A beam structure with shear-bent section filled with UHPC and a prefabrication method thereof

Abstract

This invention provides a beam structure with UHPC filling in the shear bending section and its prefabrication method, solving the problems of current beam construction methods that use only UHPC, which not only result in a large structural self-weight and high cost, but also increase the overall construction cost and extend the construction period. This invention includes ordinary concrete beam sections and UHPC beam sections, which are spaced apart along the length of the beam. Taking into account the stress characteristics of the shear bending section of reinforced concrete beams, this invention fills a certain length of UHPC material only in key areas of the reinforced concrete shear bending section to improve the mechanical properties of the main beam's shear bending section, significantly increasing the shear bearing capacity of the main beam. Simultaneously, filling a portion of the main beam's shear bending section with UHPC effectively reduces the cross-sectional area of ​​the beam near the supports, reducing the structure's self-weight and lowering the construction cost of the UHPC, thus exhibiting good economic efficiency and practicality.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, and in particular to a beam structure with a UHPC (Ultra-High-Pressure Polymer) filling section in shear bend and its prefabrication method. Background Technology

[0002] Ultra-high performance concrete (UHVPC) has a dense structure with low porosity, excellent corrosion resistance and fatigue resistance, as well as high tensile and compressive strength. If it is used in bridge structures, the shear and bending resistance of the main beam can be effectively improved.

[0003] Currently, there are more and more cases of using UHPC in bridge construction. However, research has found that UHPC structures are heavy and the product materials and construction costs are relatively high. If the main beams of the entire bridge are cast with UHPC, it will not only bring a large structural self-weight and high cost, but also require additional bridge supports to balance the force, which will increase the overall construction cost of the bridge and prolong the construction period. Summary of the Invention

[0004] To address the issues in the background art where the current method of casting beams entirely with UHPC not only results in a large structural self-weight and high cost, but also increases the overall construction cost and extends the construction period, this invention proposes a beam structure with UHPC filling in the shear bending section and its prefabrication method.

[0005] The technical solution of the present invention is: a beam structure for a shear-bending section filled with a UHPC, comprising a regular concrete beam section and a UHPC beam section, wherein the UHPC beam section and the regular concrete beam section are spaced apart along the length of the beam.

[0006] Preferably, the UHPC segment beam includes multiple UHPC beam casting layers in the vertical direction, and the ordinary concrete segment beam includes multiple ordinary concrete beam casting layers in the vertical direction. The UHPC beam casting layers and the ordinary concrete beam casting layers are connected one-to-one, and the thickness of the UHPC beam casting layer and the ordinary concrete beam casting layer in the same layer is the same.

[0007] Preferably, the connection between the UHPC beam casting layer and the ordinary concrete beam casting layer has a staggered and intersecting structure in the vertical direction.

[0008] Preferably, the intrusion length of the staggered intrusion structure of each layer is 2 / 3 of the thickness of that layer.

[0009] Preferably, the UHPC beam casting layer and the ordinary concrete beam casting layer on the same floor are integrally cast and formed into a structure.

[0010] The adjacent UHPC beam casting layer and the ordinary concrete beam casting layer are layered casting structures.

[0011] A method for prefabricating a beam structure with a partially filled UHPC section in shear bend, comprising the following steps: S1 – Based on the material properties of UHPC material and ordinary concrete, establish a shear bearing capacity model for a UHPC beam with a partially filled shear bend.

[0012] S2 – Based on the shear capacity model of a UHPC beam partially filled with shear bending section, establish the formula for the shear capacity of a simply supported UHPC beam filled with shear bending section:

[0013] In the formula, β is the UHPC crack length ratio coefficient;

[0014] b is the beam width;

[0015] c is the horizontal projection length of the distance from the intersection of the longitudinal reinforcement and the bottom of the diagonal crack to the top of the diagonal crack;

[0016] f cu,k This refers to the standard value of the compressive strength of a concrete cube.

[0017] A s This represents the area of ​​the longitudinal reinforcement.

[0018] f s For longitudinal reinforcement strength;

[0019] ρ sv The hoop ratio;

[0020] f sv For the strength of the stirrups;

[0021] α is set to 0.6;

[0022] ω is the random distribution coefficient of the steel fiber;

[0023] σ f The pull-out strength of the steel fiber;

[0024] V f This refers to the volumetric content of steel fibers.

[0025] l f The length of the steel fiber;

[0026] d f The diameter of the steel fiber;

[0027] τ f The average bond stress between the fiber and the matrix is ​​related to the uniaxial compressive strength of UHPC.

[0028] The coefficients A and B take values ​​of

[0029] S3 - Based on the relevant calculation parameters of the shear bearing capacity of the main beam and the load that the shear bending section beam needs to bear, the shear bearing capacity formula of the infill UHPC beam in the shear bending section is used to calculate the length and position of the UHPC section beam and the ordinary concrete beam.

[0030] S4 – Install main beam formwork;

[0031] S5 – Install the reinforcing cage inside the main beam formwork;

[0032] S6 - Based on the length and position of the UHPC segment beam and the ordinary concrete beam, pour the UHPC and ordinary concrete in layers at the corresponding positions in the main beam formwork to form interconnected UHPC beam pouring layers and ordinary concrete beam pouring layers.

[0033] S7 - After the pouring is completed and the main beam has solidified, the main beam formwork is removed, and the prefabrication of the main beam is completed.

[0034] Preferably, when performing the layered pouring of UHPC and ordinary concrete in step S6, each layer of UHPC beam pouring layer and ordinary concrete beam pouring layer is poured simultaneously and with equal thickness.

[0035] Furthermore, the joint between the UHPC beam casting layer and the ordinary concrete beam casting layer is treated by cross-intrusion, forming a staggered cross-intrusion structure on the left and right sides.

[0036] The intrusion length of the staggered intrusion structure of each layer is 2 / 3 of the thickness of that layer.

[0037] Preferably, the equilibrium equation for the inclined crack section of the shear bearing capacity model of the locally filled UHPC beam in step S1 is:

[0038]

[0039]

[0040]

[0041] In the formula, σ is the compressive stress borne by the concrete in the shear-compression zone;

[0042] τ represents the shear stress borne by the UHPC in the shear-compression zone;

[0043] b is the beam width;

[0044] F represents the vertical shear force on the concrete shear surface;

[0045] D represents the horizontal compressive shear force on the concrete shear surface;

[0046] T s For longitudinal reinforcement tension;

[0047] A s This represents the area of ​​the longitudinal reinforcement.

[0048] f s For longitudinal reinforcement stress;

[0049] T sv For the tensile force of the stirrups;

[0050] ρ sv The hoop ratio;

[0051] f sv Stress in the stirrups;

[0052] d is V w The length of the lever arm from point O;

[0053] z represents the height of the concrete pressure relief surface;

[0054] 'a' represents the distance from the shear surface to the support.

[0055] c is the horizontal projection length of the distance from the intersection of the longitudinal reinforcement and the bottom of the diagonal crack to the top of the diagonal crack;

[0056] V w For steel fiber pull-out force;

[0057] V w1 This is the vertical component of the steel fiber pull-out force;

[0058] V w2 The horizontal component of the steel fiber pull-out force;

[0059] h0 is the effective height of the beam section;

[0060] θ is the angle between the main diagonal crack and the beam axis.

[0061] Preferably, the UHPC crack length proportion coefficient β is calculated as follows: Let the UHPC filling length in the shear-bending section be l, the lower end position of the diagonal crack be p, and the length from the starting point of the UHPC filling in the shear-bending section to the lower end position of the diagonal crack be l. p If the projected length of the diagonal crack on the horizontal plane is c, then...

[0062] When the UHPC fill length of the shearing section l < l p At this point, the diagonal crack has not penetrated the UHPC segment beam, and the horizontal projection length of the diagonal crack through the UHPC is 0, so β ​​= 0.

[0063] When the UHPC fill length of the shearing segment is l p <l<(l) p When +c), the diagonal crack passes through two materials simultaneously, according to... Figure 9 The specific β value can be calculated by considering the proportion of diagonal cracks in the two materials in b.

[0064] When the UHPC filling length of the shearing segment l > (l p +c), the diagonal crack partially penetrates the UHPC, at which point β=1.

[0065] Preferably, the formula for calculating the projected length c of the diagonal crack on the horizontal plane is c=kλh0;

[0066] Where λ: the shear span ratio of the normal section at the top of the inclined section;

[0067] M d V d Design values ​​of bending moment and shear force at the top of the inclined section;

[0068] k: Influence coefficient.

[0069] Advantages of this invention: This invention combines the stress characteristics of the shear bending section of reinforced concrete beams, and improves the mechanical properties of the main beam's shear bending section by filling a certain length of UHPC material only in key parts of the reinforced concrete shear bending section, which can significantly improve the shear bearing capacity of the main beam; at the same time, filling a section of the main beam's shear bending section with UHPC effectively reduces the cross-sectional area of ​​the beam near the support, reduces the self-weight of the structure, and also reduces the construction cost of UHPC, thus having good economic efficiency and practicality. Attached Figure Description

[0070] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0071] Figure 1 Loading and internal force diagrams for a simply supported reinforced concrete beam;

[0072] Figure 2 A schematic diagram of the UHPC filling portion of the shear-bending section of a simply supported beam;

[0073] Figure 3 A schematic diagram of the casting of UHPC for the shear-bending section of a simply supported beam;

[0074] Figure 4 This is a schematic diagram of the connection between UHPC and ordinary concrete (NC) in a simply supported beam.

[0075] Figure 5 Location of diagonal cracks when the shear-bending section of a simply supported beam fails after filling with UHPC;

[0076] Figure 6The diagram shows the calculation of shear capacity of each inclined section when there are three types of inclined crack locations.

[0077] Figure 7 This is a schematic diagram of the projected length c of the diagonal crack.

[0078] Figure 8 This diagram shows the location of sections with relatively weak shear bearing capacity.

[0079] Figure 9 The positional relationship between the infilling of the shear bend segment with UHPC of different lengths and the occurrence of diagonal cracks;

[0080] Figure 10 A graph showing the variation of shear capacity for beams with different UHPC fill lengths;

[0081] In the diagram, 1 is the ordinary concrete beam pouring layer, 2 is the UHPC beam pouring layer, and 3 is the formwork. Detailed Implementation

[0082] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0083] Example 1: A beam structure with a UHPC filled in the shear bending section, such as... Figure 4 As shown, the beam includes ordinary concrete beam sections and UHPC beam sections, which are spaced apart along the length of the beam.

[0084] The UHPC beam section includes multiple UHPC beam casting layers 2 in the vertical direction, and the ordinary concrete beam section includes multiple ordinary concrete beam casting layers 1 in the vertical direction. The UHPC beam casting layers 2 and the ordinary concrete beam casting layers 1 are connected one-to-one. The connection between the UHPC beam casting layers 2 and the ordinary concrete beam casting layers 1 has a staggered and intersecting structure in the vertical direction. The thickness of the UHPC beam casting layers 2 and the ordinary concrete beam casting layers 1 in the same layer is the same.

[0085] During the pouring process, in order to ensure the bond strength of the connection between UHPC and ordinary concrete, the UHPC beam pouring layer 2 and the ordinary concrete beam pouring layer 1 on the same floor are poured as a whole. The adjacent UHPC beam pouring layer 2 and ordinary concrete beam pouring layer 1 are poured continuously from bottom to top, and the maximum layer thickness does not exceed 20cm, and does not exceed 15cm when the reinforcement is dense.

[0086] The intrusion length of each layer into the staggered, intersecting structure is 2 / 3 of the layer thickness. UHPC selection should refer to the "Technical Requirements for Ultra-High Performance Concrete (UHPC)" (T / CECS10107-2020), specifying a minimum strength of 100 MPa. Ordinary concrete should not be lower than C60 grade; longitudinal reinforcement and stirrups in beams should use HB400 grade steel bars; specimens should be cast and cured according to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB-T 50081-2019) and the "Technical Requirements for Ultra-High Performance Concrete (UHPC)" (T / CECS10107-2020).

[0087] A method for prefabricating a beam structure with a partially filled UHPC section in shear bend includes the following steps: S1 - Based on the material properties of UHPC material and ordinary concrete, establish a shear bearing capacity model for a partially filled UHPC beam in shear bend.

[0088] S2 – Based on the shear capacity model of a UHPC beam partially filled with shear bending section, establish the formula for the shear capacity of a simply supported UHPC beam filled with shear bending section:

[0089] In the formula, β is the UHPC crack length ratio coefficient;

[0090] b is the beam width;

[0091] c is the horizontal projection length of the distance from the intersection of the longitudinal reinforcement and the bottom of the diagonal crack to the top of the diagonal crack;

[0092] f cu,k This refers to the standard value of the compressive strength of a concrete cube.

[0093] A s This represents the area of ​​the longitudinal reinforcement.

[0094] f s For longitudinal reinforcement strength;

[0095] ρ sv The hoop ratio;

[0096] f sv For the strength of the stirrups;

[0097] α is set to 0.6;

[0098] ω is the random distribution coefficient of the steel fiber;

[0099] σ f The pull-out strength of the steel fiber;

[0100] V f This refers to the volumetric content of steel fibers.

[0101] l f The length of the steel fiber;

[0102] d f The diameter of the steel fiber;

[0103] τ f The average bond stress between the fiber and the matrix is ​​related to the uniaxial compressive strength of UHPC.

[0104] The coefficients A and B take values ​​of

[0105] S3 - Based on the relevant calculation parameters of the shear bearing capacity of the main beam and the load that the shear bending section beam needs to bear, the shear bearing capacity formula of the infill UHPC beam in the shear bending section is used to calculate the length and position of the UHPC section beam and the ordinary concrete beam.

[0106] S4 – Install main beam formwork;

[0107] S5 – Install the reinforcing cage inside the main beam formwork;

[0108] S6 - Based on the length and position of the UHPC beam and the ordinary concrete beam, pour the UHPC and ordinary concrete in layers at the corresponding positions in the main beam formwork to form the UHPC beam pouring layer 2 and the ordinary concrete beam pouring layer 1 that are connected to each other.

[0109] S7 - After the pouring is completed and the main beam has solidified, the main beam formwork is removed, and the prefabrication of the main beam is completed.

[0110] Among them, such as Figure 3 and Figure 4 As shown, when pouring UHPC and ordinary concrete in step S6, each layer of UHPC beam pouring layer 2 and ordinary concrete beam pouring layer 1 is poured simultaneously and with equal thickness.

[0111] Furthermore, the connection between the UHPC beam casting layer 2 and the ordinary concrete beam casting layer 1 is treated by cross-intrusion, forming a staggered cross-intrusion structure on the left and right sides.

[0112] The intrusion length of the staggered intrusion structure of each layer is 2 / 3 of the thickness of that layer.

[0113] The specific analysis process in steps S1 to S2 above is as follows:

[0114] 1. The specific process of establishing the shear bearing capacity model of the UHPC beam with local filling in the shear bending segment is analyzed as follows:

[0115] Under load, a simply supported reinforced concrete beam exhibits large bending moments near the mid-span section and large shear forces near the supports. Figure 1Taking the loading mode as an example, based on the distribution of bending moment and shear force diagrams of a simply supported beam under concentrated load, the beam can be divided into sections such as pure bending segment and shear bending segment. Among them, the shear bending segment bears both shear force and bending moment, and its stress is more complex than that of the pure bending segment.

[0116] Studies have shown that the failure modes of reinforced concrete shear-bending sections mainly include diagonal tension failure, shear-compression failure, and diagonal compression failure. In beam shear design, it has been found that shear capacity is mainly related to the shear span ratio, concrete compressive strength, longitudinal tensile reinforcement ratio, and stirrup reinforcement ratio and strength. In bridge design, the failure mode of the shear-bending section is usually designed as shear-compression failure. Shear-compression failure of reinforced concrete flexural members occurs when the principal compressive stress, resulting from the synthesis of normal and shear stresses in the compression zone of the inclined section, exceeds the ultimate compressive strength of the concrete, ultimately leading to failure. Therefore, significantly improving the compressive and tensile strength of the concrete in the shear-bending section of the main beam will greatly improve the shear capacity of the main beam. However, even by increasing the concrete grade to improve the compressive and tensile strength of ordinary concrete, the increase in strength is very limited.

[0117] Currently, UHPC materials exhibit high density, resulting in extremely high strength and excellent durability. Studies have shown that UHPC compressive strength can reach over 200 MPa, while its durability can exceed 200 years. Furthermore, the fine steel fibers dispersed within UHPC significantly slow the propagation of internal microcracks, thus contributing to the material's exceptional toughness and ductility.

[0118] In reinforced concrete beams with varying lengths of UHPC (ultra-high-density concrete) filling in the shear bending section, under external forces, the location of diagonal cracks within the shear bending section will vary depending on the proportion of UHPC filling length. Figure 5 The three cases shown are: 1) the diagonal crack only passes through the ordinary concrete NC; 2) the diagonal crack passes through both the UHPC and the ordinary concrete NC; 3) the diagonal crack only passes through the UHPC.

[0119] Figure 5 In the middle, due to the different material distribution in the areas where the diagonal cracks pass through the beam, therefore Figure 5 The calculation of the shear capacity of the structure differs under the three failure scenarios. To accurately calculate the shear capacity of the beam under these three conditions, we will now analyze them separately. Figure 5 Force analysis is performed on the three failure scenarios shown, such as Figure 6 As shown.

[0120] Figure 6 For the corresponding Figure 5 The diagrams shown illustrate the calculation of the shear capacity of the beam at different locations of the diagonal cracks. The calculations are now performed on each of these locations. Figure 6 Force analysis is performed for each type of damage.

[0121] 1) Figure 6 a) For the stress analysis of the failure section when the diagonal crack only penetrates through ordinary concrete, let c be the horizontal projected length from the intersection of the longitudinal reinforcement and the bottom of the diagonal crack to the top of the diagonal crack. At this time, the concrete shear surface at the top of the diagonal section bears a horizontal compressive force D and a vertical shear force F. The longitudinal reinforcement within the diagonal section provides horizontal tensile force T. s The stirrups provide a vertical tensile force T. sv .

[0122] 2) Figure 6 (b) For the stress analysis of the failure section when the diagonal crack simultaneously passes through both UHPC and ordinary concrete, a UHPC crack length proportion coefficient β is introduced, which is the horizontal projection length of the main diagonal crack βc passing through the UHPC. Therefore, the horizontal projection length of the diagonal crack passing through the ordinary concrete should be (1-β)c. At this time, the concrete shear-compression surface at the top of the diagonal section bears the horizontal compressive force D and the vertical shear force F. The longitudinal reinforcement within the diagonal section provides support against the horizontal tensile force T. s The stirrups provide a vertical tensile force T. sv The steel fibers in the UHPC, within the length βc through which the oblique section passes, provide pull-out resistance V in the direction perpendicular to the oblique section. w .

[0123] 3) Figure 6 c) Stress analysis of the failure section when the diagonal crack only passes through the UHPC. In this case, the UHPC concrete shear-compression surface at the top of the diagonal section is subjected to horizontal compressive force D and vertical shear force F. The longitudinal reinforcement within the diagonal section provides support under the horizontal tensile force T. s The stirrups provide a vertical tensile force T. sv And the steel fibers in UHPC provide pull-out resistance V perpendicular to the oblique section. w .

[0124] 2. Shear bearing capacity model of UHPC beam with localized filling in shear bending segment

[0125] Based on the above analysis, it was found that, due to Figure 6 The different locations of the three oblique sections result in different stresses on each section. The main difference in stress on each failing oblique section lies in whether the oblique section passes through the UHPC region and whether the steel fibers provide pull-out resistance.

[0126] Now, using the proposed UHPC crack length ratio coefficient β, based on the force balance relationship and the bending moment balance relationship, an applicable... Figure 6 Formulas for the shear bearing capacity of beams under three failure conditions are given, where β=0 represents the case where the diagonal crack only passes through ordinary concrete; β∈(0,1) represents the case where the diagonal crack passes through both UHPC and ordinary concrete; and β=1 represents the case where the diagonal crack only passes through UHPC.

[0127] It is evident that adjusting the UHPC crack length ratio coefficient β can reflect the above three failure scenarios. Figure 6 a) with Figure 6 c) The beam can be considered as Figure 6 b) The two extreme value forms when β takes the values ​​0 and 1. Therefore, we first consider... Figure 6 The mechanical analysis of the failure cross section in b) allows us to establish the following equilibrium equations:

[0128]

[0129]

[0130]

[0131] In the formula, σ is the compressive stress borne by the concrete in the shear-compression zone;

[0132] τ represents the shear stress borne by the UHPC in the shear-compression zone;

[0133] b is the beam width;

[0134] F represents the vertical shear force on the concrete shear surface;

[0135] D represents the horizontal compressive shear force on the concrete shear surface;

[0136] T s For longitudinal reinforcement tension;

[0137] A s This represents the area of ​​the longitudinal reinforcement.

[0138] f s For longitudinal reinforcement stress;

[0139] T sv For the tensile force of the stirrups;

[0140] ρ sv The hoop ratio;

[0141] f sv Stress in the stirrups;

[0142] d is V w The length of the lever arm from point O;

[0143] z represents the height of the concrete pressure relief surface;

[0144] 'a' represents the distance from the shear surface to the support.

[0145] c is the horizontal projection length of the distance from the intersection of the longitudinal reinforcement and the bottom of the diagonal crack to the top of the diagonal crack;

[0146] V w For steel fiber pull-out force;

[0147] Vw1 This is the vertical component of the steel fiber pull-out force;

[0148] V w2 The horizontal component of the steel fiber pull-out force;

[0149] h0 is the effective height of the beam section;

[0150] θ is the angle between the main diagonal crack and the beam axis.

[0151] 3. Formula for shear capacity of simply supported UHPC beam with shear-bending section

[0152] To facilitate the calculation of steel fiber pull-out force, we assume the direction of the diagonal crack is perpendicular to the axial direction of the steel fiber, thus deriving the expression for the steel fiber pull-out force in UHPC. Furthermore, based on the fourth strength theory, the relationship between compressive stress and shear stress in the shear-compression zone concrete can also be established. Through derivation, the final formula for calculating the shear capacity of the beam with locally filled UHPC in the shear-bending section is as follows:

[0153]

[0154] To simplify the calculation formula for the shear capacity of beams with UHPC partially filled in the shear-bending section, let:

[0155]

[0156] Then formula (4) can be simplified to:

[0157]

[0158] In formula (5), σ f The pull-out strength of the steel fiber;

[0159] b is the beam width;

[0160] ω is the random distribution coefficient of the fiber. For UHPC with 3% steel fiber content, ω = 0.7 is taken, and for UHPC with 5% steel fiber content, ω = 0.55 is taken. For other steel fiber (steel bar) contents, ω can be taken as the corresponding interpolation value.

[0161] V f This refers to the volumetric content of steel fibers.

[0162] l f The length of the steel fiber;

[0163] d f The diameter of the steel fiber;

[0164] f cu,k This refers to the standard value of the compressive strength of a concrete cube.

[0165] τ fThe average bond stress between the fiber and the matrix is ​​related to the uniaxial compressive strength of UHPC. α is set to 0.6;

[0166] Wherein, coefficients A and B take values ​​of

[0167] Observing the symbols in the formula, we find that all symbols except 'c' are currently known. 'c' is related to the location of the diagonal section where the diagonal crack fails, specifically the location from point 'p' (the intersection of the longitudinal reinforcement of the diagonal crack and the bottom of the crack) to point 'q' (the intersection of the top of the diagonal crack). Figure 7 As shown.

[0168] To determine the horizontal projection length c of the failure section, it is necessary to identify the intersection points of the longitudinal reinforcement with the bottom of the diagonal crack and the top of the diagonal crack. Only then can the shear bearing capacity of the beam after local filling of the shear bending section with UHPC of different lengths be determined.

[0169] 4. Determination of the horizontal projected length c of the failure cross section and the UHPC crack length ratio coefficient β

[0170] 4.1 Location of the bottom section of the inclined section

[0171] When calculating the shear capacity of UHPC beams with infilled shear bends of varying lengths, many factors influence the location of the main shear section where failure occurs, such as the loading point location, beam cross-sectional dimensions, the quantity, arrangement, and spacing of longitudinal and stirrup reinforcement, and the uniformity of steel fiber distribution within the UHPC. Therefore, it is theoretically difficult to accurately determine the location of the main shear section where failure occurs. Based on the Highway Bridge Code and the material distribution of UHPC beams with infilled shear bends, the following sections are considered to have relatively weak shear capacity:

[0172] 1) Section 1-1 at a distance h / 2 from the center of the support;

[0173] 2) Section 2-2 where the number or spacing of stirrups changes;

[0174] 3) Sections of the bent-up reinforcement in the tension zone and the sections of the longitudinal reinforcement anchored in the tension zone at the point where it begins to be unstressed (3-3).

[0175] 4) Section where the width of the beam's rib changes;

[0176] 5) Section 4-4 at the junction of UHPC and NC;

[0177] Figure 6 The above diagram shows the locations of the five sections with relatively weak shear bearing capacity. Figure 8 The intersection point between the longitudinal reinforcement of the diagonal crack and the bottom of the diagonal crack within the beam can be determined.

[0178] 4.2 Determination of the UHPC crack length proportion coefficient β

[0179] The location of the oblique section failure can be determined from the preceding text. Based on the relative positional relationship between the calculated location of the oblique section and the UHPC filling length, the proportion factor β of the oblique crack in the UHPC after filling the shear-bending section of the simply supported beam with different UHPCs can be determined, such as... Figure 7 As shown.

[0180] Figure 9 The positional relationship between points β, c, and p when filling the shear bend segment with different UHPC lengths l. Figure 7 It can be seen that the calculation of the crack length ratio coefficient β after filling the shear bending section with different UHPCs can be divided into the following three cases:

[0181] 1) Figure 9 a) The fill length l of the shear bending section UHPC is less than l p When the diagonal crack section does not pass through the UHPC, the horizontal projection length of the diagonal crack through the UHPC is 0, and β = 0.

[0182] 2) Figure 9 b) The fill length of the UHPC shearing section l p <l<(l) p When +c), the diagonal crack passes through two materials simultaneously, according to... Figure 9 The specific β value can be calculated by considering the proportion of diagonal cracks in the two materials in b.

[0183] 3) Figure 9 c) The fill length l of the shearing section UHPC is greater than (l p +c), the diagonal crack partially penetrates the UHPC, at which point β=1.

[0184] 4.3 Determination of the horizontal projection length c of the failure section

[0185] The magnitude of the horizontal projection length 'c' of the inclined section is related to the effective height of the beam section and the shear span ratio. Based on extensive experimental data from both domestic and international sources, it is recommended that:

[0186] c=kλh0 (3);

[0187] Where λ represents the shear span ratio of the normal section at the top of the inclined section. For simply supported beams under concentrated loads, a narrow shear span ratio can be used. For other load conditions, the generalized shear span ratio is taken. The moment of impact (M) at the top section of each diagonal crack needs to be determined based on the bending moment envelope diagram and the shear force envelope diagram. d With V d The maximum value of λ is obtained, thus determining λ.

[0188] M d V d These are the design values ​​of bending moment and shear force at the top of the inclined section;

[0189] k is the influence coefficient. When the diagonal cracks are all in ordinary concrete, k is taken as 0.6.

[0190] When diagonal cracks occur in UHPC beams, based on the statistical results of shear tests on full UHPC beams, k can be taken as 0.65.

[0191] When the diagonal cracks are partially in ordinary concrete and partially in UHPC, according to Figure 6 The geometric relationship in b) is given by k, which is an interpolation value (a positive value). The calculation method is as follows:

[0192]

[0193] When solving for c, it is necessary to first determine the position q of the top section of the inclined section, and then use formula (3) to perform trial calculations until the calculated horizontal projection length c is exactly or close to the horizontal projection length of pq. At this time, the position q is considered to be the final position of the top section of the inclined section, and the value of c is the horizontal projection length of the damaged inclined section used in the final calculation.

[0194] After determining the values ​​of c and β, the shear bearing capacity of simply supported UHPC beams with different lengths filled with shear-bending sections can be calculated using the formula in this paper, providing a reference for determining the design of external force values ​​for UHPC simply supported beams with corresponding shear-bending sections.

[0195] Using the above calculation method, the trends of the shear capacity calculation curves for ordinary concrete beams, UHPC beams, and UHPC beams with different lengths of shear-bending sections were compared under the same size and material conditions. Figure 10 Observations revealed that the shear capacity of all-ordinary concrete beams was the lowest, while that of all-UHPC beams was the highest. Furthermore, the shear capacity of beams with different UHPC proportions increased linearly with the length of the UHPC infill. This indicates that the UHPC-filled beams in the shear-bending section proposed in this patent can significantly improve the shear capacity of the beam, with a greater increase in shear capacity as the UHPC infill length increases. Additionally, given the beam cross-sectional dimensions and the design value of the beam's shear capacity, it can be determined based on… Figure 10 Determine the UHPC fill length.

[0196] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A beam structure with a shear-bending section filled with a UHPC, characterized in that: It includes ordinary concrete beam sections and UHPC beam sections, with UHPC beam sections and ordinary concrete beam sections spaced apart along the length of the beams; The UHPC beam section includes multiple UHPC beam casting layers (2) in the vertical direction, and the ordinary concrete beam section includes multiple ordinary concrete beam casting layers (1) in the vertical direction. The UHPC beam casting layer (2) and the ordinary concrete beam casting layer (1) are connected one-to-one, and the thickness of the UHPC beam casting layer (2) and the ordinary concrete beam casting layer (1) in the same layer is the same. The UHPC beam casting layer (2) and the ordinary concrete beam casting layer (1) on the same floor are integrally cast and formed structures; The adjacent UHPC beam casting layer (2) and ordinary concrete beam casting layer (1) are layered casting structures; The steps include: S1~Based on the material properties of UHPC material and ordinary concrete, establish a shear bearing capacity model for a UHPC beam with local infill in the shear-bending section; S2~Based on the shear capacity model of a UHPC beam with a partially filled shear-bending section, establish the formula for the shear capacity of a simply supported UHPC beam with a filled shear-bending section: To simplify the calculation formula for the shear capacity of beams with UHPC partially filled in the shear-bending section, let: The formula then simplifies to: In the formula, β This is the crack length ratio coefficient for UHPC. b For beam width; c It is the horizontal projection length of the distance from the intersection of the longitudinal reinforcement and the bottom of the diagonal crack to the top of the diagonal crack; f cu,k This refers to the standard value of the compressive strength of a concrete cube. A s This represents the area of ​​the longitudinal reinforcement. f s For longitudinal reinforcement strength; p sv The hoop ratio; f sv For the strength of the stirrups; α Take 0.6; w The random distribution coefficient of steel fibers; σ f The pull-out strength of the steel fiber; V f This refers to the volumetric content of steel fibers. l f The length of the steel fiber; d f The diameter of the steel fiber; τ f The average bond stress between the fiber and the matrix is ​​related to the uniaxial compressive strength of UHPC. ; S3~Based on the relevant calculation parameters of the shear bearing capacity of the main beam and the load that the shear bending section beam needs to bear, the shear bearing capacity formula of the infill UHPC beam in the shear bending section is used to calculate the length and position of the UHPC section beam and the ordinary concrete beam; S4 ~ Install main beam formwork; S5~Install the reinforcing cage inside the main beam formwork; S6~Based on the length and position of the UHPC beam and the ordinary concrete beam, UHPC and ordinary concrete are poured in layers at the corresponding positions in the main beam formwork to form the UHPC beam pouring layer (2) and the ordinary concrete beam pouring layer (1) that are connected to each other. S7 - After the pouring is completed and the main beam has solidified, the main beam formwork is removed, and the prefabrication of the main beam is completed. The connection between the UHPC beam casting layer (2) and the ordinary concrete beam casting layer (1) is a staggered, cross-intrusion structure in the vertical direction.

2. The beam structure with a UHPC filled in the shear bending section as described in claim 1, characterized in that: The intrusion length of the staggered intrusion structure of each layer is 2 / 3 of the thickness of that layer.

3. The prefabrication method for a beam structure with a UHPC filled in a shear-bending section as described in claim 1, characterized in that: When performing the layered pouring of UHPC and ordinary concrete in step S6, each layer of UHPC beam pouring layer (2) and ordinary concrete beam pouring layer (1) is poured simultaneously and with equal thickness. Furthermore, the joint between the UHPC beam casting layer (2) and the ordinary concrete beam casting layer (1) is treated by cross-intrusion, forming a staggered cross-intrusion structure on the left and right sides; The intrusion length of the staggered intrusion structure of each layer is 2 / 3 of the thickness of that layer.

4. The prefabrication method for a beam structure with a UHPC filling section as described in claim 3, characterized in that: The equilibrium equation for the inclined crack section of the shear capacity model of the locally filled UHPC beam in step S1 is: S X =0→ D = Ts + V W2 →s bz = A s f s + V w sinth S Y =0→ V = Tsv + F + Vw 1→ V =p sv f sv bc +t bz + V w cosθ In the formula, σ This refers to the compressive stress borne by the concrete in the shear-compression zone. τ The shear stress borne by the UHPC in the shear-compression zone; b For beam width; F This refers to the vertical shear force on the concrete shear surface. D This refers to the horizontal compressive shear force on the concrete shear surface. T s For longitudinal reinforcement tension; A s This represents the area of ​​the longitudinal reinforcement. f s For longitudinal reinforcement strength; T sv For the tensile force of the stirrups; p sv The hoop ratio; f sv For the strength of the stirrups; d for V w distance O The length of the lever arm at the point; z The height of the shear-compression surface concrete; a This is the distance from the shear surface to the support; c It is the horizontal projection length of the distance from the intersection of the longitudinal reinforcement and the bottom of the diagonal crack to the top of the diagonal crack; V w For steel fiber pull-out force; V w1 This is the vertical component of the steel fiber pull-out force; V w2 The horizontal component of the steel fiber pull-out force; h 0 represents the effective height of the beam section; θ The angle between the main diagonal crack and the beam axis.

5. The prefabrication method for a beam structure with a UHPC filling section as described in claim 3, characterized in that: UHPC Crack Length Ratio Coefficient β The calculation method is as follows, assuming the fill length of the shear bending section UHPC is... l The lower end of the diagonal crack is located at p The length from the starting point of the UHPC filling in the shear bending section to the lower end of the diagonal crack is... l p The projected length of the diagonal crack on the horizontal plane is c ,but, When the UHPC fill length of the shearing segment l < l p At this point, the diagonal crack has not penetrated the UHPC segment beam, and the horizontal projection length of the diagonal crack through the UHPC is 0. β =0; When the UHPC fill length of the shearing segment l p < l <( l p + c When the diagonal crack passes through two materials simultaneously, ; When the UHPC fill length of the shearing segment l >( l p + c The diagonal crack partially penetrates the UHPC, at which point... β =1.

6. The prefabrication method for a beam structure with a UHPC filled in a shear bending section as described in claim 5, characterized in that: The projected length of the diagonal crack on the horizontal plane is c The calculation formula is as follows: ; in, λ This represents the shear span ratio of the normal section at the top of the inclined section; h 0 represents the effective height of the beam section; k This is the influence coefficient.

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