Calculation (evaluation) method for the anchorage strength of mechanical reinforcement anchoring methods

Abstract

[Problem] To improve the accuracy of the estimated anchorage strength calculation in mechanical rebar anchorage. [Solution] A method for calculating an estimated anchorage strength Pn when an anchorage member 2 fails due to cone-type failure against tensile force T generated in a main reinforcement 11, in the mechanical rebar anchorage where the main reinforcement 11 with anchorage hardware 40 attached to the end is disposed in the reinforced concrete structural anchorage member 2 and is anchored by the anchorage hardware 40. The anchorage strength Pn is calculated on the basis of the value obtained by multiplying the area of the side surface of a conical shape 50, which is assumed as the failure shape of the cone-type failure, by the tensile strength of the concrete against the cone-type failure.

Description

[Technical Field]

[0001] This invention relates to a mechanical rebar anchoring method for arranging and anchoring the ends of rebars fitted with anchoring hardware within concrete, and more specifically, to a method for calculating the anchoring strength. [Background technology]

[0002] Conventionally, the bending method, in which the ends of the reinforcing bars are bent at 90 or 180 degrees to form hooks, has been commonly used as an anchoring method for reinforcing bars in reinforced concrete structures (see, for example, Patent Document 1). However, in recent years, problems have arisen such as the increasing density and complexity of reinforcement due to the heightening of structures, making concrete pouring difficult, and the increasing strength of reinforcing bars making bending difficult.

[0003] To solve these problems, a mechanical reinforcement anchoring method is employed in which anchoring hardware is attached to the ends of the anchoring reinforcement bars (see, for example, Patent Document 2). In an anchoring member of reinforced concrete constructed using this method, the reinforcement portion and the anchoring hardware, which are required for the anchoring length, form the anchoring section, and the tensile force acting on the anchoring reinforcement is resisted by the adhesion force of the reinforcement portion and the bearing pressure of the anchoring hardware.

[0004] When the tensile force acting on the anchoring reinforcement exceeds this resisting force, anchoring failure occurs, resulting in a loss of anchoring force due to the destruction of the anchoring member (concrete) around the anchoring point. During anchoring failure, the adhesive force of the reinforcement is almost completely lost, and the anchoring strength is obtained from the bearing pressure of the anchoring hardware. Two types of anchoring failure are known: cone-shaped failure, in which the anchoring member is scraped out of the anchoring hardware in a cone shape, and lateral spalling failure, in which the lateral cover portion is pushed out due to the destruction of the concrete near the end of the reinforcement. The following formula (a) exists to calculate the anchoring strength during cone-shaped failure (Non-Patent Literature 1), and the following formula (b) exists to calculate the anchoring strength during lateral spalling failure (Non-Patent Literature 2).

[0005] (Math a) P = γ·0.31√F c ·A c···(a) P: Anchoring strength at the time of cone-shaped failure (N) γ: Coefficient for reducing cracks F c : Design standard strength of concrete (N / mm 2 ) !(0.31√F c : Tensile strength of concrete against cone-shaped failure) A c : Effective horizontal projected area of the cone-shaped failure surface (mm 2 ) (Equation b) P = k·a b ·σ std ···(b) P: Anchoring strength at the time of side peeling failure (N) k: Coefficient representing the influence of the restraint effect by the reinforcement a b : Cross-sectional area of the reinforcing bar (mm 2 ) σ std : Stress of the reinforcing bar at the time of anchoring failure without reinforcement (N / mm 2 )

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] There is no continuity between the above calculation formula (a) and calculation formula (b), and each formula must be used for calculation of the anchorage strength. Furthermore, these formulas were derived from experiments at various joints of concrete structures, and calculations could not be performed when the experimental range was exceeded, requiring verification through new experiments. In particular, the experimental range for calculation formula (b) was limited in terms of joint conditions, anchorage length, and materials used.

[0009] In the above calculation formula (a), the tensile strength of concrete against cone-shaped failure is (0.31√F). c ) is the effective horizontal projection area of ​​the cone-shaped fracture surface (A c The cone-shaped fracture resistance P is calculated based on the product obtained by multiplying by ).

[0010] For example, as shown in Figure 7(A), when the tip of the upper main reinforcement 21 of a beam to which anchoring hardware 40 is attached is placed within a T-shaped joint 30 connecting a column 10 and a beam 20, and a tensile force T acts on the upper main reinforcement 21, causing a cone-shaped failure surface Cs, the calculation of the cone-shaped failure strength P uses the area of ​​the portion Cp obtained by projecting the cone-shaped failure surface Cs onto the side surface of the column 10, as shown in Figure 7(B). This reduced the accuracy of the calculation.

[0011] Furthermore, the crack reduction coefficient (γ) used in the above calculation formula (a) is a coefficient that takes into account cracks crossing the cone-shaped failure surface when anchored to a joint of a concrete structure, for example, and is an approximation of the value obtained experimentally. As a result, the application of the calculation formula was limited to the experimental range in which the formula was derived, and the calculated anchorage strength was underestimated compared to the actual anchorage strength due to the reduction coefficient (γ). [Means for solving the problem]

[0012] The present invention has been made to solve at least one of the above problems, and a method for calculating the fixing strength of a mechanical rebar fixing according to one aspect of the present invention arranges a fixing rebar having a fixing hardware attached to an end portion in a fixing member of a reinforced concrete structure, and in the mechanical rebar fixing fixed by the fixing hardware, it is a method for calculating an estimated fixing strength when the fixing member undergoes fixing failure due to conical failure with respect to the tensile force generated in the fixing rebar, and based on the product of the area of the side surface of the conical shape assumed as the failure shape of the conical failure and the tensile strength of the concrete with respect to the conical failure, it is characterized by calculating the fixing strength including not only conical failure but also side surface peeling failure.

[0013] According to the above configuration, it can be applied to the calculation of the fixing strength under various conditions. Further, by assuming a conical shape as the failure shape of the conical failure and using the area of its side surface for the calculation of the fixing strength, the accuracy of the calculation can be improved.

[0014] Preferably, in the above fixing strength calculation method, a reference value calculation step of calculating a reference value of the fixing strength by multiplying the coefficient regarding the ratio of the inner side surface of the fixing member within the fixing member among the side surfaces of the conical shape by the above product; among the inner side surfaces of the fixing member of the conical shape, a portion having a symmetric shape centered on the fixing rebar and the fixing hardware is defined as a symmetric portion, and a portion excluding the symmetric portion is defined as an asymmetric portion, and a loss strength value lost due to the asymmetry of the asymmetric portion is obtained by multiplying the coefficient regarding the ratio of the asymmetric portion by the reference value of the fixing strength, and a lower limit value calculation step of calculating the lower limit value of the fixing strength by subtracting this from the reference value; an estimated strength value calculation step of calculating the value of the estimated fixing strength by multiplying the coefficient regarding the ratio that the transmission force of the reinforcing bar crossing the inner side surface of the fixing member of the conical shape can contribute to the fixing strength by the loss strength value and adding this to the lower limit value, and is characterized by including these steps.

[0015] According to the above configuration, the accuracy of the calculation of the estimated anchorage strength can be further improved by considering the area of ​​the failure surface within the anchorage member, the symmetrical and asymmetrical portions of the failure surface within the anchorage member, and the transmission force of the reinforcing bars crossing the inner surface of the conical anchorage member. [Effects of the Invention]

[0016] According to the present invention, the accuracy of calculating the estimated anchoring strength can be improved. [Brief explanation of the drawing]

[0017] [Figure 1] This perspective view shows the conical shape expected as the failure pattern of a cone-shaped fracture when tensile force is applied to a reinforcing bar that is placed within a fixing member and to which fixing hardware is attached. [Figure 2] This is a perspective view showing a mechanically anchored column-beam joint according to a first embodiment of the present invention, and shows the failure surface that is expected to occur when tensile force is applied to the main column reinforcement located at the corner on the tip side of the main beam reinforcement, causing cone-shaped failure. [Figure 3] (A) A perspective view showing the assumed fracture surface of Figure 2 in isolation. (B) A perspective view showing the assumed fracture surface of Figure 2 in isolation, with the symmetrical and asymmetrical parts shown separately. [Figure 4] This is a perspective view showing a mechanically anchored reinforcement bar at a column-beam joint according to a second embodiment of the present invention, and shows the failure surface assumed when tensile force is generated in the main column reinforcement bar located at the inner corner of the column and beam, causing cone-shaped failure. [Figure 5] (A) A perspective view showing the assumed fracture surface of Figure 4 in isolation. (B) A perspective view showing the assumed fracture surface of Figure 4 in isolation, with the symmetrical and asymmetrical parts shown separately. [Figure 6] This is a schematic diagram of a reinforced concrete structure with columns and beams. [Figure 7] This is a schematic diagram for explaining the conventional calculation of anchorage strength, showing a state in which tensile force is applied to the main reinforcement of a beam with anchorage hardware at the tip placed inside a T-shaped column-beam joint, (A) is a view from the front, and (B) is a view from the side. [Modes for carrying out the invention]

[0018] [First Embodiment] The method for calculating the anchorage strength of a mechanically-type reinforced concrete anchorage system according to the first embodiment of the present invention will be described below with reference to Figures 1 to 3 and Figure 6. This embodiment applies the present invention to the calculation of the anchorage strength at a column-beam joint of a reinforced concrete structure.

[0019] The reinforced concrete structure 1 shown in Figure 6 has columns 10, beams 20, and column-beam joints 30 to which the columns 10 and beams 20 are connected. The column-beam joints 30 include a T-shaped joint 30a to which the end of the beam 20 is connected to the column 10, a T-shaped joint 30b to which the upper end of the column 10 is connected to the beam 20, and an L-shaped joint 30c to which the upper end of the column 10 is connected to the end of the beam 20.

[0020] Figure 2 shows the structure of the L-shaped joint 30c according to this embodiment, but the column 10 is partially omitted from the illustration. The beam 20 has a plurality of upper main reinforcement bars 21 (four in this embodiment) that extend parallel to each other in the same horizontal plane, and a plurality of lower main reinforcement bars 22 (four in this embodiment) that extend parallel to each other in another horizontal plane below. The upper main reinforcement bars 21 and lower main reinforcement bars 22 are embedded in concrete Cn, and within the L-shaped joint 30c, a hook 21a bent vertically downward is formed at the tip of each upper main reinforcement bar 21, and a hook 22a bent vertically upward is formed at the tip of each lower main reinforcement bar 22.

[0021] Column 10 is equipped with multiple main reinforcement bars 11 (anchoring bars) positioned at the corners and sides of the virtual rectangle, but Figure 2 shows only the two main reinforcement bars 11 positioned at the corners (outer corners) on the tip side of the main reinforcement bars 21 and 22 of the beam at the L-shaped joint 30c. Column 10 is equipped with multiple rectangular shear reinforcement bars 12 (reinforcement bars) surrounding the multiple main reinforcement bars 11, and the shear reinforcement bars 12 are spaced apart in the longitudinal direction of the main reinforcement bars 11. The main reinforcement bars 11 and the shear reinforcement bars 12 are connected at their intersections with wire or the like and embedded in the concrete Cn.

[0022] In this embodiment, threaded reinforcing bars having threaded joints are used for the main reinforcement bars 11, but ordinary deformed reinforcing bars having longitudinal ribs and transverse joints may also be used. Within the L-shaped joint 30c, anchoring hardware 40 having flange portions 41 that protrude radially from the main reinforcement bars 10 is attached to the tip of each main reinforcement bar 11. As a result, mechanical reinforcement is anchored in the L-shaped joint 30c by the main reinforcement bars 10 and the anchoring hardware 40.

[0023] Figure 1 shows the case where a main reinforcement bar 11 with an anchoring hardware 40 attached is placed inside a rectangular parallelepiped anchoring member 2 made of concrete Cn. Inside the anchoring member 2, the anchoring length portion 11a of the main reinforcement bar 11, which has the required length as the anchoring length, and the anchoring hardware 40 form the anchoring portion 40A. The tensile force T acting in the axial direction of the main reinforcement bar 11 is resisted by the adhesive force of the anchoring length portion 11a and the bearing pressure of the anchoring hardware 40. When the tensile force T exceeds the anchoring strength, a cone-shaped failure, which is anchoring failure, occurs, and the anchoring member 2 is scraped out from the anchoring hardware 40 in a cone shape.

[0024] When a tensile force T is applied to the main reinforcement 11, within the anchoring member 2, the adhesion force and bearing pressure transmitted to the anchoring portion 40A are supported through the stress at the part that becomes the fracture surface during cone-shaped failure. When this stress exceeds the concrete strength, cone-shaped failure occurs.

[0025] Therefore, if we assume a cone shape 50 (cone shape) as the failure shape of cone-shaped failure, the side surface 51 of the cone shape 50 becomes the expected failure surface, and the bearing capacity of the cone-shaped failure (ultimate reinforcement anchoring capacity) can be calculated by the product of the area of ​​the side surface 51 and the concrete tensile strength. The cone shape 50 is specified so that the side surface 51 is at a 45-degree angle to the main reinforcement 11.

[0026] Similarly, in the case of the L-shaped joint 30c shown in Figure 2, if we consider the L-shaped joint 30c as the anchoring member 2 and assume a conical shape 50 as the failure shape of the cone-shaped failure caused by the tensile force T generated in the main reinforcement 11 at the outer corner, then the conical shape 50 does not fit within the L-shaped joint 30c, i.e., the anchoring member 2. The assumed failure surface is the side surface 51i (inner surface of the anchoring member) of the conical shape 50 that fits within the anchoring member 2, resulting in the shape shown in Figure 3(A). Therefore, in calculating the anchoring strength, it is necessary to consider the side surface 51i that fits within the anchoring member 2 as the assumed failure surface.

[0027] Therefore, regarding the estimated anchoring strength Pn when the main reinforcement 11 shows cone-shaped failure due to tensile force T as shown in Figure 2, if we let C be the coefficient relating to the ratio of the area of ​​the side surface 51i that fits within the anchoring member 2 to the side surface 51 of the cone shape 50, then the upper limit value maxPn can be obtained using the following equation (1-1) as the upper limit equation, and the standard value Pn0 can be obtained using the following equation (1-2) as the standard equation. (Math 1-1) Upper limit formula: maxPn=A×B (1-1) (Math 1-2) Standard formula: Pn0=A×B×C (1-2) A: Area of ​​the lateral surface of the cone shape assumed as the fracture shape. B: Tensile strength of concrete considering the angle between the assumed failure surface and the anchoring reinforcement. C: Coefficient relating to the ratio of the area of ​​the side surface that fits within the fixing member to the area of ​​the side surface of the cone shape.

[0028] As shown in Figure 3(B), the side surface 51i (assumed failure surface) contained within the anchoring member 2, which is considered in the calculation of formula (1) above, has a symmetrical portion 51a, which is a part with a symmetrical shape around the main reinforcement 11 and the anchoring hardware 40, and an asymmetrical portion 51b (the part of the side surface 51i contained within the anchoring member 2 excluding the symmetrical portion 51a), which has an asymmetrical shape. In the symmetrical portion 51a, anchoring strength can be secured due to the symmetry of its shape, but in the asymmetrical portion 51b, anchoring strength is lost due to the asymmetry of its shape.

[0029] Therefore, in calculating the anchoring strength Pn, it is necessary to subtract the loss of strength due to the asymmetry of the asymmetrical part 51b, which corresponds to the ratio of the asymmetrical part 51b to the side surface 51i that fits within the anchoring member 2, from the standard value Pn0 obtained by the above formula (1-2).

[0030] Therefore, the coefficient D relating to the ratio of the area of ​​the asymmetric portion 51b to the side surface 51i is multiplied by the reference value Pn0 obtained by the above formula (1-2) to obtain the loss of load-bearing capacity D*Pn0 due to the asymmetry of the asymmetric portion 51b, and the lower limit value minPn can be obtained by subtracting this from the above reference value Pn0 using the following formula (2). (Math 2) Lower limit formula: minPn=(1-D)×Pn0...(2) D: Coefficient relating to the ratio of the area of ​​the asymmetrical portion to the area of ​​the side surface that fits within the fixing member.

[0031] In the calculation of equation (2) above, it was assumed that the anchorage strength is lost in the asymmetrical section 51b due to asymmetry. However, as shown in Figure 2, if there is a transmission force Tr of the shear reinforcement 12 (reinforcement bars) that crosses the side surface 51i (assumed failure surface) within the anchorage member 2, the transmission force Tr can contribute to the anchorage strength Pn by taking the equilibrium force Tb at the side surface 51i as the incorporated strength due to the balance of forces between the main reinforcement 11 and the shear reinforcement 12.

[0032] Therefore, by multiplying the coefficient E relating to the contribution ratio of the transmission force Tr to the anchorage strength Pn by the above-mentioned loss strength value D*Pn0, we obtain the calculated strength value D*E*Pn0 based on the transmission force Tr of the shear reinforcement 12, and by adding this to the lower limit minPn obtained in (2) above, we can calculate the estimated anchorage strength value Pn using the following equation (3) as the estimated strength equation. (Math 3) Estimated strength formula: Pn={1-D×(1-E)}×Pn0...(3) E: A coefficient relating to the proportion of the loss of strength due to asymmetry that can be contributed to by the transmission force of reinforcing bars crossing the side surface within the anchoring member.

[0033] According to the above embodiment, by assuming a conical shape 50 as the fracture shape of the cone-shaped fracture and using the area of ​​its side surface 51 to calculate the estimated anchoring strength Pn, the accuracy of the anchoring strength calculation can be improved compared to the conventional method of using the effective horizontal projection area of ​​the cone-shaped fracture surface.

[0034] Furthermore, the accuracy of the calculation of the estimated anchorage strength Pn can be further improved by considering the area of ​​the side surface 51i (assumed failure surface) contained within the anchorage member 2, the symmetrical portion 51a and asymmetrical portion 51b of the side surface 51i, and the transmission force Tr of the shear reinforcement bars 12 crossing the side surface 51i.

[0035] Furthermore, since the expected anchoring strength at the time of failure is calculated using the theoretical estimation strength formula, it can be applied to calculating the anchoring strength of cone-shaped failures under various conditions, as well as to calculating the anchoring strength of lateral delamination failures and the like.

[0036] Next, other embodiments of the present invention will be described. In the following embodiments, only configurations that differ from the above embodiments will be described, and similar components will be denoted by the same reference numerals and their descriptions will be omitted.

[0037] [Second Embodiment] Figures 4 and 5 show a second embodiment of the present invention. This embodiment calculates the anchorage strength of column main reinforcement at a different location within the column-beam joint compared to the first embodiment.

[0038] In the L-shaped joint 30c shown in Figure 4, we consider a case where a cone-shaped failure occurs due to the tensile force T generated in the main reinforcement 11 located at the inner corner (inner corner) of the column 10 and beam 20. In this case, the expected cone shape 50 does not fit within the L-shaped joint 30c, and a portion of it extends into the interior of the beam 20 adjacent to the L-shaped joint 30c.

[0039] In other words, in this embodiment, the L-shaped joint 30c and the beam 20 serve as the anchoring member 2, and the coefficient C relating to the ratio of the surface area of ​​the side that fits within the anchoring member in the above standard formula (formula (1-2)) is determined based on the shape of this anchoring member 2.

[0040] The fracture surface assumed in this embodiment, the side surface 51i that fits within the fixing member 2, has the shape shown in Figure 5(A) and has a symmetrical portion 51a and an asymmetrical portion 51b as shown in Figure 5(B).

[0041] It should be noted that the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. In the above embodiment, the conical shape 50 assumed as the fracture shape of cone-shaped fracture is defined such that the side surface 51 is inclined at a 45-degree angle with respect to the main reinforcement bar 11, but it may be defined at other inclination angles. In the above embodiment, a cone shape 50 was assumed as the fracture shape of the cone-shaped fracture, but the cone shape may be a frustocone shape or other shapes. In the above embodiment, the calculation of the anchorage strength of the mechanically anchored reinforcement bars for the main reinforcement bars 11 of the column 10 was described, but other types of reinforcement bars may also be used. In the above embodiment, the calculation of the anchoring strength of the mechanical reinforcement anchoring of the L-shaped joint 30c was described, but it may also be applied to the G-shaped joint 30a, the T-shaped joint 30b, and other anchoring members. [Industrial applicability]

[0042] This invention can be applied to a method for calculating the anchoring strength in a mechanical reinforcement anchoring method. [Explanation of symbols]

[0043] 1. Reinforced concrete structure 2 Fixing member 10 pillars 11 Main reinforcement (anchoring reinforcement) 11a Fixing length portion 12 Shear reinforcement bars 20 beams 21 Upper main reinforcement 21a Hook 22 Lower main reinforcement 22a Hook 30 Column beam joint 30a T-shaped joint 30b T-joint 30c L-shaped joint 40 Fixing hardware 40A Fixing section 41 Guard section 50 Conical shape 51 Conical side 51i Side surface that fits within the anchoring member (inner surface of the anchoring member, assumed failure surface) 51a Symmetrical part 51b Asymmetrical part Cn Concrete Cs cone-shaped fracture surface Projected portion of the cone-shaped fracture surface of Cp T Tensile force Tr Communication ability Tb balancing force

Claims

1. A method for calculating the estimated anchoring strength in a mechanical reinforced concrete anchoring system, in which anchoring reinforcement bars with anchoring hardware attached to their ends are placed within an anchoring member and anchored by the anchoring hardware, when the anchoring member fails due to cone-shaped fracture in response to tensile force generated in the anchoring reinforcement bars, A method for calculating the anchorage strength of mechanically installed reinforcing bars, characterized by calculating the anchorage strength including not only cone-shaped failure but also lateral spalling failure based on the product of the area of ​​the cone-shaped side surface, which is assumed to be the failure shape of cone-shaped failure, and the tensile strength of the concrete against cone-shaped failure.

2. In the method for calculating anchorage strength according to claim 1, A standard value calculation step involves multiplying the above product by a coefficient relating to the ratio of the inner surface of the anchoring member to the side surface of the conical shape described above, which is located within the anchoring member, to calculate a standard value for the anchoring strength. A lower limit calculation step is performed by multiplying the standard value of the anchoring strength by a coefficient relating to the proportion of the asymmetrical portion, thereby obtaining the value of the loss of anchoring strength due to the asymmetry of the asymmetrical portion, and subtracting this from the standard value to calculate the lower limit of the anchoring strength. The estimated strength value calculation process involves multiplying the above-mentioned loss of strength value by a coefficient relating to the proportion that can be contributed to the anchoring strength by the transmission force of the reinforcing bars crossing the inner surface of the above-mentioned conical anchoring member, thereby obtaining an incorporated strength value based on the transmission force of the above-mentioned reinforcing bars, and adding this to the above-mentioned lower limit value to calculate the estimated anchoring strength value. A method for calculating the anchorage strength of a mechanically constructed reinforced concrete anchorage system, characterized by having the following features.

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