Design methods for steel beams
By setting the sliding strength of the bolted joint to exceed design yield strength but be less than the actual yield strength, the steel beam design method addresses the challenge of reduced standard strength, facilitating simplified and safe design for steel beams with high yield ratio steels.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TAKENAKA CORP
- Filing Date
- 2024-11-12
- Publication Date
- 2026-05-22
AI Technical Summary
Existing steel beam design methods struggle with reduced standard strength when set below the yield point, complicating the design process, especially for high yield ratio steels like SM490YA, BTHT400C, and BTHT500C, which require confirmation against rare seismic motions or use below allowable stress.
The steel beam design method sets the sliding strength of the bolted joint to be greater than the design yield strength based on allowable stress and less than the actual yield strength, allowing the joint to slide before the load reaches the yield point, preventing plastic deformation.
This approach enables rational design of steel beams with standard strength lower than the yield point, simplifying the design process and ensuring safety against rare seismic motions without requiring plastic deformation performance.
Smart Images
Figure 2026085139000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a design method for steel beams.
Background Art
[0002] A bolted joint structure in which a steel column and a steel beam are bolted together is known (see, for example, Patent Documents 1 to 3).
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Patent Document 2
Patent Document 3
Summary of the Invention
Problems to be Solved by the Invention
[0004] By the way, the standard strength (F value) of a steel beam is generally set based on the yield point of the steel material forming the steel beam. However, for example, when 70% of the tensile strength of the steel material is smaller than the yield point of the steel material, the standard strength of the steel beam is reduced not to the yield point of the steel material but to 70% of the tensile strength of the steel material.
[0005] Also, as a steel material with a high yield ratio having the same tensile strength and a higher yield point, for example, there is SM490YA. In this SM490YA, the yield point is 355 [N / mm 2 , whereas the standard strength is reduced to 325 [N / mm 2 .
[0006] When the standard strength of the steel material forming the steel beam is smaller than the yield point in this way, even if the yield point of the steel material is high, its performance becomes surplus performance, and it is difficult to obtain, for example, the effect of reducing the amount of steel material according to the yield point.
[0007] Other steels with high yield ratios include, for example, BTHT400C and BTHT500C. While the nominal strength of BTHT400C and BTHT500C is the same as the yield point, their plastic deformation performance cannot be expected. Therefore, for example, safety must be confirmed against extremely rare seismic motions, or they must be used below the allowable stress. In this case, the design cannot be done using general design routes, potentially complicating the design process.
[0008] Considering the above facts, the present invention aims to enable rational design of steel beams whose standard strength is lower than the yield point, or to facilitate the design of steel beams that need to be used below the allowable stress for rarely occurring seismic motions, or for which safety must be confirmed against rarely occurring seismic motions. [Means for solving the problem]
[0009] The steel beam design method according to claim 1 is a steel beam design method in which the standard strength is less than the yield point, wherein the sliding strength of the bolted joint of the steel beam is set to be greater than the design yield strength of the steel beam based on the allowable stress determined by the standard strength, and less than the actual yield strength of the steel beam based on the yield point.
[0010] According to the steel beam design method of claim 1, the standard strength is less than the yield point, and the sliding strength of the bolted joint of the steel beam is set to be greater than the design yield strength of the steel beam based on the allowable stress determined by the standard strength, and less than the yield strength of the steel beam based on the yield point.
[0011] As a result, during an earthquake, the bolted joints slip before the load acting on the steel beam reaches the actual yield strength of the steel beam, preventing the steel beam from undergoing plastic deformation. In other words, in this invention, plastic deformation performance is not required for the steel beam. Therefore, in this invention, there is no need to set the design yield strength based on the allowable stress determined by the standard strength of the steel beam, and the actual yield strength based on the yield point of the steel beam can be set as the design yield strength.
[0012] Therefore, in this invention, even if the standard strength of the steel beam is lower than the yield point, the height of the yield point of the steel beam can be utilized, thus enabling a rational design.
[0013] The steel beam design method described in claim 2 is a steel beam design method that requires confirmation of safety against extremely rare seismic motions or the use of a steel beam below the allowable stress, wherein the sliding strength of the bolted joint of the steel beam is set to be smaller than the actual yield strength of the steel beam based on the yield point of the steel beam.
[0014] The steel beam design method according to claim 2 is a design method for a steel beam that needs to be used below the allowable stress level or to confirm safety against extremely rare seismic motions, and involves setting the sliding strength of the bolted joint of the steel beam to be smaller than the actual yield strength of the steel beam based on the yield point of the steel beam.
[0015] As a result, during an earthquake, the bolted joints slip before the load acting on the steel beam reaches the actual yield strength of the steel beam, preventing the steel beam from undergoing plastic deformation. In other words, in this invention, plastic deformation performance is not required for the steel beam. Therefore, in this invention, there is no need to confirm safety against rarely occurring seismic motions, or to use the steel beam below the allowable stress level for extremely rare seismic motions.
[0016] Therefore, in this invention, steel beams can be designed using a general design route, thus simplifying the design of steel beams.
[0017] The steel beam design method according to claim 3 is the steel beam design method according to claim 1 or claim 2, wherein a sliding member is provided at the bolted joint.
[0018] According to the steel beam design method of claim 3, a sliding material is provided at the bolted joint. This sliding material allows for easy adjustment of the sliding resistance of the bolted joint. [Effects of the Invention]
[0019] As described above, according to the present invention, it is possible to rationally design a steel beam whose reference strength is smaller than the yield point, or to facilitate the design of a steel beam that needs to be confirmed for safety against rarely occurring seismic motions or used below the allowable stress for extremely rarely occurring seismic motions.
Brief Description of the Drawings
[0020] [Figure 1] It is an elevation view showing a steel beam designed by the steel beam design method according to the first embodiment. [Figure 2] It is a graph showing the relationship between the deformation amount of the column-beam structure during an earthquake and the load acting on the steel beam for the column-beam structure shown in FIG. 1. [Figure 3] It is a graph showing the relationship between the deformation amount of the column-beam structure during an earthquake and the load acting on the steel beam for the steel beam design method according to the first embodiment. [Figure 4] It is an elevation view corresponding to FIG. 1 showing a deformation example of the bolt joint of the steel beam.
Modes for Carrying Out the Invention
[0021] (First Embodiment) First, the first embodiment will be described.
[0022] In FIG. 1, a steel beam 20 designed by the steel beam design method according to the present embodiment and a steel column 10 to which the steel beam 20 is joined are shown.
[0023] The steel column 10 is formed of a square steel pipe as an example. A pair of diaphragms 12 are provided at the column-beam joint portion 10S of the steel column 10. The pair of diaphragms 12 are, for example, continuous diaphragms and are arranged to face each other in the material axis direction of the steel column 10. The steel beam 20 is joined to the column-beam joint portion 10S of the steel column 10.
[0024] Furthermore, the steel column 10 is not limited to steel pipes such as square steel pipes, but may also be formed from shaped steel such as H-beams. Also, the pair of diaphragms 12 are not limited to through diaphragms, but may be external diaphragms, internal diaphragms, etc.
[0025] The steel beam 20 is erected on the steel column 10 and other steel columns (not shown), and together with these steel columns 10, it constitutes a column-beam frame. For example, the steel beam 20 is joined to the steel column 10 using a bracket method. Specifically, the steel beam 20 has a beam bracket 22 and a beam body 24. The beam bracket 22 and the beam body 24 are formed from H-shaped steel.
[0026] The beam bracket 22 has a pair of flange portions 22A that face each other in the vertical direction, and a web portion 22B that connects the pair of flange portions 22A. This beam bracket 22 is joined (rigidly joined) to the column-beam joint portion 10S of the steel column 10 by welding in a factory or the like. Specifically, the pair of flange portions 22A of the beam bracket 22 are welded in a state where they abut against the pair of diaphragms 12 of the column-beam joint portion 10S.
[0027] The beam body 24 has a pair of flange portions 24A that face each other in the vertical direction, and a web portion 24B that connects the pair of flange portions 24A. The ends of the beam body 24 and the ends of the beam bracket 22 are bolted together.
[0028] Specifically, the beam bracket 22 and the beam body 24 are arranged so that their respective flange portions 22A and 24A are continuous with each other. These flange portions 22A and 24A are sandwiched from both above and below by a pair of splice plates (flange splice plates) 30.
[0029] One end of the pair of splice plates 30 is joined (friction joined) to the flange portion 22A of the beam bracket 22 by bolts (high-strength bolts) 32 and nuts 34. Similarly, the other end of the pair of splice plates 30 is joined (friction joined) to the flange portion 24A of the beam body 24 by bolts (high-strength bolts) 32 and nuts 34.
[0030] The beam bracket 22 and beam body 24 are arranged so that their respective web portions 22B and 24B are continuous with each other. Splice plates (web splice plates) 40 are placed on one or both sides of these web portions 22B and 24B.
[0031] One end of the splice plate 40 is joined (friction joined) to the web portions 22B and 24B of the beam bracket 22 by bolts (high-strength bolts) 42 and nuts (not shown). Similarly, the other end of the splice plate 40 is joined (friction joined) to the web portions 22B and 24B of the beam body 24 by bolts (high-strength bolts) 42 and nuts (not shown).
[0032] Here, at the bolted joint J of the beam bracket 22 and the beam body 24, when the load acting on the bolted joint J during an earthquake reaches the sliding resistance PS of the bolted joint J (described later), the bolted joint J is configured to slide in the axial direction of the steel beam 20.
[0033] Specifically, in the bolted joint J, the bolt holes (not shown) for bolts 32 and 42 formed in the flange portions 22A and 24A and the web portions 22B and 24B of the beam bracket 22 and beam body 24 are elongated holes (loose holes) that extend in the direction of the material axis of the steel beam 20.
[0034] As a result, in the event of an earthquake, when the load acting on the bolted joint J reaches the sliding resistance PS of the bolted joint J (described later), the bolts 32 and 42 move along the elongated holes, causing the bolted joint J to slide in the axial direction of the steel beam 20.
[0035] The elongated holes for the bolts 32 can be formed in at least one of the flange portions 22A, 24A of the beam bracket 22 and the beam body 24 and the splice plate 30. Similarly, the elongated holes for the bolts 42 can be formed in at least one of the web portions 22B, 24B of the beam bracket 22 and the beam body 24 and the splice plate 40.
[0036] (Design methods for steel beams) Next, an example of a design method for steel beams according to the first embodiment will be described.
[0037] Generally, the tensile strength of the steel material forming the steel beam 20 is 520 [N / mm²] 2 In the following cases, the standard strength (F value) of the steel beam 20 shall, in principle, be set based on the yield point (lower limit) of the steel. However, if, for example, 70% of the tensile strength of the steel is smaller than the yield point (lower limit) of the steel, the standard strength of the steel beam 20 shall be reduced to 70% of the tensile strength of the steel, rather than the yield point of the steel.
[0038] In this way, when the standard strength of the steel beam 20 is lower than the yield point, even if the yield point of the steel is high, that performance becomes excess performance, making it difficult to obtain, for example, the effect of reducing the amount of steel required in proportion to the yield point.
[0039] Therefore, as shown in Figure 2, in this embodiment, the sliding strength PS of the bolted joint J is set so that the steel beam 20 does not yield during an earthquake. Specifically, the sliding strength PS of the bolted joint J is set to be smaller than the actual yield strength PA based on the yield point (lower limit) of the steel beam 20.
[0040] As a result, during an earthquake, the bolted joint J slides in the axial direction of the steel beam 20 before the load acting on the steel beam 20 reaches the actual yield strength PA of the steel beam 20, thus preventing the steel beam 20 from undergoing plastic deformation. In other words, in this embodiment, plastic deformation performance is not required for the steel beam 20. Consequently, in this embodiment, there is no need to reduce the standard strength of the steel beam 20 to 70% of its tensile strength.
[0041] Therefore, in this embodiment, the sliding strength PS of the bolted joint J is set to be greater than the design yield strength PD of the steel beam 20, which is based on the allowable stress determined by the standard strength (70% of the tensile strength of the steel beam 20). In other words, in this embodiment, for a steel beam 20 whose standard strength is less than the yield point, the sliding strength PS of the bolted joint J is set as shown in equation (1) below.
[0042] Design yield strength PD based on allowable stress determined by standard strength < sliding strength PS of bolted joint < actual yield strength PA based on yield point of steel beam ... (1)
[0043] Therefore, in this embodiment, even if the steel beam 20 has a standard strength based on tensile strength that is lower than the yield point, the height of the yield point of the steel beam 20 can be utilized, thus enabling a rational design.
[0044] Furthermore, even if the steel beam 20 is subjected to an unexpectedly large earthquake or repeated seismic loads, the steel beam 20 will not undergo plastic deformation, thus preventing fracture at the joint between the steel beam 20 and the steel column 10, and preventing local buckling of the steel beam 20. Moreover, because the steel beam 20 does not undergo plastic deformation even when subjected to a large earthquake, the steel beam 20 can be reused.
[0045] In this embodiment, the standard strength of the steel beam 20 is set to 70% of the tensile strength of the steel beam 20. However, the allowable stress determined by the standard strength of the steel beam 20 is not limited to 70% of the tensile strength of the steel beam 20. For example, SM490YA is a steel material with a high yield ratio. In this SM490YA (16 [mm] < plate thickness ≤ 40 [mm]), the yield point (lower limit) is 355 [N / mm]. 2 While the standard strength is 325 [N / mm²], the standard strength is 325 [N / mm²]. 2 It is reduced to ].
[0046] The first embodiment can also be applied to steel beams 20 formed from steel materials such as SM490YA. In other words, by setting the sliding strength PS of the bolted joint J to be greater than the design yield strength PD of the steel beam 20 based on the allowable stress determined by the standard strength, and less than the actual yield strength PA of the steel beam 20 based on the yield point, the same effect as the first embodiment can be obtained.
[0047] (Second embodiment) Next, a second embodiment will be described. In the second embodiment, components and the like that have the same configuration as in the first embodiment will be denoted by the same reference numerals, and their descriptions will be omitted as appropriate.
[0048] In the first embodiment described above, a steel beam 20 with a standard strength lower than the yield point was designed. In contrast, in the second embodiment, a steel beam 20 is designed that requires confirmation of safety against extremely rare seismic motions, or that needs to be used below the allowable stress.
[0049] Specifically, the steel beam 20 is formed, for example, from BTHT400C, which has a high yield ratio. BTHT400C has a yield point (lower limit) and a standard strength of 400 [N / mm²]. 2 It is stated that the yield point and standard strength are equivalent. In other words, the steel beam 20 has an actual yield strength PA based on the yield point and a design yield strength PD based on the allowable stress determined by the standard strength that are equivalent.
[0050] However, because BTHT400C cannot be expected to exhibit plastic deformation performance, it is necessary to confirm its safety against extremely rare seismic motions or to use it below its allowable stress. Therefore, steel beams 20 formed from BTHT400C cannot be designed using general design methods, which may complicate the design process.
[0051] Therefore, in this embodiment, the sliding strength PS of the bolted joint J is set so that the steel beam 20 does not yield during an earthquake. Specifically, as shown in Figure 3, the sliding strength PS of the bolted joint J is set to be smaller than the actual yield strength PA based on the yield point (lower limit) of the steel beam 20.
[0052] As a result, during an earthquake, the bolted joint J slides in the axial direction of the steel beam 20 before the load acting on the steel beam 20 reaches the actual yield strength PA of the steel beam 20, thus preventing the steel beam 20 from undergoing plastic deformation. In other words, in this embodiment, plastic deformation performance is not required for the steel beam 20. Consequently, in this embodiment, there is no need to confirm the safety of the steel beam 20 against extremely rare seismic motions or to use it below the allowable stress.
[0053] Therefore, in this embodiment, in a steel beam 20 that needs to be used below the allowable stress level or to confirm safety against extremely rare seismic motions, the sliding resistance PS of the bolted joint J is set as shown in the following formula (2).
[0054] The sliding strength of the bolted joint PS < the actual yield strength PA based on the yield point of the steel beam ... (2)
[0055] Therefore, in this embodiment, the steel beam 20 can be designed using a general design route, thus simplifying the design of the steel beam 20.
[0056] In this embodiment, the steel beam 20 is formed of BTHT400C, which has a high yield ratio. However, the steel beam 20 is not limited to BTHT400C; for example, it may be formed of BTHT500C, which also has a high yield ratio. BTHT500C has a yield point (lower limit) and a standard strength of 500 [N / mm²]. 2 It is stated that the yield point and standard strength are equivalent. In other words, the steel beam 20 has an actual yield strength PA based on the yield point and a design yield strength PD based on the allowable stress determined by the standard strength that are equivalent.
[0057] However, since BTHT500C cannot be expected to exhibit plastic deformation performance, it is necessary to confirm its safety against extremely rare seismic motions, or to use it below its allowable stress, similar to BTHT400C. Therefore, steel beams 20 formed from BTHT500C cannot be designed using general design methods, which may make the design process difficult.
[0058] Even with a steel beam 20 formed by such BTHT500C, the same effect as in the second embodiment can be obtained by setting the sliding strength PS of the bolted joint J to be smaller than the actual yield strength PA based on the yield point (lower limit).
[0059] (modified version) Next, modifications of the first and second embodiments described above will be explained. In the following, various modifications will be explained using the first embodiment as an example, but these modifications can also be appropriately applied to the second embodiment.
[0060] In the first embodiment described above, a sliding material may be provided at the bolted joint J of the steel beam 20. The sliding material is made of, for example, a stainless steel plate and is provided on the friction joint surface formed by the bolts 32.
[0061] Specifically, the sliding members are provided, for example, in the bolted joint J of the steel beam 20, between the flange portions 22A, 24A of the beam bracket 22 and the beam body 24 and the splice plate 30, or between the web portions 22B, 24B of the beam bracket 22 and the beam body 24 and the splice plate 40. These sliding members allow for easy adjustment of the sliding resistance PS of the bolted joint J.
[0062] Furthermore, if the sliding resistance PS of the bolted joint J decreases due to repeated sliding deformation, the initial performance can be restored by replacing the sliding material of the bolted joint J, thus simplifying repairs.
[0063] Furthermore, the sliding strength PS of the bolted joint J may be adjusted not only by the number of bolts 32 and 42 or the sliding material, but also, for example, by applying a roughening treatment to the friction joint surface formed by the bolts 32 and 42.
[0064] Furthermore, in the above embodiment, the sliding resistance PS of the bolted joint J between the upper and lower flange portions 22A and 24A of the steel beam 20 is set similarly. However, the sliding resistance PS of the bolted joint J between the upper and lower flange portions 22A and 24A of the steel beam 20 may be set to different values.
[0065] For example, in the modified example shown in Figure 4, the number of bolts 32 joining the lower flange portions 22A and 24A together in the steel beam 20 is less than the number of bolts 32 joining the upper flange portions 22A and 24A together. As a result, the sliding resistance PS of the bolted joint J between the lower flange portions 22A and 24A is made smaller than the sliding resistance PS of the bolted joint J between the upper flange portions 22A and 24A.
[0066] In this case, during an earthquake, the bolted joint J between the lower flange portions 22A and 24A will slip before the bolted joint J between the upper flange portions 22A and 24A. Therefore, damage to a slab (not shown) provided on the steel beam 20 can be suppressed, for example.
[0067] Furthermore, in the above embodiment, the steel beam 20 is joined to the steel column 10. However, the steel beam 20 is not limited to being joined to the steel column 10, but may also be joined to a reinforced concrete, steel-reinforced concrete, or wooden column.
[0068] Although one embodiment of the present invention has been described above, the present invention is not limited to these embodiments, and various modifications may be used in appropriate combinations with one embodiment, and of course, the invention can be implemented in various forms without departing from the spirit of the present invention. [Explanation of symbols]
[0069] 20 Steel beams J-bolt joint Actual yield strength of PA steel beams PS bolt joint slip resistance Design yield strength of PD steel beams
Claims
1. A design method for steel beams in which the standard strength is less than the yield point, The sliding strength of the bolted joints of the steel beam is set such that it is greater than the design yield strength of the steel beam based on the allowable stress determined by the standard strength, and less than the actual yield strength of the steel beam based on the yield point. Design methods for steel beams.
2. A design method for steel beams that require confirmation of safety against extremely rare seismic motions, or for use below the allowable stress, The sliding resistance of the bolted joints of the steel beam is set to be smaller than the actual yield strength of the steel beam based on the yield point of the steel beam. Design methods for steel beams.
3. A sliding material is provided at the bolted joint. A method for designing steel beams according to claim 1 or claim 2.