Decoupling experiment device and analysis method for low-temperature interfacial force of concrete filled steel tube with hollow interlayer
By designing an experimental device and analysis method for decoupling interfacial forces in hollow sandwich steel tube concrete at low temperatures, quantitative decoupling of the components of interfacial forces was successfully achieved. This solved the problem of the complex influence mechanism of interfacial forces under low temperature conditions, improved measurement accuracy and calculation accuracy, and supported the safe design and assessment of structures in cold regions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING UNIV OF CIVIL ENG & ARCHITECTURE
- Filing Date
- 2026-01-30
- Publication Date
- 2026-04-21
AI Technical Summary
Existing technologies are unable to effectively decouple the components of interfacial forces in hollow steel-concrete composite structures at low temperatures, resulting in complex interfacial force mechanisms that are difficult to extend to low-temperature environments and multi-interfacial types, thus restricting safety design and performance evaluation.
A decoupling experimental device and analysis method for low-temperature interfacial forces in hollow sandwich steel tube concrete were designed. Through innovative experimental device and step-by-step decoupling logic, the four components of interfacial forces, including chemical bonding force, low-temperature freezing force, mechanical interlocking force and friction force, were quantitatively evaluated. The measurements were performed using specially designed specimens and sensor systems.
This study enabled a refined analysis of the interfacial forces of hollow steel-concrete composite structures, revealing the damage and evolution mechanisms under low-temperature conditions. It provides a reliable basis for the safety design and assessment of structures in cold regions and improves the accuracy of measurement and interfacial force calculation.
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Figure CN121899008A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of civil engineering materials and structural testing technology, and more specifically, to an experimental apparatus and analytical method for quantitatively separating and evaluating the components of interfacial forces in hollow sandwich steel tube concrete under low-temperature conditions. Background Technology
[0002] Hollow-core steel-concrete composite structures are high-performance composite structures developed from steel-concrete composite structures, widely used in buildings, bridges, and wind turbine towers. The interfacial performance between the steel tube and concrete is fundamental to ensuring the coordinated operation of all components in hollow-core steel-concrete composite structures. Existing research is limited to ambient temperature environments and steel-concrete interface types. However, hollow-core steel-concrete composite structures exhibit two interface types: outer steel tube-concrete and concrete-inner steel tube. Furthermore, at low temperatures, the interfacial forces are multifaceted, including chemical bonding forces, freezing forces, mechanical interlocking forces, and frictional forces. The mechanisms influencing these interfacial forces are complex, encompassing pore water freezing, non-uniform temperature deformation, damage to the interfacial bonding layer material, and changes in normal pressure. Low temperatures, based on different mechanisms, couple the components of these multi-type interfacial forces, leading to difficulties in decoupling the interfacial forces and unclear mechanisms. This hinders the expansion of the application scope to low-temperature environments and multi-interfacial types, thus limiting the development of calculation formulas for interfacial forces in hollow-core steel-concrete composite structures at low temperatures. Therefore, there is an urgent need for a set of decoupled experimental apparatus and analysis method for the force composition of steel tube-concrete interface that can be applied to low-temperature environments and multiple interface types, so as to provide a reliable basis for the safety design and performance evaluation of hollow sandwich steel tube concrete in cold region engineering. Summary of the Invention
[0003] This disclosure aims to provide an experimental apparatus and analytical method for the quantitative decoupling of interfacial force components in hollow steel-concrete composite structures under low-temperature and freeze-thaw environments. The apparatus and method conduct a refined study of the bonding behavior of two interfaces in hollow steel-concrete composite structures—the outer steel tube-concrete interface and the concrete-inner steel tube interface—under complex low-temperature environments. Through innovative experimental apparatus design and step-by-step decoupling analytical logic, the effective separation and quantitative evaluation of four components in the interfacial forces—chemical bonding force, low-temperature freezing force, mechanical interlocking force, and frictional force—are achieved. This reveals the damage and evolution mechanism of interfacial performance under low-temperature environments, providing a reliable basis for the design and safety assessment of hollow steel-concrete composite structures in cold regions.
[0004] To achieve the above objectives, this disclosure provides a low-temperature interfacial force decoupling experimental device for hollow sandwich steel-concrete composite structures. The device includes a steel-concrete interfacial tension specimen, a hollow sandwich steel-concrete interfacial ejection specimen, an interfacial normal tension device, an interfacial tangential repeated ejection and sliding device, a low-temperature environment chamber, a low-temperature control system, a displacement sensor, a temperature sensor, a data acquisition system, and a bidirectional strain gauge. Its specific features are as follows: A steel-concrete interface tension test specimen includes a first steel plate, a second steel plate, a concrete block, a central threaded rod, short threaded rods, a first nut, a second nut, a third nut, a protective nut, and a central nut. Both the first and second steel plates have openings at their centers, and a certain distance is maintained between them. The central threaded rod passes through the openings in both plates, fixing the first plate with the first and second nuts, and fixing the second plate with the third nut and the protective nut. The second and third nuts are located inside the first and second steel plates. At least four short threaded rods are welded to the outer side of the second steel plate, evenly distributed at the corners. Before welding the short threaded rods, a precision connecting sleeve is used to connect the central threaded rod and a second extension threaded rod to the outside of the protective nut to fix the second and third steel plates. The short threaded rods are then fixed on the third steel plate before welding to ensure strict alignment during the tension test. After welding, the precision connecting sleeve, the second extension threaded rod, and the third steel plate are removed. A concrete block is then poured inside the first and second steel plates.
[0005] Hollow-core steel-concrete interface ejection specimens include an inner interface ejection specimen and an outer interface ejection specimen. Both the inner and outer interface ejection specimens contain an outer steel pipe and an inner steel pipe, with concrete poured between the outer and inner steel pipes. The bottom surface of the inner interface ejection specimen is flush with the outer steel pipe, concrete, and inner steel pipe, while the top surface shows the inner steel pipe protruding a certain distance from the concrete and outer steel pipe, serving as a sliding section. The top surface of the outer interface ejection specimen is flush with the outer steel pipe, concrete, and inner steel pipe, while the bottom surface shows the outer steel pipe protruding a certain distance from the concrete and inner steel pipe, serving as a sliding section.
[0006] An interface normal tension joint device includes a tensile testing machine, a first extension screw, a second extension screw, a precision connecting sleeve, a third steel plate, and a connecting nut. The first extension screw is connected to the upper clamp of the tensile testing machine and passes through a low-temperature environment chamber, while the second extension screw is connected to the lower clamp of the tensile testing machine and passes through the low-temperature environment chamber. The precision connecting sleeve is used to connect the first extension screw and the central screw of the steel plate-concrete interface tension joint specimen. The third steel plate has a hole at a position consistent with the central hole of the second steel plate and the short screw of the steel plate-concrete interface tension joint specimen, and is connected to the second extension screw and the short screw through the connecting nut. The protective nut is removed during loading.
[0007] The interface tangentially pushes out a sliding device, which includes a pressure testing machine, a loading block, and a base; the height of the loading block is greater than the sum of the wall thickness of the low temperature environment chamber and the sliding distance, and the diameter is slightly smaller than the inner diameter of the outer steel pipe of the outer interface pushing out the specimen; Displacement sensors are used to measure the displacement of steel plate-concrete interface tension specimens and hollow sandwich steel tube-concrete interface ejection specimens. Temperature sensors are used to measure the temperature of steel plate-concrete interface tension specimens and hollow sandwich steel tube-concrete interface ejection specimens. Two-dimensional strain gauges are arranged on the outer wall of the outer steel tube that pushes the specimen out at the outer interface and on the inner wall of the inner steel tube that pushes the specimen out at the inner interface, and are used to measure the circumferential strain and axial strain during the temperature change and the pushing and sliding process. The data acquisition system is used to collect load, displacement, temperature, and strain data. Loads are obtained using a tensile testing machine and a compression testing machine; strain data includes circumferential strain and axial strain measured by bidirectional strain gauges.
[0008] This device is specifically designed to address the decoupling requirements of the four components of low-temperature interfacial forces in hollow steel-tube concrete, and has the following characteristics and advantages compared to existing technologies: (1) The device can expand the scope of application for measuring interfacial forces in steel-concrete structures, including "outer steel pipe-concrete" and "concrete-inner steel pipe", as well as in low-temperature environments. (2) By accurately comparing interfacial forces at room temperature and low temperature, normal and tangential directions, and single and repeated tests, the device can achieve quantitative separation and decoupling of all components of interfacial forces in multiple interfacial types and low-temperature environments. This helps to reveal the working mechanism of each component of low-temperature interfacial forces and supports the formulation of corresponding interfacial force calculation formulas. (3) The device cleverly solves the problem of low measurement accuracy caused by loading eccentricity and accidental damage in previous interfacial tension test methods by using a central screw, protective nut, and pre-alignment connection before welding. This effectively improves measurement accuracy and meets the decoupling requirements. (4) The device can be used for single and multiple repeated tangential push-slip tests, which facilitates the study of the degradation characteristics and damage mechanism of interfacial forces during multiple slip processes. (5) The device design is based on the characteristic analysis of each component of low-temperature interfacial forces. It has a simple structure, is easy to process, has a clear loading path, and has excellent effects.
[0009] In some embodiments, in the low-temperature interface tangential repeated push-out sliding device, the strain gauge used for low-temperature testing is a low-temperature strain gauge, which is bonded with low-temperature special adhesive and sealed and protected with silicone rubber.
[0010] In some embodiments, the concrete at the interface to be tested in the steel plate-concrete interface tension specimen and the hollow sandwich steel pipe-concrete interface ejection specimen can be ordinary concrete or recycled aggregate concrete, and the steel plate or steel pipe can be made of materials with different strengths or with different surface roughness treatments.
[0011] In some embodiments, the cross-sectional dimensions of the outer steel pipe, concrete, and inner steel pipe of the hollow sandwich steel pipe concrete interface specimen can be considered in different combinations to study the influence of the interface normal pressure on the interface tangential properties.
[0012] In some embodiments, a certain number of central nuts are equidistantly arranged between the second nut and the third nut to enhance the anchoring effect between the central screw and the concrete block; during transportation, the protective nuts are tightened to prevent damage to the interface to be tested, and then removed before loading.
[0013] In some embodiments, after a single ejection, the specimen is inverted and ejected repeatedly to study the interfacial force damage in the later stages of slippage. The repeated tangential ejection-slip experiment includes four ejection loading cycles. The first ejection is a forward ejection loading cycle, the second ejection is a reverse ejection loading cycle, the third ejection is a second forward ejection loading cycle, and the fourth ejection is a second reverse ejection loading cycle.
[0014] Based on the above-mentioned device, this disclosure also provides a method for decoupling analysis of low-temperature interfacial forces in hollow sandwich steel tube concrete, used to separate all components of low-temperature interfacial forces, including chemical bonding force, low-temperature freezing force, mechanical interlocking force, and frictional force. The specific method is as follows: A normal tension test was performed on the steel plate-concrete interface tension specimen at room temperature, and the peak stress was taken to obtain the first result. The first result is the chemical bonding force between the steel plate and the concrete in the steel plate-concrete interface tension specimen. A normal tensile test was conducted on the steel plate-concrete interface tension specimen at a set low temperature, and the peak stress was taken to obtain the second result; the second result is the sum of the chemical bonding force between the steel plate and the concrete and the low-temperature freezing force in the steel plate-concrete interface tension specimen. Subtracting the first result from the second result yields the low-temperature freezing force between the steel plate and the concrete, thus establishing a quantitative relationship between low temperature and the low-temperature freezing force. At a set low temperature, the hollow steel-concrete interfacial ejection specimen was subjected to repeated tangential ejection and slippage tests. The first peak stress of the first ejection stress-displacement curve was taken to obtain the third result. The third result is the sum of the chemical bonding force, low-temperature freezing force, mechanical interlocking force, and friction force between the steel pipe and the concrete in the hollow steel-concrete interfacial ejection specimen. The temperature changes of the outer steel pipe wall of the outer interface and the inner steel pipe wall of the inner interface of the specimen were measured, as well as the circumferential and axial strains during the ejection and sliding process. The interface normal pressure was calculated according to formulas (1) and (2). p n Multiplying the interfacial normal pressure by the friction coefficient yields a fourth result, which is the frictional force between the steel pipe and the concrete in the hollow sandwich steel-concrete interface specimen. ; in, E s It is the elastic modulus of the steel pipe.t s It's the thickness of the steel pipe wall. D s It is the diameter of the steel pipe. v s It is the Poisson's ratio of the steel pipe. σ h It is the circumferential stress of the steel pipe. σ z It is the axial stress of the steel pipe. ε h It is the circumferential strain of the steel pipe. ε z It is the axial strain of the steel pipe. α s It is the coefficient of linear expansion of the steel pipe, Δ T It represents temperature change; cooling is negative.
[0015] Subtract the second result from the third result, and then subtract the fourth result to obtain the mechanical biting force.
[0016] Compared with existing technologies, this analytical method has the following characteristics and advantages: (1) By separating the interfacial normal tension and tangential slip properties under normal and low temperature environments, and combining repeated slip and interfacial normal pressure analysis, the chemical bonding force, low temperature freezing force, mechanical interlocking force and friction force of the steel pipe-concrete low temperature interface force are identified and quantitatively decoupled stepwise. This solves the problem that the mechanism is not clearly revealed and it is difficult to extend to low temperature environments due to the previous macroscopic overall interface force fitting. (2) By quantitatively decoupling the components of the interface force, the macroscopic factors of the "outer steel pipe-concrete" and "concrete-inner steel pipe" multi-interface types are brought down to the essential factors, realizing the extension of the hollow sandwich steel pipe concrete interface force analysis to multiple types and low temperature environments. (3) This method is based on the characteristic analysis of the components of the low temperature interface force. The principle is simple and easy to operate and calculate.
[0017] In some embodiments, the coefficient of friction may be selected based on the different roughness of the steel pipe wall.
[0018] In some embodiments, the loss pattern of mechanical engagement force is obtained by comparing the stress-displacement curves of the first and third ejections; and the loss pattern of friction force is obtained by comparing the stress-displacement curves of the second and fourth ejections. Attached Figure Description
[0019] To more clearly illustrate the technical solutions in this disclosure, the accompanying drawings used in this disclosure are described below. It should be understood that the accompanying drawings described below are only for the convenience of clearly illustrating some embodiments of the technical solutions in this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.
[0020] Figure 1 This is a flowchart of the experimental apparatus and analysis method for decoupling low-temperature interfacial forces in hollow sandwich steel tube concrete proposed in the embodiments of this disclosure.
[0021] Figure 2 (a), (b), and (c) are schematic diagrams of the steel plate-concrete interface tension specimens from different perspectives according to the embodiments of this disclosure.
[0022] Figure 3 This is a schematic diagram showing the positioning of the short screw of the steel plate-concrete interface tension specimen before welding, as proposed in an embodiment of this disclosure.
[0023] Figure 4 (a), (b), (c), and (d) are schematic diagrams of the inner interface of the hollow sandwich steel tube concrete interface ejection specimen from different perspectives according to the embodiments of this disclosure.
[0024] Figure 5 (a), (b), (c), and (d) are schematic diagrams of the outer interface of the hollow sandwich steel tube concrete interface ejection specimen from different perspectives according to the embodiments of this disclosure.
[0025] Figure 6 This diagram illustrates the connection relationship between the steel plate-concrete interface tension specimen, the interface normal tension device, the low-temperature environment chamber, and the low-temperature control system involved in the interface tension test proposed in this embodiment.
[0026] Figure 7 This diagram illustrates the connection relationships between the external interface ejection specimen, the interface tangential repeated ejection sliding device, the low-temperature environment chamber, the low-temperature control system, and the displacement sensor involved in the interface tangential repeated ejection sliding experiment proposed in this embodiment of the disclosure.
[0027] Figure 8 This diagram illustrates the connection relationships between the inner interface ejection specimen, the interface tangential repeated ejection sliding device, the low-temperature environment chamber, the low-temperature control system, and the displacement sensor involved in the interface tangential repeated ejection sliding experiment proposed in this embodiment of the disclosure.
[0028] Figure 9 This is a schematic diagram of the bidirectional strain gauge arrangement of the outer interface ejection specimen involved in the interface tangential repeated ejection and sliding experiment proposed in the embodiments of this disclosure.
[0029] Figure 10This is a schematic diagram of the bidirectional strain gauge arrangement of the inner interface ejection specimen involved in the interface tangential repeated ejection and sliding experiment proposed in the embodiments of this disclosure.
[0030] Figure 11 This invention relates to the experimental apparatus and analytical method for decoupling low-temperature interfacial forces in hollow sandwich steel tube concrete according to embodiments of this disclosure, and obtains the quantitative relationship between chemical bonding force and low-temperature freezing force.
[0031] Figure 12 This is a schematic diagram of the first ejection stress-displacement curve obtained from the repeated ejection and sliding experiment in the tangential direction of the interface proposed in the embodiments of this disclosure.
[0032] Figure 13 This is a schematic diagram of the stress-displacement curves obtained from four repeated push-out sliding experiments in the tangential direction of the interface proposed in this embodiment.
[0033] Figure 14 This is a schematic diagram of the decoupling of interfacial forces throughout the entire process, obtained from the experimental apparatus and analysis method for decoupling interfacial forces in hollow sandwich steel tube concrete according to the embodiments of this disclosure.
[0034] Steel plate-concrete interface tension specimen: 1-1 Concrete block; 1-2 First steel plate; 1-3 Second steel plate; 1-4 Short threaded rod; 1-5 First nut; 1-6 Second nut; 1-7 Center nut; 1-8 Third nut; 1-9 Protective nut; 1-10 Center threaded rod; 4-2 Second extension threaded rod; 4-3 Precision connecting sleeve; 4-4 Connecting nut; 4-5 Third steel plate; Hollow sandwich steel tube concrete interface ejection specimen inner interface ejection specimen: 2-1 inner steel tube; 2-2 outer steel tube; 2-3 concrete; Hollow sandwich steel tube concrete interface ejection specimen: 3-1 Inner steel tube; 3-2 Outer steel tube; 3-3 Concrete; Interface normal tension device: 4-1 First extension screw; 4-2 Second extension screw; 4-3 Precision connecting sleeve; 4-4 Connecting nut; 4-5 Third steel plate; 4-6 Low temperature environment chamber; 4-7 Tensile testing machine; Interface tangential repeated sliding device: 4-6 Low temperature environment chamber; 5-1 Loading block; 5-2 Base; 5-3 Displacement sensor; 5-4 Pressure testing machine; 5-5 Bidirectional strain gauge. Detailed Implementation
[0035] The present application is described in detail below, with examples illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be construed as limiting the present application.
[0036] The following is combined Figure 1 This document describes the implementation of the experimental apparatus and analysis method for decoupling low-temperature interfacial forces in hollow sandwich steel tube concrete, as proposed in the embodiments of this disclosure, including the experimental apparatus for decoupling low-temperature interfacial forces in hollow sandwich steel tube concrete and the analysis method for decoupling low-temperature interfacial forces in hollow sandwich steel tube concrete.
[0037] The experimental apparatus for decoupling low-temperature interfacial forces in hollow steel-concrete composite tubes includes a steel-concrete interfacial tension specimen, a hollow steel-concrete composite tube interfacial ejection specimen, an interfacial normal tension device, an interfacial tangential repeated ejection and sliding device, a low-temperature environment chamber, a low-temperature control system, a displacement sensor, a temperature sensor, a data acquisition system, and a bidirectional strain gauge.
[0038] The experiment was conducted using a low-temperature interfacial force decoupling experimental device for hollow-core steel tube concrete. The specific steps are as follows: For the fabrication of steel plate-concrete interface tension specimens, see [link / reference]. Figure 2 The system includes a first steel plate 1-2, a second steel plate 1-3, a concrete block 1-1, a central screw 1-10, a short screw 1-4, a first nut 1-5, a second nut 1-6, a third nut 1-8, a protective nut 1-9, and a central nut 1-7. Both the first steel plate 1-2 and the second steel plate 1-3 have openings in their centers. A certain distance is maintained between the first steel plate 1-2 and the second steel plate 1-3. The central screw 1-10 passes through the openings in the first steel plate 1-2 and the second steel plate 1-3. The first steel plate 1-2 is fixed in position by the first nut 1-5 and the second nut 1-6, and the second steel plate is fixed by the third nut 1-8 and the protective nut 1-9. Positions 1-3; the second nut 1-6 and the third nut 1-8 are located inside the first steel plate 1-2 and the second steel plate 1-3; short screws 1-4 are welded to the outside of the second steel plate 1-3, with no fewer than four short screws 1-4 evenly distributed at the corners of the outside of the second steel plate 1-3; before welding the short screws 1-4, a center screw 1-10 and a second extension screw 4-2 are pre-connected to the outside of the protective nut 1-9 via a precision connecting sleeve 4-3 to fix the second steel plate 1-3 and the third steel plate 4-5, and the positions of the short screws 1-4 are fixed on the third steel plate 4-5 before welding, to ensure strict alignment of the load during the tensile test, such as... Figure 3 After welding, remove the precision connecting sleeve 4-3, the second extension screw 4-2, and the third steel plate 4-5; pour concrete block 1-1 inside the first steel plate 1-2 and the second steel plate 1-3. In this example, all steel plates are made of Q355B material, all steel plates are 100mm×100mm in size, and have a wall thickness of 20mm. All screws and nuts are made of 12.9 grade high-strength material. There are 4 short screws 1-4. The concrete grade is C40, and the standard curing time is 28 days.
[0039] Fabrication of hollow-core steel-concrete composite interface ejection specimens, including inner interface ejection specimens (see [reference]). Figure 4 ), the outer interface pushes out the test piece (see Figure 5 Both the inner and outer interface ejection specimens consist of an outer steel pipe and an inner steel pipe, with concrete poured between them. On the bottom surface of the inner interface ejection specimen, the outer steel pipe 2-2, concrete 2-3, and inner steel pipe 2-1 are flush, while on the top surface, the inner steel pipe 2-1 protrudes from concrete 2-3 and outer steel pipe 2-2 by a distance, serving as the sliding section. On the top surface of the outer interface ejection specimen, the outer steel pipe 3-2, concrete 3-3, and inner steel pipe 3-1 are flush, while on the bottom surface, the outer steel pipe 3-2 protrudes from concrete 3-3 and inner steel pipe 3-1 by a distance, also serving as the sliding section. In this example, all steel pipes are made of Q355B, the concrete grade is C40, the sliding section distance is 40mm, and standard curing is 28 days.
[0040] An interfacial normal tension test was conducted on steel-concrete interfacial tension specimens using an interfacial normal tension device, a low-temperature environmental chamber 4-6, a low-temperature control system, a displacement sensor 5-3, a temperature sensor, and a data acquisition system. (See [link to relevant documentation]). Figure 6 An interfacial tangential repeated push-out sliding device, a low-temperature environmental chamber 4-6, a low-temperature control system, a displacement sensor 5-3, a temperature sensor, a data acquisition system, and a bidirectional strain gauge 5-5 were used to conduct an interfacial repeated push-out sliding experiment on hollow sandwich steel tube concrete specimens. (See [reference needed]). Figure 7 , Figure 8 .
[0041] The interface normal tension device includes a tensile testing machine 4-7, a first extension screw 4-1, a second extension screw 4-2, a precision connecting sleeve 4-3, a third steel plate 4-5, and a connecting nut 4-4. The first extension screw 4-1 is connected to the upper clamp of the tensile testing machine 4-7 and passes through the low-temperature environment chamber 4-6. The second extension screw 4-2 is connected to the lower clamp of the tensile testing machine 4-7 and passes through the low-temperature environment chamber 4-6. The precision connecting sleeve 4-3 is used to connect the first extension screw 4-1 and the central screw 1-10 of the steel plate-concrete interface tension specimen. The third steel plate 4-5 has a hole at the same position as the central hole of the second steel plate 1-3 and the short screw 1-4 of the steel plate-concrete interface tension specimen, and is connected to the second extension screw 4-2 and the short screw 1-4 through the connecting nut 4-4. The protective nut 1-9 is removed during loading. In this example, the tensile testing machine 4-7 is a 1000kN MTS testing machine with a loading speed of 70N / s.
[0042] The interface tangentially pushes out the sliding device, which includes a pressure testing machine 5-4, a loading block 5-1, and a base 5-2. The height of the loading block 5-1 is greater than the sum of the wall thickness of the low temperature environment chamber 4-6 and the sliding distance, and the diameter is slightly smaller than the inner diameter of the outer steel pipe of the outer interface pushing out the specimen. In this example, the pressure testing machine 5-4 is a 3000kN MTS testing machine. The experimental loading is controlled by displacement, and the loading rate is 1mm / min until the free end of the specimen reaches the maximum sliding amount and stops.
[0043] Displacement sensor 5-3 is used to measure the displacement of the steel plate-concrete interface tension specimen and the hollow sandwich steel tube-concrete interface ejection specimen; in this example, the displacement of the loaded end and the free end are measured respectively.
[0044] Temperature sensors are used to measure the temperature of steel plate-concrete interface tension specimens and hollow sandwich steel tube-concrete interface ejection specimens; in this example, the temperature sensor is a PT100 model, which is arranged on the surface of the specimen and inside the low-temperature environment chamber 4-6.
[0045] Bidirectional strain gauges 5-5 are arranged on the outer wall of the outer steel tube at the outer interface and the inner wall of the inner steel tube at the inner interface of the specimen ejection process. They are used to measure the circumferential and axial strains during temperature changes and the ejection and slippage process. In this example, the arrangement of bidirectional strain gauges 5-5 is shown in [reference needed]. Figure 9 , Figure 10 .
[0046] The data acquisition system is used to collect load, displacement, temperature, and strain data.
[0047] In some embodiments, in the low-temperature interface tangentially pushed-out sliding device, the strain gauge used for low-temperature testing is a low-temperature strain gauge, which is bonded with low-temperature special adhesive and sealed and protected with silicone rubber.
[0048] In some embodiments, the concrete at the interface to be tested in the steel plate-concrete interface tension specimen and the hollow sandwich steel tube-concrete interface ejection specimen can be ordinary concrete or recycled aggregate concrete, and the steel plate or steel tube can be made of materials with different strengths or with different surface roughness treatments.
[0049] In some embodiments, the cross-sectional dimensions of the outer steel tube, concrete, and inner steel tube of the hollow sandwich steel tube concrete interface specimen can be considered in different combinations to study the effect of interface normal pressure on interface tangential properties.
[0050] In some embodiments, a certain number of central nuts 1-7 are equidistantly arranged between the second nut 1-6 and the third nut 1-8 to enhance the anchoring effect between the central screw 1-10 and the concrete block 1-1; during transportation, the protective nuts 1-9 are tightened to prevent damage to the interface to be tested, and then removed before loading.
[0051] In some embodiments, after a single ejection, the specimen is inverted and ejected repeatedly to study the interfacial force damage in the later stages of slippage. The tangential repeated ejection-slip experiment consists of four ejection loading cycles. The first ejection is a forward ejection loading cycle, the second ejection is a reverse ejection loading cycle, the third ejection is a second forward ejection loading cycle, and the fourth ejection is a second reverse ejection loading cycle.
[0052] The experimental results obtained based on the low-temperature interfacial force decoupling experimental device for hollow-core steel tube concrete were used to separate the full components of the low-temperature interfacial force, including chemical bonding force, low-temperature freezing force, mechanical interlocking force, and frictional force, using the low-temperature interfacial force decoupling analysis method for hollow-core steel tube concrete. The specific method is as follows: Normal tension tests were conducted on steel-concrete interface tension specimens at room temperature, and the peak stress was taken to obtain the first result, which is the chemical bonding force between the steel plate and the concrete in the steel-concrete interface tension specimen.
[0053] Normal tensile tests were conducted on steel-concrete interface tension specimens at a set low temperature, and the peak stress was taken to obtain the second result; the second result is the sum of the chemical bonding force between the steel plate and the concrete and the low-temperature freezing force in the steel-concrete interface tension specimen.
[0054] Subtracting the first result from the second result yields the low-temperature freezing force between the steel plate and concrete. A quantitative relationship between low temperature and low-temperature freezing force is then established. (See [link to relevant documentation]). Figure 11 .
[0055] At a set low temperature, repeated tangential push-out and sliding tests were conducted on hollow steel-concrete composite interface specimens. The first peak stress of the stress-displacement curve during the first push-out was used to obtain the third result. (See [reference needed]). Figure 12 The third result is the sum of chemical bonding force, low-temperature freezing force, mechanical interlocking force, and friction force between the steel pipe and concrete in the hollow sandwich steel pipe concrete interface specimen.
[0056] The temperature changes of the outer steel pipe wall at the outer interface and the inner steel pipe wall at the inner interface of the specimen were measured, as well as the circumferential and axial strains during the ejection and sliding process. The interface normal pressure was calculated according to formulas (1) and (2). p n Multiplying the interfacial normal pressure by the friction coefficient yields the fourth result, which is the frictional force between the steel pipe and the concrete in the hollow sandwich steel-concrete interface specimen. ; in, E s It is the elastic modulus of the steel pipe. t s It's the thickness of the steel pipe wall. Ds It is the diameter of the steel pipe. v s It is the Poisson's ratio of the steel pipe. σ h It is the circumferential stress of the steel pipe. σ z It is the axial stress of the steel pipe. ε h It is the circumferential strain of the steel pipe. ε z It is the axial strain of the steel pipe. α s It is the coefficient of linear expansion of the steel pipe, Δ T It represents temperature change; cooling is negative.
[0057] Subtract the second result from the third result, and then subtract the fourth result to obtain the mechanical biting force.
[0058] In some embodiments, the coefficient of friction may be selected based on the different roughness of the steel pipe wall.
[0059] In some embodiments, the loss pattern of mechanical engagement force is obtained by comparing the stress-displacement curves of the first and third ejections; the loss pattern of frictional force is obtained by comparing the stress-displacement curves of the second and fourth ejections. (See [reference needed]). Figure 13 .
[0060] Finally, using the analytical method disclosed herein, the variation law of the full-component interfacial force of hollow steel-tube concrete at low temperature, including chemical bonding force, low-temperature freezing force, mechanical interlocking force, and frictional force, was obtained. (See [reference needed]). Figure 14 Based on this, calculation formulas (3) to (6) are proposed for the components of the outer and inner interface forces in the example, including chemical bonding force, low temperature freezing force, mechanical interlocking force and friction force. Compared with the existing technology which is limited to room temperature and the single interface type of "outer steel pipe-concrete", the application range of low temperature environment and interface type is broadened, and the safety guarantee and performance evaluation of hollow sandwich steel pipe concrete in cold regions are supported.
[0061] ; in, f bc For chemical bonding force, f bl For low-temperature freezing power, f bm For mechanical biting force, f bf This is friction.
[0062] The results of this example demonstrate that the experimental setup and analytical method of this disclosure are scientifically designed and feasible to operate. Compared with the prior art which is limited to fitting the macroscopic total interfacial force, this disclosure successfully achieves the quantitative decoupling of all components of the internal and external multi-type interfacial forces in hollow sandwich steel tube concrete under low temperature conditions. It can propose calculation formulas for each component, reveal the low temperature damage mechanism, and provide an important experimental setup and analytical method for the interface design and evaluation of hollow sandwich steel tube concrete structures in cold regions.
Claims
1. A low-temperature interfacial force decoupling experimental device for hollow sandwich steel tube concrete, characterized in that, include: Steel plate concrete interface tension specimen, hollow sandwich steel tube concrete interface push-out specimen, interface normal tension device, interface tangential repeated push-out sliding device, low temperature environment chamber, low temperature control system, displacement sensor, temperature sensor, data acquisition system and bidirectional strain gauge. The interface normal tension device is used to conduct tension tests on the steel plate-concrete interface tension specimen to decouple chemical bonding force and low-temperature freezing force. The interface tangential repeated push-out sliding device is used to conduct push-out sliding experiments on hollow sandwich steel tube concrete interface push-out specimens to decouple mechanical biting force and friction force. During the loading process, the steel plate concrete interface tension specimen and the hollow sandwich steel tube concrete interface ejection specimen are located inside the low temperature environment chamber, and the low temperature control system is used to control the internal temperature of the low temperature environment chamber. The displacement sensor is used to measure the displacement of the steel plate-concrete interface tension specimen and the hollow sandwich steel tube-concrete interface ejection specimen. The temperature sensor is used to measure the temperature of the steel plate-concrete interface tension specimen and the hollow sandwich steel tube-concrete interface ejection specimen. The bidirectional strain gauges are arranged on the outer wall of the outer steel tube that pushes the specimen out at the outer interface and on the inner wall of the inner steel tube that pushes the specimen out at the inner interface, and are used to measure the circumferential strain and axial strain during the temperature change and the pushing and sliding process. The data acquisition system is used to collect load, displacement, temperature, and strain data.
2. The apparatus according to claim 1, characterized in that, The steel plate-concrete interface tension specimen includes a first steel plate, a second steel plate, a concrete block, a central threaded rod, a short threaded rod, a first nut, a second nut, a third nut, a protective nut, and a central nut. The first steel plate and the second steel plate each have an opening in the center, and a certain distance is set between the first steel plate and the second steel plate. The central screw passes through the openings in the first steel plate and the second steel plate, and the position of the first steel plate is fixed by the first nut and the second nut, and the position of the second steel plate is fixed by the third nut and the protective nut. The second nut and the third nut are located inside the first steel plate and the second steel plate. A certain number of central nuts are equidistantly arranged between the second nut and the third nut to enhance the anchoring effect between the central screw and the concrete block. The short screws are welded to the outside of the second steel plate, and there are no fewer than four short screws, which are evenly distributed at the corners of the outside of the second steel plate. Concrete blocks are poured inside the first and second steel plates; Before loading the test specimen, tighten the protective nut to prevent accidental damage; remove the protective nut during loading.
3. The apparatus according to claim 1, characterized in that, The hollow sandwich steel tube concrete interface ejection specimen includes an inner interface ejection specimen and an outer interface ejection specimen. Both the inner interface ejection specimen and the outer interface ejection specimen include an outer steel pipe and an inner steel pipe, with concrete poured between the outer steel pipe and the inner steel pipe. The inner interface extends outward from the bottom surface of the specimen, where the outer steel pipe, concrete, and inner steel pipe are flush. The inner steel pipe on the top surface protrudes a distance from the concrete and the outer steel pipe, which is used for the sliding section. The outer interface extends outward from the top surface of the specimen, where the outer steel pipe, concrete, and inner steel pipe are flush. The outer steel pipe on the bottom surface protrudes a distance from the concrete and the inner steel pipe, which is used for the sliding section.
4. The apparatus according to claim 1, characterized in that, The interface normal tension device includes a tensile testing machine, a first extension screw, a second extension screw, a precision connecting sleeve, a third steel plate, and a connecting nut; The first extension screw is connected to the upper clamp of the tensile testing machine and passes through the low-temperature environment chamber; the second extension screw is connected to the lower clamp of the tensile testing machine and passes through the low-temperature environment chamber. The precision connecting sleeve is used to connect the first extension screw and the central screw of the steel plate-concrete interface tension specimen during loading, and the welding position of the short screw is pre-positioned when making the steel plate-concrete interface tension specimen. The third steel plate has a hole at the same position as the center hole of the second steel plate and the short screw in the tension specimen at the interface between the steel plate and the concrete, and is connected to the second extension screw and the short screw by a connecting nut.
5. The apparatus according to claim 1, characterized in that, Before welding the short screw, the center screw and the second extension screw are connected in advance using a precision connecting sleeve according to claims 2 and 4, the second steel plate and the third steel plate are fixed, the position of the short screw is fixed on the third steel plate, and then welding is performed to ensure that the load is strictly aligned during the tensile test. After welding, the second extension screw, the third steel plate and the precision connecting sleeve are removed.
6. The apparatus according to claim 1, characterized in that, The interface tangentially repeatedly pushes out the sliding device, which includes a pressure testing machine, a loading block, and a base; The height of the loading block is greater than the sum of the wall thickness of the low-temperature environment chamber and the sliding distance, and the diameter is slightly smaller than the inner diameter of the outer steel pipe from which the specimen is pushed out of the outer interface.
7. A method for decoupling interfacial forces in hollow-core steel-concrete composite at low temperatures, based on the experimental apparatus for decoupling interfacial forces in hollow-core steel-concrete composite at low temperatures according to any one of claims 1 to 6, characterized in that, include: A normal tension test was performed on the steel plate-concrete interface tension specimen at room temperature, and the peak stress was taken to obtain the first result. The first result is the chemical bonding force between the steel plate and the concrete in the steel plate-concrete interface tension specimen. A normal tension test was conducted on the steel plate-concrete interface tension specimen at a set low temperature, and the peak stress was taken to obtain the second result. Subtracting the first result from the second result yields the low-temperature freezing force between the steel plate and the concrete, thus establishing a quantitative relationship between low temperature and the low-temperature freezing force. At a set low temperature, the hollow sandwich steel tube concrete interface ejection specimen was subjected to repeated tangential ejection and slippage tests. The first peak stress of the first ejection stress-displacement curve was taken to obtain the third result. By monitoring the surface strain of the steel pipe and calculating the interface normal pressure, the interface normal pressure is multiplied by the friction coefficient to obtain a fourth result, which is the frictional force between the steel pipe and the concrete in the hollow sandwich steel pipe concrete interface ejection specimen. Subtract the second result from the third result, and then subtract the fourth result to obtain the mechanical biting force.
8. The method according to claim 7, characterized in that, The second result is the sum of the chemical bonding force and the low-temperature freezing force between the steel plate and the concrete in the steel plate-concrete interface tension specimen; The third result is the sum of the chemical bonding force, low-temperature freezing force, mechanical interlocking force, and frictional force between the steel pipe and the concrete in the hollow sandwich steel pipe concrete interface specimen.
9. The method according to claim 7, characterized in that, The interface tangential repeated push-out sliding experiment includes four push-out loadings; the first push-out is a forward push-out loading, the second push-out is a reverse push-out loading, the third push-out is a second forward push-out loading, and the fourth push-out is a second reverse push-out loading. By comparing the stress-displacement curves of the first and third push-outs, the loss pattern of mechanical engagement force is obtained; by comparing the stress-displacement curves of the second and fourth push-outs, the loss pattern of frictional force is obtained.
10. The method according to claim 7, characterized in that, Strain gauges were placed on the outer wall of the outer steel pipe of the specimen ejected at the outer interface and the inner wall of the inner steel pipe of the specimen ejected at the inner interface to measure the temperature change and the circumferential and axial strains during the ejection and sliding process. The interface normal pressure was calculated according to formulas (1) and (2). p n ; in, E s It is the elastic modulus of the steel pipe. t s It's the thickness of the steel pipe wall. D s It is the diameter of the steel pipe. v s It is the Poisson's ratio of the steel pipe. σ h It is the circumferential stress of the steel pipe. σ z It is the axial stress of the steel pipe. ε h It is the circumferential strain of the steel pipe. ε z It is the axial strain of the steel pipe. α s It is the coefficient of linear expansion of the steel pipe, Δ T It represents temperature change; cooling is negative.