Method and system for testing and determining shear capacity of steel-UHPC (Ultra High Performance Concrete) geocell

Abstract

The invention belongs to the field of steel-concrete connection section design, and discloses a steel-UHPC (Ultra High Performance Concrete) geocell shear capacity test and determination method, and all shear connectors (studs or perforated steel plates (PBLs)) of a steel-UHPC geocell longitudinal shear transfer capacity push-out test piece are located in a geocell. The invention accurately reflects a reasonable form of a steel-UHPC cell longitudinal shear transmission performance and a bearing capacity push-out test piece, and a method for determining the bearing capacity of PBL steel-UHPC cell longitudinal shear transmission.

Description

Technical Field

[0001] The present invention belongs to but is not limited to the technical field of steel-concrete connection section design, and in particular relates to a method and system for testing and determining the shear bearing capacity of a steel-UHPC cell. Background Art

[0002] The steel-concrete connection section is a key structure and key part of hybrid beams, hybrid bridge towers, hybrid arches, etc. The steel-concrete connection section usually includes three parts: steel-concrete joint section (including the concrete cross beam and steel pressure plate therein), concrete transition section (the thickness of each plate often gradually transitions from the standard section to the corresponding plate thickness of the steel-concrete joint section), and steel box transition section (the cross diaphragm is often denser, and the height of the equal-height U-ribs and T-shaped stiffening ribs gradually increases to the corresponding height of the top and bottom plates of the joint section) (this application strictly distinguishes the connection section from the joint section). Obviously, due to the strengthening of the section, the bending, compression and shear capacity of the concrete transition section and the steel box transition section, and the shear capacity of the joint section are stronger than the nearby standard concrete section or standard steel box section. Under the premise that the bearing capacity of the standard concrete section and the standard steel box section meets the design requirements, the bending and compression bearing capacity and shear bearing capacity of the transition section section, and the shear bearing capacity of the joint section are often naturally satisfied. Therefore, how to ensure the bending and compression capacity (i.e. the longitudinal shear bearing capacity) of the steel-concrete joint section becomes the key. For example, the defects in the steel-concrete joint section of the tower of Japan's Tsurumi Channel Bridge were caused by improper design and insufficient bending and compression resistance (including durability).

[0003] The cell steel-concrete joint section is an important form of steel-concrete joint section. The cell steel-concrete joint section is a partial connection filled with concrete solution ( Figure 1 a)) Because the PBL and studs are conveniently arranged inside the steel grid, the internal concrete is subjected to three-dimensional forces, and the contact area between the steel plate and the internal concrete is large, the integrity is good, and the main beam stiffness changes smoothly. This overcomes the full-section connection solution ( Figure 1 b) and c)) have complex structures, many consumables, difficult construction, and difficult to ensure construction quality. This also overcomes some of the problems of connecting the pressure plate ( Figure 1 d)) Due to the drastic change in the stiffness of the main beam, the easy cracking of the concrete near the joint surface, and the need to use ultra-thick pressure-bearing steel plates, most of the joint sections of bridges built at home and abroad are cell steel-concrete joint sections (also called cell steel-concrete joint sections).

[0004] Ultra-high performance concrete (UHPC) has the characteristics of high strength, good toughness, small creep, good anchoring performance and good durability. The use of steel-UHPC joint sections (the joint sections of poured UHPC are called steel-UHPC joint sections) is expected to solve the problems of voiding and large joint section size and complex structure caused by ordinary self-flowing dense concrete pouring materials. For this reason, the joint sections of Hubei Jiayu Yangtze River Highway Bridge, Hubei Wuxue Yangtze River Highway Bridge, Yunnan Nujiang Bridge, Foshan Tongji Bridge, etc. have adopted steel-UHPC joint sections, and most of them choose the cell type. However, due to the lack of methods to determine the longitudinal shear bearing capacity of steel-UHPC joint sections, the steel-UHPC joint sections still conservatively apply the structural dimensions and structures of steel-concrete joint sections tested by engineering or scaled model tests. Although it can solve the voiding problem caused by ordinary self-flowing dense concrete pouring materials, it has not exerted the potential of UHPC, whose mechanical properties far exceed those of ordinary concrete.

[0005] In the past, all national standards used the push-out test results as the basis for formulating the bearing capacity calculation formula. Push-out test specimens can be divided into standard type ( Figure 2 )(Partially exposed middle I-beam + two wing plates with welded studs on the outer surface or welded axially arranged perforated steel plates + concrete wrapped with studs or perforated steel plates and their steel bars; or, integral steel plates with holes on both sides + concrete wrapped with perforated steel plates on both sides and their steel bars; the size of the specimens varies, and the thickness of the concrete slab varies from 125mm in European standards to 200, 300 and 400mm, etc.), insertion type ( Figure 3 , some are called embedded type or sandwich type) (partially exposed middle open hole steel plate + concrete wrapped with open hole steel plate and its steel bars, or: partially exposed middle steel plate + welding nails on both surfaces of the steel plate + concrete wrapped with steel plate and its welding nails, or: partially exposed two side steel plates + welding studs on opposite surfaces of two side steel plates or welding open hole steel plates along the push-out direction + concrete between two steel plates) and quasi-cell type ( Figure 4 ). The essential difference between the standard type and the inserted type is that although both of them balance the axial force of the concrete on both sides with the push-out force (axial force) of the steel structure, the spacing of the axial forces of the concrete on both sides of the standard type is relatively large. The stress state of the standard type specimen can reflect the stress state of the composite beam shear connector, and its results have been applied to the formulation of the specification of composite beam bridge connectors; the inserted type can better reflect the stress state of the connector in the non-cell steel-concrete joint section, and its test results are generally slightly larger than those of the standard type; the quasi-cell type proposed so far attempts to reflect the stress state of the connector in the cell, but because half or nearly half of the steel bars and concrete are located outside the steel cell (perhaps some bolts are arranged outside the steel cell), the stress state of the connector in the test and the failure mode, crack development process and load-slip curve obtained in the test cannot fully reflect the circumferential restraint effect of the steel cell on the concrete in the cell type steel-concrete (UHPC) joint section.

[0006] In view of the above analysis, the technical problems that need to be solved urgently in the prior art are:

[0007] (1) Accurately reflect the longitudinal shear performance and bearing capacity of steel-UHPC cells and push out the reasonable form of the specimen;

[0008] (2) Method for determining the longitudinal shear capacity of PBL steel-UHPC cells (abbreviation of PBL steel-UHPC cells). Summary of the invention

[0009] In view of the problems existing in the prior art, the present invention provides a method for testing and determining the shear bearing capacity of a steel-UHPC cell.

[0010] The present invention is implemented as follows: a steel-UHPC cell shear bearing capacity test and determination system, the system comprising:

[0011] a) Test specimen preparation module, used to prepare a test specimen consisting of five steel plates forming a cell with a PBL bond and filled with UHPC;

[0012] b) Shear connector arrangement device, used to arrange all shear connectors (studs or perforated steel plates, i.e. PBL) inside the cell;

[0013] c) Mechanical properties testing module, including equipment for measuring the shear capacity of UHPC tenons and the shear capacity of through-steel bars in UHPC;

[0014] d) a calculation unit, used to calculate the longitudinal shear bearing capacity of the steel-UHPC cell according to a preset shear bearing capacity calculation method, wherein the longitudinal shear bearing capacity is jointly determined by the shear bearing capacity of the UHPC tenon, the shear bearing capacity of the through-steel in the UHPC, and the hoop effect enhancement coefficient;

[0015] e) Parameter adjustment module, used to adjust the hoop effect increase coefficient according to the steel-UHPC interface state and the cross-sectional hoop coefficient;

[0016] f) Data recording and analysis module, used to record test data and analyze calculation results to determine the shear bearing capacity of the steel-UHPC cell.

[0017] The test specimen preparation module further comprises:

[0018] a) The cross-sectional dimensions of the test piece are 400 mm x 400 mm;

[0019] b) The thickness of the steel plate is 24 mm, the height of the steel plate is 500 mm, and the height of the UHPC is 500 mm;

[0020] c) The bonding length between the steel plate and the UHPC is 400 mm, and the protruding part of the UHPC is left empty at the end of the PBL to form a 24 mm thick gap;

[0021] d) The perforated steel plate is located in the middle of the steel box or wing plate, and a hole with a diameter of 60 mm is set at a position 200 mm away from the top;

[0022] e) The diameter of the through-steel bar is 18 mm and the length is 300 mm, fixed in the center by steel wire;

[0023] f) In the type A specimen, the inner surfaces of the two steel plates parallel to the PBL steel plate are smeared with butter, and the inner surfaces of the other steel plates in contact with the UHPC are kept naturally clean.

[0024] Furthermore, in the calculation unit, the shear bearing capacity of the UHPC tenon is determined by considering factors such as the number of shear surfaces, the diameter of the hole of the perforated steel plate, the diameter of the steel bar passing through the hole, and the compressive strength of the concrete.

[0025] Furthermore, in the calculation unit, the shear bearing capacity of the through-steel in the UHPC is determined by considering factors such as the diameter and number of the through-steel and the tensile strength of the steel bars.

[0026] Further, in the parameter adjustment module, the hoop effect enhancement coefficient is set to a specific value in the PBL cell with the dimensions of the present invention, and is set to another specific value in the unbonded PBL cell, while for the inserted specimen, the hoop effect enhancement coefficient is set to 1.

[0027] Furthermore, when the steel content of the section or the degree of hoop constraint is different from the section with the dimensions marked in this specification, the hoop effect increase factor is adjusted accordingly to ensure the accuracy of the shear bearing capacity calculation.

[0028] The present invention also provides a method for testing and determining the shear bearing capacity of a steel-UHPC cell (without end bearing plates, the same below, omitted), comprising:

[0029] 1) All shear connectors (studs or perforated steel plates, i.e. PBL) of the steel-UHPC cell longitudinal shear transmission bearing capacity push-out test specimens are located inside the cell;

[0030] 2) PBL steel-UHPC cell (without end plate) longitudinal shear bearing capacity ( Figure 5 The formula for a steel-UHPC cell with a single-hole PBL in the steel-UHPC joint section shown is

[0031] V u =α(V t +V r +V C ) (1)

[0032] Where: V u is the longitudinal shear capacity of the steel-UHPC cell; V t is the shear bearing capacity of UHPC tenon (without hoop effect), V r is the shear bearing capacity of the through-steel in UHPC (without hoop effect), V C is the chemical bonding force between steel and UHPC when the load reaches the bearing capacity (without the effect of the hoop), α is the hoop effect increase coefficient - the part of α exceeding 1 is actually the friction resistance, because the friction resistance of the bearing limit state can be expressed as the hoop lateral pressure of this state multiplied by the friction coefficient, and this hoop lateral pressure is proportional to the relative stiffness and push-out force of the hoop, so the α value is related to the steel-UHPC interface state (whether oiled), cross-section hoop coefficient, etc.; when there is no hoop effect, α=1, when there is a hoop effect, α>1.

[0033] Furthermore, the shear connectors (studs or perforated steel plates or PBL) of the steel-UHPC cell longitudinal shear bearing capacity push-out test specimen are all located inside the cell:

[0034] 1) The push-out test specimen is composed of five steel plates (i.e., the middle perforated steel plate and the four outer steel plates) to form a PBL key cell and UHPC in the cell (see Figure 6 , the steel plates around the cells form peripheral constraints on UHPC).

[0035] 2) The cross-sectional size of the push-out test specimen is 400 mm × 400mm, the thickness of the steel plate is 24mm, the height of the steel plate is 500mm, the height of the UHPC is 500mm, the bonding (contact) length of the steel plate and UHPC is 400mm (the two are staggered by 100mm in height), and the protruding part of the UHPC is left at the end of the PBL to form a 24mm thick gap. The perforated steel plate is located in the middle of the steel box or wing plate, and a hole is set at a distance of 200mm from the top, with a hole diameter of 60mm. The steel plates in each specimen are connected by welding. The diameter of the through steel bar is 18mm and the length is 300mm; the through steel bar is fixed in the center by steel wire. In Class A specimens, the two steel plates parallel to the perforated steel plate have holes of 24mm to facilitate the placement of the steel bars in the steel box. (Note: The numbers in this paragraph can vary within a certain range, but must be geometrically compatible)

[0036] 3) The inner surfaces of the two steel plates parallel to the PBL steel plate are coated with butter (or not coated with butter), and the inner surfaces of the other steel plates in contact with the UHPC are kept in a naturally clean state to ensure that the bonding surface area is equivalent to the bonding area of ​​the single cell steel-UHPC in the cell steel-UHPC joint section (the bonding area is larger).

[0037] Furthermore, the longitudinal shear bearing capacity formula of the PBL steel-UHPC cell is as follows:

[0038] 1) UHPC tenon shear bearing capacity V t

[0039]

[0040] Where: n is the number of shear surfaces; d is the hole diameter of the perforated steel plate, mm; d s is the diameter of the steel bar passing through the hole, mm; f cu is the concrete cube compressive strength, MPa;

[0041] 2) Shear bearing capacity of through-steel bars in UHPC V r

[0042]

[0043] Where: f y is the tensile strength of the steel bars penetrating the hole, MPa.

[0044] 3) Chemical bond strength V between steel and UHPC when the load reaches the bearing capacity C

[0045] V C =f nj A nj

[0046] Where: f nj A is the chemical bonding strength between steel and UHPC when the load reaches the bearing capacity, MPa; nj is the bonding area between steel and UHPC.

[0047] 4) The increase coefficient of the hoop effect α - the part of α exceeding 1 is provided by the side friction resistance

[0048] For the PBL cell with the dimensions specified in the present invention (PBL is Figure 1 For the cell side plate in the invention, the same below), the hoop action coefficient α=2.715; for the unbonded (oiled) PBL cell with the dimensions specified in the invention, α=1.671; when the cross-section steel content or the degree of hoop constraint is different from the cross-section with the dimensions specified in this specification, α will also be different. The greater the steel content (degree of hoop constraint), the greater the α value; for the inserted specimen, α=1.

[0049] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0050] First, the present invention accurately reflects the longitudinal shear transfer performance and bearing capacity of steel-UHPC cells and proposes a reasonable form of test specimens, as well as a method for determining the bearing capacity of longitudinal shear transfer of PBL steel-UHPC cells.

[0051] In the field of shear bearing capacity design and testing of steel-UHPC (ultra-high performance concrete) cells, existing technologies mainly rely on empirical formulas and finite element analysis methods. These methods have the following major technical problems in actual industrial applications:

[0052] 1. High degree of model simplification: Traditional methods usually simplify the complexity of mine geological conditions and filling materials, and cannot fully reflect the mechanical behavior of steel-UHPC cells under actual working conditions, resulting in insufficient accuracy in shear bearing capacity prediction.

[0053] 2. Poor adaptability: The geological conditions and filling material properties of different mines vary significantly. The existing models lack sufficient flexibility and adaptability, and are difficult to be widely used in shear bearing capacity design under various complex working conditions.

[0054] 3. Low design efficiency: The design method based on experience and finite elements has large calculation amount and long cycle, which is difficult to meet the needs of rapid design and optimization in mining production, limiting the progress of engineering projects.

[0055] 4. Insufficient ability to comprehensively consider multiple factors: Multiple factors such as mining geological conditions, filling material characteristics, and construction technology interactively affect the strength of the filling body. Existing models are difficult to comprehensively consider these factors, affecting the reliability and practicality of the design results.

[0056] 5. Lack of real-time monitoring and feedback mechanism: During the filling construction process, there is a lack of effective real-time monitoring and feedback mechanism, and the design parameters cannot be dynamically adjusted according to the actual construction conditions, resulting in deviations between the design and actual application, affecting the ultimate shear bearing capacity of the filling body.

[0057] 2. Technical solutions to solve technical problems

[0058] The present invention proposes a method for constructing a filling body strength design model for a two-step filling mining method. Through systematic design and optimization, the key problems in the above-mentioned prior art are solved, specifically including the following aspects:

[0059] 1. Accurate test specimen design and layout: By arranging all shear connectors (studs or perforated steel plates, i.e. PBL) inside the cell, the shear force transfer is ensured to be centralized and uniform, the risk of local stress concentration and structural failure is reduced, and the accuracy of shear bearing capacity prediction is improved.

[0060] 2. Comprehensive mechanical bearing capacity calculation formula: The formula "Vu equals α multiplied by (Vt plus Vr)" is used to comprehensively consider the shear bearing capacity of UHPC tenons, the shear bearing capacity of through-steel in UHPC, and the hoop effect enhancement coefficient α, which effectively reflects the influence of multiple factors on the overall shear bearing capacity and improves the comprehensiveness and applicability of the model.

[0061] 3. Multi-factor impact analysis and weight determination: Through statistical analysis and multiple regression methods, identify and quantify the impact of multiple factors such as geological conditions, filling material characteristics, and construction technology on the strength of the filling body, ensure that the design model can fully consider the complex factors in actual working conditions, and improve the reliability of the design results.

[0062] 4. Dynamic optimization and feedback mechanism: Introduce real-time monitoring data, dynamically adjust design parameters, establish a closed-loop control system, realize real-time linkage between design and construction process, ensure that the strength design of the filling body is highly consistent with the actual construction situation, and improve the response speed and accuracy of the design.

[0063] 5. Standardization and modular design: Through standardized test specimens and modular system structure, the repeatability and promotion of design methods can be improved to meet the specific needs of different mines and enhance the adaptability and flexibility of the system.

[0064] III. Significant Technological Advances

[0065] The present invention has achieved a number of significant technical advances in the test and determination of the shear bearing capacity of steel-UHPC cells, including:

[0066] 1. Improve the accuracy and reliability of shear bearing capacity design: Through precise specimen design and comprehensive mechanical bearing capacity calculation formula, the accuracy of shear bearing capacity prediction is significantly improved, the design error is reduced, and the safety and stability of the filling body in practical application are ensured.

[0067] 2. Enhance the adaptability and flexibility of the design model: The multi-factor comprehensive analysis and weight determination method enable the design model to adapt to the complex geological conditions and diversified filling material characteristics of different mines, and is widely used in shear bearing capacity design under various working conditions.

[0068] 3. Significantly improve the efficiency of the design process: Standardized and modular design methods combined with dynamic optimization and feedback mechanisms have greatly shortened the design cycle, improved design efficiency, met the needs of rapid design and adjustment in mining production, and accelerated the advancement of engineering projects.

[0069] 4. Comprehensive consideration of multiple influencing factors: The present invention comprehensively considers the interactive influence of geological conditions, filling material characteristics, construction technology and other factors through multi-factor impact analysis, ensures the scientificity and comprehensiveness of the design results, and improves the reliability of the shear bearing capacity of the filling body.

[0070] 5. Establish a real-time monitoring and feedback mechanism: Through real-time monitoring and dynamic adjustment of the closed-loop control system of design parameters, the high consistency between the design and the actual construction process is ensured, the response speed and adaptability of the shear bearing capacity design are improved, and the safety and effectiveness of the engineering construction are enhanced.

[0071] 6. Promote the standardization and popularization of the shear bearing capacity design of steel-UHPC cells: The systematic design method and detailed implementation steps provided by the present invention provide a standardized technical solution for the shear bearing capacity design of steel-UHPC cells, promote the widespread application and promotion of this technology in mining, and improve the overall engineering design level and construction quality.

[0072] The present invention successfully solves the key problems of the prior art, such as model simplification, poor adaptability, low design efficiency, insufficient consideration of multiple factors, and lack of real-time monitoring and feedback, through a systematic two-step backfill mining method stage backfill strength design model. Through precise specimen design, comprehensive mechanical bearing capacity calculation, multi-factor influence analysis and dynamic optimization feedback mechanism, the present invention significantly improves the accuracy, reliability and adaptability of the shear bearing capacity design of steel-UHPC cells, while greatly improving the efficiency and response speed of the design process, and realizing the organic combination of long-term stability of the backfill and safe production in mines, which has important technical innovation significance and broad industrial application prospects.

[0073] Second, the expected benefits and commercial value of the technical solution of the present invention after transformation are as follows: the steel-concrete connection section can be set to be lighter, further reducing or even eliminating the concrete transition section and the steel structure transition section, thereby reducing the size and cost of the steel-concrete connection section and improving its durability.

[0074] The technical solution of the present invention fills the technical gap in the industry at home and abroad: it is the first to give the structural form of the cell-type push-out specimen; it is the first to establish a method and calculation formula for determining the longitudinal shear bearing capacity of the steel-UHPC cell that conforms to the cell-type stress characteristics.

[0075] Previous methods did not consider the effect of the hoop, which greatly underestimated the longitudinal shear transmission capacity of the cell steel-concrete (or UHPC) joint section, resulting in an overly conservative design. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 This is a connection scheme diagram of the main beam steel-concrete combined section provided by an embodiment of the present invention;

[0077] Figure 2 It is the standard type provided by the embodiment of the present invention (4 single-hole plates, with grooves at the bottom);

[0078] Figure 3 It is an insertion type (single-hole plate, bottom groove) provided in an embodiment of the present invention;

[0079] Figure 4 It is a quasi-cell type (single-hole plate case) provided in an embodiment of the present invention;

[0080] Figure 5: is a cross-sectional view of a steel cell of a steel-concrete joint section provided by an embodiment of the present invention (a cell is contained in a red frame);

[0081] Figure 6 The test specimen provided in the embodiment of the present invention is composed of 5 steel plates enclosing a PBL key cell and UHPC in the cell;

[0082] Figure 7 It is a type B test piece provided in an embodiment of the present invention - an insertion test piece;

[0083] Figure 8 is a layout diagram of a displacement sensor and a strain gauge provided in an embodiment of the present invention (unit: mm);

[0084] Fig. 9 The test loading device provided by the embodiment of the present invention;

[0085] Fig.10 It is the specimen load-relative displacement curve provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0086] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0087] The embodiment of the present invention provides a method for testing and determining the shear bearing capacity of a steel-UHPC cell, which specifically includes:

[0088] 1. Push-out specimen of longitudinal shear capacity of steel-UHPC cell - push-out specimen of steel-UHPC cell

[0089] (1) The push-out test specimen is composed of five steel plates (i.e., the middle perforated steel plate and the four outer steel plates) to form a PBL key cell and UHPC in the cell (see Figure 6 , the steel plates around the cells form peripheral constraints on UHPC)

[0090] (2) The cross-sectional size of the push-out test specimen is 400 mm ×400mm, the thickness of the steel plate is 24mm, the height of the steel plate is 500mm, the height of the UHPC is 500mm, the bonding (contact) length of the steel plate and UHPC is 400mm (the two are staggered by 100mm in height), and the protruding part of the UHPC is vacated at the end of the PBL to form a 24mm thick gap. The perforated steel plate is located in the middle of the steel box or wing plate, and a hole is set at a distance of 200mm from the top, with a hole diameter of 60mm. The steel plates in each specimen are connected by welding. The diameter of the through steel bar is 18mm and the length is 300mm; the through steel bar is fixed in the center by steel wire. In the Class A specimen, the two steel plates parallel to the perforated steel plate are both opened with a hole of 24mm to facilitate the placement of the steel bar in the steel box (Note: The numbers in this paragraph can vary within a certain range, but must be geometrically compatible).

[0091] (3) The inner surfaces of the two steel plates parallel to the PBL steel plate are coated with butter (or not coated with butter), and the inner surfaces of the other steel plates in contact with the UHPC are kept in a naturally clean state to ensure that the bonding surface area is equivalent to the bonding area of ​​the single cell steel-UHPC in the cell steel-UHPC joint section (the bonding area is larger).

[0092] 2. PBL steel-UHPC cell (without end plate) longitudinal shear bearing capacity ( Figure 6 A steel-UHPC cell with a single-hole PBL in the cross section of the steel-UHPC joint shown in Figure 2

[0093]

[0094] Where: V u is the longitudinal shear bearing capacity of the steel-UHPC cell; n is the number of shear surfaces; d is the hole diameter of the perforated steel plate, mm; d s is the diameter of the steel bar passing through the hole, mm; f cu is the compressive strength of concrete cube, MPa; f y V is the tensile strength of the steel bar penetrating the hole, MPa; C =f nj A nj , f nj A is the chemical bonding strength between steel and UHPC when the load reaches the bearing capacity, which can be taken as 0, MPa in this case; nj is the bonding area between steel and UHPC; α is the hoop action coefficient. For the PBL cells with the dimensions specified in this specification (PBL is Figure 1 For the cell side plate in the specification, the same below), α=2.715; for the unbonded (oiled) PBL cell with dimensions specified in this specification, α=1.671; when the steel content of the section or the degree of hoop constraint is different from the section with dimensions specified in this specification, α will also be different. The greater the steel content (degree of hoop constraint), the greater the α value; for the inserted specimen, α=1.

[0095] How it works

[0096] This paper proposes a method for testing and determining the shear bearing capacity of steel-UHPC (ultra-high performance concrete) cells, aiming to improve the overall shear capacity of steel-UHPC cells during longitudinal shear transmission by optimizing the arrangement of shear connectors and the bearing capacity calculation formula. The core of this method is to arrange all shear connectors (such as studs or perforated steel plates, i.e. PBL) inside the cells, so as to effectively concentrate and transmit shear force and enhance the overall stability of the structure.

[0097] First, the design of the test specimen ensures that the shear connector is completely located inside the cell, which can concentrate the shear force and avoid local failure caused by uneven force on the outside of the connector. The specimen is surrounded by five steel plates to form a cell with a PBL key, and the interior of the cell is filled with UHPC. This design not only improves the efficiency of shear force transmission, but also ensures the uniformity and stability of the specimen under stress through reasonable geometric layout and material selection.

[0098] In terms of the calculation of shear capacity, the formula V_u = α (V_t + V_r) is introduced, where V_u represents the longitudinal shear capacity of the steel-UHPC cell, V_t is the shear capacity of the UHPC tenon, V_r is the shear capacity of the through-steel in the UHPC, and α is the shear enhancement factor of the hoop effect. This formula linearly superimposes the shear contribution of the UHPC tenon and the through-steel, and takes into account the additional friction caused by the hoop through the α coefficient, thereby more accurately reflecting the shear performance of the overall structure.

[0099] Specifically, the shear bearing capacity V_t of the UHPC tenon is calculated by the formula V_t = 10.5352·nπ(d 2 -d_s 2 ) / 4(f_cu)^0.3, where n is the number of shear planes, d is the diameter of the hole in the perforated steel plate, d_s is the diameter of the steel bar in the hole, and f_cu is the compressive strength of the concrete cube. This formula takes into account the influence of the number of shear planes and geometric dimensions on the shear capacity, ensuring that the calculation of V_t has high accuracy and applicability.

[0100] The shear bearing capacity V_r of the through-steel in UHPC is given by the formula V_r=1.1261·(nπd_s 2 ) / 4f_y, where f_y is the tensile strength of the steel bars running through the hole. This formula reflects the important role of steel bars as shear components in UHPC. Combined with the material properties and geometric parameters of the steel bars, it effectively evaluates the contribution of V_r to the overall shear bearing capacity.

[0101] The introduction of the hoop effect enhancement coefficient α further improves the calculation accuracy of the shear bearing capacity. The α value not only takes into account the friction resistance brought by the hoop, but is also related to factors such as the state of the steel-UHPC interface (such as whether it is oiled) and the cross-sectional hoop coefficient. When there is no hoop effect, α=1; when there is a hoop effect, α>1, and the specific value is determined according to the actual working conditions and the size of the specimen. For example, the hoop effect coefficient of the PBL cell with marked dimensions in the present invention is α=2.715, α=1.671 for the unbonded PBL cell, and α=1 for the inserted specimen. By adjusting the α value, it is possible to flexibly adapt to sections with different steel content and degree of hoop constraint, ensuring the reliability and applicability of the shear bearing capacity calculation.

[0102] In summary, the present invention constructs a systematic shear bearing capacity design model for steel-UHPC cells by rationally arranging shear connectors, accurately calculating the shear bearing capacity of UHPC tenons and through-steel bars, and introducing the hoop effect enhancement coefficient α. This method not only improves the prediction accuracy of shear bearing capacity, but also enhances the adaptability and flexibility of the model, providing a solid theoretical and practical foundation for the safe application of steel-UHPC cells under complex working conditions.

[0103] The invention process of this part is as follows:

[0104] 1. Test Overview

[0105] 1.1 Specimen design

[0106] A total of 7 push-out specimens of two types, A and B, were designed. Type A specimens are cell-type specimens, consisting of 5 steel plates (i.e., the middle perforated steel plate and the 4 outer steel plates) enclosing a cell with a PBL key and UHPC inside the cell (see Figure 6 , the steel plates around the cells form peripheral constraints on the UHPC); Category B is an inserted specimen (see Figure 7 ), consisting of an I-shaped steel plate (i.e., a central perforated steel plate and two flange steel plates) and UHPC between the two flange steel plates (the three steel plates do not form a peripheral constraint on the UHPC). PBL end bearing concrete was not set in both types of specimens.

[0107] The cross-sectional dimensions of Class A and Class B specimens are both 400mm x 400mm. The thickness of each steel plate is 24mm, the height of the steel plate is 500mm, the height of the UHPC is 500mm, the bonding (contact) length of the steel plate and the UHPC is 400mm (the two are staggered by 100mm in height), and the protruding part of the UHPC is vacated at the end of the PBL to form a 24mm thick gap. The perforated steel plate is located in the middle of the steel box or wing plate, and a hole is set at a distance of 200mm from the top, with a hole diameter of 60mm. The steel plates in each specimen are connected by welding. Some specimens have through-steel bars with a diameter of 18mm and a length of 300mm. The through-steel bars are fixed in the center by steel wire. In Class A specimens, the two steel plates parallel to the perforated steel plate are both opened with a 24mm hole to facilitate the placement of the steel bars in the steel box.

[0108] The perimeter of the intermediate steel plate and its flange steel plate in contact with UHPC has been Figure 3 The representative character chamber has a similar perimeter, so in all type A specimens in this paper, the inner surfaces of the two steel plates parallel to the PBL steel plate are coated with butter (such as Figure 4 The orange line shows the bonding effect between the concrete and the two steel plates.

[0109] In order to investigate the contribution of bond friction, concrete tenon, through-steel and their mutual influence, the A-type specimens were set up with pure bond, unbonded pure tenon, bonded pure tenon, bonded steel bar, unbonded PBL, and PBL steel-UHPC cell specimens (a total of 6 groups); the B-type specimens were only PBL insertion specimens (opening steel plate was not oiled). The specimen grouping and numbering are shown in Table 1, and 3 identical specimens were made in each group. Considering the scale of the test, the specimens introduced in this paper only studied the single-hole PBL and no end bearing plate was set.

[0110] Table 1 Push-out specimen specifications

[0111]

[0112] Note: Explanation of specimen numbers: A—cell type specimen, B—insertion type specimen; bn—bonding condition between concrete and perforated steel plate, b0 means no bonding, b1 means bonding; tn—concrete tenon condition in the hole, t0 means no concrete tenon, t1 means concrete tenon; rn—through-rebar condition in the hole, r0 means no through-rebar, r1 means through-rebar.

[0113] 1.2 Material properties

[0114] The concrete used in the test is the UHPC developed by our team, which is composed of cement, quartz sand, quartz powder, silica fume, water reducer, expansion agent, steel fiber, and water. The proportions are shown in Table 2. The steel fiber is straight, 13 mm long, and has an aspect ratio of 65. During the casting of the push-out specimens, the material specimens were cast simultaneously, and the curing and material properties tests were carried out in accordance with the "Ultra-High Performance Concrete Basic Performance Test and Method" specification. The material properties are shown in Table 3. The steel components in the test are cast from Q345C quenched steel, and the through steel bars are HRB400. The mechanical properties are shown in Table 4.

[0115] Table 2 UHPC material mix ratio (unit: kg / m 3 )

[0116]

[0117]

[0118] Table 3 UHPC material properties

[0119]

[0120] Table 4 Mechanical properties of steel

[0121]

[0122] 4.2.1.3 Arrangement of slip and strain gauge measurement points

[0123] The relative displacement measurement points between the steel plate and UHPC of the cell-type specimen (Type A specimen) are arranged on the side of the specimen, such as Figure 8 (a) (the specimen is inverted). Four displacement sensors (numbered W1, W2, W3, and W4) are fixed at the center height of the side steel plate opening using a magnetic base. The measuring rod of the displacement sensor is in full contact with the angle steel pasted on the UHPC surface. The relative displacement measurement point arrangement of the insertion type specimen (type B specimen) is similar to that of the cell type specimen, as shown in Figure 1. Figure 8 (b) (the specimen is inverted). Vertical strain gauges (G1, G2, G3, G4) are arranged on the steel plate surface of the cell type specimen (type A specimen). Figure 8 (a) shown.

[0124] 1.4 Loading and testing plan

[0125] The test was conducted on a 500t hydraulic servo press. Since the top surface of the UHPC specimen may be uneven, a small amount of quartz sand needs to be laid on the top surface to level it in order to avoid eccentric loading. During the specific operation, the specimen is inverted so that the center of the UHPC top surface is placed at the center of the steel base, and an appropriate amount of quartz sand is laid on the upper surface of the steel base. The load in the test is controlled by a hydraulic servo press, and the relative displacement between the steel plate and the UHPC is automatically collected using a displacement sensor. The test loading device is as follows: Fig. 9 shown.

[0126] Before the specimen is loaded, the shear bearing capacity P is estimated according to the PBL shear bearing capacity calculation formula. Before the specimen is formally loaded, it is preloaded twice at 0.1P, each time for 5 minutes to eliminate the initial defects of the test device and the specimen, loaded to 10kN, and the initial reading of the displacement meter is reset to zero. The formal loading adopts a graded loading system: first, it is loaded to near P at a load increment of 40kN per level and a loading rate of 5kN / s, and then displacement control is adopted, and loading is stopped at a rate of 1mm / min until the relative displacement of the specimen is about 40mm.

[0127] 2. Test results - load-relative displacement curve and ultimate load

[0128] The load-relative displacement curves of the push-out tests of each specimen (the relative displacement here actually includes the UHPC compression from the center height of the steel bar to the top surface of the UHPC, the slip between the steel plate and the UHPC at the center height of the steel bar, and the displacement of the UHPC edge relative to the center at the height of the steel bar) are shown in Figure 2. Fig.10 As shown in (a) to (g). For perforated steel plate specimens, considering that in actual engineering, the shearing of tenons or through-steel bars is not allowed, the peak load before the shearing of tenons or through-steel bars can be defined as the ultimate load. For cell-type specimens with no holes in the middle steel plate, the load value of the load-relative displacement curve is still increasing even when the relative displacement reaches 40 mm, which is not allowed even under the most unfavorable load in actual engineering. Therefore, some references define it as the inflection point where the increase of load with relative displacement slows down significantly and the relative displacement does not exceed 20 mm ( Fig.10 The loads C1, C2, and C3 in (a) are taken as the ultimate loads.

[0129] The push-out test ultimate load Pu, ultimate relative displacement Su of each specimen and the average value and failure mode of the same specimen are shown in Table 5.

[0130] Table 5 Push-out test results

[0131] Table 5 Results of push-out test

[0132]

[0133] Note: P, Pu, Pu.ave, Su and Su.ave refer to the estimated bearing capacity, ultimate load, average ultimate load, ultimate relative displacement (relative displacement value under ultimate load) and average ultimate relative displacement (in A-b1t0r0 specimens, they refer to bond-slip ultimate strength, average bond-slip ultimate strength, bond limit slip and average bond limit slip, respectively).

[0134] 3. PBL (no pressure-bearing end) longitudinal shear bearing capacity calculation formula

[0135] Table 6 gives the bearing capacity calculation formula of PBL shear keys in domestic and international standards and some literature.

[0136] Table 6 Calculation formula for shear bearing capacity of PBL

[0137]

[0138] Note: V u is the shear bearing capacity of the PBL shear key; d is the opening diameter; d s is the diameter of the steel bar; f cu is the compressive strength of concrete cube; f st is the strength of the through-steel reinforcement; f cd is the design value of concrete axial compressive strength; f sd is the design value of the tensile strength of the through reinforcement; γ0 is the component coefficient, usually taken as 1; α is the influence coefficient of the through reinforcement, taken as 1.320125; β is the influence coefficient of the transverse ordinary reinforcement, when the stirrup ratio ρ≤0.18%, take 1.204479, otherwise take 1.042948; γ is the influence coefficient of the concrete tenon, taken as 1.95168; A c is the cross-sectional area of ​​the concrete tenon; ξ is the influence coefficient of the stirrups; t is the thickness of the perforated steel plate; λ t is the concrete constraint index; A e A is the cross-sectional area of ​​the perforated steel plate; r is the cross-sectional area of ​​the steel bar; A' r is the cross-sectional area of ​​the transverse ordinary steel bar; f y is the yield strength of the steel bar; f y ' is the yield strength of ordinary steel bars; A is the bonding area between the perforated plate and concrete; n is the number of shear surfaces.

[0139] After analysis, it can be assumed that Fig.10 (b)~10(f) The PBL bearing capacity V u The interfacial chemical bonding force V can be ignored C The contribution of VC = 0), the bearing capacity V provided by the through steel bars r , bearing capacity provided by concrete tenon V t , and friction V R Composition, that is

[0140] V u =V t +V r +V C +V R =V t +V r +V R (3)

[0141] Assume that the transverse normal pressure σ is proportional to the load (ignore the difference in transverse normal stress of each steel-UHPC interface and the difference in the area of ​​each steel-UHPC interface), and the proportional coefficient is k; Assume that the friction coefficient when not oiled is x1, and the friction coefficient when oiled is x2. If 2 surfaces are oiled and 4 surfaces are not oiled, the friction resistance is P·k(4x1+2x2), recorded as P·y1; the friction resistance when all 6 surfaces are oiled is P·k·6x2, recorded as P·y2; Obviously y1>y2. Assume that the ultimate load is V u , then: V u =V u ·y i +V t +V r (i=1,2,3) (when i=3, y3=0, indicating no hoop effect, no friction resistance is considered), that is

[0142]

[0143] Where: V u is the shear bearing capacity of PBL in UHPC, kN; V t is the concrete tenon action, kN; V r is the penetration effect of steel bars, kN; α i is the hoop effect enhancement coefficient (i=1,2,3).

[0144]

[0145] y1=k(4x1+2x2) (6)

[0146] y2=6kx2(7)

[0147] Where: α1 is the hoop action coefficient of the bonded cell type specimen, α2 is the hoop action coefficient of the oiled cell type specimen, α3 is the hoop action coefficient of the inserted type specimen, and α3=1.

[0148] From the analysis of the formulas in Table 6, we can see that the contribution of the through-steel reinforcement to the shear bearing capacity is proportional to the product of its cross-sectional area and tensile strength. r It can be written as:

[0149]

[0150] Where: γ is the influence coefficient of the steel bars penetrating the hole; n is the number of shear planes; d s is the diameter of the steel bar passing through the hole, mm; f y is the tensile strength of the steel bars penetrating the hole, MPa.

[0151] The contribution value of the concrete tenon to the shear bearing capacity in each formula in Table 6 is proportional to its cross-sectional area, but is proportional to the 0.5 power, 0.57 power, and 1 power of the concrete strength, respectively. In this paper, it is set to be proportional to the y power (0.3≤y≤1, y is determined by trial calculation), that is, V t It can be written as formula (7). Therefore, formula (8) is obtained from formula (2), (6), and (7).

[0152]

[0153] Where: β is the correction coefficient of the concrete tenon in the hole; n is the number of shear surfaces; d is the hole diameter of the perforated steel plate, mm; d s is the diameter of the steel bar passing through the hole, mm; f cu is the compressive strength of concrete cube, MPa; y is the power of the compressive strength of concrete cube, (0.3≤y≤1).

[0154]

[0155] For the six groups of specimens in Table 5 (based on the average value of each group), there is formula (8). When y is given a certain value, according to V u = The experimental value is a system of 6 equations, but there are only 4 unknowns α1, α2, γ, β, which is a contradictory system of equations. Solve it by the least square method. No matter what value y takes, the values ​​of α1, α2, γ obtained by formula (8) remain unchanged, and the calculation results in Table 8 remain unchanged (because β(f cu ) y is a constant). The six equations composed of formula (8) yield α1=5.9701, α2=2.5147, γ=1.1261, and β=10.5352 when y=0.3. Therefore, formula (10) becomes:

[0156]

[0157] In the formula: α1=5.9701, the hoop action coefficient of the bonded cell type specimen; α2=2.5147, the hoop action coefficient of the oiled cell type specimen; obviously, the size of α1 and α2 is also related to the steel content of the section, the larger the steel content, the larger the values ​​of the two; α3=1, the hoop action coefficient of the inserted specimen.

[0158] The bearing capacity of each specimen in this paper is calculated according to formula (11) (see Table 7). The average value of the ratio of the calculated value to the test value is 0.96, the standard deviation is 0.09, and the coefficient of variation is 0.10, which is in good agreement.

[0159] Table 7 Calculated values ​​of formula (11) and comparison with the experimental results in this paper

[0160]

[0161]

[0162] When y is 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0, the average values ​​and coefficients of variation of the last column of physical quantities in Table 9 are 0.85, 0.20, 0.82, 0.20, 0.78, 0.21, 0.75, 0.22, 0.73, 0.23, 0.71, 0.25, 0.68, 0.27, 0.69, and 0.27. Table 9 lists the results of y = 0.3, β = 10.5352 with better calculation results. When the test results of reference

[17] are cited in Table 8, the bonding effect is deducted from the test values; the concrete cube compressive strength of reference

[16] in Table 8 is obtained by the cylinder compressive strength given in reference

[16] / 0.8.

[0163] It can be seen from Table 8 that the calculated values ​​of ordinary concrete or RPC100 obtained by formula (6) are generally smaller than the test values ​​(the average value of the ratio of the calculated value to the test value is 0.85). The reason is that the load proportion shared by the push-out test of ordinary concrete or RPC100-steel PBL connector is relatively large. Therefore, the calculated values ​​of formula (11) ignoring the bonding effect of the two are generally smaller than the test values.

[0164] In addition, the coefficient of variation of the ratio of the calculated value to the experimental value in Table 8 is 0.20, which is slightly large. This may be due to differences in the experimental methods, test instrument accuracy, and material stability control among scholars.

[0165] Substituting the obtained α1=5.9701, α2=2.5147 into equations (3), (4), and (5), we can obtain kx1=0.15793, kx2=0.10039.

[0166] for Figure 3The number of steel-UHPC interfaces is 4. When the steel plate interfaces are not oiled, the corresponding y i =4kx1=0.63172, α i =2.715; when oil is applied, it is y i =4kx2=0.40156, α i =1.671. It can be seen from formula (11) that the longitudinal shear bearing capacity of the PBL cell type component considering the hoop effect is 2.715 times that of the PBL insert type component without the hoop effect, and the longitudinal shear bearing capacity of the oiled cell type component is 1.671 times that of the PBL insert type component without the hoop effect.

[0167] Table 8 Ratio of calculated values ​​of formula (11) to experimental values ​​in various literatures

[0168]

[0169]

[0170] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. It can be understood by a person of ordinary skill in the art that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0171] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A steel-UHPC cell shear bearing capacity test and determination system, characterized in that: The system includes: a) Test specimen preparation module, used to prepare test specimens consisting of five steel plates forming a cell with a PBL bond and filled with UHPC; b) a shear connector arrangement device, used to arrange all the shear connectors inside the cell; c) Mechanical properties testing module, including equipment for measuring the shear capacity of UHPC tenons and the shear capacity of through-steel bars in UHPC; d) a calculation unit, used to calculate the longitudinal shear bearing capacity of the steel-UHPC cell according to a preset shear bearing capacity calculation method, wherein the longitudinal shear bearing capacity is jointly determined by the shear bearing capacity of the UHPC tenon, the shear bearing capacity of the through-steel in the UHPC, and the hoop effect enhancement coefficient; e) Parameter adjustment module, used to adjust the hoop effect enhancement coefficient according to the steel-UHPC interface state and the cross-sectional hoop coefficient; f) Data recording and analysis module, used to record test data and analyze calculation results to determine the shear bearing capacity of the steel-UHPC cell.

2. The steel-UHPC cell shear bearing capacity test and determination system according to claim 1, characterized in that: The test specimen preparation module further comprises: a) The cross-sectional dimensions of the test piece are 400 mm x 400 mm; b) The thickness of the steel plate is 24 mm, the height of the steel plate is 500 mm, and the height of the UHPC is 500 mm; c) The bonding length between the steel plate and the UHPC is 400 mm, and the protruding part of the UHPC is left empty at the end of the PBL to form a 24 mm thick gap; d) The perforated steel plate is located in the middle of the steel box or wing plate, and a hole with a diameter of 60 mm is set at a position 200 mm away from the top; e) The diameter of the through-steel bar is 18 mm and the length is 300 mm, fixed in the center by steel wire; f) In the type A specimen, the inner surfaces of the two steel plates parallel to the PBL steel plate are smeared with butter, and the inner surfaces of the other steel plates in contact with the UHPC are kept naturally clean.

3. The steel-UHPC cell shear bearing capacity test and determination system according to claim 1, characterized in that: In the calculation unit, the shear bearing capacity of the UHPC tenon is determined by considering factors such as the number of shear surfaces, the diameter of the hole of the perforated steel plate, the diameter of the steel bar passing through the hole, and the compressive strength of the concrete.

4. The steel-UHPC cell shear bearing capacity test and determination system according to claim 1, characterized in that: In the calculation unit, the shear bearing capacity of the through-steel in the UHPC is determined by considering factors such as the diameter and number of the through-steel and the tensile strength of the steel.

5. The steel-UHPC cell shear bearing capacity test and determination system according to claim 1, characterized in that: In the parameter adjustment module, the hoop effect enhancement coefficient is set to a specific value in the PBL cell with the dimensions of the present invention, and is set to another specific value in the unbonded PBL cell, while for the inserted specimen, the hoop effect enhancement coefficient is set to 1.

6. The steel-UHPC cell shear bearing capacity test and determination system according to claim 1, characterized in that: When the steel content of the section or the degree of hoop restraint is different from the section with the size marked in this manual, the hoop effect enhancement factor shall be adjusted accordingly to ensure the accuracy of the shear bearing capacity calculation.

7. A method for testing and determining the shear bearing capacity of steel-UHPC cells, characterized in that: The method specifically includes: 1) All shear connectors (studs or perforated steel plates, i.e. PBL) of the steel-UHPC cell longitudinal shear transmission bearing capacity push-out test specimens are located inside the cell; 2) The longitudinal shear bearing capacity formula of PBL steel-UHPC cell is: V u =α(V t +V r ) (1) Where: V u is the longitudinal shear capacity of the steel-UHPC cell; V t is the shear bearing capacity of UHPC tenon, V r is the shear bearing capacity of the through-steel in UHPC, α is the hoop effect enhancement coefficient - the part of α exceeding 1 is actually the friction resistance, because the friction resistance of the ultimate bearing state can be expressed as the hoop lateral pressure of this state multiplied by the friction coefficient, and this hoop lateral pressure is proportional to the hoop relative stiffness and push-out force, so the α value is related to the steel-UHPC interface state, section hoop coefficient, etc.; when there is no hoop effect, α=1, when there is a hoop effect, α>1.

8. The test method for longitudinal shear bearing capacity of steel-UHPC cells and the method for determining shear bearing capacity of PBL steel-UHPC cells as claimed in claim 7 are characterized in that: All the shear connectors of the steel-UHPC cell longitudinal shear transmission bearing capacity push-out test specimen are located inside the cell: 1) The push-out test specimen is composed of 5 steel plates enclosing a PBL key cell and UHPC inside the cell; 2) The cross-sectional size of the push-out test specimen is 400 mm × 400mm, the thickness of the steel plate is 24mm, the height of the steel plate is 500mm, the height of the UHPC is 500mm, the bonding length of the steel plate and the UHPC is 400mm, the protruding part of the UHPC is vacated at the end of the PBL to form a 24mm thick gap, the perforated steel plate is located in the middle of the steel box or wing plate, and a hole is set at a distance of 200mm from the top, with a hole diameter of 60mm. The steel plates in each specimen are connected by welding, and the diameter of the through steel bar is 18mm and the length is 300mm; the through steel bar is fixed in the center by steel wire. In the type A specimen, the two steel plates parallel to the perforated steel plate are both opened with a hole of 24mm to facilitate the placement of the steel bar in the steel box; 3) Grease the inner surfaces of the two steel plates parallel to the PBL steel plate, and keep the inner surfaces of the other steel plates in contact with the UHPC in a naturally clean state to ensure that the bonding surface area is equivalent to the bonding area of ​​the single cell steel-UHPC in the cell steel-UHPC joint section.

9. The test method for longitudinal shear bearing capacity of steel-UHPC cells and the method for determining shear bearing capacity of PBL steel-UHPC cells as claimed in claim 7 are characterized in that: The longitudinal shear bearing capacity formula of the PBL steel-UHPC cell is as follows: 1) UHPC tenon shear bearing capacity V t Where: n is the number of shear surfaces; d is the hole diameter of the perforated steel plate, mm; d s is the diameter of the steel bar passing through the hole, mm; f cu is the concrete cube compressive strength, MPa; 2) Shear bearing capacity of through-steel bars in UHPC V r Where: f y is the tensile strength of the steel bars penetrating the hole, MPa. 3) The increase coefficient of the hoop effect α - the part of α exceeding 1 is provided by the side friction resistance For the PBL cells with marked dimensions, the hoop action coefficient α=2.715; for the unbonded PBL cells with marked dimensions of the present invention, α=1.671; when the cross-sectional steel content or the degree of hoop constraint is different from the cross-sectional dimensions marked in this specification, α will also be different, and the greater the steel content, the greater the α value; for the inserted specimen, α=1.

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