Design method for concrete-filled steel pipe columns
The design method for concrete-filled steel pipe columns addresses the cost and time issues of fire-resistant coatings by ensuring the concrete maintains structural integrity during fires, thus meeting fire resistance requirements without fireproofing, reducing construction costs and time.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- SHIMIZU CORP
- Filing Date
- 2022-05-11
- Publication Date
- 2026-07-22
AI Technical Summary
Existing fire-resistant coated structures for steel-framed columns are costly and time-consuming, and there is a need for a method that meets fire resistance requirements without using fire-resistant coatings.
A design method for concrete-filled steel pipe columns that ensures the cross-sectional area and design standard strength of the filling concrete exceed the long-term allowable compressive strength of the steel pipe, allowing the concrete to maintain structural integrity during fires without the need for fireproofing.
The method reduces construction costs and time by eliminating the need for fireproofing and ensures the columns maintain structural strength during fires, meeting Building Standards Act Enforcement Order requirements.
Smart Images
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Abstract
Description
[Technical Field]
[0001] This invention relates to a design method for concrete-filled steel pipe columns. [Background technology]
[0002] The Building Standards Act Enforcement Order stipulates that, for steel-framed columns with three or more stories excluding the basement, if there is a risk of easy collapse due to a decrease in load-bearing capacity caused solely by the heat of the columns, the structure of the columns must be such that no deformation, melting, or destruction that would impair their structural strength occurs for 30 minutes after being subjected to the heat of a normal fire, even if there is no requirement for fire-resistant or semi-fire-resistant measures.
[0003] Conventionally, the fire-resistant structure of columns has been defined as one of the structures specified in the Ministry of Construction's notification, all of which are fire-resistant coated structures in which the perimeter of the column is covered with a covering material. For example, Patent Document 1 discloses a fire-resistant structure that includes fire-resistant coated columns and fire-resistant coated beams made of steel material with a fire-resistant coating. [Prior art documents] [Patent Documents]
[0004] [Patent Document 1] International Publication No. 2020 / 110985 [Overview of the project] [Problems that the invention aims to solve]
[0005] Applying fire-resistant coatings to columns that do not require fire-resistant or semi-fire-resistant measures presents challenges such as extending the construction period and increasing costs. Therefore, there is a need for a column design method that can satisfy the fire resistance requirements stipulated in the Building Standards Act Enforcement Order without using fire-resistant coatings.
[0006] On the other hand, concrete-filled steel pipe columns, which have been conventionally used as a construction method for steel-framed columns, have the advantage that the load-bearing capacity of the concrete filled inside the steel pipe does not easily decrease even in the event of a fire, due to the large heat capacity of the concrete filled inside the steel pipe.
[0007] The present invention has been made in view of the above circumstances, and aims to provide a design method for concrete-filled steel pipe columns that eliminates the need for fire-resistant coating and reduces the impact of fire heating on the structural strength of the column. [Means for solving the problem]
[0008] A design method for concrete-filled steel pipe columns, applicable to concrete-filled steel pipe columns installed in buildings having three or more floors excluding the basement, wherein when the concrete-filled steel pipe column is heated, the cross-sectional area of the effective cross section in the transverse direction, excluding the portion where the load-bearing capacity is reduced due to the heating of the filling concrete, is Ace, and the design standard strength (N / mm²) of the filling concrete within the effective cross section is 2 A design method for concrete-filled steel pipe columns, characterized in that when Fc is the long-term allowable compressive force of the steel pipe, the following equation (1) holds true.
[0009]
number
[0010] With the above configuration, a concrete-filled steel pipe column designed according to the design method for concrete-filled steel pipe columns (hereinafter referred to as "designed concrete-filled steel pipe column") satisfies equation (1), so that when heated, the compressive strength of the filling concrete at the effective cross-section of the filling concrete exceeds the long-term allowable compressive strength of the steel pipe. Therefore, even after the compressive strength of the steel pipe portion of the designed concrete-filled steel pipe column decreases due to heating, the filling concrete maintains the column axial force and can continue to support the long-term compressive force. Based on the above, since the design concrete-filled steel pipe column satisfies formula (1), the design concrete-filled steel pipe column will not be impaired in terms of structural strength even when heated by fire or other causes, and therefore can satisfy the structural requirements of the Building Standards Act Enforcement Order without the need to install fireproofing. Design concrete-filled steel pipe columns eliminate the need for fireproofing and reduce the amount of steel compared to conventional steel frame construction, thus enabling a reduction in overall construction costs and a shortening of construction time for buildings to which design concrete-filled steel pipe columns are applied.
[0011] Furthermore, in the design method for concrete-filled steel pipe columns according to the present invention, the standard strength of the steel pipe is 440 N / mm². 2 The following is also acceptable.
[0012] By adopting the above configuration, the long-term allowable compressive force of the steel pipe is specified within a certain range in the design method for concrete-filled steel pipe columns, thereby improving the accuracy and ease of design for concrete-filled steel pipe columns.
[0013] Furthermore, in the design method for concrete-filled steel pipe columns according to the present invention, the concrete-filled steel pipe column is provided as a rectangular column with a substantially square cross-section, and the steel pipe may be formed with a cross-sectional member width of 500 mm or more and a thickness of 16 mm or more.
[0014] By adopting the above configuration, the range of dimensions for the rectangular steel pipe in the design method for concrete-filled steel pipe columns is specified to a certain range, thereby improving the accuracy and ease of design for concrete-filled steel pipe columns.
[0015] Furthermore, in the design method for concrete-filled steel pipe columns according to the present invention, the concrete-filled steel pipe column is provided as a cylindrical column with a substantially circular cross-section, and the steel pipe may be formed with a cross-sectional member width of 633 mm or more and a thickness of 16 mm or more.
[0016] With the above configuration, in the design method of a concrete-filled steel tubular column, since the steel pipe dimension range of the cylindrical shape is specified within a certain range, the accuracy and ease of design of the concrete-filled steel tubular column can be improved.
[0017] Also, in the design method of the concrete-filled steel tubular column according to the present invention, the thickness of the square-shaped steel pipe is such that when the member width of the cross-section of the steel pipe is 1000 mm exceed In the case, it is calculated as a thickness that is equal to or greater than the member rank FC that satisfies the following formula (2) according to the reference strength and member width of the steel pipe, and when the member width of the cross-section of the steel pipe is 1000 mm below In the case, it may also be a steel pipe thickness determined according to Table 1 below according to the reference strength and member width of the steel pipe. (Table 1 is described in the mode for carrying out the invention.)
[0018] [[ID=ll]]
Number
[0019] With the above configuration, for a concrete-filled steel tubular column having a prismatic shape, since steel pipes of the member type FD rank with brittle deformation performance can be excluded from the target, the toughness of the steel pipe can be ensured.
[0020] Also, in the design method of the concrete-filled steel tubular column according to the present invention, the thickness of the circular-shaped steel pipe is such that when the member width of the cross-section of the steel pipe is 2610 mm exceed In the case, it is calculated as a thickness that is equal to or greater than the member rank FC that satisfies the following formula (3) according to the reference strength and member width of the steel pipe, and when the member width of the cross-section of the steel pipe is 2610 mm below In the case, it may also be a steel pipe thickness determined according to Table 2 below according to the reference strength and member width of the steel pipe. (Table 2 is described in the mode for carrying out the invention.)
[0021]
Number
[0022] By adopting the above configuration, it is possible to exclude steel pipes of member type FD rank, which have brittle deformation performance, from the target for cylindrical concrete-filled steel pipe columns, thereby ensuring the toughness of the steel pipes.
[0023] Furthermore, in the design method for concrete-filled steel pipe columns according to the present invention, the design standard strength Fc of the filled concrete is 39 N / mm². 2 More than 60N / mm 2 The following is also acceptable.
[0024] By adopting the above configuration, the design range of the concrete's design strength for the concrete-filled steel pipe column is specified within a certain range, thereby improving the accuracy and ease of designing concrete-filled steel pipe columns.
[0025] Furthermore, in the design method for concrete-filled steel pipe columns according to the present invention, the cross-sectional area of the effective cross section may be the cross-sectional area in the transverse direction of the portion where the temperature of the filled concrete is 200°C or less.
[0026] By adopting the above configuration, the definition of the effective cross-sectional area in the design method for concrete-filled steel pipe columns is specified to be within a certain range, thereby improving the accuracy and ease of designing concrete-filled steel pipe columns. [Effects of the Invention]
[0027] According to the present invention, it is possible to provide a design method for concrete-filled steel pipe columns that eliminates the need for fire-resistant coating and reduces the impact of fire heating on the structural strength of the column. [Brief explanation of the drawing]
[0028] [Figure 1] This is a longitudinal cross-sectional view showing an example of a column-beam structure comprising a concrete-filled steel pipe column to which the design method for concrete-filled steel pipe columns according to an embodiment of the present invention is applied. [Figure 2]An example of a concrete-filled steel pipe column to which the design method for concrete-filled steel pipe columns according to an embodiment of the present invention is applied is shown, where (a) is a cross-sectional view of a rectangular prism-shaped concrete-filled steel pipe column, and (b) is a cross-sectional view of a cylindrical concrete-filled steel pipe column. [Figure 3] This graph shows the measurement results of the axial shrinkage amount due to heating of a concrete-filled steel pipe column to which the design method for concrete-filled steel pipe columns according to an embodiment of the present invention is applied. [Modes for carrying out the invention]
[0029] The design method for concrete-filled steel pipe columns according to embodiments of the present invention will be described below with reference to Figures 1 to 3. The concrete-filled steel pipe column design method according to this embodiment is applicable to steel-framed buildings 1 that are three stories or more in height, excluding the basement, and do not require the installation of fire-resistant structures. Building 1 is not located in a fire-prevention zone or quasi-fire-prevention zone as defined by the City Planning Act, and is not a special building as defined by the Building Standards Act.
[0030] As shown in Figure 1, the building 1 comprises a plurality of concrete-filled steel pipe columns 2 designed according to the concrete-filled steel pipe column design method of this embodiment, a plurality of beams 3, and a plurality of slabs 4 that partition each floor. In Figure 1, the horizontal direction relative to the concrete-filled steel pipe columns 2 is denoted as the X direction, the horizontal direction relative to the concrete-filled steel pipe columns 2 perpendicular to the X direction is denoted as the Y direction, and the vertical direction relative to the beams 3 (the direction in which the concrete-filled steel pipe columns 2 are arranged) is denoted as the Z direction. The beams 3 are, for example, known H-shaped steel.
[0031] The concrete-filled steel pipe columns 2 are steel pipe columns without fire-resistant coatings. Multiple concrete-filled steel pipe columns 2 are arranged at regular intervals in the X and Y directions.
[0032] Multiple beams 3 are arranged at regular intervals in the X and Y directions to form a single beam section 31. Multiple beam sections 31 are arranged at regular intervals in the Z direction according to the number of floors of the building 1. Above the multiple beam sections 31, a slab 4 corresponding to the floor or roof of the building 1 is provided. The slab 4 is made of known reinforced concrete.
[0033] Multiple concrete-filled steel pipe columns 2 and multiple beams 3 are joined at each intersection 5. The joining method at the intersection 5 is not limited; for example, the concrete-filled steel pipe columns 2 and the multiple beams 3 can be joined by welding at the intersection 5.
[0034] As shown in Figure 2, the concrete-filled steel pipe column 2 is composed of a steel pipe 21 and concrete 22 filled inside the steel pipe 21.
[0035] The concrete-filled steel pipe column 2 is designed such that, when the concrete-filled steel pipe column 2 is heated, the concrete strength of the effective cross section 23 in the transverse direction, excluding the portion where the strength of the filling concrete 22 is reduced due to heating, exceeds the long-term allowable compressive strength of the steel pipe 21. Specifically, when the cross-sectional area of the effective cross section 23 is Ace, the design standard strength of the filling concrete 22 within the effective cross section 23 is Fc, and the long-term allowable compressive strength of the steel pipe 21 is LN, then equation (1) holds. The effective cross section 23 is the smallest cross section of the shaft 2a of the concrete-filled steel pipe column 2, excluding the intersection 5 (column-beam joint). For example, if the diameter of the shaft 2a changes along the way, the effective cross section 23 takes the cross section at the smallest diameter.
[0036]
number
[0037] By satisfying the above design conditions, the steel pipe 21 alone can resist long-term stresses during normal times, and after the load-bearing capacity of the steel pipe 21 is reduced due to heating such as fire, the load-bearing capacity of the filled concrete 22 alone can resist long-term stresses.
[0038] The cross-sectional area Ace of the effective cross section 23 is the transverse cross-sectional area of the portion of the concrete-filled steel pipe column 2 where the temperature of the filled concrete 22 is 200°C or less during heating.
[0039] Steel pipe 21 meets the quality standards stipulated in the Building Standards Act. It is desirable that steel pipe 21 be BCP325. The standard strength (F value) of steel pipe 21 is 440 N / mm². 2 The following applies:
[0040] The concrete-filled steel pipe column 2 is preferably provided as a rectangular prism with a cross-section 24 that is approximately square, or as a cylindrical column with a cross-section that is approximately circular.
[0041] As shown in Figure 2(a), when the concrete-filled steel pipe column 2 is a rectangular column with a roughly square cross-section 24, the width b in the X and Y directions, which is the member width of the cross-section 24 of the steel pipe 21, is formed to be 500 mm or more, and the thickness t is 16 mm or more.
[0042] As shown in Figure 2(b), when the concrete-filled steel pipe column 2 is a cylindrical column with a substantially circular cross-section 24, the width (outer diameter) D of the cross-section 24 of the steel pipe 21 is formed to be 633 mm or more, and the thickness is 16 mm or more.
[0043] The steel pipe 21 is provided with steam vents at designated locations to release steam generated from the concrete 22 during a fire, as stipulated in the Ministry of Land, Infrastructure, Transport and Tourism notification.
[0044] The design standard strength Fc of the concrete filling 22 is 39 N / mm². 2 More than 60N / mm 2 The following applies:
[0045] The width-to-thickness ratio C of the steel pipe 21, which is the ratio of the width to the thickness of the member, is calculated when the cross-section 24 is a roughly square prism and the width b of the steel pipe 21 is 1000 mm. If it exceeds The standard strength F of steel pipe 21 is 235 N / mm². 2When it is, the width-to-thickness ratio C becomes 48, and the reference strength F of the steel pipe 21 is 295 N / mm 2 When it is, the width-to-thickness ratio C becomes 42.8, and the reference strength F of the steel pipe 21 is 325 N / mm 2 When it is, the width-to-thickness ratio C becomes 40.8. Also, the following formula (2) holds. However, when the width length b of the steel pipe 21 is 1000 mm below In the case of, the thickness t of the steel pipe 21 is the condition shown in Table 1, and the width-to-thickness ratio C is calculated from the relationship between the width length b and the thickness t described in Table 1.
[0046]
Number
[0047]
[0046]
Number
[0047]
Table 1
[0048] <
[0052] Regarding the design conditions for the concrete-filled steel pipe column 2 described above, we will consider, for example, the case where the steel pipe 21 is a BCP325 with a rectangular column length b of 500 mm. For the concrete-filled steel pipe column 2, we will appropriately change the thickness t and the design standard strength Fc of the filling concrete and examine equation (2) for each case. The standard strength F of the steel pipe 21 is 325 N / mm 2 Therefore, the calculation of the long-term allowable compressive stress Fa of the steel pipe 21 is in accordance with the steel structure design standards. The long-term allowable compressive stress Fa is determined by the standard strength F of the steel pipe 21 and the slenderness ratio of the steel pipe 21. For equation (2) to hold, the ratio of the left side to the right side of equation (2) must be 1 or less.
[0053] In a concrete-filled steel pipe column 2, if the cross-sectional dimensions (width-to-thickness ratio) of the steel pipe 21 are made larger, the range in which equation (2) for the design standard strength Fc of the filling concrete 22 is satisfied narrows, and if it is made smaller, the range in which equation (4) is satisfied for the design standard strength Fc is expanded. In a concrete-filled steel pipe column 2, if the length of the column in the Z direction is made longer, the long-term allowable compressive force LN decreases, which is favorable for the satisfaction of equation (2).
[0054] The concrete-filled steel pipe columns 2 installed in building 1 will be confirmed by the following demonstration test to be constructed in such a way that they will not undergo deformation, melting, fracture, or other damage that would impair their structural strength for 30 minutes after the start of heating when subjected to the heat of a normal fire as defined in the Building Standards Act Enforcement Order.
[0055] A concrete-filled steel pipe column specimen 20 is formed as a rectangular column with a width b of 500 mm, a thickness t of 16 mm, and a length in the Z direction of 3500 mm. The steel pipe 21 is BCP325. The width b and thickness t of the concrete-filled steel pipe column specimen 20 are formed to satisfy equation (3).
[0056] The concrete-filled steel pipe column specimen 20 (hereinafter referred to as "specimen 20"), designed according to the above design conditions, is subjected to a constant long-term allowable compressive force LN (6355kN) applied downward in the Z direction to its upper end surface, while simultaneously being heated at a constant heating rate, with a maximum heating temperature of 842°C. The heating method is the ISO standard heating method. The loading time and heating time are at least 40 minutes. The heating temperature is measured by measuring the flame temperature at four points corresponding to the four corners of the upper end surface (heated surface) of specimen 20, located 10 cm away from the upper end surface in the Z direction. These four measurement points are designated as A, B, C, and D, and the amount of shrinkage (elongation) of specimen 20 in the Z direction due to heating at each measurement point is measured. The test standard is 4.7 Column Fire Resistance Performance Test Method, "Fire Resistance Performance Test and Evaluation Work Method Manual" established by the Japan Building Research Institute. The verification test is performed by repeating tests using multiple specimens.
[0057] As shown in Figure 3, the test results indicate that the concrete-filled steel pipe column specimen 20 exhibits deformation behavior in the Z direction from the start of heating up to approximately 20 minutes later, with the steel pipe 21 extending upward in the Z direction due to heating. At this time, the upper end surface of the filled concrete 22 temporarily separates from the loading surface.
[0058] Approximately 20 minutes after the start of heating, the deformation behavior of the concrete-filled steel pipe column specimen 20 shifts to contraction in the Z direction. This behavior indicates that the long-term allowable compressive force LN of the steel pipe 21 gradually decreases due to heating, making it unable to support the applied long-term allowable compressive force LN, and thus causing the steel pipe 21 to begin contracting due to the load.
[0059] The concrete-filled steel pipe column specimen 20 shows a decrease in shrinkage per unit time in the Z direction starting approximately 21 minutes after the start of heating. This behavior indicates that by 20 minutes after the start of heating, the steel pipe 21 has almost completely contracted to compensate for the length it expanded due to heating, causing the loading surface to contact both the steel pipe 21 and the filling concrete 22, resulting in a configuration where the steel pipe 21 and the filling concrete 22 support the load of the long-term allowable compressive force LN.
[0060] The concrete-filled steel pipe column specimen 20 shows positive shrinkage approximately 24 minutes after the start of heating. This behavior indicates that the bearing capacity of the filled concrete 22 has begun to support the long-term allowable compressive force LN.
[0061] Based on the above test results, the concrete-filled steel pipe column specimen 20 showed a shrinkage in the Z direction of less than 5 mm when loaded with the long-term allowable compressive force LN 30 minutes after the start of heating. This result is significantly smaller than the allowable axial shrinkage of 35 mm calculated from the initial height h / 100 of specimen 20 according to the judgment criteria in the fire resistance performance test and evaluation work report of the Japan Building Research Institute. Furthermore, the concrete-filled steel pipe column specimen 20 also showed a shrinkage in the Z direction of less than 5 mm when loaded with the long-term allowable compressive force LN 40 minutes after the start of heating, which is similarly significantly smaller than the allowable axial shrinkage of 35 mm.
[0062] Next, the operation and effects of the design method for concrete-filled steel pipe columns according to the embodiments of the present invention described above will be explained with reference to the drawings.
[0063] The concrete-filled steel pipe column 2, designed according to the design method for concrete-filled steel pipe columns, is installed in building 1, and equation (2) holds true. With the above configuration, the compressive strength of the filled concrete 22 due to the effective cross-section 23 of the filled concrete 22 exceeds the long-term allowable compressive force LN of the steel pipe 21. Therefore, even after the compressive strength of the steel pipe 21 portion of the concrete-filled steel pipe column 2 decreases due to heating, the filled concrete 22 maintains the column axial force and can continue to support long-term compressive forces. Based on the above, the concrete-filled steel pipe column 2 does not experience any impairment in its structural strength even when heated by fire or other means, and therefore can meet the structural requirements of the Building Standards Act Enforcement Order without the need to install fireproofing.
[0064] Concrete-filled steel pipe columns 2 eliminate the need for fireproofing and reduce the amount of steel compared to conventional steel frame construction, thus enabling a reduction in overall construction costs and a shorter construction period for building 1.
[0065] In the concrete-filled steel pipe column 2, the standard strength F, width b, and thickness t of the steel pipe 21, the design standard strength Fc of the filling concrete 22, and the temperature of the effective cross-section 23 are specified within a certain range, thus improving the accuracy and ease of design of the concrete-filled steel pipe column.
[0066] The concrete-filled steel pipe column 2 can be made into a member of a member type other than FD rank, which has brittle deformation performance, by ensuring that the width b and thickness t (width-to-thickness ratio C) of the steel pipe 21 meet the conditions listed in Table 1.
[0067] When the building 1 is a production facility or the like, the concrete-filled steel pipe column 2 is fitted with support brackets for fixing equipment piping. However, since there is no fireproofing, the effort of installing the support brackets by penetrating the fireproofing is eliminated. Therefore, the support brackets can be easily attached to the concrete-filled steel pipe column 2, further shortening the overall construction period of the building 1.
[0068] Although embodiments of the design method for concrete-filled steel pipe columns according to the present invention have been described above, the present invention is not limited to the above embodiments and can be modified as appropriate without departing from the spirit of the invention.
[0069] For example, in the above embodiment, it is preferable that the concrete-filled steel pipe column 2 be provided as a rectangular prism with a substantially square cross-section 24 or as a cylindrical column with a substantially circular cross-section 24, but it may also be a rectangular prism with a substantially rectangular shape in which either the X direction or the Y direction is longer. Furthermore, the concrete-filled steel pipe column 2 may be formed with a width b, outer diameter D, and thickness t that are less than or equal to the reference values in the embodiment, taking into consideration formula (2).
[0070] In the above embodiment, the standard strength F of the steel pipe 21 is 440 N / mm². 2 The design standard strength Fc of the concrete filling 22 is 39 N / mm². 2 More than 60N / mm 2 The following is considered to be the standard strength F, but considering equation (2), the standard strength F is 440 N / mm².2 The above may be used, or the design standard strength Fc of the filling concrete 22 may be 60 N / mm². 2 It may be done this way.
[0071] In the above embodiment, the cross-sectional area Ace of the effective cross section 23 is defined as the transverse cross-sectional area of the portion of the filled concrete 22 where the temperature is 200°C or less. However, the temperature reference value may be raised and defined considering equation (2). [Explanation of symbols]
[0072] 1 Building 2. Concrete-filled steel pipe columns 21 Steel pipe 22. Filling concrete 23 Effective cross-section 24 Cross-section b Width length t thickness
Claims
1. A design method for concrete-filled steel pipe columns, which are provided in buildings having three or more stories excluding the basement, and which consist of a steel pipe and concrete filling the inside of the steel pipe, A design method for concrete-filled steel pipe columns, characterized in that when the concrete-filled steel pipe column is heated, the cross-sectional area of the effective cross section in the transverse direction, excluding the portion where the load-bearing capacity is reduced due to the heating of the filling concrete, is Ace, the design standard strength of the filling concrete within the effective cross section is Fc, and the long-term allowable compressive force of the steel pipe is LN, the following equation (1) holds true. [Math 1]
2. The standard strength of the aforementioned steel pipe is 440 N / mm². ２ The following is: The design method for concrete-filled steel pipe columns according to claim 1.
3. The aforementioned concrete-filled steel pipe column is provided as a rectangular prism with a cross-section formed to be approximately square. The steel pipe is formed with a cross-sectional member width of 500 mm or more and a thickness of 16 mm or more. The design method for concrete-filled steel pipe columns according to claim 1.
4. The aforementioned concrete-filled steel pipe column is provided as a cylindrical column with a substantially circular cross-section, The steel pipe is formed with a cross-sectional member width of 633 mm or more and a thickness of 16 mm or more. The design method for concrete-filled steel pipe columns according to claim 1.