Angle steel tower cross diagonal member bearing capacity calculation method considering overall buckling and sectional buckling

Abstract

The invention discloses an angle steel tower cross diagonal member bearing capacity calculation method considering overall buckling and sectional buckling, and the method comprises the following steps: based on a single angle steel stability bearing capacity test result, selecting a national standard type a column curve as a column curve type for angle steel tower cross diagonal member bearing capacity calculation; correcting the end eccentricity and the end constraint of the angle steel tower cross diagonal member according to design technical regulations; fitting and establishing a calculation length correction coefficient model of the angle steel tower cross diagonal member by adopting a least square method; and calculating the ultimate bearing capacity of the angle steel tower cross diagonal member by using the calculated length correction coefficient model. According to the method, the bearing capacity calculated by adopting the novel correction calculation length is better matched with a test result, the ultimate bearing capacity between plane sections, between auxiliary material sections and between space sections can be predicted more accurately, the economical efficiency of iron tower design is improved, and engineering application reference can be provided.

Description

Technical Field

[0001] This invention belongs to the technical field of transmission line tower design, specifically relating to a method for calculating the bearing capacity of cross bracing of angle steel towers considering both overall buckling and segmented buckling. Background Technology

[0002] Angle steel towers have been rapidly and widely adopted in the field of power transmission line towers due to their high production efficiency, low cost, and ease of installation and connection. Currently, equilateral angle steel towers are the most common type of angle steel tower in China. Crossing braces are crucial components for ensuring the stability of transmission towers, playing a key role in resisting lateral loads. Combined with auxiliary materials, they can improve the internal structural stress of the tower. From a stability perspective, when a transmission tower is subjected to lateral loads or one side of the transmission line breaks, the crossing braces experience both simultaneous compression and tension-compression conditions. Since their volume accounts for more than 30% of the entire transmission tower, further experimental and theoretical research on crossing braces is warranted from both safety and economic perspectives.

[0003] Currently, there are few full-scale experimental studies on intersecting diagonal bracing, and experimental data is scarce. Existing tests have design flaws and cannot accurately simulate the actual stress conditions of intersecting diagonal bracing. Theoretical research needs to be combined with scientific experimental data for analysis. my country's "Technical Specifications for Structural Design of Overhead Transmission Line Towers" (DL / T 5154-2012) provides a method for determining the calculated length of intersecting diagonal bracing. In addition, international standards such as the US ASCE10-15 and the European standard EN1993-3-1 also involve calculation methods for intersecting diagonal bracing. However, existing theories differ in their methods for determining the calculated length, and there is a lack of comparative analysis between calculated and experimental results. All of the above require further research in conjunction with experimental data.

[0004] There are various methods for calculating the stability bearing capacity of intersecting diagonal members in domestic and international standards. These standards differ in their consideration of the value of the calculated length of the compression member and the influence of the stress state of the other members on the bearing capacity of the compression member, leading to discrepancies in the calculation results. The calculation methods in current standards also suffer from insufficient reference to experimental data. Therefore, it is necessary to conduct in-depth research on the calculation method of the ultimate bearing capacity of intersecting diagonal members, and there is an urgent need to propose a method for calculating the bearing capacity of intersecting diagonal members in angle steel towers that considers both overall buckling and segmented buckling. Summary of the Invention

[0005] This invention is proposed to address the above-mentioned shortcomings and aims to provide a method for calculating the bearing capacity of cross-bracing members in angle steel towers that considers both overall buckling and segmented buckling. This method uses a novel modified calculation length to calculate the bearing capacity, which matches the experimental results better. It can more accurately predict the ultimate bearing capacity of planar sections, auxiliary material sections, and complete sections, thereby improving the economy of tower design and providing a reference for engineering applications.

[0006] To achieve the above objectives, the present invention adopts the following solution: A method for calculating the bearing capacity of intersecting diagonal members in angle steel towers considering both overall buckling and segmented buckling includes the following steps: Based on the test results of the stability bearing capacity of single angle steel, the column curve of Class A in the national standard is selected as the column curve type for calculating the bearing capacity of the cross diagonal members of the angle steel tower; The end eccentricity and end constraint of the cross diagonal members of the angle steel tower were corrected in accordance with the design technical specifications; A calculation length correction coefficient model for the intersecting diagonal members of the angle steel tower was established using the least squares method. The ultimate bearing capacity of the intersecting diagonal members of the angle steel tower is calculated using a calculation length correction coefficient model.

[0007] As a preferred implementation method, the end eccentricity and end constraint of the cross-bracing members of the angle steel tower are modified in accordance with DL / T5219-2014 "Technical Specification for Foundation Design of Overhead Transmission Lines".

[0008] As a preferred embodiment, the end eccentricity and end constraint correction of the angle steel tower cross diagonal members are corrected by selecting a slenderness ratio correction coefficient, which is determined according to DL / T 5219-2014 "Technical Specification for Foundation Design of Overhead Transmission Lines" based on the end stress state and end constraint conditions of the cross diagonal members.

[0009] As a preferred implementation method, when both ends of the angle steel tower's intersecting diagonal members are centrally compressed and unconstrained, the slenderness ratio correction factor is taken as 1; when both ends of the angle steel tower's intersecting diagonal members are constrained, the slenderness ratio correction factor is taken as 2; when the other ends of the angle steel tower's intersecting diagonal members are subjected to a combination of forces and constraints, the slenderness ratio correction factor is determined according to DL / T 5219-2014 "Technical Specification for Foundation Design of Overhead Transmission Lines".

[0010] As a preferred embodiment, the angle steel tower cross bracing is suitable for the following types of sections: simple section, consisting of two cross bracing members; auxiliary material section, with a midpoint auxiliary material connecting the two cross bracing members; and complete section, with a main material added on top of the bracing members and auxiliary materials.

[0011] As a preferred implementation method, in the calculation length correction coefficient model, when the angle steel tower's intersecting diagonal members are bent as a whole, the following formula is used: When the stress ratio is <0.0: (1); When the stress ratio is ≥0.0: (2); In the formula, L2 is the length of the intersection of the compression diagonal members, and L3 is the total length of the intersection of the compression diagonal members. For the internal force of the compression member, For the internal force of the tie rod, when the diagonal members are simultaneously under compression, take... ; As a preferred implementation method, in the calculation length correction coefficient model, when the lower half of the intersecting diagonal member of the angle steel tower buckles, the following formula is used for calculation: 1) Simple intersegment When the stress ratio R < -0.2: (3); When the stress ratio R ≥ 0.0: (4); Interpolation when the stress ratio R is between -0.2 and 0: K=1.03+(1.06-1.03) / 0.2×(R+0.2) (5); In the formula, R is the stress ratio; 2) Auxiliary material sections When the stress ratio R < -0.2: (6); When the stress ratio R ≥ 0.0: (7); Interpolation is performed when the stress ratio R is between -0.2 and 0. K=1.14+(1.25-1.14) / 0.2×(R+0.2) (8); In the formula, R is the stress ratio.

[0012] As a preferred implementation method, the calculation length correction coefficient model is applicable to angle steel tower cross bracing members with a slenderness ratio ranging from 0 to 250. The cross bracing members adopt equilateral angle steel sections, and the ends of the cross bracing members of the angle steel tower are single-limb connections or continuous connections and are connected by one or more bolts.

[0013] Compared with the prior art, the present invention has the following beneficial effects: Firstly, this invention, based on stability bearing capacity tests of commonly used single-angle steel members, typical standard planar sections, and corresponding complete sections, conducted ANSYS finite element simulations corresponding to the cross-braced planar section tests. By assuming zero stiffness at coincident nodes, the calculated length of the cross-braced member was theoretically derived, and the calculation methods for the cross-braced member bearing capacity in six major domestic and international standards were compared. Finally, based on experiments, numerical simulations, and theoretical analysis, a correction coefficient formula for the calculated length of the cross-braced member was obtained using least-squares fitting. Combining the single-angle steel stability bearing capacity column type a curve, DL / T constraints, and eccentricity correction methods, along with the correction coefficient formula for the calculated length of the cross-braced member proposed in this invention, a novel method for calculating the ultimate bearing capacity of the cross-braced member was proposed, and compared with the calculation results and experimental values ​​from various standards. The results show that the bearing capacity calculated using the new corrected calculated length agrees better with the experimental results, can more accurately predict the ultimate bearing capacity of planar sections, auxiliary section sections, and complete sections, improves the economy of tower design, and can provide a reference for engineering applications.

[0014] Secondly, the bearing capacity calculated by the modified calculation length of this invention matches the test results better, and can more accurately predict the ultimate bearing capacity of planar sections, auxiliary material sections, and complete sections. It also provides suggestions for adjusting the bearing capacity according to the actual situation of the tower, which improves the economy of tower design and can provide a reference for engineering applications.

[0015] Third, the method of this invention simultaneously considers both the overall buckling and segmented buckling of the cross-bracing members, compensating for the deviations caused by the separate analysis of these two aspects in existing design codes. This invention introduces correction coefficients based on theoretical derivation and experimental verification to comprehensively consider the two instability modes of the cross-bracing members, making the calculation model closer to actual mechanical behavior. Comparison with multiple standard methods, space tests, and full-scale tower tests has verified that the cross-bracing member bearing capacity calculated by this method is in better agreement with the measured values, and can accurately predict the ultimate bearing capacity of the joints. Therefore, compared with existing methods, this invention significantly enhances the rationality and accuracy of the cross-bracing member bearing capacity calculation, avoiding overly conservative estimates while ensuring a safety margin, and contributing to improving the engineering economy of tower design.

[0016] Fourth, this invention also provides corresponding calculation length correction measures for the special working condition where two intersecting diagonal members are simultaneously compressed. This method assesses the instability bearing capacity by setting a calculation length specific to this situation (e.g., multiplying the entire diagonal member length by a correction factor K), thus avoiding the shortcomings of existing methods that may overlook this most unfavorable working condition. Introducing calculation rules for this situation ensures that the stability calculation is not overestimated when both intersecting diagonal members are under compression, covering extreme stress conditions not explicitly addressed in previous methods. Therefore, the method of this invention remains applicable under unfavorable working conditions such as double-compression members, enhancing the robustness and adaptability of the model and ensuring that design calculations have clear criteria and reliable results under various load conditions.

[0017] Fifth, the calculation method provided by this invention has wide applicability and good engineering consistency. By classifying the stress conditions of intersecting diagonal members and the structural form of the joint, this method is applicable to different types of joint structures (such as simple joints without auxiliary materials, joints reinforced with auxiliary materials, and joints of complete tower segments), and can provide accurate load-bearing capacity assessments. This makes up for the shortcomings of existing methods in adapting to changes in joint types, ensuring that the trend of the calculation results of this method is consistent with actual laws regardless of the arrangement of diagonal members. Since the calculation boundaries and applicable conditions are clearly defined and unified, engineers no longer need to switch between different specifications or multiple empirical formulas when applying this method, thereby improving the consistency and efficiency of the design process.

[0018] In summary, this invention greatly expands the applicability of the cross-bracing load-bearing capacity calculation model in engineering, ensuring that reasonable and reliable calculation results can be obtained under various tower types and structures, and has significant practical value. Attached Figure Description

[0019] Figure 1 This is a diagram showing the arrangement of the towers in an embodiment of the present invention; Figure 2 A simplified diagram of intersegmental structure; Figure 3 A simplified finite element model diagram of a segment; Figure 4 A comparison chart of domestic and international standards for simple segmental bearing capacity; Figure 5 A comparison chart of domestic tower specifications for simple segment bearing capacity; Figure 6 Diagram of auxiliary material joint structure; Figure 7 Finite element model diagram of the auxiliary material section; Figure 8 Comparison chart of domestic and international standards for the load-bearing capacity of auxiliary materials at joints; Figure 9 Comparison chart of domestic tower specifications for the load-bearing capacity of auxiliary materials between sections; Figure 10 This is a diagram of the complete intersegmental structure; Figure 11 This is a diagram of the complete inter-segment finite element model; Figure 12 A comparison chart of measured and theoretical displacement of DT30; In the diagram, 1-tower, 2-simple section, 3-auxiliary section, 4-complete section. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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.

[0021] The present invention provides a method for calculating the bearing capacity of intersecting diagonal members in angle steel towers considering both overall buckling and segmented buckling, comprising the following steps: S1: Based on the experimental results of the single angle steel stability bearing capacity test, it was found that when the column curve adopts the national standard a type, the stability bearing capacity of the axially compressed specimen is in good agreement with the calculated value of the specification. Therefore, the a type column curve is selected when calculating the bearing capacity of the cross diagonal member. According to the "Technical Specification for Structural Design of Overhead Transmission Line Towers" (DL / T5154-2012), a type is a rolled steel pipe with a small peak value and small value of residual stress on the outer side of the cross section, and a rolled I-beam buckling about the strong axis.

[0022] S2: Based on the experimental results of the stability bearing capacity test of single angle steel, it is concluded that the end eccentricity and constraint correction shall still adopt the constraint and eccentricity correction method of the standard DL / T5154-2012, as shown in Table 1 below.

[0023] Table 1. Correction coefficients for slenderness ratio of compression members The bearing capacity calculation adopts the Class A column curve and the correction of end constraint and eccentricity in DL / T5154-2012 (Table 1) to obtain a method for calculating the bearing capacity of the cross bracing of the angle steel tower considering overall buckling and segmented buckling. Furthermore, the calculation length of the cross bracing of the angle steel tower is corrected as shown in formulas (1) to (8).

[0024] (1) Correction for the calculated length of intersecting diagonal members when the whole is bent ① Stress ratio R < 0.0 (one tension, one compression): (1); ② Stress ratio R ≥ 0.0 (same pressure): (2); Where L2 and L3 are the length of the cross-section of the pressure diagonal member and the total length, respectively. and These are the internal forces in the compression and tension members, respectively, both taken as absolute values. When the diagonal members are simultaneously under compression, take... .

[0025] (2) Correction for the calculated length of the buckling cross bracing in the lower half (longer section) Simple joints (joints consisting of only two intersecting diagonal members): Stress ratio R < -0.2: (3); Stress ratio R ≥ 0.0: (4); Interpolation is performed when the stress ratio R is between -0.2 and 0.

[0026] K=1.03+(1.06-1.03) / 0.2*(R+0.2) (5); In the formula, R is the stress ratio.

[0027] Auxiliary material section (adding a center-split auxiliary material to the two diagonal members): Stress ratio R < -0.2: (6); Stress ratio R ≥ 0.0: (7); ③ Interpolation when the stress ratio R is between -0.2 and 0.

[0028] K=1.14+(1.25-1.14) / 0.2*(R+0.2) (8); In the formula, R is the stress ratio.

[0029] (3) Applicable conditions for formulas (1) to (8): ① The slenderness ratio of cross-bracing members is 0~250; ② The intersecting diagonal members are equal-sided angle steel; ③ The ends of the intersecting diagonal members are connected on one side or continuously, and connected by one or more bolts; All the above formulas are used for calculating the ultimate bearing capacity of intersecting diagonal members; For components with high cross-bracing stress, close to 100%, empirical adjustments to the bearing capacity are made during full-scale testing, with the adjustment range not exceeding ±10%.

[0030] Example: This embodiment provides a method for calculating the bearing capacity of intersecting diagonal members in an angle steel tower, considering both overall buckling and segmented buckling, including the following steps: like Figure 1 This is the layout diagram of tower 1. The ultimate bearing capacity under the plane segment test control group was recalculated based on the calculation length correction factor. The test results, finite element calculation results, DL / T and other standard calculation results, and the calculation results using the correction method were compared.

[0031] (1) Simple joint: Simple joint 2 consists of only two intersecting diagonal members, such as Figure 2 A simplified diagram of intersegmental structure; Figure 3 The diagram shows a simple finite element model of a section; comparative data on simple sections from domestic and international standards and Chinese tower standards can be found in [link to relevant documentation]. Figure 4 and Figure 5 .

[0032] (2) Auxiliary material section: Auxiliary material section 3 is based on two diagonal members with an additional midpoint auxiliary material. The auxiliary material section is constructed as follows: Figure 6 As shown, the finite element model of the auxiliary material joint is as follows: Figure 7 As shown; comparative data on auxiliary material sections in domestic and international standards and domestic tower standards are shown in [reference needed]. Figure 8 and Figure 9 As shown.

[0033] Where Fexp, Frequency Recommendation, F_DL / T(Class b), F_DL / T(Class a), F_DL / T(2020), F_GB, F_ASCE, Nb, and Rd represent the bearing capacities of the test, recommended method, DL / T5154-2012(Class b), DL / T5154-2012(Class a), DL / T 5486-2020(Class a), GB50017-2017, ASCE10-15, and EN50341, respectively. In simple inter-segment tests, the deformation is largest in the lower half, and buckling in the lower half plays a controlling role. The figure shows that the bearing capacity calculated by the modified calculation length of this invention matches the test results better.

[0034] (3) Fully segmented: Fully segmented 4 adds main material to the diagonal and auxiliary materials, such as Figure 10 The diagram shown is of the complete segmental structure. The finite element model of the complete segmental structure is as follows: Figure 11 As shown, the load-bearing capacity of the curved joints is lower due to torsion, and differs significantly from the actual stress on the tower components. When using the recommended formula for load-bearing capacity, the experimental load-bearing capacity will inevitably be lower than that of the recommended formula; further analysis is not conducted here.

[0035] Based on the spatial test data, the bearing capacity of the cross-braced members was calculated using various standards and recommended methods. The cross-braced members in the spatial test were under a tension and compression condition. The bearing capacity of the complete joint obtained using the recommended method is in better agreement with the test value. This ensures both accuracy and structural reliability, as well as stability, and can provide a reference for engineering applications.

[0036] To verify the effectiveness and advantages of the design method of this invention, the results of the novel calculation method and standard design under the same boundary conditions, as well as the results of the cross-diagonal member failure test under similar conditions, are compared, as shown in Table 2 below. Figure 12 As shown.

[0037] Table 2. Test Analysis Table of DT30 Real-Type Iron Tower from Figure 12 It can be seen that the measured lateral displacement at the highest ground wire support of the entire tower is basically consistent with the theoretical value, while the measured longitudinal displacement is slightly smaller than the theoretical value. The trend of displacement change is basically consistent with the theoretical value.

[0038] The above embodiments are merely illustrative examples of the technical solutions of the present invention. The present invention is not limited to the content described in the above embodiments, but is defined by the scope of the claims. Any modifications, additions, or equivalent substitutions made by those skilled in the art based on these embodiments are within the scope of protection claimed by the present invention.

Claims

1. A method for calculating the load-carrying capacity of a cross-brace of an angle steel tower considering overall buckling and segmented buckling, characterized in that: The method comprises the following steps: Based on the test results of the stability bearing capacity of the single angle steel, a column curve of a national standard a type column is selected as a column curve type for calculating the bearing capacity of the cross diagonal member of the angle steel tower; According to the design technical regulation, the end eccentricity and end constraint of the cross diagonal member of the angle steel tower are corrected. The least square method is used to fit and establish a calculation length correction coefficient model of the cross diagonal member of the angle steel tower. The ultimate bearing capacity of the cross diagonal member of the angle steel tower is calculated by using the calculation length correction coefficient model.

2. The method of claim 1, wherein: The end eccentricity and end constraint of the cross diagonal member of the angle steel tower are corrected according to the DL / T5219-2014 Technical Regulation for Design of Overhead Transmission Line Foundation.

3. The method of claim 2, wherein: The end eccentricity and end constraint correction of the cross diagonal member of the angle steel tower is corrected by selecting a slenderness ratio correction coefficient, and the slenderness ratio correction coefficient is determined according to the end force state and end constraint condition of the cross diagonal member according to the DL / T5219-2014 Technical Regulation for Design of Overhead Transmission Line Foundation.

4. The method of claim 3, wherein: When the cross diagonal member of the angle steel tower is centrally compressed at both ends and is not constrained, the slenderness ratio correction coefficient is 1; when the cross diagonal member of the angle steel tower is constrained at both ends, the slenderness ratio correction coefficient is 2; and the slenderness ratio correction coefficient under other end force and constraint combinations of the cross diagonal member of the angle steel tower is determined according to the DL / T5219-2014 Technical Regulation for Design of Overhead Transmission Line Foundation.

5. The method of claim 4, wherein: The cross diagonal member of the angle steel tower is applicable to the following panel types: a simple panel composed of two cross diagonal members; an auxiliary panel in which a midpoint auxiliary member is arranged based on the two cross diagonal members; and a complete panel in which a main member is further arranged based on the diagonal member and the auxiliary member.

6. The method of claim 5, wherein: In the calculation length correction coefficient model, when the cross diagonal member of the angle steel tower is bent as a whole, the following formula is used for calculation: When the stress ratio R is less than 0.0: ； When the stress ratio R is greater than or equal to 0.0: ； In the formula, L2 is the long section of the compression diagonal member intersection point, L3 is the full length of the compression diagonal member intersection point, is the internal force of the compression bar, is the internal force of the tension bar, when the diagonal member is under compression, take .

7. The method of claim 6, wherein: In the calculation length correction coefficient model, when the lower half of the cross diagonal member of the angle steel tower buckles, the following formula is used for calculation: 1) Simple panel When the stress ratio R is less than -0.2: ； When the stress ratio R is greater than or equal to 0.0: ； When the stress ratio R is between -0.2 and 0, interpolation is performed: K = 1.03 + (1.06-1.03) / 0.2 x (R+0.2); In the formula, R is the stress ratio. 2) Auxiliary panel When the stress ratio R is less than -0.2: ； When the stress ratio R is greater than or equal to 0.0: ； When the stress ratio R is between -0.2 and 0, interpolation is performed; K =1.14+（1.25-1.14） / 0.2×（R+0.2）； In the formula, R is the stress ratio.

8. The method according to any one of claims 1 to 7, characterized in that: The calculation length correction coefficient model is applicable to the slenderness ratio range of 0-250 of the cross diagonal member of the angle steel tower, the cross diagonal member of the angle steel tower adopts an equilateral angle steel section, and the end of the cross diagonal member of the angle steel tower is single-limb connected or continuously connected and is connected by one or more bolts.

Images