Test piece for testing torsional shear strength of concrete thin-wall round pipe and construction method of test piece

Abstract

The invention provides a test piece for testing the torsional shear strength of a concrete thin-wall round pipe, and belongs to the technical field of test pieces for testing the torsional shear strength. The structure comprises a concrete thin-wall circular pipe, concrete convex ribs are uniformly distributed on the outer side wall of the concrete thin-wall circular pipe in the circumferential direction, and short ribs are uniformly distributed at the two ends of the concrete thin-wall circular pipe in the circumferential direction; the fixing ends are used for being connected to the two ends of the concrete thin-wall round pipe, rib holes allowing the short ribs to penetrate through are formed in the fixing ends, and grooves used for being connected with the concrete protruding ribs in a clamped mode are formed in the inner side walls of the fixing ends. Through uniform loading in the shear flow direction, short rib transmission and concrete convex rib transmission are adopted, and the shear bearing capacity test of the concrete thin-wall round pipe and the thin-wall pipe can be achieved.

Description

Technical Field

[0001] This invention relates to the field of torsional shear strength test specimens, and more particularly to a torsional shear strength test specimen for a thin-walled concrete circular tube and its construction method. Background Technology

[0002] There are few research reports on torsional tests of concrete members both domestically and internationally. Given the continuous advancement of architectural design methods, the torsional design of reinforced concrete members is becoming increasingly important. Torsional shear stress in concrete is considered a method for obtaining the pure shear strength index of concrete, but there has been no concrete shear strength test conducted using pure torsional specimens.

[0003] It is very difficult to test the concrete shear strength of thin-walled circular tubes, mainly because it is difficult to achieve torsion of the thin-walled concrete circular tubes by means of loading. Summary of the Invention

[0004] In view of this, in order to overcome the above-mentioned shortcomings in the prior art, on the one hand, the present invention provides a test specimen for the torsional shear strength of a thin-walled concrete circular tube, which can realize the shear bearing capacity test of the thin-walled concrete circular tube by uniformly loading along the shear flow direction and using three methods: short reinforcement transfer, concrete rib transfer, and adhesive transfer.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A test specimen for the torsional shear strength of a thin-walled concrete circular tube includes: A thin-walled concrete circular tube has concrete ribs evenly distributed along the circumference of its outer wall and short bars evenly distributed along the circumference of its two ends. The fixed end is used to connect to both ends of the thin-walled concrete tube. It has a rib hole for the short reinforcement to pass through, and a groove on its inner side wall for engaging with the concrete rib.

[0006] Preferably, the concrete rib is bonded to the groove.

[0007] Preferably, the short rib is bonded to the rib hole.

[0008] Preferably, the bottom width of the concrete rib is greater than three times its thickness, and its length is greater than three times the bottom width.

[0009] On the other hand, the present invention also provides a method for constructing a test specimen for the torsional shear strength of the above-mentioned thin-walled concrete circular tube, comprising the following steps: Step 1): Fabricate a thin-walled concrete circular tube; Step 2): Constructing the thin-walled concrete circular tube: Step 21) Short ribs are set along the end circumference of the thin-walled concrete tube to apply uniform torsional shear stress to the specimen in the form of bearing shear force. Step 22) Concrete ribs are provided circumferentially on the outer wall of the thin-walled concrete tube; Step 3): Make a fixed end. Make a rib hole in the end cap of the fixed end to transmit tangential shear force. Make a groove on its inner side wall to transmit tangential shear force. Apply tangential shear force through the groove to twist the thin-walled circular tube. Step 4): Connect an external torsion device to perform a torsional shear strength test.

[0010] Preferably, the length of the thin-walled concrete tube is more than three times the length of the constrained portion at the fixed end, in order to overcome the influence of the end constraint.

[0011] Preferably, the thickness of the thin-walled concrete tube is no more than 1 / 8 of its diameter.

[0012] The torsional shear strength test specimen for thin-walled concrete circular tubes provided by this invention can achieve the shear bearing capacity test of thin-walled concrete circular tubes by uniformly loading along the shear flow direction and employing three methods: short reinforcement transfer, convex rib transfer, and adhesive transfer. Compared with existing technologies, it has the following beneficial effects: 1) A torsional loading test was performed on a thin-walled concrete circular tube by uniformly applying torsional shear stress, and its torsional shear stress was tested. 2) Reliable uniform loading is achieved by uniformly setting short reinforcing bars to resist shear, uniformly setting protruding ribs to enhance the shear resistance of concrete, and connecting them with the loading device (preferably by bonding the loading device to the contact point of the thin-walled concrete tube, or by using structural adhesive). 3) This test method has a theoretical solution, and the shear capacity of the material can be calculated based on the loading values. It can test the theoretical torsional shear stress of concrete. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of the thin-walled concrete circular tube in this invention; Figure 2 This is a schematic diagram of the fixed end in this invention; Figure 3 This is a schematic diagram of the overall structure of the specimen formed after the thin-walled concrete circular tube and the fixed end are assembled in this invention. In the figure, 1. thin-walled concrete tube, 11. concrete rib, 12. short bar, 2. fixed end, 21. bar hole, 22. groove. Detailed Implementation

[0014] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0015] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0016] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "sleeved / connected," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0017] Torsion of thin-walled cylinders is generally considered an ideal test specimen for obtaining the pure shear strength of materials. However, for concrete, the material strength is not high and the brittleness is relatively large, making it difficult to effectively implement loading methods and prone to end breakage and loading failure.

[0018] This invention does not employ the traditional method of applying external torque, but instead applies torque by locally applying torque at the end.

[0019] The purpose of applying torque is to generate a uniformly distributed shear flow on the cross-section of the thin-walled concrete tube. After avoiding the influence range of local stress caused by the "Saint-Venant principle", the cross-section is in a pure torsional state.

[0020] like Figure 1-3 As shown, the present invention provides a test specimen for the torsional shear strength of a thin-walled concrete circular tube, comprising: A thin-walled concrete circular tube 1 has concrete ribs 11 evenly distributed circumferentially on its outer wall, and short bars 12 evenly distributed circumferentially at both ends. The anchorage length of the short bars 12 in the thin-walled concrete circular tube 1 meets the basic requirements for tensile anchorage length. The wall thickness of the thin-walled concrete circular tube 1 meets the requirement of not exceeding 1 / 8 of the diameter. The concrete ribs 11 are used to transmit tangential shear force. The bottom width of the cross section of the concrete ribs 11 should be greater than three times the thickness, and the length should be greater than three times the bottom width. Fixed end 2, which is used to connect to both ends of the concrete thin-walled circular tube 1, has a rib hole 21 for the short reinforcing bar 12 to pass through, and a groove 22 on its inner side wall for engaging with the concrete rib 11. The torsional shear force of the short reinforcing bar is transmitted through the rib hole 21, and the tangential shear force is applied through the groove 22 to torsion the concrete thin-walled circular tube 1. The concrete rib 11 and the groove 22 transmit a uniform shear force flow through mechanical interlocking force, and the uniform shear force flow is transmitted through the shear resistance of the short reinforcing bar 11 and the rib hole 21.

[0021] The length of the thin-walled concrete tube 1 should be more than three times the length of the constrained portion at the fixed end to overcome the influence of the end constraint. The constrained portion at the fixed end can be the constraint portion of the thin-walled concrete tube 1 formed by the groove 22 and the rib hole 21. The concrete ribs 11 and grooves 22 are preferably bonded together with cementitious materials, and the short bars 12 and the bars 21 are preferably bonded together with cementitious materials, so that the shear force is uniformly transmitted through chemical bonding force.

[0022] The torsional shear strength test specimen of the thin-walled concrete circular tube provided by the present invention is reliable as it will not fail when shear force is applied before shear failure occurs.

[0023] On the other hand, the present invention also provides a method for constructing a test specimen for the torsional shear strength of the above-mentioned thin-walled concrete circular tube, comprising the following steps: Step 1): Construct a thin-walled concrete circular tube 1. Its length should be more than three times the length of the constrained portion at the fixed end to overcome the influence of the end constraint. The thickness of the thin-walled concrete circular tube 1 should not exceed 1 / 8 of its diameter. Step 2): Construct the thin-walled concrete circular tube 1, specifically as follows: Step 21) Short ribs 12 are provided along the end circumference of the thin-walled concrete tube 1, preferably at the center of the thin wall, to apply uniform torsional shear stress to the specimen in the form of bearing shear force. Specifically, this can be done as follows: Step 22) Concrete ribs 11 are provided circumferentially on the outer wall of the thin-walled concrete tube. Tangential shear force is applied through the groove 22 of the fixed end 2 to twist the thin-walled concrete tube 1. Preferably, the fixed end 2 (groove 22, rib hole 21) is bonded to the concrete ribs 11 and short ribs 12 with cementitious materials, which can also transfer part of the torsional stress. Step 3): Make a fixed end 2. Make a rib hole 21 in the end cap of the fixed end 2 to transmit tangential shear force. Make a groove 22 on its inner side wall to transmit tangential shear force. Apply tangential shear force through the groove 22 to twist the thin-walled concrete tube 1. Step 4): Connect the external torsion device and conduct a torsional shear strength test. The test is conducted without removing the formwork. After assembling the fixed end 2 with the thin-walled concrete pipe 1, the entire structure is poured. A conventional torsion device can be selected for the external torsion device.

[0024] The above are merely preferred embodiments of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A test specimen for the torsional shear strength of a thin-walled concrete circular pipe, characterized in that, include: A thin-walled concrete circular tube has concrete ribs evenly distributed along the circumference of its outer wall and short bars evenly distributed along the circumference of its two ends. The fixed end is used to connect to both ends of the thin-walled concrete tube. It has a rib hole for the short reinforcement to pass through, and a groove on its inner side wall for engaging with the concrete rib.

2. The torsional shear strength test specimen for a thin-walled concrete circular tube according to claim 1, characterized in that, The concrete ribs are bonded together with the grooves.

3. The torsional shear strength test specimen for a thin-walled concrete circular tube according to claim 1, characterized in that, The short ribs are bonded together with the rib holes.

4. The torsional shear strength test specimen for a thin-walled concrete circular tube according to claim 1, characterized in that, The concrete rib has a cross-sectional bottom width greater than three times its thickness and a length greater than three times its cross-sectional bottom width.

5. A method for constructing a torsional shear strength test specimen for a thin-walled concrete circular tube according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1): Fabricate a thin-walled concrete circular tube; Step 2): Constructing the thin-walled concrete circular tube: Step 21) Short ribs are set along the end circumference of the thin-walled concrete tube to apply uniform torsional shear stress to the specimen in the form of bearing shear force. Step 22) Concrete ribs are provided circumferentially on the outer wall of the thin-walled concrete tube; Step 3): Make a fixed end. Make a rib hole in the end cap of the fixed end to transmit tangential shear force. Make a groove on its inner side wall to transmit tangential shear force. Apply tangential shear force through the groove to twist the thin-walled circular tube. Step 4): Connect an external torsion device to perform a torsional shear strength test.

6. The method for constructing a test specimen for the torsional shear strength of a thin-walled concrete circular tube according to claim 5, characterized in that, The length of the thin-walled concrete tube is more than three times that of the constrained portion at the fixed end, in order to overcome the influence of the end constraint.

7. A method for constructing a torsional shear strength test specimen for a thin-walled concrete circular tube according to claim 5 or 6, characterized in that, The thickness of the thin-walled concrete tube is no more than 1 / 8 of its diameter.

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