Steel foundation member

Abstract

One aspect of the present invention relates to a steel base member comprising a steel plate having a yield strength at 500 DEG C of 250 MPa or more and a yield strength at 600 DEG C of 125 MPa or more.

Description

Technical Field

[0001] The invention relates to a steel foundation member used in a building. Background Art

[0002] Steel foundation components are widely used in buildings, mainly for ceiling and wall foundation components. Since steel foundation components are widely used, JIS A6517:2010 specifies the shape, material, and strength of components. This JIS standard specifies that materials that comply with JIS G 3302:2019 "hot-dip galvanized steel sheets and strips" or JIS G 3321:2019 "hot-dip 55% aluminum-zinc alloy coated steel sheets and strips" be used as materials for steel foundation components.

[0003] In addition, in order to prevent the spread of damage in the event of a fire, the Building Standards Act stipulates the fire resistance properties required for each part of a building, such as damage resistance, thermal insulation, and flame retardancy.

[0004] In the case of partition walls, exterior walls, and suspended ceilings that use steel foundation members for construction, fire-resistant covering materials are installed on the steel foundation members as fire-resistant structures in order to ensure heat insulation and flame retardancy in fire resistance performance. For example, the wall structure includes: columns that are arranged at fixed intervals and made of steel foundation members; and fire-resistant covering materials such as gypsum boards that are attached to these columns.

[0005] When a fire occurs in a building having such a fire-resistant structure, the fire-resistant covering material blocks heat and flames to protect the steel base member and the building. However, when the fire-resistant covering material is damaged by cracking or the like due to the fire, the fire-resistant structure loses its fire-resistant properties such as heat insulation and flame retardancy.

[0006] In this regard, when evaluating the fire resistance of the wall structure using steel foundation components for construction, the causes of cracking of the fire-resistant covering materials were studied, and as a result, the following recognized contents were gradually clarified. In the early stage of a fire, the heat is blocked by the fire-resistant covering materials in the fire-resistant structure, so the steel foundation components for construction remain at room temperature. However, after the fire occurs, as time passes, the heat is gradually transferred from the fire-resistant covering materials to the steel foundation components, and the steel foundation components are heated and thermally expanded. It is believed that in a building, since the two ends of the steel foundation components are constrained by other components, based on the thermal expansion, the steel foundation components are constrained by other components and deform, so that the fire-resistant covering materials attached to the steel foundation components are subjected to stress and crack.

[0007] Patent document 1 discloses a technology for preventing damage to a refractory covering material in a refractory structure using the steel base member and the refractory covering material. Specifically, Patent document 1 describes a dry refractory structure of a steel column, which includes: a steel column; a refractory covering material in which a plate-like body is arranged in a manner to surround the steel column and the corners of the plate-like body are connected to form a cylindrical body; and an insulator arranged between the refractory covering material and the steel column to isolate the refractory covering material from the steel column, wherein the insulator is in contact with both the steel column and the refractory covering material and is only fixed on one of the two, the steel column and the refractory covering material can move relative to each other along the axial direction of the steel column, and the steel column and the refractory covering material are configured not to follow the change in the material length of the two caused by heating.

[0008] Patent document 1 states that the insulator is only fixed on either the steel column or the refractory covering material, and the steel column and the refractory covering material can move relative to each other along the axial direction of the steel column, so that even when the steel column undergoes thermal expansion, stress will not act on the refractory covering material and there is no risk of damage due to the thermal expansion of the steel column.

[0009] On the other hand, in the technology described in Patent Document 1, since a partition is introduced between the steel base member and the fire-resistant covering material, it is necessary to provide a space corresponding to the partition, which narrows the living space of the building.

[0010] In addition, from the economic perspective of reducing costs and the environmental perspective of reducing carbon emissions, which has received attention in recent years, it is required to reduce the amount of materials used for refractory structures including steel base components and refractory covering materials. Therefore, it is believed that if the fireproof and fire-resistant performance of the refractory structure can be ensured with thinner insulation materials, it will be advantageous both economically and environmentally.

[0011] In addition, as mentioned above, it is believed that the reason why the fire-resistant covering material is damaged is that the steel base member is deformed at high temperature, and the fire-resistant covering material pasted on the steel base member is subjected to stress and cracks, but JIS A6517: 2010 does not specify the characteristics of the steel base member at high temperature. In other words, it is not possible to suppress the deformation of the steel base member by simply meeting the JIS standard. Here, the steel base member for construction is generally not used in the load-bearing wall that bears the structure of the building together with the wall structure and the ceiling structure, but is only used in the non-load-bearing wall. For example, non-patent document 1 records the use of light steel frame as the base member in the partition wall (non-load-bearing wall) structure. In addition, non-patent document 2 records that the steel wall base member is a non-structural body. Based on this reason, it was previously believed that in terms of fire resistance, it was not necessary to ensure the non-damage related to the collapse of the building, and even if the strength was reduced during a fire, it was assumed that there would be no problem in terms of performance. Therefore, in terms of building material applications, there has been no research on applying fire-resistant galvanized steel sheets (eg, Patent Document 2) having excellent high-temperature characteristics to steel foundation members for construction.

[0012] Therefore, an object of the present invention is to provide a steel base member that is less likely to buckle at high temperatures.

[0013] Prior art literature

[0014] Patent Literature

[0015] Patent Document 1: Japanese Patent Publication No. 6970381

[0016] Patent Document 2: Japanese Patent Gazette No. 3267324

[0017] Non-patent literature

[0018] Non-patent document 1: Ministry of Land, Infrastructure, Transport and Tourism, "Design Guidelines for Wooden Fire-Resistant Buildings in Government Buildings, Chapter 2 Case Studies", page 13, [Online], March 2013, Ministry of Land, Infrastructure, Transport and Tourism, [retrieved September 7, 2023], Internet<URL:https: / / www.mlit.go.jp / common / 000993926.pdf>

[0019] Non-patent document 2: Yashio Building Materials Industry Co., Ltd., "Product Catalog Steel Foundation Members for Construction", page 6, [Online], January 2020, Yashio Building Materials Industry Co., Ltd., [Retrieved September 7, 2023], Internet<URL:https: / / www.yasio.jp / doc / catalog / catalog seihinLT_202001.pdf> Summary of the invention

[0020] A steel base member according to one aspect of the present invention includes a steel plate having a yield strength of 250 MPa or more at 500° C. and a yield strength of 125 MPa or more at 600° C. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a graph showing the relationship between yield strength and temperature.

[0022] Figure 2 This is a coordinate diagram showing the relationship between the heating time and the strain amount of the heating surface in the longitudinal direction obtained by FEM. DETAILED DESCRIPTION

[0023] The present inventors have found that by using a material that is difficult to buckle at high temperatures as a steel base member, it is not necessary to introduce a spacer between the steel base member and the fire-resistant covering material in a fire-resistant structure of a building having a steel base member and a fire-resistant covering material, and fire-resistant performance can be ensured even if the fire-resistant covering material used is thin. Therefore, according to the present invention, a steel base member that is difficult to buckle at high temperatures can be provided.

[0024] Next, a steel base member according to an embodiment of the present invention will be described.

[0025] The steel base member according to the present embodiment includes a steel plate having a yield strength of 250 MPa or more at 500°C and a yield strength of 125 MPa or more at 600°C.

[0026] According to this structure, it is possible to provide a steel base member that is unlikely to buckle at high temperatures.

[0027] As mentioned above, steel foundation components for construction are generally not used in load-bearing walls that bear the structure of the building together with the wall structure and the ceiling structure, but are only used in non-load-bearing walls. Therefore, in the past, in terms of building material use, there has been no research on the application of steel plates that can ensure strength even at high temperatures to steel foundation components for construction. The present inventors have found that by using steel plates that have sufficient high-temperature strength and are difficult to buckle at high temperatures as steel foundation components, in the fire-resistant structure of a building including steel foundation components and fire-resistant covering materials, fire-resistant performance can be ensured even if the fire-resistant covering material used is thin. Moreover, the present inventors have clarified the following content, namely: since the cracking of the fire-resistant covering material caused by the buckling of the steel foundation component can be suppressed even at high temperatures, it is not necessary to introduce an insulator between the steel foundation component and the fire-resistant covering material, so there is an advantage that the living space of the building can be further expanded.

[0028] The reason is considered to be as follows. In the event of a fire in a building, if the steel base member constituting the fire-resistant structure is heated, thermal expansion will occur. At this time, the two ends of the steel base member in the building are constrained by other members, so a compressive force acts on the steel base member from other members based on thermal expansion. When the compressive force acting on the steel base member exceeds the yield strength after a fire occurs, the steel base member is deformed due to buckling. If the refractory covering material pasted on the steel base member is subjected to stress and cracks due to the deformation of the steel base member, the fire-resistant performance of the fire-resistant structure fails. Here, the steel plate involved in this embodiment has a high yield strength at high temperatures such as 500°C and 600°C compared to the previous steel plate, so it is difficult to buckle even if it is heated. Therefore, in the fire-resistant structure of the building, even if a separator is not introduced between the steel base member and the fire-resistant covering material involved in this embodiment, damage such as cracking of the fire-resistant covering material can be suppressed for a long time after the fire occurs. Accordingly, while ensuring the fire-resistant performance, a larger living space of the building can be ensured.

[0029] In addition, according to the steel base component involved in the present embodiment, compared with the case where conventional steel plates are used for steel base components, in the following situations, namely: when the same material as the refractory covering material used in the refractory structure in which conventional steel plates are used for steel base components is used, the time from the occurrence of fire to the occurrence of buckling of the steel base component can be delayed, thereby improving the fire resistance performance.

[0030] Furthermore, according to the steel base member of the present embodiment, even if the refractory covering material used in the refractory structure is thinned or reduced, the time from the occurrence of fire to the occurrence of buckling of the steel base member can be set to the same time as that in the case of using the conventional steel plate, compared with the case of using the conventional steel plate for the steel base member. That is, even if the refractory covering material is less, the same fire resistance as in the past can be ensured, thereby reducing costs, reducing carbon emissions, and ensuring a larger living space.

[0031] 〈Steel Plate〉

[0032] The steel plate used in the steel base member according to the present embodiment has a yield strength of 250 MPa or more at 500° C. and a yield strength of 125 MPa or more at 600° C. By using a steel plate having such a structure as a steel base member, a steel base member that is less likely to buckle at high temperatures can be provided.

[0033] The yield strength at 500° C. is preferably 280 MPa or more, more preferably 300 MPa or more. The upper limit of the yield strength at 500° C. is not particularly limited, but is preferably 500 MPa or less as an achievable value.

[0034] The yield strength at 600° C. is preferably 150 MPa or more, more preferably 175 MPa or more. The upper limit of the yield strength at 600° C. is not particularly limited, but is preferably 300 MPa or less as an achievable value.

[0035] In addition, the yield strength of the steel plate used in the steel base member according to the present embodiment at room temperature is preferably 250 MPa or more, more preferably 300 MPa or more. In the present embodiment, room temperature refers to 20° C. The upper limit of the yield strength at room temperature is not particularly specified, but as an achievable value, it is preferably 1000 MPa or less.

[0036] The yield strength of the steel sheet according to the present embodiment is a value measured by the measuring method specified in JIS G 0567:2020.

[0037] In addition, the steel base member involved in the present embodiment may also have a steel plate as described above and a metal plating formed on the surface of the steel plate. In addition, in general, from the viewpoint of improving corrosion resistance, a metal plating can be formed on the surface of the steel plate, but the yield strength of the above-mentioned steel plate at 500°C, 600°C and room temperature does not change depending on the presence or absence of a plating layer. That is, the plated steel plate having a metal plating layer formed on the surface of the steel plate in the present embodiment preferably has a yield strength of 250MPa or more at 500°C and a yield strength of 125MPa or more at 600°C. The yield strength of the plated steel plate at 500°C is more preferably 280MPa or more, further preferably 300MPa or more, and on the other hand is preferably 500MPa or less. In addition, the yield strength of the plated steel plate at 600°C is more preferably 150MPa or more, further preferably 175MPa or more, and on the other hand is preferably 300MPa or less. The yield strength at room temperature is preferably 250MPa or more, more preferably 300MPa or more, and on the other hand is preferably 500MPa or less.

[0038] The chemical composition of the steel plate involved in this embodiment is not particularly specified. Elements contained in the steel plate include C (carbon), Si (silicon), Mn (manganese), Cu (copper), Ni (nickel), Cr (chromium), Mo (molybdenum), Ti (titanium), Nb (niobium), V (vanadium), P (phosphorus), S (sulfur), N (nitrogen), B (boron), etc.

[0039] 〈Metal plating〉

[0040] Examples of the metal plating layer formed on the surface of the steel plate in the steel base member of the present embodiment include a hot-dip galvanized layer, an alloyed hot-dip galvanized layer, a hot-dip 55% aluminum-zinc alloy layer, and a hot-dip zinc-aluminum-magnesium alloy layer.

[0041] <organize>

[0042] The structure of the steel plate of the steel base member involved in this embodiment is not particularly limited, and the area ratio of the recrystallized structure is preferably less than 20%. By making the area ratio of the recrystallized structure less than 20%, the yield strength at high temperature can be more reliably improved. More preferably, the area ratio of the recrystallized structure is less than 10%. In addition, the lower limit of the area ratio of the recrystallized structure is not particularly limited, and the smaller the area ratio, the more reliably the yield strength at high temperature can be improved. The area ratio of the recrystallized structure can be obtained using a photograph of the steel plate portion in the cross section of the steel base member taken using an optical microscope.

[0043] <Manufacturing method>

[0044] The manufacturing method of the steel base member is performed by a general cold-rolled steel sheet manufacturing method and a hot-dip galvanizing method. An example of the manufacturing method of the steel base member is described below.

[0045] For example, a steel having a desired chemical composition is first cast, and the cast steel is hot-rolled, pickled, and cold-rolled, and then heat-treated by a continuous annealing line (CAL or CAPL) or a continuous hot-dip galvanizing line (CGL) or the like, so that a steel sheet having a yield strength of 250 MPa or more at 500°C and a yield strength of 125 MPa or more at 600°C can be obtained. In addition, after heat-treating by the continuous annealing line (CAL or CAPL) or the like, a galvanized layer is applied by a hot-dip galvanizing line or an electroplating line, or a galvanized layer is applied by the continuous hot-dip galvanizing line (CGL) process and a hot-dip galvanized layer is applied, so that a galvanized steel sheet having a yield strength of 250 MPa or more at 500°C and a yield strength of 125 MPa or more at 600°C can be obtained. The obtained steel sheet and galvanized steel sheet can be processed into a specified size and shape and used as a steel sheet base member.

[0046] The heat treatment conditions of the cold-rolled steel sheet can be appropriately changed according to the chemical composition of the steel and the conditions of the cold rolling, and are therefore not particularly limited. For example, the cold-rolled steel sheet is preferably heated from room temperature to an annealing temperature of 650 to 900°C, and maintained at the annealing temperature for 1 to 1800 seconds. Through this annealing treatment, the area ratio of the recrystallized structure in the steel sheet structure can be made less than 20%. The annealing temperature is preferably above 680°C, and on the other hand, it is preferably below 880°C. In addition, the holding time (annealing time) at the annealing temperature is preferably above 5 seconds, and on the other hand, it is preferably below 1500 seconds.

[0047] The steel sheet after annealing is preferably cooled to 600 to 400° C. at a cooling rate of 3 to 100° C. / sec.

[0048] As described above, this specification discloses various types of technologies, and the main technologies among them are summarized as follows.

[0049] As described above, a steel base member according to one aspect of the present invention includes a steel plate having a yield strength of 250 MPa or more at 500° C. and a yield strength of 125 MPa or more at 600° C.

[0050] By using the steel plate of this configuration for a steel foundation member, it is possible to provide a steel foundation member capable of ensuring fire resistance even when a small amount of fire-resistant covering material is used in a fire-resistant structure of a building including the steel foundation member and the fire-resistant covering material.

[0051] In the steel base member having the above structure, the yield strength of the steel plate at room temperature may be 250 MPa or more.

[0052] By using the steel plate having this structure for a steel base member, it is possible to provide a steel base member capable of ensuring not only fire resistance but also more sufficient strength at room temperature.

[0053] The steel base member of the above structure further includes: a metal plating layer formed on the surface of the steel plate.

[0054] Example

[0055] 〈Sample〉

[0056] As samples, steel sheet A and steel sheet B described below were used. Steel sheet A is a comparative example, which is a commercially available hot-dip galvanized steel sheet (SGCC) specified in JIS G 3302:2019, and is a steel sheet to which Nb (niobium), Ti (titanium), and V (vanadium) are not added. In addition, steel sheet B contains C (carbon): 0.06 mass%, Si (silicon): 0.02 mass%, Mn (manganese): 1.45 mass%, Nb (niobium): 0.02 mass%, Ti (titanium): 0.04 mass%, and the remainder is Fe (iron) and unavoidable impurities, and steel sheet B is a cold-rolled steel sheet made in a laboratory according to the following manufacturing conditions, and is an example of the present invention that meets the necessary conditions of this embodiment.

[0057] Manufacturing conditions

[0058] Hot rolling conditions, cold rolling conditions

[0059] The slab was heated at 1200°C, rolled to 3.6 mm and placed in a holding furnace at 550°C to simulate coiling, and held for 30 minutes before being cooled in the furnace. The surface and back of the cooled hot-rolled steel sheet were ground to 1.6 mm. This is a laboratory process that simulates the production of 1.6 mm hot-rolled steel sheets in actual production equipment. The 1.6 mm hot-rolled steel sheet was then cold-rolled to 0.8 mm.

[0060] Annealing conditions

[0061] The cold-rolled steel sheet was held at 700°C for 60 seconds, cooled to below 200°C at a cooling rate of 10°C / second, and then allowed to cool to obtain Steel Sheet B. In order to verify the ideal state of galvanized steel sheets in the laboratory, Steel Sheet B was not coated.

[0062] The area ratio of the recrystallized structure of the manufactured steel sheet B was 0.5%. The area ratio of the recrystallized structure of the steel sheet in the steel sheet A was 100%. The area ratio of the recrystallized structure was determined using a photograph of the steel sheet taken with an optical microscope.

[0063] <evaluate>

[0064] Tensile test pieces conforming to JIS 13B specified in JIS Z 2241:2022 were extracted from Steel Plates A and B, and tensile tests were performed at temperatures ranging from 20°C to 750°C in accordance with JIS G 0567:2020 to measure yield strength. Tensile tests were performed at temperatures above 100°C and after holding at each temperature for 10 minutes. The tensile speed in the tensile tester was set to 0.004 min. -1 , until the yield strength.

[0065] Figure 1 It is a coordinate graph showing the relationship between yield strength and temperature. The yield strength of steel plate A at 20°C is 159MPa, the yield strength at 500°C is 123MPa, and the yield strength at 600°C is 101MPa. The yield strength of steel plate B at 20°C is 901MPa, the yield strength at 500°C is 382MPa, and the yield strength at 600°C is 167MPa. Figure 1 It can be seen that the yield strength of Steel Sheet B at each temperature is higher than that of Steel Sheet A, and in particular, the yield strength at high temperatures of 500° C. and 600° C. is excellent.

[0066] Next, the deformation behavior caused by heating when the steel plates A and B are used as steel base members was simulated by finite element analysis (FEM). In addition to the above-mentioned measured values, the longitudinal elastic modulus, transverse elastic modulus, and linear expansion coefficient of the steel plates A and B were used in FEM.

[0067] The conditions for the simulation by FEM are as follows: The reason for setting only one surface of the square cylindrical steel base member as the heating surface is to simulate the heating state during a fire.

[0068] Size and shape of steel foundation components

[0069] ·Plate thickness: 0.8mm

[0070] Section: A square with a side length of 45 mm

[0071] Length: 2000m

[0072] Heating surface: Only one of the four sides

[0073] Constraints: Constrain the steel foundation components at both ends of the length direction

[0074] · Temperature T (°C) of each surface at time t (minutes) from the start of heating

[0075] Heating surface: T(t) = 900 × log 10 (1+0.08t)

[0076] ·Surface facing the heating surface: T(t) = 900 × log 10 (1+0.045(t-5)), but 5 minutes from the start of heating is at room temperature (20°C)

[0077] ·Longitudinal elastic modulus E (kgf / cm2) of steel plate A and steel plate B at temperature T (℃) 2 ) and transverse elastic modulus G (kgf / cm 2 )

[0078] ·Longitudinal elastic modulus E: E = 2.14 × 10 6 ×exp(-0.000374T)

[0079] Transverse elastic modulus G: G = 8.30 × 10 6 ×exp(-0.000409T)

[0080] ·Linear expansion coefficient α (1 / °C) of steel plates A and B: α = 0.000012

[0081] Furthermore, as a reference example, FEM was also performed on a perfect elastic body without yield strength.

[0082] Figure 2 This is a coordinate diagram showing the relationship between the heating time (seconds) obtained by the above FEM and the strain amount of the heating surface in the longitudinal direction. Figure 2, the steel plate A of the comparative example began to deform plastically (bend) about 600 seconds after the start of heating. On the other hand, the steel plate B of the present invention began to deform plastically about 1800 seconds after the start of heating. It can be seen from this that the steel plate B has better fire resistance than the steel plate A. In addition, according to Figure 2 It is understood that the perfect elastic body of the reference example does not undergo plastic deformation.

[0083] This application is based on Japanese patent application No. 2022-151271 filed on September 22, 2022, and the contents are incorporated herein by reference.

[0084] In order to describe the present invention, the present invention has been appropriately and fully described above by referring to specific embodiments and drawings, but it should be recognized that those skilled in the art can easily change and / or improve the above-mentioned embodiments. Therefore, as long as the modified embodiments or improved embodiments implemented by those skilled in the art do not deviate from the protection scope of the claims recorded in the claims, the modified embodiments or improved embodiments can be interpreted as being included in the protection scope of the claims.

[0085] Industrial Applicability

[0086] The present invention has broad industrial applicability in the technical field related to steel foundation members used in buildings.

Claims

1. A steel foundation component, characterized in that include: A steel plate having a yield strength of 250 MPa or more at 500°C and a yield strength of 125 MPa or more at 600°C.

2. The steel foundation member according to claim 1, characterized in that: The yield strength of the steel plate at room temperature is 250 MPa or more.

3. The steel foundation member according to claim 1 or 2, characterized in that Also includes: A metal plating layer is formed on the surface of the steel plate.

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