A method for calculating the characteristic value of the bending bearing capacity of a combined structure beam of steel and uhpc

Abstract

The application provides a method for calculating the characteristic value of the bending bearing capacity of a combined structure beam of steel and UHPC, different constitutive models are adopted according to the performance characteristics of UHPC, T-shaped steel beams and steel bars in the combined structure beam, the contribution of the strain hardening performance of the materials to the bending bearing capacity is fully considered, and the real performance of the structure can be obtained compared with the ideal elastic-plastic model; meanwhile, the initial values of the cross-section curvature, the iterative calculation increment of the curvature and the iterative calculation increment of the position of the neutral axis for the conventional bridge calculation are given, the influence coefficient method is adopted to search the position of the neutral axis and the cross-section curvature, which is helpful to accelerate the searching speed and solve the problem of non-convergence caused by the artificial setting of the iterative increment; finally, the strain of the top of the UHPC concrete reaching the compressive ultimate strain of the UHPC or the strain of the bottom of the T-shaped steel beam reaching the ultimate strain of the steel is simultaneously taken as the judgment condition, and both the crushing of the UHPC and the reaching of the tensile ultimate strength of the steel can be considered.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bridge engineering, in particular to a method for calculating the flexural bearing capacity characteristic value of a steel and UHPC combined structure beam. BACKGROUND

[0002] Traditional fabricated bridges have the characteristics of large quantity and wide range, and the main structural forms are prestressed hollow slab bridges, prestressed T-beam bridges and prestressed small box girder bridges. The above-mentioned bridges have the following common characteristics: (1) ordinary concrete (NC) is used as the main structural material, which is heavy and easy to crack; (2) the distribution and material consumption of steel bars and prestressed steel bars are limited by the size of the concrete structure and the pouring quality requirements, resulting in that the internal force arm is not greater than the height of the concrete section when bending, which is low in efficiency.

[0003] With the popularization of ultra-high performance concrete (UHPC), in recent years, existing technologies have tried to use UHPC to replace NC as the main building material to reduce the self-weight and improve the performance, such as steel beam-UHPC bridge deck panel composite beam, but there are defects such as the material performance cannot be fully utilized, the steel consumption and welding workload are large. In order to fully utilize the excellent performance of steel and UHPC materials and further improve the economy and applicability of steel-UHPC composite beams, some new composite beam structures have been proposed. In the currently disclosed technologies, Chinese patent applications with publication numbers CN112391932A and CN112342889A both propose a UHPC-T beam using profiled steel as external reinforcement, and the idea is to use UHPC to bear the high compressive stress of the upper flange and the low tensile stress of the composite web, and use profiled steel to bear the high tensile stress of the lower part, which fully utilizes the material performance. Different from traditional concrete beams with internal steel bars and prestressed steel bars, or pure steel web composite beam bridges, the mechanical characteristics of the externally reinforced UHPC-T beam are quite different, showing multiple stress states, i.e., horizontal shear of the composite shear member, vertical shear of the composite web, and bending resistance of the composite beam. The existing technology lacks a method for calculating the flexural bearing capacity characteristic value of the steel-UHPC composite beam, which greatly limits its application and also faces structural safety risks.

[0004] In view of the above, there is an urgent need for a method for calculating the flexural bearing capacity characteristic value of a steel and UHPC combined structure beam to solve the problems existing in the prior art. SUMMARY

[0005] The present application aims to provide a method for calculating the flexural bearing capacity characteristic value of a steel and UHPC combined structure beam, and aims to solve the problem that the prior art lacks a method for calculating the flexural bearing capacity characteristic value of a steel-UHPC composite beam, which greatly limits its application and also faces structural safety risks. The specific technical solution is as follows:

[0006] A method for calculating the characteristic value of the flexural bearing capacity of a combined structure beam of steel and UHPC, comprising the following steps:

[0007] A1, setting constant parameters, including calculating error convergence value , curvature iterative calculation increment , and neutral axis position iterative calculation increment ;

[0008] A2, inputting the cross-sectional size of the combined structure beam, the properties of each material in the combined structure beam, and the nonlinear constitutive model;

[0009] A3, dividing the cross section of the combined structure beam into element layers, specifically:

[0010] The cross section of the UHPC concrete of the combined structure beam and the cross section of the part of the T-shaped steel beam outside the UHPC concrete are respectively divided into element layers, and the cross section of all longitudinal steel bars in the uppermost layer of the combined structure beam and the cross section of all longitudinal steel bars in the bottom layer of the combined structure beam are respectively taken as an element layer;

[0011] A4, assuming the initial cross-sectional curvature of the combined structure beam , wherein ;

[0012] A5, assuming the position of the neutral axis of the combined structure beam , wherein ;

[0013] A6, calculating the strain of each element layer according to the plane cross-section assumption;

[0014] A7, calculating the stress of each element layer according to the strain of each element layer and the nonlinear constitutive model corresponding to the element layer;

[0015] A8, calculating the resultant force in the cross section of the combined structure beam according to the stress and area of each element layer F ;

[0016] A9, if is not greater than , then entering step A10; if is not less than , then correcting and repeating A6-A9;

[0017] A10, judging whether there exists upper edge compressive strain of the UHPC concrete less than its compressive ultimate strain, or lower edge tensile strain of the T-shaped steel beam greater than its ultimate tensile strain; if so, then 0.1 , After repeating steps A4-A10, if not, go to step A11;

[0018] A11, judge whether the upper edge compressive strain of UHPC concrete meets the requirement Subtract the compressive ultimate strain of UHPC concrete , or the ultimate tensile strain of T-shaped steel beam minus the lower edge tensile strain of T-shaped steel beam is less than or equal to ; if yes, go to step A12, if not, modify After repeating steps A5-A11;

[0019] A12, calculate the flexural capacity characteristic value of the composite structure beam according to the force moment of each unit layer .

[0020] Preferably, in step A2, the nonlinear constitutive model of each material is:

[0021] The nonlinear constitutive model of UHPC concrete is:

[0022] (8),

[0023] Wherein, is the strain of UHPC concrete, is the stress of UHPC concrete, is the elastic modulus of UHPC concrete; is the compressive ultimate strain of UHPC concrete; is the tensile elastic ultimate strain of UHPC concrete; is the tensile ultimate strain of UHPC concrete; is the fracture strain of UHPC concrete; is the tensile elastic ultimate stress of UHPC concrete; is the tensile ultimate stress of UHPC concrete;

[0024] The nonlinear constitutive model of T-shaped steel beam and steel bar in the composite structure beam is:

[0025] (9),

[0026] Wherein, is the strain of T-shaped steel beam or steel bar, is the stress of T-shaped steel beam or steel bar, is the elastic modulus of T-shaped steel beam or steel bar; is the compressive ultimate strain of T-shaped steel beam or steel bar; is the tensile yield strain of T-shaped steel beam or steel bar; The strain hardening starting strain of the T-shaped steel beam or the steel bar; The ultimate tensile strain of the T-shaped steel beam or the steel bar; if there is no yield platform, . The yield stress of the T-shaped steel beam or the steel bar; The ultimate tensile stress of the T-shaped steel beam or the steel bar.

[0027] In the above technical solution, preferably, the calculation method of the strain of each unit layer in step A6 is:

[0028] The strain of the first unit layer in the UHPC concrete i , the positive value is the tensile strain, and the negative value is the compressive strain; the strain of the first unit layer in the T-shaped steel beam , the positive value is the tensile strain, and the negative value is the compressive strain; k The strain of the unit layer corresponding to all longitudinal steel bars of the bottom layer of the composite structure beam ; the strain of the unit layer corresponding to all longitudinal steel bars of the top layer of the composite structure beam

[0029] . Wherein, The vertical distance from the center of the first unit layer in the UHPC concrete to the upper surface of the composite structure beam

[0030] , the positive value is the tensile strain, and the negative value is the compressive strain; the vertical distance from the center of the first unit layer in the T-shaped steel beam to the upper surface of the composite structure beam , the positive value is the tensile strain, and the negative value is the compressive strain; i The vertical distance from the center of the unit layer corresponding to all longitudinal steel bars of the bottom layer of the composite structure beam to the upper surface of the composite structure beam k , the positive value is the tensile strain, and the negative value is the compressive strain; the vertical distance from the center of the unit layer corresponding to all longitudinal steel bars of the top layer of the composite structure beam to the upper surface of the composite structure beam . In the above technical solution, preferably, the calculation method of the stress of each unit layer in step A7 is:

[0031] According to formula (8), the stress of the unit layer in the UHPC concrete

[0032] , the positive value is the tensile stress, and the negative value is the compressive stress; according to formula (9), the stress of the unit layer in the T-shaped steel beam , the positive value is the tensile stress, and the negative value is the compressive stress; according to formula (9), the stress of the unit layer corresponding to all longitudinal steel bars of the bottom layer of the composite structure beam ; according to formula (9), the stress of the unit layer corresponding to all longitudinal steel bars of the top layer of the composite structure beam .

[0033] In the above technical solution, preferably, the resultant force in the cross section of the composite structure beam in step A8 is​​F , specifically:

[0034] (11),

[0035] wherein, is the area of the i-th unit layer in the UHPC concrete, i is the area of the i-th unit layer in the T-shaped steel beam, is the area of the unit layer corresponding to all longitudinal steel bars in the bottom layer of the composite structure beam, k is the area of the unit layer corresponding to all longitudinal steel bars in the top layer of the composite structure beam. In the above technical solution, preferably, in step A12, the characteristic value of the bending resistance of the composite structure beam is calculated , specifically:

[0036]

[0037] (12).

[0038] In the above technical solution, preferably, in step A9, the influence coefficient method is used for iterative correction , specifically:

[0039] A9.1, assuming the new neutral axis position of the composite structure beam , wherein ;

[0040] A9.2, repeating steps A6-A8 to calculate the resultant force in the cross section of the composite structure beam ;

[0041] A9.3, calculating the change value of the resultant force in the cross section of the composite structure beam , wherein ;

[0042] A9.4, correcting the neutral axis position of the composite structure beam , wherein .

[0043] In the above technical solution, preferably, in step A11, the influence coefficient method is used for iterative correction , specifically:

[0044] A11.1, assuming the new cross-sectional curvature of the composite structure beam , wherein ;

[0045] A11.2, repeating steps A5-A10 to calculate the corresponding upper edge compressive strain of the UHPC concrete​​ and the tensile strain of the lower edge of the T-shaped steel beam ;

[0046] A11.3, calculating the compressive strain variation value of the upper edge of the UHPC concrete and the tensile strain variation value of the lower edge of the T-shaped steel beam ; wherein , ;

[0047] A11.4, correcting the cross-section curvature of the composite structure beam ;

[0048] wherein , is the compressive ultimate strain of the UHPC concrete, is the ultimate tensile strain of the T-shaped steel beam.

[0049] In the above technical solution, preferably, in the step A3, the vertical distance of the center of each unit layer from the upper surface of the composite structure beam and the area of each unit layer are obtained.

[0050] In the above technical solution, preferably, the minimum compressive strain selected from the unit layers of the UHPC concrete is the compressive strain of the upper edge of the UHPC concrete and the maximum tensile strain selected from the unit layers of the T-shaped steel beam is the tensile strain of the lower edge of the T-shaped steel beam .

[0051] The application of the technical solution of the present application has the following beneficial effects:

[0052] The characteristic value calculation method of the bending resistance proposed in the present application is helpful for engineering and technical personnel to judge the key mechanical properties of the structure, the calculation method is scientific and has high calculation efficiency, which is helpful for promoting the engineering application of the innovative structure and creating social and economic value.

[0053] The bending resistance calculation method proposed in the present application adopts different constitutive models according to the performance characteristics of UHPC, T-shaped steel beams and steel bars, fully considers the contribution of material strain hardening performance to the bending resistance, and compared with the ideal elastic-plastic model, can obtain the real performance of the structure and reduce waste.

[0054] The bending resistance calculation method proposed in the present application gives the initial values of the cross-section curvature, the curvature iterative calculation increment and the neutral axis position iterative calculation increment for the conventional bridge calculation, adopts the influence coefficient method to search the neutral axis position and the cross-section curvature, which is helpful for speeding up the search speed and at the same time solves the problem of non-convergence caused by artificial setting of the iterative increment.

[0055] The anti-bending bearing capacity calculation method simultaneously takes the UHPC concrete top strain reaching the UHPC compression limit strain or the T-shaped steel beam bottom strain reaching the steel limit strain as a judgment condition, can simultaneously consider the UHPC crushing and the steel reaching the tensile limit strength two failure modes, and is more convenient and fast than the traditional algorithm.

[0056] In addition to the objects, features, and advantages described above, the present application has other objects, features and advantages. The present application will be described in further detail below with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0057] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application, illustrate the preferred embodiment of the application and assist in

[0058] Figure 1 is an axonometric view of a steel and UHPC composite structure beam;

[0059] Figure 2 is Figure 1 is a structural schematic view of a vertical stirrup group in the composite structure beam;

[0060] Figure 3 is Figure 1 is a structural schematic view of a steel dowel and mortise in the composite structure beam;

[0061] Figure 4 is a flow chart of the steel and UHPC composite structure beam design method of the present application;

[0062] Figure 5 is a flow chart of the anti-bending bearing capacity characteristic value calculation in the design method of the present application;

[0063] Figure 6 is a nonlinear constitutive model schematic view of UHPC concrete;

[0064] Figure 7 is a nonlinear constitutive model schematic view of a T-shaped steel beam or a steel bar;

[0065] Figure 8 is a cross-sectional schematic view of a composite structure beam;

[0066] Figure 9 is a cross-sectional internal strain distribution schematic view of a composite structure beam;

[0067] Figure 10 is a cross-sectional internal stress distribution schematic view of a composite structure beam;

[0068] Among them, 100 is the composite structural beam, 110 is the UHPC bridge deck, 111 is the transverse reinforcement of the bridge deck, 112 is the longitudinal reinforcement of the bridge deck, 120 is the UHPC rib, 121 is the bottom open stirrup, 122 is the top open stirrup, 123 is the bottom longitudinal reinforcement, 124 is the second bottom longitudinal reinforcement, 125 is the longitudinal distribution reinforcement, 126 is the transverse short reinforcement, 130 is the T-shaped steel beam, 131 is the steel bottom plate, 132 is the steel web, 133 is the steel tenon, and 134 is the mortise. Detailed Implementation

[0069] To facilitate understanding of the present invention, a more complete description is provided below, along with preferred embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0070] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0071] Example:

[0072] Figures 1-3 The diagram illustrates a composite structural beam of steel and UHPC. The composite structural beam 100 includes a UHPC bridge deck 110 and a composite rib plate (not shown) located on the bottom surface of the UHPC bridge deck 110. The composite rib plate includes a UHPC rib plate 120 and a T-shaped steel beam 130. The UHPC rib plate 120 is located between the UHPC bridge deck 110 and the T-shaped steel beam 130, that is, the UHPC rib plate 120 and the UHPC bridge deck 110 are cast together to form a T-shaped structure. The upper edge of the T-shaped steel beam 130 is embedded in the lower end of the UHPC rib plate 120.

[0073] Furthermore, the T-shaped steel beam 130 includes a steel base plate 131 and a steel web plate 132 disposed on the steel base plate 131, which together form a T-shaped structure. The upper edge of the steel web plate 132 (i.e., the side closest to the UHPC rib plate 120) is alternately provided with steel tenons 133 and mortises 134 along the longitudinal direction of the bridge. For example... Figure 3 As shown, Figure 3 The gray area in the image is mortise 134, and the spacing between two adjacent tenons 133 is... The height of the steel tenon (i.e., the depth of the mortise) is The steel tenon 133 and mortise 134 are embedded in the concrete at the lower end of the UHPC rib 120, and the distance between the lower edge of the UHPC rib 120 and the bottom edge of the mortise 134 is [missing information]. .

[0074] Further, the UHPC ribbed slab 120 comprises a ribbed slab concrete layer and a ribbed slab steel reinforcement framework located in the ribbed slab concrete layer, the ribbed slab steel reinforcement framework comprises bottommost longitudinal steel bars 123, sub-bottom longitudinal steel bars 124, longitudinal distribution steel bars 125, transverse short steel bars 126 and vertical stirrup groups (not marked in the figure), the vertical stirrup groups comprise lower open stirrups 121 and upper open stirrups 122 arranged alternately along the longitudinal bridge direction, as shown in Figure 1 and Figure 2 , wherein the lower open stirrups 121 are arranged in one-to-one correspondence with the steel dowels 133, the upper open stirrups 122 are arranged in one-to-one correspondence with the mortises 134, the lower open stirrups 121 are inserted into the steel dowels 133 at the lower ends, the lower ends of the upper open stirrups 122 are placed in the mortises 134, and the transverse short steel bars 126 are arranged on both sides of the lower ends of the upper open stirrups 122, the transverse short steel bars 126 and the lower ends of the upper open stirrups 122 are arranged in a spaced manner (i.e. not overlapped); the position of the lower end of the lower open stirrup 121 is lower than the position of the lower end of the upper open stirrup 122, the bottommost longitudinal steel bars 123 are used to connect the lower ends of the lower open stirrups 121 along the longitudinal direction, and the sub-bottom longitudinal steel bars 124 are used to connect the lower ends of the upper open stirrups 122 along the longitudinal direction, specifically, the number of the bottommost longitudinal steel bars 123 and the sub-bottom longitudinal steel bars 124 in the embodiment is two, and they are symmetrically arranged on both sides of the steel web 132; a plurality of longitudinal distribution steel bars 125 are arranged in the vertical direction inside the vertical stirrup group, specifically, a single longitudinal distribution steel bar 125 passes through the upper open stirrups 122 and the lower open stirrups 121 arranged alternately along the longitudinal direction.

[0075] Further, the UHPC bridge deck slab 110 comprises a bridge deck slab concrete layer and a bridge deck slab steel reinforcement framework located in the bridge deck slab concrete layer, the bridge deck slab steel reinforcement framework comprises an upper layer of transverse steel bars, a lower layer of transverse steel bars and bridge deck slab longitudinal steel bars 112; a plurality of bridge deck slab longitudinal steel bars 112 are arranged in a spaced manner along the transverse bridge direction, the upper layer of transverse steel bars is located on the upper side of the bridge deck slab longitudinal steel bars 112, the upper layer of transverse steel bars comprises a plurality of bridge deck slab transverse steel bars 111 arranged in a spaced manner along the longitudinal bridge direction, the bridge deck slab longitudinal steel bars 112 and the bridge deck slab transverse steel bars 111 in the upper layer of transverse steel bars are arranged in an overlapped manner; the lower layer of transverse steel bars is located on the lower side of the bridge deck slab longitudinal steel bars 112, the lower layer of transverse steel bars comprises a plurality of bridge deck slab transverse steel bars 111 arranged in a spaced manner along the longitudinal bridge direction, the bridge deck slab transverse steel bars 111 in the lower layer of transverse steel bars and the bridge deck slab longitudinal steel bars 112 are not overlapped.

[0076] Further, the upper end of the lower opening stirrup 121 is connected with the bridge deck steel reinforcement framework, specifically, overlaps with the bridge deck longitudinal reinforcement 112.

[0077] Preferably, the bridge deck concrete layer and the ribbed slab concrete layer are both poured with UHPC concrete, and the UHPC concrete is an ultra-high performance concrete, which has super high durability and super high mechanical properties.

[0078] In order to ensure the safe application of the UHPC and steel combined structure beam in the small and medium span assembled bridge, the embodiment provides a design method for the steel and UHPC combined structure beam, as shown in the formula (1) : Figure 4 The design method comprises the following steps:

[0079] S1, determining the permanent action of the combined structure beam according to the structure size of the combined structure beam, and determining the variable action according to the use requirements and environmental conditions of the combined structure beam;

[0080] Specifically, the determination method of the permanent action and the variable action can refer to the prior art, and will not be described in detail in the embodiment.

[0081] S2, obtaining the effect design value of the basic combination of actions according to the effect design value of the permanent action and the effect design value of the variable action;

[0082] Preferably, the effect design value of the combined structure beam under the permanent action and the effect design value of the combined structure beam under the variable action are determined according to the general bridge internal force calculation method, and the effect design value of the basic combination of actions is obtained according to the combination of the effect design value of the permanent action and the effect design value of the variable action in the General Specification for Design of Highway Bridges and Culverts (JTG D60-2015).

[0083] S3, respectively checking whether the interlayer horizontal shear bearing capacity characteristic value, the vertical shear bearing capacity characteristic value and the bending bearing capacity characteristic value of the combined structure beam meet the requirements according to the structure size of the combined structure beam and the effect design value of the basic combination of actions;

[0084] Specifically, the interlayer horizontal shear bearing capacity characteristic value , the vertical shear bearing capacity characteristic value and the bending bearing capacity characteristic value of the combined structure beam are determined according to the structure size of the combined structure beam.

[0085] The interlayer horizontal shear bearing capacity characteristic value is compared with the interlayer horizontal shear design value in the effect design value of the basic combination of actions, if the following formula (2) is met: then it is indicated that the interlayer horizontal shear bearing capacity characteristic value of the combined structure beam is checked and qualified;

[0086] The vertical shear capacity characteristic value of the composite structure beam The vertical shear design value in the effect design value of the basic combination of actions For comparison, if The vertical shear capacity characteristic value of the composite structure beam is qualified for checking.

[0087] The flexural capacity characteristic value of the composite structure beam The moment design value in the effect design value of the basic combination of actions For comparison, if The flexural capacity characteristic value of the composite structure beam is qualified for checking.

[0088] Wherein, The importance coefficient of the composite structure beam, which is taken as 0.9, 1.0, 1.1 according to the importance of the bridge; The material partial coefficient, which is used to convert the calculated capacity characteristic value into the corresponding capacity design value, taken as 1.25.

[0089] Further, the calculation process of the interlayer horizontal shear capacity characteristic value of the composite structure beam is as follows:

[0090] The horizontal shear failure mode of the composite structure beam can be divided into steel tenon shear failure and mortise shear failure, so the calculation process of the interlayer horizontal shear capacity characteristic value of the composite structure beam is as follows:

[0091] The corresponding horizontal shear capacity characteristic value of the steel tenon shear failure is calculated as , unit: N:

[0092] (1),

[0093] The corresponding horizontal shear capacity characteristic value of the mortise shear failure is calculated as , unit: N:

[0094] (2),

[0095] The interlayer horizontal shear capacity characteristic value of the composite structure beam is calculated as , unit: N:

[0096] (3),

[0097] Wherein, The longitudinal arrangement spacing of the steel tenon, unit: mm; The thickness of the steel web, unit: mm; Ys is the yield strength of the steel web, in MPa; Sh is the shape factor of the mortise, which is related to the shape of the steel tenon, such as the MCL type key ; fcu is the standard value of the cubic compressive strength of the UHPC concrete, in MPa; βh is the horizontal reinforcement strengthening factor in the mortise, the horizontal reinforcement in the mortise includes the transverse short steel and the horizontal segment of the upper open stirrup, , A is the sum of the cross-sectional area of the horizontal steel in the mortise, including the transverse short steel and the horizontal segment of the upper open stirrup; Sh is the area of the mortise, such as the MCL type key ; E is the elastic modulus of the steel tenon (i.e. the steel web), in MPa; E is the elastic modulus of the UHPC concrete, in MPa.

[0098] A is the sum of the cross-sectional area of the horizontal steel in the mortise should not be less than , wherein is calculated as follows:

[0099] (4),

[0100] , wherein is the interlayer horizontal shear force design value in the effect design value of the basic combination, in N; is the transverse short steel strength design value, in MPa.

[0101] The interlayer horizontal shear bearing capacity characteristic value of the composite structure beam is obtained, and then compared with the interlayer horizontal shear force design value in the effect design value of the basic combination to determine whether it meets , and the horizontal shear bearing capacity characteristic value checking of the composite structure beam can be completed.

[0102] Further, the calculation process of the vertical shear bearing capacity characteristic value of the composite structure beam is as follows:

[0103] The vertical shear bearing capacity characteristic value of the composite structure beam is provided by the steel web, the UHPC rib plate and the UHPC bridge deck plate. Since the UHPC bridge deck plate is usually thin, only the contribution of the steel web and the UHPC rib plate is considered, and thus the calculation process of the vertical shear bearing capacity characteristic value is as follows:

[0104] The vertical shear bearing capacity characteristic value of the steel web , in N:

[0105] (5),

[0106] Calculate the characteristic value of the vertical shear capacity of the UHPC rib plate. The unit is N, which consists of contributions from the UHPC matrix and the vertical stirrup group:

[0107] (6),

[0108] Calculate the characteristic value of the vertical shear capacity of the composite structural beam (i.e., composite rib plate). Unit N:

[0109] (7),

[0110] in, The yield strength of the steel web is expressed in MPa. This represents the thickness of the steel web, in mm. This represents the height of the steel web, in mm. The thickness of the UHPC rib is in mm; The height of the UHPC rib is in mm. The tensile elastic limit strength of UHPC concrete is expressed in MPa. The tensile ultimate strength of UHPC concrete is expressed in MPa. This is the sum of the cross-sectional areas of all vertical segments of a single stirrup in the UHPC rib plate (here, stirrup refers to either an upper or lower open stirrup; upper and lower open stirrups are generally of the same specification, therefore their cross-sectional areas are the same; in this embodiment, both upper and lower open stirrups are double-legged, i.e., have two vertical segments, but in some embodiments, the stirrup may be set as a single-legged stirrup, i.e., have only one vertical segment), in mm. 2 ; The spacing of the stirrups in the UHPC rib plate is in mm; This represents the yield strength of the stirrups in the UHPC rib plate, expressed in MPa.

[0111] Obtain the characteristic value of the vertical shear capacity of the composite structural beam. Then, it is combined with the vertical shear force design value in the effect design value of the basic combination of actions. Compare and determine if the conditions are met. This allows for the verification of the characteristic value of the vertical shear bearing capacity of the composite structural beam.

[0112] Furthermore, such as Figure 5 As shown, the characteristic value of the flexural bearing capacity of the composite structural beam. The calculation process is as follows:

[0113] Characteristic value of flexural capacity of composite structural beam The calculation adopts a method considering material plasticity, and obtains the flexural capacity of the section through the internal force balance condition analysis of the cross section based on the plane section assumption, and specifically includes the following steps:

[0114] A1, setting constant parameters, including calculation error convergence value , curvature iterative calculation increment , and neutral axis position iterative calculation increment ;

[0115] Preferably, The value of ( ) is generally less than or equal to ; The value of the calculation error convergence value is generally ; the value of the neutral axis position iterative calculation increment is generally 0.1mm;

[0116] A2, inputting the cross-sectional size of the composite structural beam, the characteristics of each material, and the nonlinear constitutive model;

[0117] Unlike ordinary concrete, due to the strain hardening characteristics of UHPC concrete, and the fact that the post-cracking strength still contributes to the flexural capacity (strain softening), in order to fully consider its influence, the UHPC tensile adopts a three-fold line model, the UHPC compressive adopts a linear elastic model, and the T-shaped steel beam and the steel reinforcement in the composite structural beam adopt a three-fold line model considering the yield platform and strain hardening. Because the engineering focuses on the maximum carrying capacity, therefore, except for the UHPC tensile, the material constitutive model does not consider the descending segment.

[0118] Figure 6 Preferably, as shown in , the nonlinear constitutive model of UHPC concrete is:

[0119] (8),

[0120] Wherein, is the strain of UHPC concrete, is the stress of UHPC concrete, is the elastic modulus of UHPC concrete; is the compressive ultimate strain of UHPC concrete; is the tensile elastic ultimate strain of UHPC concrete; is the tensile ultimate strain of UHPC concrete; is the fracture strain of UHPC concrete; when , , the ultimate compressive stress is reached, the compressive ultimate stress of the UHPC concrete; the tensile elastic limit stress of the UHPC concrete, = ; the tensile ultimate stress of the UHPC concrete, at which the corresponding strain is .

[0121] As shown in Figure 6 , the second segment of the first quadrant in the nonlinear constitutive model of the UHPC is to consider the contribution of the tensile strain hardening of the UHPC to the flexural capacity, and the third segment is to consider the contribution of the UHPC after cracking to the flexural capacity.

[0122] Preferably, as shown in Figure 7 , the nonlinear constitutive model of the T-shaped steel beam and the steel bar in the composite structure beam is:

[0123] (9),

[0124] wherein, is the strain of the T-shaped steel beam or the steel bar, is the stress of the T-shaped steel beam or the steel bar, is the elastic modulus of the T-shaped steel beam or the steel bar; is the compressive ultimate strain of the T-shaped steel beam or the steel bar; is the tensile yield strain of the T-shaped steel beam or the steel bar; is the strain hardening starting strain of the T-shaped steel beam or the steel bar; is the ultimate tensile strain of the T-shaped steel beam or the steel bar; for the case without yield platform, such as some specifications of steel bars, ;

[0125] When , , the compressive ultimate stress is reached, is the compressive ultimate stress of the T-shaped steel beam or the steel bar; is the yield stress of the T-shaped steel beam or the steel bar, = ; is the ultimate tensile stress of the T-shaped steel beam or the steel bar, at which the corresponding strain is .

[0126] As shown in Figure 7 , the second segment of the first quadrant in the nonlinear constitutive model is to consider the yield platform of the stress-strain relationship of the T-shaped steel beam or the steel bar, and the third segment is to consider the contribution of the strain hardening of the T-shaped steel beam or the steel bar to the flexural capacity.

[0127] Considering that the ultimate tensile strain of the T-beam will be needed in subsequent calculations, to facilitate the distinction between the ultimate tensile strain of the T-beam and the reinforcing steel, the specific method adopted is... The ultimate tensile strain of the T-shaped steel beam is expressed by using... This represents the ultimate tensile strain of the reinforcing steel.

[0128] A3, such as Figure 8 As shown, the cross-section of the UHPC concrete in the composite structural beam is divided into unit layers, and the vertical distance from the center of each unit layer to the upper surface of the composite structural beam is obtained. and the area of ​​each unit layer The cross-section of the T-shaped steel beam outside the UHPC concrete is divided into unit layers, and the vertical distance from the center of each unit layer to the upper surface of the composite structural beam is obtained. and the area of ​​each unit layer The cross-section of all longitudinal reinforcement bars at the bottom layer of the composite structural beam is taken as a single unit layer, and its area is obtained. and the vertical distance from the upper surface of the composite structural beam The cross-sections of all longitudinal reinforcement bars in the top layer of the composite structural beam are treated as a single unit layer, and their areas are recorded. and the vertical distance from the upper surface of the composite structural beam ;

[0129] Preferred, i Indicates the first in UHPC concrete i Each unit layer, k Indicates the first in the T-shaped steel beam k Each unit layer.

[0130] Specifically, the upper surface of the composite structural beam is the upper surface of the UHPC bridge deck, i.e., the bridge deck; the bottom longitudinal reinforcement of the composite structural beam refers to the bottom longitudinal reinforcement 123 in the UHPC rib plate, and the top longitudinal reinforcement of the composite structural beam refers to the bridge deck longitudinal reinforcement 112 in the UHPC bridge deck.

[0131] Preferably, all unit layers should be on the same cross-section of the composite structural beam. When dividing the cross-section of the UHPC concrete and the cross-section of the T-beam located outside the UHPC concrete into unit layers, forced dividing lines are arranged at all locations where the cross-sectional width and material change, to facilitate the calculation of the area of ​​each unit layer and subsequent internal forces. According to the above unit layer division rules, it can be seen that, except for the longitudinal reinforcement of the bottom and top layers of the composite structural beam, the remaining steel structure embedded in the UHPC concrete (referring to the reinforcement embedded in the UHPC concrete and part of the steel web) is not considered in the calculation, which facilitates the calculation.

[0132] Preferably, the area calculation method for a single unit layer in UHPC concrete and T-shaped steel beams is as follows:

[0133] (10)

[0134] in: The width of the unit cell is determined by the cross-sectional shape. The height of each unit layer is [height]. To ensure the accuracy of the calculation and analysis, the height of each unit layer is [height]. No more than 1 / 50 h , h This represents the total height of the cross-section.

[0135] A4. Assume the initial cross-sectional curvature of the composite beam. ,in Preferably, for most bridges, Possible values ( );

[0136] A5. Assume the neutral axis position of the composite structure beam. ,in Preferred, Generally, the possible values ​​are: h / 2.

[0137] A6. Calculate the strain of a single layer in UHPC concrete based on the plane section assumption. Strain of unit layer in T-shaped steel beam The strain of all longitudinal reinforcement bars at the bottom layer of the composite structural beam corresponding to the unit layer The strain of the unit layer corresponding to all longitudinal reinforcement bars in the top layer of the composite structural beam ,like Figure 9 As shown;

[0138] Specifically, in UHPC concrete, the first i strain of each unit layer Positive values ​​represent tensile strain, and negative values ​​represent compressive strain; in the T-shaped steel beam... k strain of each unit layer Positive values ​​represent tensile strain, and negative values ​​represent compressive strain; the strain of all longitudinal reinforcement bars at the bottom layer of the composite structural beam corresponds to the strain of the unit layer. The strain of all longitudinal reinforcement bars in the uppermost layer of the composite structural beam corresponds to the strain of the unit layer. .

[0139] A7. Calculate the stress in each unit layer of UHPC concrete based on the nonlinear constitutive model of the material. Stress in each unit layer of T-shaped steel beam The stress of all longitudinal reinforcement bars at the bottom layer of the composite structural beam corresponding to the unit layer. and the stress of the unit layer corresponding to all longitudinal reinforcement of the uppermost layer of the composite structural beam , as shown in formula (8). Figure 10

[0140] Specifically, the stress of the unit layer in the UHPC concrete is obtained according to formula (8) , the positive value is tensile stress, and the negative value is compressive stress; the stress of the unit layer in the T-shaped steel beam is obtained according to formula (9) , the positive value is tensile stress, and the negative value is compressive stress; the stress of the unit layer corresponding to all longitudinal reinforcement of the bottommost layer of the composite structural beam is obtained according to formula (9) ; and the stress of the unit layer corresponding to all longitudinal reinforcement of the uppermost layer of the composite structural beam is obtained according to formula (9) .

[0141] A8. Calculate the resultant force in the cross section of the composite structural beam according to the stress and area of each unit layer F .

[0142] Preferably, the resultant force in the cross section of the composite structural beam is F .

[0143] (11).

[0144] A9. If is not greater than (i.e. less than or equal to) , then step A10 is entered; if is greater than , then the influence coefficient method is used for iterative correction , and then A6-A9 is repeated;

[0145] Preferably, the influence coefficient method is used for iterative correction , specifically as follows:

[0146] A9.1. Assume the new position of the neutral axis of the composite structural beam , wherein .

[0147] A9.2. Repeat steps A6-A8 to obtain the corresponding resultant force in the cross section of the composite structural beam .

[0148] A9.3. Calculate the change value of the resultant force in the cross section of the composite structural beam , wherein .

[0149] A9.4. Correct the position of the neutral axis of the composite structural beam , wherein . ​

[0150] According to the iterative correction of steps A9.1-A9.4, the influence coefficient method can accelerate the search speed and solve the problem of non-convergence caused by setting the iteration increment artificially.

[0151] A10, judging whether there is an upper edge compressive strain of the UHPC concrete less than the compressive ultimate strain thereof , or a lower edge tensile strain of the T-shaped steel beam greater than the ultimate tensile strain thereof ; if so, let 0.1 , repeat steps A4-A10, and if not, go to step A11;

[0152] Specifically, if there is an upper edge compressive strain of the UHPC concrete less than the compressive ultimate strain thereof , or a lower edge tensile strain of the T-shaped steel beam greater than the ultimate tensile strain thereof , it indicates that the upper edge compressive strain of the UHPC exceeds the compressive ultimate strain thereof, or the lower edge tensile strain of the T-shaped steel beam exceeds the ultimate tensile strain thereof, indicating that the step distance taken in the calculation is too large.

[0153] Preferably, the upper edge compressive strain of the UHPC and the lower edge tensile strain of the T-shaped steel beam are obtained from step A6, and the minimum compressive strain from each unit layer of the UHPC concrete is , and the maximum tensile strain from each unit layer of the T-shaped steel beam is .

[0154] A11, judging whether the upper edge compressive strain of the UHPC concrete minus the compressive ultimate strain thereof is less than or equal to , or the ultimate tensile strain of the T-shaped steel beam minus the lower edge tensile strain thereof is less than or equal to ; if so, go to step A12, and if not, adopt the influence coefficient method to iteratively correct and repeat steps A5-A11;

[0155] Preferably, in the present embodiment, the influence coefficient method is adopted to iteratively correct Specifically:

[0156] A11.1, assuming a new cross-sectional curvature of the composite structure beam , wherein​ ;

[0157] A11.2, repeat steps A5-A10, calculate the corresponding UHPC concrete upper edge compressive strain and T-shaped steel beam lower edge tensile strain ;

[0158] A11.3, calculate the UHPC concrete upper edge compressive strain change value and T-shaped steel beam lower edge tensile strain change value ; wherein , ;

[0159] A11.4, correct the combined structure beam cross section curvature , wherein .

[0160] According to steps A11.1-A11.4, iterative correction can be completed , the influence coefficient method can speed up the search speed, and at the same time solve the problem of unable to converge caused by artificially setting iteration increment. When searching for the cross section curvature corresponding to the maximum bending capacity , at the same time, the UHPC concrete top strain reaches the UHPC compressive ultimate strain or the T-shaped steel beam bottom strain reaches the steel ultimate strain as the judgment condition, both UHPC crushing and steel reaching tensile ultimate strength can be considered. In order to consider the calculation efficiency and the reliability of convergence at the same time, the judgment limit is , which can ensure that the stress error is within 0.1 MPa, which is sufficient in engineering precision.

[0161] A12, according to the action moment of each unit layer in the UHPC concrete, the action moment of each unit layer in the T-shaped steel beam, the action moment of the corresponding unit layer of all longitudinal steel bars in the bottom layer of the combined structure beam and the action moment of the corresponding unit layer of all longitudinal steel bars in the top layer of the combined structure beam, calculate the bending capacity characteristic value of the combined structure beam ;

[0162] Preferably, the bending capacity characteristic value of the combined structure beam is:

[0163] (12).

[0164] Specifically, according to steps A1-A12, the bending capacity characteristic value of the combined structure beam , compare with the bending moment design value , judge whether it meets , the bending capacity checking of the combined structure beam can be completed.

[0165] S4, if the checking all meets the requirements, it is indicated that the composite structural beam meets the technical requirements; if there is an item that does not meet the requirements, the structural size of the composite structural beam is adjusted, and steps S1-S4 are repeated.

[0166] Specifically, only when the interlayer horizontal shear capacity characteristic value, the vertical shear capacity characteristic value and the bending capacity characteristic value of the composite structural beam are all checked and qualified, it is considered that the composite structural beam meets the technical requirements, if any one of them is not qualified, it is indicated that the structural design of the composite structural beam is not qualified, and the structural size of the composite structural beam needs to be adjusted and then the checking is continued.

[0167] Through steps S1-S4 in the embodiment, the structural design of the composite structural beam can be checked, which provides theoretical guidance for the structural design of the composite structural beam and helps the technical personnel to reasonably design the structural size of the composite structural beam.

[0168] Application case:

[0169] In this case, based on the specific structural size of a composite structural beam, the structural rationality of the composite structural beam is checked using the above design method, and the specific steps are as follows:

[0170] First, the interlayer horizontal shear capacity characteristic value of the composite structural beam is calculated :

[0171] The longitudinal arrangement spacing of the steel dowel is obtained , the steel web thickness is =19mm, the yield strength of the steel web (Q355 material) is , and the horizontal shear capacity characteristic value corresponding to the shear failure of the steel dowel is calculated according to formula (1) ;

[0172] According to , the shape coefficient of the mortise is obtained =2.17, the standard value of the cubic compressive strength of the UHPC concrete is , the diameter of the upper opening stirrup is 10mm, the diameter of the transverse short steel bar in the mortise is 12mm, the sum of the cross-sectional areas of the horizontal steel bars in the mortise is , the area of the mortise is obtained according to , , the elastic modulus of the steel dowel (i.e. the steel web) is , the elastic modulus of the UHPC concrete is , and the reinforcement ratio in the mortise is calculated according to , , and the horizontal shear capacity characteristic value corresponding to the shear failure of the mortise is calculated according to formula (2) ;

[0173] According to formula (3), the interlayer horizontal shear capacity characteristic value of the composite structure beam is calculated =252.9 .

[0174] Secondly, the vertical shear capacity characteristic value of the composite structure beam is calculated is:

[0175] The yield strength of the steel web is obtained , the height of the steel web is , and the vertical shear capacity characteristic value of the steel web is calculated according to formula (5) ;

[0176] The thickness of the UHPC rib plate is obtained , the height of the UHPC rib plate is =770 mm , the sum of the sectional areas of all vertical segments of a single stirrup in the UHPC rib plate is , the spacing of the stirrups in the UHPC rib plate is s= 75 mm , the yield strength of the stirrup in the UHPC rib plate is , the tensile elastic limit strength of the UHPC is , and the tensile ultimate strength is , respectively , The vertical shear capacity characteristic value of the UHPC rib plate is calculated according to formula (6) .

[0177] The vertical shear capacity characteristic value of the composite structure beam is calculated according to formula (7) =3360.5 KN .

[0178] Finally, the flexural capacity characteristic value of the composite structure beam is calculated is:

[0179] Step 01, set constant parameters: calculate error convergence value , curvature iterative calculation increment ( ), neutral axis position iterative calculation increment 0.1 mm .

[0180] Step 02, obtain the cross-sectional size of the composite structure beam, the characteristics of each material, and the nonlinear constitutive model;

[0181] Among them, the nonlinear constitutive model of UHPC is formula (8), and the nonlinear constitutive model of T-shaped steel beam and steel is formula (9).

[0182] Elastic modulus of UHPC concrete , compressive ultimate strain , ultimate compressive stress ; tensile elastic ultimate stress of UHPC concrete , tensile ultimate stress = 11.66 MPa, tensile elastic ultimate strain 174, tensile ultimate strain , fracture strain .

[0183] Elastic modulus of steel bar (HRB400) = 200 GPa, compressive ultimate strain 2, ultimate compressive stress = 400 MPa; yield stress of steel bar = 400 MPa, ultimate stress MPa, yield strain = 0.002, strain hardening starting strain without yield platform = , ultimate tensile strain .

[0184] Elastic modulus of T-shaped steel beam (Q355) , yield stress = 355 MPa, ultimate tensile stress MPa, yield strain = 0.001723, strain hardening starting strain = 0.0198, ultimate tensile strain ;

[0185] Step 03, element layer division is performed on the cross section of the composite structure beam according to step A3;

[0186] wherein the total height of the cross section is , the distance of the element layer corresponding to all longitudinal steel bars of the bottom layer of the composite structure beam from the upper edge of the cross section is , the sum of the cross-sectional areas of all longitudinal steel bars of the bottom layer of the composite structure beam (i.e. the area of the corresponding element layer) is , the distance of the element layer corresponding to all longitudinal steel bars of the top layer of the composite structure beam from the upper edge of the cross section is , the sum of the cross-sectional areas of all longitudinal steel bars of the top layer of the composite structure beam (i.e. the area of the corresponding element layer) is .

[0187] Step 04, the initial cross-sectional curvature of the composite structure beam is assumed .

[0188] Step 05, assuming the position of the neutral axis of the composite structure beam ;

[0189] Step 06, calculating the strain of the unit layer in the UHPC concrete according to step A6 respectively , the strain of the unit layer in the T-shaped steel beam , the strain of the unit layer corresponding to all longitudinal steel bars of the bottom layer of the composite structure beam and the strain of the unit layer corresponding to all longitudinal steel bars of the top layer of the composite structure beam ;

[0190] Step 07, calculating the stress of each unit layer in the UHPC concrete according to the nonlinear constitutive model of each material , the stress of each unit layer in the T-shaped steel beam , the stress of the unit layer corresponding to all longitudinal steel bars of the bottom layer of the composite structure beam and the stress of the unit layer corresponding to all longitudinal steel bars of the top layer of the composite structure beam ;

[0191] Step 08, performing the processing of steps A8-A12 to finally obtain the characteristic value of the bending resistance of the composite structure beam .

[0192] The obtained horizontal shear capacity design value , the vertical shear capacity design value , the bending moment shear capacity design value . The effect design value is obtained by establishing a finite element analysis model of the composite structure beam, and the horizontal shear design value, the vertical shear design value and the bending moment design value with the structure importance coefficient are respectively: , , , wherein . It can be seen that the capacity design value is greater than the corresponding effect design value, which indicates that the technical requirements are met.

[0193] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for calculating the characteristic value of the flexural capacity of a composite beam of steel and UHPC, characterized in that, The method comprises the following steps: A1, set constant parameters, including calculating error convergence value , curvature iterative calculation increment , and neutral axis position iterative calculation increment ; A2, inputting cross-sectional dimensions of the composite structural beam, characteristics of each material in the composite structural beam, and a nonlinear constitutive model; A3, dividing the cross section of the composite structural beam into unit layers, specifically: the cross section of the UHPC concrete of the composite structural beam and the cross section of the part of the T-shaped steel beam located outside the UHPC concrete are respectively divided into unit layers, and the cross section of all longitudinal steel bars in the uppermost layer of the composite structural beam and the cross section of all longitudinal steel bars in the bottom layer of the composite structural beam are respectively taken as one unit layer; A4. Assuming the initial cross-sectional curvature of the composite beam wherein ; A5. Assuming the position of the neutral axis of the composite structural beam wherein ; A6, calculating the strain of each unit layer according to the plane cross section assumption; A7, calculating the stress of each unit layer according to the strain of each unit layer and the nonlinear constitutive model corresponding to the unit layer; A8. Calculate the resultant force within the cross section of the combined structural beam from the stresses and areas of each unit layer F ; A9. If not greater than then go to step A10; if not not greater than then to repeat A6-A9 after correction; A10. Determine if there is a compressive strain on the top edge of the UHPC concrete less than its compressive limit strain, or, a tensile strain on the bottom edge of the T-beam greater than its tensile limit strain; if so, then 0.1 , Repeat steps A4-A10, and if not, go to step A11. A11. Determine whether the upper edge compressive strain of the UHPC concrete is satisfied. Subtract its compressive ultimate strain less than or equal to Alternatively, the ultimate tensile strain of the T-beam minus the tensile strain at its lower edge. Less than or equal to If the conditions are met, proceed to step A12; otherwise, make corrections. Then repeat steps A5-A11; A12. Calculate the characteristic value of the bending bearing capacity of the composite structure beam according to the moment of force of each unit layer .

2. The method for calculating the characteristic value of the flexural bearing capacity of a composite beam of steel and UHPC according to claim 1, characterized in that, The nonlinear constitutive model of each material in step A2 is specifically: The nonlinear constitutive model of the UHPC concrete is: （8）， wherein, is the strain of the UHPC concrete, is the stress of the UHPC concrete, is the elastic modulus of the UHPC concrete; is the compressive ultimate strain of the UHPC concrete; is the tensile elastic limit strain of the UHPC concrete; is the tensile ultimate strain of the UHPC concrete; is the fracture strain of the UHPC concrete; is the tensile elastic limit stress of the UHPC concrete; is the tensile ultimate stress of the UHPC concrete; The nonlinear constitutive model of the T-shaped steel beam and the steel bar in the composite structural beam is: （9）， wherein, ε is the strain of the T-shaped steel beam or rebar, σ is the stress of the T-shaped steel beam or rebar, E is the elastic modulus of the T-shaped steel beam or rebar; εcu is the compressive ultimate strain of the T-shaped steel beam or rebar; εty is the tensile yield strain of the T-shaped steel beam or rebar; εin is the strain hardening initiation strain of the T-shaped steel beam or rebar; εtu is the ultimate tensile strain of the T-shaped steel beam or rebar; if there is no yield plateau, then ; σy is the yield stress of the T-shaped steel beam or rebar; σtu is the ultimate tensile stress of the T-shaped steel beam or rebar.

3. The method for calculating the characteristic value of the flexural bearing capacity of the composite structural beam of steel and UHPC according to claim 2, characterized in that, The calculation method of the strain of each unit layer in step A6 is: UHPC concrete i strain of each unit layer Positive values ​​represent tensile strain, and negative values ​​represent compressive strain; in the T-shaped steel beam... k strain of each unit layer Positive values ​​represent tensile strain, and negative values ​​represent compressive strain. all longitudinal reinforcement of the bottom layer of the composite beam corresponds to the strain of the unit layer ; all longitudinal reinforcement of the uppermost composite beam layer corresponds to the strain of the unit layer ; in, For UHPC concrete, the first i The vertical distance from the center of each unit layer to the upper surface of the composite structural beam. The first in the T-shaped steel beam k The vertical distance from the center of each unit layer to the upper surface of the composite structural beam. This refers to the vertical distance from the center of each unit layer corresponding to all the longitudinal reinforcement bars at the bottom layer of the composite structural beam to the upper surface of the composite structural beam. This refers to the vertical distance from the center of each unit layer corresponding to all longitudinal reinforcement bars in the uppermost layer of the composite structural beam to the upper surface of the composite structural beam.

4. The method for calculating the characteristic value of the flexural bearing capacity of the composite structural beam of steel and UHPC according to claim 3, characterized in that, The calculation method of the stress of each unit layer in step A7 is: According to formula (8), the stress of the unit layer in the UHPC concrete is obtained , the positive value is tensile stress, and the negative value is compressive stress; according to formula (9), the stress of the unit layer in the T-shaped steel beam is obtained , the positive value is tensile stress, and the negative value is compressive stress; according to formula (9), the stress of the unit layer corresponding to all longitudinal steel bars in the bottom layer of the composite structure beam is obtained ; according to formula (9), the stress of the unit layer corresponding to all longitudinal steel bars in the top layer of the composite structure beam is obtained .

5. The method for calculating the characteristic value of the flexural bearing capacity of the composite structural beam of steel and UHPC according to claim 4, characterized in that, The resultant force within the cross section of the composite structural beam in step A8 F , in particular: （11）， wherein, A is the area of the nth unit layer in the UHPC concrete, i A is the area of the nth unit layer in the T-shaped steel beam, A is the area of the nth unit layer in the T-shaped steel beam, k A is the area of the nth unit layer in the T-shaped steel beam, A is the area of the nth unit layer in the T-shaped steel beam, A is the area of the nth unit layer in the T-shaped steel beam, 6. The method for calculating the characteristic value of the flexural bearing capacity of a composite structural beam of steel and UHPC according to claim 5, characterized in that, Step A12 calculates the flexural capacity eigenvalue of the composite beam , in particular: （12）。 7. The method of calculating the characteristic value of the flexural capacity of a composite beam of steel and UHPC according to any one of claims 1 to 6, characterized in that, The impact coefficient method is used for iterative correction in step A9 Specifically, A9.

1. Assuming new neutral axis position of the composite beam wherein ; A9.

2. Repeat steps A6-A8, calculating the resulting Corresponding resultant force within the cross section of the composite beam ; A9.

3. Calculate the value of the change in the resultant force within the cross section of the composite structural beam wherein ; A9.

4. Correcting the position of the neutral axis of a composite structural beam wherein .

8. The method of calculating the characteristic value of the flexural capacity of a composite beam of steel and UHPC according to any one of claims 1 to 6, characterized in that, The impact coefficient method is used for iterative correction in step A11 Specifically, A11.

1. Assuming a new cross-sectional curvature of the composite beam wherein ; A11.2, repeating steps A5-A10, the calculation results in Corresponding UHPC concrete upper edge compressive strain and T steel beam lower edge tensile strain ; A11.3, calculating the change in compressive strain at the top edge of the UHPC concrete and the change in tensile strain at the bottom edge of the T-beam ; wherein , ; A11.

4. Modified composite beam cross-section curvature ; wherein , is the compressive ultimate strain of the UHPC concrete, is the ultimate tensile strain of the T-shaped steel beam.

9. The method of calculating the characteristic value of the flexural capacity of a composite beam of steel and UHPC according to any one of claims 1 to 6, characterized in that, In step A3, the vertical distance of the center of each unit layer from the upper surface of the composite structural beam and the area of each unit layer are obtained.

10. The method of calculating the characteristic value of the flexural capacity of a composite beam of steel and UHPC according to any one of claims 1-6, characterized in that, The minimum compressive strain selected from each unit layer of the UHPC concrete is the upper edge compressive strain of the UHPC concrete The maximum tensile strain selected from each unit layer of the T-shaped steel beam is the lower edge tensile strain of the T-shaped steel beam .

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