Floor support structure and design method for floor support structure

Abstract

This provides a floor support structure that suppresses buckling of steel beams, even when stiffening members cannot be attached to the steel beams. [Solution] A floor support structure 10 comprising a column, a steel beam 11 rigidly connected to the column, and a floor slab 21 attached to the upper surface of the steel beam via a shear connector 16, wherein the steel beam is an H-shaped cross section member, no lateral buckling stiffener is attached to the lower flange of the steel beam to prevent lateral buckling, the standardized width-to-thickness ratio β obtained by formula is greater than 65 in the web 14 of the steel beam, no local buckling stiffener is installed in the web in the range corresponding to the height of the steel beam from the end of the material axis z of the steel beam, and the restraining stiffness K of the surrounding members 25 of the steel beam with respect to the contraction in the material axis direction of the steel beam satisfies the formula.

Description

[Technical Field]

[0001] The present invention relates to a floor support structure and a method for designing a floor support structure. [Background technology]

[0002] Traditionally, H-shaped steel members (H-section members) have been commonly used for main beams supporting floor slabs. This is because, as with main beams, when bending moments are generated in the member due to the weight of the members it supports and external forces, it is rational to use an H-shaped section, which has high bending performance around the strong axis relative to the weight of the steel and good cross-sectional efficiency.

[0003] On the other hand, while H-shaped members have excellent cross-sectional properties around the strong axis, their cross-sectional properties around the weak axis are poor, making lateral buckling (deformation in which the member twists and moves out of plane) a problem. When lateral buckling occurs in a member, a rapid deterioration in load-bearing capacity occurs, and the behavior of the member becomes unstable. Therefore, it is necessary to design members in a way that prevents lateral buckling. Specifically, in the Ministry of Land, Infrastructure, Transport and Tourism's Notification No. 1024 of 2001, "Regarding the Specification of Special Allowable Stresses and Special Material Strengths," the allowable stress for buckling of bending members is specified, and it is stipulated that the allowable stress should be reduced when the length of the member where lateral buckling can occur is long. As a result, under conditions where lateral buckling is likely to occur, such as when the length of the member is long or when the width of an H-shaped cross-section member is narrow, the allowable stress decreases, and the cross-section does not exhibit the cross-sectional performance that it originally possessed. This necessitates increasing the cross-section, which increases the amount of steel used, resulting in an uneconomical design.

[0004] In addition, as a method to prevent a decrease in allowable stress due to lateral buckling, stiffeners are sometimes installed in the members to prevent lateral buckling. In this case, if a sufficient number of stiffeners are installed, a decrease in allowable stress will not occur, but the time and cost involved in processing and installing the stiffeners makes it uneconomical.

[0005] To address these challenges, design methods are sometimes adopted that improve lateral buckling resistance by considering the restraining effect of the floor slab on the upper flange, thereby omitting stiffeners for preventing lateral buckling. Patent Document 1 derives an elastic lateral buckling resistance formula for an H-shaped beam in which the upper flange is fastened to the floor slab by a shear connector, assuming that the lateral movement of the upper flange is completely restrained, and uses this formula in the design and analysis methods. Patent Document 2 derives an elastic lateral buckling resistance formula for a floor structure having a steel beam and a floor slab joined to the upper surface of the steel beam by a shear connector, assuming that the lateral movement and rotation of the upper flange are completely restrained, and uses this formula in the design method. By using the design methods described in Patent Documents 1 and 2, lateral buckling can be suppressed and premature deterioration of load-bearing capacity can be prevented, thereby eliminating the need for lateral stiffeners and enabling the realization of a rational structure.

[0006] Furthermore, the design methods described in Patent Documents 1 and 2 assume a beam cross-section with a relatively thick web (plate thickness) and a small web-to-thickness ratio. This is because a large web-to-thickness ratio can lead to problems with local buckling. In the general design of earthquake-resistant buildings, the design system requires the use of a cross-section with a relatively thick web to prevent a significant decrease in deformation performance due to local buckling. Specifically, Ministry of Land, Infrastructure, Transport and Tourism Notification No. 1792 of 1980, "Regarding the Method for Calculating Ds and Fes," specifies the limitations on the width-to-thickness ratio and the correspondence to member types when using H-shaped steel for beams. This notification states that it is common practice to design the main beam so that the standardized web width-to-thickness ratio β, calculated by equation (1), is 65 or less, so that the member type of the main beam is FB or higher.

[0007]

number

[0008] Here, d is the web height, t w is the web thickness, and F is the standard strength of the steel material.

[0009] On the one hand, in order to reduce the material consumption of steel materials, there is a need to use a web cross-section with a thin web thickness where the web standardized width-thickness ratio β exceeds 65. In a thin web cross-section, the cross-sectional performance with respect to the mass of the beam itself is high, and the cross-sectional efficiency is good, so the economic rationality is high. In particular, when the strength of the steel beam is high-strength of 490 N class or more, or when the height of the beam is large at 600 mm or more, according to the above-mentioned design method, the required thickness of the web becomes thick, so the use of a cross-section with a thin web thickness is often desired. Regarding the flange, there is no need to reduce its thickness. It is preferable to have a cross-sectional dimension where the standardized width-thickness ratio α of the flange obtained by Equation (2) is 11 or less, so that stable structural performance can be expected.

[0010]

Number

[0011] Here, b is half the length of the width of the flange, and t f is the thickness of each flange.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0013] However, when a design method that allows for the omission of lateral stiffeners by considering the restraining effect of the floor slab is used in combination with a thin web section, there are structural performance issues. When relying on the restraining effect of the floor slab, early deterioration of load-bearing capacity due to lateral buckling can be prevented, but in the ultimate behavior that determines the deformation performance, lateral buckling becomes dominant. In such cases, when used in combination with a thin web section, problems arise such as the coupling of lateral buckling with local buckling and the web becoming more prone to bending out of plane, resulting in a decrease in deformation performance. Therefore, for cross-sections with thin webs and a web-normalized width-to-thickness ratio β exceeding 65, it becomes necessary to install local buckling reinforcements such as stiffeners or ribs within a certain range from the end of the member (for example, up to the beam height) to suppress out-of-plane deformation of the web. However, the installation of stiffeners or ribs increases the amount of steel and processing required, making it uneconomical.

[0014] In other words, for cross-sections where the web standardized width-to-thickness ratio β exceeds 65, it is difficult to realize a rational structure that saves materials and processing by omitting lateral stiffeners by considering the restraining effect of the floor slab, without providing stiffeners or the like on the web at the end of the member, due to structural performance issues.

[0015] The present invention has been made in view of these problems, and aims to provide a floor support structure and a method for designing a floor support structure that suppresses buckling of a steel beam even when a lateral stiffener cannot be attached to a steel beam that does not have a local buckling stiffener at the end of the member. [Means for solving the problem]

[0016] To solve the aforementioned problems, this invention proposes the following means. (1) Embodiment 1 of the present invention is a floor support structure comprising a column, a steel beam rigidly connected to the column, and a floor slab attached to the upper surface of the steel beam via a shear connector, wherein the steel beam is an H-shaped cross section member, no lateral buckling stiffener is attached to the lower flange of the steel beam to prevent lateral buckling, the standardized width-to-thickness ratio β obtained by equation (11) is greater than 65 in the web of the steel beam, no local buckling stiffener is attached in the web in a range corresponding to the height of the steel beam from the end of the steel beam in the axial direction of the material, and the restraining stiffness K of the steel beam by the surrounding members with respect to the contraction of the steel beam in the axial direction of the material satisfies equation (12). However, d is the height of the web, t w F is the thickness of the web, F is the standard strength of the material strength of the steel beam, E is the Young's modulus of the steel beam, A is the cross-sectional area of ​​the steel beam perpendicular to the material axis direction, and L is the length of the steel beam.

[0017]

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[0018] In this invention, the inventors diligently studied how to suppress buckling of a steel beam in a floor support structure comprising a column, a steel beam rigidly connected to the column, and a floor slab attached to the upper surface of the steel beam via a shear connector, when no lateral buckling stiffeners or local buckling stiffeners are attached to the steel beam. As a result, they found that even when the standardized width-to-thickness ratio β obtained by equation (11) for the web of the steel beam is greater than 65, if the restraining stiffness K of the surrounding members of the steel beam against axial compression of the steel beam satisfies equation (12), the steel beam becomes less likely to compress beyond a certain point in the axial direction, and buckling of the steel beam, which tends to occur when the steel beam compresses in the axial direction, can be suppressed. Therefore, even when lateral buckling stiffeners and local buckling stiffeners cannot be installed on the steel beam, buckling of the steel beam can be suppressed.

[0019] (2) In embodiment 2 of the present invention, the peripheral member is the column, and the restraining stiffness K is determined by equation (13), and the floor support structure is as described in (1). However, N is the total number of columns directly or indirectly connected to the steel beam that are on the same structural plane as the steel beam, n is the number of columns located on the starting end side of the steel beam among the columns directly or indirectly connected to the steel beam that are on the same structural plane as the steel beam, K i is the stiffness of the i-th column.

[0020]

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[0021] In this invention, the constraint stiffness K can be precisely defined using the mathematical formula (13).

[0022] (3) Embodiment 3 of the present invention is characterized in that the height of the steel beam is 600 mm or more, and the yield strength of the steel beam is 325 N / mm 2 The above applies, but the floor support structure may also be as described in (1) or (2). In this invention, the height of the steel beam is 600 mm or more, and the yield strength of the steel beam is 325 N / mm². 2 The present invention can be applied to relatively large steel beams of the above size.

[0023] (4) A fourth aspect of the present invention is a design method for a floor support structure comprising a column, a steel beam rigidly connected to the column, and a floor slab attached to the upper surface of the steel beam via a shear connector, wherein the steel beam is set to be an H-shaped cross section member, a lateral buckling stiffener to prevent lateral buckling is not attached to the lower flange of the steel beam, a local buckling stiffener to prevent local buckling is not attached to the web of the steel beam in a range corresponding to the height of the steel beam from the end of the steel beam in the axial direction of the steel beam, and the deformation performance of the steel beam is evaluated by setting the surrounding members of the steel beam to be restrained against the contraction of the steel beam in the axial direction of the steel beam.

[0024] In this invention, the inventors diligently studied how to suppress buckling of a steel beam in a floor support structure comprising a column, a steel beam rigidly connected to the column, and a floor slab attached to the upper surface of the steel beam via a shear connector, when the steel beam is not fitted with a lateral buckling stiffener or a local buckling stiffener. As a result, they found that if the surrounding members of the steel beam are set to restrain the steel beam from shrinking in the axial direction of the steel beam, the steel beam will be less likely to shrink in the axial direction beyond a certain point, thereby suppressing buckling of the steel beam, which is likely to occur when the steel beam shrinks in the axial direction of the steel beam, and that the deformation performance can be improved depending on the degree of restraint of the surrounding members. Therefore, even when lateral buckling stiffeners and local buckling stiffeners cannot be attached to the steel beam, it is possible to design the steel beam as a member with high deformation performance by suppressing buckling. [Effects of the Invention]

[0025] In the floor support structure and floor support structure design method of the present invention, buckling of a steel beam can be suppressed even when a lateral stiffener cannot be attached to a steel beam that does not have a local buckling stiffener at the end of the member. [Brief explanation of the drawing]

[0026] [Figure 1] This is a perspective view showing the outline configuration of a building equipped with a floor support structure according to one embodiment of the present invention. [Figure 2] Cross-sectional view of the cutting line A1-A1 in Figure 1. [Figure 3] This figure shows an analytical model of the bed support structure. [Figure 4] This diagram shows the relationship between (M / Mp) and (θ / θp). [Figure 5] This figure shows the difference in deformation performance due to the spring stiffness coefficient. [Figure 6] This figure shows the required values ​​for the spring stiffness coefficient based on the standardized width-to-thickness ratio of the web. [Figure 7] This diagram schematically shows a building in which a method for restraining steel beams from shrinkage in the axial direction of the material was investigated. [Modes for carrying out the invention]

[0027] Hereinafter, one embodiment of the floor support structure and the design method for the floor support structure according to the present invention will be described with reference to Figures 1 to 7.

[0028] [1. Structure of the floor support system] As shown in Figures 1 and 2, the floor support structure (column-beam structure with slab) 10 of this embodiment is provided in a building 1. The configuration of the building 1 is not limited as long as it includes the floor support structure 10. In Figure 1, a portion of the floor slab 21, which will be described later, is shown by a dashed line. Building 1 comprises a floor support structure 10, joists 27, and walls, a roof, etc. (not shown). The floor support structure 10 comprises a plurality of columns 5, steel beams 11, and a floor slab 21.

[0029] As shown in Figure 1, the columns 5 extend in the vertical direction. Columns 5 are generally composed of square steel pipes, welded box-section pipes, or circular steel pipes, but the type of column is not limited. Columns may also be made of reinforced concrete, reinforced steel-frame concrete, H-beams, etc. Multiple columns 5 are arranged at intervals from each other along the horizontal plane on a foundation (not shown). As shown in Figure 1, the steel beam 11 is an H-shaped cross-section member and is a main beam. The steel beam 11 may also be made of H-shaped steel. The steel beam 11 extends along the horizontal plane in the direction z, which is the axis of the steel beam 11. The steel beam 11 has an upper flange 12, a lower flange 13, and a web 14. The upper flange 12, lower flange 13, and web 14 are formed from steel in a flat plate shape. The upper flange 12 is positioned above the lower flange 13. The web 14 is positioned between the upper flange 12 and the lower flange 13. The web 14 is connected to the widthwise center of the upper flange 12 and the widthwise center of the lower flange 13, respectively. The cross-section of the steel beam 11 perpendicular to the material axis z is H-shaped. The steel beam 11 may be made of rolled H-shaped steel or a welded H-shaped cross-section. A headed stud (shear connector) 16 is fixed to the upper surface of the upper flange 12 (steel beam 11).

[0030] Both ends of the steel beam 11 are rigidly connected to multiple columns 5. The rigid connection referred to here is a connection as defined in, for example, "Eurocode 3: Design of steel structures - Part 1-8: Design of joints", 2004, Authority: The European Union Per Regulation 305 / 2011, Directive 98 / 34 / EC, Directive 2004 / 18 / EC. For example, both ends of the steel beam 11 are joined to multiple columns 5 by high-strength bolts and welding. For example, the secondary beam 27 is made of H-shaped steel. The secondary beam 27 is spanned between multiple steel beams 11.

[0031] The type of floor slab 21 is not limited. For example, the floor slab 21 may be a reinforced concrete slab, a composite slab, etc. For example, if the floor slab 21 is a composite slab, the shear connector may be a welded joint that welds the upper flange 12 to the deck plate of the composite slab. The floor slab 21 is formed in a flat plate shape with its thickness direction aligned with the vertical direction. The floor slab 21 is supported from below by the steel beam 11 and the secondary beam 27. Headed studs 16 are embedded within the floor slab 21. The floor slab 21 is attached to the upper surface of the upper flange 12 (steel beam 11) via the headed studs 16.

[0032] Furthermore, the lower flange 13 of the steel beam 11 is not fitted with a lateral buckling stiffener to prevent lateral buckling. A lateral buckling stiffener, as used here, refers to a member made of steel or the like that is attached to the lower flange 13 and restrains the lower flange 13 from deforming outwards (in the thickness direction x in Figure 3, which will be described later) due to lateral buckling of the steel beam 11. Angle steel or channel steel can be used as a lateral buckling stiffener. From the end in the material axis direction z of the web 14, in the material axis direction z, in the range corresponding to the height (beam depth) of the steel beam 11, no local buckling restraining stiffener is provided. The local buckling restraining stiffener mentioned here means a member made of steel or the like that is attached in the range corresponding to the height of the steel beam 11 from the end in the material axis direction z of the web 14 and restrains the deformation in the thickness direction of the web 14. As the local buckling restraining stiffener, stiffeners, ribs, etc. formed of steel are used. The local buckling restraining stiffener does not include high-strength bolts, nuts, and gusset plates used for connection to the column at the end in the material axis direction.

[0033] The wall is arranged between a plurality of columns and is supported from below by the floor slab 21. The roof is fixed to the upper ends of a plurality of columns, etc.

[0034] Here, the specifications (definitions) of the floor support structure 10 are defined. Define the height of the steel beam 11 as H (mm). Define the thickness of the flanges 12, 13 as t f (mm). Define the thickness of the web 14 as t w (mm). Define the height of the web 14 (the length in the height direction y described later) as d (mm). The height d is equal to (H - 2t f ). Define the length of the steel beam 11 as L (mm). Define the cross-sectional area perpendicular to the material axis direction z of the steel beam 11 as A (mm 2 ). Define the Young's modulus of the steel beam 11 as E (N / mm 2 ). Define the reference strength of the material strength of the steel beam 11 as F (N / mm 2 ). Define the yield strength of the steel beam 11 as σ y (N / mm 2 ).

[0035] The inventors, after examining the floor support structure 10 configured as described above, concluded that the peripheral member 25, which is at least one of the column and the floor slab 21, influences the contraction of the steel beam 11 in the material axis direction z. The peripheral member 25 holds the steel beam 11 in the material axis direction z when lateral buckling occurs in the steel beam 11 and contraction occurs in the material axis direction z, thereby making it difficult for the steel beam 11 to contract in the material axis direction z. Furthermore, the surrounding members are not limited to at least one of the columns and the floor slab 21. Below, we examine the effect of the steel beam 11 becoming less susceptible to contraction in the material axis direction z on the buckling of the steel beam 11.

[0036] [2. Examination of buckling of steel beams in floor support structures] In the following study, the difficulty of the steel beam 11 compressing in the material axis direction z was modeled as a spring constraint by the surrounding members 25. The effect of spring-restraining the compression of the steel beam 11 in the axial direction z will be used to improve its deformation performance, which will be confirmed using elastoplastic analysis with the Finite Element Method (FEM). Figure 3 shows the analysis model. The analysis model is a steel beam 11 that mimics a main beam using an H-shaped cross-section, and is composed of four-node shell elements. In the steel beam 11, the thickness direction x of the web 14 and the height direction y where the upper flange 12 and lower flange 13 face each other are defined.

[0037] At the first end 11a of the steel beam 11 in the material axis direction z, the displacement (movement) in the thickness direction x and height direction y was constrained (Ux=Uy=0). At end 11a, the rotation in the height direction y and around the material axis direction z was constrained (Uy=Uz=0). At the second end 11b of the steel beam 11 in the direction z of the material axis, the displacement in the thickness direction x, the height direction y, and the material axis direction z were constrained (Ux=Uy=Uz=0). At end 11b, rotation around the height direction y and the material axis direction z was constrained (Uy=Uz=0). At the intersection line of the upper flange 12 and the web 14 (the center line of the thickness direction x of the upper flange 12), the displacement in the thickness direction x was constrained (Ux=0).

[0038] Thus, the displacement of the steel beam 11 in the material axis direction z is not constrained at end 11a, but only at end 11b. At end 11a, an elastic spring in the material axis direction z is set up by the surrounding members 25, reproducing the effect of constraining the compression in the material axis direction z by the columns and floor slabs 21. The spring stiffness of the elastic spring in the material axis direction z is set to the constraining stiffness K. The upper flange 12 replicates the restraining effect of the floor slab 21 on lateral movement (in the thickness direction x), thereby constraining lateral displacement (in the thickness direction x). Furthermore, in the analysis model, no local buckling stiffeners, such as stiffeners, are provided on the web 14 of the steel beam 11 to suppress local buckling. No lateral buckling stiffeners are attached to the lower flange 13.

[0039] In this analysis model, a forced rotation angle of equal magnitude was applied to ends 11a and 11b to simulate inverse symmetric bending under seismic load. M1 and M2 shown in Figure 3 represent the moments generated at ends 11a and 11b due to the forced rotation angle. In addition to seismic loads, there are also static loads, wind loads, etc., but the specifications of the structural members are almost entirely determined by seismic loads.

[0040] Table 1 shows the analysis cases.

[0041] [Table 1]

[0042] The steel beams 11 were divided into three types: H-600 (490N class), H-1000 (490N class), and H-1200 (550N class). For each type, the height, width, and thickness of flanges 12 and 13 were kept constant, and only the thickness of the web 14 was changed, resulting in an analysis case where the standardized width-to-thickness ratio β of the web 14 was used as a variable. Cases 1-1, 2-1, and 3-1 involve setting the thickness of the web 14 such that the standardized width-to-thickness ratio β of the web 14, obtained by equation (a1), corresponds to 65, which is the upper limit when the member type based on the width-to-thickness ratio of the web 14 is FB. These cases represent the thinnest possible web 14 thickness, which is commonly used in general design. The types of materials are specified in the Ministry of Land, Infrastructure, Transport and Tourism's Public Notice No. 1792 of 1980, "Regarding the Method for Calculating Ds and Fes." In equation (a1), the yield strength σ of the steel beam 11 y If we use the standard strength F of the material strength of the steel beam 11 instead, we obtain equation (a1a).

[0043]

number

[0044] In contrast, analysis cases 1-2 to 3, 2-2 to 4, and 3-2 to 4 are analysis cases in which the thickness of the web 14 is made thinner. In these analysis cases, the normalized width-to-thickness ratio β of the web 14 exceeds 65 (is greater than 65), and the member type based on the web width-to-thickness ratio is FC to FD. In all cases, the standardized width-to-thickness ratio α of flanges 12 and 13 according to equation (a2) is 11 or less.

[0045]

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[0046] In each analysis case, the constraint stiffness K is used as a variable. In setting the constraint stiffness K as a variable, as shown in equation (a3), the constraint stiffness K was treated as a dimensionless spring stiffness coefficient k, which is the stiffness related to the deformation of the steel beam 11 in the axial direction z.

[0047]

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[0048] Then, the spring stiffness coefficient k was varied within the range of 0.001 to 100. Note that in analysis cases 1-1, 2-1, and 3-1, the constraint of compression in the material axis direction z is not considered, and the spring stiffness coefficient k is set to 0.

[0049] As an example of the analysis results, Figure 4 shows the load-deformation relationship for typical spring stiffness coefficients k in analysis cases 1-1 and 1-3. In Figure 4, the vertical axis represents the moment M at the end of the steel beam 11 (moment M1 at end 11a) obtained from the analysis, and the full plastic moment M, which is the moment when the entire cross-section of the steel beam 11 undergoes plastic deformation in the material axis direction z. p The dimensionless value (M / M p The horizontal axis represents the rotation angle θ around the thickness direction x at the end of the steel beam 11, and the elastic rotation angle θ at full plastic load capacity, which is the load-bearing capacity when the entire cross-section of the steel beam 11 in the material axis direction z undergoes plastic deformation. p The dimensionless value (θ / θ) p ) (M / M p After the value of ) reaches its maximum, (θ / θ p As ) increases (M / M p The smaller the value of ), the more the steel beam 11 has deteriorated in terms of load-bearing capacity. Figure 4 shows that, compared to analysis case 1-1, in analysis case 1-3, where the thickness of the web 14 is reduced, the yield strength deteriorates early in the region where the spring stiffness coefficient k is small, but in the region where the spring stiffness coefficient k is large, the yield strength deteriorates less easily, resulting in a stable load-deformation relationship.

[0050] Here, in the load-deformation relationship, due to the deterioration of load-bearing capacity, the moment M at the end of the steel beam 11 becomes the full plastic moment M p The horizontal axis (θ / θ) at the point when it becomes equal to (the point when the vertical axis in Figure 4 is less than 1) p The value of ) is defined as the deformation performance. Even in analysis case 1-3, where the web 14 is thin, it can be seen that if the spring stiffness coefficient k exceeds 1, it exhibits deformation performance that surpasses analysis case 1-1.

[0051] Figure 5 shows a comparison of the deformation performance of analysis case 1-1 and analysis case 1-3. In Figure 5, the vertical axis represents the difference obtained by subtracting the deformation performance of analysis case 1-1 from the deformation performance of analysis case 1-3. The horizontal axis represents the spring stiffness coefficient k. In addition to the results for the analysis case shown in Figure 4, Figure 5 also shows the results obtained by finely varying the spring stiffness coefficient k in the range of k = 0.01 to 10.

[0052] From Figure 5, the circles indicate that when the spring stiffness coefficient k is about 0.4, the difference in deformation performance on the vertical axis becomes 0. Therefore, even in a cross section where the thickness of the web 14 is reduced and the normalized width-to-thickness ratio β is 115.5, resulting in a member type of FD, if the spring stiffness coefficient k is about 0.4, it can be seen that it exhibits deformation performance equivalent to that of a cross section where the normalized width-to-thickness ratio β is about 65 and the member type is FB, without considering constraints in the material axis direction z.

[0053] Using the same method as described above, the spring stiffness coefficient k in the material axis direction z required to exhibit deformation performance equivalent to that of a cross section with member type FB was also determined for analysis cases 1-2, 2-2 to 2-4, and 3-2 to 3-4. The results are shown in Figure 6. In Figure 6, the vertical axis represents the required value of the spring stiffness coefficient k for each analysis case. The horizontal axis represents the normalized width-to-thickness ratio β of the web 14. As shown in Figure 6, the required value of the spring stiffness coefficient k tends to increase as the normalized width-to-thickness ratio β of the web 14 increases. This relationship is generally linear and can be seen to be about the same regardless of the cross-sectional dimensions of the steel beam 11 or the strength of the steel material.

[0054] Furthermore, Figure 6 shows the required value k for the spring stiffness coefficient shown in equation (a4). req The evaluation formula is also shown by line L1.

[0055]

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[0056] It can be seen that the evaluation formula in (a4) generally encloses each analysis case on the safe side and accurately represents the required value of the spring stiffness coefficient. Note that equation (a4) is the required value k for the spring stiffness coefficient. req Although expressed as such, the required value of constraint stiffness K can be determined from the relationship in equation (a3). req It can be expressed as equation (a5). Furthermore, considering equations (a5) and (a1a), it can be seen that the constraint stiffness K only needs to satisfy equation (a5a).

[0057]

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[0058] Note that equation (a5) is the yield strength σ of the steel. y Instead, the standard strength F, which is the strength of the steel material used in the design, is used.

[0059] Based on the above considerations, for a main beam (steel beam 11) whose lateral movement of the upper flange 12 is restrained by the floor slab 21, when lateral buckling is dominant and determines the deformation performance, even if the standardized width-to-thickness ratio β of the web 14 is greater than 65 and no lateral buckling stiffeners or local buckling stiffeners are provided within a predetermined range, the required restraint stiffness K shown in equation (a5) is still valid. req It was confirmed that by applying the above constraints in the material axis direction z, the web 14 exhibits deformation performance equivalent to or better than that of a cross section with a standardized width-to-thickness ratio β of 65 and member type FB.

[0060] In the floor support structure 10, the restraining stiffness K of the surrounding members 25 against the contraction of the steel beam 11 in the axial direction z satisfies equation (a5a). Furthermore, the height H of the steel beam 11 is 600 mm or more, and the yield strength σ of the steel beam 11 is... y 325 N / mm 2 It is desirable that it be as above. It has been found that the tendency to suppress buckling of the steel beam 11 is similar when the standardized width-to-thickness ratio β of the web 14 is 65 or less.

[0061] [3. Examination of methods to achieve constraint against contraction in the axial direction of steel beams] Next, we will describe a method for achieving constraint against contraction of the steel beam 11 in the axial direction z. In actual buildings, steel beams can be expected to be restrained by multiple surrounding members, such as columns, beams perpendicular to the steel beams, and floor slabs. This section describes a method for calculating the spring stiffness of a steel beam (a main beam) in relation to compression in the axial direction z, assuming a steel-framed building and focusing on the restraining effect of columns. In actual buildings, higher stiffness is expected due to contributions from floor slabs, etc., and these may be taken into consideration.

[0062] Figure 7 shows an image of building 2, which evaluates the restraint effect of column 31. Building 2 comprises a plurality of columns 31 and a plurality of steel beams 11 connected to the plurality of columns 31. The plurality of columns 31 are arranged in a line along the horizontal plane. Building 2 has a plurality of floors (levels). When evaluating the central steel beam 11 (hereinafter also referred to as steel beam 11A) in the vertical and horizontal directions of Figure 7, the influence of all columns 31 located above and below the steel beam 11A is taken into consideration. The constraint stiffness (rigidity) K is determined by the i-th column 31 (where i is a value in the range of 1 to N, as described later) from the first side z1 along the horizontal plane. i This is expressed by equation (a6). In this example, for the sake of simplicity, the influence of the floor slab and shear connectors was not considered, and the surrounding members of the steel beam 11A were designated as columns 31.

[0063]

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[0064] Here, i I UThis is the second moment of area (mm²) of the column 31 that is the i-th column along the horizontal plane and is adjacent to the steel beam 11A in one layer. 4 ) i I L This is the second moment of area (mm²) of the i-th column 31 that is adjacent to the steel beam 11A in the horizontal plane and is located below it. 4 ) is H U This is the floor height (story height) (mm) of one adjacent floor above the steel beam 11A. L This is the floor height (mm) of one adjacent floor below the steel beam 11A. E is the Young's modulus (N / mm²) of column 31. 2 ) N is the total number of columns 31 that are on the same structural plane (on the same surface) as the steel beam 11A and are directly or indirectly connected to the steel beam 11A. n is the number of columns 31 that are on the same structural plane as the steel beam 11A and are directly or indirectly connected to the steel beam 11A, and that are located on the side of the first end (start end) 11aA of the steel beam 11A.

[0065] In this example, we will focus on a column 31 that is directly or indirectly connected to the steel beam 11A as part of building 2 and is on the same structural plane as the steel beam 11A.

[0066] For example, let's explain the case where the first end 11aA is the first side z1 of the steel beam 11A in the material axis direction z. In this case, n means the number of columns 31 that are on the same structural plane as the steel beam 11A and are directly or indirectly connected to the steel beam 11A, and are located at the same position as the first end 11aA or at a position first to the first side z1 of the first end 11aA in the material axis direction z.

[0067] The restraining stiffness K for the steel beam 11A is expressed by equation (a7) as a series system of the sum of the restraining stiffnesses by the column 31 on the first end 11aA side of the steel beam 11A and the sum of the restraining stiffnesses by the column 31 on the second end (terminal) 11bA side of the steel beam 11A.

[0068]

number

[0069] In other words, in this example, the constraint stiffness K can be found using equation (a7). Furthermore, the column 31 on the second end 11bA side refers to a column 31 that is directly or indirectly connected to the steel beam 11A, and is located at the same position as the second end 11bA or at a position z2 further to the second end 11bA in the material axis direction z.

[0070] As an example, Table 2 shows the results of calculating the restrained stiffness K for a steel beam 11A in the middle floor of a three-story building 2, where each floor is 4m high and each span is 9m long.

[0071] [Table 2]

[0072] Analysis Case A involves a steel beam 11 with a cross-section of H-600×200×9×19 and a column 31 with a cross-section of □(welded assembled box cross-section)-400×400×19, where there are multiple columns 31 spanning 3 spans (N=4). In Analysis Case A, both the steel beam 11A located at the ends along the horizontal plane and the steel beam 11A located in the center of building 2 have a required restraining stiffness K. req It surpasses that. On the other hand, in analysis case B, where the cross-section of the steel beam 11 is H-600×200×6×19, which is thinner than the web 14, the required value of the constrained stiffness K req Because it increases, the required restraint stiffness K is K for the same number of spans and cross-section of column 31. req This will result in a failure to satisfy the requirements. In analysis case B, the thickness of web 14 was changed from 9 mm to 6 mm.

[0073] In contrast to analysis case B, in analysis case C, where the cross-sections of steel beams 11 and columns 31 remain the same but the number of spans is increased, only the central beam of building 2 has a required restraining stiffness K. req This result surpasses the previous one. In analysis case C, the number of spans has been changed from 3 to 9. Furthermore, in analysis case D, in which the cross-section and span number of the steel beam 11 remain the same as in analysis case B, and only the cross-section of the column 31 is changed, the required restraint stiffness K is set to the required value K for both the steel beam 11 at the end of building 2 and the steel beam 11 in the center of building 2. req This result surpasses the previous one.

[0074] Thus, the constraint stiffness K increases due to the large number of columns 31 and the enlargement of the cross-section of the columns 31. Therefore, the constraint stiffness K is not the required value K. req Even if it falls below this value, the required value of the restraint stiffness K can be obtained by changing the number of columns 31 or the cross-section of the columns 31. req It can satisfy that.

[0075] From the above, the restraining stiffness K of the steel beam 11 with respect to the contraction in the material axis direction z by the column 31 and floor slab 21, calculated using equation (a7), is the required stiffness K that can be obtained using equation (a5). req If it exceeds this value, even in sections where the normalized width-to-thickness ratio β of the web 14 exceeds 65, deformation performance equivalent to or better than that of a section where the normalized width-to-thickness ratio β of the web 14 is 65 can be expected. This relationship can be expressed mathematically as satisfying equation (a8), and using the normalized width-to-thickness ratio β of web 14, it can be expressed as equation (a5a).

[0076]

number

[0077] [4. Design Method for Floor Support Structures] The design method for the floor support structure of this embodiment (hereinafter referred to as the design method) is as follows: The steel beam 11 is set to be an H-shaped cross section member. The lower flange 13 of the steel beam 11 is set so that no lateral buckling stiffener is attached to prevent lateral buckling. The web 14 of the steel beam 11 is set so that no local buckling stiffener is attached in the range corresponding to the height H of the steel beam 11 from the end in the material axis direction z. Then, the surrounding members 25 of the steel beam 11 are set to restrain the contraction of the steel beam 11 in the material axis direction z, and the deformation performance of the steel beam 11 is evaluated. By performing the above steps, the floor support structure is designed.

[0078] [5. Effects of this embodiment] As described above, in the floor support structure 10 of this embodiment, the inventors diligently studied how to suppress buckling of the steel beam 11 in a floor support structure 10 comprising a column, a steel beam 11 rigidly connected to the column, and a floor slab 21 attached to the upper surface of the steel beam 11 via a headed stud 16, when the steel beam 11 is not fitted with a lateral buckling stiffener and a local buckling stiffener. As a result, they found that even when the normalized width-to-thickness ratio β obtained by equation (a1a) for the web 14 of the steel beam 11 is greater than 65, if the restraining stiffness K of the surrounding members 25 of the steel beam 11 with respect to the contraction of the steel beam 11 in the material axis direction z satisfies equation (a5a), the steel beam 11 becomes less likely to contract in the material axis direction z beyond a certain point, and buckling of the steel beam 11 can be suppressed. Therefore, even when lateral buckling stiffeners and local buckling stiffeners cannot be installed in a steel beam 11 using a cross section with a web standardized width-to-thickness ratio β exceeding 65, buckling of the steel beam 11 can be suppressed.

[0079] In the analysis in [3.], the restraint stiffness K can be determined by equation (a7). In this case, the restraint stiffness K can be precisely defined using the mathematical formula (a7). Furthermore, the restraint on the steel beam 11A can be realized by multiple columns 31 of the building 2. The height of the steel beam 11 is 600 mm or more, and the yield strength of the steel beam 11 is 325 N / mm². 2 In some cases, the above conditions apply. In this case, the height of the steel beam 11 is 600 mm or more, and the yield strength of the steel beam 11 is 325 N / mm². 2 By applying the present invention to relatively large steel beams 11, which conventionally had a cross-section with a relatively thick web thickness, making economical design difficult, a rational member can be realized.

[0080] Furthermore, in the design method of this embodiment, the inventors diligently studied how to suppress buckling of the steel beam 11 in a floor support structure 10 comprising a column, a steel beam 11 rigidly connected to the column, and a floor slab 21 attached to the upper surface of the steel beam 11 via a headed stud 16, when the steel beam 11 is not fitted with a lateral buckling stiffener and a local buckling stiffener. As a result, they found that if the surrounding members 25 of the steel beam 11 are set to restrain the contraction of the steel beam 11 in the material axis direction z, the steel beam 11 becomes less likely to contract in the material axis direction z beyond a certain point, and buckling of the steel beam 11 can be suppressed. Therefore, even if lateral buckling stiffeners and local buckling stiffeners cannot be attached to the steel beam 11, the buckling of the steel beam 11 can be suppressed and it can be designed as a member with high deformation performance.

[0081] Although one embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and modifications, combinations, deletions, etc., of the configuration are also included without departing from the spirit of the present invention. [Explanation of symbols]

[0082] 10 Floor support structure 11 Steel beam 13 Lower flange 14 Web 16 Headed Studs (Shear Connectors) 21 Floor slab 25 Peripheral components 31 pillars z Material axis direction

Claims

1. A floor support structure comprising a column, a steel beam rigidly connected to the column, and a floor slab attached to the upper surface of the steel beam via a shear connector, The aforementioned steel beam is an H-shaped cross-section member, The lower flange of the aforementioned steel beam is not fitted with a lateral buckling stiffener to prevent lateral buckling. In the web of the aforementioned steel beam, the standardized width-to-thickness ratio β obtained by equation (1) is greater than 65. In the aforementioned web, no local buckling stiffener is provided to prevent local buckling in the area corresponding to the height of the steel beam, from the end of the steel beam in the axial direction of the material. A floor support structure in which the restraining stiffness K of the steel beam by the surrounding members with respect to the axial compression of the steel beam satisfies equation (2). However, d is the height of the web, t ｗ F is the thickness of the web, F is the standard strength of the material strength of the steel beam, E is the Young's modulus of the steel beam, A is the cross-sectional area of ​​the steel beam perpendicular to the material axis direction, and L is the length of the steel beam. [Math 1]

2. The aforementioned peripheral member is the column, The restraint stiffness K is determined by equation (3), as described in claim 1. However, N is the total number of columns directly or indirectly connected to the steel beam which is on the same structural plane as the steel beam, n is the number of columns located on the first end side of the steel beam among the columns directly or indirectly connected to the steel beam which is on the same structural plane as the steel beam, K ｉ is the stiffness of the i-th column along the horizontal plane. [Math 2]

3. The height of the steel beam is 600 mm or more, and the yield strength of the steel beam is 325 N / mm². ２ The floor support structure according to claim 1 or 2.

4. A method for designing a floor support structure comprising a column, a steel beam rigidly connected to the column, and a floor slab attached to the upper surface of the steel beam via a shear connector, The aforementioned steel beam is set to be an H-shaped cross-section member. The lower flange of the aforementioned steel beam is designed so that a lateral buckling stiffener is not attached to prevent lateral buckling. In the web of the steel beam, a local buckling stiffener is not provided in the area corresponding to the height of the steel beam, from the end in the axial direction of the steel beam. A design method for a floor support structure, which evaluates the deformation performance of a steel beam by setting the surrounding members of the steel beam to restrain the steel beam's contraction in the axial direction of the steel beam.

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