On-site monitoring device and method for vertical load on concrete rectangular section columns

Abstract

This invention discloses a method for on-site monitoring of vertical loads on concrete rectangular cross-section columns, comprising the following steps: selecting a loading test area in the lower part of the column to form a column loading zone; arranging a column confining pressure loading system; placing a leveling rod and orthogonal strain gauges on the loading test area; starting the loading motor to complete the confining pressure loading of the column loading zone; calculating the vertical load of the column based on the three-dimensional static equilibrium condition of the column's small deformation and low confining pressure elastic state, plotting the column's vertical load time-effect characteristic curve, and then combining it with the column's vertical bearing capacity to assess the bearing stability of the reinforced concrete column member during service. This invention can overcome the problems of column bending, tilting, and human error caused by unreasonable vertical load monitoring schemes or monitoring results for reinforced concrete column structures, as well as the problems of technical complexity, high risk, and high monitoring costs. It has the advantages of strong environmental adaptability, rapid and simple testing method, safe operation, and low cost.

Description

Technical Field

[0001] This invention relates to the field of reinforced concrete structures, and in particular to a field monitoring device and method for vertical load on concrete rectangular cross-section columns. Background Technology

[0002] A large number of reinforced concrete column structures have been created in the renovation, expansion, and construction of civil buildings, industrial buildings, and underground engineering structures. Under conditions of adding floors, increased roof load, and uneven foundation settlement, adverse effects such as column bending deformation and tilting have occurred, severely impacting column deformation and load-bearing stability. This is especially true for illegal alterations to column structures and excessive eccentric loading, which have a more severe impact on the vertical load-bearing stability of columns. Numerous facts show that once a column structure becomes unstable, repair is extremely difficult, resulting in significant property damage and casualties. Therefore, it is essential to implement rapid and effective load-bearing monitoring and timely proactive reinforcement for reinforced concrete columns with safety hazards during their service life to control the occurrence of disasters.

[0003] Currently, the measurement of vertical loads on reinforced concrete column structures is mainly conducted before construction. This involves using stress gauges on the reinforcing bars and strain gauges in the concrete to monitor the column's load-bearing condition. This method is significant for tracking the column's load-bearing characteristics and guiding reinforcement. However, during the column's service life, this method struggles to obtain real-time load distribution and assess load-bearing reliability under non-destructive conditions. If test results and forecasts are delayed or misjudged, the optimal time for reinforcement will inevitably be missed, leading to greater property damage and social impact. Therefore, on-site monitoring of vertical loads on columns during service life remains a technical challenge, and a simple, efficient, and rapid monitoring method is still lacking. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a simple, reliable, and low-cost on-site monitoring device for the vertical load of a concrete rectangular section column, and a safe and easy-to-operate on-site monitoring method for the vertical load of a concrete rectangular section column.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is: a field monitoring device for vertical load of concrete rectangular cross-section columns, including a column body of rectangular cross-section columns, a column confining pressure loading system, a stress and strain testing system, and a data processing and analysis system, wherein the data processing and analysis system is connected to the column confining pressure loading system and the stress and strain testing system respectively;

[0006] The column confining pressure loading system includes a pressure-bearing steel plate, a connecting rod, a grooved pulley, a steel wire rope, and a loading motor. A loading test area is provided on the column, with the loading test area located below it as the column loading area. A pressure-bearing steel plate is arranged on each of the four sides of the column loading area. The outer side of each pressure-bearing steel plate is fixedly connected to one end of a connecting rod, and the other end of the connecting rod is fixedly connected to a grooved pulley. The two ends of the steel wire rope are wound in opposite directions around the screw of the loading motor, forming a loop around the four grooved pulleys. The rotation of the screw of the loading motor causes the two ends of the steel wire rope to be tensioned synchronously, but in opposite directions. The loading motor's rotation of the screw tensions the steel wire rope and compresses the connecting rod, completing the graded loading of the column loading area.

[0007] The stress-strain testing system includes strain gauges, stress meters, and leveling rods; the strain gauges are respectively arranged on the four sides of the upper part of the loading test area; the stress meters are arranged in the middle of the connecting rod; and the leveling rods are arranged on the four sides of the upper part of the loading test area; it is used to record the strain of the column during the confining pressure and graded loading process in the loading area of ​​the column.

[0008] The data processing and analysis system includes a main control computer, which is connected to strain gauges, stress meters, and a loading motor. It is used to calculate the collected stress and strain to obtain the vertical load of the column, plot the time-effect characteristic curve of the vertical load of the column, and compare and analyze the monitoring and calculation results with the vertical bearing capacity of the column to identify the bearing stability of the column component.

[0009] In the above-mentioned on-site monitoring device for vertical loads on concrete rectangular cross-section columns, the length of the bearing steel plate is less than the cross-sectional length of the column loading area, and the height of the bearing steel plate is equal to the height of the column loading area.

[0010] The above-mentioned on-site monitoring device for vertical load on concrete rectangular cross-section columns uses orthogonal strain gauges. Three sets of strain gauges are attached at equal intervals on each side of the loading test area, and are located at three positions: the side axis of the loading test area and its left and right 1 / 4 lengths.

[0011] The above-mentioned on-site monitoring device for vertical load on concrete rectangular section columns includes a leveling rod positioned between the strain gauge and the bearing steel plate. The midpoint of the leveling rod is located on the vertical axis of the side of the loading test area. Both ends of the leveling rod are fixed to the side of the loading test area by pins, and the bubble of the leveling rod is centered and horizontal. The pins move vertically within the grooves at both ends of the leveling rod as the column deforms vertically.

[0012] A method for on-site monitoring of vertical loads on concrete rectangular cross-section columns using a field monitoring device, comprising the following steps:

[0013] (1) Select a rectangular loading test area above the floor in the lower part of the column, and draw lines to determine the range of confining pressure loading in this area to form the column loading area;

[0014] (2) Arrange the pressure-bearing steel plates on the four sides of the column loading area respectively, and fix the four pressure-bearing steel plates to the four groove pulleys through four connecting rods. Wrap the two ends of the wire rope in opposite directions on the screw of the loading motor. The wire rope is wound in a ring around the outside of the four groove pulleys. Then, arrange stress gauges in the middle of each connecting rod.

[0015] (3) Leveling rods and orthogonal strain gauges are arranged sequentially from bottom to top on the four sides of the upper part of the loading test area;

[0016] (4) Start the loading motor. The screw rotates to synchronously tension both ends of the wire rope. The tension of the wire rope is transmitted to the pressure plate through the groove pulley and connecting rod to complete the confining pressure loading of the column loading area.

[0017] (5) Based on the three-dimensional static equilibrium condition of the column under small deformation and low confining pressure elastic state, the vertical load of the column is calculated, the time-effect characteristic curve of the vertical load of the column is plotted, and then combined with the vertical bearing capacity of the column, the bearing stability of the reinforced concrete column member during service is evaluated.

[0018] In the above-mentioned method for on-site monitoring of vertical loads on concrete rectangular cross-section columns, in step (1), a rectangular loading test area is selected above the floor in the lower part of the column. The marked area is: the bottom edge is 60cm to 100cm from the floor, the cross-sectional dimensions of the loading test area are a×b, and the height is 20cm.

[0019] In the above-mentioned method for on-site monitoring of vertical loads on concrete rectangular cross-section columns, in step (2), rectangular bearing steel plates with cross-sectional dimensions of a′×b′ are symmetrically arranged on the four sides of the loading test area to form a column loading area. The height of the bearing steel plates is equal to the height of the column loading area.

[0020]

[0021] In equation (1): a, b, h are the length, width, and height of the cross section of the loading test area, respectively; a', b', h' are the length, width, and height of the bearing steel plate, respectively.

[0022] The pressure-bearing steel plate is fixedly connected to the grooved pulley by a connecting rod. The connecting rod is a straight steel rod with a circular cross-section, and the center of the circle on both ends of the connecting rod coincides with the centroid of the pressure-bearing steel plate and the grooved pulley, respectively.

[0023] In the above-mentioned method for on-site monitoring of vertical load on concrete rectangular cross-section columns, in step (3), leveling rods and orthogonal strain gauges are arranged from bottom to top on the upper part of the four sides of the column loading area. First, the midpoint of the leveling rod is fixed on the vertical axis of the side of the loading test area, and the two ends of the leveling rod are fixed on the side of the loading test area by pins, so that the bubble of the leveling rod is centered and reaches a horizontal state. The pins move vertically in the grooves at both ends of the leveling rod as the column deforms vertically. Then, orthogonal strain gauges are arranged 40cm away from the upper boundary of the loading test area on the side of the loading test area. Three sets of orthogonal strain gauges are pasted parallel at equal intervals on each side of the loading test area, respectively located on the axis of the side of the loading test area and at three positions on the left and right 1 / 4 of the length.

[0024] In the above-mentioned method for on-site monitoring of vertical loads on concrete rectangular cross-section columns, in step (4), the loading motor is started, and the two ends of the steel wire rope are simultaneously tensioned by rotating the screw. The tension of the steel wire rope is transmitted to the bearing steel plate, which has been coated with a smooth coating, through the groove pulley and connecting rod to complete the confining pressure loading of the column loading area. The confining pressure loading adopts a graded loading method. First, an initial low-pressure loading of 0.2kN is implemented. After loading, the bubble in the middle of the leveling rod is adjusted so that the bubble is centered and the leveling rod is horizontal. The bearing steel plate is in close contact with the column loading area. Then, the initial values ​​of the stress gauge and strain gauge monitoring results are removed. Then, the screw tensions the steel wire rope with rotational forces of 2kN, 4kN, and 6kN respectively to complete the graded loading of the column confining pressure. Each loading is carried out for 2h to 4h. At the same time, the movement process of the bubble in the leveling rod is observed, and the stress, strain, and bubble movement monitoring results of each loading are recorded.

[0025] In the above-mentioned method for on-site monitoring of vertical loads on concrete rectangular cross-section columns, in step (5), based on the three-dimensional stress-strain relationship of the concrete column under small deformation and low confining pressure elastic state, combined with the vertical strain test data, the calculation results of the vertical load of the column are obtained, the time variation curves of stress and strain are plotted, and the distribution of vertical loads on the column is tracked. Then, combined with the results of the concrete strength test of the column by the rebound hammer and the design data of the vertical bearing capacity of the column, the bearing stability of the reinforced concrete column members during service is assessed.

[0026] First, based on the three-dimensional stress-strain relationship in the elastic state, without considering the load effect at the end of the column, at t i Vertical load σ of column at any moment z (t i )for:

[0027] σ z (t i )=Eε z (t i )+ν(σ x (t i )+σ y (t i (2)

[0028] In equation (2): σ z For the vertical load on the column, σ x and σ y The confining pressure load, transmitted from the tensioning wire rope to the bearing steel plate via a grooved pulley and connecting rod, is obtained from stress gauge tests. E and ν represent the elastic modulus and Poisson's ratio of the concrete, respectively, and ε... z The vertical strain test value is used, and the average value of the test results for each side is taken in the calculation. t i i = 1, 2, 3 are the times of the three-stage loading of 2kN, 4kN, and 6kN, respectively;

[0029] Then, based on the three-parameter linear creep model HK theory, the creep deformation of the vertical strain is obtained as follows:

[0030]

[0031] In equation (3): E0 and E1 are the instantaneous elastic modulus and viscoelastic modulus of the concrete column, respectively, and η1 is the viscosity coefficient;

[0032] Considering a constant confining pressure load, substituting equation (3) into equation (2) yields:

[0033]

[0034] By combining the time-varying curves of stress and strain, the long-term value σ of the vertical load under the three levels of confining pressure can be obtained. z (t ∞ )for:

[0035]

[0036] In equation (5), σ z (t ∞ ), σ x (t ∞ ), σ y (t ∞ E ∞ σ z σ x σ y The long-term value of E; further transformation yields:

[0037]

[0038] in

[0039] σ x (t ∞ )=σ x (t3)

[0040] σ y (t∞ )=σ y (t3) (7)

[0041] In equation (7): E ∞ The long-term elastic modulus of the three-parameter linear creep model is obtained from the creep test characteristic curve.

[0042] When σ z (t ∞ ) / E <f c When / E, the column load is stable and safe; otherwise, the column load is in an unstable state. c This refers to the design value of the compressive strength of concrete.

[0043] The beneficial effects of this invention are as follows:

[0044] 1. This invention completes the confining pressure loading of the column loading zone through a column confining pressure loading system of an on-site monitoring device. Then, based on the three-dimensional static equilibrium condition of the column under small deformation and low confining pressure elastic state, the vertical load of the column is calculated, and the time-effect characteristic curve of the vertical load of the column is plotted. Combined with the vertical bearing capacity of the column, the bearing reliability of the reinforced concrete column component during service can be identified. This invention can overcome the problems of column bending, tilting and human error caused by unreasonable vertical load monitoring schemes or monitoring results of reinforced concrete column structures, as well as the complexity of technology, high risk and high monitoring cost. It ensures that the rapid monitoring system has strong environmental adaptability, fast and simple testing methods, safe operation, low cost, and can also track the vertical load distribution and bearing stability evaluation of reinforced concrete columns in real time.

[0045] 2. Based on the real-time distribution and deformation monitoring data of the column vertical load, the monitoring method of this invention provides the time for column load stability and timely reinforcement, giving full play to the timeliness of the monitoring data. This has good theoretical significance and economic and social value for the rapid assessment and active reinforcement of the reliability of reinforced concrete rectangular section columns. Attached Figure Description

[0046] Figure 1 This is a structural block diagram of the monitoring device of the present invention.

[0047] Figure 2 This is a schematic diagram of on-site monitoring of vertical load on a rectangular cross-section column according to an embodiment of the present invention.

[0048] Figure 3 This is a schematic diagram of the loading test area and monitoring layout in an embodiment of the present invention.

[0049] Figure 4 This is a schematic diagram of the leveling rod according to an embodiment of the present invention.

[0050] Figure 5This is a schematic diagram of the column confining pressure loading system according to an embodiment of the present invention.

[0051] Figure 6 for Figure 5 Schematic diagram of the medium-loaded motor structure.

[0052] Figure 7 The creep characteristic curves for the loading test.

[0053] In the diagram, 1 is a column, 2 is a beam, 3 is the loading test area AFEGHI, 4 is the loading area AFEDCB, 5 is the floor, 6 is a leveling rod, 7 is an orthogonal strain gauge, 8 is the beam load area, 9 is the axis, 10 is a bubble, 11 is a pin, 12 is an end slot, 13 is a stress gauge, 14 is a bearing steel plate, 15 is a grooved pulley, 16 is a connecting rod, 17 is a wire rope, 18 is a loading motor, and 19 is a screw. Detailed Implementation

[0054] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0055] like Figures 1 to 6 As shown, in this embodiment, the column is a reinforced concrete rectangular section column with a design service life of 50 years, an environmental category of Class I, and is subjected to small eccentric compression. The calculated length of the column is 4800mm, the column cross-sectional dimensions are 600×500mm, the concrete strength grade is C30, asymmetric reinforcement is used, and the design value of the axial pressure it bears is 1000kN.

[0056] like Figure 1 As shown, a field monitoring device for vertical load on a concrete rectangular section column includes a column body 1, a column confining pressure loading system, a stress-strain testing system, and a data processing and analysis system. The data processing and analysis system is connected to the column confining pressure loading system and the stress-strain testing system, respectively.

[0057] The column confining pressure loading system includes a pressure-bearing steel plate 14, a connecting rod 16, a grooved pulley 15, a steel wire rope 17, and a loading motor 18. A loading test area is provided on the column 1, and the lower part of the loading test area is the column loading area. A pressure-bearing steel plate 14 is arranged on each of the four sides of the column loading area. The outer side of each pressure-bearing steel plate 14 is fixedly connected to one end of a connecting rod 16, and the other end of the connecting rod 16 is fixedly connected to a grooved pulley 15. The two ends of the steel wire rope 17 are wound in opposite directions around the screw 19 of the loading motor 18, and the steel wire rope 17 is wound in a ring around the four grooved pulleys 15. The rotation of the screw 19 of the loading motor 18 causes the two ends of the steel wire rope 17 to be tensioned synchronously, but in opposite directions. The loading motor 18 rotates the screw 19 to tension the steel wire rope 17 and compress the connecting rod 16, thus completing the graded loading of the column loading area confining pressure. The length of the pressure-bearing steel plate 14 is less than the cross-sectional length of the column loading area, and the height of the pressure-bearing steel plate 14 is equal to the height of the column loading area.

[0058] The stress-strain testing system includes strain gauges 7, stress meters 13, and a leveling rod 6. The strain gauges 7 are arranged on the four upper sides of the loading test area. The strain gauges 7 are orthogonal strain gauges, with three sets evenly spaced parallel to each side of the loading test area, located at three positions: the side axis of the loading test area and its left and right quarter lengths. The stress meters 13 are positioned in the middle of the connecting rod 16. The leveling rod 6 is arranged on the four upper sides of the loading test area to record the strain of the column 1 during the confining pressure and graded loading process. The leveling rod 6 is positioned between the strain gauges 7 and the bearing steel plate 14. The midpoint of the leveling rod 6 is located on the vertical axis 9 of the side of the loading test area. Both ends of the leveling rod 6 are fixed to the side of the loading test area by pins 11, with the bubble 10 of the leveling rod 6 centered and horizontal. The pins 11 move vertically within the grooves 12 at both ends of the leveling rod 6 as the column 1 deforms vertically.

[0059] The data processing and analysis system includes a main control computer, which is connected to strain gauges 7, stress gauges 13, and loading motors 18. It is used to calculate the collected stress and strain, obtain the vertical load of the column, plot the time-effect characteristic curve of the vertical load of the column, and compare and analyze the monitoring and calculation results with the vertical bearing capacity of the column, thereby identifying the bearing stability of the column component.

[0060] A method for on-site monitoring of vertical loads on concrete rectangular section columns includes the following steps:

[0061] (1) Select a rectangular load test area (AFEGHI)3 above the floor 5 in the lower part of column 1, and draw lines to determine the range of confining pressure loading in this area, forming column loading area (AFEDCB)4.

[0062] A rectangular loading test area is selected above the floor 5 in the lower part of column 1. The marked area is as follows: the distance from the bottom edge to the floor is c = 800mm, the cross-sectional dimensions of the loading test area are a×b = 600×500mm, and the height is 700mm.

[0063] (2) The pressure-bearing steel plates 14 are respectively arranged on the four sides of the loading area of ​​the column. The four pressure-bearing steel plates 14 are fixedly connected to the four groove pulleys 15 by four connecting rods 16. The two ends of the steel wire rope 17 are wound on the screw 19 of the loading motor 18 in opposite directions. The steel wire rope 17 is wound in a ring around the outside of the four groove pulleys 15. Then, stress gauges 13 are arranged in the middle of each connecting rod 16.

[0064] Rectangular bearing steel plates 14 with cross-sectional dimensions a′×b′ are symmetrically arranged on the four sides of the loading test area to form a column loading area. The height of the bearing steel plates 14 is equal to the height of the column loading area.

[0065]

[0066] In formula (1): a, b, h are the length, width and height of the cross section of the loading test area, respectively; a', b', h' are the length, width and height of the bearing steel plate 14, respectively; the length a' of the bearing steel plate 14 is 560mm, which is less than the cross section length a = 600mm of the column 1 in the loading area 4; the height AB = CF = DE = 200mm of the bearing steel plate 14 is equal to the height of the column loading area.

[0067] The pressure-bearing steel plate 14 is fixedly connected to the grooved pulley 15 by the connecting rod 16. The connecting rod 16 is a straight steel rod with a circular cross-section. The center of the circle of the two end faces of the connecting rod 16 coincides with the centroid of the pressure-bearing steel plate 14 and the grooved pulley 15, respectively.

[0068] (3) Leveling rods 6 and orthogonal strain gauges are arranged sequentially from bottom to top on the four sides of the upper part of the loading test area.

[0069] A leveling rod 6 and orthogonal strain gauges 7 are arranged from bottom to top within a range of e = 500 mm on the upper boundary of the four sides of the loading area of ​​the column. First, the midpoint of the leveling rod 6 is fixed on the vertical axis 9 of the side of the loading test area. The two ends of the leveling rod 6 are fixed to the side of the loading test area by pins 11, so that the bubble 10 of the leveling rod 6 is centered and reaches a horizontal state. The pins 11 move slightly vertically within the grooves 12 at both ends of the leveling rod 6 as the column deforms vertically. Then, orthogonal strain gauges are arranged on the side of the loading test area at a position d = 400 mm from the upper boundary of the loading area. Three sets of orthogonal strain gauges are attached in parallel at equal intervals of 150 mm on each side of the loading test area, located at three positions: the side axis of the loading test area and the left and right 1 / 4 of the length 150 mm.

[0070] (4) Start the loading motor 18, and the screw 19 rotates to synchronously tension both ends of the wire rope 17. The tension of the wire rope 17 is transmitted to the pressure plate 14 through the groove pulley 15 and the connecting rod 16 to complete the confining pressure loading of the column loading area.

[0071] The loading motor 18 is started, and the two ends of the steel wire rope 17 are synchronously tensioned by rotating the screw 19. The tension of the steel wire rope 17 is transmitted to the pressure-bearing steel plate 14, which has been coated with a smooth coating, through the groove pulley 15 and the connecting rod 16, thus completing the confining pressure loading of the column loading area. The confining pressure loading adopts a staged loading method. First, an initial low-pressure loading of 0.2kN is implemented. After loading, the bubble 10 in the middle of the leveling rod 6 is adjusted so that the bubble 10 is centered, the leveling rod 6 is horizontal, and the pressure-bearing steel plate 14 is in close contact with the column loading area. Then, the initial values ​​of the monitoring results of the stress gauge 13 and strain gauge 7 are removed. Then, the screw 19 tensions the steel wire rope 17 with rotational forces of 2kN, 4kN, and 6kN respectively, thus completing the staged loading of the confining pressure of the column 1. Each stage of loading lasts for 4 hours. At the same time, the movement process of the bubble 10 on the leveling rod 6 is observed, and the stress, strain, and bubble 10 movement monitoring results of each stage of loading are recorded.

[0072] (5) Based on the three-dimensional static equilibrium condition of the column under small deformation and low confining pressure elastic state, the vertical load of the column is calculated, the time-effect characteristic curve of the vertical load of the column is plotted, and then combined with the vertical bearing capacity of the column, the bearing reliability of the reinforced concrete column member during service is assessed.

[0073] Based on the three-dimensional stress-strain relationship of the concrete column under small deformation and low confining pressure elastic state, combined with the vertical strain test data, the vertical load calculation results of the column are obtained, the stress and strain time variation curves are plotted, and the vertical load distribution of the column is tracked. Then, combined with the concrete strength test results of the column by the rebound hammer and the vertical bearing capacity design data of the column, the bearing stability of the reinforced concrete column member during service is evaluated.

[0074] First, based on the three-dimensional stress-strain relationship in the elastic state, without considering the load effect at the end of the column, at t i Vertical load σ of column at any moment z (t i )for:

[0075] σ z (t i )=Eε z (t i )+ν(σ x (t i )+σ y (t i (2)

[0076] In equation (2): σ z For the vertical load on the column, σ x and σy The confining pressure load transmitted from the tensioning wire rope 17 to the bearing steel plate 14 via the grooved pulley 15 and connecting rod 16 is obtained from the test results of the stress gauge 13. E and ν are the elastic modulus and Poisson's ratio of concrete, respectively. z The vertical strain test value is used, and the average value of the test results for each side is taken in the calculation. t i i = 1, 2, 3 are the times of the three-stage loading of 2kN, 4kN, and 6kN, respectively;

[0077] Then, based on the three-parameter linear creep model HK theory, the creep deformation of the vertical strain is obtained as follows:

[0078]

[0079] In equation (3): E0 and E1 are the instantaneous elastic modulus and viscoelastic modulus of the concrete column, respectively, and η1 is the viscosity coefficient;

[0080] Considering a constant confining pressure load, substituting equation (3) into equation (2) yields:

[0081]

[0082] By combining the time-varying curves of stress and strain, the long-term value σ of the vertical load under the three levels of confining pressure can be obtained. z (t ∞ )for:

[0083]

[0084] In equation (5), σ z (t ∞ ), σ x (t ∞ ), σ y (t ∞ E ∞ σ z σ x σ y The long-term value of E; further transformation yields:

[0085]

[0086] in

[0087] σ x (t ∞ )=σ x (t3)

[0088] σ y (t ∞ )=σ y (t3) (7)

[0089] In equation (7): E ∞ The long-term elastic modulus of the three-parameter linear creep model is obtained through creep test characteristic curves.

[0090] like Figure 7 As shown, when σ z (t ∞ ) / E <f c At / E, the column load is stable and safe. c This refers to the design value of the compressive strength of concrete, when σ z (t ∞ ) / E≥f c When / E, the column is in an unstable state under load.

Claims

1. A field monitoring device for vertical load on a concrete rectangular section column, comprising a column body, a column confining pressure loading system, a stress-strain testing system, and a data processing and analysis system, wherein the data processing and analysis system is connected to the column confining pressure loading system and the stress-strain testing system respectively; characterized in that: The column confining pressure loading system includes a pressure-bearing steel plate, a connecting rod, a grooved pulley, a steel wire rope, and a loading motor. A loading test area is provided on the column, with the loading test area located below it as the column loading area. A pressure-bearing steel plate is arranged on each of the four sides of the column loading area. The outer side of each pressure-bearing steel plate is fixedly connected to one end of a connecting rod, and the other end of the connecting rod is fixedly connected to a grooved pulley. The two ends of the steel wire rope are wound in opposite directions around the screw of the loading motor, forming a loop around the four grooved pulleys. The rotation of the screw of the loading motor causes the two ends of the steel wire rope to be tensioned synchronously, but in opposite directions. The loading motor's rotation of the screw tensions the steel wire rope and compresses the connecting rod, completing the graded loading of the column loading area. The stress-strain testing system includes strain gauges, stress meters, and leveling rods; the strain gauges are respectively arranged on the four sides of the upper part of the loading test area; the stress meters are arranged in the middle of the connecting rod; the leveling rods are arranged on the four sides of the upper part of the loading test area; the stress-strain testing system is used to record the strain of the column during the confining pressure and graded loading process in the loading area of ​​the column. The data processing and analysis system includes a main control computer, which is connected to strain gauges, stress meters, and loading motors. It is used to calculate the collected stress and strain to obtain the vertical load of the column, plot the time-effect characteristic curve of the vertical load of the column, and compare and analyze the monitoring and calculation results with the vertical bearing capacity of the column to identify the bearing stability of the column component. Based on the three-dimensional stress-strain relationship of the concrete column under small deformation and low confining pressure elastic state, combined with the vertical strain test data, the vertical load calculation results of the column are obtained, the stress and strain time variation curves are plotted, and the vertical load distribution of the column is tracked. Then, combined with the concrete strength test results of the column by the rebound hammer and the vertical bearing capacity design data of the column, the bearing stability of the reinforced concrete column member during service is evaluated. First, based on the three-dimensional stress-strain relationship in the elastic state, without considering the load effect at the end of the column, in Vertical load on column for: （2）； In formula (2): For the vertical load of the column, and The confining pressure load, which is transferred from the tensioning wire rope to the bearing steel plate via a grooved pulley and connecting rod, is obtained from stress gauge test results. , These are the elastic modulus and Poisson's ratio of concrete, respectively. The values ​​are vertical strain test values; the average value of the test results for each side is used in the calculation. The times of three-level loading are 2kN, 4kN, and 6kN, respectively; Then, based on the three-parameter linear creep model HK theory, the creep deformation of the vertical strain is obtained as follows: （3）； In formula (3): , These are the instantaneous elastic modulus and viscoelastic modulus of the concrete column, respectively. The viscosity coefficient; Considering a constant confining pressure load, substituting equation (3) into equation (2) yields: （4）； By combining the time-varying curves of stress and strain, the long-term value of the vertical load under three levels of confining pressure can be obtained. for: （5）； In equation (5), , , , They represent , , , The long-term value; The long-term elastic modulus of the three-parameter linear creep model is obtained from the creep test characteristic curve; further deformation yields: （6）； in （7）； when When the load is applied correctly, the column is stable and safe; otherwise, the column is in an unstable state. This refers to the design value of the compressive strength of concrete.

2. The on-site monitoring device for vertical loads on concrete rectangular section columns according to claim 1, characterized in that: The length of the pressure-bearing steel plate is less than the cross-sectional length of the column loading area, and the height of the pressure-bearing steel plate is equal to the height of the column loading area.

3. The on-site monitoring device for vertical loads on concrete rectangular section columns according to claim 2, characterized in that: The strain gauges are orthogonal strain gauges, with three sets of them equally spaced and parallelly pasted on each side of the loading test area, located at three positions: the side axis of the loading test area and the left and right 1 / 4 of its length.

4. The on-site monitoring device for vertical loads on concrete rectangular section columns according to claim 3, characterized in that: The leveling rod is set between the strain gauge and the bearing steel plate. The midpoint of the leveling rod is located on the vertical axis of the side of the loading test area. The two ends of the leveling rod are fixed to the side of the loading test area by pins. The bubble of the leveling rod is centered and reaches a horizontal state. The pins move vertically in the grooves at both ends of the leveling rod as the column deforms vertically.

5. A method for on-site monitoring of the vertical load of a concrete rectangular section column based on the on-site monitoring device for vertical load of a concrete rectangular section column according to claim 4, characterized in that, Includes the following steps: (1) Select a rectangular loading test area above the floor in the lower part of the column, and draw lines to determine the range of confining pressure loading in this area to form the column loading area; (2) Arrange the pressure-bearing steel plates on the four sides of the column loading area respectively, and fix the four pressure-bearing steel plates to the four groove pulleys through four connecting rods. Wrap the two ends of the wire rope in opposite directions on the screw of the loading motor. The wire rope is wound in a ring around the outside of the four groove pulleys. Then, arrange stress gauges in the middle of each connecting rod. (3) Leveling rods and orthogonal strain gauges are arranged sequentially from bottom to top on the four sides of the upper part of the loading test area; (4) Start the loading motor. The screw rotates to synchronously tension both ends of the wire rope. The tension of the wire rope is transmitted to the bearing steel plate through the groove pulley and connecting rod to complete the confining pressure loading of the column loading area. (5) Based on the three-dimensional static equilibrium condition of the column under small deformation and low confining pressure elastic state, the vertical load of the column is calculated, the time-effect characteristic curve of the vertical load of the column is plotted, and then combined with the vertical bearing capacity of the column, the bearing stability of the reinforced concrete column member during service is assessed.

6. The method for on-site monitoring of vertical loads on concrete rectangular section columns according to claim 5, characterized in that: In step (1), a rectangular loading test area is selected above the floor in the lower part of the column. The marked range is: the bottom edge is 60cm to 100cm from the floor. The cross-sectional dimensions of the loading test area are a×b and the height is 20cm. a and b are the length and width of the cross-section of the loading test area, respectively.

7. The method for on-site monitoring of vertical loads on concrete rectangular section columns according to claim 6, characterized in that: In step (2), rectangular pressure-bearing steel plates are symmetrically arranged on the four sides of the loading test area to form a column loading area. The height of the pressure-bearing steel plates is equal to the height of the column loading area. The pressure-bearing steel plate is fixedly connected to the grooved pulley by a connecting rod. The connecting rod is a straight steel rod with a circular cross-section, and the center of the circle on both ends of the connecting rod coincides with the centroid of the pressure-bearing steel plate and the grooved pulley, respectively.

8. The method for on-site monitoring of vertical loads on concrete rectangular section columns according to claim 5, characterized in that: In step (3), leveling rods and orthogonal strain gauges are arranged from bottom to top on the upper part of the four sides of the loading area of ​​the column. First, the midpoint of the leveling rod is fixed on the vertical axis of the side of the loading test area. The two ends of the leveling rod are fixed on the side of the loading test area by pins, so that the bubble of the leveling rod is centered and reaches a horizontal state. The pins move vertically in the grooves at both ends of the leveling rod as the column deforms vertically. Then, orthogonal strain gauges are arranged on the side of the loading test area at a position 40 cm away from the upper boundary of the loading area. Three sets of orthogonal strain gauges are pasted parallel to each side of the loading test area at equal intervals, located at the three positions of the side axis of the loading test area and its left and right 1 / 4 lengths.

9. The method for on-site monitoring of vertical loads on concrete rectangular section columns according to claim 5, characterized in that: In step (4), the loading motor is started, and the two ends of the steel wire rope are synchronously tensioned by rotating the screw. The tension of the steel wire rope is transmitted to the pressure-bearing steel plate that has been coated with a smooth coating through the groove pulley and connecting rod to complete the confining pressure loading of the column loading area. The confining pressure loading adopts a graded loading method. First, an initial low pressure loading of 0.2 kN is implemented. After loading, the bubble in the middle of the leveling rod is adjusted so that the bubble is centered and the leveling rod is horizontal. The pressure-bearing steel plate is in close contact with the column loading area. Then, the initial values ​​of the stress gauge and strain gauge monitoring results are removed. Then, the screw tensions the steel wire rope with a rotational force of 2 kN, 4 kN and 6 kN respectively to complete the graded loading of the column confining pressure. Each loading is carried out for 2 h to 4 h. At the same time, the movement process of the bubble in the leveling rod is observed, and the stress, strain and bubble movement monitoring results of each loading are recorded.

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