Girder-beam connection structure

Abstract

To provide a girder-beam connection structure enabling rigid connection between a girder and a beam using fillet welding that is easy to construct and capable of ensuring sufficient welding length on a beam lower flange side.SOLUTION: A girder-beam connection structure 1 according to the invention comprises: a beam upper flange connection part 7 at which a beam upper flange 5a is rigidly connected to a girder upper flange 3a, or the beam upper flanges 5a facing each other are rigidly connected to each other; a beam web connection part 9 at which a beam web 5b is rigidly connected to a vertical plate 19 connected to a girder web 3b; and a beam lower flange connection part 11 at which a beam lower flange 5c is connected to a lower flange weld plate 25 connected to a lower face of a girder lower flange 3c. The lower flange weld plate 25 is a plate wider than the beam lower flange 5c extending from both side ends of the girder lower flange 3c. A material axis direction side end 5ca of the beam lower flange 5c is connected by fillet welding to the lower flange weld plate 25 at the beam lower flange connection part 11.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a girder and joist joint structure of a framework in a steel structure.

Background Art

[0002] Conventionally, a framework for supporting a concrete floor in a steel structure is composed of girders arranged in parallel at a predetermined interval and joists arranged to connect the girders. In a general girder and joist joint of a framework, the joist web is bolted to a mating member provided on the girder web, and the upper and lower flanges of the joist are designed as a pin joint that does not join. The joist with pin joints at both ends is called a simple beam. When supporting the floor, the bending moment generated in the joist is not transmitted to the girder, so the bending moment concentrates at the central portion in the longitudinal direction of the joist. Therefore, in the structure where the joist is pin-jointed to the girder, the size of the joist has to be increased to resist the bending moment at the central portion of the joist, increasing the weight of the joist and becoming a factor in cost increase.

[0003] Here, by making the joist joint a rigid joint and generating a moment at the end, the bending moment concentrated at the central portion in the longitudinal direction of the joist can be reduced. Such examples are disclosed in Patent Documents 1 and 2, for example, and these can reduce the weight of the joist compared to the case where the joist is pin-jointed to the girder. Note that a rigid joint is a joint rich in rotational restraint force that can be regarded as not generating a rotational displacement (angle) at the joint portion, and a pin joint is a joint that can be regarded as not exerting a rotational restraint force and allowing a rotational displacement (angle) to occur at the joint portion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, the upper and lower flanges of the secondary beam are welded to the main beam, so that the main beam and the secondary beam are rigidly joined. In this welded joint, as can be seen from FIG. 4 of Patent Document 1, butt welding (complete penetration welding) is used. However, since butt welding requires the skill of a welder, the work load at the site was large. In recent years, with the aging of skilled workers, the number of welders with high skills has been decreasing, so a construction method that does not depend on the skill of welders is desired.

[0006] On the other hand, in Patent Document 2, the upper and lower flanges of the secondary beam are rigidly joined to the main beam by fillet welding. Since fillet welding does not require the skill of a welder as compared with butt welding, construction at the site is easy.

[0007] In the case of joining by fillet welding, the joining strength improves as the welding length becomes longer. Therefore, when joining the upper and lower flanges of the secondary beam to the main beam by fillet welding, it is necessary to perform fillet welding with a sufficient welding length so as to be able to resist the stress acting on the joint when a bending moment occurs in the secondary beam. In this regard, Patent Document 2 proposes a method of increasing the fillet welding length by forming a notch in the upper flange of the secondary beam (see FIG. 12 of Patent Document 2). However, this requires processing the upper flange of the secondary beam, which takes time and effort in manufacturing.

[0008] Further, the structure of Patent Document 2 is a structure in which secondary beams are rigidly joined to both sides of the main beam and these secondary beams function as continuous beams. However, since the stress generated in one secondary beam is transmitted to the other secondary beam via the main beam, it may be difficult to apply when the yield strength of the main beam is lower than the yield strength of the secondary beam.

[0009] The present invention has been made to solve the above-described problems, and an object thereof is to provide a girder and joist joint structure that forms a girder and joist joint using fillet welding that is easy to construct and can easily secure a required welding length. Another object of the present invention is to provide a girder and joist joint structure that can be applied even when the yield strength of the girder is lower than the yield strength of the joist.

Means for Solving the Problems

[0010] (1) The girder and joist joint structure according to the present invention is a girder and joist joint structure in which a pair of joists made of H-shaped steel having the same beam shape as the girder are opposed to each other with the girder interposed therebetween in a direction orthogonal to the girder, and the girder is made of H-shaped steel. A joist upper flange joint portion in which the joist upper flanges of the opposing joists are rigidly joined to the girder upper flange, or the opposing joist upper flanges are rigidly joined to each other via a member. A joist web joint portion in which the joist webs of the opposing joists are rigidly joined to vertical plates joined to the girder web, respectively. A joist lower flange joint portion in which the joist lower flanges of the opposing joists are joined to a lower flange welding plate joined to the lower surface of the girder lower flange, and has: The lower flange welding plate is a plate that is orthogonal to the longitudinal direction of the girder lower flange and is wider than the joist lower flanges extending from both side ends of the girder lower flange. The joist lower flange joint portion is characterized in that the side end portion in the material axis direction of the joist lower flange is fillet welded to the lower flange welding plate in a state where the lower surface of the joist lower flange is in contact with the lower flange welding plate.

[0011] (2) Further, in the structure described in (1) above, the tip portion in the material axis direction of the joist lower flange is fillet welded to the lower flange welding plate.

[0012] (3) Further, in the structure described in (1) or (2) above, an upper flange welding plate that is orthogonal to the longitudinal direction of the upper flange of the girder and extends from both side ends of the upper flange of the girder is disposed on the upper surface of the upper flange of the girder. The upper flange welding plate is a plate that is narrower in width than the upper flange of the secondary girder. The upper flange joint of the secondary girder joins the upper flanges of the opposing secondary girders to the upper flange welding plate, and is characterized in that the outer peripheral portion of the upper flange welding plate is fillet welded to the upper flange of the secondary girder in a state where the lower surface of the upper flange welding plate is in contact with the upper flange of the secondary girder.

[0013] (4) Further, the girder-secondary girder joint structure according to the present invention is a girder-secondary girder joint structure in which a pair of secondary girders using H-shaped steel are opposed to each other with a girder using H-shaped steel interposed therebetween in a direction orthogonal to the girder, and joined together. An upper flange joint of the secondary girder that joins the upper flanges of the opposing secondary girders to an upper flange welding plate disposed on the upper surface of the upper flange of the girder. A vertical plate joined to the girder web and a secondary girder web joint that rigidly joins the secondary girder webs of the opposing secondary girders to the vertical plate, respectively. A lower flange joint of the secondary girder in which the lower flanges of the opposing secondary girders are rigidly joined to the lower flange of the girder, respectively, or the lower flanges of the opposing secondary girders are rigidly joined to each other via a member. The upper flange welding plate is a plate that is orthogonal to the longitudinal direction of the upper flange of the girder and is narrower in width than the upper flanges of the secondary girders extending from both side ends of the upper flange of the girder. The upper flange joint of the secondary girder is characterized in that the outer peripheral portion of the upper flange welding plate is fillet welded to the upper flange of the secondary girder in a state where the lower surface of the upper flange welding plate is in contact with the upper flange of the secondary girder.

Advantages of the Invention

[0014] Since the present invention constitutes a joint portion using fillet welding that is easy to construct, it can be constructed even at a site where there is no skilled welder. Further, it is possible to easily secure the welding length necessary to resist the stress acting on the joint portion. Furthermore, since it is also possible to configure the stress transmission between the small beams joined to both sides of the large beam without passing through the large beam, it is suitable even when the yield strength of the large beam is lower than the yield strength of the small beam.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0016] [Embodiment 1] A large beam - small beam joint structure 1 according to an embodiment of the present invention joins a pair of small beams facing each other with the large beam interposed therebetween to the large beam that constitutes the floor frame structure of a building steel frame. Taking the case where the beam shapes of the small beam and the large beam are the same as an example, the following description will be made with reference to Fig. 1.

[0017] As shown in Fig. 1(a), the girder - joist joint structure 1 joins a pair of joists 5 made of H - shaped steel on both sides of a girder 3 made of H - shaped steel with the joists 5 facing each other across the girder 3 in a direction perpendicular to the girder 3. The girder - joist joint structure 1 includes a joist upper - flange joint portion 7, a joist web joint portion 9, and a joist lower - flange joint portion 11. Hereinafter, each joint portion will be described in detail.

[0018] <Joist upper - flange joint portion> The joist upper - flange joint portion 7 is formed by joining the joist upper - flanges 5a of the joists 5 facing each other across the girder 3 (hereinafter simply referred to as "the facing joists 5") to the girder upper - flange 3a of the girder 3 respectively. The facing joists 5 are arranged at a height position where their respective joist upper - flanges 5a form the same plane as the girder upper - flange 3a of the girder 3, and the ends of the joist upper - flanges 5a are bevelled. A backing plate 17 is attached to the lower side of the ends of the joist upper - flanges 5a, and a scallop 13 (notch) is formed at the boundary between the joist upper - flange 5a and the joist web 5b at the axial end of the joist web 5b. And the joist upper - flange 5a is welded to the girder upper - flange 3a by the butt - weld portion 15. As described above, the joist upper - flanges 5a of the facing joists 5 are welded to the girder upper - flange 3a of the girder 3, and thus are rigidly joined to the girder 3 respectively.

[0019] <Joist web joint portion> The joist web joint portion 9 is formed by rigidly joining the joist webs 5b of the facing joists 5 to the girder web 3b of the girder 3 respectively. On both sides of the girder web 3b of the girder 3, a pair of vertical plates 19 arranged to form the same plane as the joist webs 5b of the joists 5 are provided. The vertical plate 19 is a plate - shaped member having the same shape as the region surrounded by the girder upper - flange 3a, the girder web 3b, and the girder lower - flange 3c, and is arranged to close the region and is welded to the girder upper - flange 3a, the girder web 3b, and the girder lower - flange 3c.

[0020] On both sides of the web 5b of the joist and the vertical plate 19, gusset plates 21 are arranged so as to straddle both of them, and the gusset plates 21 are fastened to the web 5b of the joist and the vertical plate 19 respectively by high-strength bolts 23. As described above, the webs 5b of the opposing joists 5 are rigidly joined to the girder 3 via the vertical plates 19, gusset plates 21, and high-strength bolts 23 respectively.

[0021] <Lower flange joint of joist> The lower flange joint 11 of the joist is formed by joining the lower flanges 5c of the opposing joists 5 via a joining member. On the lower surface of the lower flange 3c of the girder 3, a lower flange welding plate 25 is joined as the above joining member by fillet welding (not shown). As shown in Fig. 1(b), the lower flange welding plate 25 is a plate wider than the lower flanges 5c of the joist that are orthogonal to the longitudinal direction of the lower flange 3c of the girder 3 and extend from both side ends of the lower flange 3c of the girder 3, and is attached to the lower surface of the lower flange 3c of the girder 3 in advance at the factory or on-site before the steel frame construction. The fillet weld portion for welding the lower flange welding plate 25 to the lower flange 3c of the girder 3 is for the purpose of attaching the lower flange welding plate 25 and preventing buckling, and does not resist the stress acting on the joist 5. Therefore, the fillet weld portion for welding the lower flange welding plate 25 to the lower flange 3c of the girder 3 may be intermittent welding.

[0022] The lower flange welding plate 25 is preferably equal to or higher than the lower flange 5c of the joist in yield strength, so it is desirable to use the same thickness and the same strength material as the lower flange 5c of the joist. The width of the lower flange welding plate 25 is set to about the width of the lower flange 5c of the joist + 100 mm to ensure the fillet weld allowance when welding the lower flange 5c of the joist to the lower flange welding plate 25 and to ensure the allowance for absorbing manufacturing and construction errors. Alternatively, it is also effective to use a material with a yield strength higher than that of the lower flange 5c for the lower flange welding plate 25. In this case, the strength of the joint portion can be improved and the safety can be enhanced. In addition, the plate thickness can be made thinner than that of the lower flange 5c to improve workability while ensuring the strength of the joint portion.

[0023] The lower flange 5c of the joist is fillet welded (fillet weld 27) to the lower flange welding plate 25 over the entire length of the axial side end 5ca of the lower flange 5c of the joist at the contact portion in a state where the lower surface is in contact with the upper surface of the lower flange welding plate 25. Here, the expression "over the entire length" is used, but in actual welding work, in order to prevent melting at the welding ends, the welding line of the side end 5ca is stopped about 10 mm in front of the edge of the lower flange welding plate 25. Reference numeral 29 in the figure is a stitching bolt used for positioning when joining the lower flange 5c of the joist to the lower flange welding plate 25. During steel frame construction, the lower flange 5c of the joist is placed on the upper surface of the lower flange welding plate 25, and the joining position is determined using the stitching bolt 29. Then, the stitching bolt 29 is tightened to bring the lower flange 5c into close contact with the lower flange welding plate 25, and the side end 5ca of the lower flange 5c is fillet welded to the lower flange welding plate 25.

[0024] The lower flange 5c and the lower flange welding plate 25 are provided with stitching bolt holes for inserting the stitching bolt 29. The stitching bolt holes may be enlarged holes larger than the bolt diameter or may be slit holes. Also, the stitching bolt 29 may be removed after joining the joist 5 to the girder 3.

[0025] By fillet welding and joining the side end 5ca of the lower flange 5c of the joist to the lower flange welding plate 25, the opposing lower flanges 5c of the joist are joined via the lower flange welding plate 25. By joining the opposing lower flanges 5c of the joist, the stress (compressive force) acting on the lower flange 5c of one joist 5 is transmitted to the lower flange 5c of the other joist 5.

[0026] Therefore, it is necessary to design the welding length of the fillet weld 27 so that the joining strength is sufficient to sufficiently perform the above stress transmission. In this embodiment, if the length of the lower flange welding plate 25 is increased, the required welding length can be ensured.

[0027] In addition, in the present embodiment, since the sub-trabecular flange 5c is fillet-welded to the lower flange welding plate 25 at the fillet to join the opposing sub-trabecular flanges 5c, on-site labor can be reduced as compared with the case where the sub-trabecular flange 5c is butted and welded to the main-trabecular flange 3c. Specifically, operations such as beveling the sub-trabecular flange 5c, attaching backing bars, and scalloping can be made unnecessary.

[0028] Note that in FIG. 1, only the side end portion 5ca of the sub-trabecular flange 5c was fillet-welded to the lower flange welding plate 25. As another aspect, as in the main-trabecular and sub-trabecular joint structure 31 shown in FIG. 2, a fillet weld portion 27 may be provided also at the tip end portion 5cb in the material axis direction of the sub-trabecular flange 5c. When fillet-welding the tip end portion 5cb, it is necessary to form a scallop 13 at the boundary between the sub-trabecular web 5b and the sub-trabecular flange 5c to secure a welding space. However, since the welding length can be ensured, the length of the lower flange welding plate 25 can be reduced to, for example, about 50% to 60%. By reducing the length of the lower flange welding plate 25, it is possible to expect a reduction in the amount of material, a reduction in "warpage" during factory welding, and an improvement in handling ease during transportation. When the processing of the scallop 13 is complicated, it is also possible to stop the welding of the tip end portion 5cb in front of the sub-trabecular web 5b and cut it off, so as to omit (not provide) the scallop 13.

[0029] Furthermore, according to the following formula (1) defined in the Design Guidelines for Steel Structure Joints of the Architectural Institute of Japan, the fillet weld portion 27 provided at the tip end portion 5cb can be evaluated to have a greater welding strength than the fillet weld portion 27 provided at the side end portion 5ca. w q y =(1 + 0.4cosθ)×a×(Fy / √3) ···(1) Here, w q y : Yield strength per unit length of the fillet weld joint θ: Angle of the fillet weld joint with respect to the direction of the acting stress a: Effective throat thickness of the weld joint Fy: Yield strength of the base material to be joined

[0030] In the fillet weld portion 27 at the corner of the tip portion 5cb, since the weld line is perpendicular to the stress to be transmitted, cosθ = 1. In the fillet weld portion 27 at the corner of the side end portion 5ca, since the stress to be transmitted is parallel to the weld line, cosθ = 0. Therefore, from the above formula (1), the fillet weld portion 27 at the corner of the tip portion 5cb is w q y greater than that of the fillet weld portion 27 at the corner of the side end portion 5ca, and it can be said that the structure in Fig. 2 is more reasonable than the structure in Fig. 1.

[0031] Note that this embodiment is characterized by the joining method of the lower flange joint portion 11 of the secondary beam, and does not limit the joining methods of the upper flange joint portion 7 and the web joint portion 9 of the secondary beam. The upper flange joint portion 7 and the web joint portion 9 of the secondary beam only need to be rigidly joined so as to exhibit the rotational rigidity as a joint portion. For example, they may be joined by the following methods.

[0032] For example, in the case of the upper flange joint portion 7 of the secondary beam, in Figs. 1 and 2, an example of butt welding the upper flange 5a of the secondary beam to the upper flange 3a of the main beam is shown, but this may also be a bolt joint via a gusset plate. Alternatively, instead of directly joining the upper flange 5a of the secondary beam and the upper flange 3a of the main beam, the upper flanges 5a of the secondary beam may be joined via a joining member arranged so as to straddle the opposing upper flanges 5a of the secondary beam. As an example of joining the upper flanges 5a of the secondary beam, there is a method of arranging a plate so as to straddle the opposing upper flanges 5a of the secondary beam and performing high-strength bolt friction joining between the plate and the upper flange 5a of the secondary beam. Alternatively, there is also a method of providing a standing plate joined in a state standing in the axial direction of the secondary beam on the upper surface of the upper flange 5a of the secondary beam, arranging joining plates on both surfaces of the standing plate so as to straddle the opposing standing plates, and performing high-strength bolt friction joining between the standing plate and the two joining plates.

[0033] Next, in the case of the web joint portion 9 of the secondary beam, in Figs. 1 and 2, an example of bolt joining the web 5b of the secondary beam and the vertical plate 19 via a gusset plate 21 is shown, but without using the gusset plate 21, the vertical plate 19 may be projected toward the web 5b of the secondary beam and directly bolted to the web 5b of the secondary beam.

[0034] [Embodiment 2] The girder - joist joint structure 33 of this embodiment is an example in which the configuration of the lower flange joint portion 11 of the joist described in Embodiment 1 is applied to the upper flange joint portion 7 of the joist. Hereinafter, the upper flange joint portion 7 of the girder - joist joint structure 33 of this embodiment will be described with reference to FIG. 3. Note that the joist web joint portion 9 and the lower flange joint portion 11 of the girder - joist joint structure 33 are not limited to specific joining methods, similar to the joist web joint portion 9 and the upper flange joint portion 7 of Embodiment 1, so the same reference numerals as in FIG. 1 are given and the description is omitted.

[0035] <Upper flange joint portion of the joist> In the upper flange joint portion 7 of the joist of this embodiment, on the upper surface of the upper flange 3a of the girder 3, upper flange welding plates 35 that are orthogonal to the longitudinal direction of the upper flange 3a and extend from both side ends of the upper flange 3a are arranged. And through these upper flange welding plates 35, the upper flanges 5a of the opposing joists 5 are joined together.

[0036] As shown in FIG. 3(b), the upper flange welding plate 35 is a plate narrower than the upper flange 5a of the joist. After joining the joist webs 5b of the opposing joists 5 to the girder 3 at the construction site, it is arranged on the upper surface of the upper flange 3a of the girder. Since the upper flange welding plate 35 is a stress - transmission member between the upper flanges 5a of the opposing joists 5, special welding at the contact portion with the upper flange 3a is not necessary, but assembly welding for positioning may be performed.

[0037] The upper flange welding plate 35 is designed in terms of cross - section so that its load - bearing capacity is equal to or greater than that of the upper flange 5a of the joist. The plate width is about the width of the upper flange 5a of the joist - 100 mm, to ensure the fillet - welding allowance when welding the upper flange welding plate 35 to the upper flange 5a of the joist and to ensure the allowance for absorbing manufacturing and construction errors. Regarding the plate thickness, when using the same high - strength material as the joist 5, it is set thicker than the upper flange 5a of the joist to ensure the same load - bearing capacity as the upper flange 5a of the joist. When using a material with higher strength than the joist 5, the plate thickness can be reduced according to its yield strength.

[0038] The upper flange welding plate 35 is fillet welded (fillet weld portion 27) to the upper flange of the cross beam 5a over the entire circumference of the outer peripheral portion of the upper flange welding plate 35 at the contact portion in a state where the lower surface is in contact with the upper surface of the upper flange of the cross beam 5a. During the construction of the steel frame, the joining position of the upper flange welding plate 35 is determined using the stitch bolts 29 in the same manner as the lower flange joining portion 11 of the first embodiment. Then, the stitch bolts 29 are tightened to bring the upper flange welding plate 35 into close contact with the upper flange of the cross beam 5a, and the outer peripheral portion of the upper flange welding plate 35 is fillet welded to the upper flange of the cross beam 5a.

[0039] By joining the upper flange welding plate 35 to the upper flange of the cross beam 5a, the opposing upper flanges of the cross beam 5a are joined via the upper flange welding plate 35. By joining the opposing upper flanges of the cross beam 5a, the stress (tensile force) acting on the upper flange of the cross beam 5a of one cross beam 5 is transmitted to the upper flange of the cross beam 5a of the other cross beam 5.

[0040] The upper flange joining portion 7 of the present embodiment can secure the required welding length by increasing the length of the upper flange welding plate 35 in the same manner as the lower flange joining portion 11 of the first embodiment. This is more efficient because there is no need to process the upper flange of the cross beam 5a compared to the conventional example of directly fillet welding the upper flange of the cross beam 5a to the upper flange of the main beam 3a. In addition, the on-site labor can be reduced compared to the case of butt welding the upper flange of the cross beam 5a to the upper flange of the main beam 3a.

[0041] Also, when the beam width of the crossbeam 5 is, for example, 300 mm or more and the width of the upper flange welding plate 35 can be widened, as shown in FIG. 4, a slit 35a may be provided in the upper flange welding plate 35, and the inner peripheral portion of the slit 35a may be fillet-welded. By doing so, the welding length can be further ensured, and thus the length of the upper flange welding plate 35 can be reduced. Then, by reducing the length of the upper flange welding plate 35, it is possible to expect a reduction in the amount of material, a reduction in "warpage" during factory welding, and an improvement in handling ease during transportation, etc.

[0042] [Embodiment 3] As described above, the feature of the present invention lies in fillet-welding and joining the flanges of both crossbeams 5 to a plate arranged so as to straddle the opposing crossbeams 5. In Embodiment 1, an example having the feature of the present invention at the crossbeam lower flange joint 11 was shown, and in Embodiment 2, an example having the feature of the present invention at the crossbeam upper flange joint 7 was shown. In this embodiment, an example having the feature of the present invention at both the crossbeam upper flange joint 7 and the crossbeam lower flange joint 11 will be described. The girder-crossbeam joint structure 37 of this embodiment is shown in FIG. 5.

[0043] The crossbeam upper flange joint 7 of the girder-crossbeam joint structure 37 is the same as the crossbeam upper flange joint 7 (see FIG. 3) of Embodiment 2, and the crossbeam lower flange joint 11 is the same as the crossbeam lower flange joint 11 (see FIG. 1) of Embodiment 1. Also, the crossbeam web joint 9 is the same as the crossbeam web joint 9 of Embodiments 1 and 2.

[0044] The girder-crossbeam joint structure 37 joins the opposing crossbeams 5 at both the crossbeam upper flange joint 7 and the crossbeam lower flange joint 11. As a result, the tensile force generated in the crossbeam upper flange 5a of one crossbeam 5 and the compressive force generated in the crossbeam lower flange 5c are transmitted to the other crossbeam 5 without passing through the girder 3. The structure of FIG. 5 is suitable even when the yield strength of the flanges (3a, 3c) of the girder 3 is lower than the yield strength of the flanges (5a, 5c) of the crossbeam 5 because it is not necessary to consider the bearing capacity of the girder 3 in the stress transmission between the opposing crossbeams 5.

[0045] In the above description, the case where the beam configurations of the main beam 3 and the sub-beam 5 are the same has been described as an example. However, FIG. 6 shows an embodiment in which sub-beams 5 having a smaller beam configuration than the main beam 3 are joined to both sides of the main beam 3. The main beam - sub-beam joint structure 37 in FIG. 6 includes a sub-beam upper flange joint portion 7 and a sub-beam web joint portion 9 similar to those in FIG. 5, but the aspect of the sub-beam lower flange joint portion 11 is different from that in FIG. 5.

[0046] When the beam configuration of the sub-beam 5 is smaller than that of the main beam 3, the lower flange welding plate 25 cannot be arranged so as to straddle the opposing sub-beam lower flange 5c. Therefore, as shown in FIG. 6, the lower flange welding plate 25 is divided into two split pieces 39. Each of the two split pieces 39 is formed with a slit, and in a state where the vertical plate 19 of the main beam 3 is inserted into the slit, it is arranged at a height position along the lower surface of the sub-beam lower flange 5c and is welded and joined to both sides of the main beam web 3b.

[0047] And, similar to the example in FIG. 2, the lower surface of the sub-beam lower flange 5c is in contact with the split piece 39 (lower flange welding plate 25), and the side end portion 5ca and the tip end portion 5cb are fillet welded and joined (fillet weld portion 27) to the split piece 39 (lower flange welding plate 25).

[0048] In the example of FIG. 6, at the intersection of the vertical plate 19 and the split piece 39, the vertical plate 19 is recessed. However, it may also be a recessed state where the split piece 39 is recessed by eliminating the shaded portion in FIG. 6. The recessed state where the split piece 39 is recessed is more reasonable because it can reduce the material and there is no need to form a slit in the split piece 39.

[0049] Also in the example of FIG. 6, since fillet welding is used in both the sub-beam upper flange joint portion 7 and the sub-beam lower flange joint portion 11, construction is easy even at a site without skilled workers, similar to the example in FIG. 5. However, in the example of FIG. 6, since the stress (compressive force) acting on the sub-beam lower flange 5c is also transmitted to the main beam 3, it is a suitable structure when the yield strength of the main beam 3 is equal to or higher than that of the sub-beam 5.

Explanation of Symbols

[0050] 1 Girder - joist joint structure (Embodiment 1) 3 Girder 3a Upper flange of girder 3b Web of girder 3c Lower flange of girder 5 Joist 5a Upper flange of joist 5b Web of joist 5c Lower flange of joist 5ca Side end part 5cb Tip part 7 Joist upper flange joint 9 Joist web joint 11 Joist lower flange joint 13 Scallop 15 Butt weld part 17 Backing plate 19 Vertical plate 21 Gusset plate 23 High - strength bolt 25 Lower flange welding plate 27 Fillet weld part 29 Binding bolt 31 Girder - joist joint structure (Another aspect of Embodiment 1) 33 Girder - joist joint structure (Embodiment 2) 35 Upper flange welding plate 35a Slit 37 Girder - joist joint structure (Embodiment 3) 39 Split piece

Claims

1. A girder - joist joint structure in which a pair of joists made of H - shaped steel having the same beam shape as the girder are opposed to each other with the girder interposed therebetween in a direction orthogonal to the girder, and are joined to the girder made of H - shaped steel. A joist upper - flange joint part in which the joist upper flanges of the opposing joists are rigidly joined to the girder upper flange respectively, or the opposing joist upper flanges are rigidly joined to each other via a member. A joist web joint part in which the joist webs of the opposing joists are rigidly joined to the vertical plates joined to the girder web respectively. A joist lower - flange joint part in which the joist lower flanges of the opposing joists are joined to the lower - flange welding plates joined to the lower surface of the girder lower flange, and it has: The lower - flange welding plate is a plate wider than the joist lower flanges extending from both side ends of the girder lower flange and orthogonal to the longitudinal direction of the girder lower flange. The joist lower - flange joint part is characterized in that the side end part in the material axis direction of the joist lower flange is fillet - welded to the lower - flange welding plate in a state where the lower surface of the joist lower flange contacts the lower - flange welding plate. The girder - joist joint structure.

2. The girder - joist joint structure according to claim 1, characterized in that the tip part in the material axis direction of the joist lower flange is fillet - welded to the lower - flange welding plate.

3. An upper - flange welding plate orthogonal to the longitudinal direction of the girder upper flange and extending from both side ends of the girder upper flange is arranged on the upper surface of the girder upper flange. The upper - flange welding plate is a plate narrower than the joist upper flange. The joist upper - flange joint part is one in which the joist upper flanges of the opposing joists are joined to the upper - flange welding plate, and the outer peripheral part of the upper - flange welding plate is fillet - welded to the joist upper flange in a state where the lower surface of the upper - flange welding plate contacts the joist upper flange. The girder - joist joint structure according to claim 1 or 2.

4. A girder - joist joint structure in which a pair of joists made of H - shaped steel are opposed to each other with the girder interposed therebetween in a direction orthogonal to the girder, and are joined to the girder made of H - shaped steel. A joist upper - flange joint part in which the joist upper flanges of the opposing joists are joined to the upper - flange welding plate arranged on the upper surface of the girder upper flange. A joist web joint part in which the joist webs of the opposing joists are rigidly joined to the vertical plates joined to the girder web respectively. It has a lower flange joint portion of the opposite girders in which the lower flange of the opposite girders is rigidly joined to the lower flange of the main beam, or the lower flanges of the opposite girders are rigidly joined to each other via a member. The upper flange welding plate is a plate that is orthogonal to the longitudinal direction of the upper flange of the main beam and is narrower in width than the upper flange of the girder that extends from both side ends of the upper flange of the main beam. The upper flange joint portion of the girder is characterized in that the outer peripheral portion of the upper flange welding plate is fillet welded to the upper flange of the girder in a state where the lower surface of the upper flange welding plate is in contact with the upper flange of the girder.

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