A self-temperature-control testing device for slow-bonding prestressed steel bars and a testing method thereof

Abstract

This invention relates to a self-controlled temperature testing device and method for delayed-bonding prestressed tendons. The self-controlled temperature testing device for delayed-bonding prestressed tendons includes a loading and unloading device, a heating and insulation device, a measuring and sensing device, an automated control device, and a data acquisition, transmission, processing, and analysis device. This invention utilizes concrete specimens to simulate field conditions, embedding delayed-bonding prestressed tendons in the middle of the concrete specimens. Before the test, the required length of the prepared delayed-bonding prestressed tendons is calculated to ensure that the length of the prestressed tendons within the concrete specimen remains constant throughout the test. The relationship between the viscosity coefficient and temperature, and the relationship between the equivalent curing period and bond strength are fitted using selected functional relationships. Then, by recording the time and temperature at the field, the equivalent curing period, viscosity coefficient, and bond strength are directly obtained, thereby guiding the loading of delayed-bonding prestressed members in the field.

Description

Technical Field

[0001] This invention relates to the field of concrete testing equipment, and more particularly to a self-temperature-controlled testing device and testing method for slow-bonding prestressed tendons. Background Technology

[0002] In the 21st century, the application of delayed-bond prestressing technology in engineering has become increasingly widespread. Compared with bonded and unbonded prestressing technologies, delayed-bond prestressing technology has significant advantages and is more suitable for more complex building projects, such as beams and piles.

[0003] However, the practical application of loosely bonded prestressing tendons mainly faces two problems: 1. Prestress loss occurs during the prestressing process. This loss is primarily caused by the viscosity of the tendons. Therefore, to achieve precise control of prestressing, the viscosity coefficient of the loosely bonded prestressing tendons needs to be accurately measured. 2. After the construction of loosely bonded prestressed members is completed, theoretically, the members can only bear load after the adhesive has fully reached its design bond strength. However, how to assess whether the bond strength has been reached, and to what extent, remains an unresolved issue. Therefore, it is necessary to invent a self-controlled temperature testing device for loosely bonded prestressing tendons. By recording the on-site time and temperature, data such as the equivalent curing time and bond strength can be obtained directly, quickly, and accurately.

[0004] Prior art document CN111948131A provides a test apparatus and method for testing the bond strength of reinforced concrete. A servo actuator is used to pull the reinforcing steel in the middle of the concrete sample. A pressure sensor records the downward pressure applied by the servo actuator, an electronic dial gauge records the displacement value, and a signal processor connects to a computer for data processing, thereby accurately testing the bearing capacity of the reinforced concrete.

[0005] However, in the above-mentioned pull-out test and measuring device, it is not possible to directly obtain the equivalent curing time, bond strength and viscosity coefficient of concrete by only providing temperature and time values; and as the slow-bonded prestressing tendons are pulled out of the concrete specimen, there is a deviation between the actual pulling force on the concrete specimen and the value displayed by the pulling force sensor, resulting in deviations in the measured test data. Summary of the Invention

[0006] The purpose of this invention is to provide a test device and test method for slow-bonding prestressed tendons. By recording the time and temperature on site, the equivalent curing period, the bonding coefficient and bonding strength of the slow-bonding prestressed tendons can be directly obtained, and the accuracy of the measurement results can be improved.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A self-temperature controlled testing device for slow-bonded prestressed tendons includes a loading and unloading device, a heating and insulation device, a measuring and sensing device, an automatic control device, and a data acquisition, transmission, processing, and analysis device.

[0009] The loading and unloading device includes an operating frame, a telescopic rod, and a hydraulic jack; the operating frame is divided into an upper platform and a lower platform, the upper platform is equipped with a hydraulic jack to provide the pulling force for pulling out the loosely bonded prestressed tendons; the lower platform is equipped with a telescopic rod for fixing concrete specimens;

[0010] The heating and heat preservation device includes a self-regulating electric heating cable and a temperature sensing element; the self-regulating electric heating cable is evenly arranged on the concrete specimen to maintain the temperature of the concrete specimen; the temperature sensing element is bonded to the upper end of the slow-setting prestressing tendon to measure the temperature of the slow-setting prestressing tendon in real time.

[0011] The measuring and sensing device includes a temperature sensor, a displacement sensor, and a jack force sensor;

[0012] The data acquisition, transmission, processing, and analysis device processes the relevant data collected by the measurement and sensing device, specifically including the calculation of the equivalent curing period, the fitting of the functional relationship between the hysteresis coefficient and temperature, and the fitting of the functional relationship between the equivalent curing period and the bond strength.

[0013] The loading and unloading device and the heating and insulation device are controlled in real time by an automated control device.

[0014] As a further aspect of the present invention, a slow-bonding prestressing tendon is inserted through the middle of the concrete specimen. The length of the slow-bonding prestressing tendon is predetermined based on the number of tests to ensure that the length of the slow-bonding prestressing tendon placed in the concrete specimen remains unchanged throughout the entire test.

[0015] As a further embodiment of the present invention, the fixing component includes an anchor, high-strength reinforcing bars, and a steel plate; the steel plate is divided into an upper steel plate and a lower steel plate, and the high-strength reinforcing bars are divided into left reinforcing bars and right reinforcing bars; the left reinforcing bar is fixed to the left side of the steel plate by the anchor, and the right reinforcing bar is fixed to the right side of the steel plate by the anchor; the slow-bonding prestressed tendon is located in the center of the lower steel plate, and the hydraulic jack is located in the center of the upper platform of the operating frame—the upper steel plate.

[0016] As a further aspect of the present invention, the automated control device controls the heating temperature of the self-regulating electric heating tape in real time to ensure that the actual temperature is the same as the temperature set for the test.

[0017] As a further aspect of the present invention, the data acquisition, transmission, processing, and analysis device includes an initial data input module, a process data acquisition module, and an experimental data processing module; the initial data input module inputs the set temperature and the jack loading force; during the experiment, the process data acquisition module inputs data from the temperature sensor, the displacement sensor, and the jack loading force; after the experiment, the experimental data processing module processes the acquired data.

[0018] As a further aspect of the present invention, the functional fitting relationship between temperature and viscosity coefficient is as follows:

[0019] λ=Ae -BT

[0020] Where T is temperature, and A and B are fitting coefficients.

[0021] As a further aspect of the present invention, the functional relationship between the equivalent curing time and the bond strength is as follows:

[0022]

[0023] Where, τ flim τ is the ultimate bond strength; β is the normalized parameter of equivalent curing time; α is the goodness-of-fit parameter; flim α, β, and α are all determined by function fitting methods.

[0024] As another aspect of the present invention, a self-temperature-controlled test method for slow-bonding prestressed tendons includes the following steps:

[0025] S1. Adjust the telescopic rod to fix the concrete specimen, fix the displacement gauge and attach the temperature sensing sheet to the loosely bonded prestressing tendon on the upper part of the concrete specimen, and evenly arrange the self-limiting electric heating tape on the concrete specimen.

[0026] S2. Place the hydraulic jack and set the loading mode of the hydraulic jack on the control end;

[0027] S3. Set the temperature series for which the viscosity coefficient needs to be measured, the temperature series for which the bond strength needs to be measured, and the curing time for each temperature.

[0028] S4. Using a data acquisition, transmission, processing, and analysis device, calculate the functional relationship between the equivalent curing time, viscosity coefficient, and temperature, as well as the functional relationship between the equivalent curing time and bond strength. By recording the time and temperature at the construction site, the equivalent curing time and bond strength values ​​at the construction site can be directly obtained.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. The precast concrete specimen of the present invention has a slow-bonding prestressing tendon in the middle. The present invention determines the length of the prestressing tendon in contact with the concrete specimen and the perimeter of the prestressing tendon section in advance according to the number of tests required, thereby ensuring that the slow-bonding prestressing tendon in the concrete specimen has a large margin on both the upper and lower sides of the concrete specimen, so as to ensure that the length of the prestressing tendon placed in the concrete specimen remains unchanged throughout the test, and further improves the accuracy of the test data.

[0031] 2. This invention can clarify the relationship between viscosity coefficient and temperature, and the relationship between bond strength and time and temperature through a series of function fitting relationships; thus, by combining on-site time and temperature records, the equivalent curing period and bond strength of the slow-bonded prestressed tendon can be directly obtained. Attached Figure Description

[0032] Figure 1 This is a block diagram of the self-temperature controlled test device for the slow-bonding prestressed tendons in this invention;

[0033] Figure 2 This is a schematic diagram of the loading / unloading device, heating and heat preservation device, and measuring and sensing device in this invention.

[0034] Numbering in the diagram: 1-Operating frame; 2-Telescopic rod; 3-Concrete specimen; 4-Slow-bonding prestressed tendon; 5-Displacement gauge; 6-Anchorage; 7-Hydraulic jack; 8-High-strength steel bar; 9-Steel plate; 10-Self-regulating heating cable; 11-Temperature sensor. Detailed Implementation

[0035] 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.

[0036] See Figure 1 In this embodiment of the invention, a self-temperature controlled test device for slow-bonding prestressed tendons includes a loading and unloading device, a heating and heat preservation device, a measuring and sensing device, an automatic control device, and a data acquisition, transmission, processing, and analysis device.

[0037] The loading and unloading device includes an operating frame 1, a telescopic rod 2, a hydraulic jack 7, a steel plate 9, and a high-strength steel bar 8. The operating frame is divided into an upper platform and a lower platform. The upper platform holds the hydraulic jack 7 to provide the upward pulling force required for the test. The lower platform holds the concrete specimen 3, and the length of the telescopic rod 2 is adjusted to fix the concrete specimen 3.

[0038] The heating and heat preservation device includes a self-regulating electric heating tape 10 and a temperature sensing element 11; the self-regulating electric heating tape 10 is evenly arranged on the concrete specimen 3 to maintain the set temperature of the concrete specimen 3; the temperature sensing element 11 is attached to the loosely bonded prestressing tendon 4 on the upper part of the concrete specimen 3 to measure the temperature of the loosely bonded prestressing tendon 4 in real time.

[0039] The measuring and sensing device includes a temperature sensor, a displacement sensor, and a jack force sensor. The measuring and sensing device is installed in the loading and unloading device and the heating and insulation device. The measuring and sensing device collects relevant data, stores and processes it through a data acquisition, transmission, processing and analysis device, and then transmits the processed data to an automation control device. The automation control device then performs real-time control of the loading and unloading device and the heating and insulation device.

[0040] See Figure 2 This section provides a specific test method for applying a slow-bonding prestressed tendon test device. The test method includes the following steps:

[0041] S1. Preparation of concrete specimens 3

[0042] 1) Weigh water, cement, fine sand and gravel according to the mix proportions for C33 concrete grade, with a ratio of 205:410:625:1160 per cubic meter of concrete; mix thoroughly and then fill into molds.

[0043] 2) For the unbonded part of the prestressed tendon 4, use a PVC pipe with a diameter slightly larger than that of the steel bar to cover it, and seal both ends of the plastic sleeve.

[0044] 3) Place the slow-bonding prestressed tendon 4 in the middle of the prepared concrete mold in advance, pour the concrete into the mold, and then demold and cure to obtain concrete specimen 3; the curing time is 28 days and the curing temperature is 20℃.

[0045] After the concrete has cured, it bonds together with the polyethylene pipe encasing the slow-bonding prestressing tendon, forming a whole with the concrete. The upper part of the slow-bonding prestressing tendon 3 is the loading end of the component, and the lower part is the free end of the component; a displacement gauge 5 is installed at the loading end of the component to measure the displacement between the slow-bonding prestressing tendon 4 and the concrete specimen 3.

[0046] S2. Place the concrete specimen 3 on the lower platform of the operating frame 1 and adjust the telescopic rod 2 to fix the concrete specimen 3. Next, anchor the loosely bonded prestressing tendons on the upper part of the concrete specimen 3 to the steel plate 9. Install and fix the displacement gauge 5 on the upper part of the concrete specimen 3. Peel off the PE outer sleeve of the loosely bonded prestressing tendons on the lower part of the concrete specimen 3, leaving the adhesive.

[0047] S3. Temperature sensing plates 11 are attached to the loosely bonded prestressed tendons 4, and self-regulating heating cables 10 are evenly distributed on the concrete specimen 3. A hydraulic jack 7 is placed on the upper part of the operating frame, and the loading mode of the hydraulic jack 7 is set at the operating end for test control.

[0048] S4. Using a data acquisition, transmission, processing, and analysis device, fit the functional relationship between temperature and viscosity coefficient, and the functional relationship between equivalent curing time and bond strength.

[0049] Fitting principle:

[0050] Determine the viscosity coefficient and bond strength

[0051] The formula for calculating the viscosity coefficient is: λ=F / (vL); where F is the tension provided by the jack; V is the average sliding speed, which can be measured by a displacement gauge; L is the length of the prestressing tendon in contact with the concrete specimen; the formula for calculating the bond strength is: tf=F / (SL), where S is the perimeter of the prestressing tendon section.

[0052] Determine the equivalent curing period

[0053] Formula for calculating equivalent curing time:

[0054]

[0055] Where n is the number of curing time periods; Ea is the apparent activation energy of the adhesive material (kJ / mol); R is the gas constant (kJ / mol / K); Ti is the curing temperature of the i-th curing time period; Tr is the comparison temperature, taken as a constant -253.15K; Δti is the duration of the i-th curing time period (d); the formula for calculating the bond strength is t f =F / (SL), where S is the perimeter of the prestressed tendon section.

[0056] Based on the known viscosity coefficient, the functional relationship between temperature and viscosity coefficient is fitted:

[0057] λ=Ae -BT

[0058] Where T is temperature, and A and B are fitting coefficients.

[0059] Based on the known bond strength, the functional relationship between the equivalent curing time and the bond strength is fitted:

[0060]

[0061] Among them, t flim β is the ultimate bond strength; β is the normalized parameter of equivalent curing time; α is the goodness-of-fit parameter; t flim α, β, and α are all determined by function fitting methods.

[0062] Fitting method:

[0063] The length of the loosely bonded prestressing tendon 4 in contact with the concrete specimen 3 and the perimeter parameters of the loosely bonded prestressing tendon 4 section are determined according to the actual situation.

[0064] In the data acquisition, transmission, processing and analysis device, the temperature series for which the viscosity coefficient needs to be measured, such as 5℃, 7.5℃, 10℃, 12.5℃, 15.0℃, 17.5℃, 20.0℃, and 25.0℃, can be automatically obtained to obtain the viscosity coefficient corresponding to the specified temperature series and fit the functional relationship between temperature and viscosity coefficient.

[0065] Input the temperature series for which the bond strength needs to be measured, along with the curing time for each temperature, such as 20 days at 5℃, 20 days at 10℃, 10 days at 15℃, 10 days at 20℃, 5 days at 25℃, and 5 days at 30℃. The system can automatically calculate the equivalent curing period after each curing reaction and fit the functional relationship between the equivalent curing period and the bond strength.

[0066] This invention, as a concrete bond strength test, only measures the bond strength of slow-bonding prestressing tendons. Even if the slow-bonding prestressing tendons are replaced with other engineering materials, the effective curing period and bond strength in concrete and other construction materials can still be determined.

[0067] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0068] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A self-temperature controlled testing device for slow-bonding prestressed tendons, characterized in that, The test apparatus includes a loading and unloading device, a heating and insulation device, a measuring and sensing device, an automatic control device, and a data acquisition, transmission, processing, and analysis device. The loading and unloading device includes an operating frame (1), a telescopic rod (2), and a hydraulic jack (7). The operating frame is divided into an upper platform and a lower platform. The upper platform is equipped with a hydraulic jack (7) to provide the pulling force for the prestressed tendons (4). The lower platform is equipped with a telescopic rod (2) for fixing the concrete specimen (3). The heating and heat preservation device includes a self-regulating electric heating tape (10) and a temperature sensing element (11); the self-regulating electric heating tape (10) is evenly arranged on the concrete specimen (3) to maintain the temperature of the concrete specimen (3); the temperature sensing element (11) is bonded to the upper end of the loosely bonded prestressing tendon (4) to measure the temperature of the loosely bonded prestressing tendon (4) in real time. The measuring and sensing device includes a temperature sensor, a displacement sensor, and a jack force sensor; The data acquisition, transmission, processing, and analysis device processes the relevant data collected by the measurement and sensing device, specifically including the calculation of the equivalent curing period, the fitting of the functional relationship between the hysteresis coefficient and temperature, and the fitting of the functional relationship between the equivalent curing period and the bond strength. The loading / unloading device and the heating / insulation device are controlled in real time by an automated control device. The data acquisition, transmission, processing, and analysis device includes an initial data input module, a process data acquisition module, and an experimental data processing module. The initial data input module inputs the set temperature and jack loading force. During the experiment, the process data acquisition module inputs data from the temperature sensor, displacement sensor, and jack loading force. After the experiment, the experimental data processing module processes the acquired data. The functional relationship between temperature and viscosity coefficient is as follows: λ=Ae -BT Where T is the temperature, and A and B are the fitting coefficients; The functional relationship between the equivalent curing time and the bond strength is as follows: Where τflim is the ultimate bond strength; β is the normalized parameter of equivalent curing time; α is the goodness-of-fit parameter; τflim, β, and α are all determined by function fitting method.

2. The self-temperature controlled testing device for slow-bonding prestressed tendons according to claim 1, characterized in that, The concrete specimen (3) has a slow-bonding prestressing tendon (4) running through its middle. The length of the slow-bonding prestressing tendon (4) is determined in advance based on the number of tests to ensure that the length of the slow-bonding prestressing tendon (4) placed in the concrete specimen (3) remains unchanged throughout the entire test.

3. The self-temperature controlled testing device for slow-bonding prestressed tendons according to claim 1, characterized in that, The loading and unloading device also includes anchors (6), high-strength steel bars (8) and steel plates (9); the steel plates (9) are divided into upper steel plates and lower steel plates, and the high-strength steel bars (8) are divided into left steel bars and right steel bars; the left steel bars are fixed to the left side of the steel plates (9) by anchors (6), and the right steel bars are fixed to the right side of the steel plates (9) by anchors (6); the slow-bonded prestressed tendons (4) are located in the center of the lower steel plate, and the hydraulic jacks (7) are located in the center of the upper platform of the operating frame (1)—the upper steel plate.

4. The self-temperature controlled testing device for slow-bonding prestressed tendons according to claim 1, characterized in that, The automated control device controls the heating temperature of the self-regulating electric heating tape in real time to ensure that the actual temperature is the same as the temperature set for the test.

5. A method for testing the self-controlled temperature of slow-bonded prestressed tendons, comprising the self-controlled temperature testing device for slow-bonded prestressed tendons as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Adjust the telescopic rod (2) to fix the concrete specimen (3), fix the displacement gauge (5) on the prestressed tendon (4) on the upper part of the concrete specimen (3), and attach the temperature sensing sheet (11). Arrange the self-limiting electric heating tape (10) evenly on the concrete specimen (3). S2. Place the hydraulic jack (7) and set the loading mode of the hydraulic jack (7) on the control end; S3. Set the temperature series for which the viscosity coefficient needs to be measured, the temperature series for which the bond strength needs to be measured, and the curing time for each temperature. S4. Using a data acquisition, transmission, processing, and analysis device, calculate the functional relationship between the equivalent curing time, viscosity coefficient, and temperature, as well as the functional relationship between the equivalent curing time and bond strength. By recording the time and temperature at the construction site, the equivalent curing time and bond strength values ​​at the construction site can be directly obtained.

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