Reinforcing steel bar rust expansive force simulation test device and method based on trapezoidal interface stress conversion

Abstract

The invention discloses a reinforcing steel bar rust expansive force simulation test device and method based on trapezoidal interface stress conversion. The device comprises a base, two supporting frames, two stress conversion devices, two steel pressure-bearing components, a steel sleeve and a jack. Each stress conversion device comprises a steel bar, a conical steel sleeve, a conical clamping piece and a concrete test piece. By the adoption of the device, the method is based on trapezoidal interface stress conversion, compared with pressurized liquid injection equipment, interface circumferential stress can be more uniform, and meanwhile, an interface rust expansion force-rust expansion displacement corresponding relation can be rapidly established through interface stress balance on the basis of the drawing load-drawing displacement relation; moreover, by adjusting the taper angle of the conical steel sleeve, the interface rust expansive force applying speed can be controlled, and different corrosion rates or corrosion product expansive rates can be simulated; moreover, by adjusting the size of the peripheral conical clamping piece, the rust expansion under different steel bar diameters can be simulated more conveniently.

Description

Technical Field

[0001] The present invention relates to the technology in the field of simulation tests, and in particular to a simulation test device and method for the rust expansion force of steel bars based on the force conversion of a trapezoidal interface. Background Art

[0002] The corrosion of steel bars is an important factor affecting the durability of reinforced concrete structures. In environments such as humidity and chloride ion erosion, the volume of the oxide generated by the corrosion of steel bars expands (usually 2-4 times the original volume), generating a rust expansion force and a rust expansion displacement at the steel bar-concrete interface. When the circumferential tensile stress formed by the rust expansion force and the rust expansion displacement exceeds the tensile strength of the concrete, the concrete cover cracks, that is, rust expansion cracking occurs. With the development of the rust expansion force and the rust expansion displacement, the concrete wrapping the steel bars will experience the whole process from partial cracking of the interface to complete cracking. The cracked concrete will accelerate the speed of external air and chloride ions eroding the steel bars, thereby accelerating the deterioration of the structure. In addition, as a non-linear material, the energy consumption during the cracking process of concrete of different sizes is affected by the size effect, which affects the bond strength of the concrete to the steel bars. There may be a size effect on the relationship between the interface rust expansion force and the rust expansion displacement of geometrically similar components of different sizes, and the influence of factors such as the diameter of the steel bars and the size of the concrete cover needs to be considered. Therefore, studying the evolution mechanism and measurement method of the rust expansion force and the rust expansion displacement at the steel bar-concrete interface is of great significance for evaluating the structure life and optimizing the protection measures.

[0003] For the simulation test of the corrosion at the steel bar-concrete interface, currently mainly through physical experiments, such as the electrochemical accelerated corrosion method to simulate the corrosion process of steel bars, and strain gauges or displacement sensors are used to measure the surface deformation of the concrete. In addition, a finite element analysis can be used to establish a steel bar-concrete interface model to simulate the expansion stress distribution of the corrosion products.

[0004] In the prior art, for example, Chinese invention patent 2012100370438 discloses a device and method for simulating and monitoring the expansion cracking of concrete. The interface rust expansion force is applied by setting radial liquid outlet holes in the middle of the steel bar. During the process of injecting liquid and pressurizing into the steel bar, the pressure is applied to the outer heat shrinkable tube through the liquid outlet holes and transmitted to the outer concrete through the heat shrinkable tube, thereby simulating the application process of the rust expansion force, and a pressure gauge is set at the end of the steel bar to measure the internal pressure, which is used to represent the rust expansion force.

[0005] However, the pressure value inside the steel bar may not be consistent with the actual pressure value applied to the concrete, and it is susceptible to factors such as the liquid outlet hole diameter and the self-expansion resistance of the heat-shrinkable tube. Also, due to the presence of the heat-shrinkable tube, the magnitude of the force applied at the interface may be uneven; moreover, the above method cannot measure the interface corrosion-induced expansion displacement, and thus cannot establish the relationship between the corrosion-induced expansion force and the interface corrosion-induced expansion displacement; meanwhile, the acceleration rate of the interface corrosion-induced expansion force in the above method is not easy to control; in addition, the above method cannot simulate the corrosion-induced expansion under various steel bar diameters and is restricted by the thread size of the pressure gauge. Therefore, it is necessary to study a solution to solve the above problems. Summary of the Invention

[0006] In view of this, in view of the deficiencies in the prior art, the main object of the present invention is to provide a steel bar corrosion-induced expansion force simulation test device and method based on trapezoidal interface force conversion, which can effectively solve the problems existing in the existing devices and methods for simulating and monitoring concrete expansion cracking, such as uneven magnitude of the force applied at the interface, inability to establish the relationship between the corrosion-induced expansion force and the interface corrosion-induced expansion displacement, difficult control of the acceleration rate of the corrosion-induced expansion force, and inability to simulate the corrosion-induced expansion under various steel bar diameters.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A steel bar corrosion-induced expansion force simulation test device based on trapezoidal interface force conversion includes a base, two support frames, two force conversion devices, two steel bearing members, a steel sleeve, and a jack; the two support frames are symmetrically and separately arranged on the base; the two force conversion devices are symmetrically and respectively arranged on the two support frames, and each force conversion device includes a steel bar, a tapered steel sleeve, tapered clamping pieces, and a concrete specimen. The two ends of the steel bar respectively have a first threaded section and a second threaded section. The tapered steel sleeve is screwed to the first threaded section. The tapered clamping pieces are multiple, and the multiple tapered clamping pieces are sleeved outside the tapered steel sleeve and form a cylinder with the tapered steel sleeve. The concrete specimen is sleeved outside the cylinder, and a dial indicator is arranged on the concrete specimen; the two steel bearing members are opposite to each other and are respectively fixed to the inner sides of the two concrete specimens; the steel sleeve is screwed between the second threaded sections of the two steel bars; one end of the jack is fixedly connected to a steel bearing member, a pressure sensor is fixed to the other end of the jack, and the pressure sensor is fixedly connected to the other steel bearing member.

[0009] Preferably, the length of the first threaded section is greater than the length of the second threaded section, and there is a non-threaded section between the first threaded section and the second threaded section.

[0010] Preferably, the tapered clamping pieces are three, the taper angle of the tapered clamping pieces is the same as the taper angle of the tapered steel sleeve, and the three tapered clamping pieces are combined into a cylinder with an axial tapered through hole.

[0011] Preferably, through holes are formed through both ends of the steel sleeve, and the inner wall of the through hole is threaded.

[0012] Preferably, two dial gauges are arranged on the concrete specimen, and the two dial gauges are symmetrically arranged along the steel bar.

[0013] Preferably, the steel bearing member is formed by welding and combining two steel plates with circular holes in the middle and four steel columns.

[0014] Preferably, the support frame includes a T-shaped steel frame, a semi-circular connecting member is arranged above the T-shaped steel frame, circular through holes with the same diameter as the flange plates of the T-shaped steel frame are arranged at both ends of the semi-circular connecting member, the circular through holes on the same side are aligned and the steel bar is fixed by screwing a nut and a threaded nail respectively.

[0015] Preferably, the base is a steel plate, and the lower end of the T-shaped steel frame is welded and fixed to the base.

[0016] Preferably, the jack is a hollow hydraulic jack.

[0017] A method for simulating the corrosion expansion force of steel bars based on the force conversion of a trapezoidal interface, using the aforementioned device for simulating the corrosion expansion force of steel bars based on the force conversion of a trapezoidal interface, includes the following steps:

[0018] (a) Threadedly connect the tapered steel sleeve with the first threaded section of the steel bar, and rotate the tapered steel sleeve to the non-threaded section. Then, put the tapered clamping pieces on the tapered steel sleeve. Multiple tapered clamping pieces are combined into a cylinder with an axial tapered through hole. Fix multiple tapered clamping pieces with a rubber band. Then, pour a concrete specimen on the cylinder. The two ends of the concrete specimen are respectively aligned with the two ends of the cylinder to form a force conversion device with a trapezoidal interface;

[0019] (b) Fabricate two force conversion devices with the same size of trapezoidal interfaces. First, threadedly connect the steel sleeve with the second threaded section of the steel bar in one of the force conversion devices. Then, successively put on the steel bearing member, the jack, the pressure sensor, and another steel bearing member. Finally, connect another force conversion device with a trapezoidal interface to the steel sleeve through the second threaded section of the steel bar. Finally, place the combined device of the two on two T-shaped steel frames. One of the T-shaped steel frames is combined with the semi-circular connecting member, the nut, and the threaded nail to fix one of the steel bars. Finally, install dial gauges on the concrete specimen, and fix the base of the dial gauge on the base;

[0020] (c) Use a jack to pull the entire device. The pulling force is obtained through a pressure sensor. The relative slip between the steel bar and the concrete specimen, and the pulling displacement are obtained through a dial gauge to obtain the relationship between the pulling load and the pulling displacement. The pulling force is converted into the circumferential tensile stress on the concrete through the force conversion device with a trapezoidal interface, and the longitudinal pulling displacement is converted into the radial displacement of the interface to obtain the interface expansion force, that is, the relationship between the rust expansion force and the interface rust expansion displacement.

[0021] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solutions:

[0022] By adopting the device of the present invention, the method of the present invention is based on the method of force conversion of a trapezoidal interface. Compared with the pressure injection equipment, the circumferential force on the interface can be made more uniform. At the same time, based on the relationship between the pulling load and the pulling displacement, through the force balance of the interface, the corresponding relationship between the interface rust expansion force and the rust expansion displacement can be quickly established. Moreover, by adjusting the cone angle of the tapered steel sleeve, the application rate of the interface rust expansion force can be controlled to simulate different corrosion rates or corrosion product expansion rates. And by adjusting the size of the peripheral tapered clamping pieces, it is more convenient to simulate the rust expansion under different steel bar diameters. In addition, by longitudinally stacking multiple interface tapered modules, the rust expansion under different corrosion lengths can be simulated. Furthermore, the symmetric pulling design of the present invention is convenient for carrying out comparative experiments on repetitive test data. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is an assembled three-dimensional schematic diagram of a preferred embodiment of the present invention;

[0024] Figure 2 is a partial assembly schematic diagram of a preferred embodiment of the present invention;

[0025] Figure 3 is another partial assembly schematic diagram of a preferred embodiment of the present invention;

[0026] Figure 4 is an exploded schematic diagram of the T-shaped steel frame in a preferred embodiment of the present invention;

[0027] Figure 5 is an enlarged schematic diagram of the steel bearing member in a preferred embodiment of the present invention;

[0028] Figure 6 is a combined schematic diagram of the steel bar, the tapered steel sleeve and the tapered clamping piece in a preferred embodiment of the present invention;

[0029] Figure 7 is an exploded schematic diagram of the steel bar, the tapered steel sleeve and the tapered clamping piece in a preferred embodiment of the present invention;

[0030] Figure 8 is an analysis diagram of the force and displacement of the trapezoidal interface in a preferred embodiment of the present invention.

[0031] Description of the drawing reference numerals:

[0032] 10. Base 20. Support frame

[0033] 21. T-shaped steel frame 211. Flange

[0034] 22. Semi-circular connecting piece 23. Nut

[0035] 24. Threaded nail 30. Force conversion device

[0036] 31. Steel bar 311. First threaded section

[0037] 312. Second threaded section 313. Non-threaded section

[0038] 32. Tapered steel sleeve 33. Tapered clamping piece

[0039] 34. Concrete specimen 35. Dial gauge

[0040] 40. Steel bearing member 41. Steel plate

[0041] 42. Steel column 50. Steel sleeve

[0042] 60. Jack 70. Pressure sensor Detailed implementation manners

[0043] Please refer to Figures 1 to 7 shown in the figure, which shows the specific structure of a steel bar rust expansion force simulation test device based on the force conversion of a trapezoidal interface according to a preferred embodiment of the present invention, including a base 10, two support frames 20, two force conversion devices 30, two steel bearing members 40, a steel sleeve 50, and a jack 60.

[0044] The base 10 is a steel plate and has a square structure.

[0045] The two support frames 20 are symmetrically and separately arranged on the base 10; specifically, the support frame 20 includes a T-shaped steel frame 21, a semi-circular connecting piece 22 is arranged above the T-shaped steel frame 21, and circular through holes with the same diameter as the flanges 211 of the T-shaped steel frame 21 are arranged at both ends of the semi-circular connecting piece 22. The circular through holes on the same side are aligned and respectively threadedly connected to the T-shaped steel frame 21 through nuts 23 and threaded nails 24. In addition, the lower end of the T-shaped steel frame 21 is fixedly welded to the base 10.

[0046] The two force conversion devices 30 are symmetrically arranged on the two support frames 20 respectively. Each force conversion device 30 includes a steel bar 31, a tapered steel sleeve 32, tapered clamping pieces 33 and a concrete specimen 34. Both ends of the steel bar 31 respectively have a first threaded section 311 and a second threaded section 312. The tapered steel sleeve 32 is screwed and connected to the first threaded section 311. There are multiple tapered clamping pieces 33. The multiple tapered clamping pieces 33 are sleeved outside the tapered steel sleeve 32 and form a cylinder with the tapered steel sleeve 31. The concrete specimen 34 is sleeved outside the cylinder, and a dial indicator 35 is arranged on the concrete specimen 34. In this embodiment, the aforementioned nut 23 is threadedly connected to the threaded nail 24 to fix the steel bar 31. The length of the first threaded section 311 is greater than that of the second threaded section 312, and there is a non-threaded section 313 between the first threaded section 311 and the second threaded section 312. The inner wall of the through hole of the tapered steel sleeve 32 has threads for screwing and connecting with the first threaded section 311. There are three tapered clamping pieces 33. The taper angle of the tapered clamping pieces 33 is the same as that of the tapered steel sleeve 31. The three tapered clamping pieces 33 are combined into a cylinder with an axial tapered through hole. The included angle between the tapered steel sleeve 31 and the tapered clamping pieces 33 can be set arbitrarily to simulate the corrosion expansion under different corrosion rates or different corrosion product expansion rates. Moreover, the size of the ring formed by the multiple tapered clamping pieces 33 can be set arbitrarily to simulate the corrosion expansion of different steel bar diameters. There are two dial indicators 35 arranged on the concrete specimen 34, and the two dial indicators 35 are symmetrically arranged along the steel bar 31.

[0047] The two steel bearing members 40 face each other and are respectively fixed to the inner sides of the two concrete specimens 34. The steel bearing member 40 is welded and combined by two steel plates 41 with round holes in the middle and four steel columns 42.

[0048] The steel sleeve 50 is screwed and connected between the second threaded sections 312 of the two steel bars 31. Through holes (not shown in the figure) are formed through both ends of the steel sleeve 50, and the inner wall of the through hole has threads for screwing and connecting with the second threaded section 312.

[0049] One end of the jack 60 is fixedly connected to a steel bearing member 40, a pressure sensor 70 is fixed to the other end of the jack 60, and the pressure sensor 70 is fixedly connected to the other steel bearing member 40. In this embodiment, the jack 60 is a hollow hydraulic jack.

[0050] The present invention also discloses a method for simulating the corrosion expansion force of steel bars based on the force conversion of a trapezoidal interface. Using the aforementioned device for simulating the corrosion expansion force of steel bars based on the force conversion of a trapezoidal interface, it includes the following steps:

[0051] (a) Thread-connect the tapered steel sleeve 32 with the first threaded section 311 of the steel bar 31, and rotate the tapered steel sleeve 32 to the non-threaded section 313. Then, put the tapered clamping pieces 33 on the tapered steel sleeve 32. Multiple tapered clamping pieces 33 are combined into a cylinder with an axial tapered through-hole. Fix multiple tapered clamping pieces 33 with a rubber band (not shown in the figure). Then, pour the concrete specimen 34 on the cylinder. The two ends of the concrete specimen 34 are aligned with the two ends of the cylinder respectively to form a force conversion device 30 with a trapezoidal interface.

[0052] (b) Fabricate two force conversion devices 30 with the same size of trapezoidal interfaces. First, thread-connect the steel sleeve 50 with the second threaded section 312 of the steel bar 31 in one of the force conversion devices 30. Then, successively put on the steel bearing member 40, the jack 60, the pressure sensor 70 and another steel bearing member 40. Finally, connect another trapezoidal interface force conversion device 30 to the steel sleeve 50 through the second threaded section 312 of the steel bar 31. Finally, place the combined device of the two on two T-shaped steel frames 21. Combine one of the T-shaped steel frames 21 with the semi-circular connecting piece 22, the nut 23 and the threaded nail 24 to fix one of the steel bars 31. Finally, install a dial gauge 35 on the concrete specimen 34, and fix the base of the dial gauge 35 on the base 10.

[0053] (c) Use the jack 60 to pull out the whole device. The pulling force is obtained through the pressure sensor 70. The relative slip between the steel bar 31 and the concrete specimen 34 and the pulling displacement are obtained through the dial gauge 35 to get the relationship between the pulling load and the pulling displacement. The pulling force is converted into the circumferential tensile stress on the concrete through the force conversion device 30 with a trapezoidal interface, and the longitudinal pulling displacement is converted into the interface radial displacement to obtain the interface expansion force, that is, the relationship between the rust expansion force and the interface rust expansion displacement.

[0054] As Figure 8 shown, assume that the cone angles of the steel sleeve 50 and the tapered clamping pieces 33 are α, and the relationship between the bonding stress τ and the pulling force P is: τ = P / πd b l d . The relationship between the bonding stress τ and the interface radial stress σ n is: tan(α + arctanμ) = τ / σ n ; where μ is the friction coefficient. Therefore: the relationship between the pulling force P and the interface radial stress σ n is: Let the pulling displacement be u, and the interface radial displacement be u n , then the relationship between the two is: tanα = u / u n .

[0055] The design focus of the present invention is as follows: By adopting the device of the present invention, the method of the present invention is based on the force conversion of the trapezoidal interface. Compared with the pressure injection equipment, it can make the circumferential force on the interface more uniform. At the same time, based on the relationship between the pull-out load and the pull-out displacement, through the force balance on the interface, the corresponding relationship between the interface corrosion expansion force and the corrosion expansion displacement can be quickly established. Moreover, by adjusting the cone angle of the conical steel sleeve, the application speed of the interface corrosion expansion force can be controlled to simulate different corrosion rates or corrosion product expansion rates. And by adjusting the size of the peripheral conical clamping pieces, it is more convenient to simulate the corrosion expansion under different steel bar diameters. In addition, through the longitudinal superposition of multiple interface conical modules, the corrosion expansion under different corrosion lengths can be simulated. Furthermore, the symmetric pull-out design of the present invention is convenient for carrying out comparative analysis of repetitive test data.

[0056] The technical principle of the present invention has been described above in combination with specific embodiments. These descriptions are only for explaining the principle of the present invention and cannot be construed in any way as a limitation on the protection scope of the present invention. Based on the explanations herein, those skilled in the art can readily conceive of other specific embodiments of the present invention without creative efforts, and these embodiments will fall within the protection scope of the present invention.

Claims

1. A simulation test device for the rust expansion force of steel bars based on the force conversion of a trapezoidal interface, characterized in that: It includes a base, two support frames, two force conversion devices, two steel bearing members, a steel sleeve and a jack; the two support frames are symmetrically and separately arranged on the base; the two force conversion devices are symmetrically arranged on the two support frames respectively, and each force conversion device includes a steel rod, a tapered steel sleeve, tapered clamping pieces and a concrete specimen. The two ends of the steel rod respectively have a first threaded section and a second threaded section. The tapered steel sleeve is screwed to the first threaded section. The tapered clamping pieces are multiple, and the multiple tapered clamping pieces are sleeved outside the tapered steel sleeve and form a cylinder with the tapered steel sleeve. The concrete specimen is sleeved outside the cylinder, and a dial gauge is arranged on the concrete specimen; the two steel bearing members are opposite to each other and are respectively fixed to the inner sides of the two concrete specimens; the steel sleeve is screwed between the second threaded sections of the two steel rods; one end of the jack is fixedly connected to a steel bearing member, a pressure sensor is fixed at the other end of the jack, and the pressure sensor is fixedly connected to the other steel bearing member.

2. The steel bar corrosion expansion force simulation test device based on the force conversion of the trapezoidal interface according to claim 1, wherein: The length of the first threaded section is greater than that of the second threaded section, and there is a non-threaded section between the first threaded section and the second threaded section.

3. The steel bar corrosion expansion force simulation test device based on the force conversion of the trapezoidal interface according to claim 1, characterized in that: The tapered clamping pieces are three, the taper angle of the tapered clamping pieces is the same as that of the tapered steel sleeve, and the three tapered clamping pieces are combined into a cylinder with an axial tapered through hole.

4. The steel bar corrosion expansion force simulation test device based on the force conversion of the trapezoidal interface according to claim 1, characterized in that: Through holes are formed through both ends of the steel sleeve, and the inner wall of the through hole has threads.

5. The steel bar corrosion expansion force simulation test device based on the force conversion of the trapezoidal interface according to claim 1, characterized in that: Two dial gauges are arranged on the concrete specimen, and the two dial gauges are symmetrically arranged along the steel rod.

6. The simulated test device for the steel bar corrosion expansion force based on the force conversion of the trapezoidal interface as described in claim 1, wherein: The steel bearing member is welded and combined by two steel plates with round holes in the middle and four steel columns.

7. The steel bar corrosion expansion force simulation test device based on the force conversion of the trapezoidal interface according to claim 1, characterized in that: The support frame includes a T-shaped steel frame, a semi-circular connecting piece is arranged above the T-shaped steel frame, and circular through holes with the same diameter as the flange plates of the T-shaped steel frame are arranged at both ends of the semi-circular connecting piece. The circular through holes on the same side are aligned and the steel rod is fixed respectively by screwing with nuts and threaded nails.

8. The steel bar corrosion expansion force simulation test device based on the force conversion of the trapezoidal interface according to claim 1, characterized in that: The base is a steel plate, and the lower end of the T-shaped steel frame is welded and fixed to the base.

9. The simulated test device for the steel bar corrosion expansion force based on the force conversion of the trapezoidal interface according to claim 1, wherein: The jack is a hollow hydraulic jack.

10. A simulation test method for the rust expansion force of steel bars based on the force conversion of a trapezoidal interface, characterized in that, Using the steel bar corrosion expansion force simulation test device based on trapezoidal interface force conversion as described in any one of claims 1-9, it includes the following steps: (a) Thread the tapered steel sleeve to the first threaded section of the steel rod, and rotate the tapered steel sleeve to the non-threaded section. Then sleeve the tapered clamping pieces on the tapered steel sleeve. The multiple tapered clamping pieces are combined into a cylinder with an axial tapered through hole. Fix the multiple tapered clamping pieces with a rubber band. Then pour the concrete specimen on the cylinder. The two ends of the concrete specimen are respectively aligned with the two ends of the cylinder to form a force conversion device with a trapezoidal interface; (b) Fabricate two force conversion devices with trapezoidal interfaces of the same size. First, thread-connect the steel sleeve with the second threaded section of the steel bar in one of the force conversion devices. Then, successively put on the steel bearing member, the jack, the pressure sensor, and another steel bearing member. Finally, connect the force conversion device with the other trapezoidal interface to the steel sleeve through the second threaded section of the steel bar. Finally, place the combined device of the two on two T-shaped steel frames. One of the T-shaped steel frames is combined with the semi-circular connecting piece, the nut, and the threaded nail to fix one of the steel bars. Finally, install dial gauges on the concrete specimen, and fix the bases of the dial gauges on the base. (c) Use the jack to pull the entire device. The pulling force is obtained through the pressure sensor. The relative slip between the steel bar and the concrete specimen, and the pulling displacement are obtained through the dial gauge to obtain the relationship between the pulling load and the pulling displacement. The pulling force is converted into the circumferential tensile stress on the concrete through the force conversion device with the trapezoidal interface, and the longitudinal pulling displacement is converted into the radial displacement of the interface to obtain the interface expansion force, that is, the relationship between the rust expansion force and the interface rust expansion displacement.

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