JP4583299B2 - Lap joint for joining concrete members and the design method thereof - Google Patents

Description

  The present invention relates to a lap joint for joining concrete members or the like and a design method thereof.

  Of the joining methods at the joints of opposing concrete members (reinforced concrete members, steel concrete members, steel reinforced concrete members, steel grain concrete members, concrete members, steel members), closed stress materials (rebar, round steel, etc.) There is known a joint structure (a lap joint of stress materials in a closed shape) that transmits the stress of one stress material to the other stress material by making the concrete face to face each other (Patent Document 1).

  For example, as shown in FIG. 8, when joining the reinforced concrete member 1 and the reinforced concrete member 2, the reinforcing bars 3 and 4 having shapes extending from the reinforced concrete members 1 and 2, bent and returned to the joint are opposed to each other. It is a structure that transmits stress from one reinforcing bar to the other reinforcing bar by filling the joint with concrete. In this case, the overlapping length H of the reinforcing bars not including the bending portion of the reinforcing bars is the joint length handled in the present invention. In addition, although the thing in the state where the opposing couplings contacted is shown in the figure, the opposing couplings may be separated.

For example, such a joint structure is constructed by sequentially inserting steel elements into the ground by traction or propulsion while excavating the ground and combining them, and joining the steel elements together to form a closed element structure in the ground. If the element structure is used as the main body structure of an underground structure by excavating the earth and sand surrounded by the element structure, etc., it is used for joining the part (closing part) where the element structure is finally closed (Patent Document 2).
JP 2002-38607 A JP 2002-115497 A

  Conventionally, the lap joint made of a stress material having a closed shape has not yet been clarified in the proof strength as a joint. Therefore, it has been necessary to increase the lap length of the joint portion (joint length) to obtain the proof strength. However, when placing concrete after placing the concrete member in place and overlaying the joint on the joint, the amount of concrete to be placed increases as the joint length increases, resulting in poor workability and economic efficiency. become.

The present invention is intended to solve the above-mentioned problems, and analyzes and formulates the joint proof strength of a lap joint of a stress material having a closed shape, and is a lap joint excellent in workability and economy as a joint length within a reasonable range. Is to achieve.
The present invention relates to a lap joint in which a pair of closed stress materials consisting of a straight portion and a curved portion are arranged opposite to a joint portion of a concrete member or the like, and concrete is placed on the joint portion to join the concrete member or the like. ,
The relationship between the stress material diameter φ, the bending radius r of the curved portion, the concrete compressive strength f ′ _C , the joint length H, the cross-sectional area A _{S of} the joint stress material, the yield strength σ _S of the joint stress material and the joint strength P is ) And (2) are satisfied,

And the bend radius r of the curved portion of the lap joint is 2φ to 8φ,
Reinforcing bar diameter to be placed on the curved part of the lap joint is 0.5φ or more,
The joint length of the lap joint is 1φ to 13.4φ,
Stress material diameter φ is 16 to 35 mm,
The concrete compressive strength is 16 to 40 N / mm ² .
Further, the present invention is a design method of a lap joint in which a pair of stress materials closed to a joint portion such as a concrete member are arranged to face each other, and concrete is placed in the joint portion to join the concrete member or the like.
The relationship between the stress material diameter φ, the bending radius r of the curved portion, the concrete compressive strength f ′ _C , the joint length H, the cross-sectional area A _{S of} the joint stress material, the yield strength σ _S of the joint stress material and the joint strength P is ) And (2) are satisfied,

And the bend radius r of the curved portion of the lap joint is 2φ to 8φ,
Reinforcing bar diameter to be placed on the curved part of the lap joint is 0.5φ or more,
The joint length of the lap joint is 1φ to 13.4φ,
Stress material diameter φ is 16 to 35 mm,
It is designed to have a concrete compressive strength of 16 to 40 N / mm ² .

  In the present invention, the joint strength of the lap joint of the stress material in the closed shape is formulated, and the joint strength is designed to be larger than the yield strength of the stress material used for the joint, so that the workability and the economic efficiency are remarkably improved. Is possible.

Hereinafter, embodiments of the present invention will be described. In the following, description will be made taking a reinforcing bar as an example of a stress material.
FIG. 1 is a view for explaining an arrangement configuration of reinforcing bars (stress materials) of a lap joint of the present invention.
One joint rebar 3 in a closed shape that forms a lap joint for joining concrete members (reinforced concrete members, steel concrete members, steel reinforced concrete members, steel grain concrete members, concrete members, steel members) is a tensile force acting on the concrete members The other reinforcing bar 4 of the closed shape which consists of the reinforcing bars 3a and 3e of the force direction, the reinforcing bar 3c of the direction orthogonal to this, and the curved part 3b and 3d which connect these linear parts, and comprises a lap joint. Consists of straight reinforcing bars 4a and 4e in the direction of tensile force acting on the concrete member, straight reinforcing bars 4c in the direction perpendicular to the reinforcing bars 4b, and curved bars 4b and 4d connecting these straight portions. When the reinforcing bar (rebar, round steel, etc.) 5 is arranged in the direction perpendicular to the direction in which the joint reinforcing bar extends in the curved portion of each joint reinforcing bar, the reinforcing bar 5 is in contact with or not in contact with the reinforcing bar of the lap joint. Both are possible. The joint length H is the overlapping length of the reinforcing bars that do not include the curved portion of the reinforcing bars (the distance between the curved portions). Note that the joint reinforcing bar 3 and the joint reinforcing bar 4 may be in contact with each other or separated from each other, and in this case, may be separated in the vertical direction. A concrete member or the like is joined by placing concrete in the lap joint. When a bending moment acts on the lap joint, a tensile force in the direction of the arrow shown in the figure acts on the joint rebar, and a joint yield strength is required to resist this.

  Generally, the proof strength of a lap joint is composed of the fixing force of a curved part that has been bent (the degree of fixation of the reinforcing part of the curved part in the concrete) and the fixing force of the straight part (the adhesion force between the reinforcing bar and the concrete). The joint yield strength is calculated by the following equations (1) and (2).

That is, the joint yield strength P [N] is a reinforcing bar (stress material) diameter φ [mm], a curved portion bending radius r [mm], a concrete compressive strength f ′ _C [N / mm ² ], and a joint length H [mm]. It is obtained by the function form equation (1) as a variable, and is determined by the fixing force of the curved portion and the joint length. When the cross-sectional area A _{S of} the reinforcing bar (stress material) used for the joint and the yield strength of the reinforcing bar (stress material) used for the joint is σ _S , the joint yield per unit area (P / A _S) ) Is made larger than the yield strength (σ _S ) of the reinforcing bar (stress material) so that the joint is not broken before the yielding of the reinforcing bar. The fixing force of the curved portion is determined by the bending radius, the diameter of the reinforcing bar (stress material) used for the joint, the reinforcing bar diameter, and the concrete compressive strength. As will be described later, the reinforcing bar diameter is 0.5 of the joint reinforcing bar diameter. Since the same reinforcing effect can be obtained if it is twice or more, the reinforcing rod diameter is not included as a factor in equation (1).

FIG. 2 is a diagram illustrating an example of a beam-shaped test body used when the equation (1) is derived.
Equation (1) is the joint proof strength derived from the load at the time of failure in an experiment in which a lap joint is installed in the center of a beam-shaped specimen and loaded at two points on the joint. A list of specimens used in this experiment is shown.

  The test body 10 in the example of FIG. 2 is supported by fulcrum points 12 and 13 having an interval of 3000 mm with the lap joint portion 11 as the center A, and loading positions 14 and 15 at positions 500 mm (interval of 1000 mm) on both sides from the center A, respectively. A bending moment is applied to the lap joint, and a tensile force is applied to the joint rebar. In the example shown in the figure, the joint length is set to 1 time (= 1φ) of the reinforcing bar diameter φ.

As shown in Table 1, No1 to No10 were used as test specimens. The span L in Table 1 is the distance between the fulcrum, the arm is the distance between the loading point and the fulcrum, the main reinforcing bar is the joint reinforcing bar diameter and joint reinforcing bar cross section, the reinforcing bar is the reinforcing bar diameter and its cross sectional area, and the concrete compressive strength is In the range of 20.6 to 25.0 [N / mm ² ], the joint yield strength [kN] per one is the calculated value and the experimental value, and the joint length is the actual length and the length expressed as an integral multiple of the reinforcing bar diameter φ. The joint corners indicate the bending radius and the length of the bending part, respectively. In Table 1, it can be seen that the joint yield per one obtained by calculation in Formula 1 for the joint length 1φ and the joint yield per one obtained in the experiment are almost the same. In the case of the joint length 2φ, the stress material (rebar) yielded before the joint breakage, so the yield strength obtained by the calculation of Equation 1 exceeded the joint yield strength obtained by experiment. ing.

FIG. 3 is a schematic diagram of a tensile test for obtaining a bending radius of a curved portion, and FIG. 4 is a diagram showing a tensile test result. This test is for quantitatively evaluating the influence of r / φ in the equation (1).
In a tensile test using a test body made of a concrete structure having a length L, a height H, and a width W, one end of one joint rebar is fixed to the surface of the test body with a fixture 16, After passing through the horizontal portion 17 and the bending portion 18, the vertical portion 19 measures the proof strength of the bending portion from the maximum tensile load at that time by pulling the reinforcing bar upward with a jack so that there is no adhesion with concrete. Yes, this test is performed by changing the bending radius.

When the maximum tensile load with respect to (bending radius r) / (rebar diameter φ) was obtained for test bodies No1, No2, and No3, the results shown in FIG. 4 were obtained. The maximum tensile load is a value normalized by dividing by the concrete compressive strength and multiplying by 24 N / mm ² . From FIG. 4, it is desirable that the maximum bending radius is 8φ because the fixing force tends to be saturated even if the bending radius is larger than 8φ. In addition, if the bending radius is reduced, the strength of the stress material is reduced due to the bending, so the bending radius of the joint reinforcing bar must be 2φ or more. Therefore, it is desirable that the bending radius of the joint reinforcing bar is 2φ to 8φ.

FIG. 5 shows the relationship between joint strength per reinforcing bar diameter / joint reinforcing bar diameter from specimens No. 3, No. 5, and No. 6. FIG.
It can be seen that if the diameter of the reinforcing rod arranged in the bent portion is 0.5 times (= 0.5φ) or more of the joint reinforcing bar diameter, a predetermined reinforcing effect can be obtained. If the diameter is 0.5φ or less, the reinforcing effect varies greatly. If the diameter is 0.5φ or more, the same reinforcing effect can be obtained. Therefore, the diameter of the reinforcing rod is not included in the equation (1).

  FIG. 6 is a schematic diagram of a test piece of an element test of a curved portion, Table 2 is a list of element tests of the curved portion, and FIG. . This element test is for quantitatively evaluating the influence of H / φ in the equation (1).

The influence of the joint yield strength according to the joint length was confirmed by an element test on the curved portion shown in FIG. In this element test, reinforcing bars 21 simulating the reinforcing bars of the curved part of the lap joint are placed above and below the concrete block 20 (the distance H between the reinforcing bar centers corresponds to the joint length). The length was the same (120 mm in this example), and the reinforcing bars were placed and fixed in such a way that they were embedded halfway into the surface of the concrete block when the specimen was manufactured, and concrete was cast. In order to apply a load evenly to this reinforcing bar, a loading beam with sufficient rigidity is used, the loading load is transmitted to the loading plate, hard rubber is sandwiched between the loading plate and the reinforcing bar, and the local contact is corrected. The load was applied and the joint strength was evaluated from the maximum load.

In FIG. 7, the horizontal axis represents the specimen height (joint length) H / φ, and the vertical axis represents 24 N / mm ² after dividing the maximum loading load (joint curve portion proof stress) per joint rebar by the concrete compressive strength. To normalize and compensate for variations in loading force due to concrete strength. Test specimens Nos. 1 to 4 had no reinforcing reinforcing bars, and specimens Nos. 5 to 10 had reinforcing reinforcing bars, and determined the maximum load per specimen with respect to the specimen height (joint length) H / φ. As shown in Table 2, Nos. 5 to 7 in the figure are the case where two reinforcing bar diameters D25 are arranged above and below the concrete block, and Nos. 8 to 10 are the case where four reinforcing bar diameters D25 are arranged above and below the concrete block. is there.

From this test result, it can be seen that when the specimen height (joint length) is 13.4φ or more, the maximum loading load does not change with or without the reinforcing bars, and the specimen height is in the range of 4 to 13.4φ. The tendency to reduce the maximum loading load due to the shortening of the joint length by arranging the reinforcing reinforcing bars is small. Here, 4φ or less is not shown, but the proof stress can be confirmed also in the case of 1φ and 2φ from the test result of FIG. 2 (Table 1). That is, it was confirmed that the relationship between the joint length and the joint yield strength P is P = P ₀ (1-1 / 1.4exp (H / φ)) in the range of the joint length 1φ to 13.4φ. Here, P ₀ is a convergence value when the joint length is infinitely long. Thus, the joint length is desirably 1φ to 13.4φ, the joint length is in the range of 1φ to 13.4φ, and when the joint length increases, the yield strength of the joint improves. Since there is no problem with the proof stress, it may be either in contact or separated. Thus, the joint yield strength increases corresponding to the size of the joint length (the distance between the curved portions), but the distance between the curved portions between the pair of opposing joints (the distance in the parallel direction or the vertical direction) increases. However, the joint strength is increased.

The yield strength of the joint of the present invention is determined by the fixing force of the curved portion, and the form at the time of failure is a bearing failure. Formula (1) is based on the calculation formula of bearing strength (product of concrete bearing strength characteristic value (concrete compressive strength function) and bearing receiving area (function of stress material diameter)). The concrete compressive strength can be applied within the range of the concrete compressive strength to which the calculation formula of the compressive strength can be applied. Therefore, the concrete compressive strength applicable in the present invention is 16 to 40 N / mm ² applied to a general concrete structure. It is.

  According to the present invention, since the joint yield strength of a lap joint of a stress material having a closed shape can be formulated, the workability and the economic efficiency can be remarkably improved, and thus the industrial utility value is great.

It is a figure explaining the arrangement configuration of the reinforcing bar of a lap joint. It is a figure which shows the example of the beam-shaped test body used when calculating | requiring Formula 1. FIG. It is a schematic diagram of a tensile test for obtaining a bending radius of a curved portion. It is a figure which shows a tension test result. It is a figure which shows the relationship of a joint reinforcement strength per reinforcement bar diameter / joint bar diameter pair. It is a test body schematic diagram of the element test of a curve part. It is a figure which shows the relationship between joint length and the maximum load per joint. It is a figure explaining the conventional lap joint.

Explanation of symbols

3, 4 ... Reinforcing bars, 5 ... Reinforcing bars, H ... Joint length.

Claims (2)

In a lap joint that places a pair of closed stress materials consisting of a straight part and a curved part facing a joint part such as a concrete member, and places concrete in the joint part to join the concrete member,
The relationship between the stress material diameter φ, the bending radius r of the curved portion, the concrete compressive strength f ′ _C , the joint length H, the cross-sectional area A _{S of} the joint stress material, the yield strength σ _S of the joint stress material and the joint strength P is ) And (2) are satisfied,

And the bend radius r of the curved portion of the lap joint is 2φ to 8φ,
Reinforcing bar diameter to be placed on the curved part of the lap joint is 0.5φ or more,
The joint length of the lap joint is 1φ to 13.4φ,
Stress material diameter φ is 16 to 35 mm,
A lap joint for joining concrete members or the like, characterized in that the concrete compressive strength is 16 to 40 N / mm ² . In a design method of a lap joint in which a pair of stress materials closed to a joint part such as a concrete member are arranged to face each other, and concrete is placed in the joint part to join the concrete member,
The relationship between the stress material diameter φ, the bending radius r of the curved portion, the concrete compressive strength f ′ _C , the joint length H, the cross-sectional area A _{S of} the joint stress material, the yield strength σ _S of the joint stress material and the joint strength P is ) And (2) are satisfied,

And the bend radius r of the curved portion of the lap joint is 2φ to 8φ,
Reinforcing bar diameter to be placed on the curved part of the lap joint is 0.5φ or more,
The joint length of the lap joint is 1φ to 13.4φ,
Stress material diameter φ is 16 to 35 mm,
A method for designing a lap joint for joining concrete members or the like, wherein the concrete compressive strength is designed to be 16 to 40 N / mm ² .

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