Reinforcement joint design method

Abstract

To provide a design method of a reinforcement joint that is lightweight and can be densely filled with mortar.SOLUTION: A design method of a mortar-filled reinforcement joint 1 has a cylindrical sleeve 2 into which reinforcements 4 can be inserted from both sides and has no ribs formed on an inner circumferential surface 2a of the sleeve. The design method designs so as to satisfy a prescribed relational expression.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for designing a reinforcing bar joint. [Background technology]

[0002] Conventionally, one method of joining rebars extending in the axial direction of precast reinforced concrete members is to use mortar-filled rebar joints. Compared to joining methods such as pressure welding, mortar-filled rebar joints are less susceptible to environmental conditions during work, and are therefore widely adopted from the perspective of ensuring quality.

[0003] Generally, commercially available rebar joints have multiple ribs on the inner surface of the sleeve of the approximately hollow rebar joint to meet the performance standards set out in the "Rebar Joint Performance Evaluation Criteria" in the "Explanation of Technical Standards Related to Building Structures" compiled by the Building Guidance Division, Housing Bureau, Ministry of Land, Infrastructure, Transport and Tourism, the Japan Building Administration Council, and the Japan Structural Engineers Association.Other innovations include tapering the inner surface of the sleeve of the approximately hollow rebar joint.

[0004] In addition, the rebars inside the sleeve of the rebar joint are joined together by mortar filled inside the sleeve, and when a tensile load is applied to the rebars, the stress is transmitted from the deformed rib of one rebar through the filled mortar to the rib inside the sleeve and then to the other rebar. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-292862 Summary of the Invention [Problem to be solved by the invention]

[0006] However, providing multiple ribs on the inner surface of the sleeve increases the weight of the rebar joint, significantly affecting workability and construction costs. Also, although the filling of the mortar inside the sleeve is monitored by workers during construction, there is a problem in that it is impossible to confirm whether the mortar is densely packed due to the influence of the ribs inside the sleeve.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a method for designing a reinforcing bar joint that is lightweight and allows mortar to be densely filled. [Means for solving the problem]

[0008] In order to achieve the above object, the design method for a reinforcing bar joint according to the present invention is a design method for a mortar-filled reinforcing bar joint having a cylindrical sleeve into which reinforcing bars can be inserted from both sides, with no ribs formed on the inner surface of the sleeve, characterized in that the reinforcing bar joint is designed to satisfy the following relational expression (A).

[0009]

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[0010] D0 is the maximum diameter (mm) of the diameter of the thick core sleeve. t is the sleeve thickness (mm) β is the safety margin s σ y is the yield stress of the sleeve (N / mm 2 ) r σ y is the yield stress of the reinforcing bar (N / mm 2 ) d is the nominal diameter of the rebar (mm).

[0011] According to this invention, it is possible to realize a lightweight reinforcing bar joint that satisfies structural requirements and has no ribs formed on the inner peripheral surface of the sleeve. Furthermore, since no ribs are formed on the inner peripheral surface of the sleeve, it is possible to realize a reinforcing bar joint that has excellent mortar filling properties. As a result, it is possible to provide a reinforcing bar joint that has excellent workability.

[0012] In addition, in the design method of a reinforcing bar joint according to the present invention, the sleeve may have a taper that expands or contracts in diameter along the axial direction, and the taper angle of the taper may be designed to satisfy the following relational expression (B).

[0013]

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[0014] In addition, σ ex <m>< / m> is the equivalent stress at the time of mortar failure (N / mm 2 ) σ B is the compressive strength of the mortar (N / mm 2 ) α is the taper angle r 2 is the coefficient of determination.

[0015] According to this invention, the angle of the taper formed on the inner peripheral surface of the sleeve can be set appropriately. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a method for designing a reinforcing bar joint that is lightweight and allows mortar to be densely filled inside the sleeve. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a cross-sectional view of a reinforcing bar joint model according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 3 is an enlarged perspective view of part B in FIG. 2. [Figure 4] 10 is a graph showing the relationship between the equivalent stress at the time of mortar failure and the taper angle. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a method for designing a reinforcing bar joint according to an embodiment of the present invention will be described with reference to the drawings.

[0019] As shown in FIG. 1, the reinforcing bar joint 1 used in this embodiment is a mortar-filled reinforcing bar joint. The reinforcing bar joint 1 has a sleeve 2 that corresponds to the main body of the joint. The sleeve 2 has a hollow cylindrical shape, and a reinforcing bar 4 is placed in a hollow portion 3 of the sleeve 2, with mortar 5 filled between the sleeve 2 and the reinforcing bar 4. No ribs are formed on the inner surface 2a of the sleeve 2 of the reinforcing bar joint 1. As shown in FIG. 2, the sleeve 2 has a cylindrical shape with an annular cross section. Furthermore, the sleeve 2 is formed in a tapered shape such that the diameter of the hollow portion 3 varies along the axial direction.

[0020] The performance of the reinforcing bar joint 1 is thought to be greatly influenced by the taper angle α, thickness ratio D0 / t, joint length ratio h / D0, friction coefficient μ between the mortar and sleeve, and shear stress intensity τ0, but in this embodiment, the focus is on the taper angle α and thickness ratio D0 / t, which have the greatest influence.

[0021] There are four possible failure modes: 1) sliding failure between the mortar and sleeve, 2) shear failure of the mortar, 3) bond failure between the rebar and mortar, and 4) tensile yielding of the sleeve. However, since mode 1) is the dominant failure mode for rebar joint 1 and the purpose is to examine the design method for rebar joint 1 (sleeve 2), mode 1) will be the subject of consideration below.

[0022] (Relationship between rebar tensile load and internal stress) 1 to 3 show a model of the reinforcing bar joint 1 and the balance of forces in a small space. Here, the assumptions are as follows: a) the assumed failure mode is sliding failure between the mortar and the sleeve; b) the mortar 5 is rigid, the sleeve 2 is elastic (thin), and the interface 6 between the mortar 5 and the sleeve 2 is completely adhered before sliding occurs; and c) the taper angle α is small.

[0023] When the conditions are set as above, the balance of forces inside the sleeve 2 satisfies the relationship of the following formula (1) based on the balance of forces in the circumferential direction and the surface pressure direction.

[0024]

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[0025] Next, due to the balance of vertical forces, the following equation (2) holds true.

[0026]

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[0027] The stress-strain relationship of the sleeve under plane stress is expressed by the following equation (3).

[0028]

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[0029] At the interface between the mortar and the sleeve, the mortar element is in the Z direction. Z Assuming that the sleeve has come out by (mm), ε θ is expressed by equation (4).

[0030]

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[0031] From the above equations (3) and (4), the following equation (5) is derived.

[0032]

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[0033] The above formula (5) becomes the following formulas (6) and (7) from formula (1).

[0034]

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[0035]

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[0036] The relationship with τ is expressed by the following equation (8) based on equation (2).

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[0038] From the above, σ Z The relationship between σ and τ is n and Δδ Z The equivalent stress of the sleeve σ eq is given by equation (9), which makes it possible to determine whether the material will yield.

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[0040] Two cases are assumed for the boundary state between the mortar and the sleeve: a complete bond state and a sliding failure state.

[0041] (Case 1: The interface between the mortar and the sleeve is in a completely bonded state (Δδ Z = 0) σ in fully attached state n is determined by the elastic rigidity of the mortar, but in this embodiment, the mortar is assumed to be a rigid body. ZAssuming that is expressed as a quadratic function of Z, Δδ in equations (7) and (8) Z = 0, we obtain equation (10).

[0042]

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[0043] Equations (11) and (12) are derived from the relationship between load and stress.

[0044]

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[0045]

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[0046] From equations (11) and (12), C1 and C2 in equation (10) are expressed as in the following equation (13): where h (mm) is the total length of the joint (total length of the sleeve).

[0047]

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[0048] From equation (13), equation (10) can be expressed as the following equation (14): where z (mm) is an arbitrary position in the joint length direction.

[0049]

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[0050] From equations (7) and (8), τ and σ n are given by equations (15) and (16), respectively.

[0051]

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[0052]

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[0053] (Case 2: When slippage at the interface between the mortar and sleeve is allowed) τ and σ at the mortar-sleeve interface n Applying the slip resistance formula to the relationship, and allowing for slip on the interface between the mortar and sleeve, σ Z Then, the following equations (17) and (18) are derived.

[0054]

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[0055]

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[0056] Here, μ and τ0 are conventionally μ=1.0 and τ0=0.1σ, respectively. B Let's say.

[0057] Next, equation (19) is derived from the balance between the tensile load of the reinforcing bar and the shear stress inside the sleeve.

[0058]

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[0059] From the above, the equivalent stress σ due to the tensile load of the reinforcing bar ex and Δδ Z The relationship is given by equation (20) or equation (21).

[0060]

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[0061]

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[0062] σ Z is σ at equation (8) and Z=0 Z The boundary conditions are given by equation (22).

[0063]

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[0064] (Design Criteria) The equivalent stresses at the time of mortar failure and sleeve yielding required to set the design criteria for rebar joint 1 are shown below.

[0065] Equivalent stress σ when mortar breaks ex <m>< / m> is expressed by equation (23) based on the regression analysis results shown in FIG.

[0066]

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[0067] Equivalent stress degree at sleeve yield σ ex <eq>< / eq> σ changes depending on the material axis position eq In (Equation (9)), σ is maximized when Z=0. eq σ ex <eq>< / eq> Let's say.

[0068]

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[0069] Sleeve yield criteria σ eq / s σ y ≦1.0, equation (25) is derived.

[0070]

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[0071] The design criteria are the minimum value of the equivalent stress for each failure mode, σ ex <d>< / d> Equivalent stress σ at yield of reinforcing bar ex <r>< / r> This can be thought of as a ratio (safety margin).

[0072]

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[0073]

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[0074]

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[0075] (Maximum required diameter / thickness ratio D0 / t of sleeve) A limit is set for D0 / t, provided that the yield load of the sleeve is equal to or greater than the yield load of the reinforcing bar, taking into account the safety margin β. In reality, we should consider yielding under biaxial stress, but σ θ is σ Z is smaller than σ Z Considering only σ is a safe evaluation. Z Then, the following equations (29) and (30) are derived.

[0076]

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[0077]

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[0078] According to this embodiment, the design method of the mortar-filled reinforcing bar joint 1, which has a cylindrical sleeve 2 into which a reinforcing bar 4 can be inserted from both sides and has no ribs formed on the inner surface 2a of the sleeve 2, was designed to satisfy the above formula (30).

[0079] D0 is the maximum diameter (mm) of the diameters due to the thick core sleeve, t is the sleeve thickness (mm), β is the safety margin, s σ y is the yield stress of the sleeve (N / mm 2 ), r σ y is the yield stress of the reinforcing bar (N / mm 2 ), d is the nominal diameter of the reinforcing bar (mm).

[0080] According to this invention, it is possible to realize a lightweight reinforcing bar joint 1 that satisfies structural conditions and has no ribs formed on the inner peripheral surface 2a of the sleeve 2. Furthermore, because no ribs are formed on the inner peripheral surface 2a of the sleeve 2, it is possible to realize a reinforcing bar joint 1 that has excellent mortar filling properties. As a result, it is possible to provide a reinforcing bar joint 1 that has excellent workability.

[0081] In addition, in the design method of the reinforcing bar joint 1 of this embodiment, when the sleeve 2 is formed with a taper that expands or contracts in diameter along the axial direction, the taper angle α of the taper is designed to satisfy the above formula (23).

[0082] In addition, σ ex <m>< / m> is the equivalent stress at the time of mortar failure (N / mm 2 ), σ B is the compressive strength of the mortar (N / mm 2 ), α is the taper angle, r 2 is the coefficient of determination.

[0083] According to the present invention, the taper angle α of the reinforcing bar joint 1 in which the inner peripheral surface 2a of the sleeve 2 is tapered can be set appropriately.

[0084] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments and can be modified within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0085] 1 Reinforced concrete joints 2 sleeves 2a Inner surface 4. Reinforced concrete 5. Mortar α Taper angle

Claims

1. A design method for a mortar-filled reinforcing bar joint having a cylindrical sleeve into which reinforcing bars can be inserted from both sides, and no ribs formed on the inner circumferential surface of the sleeve, A design method for a reinforcing bar joint, characterized by designing it to satisfy the following relational expression (A). [Equation 1] In addition, D ０ is the maximum diameter (mm) of the diameter of the thick sleeve core t is the sleeve thickness (mm) β is the safety margin ｓ σ ｙ is the yield stress of the sleeve (N / mm ２ ) ｒ σ ｙ is the yield stress of the reinforcing bar (N / mm ２ ) d is the nominal diameter of the rebar (mm).

2. The design method for a reinforcing bar joint according to claim 1, characterized in that the sleeve has a taper that expands or contracts in diameter along the axial direction, and the taper angle of the taper is designed to satisfy the following relational expression (B). [Equation 2] In addition, σ ｅｘ＜ｍ＞ is the equivalent stress at the time of mortar failure (N / mm ２ ) σ Ｂ is the compressive strength of the mortar (N / mm ２ ) α is the taper angle r ２ is the coefficient of determination.

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