Design method and structure of PC column-beam joint

Abstract

Regarding the main reinforcement of PC beams anchored in column-beam joints where prestressing is introduced, the required anchorage length can be evaluated more appropriately to streamline the design of column-beam joints. [Solution] In the column-beam joint 50, the main reinforcement bars 13 and 14 protruding from the ends of the PC beams 10 and 20 placed on the jaw 4 of the PC column 2 are anchored to a predetermined anchorage length, and the PC tensioning members 30 and 40 placed on the PC beams 10 and 20 and the PC column 2 are passed through or anchored to the column-beam joint 50 and tensioned, thereby introducing prestress in each axial direction to the column-beam joint 50. The required anchorage length of the main reinforcement bars 13 and 14 protruding from the ends of the PC beams is calculated and set according to a predetermined formula that takes into account the restraint effect due to prestress.

Description

[Technical Field]

[0001] The present invention relates to a design method for a column-beam joint where the main reinforcement of a precast prestressed concrete beam is anchored. [Background technology]

[0002] Conventionally, there is a structure in which a prestressed concrete beam (hereinafter also called "PC beam"), which is made up of precast concrete members (hereinafter also called "PCa members") aligned in two horizontal directions (X-axis direction and Y-axis direction) and top concrete, and a prestressed concrete column (hereinafter also called "PC column"), which is made up of PCa members aligned in the vertical direction (Z-axis direction), are joined at a column-beam joint (panel zone) formed with cast-in-place concrete.

[0003] Patent Document 1 discloses a technology to solve the problem that in this type of column-beam joint, the concentration of reinforcing bars tends to result in insufficient concrete filling and density. In the technology of Patent Document 1, prestress applied to the PC beam by PC steel wire is introduced to the column-beam joint, and the anchorage length of the lower reinforcement of the PC beam at this column-beam joint is reduced to a length that does not require bent reinforcement (the lower reinforcement of the PC beam at the column-beam joint is anchored only by horizontal reinforcement). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 3873064 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, conventional designs have not specifically considered the relationship between the prestress introduced at the column-beam joint and the required anchorage length of the main reinforcement of the PC beam at the column-beam joint. In particular, no method has been established to rationally calculate the required anchorage length of the main reinforcement while taking this relationship into account.

[0006] Even in the aforementioned Patent Document 1, only the shortening of the lower reinforcement and anchoring with horizontal reinforcement is disclosed, and no specific method for calculating the required anchorage length is considered. Moreover, in the technology of Patent Document 1, the anchorage length is shortened only for the lower reinforcement which is in a compressive stress state during long-term stress and bears the tensile force during short-term stress during earthquakes. On the other hand, the upper reinforcement which also bears the tensile force during long-term stress is arranged in a 90° bent configuration according to the conventional design standard that requires an anchorage length of 35d, as in the case where prestress is not introduced. With such a configuration, the congestion of reinforcement at the column-beam joint is not sufficiently resolved, and the problems related to concrete filling and density remain unresolved.

[0007] Therefore, the present invention aims to rationalize the design of column-beam joints by more appropriately calculating the required anchorage length for the main reinforcement of a PC beam that is anchored in a column-beam joint where prestress is introduced. [Means for solving the problem]

[0008] A design method for the PC column-beam joint of a rigid frame structure formed by PC beams in two planar directions (X and Y axes) and PC columns in the vertical direction (Z axis), The PC columns are made of precast concrete members, the PC beams are formed by combining precast concrete members and top concrete, and the column-beam joints are formed of cast-in-place high-strength concrete. The design standard strength Fc of the aforementioned high-strength concrete is 50 N / mm². 2 That concludes my presentation. At the column-beam joint, main reinforcement protruding from the end of the PC beam placed on the jaw of the PC column is fixed with a predetermined fixing length, and PC tendons arranged in the PC beam and the PC column are penetrated or fixed to the column-beam joint and tension-fixed, so that prestresses σx, σy, and σz calculated by the following formulas (1), (2), and (3) in each axial direction are introduced into the column-beam joint. When the beam axis to be designed is taken as the X axis, σx ≥ 1.0 N / mm 2 is satisfied, a reduction coefficient (γ) is set according to the following formula (6), the required fixing length of the main reinforcement protruding from the end of the PC beam is calculated according to the following formula (4), and the above-mentioned predetermined fixing length is set to be not less than the calculated required fixing length.

Equation

Equation

Equation

Number

Advantages of the Invention

[0009] According to the present invention, at the column-beam joint, the required fixing length of the main reinforcement bars protruding from the end face of the PC beam can be determined reasonably and on the safe side. Therefore, at the column-beam joint, while ensuring the required strength, the congestion of the steel bars can be effectively alleviated. Thus, it is possible to improve the workability of the steel bar arrangement at the site, improve the economy by reducing the amount of steel bars used, and improve the filling property and compactness of the concrete.

Brief Description of the Drawings

[0010] [Figure 1] It is a cross-sectional view seen from the side of the joint between the middle column and the PC beam in a multi-story building to which the design method of the column-beam joint according to an embodiment of the present invention is applied. [Figure 2] It is a cross-sectional view seen from the side of the joint between the outer peripheral column and the PC beam in the same building. [Figure 3] It is a cross-sectional view of the PC beam. [Figure 4] It is a cross-sectional view seen from above of the arrangement of the lower-end steel bars of the PC beam and the PC cables at the joint with the middle column. [Figure 5] It is a cross-sectional view seen from above of the arrangement of the lower-end steel bars of the PC beam and the PC cables at the joint with the outer peripheral column. [Figure 6] It is a view showing the first specimen used in the verification experiment. [Figure 7] It is a view showing the second specimen used in the verification experiment. [Figure 8] It is a view showing the loading device used in the verification experiment. [Modes for carrying out the invention]

[0011] An embodiment of the present invention will be described below with reference to the attached drawings. The following description is essentially illustrative and is not intended to limit the present invention, its applications, or its uses.

[0012] [Overview of the building to be designed] First, with reference to Figures 1 to 5, the design method for the column-beam joint according to this embodiment and an overview of the structure and construction of Building 1 to which the column-beam joint structure is applied will be described.

[0013] In this embodiment, the present invention will be explained using Building 1 shown in Figures 1 to 5 as an example, but the present invention is not limited to Building 1 and can be applied to various structures in which PC beams are joined to PC columns via cast-in-place concrete.

[0014] Figures 1 to 5 are schematic diagrams to facilitate understanding of the present invention, and conventional components not directly related to the present invention are omitted. For example, reinforcement other than the main reinforcement of PC beams (except in Figure 3), and reinforcement arrangements for PC columns and column-beam joints are omitted. Regarding PC tensioning members, the members installed on-site are shown, and members assembled to PCa members in the factory are omitted. The foundation of building 1 is also omitted from the diagram, but the present invention is applicable to earthquake-resistant and base-isolated structures.

[0015] Figures 1 and 2 show the column-beam joints 50 (50A, 50C) and their surrounding areas on the general floors (floors below the top floor) of Building 1, and the column-beam joints 50 (50B, 50D) and their surrounding areas on the top floor. In particular, Figure 1 shows the column-beam joints 50 (50A, 50B) on the central columns, and Figure 2 shows the column-beam joints 50 (50C, 50D) on the outer perimeter columns.

[0016] As shown in Figures 1, 2, 4, and 5, Building 1 is a multi-story prestressed concrete structure. Building 1 is a rigid frame structure in which PC columns 2 and PC beams 10 and 20 are rigidly connected at column-beam joints 50. At each column-beam joint 50, the respective ends of the PC beams 10 and 20, which extend in two different directions, are placed on the jaws 4 of the same PC column 2 and connected to the PC column 2 via cast-in-place concrete. Prestress is applied to the PC columns 2 and PC beams 10 and 20 using a post-tensioning method.

[0017] The PC column 2 is composed of PCa members and is erected vertically (Z-axis direction) on the column-beam joints 50A, 50C of the lower floor or on the foundation (not shown). PC steel bars 6 are arranged in the PC column 2 as PC tensioning members, passing through in the column axis direction (Z-axis direction). The lower end of the PC steel bar 6 is connected to the upper end of the PC steel bar 6 on the lower floor via connectors 8a, 8b and connecting PC steel bars 9, or fixed to the foundation. The PC steel bar 6 is tensioned and fixed using anchoring devices 7 at the upper end of the PC column 2, with a predetermined length of length protruding upward.

[0018] As PC beams 10 and 20, a first prestressed concrete beam 10 (hereinafter also referred to as the "first PC beam") extends in the X-axis direction along the horizontal plane, and a second prestressed concrete beam 20 (hereinafter also referred to as the "second PC beam") extends in the Y-axis direction perpendicular to the X-axis direction along the horizontal plane.

[0019] Referring to the cross-sectional view in Figure 3, the configuration of the first PC beam 10 will be explained, but the configuration of the second PC beam 20 is the same as that of the first PC beam 10.

[0020] The first PC beam 10 is composed of a precast concrete beam member (hereinafter also referred to as "PCa beam member") 11 and top concrete 18 that is poured on-site onto the upper surface of the PCa beam member 11. The first PC beam 10 further comprises reinforcing bars 12. The reinforcing bars 12 include upper and lower reinforcement bars 13 and 14 as main reinforcement, stirrup reinforcement bars 15, and assembly reinforcement bars 16. Both the upper and lower reinforcement bars 13 and 14 are deformed reinforcing bars.

[0021] The reinforcing bars 12, with the exception of the upper reinforcing bars 13, are installed in the PCa beam member 11 by assembly in the factory. The stirrup reinforcing bars 15 are installed so as to protrude upward from the upper surface of the PCa beam member 11. The reinforcing bars are arranged so that only the lower reinforcing bars 14 protrude from the end face of the PCa beam member 11 and are anchored in the cast-in-place concrete at each column-beam joint 50A, 50B, 50C, and 50D. When manufactured in the factory, it is preferable to place the assembled reinforcing bars 16 inside the PCa beam member 11 so as not to protrude from the end face of the PCa beam member 11.

[0022] On site, upper reinforcement bars 13 are placed on the protruding portions of the stirrup bars 15 on the upper side of the precast concrete beam member 11. The upper reinforcement bars 13 penetrate the column-beam joints 50A and 50C of the central column, and the ends of the upper reinforcement bars 13 are anchored to the column-beam joints 50B and 50D of the outer perimeter column.

[0023] The top concrete 18 is poured after the upper reinforcement bars 13 are placed, and the upper reinforcement bars 13 are positioned within the top concrete 18. Generally, the top concrete 18 and the slab 19 are poured simultaneously. Therefore, the first PC beam 10 is considered to have a T-shaped cross-section, and its effective width (B) is determined according to the calculation formula of the Reinforced Concrete Structural Calculation Standards (the current design standards defined in the "Reinforced Concrete Structural Calculation Standards and Commentary 2024 Revision (Architectural Institute of Japan)") (hereinafter also referred to as the "RC Standards").

[0024] In the plan view shown in Figures 4(a) and 5(a), at each column-beam joint 50, the lower reinforcement bars 14 protruding in the X-axis direction from the end face of the first PC beam 10 and the lower reinforcement bars 24 protruding in the Y-axis direction from the end face of the second PC beam 20 are arranged and anchored so as to intersect. Figures 4(a) and 5(a) show the anchorage length Lx of the lower reinforcement bars 14 in the X-axis direction and the anchorage length Ly of the lower reinforcement bars 24 in the Y-axis direction.

[0025] Although not shown in the diagram, at the column-beam joints 50C and 50D of the outer perimeter columns, the upper reinforcement bars 13 in the X-axis direction and the upper reinforcement bars 23 in the Y-axis direction are arranged and anchored so as to intersect in a plan view, similar to the lower reinforcement bars 14 and 24.

[0026] For the cast-in-place construction of the column-beam joint 50, the strength should be matched to that of the PC column 2 and PCa beam member 11, with a strength of 50 N / mm². 2 High-strength concrete with the above design strength (Fc) is used. On the other hand, since the top concrete 18 is formed integrally with the cast-in-place slab 19, 30 N / mm 2 Ordinary concrete with a design strength (Fc) of a certain degree is used. Therefore, the concrete placement process is carried out in two stages. Specifically, after the high-strength concrete is placed at the column-beam joint 50, the top concrete 18 and slab 19 are placed.

[0027] As shown in Figures 1 and 2, both ends of the first PC beam 10 are rested on the jaws 4 of the PC column 2. A PC cable 30, for example, is placed through the PCa beam member 11 in the beam axis direction (X axis direction) as a PC tensioning member. The PC cable 30 passes through the column-beam joints 50A and 50C of the central column and is tensioned and anchored at the column-beam joints 50B and 50D of the outer column using a fixing device 32 (see Figure 2). This applies prestress to the first PC beam 10.

[0028] Similarly, the second PC beam 20 is also placed on the jaw 4 of the PC column 2 and prestressed by a PC cable 40 that penetrates in the beam axis direction (Y axis direction).

[0029] The tensioning and anchoring of the PC cables 30 and 40 are carried out sequentially after the cast-in-place concrete of the column-beam joint 50 and the top concrete 18 (and slab 19) has hardened. Subsequently, the PC columns 2 and PC steel bars 6 of the upper floors are positioned in the same manner as described above.

[0030] As shown in Figures 4(b) and 5(b), each column-beam joint 50 is subjected to a tension force Px in the X-axis direction applied to the first PC beam 10 by the PC cable 30, and a tension force Py in the Y-axis direction applied to the second PC beam 20 by the PC cable 40. In addition, the column-beam joints 50A and 50C on the general floors are further subjected to a tension force in the Z-axis direction applied to the PC column 2 by the PC steel bar 6 (see Figures 1 and 2). As a result, the main reinforcement bars (upper reinforcement bars 13, 23 and lower reinforcement bars 14, 24) placed in the column-beam joints 50A and 50C on the general floors are constrained by prestress introduced in three directions (X, Y, and Z axis directions).

[0031] [Design of column-beam joints] The design method for the column-beam joint 50 according to this embodiment will be described below. In this embodiment, the required anchorage length of the main reinforcement bars to be placed in the column-beam joint 50 is calculated as follows.

[0032] Specifically, the lower reinforcement bars 14 of the first PC beam 10 and 24 of the second PC beam 20, which are anchored at each column-beam joint 50A, 50B, 50C, and 50D, are included in the calculation of the required anchorage length. In addition, the upper reinforcement bars 13 of the first PC beam 10 and 23 of the second PC beam 20, which are anchored at the column-beam joints 50C and 50D of the outer perimeter columns, are also included in the calculation of the required anchorage length. Note that for the column-beam joints 50A and 50B of the central columns, it is not necessary to calculate the required anchorage length for the upper reinforcement bars 13 and 23, which are continuous reinforcement bars.

[0033] In this embodiment, considering the effect of the main reinforcement on the concrete due to the prestress introduced into the column-beam joint 50, the required anchorage length of the main reinforcement placed in the column-beam joint 50 is calculated according to the magnitude of the prestress.

[0034] With respect to the X-axis, if the prestress is σx, the tension introduction force is Px, and the cross-sectional area of ​​the beam end of the first PC beam 10 is Ax, then σx = Px / Ax. With respect to the Y-axis, if the prestress is σy, the tension introduction force is Py, and the cross-sectional area of ​​the beam end of the second PC beam 20 is Ay, then σy = Py / Ay. With respect to the Z-axis, if the prestress is σz, the tension introduction force is Pz, and the cross-sectional area of ​​the column end of the PC column 2 is Az, then σz = Pz / Az.

[0035] In this embodiment, if the prestress is below a certain level, the restraining effect may be weak. Therefore, to be on the safe side, the required anchorage length of the main reinforcement is calculated according to the conventional RC standard.

[0036] Specifically, the required anchorage length (lab) of the tensile reinforcement for deformed reinforcing bars as defined in the RC standard is calculated according to the following formula (S1). In the following formula (S1), fd is the strength that serves as the basis for bond splitting, and σ t This is the short-term allowable stress of the reinforcing bars at the joint surface, and d b α is a numerical value used in the designation of deformed reinforcing bars, where α is 1.0 (when anchored within a core restrained by lateral reinforcing bars) or 1.25 (otherwise), and S is a correction factor for the required anchorage length (1.25 in the case of straight anchorage).

number

[0037] On the other hand, if the prestress is above a certain level, specifically, 1.0 N / mm² is applied to the column-beam joint 50. 2 When the above prestressing is applied, the required anchorage length (l) of the main reinforcement bars (bottom reinforcement bars 14, 24 and top reinforcement bars 13, 23) at the column-beam joint 50 is calculated according to the following method. Note that the calculation of the required anchorage length (l) is based on deformed reinforcement bars only.

[0038] First, in order to calculate the required anchorage length (l), a reduction factor (γ) is set that takes into account the restraint effect due to prestress, and γ ≤ 0.85 is set to at least. The method for setting the reduction factor (γ) will be explained later.

[0039] Next, the required anchorage length (l) of the main reinforcement at the column-beam joint 50 is calculated according to the following formula (1), which multiplies the required anchorage length (lab) specified in the RC standard by a reduction factor (γ). This allows for a rational calculation of the required anchorage length (l) that has been reduced according to the restraint effect due to prestress.

number

[0040] The following explains how to set the reduction factor (γ).

[0041] Specifically, we will explain how to set the reduction coefficient (γ) using the example of calculating the required anchorage length (l) of the main reinforcement (bottom reinforcement 14 and top reinforcement 13) of the first PC beam 10. In this case, the prestress (σx) introduced into the column-beam joint 50 in the X-axis direction is 1.0 N / mm 2 If the above conditions are met, the reduction factor (γ) is set, and the required anchoring length (l) is calculated according to the above formula (1).

[0042] Furthermore, for the main reinforcement bars (bottom reinforcement bars 24 and top reinforcement bars 23) of the second PC beam 20, the reduction coefficient (γ) can be set and the required anchorage length (l) can be calculated according to the above formula (1) by swapping the settings for the X-axis and Y-axis directions.

[0043] First, a first coefficient (γx) is set to 0.85, taking into account the constraint effect due to prestress in the X-axis direction. Based on this first coefficient (γx), a reduction coefficient (γ) is set.

[0044] In the setting of the reduction coefficient (γ), not only the prestress in the X-axis direction (σx), but also the prestress in the Y-axis direction (σy) and the prestress in the Z-axis direction (σz) are considered. In the column-beam joints 50A and 50C of the general floors, prestresses in three directions (X, Y, and Z-axis directions) (σx, σy, σz) are introduced, but the setting of the reduction coefficient (γ) varies depending on the strength of the prestress (σx, σy, σz) in each direction. In the column-beam joints 50B and 50D of the top floor, usually no prestress in the Z-axis direction (σz) is introduced (see FIGS. 1 and 2), so in principle, the reduction coefficient (γ) is set according to the strength of the prestresses in two directions (X and Y-axis directions) (σx, σy). Specifically, the reduction coefficient (γ) is set as follows.

[0045] The prestress in the X-axis direction (σx) is 1.0 N / mm 2 or more, and the prestresses in the Y-axis direction (σy) and the Z-axis direction (σz) are less than 1.0 N / mm 2 In this case, only the prestress in the X-axis direction is evaluated as effective in restraining the main reinforcement against the concrete of the column-beam joint 50. In this case, the reduction coefficient (γ) is set according to the following formula (2).

Equation

[0046] The prestresses in the X-axis direction (σx) and the Y-axis direction (σy) are 1.0 N / mm 2 or more, and the prestress in the Z-axis direction (σz) is less than 1.0 N / mm 2 In this case, not only the X-axis direction but also the restraining effect in the Y-axis direction is evaluated as effective. In this case, after setting the second coefficient (γy) considering the restraining effect by the prestress in the Y-axis direction to 0.9, the reduction coefficient (γ) is set according to the following formula (3).

Equation

[0047] The prestresses in the X-axis direction (σx) and the Z-axis direction (σz) are 1.0 N / mm2 The above results indicate that the prestress in the Y-axis direction (σy) is 1.0 N / mm 2 If the value is less than the specified value, the constraint effect in the Z-axis direction as well as the X-axis direction is considered effective. In this case, a third coefficient (γz) that takes into account the constraint effect due to prestress in the Z-axis direction is set to 0.9, and then the reduction coefficient (γ) is set according to equation (4) below.

number

[0048] The prestress (σx, σy, σz) in all three directions (X, Y, Z axis) is 1.0 N / mm 2 If the above conditions are met, the constraint effect in all three directions is evaluated as effective. In this case, the first coefficient (γx), the second coefficient (γy), and the third coefficient (γz) are set in the same manner as above, and the reduction coefficient (γ) is set according to the following equation (5).

number

[0049] According to this embodiment, as described above, the required anchorage length (l) of the main reinforcement is determined rationally and safely using a reduction coefficient (γ) set according to the prestress introduced into the column-beam joint 50. Therefore, in the column-beam joint 50, congestion of reinforcement can be effectively alleviated while ensuring the necessary strength. Consequently, improvements can be made to the workability of reinforcement placement at the site, economic efficiency by reducing the amount of reinforcement used, and the filling and density of the concrete.

[0050] Although the present invention has been described above with reference to the embodiments described above, the present invention is not limited to the embodiments described above.

[0051] For example, regarding the restraint effect due to prestress (σz) in the vertical direction (Z-axis direction), if the restraint effect of stress due to column axial force is obtained similarly, not limited to prestress by PC tensioning members, the column to which the PC beam is connected is not limited to a PC column, but may also be an RC column. In this case, it is important to note that the axial force differs depending on the type of load. Generally, the loads acting on a building include dead loads due to the self-weight of structural members and finishes, live loads due to the weight of movable objects such as people and furniture, and horizontal loads due to wind and earthquakes. Since live loads and horizontal loads are constantly changing, the axial forces due to these loads also change. Therefore, it is preferable to consider the axial force due to prestress by PC tensioning members and / or dead loads without considering the restraint effect of axial force due to live loads and horizontal loads.

[0052] [Demonstration experiment] The inventor of this application conducted the following demonstration experiment to confirm the validity of the relationship between the prestress introduced into the column-beam joint and the required anchorage length of the main reinforcement calculated accordingly.

[0053] The demonstration experiment used the first test specimen P1 shown in Figure 6, the second test specimen P2 shown in Figure 7, and the loading device 200 shown in Figure 8. The first test specimen P1 and the second test specimen P2 were fabricated at approximately 1 / 2 scale of the actual structure.

[0054] As shown in Figures 6 and 7, the first specimen P1 and the second specimen P2 each comprise a pair of column sections 102 of the same length, a pair of first beam sections 110a and 110b of different lengths, and a pair of second beam sections 120a and 120b of the same length. The column sections 102, the first beam sections 110a and 110b, and the second beam sections 120a and 120b are arranged orthogonally to each other and joined to each other at a column-beam joint 150. The beam axis direction of the first beam sections 110a and 110b is the X-axis direction, the beam axis direction of the second beam sections 120a and 120b is the Y-axis direction, and the column axis direction of the column section 102 is the Z-axis direction.

[0055] In the first specimen P1 and the second specimen P2, an upper reinforcement bar 113 was provided that extended through the column-beam joint 150 from the beam end of one first beam section 110a to the beam end of the other first beam section 110b, and a lower reinforcement bar 114 was provided that was placed in one first beam section 110a and anchored at the column-beam joint 150. The anchorage length L of the lower reinforcement bar 114 at the column-beam joint 150 was set to 278 mm. In contrast, the required anchorage length (lab) calculated according to the RC standard is 325 mm. In other words, the anchorage length L of the first specimen P1 and the second specimen P2 is approximately 0.85 times the required anchorage length (lab) according to the RC standard.

[0056] Furthermore, in the first specimen P1 and the second specimen P2, a PC cable extending in the X-axis direction was tensioned and anchored at the beam ends of the first beam sections 110a and 110b, with the cable passing through the column-beam joint 150. The column section 102 was an RC column, and no tensioning members were placed there.

[0057] In the first specimen P1 shown in Figure 6, no tensioning members were placed in the second beam sections 120a and 120b. However, in the second specimen P2 shown in Figure 7, a PC steel bar 140 extending in the Y-axis direction was tensioned and anchored at the beam ends of the second beam sections 120a and 120b, passing through the column-beam joint 150.

[0058] The demonstration experiment was conducted on the first and second test specimens P1 and P2, which were set in the loading device 200 in the posture shown in Figure 8, based on the parameters shown in Table 1 below. In the demonstration experiment, alternating positive and negative loads were applied to the long first beam section 110a by the actuator 202 of the loading device 200. [Table 1]

[0059] Furthermore, for the first specimen P1 and the second specimen P2, σx = 1.27 N / mm² was used for the rectangular cross-section of the beam without a slab. 2 However, when converted to the T-beam section with slab in the detailed design, σx = 1.0 N / mm 2 It corresponds to a certain degree.

[0060] Table 2 below shows the results of the demonstration experiment. These results demonstrate the following: [Table 2] Note that the strain gauges shown in Table 2 were attached to the upper and lower reinforcement bars within the column-beam joint (panel zone).

[0061] Based on the experimental results of the first specimen P1, it can be evaluated that setting the reduction coefficient (γ) = first coefficient (γx) = 0.85 is appropriate and safe when only prestress in the X-axis direction (σx) is introduced and prestress in the Y-axis direction (σy) is not introduced.

[0062] While the first specimen P1 showed yielding of the tensile reinforcement, the second specimen P2 showed fracture of the tensile reinforcement. In the second specimen P2, the fracture load Ft / yield load Fy was 1.4 times higher, but no pull-out of the reinforcement occurred. From these results, it can be concluded that when prestress in the Y-axis direction (σy) is introduced in addition to prestress in the X-axis direction (σx), as in the second specimen P2, setting the second coefficient (γy) to 0.9 is appropriate and safe, taking safety into consideration.

[0063] In the demonstration experiment, no prestress (σz) was applied in the column axis direction (Z axis direction), but 1.0 N / mm² was applied in the Z axis direction. 2 When the above prestress (σz) is added, it is estimated that a similar restraint effect in the column axis direction will be obtained. Therefore, setting the third coefficient (γz) = 0.9 can be evaluated as reasonable and safe. [Explanation of symbols]

[0064] 1. Building 2 PC pillar 4. Jaw 6, 9 PC steel bar 7 Fixing device 8a, 8b Connectors 10. First PC beam 11 PCa beam members 12 Reinforcing bars 13 Top bar 14 Bottom reinforcement 15 Stirrup muscles 16 Assembly bar 18 Top Concrete 19 Slab 20. Second PC beam 23 Top bar 24 Bottom reinforcement 30. First PC cable 32 Fixing device 40. Second PC cable 50A Column-beam joint in a central column on a general floor 50B Column-beam joint at the central column on the top floor 50C Column-beam joint in the outer perimeter column of a general floor 50D Column-beam joint in the outer perimeter column of the top floor 200 Loading device 202 Actuator P1 First specimen P2 Second test specimen

Claims

1. A design method for the PC column-beam joint of a rigid frame structure formed by PC beams in two planar directions (X and Y axes) and PC columns in the vertical direction (Z axis), The PC columns are made of precast concrete members, the PC beams are formed by combining precast concrete members and top concrete, and the column-beam joints are formed of cast-in-place high-strength concrete. The design standard strength Fc of the aforementioned high-strength concrete is 50 N / mm². ２ That concludes my presentation. In the column-beam joint, the main reinforcement bars protruding from the end of the PC beam, which is placed on the jaw of the PC column, are anchored to a predetermined anchorage length, and the PC tensioning members arranged in the PC beam and PC column are passed through or anchored to the column-beam joint and tensioned, thereby introducing prestresses σx, σy, and σz calculated by the following equations (1), (2), and (3) in each axial direction to the column-beam joint. When the beam axis to be designed is the X-axis, σx ≥ 1.0 N / mm ２ year, The reduction factor (γ) is set according to the following formula (6): A design method for a PC column-beam joint, characterized in that the required anchorage length of the main reinforcement protruding from the end of the PC beam is calculated according to the following formula (4), and the predetermined anchorage length is equal to or greater than the calculated required anchorage length. [Math 1] Here, Px: Tension introduction force in the X-axis direction Ax: Cross-sectional area of ​​the PC beam end in the X-axis direction Py: Tension-inducing force in the Y-axis direction Ay: Cross-sectional area of ​​the PC beam end in the Y-axis direction Pz: Tension introduction force in the Z-axis direction Az: Cross-sectional area of ​​the PC column end in the Z-axis direction [Math 2] Here, l: Required anchorage length of main reinforcement calculated considering the restraining effect of prestress. γ: The reduction coefficient considering the restraining effect due to prestress. lab: Required anchorage length of deformed reinforcing bars in RC standards, calculated according to formula (5) below. [Math 3] Here, fd: Strength that serves as the basis for adhesion splitting σt: Short-term allowable stress of reinforcing bars at the joint surface db: A numerical value used in the naming of deformed reinforcing bars. α: 1.0 if anchored within a core constrained by lateral reinforcement, 1.25 otherwise. S: This is the correction factor for the required anchoring length; in the case of straight anchoring, it is 1.

25. [Math 4] Here, γx: This is the reduction coefficient due to the prestress σx in the X-axis direction, where γx = 0.85

2. In setting the reduction coefficient (γ), σy ≥ 1.0 N / mm ２ year, The design method for a PC column-beam joint according to claim 1, characterized in that the reduction coefficient (γ) is set according to the following formula (7) instead of the above formula (6). [Math 5] Here, γx: This is the reduction coefficient due to the prestress σx in the X-axis direction, where γx = 0.85 γy: This is the reduction coefficient due to the prestress σy in the Y-axis direction, where γy = 0.9

3. In setting the reduction coefficient (γ), σz ≥ 1.0 N / mm ２ year, The design method for a PC column-beam joint according to claim 1, characterized in that the reduction coefficient (γ) is set according to the following formula (8) instead of the above formula (6). [Math 6] Here, γx: This is the reduction coefficient due to the prestress σx in the X-axis direction, where γx = 0.85 γz: This is the reduction coefficient due to the prestress σz in the Z-axis direction, where γz = 0.9

4. In setting the reduction coefficient (γ), σy ≥ 1.0 N / mm ２ , σz≧1.0N / mm ２ year, The design method for a PC column-beam joint according to claim 1, characterized in that the reduction coefficient (γ) is set according to the following formula (9) instead of the above formula (6). [Number 7] Here, γx: This is the reduction coefficient due to the prestress σx in the X-axis direction, where γx = 0.85 γy: This is the reduction coefficient due to the prestress σy in the Y-axis direction, where γy = 0.9 γz: This is the reduction coefficient due to the prestress σz in the Z-axis direction, where γz = 0.9

5. A PC column-beam joint structure designed by the design method described in any one of claims 1 to 4.

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