CN111707541B - Concrete uniaxial tensile load and test device and its application method - Google Patents

Abstract

The single-shaft tensile load holding and testing device for the concrete and the using method thereof do not need to adopt an independent load sensor, and the method of sticking the resistance strain gauge by adopting the connecting sleeve with the internal threads and the external smooth circle is adopted to enable the connecting sleeve to be used as the load sensor, so that the testing device is simplified, and the cost problem that a large number of load sensors are occupied by long-term load holding is reduced. The invention realizes the application of axial tension to the concrete test block by simultaneously rotating the second specification of four finish rolling nuts close to one side of the upper spherical hinge. The connecting sleeve attached with the strain gauge is also used as a load sensor to obtain a load, and the second specification of the finish rolling nut is slightly rotated to realize fine adjustment of the load. For the concrete single-shaft tension testing device, a square steel plate and a through-type drawing instrument are added on the basis of a load holding device. The invention combines the single-shaft tension load holding and testing device of the concrete into a whole, has simple operation and can provide stable and effective continuous load.

Description

Concrete uniaxial tensile load and test device and its application method

technical field

The invention belongs to the field of civil engineering, and in particular relates to a concrete uniaxial tensile load and testing device and a use method thereof, and is especially suitable for studying the durability test of a concrete uniaxial tensile test piece under the coupled action of load and erosive environment.

Background technique

As we all know, concrete is one of the most widely used building materials in current engineering structures, and its compressive strength is its most prominent feature, while less attention has been paid to its tensile strength. Therefore, in modern structures, concrete is mainly used to bear the compressive strength, and the tensile strength of concrete is generally only 1/17~1/8 of the compressive strength, and a small load can reach the tensile strength of concrete, so in In structural design, the tensile strength of concrete is usually neglected and the tensile strength of the structure is borne by steel bars. Not allowing to appear the stress of drawing in some structures such as the complete prestressed stress concrete structure, but allowing the stress of drawing to appear in the part of the prestressed structure.

The tensile strength and deformation of concrete are one of the most important basic properties of concrete. It is not only an important part of the study of concrete strength theory and failure mechanism, but also an important factor affecting the cracking, deformation and durability of concrete structures. Since the tensile strength controls the whole process of the cracks in the concrete, as well as other related properties such as elastic modulus, stiffness, steel grip and durability of concrete, etc., in addition, the tensile strength also affects the resistance of concrete. It is the main factor of shear performance and an important parameter to establish the multiaxial failure criterion of concrete. In recent years, with the construction of a large number of high-rise buildings and long-span bridge projects, the proportion of high-performance concrete used in modern structures is increasing, and one of the main characteristics of high-performance concrete is high durability. Realistic structures For example, there are many macroscopic cracks on the surface of bridges, crane beams, roads, and offshore platforms, which seriously affect their durability, structural safety, reliability, and service life. The development of concrete cracks is mainly related to the tensile strength. Therefore, it is of great significance to study the tensile properties of concrete.

For a long time, people's experimental research on the tensile strength of concrete is only in the initial stage, coupled with the great discreteness of concrete, the backwardness of concrete tensile test equipment, and people's understanding of tensile strength lacks integrity. After the 1960s, researchers developed a series of concrete tensile test devices, which can realize the measurement of the full tensile stress-strain curve of concrete, but the test devices used by each researcher are different. In previous studies, there were few studies on the durability of concrete uniaxial tensile specimens under continuous load, especially in the erosion service environment (coupling of load and erosion environment), and during the test, through physical The centering method is used to realize the concrete shaft pulling, the operation is complicated, and the centering situation is not easy to control. Therefore, there is no recognized and effective method at present. If the specimen cannot be centered, the specimen will break quickly once the load is applied, and the test will fail. The durability test requires very high environmental conditions such as test temperature and humidity. Strict; in addition, the operation process of the test is very complicated, and it has high requirements on the test equipment, data acquisition system, test piece performance and test conditions. In previous studies, two sets of test devices were often required for the holding device and test device used for the uniaxial tensile test of concrete under long-term load, which was not convenient enough. Therefore, it is necessary to develop a set of concrete uniaxial tensile load and test device as soon as possible.

Contents of the invention

Aiming at the problems of difficult centering of concrete specimens and relatively complicated test operation process when using traditional concrete tensile test devices, the present invention provides a concrete uniaxial tensile load and test device and its use method. The method of adding a spherical hinge to ensure that the concrete axis is under tension.

Technical scheme of the present invention is as follows:

Concrete uniaxial tensile load and test device is characterized in that it includes a concrete test block, a top steel plate, a bottom steel plate, four second prestressed finish-rolled threaded steel bars, two spherical joints, ordinary connecting rods, extended connecting rods, Two square anchor plates; the top steel plate and the bottom steel plate pass through four second prestressed finish-rolled threaded steel bars respectively, and are respectively placed in parallel on the upper and lower parts of the second prestressed finish-rolled threaded steel bar; the top steel plate and the bottom steel plate They are respectively in rotational contact with the ball hinge, the elongated connecting rod is fixedly connected with the ball hinge at the top, and the ordinary connecting rod is fixedly connected with the ball hinge at the bottom;

Two square anchor plates are fixedly connected to the top and bottom of the concrete test block through their four corners respectively, and the middle parts of the two square anchor plates are respectively fixed with first prestressed finish-rolled threaded steel bars; two first prestressed finish-rolled threaded steel bars The ends of the two connecting sleeves are respectively screwed to the connecting sleeve, and the two connecting sleeves are respectively screwed to the ordinary connecting rod and the extended connecting rod; by driving the upper part of the first prestressed finish-rolled threaded steel bar to be stressed, the concrete uniaxial Subject to tensile load and test.

Further, the top and bottom of the concrete test block are respectively prefabricated with four fine-rolled threaded steel bars, and a certain length is exposed; the four corners of the square anchor plate are respectively provided with reserved holes, and the four finished-rolled threaded steel bars pass through Corresponding to the four reserved holes of the square anchor plate, screw the finished threaded steel bar into the finished rolled nut, and connect the two square anchor plates with the concrete test block.

Further, the bottom steel plate and the top steel plate are variable-section steel plates.

Further, four finish-rolled nuts are provided on the bottom steel plate to be screwed with the corresponding second prestressed finish-rolled rebar, and steel washers are provided between the finish-roll nuts and the bottom steel plate.

Further, the top steel plate and the bottom steel plate are respectively fixed with reinforced round steel pipes, and the two reinforced round steel pipes are respectively set on the extended connecting rod and the ordinary connecting rod;

Four rectangular stiffened steel plates are evenly arranged in the circumferential direction of the two reinforced round steel pipes, and the four rectangular stiffened steel plates are fixedly connected to the corresponding steel plates, which are used to connect the reinforced round steel pipes and the corresponding steel plates in four directions to ensure that the ball There is no local damage to the hinge.

Further, the outer surface of the upper connecting sleeve is pasted with a strain gauge and also serves as a load sensor, and the strain gauge is connected to the resistance strain gauge through a connecting wire.

Further, four finish-rolled nuts are provided at the bottom of the top steel plate to be screwed with the corresponding second prestressed finish-rolled rebar, and a steel washer is provided between the finish-rolled nuts and the top steel plate. Specifically, concrete uniaxial tensile load test:

By rotating the four finish-rolled nuts at the bottom of the top steel plate at the same time, an outward force is applied to the top steel plate, which sequentially drives the extended connecting rod, the connecting sleeve, and the first prestressed finish-rolled threaded steel bar to be stressed, and then the concrete test block is subjected to tension. ; At the same time, the bottom steel plate restricts the movement of the first prestressed finish-rolled rebar and the square anchor plate, thereby realizing the sustained load of the concrete test block; Rotate the finishing nut at the bottom of the top steel plate to fine-tune the load; during the load-holding process, it is necessary to ensure that the upper and lower variable-section steel plates are parallel.

Further, two middle steel plates are arranged between the upper connecting sleeve and the upper rectangular stiffener steel plate, and the two middle steel plates respectively pass through four second prestressed finish-rolled threaded steel bars; one of the middle steel plates is located on the upper connecting sleeve Above, its top is used to support the core-type drawing instrument, and the core-through-type drawing instrument is set on the extended connecting rod, and the bottom of the middle steel plate is provided with four finish-rolled nuts to match the corresponding second preset The stress finish-rolled threaded steel bar is screwed, and a steel washer is arranged between the finish-roll nut and the intermediate steel plate; another intermediate steel plate is located on the top of the center-piercing drawing machine. Specifically, concrete uniaxial tension test:

During the test, the core-type puller exerts an upward force against the middle steel plate above it, and the tensile force is transmitted to the concrete test block through the ball hinge at the upper end, the extended connecting rod, the connecting sleeve, and the first prestressed finish-rolled threaded steel bar. ; at the same time, the spherical joint at the bottom limits the movement of the first prestressed finish-rolled threaded steel bar and the square anchor plate, and then realizes the application of tensile force to the concrete test block until the test piece is destroyed; the tensile force is measured by the connecting sleeve that also serves as a load sensor. The tensile strength of the concrete can then be calculated using the formula.

The present invention does not need to use a separate load sensor, and adopts the method of pasting the resistance strain gauge on the connecting sleeve with internal thread and external light circle so that it can also be used as a load sensor, which simplifies the test device and reduces the need for a large number of load sensors for long-term load cost issue. The load holding device is easy to operate and can provide stable and effective continuous load. The invention combines the concrete uniaxial tensile load and testing device into one, and does not need to use the two devices to carry out the load test and test on the concrete uniaxial tensile performance under the long-term load. Form the test device.

The steel plate in the present invention is made of stainless steel; in the present invention, the axial tension is applied to the concrete test block by simultaneously rotating the four finish-rolled nuts of specification 2 on the side close to the upper spherical hinge. The load is obtained through the connecting sleeve with the strain gauge attached as the load sensor, and the fine-tuning of the load is realized by slightly rotating the finish-rolled nut specification 2. For the concrete uniaxial tension test device, a square steel plate and a through-core puller are added on the basis of the load-bearing device.

The beneficial effects of the present invention are:

1. The present invention provides a concrete uniaxial tensile bearing and testing device, which has a simple structure and is easy to operate;

2. The load-holding device can provide reliable and stable load for the concrete test block by twisting the finishing nut under the top steel plate, which can meet the requirements of long-term loading. The spherical hinge at the end will rotate when encountering eccentric force, which can ensure that the steel plate Push forward steadily and apply axial tension to the concrete test block to avoid adverse effects on the test due to eccentric tension;

3. The load-holding device can apply continuous load to the specimen without using the reaction frame, and the connecting sleeve with the strain gauge is also used as the load sensor, which greatly reduces the space occupied by the loading device;

4. The present invention can not only be used as a concrete uniaxial tension load-bearing device, but also can form a concrete uniaxial tension test device through partial modification;

5. The load-holding and testing device is made of corrosion-resistant stainless steel, which is not easy to rust. Put the test piece into the corrosion environment simulation device (such as freeze-thaw test chamber, carbonization chamber, chloride salt, sulfate corrosion solution environment, etc.) Force state, test the mechanical properties and durability of the specimen.

Description of drawings

Fig. 1 is the schematic diagram that the present invention is made concrete uniaxial tensile load test device;

Fig. 2 is the schematic diagram of square anchor plate;

Fig. 3 is A-A sectional view among Fig. 1;

Fig. 4 is the schematic diagram of steel washer;

Fig. 5 is the schematic diagram of the present invention as concrete uniaxial tension test device;

Fig. 6 is B-B sectional view among Fig. 5;

Fig. 7 is the schematic diagram of square steel plate;

In the figure, 1 is the concrete test block, 2 is the finish-rolled rebar, 3 is the square anchor plate, 4 is the prestressed finish-rolled rebar specification one (the first prestressed finish-rolled rebar), and 5 is the finish-rolled nut specification one , 6 is connecting sleeve, 7 is ordinary connecting rod, 8 is extended connecting rod, 9 is reinforced round steel pipe, 10 is rectangular stiffened steel plate, 11 is spherical hinge, 12 is prestressed finish rolled thread steel Prestressed finish-rolled rebar), 13 steel washers, 14 is finish-rolled nut specification 2, 15 is strain gauge, 16 is resistance strain gauge, 17 is connecting wire, 18 is square steel plate, and 19 is a through-core puller.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Example 1

As shown in Figure 1, a concrete uniaxial tensile load test device, including concrete test block 1, finish-rolled threaded steel bar 2, square anchor plate 3, prestressed finish-rolled threaded steel bar specification 1, finish-rolled nut specification 1 5. Connecting sleeve 6, ordinary connecting rod 7, extended connecting rod 8, reinforced round steel pipe 9, rectangular stiffened steel plate 10, ball hinge 11, prestressed finish-rolled thread steel bar specification 2 12, steel washer 13, finish-rolled nut specification Two 14, strain gage 15, resistance strain gauge 16, connecting wire 17. The concrete test block 1 (120mm×120mm×400mm) is a non-standard type. Considering the effect of reducing the stress effect at the end and ensuring that the tensile failure occurs in the middle part, the area of the middle part of the test piece is reduced, and a self-made steel mold is used. To complete the pouring and molding of the test piece, remove the formwork after 24 hours, and put it into the standard curing room for curing after the formwork removal; there are eight fine-rolled threaded steel bars 2 (150mm in length), which are pre-buried at both ends of the concrete test block respectively. In order to achieve axial tensile strength and uniform distribution of stress, provide sufficient anchoring strength, and expose it to a certain length to facilitate test operations; the concrete test block 1 and the pre-embedded finish-rolled threaded steel bar 2 divide the device into upper and lower parts. two parts.

For the upper part of this device, as shown in Figure 2, the square anchor plate 3 is arranged at the end of the concrete test block 1, and there are four reserved holes at the four corners, and the center is welded with the prestressed finish rolled threaded steel bar specification-4 Together to form a whole; the finish-rolled nut specification-5 sets the four corners of the square anchor plate 3 for connecting the finish-rolled threaded steel bar 2 and the square anchor plate 3, and then connects the concrete test block 1 and the prestressed finished-rolled threaded steel bar specification a 4. The connecting sleeve 6 has an internal thread and has a smooth outer surface, and the prestressed finish-rolled threaded steel bar specification-4 and the extended connecting rod 8 are connected together through the connecting sleeve 6; the reinforced round steel pipe 9 and the end of the spherical hinge 11 The variable-section steel plates at the top are fixed together, and are sleeved on the extension connecting rod 8, leaving a certain distance with the extension connecting rod 8.

As shown in Figure 3, the rectangular stiffener steel plate 10 is used to connect the reinforced round steel pipe 9 and the spherical hinge 11 in four directions, so as to avoid local damage to the spherical hinge; the spherical hinge 11 will rotate under eccentric force; the variable-section steel plate It is a part of the spherical hinge, and four reserved holes are set at the four corners. In order to avoid becoming bulky due to the large thickness of the steel plate, it is designed as a variable cross-section.

For the lower part of this device, the extension connecting rod 8 in the upper part is changed into common connecting rod 7, and all the other places are identical with the upper part of the above-mentioned device.

There are four prestressed finish-rolled threaded steel bars in specification 212, respectively passing through the reserved holes at the four corners of the upper and lower variable-section steel plates.

As shown in Figure 4, the steel washer 13 is circular, and is arranged between the variable-section steel plate and the finish-rolled nut specification two 14, the inner diameter is slightly larger than the diameter of the prestressed finish-rolled threaded steel bar specification two 12, and the outer diameter is larger than the precision The diameter of the circumscribed circle of the rolled nut specification 2 14; the finish-rolled nut specification 2 14 connects the prestressed finish-rolled threaded steel bar specification 2 12 with the upper and lower two variable-section steel plates.

Further, the diameter of the reserved hole on the square anchor plate 3 is larger than the diameter of the finished rolled threaded steel bar 2 .

The diameter of the prestressed finish-rolled threaded steel bar specification one 4 is greater than the diameter of the prestressed finish-rolled threaded steel bar specification two 12 .

The finish-rolled nut specification one 5 and the finish-roll nut specification two 14 are hexagonal nuts.

Both the elongated connecting rod 8 and the common connecting rod 7 are made of steel, and are integrally formed with the ball hinges 11 at the upper and lower ends respectively.

There is a certain distance between the reinforced round steel pipe 9 and the connecting sleeve 6 .

The reserved hole on the variable-section steel plate at the end of the spherical hinge 11 is a circular through hole, and the diameter of the reserved hole is greater than the diameter of the prestressed finish-rolled threaded steel bar specification 212, and a groove is reserved in the middle of the variable-section steel plate To make rotational contact with the ball hinge.

Still further, a strain gauge 15 is pasted on the surface of the connecting sleeve 6 of the upper part of the device and also serves as a load sensor. The strain gauge 15 is connected to the resistance strain gauge 16 through the connecting wire 17. When the load is sustained, the connecting sleeve 6 is pulled, and the magnitude of the tensile strain can be displayed by the resistance strain gauge 16, and converted into the force exerted on the connecting sleeve 6 through calculation. The tensile force at the connecting sleeve 6 is the continuous load on the concrete test block 1.

The device is made of corrosion-resistant stainless steel, and its durability will not be reduced under the action of erosive environment.

A concrete uniaxial tensile load test device, the continuous load in the normal use state is realized by simultaneously rotating the four finish-rolled nuts on the inner side of the variable-section steel plate at the upper end. The steel plate exerts an outward force, which sequentially drives the extended connecting rod 8, the connecting sleeve 6, and the prestressed finish-rolled threaded steel bar specification-4 to be stressed, and then the concrete test block 1 is pulled, and at the same time, the lower end variable-section steel plate limits the prestressed precision The movement of the rolled threaded steel bar specification-4 and the square anchor plate 3 realizes the bearing of the concrete test block 1. The magnitude of the continuous load is obtained by connecting the sleeve 6 with the strain gauge attached and serving as a load sensor, and the fine-tuning of the load is realized by slightly rotating the finish-rolled nut specification 2 14. During the load-bearing process, the parallelism of the upper and lower variable-section steel surfaces must be ensured. Then, put the test piece into the corrosion environment simulation device after holding the load, and let it stand for a period of time.

Example 2

As shown in Figure 5, a concrete uniaxial tension test device takes out the load-bearing device in the erosion environment simulation device, and adds a square steel plate 18 and a core-type puller 19 on the basis of the load-bearing device. Two new square steel plates 18 are added, one of which is placed between the upper part of the connecting sleeve 6 and the rectangular stiffener steel plate 10 to support the upper through-hole drawing instrument 19, and the lower steel washer 13 and finish rolling The nut specification two 14 is fixed, and the other one is arranged on the top of the through-heart drawing instrument 19 to withstand the rectangular stiffened rib steel plate 10; the rectangular stiffened rib steel plate 10 is arranged as a rectangle to facilitate the support of the square steel plate 18 below; The core-through drawing instrument 19 is arranged on the square steel plate 18 for applying tension; as shown in FIG. 6 , the steel washer 13 and the finish-rolled nut specification 2 14 inside the variable-section steel plate are removed.

Further, as shown in Figure 7, the square steel plate 18 is provided with five circular reserved holes at the four corners and the center respectively, and the diameters of the reserved holes at the four corners are greater than the diameter of the prestressed finish-rolled threaded steel bar specification 2 12, and the central reserved The diameter of hole is greater than the diameter of extension connecting rod 8.

A concrete uniaxial tension test device. During the test, the through-center puller 19 presses against the square steel plate 18 above it to apply an upward force, and the tensile force passes through the ball hinge 11, the extended connecting rod 8, and the connecting sleeve at the upper end of the device respectively. 6. The prestressed fine-rolled threaded steel bar specification-4 is passed to the concrete test block 1, and the ball hinge 11 at the lower end restricts the movement of the pre-stressed finished-rolled threaded steel bar specification-14 and the square anchor plate 3, thereby realizing the concrete test block 1 Apply tension until the specimen fails. The tensile force is measured by the connecting sleeve 6 which doubles as a load sensor, and then the tensile strength of the concrete can be calculated by using a formula.

Finally, the present invention is not limited to the above-mentioned embodiments, and many modifications can be made on the basis of the essence of the present invention. All modifications that can be directly associated by those skilled in the art on the basis of the disclosed content of the present invention should be considered as the present invention. protection scope of the invention.

Claims (6)

1. Concrete uniaxial tensile load and testing device, which is characterized by including concrete test block, top steel plate, bottom steel plate, four second prestressed finish-rolled threaded steel bars, two spherical joints, ordinary connecting rods, and extended connections rod, two square anchor plates; the top steel plate and the bottom steel plate pass through four second prestressed finish-rolled rebars respectively, and are respectively placed in parallel on the upper and lower parts of the second prestressed finish-rolled rebar; the top steel plate, The bottom steel plates are respectively in rotational contact with the ball hinge, the extended connecting rod is fixedly connected with the ball hinge at the top, and the ordinary connecting rod is fixedly connected with the ball hinge at the bottom; Two square anchor plates are fixedly connected to the top and bottom of the concrete test block through their four corners respectively, and the middle parts of the two square anchor plates are respectively fixed with first prestressed finish-rolled threaded steel bars; two first prestressed finish-rolled threaded steel bars The ends of the two connecting sleeves are respectively screwed to the connecting sleeve, and the two connecting sleeves are respectively screwed to the ordinary connecting rod and the extended connecting rod; by driving the upper part of the first prestressed finish-rolled threaded steel bar to be stressed, the concrete uniaxial Tensile loads and tests; The top and bottom ends of the concrete test block are prefabricated with four fine-rolled threaded steel bars respectively, and a certain length is exposed; the four corners of the square anchor plate are respectively provided with reserved holes, and the four finished-rolled threaded steel bars pass through the corresponding square anchors. The four reserved holes of the plate, and the finished rolled threaded steel bar is screwed into the finished rolled nut, and the two square anchor plates are integrated with the concrete test block; Four finish-rolled nuts are arranged on the bottom steel plate to be screwed with the corresponding second prestressed finish-rolled threaded steel bars, and steel washers are arranged between the finish-roll nuts and the bottom steel plate; The top steel plate and the bottom steel plate are respectively fixed with reinforced round steel pipes, and the two reinforced round steel pipes are respectively set on the extended connecting rod and the common connecting rod; Four rectangular stiffened steel plates are evenly arranged in the circumferential direction of the two reinforced round steel pipes, and the four rectangular stiffened steel plates are fixedly connected to the corresponding steel plates, which are used to connect the reinforced round steel pipes and the corresponding steel plates in four directions to ensure that the ball No local damage occurs to the hinge; The outer surface of the connecting sleeve on the upper part is pasted with a strain gauge and also serves as a load sensor, and the strain gauge is connected with a resistance strain gauge through a connecting wire. 2. The concrete uniaxial tensile load and test device according to claim 1, characterized in that, the bottom steel plate and the top steel plate are all variable-section steel plates. 3. The concrete uniaxial tensile load and testing device according to claim 1, wherein four finish-rolled nuts are arranged at the bottom of the top steel plate to be screwed with the corresponding second prestressed finish-rolled threaded steel bar. Then, a steel washer is provided between the finish-rolled nut and the top steel plate. 4. The concrete uniaxial tensile load and test device according to claim 1, characterized in that two middle steel plates are arranged between the upper connecting sleeve and the upper rectangular stiffener steel plate, and the two middle steel plates are respectively worn through Through four second prestressed finish-rolled threaded steel bars; one of the middle steel plates is located on the upper connecting sleeve, and its top is used to support the core-type drawing instrument, and the core-through-type drawing instrument is set on the extension connecting rod On the bottom of the intermediate steel plate, there are four finish-rolled nuts to be screwed with the corresponding second prestressed finish-rolled rebar, and a steel washer is arranged between the finish-rolled nuts and the intermediate steel plate; another intermediate steel plate is located The top of the piercing puller. 5. The concrete uniaxial tensile load and testing device according to claim 3, wherein the concrete uniaxial tensile load test: By rotating the four finish-rolled nuts at the bottom of the top steel plate at the same time, an outward force is applied to the top steel plate, which sequentially drives the extended connecting rod, the connecting sleeve, and the first prestressed finish-rolled threaded steel bar to be stressed, and then the concrete test block is subjected to tension. ; At the same time, the bottom steel plate restricts the movement of the first prestressed finish-rolled rebar and the square anchor plate, thereby realizing the sustained load of the concrete test block; Rotate the finishing nut at the bottom of the top steel plate to fine-tune the load; during the load-holding process, it is necessary to ensure that the upper and lower variable-section steel plates are parallel. 6. The concrete uniaxial tensile holding load and the using method of the test device according to claim 4, characterized in that, the concrete uniaxial tensile test: During the test, the core-type puller exerts an upward force against the middle steel plate above it, and the tensile force is transmitted to the concrete test block through the ball hinge at the upper end, the extended connecting rod, the connecting sleeve, and the first prestressed finish-rolled threaded steel bar. ; at the same time, the spherical joint at the bottom limits the movement of the first prestressed finish-rolled threaded steel bar and the square anchor plate, and then realizes the application of tensile force to the concrete test block until the test piece is destroyed; the tensile force is measured by the connecting sleeve that also serves as a load sensor. The tensile strength of the concrete can then be calculated using the formula.

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