Built-in inclined strut steel pipe constraint reinforced concrete joint and design method thereof

Abstract

The invention discloses a built-in inclined strut steel pipe confined reinforced concrete joint and a design method thereof, belongs to the field of building construction, and solves the problems that an existing steel pipe confined concrete joint reinforcing mode is large in mass, complex in construction, poor in reinforcing degree and the like, and pipeline layout is affected. The two steel bar frames are symmetrical from the view angle in the F direction and are arranged in a crossed mode. The first longitudinal bars are connected with the inclined bars, and the ends, deviating from the first longitudinal bars, of the inclined bars are connected with the second longitudinal bars. The inclined ribs are arranged within the range of the inclined pressing rods and are parallel to the inclined pressing rods. The ends, deviating from the inclined ribs, of the first longitudinal ribs and the second longitudinal ribs are connected with the steel pipe restrained reinforced concrete column. A plurality of stirrups are arranged on each steel bar frame, the stirrups are arranged at intervals in the extending direction of the inclined ribs, and the stirrups are arranged on the peripheries of the inclined ribs in a sleeving mode. The built-in inclined strut does not occupy extra space and does not affect pipeline layout. And meanwhile, the softening effect on the inclined pressing rod in the main pulling direction can be relieved, and brittle failure of a concrete node area is effectively prevented.

Description

Technical Field

[0001] The present application relates to the technical field of building construction, and in particular to a reinforced concrete node constrained by a steel pipe with an internal diagonal brace and a design method thereof. Background Art

[0002] The steel tube confined reinforced concrete column structure was first proposed to improve the shear failure of short columns. It is similar to the steel tube concrete column with disconnected steel tubes at the upper and lower ends in terms of structural form, but is closer to the role of stirrups in terms of mechanical properties. It is a continuous stirrup that is wrapped around the reinforced concrete column. In recent years, extensive research has been conducted on the static and seismic performance of steel tube confined reinforced concrete columns. The results show that due to the disconnection of the steel tube, within a certain range of diameter-to-thickness ratio, the steel tube confined reinforced concrete column has better axial compression performance than the steel tube concrete column, and its seismic performance is also significantly better than that of the traditional reinforced concrete column.

[0003] Although the steel pipe wrapping enhances the performance of reinforced concrete columns, it causes the node bearing capacity to become relatively weak, which makes the node easy to be damaged before the column. At present, the node area is strengthened by increasing the volume of the node area and increasing the reinforcement of the node area. Increasing the volume of the node area will occupy additional space and affect the layout of the pipeline. Increasing the stirrup ratio and the strength of the stirrups in the node area can improve the constraint on the concrete, but there is a certain angle between the concrete diagonal compression rod and the stirrups. The deformation of the diagonal compression rod parallel to the stirrup direction is effectively constrained by the stirrups, but the deformation perpendicular to the stirrup direction lacks constraint. Even if the amount of stirrups is increased, the brittle failure of the concrete node area cannot be effectively prevented. Summary of the invention

[0004] The embodiments of the present application provide a reinforced concrete node constrained by an internally braced steel pipe and a design method thereof, thereby solving the problem that the existing node area reinforcement method affects the pipeline layout and cannot effectively prevent the brittle failure of the concrete node area.

[0005] In the first aspect, an embodiment of the present invention provides a steel tube constrained reinforced concrete node with an internal diagonal brace, which includes a beam, a steel tube constrained reinforced concrete column and an internal diagonal brace; the beam and the steel tube constrained reinforced concrete column are vertically cross-connected; the internal diagonal brace includes two steel frames and a plurality of stirrups; the two steel frames are symmetrical from the perspective of the F direction, and the two steel frames are arranged crosswise with each other; the steel frame includes two longitudinal reinforcement groups; the two longitudinal reinforcement groups are centrally symmetrical; the longitudinal reinforcement group includes a plurality of longitudinal reinforcements, and the plurality of longitudinal reinforcements are mutually They are arranged parallel to each other; the longitudinal reinforcement includes a first longitudinal reinforcement, a second longitudinal reinforcement and an oblique reinforcement; the first longitudinal reinforcement is connected to the oblique reinforcement, and the end of the oblique reinforcement away from the first longitudinal reinforcement is connected to the second longitudinal reinforcement; the oblique reinforcement is arranged within the range of the oblique compression rod, and the oblique reinforcement is parallel to the oblique compression rod; the ends of the first longitudinal reinforcement and the second longitudinal reinforcement away from the oblique reinforcement are connected to the steel tube constrained reinforced concrete column; a plurality of stirrups are respectively arranged on each of the steel bar frames, and the plurality of stirrups are arranged at intervals along the extension direction of the oblique reinforcement, and each of the stirrups is sleeved on the periphery of the plurality of oblique reinforcements.

[0006] In combination with the first aspect, in a possible implementation, the built-in diagonal brace steel tube constrained reinforced concrete node also includes a connecting piece; a connecting piece is arranged on each of the first longitudinal reinforcements, one end of the connecting piece is connected to the first longitudinal reinforcement and its corresponding second longitudinal reinforcement, and the other end of the connecting piece is connected to the vertical longitudinal reinforcement of the steel tube constrained reinforced concrete column.

[0007] In a second aspect, an embodiment of the present invention provides a design method for a reinforced concrete node constrained by a built-in diagonal brace steel pipe, which is applicable to the above-mentioned built-in diagonal brace steel pipe constrained reinforced concrete node, including:

[0008] Determine the angle of the diagonal strut; determine the arrangement angle of the diagonal reinforcement according to the angle of the diagonal strut; determine the width of the diagonal strut; determine the depth of the diagonal strut; determine the size of the stirrup according to the width and depth of the diagonal strut; determine the distance between multiple longitudinal steel bars according to the depth of the diagonal strut; obtain at least one steel bar frame based on the arrangement angle of the diagonal reinforcement, the distance between multiple longitudinal steel bars and the size of the stirrup; two steel bar frames are crossed and symmetrically arranged from the perspective of direction F; multiple stirrups are respectively tied on each of the steel bar frames, the multiple stirrups are arranged at intervals along the extension direction of the diagonal reinforcement, and each stirrup is sleeved on the periphery of the multiple diagonal reinforcements to form a built-in diagonal brace; connect the built-in diagonal brace and the steel tube constrained reinforced concrete column.

[0009] In conjunction with the second aspect, in a possible implementation, the angle of the oblique pressure rod is determined as follows:

[0010] In the formula, θ represents the angle of the diagonal rod, Cb1 and C c1 H represents the pressure transmitted to the node from the column-beam compression zone. c , H b Respectively represent the distance between the longitudinal reinforcements of the column and beam, n t Indicates the axial pressure ratio.

[0011] In conjunction with the second aspect, in a possible implementation, the width of the diagonal pressure rod is determined as follows:

[0012] In the formula, a sw represents the width of the diagonal strut, a b represents the height of the compression zone of the beam, a c It represents the height of the compression zone of the column;

[0013] Among them, θ' represents the angle generated by the height of the beam-column compression zone,

[0014] In conjunction with the second aspect, in a possible implementation, the design method of the reinforced concrete node constrained by the built-in diagonal brace steel tube also includes:

[0015] Determine the shear bearing capacity of reinforced concrete nodes confined by internal diagonal steel tube braces.

[0016] In conjunction with the second aspect, in a possible implementation, determining the shear bearing capacity of the reinforced concrete node constrained by the built-in diagonal brace steel tube includes:

[0017] The steel bar yield strain is set as the initial value of the principal tensile strain, and the softening coefficient is determined; the softening coefficient formula is as follows:

[0018] In the formula, ζ represents the softening coefficient, ε r represents the principal tensile strain;

[0019] Determine the concrete stress in the direction of the principal compressive stress based on the principal tensile strain and softening formula;

[0020] Determine the resistance of the diagonal strut in the direction of the principal compressive stress as follows:

[0021] In the formula, C cb1，R represents the resistance of the diagonal compression rod in the direction of the principal compressive stress, σ d represents the concrete stress in the direction of the principal compressive stress, A s represents the area of ​​the bar in the direction of the principal compressive stress, σ br,z A represents the stress of the longitudinal reinforcement of the built-in diagonal brace. sbr represents the area of ​​the longitudinal reinforcement of the built-in diagonal brace, σ st,c A represents the stress of internal diagonal stirrups, st,ccosθ1 represents the area component of the internal diagonal stirrup in the direction of the principal compressive stress, σ ss A represents the stress of horizontal stirrups in the node area. ss1 represents the area of ​​horizontal stirrups, represents the area component of the horizontal stirrups in the direction of the principal compressive stress;

[0022] The resistance in the direction of the principal tensile stress is determined according to the principal tensile strain; the calculation formula for the resistance in the direction of the principal tensile stress is as follows:

[0023] T cb1 =σ st,t ·A st,t +σ br,t ·A br,t ·cosθ1+σ ss ·A ss2 / cosθ; where T cb1 represents the resistance in the direction of the principal tensile stress, σ st,t A represents the stress of internal diagonal stirrups. st,t represents the area of ​​the internal diagonal stirrup in the direction of the main tensile stress, σ br,t A represents the stress of the longitudinal reinforcement of the built-in diagonal brace. br,t ·cosθ1 represents the area component of the longitudinal reinforcement of the built-in diagonal brace in the direction of the principal tensile stress, σ ss A represents the stress of horizontal stirrups in the node area. ss2 / cosθ represents the area component of the horizontal stirrups in the direction of the principal tensile stress;

[0024] The principal pressure on the diagonal compression rod in the direction of the principal compressive stress is determined by the equilibrium formula, which is as follows:

[0025] T cb1 sinθ+N=C cb1 ·cosθ; where N represents the axial pressure, θ represents the angle of the diagonal rod, and C cb1 Indicates the principal pressure on the diagonal compression rod in the direction of the principal compressive stress;

[0026] Compare the principal pressure on the diagonal strut in the direction of the principal compressive stress and the resistance of the diagonal strut in the direction of the principal compressive stress;

[0027] When the principal pressure on the diagonal compression rod in the direction of the principal compressive stress is greater than or equal to the resistance of the diagonal compression rod in the direction of the principal compressive stress, a group of equilibrium relationship equations are simultaneously established, and the principal pressure on the diagonal compression rod in the direction of the principal compressive stress and the resistance of the diagonal compression rod in the direction of the principal compressive stress in the group of equilibrium relationship equations are made equal to determine multiple variable values, wherein the multiple variable values ​​include the resistance of the diagonal compression rod in the direction of the principal compressive stress, the principal pressure on the diagonal compression rod in the direction of the principal compressive stress, the resistance in the direction of the principal tensile stress, the concrete stress in the direction of the principal compressive stress, the principal tensile strain, the resultant force on the tensile side of the column, and the resultant force on the tensile side of the beam;

[0028] Among them, the equilibrium relationship equations are established based on the rotation softening truss model in the direction of the principal stress as follows: Where, T c1 represents the resultant force on the tensile side of the column, T b2 represents the resultant force on the tensile side of the beam, V b2 represents the vertical shear force at the beam end, h b Indicates the beam section height, L b Indicates that the beam length is calculated from the inflection point, approximately taking the mid-span, V c1 represents the horizontal shear force at the column end, h c Indicates the column section height, L c It means that the column length is calculated from the position of the inflection point, approximately taking the mid-span;

[0029] When the principal pressure on the oblique compression rod in the direction of the principal compressive stress is less than the resistance of the oblique compression rod in the direction of the principal compressive stress, the principal tensile strain is gradually increased to a certain value according to a fixed increment, and a plurality of variable values ​​are determined by a simultaneous equilibrium relationship equation group; the difference between the principal pressure on the oblique compression rod in the direction of the principal compressive stress and the resistance of the oblique compression rod in the direction of the principal compressive stress is determined according to the plurality of variable values, and when the difference is large, the principal tensile strain is gradually increased again according to a fixed increment, and the plurality of variable values ​​are determined by a simultaneous equilibrium relationship equation group until the difference between the principal pressure on the oblique compression rod in the direction of the principal compressive stress and the resistance of the oblique compression rod in the direction of the principal compressive stress is less than a preset value;

[0030] The node shear bearing capacity is determined based on the multiple variable values.

[0031] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0032] An embodiment of the present invention provides a steel tube restrained reinforced concrete node with built-in diagonal brace, and the steel tube restrained reinforced concrete node with built-in diagonal brace includes a beam, a steel tube restrained reinforced concrete column and a built-in diagonal brace. The beam and the steel tube restrained reinforced concrete column are vertically cross-connected. The built-in diagonal brace includes two steel bars and a plurality of stirrups. The two steel bars are symmetrical from the perspective of the F direction, and the two steel bars are arranged crosswise with each other. The steel bar frame includes two longitudinal reinforcement groups, and the two longitudinal reinforcement groups are centrally symmetrical. The longitudinal reinforcement group includes a plurality of longitudinal reinforcements, and the plurality of longitudinal reinforcements are arranged parallel to each other. The longitudinal reinforcement includes a first longitudinal reinforcement, a second longitudinal reinforcement and a diagonal reinforcement. The first longitudinal reinforcement is connected to the diagonal reinforcement, and one end of the diagonal reinforcement away from the first longitudinal reinforcement is connected to the second longitudinal reinforcement. The diagonal reinforcement is arranged within the range of the diagonal compression rod, and the diagonal reinforcement is parallel to the diagonal compression rod. One end of the first longitudinal reinforcement and the second longitudinal reinforcement away from the diagonal reinforcement is connected to the steel tube restrained reinforced concrete column. A plurality of stirrups are arranged on each steel bar frame, and the plurality of stirrups are arranged at intervals along the extension direction of the diagonal reinforcement, and each stirrup is sleeved on the periphery of the plurality of diagonal reinforcements. The built-in diagonal brace of the present application is set inside the steel tube-constrained reinforced concrete column, which does not take up extra space, and has a flexible design form and does not affect the pipeline layout. At the same time, it can significantly improve the bearing capacity and seismic performance of the node area, reduce the softening effect of the main tension direction on the diagonal compression rod, and effectively prevent the brittle failure of the concrete node area. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0034] Figure 1 A schematic diagram of the structure of the built-in diagonal brace provided in the embodiment of the present application Figure 1 ;

[0035] Figure 2 A schematic diagram of the structure of the built-in diagonal brace provided in the embodiment of the present application Figure 2 ;

[0036] Figure 3 for Figure 2 Schematic diagram of the structure from the perspective of the F direction;

[0037] Figure 4 Schematic diagram of the structure of the longitudinal reinforcement group and stirrups provided in the embodiment of the present application Figure 1 ;

[0038] Figure 5 Schematic diagram of the structure of the longitudinal reinforcement group and stirrups provided in the embodiment of the present application Figure 2 ;

[0039] Figure 6A schematic diagram of the structure of a reinforced concrete node constrained by a steel pipe with built-in diagonal bracing provided in an embodiment of the present application;

[0040] Figure 7 A flowchart of a design method for a reinforced concrete node constrained by a steel pipe with an internal diagonal brace provided in an embodiment of the present application;

[0041] Figure 8 A flowchart of determining the shear bearing capacity of a reinforced concrete node constrained by a built-in diagonal brace steel pipe provided in an embodiment of the present application;

[0042] Fig. 9 A force analysis diagram of the node area isolation body provided in the embodiment of the present application;

[0043] Fig.10 The axial pressure ratio and N / C provided in the embodiment of the present application c1 relationship;

[0044] Fig.11 The width of the concrete diagonal compression rod provided in the embodiment of the present application;

[0045] Fig.12 A force analysis diagram of a node area provided in an embodiment of the present application;

[0046] Fig.13 A comparison chart of theoretical and experimental results provided in the embodiments of the present application;

[0047] Fig.14 A comparison diagram between the theory and finite element simulation provided in the embodiments of the present application;

[0048] Fig.15 The constitutive curve provided for the embodiment of the present application;

[0049] Fig.16 A softening model provided in the embodiment of the present application;

[0050] Fig.17 Comparison of the failure characteristics of the specimens provided in the embodiments of the present application;

[0051] Fig.18 Comparison 1 of the hysteresis curves of the specimens provided in the embodiment of the present application;

[0052] Fig.19 Basic specimen construction information provided for the embodiments of this application;

[0053] Fig. 20 Comparison of the final damage morphology of the specimens provided in the embodiments of the present application;

[0054] Fig.21 The hysteresis curve of the specimen provided in the embodiment of the present application is compared with the second

[0055] Fig. 22The principal strain of concrete in the node area provided in the embodiment of the present application;

[0056] Fig.23 The principal stress of concrete in the node area provided in the embodiment of the present application;

[0057] Fig.24 The stress development of the steel bar unit at the core of the node provided by the embodiment of the present application;

[0058] Fig.25 The influence of the longitudinal reinforcement ratio provided by the embodiment of the present application;

[0059] Fig.26 The influence of the stirrup reinforcement ratio provided in the embodiment of the present application;

[0060] Fig. 27 The steel bar stress at different axial compression ratios provided in the embodiments of the present application.

[0061] Icon: 1-rebar frame; 11-longitudinal reinforcement group; 111-longitudinal reinforcement; 1111-first longitudinal reinforcement; 1112-second longitudinal reinforcement; 1113-diagonal reinforcement; 2-stirrups; 3-connectors. DETAILED DESCRIPTION

[0062] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] In the description of the embodiments of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limitations on the present invention. The terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. In addition, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to the specific circumstances.

[0064] like Figures 1 to 6As shown, an embodiment of the present invention provides a steel tube constrained reinforced concrete node with built-in diagonal braces, and the steel tube constrained reinforced concrete node with built-in diagonal braces includes a beam, a steel tube constrained reinforced concrete column and a built-in diagonal brace. The beam and the steel tube constrained reinforced concrete column are vertically cross-connected. The built-in diagonal brace includes two steel bars 1 and a plurality of stirrups 2. The built-in diagonal brace of the present application is arranged inside the steel tube constrained reinforced concrete column, does not occupy additional space, and has a flexible design form, does not affect the pipeline layout, and does not cause additional conflicts with the steel bar layout of the beam and the steel tube constrained reinforced concrete column.

[0065] like Figures 2 to 5 As shown, the two steel bars 1 are symmetrical from the perspective of the F direction, and the two steel bars 1 are arranged crosswise with each other. The steel bar frame 1 includes two longitudinal reinforcement groups 11. The two longitudinal reinforcement groups 11 are centrally symmetrical. The longitudinal reinforcement group 11 includes a plurality of longitudinal reinforcements 111, and the plurality of longitudinal reinforcements 111 are arranged parallel to each other. The longitudinal reinforcement 111 includes a first longitudinal reinforcement 1111, a second longitudinal reinforcement 1112, and an oblique reinforcement 1113. The first longitudinal reinforcement 1111 is connected to the oblique reinforcement 1113, and the end of the oblique reinforcement 1113 that is away from the first longitudinal reinforcement 1111 is connected to the second longitudinal reinforcement 1112. The oblique reinforcement 1113 is arranged within the range of the oblique compression rod, and the oblique reinforcement 1113 is parallel to the oblique compression rod. The ends of the first longitudinal reinforcement 1111 and the second longitudinal reinforcement 1112 that are away from the oblique reinforcement 1113 are both connected to the steel tube constrained reinforced concrete column. Specifically, the diagonal reinforcement 1113 is mainly used to improve the performance of the diagonal compression rod, so it is arranged within the range of the diagonal compression rod and parallel to the diagonal compression rod. The first longitudinal reinforcement 1111 and the second longitudinal reinforcement 1112 outside the node area extend into the steel tube restrained reinforced concrete column. The first longitudinal reinforcement 1111 and the second longitudinal reinforcement 1112 extending into the column can improve the plastic hinge performance of the column end to a certain extent, which is convenient for realizing the design requirements of "strong column and weak beam", and on the other hand, it is convenient for the hoisting of the built-in diagonal brace. In the actual construction process, the longitudinal reinforcement 111 is made by bending and forming a steel bar.

[0066] In practical applications, the arrangement direction of the diagonal reinforcement 1113 provided in the embodiment of the present application is the same as that of the diagonal compression rod, so as to maximize the reinforcement of the shear resistance of the node. At the same time, the diagonal reinforcement 1113 participates in shear resistance, which can reduce the softening effect of the main tension direction on the diagonal compression rod, thereby effectively preventing the brittle failure of the concrete node area. In addition, the built-in diagonal brace is mainly set up using the effective space inside the node area, and can be prefabricated separately in advance, without affecting the arrangement and binding of the longitudinal and transverse reinforcements, and can avoid the problem of difficult construction faced by on-site reinforcement.

[0067] Continue to refer to Figure 3Therefore, a plurality of stirrups 2 are respectively arranged on each steel frame 1, and the plurality of stirrups 2 are arranged at intervals along the extension direction of the diagonal bars 1113, and each stirrup 2 is sleeved on the periphery of the plurality of diagonal bars 1113. Specifically, the stirrups 2 are arranged perpendicular to the diagonal bars to effectively constrain the diagonal bars, improve the strength of the concrete diagonal bars, and thus enhance the bearing capacity of the node. Furthermore, the arrangement range of the stirrups 2 is mainly coordinated with the diagonal bars 1113 to form a cross steel cage.

[0068] An embodiment of the present invention provides a steel tube-constrained reinforced concrete node with an internal diagonal brace, and the steel tube-constrained reinforced concrete node with an internal diagonal brace includes a beam, a steel tube-constrained reinforced concrete column, and an internal diagonal brace. The beam and the steel tube-constrained reinforced concrete column are vertically cross-connected. The internal diagonal brace includes two steel bars 1 and a plurality of stirrups 2. The two steel bars 1 are symmetrical from the perspective of the F direction, and the two steel bars 1 are arranged crosswise with each other. The steel bar frame 1 includes two longitudinal bar groups 11, and the two longitudinal bar groups 11 are centrally symmetrical. The longitudinal bar group 11 includes a plurality of longitudinal steel bars 111, and the plurality of longitudinal steel bars 111 are arranged parallel to each other. The longitudinal steel bars 111 include a first longitudinal bar 1111, a second longitudinal bar 1112, and an oblique bar 1113. The first longitudinal bar 1111 is connected to the oblique bar 1113, and one end of the oblique bar 1113 that is away from the first longitudinal bar 1111 is connected to the second longitudinal bar 1112. The oblique bar 1113 is arranged within the range of the oblique compression rod, and the oblique bar 1113 is parallel to the oblique compression rod. The ends of the first longitudinal reinforcement 1111 and the second longitudinal reinforcement 1112 that are away from the diagonal reinforcement 1113 are connected to the steel tube constrained reinforced concrete column. A plurality of stirrups 2 are respectively arranged on each steel frame 1, and the plurality of stirrups 2 are arranged at intervals along the extension direction of the diagonal reinforcement 1113, and each stirrup 2 is sleeved on the periphery of the plurality of diagonal reinforcements 1113. The built-in diagonal brace of the present application is arranged inside the steel tube constrained reinforced concrete column, does not occupy additional space, and has a flexible design form and does not affect the pipeline layout. At the same time, it can significantly improve the bearing capacity and seismic performance of the node area, reduce the softening effect of the main tension direction on the diagonal compression rod, and thus effectively prevent the brittle failure of the concrete node area.

[0069] Continue to refer to Figure 1 As shown, the internal diagonal brace steel tube restrained reinforced concrete node also includes a connector 3. A connector 3 is respectively provided on each first longitudinal reinforcement 1111, one end of the connector 3 is connected to the first longitudinal reinforcement 1111 and its corresponding second longitudinal reinforcement 1112, and the other end of the connector 3 is connected to the vertical longitudinal reinforcement of the steel tube restrained reinforced concrete column. In practical applications, the internal diagonal brace is connected to the vertical longitudinal reinforcement of the steel tube restrained reinforced concrete column through the connector 3, thereby achieving the fixation of the internal diagonal brace.

[0070] This application verifies the effect of built-in diagonal brace steel tube confined reinforced concrete nodes through finite element modeling, as follows:

[0071] (1) Finite element model establishment

[0072] The analysis was performed with the help of finite element software DIANA. The total strain crack model is used to simulate the concrete characteristics. The total strain crack model disperses the cracks in the concrete unit and can consider the opening and closing states of the cracks. The Poisson's ratio in the cracked state adopts the orthogonal anisotropic theory to consider that the material stretching in the cracked state will not cause vertical contraction; the stress lateral constraint model is used to consider the constraint effect of the steel pipe and stirrup 2 on the improvement of the core concrete strength. In the analysis model, the concrete adopts the three-dimensional 8-node solid unit HX24L unit, and the concrete compressive characteristics are adopted as follows Fig.15 The constitutive curve simulation is shown in Figure 1, where n and k are the shape factors of the softening section of the curve, and ε is less than zero. Fig.16 Softening model shown.

[0073] Truss units that consider bond slip are used for the longitudinal reinforcement of columns and beams and stirrups 2. The bond slip relationship between them and concrete adopts multilinear bond slip curves, and the characteristic parameters of the curves are specified in the Code for Design of Concrete Structures. For areas where the bond slip phenomenon of stirrups 2 is not obvious, embedded truss units are used for simulation to improve the calculation efficiency. The steel bar constitutive relationship adopts a steel bar model that can reasonably consider the hardening of steel bars and the Bauschinger effect. The steel pipe adopts a two-dimensional 4-node shell unit Q20SH, and the interface unit is used to simulate the contact characteristics between the steel pipe and concrete. The material model selects the "Coulomb Friction Model". The Coulomb Friction Model can reasonably consider the effect of the increase of normal stress on the tangential stress, as well as the effect of the interface unit on the tangential stress after opening.

[0074] (2) Model Verification

[0075] Reinforced concrete node specimens, steel tube confined concrete node specimens and reinforced concrete node specimens confined by steel tubes with built-in diagonal braces were selected, and the model was established using the above method. The effectiveness of the model was verified from three aspects: failure characteristics, hysteresis characteristics, and bearing capacity.

[0076] Comparison of specimen failure characteristics Fig.17 As shown, Fig.17 (a) is the failure characteristics of reinforced concrete node specimens. Fig.17 (b) is the failure characteristics of the steel tube confined concrete node specimen. Fig.17 (c) is the failure characteristics of the reinforced concrete node specimen confined by the internal diagonal brace steel tube. Fig.17 It can be seen that the failure of the reinforced concrete node specimens and the steel tube confined concrete node specimens are concentrated in the node area, while the failure of the reinforced concrete node specimens confined by built-in diagonal braces steel tubes mainly occurs at the beam end, and there is slight damage in the node area, which is consistent with the specimen failure characteristics.

[0077] The hysteresis curve of the specimen is compared with Fig.18 As shown, Fig.18 (a) is the hysteresis curve of reinforced concrete node specimen. Fig.18 (b) is the hysteresis curve of the steel tube confined concrete node specimen. Fig.18 (c) is the hysteresis curve of the reinforced concrete node specimen confined by the internal diagonal brace steel tube. Fig.18 It can be seen that the model can better predict the unloading stiffness of the test specimen, and the reasonable simulation of the crack can better reflect the pinching characteristics and make an accurate estimate of the energy consumption of the specimen.

[0078] The bearing capacity was statistically analyzed and it was found that the average simulation deviations of the positive and negative peak bearing capacities of reinforced concrete node specimens, steel tube confined concrete node specimens and reinforced concrete node specimens with internal diagonal braces were 6%, 5.4% and 1.6% respectively. The simulation results show that the finite element model can better predict the seismic performance of the test specimens.

[0079] Specifically, the performance analysis of reinforced concrete nodes confined by steel tubes with built-in diagonal braces is as follows:

[0080] (1) Specimen parameter design

[0081] The parameter design of the foundation specimen is based on the requirements of the second-level seismic grade of the frame in the concrete structure design specification and the technical specification of steel tube confined concrete structure. The column-beam bending bearing capacity ratio is taken as 1.5, and the stirrups 2 in the core area of ​​the node are configured according to the minimum spacing requirements. The structural information of the foundation specimen is as follows: Fig.19 The concrete is C40, the diameter of the longitudinal reinforcement of the column and beam is 25mm, the reinforcement ratio is 2.9% and 2.2% respectively, and the core area stirrup 2 is HPB300 grade steel bar with a diameter of 10mm. For other information, see Fig.19 .

[0082] In order to further analyze the performance of reinforced concrete nodes confined by steel tubes with built-in diagonal braces, the seismic performance of reinforced concrete nodes confined by steel tubes with built-in diagonal braces was analyzed by adjusting the reinforcement ratio and axial compression ratio of the longitudinal reinforcement 111 in the parameter setting of the foundation specimen. The basic parameters are: the reinforcement ratio of the longitudinal reinforcement of the column is 1% to 4%; the reinforcement ratio of the longitudinal reinforcement of the beam is 1% to 3%; the reinforcement ratio of the longitudinal reinforcement 111 of the built-in diagonal brace is 0.2% to 0.66%; the reinforcement ratio of the stirrup 2 of the built-in diagonal brace is 0.1% to 0.5%; and the axial compression ratio is 0.1 to 0.7.

[0083] (2) Comparison of seismic performance

[0084] Different reinforcement ratios in the node area have different degrees of enhancement on the seismic performance of the node. In order to clarify the enhancement effect of built-in diagonal braces on node performance, three typical specimens were selected for comparative analysis. The specimens include: a comparison specimen without built-in diagonal braces; a specimen with a built-in diagonal brace longitudinal steel bar 111 with a diameter of 12mm and stirrup 2 with a diameter of 8mm (the reinforcement ratio in the node area is 0.24%); a specimen with a built-in diagonal brace longitudinal steel bar 111 with a diameter of 20mm and stirrup 2 with a diameter of 10mm (the reinforcement ratio in the node area is 0.66%), and the rest of the structural information is the same. The final damage morphology of the specimens is compared. Fig. 20 As shown, Fig. 20 (a) is the damage form of the comparison specimen without built-in diagonal bracing. Fig. 20 (b) is the damage form of the specimen with the internal diagonal bracing longitudinal reinforcement 111 having a diameter of 12 mm and stirrup 2 having a diameter of 8 mm. Fig. 20 (c) is the damage form of the specimen with the internal diagonal bracing longitudinal reinforcement 111 having a diameter of 20 mm and stirrup 2 having a diameter of 10 mm. Fig. 20 It can be seen that the damage of the comparison specimens without built-in diagonal braces is mainly concentrated in the node area, indicating that the bearing capacity of the node area is insufficient, which is a "strong component, weak node" feature. After setting up the built-in diagonal brace, the damage in the node area is significantly reduced, and the damage gradually shifts to the beam end. As the reinforcement ratio of the built-in diagonal brace increases, the damage is completely concentrated at the beam end, achieving the design requirement of "strong node, weak component".

[0085] The hysteresis curve of the specimen is compared with Fig.21 As shown, Fig.21 (a) is the hysteresis curve of the specimen with the internal diagonal brace longitudinal reinforcement 111 having a diameter of 12 mm and stirrup 2 having a diameter of 8 mm. Fig.21 (b) is the hysteresis curve of the specimen with the internal diagonal brace longitudinal reinforcement 111 having a diameter of 20 mm and stirrup 2 having a diameter of 10 mm. Fig.21 It can be seen that after adding the built-in diagonal brace, the initial stiffness of the specimen does not change significantly. As the reinforcement ratio of the built-in diagonal brace increases, the peak bearing capacity increases significantly, and the ductility gradually decreases. At the same time, the unloading stiffness of the specimen increases significantly, and the hysteresis curve becomes fuller. The main reason is that when the damage occurs in the node area, the node area undergoes significant shear deformation. After the concrete cracks, the shear force transmission capacity of the crack surface decreases significantly, and the unloading and reloading stiffness decreases significantly. The built-in diagonal brace enhances the node bearing capacity and deformation capacity, so that the deformation is mainly concentrated at the beam end and is mainly bending deformation. The longitudinal steel bar 111 deforms greatly during the force process, and the concrete is mainly subjected to tension and compression, the unloading stiffness is large, and the hysteresis curve is fuller.

[0086] Node damage and bearing capacity reduction usually start from the middle of the core area of ​​the node. The principal strain of concrete in the node area is as follows: Fig. 22 , Fig. 22 (a) is the principal tensile strain, Fig. 22 (b) is the principal compressive strain, given by Fig. 22 It can be seen that with the increase of the reinforcement amount in the core area of ​​the node, the values ​​of the principal tensile and compressive strains of the concrete at the same displacement are significantly reduced. Due to the coupling of tensile and compressive strains, the D12+8 and D20+10 specimens are greater than the uniaxial ultimate strain of concrete by 0.0033 at the peak load. However, as the displacement increases, the specimen enters the softening stage and the strain decreases. This shows that due to the arrangement of the built-in diagonal brace, after the peak load, the maximum deformation position is transferred to the beam end, and the deformation of the node area decreases. The principal stress of the concrete in the node area is as follows: Fig.23 , Fig.23 (a) Principal tensile stress, Fig.23 (b) The main compressive stress is Fig.23 It can be seen that the effect of the built-in diagonal brace on the peak value and the development of the whole process of the principal tensile stress and principal compressive stress is not obvious. The main reason is that although the concrete in the node area of ​​the comparison specimen reaches its peak stress, the peak stress has dropped significantly due to the weakening in the main tensile direction. The built-in diagonal brace can reduce the development of the principal tensile strain and reduce the weakening of the principal compressive stress. Although it has not reached the peak stress, its value is close to the peak stress of the concrete of the comparison specimen.

[0087] Further analysis is made on the development of the longitudinal reinforcement 111 in the node area, and the stress development of the reinforcement unit at the core of the node is extracted as follows: Fig.24 , Fig.24 (a) is the stress development of the longitudinal reinforcement 111, Fig.24 (b) is the stress development of stirrup 2, Fig.24 It can be seen that when the peak load is reached, the longitudinal steel bar 111 in the D12+8 specimen has yielded and has remained in the yield state as the strain increases. In the D20+10 specimen, the longitudinal steel bar 111 yields at the peak load, and the principal stress decreases as the displacement increases, indicating that the damage is mainly concentrated at the beam end, while the node area is in an unloading state. Fig.24 (c) is the stress development of stirrup 2 in the core area of ​​the node. It can be seen that with the increase of the reinforcement ratio of the built-in diagonal brace, stirrup 2 gradually changes from a yielded state to an unyielded state.

[0088] (3) Influence of reinforcement ratio

[0089] Fig.25 The influence of the longitudinal reinforcement ratio of 111 is: Fig.25 (a) and Fig.25 (b) The effects of different longitudinal reinforcement ratios on the horizontal bearing capacity and ductility of the specimens when the diameter of stirrup 2 is 8 mm, where P is the horizontal load of the specimen and ρ is the longitudinal reinforcement ratio; Fig.26 The influence of the reinforcement ratio of stirrup 2, Fig.26 (a) and Fig.26 (b) The effects of different stirrup 2 reinforcement ratios on the horizontal bearing capacity and ductility of the specimens when the diameter of the longitudinal steel bar 111 is 8 mm.

[0090] Depend on Fig.25 and Fig.26 It can be seen that the longitudinal reinforcement 111 and stirrup 2 have the same influence on the performance of the specimen. When the failure occurs in the core area of ​​the specimen node, the horizontal bearing capacity and ductility of the specimen are significantly improved with the increase of the reinforcement ratio of the longitudinal reinforcement 111 and stirrup 2 in the node area; when the specimen failure occurs at the beam end, the bearing capacity and ductility do not change much. As the axial compression ratio increases, the influence of the reinforcement ratio of the longitudinal reinforcement 111 and stirrup 2 on the bearing capacity gradually decreases. When the axial compression ratio is large, the principal tensile stress decreases, and the weakening of the concrete strength in the principal compression direction becomes smaller; when the reinforcement ratio of the longitudinal reinforcement 111 and stirrup 2 is small, the bearing capacity of the node area can be greatly improved. As the reinforcement ratio increases, the failure of the specimen gradually transfers from the node area to the beam end. At this time, increasing the reinforcement of the node area cannot significantly improve the horizontal bearing capacity.

[0091] In summary, the greater the reinforcement ratio of the longitudinal steel bars 111 and stirrup 2, the better the overall ductility of the specimen. When the failure occurs in the node area, at the same reinforcement ratio, the higher the axial compression ratio, the worse the ductility. When the failure occurs at the beam end, the axial compression ratio has little effect on the ductility.

[0092] (4) Axial pressure ratio

[0093] The specimens with the inclined compression reinforcement ratio of D12 and the inclined tension reinforcement ratio of D8 in the node area were selected to analyze the stress characteristics of the built-in diagonal brace at different axial compression ratios. Fig. 27 is the steel bar stress at different axial compression ratios, Fig. 27 (a) is the steel bar stress when the axial compression ratio is 0.1, Fig. 27 (b) is the steel bar stress when the axial compression ratio is 0.3. Fig. 27 (c) is the steel bar stress when the axial compression ratio is 0.5, Fig. 27 (d) is the steel bar stress when the axial compression ratio is 0.7. Fig. 27 It can be seen that as the axial compression ratio increases, the pressure on the compression side increases and the tension on the tension side decreases, resulting in an increase in the principal compressive stress, a decrease in the principal tensile stress, and a gradual decrease in the corresponding tensile reinforcement stress. At this time, the softening effect of the principal tensile-compression direction on the principal compression direction is small, and the built-in diagonal brace mainly enhances the node bearing capacity through the constraint of the diagonal compression rod concrete by the longitudinal steel bars 111 and stirrups 2. When the axial compression ratio is small, the principal tensile stress is high, and the built-in diagonal brace provides tensile resistance through the longitudinal steel bars 111 and stirrups 2, reducing the weakening of the principal tensile stress on the principal compressive stress.

[0094] In summary, when the axial pressure is relatively high, the longitudinal steel bars 111 and stirrups 2 in the built-in diagonal brace can improve the strength of the diagonal compression rod in the node area; when the axial pressure is relatively low, the longitudinal steel bars 111 and stirrups 2 in the built-in diagonal brace can effectively resist the principal tensile stress and reduce the weakening of the principal tensile direction on the principal compression direction.

[0095] like Figure 7As shown, an embodiment of the present invention provides a design method for a reinforced concrete node constrained by a built-in diagonal brace steel pipe, and the design method is applicable to the above-mentioned built-in diagonal brace steel pipe constrained reinforced concrete node, comprising the following steps:

[0096] Step 101: Determine the angle of the diagonal bar as follows:

[0097] In the formula, θ represents the angle of the diagonal rod, C b1 and C c1 H represents the pressure transmitted to the node from the column-beam compression zone. c , H b They respectively represent the distances between the longitudinal reinforcements of columns and beams, and nt represents the axial compression ratio.

[0098] Concrete diagonal struts are formed by the pressure from the compression zone of columns and beams being transferred to the node zone. They are mainly used to bear the principal compressive stress in the node zone. Therefore, the angle of the diagonal struts should be consistent with the resultant force of the pressure. Fig. 9 As shown, and taking the moment at the intersection of the column and beam tension lines, the first equilibrium equation is established as follows:

[0099] (C c1 +T c2 )·h c0 +V c1 ·h b1 +V c2 ·h b2 -C c2 ·(H c -h c0 )=(C b1 +T b2 )·h b0 +V b1 ·h c1 +V b2 ·h c2 -C b2 ·(H b -h b0 );Wherein, V c1 、V c2 、V b1 、V b2 They represent the shear force transmitted from the column to the node, C c1 , C c2 , C b1 , C b2 They represent the pressure transmitted to the node from the compression zone of the column and beam, T c1 、T c2 、T b1 、T b2 They represent the tensile force transmitted from the column and beam tension zone to the node, H c , H bThey represent the distance between the longitudinal reinforcements of the column and beam, h c0 、h b0 They represent the distance between the tensile longitudinal reinforcement of the column and beam and the point of action of the resultant force in the compression zone, h c1 、h c2 、h b1 、h b2 They represent the distance from the tensile longitudinal reinforcement of the column and beam to the edge of the section respectively;

[0100] The shear force transmitted from the column to the node is smaller than the pressure value transmitted from the column to the node in the compression zone, and the bending moment generated by the shear force transmitted from the beam to the column offsets each other to a certain extent. Its influence can be approximately ignored in the first equilibrium equation mentioned above. At the same time, the distance between the point of action of the resultant force in the compression zone and the point of action of the longitudinal reinforcement is relatively close, (H c -h c0 ) and (H b -h b0 ) relative to h c0 、h b0 The values ​​are small and there is a certain degree of mutual cancellation, which can be approximately ignored. Then the first equilibrium equation can be transformed into the second equilibrium equation as follows:

[0101] (C c1 +T c2 )·h c0 =(C b1 +T b2 )·h b0 ;

[0102] Since there is no axial pressure at the beam end, according to the horizontal force balance, T b1 Equal to C b1 , and due to the axial pressure at the column end, T c1 Equal to C c1 -N, where N is the column axial pressure. Then the second equilibrium equation can be further transformed into:

[0103]

[0104] According to the symmetry, C b1 Equal to C b2 , C c1 Equal to C c2 , and for ease of application, we approximate H c / H b Equal to h c0 / h b0 , the above formula can be transformed into:

[0105] Where N represents the axial force, n t represents the axial pressure ratio;

[0106] From the above formula, we can see that the angle of the diagonal rod is affected by H. c / H b In addition to the impact of N / C c1 Influence, while C c1 The value corresponds to the vertical component of the concrete diagonal strut failure in the node area, which is related to the bearing capacity of the concrete diagonal strut, and then to the concrete strength and the area of ​​the diagonal strut, which is easy to associate with N / C c1 Related to the axial pressure ratio, further study the axial pressure ratio and N / C c1 relationship, such as Fig.10 As shown;

[0107] Take the common H c / H b The angle θ of the oblique compression rod at different axial pressure ratios is shown in Table 1. It can be seen from Table 1 that the greater the axial pressure ratio, the greater the impact on the angle, and the maximum difference can reach 18.3°. c / H b When it is smaller, the angle changes relatively less with the axial pressure ratio. c / H b When the difference is 0.75, it is 16.3°, which is higher than H c / H b When the difference is 1, it decreases by 2°.

[0108]

[0109] Table 1. The angle of the diagonal compression rod at different axial pressure ratios. The angle calculation formula of the diagonal compression rod is as follows:

[0110]

[0111] Step 102: Determine the arrangement angle of the oblique ribs 1113 according to the angle of the oblique compression rod. Specifically, since the oblique ribs 1113 are mainly used to improve the performance of the oblique compression rod, the oblique ribs 1113 are arranged within the range of the oblique compression rod and are parallel to the oblique compression rod.

[0112] Step 103: Determine the width of the diagonal strut as follows:

[0113] In the formula, a sw represents the width of the diagonal strut, a b represents the height of the compression zone of the beam, a c It represents the height of the compression zone of the column;

[0114] Among them, θ' represents the angle generated by the height of the beam-column compression zone,

[0115] Specifically, the width of the concrete diagonal strut is Fig.11As shown in the figure, the concrete diagonal strut is mainly formed by the compressive stress of the concrete compression zone of the beam-column section being transmitted to the node, and the force range of the diagonal strut also matches the size of the compression zone of the beam-column section. Therefore, the following formula is used to estimate the height of the compression zone of the beam and column respectively;

[0116] In the formula, a b A represents the height of the compression zone of the beam. s represents the tensile longitudinal reinforcement area of ​​the beam, f y represents the yield strength of the longitudinal reinforcement of the beam, b b represents the width of the beam section, f c ' represents the axial compressive strength of concrete.

[0117] In the formula, a c represents the height of the column's compression zone, N represents the axial force, and h c Represents the column section height, h cb represents the column section width, f c ' represents the axial compressive strength of concrete.

[0118] The principal stress direction of the concrete compression rod should be the direction of the resultant force of the column and beam pressure, and the principal compressive stress should be consistent with the direction of the resultant force. The width of the corresponding oblique compression rod should be:

[0119] In the formula, a sw represents the width of the diagonal strut, a b represents the height of the compression zone of the beam, a c It represents the height of the compression zone of the column;

[0120] Among them, θ' represents the angle generated by the height of the beam-column compression zone,

[0121] Step 104: Determine the depth of the diagonal rod. Specifically, the depth b of the diagonal rod is c The value of is determined according to the space used in the depth direction of the node area. The two reinforcement frames 1 are arranged crosswise, so when determining b c When calculating the diameter of the longitudinal reinforcement 111 and the diameter of the stirrup 2, it is necessary to take into account.

[0122] Step 105: Determine the size of the stirrup 2 according to the width and depth of the diagonal compression rod.

[0123] Step 106: Determine the distance between the plurality of longitudinal reinforcement bars 111 according to the depth of the diagonal compression rod.

[0124] Step 107 : obtaining at least one reinforcement frame 1 based on the arrangement angle of the oblique reinforcement 1113 , the distance between the plurality of longitudinal reinforcements 111 , and the size of the stirrups 2 .

[0125] Step 108: Two steel bars 1 are crossed and symmetrically arranged from the perspective of direction F.

[0126] Step 109: Tie a plurality of stirrups 2 on each steel frame 1, the stirrups 2 are spaced apart along the extension direction of the diagonal bars 1113, and each stirrup 2 is sleeved on the periphery of the plurality of diagonal bars 1113 to form a built-in diagonal brace; connect the built-in diagonal brace and the steel tube constrained reinforced concrete column.

[0127] The design method of the reinforced concrete node constrained by the built-in diagonal brace steel tube provided in the embodiment of the present application is different from the existing node design method in that the reinforcement is parallel to the beam-column direction for shear resistance. The longitudinal steel bars 111 in the node area are consistent with the direction of the diagonal compression rod formed by the force in the node area, and the force is more reasonable, which maximizes the bearing capacity of the material, improves the shear resistance of the node, and reduces the cost. Correspondingly, the design of the built-in diagonal brace reinforcement is mainly carried out around the force in the direction of the diagonal compression rod, establishes a balance method, and considers the softening characteristics in the main direction, so that the reinforcement calculation is more in line with the actual force characteristics.

[0128] An embodiment of the present invention provides a design method for a reinforced concrete node constrained by a steel pipe with an internal diagonal brace, further comprising:

[0129] Step 110: Determine the shear bearing capacity of the reinforced concrete node confined by the internal diagonal brace steel tube.

[0130] like Figure 8 As shown in the figure, the shear bearing capacity of reinforced concrete nodes confined by built-in diagonal braces steel tubes is determined, including:

[0131] This application is based on the softening concept proposed by Hsu, takes the oblique strut area as the research object, considers the softening effect of the principal tensile stress on the principal compressive resistance in the force analysis, and considers the influence of the axial pressure based on the force balance. Fig.12 As shown, the force transmitted from the beam to the node can be synthesized into the main pressure C in the main direction. cb and the main tension T cb , from the strain development of concrete and steel bars, it can be seen that when the steel bars yield, the concrete has cracked. cb It can be deduced from the steel bar stress in reverse, T c1 and T b2 It can also be found through the composition and decomposition of forces.

[0132] Step 1101: Set the steel bar yield strain to the initial value of the principal tensile strain ε r , determine the softening coefficient; the softening coefficient formula is as follows:

[0133] In the formula, ζ represents the softening coefficient, ε r represents the principal tensile strain;

[0134] Step 1102: Determine the concrete stress in the direction of the principal compressive stress according to the principal tensile strain and softening formula;

[0135] In the formula, ε0 represents a known quantity related to the material, f c ' represents the axial compressive strength of concrete, ε d represents the principal compressive strain.

[0136] Specifically, the principal tensile strain is the peak stress, and when calculating the peak stress, the principal compressive strain ε d is equal to ζε0.

[0137] Step 1103: Determine the resistance of the diagonal compression rod in the direction of the principal compressive stress as follows:

[0138] In the formula, C cb1，R represents the resistance of the diagonal compression rod in the direction of the principal compressive stress, σ d represents the concrete stress in the direction of the principal compressive stress, A s represents the area of ​​the bar in the direction of the principal compressive stress, σ br,z A represents the stress of the longitudinal reinforcement 111 of the built-in diagonal brace. sbr represents the area of ​​the internal diagonal brace longitudinal reinforcement 111, σ st,c represents the stress of internal diagonal stirrup 2, A st,c cosθ1 represents the area component of the internal diagonal stirrup 2 in the direction of the principal compressive stress, σ ss A represents the stress of horizontal stirrups in the node area. ss1 represents the area of ​​horizontal stirrups, It represents the area component of the horizontal stirrup in the direction of the principal compressive stress. Specifically, the resistance of the diagonal compression rod in the direction of the principal compressive stress includes the resistance provided by concrete, steel bars and stirrups 2.

[0139] Step 1104: Determine the resistance in the direction of the principal tensile stress according to the principal tensile strain; wherein the calculation formula of the resistance in the direction of the principal tensile stress is as follows:

[0140] T cb1 =σ st,t ·A st,t +σ br,t ·A br,t ·cosθ1+σ ss ·A ss2 / cosθ; where T cb1 represents the resistance in the direction of the principal tensile stress, σ st,t represents the stress of internal diagonal stirrup 2, A st,t represents the area of ​​the internal diagonal stirrup 2 in the direction of the principal tensile stress, σ br,t A represents the stress of the longitudinal reinforcement 111 of the built-in diagonal brace. br,t·cosθ1 represents the area component of the internal diagonal brace longitudinal reinforcement 111 in the direction of the principal tensile stress, σ ss A represents the stress of horizontal stirrups in the node area. ss2 / cosθ represents the area component of the horizontal stirrups in the direction of the principal tensile stress.

[0141] Step 1105: Determine the principal pressure on the diagonal compression rod in the direction of the principal compressive stress by using the equilibrium formula. The equilibrium formula is as follows:

[0142] T cb1 sinθ+N=C cb1 ·cosθ; where N is the axial pressure; θ is the angle of the diagonal rod; C cb1 Indicates the principal pressure on the diagonal compression rod in the direction of the principal compressive stress.

[0143] Step 1106: Compare the magnitude of the principal pressure on the diagonal strut in the direction of the principal compressive stress and the resistance of the diagonal strut in the direction of the principal compressive stress. For the softening coefficient formula, softening formula and equilibrium relationship equation group, after assuming the diagonal brace reinforcement area, multiple variable values ​​include the resistance of the diagonal strut in the direction of the principal compressive stress, the principal pressure on the diagonal strut in the direction of the principal compressive stress, the resistance in the direction of the principal tensile stress, the concrete stress in the direction of the principal compressive stress, the principal tensile strain, the resultant force on the tensile side of the column and the resultant force on the tensile side of the beam. However, due to the nonlinearity of the steel bars and concrete materials, they cannot be solved directly, so further judgment is required in the calculation process.

[0144] Step 1107: When the principal pressure on the diagonal strut in the direction of the principal compressive stress is greater than or equal to the resistance of the diagonal strut in the direction of the principal compressive stress, a group of equilibrium relationship equations is established simultaneously, and the principal pressure on the diagonal strut in the direction of the principal compressive stress and the resistance of the diagonal strut in the direction of the principal compressive stress in the group of equilibrium relationship equations are made equal to determine multiple variable values, and the multiple variable values ​​include the resistance of the diagonal strut in the direction of the principal compressive stress, the principal pressure on the diagonal strut in the direction of the principal compressive stress, the resistance in the direction of the principal tensile stress, the concrete stress in the direction of the principal compressive stress, the principal tensile strain, the resultant force on the tensile side of the column, and the resultant force on the tensile side of the beam. Specifically, when the principal pressure on the diagonal strut in the direction of the principal compressive stress is greater than or equal to the resistance of the diagonal strut in the direction of the principal compressive stress, it indicates that the actual principal tensile strain is less than the principal tensile strain at yield, and the steel bar is in an elastic state at this time. The initial value of the principal tensile strain ε before this r Too large, at this time, the equilibrium relationship equations are combined, and the principal pressure on the oblique compression rod in the direction of the principal compressive stress and the resistance of the oblique compression rod in the direction of the principal compressive stress in the equilibrium relationship equations are made equal to solve multiple variable values.

[0145] Among them, the equilibrium relationship equations are established based on the rotation softening truss model in the direction of the principal stress as follows: Where, T c1 represents the resultant force on the tensile side of the column, T b2 represents the resultant force on the tensile side of the beam, V b2 represents the vertical shear force at the beam end, hb Indicates the beam section height, L b Indicates that the beam length is calculated from the inflection point, approximately taking the mid-span, V c1 represents the horizontal shear force at the column end, h c Indicates the column section height, L c It means that the column length is calculated based on the position of the inflection point, approximately taking the mid-span.

[0146] Step 1108: When the principal pressure on the diagonal compression rod in the direction of the principal compressive stress is less than the resistance of the diagonal compression rod in the direction of the principal compressive stress, the principal tensile strain is gradually increased to a certain value according to a fixed increment, and the values ​​of multiple variables are determined by the simultaneous equilibrium relationship equations. When the principal pressure on the diagonal compression rod in the direction of the principal compressive stress is less than the resistance of the diagonal compression rod in the direction of the principal compressive stress, it indicates that the actual principal tensile strain is greater than the yield strain. The initial value of the principal tensile strain is too small before, and the strain increases after the steel bar yields, and the stress is almost unchanged, but the softening of the principal compressive stress continues to increase, and it is no longer a linear relationship. Therefore, the principal tensile strain is first gradually increased to a certain value according to a fixed increment to determine the principal tensile strain, and then the values ​​of multiple variables are determined by the simultaneous equilibrium relationship equations.

[0147] Step 1109: Determine the difference between the principal pressure on the diagonal rod in the direction of the principal compressive stress and the resistance of the diagonal rod in the direction of the principal compressive stress according to the values ​​of multiple variables. When the difference is large, gradually increase the principal tensile strain again by a fixed increment, and continue to determine the values ​​of multiple variables by simultaneously solving the equilibrium relationship equations until the difference between the principal pressure on the diagonal rod in the direction of the principal compressive stress and the resistance of the diagonal rod in the direction of the principal compressive stress is less than a preset value. Determine the difference between the principal pressure on the diagonal rod in the direction of the principal compressive stress and the resistance of the diagonal rod in the direction of the principal compressive stress according to the values ​​of multiple variables. When the difference is large, continue to gradually increase the principal tensile strain by a fixed increment, then determine the values ​​of multiple variables by simultaneously solving the equilibrium relationship equations, and then determine the difference between the principal pressure on the diagonal rod in the direction of the principal compressive stress and the resistance of the diagonal rod in the direction of the principal compressive stress according to the values ​​of the variables again, and repeat the above steps until the difference is less than a preset value Δ.

[0148] Step 1110: Determine the shear bearing capacity of the node based on multiple variable values. In current projects, the shear force on the node is first solved, and the diagonal brace reinforcement is calculated based on the shear force. This application first presets the diagonal brace reinforcement, then reversely calculates the node shear force, and then compares it with the actual shear force, and then adjusts the reinforcement to gradually match the actual shear force.

[0149] The method for determining the shear bearing capacity of reinforced concrete nodes constrained by built-in diagonal braces and steel tubes provided in the embodiment of the present application is based on the force analysis of the isolation body in the node area and is not only applicable to reinforced concrete nodes constrained by built-in diagonal braces and steel tubes set in the present application, but also to nodes without built-in diagonal braces.

[0150] This application verifies the method of determining the shear bearing capacity of reinforced concrete nodes confined by internal diagonal braces from the following two aspects:

[0151] (1) Verify the traditional steel tube confined reinforced concrete column nodes;

[0152] 158 steel tube confined concrete column node failure specimens were analyzed, and the results are as follows: Fig.13 As shown in the figure, after calculation, for 67% of the specimens, the stirrups had yielded when the nodes reached the peak load, and for the remaining specimens, the stirrups had not yielded when the nodes reached the peak load. Fig.13 It can be seen that the calculation error is basically within 15%, and the stability of the calculation results of the statistical specimens is not affected by the change of the axial pressure ratio.

[0153] (2) Verify reinforced concrete nodes confined by steel tubes with built-in diagonal braces;

[0154] In order to verify the rationality of the calculation model applied to reinforced concrete node specimens confined by built-in diagonal braces, 54 specimens were designed by adjusting the diameter, strength and spacing of the longitudinal steel bars 111 and stirrups 2 in the built-in diagonal braces, and the failure occurred in the node area. Fig.14 As shown, the error is within 10%, indicating that this method can be effectively used to calculate the bearing capacity of reinforced concrete nodes confined by internal diagonal braces and steel tubes.

[0155] In order to verify the method of determining the shear bearing capacity of the node, the traditional steel tube confined reinforced concrete column (without built-in diagonal bracing) node is selected for calculation as follows:

[0156] 1) Calculate the angle θ of the diagonal rod

[0157]

[0158] 2) Calculate the principal tensile stress of the diagonal strut

[0159] The yield stress of the stirrups in the node area is 407MPa, the stirrup diameter is 12, the number is 9, and the elastic modulus of the steel is calculated as 206000MPa. Combined with the angle of the diagonal strut, it can be solved:

[0160] T cb1 =f yv ·A v n / cosθ=907890N;

[0161]

[0162] Combining the above formulas, we can get:

[0163] T c1 =834974N;T b2 =1285580N;

[0164] C c1 =T c1+N=834974+1420000=2254974N;

[0165] C cb1 =C c1 / cosθ=2472233N.

[0166] 3) Calculate the compressive strength of concrete diagonal compression bars

[0167] The yield strain of the longitudinal reinforcement is 0.00197, and the strain in the main direction is 0.00216. Based on this, the softening coefficient is:

[0168]

[0169] The bearing capacity of concrete struts is:

[0170] F=ζf c ·A s =0.6587×35.5×84400=197359.9N;

[0171]

[0172] The principal stress direction of the concrete compression rod should be the direction of the resultant force of the column and beam pressure, and the principal compressive stress should be consistent with the direction of the resultant force. The corresponding width of the diagonal compression rod should be:

[0173]

[0174] A s =a sw b c =211.1×400=84400mm 2 ;

[0175] 4) Judgment

[0176] C cb1 =C c1 / cosθ=2472233N>F=197359.9N, indicating that the stirrups have not yielded, so it is assumed that the principal tensile strain at the peak shear force of the node is ε r ,but:

[0177] T cb1 =Eε r cosθ·A v n / cosθ;

[0178] Solving simultaneous equations:

[0179]

[0180] C c1 =T c1 +N;

[0181] Let C cb1 =F:

[0182]

[0183] Solve for ε r =0.00064; T c1 =252823N;T b2 =396216N.

[0184] 5) Calculate horizontal shear force

[0185] V=T c1 tanθ+T b2 -V c =1050559N

[0186] The difference with the experimental value is 6.2%, which is in good agreement.

[0187] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other. Each embodiment focuses on the differences from other embodiments.

[0188] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A reinforced concrete node constrained by a built-in diagonal steel pipe, characterized in that: It includes beams, steel tube-confined reinforced concrete columns and built-in diagonal braces; The beam and the steel tube restrained reinforced concrete column are vertically cross-connected; The built-in diagonal brace comprises two steel bars (1) and a plurality of stirrups (2); The two steel bars (1) are symmetrical from the perspective of direction F, and the two steel bars (1) are arranged crosswise with each other; The steel reinforcement frame (1) comprises two longitudinal reinforcement groups (11); The two longitudinal reinforcement groups (11) are centrally symmetrical; The longitudinal reinforcement group (11) comprises a plurality of longitudinal reinforcements (111), and the plurality of longitudinal reinforcements (111) are arranged parallel to each other; The longitudinal reinforcement (111) comprises a first longitudinal reinforcement (1111), a second longitudinal reinforcement (1112) and an oblique reinforcement (1113); The first longitudinal rib (1111) is connected to the oblique rib (1113), and one end of the oblique rib (1113) away from the first longitudinal rib (1111) is connected to the second longitudinal rib (1112); The oblique rib (1113) is arranged within the range of the oblique pressure rod, and the oblique rib (1113) is parallel to the oblique pressure rod; The ends of the first longitudinal reinforcement (1111) and the second longitudinal reinforcement (1112) facing away from the oblique reinforcement (1113) are both connected to the steel tube-constrained reinforced concrete column; A plurality of stirrups (2) are respectively arranged on each of the steel bars (1); the plurality of stirrups (2) are arranged at intervals along the extension direction of the oblique bars (1113); and each stirrup (2) is sleeved on the periphery of the plurality of oblique bars (1113).

2. The reinforced concrete node constrained by an internal diagonal brace steel tube according to claim 1 is characterized in that: Also includes a connecting piece (3); A connecting piece (3) is respectively arranged on each of the first longitudinal bars (1111), one end of the connecting piece (3) is connected to the first longitudinal bar (1111) and its corresponding second longitudinal bar (1112), and the other end of the connecting piece (3) is connected to the vertical longitudinal bar of the steel tube-constrained reinforced concrete column.

3. A design method for reinforced concrete nodes constrained by internal diagonal steel pipes, characterized in that: The invention is applicable to the reinforced concrete node constrained by the internal diagonal brace steel tube as claimed in any one of claims 1 to 2, comprising: Determine the angle of the diagonal bar; Determine the arrangement angle of the oblique reinforcement (1113) according to the angle of the oblique compression rod; Determine the width of the diagonal strut; Determine the depth of the diagonal strut; The size of the stirrup (2) is determined according to the width and depth of the diagonal strut; Determining the distance between the plurality of longitudinal steel bars (111) according to the depth of the diagonal compression rod; At least one reinforcement frame (1) is obtained based on the arrangement angle of the oblique reinforcement (1113), the distance between the plurality of longitudinal reinforcements (111) and the size of the stirrups (2); The two steel bars (1) are crossed and symmetrically arranged from the perspective of direction F; A plurality of stirrups (2) are respectively tied on each of the steel bars (1), the plurality of stirrups (2) are arranged at intervals along the extension direction of the diagonal bars (1113), and each stirrup (2) is sleeved on the periphery of the plurality of diagonal bars (1113) to form a built-in diagonal brace; the built-in diagonal brace is connected to the steel tube constrained reinforced concrete column.

4. The design method of reinforced concrete nodes constrained by built-in diagonal bracing steel pipes according to claim 3 is characterized in that: The angle of the diagonal rod is determined as follows: In the formula, θ represents the angle of the diagonal rod, C b1 and C c1 H represents the pressure transmitted to the node from the column-beam compression zone. c , H b They respectively represent the distances between the longitudinal reinforcements of columns and beams, and nt represents the axial compression ratio.

5. The design method of reinforced concrete nodes constrained by internal diagonal steel pipes according to claim 3 is characterized in that: The width of the diagonal rod is determined as follows: In the formula, a sw represents the width of the diagonal strut, ab represents the height of the compression zone of the beam, and a c It represents the height of the compression zone of the column; Among them, θ' represents the angle generated by the height of the beam-column compression zone, 6. The design method of reinforced concrete nodes constrained by internal diagonal bracing steel pipes according to claim 3 is characterized in that: Also includes: Determine the shear bearing capacity of reinforced concrete nodes confined by internal diagonal steel tube braces.

7. The design method of reinforced concrete nodes constrained by internal diagonal steel pipes according to claim 6 is characterized in that: Determining the shear bearing capacity of reinforced concrete nodes restrained by built-in diagonal bracing steel tubes includes: The steel bar yield strain is set as the initial value of the principal tensile strain, and the softening coefficient is determined; the softening coefficient formula is as follows: In the formula, ζ represents the softening coefficient, ε r represents the principal tensile strain; Determine the concrete stress in the direction of the principal compressive stress based on the principal tensile strain and softening formula; Determine the resistance of the diagonal strut in the direction of the principal compressive stress as follows: In the formula, C cb1，R represents the resistance of the diagonal compression rod in the direction of the principal compressive stress, σ d represents the concrete stress in the direction of the principal compressive stress, A s represents the area of ​​the bar in the direction of the principal compressive stress, σ br,z represents the stress of the internal diagonal brace longitudinal reinforcement (111), A sbr represents the area of ​​the internal diagonal brace longitudinal reinforcement (111), σ st,c represents the stress of the internal diagonal stirrup (2), A st,c cosθ1 represents the area component of the internal diagonal stirrup (2) in the direction of the principal compressive stress, σ ss A represents the stress of horizontal stirrups in the node area. ss1 represents the area of ​​horizontal stirrups, represents the area component of the horizontal stirrups in the direction of the principal compressive stress; The resistance in the direction of the principal tensile stress is determined according to the principal tensile strain; the calculation formula for the resistance in the direction of the principal tensile stress is as follows: T cb1 =σ st,t ·A st,t +σ br,t ·A br,t ·cosθ1+σ ss ·A ss2 / cosθ; where T cb1 represents the resistance in the direction of the principal tensile stress, σ st,t represents the stress of the internal diagonal stirrup (2), A st,t represents the area of ​​the internal diagonal stirrup (2) in the direction of the principal tensile stress, σ br,t represents the stress of the internal diagonal brace longitudinal reinforcement (111), A br,t ·cosθ1 represents the area component of the internal diagonal brace longitudinal reinforcement (111) in the direction of the principal tensile stress, σ ss A represents the stress of horizontal stirrups in the node area. ss2 / cosθ represents the area component of the horizontal stirrups in the direction of the principal tensile stress; The principal pressure on the diagonal compression rod in the direction of the principal compressive stress is determined by the equilibrium formula, which is as follows: T cb1 sinθ+N=C cb1 ·cosθ; where N represents the axial pressure, θ represents the angle of the diagonal rod, and C cb1 Indicates the principal pressure on the diagonal compression rod in the direction of the principal compressive stress; Compare the principal pressure on the diagonal strut in the direction of the principal compressive stress and the resistance of the diagonal strut in the direction of the principal compressive stress; When the principal pressure on the diagonal compression rod in the direction of the principal compressive stress is greater than or equal to the resistance of the diagonal compression rod in the direction of the principal compressive stress, a group of equilibrium relationship equations are simultaneously established, and the principal pressure on the diagonal compression rod in the direction of the principal compressive stress and the resistance of the diagonal compression rod in the direction of the principal compressive stress in the group of equilibrium relationship equations are made equal to determine multiple variable values, wherein the multiple variable values ​​include the resistance of the diagonal compression rod in the direction of the principal compressive stress, the principal pressure on the diagonal compression rod in the direction of the principal compressive stress, the resistance in the direction of the principal tensile stress, the concrete stress in the direction of the principal compressive stress, the principal tensile strain, the resultant force on the tensile side of the column, and the resultant force on the tensile side of the beam; Among them, the equilibrium relationship equations are established based on the rotation softening truss model in the direction of the principal stress as follows: Where, T c1 represents the resultant force on the tensile side of the column, T b2 represents the resultant force on the tensile side of the beam, V b2 is the vertical shear force at the beam end, h b Indicates the beam section height, L b Indicates that the beam length is calculated from the inflection point, approximately taking the mid-span, V c1 represents the horizontal shear force at the column end, h c Indicates the column section height, L c It means that the column length is calculated from the position of the inflection point, approximately taking the mid-span; When the principal pressure on the oblique compression rod in the direction of the principal compressive stress is less than the resistance of the oblique compression rod in the direction of the principal compressive stress, the principal tensile strain is gradually increased to a certain value according to a fixed increment, and a plurality of variable values ​​are determined by a simultaneous equilibrium relationship equation group; the difference between the principal pressure on the oblique compression rod in the direction of the principal compressive stress and the resistance of the oblique compression rod in the direction of the principal compressive stress is determined according to the plurality of variable values, and when the difference is large, the principal tensile strain is gradually increased again according to a fixed increment, and the plurality of variable values ​​are determined by a simultaneous equilibrium relationship equation group until the difference between the principal pressure on the oblique compression rod in the direction of the principal compressive stress and the resistance of the oblique compression rod in the direction of the principal compressive stress is less than a preset value; The node shear bearing capacity is determined based on the multiple variable values.

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