JP7234084B2 - Steel beam with floor slab and its reinforcement method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a steel frame beam with a floor slab in which a concrete floor slab exists on top of the beam and the concrete floor slab and the beam are joined together, and a reinforcing method thereof.

In steel structures, a phenomenon known as lateral buckling during an earthquake can cause the steel beams to deform in the direction perpendicular to the beam axis, preventing the specified strength and deformation capacity from being exerted. It prevents lateral buckling by constraining the movement of the steel frame beam in the direction perpendicular to the material axis.
At that time, it is customary to restrain deformation of the lower flange out of the structure plane by joining a member such as an angle joined to the small beam or the sub-beam to the lower flange of the steel frame beam.

9 and 10 show a conventional configuration in which a steel beam is joined to a concrete floor slab via headed studs.
Conventional steel beams 41 with floor slabs consist of a steel beam 5 with an H-shaped cross section rigidly joined to columns 3 at both ends, and a concrete floor slab 13 joined to the top of the steel beams 5 via headed studs 11. A gusset plate 43 is provided on the side surface of the steel beam 5, a small beam 45 is bolted to the gusset plate 43 at the top of the steel beam 5, and an angle 47 is provided at the bottom of the small beam 45 It is joined so as to straddle the gusset plate 49 and the lower part of the gusset plate 43 on the side surface of the steel beam 5 . This restrains deformation out of the structural plane due to lateral buckling of the steel beams 5 . Further, the concrete floor slab 13 is provided with reinforcing bars 25 inside the concrete 23 .
The web 19 of the steel beam 5 is either welded to the column 3 or high strength bolted to a shear plate 51 welded to the column 3 .

Recently, as shown in Non-Patent Document 1, when steel beams are joined to concrete floor slabs via headed studs, the out-of-frame deformation of the upper flange is restrained, and small beams and grandsons are used to prevent lateral buckling. The idea that beams and angles can be omitted is spreading.
Based on this idea, in Patent Document 1, the torsional rigidity of the concrete floor slab that is joined to the steel beam is set to 10 times the torsional rigidity of the steel beam, so that lateral buckling can be achieved without a lateral buckling stiffener. Preventive design methods have been proposed.
In addition, Patent Document 2 proposes a _design method and floor structure for a steel beam joined to a concrete floor slab. This indicates that if the lateral buckling slenderness ratio _λb is 0.5 or less, sufficient yield strength can be expected without a lateral buckling stiffening member.

Patent No. 5885911 Japanese Patent Application Laid-Open No. 2019-56220

Architectural Institute of Japan, "Guidelines for Designing Composite Structures and Commentaries, 2010"

As described above, when the steel beam 5 is joined to the concrete floor slab 13 via the headed stud 11, deformation of the upper flange 7 of the steel beam 5 outside the structural plane is constrained. The idea that the beam 45, the sub-beam, and the angle 47 can be omitted is spreading.
However, if the beam length is long, even if the steel beam 5 is joined to the concrete floor slab 13 via the headed stud 11, there is a possibility that the steel beam 5 will not exhibit sufficient deformability due to lateral buckling.

Therefore, in the design methods disclosed in Patent Documents 1 and 2, the upper limit of the lateral buckling slenderness ratio λ _b or the slenderness ratio λ _y is defined so that the steel frame beam is too long and so on.
That is, in long steel beams, as described in Patent Document 2, the longer the beam length, the lower the bearing strength of the steel beam. It is difficult to omit the lateral buckling stiffening member because there is a risk that the deformability will be insufficient.
On the other hand, the length of beams in modern buildings sometimes exceeds 20m. Although there is a great merit in omitting the stiffening member, there is a problem that the conventional method cannot cope with this.

The present invention has been made to solve this problem. The object of the present invention is to provide a steel frame beam with a floor slab and a method of designing the steel beam with a floor slab that can secure sufficient deformation capacity by constraining the deformation of the flange outside the structural plane.

(1) A steel beam with a floor slab according to the present invention includes a steel beam with an H-shaped cross section, both ends of which are rigidly connected to columns and no lateral buckling stiffening member is provided, and the entire length of the upper flange of the steel beam. a concrete floor slab joined via headed studs extending through
The steel beam has a ratio λ _w between the beam length and the plate thickness center distance between the upper and lower flanges of 15 < λ _w ≤ 30, and a slenderness ratio λ _y about the weak axis of the steel beam is A < λ _y ,
The number of headed studs is at least twice the number required for a complete composite beam with an antisymmetric bending moment distribution,
The vertical stiffeners joined so as to connect the upper and lower flanges of the steel beam have a pitch of 0.2 times or less of the beam length over the entire length of the steel beam, and the distance between the vertical stiffener closest to the column and the column is It is characterized in that it is provided so as to be 0.125 times or less of the beam length.
However, A is a coefficient that determines the upper limit of the slenderness ratio for the weak axis of a steel beam that does not require lateral buckling stiffening when lateral stiffening is provided at equal intervals over the entire length of the steel beam. For example, if the steel material used for the steel beam 5 is 400N class steel, it is 170; if it is 490N class steel, it is 130;

(2) In addition, in the above (1), the longitudinal stiffener has a plate thickness that is 0.5 times or more the web plate thickness of the steel frame beam, and the steel material used has a design standard strength of the steel frame It is set lower than the design standard strength of the steel material used for the beam,
In addition, the steel beam has a lateral buckling slenderness ratio λ _b given by the square root √ (M _p /M _e ) of the ratio of the total plastic moment M _p and the elastic lateral buckling moment M _e given by the following equation: √(M _p /M _e ) satisfies 0.5<λ _b ≦0.54.

(3) A method for reinforcing a steel beam with a floor slab according to the present invention includes a steel beam with an H-shaped cross section, both ends of which are rigidly joined to columns and no lateral buckling stiffening member is provided, and a steel beam on the steel beam. A steel beam with a floor slab having a concrete floor slab joined via headed studs provided along the entire length of the flange,
The steel beam has a ratio λ _w between the beam length and the plate thickness center distance between the upper and lower flanges of 15 < λ _w ≤ 30, and a slenderness ratio λ _y about the weak axis of the steel beam is A < λ _y ,
A reinforcement method for a steel beam with a floor slab, wherein the number of headed studs is at least twice the number required for a complete composite beam when the bending moment distribution is antisymmetric,
A vertical stiffener is provided so as to connect the upper and lower flanges of the steel beam, and the vertical stiffener is arranged over the entire length of the steel beam at a pitch of 0.2 times or less of the beam length and is closest to the column and the vertical stiffener and the column. It is characterized in that it is provided so that the distance between the
However, A is a coefficient that determines the upper limit of the slenderness ratio for the weak axis of a steel beam that does not require lateral buckling stiffening when lateral stiffening is provided at equal intervals over the entire length of the steel beam. For example, if the steel material used for the steel beam 5 is 400N class steel, it is 170; if it is 490N class steel, it is 130; if it is 520N class steel, it is 120;

According to the present invention, even steel beams with a long beam length can be connected to concrete floor slabs via headed studs and provided with vertical stiffeners, thereby eliminating small girders, grand girders, and angles for preventing lateral buckling. However, it can exhibit sufficient deformation ability in the event of an earthquake.

1 is an explanatory diagram of a steel beam with a floor slab according to an embodiment of the present invention; FIG. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1; FIG. 4 is an explanatory diagram of an analysis model in Example 1; 4 is a graph showing the analysis results of Example 1 (No. 1); 7 is a graph showing analysis results of Example 1 (No. 2); FIG. 11 is an explanatory diagram of an analysis model in Example 2; 10 is a graph showing analysis results of Example 2 (No. 1); 7 is a graph showing the analysis results of Example 2 (No. 2); It is explanatory drawing of the conventional steel-frame beam with a floor slab. FIG. 10 is a cross-sectional view taken along line BB in FIG. 9;

A steel frame beam with a floor slab according to this embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 and 2, the same parts as in FIGS. 9 and 10 showing the conventional example are denoted by the same reference numerals.
A steel beam 1 with a floor slab according to the present embodiment includes a steel beam 5 having an H-shaped cross section, both ends of which are rigidly joined to columns 3 and no lateral buckling stiffening member is provided, and an upper flange of the steel beam 5. A steel beam 1 with a floor slab having a concrete floor slab 13 joined via headed studs 11 provided over the entire length of the steel beam 1 to connect the upper flange 7 and the lower flange 9 of the steel beam 5 is provided with a longitudinal stiffener 15.
Each configuration will be described in detail below.

<Pillar>
Although the type of the column 3 is not particularly limited, examples thereof include a welded assembled box-shaped cross-section column, a square steel pipe column, an H-shaped cross-section column, a CFT column, an RC column, an SRC column, and the like.
The column 3 is provided with a steel plate called a diaphragm 17 for transmitting the force transmitted from the upper and lower flanges 7 and 9 of the steel beam 5 to the column 3 . The diaphragm 17 is classified into a through-diaphragm type, an inner diaphragm type, and an outer diaphragm type depending on the joint type with the column 3 .

<Steel beam>
The steel beam 5 has an H-shaped cross section and is made of steel with a design standard strength of 235 N/mm ² or more and 440 N/mm ² or less. Steel materials with a design standard strength of over 440N/mm ² are not suitable for beams because of their high strength and low elongation and poor ability to deform during an earthquake. The size of the steel frame beams is H-shaped steel with a small cross section specified in JIS G3192, H-shaped steel with a maximum beam height of 1000 mm, and welded H-shaped cross-section members with a beam height exceeding 1000 mm. Applicable. Among these, for large cross-section members with a beam depth exceeding 1000 mm and H-shaped cross-section members made of high-strength steel with a design standard strength of 355 N/mm ² or more, angle 47 etc. A rigid member is often required.
Unlike the conventional examples shown in FIGS. 9 and 10, the steel beams 5 of this embodiment are not provided with the small beams 45 and angles 47 intended to restrain deformation outside the structural plane.

The steel beam 5 has a ratio _λw between the beam length and the plate thickness center distance between the upper and lower flanges 7 and 9, which is 15< _λw ≦30, and the slenderness ratio _λy about the weak axis of the steel beam 5 is A< _λy. is.
However, A is a coefficient that determines the upper limit of the slenderness ratio regarding the weak axis of the steel beam 5 that does not require lateral buckling stiffening when lateral stiffening is provided at equal intervals over the entire length of the steel beam 5 . For example, if the steel material used for the steel beam 5 is 400N class steel, it is 170; if it is 490N class steel, it is 130;

The reasons for defining λ _w and λ _y as above are as follows.
If the steel beam 5 does not require lateral buckling stiffening, and if the beam length is not so long and the concrete floor slab 13 restrains the deformation of the upper flange 7 outside the structure surface, the small beam 45 and the angle 47 can be omitted. This is because the floor slab-equipped steel frame beam 1 exhibiting a high deformation ability is excluded from the scope of the present invention.

Both ends of the steel beam 5 are rigidly joined to the column 3. In this case, the upper and lower flanges 7 and 9 of the steel beam 5 are welded to the column 3 or the diaphragm 17 provided on the column 3. When the upper and lower flanges 7 and 9 are joined to the diaphragm 17, they are joined in the following manner depending on the type of the diaphragm 17. As shown in FIG.

Since the diaphragm 17 is provided inside the column 3 in the inner diaphragm type, the upper and lower flanges 7 and 9 of the steel beam 5 are joined to the column 3 . In the through diaphragm type and the outer diaphragm type, the upper and lower flanges 7 and 9 of the steel beam 5 are welded to the diaphragm 17 .
The web 19 of the steel beam 5 is either high strength bolted with a shear plate 51 welded to the column 3 or welded to the column 3 .

A deck plate 21 for placing concrete is welded to the upper flange 7 of the steel beam 5, and a concrete floor slab 13 is provided thereon.
The deck plate 21 includes a flat deck for surrender formwork, a corrugated composite deck that behaves integrally with concrete, and a surrender formwork deck with rebar trusses to which reinforcing bars are welded.

<Concrete floor slab>
The concrete floor slab 13 has a reinforced concrete structure in which reinforcing bars 25 are arranged inside the concrete 23 . Ordinary concrete and lightweight concrete are used for the concrete 23, and deformed reinforcing bars, round steel reinforcing bars, and welded wire mesh are used for the reinforcing bars 25. Half PC slabs and void slabs that include hollow parts are also applicable, using precast concrete plates made at the factory as dual-purpose formwork on site.

<Stud with head>
The headed studs 11 are welded over the entire length of the upper flange 7 of the steel beam 5, and the number of the studs 11 is at least twice the number required for a complete composite beam when the bending moment is antisymmetrically distributed. be.
By setting the number of the headed studs 11 in this manner, an effect of improving the deformability of the steel frame beam 5 can be expected even when there is no lateral buckling stiffening member. This point is demonstrated in Example 2 described later.

It is desirable that the headed stud 11 has a shaft diameter of 16 mm or more and a height of 0.5 times or more the thickness of the floor slab, from which sufficient strength can be expected. Arrangement shapes of the headed studs 11 include single row arrangement, two or more rows arrangement, staggered arrangement, and the like.

<Vertical stiffener>
The vertical stiffener 15 is welded to the steel beam 5 so as to connect the upper and lower flanges 7 and 9 of the steel beam 5 . The vertical stiffeners 15 have a pitch of 0.2 times or less of the beam length over the entire length of the steel beam 5, and the distance between the vertical stiffener 15 closest to the column 3 and the column 3 is 0.125 times or less of the beam length. is provided as follows.
By providing the vertical stiffener 15 in this manner, an effect of improving the deformability of the steel frame beam 5 can be expected even when there is no lateral buckling stiffening member. This point is demonstrated in Example 1 described later.

The plate thickness of the longitudinal stiffener 15 is preferably 0.5 times or more the web plate thickness of the steel beam 5 . By setting the plate thickness of the vertical stiffener 15 in this manner, the deformability of the steel beam 5 can be ensured.
It is also possible to use the longitudinal stiffener 15 also as a gusset plate for joining small beams for supporting the concrete floor slab 13 . Even if joints with concrete floor slabs are taken into consideration, small beams, sub-beams, and angles for preventing lateral buckling can be omitted, but small beams are sometimes provided to suppress deflection of the floor slab. Unlike conventional small beams used to prevent lateral buckling, these small beams do not have angles or the like to suppress deformation of the lower flanges of the large beams outside the structural plane. It may be smaller than a small beam for stiffening, or the number of bolts at the joint may be reduced.

With the steel frame beam 1 with the floor slab of this embodiment configured as described above, even if the steel frame beam 5 is long and there is no lateral buckling stiffening member such as the small beam 45 or the angle 47, , deformation of the upper flange 7 of the steel frame beam 5 due to lateral buckling is restrained to ensure sufficient deformation ability.

In addition, in Patent Document 2, the steel beam 5 is given by the square root √ (M _p /M _e ) of the ratio of the total plastic moment M _p and the elastic lateral buckling moment M _e given by the following equation. It is shown that if the slenderness ratio λ _b =√(M _p /M _e ) satisfies λ _b ≦0.5, the strength of the steel frame beam 5 sufficiently exceeds M _p .

That is, if the lateral buckling slenderness ratio λ _b ≦0.5, lateral buckling of the steel frame beam 5 can be prevented against the seismic force without attaching a lateral buckling stiffener. In other words, if the steel beam 5 satisfies the lateral buckling slenderness ratio λ _b ≤ 0.5, it is not necessary to satisfy the requirements for the number of headed studs 11 and the arrangement of the longitudinal stiffeners 15 defined in the present invention, and the present invention can be applied. It can be said that there is no advantage in doing so.
From this point of view, the steel beams 5 to which the present invention is advantageous have a lateral buckling slenderness ratio _λb exceeding 0.5.
Therefore, if the steel frame beam 5 has a lateral buckling slenderness ratio λ _b of 0.5<λ _b ≦0.54, the effects of the present invention can be fully expected by applying the present invention.

The reason why the lateral buckling slenderness ratio _λb is 0.54 or less is as follows. Steel beams with a lateral buckling slenderness ratio _λb exceeding 0.54 or more include beams that are too long to be used in actual structures, or beams that are long and have thin beam webs. do. The former is a beam that is not used in the actual structure as described, and the latter is likely to cause problems other than lateral buckling such as local buckling. For the above reason, the upper limit of the lateral buckling slenderness ratio _λb is set to 0.54.

In order to confirm the effect of the longitudinal stiffener 15 in the present invention, FEM analysis was performed using the analytical model 27 shown in FIG. 3, which will be described below.
The analysis model 27 in FIG. 3 is a simplified model in which the effect of restraining the deformation of the upper flange 7 outside the structural plane by the floor slab is considered as a boundary condition of the upper flange 7 .
The analysis cases are the following four cases, and the cross section of the beam at the end of the material is assumed to be a rigid surface on the assumption that both ends are rigidly connected to the column 3 .

・Case 1: Basic case without vertical stiffener 15 ・Case 2: Vertical stiffener 15 provided only at a position 0.125L (L: length of steel frame beam 5) from beam end ・Case 3: Beam end A longitudinal stiffener 15 is installed at a position of 0.125L from the end of the beam and a pitch of 0.15L over the entire length of the beam.

The shape of each beam is H-350x125x6x12, λ _w =25.7, λ _y =310, λ _b =0.53, and the material properties are assumed to be 490N class steel. The vertical stiffener 15 has a plate thickness of 6 mm, and has material properties assuming 400N class steel.
Both the beam and the longitudinal stiffener 15 are modeled with shell elements. In the analysis, a bending moment was applied to the ends of the beams so as to obtain an anti-symmetrical bending moment distribution under seismic load.

The analysis results are shown in FIGS. 4 and 5. FIG. Fig. 4 shows the maximum yield strength (M _max ) of the beam on the negative bending side normalized by the total plastic moment (M _p ), and Fig. 5 shows the plastic deformation ratio (R _max ) at the maximum yield strength of the beam on the negative bending side. show.
As shown in FIG. 4, due to the effect of the vertical stiffener 15, the cases 2 to 4 have a higher maximum yield strength than the case 1 without the vertical stiffener 15. As shown in FIG.
However, as shown in FIG. 5, the plastic deformation ratio of case 2, in which the vertical stiffeners 15 are arranged only at the ends, is about the same as that of case 1, and although the proof stress is increased, the deformability is not improved. In contrast, in cases 3 and 4, both yield strength and deformability are improved over case 1. Further, in Case 4, where the position of the vertical stiffener 15 closest to the beam end is closer to the beam end, the yield strength is greater than in Case 3.
Therefore, it was confirmed that the strength and deformability of the steel frame beam 1 with the floor slab can be improved by reinforcing the entire length of the beam with the longitudinal stiffener 15 .

Subsequently, in order to confirm the effect of the number of headed studs 11 in the present invention, FEM analysis was performed using the analysis model 29 shown in FIG.
In the analysis, the column 3, diaphragm 17, and steel beam 5 were modeled in detail using shell models, the concrete floor slab 13 using beam elements, and the headed stud 11 using spring elements.
The headed stud 11 joint is modeled with a shear spring and a rotary spring that take into account the strength and rigidity of one headed stud.

The steel beam 5 is H-1000x350x19x36, λ _w =21.6, λ _y =268, λ _b =0.53, and the material properties are assumed to be 550N class steel (YS=385N/mm ² ). The vertical stiffener 15 is assumed to be generally used 400N class steel (YS=235N/mm ² ).
Three cases were analyzed, and the synthetic rates were set to 1.0, 2.5, and 4.7. 7 and 8 show the analysis results. Fig. 7 shows the maximum yield strength (M _max ) of the beam on the negative bending side normalized by the total plastic moment (M _p ), and Fig. 8 shows the plastic deformation ratio (R _max ) at the maximum yield strength of the beam on the negative bending side. show.

By increasing the synthesis rate, both yield strength and deformation ability increased. The difference in maximum yield strength between the cases of 1.0 and 2.5 ratios is larger than the difference between the cases of 2.5 and 4.7 ratios, suggesting that the effect of increasing the ratio tends to converge.
As a result of this analysis, it is considered that sufficient yield strength and deformability improvement effect can be obtained if the composition ratio is 2.0. From this result, it was shown that it is effective to make the number of headed studs 11 more than double the number required for a complete composite beam when the bending moment is antisymmetrically distributed.

1 Steel Beam with Floor Slab 3 Column 5 Steel Beam 7 Upper Flange 9 Lower Flange 11 Headed Stud 13 Concrete Floor Slab 15 Vertical Stiffener 17 Diaphragm 19 Web 21 Deck Plate 23 Concrete 25 Rebar <Conventional Example>
41 Steel beam with floor slab 43 Gusset plate 45 Small beam 47 Angle 49 Gusset plate 51 Shear plate

Claims (3)

A steel beam with an H-shaped cross section, both ends of which are rigidly connected to columns and which is not provided with a lateral buckling stiffening member, is joined via a headed stud provided over the entire length of the upper flange of the steel beam. A steel beam with a floor slab having a concrete floor slab with
The steel beam has a ratio λ _w between the beam length and the plate thickness center distance between the upper and lower flanges of 15 < λ _w ≤ 30, and a slenderness ratio λ _y about the weak axis of the steel beam is A < λ _y ,
The number of headed studs is at least twice the number required for a complete composite beam with an antisymmetric bending moment distribution,
The vertical stiffeners joined so as to connect the upper and lower flanges of the steel beam have a pitch of 0.2 times or less of the beam length over the entire length of the steel beam, and the distance between the vertical stiffener closest to the column and the column is A steel beam with a floor slab, characterized in that it is provided so as to be 0.125 times or less of the beam length.
However, A is a coefficient that determines the upper limit of the slenderness ratio for the weak axis of a steel beam that does not require lateral buckling stiffening when lateral stiffening is provided at equal intervals over the entire length of the steel beam. The longitudinal stiffener has a thickness equal to or greater than 0.5 times the thickness of the web of the steel beam, and the standard design strength of the steel material used is set lower than the standard design strength of the steel material used in the steel beam. ,
In addition, the steel beam has a lateral buckling slenderness ratio λ _b given by the square root √ (M _p /M _e ) of the ratio of the total plastic moment M _p and the elastic lateral buckling moment M _e given by the following equation: 2. The steel beam with floor slab according to claim 1, wherein √(M _p /M _e ) satisfies 0.5<λ _b ≦0.54.

A steel beam with an H-shaped cross section, both ends of which are rigidly connected to columns and which is not provided with a lateral buckling stiffening member, is joined via a headed stud provided over the entire length of the upper flange of the steel beam. A steel beam with a floor slab having a concrete floor slab with
The steel beam has a ratio λ _w between the beam length and the plate thickness center distance between the upper and lower flanges of 15 < λ _w ≤ 30, and a slenderness ratio λ _y about the weak axis of the steel beam is A < λ _y ,
A reinforcing method for a steel frame beam with a floor slab, wherein the number of headed studs is at least twice the number required for a complete composite beam when the bending moment distribution is antisymmetric,
A vertical stiffener is provided so as to connect the upper and lower flanges of the steel beam, and the vertical stiffener is arranged over the entire length of the steel beam at a pitch of 0.2 times or less of the beam length and is closest to the column and the vertical stiffener and the column. A method of reinforcing a steel frame beam with a floor slab, characterized in that the distance between and is set to be 0.125 times or less of the beam length.
However, A is a coefficient that determines the upper limit of the slenderness ratio for the weak axis of a steel beam that does not require lateral buckling stiffening when providing lateral stiffening at equal intervals over the entire length of the steel beam.

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