Design method of fabricated composite bent cap and fabricated composite bent cap

Abstract

The application provides a design method and an assembled combined cap beam, which utilizes material characteristics of steel structures and concrete structures, can effectively reduce beam height, increase net clearance under the bridge, fully utilizes tensile strength of steel and compressive strength of concrete, avoids transition design, ensures structural safety performance, ensures bearing capacity and structural rigidity of the cap beam, appropriately reduces material consumption of the lower structure under the design effect, improves the seismic performance, and is especially suitable for large cantilever cap beam structures. The design process is comprehensive and simple, can quickly and reasonably determine the size of the assembled cap beam, improves the design efficiency, and reduces the popularization cost and difficulty of the structure. The whole combined cap beam is realized by full assembled construction, the flange assembly is used to realize force transmission between the assembled cap beam and the pier column, greatly improves the construction efficiency, reduces the construction cost and construction period, and has obvious economic benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bridges, and particularly relates to a design method of an assembled combined cap beam and the assembled combined cap beam. BACKGROUND

[0002] Compared with the traditional cast-in-situ beam, the assembled bridge has significant advantages in efficiency, environmental protection, and quality controllability, and has become an important direction of the development of modern bridge engineering. At present, the superstructure, pier column and pile foundation of the assembled bridge have relatively mature structure forms, and the prefabricated cap beam is mainly of the reinforced concrete structure. A kind of assembled bridge cap beam is disclosed in the related technology, a connecting sleeve is arranged at one end or both ends of the cap beam, the external reinforcement reserved when the structure is segmented is inserted into the connecting sleeve, and grouting is performed in the connecting sleeve to fixedly connect the prefabricated cap beams. The reinforcement connection construction of the technical scheme is complex, the connection effect cannot be guaranteed, and the node stress and seismic performance are affected. At the same time, the ordinary reinforced concrete cap beam is heavy and difficult to hoist, and cannot be applied to the large cantilever structure cap beam commonly used in urban bridges. If the prestress system is supplemented, the construction difficulty and cycle will be further increased.

[0003] In addition, in the currently disclosed technology, a combined system cap beam with a steel skeleton stiffener is proposed, which solves some problems of the ordinary concrete structure, but the structure form of the concrete outer package steel skeleton is also not suitable for the stress mode of the double-pier large cantilever cap beam, in which the negative bending moment at the top of the pier is much larger than the positive bending moment between the piers, and cannot fully play the material properties of the steel structure in tension and the concrete structure in compression.

[0004] Therefore, it is necessary to propose a design method of an assembled combined cap beam and the assembled combined cap beam to solve or at least alleviate the above-mentioned defects. SUMMARY

[0005] The main purpose of the present application is to provide a design method of an assembled combined cap beam and the assembled combined cap beam, so as to solve the problem that the stress system of the combined system cap beam in the prior art is not suitable for the large cantilever cap beam.

[0006] To achieve the above-mentioned purpose, the present application provides a design method of an assembled combined cap beam, comprising the following steps:

[0007] S1, determining the size group of the combined cap beam according to the material performance; wherein the combined cap beam comprises a steel structure section and a reinforced concrete section;

[0008] S2, determining the effect design value group of the action basic combination according to the size group of the combined cap beam; wherein the effect design value group of the action basic combination comprises a shear design value of the action basic combination, a steel beam stress value of the action basic combination, and a concrete compressive stress value of the action basic combination;

[0009] S3, checking whether the combined cap beam structure safety parameters meet the requirements based on the effect design value group of the combined cap beam size group and the effect basic combination; wherein the combined cap beam structure safety parameters include vertical shear bearing capacity, bending bearing capacity, fatigue strength of steel structure, and deflection of the cantilever end of the combined cap beam;

[0010] S4, judging whether all the combined cap beam structure safety parameters meet the requirements; if all the combined cap beam structure safety parameters meet the requirements, determining that the combined cap beam meets the technical requirements; if any one of the combined cap beam structure safety parameters does not meet the requirements, adjusting the size of the combined cap beam, and returning to step S1.

[0011] Preferably, step S1 specifically comprises the steps of:

[0012] S11, obtaining the total cross-sectional height of the combined cap beam according to the application scenario;

[0013] S12, obtaining the concrete beam cross-sectional height according to the total cross-sectional height of the combined cap beam;

[0014] S13, determining the steel beam cross-sectional size according to the formula ; wherein,

[0015] is the ratio of the elastic modulus of steel to that of concrete, is the elastic modulus of steel, is the elastic modulus of concrete, is the cross-sectional area of steel, is the cross-sectional area of concrete, is the distance from the centroid of the steel beam to the upper surface of the concrete, is the concrete beam cross-sectional height.

[0016] Preferably, the step S12 specifically comprises the steps of:

[0017] The formula is used to determine the value of the cross-sectional height ; wherein, h is the total cross-sectional height of the combined cap beam, is the limit compression zone height, f sd is the tensile strength design value of steel.

[0018] Preferably, the checking of the vertical shear bearing capacity in the step S3 specifically comprises the steps of:

[0019] S31, determining the vertical shear bearing capacity according to the formula determining whether the vertical shear capacity design value of the composite cap beam meets the requirement, if the vertical shear capacity design value of the composite cap beam is greater than or equal to the shear design value of the basic combination of actions, the requirement is met; if the vertical shear capacity design value of the composite cap beam is less than the shear design value of the basic combination of actions, the requirement is not met; wherein,

[0020] is the structural importance coefficient, is the shear design value of the basic combination of actions, is the vertical shear capacity design value, b is the width of the concrete oblique section shear compression zone corresponding to the normal section, h 0 is the effective height of the concrete section, P is the reinforcement percentage of the longitudinal tensile steel bar in the oblique section, f cu,k is the standard value of the compressive strength of a concrete cube with a side length of 150 mm, ρ sv is the reinforcement ratio of the hoop steel bar in the concrete oblique section, f sv is the tensile strength design value of the hoop, f vd is the shear strength design value of the steel material, A w is the web section area of the steel material.

[0021] Preferably, the checking of the bending capacity in the step S3 specifically comprises the steps of:

[0022] S32, according to the formula determining whether the steel beam stress value of the basic combination of actions is less than or equal to the tensile strength design value of the steel material,

[0023] and according to the formula determining whether the concrete compressive stress value of the basic combination of actions meets the requirement, if the steel beam stress value of the basic combination of actions is less than or equal to the tensile strength design value of the steel material, and the concrete compressive stress value of the basic combination of actions is less than or equal to the compressive strength design value of the concrete, the requirement is met; if the steel beam stress value of the basic combination of actions is greater than the tensile strength design value of the steel material, and / or the concrete compressive stress value of the basic combination of actions is greater than the compressive strength design value of the concrete, the requirement is not met; wherein,

[0024] is the edge stress of the steel section, is the edge stress of the concrete section, is the axial force borne by the steel section, is the bending moment borne by the steel section, is the axial force borne by the concrete section, is the bending moment borne by the concrete section, is the sectional bending stiffness of the steel material, is the sectional bending stiffness of the concrete, fcd is the design value of the compressive strength of the concrete.

[0025] Preferably, the checking of the fatigue strength of the steel structure in the step S3 specifically comprises the steps of:

[0026] S330, establishing a composite bent model;

[0027] S331, obtaining normal stress values and shear stress values under the limit state based on the composite bent model;

[0028] S332, judging whether the limit normal stress difference value is less than or equal to the normal stress fatigue limit according to the formula and judging whether the limit shear stress difference value is less than or equal to the shear stress fatigue limit according to the formula if both are within the fatigue limit, the requirement is met; if one of them is greater than the fatigue limit, the requirement is not met; wherein,

[0029] σ pmax , σ pmin are the maximum and minimum normal stresses respectively under the limit state and loaded on the influence line, τ pmax , τ pmin are the maximum and minimum shear stresses respectively under the limit state and loaded on the influence line, is the size effect reduction factor, is the normal stress constant amplitude fatigue limit, is the shear stress constant amplitude fatigue limit.

[0030] Preferably, the checking of the deflection of the cantilever end of the composite bent in the step S3 specifically comprises the steps of:

[0031] S341, obtaining live load counterforces at each support and distances from the center of the pier column of each support based on the composite bent model;

[0032] S342, judging whether the deflection of the cantilever end of the composite bent meets the requirement according to the formula if the maximum deflection of the cantilever end of the composite bent is within the limit deflection range of the cantilever end of the composite bent, the requirement is met; if the maximum deflection of the cantilever end of the composite bent exceeds the limit deflection value of the cantilever end of the composite bent, the requirement is not met; wherein,

[0033] δ max is the maximum deflection value of the cantilever end of the composite bent, is the live load counterforce at each support, is the distance from the support to the center of the pier column, n is the number of supports in the cantilever range, and L is the cantilever length, is a stiffness reduction coefficient.

[0034] Preferably, the step S4 of "adjusting the size of the combined cap beam" specifically comprises:

[0035] adjusting the total cross-sectional height of the combined cap beam; wherein the single adjustment of the total cross-sectional height is 5cm-10cm.

[0036] The application also provides a prefabricated combined cap beam, comprising a combined cap beam and a flange assembly, the combined cap beam comprising a steel structure section and a reinforced concrete section, the steel structure section being connected above the reinforced concrete section, and the reinforced concrete section being connected to a pier column through the flange assembly; wherein the size of the combined cap beam is obtained based on the design method of the prefabricated combined cap beam as described above.

[0037] Preferably, the flange assembly comprises a pier flange and a cap beam flange, the bottom end of the pier flange being connected to the pier column, the top end of the cap beam flange being connected to the reinforced concrete section, and the pier flange and the cap beam flange being connected through bolts.

[0038] Compared with the prior art, the prefabricated combined cap beam provided by the application has the following advantages:

[0039] The design method of the prefabricated combined cap beam and the prefabricated combined cap beam provided by the application utilize the material properties of steel structure and concrete structure, and under the design of reasonable arrangement of cross-sectional layout, can effectively reduce the beam height, increase the under-bridge clearance, fully utilize the tensile strength of steel and the compressive strength of concrete, avoid transition design, ensure the structural safety performance, ensure the bearing capacity and structural stiffness of the cap beam, and under the design effect, can appropriately reduce the material consumption of the lower structure, improve the seismic performance, and is particularly suitable for large cantilever cap beam structure. The design process is comprehensive and simple, can quickly and reasonably determine the size of the prefabricated cap beam, improve the design efficiency, and also reduce the popularization cost and difficulty of such structure. The entire combined cap beam realizes full prefabricated construction, and the flange assembly realizes the force transmission between the prefabricated cap beam and the pier column, greatly improves the construction efficiency, reduces the construction cost and construction period, and has obvious economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from the structures shown in the drawings without creative labor.

[0041] Figure 1 A flowchart of a design method of the assembled combined cap beam in an embodiment of the present application;

[0042] Figure 2 An elevation view of an application scenario of the overall structure in an embodiment of the present application;

[0043] Figure 3 A side view of an application scenario of the overall structure in an embodiment of the present application.

[0044] The purposes, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings.

[0045] Explanation of reference signs:

[0046] 10, combined cap beam; 110, steel structure section; 120, reinforced concrete section; 20, flange assembly; 210, cap beam flange; 220, pier flange; 30, pier column. DETAILED DESCRIPTION

[0047] It should be understood that the specific embodiments described herein merely exemplify the present application and are not intended to limit the present application.

[0048] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0049] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present application are only used to explain the relative positional relationship, movement condition, etc. between components in a certain posture (as shown in the drawings), and if the certain posture changes, the directional indications also change accordingly.

[0050] In addition, the description of “first”, “second” and the like in the present application is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by “first”, “second” can explicitly or implicitly include at least one of the features. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of those skilled in the art, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the scope of protection claimed by the present application.

[0051] Please refer to the attached Figure 1 -attached Figure 3 In an embodiment, the application provides a design method of an assembled composite bent cap and the assembled composite bent cap, comprising the steps of:

[0052] S1, determining the size group of the composite bent cap 10 according to the material performance; wherein the composite bent cap 10 comprises a steel structure section 110 and a reinforced concrete section 120; it should be noted that the composite bent cap 10 mainly adopts the form of combination of steel structure and reinforced concrete structure, the concrete in the cross section of the composite bent cap 10 is mainly compressed, and the steel beam is mainly in tension, so as to combine the material properties of steel and concrete, improve the carrying capacity of the structure, and therefore, in order to make the cross section size of the composite bent cap 10 optimal, it is necessary to design an optimal cross section size combination form, so that the steel beam is basically in tension and the concrete is basically in compression, thereby fully exerting the material properties of each other.

[0053] As a preferred embodiment, step S1 specifically comprises the steps of:

[0054] S11, obtaining the total cross section height of the composite bent cap 10 according to the application scenario;

[0055] S12, obtaining the concrete beam cross section height according to the total cross section height of the composite bent cap 10;

[0056] S13, determining the steel beam cross section size according to formula one: ; wherein,

[0057] is the ratio of the elastic modulus of steel and concrete, is the elastic modulus of steel, is the elastic modulus of concrete, is the cross section area of steel, is the cross section area of concrete, is the distance from the centroid of the steel beam to the upper surface of the concrete, is the concrete beam cross section height.

[0058] In the application scenario of the bridge design, the total cross section height of the composite bent cap 10 is first limited, and the commonly used total cross section height of the composite bent cap 10 can be used as the initial value when the initial size is first determined. Based on the initial value, the total height of the composite bent cap 10 is determined, and the cross section height of the concrete beam is further obtained; wherein in a preferred embodiment, formula two can be used to determine the value of the cross section height of the concrete: ; wherein, h is the total cross section height of the composite bent cap 10, is the limit compression zone height, f sd ​a design value of tensile strength of steel, a design value of tensile strength of steel f sd can be obtained according to the type of steel, and the specification of steel and the grade of concrete are usually preliminarily determined, so that the value of the concrete section height obtained according to the formula, it is worth mentioning that formula two is mainly suitable for the scene of concrete grade C50 and below.

[0059] And it can be understood that in the case where the total height of the composite cap beam 10 h , the concrete section height are known, since the cross section of the composite cap beam 10 is usually a regular figure, the distance between the centroid of the steel beam and the upper surface of the concrete can be easily obtained, which will not be described in detail here, and the width of the concrete section can also be reasonably valued according to the conventional concrete cap beam, and the cross-sectional area of the concrete can be obtained by combining the preliminary determination of the width of the conventional concrete section and the height of the concrete section, the cross-sectional area refers to the cross-sectional area; it should be noted that n 0 in formula one is the ratio of the elastic modulus of steel and concrete, the elastic modulus of steel and the elastic modulus of concrete can be obtained by corresponding material grade and specification in the specification, so that the cross-sectional area of steel can be determined according to formula one after the above data are preliminarily determined, and the size group of the preliminary composite cap beam 10 is obtained, so that the subsequent structure safety calculation can be carried out according to the size group preliminarily determined.

[0060] S2, determining the effect design value group of the basic combination according to the size group of the composite cap beam 10; wherein the effect design value group of the basic combination includes the shear design value of the basic combination, the steel beam stress value of the basic combination, and the concrete compressive stress value of the basic combination. It should be noted that the effect design value group of the basic combination is the basic combination and frequent combination effect design value acting on the cap beam, specifically, the effect design value of the bridge under permanent action and variable action is determined according to the general bridge internal force calculation method, and the effect design value group of the basic combination is obtained by combining the permanent action design value and the variable action design value in the “general specification for design of highway bridges and culverts” (JTGD60-2015), in this application, the shear design value of the basic combination is mainly needed to calculate the vertical shear bearing capacity, and the steel beam stress value of the basic combination and the concrete compressive stress value of the basic combination are needed to calculate the bending bearing capacity.

[0061] S3, checking whether the effect design value group of the basic combination meets the requirement based on the size group of the combined cap beam 10 and the effect design value group of the basic combination; wherein the structure safety parameters of the combined cap beam 10 include vertical shear bearing capacity, bending bearing capacity, fatigue strength of the steel structure, and deflection of the cantilever end of the combined cap beam 10;

[0062] S4, judging whether all the structure safety parameters of the combined cap beam 10 meet the requirement; if all the structure safety parameters of the combined cap beam 10 meet the requirement, it is determined that the combined cap beam 10 meets the technical requirement; if any one of the structure safety parameters of the combined cap beam 10 does not meet the requirement, the size of the combined cap beam 10 is adjusted, and the step S1 is returned. It is worth noting that, in the case of given material specifications, based on the size group of the combined cap beam 10 which has been preliminarily determined, the structure safety parameters are obtained to ensure the safety performance of the combined cap beam 10, mainly including vertical shear bearing capacity, bending bearing capacity, fatigue strength of the steel structure, and deflection of the cantilever end of the combined cap beam 10. Only when all the above parameters meet the requirement, the safety performance of the combined cap beam 10 can be ensured. If one of the parameters does not meet the requirement, the size of one of the parameters needs to be adjusted based on the preliminarily determined size, and the adjusted value is substituted into the step S1. The improved determined size is determined again according to the adjusted size and formula one. The safety parameters are calculated again according to the improved determined size until all the above parameters meet the requirement.

[0063] Specifically, the calculation of the vertical shear bearing capacity in the step S3 specifically includes the following steps:

[0064] S31, according to formula three: judging whether the vertical shear bearing capacity design value of the combined cap beam 10 meets the requirement, if the vertical shear bearing capacity design value of the combined cap beam 10 is greater than or equal to the shear design value of the basic combination, it meets the requirement; if the vertical shear bearing capacity design value of the combined cap beam 10 is less than the shear design value of the basic combination, it does not meet the requirement; wherein,

[0065] is the structure importance coefficient, is the shear design value of the basic combination, is the vertical shear bearing capacity design value, b is the width of the corresponding normal section of the concrete oblique section shear compression zone, h 0 is the effective height of the concrete section, P is the reinforcement percentage of the longitudinal tensile steel bar in the oblique section, f cu,k is the standard value of the compressive strength of a concrete cube with a side length of 150 mm, ρ sv is the reinforcement percentage of the hoop steel bar in the concrete oblique section, svf is the tensile strength design value of the stirrup vd A is the shear strength design value of the steel material w A is the web section area of the steel material.

[0066] It is worth noting that according to the initially proposed girder structure size, the vertical shear bearing capacity design value of the girder is determined by combining formula three , and compared with the basic combined shear design value calculated in S2, wherein the basic combined shear design value is affected by the structure safety level, so the structure importance coefficient needs to be combined to obtain for comparison; if , it means that the proposed girder structure size is reasonable and meets the vertical shear bearing capacity checking of the girder structure, otherwise, the vertical shear bearing capacity does not meet the requirements; it is worth mentioning that P is the reinforcement percentage of longitudinal tensile steel in the oblique section, P = 100p, p = A sl / bh0, A sl is the longitudinal tensile steel area in the concrete section, and when P > 2.5, P = 2.5; and p sv is the reinforcement percentage of the stirrup steel in the concrete oblique section, p sv = A sv / S v b, A sv is the total section area of the stirrup arranged in the same section in the oblique section, S v is the spacing of the stirrup steel in the oblique section.

[0067] Further, the checking of the bending capacity in the step S3 specifically includes the steps of:

[0068] S32, according to formula four: determine whether the basic combined steel beam stress value is less than or equal to the tensile strength design value of the steel material,

[0069] and according to formula five: determine whether the basic combined concrete compressive stress value meets the requirements, if the basic combined steel beam stress value is less than or equal to the tensile strength design value of the steel material, and the basic combined concrete compressive stress value is less than or equal to the compressive strength design value of the concrete, it meets the requirements; if the basic combined steel beam stress value is greater than the tensile strength design value of the steel material, and / or the basic combined concrete compressive stress value is greater than the compressive strength design value of the concrete, it does not meet the requirements; wherein,

[0070] is the steel section edge stress, is the concrete section edge stress, is the axial force borne by the steel section, is the bending moment borne by the steel section, axial force borne by the concrete section, bending moment borne by the concrete section, sectional flexural rigidity of the steel material, sectional flexural rigidity of the concrete, f cd design value of the compressive strength of the concrete.

[0071] It is worth noting that the stress value σ s of the concrete under the action of the basic combination of the dimensions is obtained from step S2 c As shown in the equation of Formula Five, and at the same time, the structure safety level needs to be combined, and then the two are compared with the strength design value of the steel beam and the concrete respectively; if , Both satisfy, indicating that the proposed girder structure size is reasonable, and the bending capacity of the girder structure is satisfied, otherwise, both or one of them do not satisfy, and the bending capacity does not meet the requirements.

[0072] Further, the fatigue strength checking of the steel structure in step S3 specifically includes the steps of:

[0073] S330, establishing a composite girder model;

[0074] S331, obtaining normal stress values and shear stress values under the limit state based on the composite girder model;

[0075] S332, according to Formula Six: determine whether the limit normal stress difference is less than or equal to the normal stress fatigue limit, and according to Formula Seven: determine whether the limit shear stress difference is less than or equal to the shear stress fatigue limit, if both satisfy the fatigue limit, then the requirements are met; if one of them is greater than the fatigue limit, then the requirements are not met; wherein,

[0076] σ pmax , σ pmin respectively, the maximum and minimum normal stress obtained by loading the fatigue load model on the influence line under the limit condition, τ pmax , τ pmin respectively, the maximum and minimum shear stress obtained by loading the fatigue load model on the influence line under the limit condition, is the size effect reduction factor, is the normal stress constant amplitude fatigue limit, is the shear stress constant amplitude fatigue limit.

[0077] It should be noted that the three-dimensional geometric model of the bent cap can be established in software, the material properties (such as elastic modulus, yield strength, etc.) and boundary conditions (such as support position, fixed point, etc.) are defined, and various loads are applied, and then the normal stress value and shear stress value under the limit state (most unfavorable state) are obtained through finite element analysis, the normal stress value includes the maximum normal stress value and the minimum normal stress value, and the shear stress value includes the maximum shear stress value and the minimum shear stress value, in order to obtain the respective difference values, the most unfavorable state can be combined with the design specification to add load types, which are well known to those skilled in the art, and therefore will not be described in detail here, and then it is judged whether the normal stress fatigue limit meets the requirements through formula six, and whether the shear stress fatigue limit meets the requirements through formula seven; if both meet the requirements (i.e. the limit normal stress difference is less than or equal to the normal stress fatigue limit, and the limit shear stress difference is less than or equal to the shear stress fatigue limit), it means that the proposed bent cap steel structure size is reasonable and meets the requirements of fatigue strength, otherwise, if both or one of them do not meet the requirements, the fatigue strength does not meet the requirements.

[0078] Further, the checking of the deflection of the cantilever end of the combined bent cap 10 in step S3 specifically comprises the steps of:

[0079] S341, obtaining the live load reaction at each support and the distance from each support to the center of the pier column 30 based on the combined bent cap model;

[0080] S342, judging whether the deflection of the cantilever end of the combined bent cap 10 meets the requirements according to formula eight: If the maximum deflection of the cantilever end of the combined bent cap 10 is within the limit deflection range of the cantilever end of the combined bent cap 10, it meets the requirements; if the maximum deflection of the cantilever end of the combined bent cap 10 exceeds the limit deflection value of the cantilever end of the combined bent cap 10, it does not meet the requirements; wherein,

[0081] δ max is the maximum deflection value of the cantilever end of the combined bent cap 10, is the live load reaction at each support, is the distance from each support to the center of the pier column 30, n is the number of supports in the cantilever range, and L is the cantilever length, is the stiffness reduction coefficient.

[0082] It should be understood that based on the established three-dimensional geometric model, the live load reaction at each support and the distance from each support to the center of the pier column 30 are obtained and substituted into formula eight to obtain the maximum deflection value of the cantilever end of the combined bent cap 10 δ maxThe limit deflection of the cantilever end of the combined cap beam 10 is compared, if it is within the range, it meets the requirements, otherwise the structural stiffness does not meet the requirements; it can be understood that the total length of the combined cap beam 10 is matched based on the width of the bridge, and the pier core distance between the pier columns 30 is fixed based on the application scene (for example, in urban viaducts, the pier core distance between the pier columns 30 cannot be arbitrarily set, and there are specification requirements), so the cantilever length L of the combined cap beam 10 is a value that can be obtained.

[0083] Further, the step S4 of "adjusting the size of the combined cap beam 10" specifically includes:

[0084] Adjusting the total cross-sectional height of the combined cap beam 10; wherein the single adjustment cross-sectional height difference value is 5cm~10cm.

[0085] It should be noted that when any one of the structural safety parameters of the combined cap beam 10 does not meet the requirements, the size needs to be adjusted, and after adjustment, it returns to step S1 (specifically, it returns to step S12) to obtain the adjusted size group, and then the structural safety parameter calculation is performed again according to the adjusted size group. Specifically, the total cross-sectional height of the combined cap beam 10 is adjusted h When the total cross-sectional height of the combined cap beam 10 changes to h , the adjusted concrete cross-sectional height size h c can be obtained according to formula two, the concrete cross-sectional width remains unchanged, so that the adjusted concrete cross-sectional area A c can be obtained, and the distance between the centroid of the steel beam and the upper surface of the concrete y s also changes, and in the case of keeping the material unchanged, n 0 remains unchanged, so that the adjusted steel cross-sectional area A s is obtained according to formula one, and the structural safety performance calculation is performed again according to the adjusted size group obtained in this way; wherein the single adjustment cross-sectional height difference value is 5cm~10cm, that is, the cross-sectional total height is increased or decreased each time according to the comparison of the calculation results, and a new size group is obtained after the increase or decrease adjustment, and the calculation is performed, if it meets, the cross-sectional combined form that fully develops the material characteristics is obtained, if it does not meet, the cross-sectional total height is increased or decreased again until it meets.

[0086] For the convenience of those skilled in the art, a simple example is listed as follows:

[0087] Based on the commonly used cap beam size, the total cross-sectional height of the combined cap beam 10 is set to hThe preliminary size is 2 m (there are also application scenarios with high bridge clearance requirements that may be less than 2 m, and the actual application scenario is combined with the commonly used numerical value), and the steel material is Q355D, and the concrete is C40. In the case of determining the material specifications, the design values of various strengths (such as the design value of the tensile strength of the steel f sd , the design value of the compressive strength of the concrete f cd , etc.) and the elastic modulus values (the elastic modulus of the steel and the elastic modulus of the concrete ) can be obtained according to the specifications. According to formula two, the preliminary concrete section height can be obtained. In the case of determining the total height of the composite beam 10 h and the concrete section height , the distance between the steel beam centroid and the upper surface of the concrete can be obtained. The concrete section width can generally be a conventional width such as 2 m (usually 1.8 m to 2.4 m). According to the determined concrete section width and the concrete section height , the cross-sectional area of the concrete can be obtained. According to formula one, the cross-sectional area of the steel material can be determined to obtain the preliminary size group of the composite beam 10. Based on the preliminary size group of the composite beam 10, the structural safety parameter checking is performed to ensure that the structural safety performance meets the requirements. When one of the structural safety parameters does not meet the requirements, the total height of the composite beam 10 is adjusted h . In this example, it is adjusted to 2.05 m (an increase of 5 cm at a time), and the adjusted concrete section height ´, the adjusted distance between the steel beam centroid and the upper surface of the concrete ´, the adjusted cross-sectional area of the concrete ´, and the adjusted cross-sectional area of the steel material ´ are determined according to the new total height of the section h ´. The adjusted size group is obtained to perform the adjusted structural safety parameter checking according to the adjusted size group. If one of the adjusted structural safety parameters still does not meet the requirements, the total height of the section is increased by 5 cm again, and the above steps are repeated until all the structural safety parameters meet the requirements. It is worth mentioning that if the structural safety meets the requirements, the total height of the section can also be appropriately reduced, which can reduce the cost to form a structure that takes into account both safety performance and economic cost, and improves economic efficiency.

[0088] It should be noted that based on certain specific embodiments, when the cross-section height of the concrete is adjusted and it is found that the value of the structural safety parameter cannot be changed greatly, the material strength can be adjusted, and then the size is redesigned.

[0089] The application also provides a prefabricated composite cap beam 10, comprising a composite cap beam 10 and a flange assembly 20, the composite cap beam 10 comprising a steel structure section 110 and a reinforced concrete section 120, the steel structure section 110 being connected above the reinforced concrete section 120, the reinforced concrete section 120 being connected to the pier column 30 through the flange assembly 20; wherein the size of the composite cap beam 10 is obtained based on the design method of the prefabricated composite cap beam 10 as described above.

[0090] It should be noted that the entire composite cap beam 10 can be produced by full prefabrication, which is more reliable in quality and higher in precision compared to site pouring, and the structural arrangement mode of the steel structure section 110 being connected above the reinforced concrete section 120 fully utilizes the tensile strength of steel and the compressive strength of concrete, avoids or reduces the use of prestress, and the use of the flange assembly 20 for connection improves the convenience of installation and greatly speeds up the construction efficiency.

[0091] Further, the flange assembly 20 comprises a pier flange 220 and a cap beam flange 210, the bottom end of the pier flange 220 being connected to the pier column 30, the top end of the cap beam flange 210 being connected to the reinforced concrete section 120, and the pier flange 220 and the cap beam flange 210 being connected through bolts.

[0092] It should be noted that the cap beam flange 210 and the reinforced concrete section 120 of the composite cap beam 10 are welded and fixed together, the pier flange 220 is fixedly connected to the lower pier column 30 through a pre-embedded part, and after the pier pile foundation and the pier column 30 are constructed by site pouring, the prefabricated cap beam can be hoisted and assembled in place, and the prefabricated cap beam and the pier column 30 are connected through the cap beam flange 210 and the pier flange 220 to realize force transmission.

[0093] The above is only the preferred embodiment of the application, and does not limit the patent scope of the application, and any equivalent structure or equivalent process transformation using the content of the specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the application.

Claims

1. A design method for prefabricated composite cap beams, characterized in that, Including the following steps: S1, determine the size group of the composite cap beam based on the material properties; wherein, the composite cap beam includes a steel structure section and a reinforced concrete section; S2, determine the effect design value group of the basic combination of actions based on the size group of the combined cap beam; wherein, the effect design value group of the basic combination of actions includes the shear force design value of the basic combination of actions, the steel beam stress value of the basic combination of actions, and the concrete compressive stress value of the basic combination of actions. S3, based on the size group of the composite cap beam and the effect design value group of the basic combination of actions, verify whether the safety parameters of the composite cap beam structure meet the requirements; wherein, the safety parameters of the composite cap beam structure include vertical shear bearing capacity, bending bearing capacity, fatigue strength of steel structure and deflection of the cantilever end of the composite cap beam; S4, determine whether all safety parameters of the combined cap beam structure meet the requirements; if all safety parameters of the combined cap beam structure meet the requirements, then determine that the combined cap beam meets the technical requirements; if any one of the safety parameters of the combined cap beam structure does not meet the requirements, then adjust the size of the combined cap beam and return to step S1. S11, Obtain the total cross-sectional height of the composite cap beam according to the application scenario; S12, the concrete beam section height is obtained based on the total section height of the composite cap beam; where, the formula is used. Determine the cross-sectional height The value of , The height of the concrete beam section. h The total height of the composite cap beam section is The height of the boundary pressure zone. f sd This is the design value for the tensile strength of the steel. S13, according to formula To determine the cross-sectional dimensions of the steel beam; where, This is the ratio of the elastic modulus of steel to that of concrete. The elastic modulus of steel, This refers to the elastic modulus of concrete. Let be the cross-sectional area of ​​the steel. This represents the cross-sectional area of ​​the concrete. This is the distance from the centroid of the steel beam to the top surface of the concrete.

2. The design method for prefabricated composite cap beams according to claim 1, characterized in that, The verification of the vertical shear bearing capacity in step S3 specifically includes the following steps: S31, according to formula To determine whether the design value of the vertical shear capacity of the composite cap beam meets the requirements, if the design value of the vertical shear capacity of the composite cap beam is greater than or equal to the design value of the shear force of the basic combination of actions, then the requirements are met; if the design value of the vertical shear capacity of the composite cap beam is less than the design value of the shear force of the basic combination of actions, then the requirements are not met. This is the structural importance coefficient. The shear force design value is the value of the basic combination of forces. This represents the design value for vertical shear capacity. b This represents the width of the shear-compression zone of the concrete inclined section at the corresponding normal section. h 0 is the effective height of the concrete section, P is the percentage of longitudinal tensile reinforcement in the inclined section, and f is the effective height of the concrete section. cu,k The standard value of compressive strength for a concrete cube with sides of 150mm is ρ. sv f is the reinforcement ratio of stirrups in the inclined section of concrete. sv f is the design value of the tensile strength of the stirrup. vd A represents the design value of the shear strength of the steel. w This represents the cross-sectional area of ​​the web of the steel.

3. The design method for prefabricated composite cap beams according to claim 2, characterized in that, The verification of the flexural bearing capacity in step S3 specifically includes the following steps: S32, according to formula Determine whether the stress value of the steel beam under the basic combination of the aforementioned forces is less than or equal to the design value of the tensile strength of the steel. And according to the formula The concrete compressive stress value of the basic combination of actions is determined to meet the requirements. If the stress value of the steel beam in the basic combination of actions is less than or equal to the design value of the tensile strength of the steel, and the compressive stress value of the concrete in the basic combination of actions is less than or equal to the design value of the compressive strength of the concrete, then the requirements are met. If the stress value of the steel beam in the basic combination of actions is greater than the design value of the tensile strength of the steel, and / or the compressive stress value of the concrete in the basic combination of actions is greater than the design value of the compressive strength of the concrete, then the requirements are not met. For the edge stress of the steel section, For the edge stress of the concrete section, The axial force borne by the steel cross section The bending moment borne by the steel section. The axial force borne by the concrete section. The bending moment borne by the concrete section. The flexural stiffness of the steel section. The flexural stiffness of the concrete section. f cd This is the design value for the compressive strength of concrete.

4. The design method for prefabricated composite cap beams according to claim 3, characterized in that, The fatigue strength verification of the steel structure in step S3 specifically includes the following steps: S330, Establish the composite cap beam model; S331, Based on the composite cap beam model, obtain the normal stress value and shear stress value under the limit state; S332, according to formula Determine whether the difference in ultimate normal stress is less than or equal to the normal stress fatigue limit, and apply the formula. To determine if the difference in ultimate shear stress is less than or equal to the shear stress fatigue limit, if both conditions are met and within the fatigue limit, then the requirement is satisfied; if either condition exceeds the fatigue limit, then the requirement is not satisfied. σ pmax , σ pmin These represent the maximum and minimum normal stresses obtained under the limit condition when applied to the influence line, respectively. τ pmax , τ pmin These represent the maximum and minimum shear stresses obtained under the limit condition applied to the influence line, respectively. This is the size effect reduction factor. This represents the normal stress constant amplitude fatigue limit. This represents the constant amplitude fatigue limit of shear stress.

5. The design method for prefabricated composite cap beams according to claim 4, characterized in that, The calculation of the deflection at the cantilever end of the composite cap beam in step S3 specifically includes the following steps: S341, Based on the composite cap beam model, obtain the live load reaction force at each support and the distance from each support to the center of the pier column; S342, according to formula The deflection at the cantilever end of the composite cap beam is determined to meet the requirements. If the maximum deflection at the cantilever end of the composite cap beam is within the limit deflection range of the cantilever end, the requirements are met; if the maximum deflection at the cantilever end of the composite cap beam exceeds the limit deflection value, the requirements are not met. δ max This represents the maximum deflection value at the cantilever end of the composite cap beam. For the live load reaction at each support, Let n be the distance from each support to the center of the pier, n be the number of supports within the cantilever range, and L be the cantilever length. This is the stiffness reduction factor.

6. The design method for prefabricated composite cap beams according to claim 1, characterized in that, The step S4 of "adjusting the dimensions of the composite cap beam" specifically includes: Adjust the total height of the cross-section of the combined cap beam; wherein the difference in the total height of the cross-section in a single adjustment is 5cm to 10cm.

7. A prefabricated composite cap beam, characterized in that, The system includes a composite cap beam and a flange assembly. The composite cap beam comprises a steel structure section and a reinforced concrete section. The steel structure section is connected above the reinforced concrete section, and the reinforced concrete section is connected to the pier via the flange assembly. The dimensions of the composite cap beam are obtained based on the design method of the prefabricated composite cap beam as described in any one of claims 1-6.

8. The prefabricated composite cap beam according to claim 7, characterized in that, The flange assembly includes a pier flange and a cap beam flange. The bottom end of the pier flange is used to connect to the pier column, and the top end of the cap beam flange is connected to the reinforced concrete section. The pier flange and the cap beam flange are connected by bolts.

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