Method for experimental determination of static-dynamic characteristics of concrete

FIELD: construction.

SUBSTANCE: method is realised by fixation of an experimental concrete sample in the form of a prism in clamps of a test bench using an alignment device, providing for central application of stretching load in process of loading, and registration of a force and deformations of the sample in time using a dynamometer and a strain gauge station during loading executed via a lever system in two stages: at the first stage - stepped static loading of the sample to the specified level by means of laying of piece weights onto a load platform, at the second one - instant or stepped dynamic additional loading or unloading by means of short-term variation of the axis diameter in the point of force transfer from the lever to the compensating element, setting, if necessary, the value of movements in the elastic element.

EFFECT: simplified methodology and increased validity and reliability of test results.

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The invention relates to the construction, in particular to the determination of the parameters of deformation of concrete under static loading concrete samples to a level not exceeding the ultimate strength of the concrete in compression Rband tensile Rbt, dynamic loading to failure with a constant velocity and dynamic loading unloading.

Design of reinforced concrete structures are based static application of the load and further its impact, while using prism strength of concrete as determined during phase (degrees) loading concrete samples using press [1]. The disadvantage of this method is the relatively low loading rate of concrete prisms, which does not allow to judge about the deformation of the specimen under high-speed loading. Determination of strength of concrete in tension is carried out using a tensile machine, which also allows to obtain the characteristics of the deformation of the sample under high speed loading.

In the calculation of reinforced concrete structures to explosive and impact loading using the values of ultimate strength and ultimate strain of concrete samples defined at the moment of their destruction when dynamic loading is not superior to the similar value found during static tests�Oia.

One of the solutions that allow the testing of concrete to dynamic loading is the pneumodynamic installation for high-speed loading of concrete prisms [2].

The disadvantage of this solution is the inability to create a certain level of static loading, the previous high-speed loading of the concrete prism.

The closest solution to the claimed invention is a method for experimental determination of the static-dynamic charts of concrete, in which the instantaneous speed or dynamic loading case is falling with decreasing current in the electromagnet load [3].

The disadvantage of this solution lies in the inconvenience of the necessity of the presence of electromagnetic systems; the inability of the implementation of dynamic load cases on a predetermined displacement; in the impossibility of achieving the deformation of the sample during high-speed unloading to a preselected value different from the value of pogrujeniya; the inability to repeated dynamic loading of the sample in alternation with unloaded; in high error obtained in the experiment data.

The technical result of the invention is to facilitate the testing method, improving the accuracy of the obtained data, empowerment of experimentalgameplay static-dynamic properties of concrete, consisting in the possibility to pre-set displacement in kompensirujushhego element under dynamic loading and unloading.

The technical result is achieved in that in the method of experimental determination of static-dynamic characteristics of concrete, which consists in securing an experienced concrete sample in the form of a prism in the clamps of the test bench using a centering device which provides a Central load application in the process of loading, and registration efforts and deformations of the prism in time by using the dynamometer and tantostanze, according to the invention the loading is performed via a lever system in two stages: first - stage static loading of the specimen to a predetermined level by laying a piece of cargo on the cargo platform, the second is the instantaneous speed or dynamic loading case or unloading by short-term changes in the diameter of the axis at the connection of the lever and the compensating element.

Fig.1A presents a diagram of the device for implementing the proposed method in a tensile test. Fig.1B is a diagram of a device for compression testing. Fig.2A is a diagram of the offset axis in the implementation of dynamic loading in a tensile test. Fig.2B is illustrated a method of IP�of itania sample in case when a pre-set displacement in kompensirujushhego element under dynamic loading. Fig.3 is a diagram of the loads acting on the lever when a tensile test.

Specially designed installation comprises a frame 1, the device for centering and gripping of the specimen 2, the lever 4 to be transmitted to the test specimen 3 is connected through a rack 5 with the frame 1, the compensating element 6 resting on a base frame 1 and connected with the lever 4 through the axis 7, the metal ball 10, the bolt 9, the load platform 8 for the application of the static load, piece goods 11 and nut 12.

A compensating element 6 represents a spring or a torque ring, the rigidity of which is determined in advance by calibration.

The axis 7 is a metal rod with different diameter cross sections. At half the length of the rod is threaded for the nut 12.

The diameter of the hole in the lever 4 exceeds the larger diameter section of the axle 7. A larger diameter section of the axle 7 exceeds its smaller diameter section to a maximum amount of movement of the lever 4 along the axis of the compensating element 6 at the time dynamic loading and unloading.

Metal ball 10 and the different diameters of the cross section axis 7 necessary to implement drastic dynamic loading and unloading of the sample 3. Nut 12 �of neobhodimo for to test the axis 7 is not shifted further pre-defined value.

The bolt 9 is required to restrict movement of the metal ball 10 at the moment of fast loading and unloading at offset axis 7, i.e. at the time of decrease or increase of the diameter of the cross section axis 7 under the balloon 10.

The method is as follows.

Loading is carried out via a lever system in two stages. In the first stage, create stress in kompensirujushhego element 6 by means of the stacking unit loads 11 to the load platform 8. When the ball 10 rests on the axle 7 in place of a larger cross-section axis. In the second stage, fix the specimen 3 in the 2 clips, then move the axis 7 so that the ball 10 turned out to be over a smaller cross-section axis, wherein the load acting on the compensating element 6, abruptly jumps to the sample 3 through the lever 4, by dynamic loading of the concrete sample. If the movement of the lever 4 should be set in advance, used the nut 12.

Further displacement of the axis 7 will increase the diameter of the axle under the ball 10 and the removal of the load from the test sample.

In the process of testing a dynamometer to measure the force acting on the prism, and the parameters of deformation of the prism under static loading and dynamic loading case are measured by means of tantostanze with a built-in ten�hosilities, for connecting the load cells without the use of intermediate amplifiers, and having the ability when connected to the computer and use specialized software to record and display the converted signals of multiple input channels depending on time.

In the case of static loading in a tensile test the load acting on the sample, is determined by the formula:

N=P(l-a)-Kba,

where P is the applied load; K is the force in kompensirujushhego element; l is the length of the lever 4; a, b - distance from the rack 5 to the sample 3 and the elastic element 6, respectively.

In the case of dynamic loading is a sharp redistribution of the load compensating element 6 on the sample 3.

Examples

The tensile test samples were subjected to a rectangular shape, length 16 cm, height 4 cm and width 4 cm, made of fine concrete B20 with ratio W/C=0,741, C/N=1:to 3.789.

The distance from the sample to the column 5 a=0.1 m =100 mm from the rack 5 to the axis of the compensating element b=0.1 m =100 mm, the length of the lever 4 l=0.6 m =600 mm. elements of the communication efforts made of PT.3.

1) the Loading platform P=200 H. Napr�CAD on compensating element was K=1000 N, the deformation of the compensating element is equal to 0.2 mm. After fixing the specimen in the clamps of the stand shifted the axis 7. The compensating element is unloaded, K=0 N. Dynamic loading of the sample was N=1000 H, elongation of the sample was 0.2 mm.

2) the Loading platform P=100 H. Load compensating element amounted to K=500 N, the deformation of the compensating element is 0.1 mm. Fix the specimen in the clamps of the stand. Load the platform up to P=200 N. The total deformation of the elastic element was 0.16 mm, the deformation of the sample was 0.06 mm (static loading). Forces in the elastic element is equal to 800 H, the sample was 200 H. Displace the axis 7, reducing its diameter. Efforts in the sample was 1000 H (dynamic loading case), efforts in kompensirujushhego element become equal to 200 H. Deformation in the sample was 0.16 mm. With a sharp displacement of the axis 7 in the direction of increasing the diameter of the section's efforts in the sample amounted to 200 H (unloading), the deformation of the sample was 0.06 mm, while efforts in kompensirujushhego element become equal to 800 H.

From the examples it is seen that through the use of axis with different diameters of the cross sections, the deformation of the specimen during sudden loading of a given size. Achieved technical result: the possibility of multiple dynamic loading of the sample in alternation with the unloading, achieved high �echnosti obtained in the experiment data.

1. The state standard 24452-80 Concretes. Methods for determination of prism strength, modulus of elasticity and Poisson's ratio. - M.: NEIGBD. 1982. - 15 p.

2. Bazhenov. Y. M. Concrete under dynamic loading. - M.: Stroiizdat, 1970. - 272.

3. RF patent №2482480, CL G01N 3/00, 2006.

Method for experimental determination of static-dynamic characteristics of concrete, which consists in securing an experienced concrete sample in the form of a prism in the clamps of the test bench using a centering device which provides a Central load application in the process of loading, and registration efforts and deformations of the prism in time by using the dynamometer and tantostanze, characterized in that the loading is performed via a lever system in 2 stages: first - stage static loading of the specimen to a predetermined level by laying a piece of cargo on the cargo platform, the second is the instantaneous speed or dynamic loading case or unloading by short-term changes in the diameter of the axis at the connection of the lever and a compensating element, specifying, if necessary, the magnitude of the movements in this item.



 

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