Method for calculating ultimate bearing capacity of steel truss web member-concrete latticed column

Abstract

The invention relates to the technical field of bridge structure bearing capacity, in particular to a method for calculating ultimate bearing capacity of a steel truss web member-concrete latticed column, which comprises the following steps of: 1, regarding a single column limb of the latticed column as a combination of a steel reinforced concrete column and a reinforced concrete column to obtain axial compression bearing capacity of a short latticed column; 2, the bearing effects of the eccentricity ratio and the slenderness ratio on the latticed column are basically independent of each other, and the ultimate bearing capacity of the latticed column is calculated through the method that the eccentricity ratio and the slenderness ratio reduction coefficient are multiplied; 3, according to the crushing failure mode and the tension fracture failure mode of the latticed column, a crushing failure and tension fracture failure calculation formula is provided, and then an eccentricity ratio reduction coefficient calculation formula is obtained; and 4, deducing a conversion slenderness ratio considering shear deformation, and fitting an ultimate bearing capacity result of the latticed column to obtain a slenderness ratio reduction coefficient calculation formula. According to the calculation method, the bearing capacity can be calculated more simply and more conveniently, and the accuracy is improved.

Description

Technical Field

[0001] This invention relates to the field of bridge structural bearing capacity technology, specifically to a method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column. Background Technology

[0002] The steel truss web-concrete composite arch effectively solves the problems of heavy self-weight and difficult construction of concrete arches. It eliminates the need for concrete web pouring, simplifying the construction process, while effectively reducing the self-weight of the arch ring, making it a more rational structural form. In recent years, some researchers have conducted systematic studies on the mechanical properties of steel truss web-concrete composite arch bridges through trial design, model testing, and finite element simulation. This new type of arch bridge has already been applied in practical engineering projects.

[0003] The main methods for calculating the bearing capacity of arch bridges include the equivalent beam-column method, the empirical coefficient method, the limit analysis method, and the numerical analysis method. Among these, the equivalent beam-column method is a commonly used method. Using the equivalent beam-column method, a steel truss web-concrete composite arch can be equivalently represented as a steel truss web-concrete lattice column, which is a novel type of lattice column. The steel truss web-concrete lattice column differs in structural form from traditional lattice columns (such as steel lattice columns and steel-concrete composite lattice columns), and the traditional theories and standards for calculating the ultimate bearing capacity of lattice columns may not be applicable.

[0004] Currently, there are shortcomings in the calculation theory of bearing capacity of steel truss web-concrete lattice columns. The existing ultimate bearing capacity calculation method is a direct application of the calculation theory of steel tube concrete lattice columns. Because it uses the steel tube concrete ferrule index, it is not applicable to steel truss web-concrete lattice columns. Summary of the Invention

[0005] The purpose of this invention is to provide a method for calculating the ultimate bearing capacity of steel truss web-concrete lattice columns, which helps to simplify and improve the accuracy of bearing capacity calculation.

[0006] The technical solution of this invention is: a method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column, comprising the following steps: Step 1: Treat a single column of the lattice column as a combination of a steel-concrete composite column and a reinforced concrete column to obtain the axial compressive bearing capacity of the short lattice column; Step 2: The effects of eccentricity and slenderness ratio on the load-bearing capacity of lattice columns are basically independent of each other. The ultimate bearing capacity is calculated by multiplying the eccentricity and slenderness ratio reduction factors. Step 3: Based on the two failure modes of lattice columns, namely crushing and tensile cracking, calculation formulas for crushing and tensile cracking failure are proposed, and then the calculation formula for the eccentricity reduction coefficient is obtained. Step 4: First, derive the equivalent slenderness ratio considering shear deformation, then fit the ultimate bearing capacity result of the lattice column to obtain the formula for calculating the slenderness ratio reduction factor.

[0007] Furthermore, the lattice column includes a steel frame arranged vertically with spacing between the front and rear sections. Reinforcing steel frames are provided on the outer side between the front and rear chord steel sections on the left side of the two steel frames and on the outer side between the front and rear chord steel sections on the right side of the two steel frames, and concrete is poured on them.

[0008] Furthermore, the steel frame includes two vertically arranged chord steel sections, and several steel web members that are integrally connected with the chord steel sections are arranged between the two chord steel sections from top to bottom.

[0009] Furthermore, the steel reinforcement cage includes longitudinal steel bars that are vertically arranged around the chord steel and between two adjacent chord steels and are parallel to the chord steel. Stirrups are provided in the areas enclosed by the longitudinal steel bars around the chord steel and the areas enclosed by each longitudinal steel bar. Through steel bars are also provided at intervals from bottom to top between the two chord steels.

[0010] Furthermore, in step 1, by simplifying the calculation formula for the axial compressive bearing capacity of the steel truss web-concrete lattice short column, the axial compressive bearing capacity N0 of the lattice short column is obtained: In the formula: This refers to the axial compressive strength of concrete. For single-limb short column reinforcement and structural steel, the compressive yield strength is... This refers to the cross-sectional area of ​​the concrete, reinforcing steel, and structural steel of a single-limb short column.

[0011] Furthermore, in step 2, the ultimate bearing capacity of the lattice column... The calculation formula is: In the formula: This is the slenderness ratio reduction factor. N is the eccentricity reduction factor. 0i The ultimate bearing capacity of a single short limb lattice column under axial compression.

[0012] Furthermore, in step 3, under eccentric compression, the column members closer to the eccentrically compressed position are under compression, while those farther from the eccentrically compressed position are under tension. Therefore, the column members can be divided into tension members and compression members, i.e.: In the formula: For the ultimate bearing capacity of axial compression of short lattice columns, The ultimate bearing capacity of the axial compression of the tensioned short column. The ultimate bearing capacity of the compression leg short column; Introduce the asymmetry coefficient γ for the lattice column section (γ = 1 for symmetric sections): The distance 'a' from the center of gravity of the stretching limb and the pressing limb to the center of gravity of the pressure. t a c They are: In the formula: h is the distance between the centers of gravity of the two columns; Because the tensile strength of concrete is not considered when steel-concrete composite columns and reinforced concrete columns are subjected to tension, according to the "Code for Design of Composite Structures" (JGJ 138-2016) and the "Code for Design of Concrete Structures" (GB 50010-2010), and the calculation formulas for the axial tensile bearing capacity of steel-concrete composite columns and reinforced concrete columns are combined and simplified, the axial tensile bearing capacity of the tension member is thus... for: In the formula: For the longitudinal reinforcement of the tension leg and the tensile yield strength of the steel section, This refers to the longitudinal reinforcing bars of the tension member and the cross-sectional area of ​​the steel section.

[0013] Furthermore, assuming that when axial tensile force is applied to the pressure center of gravity of the lattice column, and the tension member reaches its ultimate tensile force... The ultimate axial tensile bearing capacity at that time is And order: In the formula, η is the ratio of compressive to tensile strength of the tension leg; Ultimate bending moment of latticed columns dominated by the compressive strength of the compression limbs and the tensile strength of the tension limbs They are: Under the combined action of bending moment and axial force, the yield condition for crushing and tensile cracking failure of lattice columns is: According to the definition: Based on the yield conditions for crushing and tensile failure of latticed columns, the reduction factors for crushing and tensile failure can be obtained as follows: By setting the reduction factors for crushing and tensile failures to be equal, the critical eccentricity at the point of failure can be obtained. for: In the formula: This is the limiting eccentricity of the axial force about the centroid of the cross section; Therefore, the formula for calculating the eccentricity reduction factor is:

[0014] Furthermore, in step 4, based on the calculation formula and unified theory for the critical load of elastically stable lattice columns, and considering the influence of shear deformation, the critical load N of the steel truss web-concrete lattice column about the imaginary axis (x-axis) can be obtained. cr Calculation formula: In the formula: (EA) sc λ is the combined compressive stiffness of the lattice column. x γ is the slenderness ratio of the lattice column about the x-axis, γ1 is the shear angle under unit shear force, and λ is the shear angle. 0x The slenderness ratio of the lattice column with respect to the x-axis is given. Therefore, the formula for calculating the slenderness ratio can be obtained: Now (EA) sc And γ1 is unknown, (EA) sc The solution for γ is relatively simple, but γ1 is difficult to solve. Therefore, the key to calculating the slenderness ratio is solving for γ1. Under a unit shear force, the flat web member undergoes compressive deformation. Since there are two parallel flat web members and diagonal web members at the same height, the internal force of a single flat web member is 1 / 2, and the internal force s of a single diagonal web member is... d for: In the formula: θ is the initial angle between the diagonal web member and the column member; Elongation Δ of a single flat web member and an oblique web member f Δ d for: In the formula: l f E is the length of the flat web member. s A is the elastic modulus of the steel section. f l is the cross-sectional area of ​​the flat web member; l1 is the internode length of the column member, l d Let A be the length of the diagonal web member. d Let be the cross-sectional area of ​​the diagonal web member; The total lateral displacement δ is: The unit shear angle is: Substituting the formula for calculating the unit shear angle into the formula for calculating the converted slenderness ratio, we get:

[0015] Furthermore, the slenderness ratio reduction factor is the ratio of the ultimate bearing capacity of the lattice column to the ultimate bearing capacity of the lattice short column.

[0016] Compared with the prior art, the present invention has the following advantages: Based on the structural form and compressive mechanical properties of steel truss web-concrete lattice columns, the present invention analyzes and extends the existing calculation theories of compressive bearing capacity of single-limb columns, steel lattice columns and steel-concrete lattice columns, and proposes a method for calculating the ultimate bearing capacity of steel truss web-concrete lattice columns by means of theoretical derivation, empirical analysis and data fitting. This calculation method has good applicability, high calculation accuracy, and the calculation formula has been simplified, which makes the calculation more convenient. Attached Figure Description

[0017] Figure 1 This is an elevation view of the steel truss web-concrete lattice column to be calculated according to the present invention. Figure 2 This is a cross-sectional view of the steel truss web-concrete lattice column to be calculated according to the present invention; Figure 3 This is a three-dimensional perspective view of the steel truss web-concrete lattice column to be calculated according to the present invention. Figure 4 This is a simplified diagram for calculating the reduction coefficient of the eccentricity of the facade of the lattice column in this invention. Figure 5 A simplified diagram for calculating the reduction factor of the eccentricity of the cross section of the lattice column to be calculated in this invention; Figure 6 This is a graph showing the correlation curves of the lattice column MN to be calculated in this invention; Figure 7 This is a diagram showing the deformation of a single web member of the lattice column under unit shear force in the present invention. Figure 8 This is a comparison chart of the calculated value and the calculation curve of the slenderness ratio reduction factor of the lattice column to be calculated in this invention; Figure 9 This is a schematic diagram of the calculation process of the present invention; In the diagram: 1-Concrete; 2-Chord steel; 3-Steel web member; 4-Stirrup; 5-Longitudinal reinforcement; 6-Through reinforcement; 7-Reinforced concrete column; 8-Steel-concrete column; 9-Compression center of gravity axis; 10-Compression center of gravity. Detailed Implementation

[0018] To make the above features and advantages of the present invention more readily understood, specific embodiments are described below in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0019] refer to Figures 1 to 9 A schematic diagram of a steel truss web-concrete lattice column structure is shown below. Figure 1 , Figure 2 and Figure 3As shown, the structure includes a steel frame arranged vertically with spacing between the front and rear sections. Reinforcing steel frames and concrete 1 are provided on the outer side between the front and rear chord steel sections 2 on the left side of the two steel frames and on the outer side between the front and rear chord steel sections 2 on the right side of the two steel frames. Specifically, the aforementioned steel frame includes two vertically arranged chord steel sections 2, and several steel web members 3, which are integrally connected with the chord steel sections, are arranged between the two chord steel sections from top to bottom.

[0020] Specifically, the aforementioned steel reinforcement cage includes longitudinal steel bars 5 vertically arranged around the chord steel and between two adjacent chord steels and parallel to the chord steel. Stirrups 4 are provided in the areas enclosed by the longitudinal steel bars around the chord steel and the areas enclosed by each longitudinal steel bar. Through steel bars 6 are also provided at intervals from bottom to top between the two chord steels.

[0021] Based on the structural form and stress characteristics of the steel truss web-concrete lattice column, a method for calculating the ultimate bearing capacity of the steel truss web-concrete lattice column is derived. A schematic diagram of the calculation process is shown below. Figure 9 As shown, it includes the following steps: Step 1: Consider the single column of the lattice column as a combination of steel-concrete composite column 8 and reinforced concrete column 7 (see...) Figure 2 According to the relevant specifications, the axial compressive bearing capacity of the lattice short column is obtained.

[0022] Since the calculation methods for the bearing capacity of steel-concrete composite columns and reinforced concrete columns are relatively well-established, the axial compressive bearing capacity N0 of the lattice short column is obtained by simplifying the calculation formula for the axial compressive bearing capacity of the steel truss web-concrete lattice short column: In the formula: This refers to the axial compressive strength of concrete. For single-limb short column reinforcement and structural steel, the compressive yield strength is... This refers to the cross-sectional area of ​​the concrete, reinforcing steel, and structural steel of a single-limb short column.

[0023] Step 2: The effects of eccentricity and slenderness ratio on the load-bearing capacity of lattice columns are basically independent of each other. The ultimate bearing capacity is calculated by multiplying the eccentricity and slenderness ratio reduction factors.

[0024] Ultimate bearing capacity of lattice column The calculation formula is: In the formula: This is the slenderness ratio reduction factor. N is the eccentricity reduction factor. 0i The ultimate bearing capacity of a single short limb lattice column under axial compression.

[0025] Step 3: Based on the two failure modes of lattice columns, namely crushing and tensile cracking, calculation formulas for crushing and tensile cracking failure are proposed, and then the calculation formula for the eccentricity reduction coefficient is obtained.

[0026] A simplified diagram for calculating the eccentricity reduction factor of steel truss web-concrete lattice columns is shown below. Figure 4 , Figure 5 As shown. Under eccentric compression, the column members closer to the eccentric compression position are under compression, while those farther away are under tension. Therefore, the column members can be divided into tension members and compression members, i.e.: In the formula: For the ultimate bearing capacity of axial compression of short lattice columns, The ultimate bearing capacity of the axial compression of the tensioned short column. This represents the ultimate axial compression bearing capacity of the short column with compression limbs.

[0027] Introduce the asymmetry coefficient γ for the lattice column section (γ = 1 for symmetric sections): The distance 'a' from the center of gravity of the stretching limb and the pressing limb to the center of gravity of the pressure. t a c They are: In the formula: h is the distance between the centers of gravity of the two columns; Because the tensile strength of concrete is not considered when steel-concrete composite columns and reinforced concrete columns are subjected to tension, according to the "Code for Design of Composite Structures" (JGJ 138-2016) and the "Code for Design of Concrete Structures" (GB 50010-2010), and the calculation formulas for the axial tensile bearing capacity of steel-concrete composite columns and reinforced concrete columns are combined and simplified, the axial tensile bearing capacity of the tension member is thus... for: In the formula: For the longitudinal reinforcement of the tension leg and the tensile yield strength of the steel section, This refers to the longitudinal reinforcing bars of the tension member and the cross-sectional area of ​​the steel section.

[0028] Assuming that axial tensile force is applied to the pressure center of gravity of the lattice column, and the tension leg reaches its ultimate tensile force. The ultimate axial tensile bearing capacity at that time is And order: In the formula, η is the ratio of compressive to tensile strength of the tension leg; Ultimate bending moment of latticed columns dominated by the compressive strength of the compression limbs and the tensile strength of the tension limbs They are: Under the combined action of bending moment and axial force, the yield condition for crushing and tensile cracking failure of lattice columns is:

[0029] According to the definition: Based on the yield conditions for crushing and tensile failure of lattice columns ( Figure 6 From this, we can obtain the reduction factors for crushing and tensile failure as follows: By setting the reduction factors for crushing and tensile failures to be equal, the critical eccentricity at the point of failure can be obtained. for: In the formula: This is the limiting eccentricity of the axial force about the centroid of the cross section.

[0030] Considering and We can obtain: The compressive and tensile yield strengths of steel are equal, that is... and Introducing coefficients Further simplification yields: Therefore, the reduction factors for the limiting eccentricity and tensile failure are respectively converted to:

[0031] For a two-limb lattice column with a symmetrical cross-section and two limbs having equal cross-sectional areas, we have: a t =a c =h / 2, γ=1, therefore, the formula for calculating the eccentricity reduction factor is:

[0032] Step 4: First, derive the equivalent slenderness ratio considering shear deformation, then fit the ultimate bearing capacity result of the lattice column to obtain the formula for calculating the slenderness ratio reduction factor.

[0033] Based on the calculation formula and unified theory for the critical load of elastically stable lattice columns, and considering the influence of shear deformation, the critical load N of the steel truss web-concrete lattice column about the imaginary axis (x-axis) can be obtained. cr Calculation formula: In the formula: (EA) sc λ is the combined compressive stiffness of the lattice column. x γ is the slenderness ratio of the lattice column about the x-axis, γ1 is the shear angle under unit shear force, and λ is the shear angle. 0x This is the equivalent slenderness ratio of the lattice column with respect to the x-axis.

[0034] Therefore, the formula for calculating the slenderness ratio can be obtained: Now (EA) sc And γ1 is unknown, (EA) sc The solution for γ is relatively simple, but γ1 is difficult to solve. Therefore, the key to calculating the slenderness ratio is solving for γ1. In a steel truss web-concrete lattice column, the web members and column legs are considered hinged, forming a truss system. The deformation of a single web member under unit shear force is shown in [reference needed]. Figure 7 Under a unit shear force, the flat web member undergoes compressive deformation. Since there are two parallel flat web members and diagonal web members at the same height, the internal force of a single flat web member is 1 / 2, and the internal force s of a single diagonal web member is... d for: In the formula: θ is the initial angle between the diagonal web member and the column member; Elongation Δ of a single flat web member and an oblique web member f Δ d for: In the formula: l f E is the length of the flat web member. s A is the elastic modulus of the steel section. f l is the cross-sectional area of ​​the flat web member; l1 is the internode length of the column member, l d Let A be the length of the diagonal web member. d Let be the cross-sectional area of ​​the diagonal web member; The total lateral displacement δ is: The unit shear angle is: Substituting the formula for calculating the unit shear angle into the formula for calculating the converted slenderness ratio, we get:

[0035] When the cross sections of the two individual members of a double column are the same, the overall stiffness of the column is converted into the stiffness of a chordal steel section: In the formula: E sc A represents the combined elastic modulus of a single column member; sc A is the combined area of ​​a single column member; s 、A c These represent the chord steel section and concrete area of ​​a single column; E c α is the elastic modulus of concrete for a single column; α is the steel content of the column, with a lower steel content for steel truss-concrete lattice columns, ranging from 0.5% to 4%; n is the ratio of the elastic modulus of the steel section to that of the concrete, n = Es / E c The value range is generally 5.6 to 6.9.

[0036] The relationship between structural steel and (EA) should be reasonably considered. sc The impact, due to The maximum difference in α is 8 times, therefore the influence of α cannot be ignored, while the influence of n is small and can be approximated as 6.3. The value of θ generally ranges from 40° to 60°, and can be taken as π. 2 tanθ = 9, Convert the slenderness ratio to: By fitting the results of the ultimate bearing capacity of the lattice column (see...) Figure 8 The slenderness ratio reduction factor for the steel truss web-concrete lattice column is derived as the ratio of the ultimate bearing capacity of the lattice column to the ultimate bearing capacity of the short lattice column. The calculation formula is as follows: when hour: When λ 0x >24.5 hours:

[0037] The above description is only a preferred embodiment of the present invention. For those skilled in the art, designing different forms of steel truss web-concrete lattice column ultimate bearing capacity calculation methods according to the teachings of the present invention does not require creative labor. All equivalent changes, modifications, substitutions and variations made in accordance with the scope of the patent application of the present invention without departing from the principles and spirit of the present invention shall be covered by the present invention.

Claims

1. A method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column, characterized in that, Includes the following steps: Step 1: Treat a single column of the lattice column as a combination of a steel-concrete composite column and a reinforced concrete column to obtain the axial compressive bearing capacity of the short lattice column; Step 2: The effects of eccentricity and slenderness ratio on the load-bearing capacity of lattice columns are basically independent of each other. The ultimate bearing capacity is calculated by multiplying the eccentricity and slenderness ratio reduction factors. Step 3: Based on the two failure modes of lattice columns, namely crushing and tensile cracking, calculation formulas for crushing and tensile cracking failure are proposed, and then the calculation formula for the eccentricity reduction coefficient is obtained. Step 4: First, derive the equivalent slenderness ratio considering shear deformation, then fit the ultimate bearing capacity result of the lattice column to obtain the formula for calculating the slenderness ratio reduction factor.

2. The method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column according to claim 1, characterized in that, The lattice column includes a steel frame arranged vertically with intervals between the front and rear sections. Reinforcing steel frames and concrete are provided on the outer side between the front and rear chord steel sections on the left side of the two steel frames and on the outer side between the front and rear chord steel sections on the right side of the two steel frames.

3. The method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column according to claim 2, characterized in that, The steel frame includes two vertically arranged chord steel sections, and several steel web members that are integrally connected with the chord steel sections are arranged between the two chord steel sections from top to bottom.

4. The method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column according to claim 2 or 3, characterized in that, The steel reinforcement cage includes vertical longitudinal steel bars that are arranged on the periphery of the chord steel and between two adjacent chord steels and are parallel to the chord steel. Stirrups are provided in the area enclosed by the longitudinal steel bars on the periphery of the chord steel and the area enclosed by each longitudinal steel bar. Through steel bars are also provided at intervals from bottom to top between the two chord steels.

5. A method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column according to claim 1, 2, or 3, characterized in that, In step 1, by simplifying the calculation formula for the axial compressive bearing capacity of the steel truss web-concrete lattice short column, the axial compressive bearing capacity N0 of the lattice short column is obtained: In the formula: f c * This refers to the axial compressive strength of concrete. f a * For single-limb short column reinforcement and structural steel, the compressive yield strength is... This refers to the cross-sectional area of ​​the concrete, reinforcing steel, and structural steel of a single-limb short column.

6. The method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column according to claim 5, characterized in that, In step 2, the ultimate bearing capacity of the lattice column The calculation formula is: In the formula: This is the slenderness ratio reduction factor. N is the eccentricity reduction factor. 0i The axial compressive bearing capacity of a single short column of a lattice column.

7. A method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column according to claim 1, 2, 3 or 6, characterized in that, In step 3, under eccentric compression, the column members closer to the eccentrically compressed position are under compression, while those farther from the eccentrically compressed position are under tension. Therefore, the column members can be divided into tension members and compression members, i.e.: In the formula: For the ultimate bearing capacity of axial compression of short lattice columns, The ultimate bearing capacity of the axial compression of the tensioned short column. The ultimate bearing capacity of the compression leg short column; Introduce the asymmetry coefficient γ for the lattice column section (γ = 1 for symmetric sections): The distance 'a' from the center of gravity of the stretching limb and the pressing limb to the center of gravity of the pressure. t a c They are: In the formula: h is the distance between the centers of gravity of the two columns; Because the tensile strength of concrete is not considered when steel-concrete composite columns and reinforced concrete columns are subjected to tension, according to the "Code for Design of Composite Structures" (JGJ 138-2016) and the "Code for Design of Concrete Structures" (GB 50010-2010), and the calculation formulas for the axial tensile bearing capacity of steel-concrete composite columns and reinforced concrete columns are combined and simplified, the axial tensile bearing capacity of the tension member is thus... for: In the formula: For the longitudinal reinforcement of the tension leg and the tensile yield strength of the steel section, This refers to the longitudinal reinforcing bars of the tension member and the cross-sectional area of ​​the steel section.

8. The method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column according to claim 7, characterized in that, Assuming that axial tensile force is applied to the pressure center of gravity of the lattice column, and the tension leg reaches its ultimate tensile force. The ultimate axial tensile bearing capacity at that time is And order: In the formula: η is the ratio of compressive to tensile strength of the tension leg; Ultimate bending moment of latticed columns dominated by the compressive strength of the compression limbs and the tensile strength of the tension limbs They are: Under the combined action of bending moment and axial force, the yield condition for crushing and tensile cracking failure of lattice columns is: According to the definition: Based on the yield conditions for crushing and tensile failure of latticed columns, the reduction factors for crushing and tensile failure can be obtained as follows: By setting the reduction factors for crushing and tensile failures to be equal, the critical eccentricity at the point of failure can be obtained. for: In the formula: This is the limiting eccentricity of the axial force about the centroid of the cross section; Therefore, the formula for calculating the eccentricity reduction factor is:

9. The method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column according to claim 1, characterized in that, In step 4, based on the calculation formula and unified theory for the critical load of the elastically stable lattice column, and considering the influence of shear deformation, the critical load N of the steel truss web-concrete lattice column about the imaginary axis (x-axis) can be obtained. cr Calculation formula: In the formula: (EA) sc λ is the combined compressive stiffness of the lattice column. x γ is the slenderness ratio of the lattice column about the x-axis, γ1 is the shear angle under unit shear force, and λ is the shear angle. 0x The slenderness ratio of the lattice column with respect to the x-axis is given. Therefore, the formula for calculating the slenderness ratio can be obtained: Now (EA) sc And γ1 is unknown, (EA) sc The solution for γ is relatively simple, but γ1 is difficult to solve. Therefore, the key to calculating the slenderness ratio is solving for γ1. Under a unit shear force, the flat web member undergoes compressive deformation. Since there are two parallel flat web members and diagonal web members at the same height, the internal force of a single flat web member is 1 / 2, and the internal force s of a single diagonal web member is... d for: In the formula: θ is the initial angle between the diagonal web member and the column member; Elongation Δ of a single flat web member and an oblique web member f Δ d for: In the formula: l f E is the length of the flat web member. s A is the elastic modulus of the steel section. f l is the cross-sectional area of ​​the flat web member; l1 is the internode length of the column member, l d Let A be the length of the diagonal web member. d Let be the cross-sectional area of ​​the diagonal web member; The total lateral displacement δ is: The unit shear angle is: Substituting the formula for calculating the unit shear angle into the formula for calculating the converted slenderness ratio, we get:

10. The method for calculating the ultimate bearing capacity of a steel truss web-concrete lattice column according to claim 9, characterized in that, The slenderness ratio reduction factor is the ratio of the ultimate bearing capacity of the lattice column to the ultimate bearing capacity of the lattice short column.

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