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.
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 . 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 . 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 .
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 . 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:
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.
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.
5 dwg, 2 ex
FIELD: test equipment.
SUBSTANCE: method relates to test methods of porous water-saturated bodies. It provides for production of a series of concrete specimens, saturation of specimens with water, measurement of specimens, determination of their initial volume, their frosting/defrosting to specified temperatures and recording of deformation. In addition, long-term strength limit of each specimen is determined by a non-destructive method under tension conditions. After defrosting, relative residual deformation of specimens is determined and energy dissipated in unit volume of each specimen is determined during its frosting/defrosting. Then, they are loaded under conditions of uniaxial compression to an extreme load meeting short-term strength limit; energy dissipated in unit volume of the specimen is determined during its compression to an extreme load, and as per the obtained results, grade is calculated as per freeze resistance of each specimen. Grade of concrete as to freeze resistance is determined as an arithmetic mean for grades of specimens.
EFFECT: increasing flexibility, reducing labour intensity and enlarging the number of hardware.
SUBSTANCE: previously prepared samples with various quantity of a filler in a highly dispersed condition for a dry construction mix are placed into a hollow part of metal washers, placed on a metal plate, are compacted by any available method under permanent load of up to 5 MPa per 1 cm2 of sample surface for 10-15 seconds, then marks are applied on the surface of each sample in the form of drops of a solution of various concentration, wetting angles of samples are measured θ, a curve of dependence is built cosθ-1=f(1/σl), where σl - surface tension of the liquid, they determine the angle of inclination of this functional dependence a for each sample of different composition, the curve of dependence a is built on quantity of mix components, and by the point of break of the curve of dependence they define the optimal content of a modifier in the tested object.
EFFECT: reduced number of tests and higher accuracy of mixture composition selection.
2 cl, 2 dwg, 1 tbl
FIELD: test equipment.
SUBSTANCE: at the first stage they determine process mode of manufacturing of ceramic items providing for required operability reserve. Using the produced operability reserve and knowing the suggested time, during which ceramic items must preserve strength parameters, they assess the permissible rated speed of produced reserves consumption. At the second stage, modelling conditions of real operation by means of reproduction of accelerated cyclic variations of temperature with simultaneous impact of possible mechanical factors, they determine actual speed of consumption of the same reserves. Received results of rated permissible speed and actual speed produced for imitation of operation conditions are compared, and results are produced, making it possible to judge on ceramic items.
EFFECT: possibility to determine durability of ceramic items with regard to certain conditions of use.
FIELD: measurement equipment.
SUBSTANCE: invention relates to the field of tests of cement plastering compounds for tensile strength under static loading. Substance: the value of the limit tensile strength is defined by testing steel beams with applied plastering compound according to the scheme of the double-point bend with smooth loading by small steps and fixation of the loading step corresponding to the moment of cracking, and the value of the limit tensile strength is calculated using the formula.
EFFECT: simplified technology for testing, exclusion of the necessity to apply strain metering facilities, higher accuracy of detection of limit tensile strength and completion of tests on plaster layers with specifically small thickness from several mm to 2-3 cm.
1 tbl, 1 dwg
SUBSTANCE: method involves measurement of hardening concrete temperature at given time moments and calculation of concrete strength over three days for hardening in standard conditions by the formula:
EFFECT: reduced labour consumption of monitoring.
1 tbl, 2 dwg
SUBSTANCE: apparatus has at least two sealed chambers with a U-shaped pipe filled with water for releasing excess pressure in the chamber, inlet and outlet gas-distributing manifolds, filters for cleaning the gas-air medium collected from the chambers and the inside of each chamber is fitted with a ventilator and a bath with a saturated salt solution for creating and maintaining given relative air humidity inside the chamber, connected to the sealed chambers through the inlet gas-distributing manifold and, installed on pipes, electromagnetic valves, a carbon dioxide gas source, an automatic gas analyser with a gas flow activator, a gas distribution switch for alternately collecting samples from the chambers and transferring the samples to the gas analyser through the gas flow activator; the gas analyser is also connected to a computer for automatic monitoring of gas concentration in the sealed chambers and feeding gas into the chambers through the electromagnetic valves.
EFFECT: high information value and faster determination.
SUBSTANCE: previously they make at least two samples with different water-cement ratios, thermal cycling and cyclic compression of the sample with the least water-cement ratio are alternated until proportion is disturbed between relative residual deformation and number of cycles, the ratio is calculated between relative reduction of threshold load and relative residual deformation, the concrete grade of frost resistance is determined, as well as relative residual deformation εm, corresponding to reduction of the strength limit specified by the standard for the frost resistance grade of the investigated concrete, they alternate thermal cycling and cyclic compression of other samples with higher water-cement ratios until residual deformation is achieved εm, the number of cycles required for this purpose is accepted as the grade of concrete frost resistance with higher water-cement ratio, using the produced results, they calculate parameters of the function that approximates experimental results.
EFFECT: expanded arsenal of technical facilities for detection of concrete frost resistance dependence on water-cement ratio.
SUBSTANCE: in the method including drying of a sample to permanent mass, hydraulic insulation of its side surfaces and water saturation, nonwetting of the upper end surface of the sample is provided, and a light-reflecting water impermeable coating is applied on it, and continuous even water saturation is carried out via the bottom end surface of the sample, at the same time the sample is installed onto fixed supports inside a reservoir for water saturation, the reservoir is filled with water, and even contact is provided between the lower end surface of the sample with water during the entire cycle of measurements, then with the help of laser radiation a series of holographic interferograms is registered on a non-wetted surface of the sample in process of water saturation, at the same time position, speed and acceleration of moisture movement front are determined by comparison of changes in the field of movements of the registered surface, produced according to interferograms, with the rated field of movements of a geometrically similar sample.
EFFECT: improved information value and reliability of detection.
2 cl, 1 dwg
SUBSTANCE: method is realised by fixation of an experimental concrete sample in the form of a prism between bearing plates of a test bench using a centring device, providing for central application of a compressing load in process of loading, and registration of a force and deformation of a prism in time using a dynamometer and a strain station with loading, realised through a lever system in two stages: at the first stage - stepped static loading of a sample to the required level in different shares of the crack formation load by means of laying of unit weights onto a loading platform, at the second stage - instantaneous or stepped dynamic additional loading with a weight dropping during reduction of current force in an electromagnet, the axis of the centre of gravity of which matches with the axis of the loading platform.
EFFECT: increased reliability of tests.
FIELD: test hardware.
SUBSTANCE: invention relates to vibrating hardware and can be used for analysis of rocks specimens and model of equivalent materials for effects of mechanical vibrations, particularly, of Relay waves. Bench comprises the bed to support with specimen gripper, loading mechanism engaged therewith and including the rotation drive. Loading mechanism consists of spinning disc with circular groove made at its end surface, two rolls opposed in said groove, two stiff parallel thrusts arranged in the plane parallel with disc spinning plane, one being coupled with appropriate roll and opposite one engaged with said gripper. Spinning disc is fitted off-centre on rotation drive shaft to adjust eccentricity while spinning drive allow rpm adjustment.
EFFECT: enlarged volume of data for analysis owing to possibility of causing the circular or elliptical oscillations inherent in Relay waves.
SUBSTANCE: invention relates to the field of construction and is intended to control the stiffness of beams, made of a material, having physically non-linear properties (in particular, reinforced concrete beams), and loaded uniformly by a distributed load. According to the declared method the reference structure is made of a physically nonlinear material for a certain type of beams in compliance with all the technological requirements for quality. The basic or the first resonant oscillation frequency ω0 is determined in the mentioned structure. The structure is loaded by a stepwise uniformly increasing distributed load, maximum deflection w0 is measured at each stage of loading, and an approximating function
EFFECT: expansion of technological capabilities of non-destructive testing method for the stiffness of beams made of a material, having physically nonlinear properties.
1 tbl, 3 dwg
FIELD: test equipment.
SUBSTANCE: proposed unit comprises bed to support rotary platform with specimen gripper, centrifugal weight to be secured at specimen end and platform drive. The latter comprises drive shaft and two rollers offset relative to shaft axis on both sides of platform rotational axis to realise frictional interaction therewith. Additionally, it incorporates the gripper drive to revolve it relative to the platform revolution.
EFFECT: enhanced performances at sign-variable flexure in two planes with centrifugal extension.
FIELD: test equipment.
SUBSTANCE: invention relates to test equipment and to strength tests. A unit includes a base and coaxially installed on it end and central grips with a common rotation axis and holes for a specimen, a rotation drive of the end grips, a pusher that is connected by one of its ends to the central grip and a loader that is connected to the other end of the pusher. The holes made in the grips have an out-of-round section and are made in compliance with the specimen cross-section.
EFFECT: increasing the volume of information by performing tests at single-cyclic and double-cyclic bending loading with the constant ratio of forces in longitudinal sections of a specimen.
2 cl, 1 dwg
FIELD: testing technology.
SUBSTANCE: invention relates to the testing technology, the study of samples and products for strength under cyclic loading. The unit comprises a housing, the platform mounted on it with the rotary drive, the additional platforms located on it, a grip for the sample located on one of the additional platforms. The additional platforms are mounted successively one on another and are provided with rotary drives, at that the number of platforms is predetermined by the number of loading cycles.
EFFECT: enhancing the technological capabilities by providing multicyclic loading at the independent regulation of the quantity and parameters of the cycles during the test.
SUBSTANCE: invention relates to construction, namely to mechanical tests of materials, in particular to testing methods for building constructions, and may be used for testing the bending of beam constructions. Essence: the controlled cyclic load is applied to the sample and by the loading or unloading rate, and its magnitude, the selected parameters of loading are maintained at the predetermined time interval. Range and place of application of loads is regulated by the loading device and power device, and the strength and deformation parameters of the test structure are measured in the given time interval. Device contains the supports for the placement of the test specimen fixed in the reinforced floor, loading device with the power device. Loading device is designed in the form of, at least, one lever and the power device is designed in the form of cargo tank, which is positioned on each lever of loading device and designed with possibility to fill it with liquid.
EFFECT: possibility to evaluate the strength and operating parameters of flexible constructions in real modes of load measurement during operation after the complete and partial unloading.
5 cl, 2 dwg
FIELD: testing technology.
SUBSTANCE: unit comprises a base, a turntable platform mounted on it, grip of the sample mounted on the platform, two centrifugal weights designed to secure at the ends of the sample, rotary drive of the platform, comprising a shaft with the rotary drive, a pair of rollers mounted eccentrically on opposite sides of the rotation axis of the platform and designed for frictional interaction with it, one of which is mounted on the shaft. The unit is additionally provided with a second shaft mounted coaxially with the first shaft and the rotary drive of the second shaft, at that the second roller is mounted on the second shaft.
EFFECT: enhanced functionality of the unit through providing tests both at alternating bending in two planes, and at alternating bending in one plane and constant bending in a second plane, as well as at circular bending and circular bending with stretching.
FIELD: testing equipment.
SUBSTANCE: centrifugal plant comprises a base, a rotation platform installed on it, sample grips radially arranged on the platform, one of which is connected to the platform, a centrifugal weight connected to the second grip, and two coaxially installed rotation drives kinematically connected to the platform. The centrifugal plant is additionally equipped with two electromagnetic fixators for connection of the platform with the appropriate rotation drives.
EFFECT: increased volume of information in research of energy exchange during deformation and damage of solid bodies by provision of tests under stepped variations of axial load with development of pulse bending loads at moments of stepped variations of axial load, which are proportionate to values of steps of axial load variation and having identical or different directions of bending.
SUBSTANCE: device comprises a frame, lifting table, capable to change the height, positioning node of test beam, load node of test beam made with possibility to apply cyclic dynamic load and possibility to measure displacements and loading force, comprising rod and slide mechanism. Positioning nod of the test beam comprises clamping jaws mounted on the ends of the test beam parallel to the transverse symmetry axis of the frame and intermediate elastic foundation made as a container filled with model soil with the possibility of tight contact with the place of test beam facing to it. Loading element of load node of the test beam is designed with the possibility of its positioning in the middle of the test beam.
EFFECT: increase of reliability of assessment of asphalt concrete fatigue strength parameters under cyclic dynamic impacts, reduction of the structure materials consumption.
5 cl, 2 dwg
FIELD: test equipment.
SUBSTANCE: invention refers to test equipment, to strength tests. Setup includes a bed carrying sample grips and cyclic load device in the form of cog wheel interacting with mobile rack linked to one of the grips, a bar connected by an end to the cog wheel, and load mounted on the other bar end. In addition, the setup includes second rack linked to the second grip, and shock load devices matching the number of shock momentums, each device in the form of cog wheel interacting with the second rack, arm with rotation axis coaxial to the cog wheel and rotating independently, load mounted on the arm, and two rests mounted on the cog wheel and interacting with the arm, the load is located higher than arm rotation axis, the arm is positioned between the rests with a gap, and the rests on each cog wheel are tilted in comparison to the rests of the other cog wheels.
EFFECT: increased information content of material sample tests by superposition of compressing and extending shock momentums on damped load oscillation cycles.
2 cl, 1 dwg
FIELD: testing engineering.
SUBSTANCE: bench comprises asynchronous electric motor and balancing machine interconnected through the shaft to be tested, control unit, and resonance pickup mounted on the shaft and connected with the input of the control unit. The bench is provided with the frequency converter, DAC unit, thyristor controller of voltage, and inverter. The first output of the control unit is connected with the frequency converter connected to the circuit for power supply to the asynchronous motor. The second output of the control unit is connected in series with the DAC unit and thyristor voltage controller connected with the exciting winding of the balancing machine. The circuit of the armature of the balancing machine is connected to the inverter.
EFFECT: enhanced reliability of testing.