with opposite projections. As in the prototype, the ends of the distributing crosshead are placed on the departures of the headbands, then the test specimen is loaded through the distributing crosshead and its deformed state is investigated, which is caused by simultaneous bending and torsion under the influence of the load, fixing movements in the sections of the test specimen.

In contrast to the prototype, the deformed state of the test sample is evaluated by the absolute value of the vertical deflections of the test sample and the absolute twist angle of the test sample. According to the claimed method, simultaneously from two sides of the longitudinal axis of the test sample near each of the head-ends and symmetrically relative to the longitudinal axis of the test sample, deflection gauges are installed and the vertical displacements of opposite sides of the test sample are measured under the influence of a given load. Each deflection meter is installed with the ability to ensure strictly vertical position of the movable rod. The absolute vertical deflection f _CR in the considered section of the test sample is determined by the formula:

,

,

where f _max and f _min are the values of the vertical displacements of the opposite sides of the test sample, respectively, the maximum and minimum,

while the total absolute twist angle φ of the test sample is determined by the formula:

φ = φ ₁ + φ ₂ ,

Where

φ ₁ - the absolute angle of twist of the test sample at one end of the sample near the headband;

f _{max, 1} and f _{min, 1} are the values of the vertical displacements of the opposite sides of the test sample, respectively, the maximum and minimum, at one end of the test sample near the headband;

φ ₂ is the absolute twist angle of the test sample at the second end of the sample near the headband;

f _{max, 2} and f _{min, 2} are the values of the vertical displacements of the opposite sides of the test sample, respectively, the maximum and minimum, at the second end of the test sample near the headband;

L is the distance from the longitudinal axis of the test sample to the axis of the deflection meter.

It is possible to ensure a strictly vertical position of the moving rod of the deflection meter with its free fixing at the upper point as follows: close the beam to the test specimen perpendicular to its longitudinal axis to secure the beam, ensuring the same projections of the ends of the beam over the side face. On the beam with the ability to move along it, install carriages, and move the movable rods to the carriages pivotally. The bases of the deflection meters are fixed rigidly on the force floor. The test sample is loaded with a static load, as in the prototype method, or with a short-term dynamic load.

The formula for determining the twist angle of an arbitrarily selected section of an element subject to bending with torsion is obtained from the geometric properties of a right triangle with the following assumptions. As you know, structures working on bending with torsion move in space under the action of two force factors, and in order to reliably determine the movements caused by torsion, it is necessary to separate them from the movements caused by the bending of the structure. This can be done by averaging the total displacements of two points taken on opposite sides of the sample and located in the same plane of its cross section. Then the movement of the sample from the action of the bending moment will be defined as:

where f _CR - structural displacement (deflection), due to the action of the bending moment;

f _max , f _min - the values of the vertical displacements of two points taken on opposite sides of the sample and located in the same plane of its cross section (design section).

The movement of the sample arising from the action of the torque can be determined taking into account the formula (1) as follows:

Now, knowing the horizontal displacement of the sample, using the well-known properties of a right-angled triangle, taking into account formulas (1) and (2), you can determine the angle of the triangle using known legs, which in turn will be the twist angle of the sample in the calculated cross section under consideration:

where L is the distance from the longitudinal axis of the reinforced concrete element to the axis of the deflection meter.

Determination of the full twist angle by this method involves the device of two nodes for determining the twist angle located in sections experiencing maximum torsion. Due to the fact that the load is transferred to the structure through the departures of the head ends directed in different directions, the building structure will be subjected to simultaneous bending and torques, and accordingly it will experience deformations due to two force factors: the bending of the structure and the multidirectional torsion of the two halves of the structure due to the action opposing torques. Accordingly, the full twist angle of the structure will be defined as the sum of the twist angles of both parts.

According to the above formulas, the calculation of the twist angle and deflection of the considered section is performed. It should be noted that this test method allows you to determine the change in the twist angle and deflection of the calculated cross-section at all stages of loading the sample. Moreover, the use of electronic deflection meters, for example, WayCon type SL50-G-SR, allows one to determine the twisting angles and deflection of the sections under consideration when a short-term dynamic load is applied to the sample.

The application of this method, in contrast to the prototype, allows us to determine not only the strength characteristics of the studied samples, but also the qualitative and quantitative value of the displacements arising under the influence of two force factors: bending with torsion. Methods are not known in the art that make it possible to directly or indirectly determine the twist angle of a structure under short-term dynamic action, as well as reliably determine the deflection of a structure during its complex deformation. The application of this method allows you to track changes in the rotation angles and deflection of the structure over the entire time interval of its loading, regardless of its transience.

The specified set of technical features characterizing the claimed method was obtained for the first time and is not found in the known technical solutions, which confirms the novelty of the invention. The invention meets the condition of an inventive step, since the explicitly proposed technical solution does not follow from the prior art.

The invention is industrially applicable, since it can be repeatedly used when testing building elements or structures of buildings and structures.

The invention is illustrated by drawings.

In FIG. 1 shows a stand for testing a reinforced concrete element for bending with torsion under short-term dynamic loading (photo).

In FIG. 2 shows a stand for testing a reinforced concrete element for bending with torsion under static loading (photo).

In FIG. Figure 3 shows the option of attaching the deflection meters to the building structure.

In FIG. 4 shows the option of attaching the deflection meters to the force floor.

In FIG. 5 shows a model of a test bench for the effects of bending and torque during short-term dynamic loading before applying the load.

In FIG. 6 is the same as in FIG. 5, but after application of the load.

In FIG. 7 is a schematic diagram of the operation of a device for determining the twist angle of one of the parts of the test sample.

In FIG. Figure 8 shows graphs of the dependence of the twist angle φ ₁ and φ ₂ on the magnitude of the applied load P for each design section.

In FIG. 9 is a graph of the dependence of the total twist angle φ on the magnitude of the applied load P obtained by adding the curves in FIG. 8.

The method is as follows.

As an example of the application of the proposed method, the test of a reinforced concrete element with a cross section b × h = 200 × 100 mm 2000 mm long for the action of bending and torque under short-term dynamic loading is considered.

First, as in the prototype, the reinforced concrete element 1 is installed on the supports 2, at the specified places ogolovniki with levers 3 are mounted, at the ends of the ogolovniki installed distribution beam 4, which transfers the load to the ogolovniki 3. In this case, the applied load can be static and can be created using hydraulic equipment providing the required pressure (impact) on the distribution beam (Fig. 2), or short-term dynamic due to the transfer of increasing energy falling on the distribution grass RSU cargo (Fig. 1).

After assembling the test bench (Fig. 1, Fig. 2), a device for measuring the twist angle of the structure is made in two previously calculated design sections. The bases of the electronic deflection meters 6 are rigidly fixed on the force floor (Fig. 4). On each of the two halves of the structure in close proximity to the arm of the headband, a beam 5 (Fig. 3) is installed symmetrically with respect to the central axis of the element in its transverse direction, having the same projections beyond the edge of the reinforced concrete element. To the beam 5 at the same distance from the longitudinal axis of the element are attached the rods of electronic deflection meters 6 connected to the measuring system. In this case, the connection of the rods to the beam should exclude horizontal movement of the rod together with the beam when it is rotated. In this particular example, this is accomplished by hinging the rod on a movable carriage 7, capable of moving freely along the length of the beam.

Next, the sample is loaded by dropping the load onto the distribution beam, as a result of which the reinforced concrete sample bends under the action of the applied load and experiences intense torsion due to the presence of the eccentricity of the load application (Fig. 6). Electronic deflection meters 6 record the change in the position of points located on the beam 5, throughout the duration of the load.

The principle of operation of the device for measuring the angle of twist of the structure is as follows. On the beam 5 mounted on the sample 1, two points A and B are selected, located at opposite ends of the beam at the same distance from the longitudinal axis of the element O, where the rods of the electronic deflection meters 6 are installed. Under the simultaneous action of bending and torque sections of the sample change their position in space, and previously marked points are in position A ″ and B ″ (Fig. 7), respectively. These vertical displacements are recorded by the deflection meters and are the initial information f _max and f _min necessary and sufficient to determine the angle of twist of the sample and deflection in this section. The displacement data can be represented as the sum of the displacements caused by the action of the bending moment f _pr = AA ′ = BB ′ and the displacements caused by the action of the torques f _cr = A′A ″ = B′B ″. Then the movement of the sample from the action of the bending moment (deflection) will be defined as:

where f _CR - structural displacement (deflection), due to the action of the bending moment;

f _max , f _min - the values of the vertical displacements of two points taken on opposite sides of the sample and located in the same plane of its cross section (design section).

The movement of the sample arising from the action of torque can be determined as follows:

where f _cr - displacement of the structure due to the action of torque.

Knowing the horizontal displacements of the sample, using the well-known properties of a right-angled triangle, you can determine the angle of the triangle using known legs, which in turn will be the twist angle of the sample in the considered design section:

The full twist angle is defined as the sum of the twist angles of two different parts having torsional strains of the same sign along the entire length of the part:

φ = φ ₁ + φ _2,

where φ ₁ is the absolute twist angle of the test sample at one end of the sample near the headband;

φ ₂ is the absolute twist angle of the test sample at the second end of the sample near the headband.

Thus, by measuring the change in the position of two points of the calculated cross section in space, using the proposed method, it is possible to determine the deflections and twist angles for each cross section of the sample, as well as the full twist angle of the structure (Fig. 6, Fig. 9).

Define the full twist angle for the given example. During the tests, the displacements of the points f _{max, 1} , f _{min, 1} and f _{max, 2} , f _{min, 2} , pairwise located in the calculated sections 1 and 2 of the reinforced concrete element (from two opposite ends, near the head-ends), which are presented in table:

The calculations of the absolute vertical deflections of the reinforced concrete element for sections 1 and 2 are shown as an example for the maximum load achieved during the test of 39.24 kN, which is performed as follows:

Absolute torsion angles for design cross-sections, taking into account the distance from the central axis of the element to the design points:

And accordingly, the absolute (full) twist angle of the structure will be:

φ = φ ₁ + φ ₂ = 0.0122 + 0.0076 = 0.0198 rad.

Applying this method of calculating the twist angles for all points, one can obtain graphs of the dependence of the development of the absolute values of the twist angles on the load (Fig. 8, Fig. 9).

Thus, the claimed method allows to obtain a complete picture of the stress-strain state of the test sample from the effects of the load.

Claims (4)

1. A method of testing building structures for bending with torsion under static and short-term dynamic effects, according to which the test specimen is first mounted on rigid supports, at the specified places on the test specimen, head-ends with oppositely directed outlets are fixed, the ends of the distribution traverse are placed on the outriggers, then through distribution beam, the test specimen is loaded and its deformed state, caused by simultaneous bending and torsion under load, fixing the movement in the cross sections of the test sample, characterized in that the deformed state of the test sample is estimated by the absolute value of the vertical deflections of the test sample and the absolute twist angle of the test sample, for this simultaneously from two sides of the longitudinal axis of the test sample near each of the head-ends and symmetrically relative to the longitudinal axis of the test sample, deflection gauges are installed, with which the vertical displacements of opposite the sides of the test sample under the influence of a given load, and each deflection meter is installed with the ability to ensure strictly vertical position of the movable rod, and the absolute vertical deflection f _CR in the considered section of the test sample is determined by the formula:

where f _max and f _min are the values of the vertical displacements of the opposite sides of the test sample, respectively, the maximum and minimum,
while the total absolute twist angle φ of the test sample is determined by the formula:
φ = φ ₁ + φ ₂ ,
Where

φ ₁ - the absolute angle of twist of the test sample at one end of the sample near the headband;
f _{max, 1} and f _{min, 1} are the values of the vertical displacements of the opposite sides of the test sample, respectively, the maximum and minimum, at one end of the test sample near the headband;
φ ₂ is the absolute twist angle of the test sample at the second end of the sample near the headband;
f _{max, 2} and f _{min, 2} are the values of the vertical displacements of the opposite sides of the test sample, respectively, the maximum and minimum, at the second end of the test sample near the headband;
L is the distance from the longitudinal axis of the test sample to the axis of the deflection meter. 2. The method of testing building structures according to claim 1, characterized in that a beam is fixed perpendicular to its longitudinal axis near the headbands on the test specimen, ensuring the same projections of the ends of the beam over the side face, the bases of the deflection meters are fixed rigidly on the force floor, and their movable rods are pivotally connected with carriages mounted to move along the beam. 3. The method of testing building structures according to claim 1, characterized in that the test sample is loaded with a static load. 4. The method of testing building structures according to claim 1, characterized in that the test sample is loaded with a short-term dynamic load.

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