Method for determining equivalent cycle number of dynamic wind uplift fatigue test of metal roof system

Abstract

The application discloses a kind of equivalent cycle number determination methods of dynamic wind uncover fatigue test of metal roof system, it is characterized in that, step 1, the fatigue performance parameter of target metal roof system is obtained;Step 2, based on target area typhoon wind climate model, form fatigue load mean-range-cycle number distribution matrix;Step 3, according to fatigue load mean-range-cycle number distribution matrix is divided into several loading sequences Nk;Step 4, the function relationship between equivalent cycle and fatigue index is established;Step 5, based on damage equivalent principle, determine the critical fatigue index m_crit of target structure corresponding;Step 6, according to critical fatigue index m_crit, obtain the loading sequence and cycle number suitable for dynamic wind uncover fatigue test of target structure under target area typhoon wind climate.The application can improve test efficiency while accurately detecting the fatigue damage condition of different metal roof structures, so as to ensure the safety of metal roof system structure in use.

Description

Technical Field

[0001] This invention relates to the field of wind resistance testing technology for building structures, and in particular to an equivalent cycle determination method for wind uplift fatigue testing of metal roof systems under dynamic typhoon / strong wind conditions (wind tunnel testing). Background Technology

[0002] In typhoon-prone areas, metal roofs often fail due to wind-induced fatigue within their design service life. Current international standards, such as AS 4040.3, employ the damage equivalence principle to perform tests on complex wind load time histories (Real wind load-time history). For specific structural principles, please refer to [link / reference needed]. Figure 1 This includes wind suction and wind pressure loads, simplified into several load sequences and load cycles (collectively referred to as simplified loads). See details. Figure 2 However, its fatigue index m is taken as a fixed value (such as m=1 or m=3), without taking into account the differences in fatigue performance of different structural forms.

[0003] For example, the AS 4040.3 standard (Traditional method) uses a low-high-low (LHL) loading sequence to simplify typhoon loads into four amplitude levels. However, its fatigue index uses conservative assumptions (m=1 and m=3), which leads to: ① excessive test cycles and low efficiency for structures with good fatigue performance (such as continuously welded roofs); ② failure to accurately reflect the fatigue damage process for structures with poor fatigue performance (such as screw-fixed roofs). As a result, the traditional method is unable to balance the safety and efficiency of the test.

[0004] Existing research has shown that the fatigue index m of different metal roofing systems varies significantly (ranging from approximately 2.9 to 8.5), and the ultimate bearing capacity P_u also varies considerably (7.0 to 12.5 kPa).

[0005] Therefore, there is an urgent need for a method that can dynamically determine the equivalent number of cycles based on the actual fatigue performance of the structure. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, the present invention aims to solve the problems of fixed / single equivalent cycle methods in the testing of existing metal roofing systems, which cannot reflect true fatigue damage and result in low testing efficiency. The invention provides a method for determining the equivalent cycle number in dynamic wind uplift fatigue testing of metal roofing systems. This method can improve testing efficiency while accurately detecting fatigue damage in different metal roofing structures, thereby ensuring the safety of the metal roofing system structure during use.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for determining the equivalent number of cycles in a dynamic wind uplift fatigue test of a metal roofing system, characterized by comprising the following steps:

[0008] Step 1: Obtain the fatigue performance parameters of the target metal roofing system, including the SN curve, fatigue index m, and ultimate bearing capacity P_u;

[0009] Step 2: Based on the typhoon climate model of the target area, construct the wind-induced fatigue load spectrum within the design service life, and use the rainflow counting method to extract the load cycle number to form a fatigue load mean-range-cycle number distribution matrix;

[0010] Step 3: Based on the fatigue load mean-range-cycle number distribution matrix obtained in Step 2, divide it into several loading sequences Nk according to the amplitude level, and use the Goodman correction model to correct the non-zero mean load.

[0011] Step 4: Based on Miner's linear cumulative damage criterion, establish the functional relationship between the equivalent cycle and the fatigue index;

[0012] Step 5: Based on the damage equivalence principle, determine the critical fatigue index m_crit corresponding to the target structure;

[0013] Step 6: Based on the critical fatigue index m_crit obtained in Step 5, calculate the equivalent number of cycles for each loading sequence; obtain the loading sequence and number of cycles applicable to the target structure under typhoon wind climate in the target area for dynamic wind uplift fatigue testing.

[0014] Furthermore, in step 1, the target metal roofing system is fixed using screw fixing, standing seam locking, or continuous welding, and its fatigue life model N is specifically as follows:

[0015] ;

[0016] Where c is the fatigue constant and m is the Basquin exponent.

[0017] Furthermore, in step 2, the typhoon wind climate model simulates virtual typhoon parameters based on the Monte Carlo method, uses a piecewise probability model to simulate the wind speed probability distribution, and uses a Von Mises distribution model to simulate the wind direction probability distribution. The piecewise probability model includes the Weibull distribution model and the generalized Pareto distribution model.

[0018] Furthermore, in step 3, the loading sequence is divided into four load range levels: 0.4P_d, 0.6P_d, 0.8P_d, and 1.0P_d, where P_d is the design wind load.

[0019] Furthermore, in step 3, the process of correcting the non-zero mean load using the Goodman formula is as follows:

[0020] ;

[0021] Where Sre is the corrected load, Sr is the load amplitude, Sm is the load mean, and Su is the ultimate bearing capacity of the structure.

[0022] The Goodman method is used to correct the SN fatigue life curve of the structure. When correcting the fatigue load of the ij-th element and the Nk-th sequence, the corrected loads are denoted as Pij and PNk, respectively, and the corrected Pre-N curves are obtained accordingly.

[0023] Furthermore, in step 4, the functional relationship between the equivalent cycle and the fatigue index is as follows:

[0024] ;

[0025] In the formula, Let Nk be the equivalent number of cycles in the Nk-th sequence. For the corrected load range of the Nk-th sequence, These are the fatigue performance parameters of the structure. This is the modified load range load for the ij-th element. denoted as the number of cycles belonging to all units in the Nk-th sequence.

[0026] Further, in step 5, the critical fatigue index m_crit is determined in the following way:

[0027] Under a given load spectrum, the total damage D(m) is calculated by iterating through the fatigue index m within a predetermined range with a certain step size, and the total damage D(m) corresponding to each m value is calculated. The m value when D(m) = 1 is m_crit; where the total damage of the Nk-th sequence is denoted as... for:

[0028] ;

[0029] In the formula, To determine the fatigue life of the ij-th unit in the Nk-th sequence, sum N1-N4 to obtain the damage D. Then, by traversing the fatigue index m, determine the critical fatigue index m_crit for damage D=1.

[0030] Furthermore, in step 6, based on the critical fatigue index m_crit, fatigue cycles with different load levels are converted into equivalent cycles using the principle of damage equivalence, expressed as:

[0031] ;

[0032] in, For the equivalent number of iterations, The number of cycles within the fatigue load mean-range-cycle number distribution matrix. The equivalent load range within the fatigue load mean-range-cycle number distribution matrix. This represents the equivalent load range for the load sequence N1-N4;

[0033] Based on the above formula, the total number of cycles in the Nk-th sequence is determined by summing the equivalent number of cycles in the ij-th unit within the Nk-th sequence; then, based on the formula in step 4, the number of cycles for N1-N4 is determined.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1. The impact of the structure's own fatigue performance on the equivalent cycle is considered, avoiding the bias caused by the "one-size-fits-all" approach of traditional methods;

[0036] 2. By inverting the critical fatigue index, a balance between safety and efficiency can be achieved, and the test time can be shortened by more than 19%;

[0037] 3. It has a wide range of applications and can be extended to wind fatigue testing of metal roofing systems with different structural forms and in different wind zones;

[0038] 4. Compared with existing standards such as AS 4040.3 and CSA A123.21, this method is more accurate in responding to fatigue risks in low amplitude high cycle and high amplitude low cycle conditions. Attached Figure Description

[0039] Figure 1 This is a schematic diagram illustrating the principle of dynamic wind exposure fatigue testing.

[0040] Figure 2 A schematic diagram illustrating the principle of simplifying complex wind load time histories into several loading sequences and load cycles.

[0041] Figures 3 to 5 This is a schematic diagram of a metal roofing system using screw-fixed connections.

[0042] Figure 6 This is a schematic diagram of a metal roofing system fixed with a standing seam method.

[0043] Figure 7 This is a schematic diagram of a metal roofing system that is fixedly connected using a continuous welding method.

[0044] Figure 8 A comparison chart of SN curves for five fixed connection methods used in a metal roofing system.

[0045] Figure 9 This is a schematic diagram of the fatigue performance distribution of a known metal roofing system in the embodiment.

[0046] Figure 10 This is a schematic diagram showing the distribution of known fatigue loads in the embodiment.

[0047] Figure 11 This is a schematic diagram of the normalized fatigue load distribution in the embodiment.

[0048] Figure 12 This is a schematic diagram illustrating the classification of load sequences in the embodiment.

[0049] Figure 13 A schematic diagram of the equivalent theoretical load sequence in the embodiment.

[0050] Figure 14 This is a schematic diagram showing the effect of different fatigue indices m on damage D.

[0051] Figure 15 This is a schematic diagram showing a cyclical comparison between the method of the present invention and existing standard methods. Detailed Implementation

[0052] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 a part of the embodiments of the present invention, not all of them. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0054] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship commonly used when the product is in use. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. In addition, the terms "horizontal," "vertical," etc., do not indicate that the component is required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0055] Example: A method for determining the equivalent number of cycles in a dynamic wind uplift fatigue test of a metal roofing system, comprising the following steps:

[0056] Step 1: Obtain the fatigue performance parameters of the target metal roofing system, including the SN curve, fatigue index m, and ultimate bearing capacity P_u; wherein, the fixing method of the target metal roofing system includes three types of screw-type fixing (S1-S3 curved plates, trapezoidal plates, and rib plates), such as... Figure 3-5 As shown; upright locking type with wind-resistant clamp (S4), as Figure 6 As shown; continuous welding type (S5), such as Figure 7 As shown; fatigue performance parameters corresponding to each fixing method are shown in the figure. Figure 8 See Table 1.

[0057] During implementation, fatigue tests were conducted to obtain the fatigue index m and ultimate bearing capacity P_u of the target metal roofing system. The expression for the fatigue index m is as follows:

[0058] ;

[0059] In the formula, N is fatigue life, S is load amplitude, c is fatigue constant, and m is fatigue index.

[0060] During implementation, fatigue life N is obtained based on fatigue tests S with 5-8 load ranges. The S and N data are then used to fit the data and determine the parameters c and m.

[0061] The following table shows examples of fatigue performance parameters for typical metal roofing systems:

[0062] Table 1

[0063]

[0064] Step 2: Based on the typhoon wind climate model of the target area, construct the wind-induced fatigue load spectrum within the design service life, and extract load cycles using the rainflow counting method to form a fatigue load mean-range-cycle number distribution matrix. In implementation, the typhoon wind climate model simulates virtual typhoon parameters based on the Monte Carlo method, uses a piecewise probability model to simulate the wind speed probability distribution, and a Von Mises distribution model to simulate the wind direction probability distribution. The piecewise probability model includes both the Weibull distribution model and the generalized Pareto distribution model. The rainflow counting method is used to count the number of cycles for different stress amplitudes by counting rainflows on the load time series, thus obtaining the fatigue load mean-range-cycle number distribution matrix. , where i is the mean fatigue load and j is the fatigue load range, with both i and j ranging from 1 to 10. The matrix is ​​composed of and The components represent the proportions of the mean and amplitude ranges to the design wind pressure coefficient value, respectively, and the matrix values ​​represent the number of cycles.

[0065] As one specific embodiment, see Figure 9 Based on historical typhoon data for a target region, several virtual typhoons (e.g., 10,000) were simulated using the Monte Carlo method. A piecewise probability model (Weibull + GPD) was used to simulate wind speed distribution, and the Von Mises distribution was used to simulate wind direction distribution. The typhoon-induced fatigue load was determined using an ascent method. (See [link to documentation]). Figure 10 To obtain the normalized histogram of fatigue load, see [link / reference]. Figure 11 After statistical analysis using the rainflow counting method, the fatigue load mean-range-cycle number distribution matrix was obtained. As shown in Table 2, the values ​​of ii and jj range from 1 to 10, representing the mean and range, respectively. For example, element M1R1 is denoted as [n]11, with a value of 178,274, representing the number of load cycles within the range of mean ratio 0–0.1 and range ratio 0–0.1, and a total number of cycles of 424,706.

[0066] Table 2

[0067]

[0068] Step 3: Divide the mean-range-cycle number distribution matrix into several loading sequences according to amplitude levels. Use the Goodman formula to correct for non-zero mean loads. In this scheme, based on Table 2 above, the loading sequences are divided into four amplitude levels: N1 (0.4P_d), N2 (0.6P_d), N3 (0.8P_d), and N4 (1.0P_d); where P_d is the design wind load. The specific steps are as follows:

[0069] (a) Determine the maximum load of the element The maximum load is calculated using the average value of the elements. Add range Determine half of it, the expression is: For example, the M2R3 cell has a mean of 0.2 and a range of 0.3. It is 0.35.

[0070] (b) Determine the maximum load range of the load sequence of the standard AS. The limits for each sequence are: N1 (≤ 0.5), N2 (0.5–0.7), N3 (0.7–0.9) and N4 (≥ 0.9).

[0071] (c) Determine the classification of unit M2R3. Because And since it does not exceed 0.5, M2R3 is classified as N1.

[0072] (d) Repeat the above steps for each element in matrix [n]ij to complete the classification. See details. Figure 12 For example, N1 contains units such as M1R1–8, M2R1–6, M3R1–4, and M4R1–2.

[0073] Through the above steps, fatigue wind loads are sorted and classified into sequences N1-N4, providing fatigue load data for further cyclic testing of all units in each sequence based on damage equivalent cycles.

[0074] In this scheme, the units located in all cycles of the sequence N1-Nk are... .

[0075] The process of correcting for non-zero mean loads using the Goodman formula is as follows:

[0076] (2);

[0077] In the formula, This is the corrected fatigue load range. It is the fatigue load range. It is the average fatigue load. Let be the ultimate bearing capacity of the structure. Based on this formula, the fatigue loads of the Nk-th sequence and the ij-th element are modified to determine the corresponding modified load range.

[0078] Step 4, see Figure 13 Based on the Miner linear cumulative damage criterion, a functional relationship between the equivalent cycle and the fatigue index is established; specifically, the equivalent cycle [n]_{eq,Nk} of each sequence is represented as:

[0079] (3);

[0080] In the formula, Let Nk be the equivalent number of cycles in the Nk-th sequence. For the corrected load range of the Nk-th sequence, These are the fatigue performance parameters of the structure. This is the modified load range load for the ij-th element. denoted as the number of cycles belonging to all units in the Nk-th sequence.

[0081] Step 5: Based on the principle of damage equivalence, with the total damage D = 1 as the target, when D = 1, the fatigue index m is the critical fatigue index m_crit corresponding to the target structure.

[0082] Under a given load spectrum, within a predetermined range of fatigue index m (preferably 1 to 10), the total damage D(m) corresponding to each m value is calculated by traversing the range with a certain step size (e.g., 0.01). The m value when D(m) = 1 is m_crit.

[0083] Based on the principle of damage equivalence, numerical iteration is performed within a reasonable range of m. The total damage D shows a monotonically increasing relationship with the fatigue index m, expressed as:

[0084] (4);

[0085] in, Let be the equivalent number of iterations for the k-th level sequence. Let m be the fatigue life with exponent m. Summing N1-N4 yields the damage D. Then, by iterating through the fatigue exponents m, the critical fatigue exponent m_crit for damage D=1 is determined.

[0086] Wherein, the total damage of the Nk-th sequence is denoted as for:

[0087] (5);

[0088] In the formula, Let be the fatigue life of the ij-th unit in the Nk-th sequence.

[0089] Taking a continuously welded roof (S5) as an example, when m = 2.54, D = 1, which is the critical fatigue index m_crit.

[0090] Step 6: Based on the critical fatigue index m_crit obtained in Step 5, calculate the equivalent number of cycles for each loading sequence; obtain the loading sequence and number of cycles applicable to the target structure under typhoon wind climate in the target area for dynamic wind uplift fatigue testing.

[0091] Using the principle of damage equivalence, fatigue cycles at different load levels are converted into equivalent cycle numbers, expressed as:

[0092] (6);

[0093] in, For the equivalent number of iterations, The number of cycles within the fatigue load mean-range-cycle number distribution matrix. This represents the corrected load range within the fatigue load mean-range-cycle number distribution matrix. To simplify the load sequence, a modified load range is provided. This is the fatigue load correction value for the mean-range of the ij-th value (i.e., the fatigue load correction value under the mean and amplitude of the ith value). The correction value for the sequence is shown in equation (6), which is the fatigue load correction value for the mean-range of the Nkth sequence.

[0094] Based on the above formula, the total number of cycles in the Nk-th sequence is determined by summing the equivalent number of cycles in the ij-th unit within the Nk-th sequence; then, based on the formula in step 4, the number of cycles for N1-N4 is determined.

[0095] As a specific embodiment: This embodiment takes a continuous welded stainless steel roofing system (S5) as the object, with a design wind load P_d = 10.2 kPa, fatigue index m = 2.934, and ultimate bearing capacity P_u = 12.5 kPa.

[0096] 1. Typhoon wind climate simulation:

[0097] Based on historical typhoon data for the Shenzhen area, 10,000 virtual typhoons were simulated using the Monte Carlo method. A Weibull+GPD piecewise model was used to describe wind speed distribution, and a first-order Von Mises distribution was used to describe wind direction distribution. The probability of occurrence of wind speeds and directions within the 50-year design lifespan was obtained.

[0098] 2. Wind pressure coefficient and load spectrum:

[0099] The wind pressure coefficient of the saddle-shaped roof surface was obtained through wind tunnel testing, and a sensitive point at the corner (x590y565) was selected for analysis. The load cycles were extracted using the rainflow counting method, forming a 10×10 mean-amplitude frequency distribution matrix, with a total of 424,706 cycles.

[0100] 3. Load Classification and Correction:

[0101] According to the AS 4040.3 standard, the load spectrum is divided into four sequences, N1 to N4. The Goodman formula is used to correct the non-zero mean load, and the corrected equivalent load amplitude is used for subsequent damage calculation.

[0102] 4. Equivalent cycle calculation and critical index inverse calculation, see Figure 14 .

[0103] Based on the damage equivalence principle, the equivalent cycles and total damage D under different fatigue indices m are calculated. When m = 2.54, D = 1, which is the critical fatigue index m_crit. Based on this, the equivalent cycle number for each sequence is:

[0104] in,

[0105] N1: 31,640 times;

[0106] N2: 1,570 times;

[0107] N3: 570 times;

[0108] N4: 110 times;

[0109] The total number of cycles was 33,890, which is 7,949 fewer than the traditional method (41,839 cycles).

[0110] 5. For a comparison of the effects, see... Figure 15 :

[0111] Compared with the traditional AS 4040.3 method, the method of this invention reduces the total number of test cycles by 19% and the test time from 93.1 hours to 75.3 hours while ensuring structural fatigue safety. Furthermore, this method can be extended to other structural forms (such as screw fixing and upright seam) and other typhoon-prone areas.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for determining the equivalent number of cycles in a dynamic wind uplift fatigue test of a metal roofing system, characterized in that, Includes the following steps: Step 1: Obtain the fatigue performance parameters of the target metal roofing system, including the SN curve, fatigue index m, and ultimate bearing capacity P_u; Step 2: Based on the typhoon wind climate model of the target area, construct the wind-induced fatigue load spectrum within the design service life, and use the rainflow counting method to extract the load cycle number to form a fatigue load mean-range-cycle number distribution matrix; Step 3: Based on the fatigue load mean-range-cycle number distribution matrix obtained in Step 2, divide it into several loading sequences Nk according to the amplitude level, and use the Goodman correction model to correct the non-zero mean load. Step 4: Based on Miner's linear cumulative damage criterion, establish the functional relationship between the equivalent cycle and the fatigue index; Step 5: Based on the damage equivalence principle, determine the critical fatigue index m_crit corresponding to the target structure; Step 6: Based on the critical fatigue index m_crit obtained in Step 5, calculate the equivalent number of cycles for each loading sequence; obtain the loading sequence and number of cycles applicable to the target structure under typhoon wind climate in the target area for dynamic wind uplift fatigue testing.

2. The method for determining the equivalent number of cycles in a dynamic wind uplift fatigue test of a metal roofing system according to claim 1, characterized in that, In step 1, the target metal roofing system is fixed using screw fixing, standing seam locking, or continuous welding, and its fatigue life model N is specifically as follows: ； Where c is the fatigue constant and m is the Basquin exponent.

3. The method for determining the equivalent number of cycles in a dynamic wind uplift fatigue test of a metal roofing system according to claim 1, characterized in that, In step 2, the typhoon wind climate model simulates virtual typhoon parameters based on the Monte Carlo method, uses a piecewise probability model to simulate the wind speed probability distribution, and uses a Von Mises distribution model to simulate the wind direction probability distribution. The piecewise probability model includes the Weibull distribution model and the generalized Pareto distribution model.

4. The method for determining the equivalent number of cycles in a dynamic wind uplift fatigue test of a metal roofing system according to claim 1, characterized in that, In step 3, the loading sequence is divided into four load range levels: 0.4P_d, 0.6P_d, 0.8P_d, and 1.0P_d, where P_d is the design wind load.

5. The method for determining the equivalent number of cycles in a dynamic wind uplift fatigue test of a metal roofing system according to claim 1, characterized in that, In step 3, the process of correcting the non-zero mean load using the Goodman formula is as follows: ； Where Sre is the corrected load, Sr is the load amplitude, Sm is the load mean, and Su is the ultimate bearing capacity of the structure. The Goodman method is used to correct the SN fatigue life curve of the structure. When correcting the fatigue load of the ij-th element and the Nk-th sequence, the corrected loads are denoted as Pij and PNk, respectively, and the corrected Pre-N curves are obtained accordingly.

6. The method for determining the equivalent number of cycles in a dynamic wind uplift fatigue test of a metal roofing system according to claim 1, characterized in that, In step 4, the functional relationship between the equivalent cycle and the fatigue index is as follows: ； In the formula, Let Nk be the equivalent number of iterations in the Nk-th sequence. For the corrected load range of the Nk-th sequence, These are the fatigue performance parameters of the structure. This is the modified load range load for the ij-th element. denoted as the number of cycles belonging to all units in the Nk-th sequence.

7. The method for determining the equivalent number of cycles in a dynamic wind uplift fatigue test of a metal roofing system according to claim 1, characterized in that, In step 5, the critical fatigue index m_crit is determined in the following way: Under a given load spectrum, the total damage D(m) is calculated by iterating through the fatigue index m within a predetermined range with a certain step size, and the total damage D(m) corresponding to each m value is calculated. The m value when D(m) = 1 is m_crit; where the total damage of the Nk-th sequence is denoted as... for: ； In the formula, To determine the fatigue life of the ij-th unit in the Nk-th sequence, sum N1-N4 to obtain the damage D. Then, by traversing the fatigue index m, determine the critical fatigue index m_crit for damage D=1.

8. The method for determining the equivalent number of cycles in a dynamic wind uplift fatigue test of a metal roofing system according to claim 1, characterized in that, In step 6, based on the critical fatigue index m_crit, fatigue cycles with different load levels are converted into equivalent cycles using the principle of damage equivalence. The expression is: ； in, For the equivalent number of iterations, The number of cycles within the fatigue load mean-range-cycle number distribution matrix. The equivalent load range within the fatigue load mean-range-cycle number distribution matrix. This represents the equivalent load range for the load sequence N1-N4; Based on the above formula, the total number of cycles in the Nk-th sequence is determined by summing the equivalent number of cycles in the ij-th unit within the Nk-th sequence; then, based on the formula in step 4, the number of cycles for N1-N4 is determined.

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