JP2022007957A - Method for designing structure - Google Patents

Abstract

To provide a method for designing a structure equipped with a hybrid beam.SOLUTION: The ultimate strength qfr of a joint surface between a beam concrete and a slab concrete included in a hybrid beam is calculated according to the following expression, where μeq is the coefficient of friction of a joint surface, s aw is the sum of the cross-sectional areas of a plurality of intermediate lateral reinforcing bars, s σwy is the yield strength or reference strength of a plurality of lateral reinforcing bars 124, swaw is the sum of the cross-sectional areas of a plurality of insertion bars, sw σwy is the yield strength or reference strength of a plurality of insertion bars, Aaw is the sum of the cross-sectional areas of a plurality of beam center side concentrated lateral reinforcing bars, A σwy is the yield strength or reference strength of a plurality of beam center side concentrated lateral reinforcing bars, σ0 is the average external vertical stress generated in a reinforced concrete, b'is the effective width of the reinforced concrete at the position of a flange, and lc is the length of the reinforced concrete in the direction in which a steel frame 122 extends.SELECTED DRAWING: Figure 2

Description

One of the embodiments of the present invention relates to a structure and a method for designing the structure.

In recent years, in structures such as office buildings, hospitals, and commercial facilities that require a large indoor space, steel frames are used as beams connecting a pair of columns, and both ends of the steel frames are covered with reinforced concrete. Beams (mixed structure beams or hybrid beams) are used. By using a hybrid beam, the number of columns can be significantly reduced compared to the case where all the beams are constructed with reinforced concrete, and as a result, it is possible to design and build a structure with a large space (patented). See Document 1).

Japanese Unexamined Patent Publication No. 2013-170386

One of the objects of the embodiment of the present invention is to provide a structure provided with a hybrid beam, which can be constructed at a lower cost. Alternatively, one of the embodiments of the present invention is to provide a method for designing a structure including a hybrid beam.

One of the embodiments of the present invention is a method of designing a structure including a hybrid beam. The hybrid beam comprises a steel frame and reinforced concrete covering both ends of the steel frame. Reinforced concrete has a plurality of beam main bars, a plurality of lateral reinforcing bars, a plurality of barbs, a beam concrete, and a slab concrete. The plurality of beam main bars extend in the extending direction of the steel frame. The plurality of lateral reinforcing bars intersect the steel frame and the plurality of beam main bars, and surround the steel frame and the plurality of beam main bars. The plurality of inserts intersect the steel frame and the plurality of beam main bars, and surround the steel frame and a part of the plurality of beam main bars. Beam concrete embeds a part of a steel frame, a part of a plurality of beam main bars, a part of a plurality of lateral reinforcing bars, and a part of a plurality of reinforcing bars. The slab concrete is located on the beam concrete and is in contact with the beam concrete, the other part of the steel frame, the other part of the multiple beam main bars, the other part of the multiple lateral reinforcing bars, and the multiple barbs. Embed other parts. The plurality of lateral reinforcing bars are the plurality of beam end side concentrated lateral reinforcing bars arranged at the beam end side at the first density, and the plurality of beam center side concentrated lateral reinforcements arranged at the beam center side at the second density. Reinforcing bars, and multiple intermediate lateral reinforcements placed between the beam end-side concentrated lateral reinforcements and the beam center-side concentrated lateral reinforcements at a density lower than the first and second densities. It is composed of muscles. This design method does not consider the contribution of the beam end side concentrated lateral reinforcement, the contribution of multiple beam center side concentrated lateral reinforcements, multiple intermediate lateral reinforcements, and multiple inserts, as well as the beam concrete and the above. It includes calculating the ultimate strength of the joint surface in consideration of the vertical stress component applied to the joint surface between the slab concrete.

（１）
式（１）において、μ_ｅｑは接合面の等価摩擦係数であり、_ｓａ_ｗは複数の中間横補強筋の断面積の総和であり、_ｓσ_ｗｙは複数の横補強筋の降伏強度または基準強度（Ｆ値）であり、_ｓｗａ_ｗは複数の差し筋の断面積の総和であり、_ｓｗσ_ｗｙは複数の差し筋の降伏強度または基準強度（Ｆ値）であり、_Ａａ_ｗは複数の梁中央側集中横補強筋の断面積の総和であり、_Ａσ_ｗｙは複数の梁中央側集中横補強筋の降伏強度または基準強度（Ｆ値）であり、σ_０は鉄筋コンクリートに生じる平均外部鉛直応力であり、ｂ´はフランジの位置における鉄筋コンクリートの有効幅であり、ｌ_ｃは鉄骨が延伸する方向における鉄筋コンクリートの長さである。 One of the embodiments of the present invention is a method for designing a structure including a hybrid beam. The hybrid beam comprises a web and a steel frame having a pair of flanges connected to the web, and reinforced concrete covering both ends of the steel frame. Reinforced concrete has beam main bars, multiple lateral reinforcements, multiple barbs, beam concrete, and slab concrete. The beam main bar extends in the extending direction of the steel frame. The plurality of lateral reinforcing bars intersect the steel frame and the plurality of beam main bars, and surround the steel frame and the plurality of beam main bars. The plurality of inserts intersect the steel frame and the plurality of beam main bars, and surround the steel frame and a part of the plurality of beam main bars. Beam concrete embeds a part of a steel frame, a part of a plurality of beam main bars, a part of a plurality of lateral reinforcing bars, and a part of a plurality of reinforcing bars. The slab concrete is located on the beam concrete and is in contact with the beam concrete, the other part of the steel frame, the other part of the multiple beam main bars, the other part of the multiple lateral reinforcing bars, and the multiple barbs. Embed other parts. The plurality of lateral reinforcing bars are the plurality of beam end side concentrated lateral reinforcing bars arranged at the beam end side at the first density, and the plurality of beam center side concentrated lateral reinforcements arranged at the beam center side at the second density. From the reinforcing bars and from multiple intermediate lateral reinforcing bars placed between the beam end-side concentrated lateral reinforcement and the beam center-side concentrated lateral reinforcement at a density lower than the first density and the second density. It is composed. This design method includes calculating the ultimate strength q _fr of the joint surface between the beam concrete and the slab concrete according to the following equation (1).

(1)
In equation (1), μ _eq is the equivalent friction coefficient of the joint surface, _s a is the sum of the cross-sectional areas of the plurality of intermediate lateral reinforcing bars, and _s σ _wy is the yield strength or the reference of the plurality of lateral reinforcing _bars . It is the strength (F value), _sw a _w is the sum of the cross-sectional areas of a plurality of barbs, _sw σ _wy is the yield strength or the reference strength (F value) of a plurality of barbs, and _A a _w is a plurality. _A σ _wy is the yield strength or reference strength (F value) of multiple beam center-side concentrated lateral reinforcements, and σ ₀ is the average outside of the reinforced concrete. It is a vertical stress, b'is the effective width of the reinforced concrete at the position of the flange, and _lc is the length of the reinforced concrete in the direction in which the steel frame is stretched.

According to the embodiment of the present invention, the ultimate strength of the hybrid beam can be easily calculated, whereby the design of the structure including the hybrid beam can be performed more precisely.

The schematic perspective view of the structure which is one of the embodiments of this invention. The schematic side view which shows the appearance and the internal structure of the hybrid beam of the structure which is one of the embodiments of this invention. The schematic side view of the hybrid beam of the structure which is one of the embodiments of this invention. Schematic cross-sectional view of a hybrid beam of a structure which is one of the embodiments of the present invention. Schematic cross-sectional view of a hybrid beam of a structure which is one of the embodiments of the present invention. Schematic side view of the test piece used in the Example. Plot of lateral reinforcement strain strain relative to beam tip deformation angle of specimen. A plot of the slip displacement of the joint position with respect to the beam tip deformation angle of the specimen. Coefficient of friction between steel and slab concrete in each specimen.

Hereinafter, each embodiment of the present invention will be described with reference to the drawings and the like. However, the present invention can be carried out in various embodiments without departing from the gist thereof, and is not construed as being limited to the description contents of the embodiments exemplified below.

In order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc. of each part as compared with the actual embodiment, but the drawings are merely examples and limit the interpretation of the present invention. It's not something to do. In the present specification and each figure, elements having the same functions as those described with respect to the above-mentioned figures may be designated by the same reference numerals and duplicate description may be omitted. When noting a part of a coded element, the sign is accompanied by a lowercase alphabet. When noting multiple elements having the same or similar structure separately, a hyphen and a natural number are added after the sign. When expressing multiple elements having the same or similar structure together, only the code is used.

Hereinafter, the expression "a structure is exposed from another structure" means an aspect in which a part of one structure is not covered by another structure, and is not covered by another structure. The portion also includes an embodiment covered by yet another structure.

Hereinafter, concrete refers to concrete that does not show fluidity due to the hardening of the hydrate produced by the reaction of cement, which is one of the raw materials, with water, and the mixture containing cement and water does not completely harden. It is distinguished from the state with fluidity (ready-mixed concrete, ready-mixed concrete).

<First Embodiment>
Hereinafter, the structure of the structure 100, which is one of the embodiments of the present invention, will be described. In the drawings shown below, for convenience, the plane parallel to the horizontal ground surface is defined as the xy plane, and the vertical direction perpendicular to the xy plane is assumed to be the z direction.

1. 1. Overall structure A schematic perspective view of the structure 100 is shown in FIG. As shown in FIG. 1, the structure 100 has a plurality of columns 110 extending in the vertical direction (z direction), and a plurality of beams 120 connected to a pair of columns 110 and extending in the horizontal direction (x direction or y direction). And a floor slab 150 provided on the beam 120 is provided as a basic configuration. Each beam 120 is connected to a pair of adjacent columns 110.

At least one of the beams 120 provided in the structure 100 is a hybrid beam. All of the beams 120 provided in the structure 100 may be hybrid beams, or a part of the beams 120 are hybrid beams, and the other beams 120 are beams entirely made of reinforced concrete (reinforced concrete beams, hereinafter referred to as RC beams). (Note) may be used. For example, in the structure 100 shown in FIG. 1, the first beam 120-1 and the third beam 120-3 are hybrid beams, and the second beam 120-2 and the fourth beam 120-4 are RC beams. Is. Here, a pair of pillars 110 provided at long intervals (spans) (for example, a pair of the first pillar 110-1 and the second pillar 110-2, a third pillar 110-3 and a fourth pillar 110-4). A hybrid beam is used as the beam 120 connected to the pair of the fifth column 110-5 and the sixth column 110-6, and the pair of columns 110 provided at short intervals (for example, the first column 110). -1, the pair of the third pillar 110-3, the pair of the second pillar 110-2 and the fourth pillar 110-4, the pair of the third pillar 110-3 and the fifth pillar 110-5, the third RC beams are used for the pair of the 4th pillar 110-4 and the 6th pillar 110-6). Although the arrangement of the hybrid beam and the RC beam can be arbitrarily determined, it is preferable to use the hybrid beam between the pair of columns 110 provided at long intervals as in the example shown in FIG. This is because the hybrid beam is lighter than the RC beam, so by using the hybrid beam for the beam with a large span (here, the first beam 120-1, the third beam 120-3, etc.), a large interior space is created. This is because it is possible to impart sufficient strength to the structure 100 while ensuring the above.

2. 2. Pillars 2 (A) and 2 (B) show schematic side views of a pair of pillars 110 (first pillar 110-1, second pillar 110-2) and a beam 120 connected to the pair of pillars 110. In FIG. 2B, the concrete of the columns 110 and the beams 120 is shown by dotted lines to show the internal structure. Further, in FIGS. 2 (A) and 2 (B), the floor slab 150 is not shown.

As long as the number of columns 110 is 4 or more, there is no particular limitation, and the number and arrangement thereof may be appropriately determined according to the size and shape of the structure 100. The columns 110 are connected to piles and foundation beams (not shown). The shape of the pillar 110 (cross-sectional shape in the xy plane) is also arbitrary, and may be appropriately selected from a quadrangle, a circle, an ellipse, and the like. The length of the pillar 110 is also appropriately designed according to the size of the structure 100 and the height of each layer.

Each column 110 is provided with at least one column main bar 112 extending in the vertical direction, and a reinforcing bar unit including a plurality of band bars 114 which intersect with the column main bar 112 and are provided so as to surround the column main bar 112. Concrete 116 is placed so as to surround the unit (FIG. 2B). The number of column main bars 112 and the arrangement density of the band bars 114 are also appropriately determined by the length and thickness of the columns 110 and the required strength.

3. 3. Floor slab The floor slab 150 is reinforced concrete constituting the floor surface of each layer, and is provided on the beam 120 (FIG. 1). The floor slab 150 is provided on each floor. In addition, in FIG. 1, only a part of the floor slab 150 is shown in consideration of legibility. Although not shown, the floor slab 150 has a wooden plate or a metal deck plate forming the floor surface, or a plurality of reinforcing bars or reinforcing bar units called reinforcing bars trusses arranged in a mesh pattern on the plate material or the deck plate. , It is formed by placing concrete (slab concrete 128b described later) so as to embed this reinforcing bar unit.

4. Hybrid beam As shown in FIGS. 2A and 2B, the beam 120, which is a hybrid beam, has a steel frame 122 connected to a pair of columns 110 and reinforced concrete arranged at both ends of the steel frame 122. The portion where the reinforced concrete is arranged is called RC section 120a. On the other hand, since reinforced concrete is not provided between the two RC sections 120a, this portion is also called a steel frame section 120b. As will be described later, the reinforced concrete includes various reinforcing bars and concrete 128 covering both ends of the steel frame 122 and the reinforcing bars. The reinforced concrete arranged at both ends of the steel frame 122 is separated from each other, and the steel frame 122 is exposed between them, that is, in the steel frame section 120b.

The steel frame 122 contains iron, and its cross-sectional shape may be H-shaped, I-shaped, T-shaped, L-shaped, or the like. Typically, H steel having an H-shaped cross section can be used. When H steel is used, the steel frame 122 is arranged so that the upper surfaces of the two flanges extend horizontally. The steel frame 122 is provided so as not to invade the inside of the reinforcing bar unit of the column 110 constructed by the column main bar 112 and the band bar 114.

A schematic side view of one RC section 120a is shown in FIG. As shown in FIGS. 2B and 3, each RC section 120a is provided with reinforcing bars such as a plurality of beam main bars 126 and a plurality of lateral reinforcing bars 124, respectively. A fixing plate 126a having a larger cross-sectional area than the beam main bar 126 may be formed on the beam center side of each beam main bar 126 (FIG. 2B). A plurality of additional bars 125 may be further arranged in the RC section 120a section. The plurality of insertion bars 125 may be provided so as to be in contact with the plurality of lateral reinforcing bars 124. With these reinforcing bars, the beam main reinforcing bar 126 is firmly fixed to the reinforcing bar unit of the column 110. The steel frame 122 may be in contact with the column 110. More specifically, both ends of the steel frame 122 may be in contact with the strips 114 of the pair of columns 110, respectively, or may be in contact with the concrete 116 or may be embedded by the concrete 116.

The beam main bar 126 extends in a direction parallel to the longitudinal direction (horizontal direction) of the steel frame 122, and a part of the beam main bar 126 is inserted into the reinforcing bar unit of the column 110. The beam main bar 126 is arranged above and below the steel frame 122. The beam main bar 126 may be separated from or in contact with the steel frame 122.

The lateral reinforcing bar 124 intersects the steel frame 122 and the beam main bar 126. As shown in the schematic cross section (FIG. 4B) of the cross section along the chain line AA'in FIG. 3, the lateral reinforcing bar 124 is arranged so as to surround the outer periphery of the steel frame 122 and the beam main bar 126. The lateral reinforcing bar 124 may be arranged so as to surround all the beam main bars 126. Here, as shown in FIG. 3, the lateral reinforcing bars 124 are arranged at high density on the column 110 side (that is, the end side of the beam 120) and the central portion side of the beam 120. Hereinafter, the lateral reinforcing bars 124 arranged at high density on the column 110 side and the central portion side of the beam 120 are referred to as beam end side concentrated lateral reinforcing bars 124a and beam central side concentrated lateral reinforcing bars 124b, respectively. On the other hand, between the beam end side concentrated lateral reinforcing bar 124a and the beam center side concentrated lateral reinforcing bar 124b, the lateral reinforcing bar 124 is the beam end side concentrated lateral reinforcing bar 124a and the beam center side concentrated lateral reinforcing bar 124b. It is placed at a density lower than the placement density. The lateral reinforcing bars 124 arranged at this low density are hereinafter referred to as intermediate lateral reinforcing bars 124c. The lateral reinforcing bar 124 farthest from the column 110 among the beam end side concentrated lateral reinforcing bars 124a, the lateral reinforcing bar 124 closest to the column 110 among the beam center side concentrated lateral reinforcing bars 124b, and a plurality of intermediate lateral reinforcing bars 124c. May be arranged at a constant pitch S. Due to the difference in the placement density of the lateral reinforcing bars 124, the distance between the two adjacent beam end-side concentrated lateral reinforcing bars 124a and the spacing between the two adjacent beam center-side concentrated lateral reinforcing bars 124b are compared with those of the two adjacent beam ends. The spacing between the intermediate lateral reinforcing bars 124c is small. The distance between the two adjacent beam end-side concentrated lateral reinforcements 124a and the distance between the two adjacent beam center-side concentrated lateral reinforcements 124b may be the same or different. The number of each of the beam end side concentrated lateral reinforcing bar 124a, the beam center side concentrated lateral reinforcing bar 124b, and the intermediate lateral reinforcing bar 124c is arbitrary, and may be different from each other or may be the same.

As shown in FIG. 3 and a schematic cross-sectional view (FIG. 4 (B)) along the chain line BB'in FIG. 3, the reinforcing bar 125 having an arbitrary configuration is an inverted U-shaped reinforcing bar and is a steel frame. It intersects the 122 and two or more beam main bars 126, surrounds a part of the steel frame 122 and the beam main bars 126, and is arranged so that the U-shaped opening faces downward. Each insert bar 125 can be arranged so as to be sandwiched between two adjacent lateral reinforcing bars 124 and in contact with one lateral reinforcing bar 124, for example. The number, placement density, and length of the insertion bars 125 may be arbitrarily determined.

In each RC section 120a, the end portion of the steel frame 122, the beam main bar 126, the lateral reinforcing bar 124, and the reinforcing bar 125 are embedded in the concrete 128 (FIG. 3). Here, as shown in FIGS. 4A and 4B, a part of the concrete 128 includes an end portion of the steel frame 122, a part of the beam main bar 126, a part of the lateral reinforcing bar 124, and a reinforcing bar. Embed a part of 125. This concrete is hereinafter referred to as beam concrete 128a. At least a part of the upper flange of the steel frame 122 is exposed from the beam concrete 128a. The other part of the concrete 128 is concrete to be laid on the beam concrete 128a, and hereinafter, this concrete is referred to as a slab concrete 128b. The slab concrete 128b is in contact with the upper surface of the beam concrete 128a and at least a part of the upper flange of the steel frame 122, and is in contact with the other part of the beam main bar 126, the other part of the lateral reinforcing bar 124, and the other part of the reinforcing bar 125. Embed a part of. The slab concrete 128b is concrete constituting the floor slab 150 and is integrated with the floor slab 150.

Therefore, in addition to at least a part of the upper flange of the steel frame 122, a part of the beam main bar 126, a part of the lateral reinforcing bar 124, and a part of the reinforcing bar 125 are exposed from the beam concrete 128a. The portion exposed from the beam concrete 128a of these reinforcing bars is embedded in the slab concrete 128b. As shown in FIG. 4 (A), the beam concrete 128a may be provided so that its upper surface is located on the same plane as the upper surface of the upper flange of the steel frame 122, or as shown in FIG. 5 (A). , It may be provided so as to cover a part of the upper surface of the flange and expose the other part. That is, the beam concrete 128a may be provided so that the upper surface is higher than the upper surface of the steel frame 122. Alternatively, as shown in FIG. 5B, the beam concrete 128a may be provided so that the upper surface is located lower than the upper surface of the flange and a part of the web connecting the pair of flanges is exposed from the beam concrete 128a. ..

Although not shown, the upper surface of the beam concrete 128a may have irregularities formed by a brushing process or the like. The depth of the unevenness (that is, the height of the convex portion) may be 2 mm or more and 10 mm or less, and 3 mm or more and 7 mm or less. By forming the unevenness on the upper surface of the beam concrete 128a, the friction coefficient of the joint surface (hereinafter referred to as the joint surface) 130 between the beam concrete 128a and the slab concrete 128b can be increased, and as a result, the beam concrete 128a and the slab can be increased. The concrete 128b can be more firmly fixed to each other.

The beam concrete 128a and the slab concrete 128b may be placed so that the compressive strength is in the range of 21 N / mm ² or more and 150 N / mm ² or less, or 24 N / mm ² or more and 120 N / mm ² or less. The beam concrete 128a and the slab concrete 128b may have the same composition and strength, or may differ from each other. In the latter case, the beam concrete 128a may have higher strength or lower strength than the slab concrete 128b. For example, one of the beam concrete 128a and the slab concrete 128b is cast so that the compression strength is 21 N / mm ² or more and 33 N / mm ² or less, or 24 N / mm ² or more and 27 N / mm ² or less, and the other is the compression strength. It may be placed so that the value is 27 N / mm ² or more and 150 N / mm ² or less, 36 N / mm ² or more and 120 N / mm ² or less, or 36 N / mm ² or more and 48 N / mm ² or less. By making the strength of one concrete (for example, slab concrete 128b) lower than that of the other, the structure 100 can be constructed at low cost. The strength of the beam concrete 128a and the slab concrete 128b may be substantially the same as or different from the strength of the concrete 116 used in the column 110.

As described above, the hybrid beam used in the structure 100 according to the present embodiment has a surface in which the beam concrete 128a and the slab concrete 128b are joined, that is, a joint surface 130 (see FIG. 4A). .. In such a structure, by using the design method described in the second embodiment, the ultimate shear strength at the joint surface 130 can be accurately calculated, and as a result, the beam concrete 128a-slab concrete at the joint surface 130. Horizontal slip fracture between 128b can be effectively prevented. Therefore, even if a low-strength slab concrete 128b is used for a part of the RC section 120a and the floor slab 150, the structure 100 having excellent earthquake resistance can be provided.

<Second Embodiment>
In this embodiment, a method for designing the structure 100 including the hybrid beam described in the first embodiment will be described. More specifically, a design method for preventing horizontal slip fracture due to an external force at the joint surface 130 of the RC section 120a of the beam 120 will be described. The description may be omitted for the configuration similar to or similar to the configuration described in the first embodiment.

（１） The detailed introduction process will be described in Examples, but as a method for effectively preventing horizontal slip fracture on the joint surface 130, in the design method according to the present embodiment, the joint between the beam concrete 128a and the slab concrete 128b in the RC section 120a is joined. The ultimate intensity q _fr of the surface 130 is calculated by the following equation (1).

(1)

The variables in the above equation are as follows (see FIGS. 4 (A), 6 (A), 6 (B)).

（２）
ここで、μ_ｓは鉄骨１２２とコンクリート間の摩擦係数であり、μ_ｒｃはコンクリートとコンクリート間の摩擦係数である。μ_ｓは０．３０以上０．９０以下、０．４０以上０．９０以下、０．５０以上０．９０以下、または０．５６以上０．８０以下の範囲から選択され、例えば０．５６である。梁コンクリート１２８ａの上面に凹凸を設けない場合にはμ_ｒｃはそれぞれ０．６λであり、凹凸を設ける場合にはμ_ｒｃは１．０λとする。λはコンクリートの種類に依存する係数であり、軽量コンクリートの場合には０．７５が、普通コンクリートの場合には１．０が採用される。Ｂｓはフランジの幅（鉄骨幅とも呼ばれ、ウェブの法線に平行な方向における長さ）であり、ｂはＲＣ区間１２０ａの梁コンクリート１２８ａの幅ｂ（ウェブの法線に平行な方向における長さ）である。ｂ´は、鉄骨１２２のフランジ位置でのＲＣ区間１２０ａの梁コンクリート１２８ａの有効幅であり、幅ｂから幅Ｂｓを引いた値である。実施例で述べるように、等価摩擦係数μ_ｅｑを上述した仮定に従って計算することで、水平すべり破壊試験から得られる終局強度と計算結果から得られる終局強度の間に高い整合性が得られることが確認されている。 μ _eq is the equivalent friction coefficient, which is the coefficient of friction of the joint surface 130. Since the joint surface 130 is mainly formed at the interface between the steel frame 122 and the slab concrete 128b and the interface between the beam concrete 128a and the slab concrete 128b, the equivalent friction coefficient μ _eq is the friction coefficient between these two interfaces, respectively. It is assumed that it contributes according to the area ratio of. Therefore, μ _eq is expressed by the following equation (2).

(2)
Here, μ _s is the coefficient of friction between the steel frame 122 and concrete, and μ _rc is the coefficient of friction between concrete and concrete. _μs is selected from the range of 0.30 or more and 0.90 or less, 0.40 or more and 0.90 or less, 0.50 or more and 0.90 or less, or 0.56 or more and 0.80 or less, for example, 0.56. be. When the upper surface of the beam concrete 128a is not provided with unevenness, μ _rc is 0.6λ, and when the upper surface is provided with unevenness, μ _rc is 1.0λ. λ is a coefficient depending on the type of concrete, 0.75 is adopted in the case of lightweight concrete, and 1.0 is adopted in the case of ordinary concrete. Bs is the width of the flange (also called the steel width, which is the length in the direction parallel to the normal of the web), and b is the width b of the beam concrete 128a of the RC section 120a (the length in the direction parallel to the normal of the web). It is). b'is the effective width of the beam concrete 128a of the RC section 120a at the flange position of the steel frame 122, and is a value obtained by subtracting the width Bs from the width b. As described in the examples, by calculating the equivalent friction coefficient μ _eq according to the above assumptions, a high degree of consistency can be obtained between the ultimate strength obtained from the horizontal slip fracture test and the ultimate strength obtained from the calculation result. It has been confirmed.

_s a _w is the total cross-sectional area of the lateral reinforcing bars 124 arranged in the RC section 120a, excluding the beam end side concentrated lateral reinforcing bars 124a and the beam center side concentrated lateral reinforcing bars 124b. ..

Since _s σ _wy is the yield strength or the reference strength (F value) of the lateral reinforcing bar 124, the first term ( _s a _w σ _wy ) in parentheses in the equation (1) is an intermediate lateral reinforcement with respect to the ultimate strength q _fr . It represents the contribution of muscle 124c.

_sw a _w is the total cross-sectional area of the bar 125, and _sw σ _wy is the yield strength or the reference strength (F value) of the bar 125. Therefore, the second term ( _sw a _w · _sw σ _wy ) in parentheses in equation (1) represents the contribution of the bar 125 to the ultimate strength q _fr . If the insertion bar 125 is not arranged, the second term becomes 0.

_{Aa w} is the sum of the cross-sectional areas of the centralized lateral reinforcing bars 124b on the center side of the beam. _A σ _wy is the yield strength or the reference strength (F value) of the centralized lateral reinforcing bar 124b on the center side of the beam. Therefore, the third term ( _A a _wA σ _wy ) in parentheses in the equation (1) represents the contribution of the beam center side concentrated lateral reinforcing bar 124b to the ultimate strength q _fr .

σ ₀ is the average external normal stress generated in the RC section 120a. F _c is the design standard strength of the slab concrete 128b. l _c is the length of the reinforced concrete in the direction in which the steel frame is stretched.

From the formula (1), it can be seen that in the design method according to one of the embodiments of the present invention, the beam end side concentrated lateral reinforcing bar 124a is not taken into consideration in the calculation of the ultimate strength q _fr of the joint surface 130. This is because, as described in the examples, it has been clarified from the test results by the inventors that the beam end side concentrated lateral reinforcing bar 124a hardly contributes to the ultimate strength _qfr of the joint surface 130. Therefore, in the calculation of the ultimate strength q _fr of the joint surface 130, the contribution of the beam end side concentrated lateral reinforcing bar 124a in resisting the horizontal shear force can be ignored, and the beam center side concentrated lateral reinforcing bar 124b, The contribution of the intermediate lateral reinforcing bars 124c and the insertion bars 125, and the vertical stress component applied to the joint surface 130 may be taken into consideration. This provides a high degree of consistency between the test results and the calculated results, as described in the examples.

As described above, the method for designing the structure 100 including the hybrid beam according to the embodiment of the present invention is at the interface between the beam concrete 128a and the slab concrete 128b existing in the RC section 120a (that is, the joint surface 130). Includes calculating the ultimate intensity q _fr . In the calculation of the ultimate strength q _fr , the equivalent friction coefficient μ _eq is used as the friction coefficient of the joint surface 130. The equivalent friction coefficient μ _eq is a value obtained by multiplying the friction coefficient of the interface between the steel frame 122 and the slab concrete 128b constituting the joint surface 130 and the interface between the beam concrete 128a and the slab concrete 128b by the area ratio of each interface. Is calculated by adding up. From the test results, μ _eq is selected from the range of 0.40 or more and 0.9 or less or 0.56 or more and 0.8 or less, and may be 0.56, for example, when a wide margin is secured with respect to the ultimate intensity q _fr . .. At the same time, the contribution of some of the reinforcing bars provided in the RC section 120a is not considered. More specifically, although the insertion bar 125, the beam center side concentrated lateral reinforcing bar 124b, and the intermediate lateral reinforcing bar 124c are considered for the calculation of the ultimate strength q _fr , the beam end side concentrated lateral reinforcing bar 124a is finally considered. The contribution to the intensity q _fr is not considered. By this method, the ultimate intensity q _fr that matches the test result can be calculated more easily.

In this example, the result of the fracture test of the hybrid beam will be described. Based on this test result, a design method of the structure 100 including the hybrid beam, which is one of the embodiments of the present invention, was established.

1. 1. Test body and test method A schematic diagram showing the entire test body 200 is shown in FIG. 6 (A), and a schematic diagram centering on the RC section 120a is shown in FIG. 6 (B). The test piece 200 shown in FIG. 6A was subjected to a destructive test by repeated positive and negative loading. The loading is performed on the steel frame 122 (see the white arrow), the upward loading is compression on the slab concrete 128b (slab compression), and the downward loading is tension on the slab concrete 128b (slab tension). In the RC section 120a, beam concrete 128a and slab concrete 128b were laminated. The slab concrete 128b was placed after removing the latency from the upper surface of the beam concrete 128a and then forming an unevenness of about 5 mm with respect to the upper surface. Ordinary concrete was used for both the beam concrete 128a and the slab concrete 128b, but as shown in Table 1, their strengths are different from each other. Further, as shown in FIG. 6B, strain gauges were attached to three places (A, B, C) near the joint surface 130. A is a place where the concentrated lateral reinforcing bar 124a on the beam end side is arranged, B is a place where the intermediate lateral reinforcing bar 124c is arranged, and C is a place where the concentrated lateral reinforcing bar 124b on the beam center side is arranged. be. Tests were performed on 22 test pieces 200, and horizontal slip fracture occurred in 4 of the test pieces 200. The specifications of these four test bodies 200 are summarized in Table 1.

2. 2. Contribution of lateral reinforcement to ultimate strength The strain ε of the lateral reinforcement 124 at each location A to C obtained from the strain gauges of the four test specimens 200 that caused the horizontal slip fracture, that is, the concentrated lateral reinforcement on the beam end side. The strains ε of the reinforcement 124a, the intermediate lateral reinforcement 124c, and the beam center-side concentrated lateral reinforcement 124b were calculated. In addition, the tip deformation angle Rb of the beam 120 at the time of horizontal slip fracture was measured. A plot of the strain ε with respect to the tip deformation angle Rb is shown in FIG.

From FIG. 7, it can be seen that the intermediate lateral reinforcing bar 124c and the beam center side concentrated lateral reinforcing bar 124b yield when the tip deformation angle Rb reaches from 5 × 10 ^-3 rad to 10 × 10 ^-3 rad. On the other hand, the strain of the beam end side concentrated lateral reinforcing bar 124a is small. From this, it was confirmed that the beam end side concentrated lateral reinforcing bar 124a has a small resistance to the horizontal shear force and hardly contributes to the ultimate strength _fqr with respect to the joint surface 130.

（３）
ただし、τ_ｕ＜０．３σ_Ｂであり、σ_Ｂは用いられるコンクリートの圧縮強度である。σ_Ｂτ_ｕはせん断摩擦を接合要素の応力伝達機構とする場合の単位面積当たりの終局強度であり、μは接合面を形成するコンクリート間の摩擦係数、Ｐｓは接合面を横切る鉄筋の単位面積当たりの断面積であり、σ_ｙは接合面を横切る鉄筋の降伏強度または基準強度である。σ_０は単位面積当たりの応力の鉛直方向成分であり、式（１）における括弧内の第４項と等価である。この式（３）を用いる終局強度の算出方法では、接合面を横切る鉄筋の全てが考慮される。すなわち、試験体２００の場合では、差し筋１２５や中間横補強筋１２４ｃ、梁中央側集中横補強筋１２４ｂのみならず、梁端部側集中横補強筋１２４ａも考慮される。 Conventionally, the ultimate strength of the joint surface 130 is "Site cast equivalent precast reinforced concrete structure design guideline (draft) / Explanation (2002)" (edited by Architectural Institute of Japan, 1st edition, published by Maruzen Co., Ltd., October 2002. On the 20th, it was calculated using the following intensity formula (hereinafter, formula (3)) described in p.60).

(3)
However, τ _u <0.3σ _B , where σ _B is the compressive strength of the concrete used. σ _B τ _u is the ultimate strength per unit area when shear friction is used as the stress transmission mechanism of the joint element, μ is the friction coefficient between the concrete forming the joint surface, and Ps is the unit area of the reinforcing bar crossing the joint surface. It is the cross-sectional area of the hit, and σ _y is the yield strength or the reference strength of the reinforcing bar crossing the joint surface. σ ₀ is a vertical component of stress per unit area, and is equivalent to the fourth term in parentheses in the equation (1). In the method of calculating the ultimate strength using this equation (3), all the reinforcing bars crossing the joint surface are taken into consideration. That is, in the case of the test body 200, not only the insertion bar 125, the intermediate lateral reinforcing bar 124c, and the beam center side concentrated lateral reinforcing bar 124b, but also the beam end side concentrated lateral reinforcing bar 124a is considered.

However, as described above, it was clarified from the fracture test that the beam end side concentrated lateral reinforcing bar 124a hardly contributes to the ultimate strength with respect to the joint surface 130. Therefore, as expressed by the formula (1) of the second embodiment, it was found that the calculation can be performed by ignoring the beam end side concentrated lateral reinforcing bar 124a in the calculation of the ultimate strength.

3. 3. Friction coefficient As described above, in the conventional calculation method (formula (3)), the friction coefficient μ between the concretes forming the joint surface 130 is adopted as the friction coefficient μ of the joint surface 130 (that is, μ _rc ). There is. However, when the ultimate strength q _fr was calculated using μ _rc instead of the equivalent friction coefficient μ _eq in the equation (1), it was confirmed that the calculated value greatly deviated from the value obtained from the test results. This is because the joint surface 130 has not only the interface between the beam concrete 128a and the slab concrete 128b to be joined, but also the interface between the steel frame 122 and the slab concrete 128b. It is considered that the latter friction coefficient is not taken into consideration in the equation (3).

Therefore, in each of the four test bodies 200 in which the horizontal slip fracture occurred, the slip displacement δ of the joint during the negative load (slab tension) was calculated. The measurement points were substantially the same as those at three points A to C provided with the strain gauges of each test piece 200. FIG. 8 shows a plot of the slip displacement δ with respect to the beam tip deformation angle Rb. As shown in FIG. 8, it can be seen that the sliding displacement δ greatly increases when the beam tip deformation angle Rb reaches about 10 × 10 ^-3 rad. Here, as can be understood from FIG. 7, the beam center side concentrated lateral reinforcing bar 124b and the intermediate lateral reinforcing bar 124c also yield when the beam tip deformation angle Rb reaches about 10 × 10 ^-3 rad. These results mean that the load when the beam tip deformation angle Rb is about 10 × 10 ^-3 rad corresponds to the horizontal shear endurance q _exp at the joint surface 130 between the beam concrete 128a and the slab concrete 128b. ing.

Based on this result, the horizontal shear endurance force _qexp obtained from the test results was substituted into the ultimate strength _qfr in the equation (1) to obtain the equivalent friction coefficient μ _eq . Further, as described in the second embodiment, the coefficient of friction at the joint surface 130 is the sum of the values obtained by multiplying the coefficient of friction between concrete and the coefficient of friction between concrete and steel by the respective area ratios. Under the assumption (Equation (2)), the coefficient of friction μ _s between concrete and steel, that is, between slab concrete 128b and steel 122 was calculated. The results are shown in FIG. From FIG. 9, it is understood that the coefficient of friction _μs between the slab concrete 128b and the steel frame 122 is generally in the range of 0.50 to 0.90. In order to secure a large margin for horizontal slip fracture, it can be said that it is preferable to design a hybrid beam by adopting a lower limit value in this range or a value close to it (for example, 0.56).

From the above results, in the design of the structure 100 including the hybrid beam having the RC section 120a in which the concrete is spliced and the upper concrete (that is, the slab concrete 128b) is in contact with the steel frame, the hybrid is based on the following design method. The horizontal shear force of the beam can be calculated.

(1) In the calculation of the horizontal shear force, the contribution of the concentrated lateral reinforcing bar 124a on the beam end side is not taken into consideration among the lateral reinforcing bars 124 arranged in the RC section 120a. Therefore, the cross-sectional area and yield strength or reference strength (F value) of the central lateral reinforcing bar 124b on the beam center side, the intermediate lateral reinforcing bar 124c, and the insert bar 125, and the stress component in the vertical direction of the joint surface 130 with respect to the ultimate strength _qfr . The formula (1), which is a strength formula in consideration of the above, is adopted.

(2) A value selected from the range of 0.50 to 0.90, or 0.56 or more and 0.8 as the coefficient of friction between the steel frame 122 and the concrete provided on the steel frame 122 (here, the slab concrete 128b). Is adopted.

(3) As the coefficient of friction of the joint surface 130, the coefficient of friction between the beam concrete 128a and the slab concrete 128b forming the joint surface 130 and the space between the steel frame 122 and the concrete provided on the steel frame 122 (here, the slab concrete 128b). The equivalent friction coefficient μ _eq obtained by multiplying the friction coefficient of 1 by the respective area ratios is used.

Each of the above-described embodiments of the present invention can be appropriately combined and implemented as long as they do not contradict each other. Those skilled in the art who appropriately add, delete, or change the design based on each embodiment are also included in the scope of the present invention as long as the gist of the present invention is provided.

Of course, other effects different from those brought about by each of the above-described embodiments, which are obvious from the description of the present specification or which can be easily predicted by those skilled in the art, are of course the present invention. It is understood that it is brought about by.

100: Structure, 110: Pillar, 110-1: First pillar, 110-2: Second pillar, 110-3: Third pillar, 110-4: Fourth pillar, 110-5: First 5 pillars, 110-6: 6th pillar, 112: pillar main bar, 114: strip bar, 116: concrete, 120: beam, 120-1: 1st beam, 120-2: 2nd beam, 120 -3: 3rd beam, 120-4: 4th beam, 122: Steel frame, 124: Lateral reinforcing bar, 124a: Beam end side concentrated lateral reinforcing bar, 124b: Beam center side concentrated lateral reinforcing bar, 124c: Intermediate lateral reinforcing bar, 125: Insert bar, 126: Beam main bar, 126a: Fixing plate, 128: Concrete, 128a: Beam concrete, 128b: Slab concrete, 130: Joint surface, 150: Floor slab, 200: Specimen

Claims (11)

It is a method of designing a structure including a hybrid beam.
The hybrid beam is
With steel and reinforced concrete covering both ends of the steel,
The reinforced concrete is
A plurality of beam main bars extending in the extending direction of the steel frame,
A plurality of lateral reinforcing bars that intersect the steel frame and the plurality of beam main bars and surround the steel frame and the plurality of beam main bars.
A plurality of reinforcing bars that intersect the steel frame and the plurality of beam main bars and surround the steel frame and a part of the plurality of beam main bars.
Located on the beam concrete, which embeds the end of the steel frame, a part of the beam main bar, a part of the lateral reinforcing bar, and a part of the beam bar, and said. It has a slab concrete that is in contact with the beam concrete and embeds the other part of the plurality of beam main bars, the other part of the plurality of lateral reinforcing bars, and the other part of the plurality of reinforcing bars.
The plurality of lateral reinforcing bars
Multiple beam end side concentrated lateral reinforcements arranged at the first density on the beam end side,
A plurality of beam center-side concentrated lateral reinforcements arranged at a second density on the beam center side, and the first among the plurality of beam end-side concentrated lateral reinforcements and the beam center-side concentrated lateral reinforcement. Consists of a plurality of intermediate lateral reinforcing bars arranged at a density lower than that of the second density.
The design method does not consider the contribution of the beam end side concentrated lateral reinforcing bar, and the contribution of the plurality of beam center side concentrated lateral reinforcing bars, the plurality of intermediate lateral reinforcing bars, and the plurality of insertion bars, and the contribution of the plurality of insertion bars. A method for designing a structure, which comprises calculating the ultimate strength of the joint surface in consideration of a stress component in the vertical direction applied to the joint surface between the beam concrete and the slab concrete. The contributions of the plurality of beam center-side concentrated lateral reinforcements are the sum of the cross-sectional areas of the plurality of beam center-side concentrated lateral reinforcements, the yield strength or reference strength of the plurality of lateral reinforcements, and the beam concrete and the said. The method for designing a structure according to claim 1, which is represented by the product of the coefficient of friction between slab concrete. The contribution of the plurality of intermediate lateral reinforcing bars is the product of the sum of the cross-sectional areas of the plurality of intermediate lateral reinforcing bars, the yield strength or the reference strength of the lateral reinforcing bars, and the coefficient of friction between the beam concrete and the slab concrete. The method for designing the structure according to claim 1, which is represented by. The contribution of the plurality of barbs is expressed as the product of the sum of the cross-sectional areas of the plurality of barbs, the yield strength or reference strength of the barbs, and the coefficient of friction between the beam concrete and the slab concrete. The method for designing a structure according to claim 1. The friction coefficient is the friction coefficient between the beam concrete and the slab concrete and the friction coefficient between the steel frame and the slab concrete, respectively, the interface between the beam concrete and the slab concrete at the joint surface, the steel frame and the steel frame, respectively. The method for designing a structure according to any one of claims 2 to 4, which is the sum of the products of the area ratios of the interfaces between the slab concretes. The method for designing a structure according to claim 5, wherein the coefficient of friction between the steel frame and the slab concrete is selected from the range of 0.40 or more and 0.90 or less. The method for designing a structure according to claim 5, wherein the coefficient of friction between the steel frame and the slab concrete is selected from the range of 0.56 or more and 0.80 or less. It is a method of designing a structure including a hybrid beam.
The hybrid beam is
A steel frame having a web and a pair of flanges connected to the web, and reinforced concrete covering both ends of the steel frame.
The reinforced concrete is
A plurality of beam main bars extending in the extending direction of the steel frame,
A plurality of lateral reinforcing bars that intersect the steel frame and the plurality of beam main bars and surround the steel frame and the plurality of beam main bars.
A plurality of reinforcing bars that intersect the steel frame and the plurality of beam main bars and surround the steel frame and a part of the plurality of beam main bars.
Located on the beam concrete, which embeds the end of the steel frame, a part of the beam main bar, a part of the lateral reinforcing bar, and a part of the beam bar, and said. It has a slab concrete that is in contact with the beam concrete and embeds the other part of the plurality of beam main bars, the other part of the plurality of lateral reinforcing bars, and the other part of the plurality of reinforcing bars.
The plurality of lateral reinforcing bars
Multiple beam end side concentrated lateral reinforcements arranged at the first density on the beam end side,
A plurality of beam center-side concentrated lateral reinforcements arranged at a second density on the beam center side, and the first among the plurality of beam end-side concentrated lateral reinforcements and the beam center-side concentrated lateral reinforcement. Consists of a plurality of intermediate lateral reinforcing bars arranged at a density lower than that of the second density.
The design method includes calculating the ultimate strength q _fr of the joint surface between the beam concrete and the slab concrete according to the following equation (1).

(1)
In equation (1)
μ _eq is the coefficient of friction of the joint surface, and is
_s a _w is the sum of the cross-sectional areas of the plurality of intermediate lateral reinforcing bars.
_s σ _wy is the yield strength or reference strength of the plurality of lateral reinforcing bars.
_{swa w} is the sum of the cross-sectional areas of the plurality of inserts.
_sw σ _wy is the yield strength or reference strength of the plurality of inserts.
_{Aa w} is the sum of the cross-sectional areas of the plurality of beam center-side concentrated lateral reinforcing bars.
_A σ _wy is the yield strength or the reference strength of the plurality of beam center-side concentrated lateral reinforcing bars.
σ ₀ is the average external vertical stress generated in the reinforced concrete.
b'is the effective width of the reinforced concrete at the position of the flange.
l _c is the length of the reinforced concrete in the direction in which the steel frame is stretched, which is a method for designing a structure. The coefficient of friction μ _eq is expressed by the following equation.

In the above formula
_μs is the coefficient of friction between the steel frame and the slab concrete.
B _s is the length of the flange in a direction parallel to the normal of the web.
_μrc is the coefficient of friction between the beam concrete and the slab concrete.
The method for designing a structure according to claim 8, wherein b is the length of the beam concrete in the direction parallel to the normal line. The method for designing a structure according to claim 9, wherein the friction coefficient _μs between the steel frame and the slab concrete is selected from the range of 0.40 or more and 0.90 or less. The method for designing a structure according to claim 9, wherein the friction coefficient _μs between the steel frame and the slab concrete is selected from the range of 0.56 or more and 0.80 or less.

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