Concrete simply supported beam deflection test system based on distributed optical fiber test

Abstract

The invention discloses a concrete simply supported beam deflection test system based on distributed optical fiber testing, which is characterized in that through distributed optical fibers on the surface of concrete and reinforcing steel bars, the strain of the reinforcing steel bars and the concrete of a beam body under the action of prestress and operation dynamic load is tested, and the deflection of the beam body is analyzed according to the strain; therefore, the concrete simply supported beam deflection test system based on the distributed optical fiber test is formed. According to the invention, full-size measurement is carried out on the strain of steel bars and concrete in the full-length range of the existing concrete simply supported beam, and the deflection deformation of the simply supported beam is analyzed according to the strain.

Description

Technical Field

[0001] This invention relates to the field of testing, specifically to a deflection testing system for simply supported concrete beams based on distributed optical fiber testing. Background Technology

[0002] Simply supported concrete beam structures are widely used in highway, railway, and municipal bridges due to their excellent technical and economic efficiency, high strength, stability, and durability. The concrete exterior of a simply supported beam structure fully utilizes the excellent durability of concrete, while the internal reinforcement and prestressed steel strands utilize their excellent tensile strength. Under prestressed loads and dynamic vehicle loads, simply supported beam structures experience continuous deflection deformation due to the shrinkage and creep characteristics of the concrete. Under long-term environmental conditions and repeated loading, the beam structure will deteriorate and deform, and may also experience sudden deformation in the event of unexpected failure. Beam deflection is an important indicator of structural stiffness, load-bearing capacity, and stability. However, for simply supported concrete beams operating in long-term environments, there is currently no reliable testing technology to obtain stable and continuous deflection characteristics.

[0003] Traditional deflection testing systems require the installation of a displacement testing device on a flat bottom surface of the beam, connected to a steel wire on the beam's underside. This method is only suitable for bridges with a flat and stable underside and pier heights less than 30m. Furthermore, this system is unstable and significantly affected by environmental factors such as wind and temperature, making it suitable only for short-term static load testing of simply supported concrete beams. While the water balance testing method reduces the requirements on the beam's underside, it is significantly affected by ambient temperature and unsuitable for long-term testing of beam deformation. Using leveling instruments or total stations results in large measurement errors, and the difference in measurement positions exceeds the beam's deformation, making continuous and stable measurements impossible.

[0004] A new deflection testing system for simply supported concrete beams is needed to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to address the problems in existing technologies where traditional deflection testing systems require the installation of displacement testing devices on a flat bottom surface of the beam and connection to steel wires on the beam bottom. This testing method is only suitable for bridges with a flat and stable bottom surface and pier height less than 30m. Furthermore, this testing system is unstable and greatly affected by environmental factors such as wind and temperature. It is suitable for deflection testing of simply supported concrete beams in short-term static load tests. While the water balance testing method can reduce the requirements on the bottom surface of the beam, this method is greatly affected by environmental temperature and is not suitable for long-term testing of beam deformation. Using measurement methods such as levels and total stations results in large measurement errors, and the difference in measurement positions exceeds the amount of beam deformation, making continuous and stable measurement impossible. This invention provides a concrete simply supported beam deflection testing system based on distributed optical fiber testing, using fiber optic grating technology to solve the problems mentioned in the background.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A deflection test system for simply supported concrete beams based on distributed optical fiber testing includes a concrete surface strain testing module, which consists of several distributed optical fibers arranged along the length of the beam on the bottom surface of the beam. The steel bar strain testing module consists of several distributed optical fibers that are pre-embedded along the length of the beam and are installed together with the bottom steel bars of the beam. The fiber optic demodulator acquires and demodulates the test data from the bottom concrete surface strain test module and the steel bar strain test module. The overall structural module is used to collect current beam data; The deflection analysis module uses the demodulated data from the bottom fiber optic demodulator and the data obtained from the bottom overall structure module as the data basis to analyze and obtain deflection data.

[0007] This invention provides a deflection testing system for simply supported concrete beams based on distributed optical fiber testing. As a preferred embodiment, the analysis process of the bottom deflection analysis module is as follows: The structural deflection obtained from the integral of the steel strain is R. g Assume there are n measuring points for the reinforcing bars: ; Where, ε g i represents the longitudinal strain of the i-th reinforcing bar in the structure, ε gT i represents the strain at the i-th steel reinforcement temperature measurement point in the structure, and L represents the length of the simply supported concrete beam. The structural deflection obtained from the concrete strain integral is R. c Assume there are m measuring points for the reinforcing bars: ; Where, ε c i represents the longitudinal strain of the i-th concrete in the structure, ε cTi represents the strain at the i-th concrete temperature measurement point in the structure.

[0008] Based on the relationship between the test location of the reinforcing bars and the vertical spatial position of the beam structure, the deflection test value of the bottom surface of the beam is calculated in reverse. Calculate the bottom deflection R of a simply supported beam obtained by back-calculation based on the deflection at the position of the reinforcing bars. Dg： ； Where Lc is the height of the neutral axis of the simply supported beam, and Lg is the distance from the center of the reinforcement measuring point to the neutral axis of the simply supported beam; Calculate the deflection R at the bottom of the simply supported beam obtained by back-calculation based on the deflection at the concrete test location. Dc : ; Where Lc is the height of the neutral axis of the simply supported beam, and Lcc is the distance from the center of the concrete measuring point to the neutral axis of the simply supported beam; The R obtained from the analysis Dg With R Dc Comparison, If the difference between the two values ​​is less than 5% compared to the average, then the average of the two values ​​is taken. Otherwise, the structure should be retested and analyzed.

[0009] This invention provides a concrete simply supported beam deflection test system based on distributed optical fiber testing. As a preferred embodiment, the bottom concrete simply supported beam deflection test system further includes a time sequence module and a dynamic evaluation module. The bottom time sequence module generates timestamps according to the time sequence, and the bottom dynamic evaluation module rates the state of the concrete simply supported beam according to the timestamp interval and the amount of deflection change, and outputs the evaluation results based on the rating.

[0010] This invention provides a test system for the deflection of simply supported concrete beams based on distributed optical fiber testing. As a preferred solution, the bottom evaluation results consist of the impact on the structural function of the beam and corresponding measures.

[0011] This invention provides a deflection test system for simply supported concrete beams based on distributed optical fiber testing. As a preferred embodiment, the data demodulated by the bottom optical fiber demodulator is the strain data of the corresponding position of the beam.

[0012] The beneficial effects of this technical solution are as follows: This distributed optical fiber testing method is applied to test the strain of steel reinforcement and concrete along the entire length of a simply supported concrete beam. Optical fibers are installed on the surface of the object under test. When the object is subjected to load, its surface deforms, causing a corresponding change in the characteristics of the distributed optical fiber. The wavelength of the reflected light passing through the fiber is altered, and after testing and analysis, the strain on the surface of the object can be accurately measured. This testing method, based on the principles of light propagation and reflection, has advantages such as high accuracy, good stability, and small size. Multiple points are continuously measured using a single distributed optical fiber. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a concrete simply supported beam deflection test system based on distributed optical fiber testing. Figure 2 This is a schematic diagram of the cross-sectional arrangement of optical fibers in a distributed optical fiber testing system for deflection of simply supported concrete beams. Figure 3 This is a schematic diagram of the fiber optic cable arrangement in a distributed fiber optic testing system for deflection of simply supported concrete beams. Figure 4 This is a schematic diagram of the installation of a fiber Bragg grating testing device in a distributed optical fiber testing system for deflection of simply supported concrete beams. Figure 5 This is a schematic diagram of the fiber optic connection for a distributed fiber optic testing system for deflection of simply supported concrete beams.

[0014] Figure label: 1. Concrete surface strain testing module; 2. Reinforcing steel strain testing module; 3. Fiber optic demodulator; 4. Overall structure module; 5. Deflection analysis module. Detailed Implementation

[0015] 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1 like Figure 1As shown, a concrete simply supported beam deflection test system based on distributed optical fiber testing includes a concrete surface strain testing module 1, a steel bar strain testing module 2, an optical fiber demodulator 3, an overall structure module 4, and a deflection analysis module 5. The data collected by the concrete surface strain testing module 1 and the steel bar strain testing module 2 are transmitted to the optical fiber demodulator 3 for demodulation. The overall structure module 4 collects the overall data in real time. The output data of the overall structure module 4 and the optical fiber demodulator 3 are output to the deflection analysis module 5 for deflection analysis.

[0017] The concrete surface strain testing module 1 consists of several distributed optical fibers arranged along the length of the beam on the bottom surface of the beam. The steel bar strain testing module 2 consists of several distributed optical fibers that are pre-embedded along the length of the beam and are installed together with the bottom steel bars of the beam. The specific arrangement of the concrete surface strain testing module 1 and the steel reinforcement strain testing module 2 is as follows: Figure 2 , 3 As shown; Fiber Bragg grating (FBG) technology offers advantages such as precise and stable measurement due to its measurement principle, small measuring element size, high precision, good anti-interference ability, and minimal impact from repeated loading. It is suitable for applications requiring high precision and subjected to repeated loading. Since its emergence, this technology has been widely used in strain testing of structures such as building structures, bridge structures, tall structures, dams, and airports. Distributed optical fibers are installed on the surface of the object being tested; structural deformation occurs on the fiber surface, and the amount of change is determined by the refraction parameters of the light, exhibiting good accuracy and stability. Currently, resistance-type and steel-wire-type strain gauges are widely used. Resistance-type strain gauges are easily affected by strong ambient currents, impacting measurement accuracy. In steel-wire-type strain gauges, the steel wire itself relaxes under repeated loading, causing frequency changes and affecting measurement accuracy.

[0018] The key to testing the deflection of simply supported concrete beams is to use a stable and precise method for continuous testing without damaging the original structure. Distributed optical arrays, which are small in size, highly accurate, and have good stability, have significant advantages in this regard.

[0019] Using distributed optical fibers to measure the full-length strain along the beam and obtaining the beam's deformation deflection through strain integration is a key process and technology for completing the deflection test of simply supported concrete beams.

[0020] In this embodiment, the installation of the fiber optic measurement element is carried out as follows: Figure 4 As shown.

[0021] Distributed optical fibers are installed on the reinforcing steel and concrete surface within a simply supported concrete beam using adhesive bonding. They are connected to a demodulator via optical fibers. The distributed optical fiber demodulator includes a broadband light source, a signal processor, and an optical fiber coupler. The demodulator is connected to a computer via a cable, and the demodulator transmits the test signals to the computer for calculation and analysis.

[0022] The installation process is as follows: ① Surface treatment at the measurement location to ensure effective adhesion between the fiber optic measuring element and the surface being measured; ② Install fiber optic measuring elements at the measurement location and adhere them to the surface of the object being measured using fast-drying 502 glue. During the load-bearing process, the measuring elements and the object being measured deform together. Based on the stress-deformation characteristics of the object being measured, apply prestress to the measuring elements and place the fiber optic elements in the optimal testing position; simultaneously, place a control fiber optic cable at the same location that is not adhered to the surface of the object being measured, and test the fiber optic strain change caused by temperature variations. ③ After the test element is fixed, apply 704 glue around the test element for soft isolation to prevent deformation and obstruction of the test element and improve test accuracy; ④ Apply epoxy resin glue to the outside of the 704 coating layer to waterproof and protect the test element from damage.

[0023] The fiber optic demodulator 3 acquires and demodulates the test data from the concrete surface strain test module 1 and the steel bar strain test module 2.

[0024] For details on the connection method between fiber demodulator 3 and the optical fiber, please refer to [link / reference]. Figure 5 .

[0025] Overall structural module 4 is used to collect current beam data.

[0026] The deflection analysis module 5 uses the demodulated data from the fiber optic demodulator 3 and the data obtained from the overall structure module 4 as the basis for analysis to obtain deflection data.

[0027] The analysis process of deflection analysis module 5 is as follows: The structural deflection obtained from the integral of the steel strain is R. g Assume there are n measuring points for the reinforcing bars: ; Where, ε g i represents the longitudinal strain of the i-th reinforcing bar in the structure, ε gT i represents the strain at the i-th steel reinforcement temperature measurement point in the structure, and L represents the length of the simply supported concrete beam. The structural deflection obtained from the concrete strain integral is R. c Assume there are m measuring points for the reinforcing bars: ; Where, ε ci represents the longitudinal strain of the i-th concrete in the structure, ε cT i represents the strain at the i-th concrete temperature measurement point in the structure.

[0028] Based on the relationship between the test location of the reinforcing bars and the vertical spatial position of the beam structure, the deflection test value of the bottom surface of the beam is calculated in reverse. Calculate the bottom deflection R of a simply supported beam obtained by back-calculation based on the deflection at the position of the reinforcing bars. Dg： ； Where Lc is the height of the neutral axis of the simply supported beam, and Lg is the distance from the center of the reinforcement measuring point to the neutral axis of the simply supported beam; Calculate the deflection R at the bottom of the simply supported beam obtained by back-calculation based on the deflection at the concrete test location. Dc : ; Where Lc is the height of the neutral axis of the simply supported beam, and Lcc is the distance from the center of the concrete measuring point to the neutral axis of the simply supported beam; The R obtained from the analysis Dg With R Dc Comparison, If the difference between the two values ​​is less than 5% compared to the average, then the average of the two values ​​is taken. Otherwise, the structure should be retested and analyzed.

[0029] This invention employs a distributed optical fiber testing technology to determine the deflection of a simply supported concrete beam: ① It proposes using a distributed optical fiber device to test the strain of the reinforcing steel and concrete along the beam length; ② It proposes to obtain the deflection of the simply supported beam based on the strain analysis of the reinforcing steel and concrete along the beam length, thereby evaluating the dynamic safety performance of the beam.

[0030] Example 2 Based on Example 1, the concrete simply supported beam deflection test system also includes a time sequence module and a dynamic evaluation module. The time sequence module generates timestamps according to the time sequence, and the dynamic evaluation module rates the state of the concrete simply supported beam according to the timestamp interval and the amount of deflection change, and outputs the evaluation results based on the rating.

[0031] The dynamic assessment method is shown in the table below. Based on the dynamic changes in the final deflection results, the simply supported beam structure is divided into five damage levels: slight, moderate, relatively severe, severe, and extremely severe.

[0032]

[0033] The condition of simply supported concrete beams is classified into four levels: A, B, C, and D. Level A is further divided into two grades: AA and A1. Grade D represents slight deterioration, Grade C represents moderate deterioration, Grade B represents relatively severe deterioration, Grade A1 represents severe deterioration, and Grade AA represents extremely severe deterioration. The evaluation and measures involved for each deterioration level are shown in the table below:

[0034] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A test system for the deflection of a simply supported concrete beam based on distributed optical fiber testing, characterized in that: It includes a concrete surface strain testing module (1), which consists of several distributed optical fibers arranged along the length of the beam on the bottom surface of the beam; The steel bar strain testing module (2) consists of several distributed optical fibers that are pre-embedded along the bottom steel bars of the beam and set along the length of the beam. The fiber optic demodulator (3) acquires the test data of the concrete surface strain test module (1) and the steel bar strain test module (2) and performs data demodulation. The overall structural module (4) is used to collect the current beam data; The deflection analysis module (5) uses the demodulated data from the fiber optic demodulator (3) and the data obtained by the overall structure module (4) as the basis for data analysis to obtain deflection data.

2. The concrete simply supported beam deflection test system based on distributed optical fiber testing according to claim 1, characterized in that: The specific analysis process of the deflection analysis module (5) is as follows: The structural deflection obtained from the integral of the steel strain is Rg, assuming there are n measuring points on the steel reinforcement; ; Where, ε g i represents the longitudinal strain of the i-th reinforcing bar in the structure, ε gT i represents the strain at the i-th steel reinforcement temperature measurement point in the structure, and L represents the length of the simply supported concrete beam. The structural deflection obtained from the concrete strain integral is R. c Assume there are m measuring points for the reinforcing bars: ; Where, ε c i represents the longitudinal strain of the i-th concrete in the structure, ε cT i represents the strain at the i-th concrete temperature measurement point in the structure; Based on the relationship between the test location of the reinforcing bars and the vertical spatial position of the beam structure, the deflection test value of the bottom surface of the beam is calculated in reverse. Calculate the bottom deflection R of a simply supported beam obtained by back-calculation based on the deflection at the position of the reinforcing bars. Dg； ； Where Lc is the height of the neutral axis of the simply supported beam, and Lg is the distance from the center of the reinforcement measuring point to the neutral axis of the simply supported beam; Calculate the deflection R at the bottom of the simply supported beam obtained by back-calculation based on the deflection at the concrete test location. Dc : ; Where Lc is the height of the neutral axis of the simply supported beam, and Lcc is the distance from the center of the concrete measuring point to the neutral axis of the simply supported beam; The R obtained from the analysis Dg With R Dc Comparison, If the difference between the two values ​​is less than 5% compared to the average, then the average of the two values ​​is taken. Otherwise, the structure should be retested and analyzed.

3. The concrete simply supported beam deflection test system based on distributed optical fiber testing according to claim 1, characterized in that: The concrete simply supported beam deflection test system also includes a time sequence module and a dynamic evaluation module. The time sequence module generates timestamps according to the time sequence, and the dynamic evaluation module rates the state of the concrete simply supported beam according to the timestamp interval and the amount of deflection change, and outputs the evaluation results based on the rating.

4. The concrete simply supported beam deflection test system based on distributed optical fiber testing according to claim 3, characterized in that: The assessment results consist of the impact on the structural function of the beam and the corresponding measures.

5. The concrete simply supported beam deflection test system based on distributed optical fiber testing according to claim 1, characterized in that: The data demodulated by the fiber optic demodulator (3) is the strain data of the corresponding position of the beam.

Images