JP6267905B2 - Calculation method for bending strength of flat beams - Google Patents

Description

The present invention relates to a bending strength calculating how flat beams, flat to properly calculate the flexural strength corresponding to the actual stress state of the column outside of the flat beam, based on it, to allow a reasonable beam design about the beams of the bending strength calculation how.

  Conventionally, in order to secure a predetermined bending strength, beams used for reinforced concrete buildings have been made to increase the beam length or increase the amount of reinforcing bars. In this case, since the normal beam width is set narrower than the column width, the number of bars arranged within the beam width is limited. On the other hand, there is a method of increasing the beam length, but the indoor space under the beam is narrowed, and it is necessary to increase the height of the building to secure the space under the beam. In order to solve such a problem, for example, in a reinforced concrete apartment house, flat beams are used for the beams located on the opening side of a balcony or the like in order to reduce the height of the building and effectively use the floor height. Proposals have been made (Patent Document 1, Patent Document 2).

JP 2003-82869 A JP, 2007-107367, A Since flat beams have a beam width wider than a column width and less than that of a column, the resistance behavior and the proof strength of a beam with respect to external forces (bending moment, shearing force) acting on a column beam connection portion have been reduced. It is recognized that the beam is different from the beam of the beam-column joint, and the conventional design method for the beam-column joint cannot be applied as it is. Studies for elucidating the behavior of flat beams at the column beam joints of flat beams with many unclear points are also in progress (Non-patent Documents 1 and 2). According to the research of Non-Patent Document 1, it is said that the ratio of the main bars located outside the column width among the main bars of the flat beam decreases as the distance from the column decreases. According to the research of Non-Patent Document 2, it is said that if the beam width of a flat beam is about twice the column width, it will show the bending strength as a beam, and if the concrete restraint of the beam near the column is strengthened, it will show good properties. Yes.

Bessho Sato, Matsuzaki Ikuhiro, et al., “Horizontal Loading Experiments on Wide Beam / Column Joints (Part 1 Outline of Experimental Results, Part 2 Examination of Experimental Results)”, Architectural Institute of Japan Annual Meeting Abstracts, pp.445-448 October 1988 Yashiro Nishimura, Katsumi Higuchi et al., “Development Research on Reinforced Concrete Flat Beam Construction”, Architectural Institute of Japan, 616, pp. 179-186, June 2007

  By the way, as described in each non-patent document, in the present situation where the design method has not been established, each designer has advanced the design of the bending strength calculation method of the flat beam by the original design method. As an example, it is assumed that the beam main bars from the column to a predetermined range (for example, column width C × n times) contribute to the bending strength with reference to the column width C, and the beam main bars included in the range are uniform. The bending strength was calculated assuming that the degree of stress was borne.

  Conventionally, it is important to accurately calculate the bending strength of a beam in order to calculate the retained horizontal strength and to guarantee the design against shear, and it is dangerous to perform empirical design as described above in the design of flat beams. There was a problem that it was a side design or, on the contrary, an uneconomical design that required more than necessary reinforcement.

  In addition, in the conventional beam design, in order to make all the main bars of the beam contribute to the bending strength, the beam outside the column width has sufficient torsional rigidity, and the main bars arranged in a row in the beam yield simultaneously. However, in the experiments conducted by the inventors, it has been confirmed that the main bars in the flat beams yield sequentially from the side close to the column. For this reason, if it is designed on the assumption that beam main bars arranged in a row over the entire width of a flat beam having a large beam width yield at the same time, the proof stress of the member will be overestimated. Therefore, in order to yield the main beam of the beam at the same time, limit the length of the flat beam protruding from the column (beam width), or arrange many torsion reinforcement bars that penetrate the beam and column in the direction perpendicular to the material axis. Therefore, a design that increases the torsional rigidity of the beam was necessary.

  From experiments conducted by the inventors, it was confirmed that the degree of stress borne by the beam main bars decreases as the distance from the column increases. That is, as the flat beam becomes wider, the torsional deformation of the column becomes larger. It has been confirmed that the stress burden is reduced in the reinforcing bars located away from the column due to this torsional deformation.

Here, the beam deformation behavior causing the stress state of the beam main reinforcement of the flat beam considered by the inventor will be described with reference to FIGS. As shown in FIG. 4, in the column beam joint 1 of the flat beam 20 having a beam width wider than the column width of the column 10, when a bending moment M as shown by an arrow acts, The beam 20 includes a beam portion 20A integrated with the column 10 (indicated as a beam (inside the column) in the drawing) and a beam portion 20B projecting on both sides of the column (indicated as a beam (outside of the column) in the drawing). The deformation behavior is different. That is, as schematically shown in cross section in FIG. 5, in the beam (inside the column) 20A, the root portion of the flat beam 20 is integrated with the column 10, so that the bending of the beam (inside the column) 20A The behavior (the amount of deflection _i δ _B at a predetermined position from the column end) is the same as that of the conventional beam. For this reason, the beam tension main bar contributes to all the bending strengths (Fig.5 (a)). On the other hand, in the beam (outside the column) 20B, when a bending external force is applied, the beam portion projecting from both sides from the column 10 is twisted, and thereafter a bending moment is borne as the beam. Therefore, the deflection amount at a predetermined position from the column end is the deflection _o deflection caused by bending [delta] _t and the beam _o [delta] a sum of _{B (o δ t + o δ} B = i δ B) caused by the torsion. For this reason, appropriately evaluating the bending behavior of the flat beam 20 leads to economic design. In FIG. 5, the bending shape of the flat beam 20 is schematically drawn as a straight line for explanation.

Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, evaluate the bending strength of the flat beam in consideration of the stress state suitable for the behavior of the flat beam, and to obtain the bending strength by a rational method. to provide a bending strength calculating how the squamous beam to be able to calculate.

In order to achieve the above object, a bending strength calculation method according to the present invention is a method for calculating a bending strength of a flat beam at a column beam joint where a flat beam is bonded to a column. By reducing the material strength or the main reinforcement amount of the tensile reinforcement bar arranged outside the column width with respect to the total tensile reinforcement amount, the bending strength of the flat beam positioned outside the column width is determined from the portion within the column width. The flat beam is designed to be lowered.

A method for calculating the bending strength of the flat beam in a column beam joint where the flat beam is bonded to a column, the tension being arranged outside the column width with respect to the total tension main bar amount of the flat beam The flat beam is designed by reducing the strength of the main bar or the amount of the main bar, and lowering the bending rigidity of the flat beam located outside the column width from the portion within the column width .

In the bending strength calculation method to reduce the bending strength of the beam, the reduction function β
β = {A-B · ( Σa to / ΣBa t)} <1
Here, 1.0 ≦ A ≦ 1.05, 0.05 <B <0.25
It is preferable to reduce the bending strength by multiplying.

It is preferable to make the diameter of the main bar arranged outside the column width smaller than the diameter of the main bar arranged within the column width of the flat beam.

  According to the present invention, by evaluating the beam strength so as to reduce the bending strength according to the ratio of the amount of the main beam bars arranged outside the column width that affects the torsional deformation, Thus, it is possible to calculate the bending strength, and it is possible to realize a rational design that does not require both the limitation of the width of the flat beam and the excessive torsional reinforcement, which are the conventional problems.

The schematic explanatory drawing which showed the column beam joint part of the flat beam used as the object which performs the bar arrangement by the bending strength calculation method of the flat beam of this invention. The beam schematic cross section which showed one Embodiment of the bar arrangement structure by the bending strength calculation method of the flat beam of this invention. The relationship graph which showed the relationship between the calculation formula in the bending strength calculation method of the flat beam of this invention, and an experimental value. The model figure for showing the deformation behavior in the column beam junction of a flat beam. The model figure which showed typically the bending behavior in each beam (inside a column) and (outside a column) of the flat beam shown in FIG.

ここに、
Ｍy：梁の曲げ耐力、β：低減関数（≦１）、
σy：梁主筋の材料強度、d：梁の有効せい、
Σ_Bａ_t：引張側の全梁主筋の断面積、
Σａ_to：柱の外側に配される引張側の梁主筋の断面積
本実施形態では、実験結果より、Ａ＝１．０５、Ｂ＝０．２５として、扁平梁の算定式を求めた。なお、（式１）は、従来、設計に適用されている梁の曲げ耐力算定式
Ｍy＝Σ_Bａ_t・σy・d …（式２）
に、扁平梁の形状による影響を考慮した低減係数βを乗じて作成したものである。 Hereinafter, the basic structure of the flat beam bending strength calculation method and the flat bar arrangement structure of the present invention will be described with reference to FIGS.
[Proposal of a formula for calculating the strength of flat beams at column beam connections]
The inventor, in the test specimen of the beam-to-column connection part of the flat beam shown in FIG. 1, the schematic cross-sectional view shown in FIG. 2 beam reinforcement (inside the column), bar arrangement ratio in the beam reinforcement (outside the column), orthogonal principal reinforcement A bending strength test of a flat beam with a plurality of test specimens was performed with or without (twist reinforcement) as a factor. Based on the results, we propose a formula for calculating the proof strength of flat beams shown in FIG.
According to this calculation formula, it is possible to reflect the behavior in which the bending strength of the beam is lowered depending on the ratio of the beam main bars arranged outside the column. Hereinafter, (Equation 1) is proposed in which the reduction start point and the reduction rate are taken into account by the reduction function β.

here,
My: bending strength of beam, β: reduction function (≦ 1),
σy: material strength of beam main bar, d: effective beam effect,
Σ _B a _t: tensile side of the cross-sectional area of the entire beam main reinforcement,
Σa _to : Cross-sectional area of the main beam on the tension side arranged outside the column In this embodiment, the calculation formula of the flat beam was obtained from the experimental results with A = 1.05 and B = 0.25. Incidentally, (Equation 1) is conventionally bending strength calculation formula of the beam that is applied to the design _{My = Σ B a t · σy} · d ... ( Equation 2)
Is multiplied by a reduction factor β that takes into account the influence of the shape of the flat beam.

FIG. 3 is a relationship graph showing the relationship between the above calculation formula and the bending strength test result of the flat beam. As shown in the figure, according to the ratio of the outer main bars cross-sectional area to the total sectional area of the beam main reinforcement _{(Σa to / Σ B a t} ) is increased, the behavior of the beam bending strength is lowered Formula 1 cover I can read that

[Proposal of reinforcement structure of flat beam at column beam joint]
FIG. 2 is a reinforcing bar cross-sectional view schematically showing the bar arrangement structure in the beam-column joint 1 of the flat beam 20 divided by parts. As can be seen from the above-described calculation formula (Formula 1), if the method of reducing the effect of the main bars outside the column 10 is calculated, the ability of the reinforcing bars will not be sufficiently exhibited. Therefore, in the present invention, the material strength (σ _yo ) of the beam main bars 30 arranged on the outer side of the column that contributes to the bending strength is reduced, and the material strength (σ _yi ) of the beam main bars 31 arranged in the column. The lower cross-sectional area (diameter) (a _to (φ _to )) of one beam reinforcing bar 30 on the outer side of the column is set _to a lower material. A bar arrangement structure at the column beam joint of a flat beam is proposed by making it smaller than a _ti (φ _ti ).
That is,
(Σ _yo ) <(σ _yi ) or (a _to ) <(a _ti ) ((φ _to ) <(φ _ti ))
By doing so, a rational design that does not require a torsion reinforcing bar or the like becomes possible.

  In addition, this invention is not limited to the Example mentioned above, A various change within the range shown to each claim is possible. In other words, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

1 Beam-column joint 10 Column 20 Flat beams 30, 31 Beam reinforcement

Claims (4)

A method of calculating the bending strength of the flat beam at Column Joints flat beams are joined to the pillar, tensile main reinforcement that said is Haisuji outside the column width to the total tensile main reinforcement of flat beams The flat beam is designed by reducing the material strength or the amount of main reinforcement, and lowering the bending strength of the flat beam located outside the column width from the portion within the column width. Bending strength calculation method. A method of calculating the bending strength of the flat beam at Column Joints flat beams are joined to the pillar, tensile main reinforcement that said is Haisuji outside the column width to the total tensile main reinforcement of flat beams The flat beam is designed by reducing the material strength or the amount of main reinforcement, and lowering the bending rigidity of the flat beam located outside the column width from the portion within the column width. Bending strength calculation method. In the bending strength calculation method to reduce the bending strength of the beam, the reduction function β
β = {A-B · ( Σa to / ΣBa t)} <1
Here, 1.0 ≦ A ≦ 1.05, 0.05 <B <0.25
The bending strength calculation method for flat beams according to claim 1, wherein the bending strength is reduced by multiplying by. Flat beam according to claim 1 or claim 2, characterized in that to reduce the diameter of the main reinforcement that is Haisuji outside the pillar width than the diameter of the main reinforcement that is Haisuji to said post within the width of said flat beam Bending strength calculation method.

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