Method for testing crack resistance of prefabricated curved plate of thin-wall concrete irrigation canal

Abstract

The invention discloses a method for testing the crack resistance of a prefabricated curved plate of a thin-wall concrete irrigation canal. The method comprises the following steps: measuring key dimension parameters of the prefabricated concrete curved plate; building a three-point bending test loading platform; performing stress state classification on the prefabricated curved plates according to the position of the action point of the resultant force of the water pressure; calculating a horizontal positioning parameter of a load acting point and a base supporting height parameter, and completing positioning of loading and supporting; calculating a loading maximum value based on a bidirectional load synthesis effect, and applying the load according to a set loading rate; calculating a fatigue lower limit equivalent value under the action of a bidirectional load, and implementing multi-cycle fatigue loading; after the loading is stopped, the cracking or damage state of the prefabricated concrete curved plate is observed, the crack width is detected, and an anti-cracking performance evaluation conclusion is given in combination with standard requirements. According to the method, the synthetic action of water pressure, top pressure beams and live loads in different directions in actual loads is comprehensively considered, and the crack resistance of the prefabricated bent plates of different sizes is accurately and directly evaluated.

Description

Technical Field

[0001] This invention relates to the field of concrete testing technology, and in particular to a method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals. Background Technology

[0002] Currently, precast concrete irrigation canal slabs have become one of the main forms of high-standard farmland irrigation canals due to their advantages such as convenient construction, reduced on-site wet work, and factory production. However, in practical applications, these precast slabs generally face the threat of cracking, a critical problem. Cracking not only reduces the durability of the canal structure but may also lead to leakage losses, directly weakening the water-saving and yield-increasing benefits of high-standard farmland and posing a potential risk to food security. Currently, there is a lack of effective and widely accepted standard methods for testing the crack resistance of such precast bending slabs. This technological gap is mainly caused by the following factors: The special limitations of structural size and shape: Precast slabs for irrigation canals are usually thin-walled (40–80 mm) curved slab structures, which makes it difficult to directly apply conventional non-destructive testing methods and some destructive testing methods for thick-walled or flat concrete components; The complexity of the actual stress state has not been fully considered: During the service of irrigation canal precast slabs, they are subjected to a complex stress state caused by the combined action of internal water pressure and external loads on the top of the canal, and the load direction is specific. Existing general component testing methods often fail to effectively simulate the combined effect of water pressure and top load, resulting in a deviation between the test results and the actual crack resistance of the component. The testing methods lack universality: the sizes and specifications of precast irrigation canal slabs on the market are not the same, and the existing special component testing methods are usually designed for specific sizes, lacking a universal loading and evaluation scheme that can flexibly adapt to precast slabs with different radii of curvature and different sizes.

[0003] Currently, the relevant testing technologies and methods in the industry mainly include: Ultimate strength testing methods for flat concrete slabs: This type of method is technically mature, but it is mainly applicable to flat slab components. As a curved slab, the precast slab of irrigation canals has fundamentally different internal force distribution, crack propagation mode and critical failure state from that of flat slabs. Therefore, the testing methods and corresponding specifications for flat slabs cannot be directly applied. On-site testing methods for concrete material strength include core sampling, rebound hammer method, and ultrasonic method. These methods have been standardized, but they are testing methods for concrete materials. The results obtained are the strength of the material, which is different from the cracking of the monolithic slab. Generally, the strength is significantly greater than the cracking load of the monolithic component. In addition, all of the above methods require the concrete slab thickness to be greater than 100mm, which does not meet the requirements for concrete slabs in irrigation canals and does not meet the standard usage conditions. Ultimate load testing methods for specific components: There are some dedicated testing methods for other types of components, but their testing requirements are significantly different from those for precast slabs of irrigation canals. First, the components are significantly different, and testing methods for precast concrete slabs of irrigation canals are still lacking. Second, the bidirectional superposition effect of the actual load is not considered, and the results obtained cannot be directly used to determine whether the component quality is qualified. Conversion is still required, which reduces the accuracy of the conclusion.

[0004] In summary, existing technologies suffer from systemic defects and applicability bottlenecks when testing the crack resistance of precast curved concrete slabs for high-standard farmland irrigation canals. Therefore, there is an urgent need to develop a dedicated testing method and technology that can accurately simulate actual stress conditions, is applicable to thin-walled curved panels of different sizes, and effectively evaluate their crack resistance and fatigue durability. Summary of the Invention

[0005] The purpose of this invention is to provide a method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals. Considering the characteristics of thin-walled concrete and curved panels in irrigation canals, and taking into account the combined effects of water pressure, top beam pressure, and live load in different directions under actual loads, a method for detecting crack resistance strength is established. This method is used to test the crack resistance of precast curved panels for irrigation canals, enabling accurate and direct evaluation of the crack resistance of precast curved panels of different sizes, and providing a reliable criterion for the quality of key components in the construction of high-standard farmland.

[0006] To achieve the above objectives, the present invention provides the following solution: A method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals includes the following steps: S1, determine the key dimensional parameters of the precast concrete curved panel and obtain load-related data; the precast concrete curved panel consists of straight segments and curved segments; S2, Construct a three-point bending test loading platform that includes an adjustable base support and a precision loading mechanism; S3. Based on the location of the resultant force of water pressure, the stress state of the precast curved panel is classified. S4, calculate the horizontal positioning parameters of the load application point and the base support height parameters to complete the positioning of loading and support; S5, calculate the maximum load value based on the bidirectional load synthesis effect, and apply the load at the set loading rate; S6, calculate the equivalent value of the lower limit of fatigue under bidirectional load, and implement multi-cycle fatigue loading; S7. After loading is stopped, observe the cracking or damage state of the precast concrete curved panel and detect the crack width. Based on the specifications, give a conclusion on the crack resistance performance.

[0007] Furthermore, in step S1, the key dimensional parameters include the width of the precast concrete curved panel. l w Horizontal projection length of the inner diameter straight segment a 1. Horizontal projection length of the inner diameter curve segment a 2. Total horizontal projection length of the inner diameter a Height of the straight section of the inner diameter h 1. Height of the inner diameter curve section h 2. Total height of inner diameter h ,in, a = a 1+ a 2, h = h 1+ h 2; Load-related data include the influence coefficient of the resultant force of water pressure at the working state water level. or 1 and the influence coefficient of top load amplification or 2.

[0008] Furthermore, in step S2, the three-point bending test loading platform adopts a steel frame portal frame with a width of not less than 2.0m and a height of not less than 2.0m. The crossbeam of the steel frame is equipped with movable pulley jacks, which are either equipped with built-in pressure sensors or separately configured with pressure sensors. The cylindrical loading head and support roller are at least 1.2m long. One end of the base supports a height-adjustable clamp, and the other end is a fixed fulcrum. The distance between the fixed fulcrum and the upper edge of the precast concrete curved panel is... l z Determined according to the following rules: Ordinary components l z =100mm, upper flange thickness >100mm, l z = Upper flange thickness + 50mm; The arc segment of the precast concrete curved panel is fixed with a clamp with a contact surface length of 100mm, and the flange segment is supported by a fixed support point 50mm away from the flange.

[0009] Furthermore, in step S3, the criterion for classifying the force state is: or 1 h-h 2 When the pressure is ≥0, the precast concrete curved panel is under Class A stress state, that is, the point of application of the resultant force of water pressure is on the straight section of the inner diameter; or 1 h-h 2 When the pressure is less than 0, the precast concrete curved panel is in a Class B stress state, that is, the point of application of the resultant force of water pressure is in the inner diameter curve segment.

[0010] Further, in step S4, the horizontal positioning parameters of the load application point are calculated according to the following formula: l p =0.7 (1 - or 1) h - l z in, l p The distance from the load application point to the right support point. l z The distance between the fixed support point and the upper edge of the precast concrete curved panel.

[0011] Furthermore, the base support height parameter is calculated according to the following formula: For type A stress state:

[0012] For type B stress state:

[0013] In the formula, d A The support elevation is for Class A stress conditions. d B The support elevation is for Class B stress conditions; x Indicates the water level height.

[0014] Further, in step S5, the maximum loading value is calculated according to the following formula: For type A stress state:

[0015] For type B stress state:

[0016] The loading rate shall not exceed 1.0 N / min, where, P A1 The maximum load is applied for stress state A. The maximum load is applied for stress state B.

[0017] Further, in step S6, the equivalent value of the fatigue lower limit is calculated according to the following formula: For type A stress state:

[0018] For type B stress state:

[0019] Among them, P A2P is the equivalent value of the lower limit of fatigue under Class A stress state. B2 This is the equivalent value of the lower limit of fatigue under Class B stress conditions; The fatigue loading cycle process is as follows: unload to P A2 or P B2 And keep it for 15 minutes, then load it to P. A1 or P B1 The loading rate should not exceed 1.0 N / min, and loading should stop after 4 cycles.

[0020] Furthermore, in step S7, cracks in the component are detected by a crack width detector. Based on the "Code for Acceptance of Construction Quality of Concrete Structures" and the engineering design requirements, it is determined whether the crack width exceeds the limit and whether there are through cracks, thereby assessing whether the crack resistance performance of the precast curved panel is qualified.

[0021] As can be seen from the above technical solution, compared with the prior art, the method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals provided by the present invention has the following beneficial effects: (1) Accurately simulate the actual working conditions. By using the water pressure and top bidirectional load positioning algorithm, combined with the stress state classification (A / B class), the combined effect of water pressure on the precast curved panel, top pressure beam and live load is restored. The detection results are highly consistent with the actual cracking of the project, solving the defect of conventional methods that do not consider multi-directional loads. (2) It has strong adaptability, and the loading point position and support height are adjustable. Combined with clear dimensional parameter measurement and calculation logic, it can detect precast curved panels of different sizes, breaking through the limitations of conventional methods on panel thickness and shape, and significantly improving versatility. (3) Introducing a fatigue loading mechanism, the dynamic changes of the load are simulated through multi-cycle loading, taking into account both short-term crack resistance and long-term fatigue performance evaluation. This method is more in line with actual service conditions than the method that only measures the ultimate strength, and provides a more comprehensive criterion for component quality. (4) The operation is controllable, the loading rate, data accuracy and evaluation standards are clear, and the testing process is easy to implement. It can provide reliable technical support for the quality control of precast slabs for high-standard farmland irrigation canals and reduce the risk of cracking and leakage. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of the crack resistance test method for the precast curved panel of thin-walled concrete irrigation canal according to the present invention. Figure 2 This is a schematic diagram of an irrigation canal composed of two precast concrete curved panels according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the dimensional parameters of the precast concrete curved panel according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the load action in an embodiment of the present invention; Figure 5 This is a schematic diagram of the loading platform structure according to an embodiment of the present invention; Explanation of reference numerals in the attached drawings: 1. Loading platform for three-point bending test; 2. Loading device; 3. Fixing clamp; 4. Precast concrete curved panel; 5. Height-adjustable support point. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The purpose of this invention is to provide a method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals. Considering the characteristics of thin-walled and curved slabs in concrete for irrigation canals, and taking into account the combined effects of water pressure, top beam pressure, and live load in different directions under actual loads, a method for detecting crack resistance strength is established. This method is used to test the crack resistance of precast curved slabs for irrigation canals and has a high degree of consistency with actual cracking conditions in engineering projects.

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 1-Figure 5 As shown, the present invention provides a method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation channels, comprising the following steps: S1, determine the key dimensional parameters of the precast concrete curved panel and obtain load-related data; the precast concrete curved panel consists of straight segments and curved segments; like Figure 2 As shown, the key dimensional parameters include the width of the precast concrete curved panel. l w Horizontal projection length of the inner diameter straight segment a 1. Horizontal projection length of the inner diameter curve segment a 2. Total horizontal projection length of the inner diameter a Height of the straight section of the inner diameter h 1. Height of the inner diameter curve section h 2. Total height of inner diameterh ,in a = a 1+ a 2, h = h 1+ h 2; Load-related data include the influence coefficient of the resultant force of water pressure at the working state water level. or 1 and the influence coefficient of top load amplification or 2, or 1 takes the value 0.28. or The value of 2 is 2.0.

[0028] S2, Construct a three-point bending test loading platform that includes an adjustable base support and a precision loading mechanism; like Figure 5 As shown, the three-point bending test loading platform 1 adopts a steel frame portal frame with a width of not less than 2.0m and a height of not less than 2.0m. The crossbeam of the steel frame is equipped with movable pulley jacks, which have built-in pressure sensors or are equipped with separate pressure sensors to control the output load. The cylindrical loading head and support roller of the loading device 2 have a length of not less than 1.2m. One end of the base supports a fixed clamp 3, and the other end is a height-adjustable support point 5. The distance between the height-adjustable support point 5 and the upper edge of the precast concrete curved panel 4 is... l z Determined according to the following rules: For ordinary components l z The value is 100mm. If the thickness of the upper flange of the precast component is greater than 100mm, then... l z The value should be the thickness of the upper flange of the component plus 50mm.

[0029] The arc segment of the precast concrete curved panel 4 is fixed by a fixing clamp 3 with a contact surface length of 100mm. The flange segment is supported by a height-adjustable support point 5, which is 50mm away from the flange. d is the height from the bottom of the inner side of the U-shaped panel to the top of the height-adjustable support point.

[0030] S3. Based on the location of the resultant force of water pressure, the stress state of the precast curved panel is classified. Due to the special shape of the precast slabs for irrigation canals, which consist of straight sections and curved sections, it is necessary to determine whether the point of action of the combined water pressure is on the straight or curved section. When the slab is under a type A stress state, it means that the point of action of the combined water pressure is on the straight section; when the slab is under a type B stress state, it means that the point of action of the combined water pressure is on the curved section. or 1 is the coefficient of influence of the resultant force of water pressure under working conditions, for general farmland irrigation canal projects. or The value of 1 is 0.28. h and hBoth 2 were obtained from step S1.

[0031] Specifically, the criteria for classifying the force state are as follows: or 1 h-h 2 When the pressure is ≥0, the precast concrete curved panel is under Class A stress state, that is, the point of application of the resultant force of water pressure is on the straight section of the inner diameter; or 1 h-h 2 When the pressure is less than 0, the precast concrete curved panel is in a Class B stress state, that is, the point of application of the resultant force of water pressure is in the inner diameter curve segment.

[0032] S4, calculate the horizontal positioning parameters of the load application point and the base support height parameters to complete the positioning of loading and support; Specifically, based on the bidirectional force characteristics under full load, the location of the resultant force application point is determined, and the horizontal location of the top load application point is determined. The bottom left support point of the component is taken as the zero point, and the distance between the application point and the height-adjustable support point 5 is adjusted. l p The formula for determining the value is as follows. Adjust the top jack to the specified position based on the calculated value.

[0033] l p =0.7 (1 - or 1) h - l z in, l p The distance from the load application point to the right support point. l z The distance between the fixed support point and the upper edge of the precast concrete curved panel.

[0034] Based on the bidirectional force characteristics under full load, the direction of the resultant force is determined, and thus the height of the bottom support of the curved panel is determined. The horizontal placement of the straight section of the precast curved panel is taken as the zero point of elevation, and the adjusted elevation is then determined. d A or d B The formula for determining the value is: For type A stress state:

[0035] For type B stress state:

[0036] In the formula, d A The support elevation is for Class A stress conditions. d BThe support elevation is for Class B stress conditions; x This represents the water level. The resultant force of the water pressure, a gradually changing and continuous load, is calculated through integration.

[0037] S5, calculate the maximum load value based on the bidirectional load synthesis effect, and apply the load at the set loading rate; Based on the bidirectional force characteristics under full load, the magnitude of the resultant force is determined, the maximum loading value under bidirectional load is calculated using the following formula, and the load is applied to the calculated value at a rate not exceeding 1.0 N / min. or 2 is the top load amplification influence coefficient, which takes into account the influence of the live load in the working state, and is set to 2.0.

[0038] For type A stress state:

[0039] For type B stress state:

[0040] The loading rate shall not exceed 1.0 N / min, where, P A1 The maximum load is applied for stress state A. The maximum load is applied for stress state B.

[0041] S6, calculate the equivalent value of the lower limit of fatigue under bidirectional load, and implement multi-cycle fatigue loading; Calculate the equivalent value of the lower fatigue limit under bidirectional load. P A2 or P B2 First, control the top loading device to unload to the calculated... P A2 or P B2 Continue loading after 15 minutes. P A1 or P B1 The loading rate should not exceed 1.0 N / min, and loading should stop after 4 cycles.

[0042] For type A stress state:

[0043] For type B stress state:

[0044] Among them, P A2 P is the equivalent value of the lower limit of fatigue under Class A stress state. B2 This is the equivalent value of the lower limit of fatigue under Class B stress conditions.

[0045] S7. After stopping loading, remove the loading equipment and fixing fixture, observe the cracking or damage state of the precast concrete curved panel and detect the crack width, and give a recommendation on whether the curved panel component is qualified according to relevant specifications and specific engineering requirements.

[0046] Specifically, cracks in components are detected by a crack width detector. Based on the "Code for Acceptance of Construction Quality of Concrete Structures" and engineering design requirements, it is determined whether the crack width exceeds the limit and whether there are through cracks, thereby assessing whether the crack resistance performance of the precast curved panel is qualified.

[0047] In summary, this invention proposes a method for testing the crack resistance of precast bending slabs in concrete irrigation canals based on a positioning algorithm for water pressure and top bidirectional load. Its innovations are: (1) a loading calculation method and device that includes adjustable loading point angle and position, applicable to precast slabs of different sizes; (2) the establishment of a method that considers the combined effect of water pressure and top load from different directions, which is consistent with the actual stress state and can be used as a basis for quality inspection of precast slabs in irrigation canals; (3) the detection process uses fatigue loading to simulate the actual cracking situation, taking into account the fatigue effect caused by the changes in water pressure and top load under different states.

[0048] Furthermore, embodiments of the present invention provide a computer-readable storage medium storing executable instructions, which, when executed, cause a processor to perform the data processing and calculation portion of the above-described method for testing the crack resistance performance of precast curved panels for thin-walled concrete irrigation canals.

[0049] Matters not covered in this invention are common knowledge.

[0050] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals, characterized in that, Includes the following steps: S1, determine the key dimensional parameters of the precast concrete curved panel and obtain load-related data; the precast concrete curved panel consists of straight segments and curved segments; S2, Construct a three-point bending test loading platform that includes an adjustable base support and a precision loading mechanism; S3. Based on the location of the resultant force of water pressure, the stress state of the precast curved panel is classified. S4, calculate the horizontal positioning parameters of the load application point and the base support height parameters to complete the positioning of loading and support; S5, calculate the maximum load value based on the bidirectional load synthesis effect, and apply the load at the set loading rate; S6, calculate the equivalent value of the lower limit of fatigue under bidirectional load, and implement multi-cycle fatigue loading; S7. After loading is stopped, observe the cracking or damage state of the precast concrete curved panel and detect the crack width. Based on the specifications, give a conclusion on the crack resistance performance.

2. The method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals according to claim 1, characterized in that, In step S1, the key dimensional parameters include the width of the precast concrete curved panel. l w Horizontal projection length of the inner diameter straight segment a 1. Horizontal projection length of the inner diameter curve segment a 2. Total horizontal projection length of the inner diameter a Height of the straight section of the inner diameter h 1. Height of the inner diameter curve section h 2. Total height of inner diameter h ,in a = a 1+ a 2, h = h 1+ h 2; Load-related data include the influence coefficient of the resultant force of water pressure at the working state water level. η 1 and the influence coefficient of top load amplification η 2.

3. The method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals according to claim 1, characterized in that, In step S2, the three-point bending test loading platform adopts a steel frame portal frame with a width of not less than 2.0m and a height of not less than 2.0m. The crossbeam of the steel frame is equipped with movable pulley jacks, which are either equipped with built-in pressure sensors or have separate pressure sensors. The cylindrical loading head and support rollers are at least 1.2m long. One end of the base supports a height-adjustable clamp, and the other end is a fixed support point. The distance between the fixed support point and the upper edge of the precast concrete curved panel is... l z Determined according to the following rules: Ordinary components l z =100mm, upper flange thickness >100mm l z = Upper flange thickness + 50mm; The arc segment of the precast concrete curved panel is fixed with a clamp with a contact surface length of 100mm, and the flange segment is supported by a fixed support point 50mm away from the flange.

4. The method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals according to claim 2, characterized in that, In step S3, the criterion for classifying the force state is: η 1 h-h 2 When the pressure is ≥0, the precast concrete curved panel is under Class A stress state, that is, the point of application of the resultant force of water pressure is on the straight section of the inner diameter; η 1 h-h 2 When the pressure is less than 0, the precast concrete curved panel is in a Class B stress state, that is, the point of application of the resultant force of water pressure is in the inner diameter curve segment.

5. The method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals according to claim 4, characterized in that, In step S4, the horizontal positioning parameters of the load application point are calculated according to the following formula: l p =0.7（1－ η 1） h － l z in, l p The distance from the load application point to the right support point. l z The distance between the fixed support point and the upper edge of the precast concrete curved panel.

6. The method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals according to claim 5, characterized in that, The base support height parameter is calculated using the following formula: For stress state A: For type B stress state: In the formula, d A The support elevation is for Class A stress conditions. d B The support elevation is for Class B stress conditions; x Indicates the water level height.

7. The method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals according to claim 6, characterized in that, In step S5, the maximum loading value is calculated according to the following formula: For stress state A: For type B stress state: The loading rate shall not exceed 1.0 N / min, where, P A1 The maximum load is applied for stress state A. The maximum load is applied for stress state B.

8. The method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals according to claim 7, characterized in that, In step S6, the equivalent value of the fatigue lower limit is calculated according to the following formula: For stress state A: For type B stress state: Among them, P A2 P is the equivalent value of the lower limit of fatigue under Class A stress state. B2 This is the equivalent value of the lower limit of fatigue under Class B stress conditions; The fatigue loading cycle process is as follows: unload to P A2 or P B2 And keep it for 15 minutes, then load it to P. A1 or P B1 The loading rate should not exceed 1.0 N / min, and loading should stop after 4 cycles.

9. The method for testing the crack resistance of precast curved panels for thin-walled concrete irrigation canals according to claim 1, characterized in that, In step S7, cracks in the component are detected by a crack width detector. Based on the "Code for Acceptance of Construction Quality of Concrete Structures" and the engineering design requirements, it is determined whether the crack width exceeds the limit and whether there are through cracks, and then the crack resistance performance of the precast curved panel is evaluated.

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