Steel guard fence, beam for steel guard fence, and method of selecting beam material for steel guard fence

Abstract

A beam for a steel guard fence according to the present invention is formed from a plated steel material comprising: a steel base material having a sheet thickness of 3.2 mm or less and a yield stress of greater than 400 MPa but not greater than 800 MPa; and a plating layer that covers the surface of the base material and is composed of a Zn-Al-Mg plating. The beam for a steel guard fence has a cut end surface formed on at least one end surface of the plated steel material, and the plated steel material has a sheet thickness of not less than 2.0 mm but less than 4.0 mm.

Description

Steel guardrails, beams for steel guardrails, and selection method for beam materials for steel guardrails

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

[0002] Steel protective fences are installed as so-called infrastructure facilities, for example, on the roadside of a roadway or in a median strip. In some documents, steel protective fences are referred to as guardrails. Japanese Patent Application Laid-Open No. 2002-121659, International Publication No. 2018 / 139619, and International Publication No. 2020 / 261723 disclose the use of plated steel material, for example, zinc (Zn), aluminum (Al), and magnesium (Mg), as the steel material for the beams of a steel protective fence.

[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] A steel guardrail is constructed by connecting a beam to the roadway side of a support post whose lower part is installed, for example, by burying it in the ground or road surface. When a vehicle collides with the steel guardrail, the beam is required to resist the load of the vehicle collision, absorb the energy of the collision, and push the vehicle back, while preventing the vehicle from jumping off the roadway. In addition, from the perspective of occupant protection, the beam is also required to prevent injury 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 new beam installed after the replacement will be required to have performance (e.g., load resistance) equal to or greater than that of the existing beam, such as the beam adjacent to the damaged beam.

[0006] Patent Document 1: JP 2002-121659 A Patent Document 2: WO 2018 / 139619 Patent Document 3: WO 2020 / 261723

[0007] Heavy beams in steel safety fences can weigh more than 60 kgf per beam. In beam replacement work, damaged or worn beams are removed from the supports, and new beams are transported and installed in their designated positions relative to the supports. The same work is also performed when installing new beams. In beam replacement and installation work, workers must hold the beams while transporting and installing them, which requires manual labor and places a heavy burden on the workers. Generally, when the weight of a beam exceeds 60 kgf, more than two workers are often required to transport and install one beam. On the other hand, reducing the weight of the beams to less than 60 kgf reduces the burden on each worker and may even reduce the number of workers required for transportation and installation, thereby streamlining the work process.

[0008] In particular, when the replacement work site is a site such as a highway where the access space and working space to the work site are limited, it is often difficult to use heavy machinery or other transport machinery that can replace human power at the work site. For this reason, the beam replacement work has to rely on human power, which results in 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 of a declining birthrate and aging population, there is a demand for technology to reduce the workload during beam replacement and new installation work so that workers from various backgrounds, such as the elderly and women, can participate 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 materials, for example, by thinning the thickness of the steel material for the beams, i.e., by thinning the material. However, simply thinning the steel material for existing beams will result in a beam formed from the thinned steel having lower strength and energy absorption performance than existing beams. In other words, it is difficult to ensure the strength required for steel guardrails that use thinned beams. Note that, hereinafter, steel materials that are subject to thinning and have a predetermined strength, such as steel materials for existing beams, will be referred to as "standard steel materials."

[0011] Furthermore, when plated steel is used as a steel material for beams, for example, when a pre-plated steel sheet is cut to a predetermined width during beam manufacturing, a cut edge is generated in which the steel sheet base is exposed without a plating layer. It is known that plated steel sheets having a plating layer containing Zn, Al, and Mg exhibit corrosion resistance at the cut edge, suppressing the formation of red rust at the cut edge, by allowing corrosion products resulting from the plating on the front and back surfaces of the steel sheet to move around (i.e., migrate) to the cut edge. The corrosion products are generated by the reaction between the plating layer and moisture. The corrosion products disclosed herein contain Mg. However, as the sheet thickness increases, the amount of plating that moves around decreases, making it impossible to expect sufficient end-face corrosion resistance. This requires rust prevention treatment, such as thermal spraying or touch-up painting, on the cut edge, which results in increased effort during beam manufacturing.

[0012] Furthermore, when a beam with a corrugated cross section is installed, the position of the cut end faces can change in various directions, such as up, down, left, and right. In other words, it is difficult to uniformly set the facing direction of the cut end faces in advance. Therefore, regardless of the facing direction of the cut end faces, it is necessary for the corrosion products to easily move around or wrap around and for a uniform coating of corrosion products to be formed.

[0013] In this regard, JP 2002-121659 A, WO 2018 / 139619 A, and WO 2020 / 261723 A do not consider a technology for ensuring edge corrosion resistance in addition to a technology for achieving both thinning and ensuring strength. Furthermore, WO 2020 / 261723 A simply mentions that high-tensile steel, i.e., high-strength steel sheet, may be used as the plated steel material, but no specific consideration has been made regarding strength requirements, such as the yield stress of high-strength steel sheet, nor has any specific consideration been made regarding thinning and edge corrosion resistance achieved by using high-strength steel sheet.

[0014] Furthermore, for example, in beams processed by cold roll forming, the beam has an open cross section formed by bending a steel plate in the width direction, which is prone to cross-sectional distortion. Furthermore, since the beam has a very large width-to-length ratio (i.e., aspect ratio), there is a problem that the entire member is prone to twisting. Furthermore, when high-strength steel plates are used for beams, i.e., when the steel plates for beams are made stronger, the residual stress introduced into the beam by beam processing increases. Beam processing includes slittering, which cuts steel plates to a predetermined width, rolling, which forms the cross-sectional shape of the beam on the steel plate, and shearing, which cuts steel plates to a predetermined length (i.e., a fixed length).

[0015] Here, if the beam is subjected to a hot-dip plating process (i.e., an immersion process) using a high-temperature plating bath of approximately 420°C to 480°C after processing, residual stress is released, resulting in distortion of the beam. The higher the strength of the steel plate, the greater the distortion that occurs, resulting in greater cross-sectional distortion and torsion of the entire member. In addition, thinning the steel plate of the beam reduces its rigidity, resulting in more pronounced cross-sectional distortion and torsion of the entire member. That is, when a beam for a steel safety fence is manufactured by hot-dip plating after residual stress has been introduced into the beam through processing, the thinning of the high-strength steel plate amplifies the cross-sectional distortion and torsion of the entire member due to the release of residual stress, making it difficult to manufacture the beam.

[0016] The present disclosure has been made in consideration of the above, and provides a steel guardrail, a beam for a steel guardrail, and a method for selecting beam material for a steel guardrail, which can achieve both thinning of the beam and ensuring its strength, suppress distortion of the cross section and twisting of the entire member, and further improve the corrosion resistance of the cut end surface of the beam.

[0017] A beam for a steel safety fence according to a first aspect of the present disclosure is formed from a plated steel material comprising a steel base material having a plate thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa, and a plating layer made of a Zn-Al-Mg-based plating that covers the surface of the base material, and has a cut end face formed on at least one end face of the plated steel material, and the plated steel material has a plate thickness of 2.0 mm or more and less than 4.0 mm.

[0018] A beam for a steel safety fence according to a second aspect of the present disclosure is formed from a plated steel material comprising: a steel base material having a plate thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa; and a plating layer made of a Zn-Al-Mg-based plating that coats the surface of the base material; the plated steel material has a cut end surface formed on at least one end face thereof; and a burr formed at the boundary between the cut end surface and the plate surface of the plated steel material; and the plated steel material has a plate thickness of 2.0 mm or more and less than 4.0 mm.

[0019] A steel protective fence according to a third aspect of the present disclosure comprises a beam formed of plated steel comprising a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa, and a plating layer made of Zn-Al-Mg-based plating covering the surface of the base material, the beam having a cut end face formed on at least one end face of the plated steel, the plated steel having a thickness of 2.0 mm or more and less than 4.0 mm, posts supporting the beam, and connectors connecting the posts to the beam.

[0020] A steel protective fence according to a fourth aspect of the present disclosure comprises a beam formed of plated steel comprising a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa, and a plating layer made of Zn-Al-Mg plating that covers the surface of the base material, the beam having a cut end surface formed on at least one end face of the plated steel and a burr formed at the boundary between the cut end surface and the plate surface of the plated steel, the plated steel having a thickness of 2.0 mm or more and less than 4.0 mm, supports supporting the beam, and connectors connecting the supports to the beam.

[0021] A beam material selection method according to a fifth aspect of the present disclosure is a method for selecting a beam material, the method being formed of a plated steel material including a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa, and a plating layer made of Zn-Al-Mg based plating covering the surface of the base material, the plated steel material having at least one cut end surface and a burr formed at the boundary between the cut end surface and the plate surface of the plated steel material, the plate thickness being set to 2.0 mm or more and less than 4.0 mm, wherein the yield stress YS' of a reference steel material satisfying a positive bending yield strength and a negative bending yield strength of a preset beam material, the yield stress YS of the plated steel material, the plate thickness t' of the reference steel material, and the plate thickness t of the plated steel material satisfy the following 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, The method includes a process of determining a combination of the yield stress YS of the plated steel material and the plate thickness t of the plated steel material so as to satisfy the formula: YS / YS'≧1 / (t / t')+5.33×(0.575−t / t') ... formula (2), and selecting the plated steel material having the determined combination as a beam material for a steel protective fence.

[0022] A method for selecting beam material for a steel protective fence according to a sixth aspect of the present disclosure selects, as beam material for a steel protective fence, plated steel material that is formed from a plated steel material comprising a steel base material having a plate thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa, and a plating layer that covers the surface of the base material and is made of a Zn-Al-Mg-based plating, the plated steel material having at least one cut end surface and a burr formed at the boundary between the cut end surface and the plate surface of the plated steel material, and that has a plate thickness set to 2.0 mm or more and less than 4.0 mm, and in which the bending yield strength Pb at which the beam for the steel protective fence yields and the bending yield strength Pc at which the post yields satisfy the relationship of the following equations (3) to (5). Pb < 2 x Pc ...Equation (3) Pb = 4 (MBP + MBN) / L ...Equation (4) Pc = MC / H ...Equation (5) Pb: Strength at which the beam yields in bending (kN) Pc: Strength at which the column yields in bending (kN) MBP: Positive bending strength of the beam (kNm) MBN: Negative bending strength of the beam (kNm) L: Support span of the beam (m) MC: Bending strength of the column (kNm) H: Support length of the column (m)

[0023] According to the present disclosure, it is possible to provide a steel guardrail, a beam for a steel guardrail, and a method for selecting beam materials for a steel guardrail, which can achieve both thinning of the beam and ensuring its strength, suppress distortion of the cross section and twisting of the entire member, and further improve the corrosion resistance of the cut end surface of the beam.

[0024] FIG. 1A is a perspective view illustrating a steel protective fence according to an embodiment of the present disclosure. FIG. 1B is a plan view illustrating a steel protective fence according to the embodiment. FIG. 1C is a cross-sectional view taken along line 1C-1C in FIG. 1B. FIG. 2A is a perspective view illustrating a steel protective fence according to the embodiment. FIG. 2B is a plan view illustrating a steel protective fence according to the embodiment. FIG. 2B is a cross-sectional view illustrating a beam of a steel protective fence according to the embodiment. FIG. 2B is a cross-sectional view illustrating a beam-to-beam lap joint and a beam-to-post connection of a steel protective fence according to the embodiment. FIG. 7A is a perspective view illustrating a state in which a load is applied to a beam of a steel protective fence according to the embodiment, causing the beam to deform. FIG. 7B is a plan view illustrating a state in which a load is applied to a beam of a steel protective fence according to the embodiment, causing the beam to deform. FIG. 7B is a plan view illustrating a state in which a load is applied to a beam of a steel protective fence according to the embodiment, causing the beam to deform. FIG. 2A is a perspective view illustrating a steel protective fence according to the embodiment, causing the beam to deform, causing positive bending, negative bending, and tensile cross-sectional forces acting on the beam when a load is applied to the beam of a steel protective fence according to the embodiment, causing the beam to deform. FIG. 9A is a schematic diagram of an analytical model for evaluating the positive bending strength of a beam in response to a positive bending load component applied to the beam. FIG. 9B is a schematic diagram of an analytical model for evaluating the negative bending strength of a beam in response to a negative bending load component applied to the beam. FIG. 9C is a schematic diagram of an analytical model for evaluating the tensile strength of a beam in response to a tensile load component applied to the beam. FIG. 10A is a graph showing the relationship between the positive bending strength and yield stress of a beam. FIG. 10B is a graph showing the relationship between the positive bending strength ratio and the yield stress ratio when a reference steel material is used as a comparison standard. FIG. 11A is a graph showing the relationship between the negative bending strength and yield stress of a beam. FIG. 11B is a graph showing the relationship between the negative bending strength ratio and the yield stress ratio when a reference steel material is used as a comparison standard. FIG. 12A is a graph showing the relationship between the tensile strength and yield stress of a beam. FIG. 12B is a graph showing the relationship between the tensile strength ratio and the yield stress ratio when a reference steel material is used as a comparison standard. Fig. 13A 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. Fig. 13B is a graph showing the relationship between the bending rigidity ratio and the yield stress ratio when a reference steel material is used as a comparison standard. Fig. 14A shows the relationship between the weight and plate thickness of a beam formed to a specified dimension.14B is a graph showing the relationship between weight ratio and plate thickness when a reference steel material is used as a comparison standard. FIG. 14B is a graph explaining the relationship between the plate thickness ratio and yield stress ratio between a reference steel material and a thinned steel material when the positive bending strength ratio to the reference steel material is 1. FIG. 14C is a graph explaining the relationship between the plate thickness ratio and yield stress ratio between a reference steel material and a thinned steel material when the negative bending strength ratio to the reference steel material is 1. FIG. 14D is a graph explaining the relationship between the plate thickness ratio and 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. FIG. 14E is a schematic diagram explaining the bending yield strength Pb of a beam. FIG. 14F is a schematic diagram explaining the bending yield strength Pc of a column.

[0025] 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.

[0026] In addition, in this disclosure, the "%" representation of the content of each element in the chemical composition means "mass %." Furthermore, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. Furthermore, when "greater than" or "less than" is added to the numerical values ​​written before and after "to", the numerical range does not include these numerical values ​​as the lower or upper limit. Furthermore, 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.).

[0027] <Configuration of Steel Guard Fence> A steel guard fence 10 according to this embodiment will be described with reference to Figures 1 to 19. As shown in Figures 1A, 1B, and 1C, the steel guard fence 10 comprises posts 12, connectors 14, and beams 16. As shown in Figure 1, in this specification, the up-down direction refers to the direction in which the posts 12 extend, and is referred to as the upward direction UD and the downward direction LD. Furthermore, in the direction perpendicular to the beam, the roadway side is referred to as the inward direction ID, and the opposite direction (i.e., the outside of 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.

[0028] 1A to 1C and 2A to 2B, the support 12 is a tubular steel member having a cylindrical shape, etc. As shown in Figures 2A and 2B, in addition to end supports 12A arranged near both ends of the beam with a support distance L, intermediate supports 12B may be provided in the middle of the beam with a support distance L1.

[0029] (Connector) The connector 14 is a connecting hardware that connects the support 12 to a connecting portion 20 provided on the fourth wall 24 located at the center of the beam 16 in the vertical direction (the horizontal direction in FIG. 3 ). The connector 14 and the support 12 are connected by a fastener 34 such as a bolt, and the connector 14 and the connecting portion 20 of the beam 16 are connected by a fastener 31 such as a bolt. Figures 1A and 2A illustrate 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. Figures 1B and 2B also illustrate 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 12 and the connector 14.

[0030] (Beam) As shown in FIG. 1B , the beam 16 is an elongated member having a length L0 along the left-right direction. The beam 16 is formed by bending a plated steel sheet constituting the plated steel material of the present disclosure. 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. Note that, 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 of the beam 16. 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 form substantially parallel surfaces. Also, in Figure 3, the symbols for the beam width B, the beam central height D1 (i.e., the distance between the fourth wall 24 and the second wall 22), the beam end height D3 (i.e., the distance between the end of the third wall 23 and the second wall 22), the projected width W1 of the first wall 21, the width W2 of the second wall 22, the projected width W3 of the third wall 23, and the width W4 of the fourth wall 24 are illustrated as dimensions at the center of the plate thickness.

[0031] (First Wall, Second Wall, Third Wall, Fourth Wall, and Connecting Portion) As shown in the cross-sectional views of FIGS. 3 and 4 , the connecting portion 20 provided on the fourth wall 24 extending in the up-down direction (the left-right direction in FIGS. 3 and 4 ) is connected to the support 12 via a connector 14. Each of the pair of first walls 21 extends from the upper and lower ends (the left and right ends in FIGS. 3 and 4 ) of the fourth wall 24 (i.e., the connecting portion 20) toward the opposite side from the support 12 (the upper side in FIGS. 3 and 4 ). 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 (the left-right direction in FIGS. 3 and 4 ) so as to form a plane parallel to the fourth wall 24 (i.e., the connecting portion 20) in the cross-section. The pair of third walls 23 extend from the tips of the pair of second walls 22 toward the support 12 side (the lower side in FIGS. 3 and 4 ).

[0032] In this embodiment, the beam 16 for the steel safety fence is a plated steel sheet manufactured as a pre-plated steel sheet. In the case of a pre-plated steel sheet, the surface layer of the steel sheet is plated, and then the steel sheet is cut into strips in the longitudinal direction. In this case, the cutting produces a cut end surface that is not completely covered with plating, i.e., a surface where the steel base material is exposed over at least a portion of the thickness direction.

[0033] (Burs) The beam 16 has burrs (in other words, burrs) formed at the boundary between the cut end surface and the surface of the plated steel sheet as the plated steel material. The shearing process used to manufacture the beam 16 generates burrs on the sheared surface. The shearing process includes, for example, slitting the widthwise end, shearing the longitudinal end, and punching the periphery of the hole. The holes are, for example, bolt holes into which bolts serving as the fasteners 31 and 32 in FIG. 2A are inserted.

[0034] The beam in Fig. 5 illustrates a cut end surface ST1 formed by shearing, a cut end surface ST2 formed by slitting, and a cut end surface ST3 formed by punching the periphery of the bolt hole. As shown in Fig. 6, the cut end surfaces ST1, ST2, and ST3, which are sheared surfaces, are each formed with a burr BT1, a fracture surface BT2, a shear surface BT3, and a sag BT4. Also shown in Fig. 6 are the height BH1 of the burr BT1, the height BH2 of the fracture surface BT2, the height BH3 of the shear surface BT3, and the height BH4 of the sag BT4. The direction from top to bottom in Fig. 6 is the shear direction.

[0035] The height of the burrs measured along the shear direction varies depending on the clearance and wear level of the die used in shearing, the thickness of the steel plate, and the elongation performance of the steel (i.e., uniform elongation). The height of the burrs that occur is, for example, approximately 0.5% to 5% of the thickness of the steel plate. For example, in the case of a beam with a plate thickness t of 4.0 mm, the height of the burrs that occur is approximately 0.02 mm to 0.2 mm. Furthermore, the height of the burrs is not constant but varies along the shear plane, in other words, along the direction perpendicular to the shear direction within the shear plane. The height of the burrs is roughly proportional to the thickness of the steel plate and the elongation performance of the steel plate.

[0036] In the present disclosure, the height of the burr can be measured by a non-contact measurement method using a digital microscope, a precision measuring microscope, etc. In non-contact measurement, the burr does not come into contact with the measuring instrument, and therefore, compared to contact methods, it is easier to measure the burr efficiently and accurately.

[0037] In this embodiment, the height of burrs can be reduced by thinning the steel plate by using high-strength steel plates, reducing the uniform elongation of the steel material due to the increased strength, and by the synergistic effect of these. For example, consider a case in which the tensile strength of a steel material is increased from 400 MPa to 590 MPa, the thickness of the steel plate is reduced from 4.0 mm to 2.8 mm, and the uniform elongation of the steel material is reduced from 12% to 8%. The increase in tensile strength from 400 MPa to 590 MPa corresponds to an increase in yield stress from 295 MPa to 440 MPa. In this case, the burr height can be reduced by half by multiplying the 70% reduction in thickness by the 67% reduction in uniform elongation. Specifically, when the tensile strength of the steel material is 400 MPa class and the thickness of the steel plate is 4.0 mm, the height of the burrs is about 0.02 mm to 0.2 mm. However, when the high-strength steel plate of this embodiment is used, the height of the burrs can be halved to 0.01 to 0.1 mm.

[0038] In this way, in the beam 16 for a steel safety fence, the thinning makes it easier for the highly corrosion-resistant corrosion products of the plated steel sheet to spread around the entire cut end surface. In addition, the synergistic effect of the high strength and thinning reduces the height of burrs on the cut end surface of the beam 16 caused by shearing, making it even easier for the highly corrosion-resistant corrosion products of the plated steel sheet to spread around the cut end surface. This significantly improves the corrosion resistance of the end surface of the beam 16.

[0039] The thickness of the base material of the plated steel sheet constituting the beam is 3.2 mm or less. The upper limit of 3.2 mm for the base material thickness of the plated steel sheet is set in consideration of the corrosion resistance of the end surface, as will be described later using Example 3. Furthermore, the thickness of the plated steel sheet when the thickness of the plating layer is added to the base material is 2.0 mm or more and less than 4.0 mm. Therefore, the lower limit of the base material thickness of the plated steel sheet can be set so that the thickness of the plated steel sheet when the thickness of the plating layer is added is 2.0 mm or more. The upper and lower limit values ​​for the thickness of the plated steel sheet will be described later in Example 1. Furthermore, the yield stress of the plated steel sheet, in other words, the yield stress of the base material, is greater than 400 MPa and less than 800 MPa. Note that in the present disclosure, the lower limit value of the yield stress of the plated steel material may include 400 MPa. The upper and lower limit values ​​for the yield stress of the base material of the plated steel sheet will be described later in Example 1.

[0040] In this embodiment, the steel material is set so that the yield stress YS' of a reference steel material that satisfies a preset bending strength of the 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 satisfy the following formulas (1) and (2): 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) Note that in the present disclosure, it is not essential to satisfy formulas (1) and (2). Formulas (1) and (2) will be specifically described later in Example 1.

[0041] Furthermore, in this embodiment, the yield strength Pb at which the steel material of the beam 16 yields in bending and the yield strength (2×Pc) at which the two pillars 12 supporting the beam 16 yield in bending are set to satisfy the following formula (3): Pb < 2×Pc Formula (3) Note that in the present disclosure, the magnitude relationship between the yield strength at which the steel material of the steel guardrail 10 yields in bending and the yield strength at which the pillars 12 yield in bending can be set as desired. Formula (3) will be described in detail later in Example 2.

[0042] In this embodiment, the steel material constituting the beam is a plated steel material having a plating layer made of a Zn-Al-Mg plating. The specifications, thickness, and end surface corrosion resistance of the plating layer of the steel material constituting the beam will be specifically described later in Example 3.

[0043] (Example 1: Beam achieving both strength and weight reduction) Next, Example 1 will be described with reference to FIGS. 1 to 17. In Example 1, an analysis was performed to confirm the relationship between the beam plate thickness and the yield stress of the steel material and the strength. Specifically, the elastic buckling stress was calculated for the cross section of the beam by a buckling analysis using the finite strip method as shown in Technical Document 1 below. Then, the positive bending strength and negative bending strength of the beam were derived by applying the Direct Strength Method as shown in Technical Document 2 below. Note that in the present disclosure, the means for analyzing the bending strength of the beam is not limited to this, and any method can be used to perform the analysis.・Technical document 1: BW Schafer, S. Adany: Buckling analysis of cold-formed steel members using CUFSM: and constrained finite strip conventional methods, 18th International Specialty Conference on Cold-Formed Steel Structures, 2006 ・Technical document 2: BW Schafer: The Direct Strength Method of cold-formed steel member design, Journal of Constructional Steel Research 64, pp.766-778, 2008

[0044] Regarding the strength of a steel safety fence, the yield strength of the beam 16 is examined assuming a condition in which a load Pr perpendicular to the beam is input, as shown in Figures 7A and 7B. The load Pr corresponds to the load component perpendicular to the beam of the load acting when a vehicle collides with the steel safety fence. Due to the influence of the load Pr corresponding to the perpendicular load component, a positive bending moment M+ acts on the beam 16 in the vicinity of the position where the load acts, as shown in Figure 8. In addition, a negative bending moment M- acts on the vicinity of the support pillars 12 that support the beam 16 in the section where the load acts. In addition, a tensile yield strength T+ is generated due to deformation Def of the beam 16.

[0045] In Example 1, the following dimensions and material properties were set as the specifications for the steel safety fence using the symbols shown in Figures 1 to 3, and the performance of the beam was also studied. However, the specifications for the steel safety fence are not limited to these dimensions. Note that W1, W2, W3, W4, D1, and D3, which represent the dimensions of each face of the beam that makes up the cross section of the beam, are expressed as the dimensions at the center of the beam thickness t. L0 = 4330 mm L = 4000 mm L1 = 2000 mm H = 600 mm B = 350 mm W1 = 41 mm W2 = 63 mm W3 = 36 mm W4 = 70 mm D1 = 71 mm D3 = 52 mm t = 2.0 mm to 4.0 mm YS = 295 MPa to 800 MPa

[0046] The cross section of the beam of the above-mentioned steel guardrail corresponds to the cross section of the Type A beam defined in the following technical document 3: Japan Road Association, Standard Specifications and Commentary for Vehicle Guardrails (Revised Edition), March 31, 2004 (Heisei 16).

[0047] The bending radius R of the bending portion that forms the ridge line of each surface of the beam is set according to the manufacturing conditions of the beam that involve bending and the plate thickness, but for convenience in examining the strength and weight of the beam, which will be described later, the bending radius R is considered to be 0. By setting the bending radius R = 0, the absolute evaluation of the buckling strength and weight changes slightly, but there is almost no effect on the relative evaluation of the reference steel material and the steel material of the present disclosure.

[0048] The specifications for the existing steel beams targeted for thinning, i.e., the standard steel, were set based on the following dimensions and material properties, which are the specifications commonly used for steel safety fences installed on expressways in Japan. Yield stress of standard steel: YS' = 295 MPa Thickness of standard steel: t' = 4.0 mm Here, the yield stress YS' of the standard steel (YS' = 295 MPa) was set with reference to the steel standards SS400 and SGH400, which are used for existing steel beams. The standard yield stress of steel standard SS400 is 235 MPa. The standard yield stress of steel standard SGH400 is 295 MPa. The yield stress YS' of the standard steel was set to 295 MPa, targeting the larger of these yield stresses, so as to ensure a safe material replacement.

[0049] The beam strength against the positive bending moment M+, negative bending moment M-, and tensile strength T+ shown in Figure 8 was examined using partial elements (member length 1000 mm) of a beam subjected to the uniform positive bending moment shown in Figure 9A, the uniform negative bending moment shown in Figure 9B, and the tensile strength shown in Figure 9C. Here, the positive bending strength and negative bending strength were derived as bending strengths taking into account buckling behavior, which is a concern when thinning, using the analytical methods described in 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.

[0050] FIG. 10A shows the positive bending strength of a beam when the steel plate thickness (t = 2.0 mm to 4.0 mm) and yield stress (YS = 295 to 800 MPa) are changed relative to a standard steel plate (t' = 4.0 mm, YS' = 295 MPa). FIG. 10B also shows the relationship between the positive bending strength ratio and the yield stress ratio relative to the standard steel plate. In the range of plate thickness t = 2.3 mm to 4.0 mm, no local buckling occurs in the cross section of the beam, and the positive bending strength increases linearly in proportion to the yield stress of the steel. On the other hand, at a plate thickness t = 2.0 mm, local buckling occurs in the second wall (see second wall 22 in FIG. 3 ) that is subjected to compressive stress in the cross section of the beam, so the positive bending strength increases nonlinearly in the range where the yield stress of the steel is 600 MPa or higher.

[0051] FIG. 11A shows the negative bending strength of a beam when the steel plate thickness (t = 2.0 mm to 4.0 mm) and yield stress (YS = 295 MPa to 800 MPa) are changed relative to a standard steel plate (t' = 4.0 mm, YS' = 295 MPa). FIG. 11B also shows the relationship between the negative bending strength ratio and the yield stress ratio relative to the standard steel plate. When the plate thickness t is in the range of 3.0 mm to 4.0 mm, 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. On the other hand, when the plate thickness t is less than 3.0 mm, that is, when the plate thickness t is 2.0 mm to 2.5 mm, local buckling occurs at the outward OD-side edges of the fourth wall (see fourth wall 24 in FIG. 3 ) and third wall (see third wall 23 in FIG. 3 ), which are subjected to compressive stress in the cross section of the beam. For this reason, the negative bending strength increases nonlinearly when the yield stress of the steel material is in the range of 500 MPa or more in the range of t = 2.3 mm to 2.5 mm, and when the yield stress of the steel material is in the range of 400 MPa or more in the range of t = 2.0 mm. In other words, the rate of change in the negative bending strength is small when the yield stress of the steel material is in the range of 500 MPa or more in the range of t = 2.3 mm to 2.5 mm, and when the yield stress of the steel material is in the range of 400 MPa or more in the range of t = 2.0 mm.

[0052] 11A and 11B, it is clear that if the thickness of the steel material is less than 2.0 mm, it is difficult to ensure a negative bending strength equal to or greater than that of the reference steel material. Based on this result, in this embodiment, the lower limit of the thickness is set to 2.0 mm.

[0053] Figure 12A shows the tensile strength of a beam when the steel plate thickness (t = 2.0 to 4.0 mm) and yield stress (YS = 295 MPa to 800 MPa) are changed relative to a standard steel material (t' = 4.0 mm, YS' = 295 MPa). Figure 12B also shows the relationship between the tensile strength ratio and yield stress ratio relative to the standard steel material. Since 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.

[0054] Regarding the bending strength of the beam, as shown in Figures 8 and 9, local buckling occurs in the area of ​​the cross section of the beam that is subjected to compressive stress, so in order to thin the beam, an appropriate combination of plate thickness and yield stress is required.

[0055] As an index of the appropriate combination of steel thickness t and yield stress YS for thinning a beam, the relationship between the thickness ratio (t / t') and yield stress ratio (YS / YS') for a standard steel material, where the yield strength ratios for positive bending, negative bending, and tension are equal (i.e., yield strength ratio = 1.0), is plotted in Figures 15 (positive bending), 16 (negative bending), and 17 (tension), respectively. In the range of 0.5≦t / t'<1.0 in Figures 15 and 17 and the range of 0.575≦t / t'<1.0 in Figure 16, the relationship between the thickness ratio and yield stress ratio is expressed by the following formula (1'): YS / YS'=1 / (t / t') ...formula (1'). Furthermore, in the range of 0.5≦t / t'<0.575 in Figure 16, the relationship between the thickness ratio and yield stress ratio is expressed by the following formula (2'). YS / YS'=1 / (t / t')+5.33×(0.575-t / t')...Formula (2')

[0056] 15 to 17, the present disclosure provides a beam that can ensure a proof stress ratio equal to or greater than that of a reference steel material for all resistance mechanisms, including positive bending, negative bending, and tension, and that satisfies the following relationships between the plate thickness ratio (t / t') and the 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)

[0057] In addition, cases where the yield stress YS' of the reference steel material was other than 295 MPa and cases where the plate thickness t' of the reference steel material was other than 4.0 mm were also investigated. In both cases, the same results as those in this example were obtained.

[0058] Furthermore, by thinning the beam, the moment of inertia, which is an indicator of the bending rigidity of the beam, can be reduced, as shown in Figures 13A and 13B. Figure 13A shows the relationship between the moment of inertia and the yield stress of the beam. Furthermore, Figure 13B shows the relationship between the bending rigidity ratio and the yield stress ratio when the reference steel material is used as the comparison standard. This allows the rigidity of the beam against deformation (see the beam deformation Def in Figure 8) when a vehicle collides with a steel safety fence using a thinned beam to be kept low. This provides the effect of absorbing the impact load (in other words, reducing the effects of the impact load). As a result, the acceleration acting on the occupant when the steel safety fence pushes back the vehicle is kept low, thereby improving the function of preventing injury to the occupant.

[0059] The weight reduction effect of thinning the beam is shown in Figures 14A and 14B. Figure 14A shows the relationship between the weight and plate thickness of a beam formed to a specified dimension. Figure 14B shows the relationship between the weight ratio and plate thickness when a reference steel material is used as the comparison standard. By reducing the plate thickness t to less than 4.0 mm compared to the reference steel material (t' = 4.0 mm), the weight per beam can be kept to less than 60 kgf. This reduces the burden on each worker and reduces the number of workers required for transportation and installation, resulting in streamlining of work.

[0060] (Thickness of Steel Plate) If the lower limit of the steel plate thickness is less than 2.0 mm, it is difficult to ensure beam performance equivalent to or better than that of a standard steel plate (t' = 4.0 mm, YS' = 295 MPa), particularly in terms of negative bending strength. Furthermore, if the steel plate thickness is 4.0 mm or more, it is not possible to achieve a weight reduction effect compared to a beam made of standard steel. In this embodiment, the lower limit of the plate thickness is set to 2.0 mm or more and the upper limit is set to less than 4.0 mm, so that the beam for a steel safety fence can be thinned, i.e., lightweight, while still maintaining strength.

[0061] (Yield Stress of Steel Material) 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 greater than that of a reference 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, it is more preferable that the yield stress of the steel material be greater than 400 MPa and less than or equal to 700 MPa. It is even more preferable that the yield stress of the steel material be greater than 400 MPa and less than or equal to 600 MPa. Furthermore, it is more preferable that the yield stress of the steel material is more than 400 MPa and not more than 500 MPa.

[0062] Example 2: Steel guardrail that suppresses damage to posts Next, Example 2 will be described with reference to Figures 18 and 19. In Example 2, in order to provide a steel guardrail that suppresses damage to posts, an analysis was carried out to confirm the relationship between the bending strength Pb of the beam and the bending strength Pc of the posts. The bending strength Pb of the beam and the bending strength Pc of the posts are set from the positive bending strength and negative bending strength of the beam shown in Example 1.

[0063] 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 in Technical Literature 1. The positive bending strength and negative bending strength of the beam were derived using the Direct Strength Method in Technical Literature 2. Furthermore, based on the mechanical model diagram 18 of the plastic analysis (i.e., limit analysis) shown in FIG. 18, the balance between the internal work Wi and the external work Wo was determined, and the bending yield strength Pb of the beam was set using Equation (4). In FIG. 18, δ is the displacement due to an external force, and θ (= 2δ / L) is the rotation angle of the bending hinge. 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 in bending (kN) MBP: Positive bending strength of the beam (kNm) MBN: Negative bending strength of the beam (kNm) L: Support span of the beam (m) For the support span of the beam (i.e., the distance between the supports) L, if there is no intermediate support as in Figure 1B, the distance between the supports L of the supports 12 at both ends of the beam 16 can be adopted. Also, if there is an intermediate support 12B as in Figure 2B, the distance L1 between the end supports 12A and the intermediate support 12B can be adopted.

[0064] Furthermore, the bending strength MC of the support, which is calculated by multiplying the yield stress of the support by the plastic section modulus, and the bending moment distribution diagram 19 of the support, were used to set the bending yield strength Pc of the support by equation (5). As shown in FIG. 19, the maximum moment is Pc x H. Pc = MC / H ... equation (5) Where, Pc: bending yield strength of the support (kN) MC: bending strength of the support (kNm) H: supporting length of the support (m)

[0065] In an installation situation where a steel guardrail is installed in which one beam is supported by two posts, a steel guardrail can be provided that suppresses damage to the posts by satisfying the condition of equation (3) in which the bending strength Pc of the two posts supporting one beam is greater than the bending strength Pb of one beam: Pb < 2 × Pc ... equation (3) As in Example 2, in this embodiment, the bending strength Pb at which the beam yields and the bending strength Pc at which the posts yield satisfy the relationships of equations (3) to (5).

[0066] Example 3: Beam with Improved Edge Corrosion Resistance by Thinning) Next, Example 3 will be described with reference to Tables 1 and 2. In Example 3, to provide a beam with improved edge corrosion resistance by thinning, a plated steel material having a Zn-Al-Mg-based plating layer was used for the steel material for the beam, which was thinned to a thickness of less than 4.0 mm as in Example 1. Then, using the plated steel material, cut sheet samples of 50 × 100 mm were prepared. The prepared cut sheet samples were subjected to a cyclic corrosion test (CCT, JIS H 8502:1999 Neutral Salt Spray Cycle Test) to accelerate corrosion. The corrosion resistance was confirmed by visually inspecting the state of red rust on the cut edge of the cut sheet sample.

[0067] The sample steel was subjected to a plating treatment, thereby forming a plating layer made of a Zn-Al-Mg-based plating. The plating treatment included a hot-dip plating process using a hot-dip plating bath of the plating type shown in Table 1. Table 1 shows the chemical composition of the plating layer in terms of mass %. Table 1 explains the chemical composition of the plating type in the hot-dip plating bath used for the samples that underwent the neutral salt spray cycle test, in terms of mass %. All of the plating types a to p in Table 1 have a plating layer made of a Zn-Al-Mg-based plating. Furthermore, plating types a to n in Table 1 have a plating layer made of a Zn-Al-Mg-based plating and have a chemical composition, in mass %, of Al: more than 15.0 to 30.0%, Mg: more than 5.0 to 15.0%, Sn: 0 to 0.70%, Ca: 0 to 0.60%, Si: 0 to 0.75%, Ti: 0 to 0.25%, Ni: 0 to 1.00%, Co: 0 to 0.25%, Fe: 0 to 5.0%, B: 0 to 0.50%, and the balance: Zn and impurities. Note that plating type q in Table 1 has a plating layer made of a Zn-based plating containing a trace amount of Al of 0.2%.

[0068]

[0069] Tables 2A, 2B, 2C, and 2D show the evaluation results of corrosion resistance of the end faces of steel materials according to the type and average thickness of the coating layer for samples with thicknesses of 4.0 mm, 3.2 mm, 2.3 mm, and 2.0 mm and coated with the coating types a to q shown in Table 1. For the Zn-based coating type q, the end faces to be evaluated were plated by hot-dip plating. On the other hand, for the Zn-Al-Mg-based coating types a to p, pre-plating was applied, and the end faces to be evaluated were cut end faces. Blank values ​​in Table 1 indicate the presence of zero or trace amounts of the coating.

[0070] Tables 2A to 2D explain the relationship between the specifications (i.e., plate thickness, plating layer, and edge treatment) of the 68 samples used in the neutral salt spray cycle test and the corrosion resistance of the edge. Table 2A explains Samples No. 1 to 17, Table 2B explains Samples No. 18 to 34, Table 2C explains Samples No. 35 to 51, and Table 2D explains Samples No. 52 to 68.

[0071]

[0072]

[0073]

[0074]

[0075] The occurrence of red rust on the end face of the evaluation object was confirmed visually. The evaluation results of corrosion resistance shown in Tables 2A to 2D are represented as follows: "AA" for a red rust occurrence rate of 10% or less at 120 and 180 cycles, "A" for a rate of more than 10% but not exceeding 30%, "B" for a rate of more than 30% but not exceeding 50%, and "C" for a rate of more than 50%. The red rust occurrence rate is the ratio of the area where red rust has occurred to the total area of ​​the end face of the evaluation object.

[0076] Referring to Tables 2A to 2D, for Zn-based plating type q, the end surfaces of the evaluation targets were plated, so the red rust occurrence rate was kept to 30% or less regardless of the plate thickness at 120 cycles. However, at 180 cycles, the red rust occurrence rate exceeded 50% regardless of the plate thickness.

[0077] On the other hand, for Zn-Al-Mg plating types a-p, when the plate thickness is 3.2 mm or less, the effect of corrosion resistance on the edge due to sacrificial corrosion protection is exerted, and as a result, the red rust occurrence rate can be suppressed to 50% or less even after 180 cycles, as shown in Tables 2B to 2D. Of the Zn-Al-Mg plating types a-p, particularly for types a-n, when the plate thickness is 3.2 mm or less, the red rust occurrence rate can be suppressed to 10% or less after 120 cycles and to 30% or less after 180 cycles, as shown in Tables 2B to 2D. In other words, it is clear that excellent corrosion resistance on the edge is exerted.

[0078] (Effects) The plated steel material forming the beam 16 for the steel safety fence according to this embodiment has a plate thickness of 3.2 mm or less and includes a steel base material having a yield stress of more than 400 MPa and less than 800 MPa, and a plating layer made of a Zn-Al-Mg-based plating that coats the surface of the base material. The beam 16 also has at least one cut end surface and a burr formed at the boundary between the cut end surface and the plated steel surface. The plated steel material has a plate thickness of 2.0 mm or more and less than 4.0 mm.

[0079] Because the plated steel base material has a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and 800 MPa or less, the plated steel has a smaller uniform elongation than, for example, a base material having the same thickness and a yield stress of 400 MPa or less, as in the above example. As a result, the height of burrs formed on the corners of the cut end surface during cutting of the plated steel can be reduced.

[0080] Therefore, compared with a plated steel material having a thickness of 4.0 mm or more and having similar specifications other than the thickness, corrosion products generated by a reaction between elements contained in the Zn-Al-Mg plating on the plated steel surface and moisture are more likely to migrate from the plate surface, over the burrs, to the cut edge. The migrated corrosion products form a coating that covers the cut edge.

[0081] This makes it possible to thin the beams 16 for the steel protective fence, i.e., to achieve both weight reduction and strength, and also to improve the corrosion resistance of the cut end surfaces of the beams 16. Similarly, it is possible to realize a steel protective fence 10 having beams 16 that are thin and strong, and that have improved corrosion resistance of the cut end surfaces.

[0082] Furthermore, for example, if the beam is subjected to a hot-dip plating process using a high-temperature plating bath of approximately 420°C to 480°C after processing, residual stress is released, resulting in distortion of the beam. The higher the strength of the steel plate, the greater the distortion, resulting in greater cross-sectional distortion and overall torsion of the member. Furthermore, thinning the steel plate of the beam reduces its rigidity, resulting in more pronounced cross-sectional distortion and overall torsion problems. That is, when manufacturing a beam for a steel safety fence by hot-dip plating after introducing residual stresses through beam processing, the thinning of the high-strength steel plate amplifies cross-sectional distortion and overall torsion due to the release of residual stresses, making beam manufacturing difficult. However, in this embodiment, by using a pre-plated steel plate for the beam 16, hot-dip plating, which involves the release of residual stresses, is not required after processing the beam 16. This makes it possible to suppress distortion of the cross section of the beam 16 and twisting of the entire member, making it easier to manufacture a beam 16 having the desired shape and a steel safety fence 10 having the beam 16.

[0083] In this embodiment, the beam 16 has a burr formed at the boundary between the cut end surface and the plated steel sheet surface. However, in the present disclosure, it is not essential that the beam have a burr. Even if the beam does not have a burr, corrosion products may migrate from the plate surface to the cut end surface, forming a coating covering the cut end surface. This allows for the thinning of the beam for a steel safety fence, i.e., achieving both weight reduction and strength, suppressing cross-sectional distortion and twisting of the entire member, and improving the corrosion resistance of the cut end surface of the beam. Similarly, a steel safety fence can be realized that has a beam that is thin and strong, suppressing cross-sectional distortion and twisting of the entire member, and improving the corrosion resistance of the cut end surface.

[0084] Furthermore, in the method for selecting beam materials for a steel safety fence according to 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 having a yield stress YS' and a plate thickness t'. The steel safety fence according to this embodiment satisfies formulas (1) and (2). Therefore, while maintaining strength equivalent to or greater than that of the reference steel material, the weight per beam can be reduced by making the beam thinner and lighter than the reference steel material. This reduces the burden on each worker and also reduces the number of workers required for transportation and installation, thereby streamlining the work. Furthermore, because the thinning reduces the bending rigidity of the beam, the steel safety fence can reduce the acceleration acting on the occupant when pushing back a vehicle that has collided with the steel safety fence, thereby improving the ability to prevent injury to the occupant.

[0085] In this embodiment, the chemical composition of the plating layer is, in mass %, Al: more than 15.0 to 30.0%, Mg: more than 5.0 to 15.0%, Sn: 0 to 0.70%, Ca: 0 to 0.60%, Si: 0 to 0.75%, Ti: 0 to 0.25%, Ni: 0 to 1.00%, Co: 0 to 0.25%, Fe: 0 to 5.0%, B: 0 to 0.50%, and the balance: Zn and impurities. In this embodiment, the plating layer having the above chemical composition can improve the corrosion resistance of the beam surface, including the cut end faces.

[0086] Furthermore, in the method for selecting beam materials for a steel guardrail according to this embodiment, the bearing strength Pb at which the beam 16 yields in bending and the bearing strength 2×Pc at which the two posts 12 supporting the beam 16 yield in bending 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 difficult to replace because they are installed in the ground, for example, by burying them, need to be replaced, and as a result, the burden of replacing the steel guardrail can be reduced.

[0087] <Other Embodiments> The present disclosure has been described using the above embodiments, but this description does not limit the present disclosure. It should be understood that various alternative embodiments, examples, and operational 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.

[0088] <<Additional Notes>> The following aspects are conceptualized from this specification.

[0089] Aspect 1 is a beam for a steel guardrail, which is formed from a plated steel material comprising: a steel base material having a plate thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa; and a plating layer made of a Zn-Al-Mg-based plating that coats the surface of the base material; the plated steel material has a cut end face formed on at least one end face; and the plated steel material has a plate thickness of 2.0 mm or more and less than 4.0 mm.

[0090] Aspect 2 is a beam for a steel guardrail formed of a plated steel material comprising: a steel base material having a plate thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa; and a plating layer made of a Zn-Al-Mg-based plating covering the surface of the base material; wherein the beam has a cut end surface formed on at least one end surface of the plated steel material and a burr formed at the boundary between the cut end surface and the plate surface of the plated steel material; and the plate thickness of the plated steel material is 2.0 mm or more and less than 4.0 mm.

[0091] Aspect 3 is a beam for a steel guardrail according to Aspect 1 or 2, wherein the plated steel material has a yield stress YS' of 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 plated steel material, a plate thickness t' of the standard steel material, and a plate thickness t of the plated steel material, which satisfy the following: YS / YS'≧1 / (t / t') ...Equation (1) in the range of 0.575≦t / t'<1.0, and YS / YS'≧1 / (t / t')+5.33×(0.575−t / t') ...Equation (2) in the range of 0.5≦t / t'<0.575.

[0092] Aspect 4 is the beam for a steel safety fence according to any one of Aspects 1 to 3, wherein the plating layer of the plated steel material has a chemical composition consisting of, in mass %, Al: more than 15.0 to 30.0%, Mg: more than 5.0 to 15.0%, Sn: 0 to 0.70%, Ca: 0 to 0.60%, Si: 0 to 0.75%, Ti: 0 to 0.25%, Ni: 0 to 1.00%, Co: 0 to 0.25%, Fe: 0 to 5.0%, B: 0 to 0.50%, and the balance: Zn and impurities.

[0093] Aspect 5 is a steel protective fence comprising: a beam formed of a plated steel material comprising: a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa; and a plating layer made of Zn-Al-Mg-based plating covering the surface of the base material, the beam having a cut end face formed on at least one end face of the plated steel material, the plated steel material having a thickness of 2.0 mm or more and less than 4.0 mm; supports supporting the beam; and connectors connecting the supports and the beam.

[0094] Aspect 6 is a steel protective fence comprising: a beam formed of plated steel material comprising a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa, and a plating layer made of Zn-Al-Mg-based plating covering the surface of the base material, wherein the beam has a cut end surface formed on at least one end surface of the plated steel material and a burr formed at the boundary between the cut end surface and the plate surface of the plated steel material, and the plated steel material has a thickness of 2.0 mm or more and less than 4.0 mm; supports supporting the beam; and connectors connecting the supports and the beam.

[0095] Aspect 7 is the steel safety fence according to Aspect 5 or 6, wherein the bending yield strength Pb of the beam and the bending yield strength Pc of the post 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) Pb: bending yield strength of the beam (kN) Pc: bending yield strength of the post (kN) MBP: positive bending strength of the beam (kNm) MBN: negative bending strength of the beam (kNm) L: supporting span of the beam (m) MC: bending strength of the post (kNm) H: supporting length of the post (m)

[0096] Aspect 8 is formed of a plated steel material including a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa, and a plating layer made of Zn-Al-Mg based plating covering the surface of the base material, the plated steel material having at least one cut edge and a burr formed at the boundary between the cut edge and the surface of the plated steel material, and the plated steel material has a thickness set to 2.0 mm or more and less than 4.0 mm, and is used to obtain a beam material having a predetermined positive bending yield strength and negative bending yield strength, wherein the yield stress YS' of a reference steel material, the yield stress YS of the plated steel material, the plate thickness t' of the reference steel material, and the plate thickness t of the plated steel material satisfy the following in the range of 0.575≦t / t'<1.0: YS / YS'≧1 / (t / t') ...Equation (1); and in the range of 0.5≦t / t'<0.575: A method for selecting beam materials for a steel protective fence, comprising a process for determining a combination of the yield stress YS of the plated steel material and the plate thickness t of the plated steel material so as to satisfy the formula: YS / YS'≧1 / (t / t')+5.33×(0.575−t / t') ... formula (2), and selecting the plated steel material having the determined combination as a beam material for the steel protective fence.

[0097] A ninth aspect is a method for selecting a beam material for a steel guardrail fence, the method comprising: a plated steel material comprising a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa; and a plating layer made of a Zn-Al-Mg-based plating covering the surface of the base material; the plated steel material having at least one cut end surface and a burr formed at the boundary between the cut end surface and the plate surface of the plated steel material; and a thickness set to 2.0 mm or more and less than 4.0 mm, wherein a bending yield strength Pb at which a beam for the steel guardrail yields and a bending yield strength Pc at which a post yields satisfy the relationships of the following equations (3) to (5) are selected as the beam material for the steel guardrail fence. Pb < 2 x Pc ...Equation (3) Pb = 4 (MBP + MBN) / L ...Equation (4) Pc = MC / H ...Equation (5) Pb: Strength at which the beam yields in bending (kN) Pc: Strength at which the column yields in bending (kN) MBP: Positive bending strength of the beam (kNm) MBN: Negative bending strength of the beam (kNm) L: Support span of the beam (m) MC: Bending strength of the column (kNm) H: Support length of the column (m)

[0098] <Other Aspects> Furthermore, the following other aspects are conceptualized from this specification.

[0099] Another aspect 1 is a beam for a steel safety fence, which is formed from a steel material, and the yield stress of the steel material is greater than 400 MPa and less than 800 MPa, and the sheet thickness of the steel material is 2.0 mm or more and less than 4.0 mm, and the steel material is a plated steel material having a base material thickness of 3.2 mm or less and provided with a plating layer made of a Zn-Al-Mg-based plating, and at least one end face of the steel material coated with the plating layer is a cut end face.

[0100] In another aspect 2, the steel material is a beam for a steel guardrail according to aspect 1, characterized in that 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, and the plate thickness t' of the standard steel material and the plate thickness t of the steel material satisfy the following: YS / YS'≧1 / (t / t') ...formula (1) in the range of 0.575≦t / t'<1.0, and YS / YS'≧1 / (t / t')+5.33×(0.575−t / t') ...formula (2) in the range of 0.5≦t / t'<0.575.

[0101] Another aspect 3 is the beam for a steel safety fence according to aspect 1 or 2, characterized in that the plating layer of the steel material has a chemical composition consisting of, in mass %, Al: more than 15.0 to 30.0%, Mg: more than 5.0 to 15.0%, Sn: 0 to 0.70%, Ca: 0 to 0.60%, Si: 0 to 0.75%, Ti: 0 to 0.25%, Ni: 0 to 1.00%, Co: 0 to 0.25%, Fe: 0 to 5.0%, B: 0 to 0.50%, and the balance: Zn and impurities.

[0102] Alternative aspect 4 is a steel protective fence comprising: a beam formed of a steel material, the steel material having a yield stress of more than 400 MPa and not more than 800 MPa and a plate thickness of the steel material of 2.0 mm or more and less than 4.0 mm; a support post supporting the beam; and a connector connecting the support post and the beam, wherein the steel material is a plated steel material having a base material plate thickness of 3.2 mm or less and provided with a plating layer made of Zn-Al-Mg plating, and at least one end face of the steel material coated with the plating layer is a cut end face.

[0103] Another aspect 5 is the steel safety fence according to aspect 4, characterized in that the bending yield strength Pb of the beam and the bending yield strength Pc of the post 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: bending yield strength of the beam (kN) Pc: bending yield strength of the post (kN) MBP: positive bending strength of the beam (kNm) MBN: negative bending strength of the beam (kNm) L: support span of the beam (m) MC: bending strength of the post (kNm) H: support length of the post (m)

[0104] Another aspect 6 is a method for manufacturing a beam beam having a beam steel material with a yield stress of more than 400 MPa and not more than 800 MPa, a beam steel material with a thickness of 2.0 mm or more and less than 4.0 mm, a base metal thickness of the beam steel being 3.2 mm or less and a plated steel material having a plating layer made of a Zn-Al-Mg-based plating, and at least one end face of the beam steel material coated with the plating layer is a cut end face, and a standard steel material having a yield stress YS' and a standard steel material having a thickness t' and a thickness t of the standard steel material satisfying a preset beam beam positive bending yield strength and a preset negative bending yield strength are in the range of 0.575≦t / t'<1.0, YS / YS'≧1 / (t / t') ...Equation (1), and 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: YS / YS'≧1 / (t / t')+5.33×(0.575−t / t') ...Equation (2).

[0105] Another aspect 7 is a method for selecting beam material for a steel guardrail, 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 2.0 mm or more and less than 4.0 mm, the steel material is a plated steel material having a base plate thickness of 3.2 mm or less and provided with a plating layer made of Zn-Al-Mg based plating, at least one end face of the steel material coated with the plating layer is a cut end face, and the bending yield strength Pb of the beam and the bending yield strength Pc of the post satisfy the relationships of the following equations (3) to (5). Pb < 2 x Pc ...Equation (3) Pb = 4 (MBP + MBN) / L ...Equation (4) Pc = MC / H ...Equation (5) Where, Pb: Strength at which beam yields in bending (kN) Pc: Strength at which column yields in bending (kN) MBP: Positive bending strength of beam (kNm) MBN: Negative bending strength of beam (kNm) L: Support span of beam (m) MC: Bending strength of column (kNm) H: Support length of column (m)

[0106] According to another aspect, it is possible to achieve both a thin beam and a sufficient strength, and further to improve the corrosion resistance of the surface of the beam.

[0107] The disclosure of Japanese Patent Application No. 2024-112060, filed on July 11, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

[0108] 10 Steel protective fence 12 Support 12A Both end supports 12B Intermediate support 14 Connector 16 Beam 20 Connection section 21 First wall 22 Second wall 23 Third wall 24 Fourth wall 31 Fastener connecting connector and beam 32 Fastener connecting beams to each other 33 Lap joint between beams 34 Fastening section connecting support and connector BH1 Burr height BH2 Height of fracture surface BH3 Height of shear surface BH4 Height of sagging BT1 Burr BT2 Fracture surface BT3 Shear surface BT4 Sagging L0 Member length of beam L Distance between supports at both ends of beam L1 Distance between supports of intermediate supports H Support length of support UD Upward direction LD Downward direction ID Inward direction OD Outward direction FD Forward direction BD Backward direction Pr Load corresponding to the orthogonal load component of the collision load Def Deformation of the beam due to the collision load M+ Positive bending moment acting on the beam M- Negative bending moment acting on the beam ST1 Cut end surface due to shearing ST2 Cut end surface due to slitting ST3 Cut end surface due to punching around the bolt hole T+ Tensile strength of the beam t Plate thickness

Claims

1. A beam for a steel guardrail, formed from a plated steel material comprising a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and less than 800 MPa, and a plating layer made of Zn-Al-Mg plating covering the surface of the base material, the beam having a cut end surface formed on at least one end face of the plated steel material, and the plated steel material having a thickness of 2.0 mm or more and less than 4.0 mm.

2. A beam for a steel guardrail, formed from a plated steel material comprising a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and less than 800 MPa, and a plating layer made of Zn-Al-Mg plating covering the surface of the base material, the beam having a cut edge formed on at least one end face of the plated steel material and a burr formed at the boundary between the cut edge and the plate surface of the plated steel material, the plate thickness of the plated steel material being 2.0 mm or more and less than 4.0 mm.

3. A beam for a steel guardrail according to claim 1 or 2, wherein the plated steel material satisfies the following: YS / YS'≧1 / (t / t') ...formula (1) in the range of 0.575≦t / t'<1.0, where the yield stress YS' of a standard steel material and the yield stress YS of the plated steel material satisfy the preset positive bending strength and negative bending strength of the beam, and the plate thickness t' of the standard steel material and the plate thickness t of the plated steel material. YS / YS'≧1 / (t / t') ...formula (2) in the range of 0.5≦t / t'<0.

575.

4. A beam for a steel safety fence according to any one of claims 1 to 3, wherein the chemical composition of the plating layer of the plated steel material consists, in mass %, of Al: more than 15.0 to 30.0%, Mg: more than 5.0 to 15.0%, Sn: 0 to 0.70%, Ca: 0 to 0.60%, Si: 0 to 0.75%, Ti: 0 to 0.25%, Ni: 0 to 1.00%, Co: 0 to 0.25%, Fe: 0 to 5.0%, B: 0 to 0.50%, and the balance: Zn and impurities.

5. A steel protective fence comprising: a beam formed from plated steel material comprising a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and less than 800 MPa, and a plating layer made of Zn-Al-Mg plating covering the surface of the base material, the beam having a cut end face formed on at least one end face of the plated steel material, the plated steel material having a thickness of 2.0 mm or more and less than 4.0 mm; posts supporting the beam; and connectors connecting the posts and the beam.

6. A steel protective fence comprising: a beam formed from plated steel comprising a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and less than 800 MPa, and a plating layer made of Zn-Al-Mg plating covering the surface of the base material, wherein the beam has a cut end surface formed on at least one end face of the plated steel and a burr formed at the boundary between the cut end surface and the plate surface of the plated steel, and the plated steel has a thickness of 2.0 mm or more and less than 4.0 mm; supports supporting the beam; and connectors connecting the supports to the beam.

7. A steel safety fence according to claim 5 or 6, wherein the bending yield strength Pb of the beam and the bending yield strength Pc of the post satisfy the relationships of the following formulas (3) to (5): Pb < 2 x Pc ... formula (3) Pb = 4 (MBP + MBN) / L ... formula (4) Pc = MC / H ... formula (5) Pb: bending yield strength of the beam (kN) Pc: bending yield strength of the post (kN) MBP: positive bending strength of the beam (kNm) MBN: negative bending strength of the beam (kNm) L: supporting span of the beam (m) MC: bending strength of the post (kNm) H: supporting length of the post (m) 8. A plated steel material is formed from a plated steel material comprising a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa, and a plating layer made of Zn-Al-Mg plating covering the surface of the base material, the plated steel material having at least one cut edge and a burr formed at the boundary between the cut edge and the plated steel surface, the plated steel material having a thickness set to 2.0 mm or more and less than 4.0 mm, wherein the yield stress YS' of a reference steel material satisfying the positive bending yield strength and negative bending yield strength of a preset beam material, the yield stress YS of the plated steel material, the plate thickness t' of the reference steel material and the plate thickness t of the plated steel material satisfy the following in the range of 0.575≦t / t'<1.0: YS / YS'≧1 / (t / t') ...Equation (1); and in the range of 0.5≦t / t'<0.575: A method for selecting beam materials for a steel protective fence, comprising a process for determining a combination of the yield stress YS of the plated steel material and the plate thickness t of the plated steel material so as to satisfy the formula: YS / YS'≧1 / (t / t')+5.33×(0.575−t / t') ... formula (2), and selecting the plated steel material having the determined combination as a beam material for the steel protective fence.

9. A method for selecting beam material for a steel guardrail, comprising: a plated steel material comprising a steel base material having a thickness of 3.2 mm or less and a yield stress of more than 400 MPa and not more than 800 MPa; and a plating layer made of a Zn-Al-Mg plating coating covering the surface of the base material; the plated steel material having at least one cut edge and a burr formed at the boundary between the cut edge and the plate surface of the plated steel material; and a thickness set to 2.0 mm or more and less than 4.0 mm, wherein the bending yield strength Pb of the beam for the steel guardrail and the bending yield strength Pc of the post satisfy the relationships of the following equations (3) to (5), and selecting the plated steel material as beam material for the steel guardrail. Pb < 2 x Pc ...Equation (3) Pb = 4 (MBP + MBN) / L ...Equation (4) Pc = MC / H ...Equation (5) Pb: Strength at which the beam yields in bending (kN) Pc: Strength at which the column yields in bending (kN) MBP: Positive bending strength of the beam (kNm) MBN: Negative bending strength of the beam (kNm) L: Support span of the beam (m) MC: Bending strength of the column (kNm) H: Support length of the column (m)

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