JPH0820347B2 - Concrete pure tensile test method and tester jig - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a concrete tensile test method for concrete and a tester jig used therefor.

[0002]

2. Description of the Related Art Conventionally, a tensile fracture test method for concrete and fiber reinforced concrete has been carried out by using a tensile tester as shown in FIG.
As shown in, a horizontal plate 5, which holds the concrete specimen 2 by surrounding the upper and lower sides of the concrete specimen 2,
5'is adhered and the concrete specimen 2 is attached to the upper and lower loading plates 3 and 3'of the tensile tester, and the concrete specimen is gradually increased in load through the upper loading plate 3 to the specimen 2. 2 until the concrete specimen 2 breaks, the load at and after the concrete specimen 2 breaks, and the elongation displacement until the concrete specimen 2 breaks are measured, and the tensile stress is measured as shown in FIG. There is a so-called pure tensile test method in which the strength of concrete is grasped by obtaining the relationship between the above and the elongation displacement of the concrete specimen 2. The load applied to the concrete specimen 2 until the concrete specimen 2 breaks here is equal to the tensile stress of the concrete specimen 2.

[0003]

The concrete pure tensile test method using the conventional tensile test as described above is performed when the concrete specimen is fractured by loading while gradually increasing the load as shown in FIG. It is possible to obtain the load of and the elongation displacement of the concrete specimen immediately before fracture,
When a concrete specimen cracks and develops and breaks, the strength of the concrete specimen drops sharply and the tensile stress of the concrete specimen also falls sharply. It is not possible to reduce the load with a fast response speed to cope with the stress, and it is not possible to obtain the relationship between the load applied to the concrete specimen and the crack opening width, so-called tensile softening curve, by continuing the tensile test. There is a problem. As a measure to solve this problem, the tensile softening curve is obtained by performing a tensile test using a tensile tester equipped with a loading mechanism that rapidly reduces the load applied to the concrete specimen in response to the occurrence of cracks and the rate of its development. Seeking is done. Such a tensile tester is expensive, and there is a problem in that an accurate tensile softening curve cannot be obtained because the response speed to cracking and its growth rate is insufficient.

Therefore, an object of the present invention is to inexpensively use a tensile tester which does not have a loading mechanism for sharply lowering the load in response to the occurrence of cracks and the speed of its development, and
Used for concrete pure tensile test method and tensile tester, which can easily obtain accurate tension-softening curve and can trace the occurrence of cracks in concrete specimens and the decrease of tensile stress corresponding to the growth rate thereof Providing a testing machine jig.

[0005]

In order to achieve the above-mentioned object, the present invention according to claim 1 provides a tensile test through a loading plate sandwiching an upper surface and a lower surface of a specimen. In the tensile test method of pulling the test piece attached to the machine, the loading plates are connected by the tension spring attached to the test piece, and the tensile load is loaded in the vertical direction, and the tensile load is the spring sharing load and the test piece sharing load. It is characterized in that the tensile stress of the test piece, the load causing cracking of the test piece, and the displacement of the test piece are obtained by dividing into two parts. The invention according to claim 2 is
In a tensile tester that pulls a specimen mounted on a tensile tester via a loading plate that sandwiches the upper and lower surfaces of the specimen, a tester jig is attached to the specimen and a tension spring that connects between the loading plates. Is provided on the loading plate.

[0006]

In this invention as described above, in the invention as set forth in claim 1, in the tensile test method as described above, the loading plates are connected by a tension spring provided in parallel with the specimen, and the loading plate is pulled vertically. The load is applied, the spring-bearing load is subtracted from the total load, and the load-bearing load of the specimen is obtained. The tensile stress of the specimen, the load causing cracking in the specimen, and the displacement of the specimen are obtained. According to the invention of claim 2, in the tensile tester as described above, the tensile spring of the tester jig, which is provided alongside the test piece and connects between the loading plates, shares the entire load with the tension spring and the test piece. .

[0007]

EXAMPLE A tensile tester for carrying out the present invention is a conventional tensile tester which does not have a loading mechanism for rapidly reducing the load in accordance with the rate of progress of cracking. The tool 1 is attached. The tester jig 1 has a tensile spring 4, and when the concrete test piece 2 is installed in a tensile tester (not shown), the load of the tensile tester placed on the upper surface and the lower surface of the concrete test piece 2 is set. Tensile springs 4 are provided on both sides of the concrete specimen 2 between the plates 3 and 3'to connect the two. As the tension spring 4, one having a suitable spring coefficient is appropriately selected and used depending on the type of the concrete specimen 2 and the composition of its components. The spring modulus for steel fiber reinforced concrete is 66000-227000 Kgf / cm. In addition, concrete specimen 2 is loaded with loading plates 3 and 3'and concrete specimen 2
The upper side surface and the lower side surface are attached to the transverse plates 5 and 5'which are provided so as to surround the upper side surface and the lower side surface, and then mounted on a tensile tester. When the tensile load of the tensile tester is zero, the attachment of the tension spring 4 is adjusted so that the displacement of the tension spring 4 becomes zero.

The concrete pure tensile test method of the present invention is the concrete test piece 2 mounted as described above.
In the same manner as in the conventional case, the load P ₁ ,
Loading is performed while gradually increasing P ₂ ... P _n . On this occasion,
Loading the load P _1, P ₂ ... vertical loading plate 3, 3 'displacement [delta] ₁ while corresponding to _{P n ..., δ 2 ... δ} n ... the measured displacement meter. The measured displacements δ ₁ , δ ₂ ... δ _n ... and the loads P ₁ , P ₂
.. P _n is shown in Equation 1 (Equation 1) and FIG.

[0009]

## EQU1 ## P = kδ + α where k is the spring coefficient, and α is the shared load of the concrete test piece 2.

In such a case, the relational characteristic between the displacement and the load k · δ shown in the general formula 1 of the tension spring 4 is obtained in advance, and the load P ₁ applied to the upper and lower loading plates 3 and 3 ′ is obtained. , P ₂ ... P _n ... Part of the load of the specimens α ₁ , α ₂ ... α _n ... which is applied to the concrete specimen 2 as shown in FIG. From the loads P ₁ , P ₂ ... P _n ... To the respective loads P ₁ , P ₂ ... P _n
The spring sharing load k · δ shared by the tension spring 4 corresponding to
₁ , k · δ ₂ … k ・ δ _n … remaining residuals, and after cracking, as shown in Fig. 3, even if the load increases, the load allotted to the specimen decreases. It will be. This specimen load sharing is equal to the tensile stress of the concrete specimen 2.

[0011] The relationship between the crack opening width and the tensile stress of the concrete specimen 2 (tensile softening curve) measured by applying a dynamic load increasing as P ₁ , P ₂ ... P _n ...
In the crack zone and the bridging zone (see FIG. 4), the tensile stress of the concrete test piece 2 decreases as the crack opening width of the concrete test piece 2 increases, and the load P _{n of the} trailing load is reduced to the load of the preceding load. Even if the tensile test is continued after increasing the load from P _n-1, the load increase corresponding to the displacement δ _n between the upper and lower loading plates 3 and 3 ′ is shared by the tension spring 4, and the concrete load at the load P _n is The sample-bearing load α _n applied to the sample 2 is α _n = P _n −k · δ _n according to Equation 1.
Therefore, the load α _n applied to the concrete specimen 2 decreases corresponding to the displacement δ _n between the upper and lower loading plates 3 and 3 ′.

When the loads P ₁ , P ₂ ... P _n , which are loaded between the upper and lower loading plates 3 and 3'in the above-described one, are increased, the concrete specimen 2 is applied to the concrete specimen 2 from the time when the crack is generated. The applied load decreases immediately in response to the crack propagation speed and the increase in displacement between the upper and lower loading plates 3, 3 '. Then, the displacement δ _n after cracking and the displacement δ _m after cracking were measured, and the difference between them was the crack opening width δ _{cn of} the concrete specimen 2, and the contribution of the concrete specimen 2 corresponding to the displacement δ _n was shared. The load α _n is obtained by Equation 1, and this measurement is similarly performed at a plurality of points to show the correlation between the crack opening width and the shared load (equal to the tensile stress) of the concrete specimen 2 as shown in FIG. It is possible to obtain the correct tensile softening characteristics. This tensile softening property can be used to trace the relationship between the decrease in tensile stress and the crack opening width. In FIG. 4, the vertical axis represents tensile stress:
σ (kgf / cm ² ), the horizontal axis represents the crack opening width: δ _C (mm), and the micro crack zones in the A to B areas on the characteristic curve are different due to delamination of the concrete aggregate interface. The bridging zone of B to C areas on the characteristic curve means the area where a crack is generated, and the area where the stress is transmitted by the meshing of the aggregate although there is only one crack.

[0013]

The present invention is as described above, and the invention according to claim 1 pulls the test piece mounted on the tensile tester via a loading plate that sandwiches the upper surface and the lower surface of the test piece. In the tensile test method, the tension springs attached to the specimen are used to connect the loading plates together, and the tensile load is applied in the vertical direction.The tensile load is divided into the spring-balanced load and the specimen-balanced load, and the tension of the specimen is Since the stress, the load that causes cracks in the test piece, and the displacement of the test piece are calculated, it is cheap to use a tensile tester that does not have a loading mechanism that sharply reduces the load in response to the progress rate of cracking. In addition, an accurate tension softening curve can be easily obtained, and it is possible to trace the occurrence of cracks in the specimen and the decrease in tensile stress corresponding to the growth rate thereof. The invention according to claim 2 is
In a tensile tester that pulls a specimen mounted on a tensile tester via a loading plate that sandwiches the upper and lower surfaces of the specimen, a tension spring that connects the loading plates to the tester jig is attached to the specimen. Since it is provided, it is possible to share the total load between the tension spring and the specimen, and use a tensile tester that does not have a loading mechanism that sharply lowers the load according to the progress rate of crack initiation. Thus, an accurate tensile softening curve can be obtained easily and inexpensively, and it is possible to trace the occurrence of cracks in the specimen and the decrease in tensile stress corresponding to the rate of its development.

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view showing a state in which a concrete specimen for carrying out the present invention is attached to a loading plate of a tensile tester using a tester jig.

FIG. 2 is a characteristic diagram showing the relationship between the load obtained by the pure tensile test method of the present invention and the displacement of the concrete specimen.

FIG. 3 is a characteristic diagram showing a relationship between a shared load and a displacement of a concrete specimen obtained by the above pure tensile test method.

FIG. 4 is a tensile softening characteristic diagram showing the relationship between the displacement and the tensile stress of the concrete specimen after the crack in FIG. 3 has occurred.

FIG. 5 is a schematic vertical cross-sectional view showing a state in which a concrete specimen for performing a conventional tensile test method is attached to a loading plate of a tensile tester.

FIG. 6 is a characteristic diagram showing the relationship between the load obtained by the above tensile test method and the displacement of the concrete specimen.

[Explanation of symbols]

 1 Tester jig 2 Concrete specimen 3,3 'Loading plate 4 Tension spring 5,5' Horizontal plate

Claims (2)

[Claims] 1. In a tensile test method for pulling a specimen mounted on a tensile tester through a loading plate that sandwiches the upper surface and the lower surface of the specimen, a tension spring is attached to the specimen to connect the loading plates. , Loading a tensile load in the up-and-down direction, dividing the tensile load into a spring-bearing load and a specimen-bearing load, tensile stress of the specimen, load causing cracking in the specimen, and displacement of the specimen. A method for determining the pure tensile strength of concrete, which is characterized in that 2. A tensile tester for pulling a specimen mounted on a tensile tester via a loading plate sandwiching the upper surface and the lower surface of the specimen, in which a tension spring for connecting between the loading plates is provided alongside the specimen. A tester jig for a concrete pure tensile tester, which is provided on a loading plate.