A calculation method for the crack opening displacement of a fan foundation and a foundation safety evaluation method

Abstract

The present invention discloses a method for calculating the crack opening displacement of a wind turbine foundation and a method for evaluating the foundation safety, including: the calculation method of the crack initiation opening displacement COD ini based on the fracture toughness #imgabs0#, the calculation method of the critical opening displacement COD c for crack unstable propagation, and the foundation safety evaluation; predicting the expansion stage of the foundation concrete cracks and evaluating the safety of the wind turbine foundation. This method analyzes and compares the foundation ring displacement with the concrete crack initiation opening displacement and the unstable opening displacement, and evaluates the safety and stability of the wind turbine foundation concrete cracking. According to the evaluation results, the concrete foundation is repaired and reinforced in a timely manner, which is of great significance for improving the safety of the wind turbine foundation joints.

Description

Technical Field

[0001] The present invention relates to the fields of wind power generation and new energy, and particularly to a method for calculating the crack opening displacement of a wind turbine foundation and a method for evaluating the foundation safety. Background Art

[0002] In recent years, the development of wind power generation in China has been rapid, and the installed capacity has increased rapidly. A wind turbine mainly consists of a nacelle, blades, a tower, a foundation ring, a foundation, etc. Among them, the nacelle and blades are located at the top of the tower, and the tower and the foundation are connected by an embedded foundation ring. The foundation ring is a large-diameter steel cylinder component, the lower part of which is buried in the concrete foundation, and the top of which is slightly higher than the top surface of the concrete foundation. Usually, the design life of a wind turbine foundation exceeds 20 years. However, in past engineering examples, it has been found that the concrete in the wind turbine foundation structure will crack and be damaged in the early stage, affecting the safety and reliability of the overall structure of the wind turbine.

[0003] Due to the connection force transmission mechanism between the foundation ring and the concrete foundation, the initiation and propagation of cracks in the concrete foundation are inevitable. The bottom of the foundation ring is connected to the concrete foundation by a flange (as shown in Figure 1 ), and the force received by the wind turbine body is transmitted to the concrete foundation through the flange at the bottom of the ring, thus avoiding the pulling out of the foundation ring and the penetration of the concrete. This also results in high stress concentration around the flange at the bottom of the ring. When the stress reaches the tensile strength of the concrete, cracks will occur on the tensile side of the concrete, reducing the connection strength between the foundation ring and the concrete foundation. As the cracks propagate, it is possible for them to penetrate the entire foundation. Stable crack propagation is acceptable in engineering, but unstable crack propagation will lead to the sudden failure of the overall foundation. Therefore, evaluating the stability of crack propagation in the concrete foundation of a wind turbine and repairing and strengthening the concrete foundation in a timely manner according to the evaluation results are of great significance for improving the safety of the connection nodes of the wind turbine foundation. Summary of the Invention

[0004] The purpose of the present invention is to propose a method for calculating the crack opening displacement of a wind turbine foundation and a method for evaluating the safety of a wind turbine foundation in view of the difficulty in evaluating the stability of internal cracks in a concrete foundation of a wind turbine.

[0005] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0006] A method for calculating the crack opening displacement of a wind turbine foundation and a method for evaluating the foundation safety, characterized by comprising: a calculation method for the crack initiation opening displacement COD based on the fracture toughness of the crack initiation, a calculation method for the critical opening displacement COD of the crack unstable propagation ini and a foundation safety evaluation; c ;

[0007] Based on the fracture toughness Crack initiation opening displacement COD ini The calculation method specifically includes:

[0008] It is known that the width of the lower anchor plate of the fan foundation ring buried in concrete is a 0 , the initial crack length of the concrete foundation is a 0 , the cracking moment is M ini , through the fracture toughness of concrete Calculate the crack initiation opening displacement COD at the foundation ring ini , including the following three steps:

[0009] (1) Calculate the concrete cracking moment M ini , and its expression is:

[0010]

[0011] In the formula, D m is the average diameter of the concrete pedestal, t is the thickness of the outer concrete pedestal of the foundation ring, is the geometric correction function of the edge crack under the bending load, and its expression is:

[0012]

[0013] (2) Calculate the maximum normal stress σ N , because of the cracking moment M ini The maximum normal stress caused is calculated by the following formula:

[0014]

[0015] Among them, r o and r i are the inner and outer radii of the concrete pedestal respectively;

[0016] (3) Calculate the crack initiation opening displacement COD ini , and its expression is:

[0017]

[0018] In the formula, E and v are the elastic modulus and Poisson's ratio of concrete respectively, D P (a 0 / t) is the geometric factor of the edge crack under the bending load, and its expression is:

[0019]

[0020] Critical opening displacement COD for unstable crack propagation c The calculation method specifically includes:

[0021] At the initial stage of the unstable crack propagation, it is assumed that the shear reinforcement passing through the crack has reached the yield strength. The critical crack opening displacement (COD) at the start of the unstable crack propagation is calculated through the following four steps. c :

[0022] (1) Calculate the maximum normal stress σ N

[0023] The maximum normal stress of the concrete is calculated by the following formula:

[0024]

[0025] where M is the bending moment of the external load;

[0026] (2) Define the relationship between and

[0027] The unstable toughness of the concrete and the stress intensity factor related to the external load and the stress intensity factor related to the crack closing force of the reinforcement The balance relationship between them is:

[0028]

[0029] where Under the known elastic modulus E′ and fracture energy G under the plane hypothesis of the concrete F conditions, the relationship expression of the above three is extended as:

[0030]

[0031] In the above formula, is the maximum crack closing force caused by the reinforcement in the unstable crack state, B is the circumferential distance between the centers of two rows of shear reinforcement, is the geometric correction function related to the crack closing force of the reinforcement, and its expression is:

[0032]

[0033] (3) Using the trial-and-error method, solve the formula in step (2) to calculate the solution crack length a c ;

[0034] (4) Calculate the crack opening displacement COD at the start of the unstable crack propagation c , substitute the crack length a c obtained in step (3) and the maximum normal stress σ N obtained in step (1) into the following formula to solve for COD c :

[0035]

[0036] Among them, is the geometric factor of the solution crack under the bending load.

[0037] The foundation safety evaluation includes:

[0038] The crack opening displacement COD at the foundation ring during the service of the fan is obtained through actual measurement or calculation. By comparing COD with the critical crack initiation opening displacement COD ini and the critical crack instability opening displacement COD c , the expansion stage of the foundation concrete crack is predicted and the safety of the fan foundation is evaluated. The comparison results include the following three situations:

[0039] (1) COD < COD ini , the crack will not expand;

[0040] (2) COD ini ≤ COD < COD c , the crack expands stably;

[0041] (3) COD ≥ COD c , the crack expands unstably and repair and remedial measures need to be taken.

[0042] Alternatively, the foundation safety evaluation includes:

[0043] After the concrete around the foundation ring cracks, it will cause the foundation ring to displace FCOD. By installing sensors (including displacement sensors, and / or tilt sensors and / or vibration sensors, etc.) on the fan foundation and / or the foundation ring and / or the fan tower barrel, the corresponding displacement FCOD can be calculated through actual measurement by the sensors. By comparing FCOD with the critical crack initiation opening displacement COD ini and the critical crack instability opening displacement COD c , the expansion stage of the foundation concrete crack is predicted and the safety of the fan foundation is evaluated. The comparison results include the following three situations:

[0044] (1) FCOD < COD ini , the crack will not expand;

[0045] (2) COD ini ≤ FCOD < COD c , the crack expands stably;

[0046] (3) FCOD ≥ COD c , the crack expands unstably and repair and remedial measures need to be taken.

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] The method of the present invention can evaluate the cracking state of the concrete matrix on both sides of the foundation ring and the stability of the cracks according to the opening displacement of the basic crack and the displacement of the foundation ring. According to the evaluation results, remedial measures can be taken in a timely manner for the damaged concrete foundation, shortening the downtime, which is of great significance for improving the safety of the wind turbine foundation connection node. Description of the Drawings

[0049] Figure 1 It is a schematic diagram of the wind turbine foundation structure;

[0050] Figure 2 It is a schematic diagram of the cracked concrete foundation. Detailed Embodiments

[0051] The present invention will be further described below with reference to the drawings and embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and gives the detailed implementation manners and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0052] A method for calculating the opening displacement of a wind turbine foundation crack and a method for evaluating the foundation safety include:

[0053] Approximate the crack opening displacement COD of the wind turbine foundation by the vertical displacement of the embedded foundation ring. By comparing COD with the crack initiation opening displacement COD ini and the critical opening displacement COD c at which the crack becomes unstable, predict the expansion stage of the foundation concrete crack and evaluate the safety of the wind turbine foundation. The comparison results include the following three situations:

[0054] (1) COD < COD ini , the crack will not expand;

[0055] (2) COD ini ≤ COD < COD c , the crack expands stably;

[0056] (3) COD ≥ COD c , the crack expands unstably and repair and remedial measures need to be taken.

[0057] The method of the present invention uses the vertical displacement of the foundation ring to approximate the crack width in the wind turbine foundation concrete. Adopting the double-K fracture theory, analyze and compare the vertical displacement of the foundation ring with the crack initiation opening displacement and the unstable opening displacement of the concrete, and evaluate the safety and stability of the cracking of the wind turbine foundation concrete. According to the evaluation results, repair and reinforce the concrete foundation in a timely manner, which is of great significance for improving the safety of the wind turbine foundation connection node.

[0058] A crack initiation opening displacement COD based on the initiation toughness iniCalculation method, given the initial crack length a of the concrete foundation 0 and the cracking moment M ini Under the condition, through the cracking toughness of the concrete Calculate the crack opening displacement COD at crack initiation ini , and its calculation includes the following three steps:

[0059] (1) Calculate the cracking moment M of the concrete ini , and its expression is:

[0060]

[0061] In the formula, D m is the average diameter of the concrete pedestal, t is the thickness of the outer concrete pedestal of the foundation, is the geometric correction function of the edge crack under the bending load, and its expression is:

[0062]

[0063] (2) Calculate the maximum normal stress σ N , and the maximum normal stress caused by the cracking moment M ini is calculated by the following formula:

[0064]

[0065] Among them, r o and r i are the inner and outer radii of the concrete pedestal respectively;

[0066] (3) Calculate the crack opening displacement COD at crack initiation ini , and its expression is:

[0067]

[0068] In the formula, E and v are the elastic modulus and Poisson's ratio of the concrete respectively, D P (a 0 / t) is the geometric factor of the edge crack under the bending load, and its expression is:

[0069]

[0070] A calculation method for the critical opening displacement COD of crack unstable propagation c , at the beginning stage of crack unstable propagation, it is assumed that the shear reinforcement passing through the crack has reached the yield strength. The critical crack opening displacement COD at the beginning of crack unstable propagation can be calculated through the following four steps c :

[0071] (1) Calculate the maximum normal stress σ N

[0072] The maximum normal stress of the concrete is calculated by the following formula:

[0073]

[0074] Among them, M is the bending moment of the external load, and the ultimate design bending moment of the fan can be referred to;

[0075] (2) Definition The relationship between and

[0076] The instability toughness of concrete and the stress intensity factor related to the external load and the stress intensity factor related to the steel bar crack closing force The equilibrium relationship between them is:

[0077]

[0078] Among them, Under the known elastic modulus E' and fracture energy G under the plane assumption of concrete F Under the conditions, it can be obtained according to the definition in the double-K fracture theory. Therefore, the relationship expression of the above three can be extended to:

[0079]

[0080] In the above formula, is the maximum crack closing force caused by the steel bar in the unstable state of the crack, B is the circumferential distance between the centers of two rows of shear-resistant steel bars, is the geometric correction function related to the steel bar crack closing force, and its expression is:

[0081]

[0082] (3) Adopt the trial method to solve and calculate the crack length a in the formula in step (2) c ;

[0083] (4) Calculate the crack opening displacement COD at the beginning of the unstable crack propagation c , substitute the crack length a obtained in step (3) c and the maximum normal stress σ obtained in step (1) N into the following formula to solve COD c :

[0084]

[0085] Example:

[0086] Given a fan foundation structure as Figure 1As shown, 1 is the base ring, 2 is the extended base, 3 is the surface of the concrete foundation, 4 is the shear reinforcement, and the average diameter D of the concrete foundation m is 5550 mm, the outer thickness t of the base ring 1 is 1250 mm, and the length a on one side of the bottom flange of the base ring 1 0 is 146 mm. The circumferential distance B between the centers of two rows of shear reinforcement is 275 mm, and the maximum design bending moment M of the fan is 58100 kNm. The compressive strength f of the foundation concrete cu is 20 MPa, the elastic modulus E is 27000 MPa, the Poisson's ratio v is 0.167, and the yield strength of the reinforcement is 400 MPa. The measured vertical displacement of the base ring is 5 mm.

[0087] First, it is necessary to determine the crack initiation opening displacement COD ini and the instability critical opening displacement COD c . For the crack initiation opening displacement COD ini , it can be calculated according to the initial crack length a of the concrete 0 , the crack initiation toughness and the crack initiation bending moment M ini . For the condition of concrete cracking around the bottom of the base ring, the initial crack length is the width of the bottom flange of the ring. The concrete crack initiation toughness can be determined according to the concrete compressive strength f cu

[0088] The external load bending moment is applied to the top of the base ring. The critical bending moment M corresponding to crack initiation ini is:

[0089]

[0090] In the formula, D m is the average diameter of the concrete pedestal, t is the thickness of the concrete pedestal outside the base ring, and a 0 is the width of the bottom flange of the ring (as Figure 2 shown); is the geometric correction function of the edge crack under the bending load, and its expression is:

[0091]

[0092] Since the maximum principal stress σ ini formed on the tensile side of the concrete foundation due to the critical bending moment M N has the following expression:

[0093]

[0094] Among them, r o and r i ​are the inner and outer radii of the concrete foundation respectively; the final crack initiation opening displacement COD of the concrete ini The expression is:

[0095]

[0096] Substitute the parameters in the embodiments into formulas (1)-(4), and the COD can be obtained ini = 0.10mm

[0097] For the critical opening displacement COD of the unstable crack propagation of the concrete c , it can be calculated according to the crack length a of the concrete c , the instability toughness and the design bending moment M of the fan. The instability toughness can be regarded as the material property of the concrete, and is calculated from the elastic modulus E, Poisson's ratio v and fracture energy G of the concrete f

[0098] The expression of the maximum principal stress σ formed on the tension side of the concrete foundation under the action of the bending moment M N is:

[0099]

[0100] At the beginning of the unstable crack propagation, since the interfacial bonding force provided by the concrete at this stage can be ignored, it can be assumed that the crack closing force is only provided by the steel bars. Therefore, the concrete instability toughness and the stress intensity factor related to the external load and the stress intensity factor related to the steel bar crack closing force The balance relationship among the three is written as:

[0101]

[0102] Furthermore, it is expanded to:

[0103]

[0104] In the above formula, is the maximum crack closing force caused by the steel bars in the unstable crack state, B is the circumferential distance between the centers of two rows of shear steel bars, is the geometric correction function related to the steel bar crack closing force, and its expression is:

[0105]

[0106] According to formulas (6)-(7), the trial method can be used to solve the crack length a c , the crack length a obtained from the above formula c and the maximum normal stress σ involved N ​Substitute into the following formula to solve for COD c :

[0107]

[0108] Substitute the parameters in the examples into formulas (5)-(9) to obtain COD c = 10.05 mm.

[0109] For the fan foundation, it is difficult to directly measure the crack opening displacement (COD) in the concrete. The vertical displacement of the foundation ring can be approximated. Given the crack initiation opening displacement COD ini and the critical crack instability opening displacement COD c , by comparing the relationship between COD and COD ini as well as COD c , the three stages of crack propagation can be judged:

[0110] (1) COD < COD ini , the crack will not propagate;

[0111] (2) COD ini ≤ COD < COD c , the crack propagates stably;

[0112] (3) COD ≥ COD c , the crack propagates unstably and repair and remedial measures need to be taken.

[0113] In this example, the vertical displacement of the foundation ring COD = 5 mm, which belongs to the second stage of the above crack propagation, and it can be determined that the crack in the fan foundation is in the stage of stable propagation.

Claims

1. A method for evaluating the safety of a cracked foundation of a wind turbine foundation, Characterized in that, Comprising: Based on the crack initiation toughness Calculation method of crack initiation opening displacement COD ini Calculation method of critical opening displacement COD for crack unstable propagation c And basic safety evaluation; Based on the crack initiation toughness The crack initiation opening displacement COD ini The calculation method specifically includes: The width of the lower anchor plate of the fan foundation ring embedded in concrete is a 0 , the initial crack length of the concrete foundation is a 0 , the cracking moment is M ini , and the crack opening displacement COD at the foundation ring is calculated through the fracture toughness of the concrete, which includes the following three steps: ini ​ (1) Calculate the cracking moment \(M\) of concrete ini , and its expression is as follows: where D m is the average diameter of the concrete pedestal, t is the thickness of the concrete pedestal outside the foundation ring, is the geometric correction function of the edge crack under the bending load, and its expression is: (2) Calculate the maximum normal stress σ N , due to the cracking moment M ini , the maximum normal stress caused is calculated by the following formula: where r o and r i are the inner and outer radii of the concrete pedestal, respectively; (3) Calculate the crack initiation opening displacement COD ini , and its expression is: where E and v are the elastic modulus and Poisson's ratio of concrete, respectively, and D P (a 0 / t) is the geometric factor of the edge crack under the flexural load, and its expression is: The foundation safety evaluation includes: The crack opening displacement COD at the foundation ring during the service of the fan is obtained through actual measurement or calculation. By comparing COD with the critical crack initiation opening displacement COD ini and the critical crack instability opening displacement COD c , the expansion stage of the foundation concrete crack is predicted and the safety of the fan foundation is evaluated. The comparison results include the following three situations: (1)COD < COD ini , the crack will not expand; (2)COD ini ≤COD < COD c , crack steadily propagates; (3) COD ≥ COD c , the crack undergoes unstable propagation, and repair and remedial measures need to be taken.

2. The method for evaluating the safety of a cracked foundation of a wind turbine foundation according to claim 1, Characterized in that, Critical opening displacement COD for unstable crack propagation c The calculation method specifically includes: At the initial stage of the unstable crack propagation, it is assumed that the shear reinforcement passing through the crack has reached the yield strength, and the critical crack opening displacement COD at the start of the unstable crack propagation is calculated through the following four steps c : (1) Calculate the maximum normal stress σ N The maximum normal stress of the concrete is calculated by the following formula: Wherein, M is the bending moment of the external load; (2) Definition and the relationship between Concrete instability toughness Stress intensity factor related to external load And stress intensity factor related to steel bar crack closure force The equilibrium relationship between them is as follows: Among them, the elastic modulus E′ and fracture energy G under the assumption of a known concrete plane F Under the condition, the relationship expression of the above three is extended to: In the above formula, is the maximum crack closing force caused by steel bars under the unstable state of cracks, B is the circumferential distance between the centers of two rows of shear-resistant steel bars, is the geometric correction function related to the crack closing force of steel bars, and its expression is: (3) Use the trial calculation method to solve and calculate the solution crack length a from the formula in step (2). c ; (4) Calculate the crack opening displacement COD at the start of unstable crack propagation c , substitute the crack length a obtained in step (3) c and the maximum normal stress σ obtained in step (1) N into the following formula to solve for COD c : Among them, is the geometric factor of the edge crack under the flexural load.

3. The method for evaluating the safety of a cracked foundation of a wind turbine foundation according to claim 1, Characterized in that, The foundation safety evaluation includes: After the concrete around the foundation ring cracks, it will cause the foundation ring to produce displacement FCOD. By installing sensors on the wind turbine foundation and / or the foundation ring and / or the wind turbine tower barrel, the corresponding displacement FCOD is obtained through actual measurement and calculation by the sensors. By comparing FCOD with the critical crack initiation opening displacement COD ini and the critical unstable crack opening displacement COD c , the expansion stage of the foundation concrete crack is predicted and the safety of the wind turbine foundation is evaluated. The comparison results include the following three situations: (1)FCOD < COD ini , the crack will not expand; (2)COD ini ≤FCOD < COD c , crack steadily propagates; (3) FCOD ≥ COD c , the crack is unstable and needs to be repaired and remedied.

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