JP2017071912A - Joint structure for beam and column - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joint structure for a beam and a column, which enables the beam and the column to be suitably joined together by using a clearance lap joint for lapping a column joining reinforcement and a main reinforcement of a half PCa beam with a clearance therebetween.SOLUTION: In a structure A, a column joining reinforcement 10 laterally protruding from a column 6, and a main reinforcement 3 of a beam 1 are connected together by a clearance lap joint 5 for lapping them at a predetermined interval, and the beam 1 and the column 6 are joined together. The length L of the lap joint for the joining reinforcement 10 and the main reinforcement 3 is set equal to or greater than the necessary joint length Lof the clearance lap joint, which is calculated by a specific expression.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a joint structure between a beam and a column, and more particularly, to a structure of a joint part between a half precast concrete (half PCa) beam and a pillar.

  Conventionally, it has many advantages, such as shortening the construction period, improving safety, improving quality, and eventually reducing costs. Therefore, it is assumed that the beams and pillars of concrete buildings have been pre-manufactured in factories, etc., and these are on-site. Assemble and build a building.

  In addition, as a method of joining a PCa beam and a column (joint structure), for example, a reinforcing bar for joining is provided on the side surface of the column or a side end surface (joining end) of the beam to be joined to the side surface of the column. In-situ concrete is placed between the side end surface of the beam and the side surface of the column, and the beam and the column are joined and integrated via these jointing reinforcing bars and the in-situ concrete.

  Further, the lower main bar and the lower side of the shear reinforcement bar are embedded in concrete to form a half PCa beam, and the lower reinforcing bar for connection (field reinforcement main bar) protruding from the column protrudes from the joint end face of the half PCa beam The upper main bar is arranged by connecting to the shear reinforcement bar that is exposed upward from the upper surface, and the upper reinforcing bar (joint bar) that protrudes from the column is superimposed on the upper main bar and protrudes from the column A construction method has been put into practical use, in which the connecting reinforcing bars and the main bars of the beams are connected by lap joints, and the concrete and PCa beams and columns are joined together by casting concrete on the joints between the half PCa beams and the columns. Yes.

  In addition, as disclosed in, for example, Patent Document 1, a construction method in which a connecting reinforcing bar protruding from a column and a main reinforcing bar of a half PCa beam are connected with an overlap joint that is overlapped with a gap is proposed and put into practical use. .

JP-A-11-81452

  On the other hand, as described above, the design method has been established for connecting the column reinforcing bars and the main bars of the half PCa beam with the lap joint, but the column connecting bars and the main bars of the half PCa beam are spaced apart. The design method of the construction method that connects with the overlapping lap joint is not well established.

  In view of the above circumstances, the present invention provides a beam and a column that can be suitably bonded to each other by using an overlap joint that overlaps the column reinforcing bars and the main bars of the half PCa beam with a space therebetween. An object is to provide a joint structure.

  In order to achieve the above object, the present invention provides the following means.

The beam-column joint structure of the present invention is a structure in which a beam and a column are joined by connecting a reinforcing bar that protrudes laterally from the column and a main bar of the beam with an overlap joint that overlaps at a predetermined interval. there are, lap joint length L of the said joining rebar main reinforcement, characterized in that it is set to be required coupling length L _d or more perforated lap joint calculated by the following formula (1) .

Here, L _p is the joint invalid length (mm). _fy is the yield strength (N / mm ² ) of the reinforcing bar, which is the standard point strength. a _s the cross-sectional area per one beam main reinforcement ^(mm 2), φ is the circumferential length per one beam main reinforcement (mm), τ _bmax is the adhesion strength of the beam main reinforcement (N / mm ^2).

The joint invalid length L _p is the following formula (2) when 1 ≦ R _b / R _e ≦ 2.5 × γ + 1, and the following formula (2.5 × γ + 1 <R _b / R _e Obtained by 3). When L _p > 1.5d, L _p = 1.5d.

a is the beam clear span length (mm), D is the total beam length (mm), and _Rd is the design target member angle (rad). R _e is ACI (American Concrete Institute) surrender deformation angle defined the criteria (rad). d is the effective length (mm) of the beam when the beam lower end is pulled. γ and β are influencing factors based on the shear span ratio (a / D), and are obtained by the following equations (4) and (5).

  According to the beam-column joint structure of the present invention, it is possible to realize a highly reliable beam-column joint structure by using an lap joint for which the design method has not been established. .

It is sectional drawing which shows the junction part structure of the beam and column which concerns on one Embodiment of this invention. It is the X1-X1 arrow view figure of FIG. It is the figure which illustrated the reinforcing bar stress distribution of the joint part of the junction structure of a beam and a column concerning one embodiment of the present invention. It is a conceptual diagram which shows the joint sliding proof stress of the junction part structure of the beam and column which concerns on one Embodiment of this invention. It is a X1-X1 arrow directional view of FIG. 4, and is a conceptual diagram which shows the joint sliding surface of the junction part structure of the beam and column which concerns on one Embodiment of this invention. It is a figure which shows the stress block method in ACI318. It is a figure which shows the relationship of ratio ( _Lp / d) with respect to the effective beam length of a joint invalid length. It is sectional drawing which shows the test body used in order to confirm the validity of the design method of the junction part structure of the beam and column which concerns on one Embodiment of this invention. It is a X1-X1 line arrow directional view of FIG. FIG. 9 is a view taken along line X2-X2 in FIG. It is the X3-X3 line arrow figure of FIG.

  Hereinafter, a beam-column joint structure according to an embodiment of the present invention will be described with reference to FIGS. 1 and 11. Here, this embodiment relates to a structure for joining a reinforced concrete (RC) column and a precast concrete beam (PCa beam).

  First, the PCa beam 1 according to the present embodiment is a U-shaped half PCa beam as shown in FIGS. 1 and 2, and the central portion in the width direction on the side of the axis O1 direction side is recessed from the upper end to the lower end. A U-shaped section is formed by providing a concrete placement space (site-cast concrete portion) 2 for placing the cast-in-place concrete.

  The half PCa beam 1 is formed such that the concrete placement space 2 is recessed from the upper end to the lower side than the center of the beam (the center in the height direction).

  Thereby, the lower main reinforcement 3 of the half PCa beam 1 is embedded in the concrete of the half PCa. Further, the half reinforcement plate 4 is embedded in the concrete so that the lower end side is embedded in the concrete, and the upper end side is protruded upward from the central portion in the axis O1 direction of the half PCa beam 1 and the upper surface of the concrete placing space 2. Is formed.

  The cover thickness between the upper surface of the concrete placement space 2 of the half PCa beam 1 and the lower main reinforcing bar 3 is set so as to ensure a predetermined interval of the lap joint 5 described later. Moreover, the thickness of the half PCa of the U-shaped part which forms the concrete placement space 2 is about 80 mm.

  On the other hand, the column 6 of this embodiment is a PCa column or an RC column, and a joining end face (column face) for joining the half PCa beam 1 while embedding the joining lower rebar 10 (or the joining upper rebar) integrally in concrete. Part) is formed so as to project laterally from 6a.

  In the beam-column joint structure A of the present embodiment, the upper reinforcing bar 7 for connection protruding from the column 6 is the upper main bar of the half PCa beam 1, and the shear reinforcement bar protruding upward from the upper surface of the half PCa beam 1 is used. 4 is connected to the upper end side. Further, the cap bar 8 is arranged so as to surround the upper main bar 7 together with the shear reinforcement bar 4.

  Further, a joining lower reinforcing bar 10 projecting from the column 6 is arranged close to the upper surface of the concrete placement space 2 of the half PCa beam 1 and has a predetermined interval above the lower main reinforcing bar 3 of the half PCa beam 1 embedded in the concrete. Arranged.

  Then, the half PCa beam 1 and the column 6 are joined by placing concrete so that the shear reinforcing bar 4, the upper main bar 7, and the cap bar 8 are embedded in the concrete placing space 2 and the half PCa.

  As described above, in the beam-to-column joint structure A of the present embodiment in which the half PCa beam 1 and the column 6 are joined, the joining lower reinforcing bar 10 protruding from the column 6 and the lower main reinforcing bar 3 of the half PCa beam 1 are separated by a predetermined distance. A joint portion connecting the lower reinforcing bar 10 for joining and the lower main reinforcing bar 3 is formed as a lap joint 5.

  Here, a design method in the case where the joint portion between the lower reinforcing bar 10 for bonding protruding from the column 6 and the lower main reinforcing bar 3 of the half PCa beam 1 as described above is used as the lap joint 5 will be described.

(Calculation for bending moment)
First, the calculation for the bending moment of the beam-column joint structure of the present embodiment is performed based on the following 1-1) and 1-2).

1-1) Based on the Japan Society for Architectural Architects "Reinforced Concrete Structure Calculation Standards / Comment: 2010 Edition" (hereinafter referred to as RC Standard) or ACI318, the stress level in the cross section is calculated, and the allowable bending moment or ultimate bending is calculated. Seek strength. In addition, you may make it obtain | require based on the reference | standard criteria applied in the said country or the said area.
1-2) The minimum principal bar amount of the beam follows the provisions of the applicable design criteria.

(Calculation for shear)
Next, the calculation for the shear of the joint structure between the beam and the column of the present embodiment is performed based on the following 2-1), 2-2), and 2-3).

2-1) Obtain allowable shear force or ultimate shear strength based on RC standard or ACI318. It may be based on standards applied in the country or region.
2-2) The minimum shear reinforcement ratio is in accordance with the provisions of the applicable design criteria.
2-3) Shear is calculated at the U-shaped fore edge (concrete placement part) and the end of the joint.

(Design of lap joint)
And the lap joint of the junction structure of the beam and the column of this embodiment is designed by the following procedures 3-1) to 3-5).

3-1) A design target maximum deformation angle _Rd is determined.
3-2) calculates the required joint length _{L d.}
3-3) Calculate the required lateral reinforcing _bar amount p _wd of the joint.
3-4) Confirm the conformity of the lap joint length L to the ACI standard.
3-5) Design a shear other than the joint.

  In this design method, the beam critical cross section is the column face portion, and the stress distribution of the joint rebar is assumed to have a shape as shown in FIG. Further, it is the friction properties of the joint interface of the joint and the dowel shear strength of the lateral reinforcing bars that contribute to the joint sliding strength, and the setting of the joint sliding surface is as shown in FIGS.

(Design target maximum deformation angle _Rd setting)
Design goal member angle R _d of the case of providing the lap joint to yield a hinge portion of the beam end, as shown in equation (6), is chosen to be less critical drift angle R _x based on the ACI Standards.
Further, R _x is obtained by equation (7), and _Re is obtained by equation (8). Furthermore, when providing a lap joint other than a yield hinge part, it is set as _Rd = _Re .

Here, R _x is a critical deformation angle (rad). C _d is the plastic magnification, and is according to Table 1 below.

Further, φ · M _n is a design bending ultimate strength (N · mm) at the time of lower end tension of the beam, and is obtained by the following equations (9) and (10) based on the stress block method shown in FIG.

Further, _Lb is a beam clear span length (mm). E _c is the Young's modulus (N / mm ² ) of concrete and is according to equation (11). Further, I _cr is a reduced cross-sectional second moment (mm ⁴ ) of the beam, and is according to the equation (12).

Further, f _c ′ is the design standard strength (N / mm ² ) of the cast-in-place concrete, and b is the beam width (mm). _Ig is the cross-sectional second moment (mm ⁴ ) of the beam.

(Calculation of required joint length L _d for perforated lap joint)
Next, describing calculation of required joint length L _d of the vacant lap joint.
In the present embodiment, the required joint length L _d of the lap joint portion is calculated by the equation (13), and the lap joint length L is ensured to be L _d or more.

Here, L _p is the joint invalid length (mm). _fy is the yield strength (N / mm ² ) of the reinforcing bar, which is the standard point strength. a _s the cross-sectional area per one beam main reinforcement ^(mm 2), φ is the circumferential length per one beam main reinforcement (mm), τ _bmax is the adhesion strength of the beam main reinforcement (N / mm ^2).

The joint invalid length L _p is the following equation (14) when 1 ≦ R _b / R _e ≦ 2.5 × γ + 1, and the following equation (15 when 2.5 × γ + 1 <R _b / R _e : 15 ) When L _p > 1.5d, L _p = 1.5d.

Here, a is the beam of Shiasupan (mm), D is the total blame the beam (mm), _{R d} is the design goals member angle (rad). R _e is a yield drift angle stipulated in ACI criterion (rad), obtained by the above equation (8). D is the effective length (mm) of the beam when the beam lower end is pulled. γ and β are influencing factors based on the shear span ratio (a / D), and are obtained by the following equations (16) and (17).

Table 2 shows a calculation example of the ratio of the joint invalid length to the effective beam length (L _p / d), and FIG. 7 shows the relationship of the ratio of the joint invalid length to the effective beam length (L _p / d). .

The _bond strength τ _bmax of the beam main reinforcement is calculated by the following equation (18). However, when √ (22 / d _b ) <1.0, √ (22 / d _b ) = 1.0.
Here, f _c ′ is the cylinder compressive strength (N / mm ² ) of the cast-in-place concrete, which is the design standard strength. d _b is the nominal diameter of the beam main reinforcement (mm).

(Calculation of necessary lateral reinforcing _bar amount p _wd )
The required lateral reinforcing _bar amount p _wd is calculated according to the following equation (19).
Here, α is 1.3 as a joint sliding margin. A _vf is the total cross-sectional area (mm ² ) of the beam bottom tensile reinforcement. _fy is the yield strength (N / mm ² ) of the beam main reinforcement, which is the standard point strength. μ is a coefficient of friction at the concrete joint interface, and 1.0 when treated with a striped steel plate. f _yt is the yield strength (N / mm ² ) of the lateral reinforcement, which is the standard point strength. B is the beam width (mm). L is a lap joint length (mm), ensuring requires joint length _{L d} or more.

(Conformity confirmation of lap joint length L to ACI standard)
Next, lap joint length L was set to be required coupling length L _d or higher, it will be described a result of the check that is required joint length L _d2 or more of the total number joint tensile by ACI criteria.

L _d2 is calculated by the following equation (20).
However, when (C _b + K _tr ) / + d _b > 2.5, (C _b + K _tr ) / + d _b = 2.5.

Here, _fy is the yield strength (N / mm ² ) of the beam main reinforcement, which is the standard point strength. f _c ′ is the cylinder compressive strength (N / mm ² ) of cast-in-place concrete and is the design reference strength. d _b is the nominal diameter of the beam main reinforcement (mm), λ is set to 1.0 in the usual concrete coefficient by the concrete type.

φ _s is a safety factor, and is 1.0 when a reinforcing bar diameter: D22 or more is used, and 0.7 otherwise. C _b is a minimum of one-half of the distance C _b1, the distance C _b2 to bottom edge than rebar _core, rebar arrangement direction of the reinforcing bar center distance C _b3 to side edge than the reinforcement core (mm) .

K _tr is a coefficient related to the lateral reinforcing _{bars, and} is according to the following equation (21).
A _tr is a set of transverse reinforcing bar cross-sectional areas (mm ² ), S is the lateral reinforcing bar pitch (mm), and N is the number of beam main bars (the number) restrained by the lateral reinforcing bars.

(Shear design other than joints)
Next, the parts other than the joint part (ordinary part) are designed so that the beam shear strength V _u exceeds the designed maximum beam shear force V _pr as shown in Expression (22).

Here, V _u is the beam shear strength of the normal part, and is according to equation (23). V _pr is the assumed maximum beam shear force for designing the normal part, and is according to equation (24). Note that V _C = 0 because V _E > (V _D + V _E ) / 2.

Φ ₁ is a reduction coefficient, which is 0.75. V _S is the shear strength of the beam, according to equation (25). M _pr is the assumed maximum bending moment of the beam and is according to equation (26). l _b is the clear span of the beam.

Furthermore, A _tr is the cross-sectional area (mm ² ) of one set of lateral reinforcing bars. f _yt is the yield strength (N / mm ² ) of the lateral reinforcing _{bars and} is the standard point strength. d is the effective beam length (mm), and s is the lateral reinforcing bar pitch (mm). phi ₂ is reduction factor, and 1.0. A _s is the total cross-sectional area of the beam tensile reinforcement ^(mm 2), _{f y} is the standard point strength at yield strength of the beam main reinforcement (N / mm ^2). a _st is the stress block length (mm) of the concrete, f _c ′ is the design reference strength (N / mm ² ) of the cast-in-place concrete, b is the beam width (mm), and is given by equation (27).

The above design method is applied under the following conditions (4-1) to 4-11) (see FIG. 1).
4-1) Fixing section to pillar The beam lower main bar of the beam and the diameter, number and material of the beam main bar in PCa are the same.
4-2) The main lower end of the PCa end portion is a single streak.
4-3) The design of the upper main reinforcement follows the provisions of the applicable design criteria.
4-4) The minimum joint length is 40 times or more of the main muscle diameter.
4-5) The joint length is determined in consideration of construction errors as well as the length necessary for calculation.
4-6) When the structural form is IMF (Intermediate Moment Frame), the diameter of the lateral reinforcing bar of Zone A is 10 mm or more, and the interval is 200 mm or less. Zone B lateral reinforcement follows the applicable design criteria.
4-7) When the structural type is SMF (Special Moment Frame) and lap joints are provided in areas other than the plastic region, the provisions of ACI 21.5.2.2.3 (maximum spacing between lateral reinforcing bars is d / 4 or less and 100 mm or less) Follow.
4-8) The top wrap of the star wrap and the core is a 135-degree hook or a 180-degree hook having a surplus length of 6d or more.
4-9) The beam reinforcement should be 4/3 times the coarse aggregate diameter and not less than the main reinforcement diameter.
4-10) As a general rule, the concrete and the beam end of the column joint are cast simultaneously.
4-11) The interval between the lower reinforcing bar for joining projecting from the column and the lower main reinforcing bar of the half PCa beam is defined as 1/5 of the lap joint length and 150 mm or less.

  Next, the result of confirming the validity of the design method when using the above-described lap joint of the present embodiment will be described.

  Here, the test bodies shown in FIGS. 8 to 11 and Table 3 were used. Further, 4-D25 (SD390) is used as the beam main reinforcing bar, 2-D13 @ 90 (SD390) is used as the joint part, and 2-D13 @ 135 (SD390) is used as the normal part.

Table 4 shows the setting of the design target member angle R _d , Table 5 shows the calculation result of the required joint length L _d1 , and Table 6 shows the calculation result of the required lateral reinforcing _bar amount p _wd .

Table 7 shows the confirmation result of the lap joint length L> L _d2 (ACI), and Table 8 shows the confirmation result of the shear design other than the joint part. From these results, it was confirmed that the design using the lap joint was possible by using the design method of the present embodiment.

  Therefore, in the beam-column joint structure of the present embodiment, it is possible to realize a highly reliable beam-column joint structure by using the lap joint for which the design method has not been established conventionally. become.

  As mentioned above, although one Embodiment of the junction structure of the beam and the column which concerns on this invention was described, this invention is not limited to said one Embodiment, It can change suitably in the range which does not deviate from the meaning. .

DESCRIPTION OF SYMBOLS 1 Half PCa beam 2 Concrete placement space 3 Lower main reinforcement 4 Shear reinforcement 5 Perforated lap joint 6 Column 6a Column face part 7 Upper main reinforcement 8 Cap reinforcement 10 Joint lower reinforcement A Beam-column connection structure O1 Beam axis

Claims (1)

It is a structure that joins the beam and the column by connecting the reinforcing bars for projection protruding laterally from the column and the main bar of the beam with an lap joint that overlaps with a predetermined interval,
Lap joint length L of the said joining rebar main reinforcement are, beams and columns, characterized in that it is set to be required coupling length L _d or more perforated lap joint calculated by the following formula (1) Joint structure.

Here, L _p is the joint invalid length (mm). _fy is the yield strength (N / mm ² ) of the reinforcing bar, which is the standard point strength. a _s the cross-sectional area per one beam main reinforcement ^(mm 2), φ is the circumferential length per one beam main reinforcement (mm), τ _bmax is the adhesion strength of the beam main reinforcement (N / mm ^2).
The joint invalid length L _p is the following formula (2) when 1 ≦ R _b / R _e ≦ 2.5 × γ + 1, and the following formula (2.5 × γ + 1 <R _b / R _e Obtained by 3). When L _p > 1.5d, L _p = 1.5d.

a is the beam clear span (mm), D is the total beam length (mm), and _Rd is the design target member angle (rad). R _e is yield drift angle stipulated in ACI criterion (rad). d is the effective length (mm) of the beam when the beam lower end is pulled. γ and β are influencing factors based on the shear span ratio (a / D), and are obtained by the following equations (4) and (5).

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