Concrete experiment beam capable of monitoring full-length strain of reinforcing steel bar

Abstract

The invention discloses a concrete experiment beam capable of realizing full-length strain monitoring of reinforcing steel bars, the concrete experiment beam internally comprises multiple layers of longitudinal bars with measurable full-length strain and multiple columns of stirrups with measurable full-length strain, each stirrup is composed of two hooked reinforcing steel bars with consistent structures and two stirrup limbs, the free ends of the two hooked reinforcing steel bars are welded with a steel sleeve, and the steel sleeve is welded with a steel beam. Sleeves at the ends of the hook steel bars are connected through stirrup limbs to form a closed annular stirrup structure, long and straight grooves extending longitudinally are formed in the two sections of stirrup limbs, optical fibers are attached to the inner walls of the long and straight grooves, and the optical fibers extend out of the concrete beam to be connected to an optical fiber demodulator to read data. The surface non-transverse rib area of the longitudinal rib is provided with a small-size groove penetrating in the axial direction of the longitudinal rib, and an optical fiber sensor is attached to the small-size groove and also extends out of the concrete beam. The method can effectively improve adverse factors which cannot be monitored by a traditional testing technology, and is convenient to evaluate and ensure the safety of the concrete structure.

Description

Technical Field

[0001] The invention belongs to the technical field of reinforced concrete performance testing, and in particular relates to a concrete test beam capable of realizing full-length strain monitoring of reinforced concrete. Background Art

[0002] Steel bar strain measurement plays a vital role in the field of civil engineering. It is essential for evaluating and ensuring the safety, durability and functionality of concrete structures. It is directly related to the structural safety, performance evaluation and life prediction of buildings and infrastructure. Through the accurate measurement of steel bar strain, engineers can verify and optimize the structural design to ensure the reliability and stability of the structure under various loading conditions. This measurement capability enables engineers to monitor the response of the structure in real time, so as to promptly detect and repair potential structural damage and avoid catastrophic accidents. Steel bar strain measurement is also crucial for construction quality control. It can ensure the accurate placement of steel bars and the correct pouring of concrete during construction, thereby ensuring the overall performance of the structure. In addition, this measurement technology is also very useful in structural reinforcement and renovation projects, which can help evaluate the effectiveness of reinforcement measures and provide data support for future maintenance and repair.

[0003] One of the commonly used methods for measuring steel bar strain is to use strain gauges, which are pasted or embedded in concrete structures to measure the strain of concrete. Strain gauges can sense tiny deformations of concrete and convert them into electrical signals for output. After amplification and processing, these electrical signals can be used to calculate the strain of concrete. However, this type of steel bar strain measurement technology has the following limitations and shortcomings: 1. It destroys the bond between steel bars and concrete, changes the stress performance of reinforced concrete components, and cannot obtain the stress conditions of steel bars under real stress conditions.

[0004] 2. There is locality and lack of data continuity. Existing technologies can usually only provide strain information in local areas and cannot provide continuous strain distribution data along the entire length of the steel bars, which limits the comprehensive understanding of the overall behavior of the structure.

[0005] 3. Increased construction complexity. Traditional strain gauges need to be pasted or fixed on steel bars during construction. Welding and other operations during construction will inevitably cause damage to the strain gauges, increasing construction complexity and cost.

[0006] 4. Durability issue: The strain gauges attached to the surface of the steel bars may be damaged by environmental factors (such as humidity, temperature changes, and chemical corrosion), affecting their long-term durability and reliability.

[0007] 5. Existing technologies may not be able to achieve real-time data transmission or require a complex data acquisition system, affecting the safety and reliability of the design.

[0008] The above shortcomings have resulted in the inability to quickly and easily obtain real and accurate concrete reinforcement strain data for a long time, which in turn has had an adverse impact on the accuracy and safety of reinforced concrete component design. Summary of the invention

[0009] In order to solve the above problems, the present invention discloses a concrete test beam which can realize full-length strain monitoring of steel bars, effectively improving the disadvantages of traditional testing technology and facilitating the evaluation and ensuring the safety of concrete structures.

[0010] To achieve the above object, the technical solution of the present invention is as follows: A concrete test beam capable of realizing full-length strain monitoring of steel bars comprises multiple layers of full-length strain-measurable longitudinal bars and multiple rows of full-length strain-measurable stirrups, wherein the full-length strain-measurable stirrups comprise two U-shaped hook steel bars of the same structure, the two hook steel bars are arranged opposite to each other and clamp the full-length strain-measurable longitudinal bars, a sleeve is welded to the free end of each hook steel bar, the sleeves at both ends of the two hook steel bars are connected to form a whole through a stirrup limb respectively, the top and bottom of the beam of the full-length strain-measurable longitudinal bars are provided with two anchoring end plates, each of the anchoring end plates is respectively fixed at the ends of the longitudinal bars at the top and bottom of the beam; each full-length strain-measurable stirrup limb is provided with a long straight groove penetrating along its axial direction, the inner wall of the long straight groove is pasted with an optical fiber, the optical fiber extends out of the stirrup limb and is connected to a demodulation device, and a small-sized groove penetrating along its axial direction is provided in the surface of each full-length strain-measurable longitudinal bar without a transverse rib area, the inner wall of the small-sized groove is continuously pasted with an optical fiber, the optical fiber extends out of the longitudinal bar and is connected to a demodulation device.

[0011] As a supplement to the present invention, each of the stirrup limbs with full-length strain measurable has external thread sections at both ends, and the two ends of the stirrup limb pass through the sleeve and are fixed by nuts assembled on the stirrup limb.

[0012] As a supplement to the present invention, each of the longitudinal bars with full-length strain measurable has external thread sections at both ends, and the longitudinal bars pass through the bar holes of the anchor end plate and are fixed by nuts assembled on the longitudinal bars on both sides of the anchor end plate.

[0013] As a supplement to the present invention, the length of the external thread sections at both ends of the steel bar is 5mm-20mm.

[0014] As a supplement to the present invention, the nuts on the stirrup limbs or the nuts on the longitudinal bars are all hexagonal nuts or threaded steel sleeves, and the diameter of the hexagonal nuts is the same as the diameter of the steel bars.

[0015] As a supplement to the present invention, the optical fiber adopts a nylon coated cable, the optical fiber is bonded with a cyanoacrylate adhesive, and an epoxy resin protective layer is applied on the surface of the optical fiber.

[0016] As a supplement to the present invention, the length of the optical fiber is 400 mm-2400 mm.

[0017] As a supplement to the present invention, the stirrup limb with full-length strain measurable is made of ribbed steel bars or plain round steel bars, and the diameter thereof is 8mm-20mm.

[0018] As a supplement to the present invention, the long straight groove of the stirrup with full-length strain measurable has a depth of 3mm-5mm and a width of 3mm-5mm.

[0019] As a supplement to the present invention, the width of the small-size groove of the longitudinal reinforcement with full-length strain measurable is 3mm-5mm, and the depth is 3mm-5mm.

[0020] As a supplement to the present invention, anchor end plates are provided at both ends of the longitudinal reinforcement with full-length strain measurable, and the thickness of the anchor end plates is 10mm-20mm.

[0021] As a supplement to the present invention, the optical fiber wire extending out of the end of the longitudinal reinforcement with full-length strain measurable is sheathed with a polyvinyl chloride (PVC) tube, and the connection between the PVC tube and the longitudinal reinforcement is fixed by steel wire binding, and the diameter of the PVC tube is 2-3mm.

[0022] The concrete test beam capable of realizing full-length strain monitoring of steel bars of the present invention adopts a four-point bending loading scheme, and a full-length strain testing scheme of steel bars is adopted only in the left half-span beam section, the steel bars in the right half-span beam section are not grooved, and dense stirrups are arranged.

[0023] The beneficial effects of the present invention are: Without destroying the bonding performance between steel bars and concrete, the strain of the entire length of the steel bars can be measured. The closed connection form can effectively ensure the restraint performance of the stirrups on the concrete. The stirrups are all made of welding-free mechanical connections, which can effectively avoid damage to the optical fiber sensor caused by high welding temperature. The slotted and pasted optical fiber sensor greatly guarantees long-term durability. The full-length strain measurement obtains data from each part in real time, ensures the safety and rationality of the design, and can promptly discover potential structural problems for existing structures.

[0024] 1. The present invention effectively eliminates the influence of the traditional measurement method on the bonding performance between steel bars and concrete by grooving and continuously pasting the optical fiber sensor.

[0025] 2. The optical fiber sensor is continuously pasted along the length direction of the inner side of the stirrup limb of the present invention, and the continuous strain along the entire length of the stirrup limb can be obtained, so that the actual stress condition of the steel bar can be accurately obtained, which greatly reduces the error of the traditional measurement method and ensures a comprehensive understanding of the overall behavior of the structure.

[0026] 3. The stirrup limbs of the present invention are combined with the hook steel bars into stirrups by mechanical connection, which effectively avoids damage to the optical fiber sensor caused by high welding temperature, thereby ensuring the readability of the measurement data and reducing the complexity and cost of construction.

[0027] 4. The present invention provides a certain degree of physical protection for the optical fiber sensor by slotting inside the stirrups and digging grooves on the surface of the longitudinal reinforcement, making it less susceptible to external damage or environmental erosion, thereby ensuring its long-term durability to a great extent.

[0028] 5. The full-length strain measurement of the present invention can help verify and calibrate the structural design theory to ensure the safety and rationality of the design. For existing structures, measuring the full-length strain of the steel bars can monitor the use status and health of the structure and discover potential structural problems in a timely manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a stereogram of the experimental beam of the present invention.

[0030] Figure 2 It is a loading schematic diagram of the present invention.

[0031] Figure 3 It is a three-dimensional view of the interior of the concrete test beam of the present invention.

[0032] Figure 4 It is a three-dimensional diagram of stirrup assembly of the present invention.

[0033] Figure 5 It is a cross-sectional view of the stirrup assembly of the present invention.

[0034] List of Figure Symbols: 1. Longitudinal reinforcement, 2. Stirrups, 3. Hooked steel bars, 4. Casing, 5. Stirrup limbs, 6. Anchor end plates at the top of the beam, 7. Anchor end plates at the bottom of the beam, 8. Optical fiber, 9. Nuts on the stirrup limbs, 10. Anchor end plates, 11. Nuts on the longitudinal reinforcement. DETAILED DESCRIPTION

[0035] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0036] As shown in the figure, a concrete test beam capable of realizing full-length strain monitoring of steel bars described in the present invention comprises longitudinal bars 1 with measurable full-length strain and stirrups 2 with measurable full-length strain, the longitudinal bars 1 are divided into upper and lower layers, a plurality of stirrups 2 clamp the longitudinal bars 1 at intervals, and grooves are provided inside the longitudinal bars 1 and the stirrups 2 for setting optical fibers 8, the longitudinal bars 1 and the stirrups 2 are both in the concrete test beam, and the optical fibers extend out of the concrete test beam and are connected to a demodulation device.

[0037] The production process is as follows: The first step is to make stirrup limb 5. The specific process is as follows: 1. First, thread the two ends of the steel bar with a thread section length of 5mm-20mm.

[0038] 2. Then cut the steel bar (cylindrical) into two halves (semi-cylindrical) along the axis of the length of the steel bar by wire cutting.

[0039] 3. Use wire cutting or punching to cut long straight grooves along the axis of the steel bar on two sections. The depth is 3mm-5mm, the width is 3mm-5mm, and the length is the same as the length of the steel bar.

[0040] 4. Optical fibers are attached to the inner wall of the groove along the axis of the steel bar, such as Figure 3 As shown, the optical fiber extends out of the steel bar and is connected to the demodulation device.

[0041] 5. Finally, the two cut sections of steel bars (semi-cylindrical) are re-bonded into stirrup limb 5 (cylindrical) by high-strength epoxy glue, and the optical fiber is led out from one end of the steel bar, or from both ends.

[0042] In the second step, the method for making the hook steel bar 3 with sleeves 4 at both ends is as follows: 1. First, bend the steel bar into hook steel bar 3 (U-shaped) with hooks at both ends by using a steel bar bending machine or manual hook bending. The hook section is 90 degrees to the straight section, and the length of the hook section is 50mm-100mm.

[0043] 2. Secondly, the sleeve 4 and the hook section of the hook steel bar 3 are connected to form a whole by welding.

[0044] The third step is to assemble the stirrups that can measure the full-length strain as follows: 1. Connect the two ends of stirrup limb 5 with the matching nuts respectively and screw them to the root of the threaded section.

[0045] 2. Then, pass the two ends of the stirrup limb 5 through the sleeves at the ends of the two hook steel bars respectively, and one end of the sleeve is close to the nut at the root of the threaded section.

[0046] 3. Finally, connect the threaded section of the stirrup limb with another matching nut and screw it until it fits tightly with the other end face of the casing to finally form a closed stirrup 2.

[0047] Step 4: The method for making the longitudinal reinforcement 1 is as follows: (1) Use a thread lathe to make threads on both ends of the steel bar. This threaded section, combined with the steel bar thread sleeve, can provide effective end anchoring when assembling the steel bar skeleton in the later stage.

[0048] (2) A groove with a width of 3 mm and a depth of 5 mm was punched and milled on the surface of the steel bar. Since in the later test, only the steel bars in the half-span beam section were subjected to the continuous strain measurement system (the other half-span was the stirrup reinforcement densification area), the longitudinal bars did not need to be grooved throughout the entire length, but only half the length. Two optical fibers were attached to the inner wall of the long straight groove, and the optical fibers extended out of the stirrup limb and were connected to the demodulation equipment.

[0049] (3) In the groove of the steel bar, the optical fiber is bonded with a nylon-coated cable using a cyanoacrylate adhesive, and an epoxy resin protective layer is applied to the surface of the optical fiber. Then, silicone is fully coated in the groove.

[0050] In order to reduce the test cost, for the four-point bending test beam, the full-length strain test scheme of the steel bars is only used in the left half-span beam section. The steel bars in the right half-span beam section are not grooved, and dense stirrups are configured to prevent shear failure, as shown in Figure 1. Regarding the anchoring of the longitudinal reinforcement, the conventional end hook processing method will make it difficult to lead the optical fiber, and the wire cannot be smoothly led out of the beam end. Therefore, this test sets anchor end plates at both ends of the longitudinal reinforcement, which, on the one hand, facilitates the precise positioning of the longitudinal reinforcement, and on the other hand, can provide effective anchoring for the longitudinal reinforcement. The specific plan is as follows: (4) Use 10 mm thick steel plates to make the top longitudinal reinforcement anchorage end plate 6 and the bottom longitudinal reinforcement anchorage end plate 7 of the beam respectively. The anchorage end plates are provided with reinforcement holes. The upper and lower end plates are positioned and connected as a whole by welding short steel bars to provide support for the longitudinal reinforcement skeleton.

[0051] (5) Pass the longitudinal reinforcement 1 through the reinforcement hole of the end plate and embed it with a hexagonal nut or a threaded steel sleeve. During the installation process, the grooved side of the longitudinal reinforcement should face the side of the beam.

[0052] (6) Plastic corrugated tubes are used to protect the conductors extending out of the ends of the longitudinal reinforcement. Steel wires are used to tie and fix the connections between the corrugated tubes and the reinforcement. Stirrup reinforcement is used within the range of the beam end supports to further enhance the anchorage and prevent local concrete damage.

[0053] (7) In order to achieve accurate positioning of the longitudinal reinforcement skeleton, the ends of the beam spans with denser stirrups are also anchored with perforated steel plates.

[0054] The present invention adopts a stirrup distributed strain test scheme, which is closer to the actual stress condition of traditional closed stirrups, and can form effective anchoring and restraint, and protect the internal optical fiber. The specific scheme is as follows: (1) Make a hook steel bar 3 as the bottom component of the closed stirrup, and weld a connecting ring (sleeve 4) at both ends of the hook steel bar. To prevent the out-of-plane bending moment from being generated when the stirrup limb is under tension, the sleeve 4 needs to be symmetrically welded to the opposite ends of the hook steel bar with the axis of the hook steel bar as the center.

[0055] (2) The stirrup 5 with the distributed optical fiber sensor pasted inside is passed through the casing 4 and fixed with a hexagonal nut.

[0056] (3) It is necessary to make a hook steel bar segment as the top component of the stirrup and tie it with the stirrup limb as a whole, which can effectively restrain the lateral buckling of the compressive longitudinal reinforcement.

[0057] (4) After the concrete is poured and demoulded, a perforated steel plate is installed on the top of the beam and connected to the stirrups through nuts.

[0058] Working process: When measuring the strain of the experimental beam during the stress deformation process, the optical fiber led out from the stirrup limbs and the ends of the longitudinal reinforcement is connected to the strain demodulator, and the full-length continuous strain distribution of the steel bars inside the experimental beam can be measured in real time.

[0059] It should be noted that the above content only illustrates the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications all fall within the protection scope of the claims of the present invention.

Claims

1. A concrete test beam capable of realizing full-length strain monitoring of steel bars, characterized in that: The structure comprises a plurality of layers of full-length strain-measurable longitudinal reinforcement (1) and a plurality of rows of full-length strain-measurable stirrups (2), wherein the full-length strain-measurable stirrups (2) comprise two U-shaped hook steel bars (3) of the same structure, the two hook steel bars (3) are arranged opposite to each other and clamp the full-length strain-measurable longitudinal reinforcement (1), a sleeve (4) is welded to the free end of each hook steel bar (3), the sleeves at both ends of the two hook steel bars are connected to form a whole by a stirrup limb (5), and the top and bottom of the full-length strain-measurable longitudinal reinforcement (1) are provided with two anchor end blocks. Plates (6), (7), each of the anchoring end plates is respectively fixed at the ends of the longitudinal reinforcement at the top and bottom of the beam; each stirrup limb (5) with full-length strain measurable is provided with a long straight groove extending through the axial direction thereof, an optical fiber (8) is attached to the inner wall of the long straight groove, the optical fiber extends out of the stirrup limb (5) and is connected to a demodulation device; each longitudinal reinforcement (1) with full-length strain measurable is provided with a small-sized groove extending through the axial direction thereof in a surface area without transverse ribs, an optical fiber (8) is continuously attached to the inner wall of the small-sized groove, the optical fiber extends out of the longitudinal reinforcement (1) and is connected to a demodulation device.

2. A concrete test beam capable of realizing full-length strain monitoring of steel bars according to claim 1, characterized in that: Each stirrup limb (5) with full-length strain measurable has external thread sections at both ends, the length of the external thread sections is 5 mm-20 mm, and the two ends of the stirrup limb (5) pass through the sleeve (4) and are fixed by nuts (9) assembled on the stirrup limb.

3. The concrete test beam capable of realizing full-length strain monitoring of steel bars according to claim 1, characterized in that: Each longitudinal reinforcement (1) with full-length strain measurable has external thread sections at both ends, the length of the external thread sections is 5 mm-20 mm, and the longitudinal reinforcement passes through the reinforcement holes of the anchor end plate and is fixed by nuts (11) assembled on the longitudinal reinforcement at both sides of the anchor end plate.

4. The concrete test beam capable of realizing full-length strain monitoring of steel bars according to claim 1, characterized in that: The length of the optical fiber (8) is 400 mm-2400 mm.

5. The concrete test beam capable of realizing full-length strain monitoring of steel bars according to claim 1, characterized in that: The optical fiber (8) adopts a nylon coated cable, and is bonded with a cyanoacrylate adhesive, and an epoxy resin protective layer is applied on the surface of the optical fiber.

6. The concrete test beam capable of realizing full-length strain monitoring of steel bars according to claim 1, characterized in that: The stirrup limb (5) with full-length strain measurable is made of ribbed steel bars or plain round steel bars, and has a diameter of 8 mm to 20 mm.

7. The concrete test beam capable of realizing full-length strain monitoring of steel bars according to claim 1, characterized in that: The long straight groove of the full-length strain-measurable stirrup (2) and the small-sized groove of the full-length strain-measurable longitudinal reinforcement (1) are both 3mm-5mm in depth and 3mm-5mm in width.

8. The concrete test beam capable of realizing full-length strain monitoring of steel bars according to claim 1, characterized in that: Anchor end plates are arranged at both ends of the longitudinal reinforcement (1) with full-length strain measurable, and the thickness of the anchor end plates is 10 mm to 20 mm.

9. The concrete test beam capable of realizing full-length strain monitoring of steel bars according to claim 1, characterized in that: The optical fiber wire extending out of the end of the longitudinal reinforcement (1) with full-length strain measurable is sheathed with a PVC tube, and the connection between the PVC tube and the longitudinal reinforcement is fixed by binding with steel wire, and the diameter of the PVC tube is 2-3 mm.

10. The method for monitoring the full-length strain of steel bars in a concrete test beam according to claim 1, characterized in that: The following steps are involved: The prepared concrete test beam has multiple layers of full-length strain-measurable longitudinal reinforcement (1) and multiple rows of full-length strain-measurable stirrups (2), and the optical fibers led out from the stirrup limbs and the ends of the longitudinal reinforcement are connected to an external strain demodulator. The two sides of the bottom of the concrete test beam are leveled, and pressure is applied downward from the middle of the top of the concrete test beam, so that the full-length continuous strain distribution of the steel bars inside the test beam can be measured in real time.

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