Steel protective fence, beam, and method for selecting beam material

Abstract

To provide a steel guard fence, a beam, and a method for selecting a beam material capable of achieving both thinning of the beam and securing of strength.SOLUTION: The beam 16 for the steel guard fence is formed of steel, the yielding stress of the steel is more than 400MPa and not more than 800MPa, and the plate thickness of the steel is not less than 2. 0mm and less than 4. 0mm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a steel safety fence, a beam, and a method for selecting beam materials. [Background technology]

[0002] Steel protective fences are installed as so-called infrastructure facilities, for example, on the roadside of roadways, medians, etc. Patent Documents 1 to 3 disclose that plated steel materials containing zinc (Zn), aluminum (Al), and magnesium (Mg) are used as steel beam materials for steel protective fences (sometimes referred to as guardrails).

[0003] A steel guardrail generally comprises posts erected on the ground or road surface, long plate-shaped beams connected to the posts and extending in the direction of travel of the roadway, and connectors such as connecting hardware that connect the posts to the beams. Steel guardrails have the function of preventing vehicles such as automobiles from veering off the road, into oncoming traffic lanes, or onto sidewalks, while minimizing injury to vehicle occupants and damage to the vehicle and restoring the vehicle to its normal course.

[0004] Steel guardrails are made up of beams connected to the roadway side of posts whose lower parts are installed (buried, etc.) in the ground or road surface. When a vehicle collides with a steel guardrail, it is required to resist the load of the collision, absorbing the energy and pushing the vehicle back, preventing it from flying off the roadway. In addition, from the perspective of protecting occupants, the steel guardrail is also required to have the function of minimizing injuries to occupants when the steel guardrail pushes the vehicle back in the event of a collision.

[0005] Furthermore, if a beam is damaged by a vehicle collision or worn down due to aging, it is expected that the beam will need to be replaced. In this case, the newly installed beam will be required to have performance (load resistance, etc.) equal to or greater than that of the existing beam. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-121659 [Patent Document 2] International Publication No. 2018 / 139619 [Patent Document 3] International Publication No. 2020 / 261723 Summary of the Invention [Problem to be solved by the invention]

[0007] Heavy beams in steel guardrails can weigh more than 60 kg per beam. When replacing a beam, the damaged or worn beam is removed from the support, and a new beam is transported and installed in its designated position relative to the support. The same process is also required for installing a new beam. When replacing or installing a new beam, workers must hold the beam while transporting and installing it, which requires manual labor and places a heavy burden on the workers. Generally, when a beam weighs more than 60 kg, more than two workers are required to transport and install a single beam. On the other hand, reducing the weight of the beam to less than 60 kg reduces the burden on each worker and may even reduce the number of workers required for transportation and installation, streamlining the work process.

[0008] In particular, when the replacement work site is a location where access space and working space to the work site are limited, such as a highway, it is often difficult to use heavy machinery or other transport machinery that can replace human power at the work site, so the beam replacement work must rely on human power, which places a heavy burden on the workers.

[0009] Furthermore, on routes with heavy traffic such as expressways, the beam replacement work must be completed quickly in order to minimize traffic congestion, which places an even heavier burden on workers. Furthermore, with the recent trend toward a declining birthrate and aging population, there is a demand for technology to reduce the workload of beam replacement and new installation work so that workers from various backgrounds (such as the elderly and women) can be involved in the work.

[0010] To reduce the workload during beam replacement or new construction, it is conceivable to reduce the weight of beams formed from steel material, for example, by thinning the thickness of the steel material used for the beams, i.e., by thinning the material. However, simply thinning the steel material used for existing beams will result in a beam with reduced strength and energy absorption performance compared to existing beams. In other words, it is difficult to ensure the strength required for steel safety fences using such beams. Note that, hereinafter, steel material that is subject to thinning and has a predetermined strength, such as steel material used for existing beams, will be referred to as "standard steel material."

[0011] In this regard, no technology is considered that achieves both thinning and ensuring strength in Patent Documents 1 to 3. Furthermore, Patent Document 3 simply mentions the possibility of using high-tensile steel as plated steel, but does not specifically consider what is required in terms of strength, such as the yield stress of high-tensile steel.

[0012] The present disclosure has been made in consideration of the above, and provides a steel protective fence, a beam, and a method for selecting beam materials that can achieve both thinning of the beams and ensuring their strength. [Means for solving the problem]

[0013] The beam for a steel protective fence according to the first aspect of the present disclosure is formed from steel material, the yield stress of the steel material being greater than 400 MPa and equal to or less than 800 MPa, and the plate thickness of the steel material being equal to or greater than 2.0 mm and less than 4.0 mm.

[0014] A steel protective fence according to a second aspect of the present disclosure comprises a beam formed of steel, the yield stress of which is greater than 400 MPa and less than 800 MPa, and the thickness of which is greater than or equal to 2.0 mm and less than 4.0 mm, a support post supporting the beam, and a connector connecting the support post and the beam.

[0015] A beam material selection method according to a third aspect of the present disclosure includes: setting the yield stress of a steel material for a beam to more than 400 MPa and not more than 800 MPa; setting the plate thickness of the steel material to 2.0 mm or more and less than 4.0 mm; and selecting a standard steel material that satisfies a preset positive bending yield strength and negative bending yield strength of the beam; a yield stress YS' of the standard steel material; a plate thickness t' of the standard steel material; and a plate thickness t of the steel material. In the range of 0.575≦t / t'<1.0, YS / YS'≧1 / (t / t') Equation (1) In the range of 0.5≦t / t'<0.575, YS / YS'≧1 / (t / t')+5.33×(0.575-t / t') Equation (2) The method includes a process of determining a combination of the yield stress YS of the steel material and the plate thickness t of the steel material so as to satisfy the formula:

[0016] A method for selecting beam material for a steel protective fence according to a fourth aspect of the present disclosure is characterized in that the yield stress of the steel material for the beam is set to more than 400 MPa and not more than 800 MPa, the plate thickness of the steel material is set to be not less than 2.0 mm and less than 4.0 mm, and the bending yield strength Pb of the beam and the bending yield strength Pc of the support satisfy the relationships of the following equations (3) to (5). Pb < 2×Pc Equation (3) Pb = 4(MBP+MBN) / L Equation (4) Pc = MC / H Equation (5) where: Pb: Strength at which the beam yields (kN) Pc: Strength at which the column yields in bending (kN) MBP: Positive bending strength of beam (kNm) MBN: Negative bending strength of beam (kNm) L: beam support span (m) MC: Bending strength of support (kNm) H: Support length of the support column (m) [Effects of the Invention]

[0017] According to the present disclosure, it is possible to provide a steel protective fence, beam, and beam material selection method that can achieve both thinning of the beam and ensuring strength. [Brief explanation of the drawings]

[0018] [Figure 1] Figure 1(a) is an oblique view illustrating a steel protective fence according to an embodiment of the present disclosure, Figure 1(b) is a plan view illustrating a steel protective fence according to this embodiment, and Figure 1(c) is a cross-sectional view taken along line 1c-1c in Figure 1(b). [Figure 2] FIG. 2(a) is a perspective view illustrating the steel protective fence according to this embodiment, and FIG. 2(b) is a plan view illustrating the steel protective fence according to this embodiment. [Figure 3] FIG. 2 is a cross-sectional view illustrating a beam of the steel safety fence according to the present embodiment. [Figure 4] FIG. 1 is a cross-sectional view illustrating the lap joints between beams and the connection between beams and posts of the steel protective fence according to this embodiment. [Figure 5] Figure 5(a) is an oblique view illustrating the state in which a load is applied to the beam of the steel protective fence according to this embodiment, causing the beam to deform, and Figure 5(b) is a plan view illustrating the state in which a load is applied to the beam of the steel protective fence according to this embodiment, causing the beam to deform. [Figure 6] FIG. 1 is a plan view illustrating the positive bending, negative bending, and tensile cross-sectional forces acting on the beam when a load is applied to the beam of the steel safety fence according to this embodiment, causing the beam to deform. [Figure 7] Figure 7(a) is a schematic diagram of an analytical model for evaluating the positive bending strength of a beam against a positive bending load component applied to the beam, Figure 7(b) is a schematic diagram of an analytical model for evaluating the negative bending strength of a beam against a negative bending load component applied to the beam, and Figure 7(c) is a schematic diagram of an analytical model for evaluating the tensile strength of a beam against a tensile load component applied to the beam. [Figure 8] Figure 8(a) is a graph showing the relationship between the beam's positive bending strength and yield stress, and Figure 8(b) is a graph showing the relationship between the positive bending strength ratio and yield stress ratio, using a standard steel material as a comparison standard. [Figure 9] Figure 9(a) is a graph showing the relationship between the negative bending strength and yield stress of the beam, and Figure 9(b) is a graph showing the relationship between the negative bending strength ratio and yield stress ratio, using a standard steel material as a comparison standard. [Figure 10] FIG. 10(a) is a graph showing the relationship between the tensile strength and yield stress of the beam, and FIG. 10(b) is a graph showing the relationship between the tensile strength ratio and yield stress ratio, using a standard steel material as a comparison standard. [Figure 11] Figure 11(a) is a graph showing the relationship between the moment of inertia, which is an index of the bending rigidity of a beam, and the yield stress, and Figure 11(b) is a graph showing the relationship between the bending rigidity ratio and the yield stress ratio, using a standard steel material as a comparison standard. [Figure 12] FIG. 12(a) shows the relationship between the weight and thickness of a beam of a predetermined size, and FIG. 12(b) is a graph showing the relationship between the weight ratio and thickness using a standard steel material as a comparison standard. [Figure 13] 1 is a graph illustrating the relationship between the plate thickness ratio and the yield stress ratio between a standard steel material and a thinned steel material when the normal bending strength ratio to the standard steel material is 1. [Figure 14] 1 is a graph illustrating the relationship between the plate thickness ratio and the yield stress ratio between a reference steel material and a thinned steel material when the negative bending strength ratio relative to the reference steel material is 1. [Figure 15] 1 is a graph illustrating the relationship between the plate thickness ratio and the yield stress ratio between a reference steel material and a thinned steel material when the tensile strength ratio to the reference steel material is 1. [Figure 16] FIG. 1 is a schematic diagram illustrating the bending yield strength Pb of a beam. [Figure 17] FIG. 1 is a schematic diagram illustrating the strength Pc at which a column yields in bending. DETAILED DESCRIPTION OF THE INVENTION

[0019] An embodiment of the present disclosure will be described below. In the following description of the drawings, identical or similar parts are designated by the same or similar reference numerals. However, the relationship between thickness and planar dimensions in the drawings, the thickness ratios of each device and each component, etc., differ from the actual ones. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. Furthermore, parts with different dimensional relationships and ratios are included between the drawings. Furthermore, unless otherwise specified in the specification, the number of each component element of the present disclosure is not limited to one and may be present in multiple numbers.

[0020] In addition, in this disclosure, the "%" representation of the content of each element in the chemical composition means "% by mass." A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. When "to" is followed by "more than" or "less than," the numerical range does not include the numerical value as the lower or upper limit. The content of an element in the chemical composition may be expressed as the element amount (e.g., Zn amount, Mg amount, etc.) or element concentration (e.g., Zn concentration, Mg concentration, etc.).

[0021] <Configuration of steel protective fence> A steel guardrail 10 according to this embodiment will be described with reference to Figs. 1 to 17. As shown in Figs. 1(a), 1(b), and 1(c), the steel guardrail 10 comprises posts 12, connectors 14, and beams 16. As shown in Fig. 1, in this specification, the up-down direction is the direction in which the posts 12 extend, and is referred to as the upward direction UD and the downward direction LD. In addition, in the direction perpendicular to the beam, the roadway side is referred to as the inward direction ID, and the opposite direction (outside the roadway) is referred to as the outward direction OD. Furthermore, in the direction in which the beam extends, the direction in which a vehicle moves forward is referred to as the forward direction FD, and the opposite direction is referred to as the reverse direction BD.

[0022] (post) As shown in Figures 1(a) to 1(c) and 2(a) to 2(b), the support columns 12 are cylindrical or other tubular steel members. In addition to the end support columns 12A arranged near both ends of the beam with a support distance of L, intermediate support columns 12B may be provided in the middle of the beam with a support distance of L1 (Figure 2).

[0023] (Connector) The connector 14 is a connecting hardware that connects a connecting portion 20 provided on the fourth wall 24 located in the center of the beam 16 in the vertical direction to the support column 12. The connector 14 and the support column 12 are connected by a fastener 34 such as a bolt, and the connector 14 and the connecting portion 20 are connected by a fastener 31 such as a bolt. FIGS. 1(a) and 2(a) show examples of the fastener 31 that connects the connector 14 and the beam 16, and the fastener 32 that connects the beams 16 to each other. Additionally, FIGS. 1(b) and 2(b) show examples of a lap joint 33 between the beams 16, a fastener 32 that connects the beams 16 to each other at the lap joint 33, and a fastener 34 that connects the support column 12 to the connector 14.

[0024] (beam) The beam 16 is a long member having a length L0 and is formed by bending a steel plate. As shown in FIGS. 1 and 2, the cross-sectional shape of the beam 16 is substantially constant along the longitudinal direction of the beam 16. In this specification, the longitudinal direction of the beam 16 is illustrated as the forward direction FD and the reverse direction BD in which the vehicle moves forward. As shown in FIG. 3, the plate thickness t of the beam 16 is substantially constant along the entire cross section. The beam 16 has a fourth wall 24 on which the connecting portion 20 is provided, a pair of first walls 21, a pair of second walls 22, and a pair of third walls 23. The fourth wall 24 and the second walls 22 are formed to be substantially parallel surfaces. In addition, Figure 3 shows the symbols for the beam width B, beam center height D1 (distance between the fourth wall 24 and the second wall 22), beam end height D3 (distance between the end of the third wall 23 and the second wall 22), projected width W1 of the first wall 21, width W2 of the second wall 22, projected width W3 of the third wall 23, and width W4 of the fourth wall 24 as dimensions at the center of the plate thickness.

[0025] (First wall, second wall, third wall, fourth wall and connecting part) As shown in Figures 3 and 4, a connecting portion 20 provided on a fourth wall 24 extending in the up-down direction is connected to the support 12 via a connector 14. The pair of first walls 21 extend from the upper and lower ends of the fourth wall 24 (connecting portion 20) toward the opposite side from the support 12 in cross section. The pair of second walls 22 extend from the tips of the pair of first walls 21 in directions away from each other in the up-down direction so as to be on planes parallel to the fourth wall 24 (connecting portion 20) in cross section. The pair of third walls 23 extend from the tips of the pair of second walls 22 toward the support 12 in cross section.

[0026] The thickness of the steel material constituting the beam is 2.0 mm or more and less than 4.0 mm. The yield stress of the steel material is more than 400 MPa and less than 800 MPa. In the present disclosure, the lower limit of the yield stress of the steel material may include 400 MPa. The upper and lower limit values ​​of the steel material thickness and the upper and lower limit values ​​of the steel material yield stress will be described later in Example 1.

[0027] In addition, in this embodiment, the steel material is set so that the yield stress YS' of a standard steel material that satisfies the bending strength of a preset beam, the yield stress YS of the steel material, the plate thickness t' of the standard steel material, and the plate thickness t of the steel material satisfy the following equations (1) and (2). In the range of 0.575≦t / t'<1.0, YS / YS'≧1 / (t / t') Equation (1) In the range of 0.5≦t / t'<0.575, YS / YS'≧1 / (t / t')+5.33×(0.575-t / t') Equation (2) In the present disclosure, it is not essential to satisfy formula (1) and formula (2). Formula (1) and formula (2) will be specifically explained in Example 1 later.

[0028] In addition, in this embodiment, the strength Pb at which the steel material of the beam 16 yields in bending and the strength (2×Pc) at which the two pillars 12 supporting the beam 16 yield in bending are set to satisfy the following equation (3). Pb < 2×Pc Equation (3) In the present disclosure, the magnitude relationship between the strength at which the steel material of the steel protective fence 10 bends and the strength at which the support posts 12 bend and yield can be set arbitrarily. Formula (3) will be specifically explained later in Example 2. [Example]

[0029] (Example 1: Beam that is both strong and lightweight) Next, Example 1 will be described with reference to FIGS. 1 to 15. In Example 1, an analysis was performed to confirm the relationship between the beam plate thickness and the yield stress and strength of the steel material. Specifically, the elastic buckling stress was calculated by buckling analysis using the finite strip method (Technical Document 1) for the cross section of the beam, and the positive bending strength and negative bending strength of the beam were derived by applying the Direct Strength Method (Technical Document 2). Note that in the present disclosure, the means for analyzing the bending strength of the beam is not limited to this, and any analytical method can be used. Technical literature 1: BW Schafer, S. Adany: Buckling analysis of cold-formed steel members using CUFSM: conventional and constrained finite strip methods, 18th International Specialty Conference on Cold-Formed Steel Structures, 2006 Technical literature 2: BW Schafer: The Direct Strength Method of cold-formed steel member design, Journal of Constructional Steel Research 64, pp.766-778, 2008

[0030] Regarding the strength of a steel safety fence, the strength of the beam 16 will be examined assuming a condition in which a load Pr perpendicular to the beam is input (corresponding to the load component perpendicular to the beam in the load that acts when a vehicle collides with a steel safety fence), as shown in Figures 5(a) and 5(b). Due to the influence of the load Pr corresponding to the perpendicular load component, a positive bending moment M+ acts on the beam 16 near the position where the load acts, as shown in Figure 6, and a negative bending moment M- acts on the beam 16 near the support columns 12 that support the beam 16 in the section where the load acts, and a tensile strength T+ is generated due to deformation Def of the beam 16.

[0031] In Example 1, the following dimensions and material properties were set as the specifications for the steel guardrail, using the symbols shown in Figures 1 to 3, and the performance of the beam was examined. However, the specifications for the steel guardrail are not limited to these dimensions. Note that W1, W2, W3, W4, D1, and D3, which represent the dimensions of each face that makes up the cross section of the beam, are expressed as the dimensions at the center of the beam thickness t. L0=4330mm L=4000mm L1=2000mm H=600mm B=350mm W1=41mm W2=63mm W3=36mm W4=70mm D1=71mm D3=52mm t=2.0~4.0mm YS=295~800MPa

[0032] The cross section of the beam of the aforementioned steel guardrail corresponds to the cross section of a Type A beam defined in the following Technical Document 3. Technical Document 3: Japan Road Association, Standard Specifications and Commentary for Vehicle Guard Barriers (Revised Edition) (March 31, 2004)

[0033] The bending radius R of the ridges of each surface is set according to the manufacturing conditions of the beam that involves bending and the plate thickness, but for convenience, in the study of the beam strength and weight described below, the bending radius R is set to 0. Setting R to 0 slightly changes the absolute evaluation of the buckling strength and weight, but has almost no effect on the relative evaluation of the reference steel material and the steel material disclosed herein.

[0034] The steel material for existing beams to be thinned, i.e., the standard steel material, was selected to have the dimensions and material properties shown below, which are specifications commonly used for steel guardrails installed on expressways in Japan. Yield stress of standard steel YS'=295MPa Standard steel plate thickness t' = 4.0 mm Here, the yield stress of the reference steel material is based on the steel standards SS400 (standard yield stress 235 MPa) and SGH400 (standard yield stress 295 MPa) used for existing beam steel materials, and a larger yield stress (YS' = 295 MPa) is targeted to ensure a safe material replacement.

[0035] The beam strength against the positive bending moment M+, negative bending moment M-, and tensile strength T+ shown in Figure 6 was examined using a partial beam element (member length 1000 mm) subjected to the uniform positive bending moment shown in Figure 7(a), the uniform negative bending moment shown in Figure 7(b), and the tensile strength shown in Figure 7(c). Here, the positive bending strength and negative bending strength were derived as bending strengths that take into account buckling behavior, which is a concern when thinning the walls, using analytical methods from technical literature 1 and 2. On the other hand, since buckling does not need to be considered for the tensile strength, it was derived as the strength obtained by multiplying the cross-sectional area by the yield stress.

[0036] Figure 8(a) shows the positive bending strength of a beam when the steel thickness (t = 2.0 mm to 4.0 mm) and yield stress (YS = 295 to 800 MPa) are varied for a standard steel material (t' = 4.0 mm, YS' = 295 MPa). Figure 8(b) shows the relationship between the positive bending strength ratio and the yield stress ratio for the standard steel material. For thicknesses t = 2.3 mm to 4.0 mm, no localized buckling occurs in the beam cross section, and the positive bending strength increases linearly in proportion to the steel's yield stress. On the other hand, for thicknesses t = 2.0 mm, localized buckling occurs in the second wall (see second wall 22 in Figure 3) that is subjected to compressive stress in the beam cross section, so the increase in positive bending strength is nonlinear when the steel's yield stress is above 600 MPa.

[0037] Figure 9(a) shows the negative bending strength of a beam when the steel plate thickness (t = 2.0mm to 4.0mm) and yield stress (YS = 295 to 800MPa) are changed for a standard steel material (t' = 4.0mm, YS' = 295MPa). Figure 9(b) shows the relationship between the negative bending strength ratio and yield stress ratio for the standard steel material. Within the plate thickness range of t = 3.0mm to 4.0mm, no local buckling occurs in the cross section of the beam, and the negative bending strength increases linearly in proportion to the yield stress of the steel material. On the other hand, when the plate thickness t is less than 3.0 mm, local buckling occurs at the edges of the OD (outward direction) of the fourth wall (see fourth wall 24 in Figure 3) and the third wall (see third wall 23 in Figure 3) that are subjected to compressive stress in the cross section of the beam. Therefore, the increase in negative bending strength is nonlinear when the steel yield stress is 500 MPa or higher in the t range of 2.3 mm to 2.5 mm, and when the steel yield stress is 400 MPa or higher in the t range of 2.0 mm. In other words, the rate of change in negative bending strength is small when the steel yield stress is 500 MPa or higher in the t range of 2.3 mm to 2.5 mm, and when the steel yield stress is 400 MPa or higher in the t range of 2.0 mm.

[0038] 9(a) and 9(b) show that if the steel plate thickness is less than 2.0 mm, it is difficult to ensure a negative bending strength equal to or greater than that of the standard steel. Based on this result, the lower limit of the plate thickness is set at 2.0 mm.

[0039] Figure 10(a) shows the tensile strength of a beam when the steel plate thickness (t = 2.0 to 4.0 mm) and yield stress (YS = 295 to 800 MPa) are changed for a standard steel material (t' = 4.0 mm, YS' = 295 MPa). Figure 10(b) shows the relationship between the tensile strength ratio and yield stress ratio for the standard steel material. Because no local buckling occurs in the cross section of the beam, the tensile strength increases linearly in proportion to the yield stress of the steel material.

[0040] Regarding the bending strength of a beam, as shown in Figures 8 and 9, local buckling occurs in the area of ​​the beam cross section that is subjected to compressive stress, so in order to make the beam thinner, an appropriate combination of plate thickness and yield stress is required.

[0041] As an index of the appropriate combination of steel plate thickness t and yield stress YS for thinning the beam, the relationship between plate thickness ratio (t / t') and yield stress ratio (YS / YS') at which the proof stress ratio (positive bending, negative bending, tension) to the standard steel is equivalent (=1.0) is plotted in Figure 13 (positive bending), Figure 14 (negative bending), and Figure 15 (tension). In the range of 0.5≦t / t'<1.0 in Figures 13 and 15, and in the range of 0.575≦t / t'<1.0 in Figure 14, the plate thickness ratio and yield stress ratio have the relationship shown in equation (1') below. YS / YS'=1 / (t / t') Equation (1') In addition, in the range of 0.5≦t / t'<0.575 in Figure 14, the relationship between the plate thickness ratio and the yield stress ratio is expressed by the following equation (2'). YS / YS'=1 / (t / t')+5.33×(0.575-t / t') Formula (2')

[0042] Based on the results shown in Figures 13 to 15, the present disclosure provides a beam that can ensure a strength ratio equal to or greater than that of a standard steel material for all resistance mechanisms, including positive bending, negative bending, and tension, and satisfies the relationship shown below for the plate thickness ratio (t / t') and yield stress ratio (YS / YS'). In the range of 0.575≦t / t'<1.0, YS / YS'≧1 / (t / t') Equation (1) In the range of 0.5≦t / t'<0.575, YS / YS'≧1 / (t / t')+5.33×(0.575-t / t') Equation (2)

[0043] Additionally, when the yield stress YS' of the reference steel material was other than 295 MPa and the plate thickness t' of the reference steel material was other than 4.0 mm, the same results as those of this example were obtained.

[0044] Furthermore, by thinning the beam, the moment of inertia, which is an indicator of the beam's bending rigidity, can be reduced, as shown in Figures 11(a) and 11(b). Figure 11(a) shows the relationship between the moment of inertia and yield stress of the beam. Figure 11(b) shows the relationship between the bending rigidity ratio and yield stress ratio, using a standard steel material as a comparison standard. This reduces the rigidity of the beam against deformation (see beam deformation Def in Figure 6) when a vehicle collides with a steel safety fence using a thinned beam. This effectively absorbs the impact load and reduces the acceleration acting on the occupants when the steel safety fence pushes the vehicle back, thereby improving the ability to prevent injury to the occupants.

[0045] The weight reduction effect of thinning the beam is shown in Figures 12(a) and 12(b). Figure 12(a) shows the relationship between the weight and plate thickness of a beam with specified dimensions. Figure 12(b) shows the relationship between the weight ratio and plate thickness, using a standard steel material as a comparison standard. By reducing the plate thickness t to less than 4.0 mm compared to the standard steel material (t' = 4.0 mm), the weight per beam can be kept to less than 60 kg. This reduces the burden on each worker and may even reduce the number of workers required for transportation and installation, streamlining the work process.

[0046] (Steel plate thickness) If the lower limit of the steel plate thickness is less than 2.0 mm, it is difficult to ensure beam performance (particularly negative bending strength) equivalent to or better than that of a standard steel plate (t' = 4.0 mm, YS' = 295 MPa). Furthermore, if the steel plate thickness is 4.0 mm or more, it is not possible to achieve the weight reduction effect compared to a beam made from a standard steel plate. In this embodiment, the lower limit of the plate thickness is set to 2.0 mm or more and the upper limit to less than 4.0 mm, so that the beam for a steel safety fence can be made thinner, i.e., lightweight, while still maintaining strength.

[0047] (yield stress of steel) Furthermore, if the lower limit of the yield stress of the steel material is less than 400 MPa, it is not possible to obtain a sufficient thinning effect, i.e., weight reduction, to ensure beam performance equivalent to or better than that of a standard steel material (t' = 4.0 mm, YS' = 295 MPa). In this embodiment, the lower limit is set to 400 MPa, making it easy to achieve both ensuring beam strength and weight reduction. Furthermore, if the upper limit of the yield stress of the steel material exceeds 800 MPa, the strength becomes too high, making it difficult to process the steel material (such as bending or drilling). In this embodiment, the upper limit is set to 800 MPa, making it easy to process the steel material. In the present disclosure, the yield stress of the steel material is more preferably greater than 400 MPa and not greater than 700 MPa. Furthermore, the yield stress of the steel material is even more preferably greater than 400 MPa and not greater than 600 MPa. Furthermore, the yield stress of the steel material is even more preferably greater than 400 MPa and not greater than 500 MPa.

[0048] (Example 2: Steel guardrail to prevent damage to posts) Next, Example 2 will be described with reference to Figures 16 and 17. In Example 2, in order to provide a steel protective fence that suppresses damage to the posts, an analysis was carried out to confirm the relationship between the bending strength Pb of the beam, which is determined from the positive bending strength and negative bending strength of the beam shown in Example 1, and the bending strength Pc of the posts.

[0049] Specifically, as in Example 1, the elastic buckling stress was calculated for the cross section of the beam by buckling analysis using the finite strip method (Technical Document 1), and the direct strength method (Technical Document 2) was applied to derive the positive bending strength and negative bending strength of the beam. Based on the mechanical model of plastic analysis (limit analysis) shown in Figure 16 (δ in Figure 16 is the displacement due to external force, and θ (= 2δ / L) is the rotation angle of the bending hinge), the balance between the internal work Wi and the external work Wo was found, and the bending yield strength Pb of the beam was determined using equation (4). Internal work: Wi=2(MBP+MBN)θ External work: Wo=Pδ where θ=2δ / L Pb = 4(MBP+MBN) / L Equation (4) where: Pb: Strength at which the beam yields (kN) MBP: Positive bending strength of beam (kNm) MBN: Negative bending strength of beam (kNm) L: beam support span (m) The beam support span (distance between supports) L can be the distance L between the supports 12 at both ends of the beam 16 when there is no intermediate support as in Figure 1(b), or the distance L1 between the end supports 12A and the intermediate support 12B when there is an intermediate support 12B as in Figure 2(b).

[0050] In addition, the bending strength of the column, MC, was calculated by multiplying the column's yield stress by the plastic section modulus, and based on the distribution of the bending moment occurring in the column (maximum moment = Pc × H, see Figure 17), the bending yield strength of the column, Pc, was determined using equation (5). Pc = MC / H Equation (5) where: Pc: Strength at which the column yields in bending (kN) MC: Bending strength of support (kNm) H: Support length of the support column (m)

[0051] In the installation of a steel protective fence in which one beam is supported by two posts, by satisfying the condition of equation (3) that the bending strength Pc of the two posts supporting the single beam is greater than the bending strength Pb of the single beam, it is possible to provide a steel protective fence that suppresses damage to the posts. Pb < 2×Pc Equation (3) As in Example 2, in this embodiment, the bending yield strength Pb of the beam and the bending yield strength Pc of the column satisfy the relationships of formulas (3) to (5).

[0052] (Action and effect) The beam 16 for the steel safety fence according to this embodiment is made of steel, and the yield stress of the steel is greater than 400 MPa and less than 800 MPa. The steel plate thickness is greater than or equal to 2.0 mm and less than 4.0 mm. This allows the beam 16 for the steel safety fence to be made thinner, i.e., lighter, while still maintaining its strength.

[0053] In this embodiment, the combination of the yield stress YS and plate thickness t of the steel material of the beam 16 is determined based on formulas (1) and (2) that are preset between the steel material and a reference steel material (yield stress YS', plate thickness t'). Therefore, while maintaining strength equivalent to or greater than that of the reference steel material, the beam can be made lighter by being thinner than the reference steel material, thereby reducing the weight per beam. This reduces the burden on each worker and also reduces the number of workers required for transportation and installation, thereby streamlining the work. Furthermore, the thinner beam reduces the bending rigidity of the beam, thereby reducing the acceleration acting on the occupant when the steel safety fence pushes back a collided vehicle, thereby improving the ability to prevent injury to the occupant.

[0054] Furthermore, in this embodiment, the bending yield strength Pb of the beam 16 and the bending yield strength 2×Pc of the two posts 12 supporting the beam 16 satisfy Pb < 2×Pc, as explained in equation (3) above. This condition provides a steel guardrail 10 that suppresses damage to the posts 12. This leads to a reduction in the number of times the posts, which are installed (buried, etc.) in the ground and are difficult to replace, and reduces the burden of the work involved in replacing the steel guardrail.

[0055] <Other embodiments> Although the present disclosure has been described using the above embodiments, this description does not limit the present disclosure. It should be understood that various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure. The present disclosure includes various embodiments not described above, and the technical scope of the present disclosure is defined only by the inventive features of the claims that are appropriate from the above description.

[0056] <<Additional Notes>> The following aspects are conceptualized from this specification.

[0057] Aspect 1 is It is made of steel, The yield stress of the steel material is more than 400 MPa and 800 MPa or less, The thickness of the steel material is 2.0 mm or more and less than 4.0 mm, Beams for steel guardrails.

[0058] Aspect 2 is The steel material is The yield stress YS' of a standard steel material that satisfies the positive bending strength and negative bending strength of a preset beam, the yield stress YS of the steel material, the plate thickness t' of the standard steel material, and the plate thickness t of the steel material, In the range of 0.575≦t / t'<1.0, YS / YS'≧1 / (t / t') Equation (1) In the range of 0.5≦t / t'<0.575, YS / YS'≧1 / (t / t')+5.33×(0.575-t / t') Equation (2) characterized in that A beam for the steel safety fence according to embodiment 1.

[0059] Aspect 3 is A beam formed of a steel material, wherein the yield stress of the steel material is more than 400 MPa and less than 800 MPa, and the plate thickness of the steel material is 2.0 mm or more and less than 4.0 mm; A support column supporting the beam; A connector that connects the support column and the beam; A steel protective fence equipped with:

[0060] Aspect 4 is The bending yield strength Pb of the beam and the bending yield strength Pc of the column satisfy the relationships of the following formulas (3) to (5), The steel protective fence according to aspect 3. Pb < 2×Pc Equation (3) Pb = 4(MBP+MBN) / L Equation (4) Pc = MC / H Equation (5) where: Pb: Strength at which the beam yields (kN) Pc: Strength at which the column yields in bending (kN) MBP: Positive bending strength of beam (kNm) MBN: Negative bending strength of beam (kNm) L: beam support span (m) MC: Bending strength of support (kNm) H: Support length of the support column (m)

[0061] Aspect 5 is The yield stress of the steel for the beam is set to over 400 MPa and below 800 MPa. The plate thickness of the steel material is set to 2.0 mm or more and less than 4.0 mm, The yield stress YS' of a standard steel material that satisfies the positive bending strength and negative bending strength of a preset beam, the yield stress YS of the steel material, the plate thickness t' of the standard steel material, and the plate thickness t of the steel material, In the range of 0.575≦t / t'<1.0, YS / YS'≧1 / (t / t') Equation (1) In the range of 0.5≦t / t'<0.575, YS / YS'≧1 / (t / t')+5.33×(0.575-t / t') Equation (2) A beam material selection method including a process of determining a combination of the yield stress YS of the steel material and the plate thickness t of the steel material so as to satisfy the formula:

[0062] Aspect 6 is The yield stress of the steel for the beam is set to over 400 MPa and below 800 MPa. The plate thickness of the steel material is set to 2.0 mm or more and less than 4.0 mm, The beam bending yield strength Pb and the column bending yield strength Pc satisfy the relationship of the following formulas (3) to (5): How to select beam materials for steel guardrails. Pb < 2×Pc Equation (3) Pb = 4(MBP+MBN) / L Equation (4) Pc = MC / H Equation (5) where: Pb: Strength at which the beam yields (kN) Pc: Strength at which the column yields in bending (kN) MBP: Positive bending strength of beam (kNm) MBN: Negative bending strength of beam (kNm) L: beam support span (m) MC: Bending strength of support (kNm) H: Support length of the support column (m) [Explanation of symbols]

[0063] 10 Steel protective fence 12 pillars 12A Double-end support 12B Intermediate post 14 Connector 16 Beam 20 Connection part 21 First wall 22 Second wall 23 Third Wall 24 Fourth Wall 31 Fasteners connecting connectors to beams 32 Fasteners connecting beams together 33 Beam-to-beam lap joint 34 Fastening part connecting the support and connector L0 Beam member length L Distance between the supports at both ends of the beam L1 Distance between intermediate supports H Support length of the support column UD Upper direction LD downward direction ID inward direction ОD outward direction FD forward direction BD Reverse direction Pr Load corresponding to the orthogonal load component of the collision load Def Deformation of the beam due to collision load M+ Positive bending moment acting on the beam M- Negative bending moment acting on the beam T+ beam tensile strength

Claims

1. It is made of steel, The yield stress of the steel material is more than 400 MPa and 800 MPa or less, The thickness of the steel material is 2.0 mm or more and less than 4.0 mm, Beams for steel guardrails.

2. The steel material is The yield stress YS' of a reference steel material that satisfies the preset positive bending strength and negative bending strength of a beam, the yield stress YS of the steel material, the plate thickness t' of the reference steel material, and the plate thickness t of the steel material, In the range of 0.575≦t / t′<1.0, YS / YS'≧1 / (t / t') Formula (1) In the range of 0.5≦t / t′<0.575, YS / YS'≧1 / (t / t')+5.33×(0.575-t / t') Formula (2) characterized in that A beam for a steel safety fence according to claim 1.

3. A beam formed of a steel material, wherein the yield stress of the steel material is more than 400 MPa and less than 800 MPa, and the plate thickness of the steel material is 2.0 mm or more and less than 4.0 mm; A support column supporting the beam; A connector that connects the support column and the beam; A steel protective fence equipped with:

4. The bending yield strength Pb of the beam and the bending yield strength Pc of the column satisfy the relationships of the following formulas (3) to (5): The steel protective fence according to claim 3. Pb < 2 × Pc Equation (3) Pb = 4(MBP+MBN) / L Formula (4) Pc = MC / H Formula (5) where: Pb: Strength at which the beam yields (kN) Pc: Strength at which the column yields in bending (kN) MBP: Positive bending strength of beam (kNm) MBN: Negative bending strength of beam (kNm) L: beam support span (m) MC: Bending strength of the support (kNm) H: Support length of the support (m)

5. The yield stress of the steel material for the beam is set to more than 400 MPa and not more than 800 MPa, The plate thickness of the steel material is set to 2.0 mm or more and less than 4.0 mm, The yield stress YS' of a reference steel material that satisfies the preset positive bending strength and negative bending strength of a beam, the yield stress YS of the steel material, the plate thickness t' of the reference steel material, and the plate thickness t of the steel material, In the range of 0.575≦t / t′<1.0, YS / YS'≧1 / (t / t') Formula (1) In the range of 0.5≦t / t′<0.575, A beam material selection method including a process of determining a combination of the yield stress YS of the steel material and the plate thickness t of the steel material so as to satisfy the formula (2): YS / YS'≧1 / (t / t')+5.33×(0.575−t / t').

6. The yield stress of the steel material for the beam is set to more than 400 MPa and not more than 800 MPa, The plate thickness of the steel material is set to 2.0 mm or more and less than 4.0 mm, The beam bending yield strength Pb and the column bending yield strength Pc satisfy the following formulas (3) to (5): How to select beam materials for steel guardrails. Pb < 2 × Pc Equation (3) Pb = 4(MBP+MBN) / L Formula (4) Pc = MC / H Formula (5) where: Pb: Strength at which the beam yields (kN) Pc: Strength at which the column yields in bending (kN) MBP: Positive bending strength of beam (kNm) MBN: Negative bending strength of beam (kNm) L: beam support span (m) MC: Bending strength of the support (kNm) H: Support length of the support (m)

Images