A design method for embedded concrete-filled steel tube column base with boot beam

Abstract

The present invention discloses a design method for an embedded steel tube concrete column foot with a boot beam. The method comprises: first, obtaining the design parameters corresponding to the upper steel tube concrete column and the lower pile foundation and the force transmitted from the column bottom to the pile foundation, and presetting the column foot embedding depth, the pedestal height, the design parameters of the boot beam and the column bottom plate size; then, adjusting the column foot embedding depth in combination with the design value of the bearing capacity of the steel tube concrete column to obtain an optimized column foot embedding depth; finally, respectively checking the stiffness of the steel tube concrete column foot with the boot beam, checking the pull-out resistance of the boot beam, checking the local bearing pressure of the column bottom plate concrete, checking the shear bearing capacity of the foundation under the column and the shearing of the corner pile on the pedestal, and if the calculation fails, adjusting the column foot embedding depth / pedestal height / design parameters of the boot beam / column bottom plate size until all calculations pass, and completing the design of the steel tube concrete column foot. The design method proposed by the present invention is quick and simple to calculate, accurate and reliable.

Description

Technical Field

[0001] The invention relates to a design method of a steel tube concrete composite structure, in particular to a design method of an embedded steel tube concrete column foot with a boot beam. Background Art

[0002] Steel tube concrete composite structure refers to a composite structure in which concrete is poured into steel tubes, and the external steel tubes and the internal core concrete work together to exert mechanical properties. Due to its unique combination form, it has the characteristics of convenient construction, high bearing capacity, good seismic performance and fire resistance. The column foot is a key structure connecting the upper steel tube concrete column and the lower reinforced concrete foundation in the building structure. A solid column foot can effectively fix the column end in the foundation and transfer the axial force, shear force and bending moment at the bottom of the column to the foundation. Therefore, the design of the column foot is also an important part of the overall design of the structure that cannot be ignored.

[0003] Considering the geometric similarity between steel tube concrete structure and steel structure, the steel tube concrete column foot can generally follow the structural form of steel column foot. According to the summary in the Technical Code for Steel Structure of High-rise Civil Buildings JGJ99-2015 (hereinafter referred to as the "High-rise Steel Code"), there are three main types of column foot forms in steel structures: exposed, embedded and external. Among them, the embedded column foot is to fix the upper structure column by extending the column end into the foundation and providing vertical and lateral support by the foundation concrete. Although this column foot form has the advantages of high rigidity and good seismic performance, it also has some problems. For example, when the upper structure column has a large bearing capacity, the column end will be buried deeper to meet the calculation requirements of the specification. The increase in the buried depth will undoubtedly increase the foundation height, inaccurate positioning of embedded parts and increase the difficulty of construction, thereby affecting the reliability of the column foot and the stability of the overall structure; the size of some column base plates is limited. In order to meet the foundation shear resistance calculation requirements, the designer has to increase the height of the foundation below the column base plate. The above two factors overlap and cause the total height of the foundation to exceed the acceptable range.

[0004] At present, with the continuous development and application of steel tube concrete structure, the structural form and design method of steel tube concrete column foot node have attracted close attention from relevant practitioners. In order to solve the above pain points encountered in the design of column foot, a buried steel tube concrete column foot with a boot beam came into being, and related studies have proved its effectiveness in reducing the buried depth of the column end and increasing the punching shear capacity. After adopting this type of column foot, the foundation height can be greatly reduced compared with the ordinary buried column foot. Despite this, there is no calculation and design method for this type of column foot in the current "High Steel Code" and "Steel Structure Design Standard" GB50017-2017 (hereinafter referred to as "Steel Standard") and other specifications. Under limited conditions, if it is to be accurately analyzed, it can only be done through cumbersome and inefficient numerical simulation methods, which requires a lot of learning and time costs for designers and cannot be widely applied. Therefore, it is necessary to propose a set of accurate, simple and easy-to-use design methods for this type of column foot, so as to provide technical support and reliable guarantee for its promotion and application. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a design method for embedded steel tube concrete column foot with boot beam for currently commonly used steel tube concrete structure and pile foundation. The design method proposed by the present invention is quick, simple, accurate and reliable.

[0006] The technical solution adopted by the present invention comprises the following steps:

[0007] 1. Design method of embedded steel tube concrete column base with boot beam

[0008] Step 1: Obtain the design parameters of the CFST column at the top of the CFST column foot and the pile foundation at the bottom, as well as the force transmitted from the column bottom to the pile foundation, and preset the column foot embedment depth h according to design experience c , Platform height h j , design parameters of the boot beam and dimensions of the column base plate;

[0009] The design parameters of the steel tube concrete column include the column section diameter D of the circular steel tube concrete column, the column section width b and column section height h of the rectangular steel tube concrete column, and the steel tube cross-sectional area A. s , core concrete cross-sectional area A c , column section wall thickness t, steel and concrete material properties and the height of the floor where the column foot is located l h .

[0010] The design parameters of the pile foundation include the foundation concrete strength, the thickness of the protective layer a s , the characteristic value of the vertical compressive bearing capacity of a single pile R, the column foot connection coefficient α and the seismic adjustment coefficient γ RE .

[0011] The force transmitted from the column bottom to the pile foundation is the design value of the column bottom force calculated after the basic load combination. The data is extracted from the general structural design software. The column bottom force includes the axial force N c , shear force V c , bending moment M c He Pull T c .

[0012] The design parameters of the shoe beam include the shoe beam height h 1 、Bridge width b 1 、Boot beam web thickness t w1 、Boot beam flange thickness t f1 and shoe beam length L 1 .

[0013] The column base plate size includes the column base plate side width b d 、Height of column base plate h d , column base plate thickness t d .

[0014] Step 2: According to all the design parameters of the CFST column foot in step 1, and combined with the bearing capacity design value of the CFST column, the column foot embedment depth h c Adjust to obtain the optimal column foot embedment depth h c ;

[0015] Step 2 is as follows:

[0016] First, according to all the design parameters of the CFST column foot in step 1 and the cross-sectional form of the CFST column, the design value of the bearing capacity of the CFST column is calculated, which includes the design value of the cross-sectional axial compressive bearing capacity of the CFST column N u , Design value of section bending bearing capacity M u , Design value of bending bearing capacity of section considering the influence of axial force M pc The shear capacity V corresponding to the bending capacity pc ; Then, according to the design value of the bearing capacity of the steel tube concrete column, the buried depth of the embedded column foot of the steel tube concrete column with the boot beam is calculated to obtain the calculated column foot buried depth d; if the current column foot buried depth h c < calculated column foot burial depth d, then the current column foot burial depth h c Does not meet the requirements, need to increase the current column foot burial depth h c , and update the calculated column foot burial depth d until the latest column foot burial depth h c ≥Calculated column foot embedment depth d, obtain optimized column foot embedment depth h c ; Otherwise, bury the current column foot to depth h c As the optimized column foot embedment depth h c .

[0017] In step 2, the cross-section of the upper steel tube concrete column is divided into circular and rectangular. When the cross-section of the steel tube concrete column is circular, the bearing capacity design value of the steel tube concrete column should be calculated according to the relevant contents of Chapter 5 of the Technical Specification for Steel Tube Concrete Structure GB50936-2014;

[0018] When the cross-section of the steel tube concrete column is a rectangular section, the design value of the column's bearing capacity should be calculated based on the relevant contents of Chapter 6 of the Technical Code for Rectangular Steel Tube Concrete Structures CECS159:2004.

[0019] When the cross-section of the steel tube concrete column is a circular cross-section, the buried depth of the embedded column foot of the steel tube concrete column with a boot beam is calculated according to the design value of the bearing capacity of the steel tube concrete column, and the calculated column foot buried depth d is obtained, including:

[0020] If the design value of the bending bearing capacity of the section under the influence of axial force is considered, M pc The bending moment M borne by the column foot beam ul If the ratio is greater than or equal to 0.5, the calculated column foot embedment depth d satisfies the following formula:

[0021] d=V pc / (0.8Df cj )+(2(V pc / (0.8Df cj )) 2 + 4(M pc -0.5M ul ) / (0.8Df cj )) 0.5

[0022] Among them, if the axial force of the steel tube concrete column N c and the design value of the cross-section axial compressive bearing capacity N u The ratio is greater than 0.255, then the design value of the bending bearing capacity of the section considering the influence of axial force is M pc Calculated using the following formula:

[0023] M pc = 1.5(1-N c / N u )M u

[0024] Otherwise, the design value of the bending bearing capacity of the section considering the influence of axial force is M pc Calculated using the following formula:

[0025] M pc = (1+N c / 2.17 / N u )M u

[0026] If the design value of the bending bearing capacity of the column section is M pc The bending moment M borne by the column foot beam ul If the ratio is less than 0.5, the calculated column foot embedment depth d satisfies the following formula:

[0027] d=V pc / (0.8Df cj )

[0028] M ul =min(M ula ,M ulb )

[0029] M ula =b 1 L 1 f cj (L 1 +D)

[0030] M ulb =[3(h c -h 1 -a s )+ b 1 +2 L 1 ]( h c -h 1 -a s ))(L 1 +D)f tj

[0031] Where D is the diameter of the circular concrete-filled steel tube column; V pc represents the shear capacity corresponding to the bending capacity, f cj Indicates the design value of the axial compressive strength of the foundation concrete, in N / mm 2 , M ula It represents the bending moment borne by the shoe beam under bending action, in N·mm; M ulb It indicates the bending moment that the shear failure cone on the upper part of the shoe beam can withstand, in N·mm; f tj Indicates the design value of the axial tensile strength of the foundation concrete, in N / mm 2 .

[0032] When the cross-section of the CFST column is a rectangular cross-section, the buried depth of the embedded column foot of the CFST column with a boot beam is calculated according to the design value of the bearing capacity of the CFST column, and the calculated buried depth of the column foot d is obtained, which is specifically:

[0033] If the design value of the bending bearing capacity of the section under the influence of axial force is considered, M pc The bending moment M borne by the column foot beam ulIf the ratio is greater than or equal to 0.5, the calculated column foot embedment depth d satisfies the following formula:

[0034] d=V pc / (bf cj )+(2(V pc / (bf cj )) 2 + 4(M pc -0.5M ul ) / (bf cj )) 0.5

[0035] Among them, if the axial force of the steel tube concrete column N c and the design value of the cross-section axial compressive bearing capacity N u The ratio is greater than α c , then the design value of the bending bearing capacity of the section considering the influence of axial force is M pc Calculate as follows:

[0036] M pc = (1-N c / N u )M u / (1-α c )

[0037] Otherwise, the design value of the bending bearing capacity of the section considering the influence of axial force is M pc Calculate as follows:

[0038] M pc = M u

[0039] Among them, α c =f c A c / N u , f c A represents the design value of the axial compressive strength of the column concrete. c Represents the concrete area of ​​the column section; α c Represents the concrete work load coefficient.

[0040] If the design value of the bending bearing capacity of the section under the influence of axial force is considered, M pc The bending moment M borne by the column foot beam ul If it is less than 0.5, the calculated column foot embedment depth d satisfies the following formula:

[0041] d=V pc / (bf cj )

[0042] M ul =min(M ula ,M ulb )

[0043] M ula =b 1 L 1 f cj (L 1 + h)

[0044] M ulb =[3(h c -h 1 -a s )+ b 1 +2 L 1 ]( h c -h 1 -a s ))(L 1 +h)f tj

[0045] Among them, V pc represents the shear capacity corresponding to the bending capacity, f cj It represents the design value of the axial compressive strength of the foundation concrete, and b is the column section width of the rectangular steel tube concrete column.

[0046] Step 3: According to the current column foot burial depth h c As well as other design parameters of the CFST column foot, the rigidity of the CFST column foot with boot beam, the pull-out resistance of the boot beam, the local bearing capacity of the column bottom plate concrete, the shear bearing capacity of the foundation under the column and the shearing of the corner pile on the cap are checked. If the calculation fails, the buried depth of the column foot h is adjusted. c / Height of the support h j / Design parameters of boot beam / Column base plate dimensions, until all verifications are passed, the design of the steel tube concrete column foot is completed.

[0047] Among them, the stiffness calculation process of the steel tube concrete column base with boot beam specifically includes:

[0048] If the column foot is buried at a depth of h c +Effective embedding length of shoe beam d l ≥Effective embedment depth of embedded concrete-filled steel tube column foot without shoe beam h c1 , it means that the stiffness of the steel tube concrete column foot with boot beam meets the design requirements and the stiffness verification is passed. Otherwise, it means that the stiffness of the steel tube concrete column foot with boot beam does not meet the design requirements and the buried depth of the column foot is increased. c Or the size of the shoe beam; if you choose to increase the column foot embedment depth h c According to all the design parameters of the CFST column foot and the design value of the bearing capacity of the CFST column, the buried depth h of the column foot is c Adjust to obtain the optimal column foot embedment depth h c, and then judge the stiffness of the steel tube concrete column foot with boot beam. If you choose to increase the size of the boot beam, directly judge the stiffness of the steel tube concrete column foot with boot beam until the stiffness of the steel tube concrete column foot with boot beam meets the design requirements, and obtain the final column foot embedment depth h c and design parameters of the boot beam.

[0049] Effective embedment depth h of embedded concrete-filled steel tube column footing without shoe beam c1 The calculation formula is as follows:

[0050] h c1 =4(E scm (I c +I s ) / E c ) 0.25

[0051] δ = I s / I c

[0052] n cs = E c / E s

[0053] E sc =1.3k E f sc

[0054] E scm =E sc (1+δ / n cs )(1+α sc ) / ((1+α sc / n cs )( 1+δ))

[0055] Among them, E scm Indicates the elastic bending modulus of the steel tube concrete column, unit N / mm 2 ; E sc Indicates the elastic modulus of the steel tube concrete column, unit N / mm 2 ;I c ,I s Respectively represent the moments of inertia of the concrete and steel tube parts of the steel tube concrete column, unit: mm 4 ;k E represents the conversion coefficient of axial compression elastic modulus of steel tube concrete column; δ represents the ratio of the moment of inertia of the steel tube part to the concrete part of the steel tube concrete column; n cs Represents the ratio of the elastic modulus of concrete to steel tube in concrete-filled steel tube columns; α sc It represents the ratio of the cross-sectional area of ​​the steel tube to the concrete part of the steel tube concrete column.

[0056] Effective embedding length d of the shoe beaml The calculation formula is as follows:

[0057] d l =4((E s I lx ) / E c ) 0.25

[0058] Among them, I lx Indicates the moment of inertia of the shoe beam, unit: mm 4 ; E c 、E s Represents the elastic modulus of concrete and steel, in N / mm 2 .

[0059] The process of checking the pull-out resistance of the boot beam of the steel tube concrete column foot specifically includes:

[0060] If the upper limit of local concrete bearing pressure F lc >Design value of axial force at column base N c , then the design requirements are met, otherwise they are not met. The column base plate size is increased and then judged again until the upper limit of the local bearing pressure of the concrete is reached. lc Meet the design requirements and obtain the final column base plate size. Upper limit of local concrete bearing pressure F lc According to the following formula to obtain:

[0061] F lc =1.35β c β l f c A l

[0062] β l = (A b / A l ) 0.5

[0063] A l =b d 2 +4 b 1 [L 1 -0.5(b d -D)]

[0064] A b =9 b d 2

[0065] Among them, β c It represents the influence coefficient of concrete strength. When the concrete strength grade does not exceed C50, it is taken as 1.0; when the concrete strength grade is C80, it is taken as 0.8. The linear interpolation method is used in between. β lIndicates the strength enhancement factor of concrete when it is locally compressed; A l Indicates the local compression area of ​​concrete, unit: mm 2 ; A b Indicates the calculated bottom area of ​​local pressure, unit: mm 2 .f c Indicates the design value of the axial compressive strength of the core concrete, in N / mm 2 .

[0066] The verification process of the punching bearing capacity of the foundation under the column and the punching bearing capacity of the corner pile on the cap specifically includes:

[0067] If the punching force design value F acting on the punching failure cone l < the upper limit of the design value of the shear resistance of the cap F, it means that the shear of the steel tube concrete column on the cap meets the design requirements, and the shear bearing capacity of the foundation under the column passes the shear calculation of the cap; otherwise, it does not meet the design requirements, and the cap height h is increased. j Or increase the shoe beam length L 1 After that, calculate the upper limit F of the punching force design value of the abutment and re-judge until the punching force design value F acting on the punching failure cone is l <The upper limit of the design value of the shear resistance of the abutment F;

[0068] If the design value of the vertical force at the top of the corner pile is N l < the upper limit of the shear force of the corner pile on the cap N, it means that the shear force of the corner pile on the cap meets the design requirements and the shear force verification of the corner pile on the cap has passed; otherwise, it does not meet the design requirements and the cap height h is increased. j Or adjust the position of the corner pile, and then calculate the upper limit N of the shear force of the corner pile of the cap, and re-judge until the vertical force design value N of the corner pile top is reached. l <The upper limit of the shear force of the corner pile of the cap N; get the final cap height h j .

[0069] The design value of the punching force acting on the punching failure cone is F l The calculation formula is as follows:

[0070] F l =N c -∑N i

[0071] Among them, N i It represents the sum of the net reaction force design values ​​of each pile within the range of the shear failure cone. The shear failure cone should be a cone formed by the line from the upper boundary of the cone to the edge of the corresponding pile top. The angle between the cone and the bottom surface of the cap should not be less than 45°. The upper boundary of the shear cone is the rectangle formed by the line connecting the midpoints of each shoe beam. N c It represents the axial force in the column base force;

[0072] The calculation formula for the upper limit F of the design value of the shear resistance of the abutment is as follows:

[0073] F=4α o (h a +a o )β hp f tj h 0

[0074] α o =0.84 / (0.2+λ o )

[0075] λ o =a o / h a

[0076] h 0 = h j -h c -α s

[0077] h a =(L 1 +D) / 2 0.5

[0078] Among them, h 0 Indicates the effective height of the shear failure cone, in mm; λ o Indicates the collapse ratio of the shear failure cone; a o represents the horizontal distance from the upper boundary of the punching cone to the pile edge. o <0.2h 0 When o =0.2h 0 , when a o >h 0 When o =h 0 , unit: mm; α o Represents the shear coefficient of the shear failure cone; β hp It indicates the influence coefficient of the section height on the punching shear bearing capacity. When h 0 When it is not greater than 800mm, take 1.0. 0 When it is greater than 2000mm, take 0.9, and use linear interpolation method in between. tj It indicates the design value of the axial tensile strength of the foundation concrete. a Represents the length of the upper boundary of the punching cone.

[0079] The calculation formula for the upper limit N of the design value of the punching force of the cap anti-corner pile is as follows:

[0080] N=[α lx (c y + a y / 2)+α ly (c x + a x / 2)] β hp f tj h 0

[0081] α lx =0.56 / (0.2+λ lx ), α ly =0.56 / (0.2+λ ly )

[0082] λ lx = a x / h 0 ,λ ly = a y / h 0

[0083] Among them, λ lx , ly Indicates the collapse ratio of the corner piles in the length and width directions of the rectangular cap; a x 、a y They represent the horizontal distances from the 45° punching line on the inner edge of the corner pile to the upper boundary 8 of the punching cone in the length and width directions of the rectangular cap. x or a y <0.2h 0 When x or a y =0.2h 0 ;when a x or a y >h 0 When x or a y =h 0 , unit: mm; α lx , α ly They represent the punching coefficients of the corner piles in the length and width directions of the rectangular cap; c x 、c y Respectively represent the distance from the inner edge of the corner pile to the outer edge of the cap in the length and width direction of the rectangular cap, in mm. hp represents the influence factor of the section height on the punching shear bearing capacity, f tj Indicates the design value of the axial tensile strength of the foundation concrete, h 0 Represents the effective height of the shear failure cone.

[0084] The anti-pullout calculation process of the boot beam specifically includes:

[0085] Conduct the uplift check of the shoe beam for the concrete-filled steel tube column foot under the action of uplift force. If the result of the uplift check of the column foot does not meet the design requirements, adjust the size of the shoe beam and re-conduct the uplift check of the shoe beam until the uplift check of the column foot meets the design requirements to obtain the final design parameters of the shoe beam.

[0086] Specifically as follows:

[0087] Judge by comparing the shear stress f vb generated on the web of the shoe beam with the design value of the shear strength of the steel f v , the tensile stress f bb generated on the flange of the shoe beam with the design value of the tensile strength of the steel f, the local compressive stress σ b generated by the shoe beam on the upper concrete with the design value of the compressive strength of the concrete f c , and the upper limit of the punching shear force V of the upper concrete of the shoe beam and the design value of the punching shear force V T acting on the punching failure cone:

[0088] If f vb < f v , f bb < f, σ b < f c , V T < V are satisfied simultaneously, it indicates that the uplift resistance of the concrete-filled steel tube column foot with a shoe beam meets the design requirements;

[0089] If f vb > f v , it indicates that the web of the shoe beam does not meet the shear design requirements under the action of uplift force. After increasing the web thickness, recalculate f vb and make a judgment until f vb < f v ;

[0090] If f bb > f c , it indicates that the flange of the shoe beam does not meet the bending design requirements under the action of uplift force. After increasing the flange thickness or increasing the size of the shoe beam, recalculate f bb and make a judgment until f bb < f;

[0091] If σ b > f c , it indicates that the upper concrete of the shoe beam does not meet the local compressive design requirements under the action of uplift force. After increasing the width or length of the shoe beam, recalculate σ b and make a judgment until σ b < f c ;

[0092] If V T>V, it means that the shear resistance of the concrete on the upper part of the boot beam does not meet the design requirements when subjected to pullout force. It is necessary to increase the column foot burial depth, boot beam width or length, and recalculate V T And make judgments until V T <V。

[0093] The shear stress f generated by the bottom pull-out force of the steel tube concrete column on the web of the boot beam vb The calculation formula is as follows:

[0094] f vb =(γ RE T) / (4(h 1 -2t f1 ) w1 )

[0095] Where T represents the upward pull force transmitted from the upper steel tube concrete column to the foundation.

[0096] The tensile stress f generated by the pull-out force on the flange of the shoe beam bb The calculation formula is as follows:

[0097] f bb =(γ RE T×0.5 L 1 ) / (4γ x W x )

[0098] Among them, W x represents the net section modulus of the shoe beam along the main axis; γ x It represents the plastic development coefficient of the section of the shoe beam along the main axis.

[0099] The local compressive stress σ generated by the boot beam on the upper concrete b The calculation formula is as follows:

[0100] σ b =(γ RE T) / (4 b 1 L 1 )

[0101] The calculation formula for the upper limit of the punching shear force V of the concrete on the upper part of the boot beam is as follows:

[0102] V = 0.7 (3 h 0T +2 L 1 + b 1 )β hp f tj h 0T

[0103] h 0T =h c -h 1

[0104] Among them, h 0T It indicates the effective height of the anti-shear concrete cone on the upper part of the boot beam;

[0105] The design value of the punching force acting on the punching failure cone is V T The calculation formula is as follows:

[0106] V T =γ RE T / 4

[0107] 2. A computer device

[0108] The method comprises a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the method for designing an embedded steel tube concrete column base with a shoe beam are implemented.

[0109] The method proposed in the present invention firstly gives a calculation formula for the embedding depth of the embedded steel tube concrete column base with a boot beam, and then proposes a verification method for the column base according to the specifications from the aspects of stiffness, local concrete pressure bearing, shearing and pull-out resistance. After all the verifications are passed, it can be judged that the column base is available and reliable, and therefore has strong applicability.

[0110] The beneficial effects of the present invention are:

[0111] 1. Currently, none of the specifications provide a corresponding calculation formula for the buried depth of the embedded steel tube concrete column base with a boot beam. If the effectiveness of the column base is to be verified, it can only be verified through a numerical simulation method with cumbersome steps and low efficiency. There are problems such as high learning and time costs and inconvenience in use. The present invention provides a simplified calculation method suitable for solving the buried depth of the embedded steel tube concrete column base with a boot beam.

[0112] 2. At present, when ordinary embedded column bases are used, the buried depth needs to meet 2-3 times the length of the column side according to the specifications. This will make the total height of the pedestal foundation larger, resulting in material waste, construction difficulties and increased costs. The present invention proposes a design method for an embedded steel tube concrete column base with a boot beam to solve the pain point of the pedestal foundation being too high, and therefore has broad engineering application prospects.

[0113] 3. The present invention takes into account the calculation of the embedded steel tube concrete column base with boot beam in terms of stiffness, shearing, pull-out resistance and concrete bearing pressure. The design process has high integrity and systematicity, and is easy to learn and use for designers, and is efficient and friendly.

[0114] 4. The design method proposed in the present invention takes into account the situation that the upper structure columns are circular and rectangular steel tube concrete columns, making its application scope wider.

[0115] 5. The present invention can be widely used in the design of various structural column bases such as multi-story structures, large-span space structures and bridge structures, and can provide technical support and reliable guarantee for the promotion of such column base structures in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0116] Figure 1 This is a flow chart of the method proposed by the present invention.

[0117] Figure 2 A three-dimensional model diagram of the embedded steel tube concrete column base with a boot beam.

[0118] Figure 3 This is a side view of the embedded steel tube concrete column base structure with a boot beam.

[0119] Figure 4 Top view of the embedded circular steel tube concrete column base with boot beam.

[0120] Figure 5 This is a top view of the embedded rectangular steel tube concrete column base structure with a boot beam.

[0121] Figure 6 Schematic diagram of the pile foundation of circular steel tube concrete column.

[0122] Figure 7 Schematic diagram of pile foundation of rectangular steel tube concrete column.

[0123] Figure 8 This is a comparison chart of the buried depths actually obtained by adopting the design method proposed in the present invention for multiple rectangular steel tube concrete columns under the same working condition and the buried depth lines of 1.5 to 2 times the column width required by the specification.

[0124] In the figure: 1. Steel tube concrete column, 2. Boot beam, 3. Studs, 4. Stand steel bars, 5. Stirrups, 6. Column base plate, 7. Pile foundation, 8. Upper boundary of punching cone. DETAILED DESCRIPTION

[0125] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form.

[0126] like Figure 2 , Figure 3 and Figure 4As shown, the CFST column foot includes a CFST column 1, a boot beam 2, a bolt 3, a frame steel bar 4, a stirrup 5, a column bottom plate 6 and a pile foundation 7; the frame steel bar 4 is installed on the cap, and a plurality of stirrups 5 are welded to the outside of the frame steel bar 4 from top to bottom. The CFST column 1 is arranged inside the frame steel bar 4, and a column bottom plate 6 is welded to the lower end surface of the CFST column 1. A cross-structured boot beam 2 is welded to the lower part of the CFST column 1. The CFST column 1 is located at the center of the cross, and the side surfaces of the column bottom plate 6 are respectively welded to the lower flanges of the corresponding boot beams 2, so that the CFST column 1 is fixedly installed in the frame steel bar 4 through the boot beam 2. The bolt 3 is welded to the outer circumferential side surface of the lower part of the CFST column 1, and the bolt 3 is welded to the upper and lower flanges and the web of the boot beam 2. Example

[0127] like Figure 4 and Figure 6 As shown in the figure, the upper part of the steel tube concrete column foot adopts a circular steel tube concrete column, the lower part of the cap has 4 pile foundations, and there is no pile foundation within the punching cone. The steel tube column is made of Q355, the concrete strength in the column is C50, the concrete strength of the foundation is C35, and the thickness of the protective layer is a s =50mm, height of the column foot l h =12400mm, design value of vertical force at top of corner pile N 1 =3500kN, column foot design flow chart as follows Figure 1 As shown:

[0128] Step 1: Obtain the design parameters of the CFST column at the top of the CFST column foot and the pile foundation at the bottom, as well as the force transmitted from the column bottom to the pile foundation. All design parameters are given in Table 1.

[0129] Table 1 shows the design parameters of Example 1

[0130]

[0131] According to the size of the structural column and the force at the bottom of the column, the initial depth of the column foot h is determined. c =900mm, platform height h j =2100mm.

[0132] Step 2 is as follows:

[0133] First, according to all the design parameters of the CFST column foot in step 1 and the cross-sectional form of the CFST column, the design value of the bearing capacity of the CFST column is calculated, which includes the design value of the cross-sectional axial compressive bearing capacity of the CFST column N u , Design value of section bending bearing capacity M u , Design value of bending bearing capacity of section considering the influence of axial force M pc The shear capacity V corresponding to the bending capacity pc; Then, according to the design value of the bearing capacity of the steel tube concrete column, the buried depth of the embedded column foot of the steel tube concrete column with the boot beam is calculated to obtain the calculated column foot buried depth d; if the current column foot buried depth h c < calculated column foot burial depth d, then the current column foot burial depth h c Does not meet the requirements, need to increase the current column foot burial depth h c , and update the calculated column foot burial depth d until the latest column foot burial depth h c ≥Calculated column foot embedment depth d, obtain optimized column foot embedment depth h c ; Otherwise, bury the current column foot to depth h c As the optimized column foot embedment depth h c In this embodiment, the design value of the bearing capacity of the steel tube concrete column should be calculated according to the relevant contents of Chapter 5 of the Technical Specification for Steel Tube Concrete Structure GB50936-2014.

[0134] The details are as follows:

[0135] In the case of a circular concrete-filled steel tube column, the cross-sectional area of ​​the steel tube is A s According to the following formula:

[0136] A s =0.25πD 2 -0.25π(D-2t) 2 =3.35×10 4 mm 2

[0137] Core concrete cross-sectional area A of circular concrete-filled steel tube column c According to the following formula:

[0138] A c =0.25π(D-2t) 2 =6.03×10 5 mm 2

[0139] Design value of compressive bearing capacity of circular concrete-filled steel tube column section N u Obtained by the following process:

[0140] α sc = A s / A c =0.056

[0141] θ = α sc f / f sc =0.733

[0142] B = 0.176 f / 213 + 0.974 = 1.226

[0143] C=-0.104 f c / 14.4+0.031=-0.136

[0144] f sc =(1.212+ Bθ+Cθ 2 ) c =47.1MPa

[0145] N u =( A s + A c ) sc =3.0×10 4 kN

[0146] Among them, α sc represents the steel content of the steel tube concrete column; θ represents the hoop coefficient of the steel tube concrete column; B and C represent the two influence coefficients of the cross-sectional shape on the hoop effect; f sc Indicates the design value of compressive strength of steel tube concrete column, unit (N / mm 2 ).

[0147] Design value of bending bearing capacity of circular steel tube concrete column under bending moment only u Obtained by the following process:

[0148] W sc =π(r 0 4 -r ci 4 ) / (4 r 0 ) = 7.16 × 10 7 mm 3

[0149] M u =γ m W sc f sc =4.04×10 3 kN·m

[0150] Among them, γ m represents the plastic development coefficient; W sc Represents the section modulus of the circular steel tube concrete column, unit (mm 3 );r 0 Indicates the radius of the circular steel tube concrete column, unit (mm); r ci It represents the hollow radius of circular concrete-filled steel tube columns, which is taken as 0 for solid components. Unit: (mm).

[0151] Design value of axial force of concrete-filled steel tube column N c The design value of the compressive bearing capacity of its section N u The ratio is 0.534.

[0152] Since the ratio is greater than 0.255, the design value of the bending bearing capacity of the circular concrete-filled steel tube column considering the influence of axial force is M pc Obtained by the following process:

[0153] M pc =1.5(1- N c / N u )M u =2.83×10 3 kN·m

[0154] Shear design value V corresponding to the bending bearing capacity of the circular steel tube concrete column pc Obtained by the following process:

[0155] V pc = 3M pc / 2l h =341.7 kN

[0156] Next, calculate the ultimate bending moment that the shoe beam can bear according to the following formula:

[0157] M ula = b 1 L 1 f cj (L 1 + D) = 1.35 × 10 4 kN·m

[0158] M ulb =[3(h c -h 1 -a s )+ b 1 +2 L 1 ]( h c -h 1 -a s ))(L 1 +D)f tj =3.31×10 3 kN·m

[0159] M ul =min(M ula ,M ulb ) = 3.31 × 10 3 kN·m

[0160] The ultimate bending moment that the shoe beam can bear is calculated by the above formula to be 3.31×10 3 kN·m, the column foot burial depth can be calculated by the following formula:

[0161] d=V pc / (0.8Dfcj )+(2(V pc / (0.8Df cj )) 2 + 4(M pc -0.5M ul ) / (0.8Df cj )) 0.5 = 0.65m

[0162] D and h c Compare and get h c >d, indicating that the initially determined column base embedment depth meets the calculation requirements and does not need to be modified.

[0163] Step 3: According to the current column foot burial depth h c As well as other design parameters of the CFST column foot, the rigidity of the CFST column foot with boot beam, the pull-out resistance of the boot beam, the local bearing capacity of the column bottom plate concrete, the shear bearing capacity of the foundation under the column and the shearing of the corner pile on the cap are checked. If the calculation fails, the buried depth of the column foot h is adjusted. c / Height of the support h j / Design parameters of boot beam / Column base plate dimensions, until all verifications are passed, the design of the steel tube concrete column foot is completed.

[0164] Among them, the stiffness calculation process of the steel tube concrete column base with boot beam specifically includes:

[0165] If the column foot is buried at a depth of h c +Effective embedding length of shoe beam d l ≥Effective embedment depth of embedded concrete-filled steel tube column foot without shoe beam h c1 , it means that the stiffness of the steel tube concrete column foot with boot beam meets the design requirements and the stiffness verification is passed. Otherwise, it means that the stiffness of the steel tube concrete column foot with boot beam does not meet the design requirements and the buried depth of the column foot is increased. c Or the shoe beam size (i.e. the shoe beam height h 1 、Bridge width b 1 、Boot beam web thickness t w1 、Boot beam flange thickness t f1 ); If you choose to increase the column foot burial depth h c According to all the design parameters of the CFST column foot and the design value of the bearing capacity of the CFST column, the buried depth h of the column foot is c Adjust to obtain the optimal column foot embedment depth h c , and then judge the stiffness of the steel tube concrete column foot with boot beam. If you choose to increase the size of the boot beam, directly judge the stiffness of the steel tube concrete column foot with boot beam until the stiffness of the steel tube concrete column foot with boot beam meets the design requirements, and obtain the final column foot embedment depth h cand design parameters of the boot beam.

[0166] Effective embedment depth h of embedded concrete-filled steel tube column footing without shoe beam c1 The calculation formula is as follows:

[0167] δ = I s / I c =0.114

[0168] n cs = E c / E s =0.153

[0169] E sc =1.3k E f sc = 4.4 × 10 4 Mpa

[0170] E scm =E sc (1+δ / n cs )(1+α sc ) / ((1+α sc / n cs )(1+δ))= 5.35×10 4 Mpa

[0171] h c1 =4(E scm (I c +I s ) / E c ) 0.25 = 1.93 × 10 3 mm

[0172] Among them, E scm Indicates the elastic bending modulus of the steel tube concrete column, unit N / mm 2 ; E sc Indicates the elastic modulus of the steel tube concrete column, unit N / mm 2 ;I c ,I s Respectively represent the moment of inertia of the concrete and steel pipe parts, unit: mm 4 ;k E represents the conversion coefficient of axial compression elastic modulus of steel tube concrete column; δ represents the ratio of the moment of inertia of the steel tube part to the concrete part of the steel tube concrete column; n cs Represents the ratio of the elastic modulus of concrete to steel tube in concrete-filled steel tube columns; α sc It represents the ratio of the cross-sectional area of ​​the steel tube to the concrete part of the steel tube concrete column.

[0173] Effective embedding length d of the shoe beam l The calculation formula is as follows:

[0174] d l =4((E s I lx ) / E c ) 0.25 = 1.22 × 10 3 mm

[0175] Among them, I lx Indicates the moment of inertia of the shoe beam, unit: mm 4 ; E c 、E s Represents the elastic modulus of concrete and steel, in N / mm 2 .

[0176] The effective embedding depth h of the steel tube concrete column foot with boot beam is determined by the above calculation results. c +d l 2.12×10 3 mm.

[0177] h c +d l With h c1 Compare and get h c +d l >h c1 , indicating that the stiffness of the steel tube concrete column base with boot beam meets the design requirements and does not need to be modified.

[0178] The process of checking the pull-out resistance of the boot beam of the steel tube concrete column foot specifically includes:

[0179] If the upper limit of local concrete bearing pressure F lc >Design value of axial force at column base N c , then the design requirements are met, otherwise they are not met. The column base plate size is increased and then judged again until the upper limit of the local bearing pressure of the concrete is reached. lc Meet the design requirements and obtain the final column base plate size. Upper limit of local concrete bearing pressure F lc According to the following formula:

[0180] F lc =1.35β c β l f c A l = 1.39 × 10 5 kN

[0181] β l = (A b / A l ) 0.5 =2.1

[0182] A l=b d 2 +4 b 1 [L 1 -0.5(b d -D)] =2.94m 2

[0183] A b =9 b d 2 =12.94m 2

[0184] Among them, β c It represents the influence coefficient of concrete strength. When the concrete strength grade does not exceed C50, it is taken as 1.0; when the concrete strength grade is C80, it is taken as 0.8. The linear interpolation method is used in between. β l Indicates the strength enhancement factor of concrete when it is locally compressed; A l Indicates the local compression area of ​​concrete, unit: mm 2 ; A b Indicates the calculated bottom area of ​​local pressure, unit: mm 2 .f c Indicates the design value of the axial compressive strength of the core concrete, in N / mm 2 .

[0185] F lc With N c Compare and get N c <F lc , indicating that the local pressure bearing of the column base slab concrete meets the design requirements and does not need to be modified.

[0186] The verification process of the punching bearing capacity of the foundation under the column and the punching bearing capacity of the corner pile on the cap specifically includes:

[0187] If the punching force design value F acting on the punching failure cone l < the upper limit of the design value of the shear resistance of the cap F, it means that the shear of the steel tube concrete column on the cap meets the design requirements, and the shear bearing capacity of the foundation under the column passes the shear calculation of the cap; otherwise, it does not meet the design requirements, and the cap height h is increased. j Or increase the shoe beam length L 1 After that, calculate the upper limit F of the punching force design value of the abutment and re-judge until the punching force design value F acting on the punching failure cone is l <The upper limit of the design value of the shear resistance of the abutment F;

[0188] If the design value of the vertical force at the top of the corner pile is N l < the upper limit of the shear force of the corner pile on the cap N, it means that the shear force of the corner pile on the cap meets the design requirements and the shear force verification of the corner pile on the cap has passed; otherwise, it does not meet the design requirements and the cap height h is increased.j Or adjust the position of the corner pile, and then calculate the upper limit N of the shear force of the corner pile of the cap, and re-judge until the vertical force design value N of the corner pile top is reached. l <The upper limit of the shear force of the corner pile of the cap N; get the final cap height h j .

[0189] The design value of the punching force acting on the punching failure cone is F l The calculation formula is as follows:

[0190] F l =N c -∑N i =1.6×10 4 kN

[0191] Among them, N i It represents the sum of the net reaction force design values ​​of each pile within the range of the shear failure cone. The shear failure cone should be a cone formed by the line from the upper boundary of the cone to the edge of the corresponding pile top. The angle between the cone and the bottom surface of the cap should not be less than 45°. The upper boundary of the shear cone is the rectangle formed by the line connecting the midpoints of each shoe beam. N c It represents the axial force in the column base force;

[0192] The calculation formula for the upper limit F of the design value of the shear resistance of the abutment is as follows:

[0193] F=4α o (h a +a o )β hp f tj h 0 =1.92×10 4 kN

[0194] α o =0.84 / (0.2+λ o )=1.704

[0195] λ o =a o / h a =0.293

[0196] h 0 = h j -h c -α s =1.15m

[0197] h a =(L 1 +D) / 2 0.5 =1.27m

[0198] Among them, h 0 Indicates the effective height of the shear failure cone, in mm; λo Denotes the punching ratio of the punching failure cone; a o Denotes the horizontal distance from the upper boundary of the punching cone to the edge of the pile. When a o <0.2h 0 When, a o =0.2h 0 When a o >h 0 When, a o =h 0 , unit: mm; α o Denotes the punching coefficient of the punching failure cone; β hp Denotes the influence coefficient of the section height of the punching bearing capacity. When h 0 Is not greater than 800 mm, take 1.0. When h 0 Is greater than 2000 mm, take 0.9, and interpolate linearly in between. f tj Denotes the design value of the axial tensile strength of the foundation concrete. h a Denotes the side length of the upper boundary of the punching cone.

[0199] Compare the design value of the punching force F l Acting on the punching failure cone with the upper limit F of the punching resistance design value of the bearing platform to obtain F l <F, indicating that the punching of the concrete-filled steel tube column on the bearing platform meets the design requirements and does not need to be modified.

[0200] The calculation formula for the upper limit N of the punching resistance design value of the bearing platform against corner piles is as follows:

[0201] N = [α lx (c y + a y / 2) + α ly (c x + a x / 2)] β hp f tj h 0 = 3.86×10 3 kN,

[0202] α lx = 0.56 / (0.2 + λ lx ) = 0.867, α ly = 0.56 / (0.2 + λ ly ) = 0.596

[0203] λ lx = a x / h 0 = 0.446, λ ly = a y / h 0 = 0.739

[0204] Among them, λ lx and λ ly represent the punching shear ratios of the corner piles in the length and width directions of the rectangular pile cap; a x and a y respectively represent the horizontal distances from the inner edge of the corner pile to the upper boundary 8 of the punching shear cone along the 45° punching shear line in the length and width directions of the rectangular pile cap. When a x or a y <0.2h 0 , a x or a y = 0.2h 0 . When a x or a y > h 0 , a x or a y = h 0 , with the unit of mm; α lx and α ly respectively represent the corner pile punching shear coefficients in the length and width directions of the rectangular pile cap; c x and c y respectively represent the distances from the inner edge of the corner pile to the outer edge of the pile cap in the length and width directions of the rectangular pile cap, with the unit of mm. β hp represents the influence coefficient of the section height of the punching shear bearing capacity, f tj represents the design value of the axial tensile strength of the foundation concrete, and h 0 represents the effective height of the punching shear failure cone.

[0205] Compare the upper limit N of the design value of the punching shear force of the pile cap against the corner pile with the design value N 1 of the vertical force at the top of the corner pile. If N l < N, it indicates that the punching shear of the corner pile against the pile cap meets the design requirements and no modification is needed.

[0206] The process of checking the uplift resistance of the shoe beam specifically includes:

[0207] Conduct the uplift resistance check of the shoe beam for the concrete-filled steel tubular column foot under the action of the uplift force. If the result of the uplift resistance check of the column foot does not meet the design requirements, adjust the size of the shoe beam and re-conduct the uplift resistance check of the shoe beam until the uplift resistance check of the column foot meets the design requirements to obtain the final design parameters of the shoe beam.

[0208] Specifically as follows:

[0209] Respectively, by comparing the shear stress f vb generated on the web of the shoe beam with the design value f v of the shear strength of the steel, the tensile stress f bb generated on the flange of the shoe beam with the design value f of the tensile strength of the steel, and the local compressive stress σ generated by the shoe beam on the upper concreteb With the design value of concrete compressive strength f c , the upper limit V of the punching shear force of the concrete above the shoe beam and the design value V of the punching shear force acting on the punching failure cone T are judged as follows:

[0210] If f vb < f v , f bb < f, σ b < f c , V T < V are satisfied simultaneously, it indicates that the uplift resistance of the concrete-filled steel tubular column foot with a shoe beam meets the design requirements;

[0211] If f vb > f v , it indicates that when subjected to the uplift force, the web of the shoe beam does not meet the shear design requirements. After increasing the web thickness, f vb should be recalculated and judged until f vb < f v ;

[0212] If f bb > f c , it indicates that when subjected to the uplift force, the flange of the shoe beam does not meet the bending design requirements. After increasing the flange thickness or increasing the size of the shoe beam, f bb should be recalculated and judged until f bb < f;

[0213] If σ b > f c , it indicates that when subjected to the uplift force, the concrete above the shoe beam does not meet the local compressive design requirements. After increasing the width or length of the shoe beam, σ b should be recalculated and judged until σ b < f c ;

[0214] If V T > V, it indicates that when subjected to the uplift force, the punching shear resistance of the concrete above the shoe beam does not meet the design requirements. After increasing the embedment depth of the column foot, the width or length of the shoe beam, V T should be recalculated and judged until V T < V.

[0215] The calculation formula for the shear stress f vb generated by the uplift force at the bottom of the concrete-filled steel tubular column acting on the web of the shoe beam is as follows:

[0216] f vb = (γ RE T) / (4(h 1 - 2t f1 ) t w1)=71.33Mpa

[0217] Where T represents the upward pull force transmitted from the upper steel tube concrete column to the foundation.

[0218] The tensile stress f generated by the pull-out force on the flange of the shoe beam bb The calculation formula is as follows:

[0219] f bb =(γ RE T×0.5 L 1 ) / (4γ x W x ) =53.47Mpa

[0220] Among them, W x represents the net section modulus of the shoe beam along the main axis; γ x It represents the plastic development coefficient of the section of the shoe beam along the main axis.

[0221] The local compressive stress σ generated by the boot beam on the upper concrete b The calculation formula is as follows:

[0222] σ b =(γ RE T) / (4 b 1 L 1 ) =1.653Mpa

[0223] The calculation formula for the upper limit of the punching shear force V of the concrete on the upper part of the boot beam is as follows:

[0224] V = 0.7 (3 h 0T +2 L 1 + b 1 )β hp f tj h 0T =2.45×10 3 kN

[0225] h 0T =h c -h 1 =0.4m

[0226] Among them, h 0T It indicates the effective height of the anti-shear concrete cone on the upper part of the boot beam;

[0227] The design value of the punching force acting on the punching failure cone is V T The calculation formula is as follows:

[0228] V T =γ RE T / 4=743.75kN

[0229] fvb With f v 、f bb With f, σ b With f c 、V T Compare with V to obtain f vb < f v 、f bb < f, σ b < f c 、V T < V, indicating that the uplift resistance of the concrete - filled steel tube column foot with boot beam meets the design requirements and does not need to be modified.

[0230] So far, all design requirements have been met. Therefore, the above - mentioned parameters can be used to design this column foot.

[0231] Example 2

[0232] As Figure 5 and Figure 7 shown, the upper part of the concrete - filled steel tube column foot adopts a rectangular concrete - filled steel tube column. There are a total of 5 pile foundations at the lower part of the bearing platform, and 1 pile foundation is within the punching cone range. The material of the steel tube column is Q355, the strength of the concrete in the column is C50, the strength of the foundation concrete is C35, the protective layer thickness a s = 50mm, the storey height l h where the column foot is located = 12400mm, the characteristic value of the vertical compressive bearing capacity of a single pile R = 3500kN, and the design flow chart of the column foot is as Figure 1 shown:

[0233] Step 1: Obtain the design parameters of the upper concrete - filled steel tube column and the lower pile foundation and the force transmitted from the column bottom to the foundation. All design parameters are given in Table 2.

[0234] Table 2 is the design parameters of Example 2

[0235]

[0236] According to the size of the structural column and the magnitude of the column bottom force, initially determine the embedment depth h c = 1300mm of the column foot and the height h j = 2600mm of the bearing platform.

[0237] Step 2: According to all the design parameters of the concrete - filled steel tube column foot in Step 1, and combined with the design value of the bearing capacity of the concrete - filled steel tube column, adjust the embedment depth h c of the column foot to obtain the optimized embedment depth h c ;

[0238] Step 2 is specifically as follows:

[0239] First, according to all the design parameters of the CFST column foot in step 1 and the cross-sectional form of the CFST column, the design value of the bearing capacity of the CFST column is calculated, which includes the design value of the cross-sectional axial compressive bearing capacity of the CFST column N u , Design value of section bending bearing capacity M u , Design value of section bending bearing capacity considering the influence of axial force M pc The shear capacity V corresponding to the bending capacity pc ; Then, according to the design value of the bearing capacity of the steel tube concrete column, the buried depth of the embedded column foot of the steel tube concrete column with the boot beam is calculated to obtain the calculated column foot buried depth d; if the current column foot buried depth h c < calculated column foot burial depth d, then the current column foot burial depth h c Does not meet the requirements, need to increase the current column foot burial depth h c , and update the calculated column foot burial depth d until the latest column foot burial depth h c ≥Calculated column foot embedment depth d, obtain optimized column foot embedment depth h c ; Otherwise, bury the current column foot to depth h c As the optimized column foot embedment depth h c .

[0240] The details are as follows:

[0241] In the case of rectangular steel tube concrete columns, the cross-sectional area of ​​the steel tube is A s According to the following formula:

[0242] A s =2bt+2ht-4t 2 =9.37×10 4 mm 2

[0243] Core concrete cross-sectional area A of rectangular steel tube concrete column c According to the following formula:

[0244] A c =(b-2t)( h-2t) =9.06×10 5 mm 2

[0245] Design value of compressive bearing capacity of rectangular steel tube concrete column section N u Obtained by the following process:

[0246] N u =fA s + f c A c =4.86×10 4 kN

[0247] Design value of bending bearing capacity of circular steel tube concrete column under bending moment only u Obtained by the following process:

[0248] d n =(A s -2bt) / (f c (b-2t) / f+4t)=267.94mm

[0249] M u =f[0.5 A s (h-2t-d n )+bt(t+ d n )]=1.15×10 4 kN·m

[0250] Among them, d n Indicates the height of the concrete compression zone in the pipe, unit (mm);

[0251] Design value of axial force of concrete-filled steel tube column N c The design value of the compressive bearing capacity of its section N u The ratio is 0.247<f c A c / N u =0.431.

[0252] The design value of the bending bearing capacity of the rectangular steel tube concrete column considering the influence of axial force is M pc =M u =1.15×10 4 kN·m.

[0253] Shear design value V corresponding to the bending bearing capacity of the rectangular steel tube concrete column pc Obtained by the following process:

[0254] V pc = 3M pc / 2l h =1.39×10 3 kN

[0255] Then, calculate the ultimate bending moment that the shoe beam can bear according to the following formula:

[0256] M ul =min(M ula ,M ulb )=1.23×10 4 kN

[0257] M ula =b 1 L 1 f cj (L1 +h) = 1.43 × 10 4 kN·m

[0258] M ulb =[3(h c -h 1 -a s )+ b 1 +2 L 1 ]( h c -h 1 -a s ))(L 1 +h)f tj = 1.23 × 10 4 kN·m

[0259] The ultimate bending moment that the shoe beam can bear is calculated by the above formula to be 1.23×10 4 kN·m, the column foot burial depth can be calculated by the following formula:

[0260] d=V pc / (bf cj )+(2(V pc / (bf cj )) 2 + 4(M pc -0.5M ul ) / (bf cj )) 0.5 =1.22m

[0261] D and h c Compare and get h c >d, indicating that the initially determined column base embedment depth meets the calculation requirements and does not need to be modified.

[0262] Step 3: According to the current column foot burial depth h c As well as other design parameters of the CFST column foot, the rigidity of the CFST column foot with boot beam, the pull-out resistance of the boot beam, the local bearing capacity of the column bottom plate concrete, the shear bearing capacity of the foundation under the column and the shearing of the corner pile on the cap are checked. If the calculation fails, the buried depth of the column foot h is adjusted. c / Height of the support h j / Design parameters of boot beam / Column base plate dimensions, until all verifications are passed, the design of the steel tube concrete column foot is completed.

[0263] Among them, the stiffness calculation process of the steel tube concrete column base with boot beam specifically includes:

[0264] If the column foot is buried at a depth of h c +Effective embedding length of shoe beam d l≥Effective embedment depth of embedded concrete-filled steel tube column foot without shoe beam h c1 , it means that the stiffness of the steel tube concrete column foot with boot beam meets the design requirements and the stiffness verification is passed. Otherwise, it means that the stiffness of the steel tube concrete column foot with boot beam does not meet the design requirements and the buried depth of the column foot is increased. c Or the shoe beam size (i.e. the shoe beam height h 1 、Bridge width b 1 、Boot beam web thickness t w1 、Boot beam flange thickness t f1 ); If you choose to increase the column foot burial depth h c According to all the design parameters of the CFST column foot and the design value of the bearing capacity of the CFST column, the buried depth h of the column foot is c Adjust to obtain the optimal column foot embedment depth h c , and then judge the stiffness of the steel tube concrete column foot with boot beam. If you choose to increase the size of the boot beam, directly judge the stiffness of the steel tube concrete column foot with boot beam until the stiffness of the steel tube concrete column foot with boot beam meets the design requirements, and obtain the final column foot embedment depth h c and design parameters of the boot beam.

[0265] The effective embedding depth of the embedded steel tube concrete column foot without boot beam is calculated according to the following formula:

[0266] h c1 =4((0.8E c I c +E s I s ) / E c ) 0.25 =2.5×10 3 mm

[0267] The effective embedding length d of the shoe beam is calculated according to the following formula l :

[0268] d l =4((E s I lx ) / E c ) 0.25 = 1.22 × 10 3 mm

[0269] The effective embedding depth of the steel tube concrete column foot with boot beam is determined to be 2.52×10 3 m.

[0270] h c +d l With h c1 Compare and get h c +d l>h c1 , indicating that the stiffness of the steel tube concrete column base with boot beam meets the design requirements and does not need to be modified.

[0271] The process of checking the pull-out resistance of the boot beam of the steel tube concrete column foot specifically includes:

[0272] If the upper limit of local concrete bearing pressure F lc >Design value of axial force at column base N c , then the design requirements are met, otherwise they are not met. The column base plate size is increased and then judged again until the upper limit of the local bearing pressure of the concrete is reached. lc Meet the design requirements and obtain the final column base plate size. Upper limit of local concrete bearing pressure F lc According to the following formula:

[0273] F lc =1.35β c β l f c A l = 1.57 × 10 5 kN

[0274] β l = (A b / A l ) 0.5 =2.184

[0275] A l =b d h d +2b 1 [L 1 -0.5(b d -b)]+2 b 1 [L 1 -0.5(h d -h)]=3.19m 2

[0276] A b =3b d (2b d + h d )=15.21m 2

[0277] F lc With N c Compare and get N c <F lc , indicating that the local pressure bearing of the column base slab concrete meets the design requirements and does not need to be modified.

[0278] The verification process of the punching bearing capacity of the foundation under the column and the punching bearing capacity of the corner pile on the cap specifically includes:

[0279] If the punching force design value F acting on the punching failure cone l < the upper limit of the design value of the shear resistance of the cap F, it means that the shear of the steel tube concrete column on the cap meets the design requirements, and the shear bearing capacity of the foundation under the column passes the shear calculation of the cap; otherwise, it does not meet the design requirements, and the cap height h is increased. j Or increase the shoe beam length L 1 After that, calculate the upper limit F of the punching force design value of the abutment and re-judge until the punching force design value F acting on the punching failure cone is l <The upper limit of the design value of the shear resistance of the abutment F;

[0280] If the design value of the vertical force at the top of the corner pile is N l < the upper limit of the shear force of the corner pile on the cap N, it means that the shear force of the corner pile on the cap meets the design requirements and the shear force verification of the corner pile on the cap has passed; otherwise, it does not meet the design requirements and the cap height h is increased. j Or adjust the position of the corner pile, and then calculate the upper limit N of the shear force of the corner pile of the cap, and re-judge until the vertical force design value N of the corner pile top is reached. l <The upper limit of the shear force of the corner pile of the cap N; get the final cap height h j .

[0281] The punching force on the shear failure cone is calculated according to the following formula:

[0282] F l =N c -∑N i =9.6×10 3 kN

[0283] The upper limit of the design value of the shear resistance of the cap is calculated according to the following formula:

[0284] F=4α o (h a +a o )β hp f tj h 0 =1.323×10 4 kN

[0285] α o =0.84 / (0.2+λ o )=0.827

[0286] λ o =a o / h a =0.816

[0287] h 0 = h j -h c -α s =1.15m

[0288] h a =( (L 1 +h) 2 / 4+ (L 1 +b) 2 / 4) 0.5 =1.344m

[0289] Compare F l with F, and obtain F l <F, indicating that the punching shear of the concrete-filled steel tube column on the pile cap meets the design requirements and no modification is required.

[0290] Calculate the upper limit of the design value of the punching shear force of the pile cap against the corner pile according to the following formula:

[0291] N = [α lx (c y + a y / 2)+α ly (c x + a x / 2)] β hp f tj h 0 =3.829×10 3 kN,

[0292] α lx =0.56 / (0.2 + λ lx ) = 0.742, α ly =0.56 / (0.2 + λ ly ) = 0.742

[0293] λ lx = a x / h 0 =0.554, λ ly = a y / h 0 =0.554

[0294] Compare N with N 1 and obtain N l <N, which indicates that the punching shear of the corner pile on the pile cap meets the design requirements and no modification is required.

[0295] The specific process of the uplift resistance check of the shoe beam includes:

[0296] Conduct the uplift resistance check of the shoe beam for the concrete-filled steel tube column foot under the action of the uplift force. If the result of the uplift resistance check of the column foot does not meet the design requirements, adjust the size of the shoe beam and re-conduct the uplift resistance check of the shoe beam until the uplift resistance check of the column foot meets the design requirements to obtain the final design parameters of the shoe beam.

[0297] Specifically as follows:

[0298] By comparing the shear stress f vb generated on the web of the shoe beam with the design value of the shear strength of the steel f v , the tensile stress f bb generated on the flange of the shoe beam with the design value of the tensile strength of the steel f, and the local compressive stress σ b generated by the shoe beam on the upper concrete with the design value of the compressive strength of the concrete f c , as well as the upper limit V of the punching shear force of the upper concrete of the shoe beam and the design value V of the punching shear force acting on the punching failure cone T to make a judgment:

[0299] If f vb < f v , f bb < f, σ b < f c , V T < V are satisfied simultaneously, it indicates that the uplift resistance of the concrete-filled steel tubular column foot with a shoe beam meets the design requirements;

[0300] If f vb > f v , it indicates that when subjected to the uplift force, the web of the shoe beam does not meet the shear design requirements. After increasing the web thickness, f vb needs to be recalculated and judged until f vb < f v ;

[0301] If f bb > f c , it indicates that when subjected to the uplift force, the flange of the shoe beam does not meet the bending design requirements. After increasing the flange thickness or increasing the size of the shoe beam, f bb needs to be recalculated and judged until f bb < f;

[0302] If σ b > f c , it indicates that when subjected to the uplift force, the upper concrete of the shoe beam does not meet the local compressive design requirements. After increasing the width or length of the shoe beam, σ b needs to be recalculated and judged until σ b < f c ;

[0303] If V T > V, it indicates that when subjected to the uplift force, the punching shear resistance of the upper concrete of the shoe beam does not meet the design requirements. After increasing the embedment depth of the column foot, the width or length of the shoe beam, V T needs to be recalculated and judged until V T < V.

[0304] The shear stress generated by the pull-out force at the bottom of the steel tube concrete column on the web of the boot beam is calculated according to the following formula:

[0305] f vb =(γ RE T) / (4(h 1 -2t f1 ) w1 )=101.9Mpa

[0306] The tensile stress generated by the pull-out force on the flange of the shoe beam is calculated according to the following formula:

[0307] f bb =(γ RE T×0.5 L 1 ) / (4γ x W x ) =76.39Mpa

[0308] The local compressive stress generated by the shoe beam on the upper concrete is calculated according to the following formula:

[0309] σ b =(γ RE T) / (4 b 1 L 1 ) =2.361Mpa

[0310] The upper limit of the punching shear force of the concrete on the upper part of the boot beam is calculated according to the following formula:

[0311] V = 0.7 (3 h 0T +2 L 1 + b 1 )β hp f tj h 0T =5.521×10 3 kN

[0312] h 0T =h c -h 1 =0.9m

[0313] The design value of the punching force acting on the punching failure cone is calculated according to the following formula:

[0314] V T =γ RE T / 4=1.063×10 3 kN

[0315] f vb With f v 、f bb With f, σ b With f c 、V TCompare with V to obtain f vb <f v 、f bb <f, σ b <f c 、V T <V indicates that the uplift resistance of the concrete - filled steel tube column foot with a boot beam meets the design requirements and no modification is required.

[0316] All design requirements have been met至此所有设计要求都已满足,因此可利用以上参数对该柱脚进行设计。

[0317] Design the embedment depths of the rectangular concrete - filled steel tube columns with boot beams in Example 2 and those used in actual projects. The width range of the columns is 750 - 1200 mm. After calculation, the range of the designed embedment depth of the columns is 1100 - 1500 mm. The distribution diagram is as Figure 8 所示。 Figure 8 It also shows the comparison result of the designed column embedment depth with the embedment depth line of 1.5 - 2 times the column width required by relevant codes. It can be seen that the required embedment depth of the rectangular concrete - filled steel tube column with a boot beam is greatly reduced compared with the code requirements, which reflects the broad engineering application prospects of the method of the present invention.

[0318] It should be noted that the above - mentioned embodiments are only used to illustrate the technical solutions of the present invention, not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A design method for an embedded steel tube concrete column base with a boot beam, characterized in that: The following steps are involved: Step 1: Obtain the design parameters of the CFST column at the top of the CFST column foot and the pile foundation at the bottom, as well as the force transmitted from the column bottom to the pile foundation, and preset the buried depth h of the column foot. c , Platform height h j , design parameters of the boot beam and dimensions of the column base plate; Step 2: According to all the design parameters of the CFST column foot in step 1, and combined with the bearing capacity design value of the CFST column, the column foot embedment depth h c Adjust to obtain the optimal column foot embedment depth h c ; Step 3: According to the current column foot burial depth h c As well as other design parameters of the CFST column foot, the rigidity of the CFST column foot with boot beam, the pull-out resistance of the boot beam, the local bearing capacity of the column bottom plate concrete, the shear bearing capacity of the foundation under the column and the shearing of the corner pile on the cap are checked. If the calculation fails, the buried depth of the column foot h is adjusted. c / Height of the support platform h j / Design parameters of boot beam / Column base plate dimensions, until all verifications are passed, the design of the steel tube concrete column foot is completed.

2. The design method of an embedded steel tube concrete column base with a boot beam according to claim 1 is characterized in that: The step 2 is specifically as follows: First, according to all the design parameters of the steel tube concrete column foot in step 1 and the cross-sectional form of the steel tube concrete column, the bearing capacity design value of the steel tube concrete column is calculated; then, according to the bearing capacity design value of the steel tube concrete column, the buried depth of the embedded column foot of the steel tube concrete column with the boot beam is calculated to obtain the calculated column foot buried depth d; if the current column foot buried depth h c < calculated column foot burial depth d, then increase the current column foot burial depth h c , and update the calculated column foot burial depth d until the latest column foot burial depth h c ≥Calculated column foot embedment depth d, obtain optimized column foot embedment depth h c ; Otherwise, bury the current column foot to depth h c As the optimized column foot embedment depth h c .

3. The design method of an embedded steel tube concrete column base with a boot beam according to claim 2 is characterized in that: In step 2, when the cross-section of the steel tube concrete column is a circular cross-section, the buried depth of the embedded column foot of the steel tube concrete column with a boot beam is calculated according to the design value of the bearing capacity of the steel tube concrete column to obtain the calculated buried depth d of the column foot, including: If the design value of the bending bearing capacity of the section under the influence of axial force is considered, M pc The bending moment M borne by the column foot beam ul If the ratio is greater than or equal to 0.5, the calculated column foot embedment depth d satisfies the following formula: d=V pc / (0.8Df cj )+(2(V pc / (0.8Df cj )) 2 + 4(M pc -0.5M ul ) / (0.8Df cj )) 0.5 If the design value of the bending bearing capacity of the steel tube concrete column is M pc The bending moment M borne by the column foot beam ul If the ratio is less than 0.5, the calculated column foot embedment depth d satisfies the following formula: d=V pc / (0.8Df cj ) Where D is the diameter of the circular concrete-filled steel tube column; V pc represents the shear capacity corresponding to the bending capacity, f cj Indicates the design value of the axial compressive strength of foundation concrete.

4. The design method of an embedded steel tube concrete column base with a boot beam according to claim 2, characterized in that: In step 2, when the cross-section of the steel tube concrete column is a rectangular cross-section, the buried depth of the embedded column foot of the steel tube concrete column with a boot beam is calculated according to the design value of the bearing capacity of the steel tube concrete column to obtain the calculated column foot buried depth d, which is specifically: If the design value of the bending bearing capacity of the section under the influence of axial force is considered, M pc The bending moment M borne by the column foot beam ul If the ratio is greater than or equal to 0.5, the calculated column foot embedment depth d satisfies the following formula: d=V pc / (bf cj )+(2(V pc / (bf cj )) 2 + 4(M pc -0.5M ul ) / (bf cj )) 0.5 If the design value of the bending bearing capacity of the section under the influence of axial force is considered, M pc The bending moment M borne by the column foot beam ul If it is less than 0.5, the calculated column foot embedment depth d satisfies the following formula: d=V pc / (bf cj ) M ul =min(M ula ,M ulb ) M ula =b1L1f cj (L1+D) M ulb =[3(h c - h1 -a s )+ b1+2 L1]( h c - h1 -a s )(L1+D)f tj Where D is the diameter of the circular concrete-filled steel tube column; V pc represents the shear capacity corresponding to the bending capacity, f cj Indicates the design value of the axial compressive strength of the foundation concrete, M ula It represents the bending moment borne by the shoe beam under bending action; M ulb Indicates the bending moment that the shear failure cone on the upper part of the shoe beam can withstand; f tj Indicates the design value of the axial tensile strength of the foundation concrete.

5. The design method of an embedded steel tube concrete column base with a boot beam according to claim 1, characterized in that: In step 3, the stiffness calculation process of the steel tube concrete column foot with boot beam specifically includes: If the column foot is buried at a depth of h c +Effective embedding length of shoe beam d l ≥Effective embedment depth of embedded concrete-filled steel tube column foot without shoe beam h c1 , it means that the stiffness of the steel tube concrete column foot with boot beam meets the design requirements and the stiffness verification is passed. Otherwise, it means that the stiffness of the steel tube concrete column foot with boot beam does not meet the design requirements and the buried depth of the column foot is increased. c Or the size of the shoe beam; if you choose to increase the column foot embedment depth h c According to all the design parameters of the CFST column foot and the design value of the bearing capacity of the CFST column, the buried depth h of the column foot is c Adjust to obtain the optimal column foot embedment depth h c , and then judge the stiffness of the steel tube concrete column foot with boot beam. If you choose to increase the size of the boot beam, directly judge the stiffness of the steel tube concrete column foot with boot beam until the stiffness of the steel tube concrete column foot with boot beam meets the design requirements, and obtain the final column foot embedment depth h c and design parameters of the boot beam.

6. The design method of an embedded steel tube concrete column base with a shoe beam according to claim 5, characterized in that: The effective embedding length d of the shoe beam l The calculation formula is as follows: d l =4((E s I lx ) / E c ) 0.25 Among them, I lx represents the moment of inertia of the shoe beam; E c 、E s represent the elastic modulus of concrete and steel respectively.

7. The design method of an embedded steel tube concrete column base with a boot beam according to claim 1, characterized in that: In step 3, the process of checking the pull-out resistance of the boot beam of the steel tube concrete column foot specifically includes: If the upper limit of local concrete bearing pressure F lc >Design value of axial force at the column base N c , then the design requirements are met, otherwise they are not met. The column base plate size is increased and then judged again until the upper limit of the local bearing pressure of the concrete is reached. lc Meet the design requirements and obtain the final column base plate size.

8. The design method of an embedded steel tube concrete column base with a boot beam according to claim 1, characterized in that: In step 3, the calculation process of the punching bearing capacity of the foundation under the column and the punching of the corner pile on the cap specifically includes: If the punching force design value F acting on the punching failure cone l < the upper limit of the design value of the shear resistance of the cap F, it means that the shear of the steel tube concrete column on the cap meets the design requirements, and the shear bearing capacity of the foundation under the column passes the shear calculation of the cap; otherwise, it does not meet the design requirements, and the cap height h is increased. j Or increase the shoe beam length L1, and then calculate the upper limit F of the design value of the shear force of the cap, and re-judge until the design value F of the shear force acting on the shear failure cone is l <The upper limit of the design value of the shear resistance of the abutment F; If the design value of the vertical force at the top of the corner pile is N l < the upper limit of the shear force of the corner pile on the cap N, it means that the shear force of the corner pile on the cap meets the design requirements and the shear force verification of the corner pile on the cap has passed; otherwise, it does not meet the design requirements and the cap height h is increased. j Or adjust the position of the corner pile, and then calculate the upper limit N of the shear force of the corner pile of the cap, and re-judge until the vertical force design value N of the corner pile top is reached. l <The upper limit of the shear force of the corner pile of the cap N; get the final cap height h j .

9. The design method of an embedded steel tube concrete column base with a boot beam according to claim 1, characterized in that: In step 3, the anti-pullout calculation process of the shoe beam specifically includes: The pull-out resistance of the boot beam of the steel tube concrete column base subjected to pull-out force is checked. If the pull-out resistance calculation result of the column base does not meet the design requirements, the size of the boot beam is adjusted and the pull-out resistance of the boot beam is re-checked until the pull-out resistance calculation of the column base meets the design requirements and the final design parameters of the boot beam are obtained.

10. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, the steps of the method for designing an embedded steel tube concrete column base with a boot beam as described in any one of claims 1 to 9 are implemented.

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