Method for determining precast concrete retaining wall of manual hole digging pile under action of non-uniform confining pressure

Abstract

The invention belongs to the field of safety protection of manual hole digging piles, and discloses a method for determining a precast concrete retaining wall in manual hole digging pile construction, which comprises the following steps of: preliminarily determining the composition number, the thickness, the height and the aperture ratio of segments of the precast concrete retaining wall according to the pile length and the diameter of the manual hole digging pile; selecting a load non-uniform distribution degree coefficient according to the soil texture condition, and establishing a non-uniform confining pressure equation on the retaining wall duct piece; building a dado structure calculation model under the action of the non-uniform confining pressure; carrying out stress analysis on the retaining wall structure under the action of non-uniform confining pressure; the protection wall segment reinforcement design under the non-uniform confining pressure effect is determined; and if the thickness of the retaining wall and the aperture ratio do not meet the reinforcement design requirement, the thickness of the retaining wall, the aperture ratio or the steel bar arrangement parameters are adjusted until the reinforcement design meets the design requirement. According to the design method, the situation that the pressure acting on the upper side of the prefabricated retaining wall segment is not uniform due to various reasons is considered, and the design calculation of the prefabricated retaining wall of the manual hole digging pile foundation can be more accurate and reasonable through the method.

Description

Technical Field

[0001] The invention belongs to the field of safety protection of artificial bored piles, and in particular relates to a method for determining a precast concrete protective wall of an artificial bored pile under the action of non-uniform confining pressure. Background Art

[0002] In recent years, with the continuous improvement of the voltage level of transmission lines and the continuous optimization of foundation design, excavation foundations such as hole foundations and excavation foundations that make full use of the original soil performance and are economical and environmentally friendly have become one of the main types of transmission line tower foundations. When excavating the foundation pit of an excavation type foundation, a retaining wall is generally set up to ensure the safety of the pit workers. Considering the economy and construction convenience, the current artificial excavation type foundation retaining wall type in transmission line projects generally adopts cast-in-place reinforced concrete retaining walls. Although the design results of these cast-in-place retaining walls meet the needs of engineering applications, they have never solved the inherent problems of cast-in-place retaining walls, such as the need for on-site maintenance, low early strength, susceptibility to environmental and human factors, and long construction period.

[0003] In my country, the railway, highway, bridge and other industries have carried out research on prefabricated retaining walls and their construction methods in factories and on-site assembly in combination with the characteristics of industry projects, and have achieved some theoretical research. There are few related studies in the power industry, and it is urgent to carry out research and design work on prefabricated retaining walls in combination with the stress characteristics of the transmission line foundation. In general, when conducting stress analysis on precast concrete prefabricated retaining wall structures, the uniformly distributed confining pressure on the outside of the retaining wall is mainly considered. However, in actual projects, due to various reasons such as construction conditions, stratum structure, and differences in rock and soil properties, the lateral pressure acting on the retaining wall will be unevenly distributed. If the design is based on uniform confining pressure, it will bring safety hazards to the retaining wall structure. Summary of the invention

[0004] Aiming at the situation that the cast-in-place retaining wall is subjected to irregular hole excavation and uneven soil in actual engineering, which results in different confining sizes of prefabricated retaining wall at the same height section, the present invention proposes a method for determining prefabricated concrete retaining wall of bored piles under non-uniform confining pressure, so as to make the design more objective and reasonable and increase the safety of temporary support retaining wall structure during construction.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for determining a precast concrete retaining wall of a bored pile under non-uniform confining pressure comprises the following steps:

[0007] Step 1: Preliminarily determine the number of components, thickness, height and opening ratio of precast concrete wall segments according to the length and diameter of the bored piles;

[0008] Step 2: Select the load non-uniform distribution coefficient according to the soil conditions and establish the non-uniform confining pressure equation on the wall segment;

[0009] Step 3: Establish a calculation model of precast concrete prefabricated wall protection structure under non-uniform confining pressure;

[0010] Step 4: Conduct stress analysis of precast concrete prefabricated wall protection structure under non-uniform confining pressure;

[0011] Step 5: Determine the reinforcement design of precast concrete prefabricated wall segment under non-uniform confining pressure;

[0012] Step 6: If the wall thickness and opening ratio do not meet the reinforcement design requirements in the "Concrete Structure Design Standard" (GB / T50010-2010), adjust the wall thickness, opening ratio or steel bar arrangement parameters until the reinforcement design meets the design requirements.

[0013] The number of precast concrete wall segments in step 1 is 3 to 6, wherein the diameter of the bored pile is less than 1.2m, 3 segments are used, the diameter is 1.2m to 1.8m, 4 segments are used, the diameter is 1.8m to 2.2m, 5 segments are used, and the diameter is greater than 2.2m, 6 segments; the thickness of the segment is not less than 60cm, the length of the bored pile is 60cm when it is less than 20m, and 80cm when it is greater than 20m; the height of the segment is 50cm under the geological conditions of silt and silty clay, and 20cm under the geological conditions of sand, gravel, soft soil and miscellaneous fill; the opening rate of the segment is not less than 40%, 40%-50% for soft soil, and up to 60% for hard soil.

[0014] Step 2: Select the load non-uniform distribution coefficient according to the soil conditions, and the steps to establish the non-uniform confining pressure equation on the wall segment are:

[0015] The distribution curve of the non-uniform confining pressure equation is q k =q A (1+msinα)

[0016] In the formula, q k is the lateral earth pressure at each point on the retaining wall; q A is the minimum lateral pressure, where point A is located at the intersection of the horizontal line passing through the center of the retaining wall and the retaining wall; α is the angle between the line connecting the calculation point of the lateral earth pressure on the retaining wall and the center of the retaining wall and the horizontal line passing through the center of the retaining wall; m is the load non-uniform distribution coefficient, m = 0 means that the load is evenly distributed, where the value of m is determined according to the soil characteristics and the smoothness of the hole wall. When the soil is silt, clay and the hole wall is relatively flat and regular, m is 0-0.5; when the soil is gravel soil, miscellaneous fill or the hole wall is not very flat and regular, m is 1.0;

[0017] The lateral pressure acting on the retaining wall is q B =K'∑γ i h i

[0018] q B is the maximum lateral pressure, where point B is located at the intersection of the vertical line through the center of the retaining wall and the retaining wall; K′ is the lateral earth pressure coefficient of the retaining wall; γ i h is the weight of the i-th layer of soil above the calculation point of the lateral earth pressure on the retaining wall; i is the thickness of the i-th soil layer above the calculation point of the lateral earth pressure on the retaining wall;

[0019] When α=90°

[0020] Preferably, in step 2, the lateral earth pressure coefficient of the retaining wall is K0, K a are the static earth pressure and active earth pressure coefficient acting on the retaining wall, respectively.

[0021] When establishing the calculation model of the precast concrete assembled wall protection structure under non-uniform confining pressure in step 3, the wall protection is regarded as a closed circular ring subjected to symmetrical non-uniform pressure, and the calculation model of the precast concrete assembled wall protection structure under non-uniform confining pressure is established.

[0022] Step 4 is to carry out stress analysis of the precast concrete assembled wall protection structure under the action of non-uniform confining pressure, where the internal forces at points A and B are:

[0023] N A =Tq A b(1+0.7854m)

[0024] Where N A is the axial force on section A (kN), T is the vertical calculated height of the retaining wall (m), and b is the outer radius of the retaining wall (m);

[0025] N B =Tq A b(1+0.5m)

[0026] Where N B is the axial force on section B (kN);

[0027] M A =-0.1488Tq A b 2 m

[0028] Where M A is the bending moment on section A (kN·m);

[0029] M B =-0.1366Tq A b 2 m

[0030] Where M Bis the bending moment on section B (kN·m).

[0031] The reinforcement design process of the precast concrete assembled wall segment under the non-uniform confining pressure described in step 5 is as follows: the precast concrete assembled wall section under the non-uniform confining pressure generates bending moment and axial force under the load. According to the calculation theory of eccentrically compressed components, the reinforcement of the segment is determined in combination with the concrete strength grade and the bending moment. The process is as follows:

[0032] N≤N u =α1f c bx-f y A s

[0033] Where, N is the design value of axial pressure, N u is the ultimate bearing capacity under axial compression, α1 is the equivalent rectangular stress diagram coefficient of the concrete compression zone, f c is the design value of concrete axial compressive strength, b is the width of the rectangular section, x is the height of the concrete compression zone, f y is the design value of steel bar tensile strength, As is the reinforcement area;

[0034]

[0035] Where N is the design value of the axial pressure, e is the distance between the axial pressure point and the longitudinal tensile reinforcement force point, M u is the design value of the ultimate resistance moment of the positive section, h0 is the effective height of the section;

[0036] Calculate the eccentricity as:

[0037] Where M mzx is the maximum design bending moment value, N max is the maximum design axial force value;

[0038] The additional eccentricity is:

[0039] The initial eccentricity is: e i =e0+e a

[0040] Determine bias category: e i =e0+e a >0.3h0 is large bias

[0041]

[0042] e i =e0+e a ≤0.3h0 is small bias

[0043]

[0044] Where, β1 is the conversion height coefficient of the equivalent rectangular stress diagram of the concrete compression zone;

[0045]

[0046] Where ξ is the relative height of the compression zone, b is the relative height of the compression zone;

[0047]

[0048] In the formula, ρ min is the minimum reinforcement ratio and h is the section height.

[0049] When the reinforcement area is too large and does not meet the structural requirements according to the specifications, the wall section thickness is increased or the concrete strength grade is increased or the opening ratio is reduced, and the reinforcement area is recalculated until the force requirements are met.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] 1. During the construction of the pile hole retaining wall of the excavated type, the soil pressure on the rock and soil of the pile hole retaining wall in the initial state is the static soil pressure. During the hole forming process of the bored pile, the lateral stress of the pile hole wall is relieved, the soil body undergoes radial centripetal displacement, and lateral relaxation deformation occurs. The soil pressure begins to change from the static soil pressure to the active soil pressure instantly. The soil pressure actually borne by the retaining wall should be between the static soil pressure and the active soil pressure. However, there is no detailed calculation method at present. Therefore, the present invention proposes a standard value of soil pressure between the static soil pressure and the active soil pressure based on the actual construction situation of the project (unloading effect and arch effect), combined with the small hole expansion relaxation theory and the existing specifications and standards, that is, a method for taking the average value of the static soil pressure and the active soil pressure coefficient on the retaining wall: compared with the traditional static soil pressure calculation theory and active soil pressure calculation theory, it takes into account both safety and economy, and is more reasonable and scientific.

[0052] 2. The present invention proposes to approximate the uneven confining pressure distribution on the outer side of the precast concrete retaining wall by using a function and an uneven coefficient, which fully considers the influence of uneven factors such as different soil qualities, different construction levels and whether the excavation surface is standardized on the stress of the precast concrete retaining wall. It is more practical, more reasonable and more accurate than the uniformly distributed pressure on the traditional retaining wall. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a flow chart of the calculation method of the precast concrete retaining wall of the artificial bored pile of the present invention;

[0054] Figure 2 It is a non-uniformly distributed confining pressure load curve diagram of the precast concrete assembled wall protection structure of the present invention;

[0055] Figure 3 It is a schematic diagram of a calculation model of a precast concrete assembled wall protection structure under non-uniform confining pressure of the present invention;

[0056] Figure 4 It is a schematic diagram of loading the open-hole precast concrete assembled wall protection segment model of the present invention;

[0057] Figure 5 It is a schematic diagram of reinforcement cross section calculation of the present invention;

[0058] Figure 6 It is a cloud diagram of stress calculation results of the precast concrete wall protection segment with an opening rate of 40% according to the present invention. DETAILED DESCRIPTION

[0059] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application are further described in detail below.

[0060] Example 1

[0061] A method for determining the precast concrete retaining wall of artificial bored piles under non-uniform confining pressure, the process of the method is as follows: Figure 1 , including the following steps:

[0062] Step 1: The diameter of the bored pile to be designed is 1.2m, and the pile hole depth is 16m; the number of precast concrete retaining wall single-ring segments is initially determined to be 3, the vertical height of a single retaining wall is 500mm, the thickness is 0.6m, the opening rate is 40%, and the concrete strength grade is C50.

[0063] Step 2: Select the uneven coefficient of action according to the soil conditions and establish the uneven confining pressure equation on the wall segment. The uneven confining pressure distribution is approximately expressed by a function, and the load curve is as follows: Figure 2 As shown,

[0064] The distribution curve of the non-uniform confining pressure equation is q k =q A (1+msinα)

[0065] In the formula, q k is the lateral earth pressure at each point on the retaining wall; q A is the minimum lateral pressure, where point A is located at the intersection of the horizontal line passing through the center of the retaining wall and the retaining wall; α is the angle between the line connecting the calculation point of the lateral earth pressure on the retaining wall and the center of the retaining wall and the horizontal line passing through the center of the retaining wall; m is the load non-uniform distribution coefficient, m = 0 means that the load is evenly distributed, where the value of m is determined according to the soil characteristics and the smoothness of the hole wall. When the soil is silt, clay and the hole wall is relatively flat and regular, m is 0-0.5; when the soil is gravel soil, miscellaneous fill or the hole wall is not very flat and regular, m is 1.0;

[0066] The lateral pressure acting on the retaining wall is q B =K'Σγ i h i

[0067] In the formula, q B is the maximum lateral pressure, where point B is located at the intersection of the vertical line through the center of the retaining wall and the retaining wall; K is the lateral earth pressure coefficient of the retaining wall; γ i is the weight of the i-th layer of soil above the calculation point of the lateral earth pressure on the retaining wall, and the soil weight is unified to γ ​​= 25 kN / m 3 ;h i is the thickness of the i-th soil layer above the calculation point of the lateral earth pressure on the retaining wall, h = 16m;

[0068] in K0, K a are the static earth pressure and active earth pressure coefficient acting on the retaining wall, K = 0.325;

[0069] q B =K'γh=0.325×25×16×500 / 220=295.455kPa

[0070] The actual height of the pipe segment is 500mm, the height of a single opening is 140mm, and the calculated height of the pipe segment is 220mm. B During calculation, the load on the actual height of the segment is evenly distributed to the calculated height portion without openings.

[0071] When α=90°, we can find

[0072] The proposed site is clay soil, and it is easy to ensure the regularity of the hole wall during construction, with the coefficient of unevenness m=0.5.

[0073] Step 3: Consider the retaining wall as a closed ring subjected to symmetrical non-uniform pressure, and establish a calculation model of the precast concrete assembled retaining wall structure under non-uniform confining pressure, such as Figure 3 shown.

[0074] Step 4: Conduct stress analysis on the precast concrete prefabricated wall structure under non-uniform confining pressure. The internal forces at points A and B can be obtained from the non-uniform confining pressure equation:

[0075] N A =Tq A b(1+0.7854m)

[0076] Where N A is the axial force on section A (kN), T is the vertical calculated height of the retaining wall (m), T is taken as 0.22m, b is the outer radius of the retaining wall (m), b is taken as 0.66m;

[0077] NB =Tq A b(1+0.5m)

[0078] Where N B is the axial force on section B (kN);

[0079] M A =-0.1488Tq A b 2 m

[0080] Where M A is the bending moment on section A (kN·m);

[0081] M B =-0.1366Tq A b 2 m

[0082] Where M B is the bending moment on section B (kN·m).

[0083] The internal forces of precast concrete wall segments are shown in Table 1.

[0084] Table 1 Internal forces of precast concrete wall segments

[0085]

[0086] The schematic diagram of the loading of the precast concrete assembled wall segment model is as follows: Figure 4 As shown, Figure 4 The load distribution curve function is q k =q A (1+msinα),α∈[0,π],q k =q A (1-msinα),α∈[-π,0], where m is the load non-uniform distribution coefficient, and the value of m is 0.5.

[0087] Step 5: Under the action of non-uniform confining pressure, the precast concrete assembled retaining wall section generates bending moment and axial force under load. The thickness of the retaining wall section can be determined based on the calculation theory of eccentrically compressed components, combined with factors such as concrete strength grade, bending moment size and reinforcement area. The cross-sectional force analysis is as follows: Figure 5 shown.

[0088] N≤N u =α1f c bx-f y A s

[0089] Where, N is the design value of axial pressure, N u is the ultimate bearing capacity under axial compression, α1 is the equivalent rectangular stress diagram coefficient of the concrete compression zone, fc is the design value of concrete axial compressive strength, b is the width of the rectangular section, x is the height of the concrete compression zone, f y is the design value of steel bar tensile strength, A s is the reinforcement area;

[0090]

[0091] Where N is the design value of the axial pressure, e is the distance between the axial pressure point and the longitudinal tensile reinforcement force point, M u is the design value of the ultimate resistance moment of the positive section, h0 is the effective height of the section;

[0092] Calculate the eccentricity:

[0093] Where M mzx is the maximum design bending moment value, N max is the maximum design axial force value;

[0094] Additional eccentricity:

[0095] Initial eccentricity: e i =e0+e a

[0096] Determine bias category: e i =e0+e a >0.3h0 is large bias

[0097]

[0098] e i =e0+e a ≤0.3h0 is small bias

[0099]

[0100] Where, β1 is the conversion height coefficient of the equivalent rectangular stress diagram of the concrete compression zone;

[0101]

[0102] Where ξ is the relative height of the compression zone, b is the relative height of the compression zone;

[0103]

[0104] In the formula, ρ min is the minimum reinforcement ratio and h is the section height.

[0105] The equivalent rectangular stress diagram coefficient of the compression zone of C50 concrete is α1=1.00, and the design value of the strength of C50 concrete is fc =23.1N / mm 2 . Design value of steel bar tensile strength f y =270N / mm 2 , calculated section height h = 60mm, calculated section width b = 220mm, minimum reinforcement ratio ρ m i n =0.2%.

[0106] e a =20mm

[0107] e i =e0+e a =35.15+20=55.15mm

[0108] h0=35mm,e i >0.3h0 is large bias

[0109]

[0110] The height of the concrete compression zone is x = 16 mm, and the axial pressure design value N is N A =39.83kN.

[0111] The final segment design parameters are shown in Table 2.

[0112] Table 2 Design parameters of precast concrete wall segments

[0113]

[0114] Step 6: The above design meets the parameter selection requirements in the "Concrete Structure Design Standard" (GB / T50010-2010).

[0115] Figure 6 The circumferential stress distribution cloud diagram of the precast concrete segment with an opening ratio of 40% and an m value of 0.5 is shown in the figure. Figure 6 It can be seen that under this load and structural design parameter conditions, the maximum compressive stress of the segment is 8.53MPa and the maximum tensile stress is 1.423MPa, both of which are less than the maximum compressive strength and tensile strength of C50 concrete, and can meet the design requirements.

[0116] The above-mentioned design and calculation principles of the present invention and the advantages of the present invention. Any simple modification, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention belong to the protection scope of the present invention.

Claims

1. A method for determining a precast concrete retaining wall of a bored pile under non-uniform confining pressure, characterized in that: The following steps are involved: Step 1: Preliminarily determine the number of components, thickness, height and opening ratio of precast concrete wall segments according to the length, diameter and soil properties of the bored piles; Step 2: Select the load non-uniform distribution coefficient according to the soil conditions and establish the non-uniform confining pressure equation on the wall segment; Step 3: Establish a calculation model of precast concrete prefabricated wall protection structure under non-uniform confining pressure; Step 4: Conduct stress analysis of precast concrete prefabricated wall protection structure under non-uniform confining pressure; Step 5: Determine the reinforcement design of precast concrete prefabricated wall segment under non-uniform confining pressure; Step 6: If the wall thickness and opening ratio do not meet the reinforcement design requirements, adjust the wall thickness, opening ratio or steel bar arrangement parameters until the reinforcement design meets the design requirements.

2. The determination method according to claim 1, characterized in that: The number of precast concrete wall segments in step 1 is 3 to 6, wherein the diameter of the bored pile is less than 1.2m, 3 segments are used, the diameter is 1.2m to 1.8m, 4 segments are used, the diameter is 1.8m to 2.2m, 5 segments are used, and the diameter is greater than 2.2m, 6 segments; the thickness of the segment is not less than 60cm, the length of the bored pile is 60cm when it is less than 20m, and 80cm when it is greater than 20m; the height of the segment is 50cm under the geological conditions of silt and silty clay, and 20cm under the geological conditions of sand, gravel, soft soil and miscellaneous fill; the opening rate of the segment is not less than 40%, 40%-50% for soft soil, and up to 60% for hard soil.

3. The determination method according to claim 2, characterized in that: In step 2, the load non-uniform distribution coefficient is selected according to the soil conditions, and the steps to establish the non-uniform confining pressure equation on the wall segment are: The distribution curve of the non-uniform confining pressure equation is: q k =q A (1+msinα) In the formula, q k is the lateral earth pressure at each point on the retaining wall; q A is the minimum lateral pressure, where point A is located at the intersection of the horizontal line passing through the center of the retaining wall and the retaining wall; α is the angle between the line connecting the calculation point of the lateral earth pressure on the retaining wall and the center of the retaining wall and the horizontal line passing through the center of the retaining wall; m is the coefficient of load non-uniform distribution, m = 0 means that the load is evenly distributed, where the value of m is determined according to the soil characteristics and the smoothness of the hole wall. When the soil is silt, clay and the hole wall is relatively flat and regular, m is 0-0.5; when the soil is gravel soil, miscellaneous fill or the hole wall is not very flat and regular, m is 1.0; The lateral pressure acting on the retaining wall is: q B =K'∑γ i h i In the formula, q B is the maximum lateral pressure, where point B is located at the intersection of the vertical line through the center of the retaining wall and the retaining wall; K is the lateral earth pressure coefficient of the retaining wall; γ i h is the weight of the i-th layer of soil above the calculation point of the lateral earth pressure on the retaining wall; i is the thickness of the i-th soil layer above the calculation point of the lateral earth pressure on the retaining wall; When α=90° 4. The determination method according to claim 3, characterized in that: In step 2, the lateral earth pressure coefficient of the retaining wall is K0, K a are the static earth pressure and active earth pressure coefficient acting on the retaining wall, respectively.

5. The determination method according to claim 3, characterized in that: When establishing the calculation model of the precast concrete assembled wall retaining structure under non-uniform confining pressure in step 3, the retaining wall is regarded as a closed circular ring subjected to symmetrical non-uniform pressure, and the calculation model of the precast concrete assembled wall retaining structure under non-uniform confining pressure is established.

6. The determination method according to claim 5, characterized in that: Step 4 is to carry out stress analysis of the precast concrete assembled wall protection structure under the action of non-uniform confining pressure, where the internal forces at points A and B are: OF A =Tq A b(1+0.7854m) Where N A is the axial force on section A (kN), T is the vertical calculated height of the retaining wall (m), and b is the outer radius of the retaining wall (m); <h2 style=";text-align:left;direction:ltr">N<h2 style=";text-align:left;direction:ltr"> B <h2 style=";text-align:left;direction:ltr"> =Tq<h2 style=";text-align:left;direction:ltr"> A <h2 style=";text-align:left;direction:ltr"> b(1+0.5m) Where N B is the axial force on section B (kN); M A =-0.1488Tq A b 2 m Where M A is the bending moment on section A (kN·m); M B =-0.1366Tq A b 2 m Where M B is the bending moment on section B (kN·m).

7. The determination method according to claim 6, characterized in that: The reinforcement design process of the precast concrete assembled wall segment under the action of non-uniform confining pressure described in step 5: Under the action of non-uniform confining pressure, the precast concrete assembled wall section generates bending moment and axial force under the action of load. According to the calculation theory of eccentrically compressed components, combined with the concrete strength grade and the bending moment size, the segment reinforcement is determined. The process is as follows: N≤N u =α1f c bx-f y A s Where N is the design value of axial pressure, N u is the ultimate bearing capacity under axial compression, α1 is the equivalent rectangular stress diagram coefficient of the concrete compression zone, f c is the design value of concrete axial compressive strength, b is the width of the rectangular section, x is the height of the concrete compression zone, f y is the design value of steel bar tensile strength, A s is the reinforcement area; Where N is the design value of the axial pressure, e is the distance between the axial pressure point and the longitudinal tensile reinforcement force point, M u is the design value of the ultimate resistance moment of the positive section, h0 is the effective height of the section; Calculate the eccentricity: Where M mzx is the maximum design bending moment value, N max is the maximum design axial force value; Additional eccentricity: Initial eccentricity: e i =e0+e a Determine bias category: e i =e0+e a >0.3h0 is large bias e i =e0+e a ≤0.3h0 is small bias Where, β1 is the conversion height coefficient of the equivalent rectangular stress diagram of the concrete compression zone; Where ξ is the relative height of the compression zone, b is the relative height of the compression zone; In the formula, ρ min is the minimum reinforcement ratio and h is the section height.

8. The determination method according to claim 7, characterized in that: When the reinforcement area is too large and does not meet the structural requirements according to the specifications, the wall section thickness is increased or the concrete strength grade is increased or the opening ratio is reduced, and the reinforcement area is recalculated until the force requirements are met.

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