Design method of directional maintenance ladder for storage tank and maintenance ladder

Abstract

The invention discloses a design method of a directional maintenance ladder for a storage tank and a maintenance ladder. The maintenance ladder comprises a lower bearing platform and an upper bearing platform installed above the lower bearing platform, an elastic flat plate sliding support is arranged between the lower bearing platform and the upper bearing platform, wind load limiting columns are arranged at the two ends of the upper bearing platform, and limiting short columns used for limiting are arranged at the two ends above the lower bearing platform; earthquake limiting brackets used for preventing overturning are arranged on the inner sides of the limiting short columns, and a plurality of steel ladder steel columns used for fixing the LNG storage tank are arranged in the middle of the upper bearing platform; the method comprises the following steps: S1, setting parameters of the storage tank limiting maintenance ladder; s2, setting boundary conditions; s3, inputting the parameters in the S1 and the boundary conditions in the S2 into finite element software to extract shearing force and uplift force borne by the limiting short column; and S4, calculating a limiting short column, an earthquake limiting bracket and a wind load limiting column. According to the design method, the overall overhaul ladder can be prevented from overturning; the problem that when the LNG storage tank displaces, the overhauling ladder is greatly deformed and even damaged is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of petrochemical industrial construction technology, specifically to a design method and maintenance ladder for storage tanks. Background Technology

[0002] As the core storage facility for cryogenic natural gas, most LNG storage tanks are now equipped with seismic isolation bearings, commonly lead-core rubber bearings and high-damping seismic isolation bearings. These bearings, designed to meet the heavy load and seismic resistance requirements of the tanks, have high stiffness values, significantly exceeding the stiffness of the superstructure above the tank's elevator. Since the seismic isolation bearings must exceed their own stiffness limits to produce effective deformation, when the LNG storage tank shifts under conditions such as earthquakes, regardless of whether the tank is equipped with these types of seismic isolation bearings or not, the elevator will experience significant structural deformation due to stiffness mismatch, potentially even leading to damage to elevator components. The "Code for Design of Liquefied Natural Gas Receiving Terminal Engineering" GB51156-2015 clearly stipulates that the auxiliary structures of LNG storage tanks should be designed according to the Operating Basis Earthquake (OBE). Under the OBE, the horizontal displacement of LNG storage tanks using seismic isolation technology (generally above 0.15g for seismic fortification intensity of 7 degrees) can reach 200mm to 400mm. However, according to the requirements of the "Standard for Seismic Isolation Design of Buildings" GB / T51408-2021, LNG storage tanks should also consider the horizontal displacement under rare earthquakes (SSE). Under rare earthquakes (SSE), the displacement of LNG storage tanks can reach 400mm to 600mm, which will cause the LNG storage tank elevators that do not adopt directional horizontal movement technology to undergo large deformations that they cannot adapt to, resulting in irreparable damage. Summary of the Invention

[0003] This invention addresses the problems in existing technologies by disclosing a design method and a maintenance ladder for storage tanks. The invention limits the horizontal displacement of the maintenance ladder by setting a limiting structure and designing the parameters of the limiting structure. This allows the maintenance ladder manufactured according to this method to, under extreme weather conditions, limit the small displacement sliding of the sliding support against its own friction through wind load limiting columns, and under seismic loading, limit the large displacement sliding of the sliding support against its own friction through seismic limiting brackets and limiting short columns, preventing the entire maintenance ladder from overturning. This effectively avoids the problem of significant deformation or even damage to the maintenance ladder when the LNG storage tank shifts.

[0004] This invention is achieved through the following technical solution:

[0005] This invention first provides a design method for a directional maintenance ladder for storage tanks. The maintenance ladder includes a lower support platform and an upper support platform installed above it. An elastic flat sliding support is provided between the lower support platform and the upper support platform. Wind load limiting columns are provided at both ends of the upper support platform for limiting the position. Short limiting columns are provided at both ends of the lower support platform for limiting the position. Seismic limiting brackets for preventing overturning are provided on the inner side of the short limiting columns. Several steel ladder columns for fixing LNG storage tanks are provided in the middle of the upper support platform.

[0006] The method includes the following steps:

[0007] S1. Determine the parameters of the tank limit maintenance ladder under a custom load condition;

[0008] S2, Set boundary conditions;

[0009] S3. Input the parameters in S1 and the boundary conditions in S2 into the finite element software to generate a finite element model for structural analysis, and extract the shear force V1 and the upward pull force F1 on the limiting short column.

[0010] S4. Calculate the data information of the limiting short column, the seismic limiting corbel, and the wind load limiting column.

[0011] As a further option, the custom load cases in S1 include: dead load, live load, wind load, seismic load, and temperature load.

[0012] As a further option, the parameters for determining the tank-limiting maintenance ladder in S1 include the transverse column spacing of the limiting short columns, the longitudinal column spacing of the limiting short columns, the shortest distance between the maintenance ladder and the outer edge of the tank, the total height and total number of floors of the maintenance ladder, the concrete material strength, the steel grade of the steel components, the basic wind pressure value A, the ground roughness category C1, the seismic fortification group C2, the fortification intensity C3, the site category C4, the characteristic period Tg, and the parameters of the elastic sliding support.

[0013] As a further option, the boundary conditions in S2 include

[0014] S21. Install steel supports, with both ends of the steel supports hinged to the steel ladder and steel column, and the LNG storage tank, respectively.

[0015] S22. The direction of the seismic limiting bracket is set perpendicular to the direction of the LNG storage tank;

[0016] S23. The upper and lower supports are set in a direction parallel to the LNG storage tank.

[0017] As a further option, the calculation method in S4 includes:

[0018] S41. Calculate the reinforcement of the limiting short column;

[0019] S42. Calculate the cross-sectional reinforcement of the seismic restraint bracket;

[0020] S43. Calculate the reinforcement of the wind load limiting column.

[0021] As a further option, the specific methods of S41 include:

[0022] S411. Calculate the longitudinal reinforcement of the limiting short column:

[0023] (1) Calculate the relative limit pressure zone height ξ b The specific formula is as follows:

[0024] in,

[0025] β1 is a coefficient; f y E represents the design tensile strength of the reinforcing steel. s ε is the elastic modulus of the steel reinforcement; cu ε represents the ultimate compressive strain of concrete under non-uniform compression. cu =0.0033-(f cu,k -50)×10 -5 If the value is greater than 0.0033, then ε is taken. cu =0.0033;

[0026] (2) Calculate the reinforcement area A of the compression zone. s The specific formula is as follows:

[0027]

[0028] Where M1 is the design bending moment; α1 is a coefficient; f c ξ is the design value of the axial compressive strength of concrete; b is the width of the concrete column; h0 is the effective height of the section; b f represents the relative height of the limit pressure zone. y This refers to the design tensile strength of the reinforcing steel; a s ′ represents the thickness of the protective layer;

[0029] (3) Calculate the reinforcement area As in the tension zone using the following formula:

[0030]

[0031] Where α1 is the coefficient; f c b is the design value of the axial compressive strength of concrete; h0 is the width of the concrete column; f is the effective height of the section; y ′ represents the design value of compressive strength; A s ′ Reinforcement area in the compression zone; N is the axial force; f y This refers to the design value of the tensile strength of the reinforcing steel.

[0032] S412. Calculate the stirrup reinforcement of the limiting short column:

[0033] (1) The concrete column with a rectangular cross-section of the limit short column shall meet the following conditions:

[0034] When hw / b < 4, the maximum shear design value Vx of the component cross-section needs to satisfy:

[0035] Vx ≤ 0.25β c f c bh0, (4);

[0036] Where, hw is the web height of the cross-section; b is the width of the rectangular cross-section; h0 is the effective height of the cross-section; β c is the concrete cross-section influence coefficient; f c is the design value of the axial compressive strength of concrete;

[0037] (2) When the limit short column meets the following requirements, the calculation of the shear bearing capacity S1 of the inclined section may not be carried out:

[0038]

[0039] Where, V1 is the shear design value; λ x is the shear span ratio of the calculated cross-section, that is, M / (Vh0); f t is the design value of the axial tensile strength of concrete; b is the width of the rectangular cross-section; h0 is the effective height of the cross-section; N is the axial force. When N is greater than 0.3f c A, take N = 0.3f c A, A is the cross-sectional area;

[0040] (3) If S1 < V1, the calculation of the shear bearing capacity S1 of the inclined section needs to be carried out, and the following formula should be satisfied:

[0041]

[0042] Where, A svx is the total cross-sectional area of all limbs of the stirrups arranged in the cross-section; S is the stirrup spacing along the length direction of the component; V1 is the shear design value; λ x is the shear span ratio of the calculated cross-section, that is, M / (Vh0); f t is the design value of the axial tensile strength of concrete; b is the width of the rectangular cross-section; h0 is the effective height of the cross-section; N is the design value of the axial pressure. When it is greater than 0.3f c A, take 0.3f c A, A is the cross-sectional area; f yv is the design value of the tensile strength of the stirrups.

[0043] As a further solution, the specific method of S42 includes:

[0044] S421. Calculate the local compression on the top surface of the seismic limit bracket, and the calculation formula is as follows:

[0045]

[0046] Where F1 is the standard value of the horizontal load; A b The calculated base area is for localized compression;

[0047] S422. Calculate the area of ​​the longitudinal reinforcing steel bars in the seismic restraint bracket:

[0048]

[0049] Where F1 is the design value of the vertical force acting on the corbel; Fh is the design value of the horizontal tension acting on the corbel; a is the horizontal distance from the point of application of the vertical force to the edge of the lower column; f y h0 is the design tensile strength of the reinforcing steel; h0 is the effective height of the section.

[0050] S423. Calculate the cross-sectional area of ​​the horizontal stirrups and bent-up bars at the top of the seismic limiting bracket;

[0051] (1) The cross-sectional calculation of horizontal reinforcement should meet the following requirements:

[0052] Among them, A sh lg is the cross-sectional area of ​​the horizontal stirrups; h0 is the effective height of the cross-section; lg is the stirrup spacing; A sv The area of ​​a single stirrup;

[0053] (2) When the shear span ratio of the corbel is not less than 0.3, bent-up bars should be provided, and the cross-sectional area of ​​the bent-up bars should meet the following requirements:

[0054] A sb >0.5A s1 (10);

[0055] Among them, A s1 Indicates the area of ​​steel reinforcement in the tension zone;

[0056] S424. Calculate crack control for seismic restraint brackets:

[0057]

[0058] Where F1 is the vertical force value acting on the top of the corbel, calculated according to the standard combination of load effects; F hk The horizontal tensile force acting on the top of the corbel, calculated according to the standard combination of load effects; a is the horizontal distance from the point of application of the vertical force to the edge of the lower column; b is the width of the corbel; f tk f is the standard value of the axial tensile strength of concrete; y β is the design value of the tensile strength of the steel reinforcement; β is the crack control coefficient; h0 is the effective height of the section.

[0059] As a further step, the specific steps of S43 include:

[0060] S431. Calculate the longitudinal reinforcement of the wind load limiting column;

[0061] S432. Calculate the stirrup reinforcement of the wind load limiting column.

[0062] The present invention also provides a maintenance ladder, including a limiting structure, which is manufactured using the design method of the directional maintenance ladder for storage tanks described above.

[0063] As a further embodiment, the maintenance ladder also includes a camera for monitoring the horizontal displacement of the elastic flat sliding support, and the camera signal is connected to an external control room.

[0064] The features and beneficial effects of this invention are as follows:

[0065] (1) This invention limits the horizontal displacement of the maintenance ladder by setting a limiting structure and designing the parameters of the limiting structure, so that the maintenance ladder made according to this method can limit the sliding support to make small displacement sliding against its own friction under extreme weather conditions by wind load limiting columns, and limit the sliding support to make large displacement sliding against its own friction under earthquake action by earthquake limiting brackets and limiting short columns, thus preventing the maintenance ladder from overturning as a whole; effectively avoiding the problem of large deformation or even damage to the maintenance ladder when the LNG storage tank is displaced.

[0066] (2) The present invention monitors the horizontal displacement value of the directional plate sliding support in real time through the camera and transmits it to the external control room, which serves as an early warning function. Attached Figure Description

[0067] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0068] Figure 1 This is a flowchart illustrating the design method of a directional maintenance ladder for storage tanks according to an embodiment of the present invention;

[0069] Figure 2 This is a schematic diagram of the maintenance ladder according to an embodiment of the present invention;

[0070] Figure 3 for Figure 2 Enlarged view of section A;

[0071] Figure 4 for Figure 3 Side view;

[0072] Figure 5 This is a schematic diagram of the support structure for the maintenance ladder and storage tank according to an embodiment of the present invention.

[0073] Explanation of reference numerals in the attached figures:

[0074] 1-Steel ladder short column; 2-Earthquake limiting bracket; 3-Limiting short column; 4-Upper pile cap; 5-Wind load limiting column; 6-Pile cap short column; 7-Lower pile cap; 8-Foundation pile; 9-Embedded part; 10-Camera; 11-Sliding bearing; 12-LNG storage tank; 13-Steel ladder steel column; 14-Steel support. Detailed Implementation

[0075] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0076] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0077] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0078] In the engineering field, existing maintenance ladders utilize lead-core rubber seismic isolation bearings or high-damping seismic isolation bearings. However, these bearings share a common characteristic: their inherent stiffness is sufficiently high. Consequently, during large vibrations or earthquakes, the steel frame above the bearings fails preferentially before the bearings deform. Therefore, we need a method to design a directional maintenance ladder with a limiting function. This ladder would limit the movement of the storage tank, preventing it from undergoing significant displacement or overturning under extreme weather or earthquake conditions, and minimizing damage to the tank and its auxiliary equipment. This application provides a design method for a directional maintenance ladder for storage tanks. The directional maintenance ladder manufactured using this method is suitable for different installation environments and requirements of storage tanks. It adopts a lower support, seismic limiting bracket, limiting short column, and wind load limiting column working together. Under extreme weather conditions, the wind load limiting column restricts the sliding support from small displacement sliding due to its own friction. Under seismic action, the seismic limiting bracket and limiting short column restrict the sliding support from large displacement sliding due to its own friction, preventing the maintenance ladder from overturning. This effectively avoids the problem of large deformation or even damage to the maintenance ladder when the LNG storage tank is displaced.

[0079] like Figures 1 to 5 As shown, a design method for a directional maintenance ladder for a storage tank is provided. The maintenance ladder includes a lower support platform 7 and an upper support platform 4 installed above it. An elastic flat sliding support 11 is provided between the lower support platform 7 and the upper support platform 4. Wind load limiting columns 5 are provided at both ends of the upper support platform 4 to limit the upper support platform under extreme weather conditions. Short limiting columns 3 are provided at both ends above the lower support platform 7 to limit the upper support platform under seismic conditions. Seismic limiting brackets 2 for preventing overturning are provided on the inner side of the short limiting columns. Several steel ladder columns for fixing LNG storage tanks 12 are provided in the middle of the upper support platform 4.

[0080] The method includes the following steps:

[0081] S1. Set a custom load condition and design the parameters of the tank limit maintenance ladder under the custom load condition;

[0082] S11. Due to wind, earthquakes, temperature and occasional adverse conditions of the storage tank, the maintenance ladder column base may experience large horizontal displacement. Therefore, the custom load conditions include: dead load, live load, wind load, seismic load, temperature load, etc.

[0083] To achieve a more rational design, maximize the utilization of forces, and simplify the structure, this method includes the following working conditions:

[0084] (1) Dead load + live load;

[0085] (2) Dead load + live load + wind load;

[0086] (3) Dead load + live load + wind load + seismic load (OBE / SSE);

[0087] (4) Dead load + live load + temperature load (normal use / extreme conditions);

[0088] (5) Other unfavorable horizontal displacement conditions caused by accidental operating conditions of the storage tank body (such as large leakage).

[0089] S22, The parameters of the tank limit maintenance ladder include:

[0090] The parameters include: transverse spacing of limiting short columns, longitudinal spacing of limiting short columns, shortest distance of the maintenance ladder from the outer edge of the storage tank, total height and number of floors of the maintenance ladder, concrete material strength, steel grade of steel components, basic wind pressure value A, ground roughness category C1, seismic fortification group C2, fortification intensity C3, site category C4, characteristic period Tg, and parameters of the sliding bearing. The parameters of the elastic plate sliding bearing include: initial stiffness K0, dynamic friction coefficient μ, vertical stiffness K1, first shape factor S1, second shape factor S2, and ultimate compressive strength f0 of the sliding material. The initial stiffness K0 is determined by... The dynamic friction coefficient μ directly affects the seismic isolation effect and energy dissipation capacity. The initial stiffness and the dynamic friction coefficient together determine the turning point of the seismic isolation performance. The vertical stiffness K1 controls the vertical deformation and stability of the structure. If the value is insufficient, it may lead to the instability of the sliding support or damage to the internal steel plate. The first shape factor S1 affects the vertical stiffness and vertical bearing capacity of the support, while the second shape factor S2 affects the buckling resistance and horizontal stiffness of the support. The ultimate compressive strength f0 of the sliding material determines the safety of the support under extreme loads.

[0091] S2. Considering the direction of force propagation and to avoid wasting force, the following boundary conditions are set:

[0092] S21. A steel support 14 is provided, and the two ends of the steel support 14 are respectively hinged to the steel ladder and steel column 13 and the LNG storage tank 12, so that the steel ladder and steel column 13 can not only support and fix the LNG storage tank 12 through the steel support 14, but also give the LNG storage tank 12 a margin of freedom of movement, effectively avoiding damage to the connection between the two due to slight vibration.

[0093] S22. Considering the direction of force and the direction of limit, there is no risk of overturning in the direction perpendicular to the LNG storage tank, but there may be a risk of overturning in the direction parallel to the LNG storage tank. Therefore, the direction of the seismic limit bracket 2 is set to be perpendicular to the direction of the LNG storage tank 12.

[0094] S23. Considering the impact of extreme weather on the LNG storage tank and maintenance ladder itself, the upper support platform 4 and the lower support platform 7 are set in a direction parallel to the LNG storage tank.

[0095] S3. Input the parameters from S1 and the boundary conditions from S2 into the finite element software to generate a finite element model for structural analysis.

[0096] Finite element components can be PKPM, Yingjianke, SAP2000, etc.

[0097] Taking PKPM as an example: Input the above parameters into the upper structural unit, click preprocessing calculation, and the calculation is completed. Extract the data from the finite element model in the "Postprocessing Module Internal Force Results": Extract the shear force V1 and the upward pull force F1 (unit kN) of the limiting short column 3, where the bending moment M1 = V1 * L, and L represents the distance from the upper edge of the upper bearing to the lower edge of the upper bearing.

[0098] S4. Manually calculate the cross-section and reinforcement of limiting short columns, seismic limiting corbels, and wind load limiting columns.

[0099] S41. Calculate the reinforcement of the restrained short column:

[0100] S411. Calculate the longitudinal reinforcement of the limiting short column:

[0101] (1) Calculate the relative limit pressure zone height ξ b The specific formula is as follows:

[0102] in,

[0103] β1 is a coefficient; f y E represents the design tensile strength of the reinforcing steel. s ε is the elastic modulus of the steel reinforcement; cu ε represents the ultimate compressive strain of concrete under non-uniform compression. cu =0.0033-(f cu,k -50)×10 -5 If the value is greater than 0.0033, then ε is taken. cu =0.0033;

[0104] From formula (1), it can be seen that the ultimate compressive strain ε of concrete under non-uniform compression is cu It is related to the strength of concrete materials, and ε cu The maximum value is 0.0033. Therefore, when selecting the strength of concrete materials, as long as the above conditions are met, the selected materials can easily meet the above requirements; when selecting the tensile design value f of the steel reinforcement, y When the height of the relative limit compression zone ξ increases, b It will decrease, depending on the elastic modulus E of the selected steel reinforcement. s As the value increases, the relative height of the boundary pressure zone ξ b The tensile design value f of the steel bar will increase, but if the same steel bar is used, the tensile design value f of the steel bar will increase. y and elastic modulus E sSince the value is fixed, the type of steel reinforcement is determined first, and then the concrete material is selected based on the usage environment of the maintenance ladder. This makes it easy to determine the relative limit compression zone height of the limiting short column.

[0105] (2) Calculate the reinforcement area A of the compression zone. s The specific formula is as follows:

[0106]

[0107] Where M1 is the design bending moment; α1 is a coefficient; f c ξ is the design value of the axial compressive strength of concrete; b is the width of the concrete column; h0 is the effective height of the section; b f represents the relative height of the limit pressure zone. y This refers to the design tensile strength of the reinforcing steel; a s ′ represents the thickness of the protective layer; from formula (2), it can be seen that the relative height of the boundary pressure zone ξ b When the height is higher, the reinforcement area A of the compression zone is increased. s ′ will increase, as can be seen from formula (1), when the relative limit pressure zone height ξ b The premise is that both the steel reinforcement and concrete materials are determined. The above parameters have already been determined in formula (1). Therefore, the design value of the axial compressive strength of concrete, f, is... c and the tensile design value f of steel reinforcement y It will also be determined that; the larger the width b of the concrete column, the larger the reinforcement area A of the compression zone. s The smaller the angle, the larger the effective height h0 of the cross section, and the larger the reinforcement area A in the compression zone. s The smaller the value of ′, the larger the width and height of the limiting short column, and the larger the area of ​​reinforcement A in the compression zone. s The smaller the value of ', the more reasonable the width and height of the limiting short column can be determined according to the actual situation, while the thickness of the protective layer 'a' is... s The thicker the layer, the larger the area of ​​reinforcement A in the compression zone. s The larger the angle ′, the greater the thickness of the protective layer a. s When the conditions are met, the reinforcement area A of the compression zone can be finely adjusted. s When the design bending moment M1 increases, the reinforcement area A in the compression zone increases. s ′ will increase accordingly.

[0108] (3) Calculate the reinforcement area As in the tension zone using the following formula:

[0109]

[0110] Where α1 is the coefficient; f c b is the design value of the axial compressive strength of concrete; h0 is the width of the concrete column; f is the effective height of the section; y′ is the design value of compressive strength; A s ′ is the area of longitudinal reinforcement in the compression zone; N is the axial force; f y is the design value of tensile strength of steel bars. As can be seen from the above, all parameters in formula (3) except the axial force N have been determined. When the axial force N increases, the area of longitudinal reinforcement As in the tension zone will decrease, and when the axial force N decreases, the area of longitudinal reinforcement As in the tension zone will increase. Therefore, for the increase or decrease of the area of longitudinal reinforcement As in the tension zone, the axial force N is the key parameter.

[0111] S412. Calculate the stirrup reinforcement of the limited short column:

[0112] (1) The concrete column with a rectangular cross-section of the limited short column shall meet the following conditions:

[0113] When hw / b < 4, the maximum shear force design value Vx on the component cross-section needs to satisfy:

[0114] Vx ≤ 0.25β c f c bh0, (4);

[0115] where, hw is the web height of the cross-section; b is the width of the rectangular cross-section; h0 is the effective height of the cross-section; β c is the influence coefficient of the concrete cross-section; f c is the design value of the axial compressive strength of concrete; the remaining parameters have been determined in the above steps. The influencing parameter in formula (4) is the influence coefficient β c of the concrete cross-section. When this coefficient decreases, Vx will decrease accordingly, and this coefficient can determine the minimum value of Vx.

[0116] (2) When the limited short column meets the following requirements, the calculation of the shear bearing capacity S1 of the inclined section may not be carried out:

[0117]

[0118] where, V1 is the shear force design value; λ x is the shear span ratio of the calculated cross-section, that is, M / (Vh0); f t is the design value of the axial tensile strength of concrete; b is the width of the rectangular cross-section; h0 is the effective height of the cross-section; N is the axial force. When N is greater than 0.3f c A, take N = 0.3f c A, A is the cross-sectional area; As can be seen from the previous steps, when the value of λ x decreases, the shear bearing capacity S1 of the inclined section will increase, and when the value of λ x increases, the shear bearing capacity S1 of the inclined section will decrease.

[0119] (3) If S1 < V1, the calculation of the shear bearing capacity S1 of the inclined section needs to be carried out, and the following formula should be satisfied:

[0120]

[0121] Among them, A svx The total cross-sectional area of ​​each leg of the stirrups within the section; S is the stirrup spacing along the length of the member; V1 is the design shear force; λ x To calculate the shear span ratio of the cross section, i.e., M / (Vh0); f t denoted by , b is the design value of the axial tensile strength of concrete; b is the width of the rectangular section; h0 is the effective height of the section; N is the design value of the axial compressive strength, which is greater than 0.3f. c When A, take 0.3f. c A, where A is the cross-sectional area; f yv This is the design value for the tensile strength of the stirrups.

[0122] S42. Calculate the cross-sectional reinforcement of the seismic restraint bracket:

[0123] S421. Calculate the local compression on the top surface of the seismic restraint bracket. The calculation formula is as follows:

[0124]

[0125] Where F1 is the standard value of the horizontal load; A b The calculated base area is for localized compression;

[0126] S422. Calculate the area of ​​the longitudinal reinforcing steel bars in the seismic restraint bracket:

[0127] To ensure the safety and durability of the seismic restraint bracket under combined stress, the sum of the cross-sectional area of ​​the tensile reinforcement required to withstand vertical force and the cross-sectional area of ​​the reinforcement required to withstand horizontal tensile force should meet the following requirements:

[0128]

[0129] Where F1 is the design value of the vertical force acting on the corbel; Fh is the design value of the horizontal tension acting on the corbel; a is the horizontal distance from the point of application of the vertical force to the edge of the lower column; f y h0 is the design value of the tensile strength of the steel reinforcement; h0 is the effective height of the section.

[0130] S423. Calculate the cross-sectional area of ​​the horizontal stirrups and bent-up bars at the top of the seismic limiting bracket;

[0131] (1) Horizontal reinforcement bars should be provided for earthquake-resistant brackets, and the cross-sectional calculation of the horizontal reinforcement bars should meet the following requirements:

[0132]

[0133] Among them, A shlg is the cross-sectional area of ​​the horizontal stirrups; h0 is the effective height of the cross-section; lg is the stirrup spacing; A sv This represents the area of ​​a single stirrup.

[0134] (2) The cross-sectional area of ​​the stirrups within 2h0 / 3 of the upper part of the corbel should not be less than half of the cross-sectional area of ​​the tensile reinforcement bearing the vertical force; when the shear span ratio of the corbel is not less than 0.3, bent-up reinforcement should be provided, and the cross-sectional area of ​​the bent-up reinforcement should meet the following requirements:

[0135] A sb >0.5A s1 (10);

[0136] Among them, A s1 This indicates the area of ​​steel reinforcement in the tension zone.

[0137] S424. Calculate crack control for seismic restraint brackets:

[0138] To control crack width, ensure structural durability, and prevent concentrated crack propagation, it is necessary to verify the crack control of the seismic restraint bracket. The cracks in the bracket must meet the following requirements:

[0139]

[0140] Where F1 is the vertical force value acting on the top of the corbel, calculated according to the standard combination of load effects; F hk The horizontal tensile force acting on the top of the corbel, calculated according to the standard combination of load effects; a is the horizontal distance from the point of application of the vertical force to the edge of the lower column; b is the width of the corbel; f tk Standard value of axial tensile strength of concrete (N / mm²) 2 );f y β is the design value of the tensile strength of the steel reinforcement; β is the crack control coefficient; h0 is the effective height of the section.

[0141] S43. Calculate the reinforcement of the wind load limiting column:

[0142] S431. Calculate the longitudinal reinforcement of the wind load limiting column:

[0143] (1) Calculate the relative limit pressure zone height ξ b The specific formula is as follows:

[0144] in,

[0145] β1 is a coefficient; f y E represents the design tensile strength of the reinforcing steel. s ε is the elastic modulus of the steel reinforcement; cu ε represents the ultimate compressive strain of concrete under non-uniform compression. cu =0.0033-(f cu,k -50)×10-5 If the value is greater than 0.0033, then ε is taken. cu =0.0033;

[0146] (2) Calculate the reinforcement area A of the compression zone. s The specific formula is as follows:

[0147]

[0148] Where M1 is the design bending moment; α1 is a coefficient; f c ξ is the design value of the axial compressive strength of concrete; b is the width of the concrete column; h0 is the effective height of the section; b f represents the relative height of the limit pressure zone. y This refers to the design tensile strength of the reinforcing steel; a s ′ represents the thickness of the protective layer;

[0149] (3) Calculate the reinforcement area As in the tension zone using the following formula:

[0150]

[0151] Where h0 is the effective height of the cross-section; f y ′ represents the design value of compressive strength; A s ′ Reinforcement area of ​​the compression zone; M1 is the design bending moment; f y This refers to the design tensile strength of the reinforcing steel; a s ′ represents the thickness of the protective layer;

[0152] S432. Calculate the stirrup reinforcement of the wind load limiting column:

[0153] (1) Concrete columns with rectangular cross-sections that are wind load limiting columns should meet the following conditions:

[0154] When hw / b < 4, the maximum shear force design value Vx on the member section needs to satisfy:

[0155] Vx≤0.25β c f c bh0, (15);

[0156] Where hw is the web height of the cross section; b is the width of the rectangular cross section; h0 is the effective height of the cross section; β c f is the influence coefficient of the concrete section; c This is the design value for the axial compressive strength of concrete.

[0157] (2) When the wind load limiting column meets the following requirements, the calculation of the shear capacity S1 of the inclined section is not required:

[0158]

[0159] Among them, V1 is the shear design value; λ x is the shear span ratio of the calculated section, that is, M / (Vh0); f t is the design value of the axial tensile strength of concrete; b is the width of the rectangular section; h0 is the effective height of the section; N is the axial force. When N is greater than 0.3f c A, take N = 0.3f c A, A is the sectional area;

[0160] (3) If S1 < V1, it is necessary to calculate the shear bearing capacity S1 of the inclined section, and the following formula should be satisfied:

[0161]

[0162] Among them, A svx is the total sectional area of all limbs of the stirrups arranged in the section; S is the stirrup spacing along the length direction of the member; V1 is the shear design value; λ x is the shear span ratio of the calculated section, that is, M / (Vh0); f t is the design value of the axial tensile strength of concrete; b is the width of the rectangular section; h0 is the effective height of the section; N is the design value of the axial pressure. When it is greater than 0.3f c A, take 0.3f c A, A is the sectional area; f yv is the design value of the tensile strength of the stirrups.

[0163] An elastic plate sliding support 11 is provided between the lower bearing platform 7 and the upper bearing platform 4. The designed sliding displacement of the support is calculated according to the seismic conditions of the main structure LNG storage tank, etc. (1.2 times of OBE and 1.05 times of SSE) (the maximum horizontal displacement value in this patent is the larger value of 1.2 times of the maximum relative displacement of the storage tank calculated by OBE and 1.05 times of the maximum relative displacement of the storage tank calculated by SSE). The general displacement range is 0 - 600mm, and the dynamic friction coefficient is generally taken as 0.04 - 0.06. The frictional resistance is provided by the gravity load of the maintenance ladder and the friction coefficient, and this frictional resistance is used to resist the horizontal load under wind load or other non-seismic actions.

[0164] The provided elastic plate sliding support 11 will not move under normal service conditions, and will slide under extreme weather conditions or seismic actions. That is, when the horizontal force acting on the structure caused by seismic action or wind load exceeds the dynamic frictional force (the product of the sum of the upper structure load and the seismic overturning force and the dynamic friction coefficient), the support slides.

[0165] When an earthquake occurs, displacement constraints are carried out perpendicular to the direction of the steel ladder and the storage tank through the seismic limit bracket. At the same time, the seismic limit bracket also has an anti-overturning effect on the upper structure.

[0166] A design method for a directional maintenance ladder for storage tanks also includes a camera. The camera is used to monitor the horizontal displacement of the elastic flat plate sliding support and transmits the monitored information to the external control room in real time for early warning purposes.

[0167] This invention also protects a maintenance ladder designed using the aforementioned design method for directional maintenance ladders for storage tanks. The maintenance ladder includes a lower foundation 7, which is connected to the ground via multiple foundation piles 8. The middle section of the lower foundation 7 is connected to an upper foundation 4 via multiple short foundation columns 6 (bolted anchor connections). A sliding support 11 is installed between each short foundation column 6 and the upper foundation 4. Wind load limiting columns 5 are provided at both ends of the upper foundation 4 to limit its movement. A steel ladder is connected to the middle section of the upper foundation 4. Multiple steel ladder columns 13 are installed on column 1, and steel ladders are installed between the multiple steel ladder columns 13. The external structure is used to fix the LNG storage tank 12. At both ends above the lower support platform 7, there are limiting short columns 3 for limiting the upper support platform. Seismic limiting brackets 2 and cameras 10 are fixedly installed on the inner side of the limiting short columns 3. The seismic limiting brackets 2 are higher than the upper support platform 4 in the horizontal direction and are located outside the wind load limiting column 5. The camera 10 is located between the limiting short column 3 and the upper support platform 4 and transmits signals to the external control room through the signal.

[0168] Both the upper foundation 4 and the lower foundation 7 are rectangular plates, with their transverse centerlines coinciding and arranged parallel to the direction of the LN storage tank. Multiple foundation piles 8, multiple foundation short columns 6, and each group of limiting short columns 3 are arranged in two columns, A and B. The transverse centerlines of the foundation piles 8, foundation short columns 6, and limiting short columns 3 in the same column coincide, ensuring that the load-bearing and stress-bearing elements are located on the same vertical plane, maximizing the utilization of the supporting force. An earthquake-resistant limiting bracket 2 is installed inside each limiting short column 3; similarly, the earthquake-resistant limiting bracket 2 and the wind load limiting column 5 also coincide with the transverse centerline of the limiting short column 3. The lower foundation 7 is equipped with drainage channels to prevent rainwater accumulation and facilitate drainage.

[0169] Example

[0170] Basic information of the maintenance ladder for a 220,000 LNG storage tank:

[0171] There are a total of 8 short columns 6 on the foundation, arranged in groups of two. They are installed in 4 groups laterally on the lower foundation 7. The horizontal column spacing of each group of short columns 6 is 2400mm, 3000mm, and 6000mm, respectively. The longitudinal column spacing of the short columns 6 in the same group is 2600mm. The distance between the maintenance ladder and the outer edge of the storage tank is 10800mm. The total height of the maintenance ladder is 67.330m, with 19 floors above ground. The concrete material strength is C40, the steel component grade is Q355-B, the basic wind pressure is A=0.45kN / m2, the ground roughness category is C1=A, the seismic fortification group is C2=Group 3, the fortification intensity is C3=7 (0.15g), the site category is C4=Class II, and the characteristic period is Tg=0.45s. The elastic plate sliding uses model ESB400, and its support geometric design parameters are shown in Table 1 below:

[0172] Table 1

[0173] Serial Number parameter numerical values unit 1 <![CDATA[Initial stiffness K0]]> ≤13 kN / mm 2 Coefficient of kinetic friction μ 0.06 / 3 <![CDATA[Vertical stiffness K1]]> 5500 kN / mm 4 First shape factor S1 ≥30 / 5 Second shape factor S2 ≥7 / 6 <![CDATA[Ultimate compressive strength f0 of the sliding material]]> ≥80 MPa

[0174] The limiting short column 3 has dimensions of 800mm x 800mm and is 3500mm higher than the surface of the lower foundation. The cross-section of the seismic limiting bracket 2 is as follows: upper column width 800mm, lower column width 800mm, bracket width b = 800mm, bracket width beyond the lower column c = 900mm, bracket height h = 1400mm. The dimensions of the wind load limiting column are 300mm x 500mm. Based on the above parameters, a seismic isolation finite element model of the LNG storage tank maintenance ladder is established, in which the steel support is hinged to the storage tank and the steel support is hinged to the steel ladder.

[0175] Considering the building envelope, the wind load shape coefficient is taken as 1.5 in the X direction and 1.0 in the Y direction. Calculations using the finite element software PKPM show that the stress ratio and inter-story drift angle of the components meet the requirements. Finite element analysis yields the total weight of the escape ladder, m1 = 389150 kg; under extreme conditions, the total horizontal shear force in the X direction under wind load is 87 kN; the OBE state seismic influence coefficient is 0.26, therefore the seismic acceleration under moderate earthquake is a1 = 0.29g = 2.842 m / s². 2 Horizontal force V under moderate earthquake 中 =m1×a1=389150×2.842÷1000=1106kN.

[0176] The maximum shear force V1 under moderate earthquake (half the shear force borne by a single column) is obtained by the most unfavorable combination: 1.3 × constant force + 1.05 × live force + 0.3 × wind force + 1.4 × E.

[0177] V1=(1.3×0+1.05×0+0.3×87+1.4×1106)*0.5=788kN;

[0178] The maximum bending moment M1 = V1 * L = 788 kN * 1.5 m = 1182 kN.m.

[0179] The calculation process for each parameter of the maintenance ladder is as follows:

[0180] 1. Calculate the reinforcement of the short column with limiting:

[0181] 1.1 Calculate the longitudinal reinforcement of the limiting short column:

[0182] ε cu =0.0033-(f cu,k -50)×10 -5 =0.0033-(40-50)×10 -5 =0.00340>0.0033, take ε cu =0.0033;

[0183] (1) Relative height of the pressure zone:

[0184] (2) Calculate the reinforcement area A of the compression zone. s ′:

[0185] To minimize the total steel consumption, let the relative pressure zone height ξ = ξ b =0.52, then the reinforcement of the compression zone is:

[0186]

[0187] (3) Calculate the reinforcement area As in the tension zone:

[0188] To fully utilize the reinforcement in the compression zone, the relative height of the concrete to the compression zone is recalculated:

[0189]

[0190] Take As = 4511.28 mm 2 ;

[0191] Total longitudinal reinforcement area A s ′+A s =5791.25mm 2 >ρ min bh = 3200mm 2 It meets the reinforcement requirements.

[0192] The final tensile reinforcement of the corbel column is taken A s =4826mm 2 ;

[0193] Take the compression steel bars A s =1473mm2

[0194] 1.2 Calculation of stirrup reinforcement for the limiting short column:

[0195] Given the shear span ratios of the concrete column: λx = 1.50, λy = 1.50, β = 1.0, and the design value of the axial compressive force N = 0 kN;

[0196] A uniaxial shear concrete column must meet the following formula requirements:

[0197]

[0198] Furthermore, the calculated shear capacity of the inclined section in the X direction is required:

[0199]

[0200] Therefore, it is necessary to calculate the shear capacity of the inclined section.

[0201] 1.3 The shear capacity of the inclined section is calculated as follows:

[0202]

[0203] The final calculation yielded 2 stirrup legs, 10mm stirrup diameter, and 300mm stirrup spacing; the final stirrup configuration was 10@150.

[0204] 2. Calculate the cross-sectional reinforcement of the seismic restraint bracket:

[0205] Through finite element analysis, the vertical force F1 = 260kN was extracted from the section of a single corbel under a single wind load condition. The reinforcement calculation process for the corbel section is as follows:

[0206] 2.1 Calculation of local compression on the top surface of the seismic restraint bracket

[0207] Calculation area A of localized pressure on the cow leg b =900×800=720000mm 2 ;

[0208] Local compressive stress:

[0209]

[0210] The requirements are met.

[0211] 2.2 Calculate the area of ​​the longitudinal reinforcing bars in the seismic restraint bracket:

[0212] To ensure the safety and durability of the corbel under combined stress, the sum of the cross-sectional area of ​​the tensile reinforcement required to withstand vertical force and the cross-sectional area of ​​the reinforcement required to withstand horizontal tensile force should conform to the following formula:

[0213]

[0214] Where A s =A s1 +A s2 , Furthermore, the longitudinal reinforcement ratio required to withstand vertical forces must not be less than the minimum reinforcement ratio ρ. min This ensures that the concrete does not break down brittlely.

[0215]

[0216] A smin =ρ min bh=0.21%×800×1400=2394.00mm 2 >311.24mm 2 ;

[0217] Then A s1 =2394mm 2 ,

[0218]

[0219] A s =A s1 +A s2 =2394mm 2 ,

[0220] Actual selection A s =2463mm 2 >2394mm 2 .

[0221] 2.3 Calculate the cross-sectional area of ​​horizontal stirrups and bent-up bars:

[0222] Horizontal stirrups should be provided at the top of the corbel, and the cross-sectional area of ​​the horizontal stirrups within 2h0 / 3 of the top of the corbel should not be less than half the cross-sectional area of ​​the tensile reinforcement bearing the vertical force. This ensures that the corbel has sufficient tensile strength in the horizontal direction.

[0223] A sh >0.5A s1 =0.5×2394=1197mm 2 ;

[0224] The stirrups are 10mm in diameter and are double-legged.

[0225] The area of ​​a single stirrup is A sv =π×10×10 / 4=78.54mm 2 ;

[0226] Stirrup spacing lg =100mm, then:

[0227]

[0228] When the shear span ratio a / h0 = 0.37 > 0.3, bent-up bars should be provided. Therefore:

[0229] A sb >1 / 2 × 2394.00 = 1197.00 mm 2 ;

[0230] Bent-up bars are selected as A sb =1234.5mm 2 .

[0231] 2.4 Calculation of crack control for seismic restraint brackets

[0232] To control crack width, ensure structural durability, and prevent concentrated crack propagation, it is necessary to verify the crack control of the seismic restraint bracket.

[0233] Given f tk = 2.39 N / mm², f y =360 N / mm², crack control coefficient β = 0.80

[0234] The effective height of the cow leg is:

[0235] h0 = h1 - a s +ctanα=500-35+500×1.00=765mm,

[0236]

[0237] It meets the requirements for crack control.

[0238] 3. Wind load limiting column design:

[0239] Finite element analysis revealed a shear force of 81 kN under a single wind load condition, and a column base bending moment of 81 x 0.4 = 33 kN·m under wind load. The shear force under minor earthquakes was also calculated.

[0240] V2 = 389150 x 0.08 x 9.8 / 1000 = 306 kN. The bending moment at the base of the wind load limiting column is 306 x 0.4 = 123 kN·m. (0.4 m is half the height of the wind load limiting column.)

[0241] The wind load limiting column has a cross-section of 300mm x 500mm. The reinforcement calculation for the column cross-section is as follows:

[0242] 3.1 Reinforcement calculation for wind-load-limited columns:

[0243] 3.1.1 Calculate the longitudinal reinforcement of the wind load limiting column:

[0244] ε cu =0.0033-(f cu,k -50)×10 -5 =0.0033-(40-50)×10 -5 =0.00340>0.0033,

[0245] Take ε cu =0.0033;

[0246] (1) Relative height of the pressure zone:

[0247] (2) Calculate the reinforcement area A of the compression zone. s ′:

[0248] To minimize the total steel consumption, let the relative pressure zone height ξ = ξ b =0.52, then the reinforcement of the compression zone is:

[0249]

[0250] (3) Calculate the reinforcement area As in the tension zone:

[0251] To fully utilize the reinforcement in the compression zone, the relative height of the concrete to the compression zone is recalculated:

[0252]

[0253] Take As = 300mm 2 ;

[0254] Total longitudinal reinforcement area A s ′+A s =600mm 2 <ρ min bh = 750mm 2

[0255] Final tensile reinforcement A s =509mm 2 ;

[0256] Take the compression steel bars A s =509mm 2

[0257] 3.1.2 Calculation of stirrup reinforcement for wind-load-limited columns under wind load:

[0258] Given the shear span ratios of the concrete column: λx = 1.50, λy = 1.50, β = 1.0, and the design value of the axial compressive force N = 0 kN;

[0259] A uniaxial shear concrete column must meet the following formula requirements:

[0260]

[0261] Furthermore, the calculated shear capacity of the inclined section in the X direction is required:

[0262]

[0263] Therefore, shear capacity calculation for inclined sections is not required. Actual stirrup configuration: 8@200.

[0264] 3.2 Reinforcement calculation for columns restrained by wind load under minor earthquakes:

[0265] 3.2.1 Calculate the longitudinal reinforcement of the wind load limiting column:

[0266] ε cu =0.0033-(f cu,k -50)×10 -5 =0.0033-(40-50)×10 -5 =0.00340>0.0033, take ε cu =0.0033;

[0267] (1) Relative height of the pressure zone:

[0268] (2) Calculate the reinforcement area A of the compression zone. s ′:

[0269] To minimize the total steel consumption, let the relative pressure zone height ξ = ξ b =0.52, then the reinforcement of the compression zone is:

[0270]

[0271] (3) Calculate the reinforcement area As in the tension zone:

[0272] To fully utilize the reinforcement in the compression zone, the relative height of the concrete to the compression zone is recalculated:

[0273]

[0274] Take As = 795mm 2 ;

[0275] Total longitudinal reinforcement area A s ′+A s =1095mm 2 >ρmin bh = 750mm 2

[0276] Final tensile reinforcement A s =1018mm 2 ;

[0277] Take the compression steel bars A s =1018mm 2 .

[0278] Given the shear span ratios of the concrete column: λx = 1.50, λy = 1.50, β = 1.0, and the design value of the axial compressive force N = 0 kN;

[0279] A uniaxial shear concrete column must meet the following formula requirements:

[0280]

[0281] Furthermore, the calculated shear capacity of the inclined section in the X direction is required:

[0282]

[0283] Therefore, it is necessary to calculate the shear capacity of the inclined section.

[0284] 3.2.2 The shear capacity of the inclined section is calculated as follows:

[0285]

[0286] The final calculation yielded 2 stirrup legs, 8mm stirrup diameter, and 100mm stirrup spacing; the final stirrup configuration was 10@150.

[0287] To ensure no displacement under wind load, the elastic plate sliding support can slide under minor earthquakes. Therefore, the reinforcement of the wind-load-limiting column is as follows: X direction: Y direction: Stirrups: 10@150.

[0288] The maintenance ladder manufactured using this method will not move under normal operating conditions. Under extreme weather conditions, when wind load causes the horizontal force on the structure to exceed the dynamic friction value, the upper platform 4 will not continue to slide when the wind load limiting column 5 contacts the seismic limiting bracket 2. This allows the wind load limiting column 5 and the seismic limiting bracket 2 to work together to limit the upper platform 4. Under seismic action, sliding will occur. When an earthquake occurs, the left and right movement of the upper platform 4 will destroy the wind load limiting column 5. At this time, the seismic limiting bracket 2 and the limiting short column 3 restrict the large displacement sliding of the sliding support against its own friction, thereby limiting the upper platform 4. At the same time, the seismic limiting bracket 2 constrains the displacement in the direction perpendicular to the steel ladder and LNG storage tank 12, and the seismic limiting bracket 2 also has the function of preventing overturning of its upper structure.

[0289] In summary, the maintenance ladder of this method employs a combination of a lower support, seismic limiting brackets, limiting short columns, and wind load limiting columns. Under extreme weather conditions, the wind load limiting columns restrict small displacement sliding of the sliding bearings against their own friction. Under seismic loading, the seismic limiting brackets and limiting short columns restrict large displacement sliding of the sliding bearings against their own friction, preventing the maintenance ladder from overturning. This effectively avoids the problem of significant deformation or even damage to the maintenance ladder when the LNG storage tank shifts.

[0290] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A design method for a directional maintenance ladder for a storage tank, characterized in that: The maintenance ladder includes a lower bearing platform and an upper bearing platform installed above it, and an elastic flat plate sliding support is provided between the lower bearing platform and the upper bearing platform. Wind load limiting columns for limiting are provided at both ends of the upper bearing platform, and limiting short columns for limiting are provided at both ends above the lower bearing platform. Earthquake limiting corbels for anti-overturning are provided inside the limiting short columns, and several steel ladder steel columns for fixing the LNG storage tank are provided in the middle of the upper bearing platform; The method includes the following steps: S1. Determine the parameters of the storage tank limiting maintenance ladder under a custom load condition; S2. Set boundary conditions; S3. Input the parameters in S1 and the boundary conditions in S2 into finite element software, and extract the shear force and uplift force received by the limiting short columns; S4. Calculate the data information of the limiting short columns, earthquake limiting corbels and wind load limiting columns.

2. The design method of a directional maintenance ladder for a storage tank according to claim 1, characterized in that: The custom load conditions in S1 include: dead load, live load, wind load, earthquake load and temperature action load.

3. The design method for a directional maintenance ladder for a storage tank according to claim 1, characterized in that: The parameters determined for the storage tank limiting maintenance ladder in S1 include the transverse column spacing of the limiting short columns, the longitudinal column spacing of the limiting short columns, the shortest distance between the maintenance ladder and the outer edge of the storage tank, the total height and total number of floors of the maintenance ladder, the strength of the concrete material, the steel grade of the steel members, the basic wind pressure value A, the ground roughness category C1, the seismic fortification grouping C2, the seismic fortification intensity C3, the site category C4, the characteristic period Tg, and the parameters of the elastic sliding support.

4. The design method of a directional maintenance ladder for a storage tank according to claim 2, characterized in that: The boundary conditions in S2 include S21. Set steel supports, and both ends of the steel supports are hinged to the steel ladder steel columns and the LNG storage tank respectively; S22. The direction of the earthquake limiting corbel is set perpendicular to the direction of the LNG storage tank; S23. The upper bearing platform and the lower bearing platform are set in the parallel direction of the LNG storage tank.

5. The design method of a directional maintenance ladder for a storage tank according to claim 1, characterized in that: The calculation methods in S4 include: S41. Calculate the reinforcement of the limiting short columns; S42. Calculate the sectional reinforcement of the earthquake limiting corbels; S43. Calculate the reinforcement of the wind load limiting columns.

6. The design method of a directional maintenance ladder for a storage tank according to claim 5, characterized in that: The specific method of S41 includes: (1) Calculate the relative limit pressure zone height ξ b The specific formula is as follows: in, β1 is a coefficient; f y E represents the design tensile strength of the reinforcing steel. s ε is the elastic modulus of the steel reinforcement; cu ε represents the ultimate compressive strain of concrete under non-uniform compression. cu =0.0033-(f cu,k -50)×10 -5 If the value is greater than 0.0033, then ε is taken. cu =0.0033; (2) Calculate the reinforcement area A in the compression zone. s The specific formula is as follows: Where M1 is the design bending moment; α1 is a coefficient; f c ξ is the design value of the axial compressive strength of concrete; b is the width of the concrete column; h0 is the effective height of the section; b f represents the relative height of the limit pressure zone. y This refers to the design tensile strength of the reinforcing steel; a s ′ represents the thickness of the protective layer; S411. Calculate the longitudinal reinforcement of the limiting short columns: Where α1 is the coefficient; f c b is the design value of the axial compressive strength of concrete; h0 is the width of the concrete column; f is the effective height of the section; y ′ represents the design value of compressive strength; A s ′ Reinforcement area in the compression zone; N is the axial force; f y This refers to the design tensile strength of the reinforcing steel. (3) Calculate the reinforcement area As of the tension zone steel bars, and the specific formula is as follows: S412. Calculate the stirrup reinforcement of the limiting short columns; (1) The concrete columns of the rectangular section of the limiting short columns should meet the following conditions: Vx≤0.25β c f c bh0, (4); Where hw is the web height of the cross section; b is the width of the rectangular cross section; h0 is the effective height of the cross section; β c f is the influence coefficient of the concrete section; c This is the design value for the axial compressive strength of concrete. Where V1 is the design shear force; λ x To calculate the shear span ratio of the cross section, i.e., M / (Vh0); f t denoted as , where is the design value of the axial tensile strength of concrete; b is the width of the rectangular section; h0 is the effective height of the section; and N is the axial force, where N is greater than 0.3f. c When A is reached, N = 0.3f. c A, where A is the cross-sectional area; When hw / b < 4, the maximum shear force design value Vx on the component section needs to meet: Among them, A svx The total cross-sectional area of ​​each leg of the stirrups within the section; S is the stirrup spacing along the length of the member; V1 is the design shear force; λ x To calculate the shear span ratio of the cross section, i.e., M / (Vh0); f t denoted by , b is the design value of the axial tensile strength of concrete; b is the width of the rectangular section; h0 is the effective height of the section; N is the design value of the axial compressive strength, which is greater than 0.3f. c When A, take 0.3f. c A, where A is the cross-sectional area; f yv This is the design value for the tensile strength of the stirrups.

7. The design method of a directional maintenance ladder for a storage tank according to claim 5, characterized in that: (2) When the limiting short columns meet the following requirements, the calculation of the shear bearing capacity S1 of the inclined section may not be carried out: (3) If S1 < V1, the calculation of the shear bearing capacity S1 of the inclined section needs to be carried out, and the following formula should be satisfied: Where F1 is the standard value of the horizontal load; A b The calculated base area is for localized compression; The specific method of S42 includes: Where F1 is the design value of the vertical force acting on the corbel; Fh is the design value of the horizontal tension acting on the corbel; a is the horizontal distance from the point of application of the vertical force to the edge of the lower column; f y h0 is the design tensile strength of the reinforcing steel; h0 is the effective height of the section. S421. Calculate the local compression on the top surface of the earthquake limiting corbel, and the calculation formula is as follows: (1) The cross-sectional calculation of horizontal reinforcement should meet the following requirements: Among them, A sh lg is the cross-sectional area of ​​the horizontal stirrups; h0 is the effective height of the cross-section; lg is the stirrup spacing; A sv The area of ​​a single stirrup; (2) When the shear span ratio of the corbel is not less than 0.3, bent-up bars should be provided, and the cross-sectional area of ​​the bent-up bars should meet the following requirements: A sb >0.5A s1 (10), Among them, A s1 Indicates the area of ​​steel reinforcement in the tension zone; S422. Calculate the area of the longitudinal stressed steel bars of the earthquake limiting corbel; Where F1 is the vertical force value acting on the top of the corbel, calculated according to the standard combination of load effects; F hk The horizontal tensile force acting on the top of the corbel, calculated according to the standard combination of load effects; a is the horizontal distance from the point of application of the vertical force to the edge of the lower column; b is the width of the corbel; f tk f is the standard value of the axial tensile strength of concrete; y β is the design value of the tensile strength of the steel reinforcement; β is the crack control coefficient; h0 is the effective height of the section.

8. The design method of a directional maintenance ladder for a storage tank according to claim 5, characterized in that: S423. Calculate the cross-sectional areas of the upper horizontal stirrups and bent-up steel bars of the earthquake limiting corbel; S424. Calculate the crack control of the earthquake limiting corbel; The specific steps of S43 include:

9. A maintenance ladder, comprising a limiting structure, characterized in that: S431. Calculate the longitudinal reinforcement of the wind load limiting columns; S432. Calculate the stirrup reinforcement of the wind load limiting columns. Manufactured by applying the design method of the directional maintenance ladder for a storage tank described in any one of claims 1 to 8.

10. The maintenance ladder according to claim 9, characterized in that: It also includes a camera for monitoring the horizontal displacement of the elastic plate sliding support, the camera signal being connected to an external control room.

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