Method of experimental determination of static-dynamic characteristics of concrete under conditions of cyclic loading

FIELD: testing technology.

SUBSTANCE: invention relates to construction, in particular to determining the parameters of deformation of concrete under conditions of cyclic loading to a level not exceeding the tensile strength of concrete to compression Rb and extension Rbt. Essence: securing a test concrete sample in the form of a prism in the jaws of the test stand is carried out using a centring device which provides a central application of load during loading. The force and deformation of the prism in time is registered by using the dynamometer and the strain-gauge station. The multiple static or dynamic loading is performed by rotating and short-term changing the diameter of the axis in the place of junction of the lever and the compensating element.

EFFECT: simplification of the test method, expanding the functional capabilities of the experimental determination of the static-dynamic characteristics of concrete under conditions of cyclic loading, which consists in alternating application of static and dynamic loads on the sample.

4 dwg

 

The invention relates to the construction, in particular to the determination of the parameters of deformation of concrete under cyclic loadings to a level not exceeding the ultimate strength of the concrete in compression Rband tensile Rbt.

Design of reinforced concrete structures are based static application of the load, while using prism strength of concrete as determined during phase (degrees) loading concrete samples using a press. Determination of strength of concrete in tension is carried out using tensile machine [1]. The disadvantages of these methods are relatively low loading rate of concrete samples, and the impossibility of application short-term dynamic or static loads on the specimen.

In the calculation of building 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 testing. With repeated application of loads on construction work of concrete is characterized by the values obtained from experimental tests under cyclic static-dynamic loading.

One of izlesene, allows 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 short-term cyclic loadings concrete sample.

There is the solution, allowing to test the material under repeated loadings, - way cyclic loading of the material, which consists in the fact that we create in a tubular specimen tensile stresses along different axes by annexes axial force, internal pressure and torque. In this way to the end of the sample applied axial force, balancing the axial component of the internal pressure, axial force and internal pressure is applied in opposite phase to the zero cycle, and torque - with the lagging phase [3].

The disadvantage of this solution is that to obtain a prismatic concrete strength required additional mathematical processing of data obtained in the experiment, which increases the computational error. In addition, the composition of the working fluid used to create the loading can affect the strength characteristics of the material under test. This method also does not allow to implement kratkofil�nye dynamic loading.

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 [4]. The cyclic loading conditions are created through multiple loading case loads.

The disadvantage of this solution is the limited number of cycles; the inability to implement multiple static loadings; the inability to pre-specify the sequence and magnitude of the applied loads.

The technical result of the invention is to facilitate the testing method, expanding the functionality of the experimental determination of the static-dynamic properties of concrete under cyclic loadings, consisting in the alternation of static and dynamic loads on the specimen.

The technical result is achieved in that in the method of experimental determination of static-dynamic properties of concrete under cyclic loadings, 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 nehruji�Oia, 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 multiple of the instantaneous speed or dynamic loading by rotation and short-term changes in the diameter of the axis at the connection of the lever and the compensating element. Alternating dynamic and static cyclic loading is carried out by shifting the axis.

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 testing the compression. Fig.2A presents a schematic variants of the cross-section axis. Fig.2B presents the scheme of interaction between the lever and the axis. Fig.4 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, metallic�the cue ball 10, the bolt 9, the load platform 8 for the application of the static load, the unit loads.

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 shapes of cross sections.

The diameter of the hole in the lever 4 exceeds the larger diameter section of the axle 7.

Metal ball 10 and the different forms of the cross sectional axis 7 necessary to implement short-term static or dynamic loading of the sample 3.

The bolt 9 is required to restrict movement of the metal ball 10 at the moment of fast loading and unloading a turning axis 7.

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 the second stage, fix the specimen 3 in the 2 clips, then carry out a multiple static or dynamic loading by rotation and short-term changes in the diameter of the axis at the connection of the lever and the compensating element. If necessary the test specimen under static cyclic loading after testing� under dynamic cyclic loads shall implement the offset of the axis.

In the process of testing a dynamometer to measure the force acting on the specimen, and the deformation of the specimen under static or dynamic loading under cyclic loads are measured by means of tantostanze equipped with a built-in Centocelle 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;ab - 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.

Fig.3 shows the diagram of stress (σ) - strain (ε) for concrete under cyclic conditions�die loadings for different types of cross-sections of the axis 7.

Sources of information

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

2. Bazhenov Yu. M. Concrete under dynamic loadings. - M.: Stroiizdat, 1970. - 272.

3. Copyright certificate of the USSR No. 1619117 A1, CL G01N 3/32, 1987.

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

Method for experimental determination of static-dynamic properties of concrete under cyclic loadings, 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 multiple static or dynamic loading is carried out by rotation and short-term changes in the diameter of the axis at the connection of the lever and the compensating element.



 

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