A slip-cast grouting connecting piece with variable constraints along the path and a design method thereof

Abstract

The application discloses a kind of along the way variable restraint steel sleeve grouting connector and its design method.Sleeve inner cavity is divided into high restraint area close to tension end and conventional / low restraint area away from tension end along anchoring length direction, high restraint area improves local restraint stress by increasing sleeve wall thickness, improving or encrypting inner rib, reducing equivalent inner diameter and other measures;And grouting layer thickness is controlled in the preferred range of 8-11mm.Based on sleeve-grouting material separator restraint stress model and bonding strength formula, along the way variable restraint design equation is established, and each subsection geometric parameter is calculated and optimized, so that the local restraint capacity at any point meets the design bonding requirement, realizes the nearly uniform distribution of bonding stress along anchoring length, significantly shortens anchoring length under the premise of meeting the design requirement of "steel bar first break", improves material utilization and the reliability of grouting sleeve connection.

Description

Technical Field

[0001] This invention relates to the field of mechanical connection technology for steel bars in prefabricated concrete structures, specifically to a grouting connector with variable constraint steel sleeve for connecting steel bars in prefabricated components and its parametric design method based on a constraint-bond synergy model. Background Technology

[0002] In prefabricated concrete structures, the longitudinal reinforcing bars of precast components are often connected by grouting with metal sleeves. The basic principle is to insert the end reinforcing bars of the precast component into a steel sleeve with inner ribs on its inner surface, and then inject high-strength cement-based grout between the reinforcing bars and the sleeve. The sleeve constrains the grout, creating positive pressure at the interface between the reinforcing bars and the sleeve. This transfers tensile force through an adhesion-friction mechanism, achieving continuous stress on the reinforcing bar joint.

[0003] The L-shaped, S-shaped, and B-shaped grouting sleeves widely used in existing engineering applications and related standard drawings share the following characteristics: the wall thickness along the anchorage length is basically constant, the height of the inner ribs and the rib spacing are basically consistent, and the inner diameter of the sleeve is enlarged as a whole only according to the diameter of the reinforcing bar and construction deviations, presenting an "overall uniform structure". To improve the bearing capacity, the constraint capacity can usually only be improved by lengthening the anchorage length or enlarging the overall sleeve cross-sectional dimensions.

[0004] On the other hand, existing experimental studies have shown that:

[0005] The bond stress between the reinforcing bar and the grout is significantly unevenly distributed along the anchorage length. The peak bond stress is larger near the tension end and significantly lower further away from the tension end. As the anchorage length increases, the average bond strength decreases, resulting in reduced material utilization and stress concentration in the anchorage area.

[0006] In existing theoretical analyses, to simplify the derivation, it is often assumed that the circumferential constraint stress provided by the sleeve to the grouting layer is uniformly distributed along the anchorage length. This is then coupled with the bond strength formula to obtain the minimum anchorage length or bearing capacity of the sleeve. However, the actual stress and deformation of the sleeve cause the constraint stress to be unevenly distributed along the length. This assumption deviates significantly from the actual stress state, affecting the calculation accuracy and safety margin configuration.

[0007] In actual engineering projects, in order to ensure that the joint performance reaches or exceeds the tensile performance of the parent material steel bars, the design often adopts a large safety factor and a conservative uniform anchorage length, without distinguishing the differences in bonding requirements along the line for steel bars of different diameters and strength grades. This results in excessively long sleeves, large steel consumption, and limited construction space. At the same time, the stress in the anchorage zone is highly concentrated in a small area near the tension end, increasing the risk of interface peeling and local cracking.

[0008] In addition, although there are some local improvements to the geometry of existing grouting sleeves, such as end micro-contraction and corrugated sleeve walls, they are still mainly local modifications to the overall geometry and are not based on the system design concept of "adjustment constraint along the anchorage - bonding matching relationship". That is, they do not actively change the sleeve constraint capacity at each position according to the bonding requirements at each position of the anchorage length, so as to make the bonding stress more uniform along the anchorage.

[0009] Existing theoretical studies, when establishing the constraint stress model and bond strength formula for the sleeve-grout separator, generally still use the simplified assumption of uniform or distributed constraint stress along the anchorage. This is mainly used to explain experimental phenomena and calibrate average bond strength parameters, without further proposing: to back-calculate the "local constraint stress-local bond bearing capacity" relationship in this type of model into a specific sleeve geometric parameter distribution; to divide the anchorage length direction into a high constraint zone, a transition zone, and a conventional / low constraint zone, and to perform parameter optimization configuration for each zone; and to form a set of engineering-applicable "variable constraint sleeve" construction and its parametric design method.

[0010] In summary, the existing technology has at least the following problems:

[0011] (1) The sleeve constraint capacity is basically uniform along the anchorage length direction, while the bonding requirement is uneven along the height. The two are seriously mismatched, resulting in excessive anchorage length, low material utilization, and local stress concentration.

[0012] (2) The theoretical models are mostly based on the assumption of uniform distribution of constraint stress, which differs from the actual deformation and cracking process along the process. The calculation results are conservative or deviate from the actual failure mode.

[0013] (3) Existing sleeve structure design lacks the concept of "variable constraint along the process" and has not yet formed a systematic method to match "local constraint stress × local bonding surface length" with actual bonding requirements by optimizing geometric parameters such as wall thickness, inner rib height and spacing, and local inner diameter in segments along the process.

[0014] (4) Studies on the influence of grout layer thickness show that when the grout layer is too thick, the constraint of the sleeve on the grout layer lags behind the development of interface cracks, and the bond strength decreases significantly. Existing sleeves mostly determine the inner diameter according to construction needs, and lack clear design control over the upper limit of grout layer thickness.

[0015] Therefore, there is an urgent need for a grouting sleeve connector that can adjust the distribution of sleeve constraint capacity along the anchorage length to coordinate with the bonding requirements of the rebar-grout interface. In addition, a set of parametric design methods based on the constraint-bond model should be proposed to significantly shorten the anchorage length, improve material utilization, and improve the distribution of bonding stress along the length while meeting the design goal of "rebar breaks first", so as to achieve a more uniform and reliable grouting sleeve connection. Summary of the Invention

[0016] This invention addresses the following shortcomings of existing rebar grouting sleeves:

[0017] 1. The existing sleeve has a basically constant wall thickness and inner rib arrangement along the anchorage length. However, experimental studies show that the bond stress at the steel bar-grout interface is uneven along the length, with stress peaks near the tension end and insufficient bond utilization at the far end. This often requires excessively long anchorage lengths to meet the bearing capacity requirements, resulting in low material utilization and significant stress concentration.

[0018] 2. Existing theoretical models often simplify the constraint stress of the sleeve on the grouting layer to be uniform along the anchorage length or distributed according to experience, which deviates from the actual stress state and makes it difficult to guide the reasonable configuration of the sleeve's geometric parameters along the anchorage.

[0019] 3. Existing improvements to the sleeve structure mainly focus on local variations such as micro-shrinkage at the overall end and corrugated walls. They lack a systematic design concept of "constraint-bonding matching relationship along the process" and have not yet established an engineering design method based on constraint-bonding collaborative model to back-calculate and optimize the geometric parameters of each segment.

[0020] 4. When the grouting layer is too thick, the constraint of the sleeve on the grouting layer lags behind the development of interface cracks, and the bond strength decreases significantly. However, existing designs mostly determine the inner diameter of the sleeve based on construction convenience, lacking clear control over the upper limit of the grouting layer thickness.

[0021] Therefore, the technical problem to be solved by the present invention is to provide a grouting connector for a reinforcing bar sleeve with variable constraint along the anchorage length and its design method, so that the constraint capacity of the sleeve along the anchorage length direction matches the actual bonding requirements, significantly shortens the anchorage length, improves the material utilization rate, improves the distribution of bonding stress along the anchorage length, and suppresses the constraint hysteresis phenomenon under the premise of satisfying "the reinforcing bar yields or fractures first".

[0022] To address the aforementioned technical problems, this invention proposes a grouting connector for a variable constraint reinforcing bar sleeve and its design method.

[0023] 1. Grouting connector for variable constraint steel sleeve along the line

[0024] The connector includes: a sleeve body, a grouting layer, and reinforcing bars inserted into the sleeve. The inner cavity of the sleeve is divided into at least two sections along the anchorage length of the reinforcing bars, preferably including: a high-constraint zone near the tension end; a conventional-constraint zone located away from the tension end; and, if necessary, a low-constraint zone with relatively low constraint capacity; a transition zone with smooth transition of constraint stiffness may be provided between the high-constraint zone and the conventional / low-constraint zone.

[0025] The high-constraint region has a geometric structure that enhances constraint capabilities compared to the normal / low-constraint region, and can specifically be one or more combinations of the following:

[0026] (1) Differential wall thickness configuration: wall thickness of cylinder wall in high constraint area Greater than the wall thickness of the conventional / low-constraint zone cylinder ,Right now This is to improve the circumferential stiffness of the high-constraint zone and the constraint capacity of the grouting layer.

[0027] (2) Configuration of inner rib parameters: Inner ribs are set in the high constraint area, and the height of the inner ribs in the high constraint area is... Greater than the height of the ribs in the normal / low constraint zone and / or rib spacing within the high constraint zone Smaller than the rib spacing in the normal / low constraint zone ,Right now By increasing the rib height and densifying the rib spacing, the local contact area and mechanical interlocking effect are improved.

[0028] (3) Equivalent inner diameter difference configuration: In the high constraint area, the equivalent inner diameter of the sleeve is appropriately reduced. This makes it smaller than the equivalent inner diameter of the normal / low-constraint region. ,Right now This reduces the radial gap between the reinforcing bar and the inner wall of the sleeve, thereby reducing the grout layer thickness and improving the constraint efficiency, while ensuring the requirements for construction grouting and reinforcing bar positioning deviation.

[0029] To suppress constraint hysteresis and avoid a decrease in bond strength caused by excessive grout layer thickness, this invention controls the grout layer thickness along the entire length of the sleeve: the grout layer thickness at any cross-section of the sleeve... Limited to Within the interval, where To ensure full grouting and minimize construction deviations, The maximum thickness that can effectively transfer restraint stress without significantly reducing bond strength. Preferably, It is about 8 mm. It is approximately 11 mm.

[0030] The geometric parameter configuration of the high-constraint zone, transition zone, and conventional / low-constraint zone adopted in this invention is not a simple linear change along the anchorage, but rather a back-calculation and optimization based on the sleeve-grout separator constraint stress model and the steel bar-grout interface bond strength formula: for any position along the anchorage length Establish a local bonding demand function And calculate the corresponding local constraint stress of the sleeve. and the effective bonding surface area near that location The segmented geometric parameters of the sleeve are designed to satisfy: ,in This represents the cross-sectional area of ​​the connected reinforcing bars.

[0031] By applying the above constraints, the "local constraint capacity × local bonding surface length" along the anchorage length is matched with the design bonding requirements, thereby achieving an approximately uniform distribution of bonding stress along the anchorage.

[0032] Under the premise of satisfying the requirements that "the reinforcing bar yields or fractures first, and the joint strength is not lower than that of the parent material", this invention increases the total anchorage length of the sleeve. The design aims to minimize the local constraint conditions and grout layer thickness constraint conditions mentioned above; simultaneously, it prioritizes maximizing the length of the high-constraint zone. Percentage of total anchorage length 20% to 60% of the adhesive is placed on the side closest to the tension end to specifically address the peak bond stress near the tension end.

[0033] 2. Design method for grouted sleeve connectors for variable constraint reinforcement along the line

[0034] This invention also proposes a parametric design method for the above-mentioned sleeve structure, including but not limited to the following steps:

[0035] (1) Input design parameters: Input the diameter, strength grade, design tensile force or design stress of the connected steel bars, the range of compressive strength of the selected grouting material, the allowable construction deviation, and the allowable range of grouting layer thickness. .

[0036] (2) Establishing a constraint-bond coordination model: Based on the mechanical model of the sleeve-grout separator and the bond strength formula of the steel bar-grout interface, a bond demand function along the anchorage length is established. Local constraint capability of sleeve The relationship between these factors clarifies the requirements for the circumferential stiffness of the sleeve and the arrangement of the inner ribs at different locations.

[0037] (3) Anchorage length segmentation and parameter setting: The proposed anchorage length direction is divided into high constraint zone, transition zone and normal / low constraint zone. The geometric parameters such as the wall thickness of the cylinder, the height and spacing of the inner ribs, the equivalent inner diameter and the thickness of the grouting layer of each segment are set as variables to be determined.

[0038] (4) Back calculation and optimization solution: Taking "minimum total anchorage length" as the objective function, with , The constraints are that the strength of the sleeve material does not exceed the design allowable value and "the steel bar yields or fractures first". Parametric modeling and numerical iteration methods are used to back-calculate and solve the geometric parameters of each segment through multi-constraint optimization.

[0039] (5) Determine the minimum anchorage length and segmentation parameters: Under the premise of satisfying the above constraints, the minimum anchorage length of the sleeve is obtained. Length of high-constraint region The geometric parameters, such as the wall thickness of each section of the cylinder, the height and spacing of the inner ribs, and the equivalent inner diameter, are output as the structural design results.

[0040] (6) Priority adjustment order (optional): In the process of parameter optimization in the high constraint area, local constraint stress is improved by increasing the height of the inner ribs and decreasing the spacing between the inner ribs. Only when the adjustment of the inner rib parameters is insufficient to meet the local bonding requirements, the wall thickness of the cylinder or the equivalent inner diameter is further increased to achieve a balance between constraint capacity, manufacturing difficulty and cost.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. Matching Bonding Requirements with Variable Constraints Along the Anchorage Length: By dividing the sleeve into a high-constraint zone, a transition zone, and a normal / low-constraint zone along the anchorage length, and calculating the geometric parameters of each segment based on the constraint-bond synergy model, the local constraint capacity of the sleeve is quantitatively matched with the bonding requirements of the steel bar-grout interface. This transforms the bond stress along the anchorage length from a highly concentrated state to an approximately uniform distribution, reducing the risk of interface peeling and local cracking.

[0043] 2. Significantly shortens anchorage length and improves material utilization: Under the premise of satisfying the condition that "the steel bar yields or fractures first", this invention can significantly shorten the required anchorage length by setting a high constraint zone near the tension end and optimizing its length and stiffness configuration, thereby reducing the amount of steel used in the sleeve and the length requirement of the precast component end, improving material utilization and the economy of prefabricated structures.

[0044] 3. Control the thickness of the grouting layer to suppress constraint lag: By clearly controlling the upper and lower limits of the grouting layer thickness in the design, we can avoid the construction difficulties and deviation sensitivity caused by the grouting layer being too thin, and also avoid the constraint initiation lag and the decrease in bond strength caused by the grouting layer being too thick, so as to ensure that the sleeve constraint can participate in the stress process in a timely and effective manner.

[0045] 4. System design method from theoretical model to construction parameters: This invention no longer uses the constraint stress model and bond strength formula only to explain experimental phenomena, but transforms them into an engineering-executable parametric design method. By "back calculation + optimization", the segmented geometric parameters of the friction-variable constraint sleeve are determined, realizing a tight coupling from theoretical model to actual construction design.

[0046] 5. High adaptability and programmable implementation: The design method of this invention takes the diameter of the steel bar, the strength grade, the design tensile force and the performance of the grouting material as inputs. It can adapt to the connection requirements of steel bars of different specifications and grouting materials of different strength grades. It can be automatically designed through programming, which is convenient for engineering promotion and application and standardization and serialization development. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the embodiments will be briefly described below with reference to the accompanying drawings. The same or similar components in the drawings are represented by the same reference numerals. Obviously, the drawings are only for illustrating the principles of the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0048] Figure 1 This is a schematic diagram of the overall structure of the friction-variable constraint steel sleeve grouting connector of the present invention;

[0049] Figure 2 For along Figure 1 A longitudinal sectional view along the sleeve axis shows the distribution of the high constraint zone, transition zone, and conventional constraint zone;

[0050] Figure 3 For along Figure 2 A schematic diagram of the cross-section of the medium-high constraint zone shows the thickness of the grouting layer and the arrangement of ribs in the high constraint zone;

[0051] Figure 4 This is a flowchart illustrating the design method of the grouting connector for the variable constraint steel sleeve of the present invention.

[0052] Explanation of reference numerals in the attached drawings: 1 — Sleeve body; 2 — Reinforcing steel; 3 — Grouting layer; 4 — High constraint zone; 5 — Transition zone; 6 — Conventional constraint zone; 7 — Inner rib; 71 — Inner rib in the high constraint zone; 72 — Inner rib in the conventional constraint zone; 8 — Sleeve wall; 81 — Sleeve wall in the high constraint zone; 82 — Sleeve wall in the conventional constraint zone; 9 — Tension end; 10 — Sleeve axis; 11 — Anchorage length ;12 — Length of the high-constraint region ; 101 — Design parameter input steps; 102 — Constraint-bonding model establishment steps; 103 — Anchorage length segment setting steps; 104 — Segmented geometric parameter back calculation and optimization steps; 105 — Minimum anchorage length and parameter solution steps; 106 — Design result output steps. Detailed Implementation

[0053] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only for illustrating the present invention and do not constitute a limitation on the scope of protection of the present invention; various modifications or substitutions can be made by those skilled in the art without departing from the core concept of the present invention, and these should all fall within the scope of protection of the present invention.

[0054] Unless otherwise stated, the reference numerals used in this section are consistent with the reference numerals in the foregoing “Description of Drawings”.

[0055] Example 1: Typical three-segment friction-variable constraint sleeve structure

[0056] This embodiment provides a typical structure for a grouted sleeve connector with variable constraint along the anchorage length. The sleeve is divided into a high constraint zone, a transition zone, and a conventional constraint zone along the anchorage length, and the variable constraint along the anchorage is achieved through differences in wall thickness and inner ribs.

[0057] 1.1 Overall Structural Layout

[0058] like Figures 1-3 As shown, the grouting connector for the variable constraint rebar sleeve in this embodiment mainly includes: a sleeve body 1; a rebar 2 inserted into the sleeve; a grouting layer 3 filling the annular space between the rebar 2 and the sleeve body 1; a high constraint zone 4 near the tension end 9; a transition zone 5 arranged between the high constraint zone 4 and the conventional constraint zone 6; a conventional constraint zone 6 away from the tension end 9; inner ribs 7 distributed on the inner wall of the sleeve, including inner ribs 71 in the high constraint zone and inner ribs 72 in the conventional constraint zone; a sleeve wall 8, including inner wall 81 in the high constraint zone and inner wall 82 in the conventional constraint zone; a sleeve axis 10 along the length of the sleeve; and a total anchorage length 11 of the sleeve (denoted as...). The length of the high-constraint region is 12 (denoted as...). ).

[0059] The reinforcing bars 2 can be butt-welded reinforcing bars of the same diameter or transitional connections between reinforcing bars of different diameters. In this embodiment, butt-welded reinforcing bars of the same diameter are used as an example for explanation. The two reinforcing bars 2 extend into the sleeve body 1 from both ends, forming a certain anchorage length inside the sleeve.

[0060] 1.2 Anchorage Length and Segment Ratio

[0061] In this embodiment, the total anchoring length 11 of the sleeve is denoted as... The length of the high-constraint region is 12, denoted as Based on theoretical analysis and experimental fitting results, the preferred length of the high-constraint zone 4 is the total anchorage length. 20% to 60%.

[0062] For example, when the nominal diameter of the connected reinforcing bar 2 is 20 mm, the strength grade is HRB400, and the design objective is that the tensile bearing capacity of the joint is not less than the tensile bearing capacity of the parent material of the reinforcing bar, the total anchorage length can be calculated using the design method of this invention (see Example 3). The length is approximately 12d to 16d (d is the diameter of the reinforcing bar), significantly shorter than the 20d to 25d commonly used in current engineering projects; the length of the high-confinement zone... It accounts for approximately 30% to 40% of the total anchorage length.

[0063] exist Figure 2In the diagram, the total anchorage length 11 and the high constraint zone length 12 can be indicated by dimension lines, which makes it easier to understand the position and proportion of each segment in the axial direction.

[0064] 1.3 Variable Thickness Structure of Cylinder Wall

[0065] like Figure 2 As shown, the sleeve body 1 has different wall thicknesses in different segmented regions: the sleeve wall in the high-constraint region 4 is denoted as the high-constraint region sleeve wall 81, with a wall thickness of... The wall of the conventional constraint zone 6 is designated as conventional constraint zone wall 82, with a wall thickness of [missing information]. .

[0066] This embodiment is designed This is to improve the circumferential stiffness of the high-constraint zone 4 and its constraint on the grouting layer 3. A typical value relationship can be: Preferred Compare Increase by 20% to 50%.

[0067] The cylinder wall 8 within the transition zone 5 can adopt a graded or continuous transition method: Graded method: The transition zone 5 is divided into several short sections, and the wall thickness of each short section ranges from... Towards Decrease step by step, such as in a three-stage form Continuous method: Through machining or forging, the wall thickness of the transition zone 5 is smoothly varied along the axial direction, transitioning from the high-constraint zone wall 81 to the conventionally constrained zone wall 82. This avoids abrupt changes in wall thickness stiffness at the segment boundaries, reducing the risk of local stress concentration.

[0068] 1.4 Arrangement of Inner Ribs with Variable Parameters Along the Friction

[0069] like Figure 2 , Figure 3 As shown, the inner wall of the sleeve body 1 is provided with inner ribs 7 to enhance the mechanical interlocking and interfacial bonding performance between the reinforcing bar 2 and the grouting layer 3.

[0070] Within the high-constraint region 4, the inner rib is called the high-constraint region inner rib 71; within the normal-constraint region 6, the inner rib is called the normal-constraint region inner rib 72.

[0071] In this embodiment, variable constraint along the friction is achieved through the difference between the inner rib height and the rib spacing: the inner rib height in the high constraint region... Greater than the height of the ribs within the conventional constraint zone ,Right now Typical values ​​can make for 1.1 to 1.5 times; rib spacing in the high-constraint zone Smaller than the rib spacing within the conventional constraint zone ,Right now Typical values ​​can make for 0.5 to 0.8 times that.

[0072] In practical implementation, 4 to 8 inner ribs 7 can be evenly distributed circumferentially, with each inner rib either continuous or segmented along the axial direction. In the high-restraint zone 4: continuous or nearly continuous inner ribs 71 are preferred, with the top surface of the inner rib close to the reinforcing bar 2 to increase local contact pressure and interlocking effect; Figure 3 The inner ribs can be represented as multiple circumferentially raised ribs with small spacing. Within the conventional constraint zone 6, the inner ribs 72 have a relatively low height and a large rib spacing to meet general bonding requirements while reducing processing costs. Within the transition zone 5, the height and spacing of the inner rib cross-section can gradually transition from the parameters of the high constraint zone to the parameters of the conventional zone, achieving a smooth change in axial stiffness and bonding ability.

[0073] 1.5 Grouting layer thickness control

[0074] like Figure 3 As shown, an annular space is formed between the reinforcing bar 2 and the inner wall of the sleeve body 1, and the grouting layer 3 fills this space. The thickness of the grouting layer at any cross-section is denoted as . .

[0075] In this embodiment, the inner cavity size of the sleeve is designed to ensure that the grout layer thickness varies along the entire length of the sleeve. satisfy: Preferably: This is to ensure that the grout is fully injected during construction and to take into account the positioning deviation of the reinforcing bars; This is to avoid the sleeve's constraint effect on the grouting layer being delayed when the grouting layer is too thick, which would lead to a significant decrease in bond strength.

[0076] Within the high-constraint zone 4, the equivalent inner diameter of the sleeve can be appropriately reduced. This allows the grouting layer 3 to be slightly thinner while still meeting the aforementioned thickness range, thereby improving local constraint efficiency; a slightly larger equivalent inner diameter is used within the conventional constraint zone 6. This ensures that the grout layer is evenly filled and meets the construction requirements.

[0077] In the specific design, the design method described in Example 3 is used to comprehensively consider the inner diameter of the sleeve, the diameter of the reinforcing bar, and construction errors. Perform a check to ensure that there are no significant deviations throughout the entire length range. The cross section.

[0078] 1.6 Materials and Manufacturing

[0079] In this embodiment: the sleeve body 1 is preferably made of low-alloy high-strength steel or high-quality carbon structural steel, such as Q345 grade steel or materials with equivalent performance, and is formed by machining or hot extrusion; the inner rib 7 can be processed by turning, rolling, cold extrusion or casting, etc., preferably by integral forming process to ensure the integrity and reliability of the inner rib and the cylinder wall 8; the reinforcing bar 2 is a conventional hot-rolled ribbed reinforcing bar, such as HRB400, HRB500, etc.; the grouting layer 3 is a premixed high-strength non-shrink cement-based grout, and its compressive strength grade is determined according to the design requirements, for example, 60 MPa to 90 MPa.

[0080] During manufacturing, a uniformly shaped sleeve blank can be machined first, and then the inner diameter, wall thickness and inner rib parameters of different segments can be formed by machining the inner hole. Alternatively, it can be formed in one step by die forging or hot extrusion and then subjected to a small amount of finishing.

[0081] 1.7 Usage and Force Process

[0082] In engineering applications, the steps for using the friction-dependent constraint sleeve in this embodiment include: inserting the reinforcing bar 2 into the inner cavity of the sleeve body 1, ensuring that the length of the reinforcing bars at both ends meets the design requirements, and ensuring that the ends of the reinforcing bars are basically located in the middle of the sleeve or positioned according to the design; using positioning measures to control the coaxiality of the reinforcing bar 2 within the sleeve body 1, ensuring that the thickness of the grouting layer 3 is within the allowable error range; injecting grouting material into the sleeve body 1 through the reserved grouting port until the grout overflows evenly from the overflow port without obvious air bubbles or voids; and putting the grouting material into use after it has hardened and reached the design strength.

[0083] Under tension, the high-constraint zone 4 near the tension end 9 first bears the larger bond stress at the steel-grout interface, and provides higher circumferential confinement stress to the grout layer 3 through the increased cylinder wall thickness 81 and the reinforced inner ribs 71. This satisfies the localized high bonding requirements. .

[0084] As the load increases further, the bond force transmission gradually extends to the conventional constraint zone 6, and the bond stress distribution within the entire anchorage length 11 tends to be uniform, avoiding the phenomenon of excessive bond stress concentration near the tension end and insufficient utilization of the bond at the far end in traditional sleeves.

[0085] Under the design load, the joint area will preferentially experience yielding and fracture of the reinforcing bar 2, without overall bond peeling or yielding and bulging of the sleeve body 1, thus achieving the design goal of "reinforcing bar fracture first".

[0086] Example 2: Structural modification of the high-constraint region by changing the equivalent inner diameter

[0087] Based on Example 1, this embodiment focuses on changing the inner diameter of the sleeve to achieve variable constraint along the process. The wall thickness can remain basically the same or be slightly adjusted, which is suitable for occasions where the processing equipment has high requirements and the wall thickness cannot be changed significantly.

[0088] 2.1 Structural differences

[0089] Compared with Example 1, the main differences in this example are: the outer diameter of the sleeve body 1 remains basically unchanged along the anchorage length direction; the nominal wall thickness difference of the sleeve wall 8 is small or there are no obvious segments; the equivalent inner diameter of the high constraint zone 4... The equivalent inner diameter is significantly smaller than that of the conventional constraint region 6. ,Right now This forms a relatively thin grouting layer 3 on the outside of the reinforcing bar 2, improving the constraint efficiency of the area; 3. The height and spacing of the inner ribs 7 can be configured differently from those in Example 1, or they can be kept approximately the same, mainly relying on the change of inner diameter to adjust the constraint capacity.

[0090] 2.2 Inner Diameter Design of High Constraint Zone

[0091] like Figure 2 , Figure 3 As shown, during the machining of the inner hole of the sleeve body 1, a smaller equivalent inner diameter can be machined in the high-constraint zone 4 near the tension end 9 by using boring tools or mandrels of different specifications. In the conventional constraint region 6, far from the tension end, a larger equivalent inner diameter is machined. .

[0092] The difference between the two The equivalent inner diameter of the high-restraint zone 4 can be determined based on the rebar diameter d and the allowable fluctuation in grout layer thickness. For example, for a rebar with d = 20 mm, if the target grout layer thickness is 8–11 mm, then the equivalent inner diameter of the high-restraint zone 4 is... Approximately 36–40 mm can be used; the equivalent inner diameter of conventional constraint zone 6 The value can be approximately 38–42 mm; the specific value needs to be optimized using the design method of Example 3 and in combination with construction deviations.

[0093] By reducing A thinner grout layer 3 is formed within the high-constraint zone 4, making it easier for the radial deformation of the sleeve body 1 to directly compress the grout layer, thus reducing the constraint stress. It starts up faster, and with the mechanical interlocking of the inner rib 7, it gives the area a higher local bond load capacity.

[0094] 2.3 Applicable Situations

[0095] This embodiment is suitable for the following situations: the outer diameter of the sleeve is limited by the component cross-section or reserved hole diameter, and it is not appropriate to increase the constraint by increasing the local wall thickness; the production process is more suitable to achieve segmentation by changing the inner hole size rather than the outer shape; and it is necessary to locally enhance the constraint capacity without significantly increasing the sleeve's self-weight and steel consumption.

[0096] Apart from the differences mentioned above, the remaining structure, materials, and usage methods can be referred to Example 1.

[0097] Example 3: Parametric Design Method for Friction-Variable Constraint Sleeves

[0098] This embodiment presents a design method based on a constraint-bond synergy model to determine the minimum anchorage length and geometric parameters of each segment of the sleeve structure in Embodiment 1 or Embodiment 2. This method can be implemented via a computer program or with the assistance of engineering calculation software.

[0099] like Figure 4 As shown, the design process of this embodiment includes the following steps.

[0100] 3.1 Inputting Design Parameters (Step 101)

[0101] Based on project requirements, designers input the following design parameters:

[0102] 1. Basic parameters of the connected reinforcing bars 2: nominal diameter d of the reinforcing bar; strength grade of the reinforcing bar (e.g., HRB400, HRB500) and corresponding yield strength. Ultimate strength .

[0103] 2. Joint design objective: Joint design tensile strength Or design stress; whether it is required that "the tensile bearing capacity of the joint is not lower than the tensile bearing capacity of the parent material of the steel bar" or "the steel bar breaks first".

[0104] 3. Grouting material performance parameters: compressive strength grade The design range; the corresponding empirical formula or test calibration parameters for bond strength.

[0105] 4. Construction and Geometric Constraints: Reinforcement positioning deviation, allowable grout layer thickness range The maximum allowable outer diameter and length range of the sleeve.

[0106] These parameters serve as input conditions for subsequent calculations.

[0107] 3.2 Constraint – Bonding Model Establishment (Step 102)

[0108] Based on the publicly available constraint mechanics model of the sleeve-grout separator and the bond strength formula of the rebar-grout interface, this embodiment establishes a bond demand function along the anchorage length direction without limiting the specific model form. Local constraint capacity of the sleeve The relationship between them.

[0109] The design objective is: to apply the design tensile force... At that time, at each point along the anchorage length At this location, the local bonding load-bearing capacity is not lower than the local bonding requirement, which can be expressed in the form of: ,in: The sleeve 1 provides local circumferential constraint stress to the grouting layer 3 through the sleeve wall 8 and the inner rib 7; :Location The effective bonding surface area in the vicinity is related to the shape and circumferential distribution of the inner ribs; Local bond requirements are determined by the stress distribution of reinforcing bars and the bond force transfer mechanism. : Cross-sectional area of ​​steel bar 2.

[0110] In practical calculations, the selected theoretical model can be used to... Determined by assuming bond-slip relationship or experimental calibration results, and derived in conjunction with sleeve geometry parameters. The expression.

[0111] 3.3 Setting the Anchorage Length in Segments (Step 103)

[0112] Preliminary estimate of total anchorage length Based on this, the anchorage length direction is divided into multiple functional segments:

[0113] 1. High-constraint zone 4: Located on the side closest to the tension end 9; its length is denoted as... The initial value can be set according to Selected; mainly responsible for transmitting the bonding peak force near the tension end.

[0114] 2. Transition zone 5 (optional): Located between high constraint zone 4 and normal constraint zone 6; its length can be adjusted according to... Selecting progressively varying wall thickness and internal rib parameters achieves a smooth transition in constraint capacity.

[0115] 3. Conventional constraint zone 6: Located on the side furthest from the tension end 9; its length is approximately... ,in The length of the transition zone is used; the wall thickness and inner rib parameters are close to those of the existing sleeve conventional configuration, which are used to bear the bond force transmission of the remaining anchorage length.

[0116] For each segment, the following geometric parameters are set as variables to be determined: cylinder wall thickness. Inner rib height Spacing Equivalent inner diameter Grouting layer thickness distribution (Determined by the inner diameter, the diameter of the reinforcing bar, and the deviation).

[0117] 3.4 Inverse calculation and optimization of piecewise geometric parameters (step 104)

[0118] In this step, parametric modeling and numerical optimization algorithms are used to solve for the parameters to be determined, so that they satisfy the constraints and optimize the objective function.

[0119] 1. Objective function: Preferably based on "total anchorage length". The goal is to minimize the length of the sleeve while meeting safety requirements; alternatively, the goal can be to take into account the amount of material used, with "minimum steel consumption" or "lowest cost" as secondary objectives.

[0120] 2. Constraints: These mainly include: Bond safety constraints: ,in For bonding safety factors, a value of 1.1 to 1.3 is typically used. Grout layer thickness constraints: Sleeve material strength constraints: The circumferential stress, axial stress, and stress at the root of the inner rib of sleeve body 1 shall not exceed the allowable values ​​of the material design strength. Failure mode constraints: Under the design tensile force... Under the action, the steel bar 2 will yield or fracture first, and the sleeve body 1 and the grouting layer 3 will not undergo overall bond peeling or yielding bulging failure.

[0121] 3. Solution Process: The following solution strategy can be adopted: Initial estimation: Based on experience or existing test results, an initial anchorage length is given. Initial values ​​of segmented parameters; iterative updates: using gradient search, heuristic optimization, or other numerical methods, gradually adjust parameters such as wall thickness, inner rib height and spacing, and equivalent inner diameter of the high-constraint zone 4, transition zone 5, and conventional constraint zone 6; each iteration calculates the values ​​along the anchorage length. , and Check whether the above constraints are met; if there are sections that do not meet the constraints, prioritize improving the local constraint capacity in those sections by increasing the height of the inner ribs, decreasing the spacing between the inner ribs, or decreasing the equivalent inner diameter, and then appropriately increase the wall thickness if necessary; once all constraints are met, attempt to reduce the total anchorage length. And re-optimize until it is further reduced. This will cause the constraints to be broken, and in this case, the current solution will be taken as the optimal solution.

[0122] 3.5 Minimum Anchorage Length and Parameter Determination (Step 105)

[0123] Through the optimization iteration in step 104, the minimum anchorage length that can satisfy the design objectives and all constraints is finally obtained. Length of high-constraint region Length of transition zone Wall thickness of each section Parameters of inner ribs Equivalent inner diameter and the corresponding grout layer thickness distribution .

[0124] Based on this, some parameters can be modified in an engineering manner: the obtained wall thickness and inner diameter can be adjusted to the specifications that can be achieved by standard steel pipes or profiles; the height and spacing of the inner ribs can be adjusted to an integer multiple that is easy to process or the size of standard cutting tools; and the parameter differences between adjacent segments can be smoothly corrected to avoid sharp transitions or stress concentrations during manufacturing.

[0125] 3.6 Design Result Output (Step 106)

[0126] The final design output includes: the total anchorage length 11 of the sleeve and the lengths of each segment (such as the lengths of the high-restraint zone 4, transition zone 5, and conventional zone 6); the wall thicknesses 81 and 82 of each segment; the height, spacing, and cross-sectional shape of the inner ribs 71 and 72 of each segment; and the equivalent inner diameter of each segment. The corresponding grouting layer thickness range ; Insertion length and positioning requirements of reinforcing bar 2; Performance requirements and construction points of grouting material 3.

[0127] The above results can be directly used for engineering drawing, processing and production, and construction guidance. They can also be used to form a standardized product series, providing matching friction-restraint sleeve models for steel bars of different diameters and strength grades.

[0128] Without departing from the basic concept of the present invention, those skilled in the art can make various modifications and improvements to the above embodiments, such as changing the number of segments (two-segment or multi-segment), using different forms of internal rib cross sections (trapezoidal, arc-shaped, sawtooth, etc.), arranging the high constraint area at symmetrical positions at both ends to simultaneously bear bidirectional tensile forces, etc., all of which should fall within the protection scope of the present invention.

Claims

1. A grouting connector for a reinforcing bar sleeve with variable restraint along the friction path, comprising a metal sleeve having an inner cavity and a grouting layer disposed within the inner cavity, characterized in that: The inner cavity of the sleeve is divided into at least two sections along the anchorage length of the reinforcing bar, including a high-constraint zone near the tension end and a conventional or low-constraint zone away from the tension end; the high-constraint zone has a geometric structure that enhances the constraint capacity compared to the conventional or low-constraint zone, and the geometric structure that enhances the constraint capacity includes at least one or more of the following: (1) the wall thickness of the sleeve in the high-constraint zone. ,in (1) The wall thickness of the cylinder in the conventional or low-constraint zone; (2) The rib height in the high-constraint zone. and / or the spacing between inner ribs ,in (2) The height and spacing of the inner ribs in the conventional constraint zone or the low constraint zone, respectively; (3) The equivalent inner diameter of the high constraint zone. ,in It is the equivalent inner diameter of the conventional or low-constraint zone to reduce the thickness of the grout layer between the reinforcing bar and the sleeve.

2. The grouting connector for the friction-adjustable reinforcing bar sleeve according to claim 1, characterized in that: Grouting layer thickness at any point inside the sleeve satisfy ,in To ensure sufficient thickness and minimal geometric deviation during construction, To achieve the maximum thickness that does not significantly reduce bond strength and suppress constraint hysteresis, the preferred thickness is... , .

3. The grouting connector for a variable constraint reinforcing bar sleeve according to claim 1 or 2, characterized in that: A transition zone is provided between the high-constraint zone, the conventional-constraint zone, and / or the low-constraint zone. Within the transition zone, the sleeve wall thickness, the height of the inner rib, and / or the inner diameter change continuously or in stages along the length direction to avoid stress concentration caused by abrupt changes in constraint stiffness.

4. The grouting connector for a variable constraint reinforcing bar sleeve according to any one of claims 1 to 3, characterized in that: The friction bond demand function determined based on the sleeve-grout separator confinement stress model and the steel bar-grout interface bond strength formula. The geometric parameters of the high-constraint zone, the conventional-constraint zone, and / or the low-constraint zone are designed to satisfy: for any position along the anchorage length ,have ,in The local constraint stress provided by the sleeve to the grouting layer This represents the effective bonding surface area near this location. This represents the cross-sectional area of ​​the connected reinforcing bars.

5. The grouting connector for a variable constraint reinforcing bar sleeve according to any one of claims 1 to 4, characterized in that: Total anchorage length of the sleeve Designed to minimize the following conditions: (1) no overall debonding failure of the interfacial bond before the reinforcing bars reach their yield strength or ultimate strength at the joint; (2) the total length of the high-restraint zone. Percentage of total anchorage length 20% to 60% of the sleeve material and arranged close to the tension end; (3) The yield strength of the sleeve material is not exceeded to avoid local yielding or bulging damage of the sleeve.

6. A design method for a grouting connector for a reinforcing steel sleeve with variable constraint along the friction path, characterized in that, The steps include: (1) Input design parameters: diameter and strength grade of the connected steel bars, design tensile force or corresponding design stress, range of compressive strength of the selected grout and construction deviation, and allowable range of grout layer thickness; (2) Use the sleeve-grout isolation body constraint stress model and the steel bar-grout interface bond strength formula to establish the bond demand function along the anchorage length. Local constraint capacity of the sleeve The relationship; (3) Divide the anchorage length direction into a high constraint zone, a transition zone and a normal / low constraint zone, and set the parameters such as the wall thickness of the cylinder, the height and spacing of the inner ribs, the equivalent inner diameter and the thickness of the grouting layer for each segment respectively; (4) Solve the parameter variables by inverse calculation and optimization so that the anchorage length can be adjusted at any position. All satisfy And the grouting layer thickness constraint condition; (5) Under the premise of satisfying "the steel bar yields first or breaks first", the minimum anchorage length and geometric parameters of each segment that satisfy the above constraints are obtained.

7. The design method according to claim 6, characterized in that: In step (4), the back calculation and optimization adopts parametric modeling and numerical iterative calculation. The preferred method is a multi-constraint optimization algorithm based on the objective function "minimum total anchorage length" and the constraints include local bonding safety factor, sleeve material strength utilization rate and upper and lower limits of grouting layer thickness.

8. The design method according to claim 6 or 7, characterized in that: When determining the parameters of the high-constraint zone, the local constraint stress is adjusted by increasing the height of the inner ribs or decreasing the spacing between the inner ribs. Only when the adjustment of the inner rib parameters is insufficient to meet the local bonding requirements is the wall thickness of the cylinder wall or the equivalent inner diameter reduced, so as to take into account the overall stiffness of the sleeve, the processing difficulty and cost.

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