Floor structure

Abstract

To provide a floor structure suppressed in generation of lateral buckling in a girder.SOLUTION: A floor structure 10 is formed of an H-section steel, and includes a girder 21 to which no lateral stiffener is attached, a pair of pillars joined to both ends of the girder 21 with rigid joint or semi-rigid joint, and a floor slab attached to the girder 21. A non-reinforced through hole 24a is formed only in a specific area in an intermediate part in a material axis direction X of the girder in a web 24 that the girder 21 has.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a floor structure. [Background technology]

[0002] Traditionally, structural members of buildings consist of vertical columns and horizontal beams that span between the columns. In steel-structure buildings in Japan, square steel pipes with a rectangular cross section and rounded corners are mainly used as columns. An H-shaped steel 100 with an H-shaped cross section, as shown in Figure 17, is used for a beam. The H-shaped steel 100 has high cross-sectional performance around the x-axis, which is the strong axis, and is an efficient cross-sectional shape. On the other hand, the H-shaped steel 100 has low cross-sectional performance around the y-axis, which is the weak axis. For this reason, when the H-shaped steel 100 is subjected to a bending moment, a phenomenon called lateral buckling occurs, in which the part of the H-shaped steel 100 that is subjected to a compressive force twists and collapses out of plane, reducing the strength and deformation performance of the H-shaped steel 100.

[0003] Furthermore, the beam is provided with through holes for facility piping. In the case of a steel beam (steel beam) using H-shaped steel 100, through holes (not shown) are provided in the web 101 of the H-shaped steel 100. In Japan, through holes are often circular in shape. Beams with through holes not only have reduced strength and deformation performance due to the influence of cross-sectional loss, but are also more susceptible to lateral buckling and the like compared to beams without through holes. Therefore, beams are generally used with reinforcement around the through holes.

[0004] The reinforcing members that reinforce the area around the through-holes are welded to the beams, which makes installing the reinforcing members time-consuming. Furthermore, there are many through-holes in the beams for equipment piping in a single building, and reinforcing them requires a great deal of time and effort. Therefore, it would be desirable to eliminate the need to reinforce the through-holes in the beams.

[0005] Prior art related to the lateral buckling of steel beams largely relates to reducing the weight of the lateral stiffeners of steel beams, or to steel beams and floor structures that omit lateral stiffeners in consideration of the restraining effect of floor slabs, as well as to their design methods (see, for example, Patent Documents 1 to 8). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-113494 [Patent Document 2] Japanese Patent Publication No. 2023-078554 [Patent Document 3] Japanese Patent Application Publication No. 2019-190109 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-161124 [Patent Document 5] Japanese Patent Application Publication No. 2018-172876 [Patent Document 6] Japanese Patent Publication No. 2022-144692 [Patent Document 7] Japanese Patent Application Publication No. 2023-114887 [Patent Document 8] Patent Publication No. 2021-055464 Summary of the Invention [Problem to be solved by the invention]

[0007] Generally, there is a floor slab above the steel beam, and the steel beam and floor slab are fixed together via a shear connector. When the floor slab fixes the top flange of the steel beam and restricts its lateral movement and rotation, the area of ​​the steel beam where the top flange is subjected to compressive force is suppressed from twisting or collapsing, making it less susceptible to lateral buckling than if the steel beam were a single unit. It should be noted that Patent Documents 1 to 8 are directed to steel beams without through holes, and do not describe steel beams with through holes. Therefore, Patent Documents 1 to 8 cannot be used to determine whether or not lateral stiffeners are required for steel beams with through holes, or to consider the placement area of ​​the through holes. In order to use Patent Documents 1 to 8, it is necessary to reinforce the through holes so that the performance is equivalent to that of steel beams without through holes.

[0008] When the restraining effect of the floor slab is taken into account, it is believed that even for steel beams with through holes, the area of ​​the steel beam where the upper flange is subjected to compressive force will be less susceptible to lateral buckling. In other words, by taking into account the restraining effect of the floor slab, it is believed that there is an area in steel beams with through holes where the presence or absence of a through hole is less likely to affect the likelihood of lateral buckling, and if this area can be clarified, it will be possible to omit reinforcement of the through holes in the steel beams. Furthermore, among steel beams, large girders, which are joined at both ends to a pair of columns, are subject to load conditions specific to large girders.Measures to prevent lateral buckling are also being considered for large girders.

[0009] The present invention has been made in consideration of such problems, and has as its object to provide a floor structure that suppresses the occurrence of lateral buckling in the girders. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention proposes the following means. (1) Aspect 1 of the present invention is a floor structure comprising a girder made of H-shaped steel and having no lateral stiffeners attached thereto, a pair of columns rigidly or semi-rigidly joined to both ends of the girder, and a floor slab attached to the girder, in which an unreinforced through-hole is formed in the web of the girder only in a specific region in the middle of the girder in the material axis direction.

[0011] In this invention, the inventors have conducted extensive research into lateral buckling that occurs in a floor structure that includes a girder made of H-shaped steel with no lateral stiffeners attached, a pair of columns rigidly or semi-rigidly joined to both ends of the girder, and a floor slab attached to the girder, and in which the web of the girder has an unreinforced through-hole with no reinforcing member attached.As a result, they have found that lateral buckling in the girder can be suppressed when a through-hole is formed only in a specific region in the middle of the girder in the material axis direction. Therefore, by configuring in this way, it is possible to suppress lateral buckling of the main girder.

[0012] (2) Aspect 2 of the present invention may be a floor structure as described in (1), in which the specific area is an area of ​​0.5L in the material axis direction, with the center of the material axis direction of the girder being the center of the specific area, when the length of the main girder in the material axis direction is defined as L. In this invention, it is possible to suppress lateral buckling of the girder in a specific region that is a region of 0.5L in the axial direction, with the center of the specific region being the center of the axial direction of the girder.

[0013] (3) Aspect 3 of the present invention may be the floor structure according to (1) or (2), in which all of the through holes formed in the specific region are unreinforced. In this invention, all of the unreinforced through holes can more reliably prevent lateral buckling of the girder. [Effects of the Invention]

[0014] The floor structure of the present invention can prevent lateral buckling from occurring in the girders. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing a schematic configuration of a floor structure according to an embodiment of the present invention. FIG. [Figure 2] FIG. 2 is a perspective view of a girder in the floor structure. [Figure 3] FIG. 10 is a diagram showing the bending moment acting on the girder when a horizontal load is applied. [Figure 4] FIG. 10 is a diagram showing the shear force acting on a girder when a horizontal load is applied. [Figure 5] FIG. 10 is a diagram showing the change in the load capacity of a girder due to deformation of the girder, depending on whether lateral buckling occurs or not. [Figure 6] FIG. 10 is a diagram showing the change in elastic buckling strength with respect to shear span ratio due to the opening area. [Figure 7] This is a contour diagram showing the buckling mode of the girder when the shear span ratio is 6. [Figure 8] This is a contour diagram showing the buckling mode of the girder when the shear span ratio is 20. [Figure 9] This is a contour diagram showing the buckling mode of the girder when the shear span ratio is 30. [Figure 10] FIG. 10 is a graph showing the change in yield strength reduction rate with respect to shear span ratio in the case of H-500×200. [Figure 11] FIG. 10 is a graph showing the change in yield strength reduction rate with respect to shear span ratio in the case of H-700×200. [Figure 12] FIG. 10 is a graph showing the change in yield strength reduction rate with respect to shear span ratio in the case of H-900×300. [Figure 13] FIG. 10 is a graph showing the change in yield strength reduction rate with respect to shear span ratio. [Figure 14] FIG. 10 is a diagram showing the change in the opening area relative to the aspect ratio. [Figure 15] FIG. 10 is a diagram showing the change in elastic buckling strength with respect to shear span ratio due to the opening area. [Figure 16] FIG. 10 is a diagram showing the change in yield strength reduction rate with respect to shear span ratio due to the opening area. [Figure 17] FIG. 1 is a front view of a conventional H-beam. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of a floor structure according to the present invention will be described with reference to FIGS.

[0017] [1. Floor structure] As shown in Fig. 1, a floor structure 10 of this embodiment is provided in a building 1. The floor structure 10 has a pair of columns 16, a girder 21, and a floor slab (not shown). There are no limitations on the configuration of the column 16. For example, the column 16 is formed of a square steel pipe. The column 16 extends in the vertical direction Z from a support member S1 such as a foundation. The pair of pillars 16 are spaced apart from each other along a horizontal plane. The pillar 16 may be formed of H-beam, steel-reinforced concrete, concrete-filled steel pipe, reinforced concrete, or the like.

[0018] As shown in FIG. 2 , the girder 21 is formed of an H-shaped steel. The girder 21 extends in the material axis direction (longitudinal direction) X along a horizontal plane. Specifically, the girder 21 has an upper flange 22, a lower flange 23, and a web 24. The upper flange 22, the lower flange 23, and the web 24 are each formed into a flat plate shape from steel. The upper flange 22 is located above the lower flange 23. The web 24 is located between the upper flange 22 and the lower flange 23. The web 24 is joined to the center of the upper flange 22 in the width direction and the center of the lower flange 23 in the width direction, respectively.

[0019] A plurality of through holes 24a are formed in the web 24. For example, when viewed in the thickness direction of the web 24, each of the through holes 24a has a circular shape. The number of through holes 24a formed in the web 24 may be one. No reinforcing member that reinforces the periphery of each through hole 24a is provided in each through hole 24a. In other words, each through hole 24a is unreinforced. The reinforcing member referred to here means, for example, a member fixed to a portion of the web 24 that is located within the radius of the through hole 24a from the periphery of the through hole 24a when viewed in the thickness direction of the web 24. A shear connector, such as a headed stud, is preferably fixed to the upper flange 22. The shear connector protrudes upward from the upper flange 22.

[0020] As shown in Fig. 1, both ends of the girder 21 in the material axis direction X are rigidly or semi-rigidly joined to a pair of columns 16. The rigid and semi-rigid joints referred to here are joints specified in, for example, "Eurocode 3: Design of steel structures - Parts 1-8: Design of joints", 2004.

[0021] The floor slab is formed in a flat plate shape. For example, the floor slab is formed of a reinforced concrete slab with reinforcing bars installed in the concrete. The floor slab is supported from below by the upper flange 22 of the main beam 21. The shear connectors of the girders 21 are embedded in the concrete of the floor slab. The floor slab is attached to the girders 21 via the shear connectors. The floor slab may be formed of a composite slab having a deck plate and concrete placed on the deck plate.

[0022] No horizontal stiffeners are attached to the girder 21. The horizontal stiffener here refers to a member that connects the member to be stiffened by this horizontal stiffener to another girder, column, etc.

[0023] [2. Study of the effect of through holes on lateral buckling] As shown in Figure 1, it is believed that a horizontal load P along the material axis direction X acts primarily on the girder 21, for example, due to an earthquake. Here, the length of the girder 21 in the material axis direction X is defined as L. As shown in Figure 17, the beam depth (height) of the girder 21 is defined as H. The width of the girder 21 is defined as B. This horizontal load P causes a bending moment shown in FIG. 3 and a shear force shown in FIG. Figure 5 shows the change in the load capacity of the girder 21 depending on whether or not lateral buckling occurs in the girder 21. It can be seen that when lateral buckling occurs in the girder 21, the load capacity of the girder 21 decreases compared to when lateral buckling does not occur in the girder 21.

[0024] [2.1. Effect of opening area on lateral buckling] First, we used finite element numerical analysis to study the effect of the opening region (arrangement region) in which the through holes 24a are formed in the material axis direction X of the girder 21 on the strength of the girder 21. Figure 2 shows an example of an analytical model of the girder 21. The xyz coordinates were defined for the girder 21 as shown in Figure 2. The center of the opening region was set to the center in the material axis direction X of the main girder 21. The opening region was then expanded in the material axis direction X from 0 times (no through-holes) to 1 time (through-holes along the entire length) of the length L in increments of 0.1 times the length L. Note that only the results in increments of 0.2 times are shown in Fig. 6 and other figures described later. When arranging the through holes 24a in the opening areas, the through holes 24a with a diameter of H / 2 were provided to fill the opening areas to the fullest extent, with the beam depth H as the reference, and at intervals of the center pitch H between the through holes 24a. In other words, in each opening area, through holes with the maximum opening area actually expected for the main beam were formed.

[0025] A shell was used to model the girder 21. All degrees of freedom of the first end 21a of the girder 21 in the material axis direction X were fixed. At the second end 21b of the girder 21 in the material axis direction X, rotation around the x-axis was restricted. Furthermore, warping at the second end 21b was fixed. Specifically, movement in the x-axis direction and rotation around the y-axis at the second end 21b were restricted. In this state, a forced displacement is applied to the second end 21b and a load is applied, thereby reproducing the stress state shown in Figures 3 and 4. In addition, in order to reproduce the restraining effect of the floor slab, the upper flange 22 restrains the movement in the x-axis direction and the rotation around the z-axis over the entire length of the girder 21. The analysis variable was the shear span ratio (L / H), which is the length L divided by the beam depth H. The shear span ratio was varied in increments of 2 within the range of 6 to 50.

[0026] The analysis results are shown in Figures 6 to 9. In Figure 6, the vertical axis shows the elastic buckling strength of each analysis model obtained from the analysis, and the horizontal axis shows the shear span ratio. Figure 6 shows that the elastic buckling strength decreases as the opening area of ​​the through-hole 24a increases. Furthermore, regardless of the opening area of ​​the through-hole 24a, as the shear span ratio increases, the elastic buckling strength shows a mountain-shaped distribution with a maximum value as the shear span ratio increases. The reason for this is that in the region where the shear span ratio is small, shear buckling becomes the dominant mode in the girder 21, as shown in Figure 7, and the elastic buckling strength drops sharply as the shear span ratio decreases. Note that in Figures 7 to 9, the shades of gray represent the out-of-plane deformation of the flanges 22, 23 and web 24, non-dimensionalized by the maximum out-of-plane deformation of the girder 21. In each figure, the darker the gray in a certain area, the greater the out-of-plane deformation in that area.

[0027] On the other hand, in the region where the shear span ratio is large, lateral buckling becomes the dominant mode in the girder 21, and the elastic buckling strength decreases gradually as the shear span ratio increases, as shown in Figure 9. In the region where the shear span ratio is intermediate, the buckling mode in the girder 21 is a region where shear buckling and lateral buckling are coupled (see Figure 8).

[0028] In this embodiment, in order to clarify the opening area of ​​the through hole 24a that does not affect lateral buckling, the minimum value of the shear span ratio at which only lateral buckling affects the elastic buckling strength was determined to be 30 based on the distribution of elastic buckling strength in Figure 6 and the buckling modes shown in Figures 7 to 9. Hereafter, a method for designing the opening area of ​​the through-hole 24a that does not affect lateral buckling will be considered, based on a shear span ratio of 30.

[0029] As can be seen from Figure 6, even when the shear span ratio is 30 or more, the provision of the through holes 24a reduces the elastic buckling strength of the main girder 21 (steel beam), albeit slightly. In other words, to clarify the opening area of ​​the through holes 24a that does not affect lateral buckling, it is necessary to determine the allowable value for the rate of reduction in elastic buckling strength (rate of reduction in strength).

[0030] [2.2. Consideration of the allowable value of the rate of decrease in elastic buckling strength] The cross-sectional size and steel type of the girders of a building are selected to ensure safety against the loads acting on them. H-shaped steel is generally used for the girders. The height, width, and thickness of the H-shaped steel vary in stages. Therefore, when designing the girder 21 using H-shaped steel, the most efficient cross-sectional size that meets or exceeds the performance required for the girder 21 is selected from the standardized H-shaped steel cross-section list shown in Table 1. Therefore, the girder 21 is designed with a cross-sectional size that has a slightly larger margin of performance than the performance required for the girder 21.

[0031] [Table 1]

[0032] Table 1 is an excerpt from the table of cross-sectional sizes for fixed outer dimensions H-shaped steel in the H-shaped steel catalog (Nippon Steel Corporation. https: / / www.nipponsteel.com / product / catalog_download / pdf / K004.pdf). For example, if calculations show that a cross-sectional size of H-700 x 200 x 12 x 17 is sufficient, then select H-700 x 200 x 12 x 19 from the cross-section list. In other words, select an H-shaped steel beam with a beam depth H of 700 mm, width B of 200 mm, web thickness t1 of 12 mm, and flange thickness t2 of 19 mm from the cross-section list. Therefore, even if the elastic buckling strength is slightly reduced by providing through holes 24a in a limited area of ​​girder 21, it was thought that this could be absorbed by the margin of strength of girder 21. It was also thought that this margin of strength would be the allowable value for the rate of reduction in elastic buckling strength. For example, let us consider a case where girder A, which is part of a building, has a cross-sectional size of H-700 x 200 x 12 x 19, designed based on the load acting on girder A. In this case, providing through holes in a wide area in the material axis direction of girder A reduces the elastic buckling strength of girder A, and it was thought that it would be impossible to provide through holes 24a in an area where the performance of girder A would be reduced to the same level as the elastic buckling strength of a girder with a cross section of H-700 x 200 x 12 x 16.

[0033] In other words, we thought that the rate of decrease in elastic buckling strength when the cross-sectional size changed from H-700×200×12×19 to H-700×200×12×16 would be the acceptable rate of decrease in elastic buckling strength due to a through hole.

[0034] Furthermore, in buildings, wider column spacing is more convenient for use, so the length of the girders spanning between columns is often long. As a result, bending moments and shear forces occur in the girders, as shown in Figures 3 and 4, and the cross-sectional size of the girders is generally determined by the bending moment. In the case of H-shaped cross-section members, a larger cross-sectional area at a position away from the neutral axis (x-axis in Figure 17) can efficiently increase the bending moment (= bending performance) that can be borne. In other words, when the height and width of the H-shaped steel are fixed, the flange thickness (thickness) has a significant effect on the bending performance of the H-shaped steel. Therefore, in order to determine the allowable value for the rate of decrease in elastic buckling strength, analytical studies were carried out for H-shaped steels of various heights, with the flange thickness as a variable, and the allowable value for the rate of decrease in elastic buckling strength was confirmed.

[0035] 2 shows an analytical model of the girder 21A. The girder 21A does not have through holes 24a formed in each configuration of the girder 21. A list of analytical models is shown in Table 2.

[0036] [Table 2]

[0037] For three cross sections of H-shaped steel with heights and widths of H-500×200, 700×200, and 900×300, the plate thickness of flanges 22 and 23 was changed to three levels. The length of the analytical model in the material axis direction was also changed so that the shear span ratio changed in increments of 2 in the range of 6≦L / H≦50.

[0038] 10 to 12 show the rate of decrease in elastic buckling strength when the plate thickness of the flanges 22 and 23 is reduced. Note that tf in FIGS. Although the magnitude of the strength reduction rate differs depending on the beam height, the change in the strength reduction rate is large in the region where shear span ratio is small and shear buckling is dominant. On the other hand, in the region where shear span ratio is 30 or more and lateral buckling is dominant, the strength reduction rate converges to a constant value, with the minimum convergence value being around 7%. Therefore, the allowable rate of decrease in elastic buckling strength when only lateral buckling affects the elastic buckling strength is set at 5%, which is a safer value than 7%.

[0039] [2.3. Consideration of the opening area of ​​the through-hole] Next, a design method for the opening area of ​​the through-hole 24a will be analyzed and examined. As mentioned above, lateral buckling occurs in the parts that receive compressive force when the girder is subjected to a bending moment due to low cross-sectional performance around the weak axis (y-axis in Figure 17). Therefore, we focused on the aspect ratio H / B, which is the ratio of the girder's height H to its width B, as a girder specification that improves performance around the weak axis. Note that the aspect ratio is one example of a variable that organizes the cross-sectional shape of the girder, and the cross-sectional shape of the girder may also be organized using variables other than the aspect ratio. Table 3 shows a list of analytical models in which the aspect ratio of the girder is used as a variable and is changed in increments of 0.5 within the range of 2≦H / B≦4.

[0040] [Table 3]

[0041] For the girders shown in Table 3, the shear span ratio was changed in increments of 2 within the range of 6≦L / H≦50. The center of the opening area of ​​the through hole 24a was set to the center of the material axis direction X of the girder 21. The opening area was changed in increments of 0.1 times the length L in the material axis direction X within the range of 0 times (no through hole) to 1 time (through hole over the entire length). The analysis conditions were the same as in [2.1].

[0042] The elastic buckling strength obtained from the analysis when no through holes 24a are formed is compared with the elastic buckling strength when through holes 24a are formed in each region, and an example of the relationship between the strength reduction rate of the elastic buckling strength when through holes 24a are formed and the shear span ratio (L / H) when through holes 24a are formed is shown in Figure 13. Figure 13 shows the case of a cross section of H-700 x 200 x 12 x 19. In Figure 13, the state where the strength reduction rate is 5% is indicated by line L1, and the state where the shear span ratio is 30 is indicated by line L2.

[0043] The rate of decrease in elastic buckling strength increases as the opening area of ​​the through hole 24a is widened. Also, in the range of this study where the rate of decrease in strength is 5% or less and the shear span ratio is 30 or more, the rate of decrease in strength is greatest when the shear span ratio is 30. In other words, to design an opening area of ​​the through hole 24a that does not affect lateral buckling, it is sufficient to find the largest opening area where the rate of decrease in elastic buckling strength is 5% or less when the shear span ratio is 30. More specifically, among the plots on line L2 and below line L1 in Fig. 13, the largest opening area is when the opening area is 0.6L. Therefore, the opening area in which the through-hole 24a can be provided is the area of ​​0.6L in the material axis direction X, centered at the center of the material axis direction X of the main girder 21.

[0044] Figure 14 shows the relationship between the opening area and aspect ratio of through-hole 24a, which has little effect on lateral buckling for the H-shaped cross-sectional sizes shown in Table 3. Figure 14 shows that the opening area of ​​through-hole 24a, which has little effect on lateral buckling, changes little with the aspect ratio. In other words, there is no clear correlation between the opening area and aspect ratio of through-hole 24a. Based on the above considerations, in this embodiment, the opening region of the through hole 24a is set to a region (specific region) having a length of 0.5L in the material axis direction X and centered at the center of the material axis direction X of the main girder 21. The through hole 24a is formed only in a region having a length of 0.5L at a middle part of the main girder 21 in the material axis direction X. The specific region is a region between positions of length 0.25L on both sides in the material axis direction X, with the center of the region being the center of the region in the material axis direction X of the main girder 21.

[0045] [2.4. When the shear span ratio is less than 30] In this study, the analysis results were used for shear span ratios (L / H) of 30 or more, so that lateral buckling would be the dominant mode. However, it was confirmed that the same tendency occurs even in areas where the shear span ratio is less than 30, when lateral buckling is the dominant mode. As an example, for a cross section of H-500x50x9x16, the shear span ratio was changed in increments of 2 within the range of 6≦L / H≦50, as before, and the opening area of ​​the through-hole 24a was changed in increments of 0.1 from the center of the main girder within the range of 0 times the length L (no through-hole) to 1 time (through-holes along the entire length). The relationship between the elastic buckling strength and the shear span ratio is shown in Figure 15, and the relationship between the strength reduction rate of the elastic buckling strength and the shear span ratio is shown in Figure 16. In Figure 16, the state where the strength reduction rate is 5% is also shown with line L5.

[0046] In a cross section prone to lateral buckling, such as the H-500 × 50 × 9 × 16 cross section, lateral buckling is dominant even in the region where the shear span ratio (L / H) is less than 30, as shown in Fig. 15. Also, Fig. 16 confirms that the range where the shear span ratio is less than 30 can be evaluated in the opening region of the through hole 24a obtained from the result where the shear span ratio is 30. In addition, the strength reduction rate exceeds 5% when the shear span ratio is less than 12, but this is because even with a cross section of H-500 x 50 x 9 x 16, the shear span ratio range of less than 12 is a range in which lateral buckling and shear buckling are coupled, and this is the reason why the strength reduction rate exceeds 5%. However, in cross sections where lateral buckling is more likely to occur, lateral buckling can become dominant even when the shear span ratio is less than 12, so the method (configuration) of this embodiment can also be applied to steel beams with a shear span ratio of less than 12.

[0047] 3. Effects of this embodiment As explained above, in the floor structure 10 of this embodiment, the inventors have conducted extensive research into lateral buckling that occurs in a floor structure 10 that includes a girder 21 formed of H-shaped steel and to which no lateral stiffeners are attached, a pair of columns 16 rigidly or semi-rigidly joined to both ends of the girder 21, and a floor slab attached to the girder 21, and in which unreinforced through-holes 24a to which no reinforcing members are attached are formed in the webs 24 of the girder 21. As a result, it has been found that lateral buckling in the girder 21 is suppressed when the through-holes 24a are formed only in a specific region in the middle of the girder 21 in the material axis direction X. Therefore, by configuring in this way, it is possible to prevent lateral buckling of the main girder 21.

[0048] The specific region is a region of 0.5L in the material axis direction X, with the center of the specific region being the center of the material axis direction X of the girder 21. Therefore, it is possible to suppress lateral buckling of the girder 21 in the specific region, which is a region of 0.5L in the material axis direction, with the center of the specific region being the center of the material axis direction X of the girder 21.

[0049] [4. Notes] 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 configuration changes, combinations, deletions, etc. are also included within the scope that does not deviate from the gist of the present invention. For example, the above embodiment is not limited to cases where the shear span ratio (L / H) is equal to or greater than 30. Furthermore, in the case of a girder that is reinforced with stiffeners or the like against local buckling or shear buckling, buckling modes other than lateral buckling are unlikely to occur, so in these cases as well, lateral buckling becomes dominant even when the shear span ratio is less than 30, and the method (configuration) of this embodiment can be applied.

[0050] The girders, floor slabs, and shear connectors that constitute the floor structure of this embodiment will be described. The main girder has an H-shaped cross section and may be H-shaped steel (rolled H-shaped steel) manufactured by rolling, or built H-shaped steel (welded and assembled H-shaped steel) made by welding steel plates of different thicknesses together into an H shape. The floor slab may be a composite deck slab using a deck plate. The shear connectors may be burnt plug welds, perforated steel dowels, or the like. The girders, floor slabs, columns, and shear connectors are not limited to those described in this embodiment.

[0051] The through-hole 24a is preferably formed below the center of the web 24 in the up-down direction.

[0052] The number of through-holes 24a formed in a particular region may be one or more. Furthermore, by forming the through holes 24a only in specific areas, even if all the through holes 24a formed in the specific areas are unreinforced through holes to which no reinforcing members are attached, lateral buckling of the main girder 21 can be more reliably suppressed.

[0053] The shape of the through-hole may be circular, rectangular, square, etc., and the size of the through-hole is not limited. Furthermore, the effect of [3] can be obtained regardless of the shape and size of the through-hole. The height and width of the through-hole 24a may be smaller or larger than half the beam depth. [Explanation of symbols]

[0054] 10 Floor structure 16 pillars 21 Large beam 24 Web 24a through hole X Material axis direction

Claims

1. A girder formed by H-shaped steel and to which no horizontal stiffener is attached; A pair of columns joined to both ends of the girder by rigid or semi-rigid joints; a floor slab attached to the girder; Equipped with A floor structure in which unreinforced through holes are formed in the webs of the girder only in specific regions in the middle of the girder in the material axis direction.

2. 2. The floor structure according to claim 1, wherein the specific area is an area of ​​0.5L in the material axis direction, with the center of the material axis direction of the girder being the center of the specific area, when the length of the girder in the material axis direction is defined as L.

3. The floor structure according to claim 1 or 2, wherein all of the through holes formed in the specific region are unreinforced.

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