JP4867370B2 - Shear reinforcement structure, shear reinforcement method, reinforced concrete member - Google Patents

Description

  The present invention relates to a shear reinforcement structure and method for a reinforced concrete member subjected to a shear load.

  A method of improving the shear strength of a reinforced concrete member by using a method in which a shear reinforcing bar is previously installed in the concrete member is widely used so that the reinforced concrete member on which the shear load acts does not cause a shear failure. In order to reliably perform shear reinforcement by such a method, it is ensured that stress is transmitted between the shear reinforcement bar and the concrete member constituting the reinforced concrete member. It is necessary to have a shear reinforcement structure fixed in the area. As such a shear reinforcing structure, a structure in which both ends of the shear reinforcing bar are bent into a hook shape and the shear reinforcing bar is arranged so that the hook-shaped portion is locked to the main reinforcing bar is widely used. ing.

  However, if the shear reinforcement bars are bent like hooks at both ends in this way, it becomes difficult to insert them between the main bars and place them at predetermined positions. Further, when the diameter of the shear reinforcing bar is increased, much labor is required to bend both ends of the deformed reinforcing bar into a hook shape. Therefore, as shown in FIG. 6, there may be used a shear reinforcement structure 20 in which shear reinforcement bars 32 each having a fixing tool 31 processed into a disk shape are arranged at both ends. According to such a configuration, the fixing tool 31 provided at both ends of the shear reinforcement bar 32 can improve the fixing strength, improve the shear strength of the concrete member, and improve the workability.

Further, as a construction method similar to this, Patent Document 1 describes a shear reinforcement structure having a fixing tool provided with a mechanical joint that is screwed into a thread reinforcing bar as a shear reinforcement bar.
Japanese Patent Laid-Open No. 2001-140405

  However, since the shear reinforcement structure having these fixing tools has a fixing structure larger than the shear reinforcement bars at both ends, it may be difficult to arrange the bars when the interval between the main reinforcing bars is narrow. Further, since the shear reinforcing bar having the fixing tool is expensive, there is a possibility that the cost required for the shear reinforcement is increased. The present invention has been made in view of the above problems, and an object thereof is to provide an inexpensive shear reinforcement structure that is easy to construct.

The shear reinforcement structure of the present invention is a shear reinforcement structure of a reinforced concrete member to which a shear load is applied, and is mainly embedded in the reinforced concrete member so as to intersect an oblique crack surface generated by the shear load. It is characterized in that a steel pipe is buried in a direction intersecting with the reinforcing bar.

Here, the steel pipe may have a shear strength greater than a shear load acting on the oblique crack surface. The steel pipe may be embedded in a reinforced concrete member substantially parallel to the direction of action of the shear load. According to the above-mentioned shear reinforcement structure, the steel pipe acts like a tenon on the oblique crack surface, so that the shear strength can be improved.
Further, the main reinforcing bars, the respective are set embedded in a predetermined overburden thickness from opposing surfaces of the reinforced concrete member, said steel pipe, so that its two ends extend to the surface side of the reinforced concrete than the main reinforcing bars It may be arranged.

Moreover, this invention shall include the reinforced concrete member provided with said shear reinforcement structure. Furthermore, the present invention is a method for reinforcing a reinforced concrete member on which a shear load acts, wherein the reinforced concrete member includes a main reinforcement embedded in the reinforced concrete member so as to intersect an oblique crack surface generated by the shear load. It shall include a shear reinforcement method characterized by embedding steel pipes in the intersecting direction .

  According to the present invention, the cost required for shear reinforcement can be reduced because the steel pipe is cheaper than the shear reinforcement having mechanical anchoring. Moreover, since there is no fixing tool provided at the end of the shear reinforcement bar of the conventional shear reinforcement structure in the steel pipe, the bar arrangement work is not difficult and the construction is facilitated.

Hereinafter, an embodiment of the shear reinforcement structure of the present invention will be described with reference to the drawings.
FIG. 1A is a cross-sectional view in the member axial direction of a reinforced concrete member 10 provided with a shear reinforcement structure 20 of the present embodiment, and FIG. 1B is a vertical cross-sectional view. As shown in the figure, the reinforced concrete member 10 includes a concrete member 12, a main reinforcing bar 11, and a distribution bar 13 provided so as to be orthogonal to the main reinforcing bar 11. Here, as shown in FIG. 1, it is assumed that a shear load P and a reaction force P ′ act on the reinforced concrete member 10. As will be described later, the shear load P and the reaction force P ′ cause an oblique crack surface (a surface on which cracks are likely to occur due to the shear load) as indicated by a dashed line in FIG.

The shear reinforcement structure 20 of the present embodiment is configured by a steel pipe 22 embedded in the concrete member 12 so as to intersect with the oblique crack surface. Further, the steel pipe 22 is arranged such that the axial direction is substantially parallel to the direction in which the shearing force is applied .

  Such a shear reinforcement structure 20, for example, when constructing a reinforced concrete member, restrains the steel pipe 22 with the main reinforcing bar 11 using a binding wire or the like when the main reinforcing bar 11 or the reinforcing bar 13 is arranged in advance. It can be constructed by placing the concrete by a method such as, and placing concrete.

  Examples of the reinforced concrete member 10 to be subjected to shear reinforcement by the shear reinforcement structure 10 of the present embodiment include, for example, columns and beams of reinforced concrete structures on which an out-of-plane shear force acts. The shear reinforcement structure of the present embodiment can be applied to any reinforced concrete member on which a shearing force acts.

  As an example, suppose that a shear load is applied to a simple beam of reinforced concrete members at any two locations symmetrical about the center of the beam (a constant shear force is generated in the concrete member between the action point and the fulcrum). The principle of improving the shear strength of the reinforced concrete member by the shear reinforcement structure will be described. In the following description, since the load acting on the reinforced concrete member is symmetric with respect to the center surface of the reinforced concrete member, an analysis model of one half of the reinforced concrete member is considered.

FIG. 2 is a diagram illustrating stress transmission in a reinforced concrete member in a state where a shear load is applied. As shown in the figure, in consideration of symmetry, the reinforced concrete member is in a balanced state by the acting load P ₁ and the fulcrum reaction force P ₂ (= P ₁ ) due to the reaction.

The concrete member in a balance state, the stress transmission mechanism for transmitting a compressive stress acting in the direction connecting the point P ₂ acting point and the fulcrum reaction force acting load P ₁ is formed. In addition, the stress transmission mechanism has a tensile stress that is substantially perpendicular to the direction in which the compressive stress acts, according to the theory of the Mole's stress circle. When the shear load acting on the reinforced concrete member increases, Tensile stress also increases. If the tensile stress becomes excessive and the concrete member 12 cannot withstand this tensile stress, the concrete member 12 will be obliquely cracked along the stress transmission mechanism, causing shear failure. That is, the oblique crack surface is generated in the direction connecting the point where the load acts and the point where the fulcrum reaction force acts.

  In the conventional shear reinforcement structure 30 as shown in FIG. 6, based on the idea that an excessive tensile stress that cannot be borne by the concrete member 12 is borne by the shear reinforcement bar 32, the tensile force of the stress transmission mechanism is increased in the reinforced concrete member. Shear reinforcement bars 32 having fixing devices 31 at both ends are arranged so as to resist. Thereby, the tensile stress borne by the concrete member 12 is transmitted to the shear reinforcement 32, and the shear reinforcement 32 is firmly fixed in the concrete member by the fixing tool 31. Was able to bear a sufficient tensile stress and improve the shear strength.

On the other hand, the shear reinforcement structure 20 of the present invention does not burden other members with the tensile stress acting on the concrete member 12 as in the conventional shear reinforcement structure, as shown in FIG. so as to intersect the diagonal crack surface (dashed line in FIG. 1) is provided a steel pipe 2 2, the effect of acting as a steel pipe 22 Gahozo (so-called dowel effect) by using, the idea of preventing shear failure Is based.

  Since the shear reinforcing bar 32 used in the conventional shear reinforcing structure is provided for the purpose of bearing a tensile stress, a reinforcing bar having a small bending strength is used. Therefore, since the shear reinforcement bars are deformed together with the concrete member, the function as a tenon is low, allowing the shear fracture to proceed with an increase in the shear load, and finally before the Dowel effect is fully generated. The reinforced concrete member breaks and the shear strength cannot be improved.

  On the other hand, the steel pipe 22 used in the shear reinforcement structure 20 of the present embodiment has a larger diameter than the shear reinforcement bar 32 and a large bending rigidity. For this reason, the function as a tenon is high, a sufficient dowel effect can be expected from the beginning of loading of the shear load, and the shear strength can be improved. In addition, if a steel pipe having a shear strength greater than the shear force generated on the oblique crack surface is used as the steel pipe 22, it can resist the force to be separated along the oblique crack surface, so that the shear strength is reliably improved. it can.

  Further, as shown in FIG. 1A, the shear reinforcement structure 20 of the present embodiment has a steel pipe 22 arranged in a direction orthogonal to the member axis. Normally, oblique cracks follow the stress transmission mechanism. That is, since the steel pipe 22 is generated in an oblique direction with respect to the member axis, the steel pipe 22 intersects with the oblique crack. For this reason, even if the steel pipe 22 is arranged in a direction orthogonal to the member axis, similarly to the shear reinforcement in the conventional shear reinforcement structure, a shear reinforcement effect can be obtained.

  As described above, according to the shear reinforcement structure of the present embodiment, since the shear reinforcement is performed using the dowel effect of the steel pipe, the fixing tool used for fixing to the concrete member is not necessary, and the construction is performed. Cost can be reduced. Further, since the steel pipe is provided so as to intersect with the crack surface caused by the shear load, efficient reinforcement is possible. For this reason, compared with the shear reinforcement used by the conventional method, since a steel pipe can carry out shear reinforcement with few numbers, economical efficiency and workability | operativity are improved. Furthermore, since there is no fixing tool at the end, the bar arrangement work is facilitated.

  Here, the numerical analysis simulation using FEM examined whether or not the reinforced concrete member having the shear reinforcement structure of the present embodiment has sufficient shear strength, and will be described below. In this simulation, one end of an RC model modeling a reinforced concrete member having a height of 1200 mm and a width of 500 mm was used as a fixed support, a load was applied to the other end, and the relationship between the load and the displacement was examined. A steel pipe having a diameter of 48.6 mm and a thickness of t3.2 mm was modeled.

In addition, about the adhesion of the steel pipe and the concrete member in the shear reinforcement structure of this embodiment, it shall represent with the line element as shown in FIG. FIG. 4 is a diagram for explaining the load-displacement characteristics of the line elements. FIGS. 9A and 9B show the displacement state of the line elements, and FIGS. 8C and 9D show the displacements (horizontal axis) when displaced as shown in FIGS. And the stress τ (vertical axis). When displacement occurs in parallel with the line element as shown in FIG. 9A, until the stress τ corresponding to the displacement δ reaches the limit value τ _max of the adhesion stress as shown in FIG. It is assumed that a stress τ proportional to the displacement δ acts, and when the stress τ corresponding to the displacement δ exceeds the limit value τ _max of the adhesion stress, a constant stress τ (= τ _max ) acts. Represents. In addition, when a displacement occurs perpendicular to the line element as shown in FIG. 4B, a stress σ proportional to the displacement δ is obtained when the displacement δ is zero or less as shown in FIG. When the displacement δ exceeds zero, the stress is expressed as not acting.

In this simulation, when a shear reinforcement structure is not provided (Condition 1), a steel pipe is provided, and there is a minimum adhesion stress between the steel pipe and the concrete member, but no friction force is generated (Condition 2). When a steel pipe is provided, there is a certain amount of adhesion stress between the steel pipe and the concrete member, and a frictional force is generated (Condition 3), and when the steel pipe and the concrete member are completely adhered ( Regarding condition 4), numerical analysis was performed to investigate the relationship between load and displacement. That is, the condition 2 corresponds to the case where the shear force is resisted only by the Dowel effect, and the conditions 3 and 4 correspond to the case where the shear force is resisted by the Dowel effect and the tensile strength of the steel pipe.
In the case where no frictional force is generated (condition 2), _{τmax is set} to 0.2 [N / mm ² ] and the friction coefficient μ = 0. In the case where the frictional force is generated (condition 3), τ _{max is set} to 0.5 [N / mm ² ] and the friction coefficient is set to μ = 0.3.

  FIG. 5 is a graph showing the load-displacement relationship of each specimen. The design shear strength of a reinforced concrete member without a shear reinforcement structure calculated using the formula for calculating the shear strength of an RC bar member described in the Standard Specification for Concrete, etc. ), And the design shear strength (upper broken line in FIG. 5) of a reinforced concrete member provided with a shear reinforcement structure in which a fixing tool is connected to both ends of the shear reinforcement, which is a conventional technique.

  As shown in FIG. 5, the reinforced concrete member provided with the shear reinforcement structure by the steel pipe of the present embodiment has no friction (condition 2), friction is considered (condition 3), and complete adhesion (condition 4). When the steel pipe is not provided (condition 1), the shear strength is greatly exceeded. From this, it was confirmed that the shear strength of the reinforced concrete member is improved by providing the shear reinforcement structure of the present embodiment.

  In addition, when the design shear strength of the shear reinforcement structure using the conventional fixing tool, which is a comparison object, is compared with the maximum shear load of the conditions 2 to 4, the maximum shear load of the conditions 2 to 4 is the conventional shear reinforcement structure. The design shear strength is greatly exceeded. Thereby, according to the shear reinforcement structure of this invention, it was confirmed that the shear strength equivalent to or more than the conventional shear reinforcement structure can be ensured.

(A) is a cross-sectional view in the member axial direction of a reinforced concrete member provided with the shear reinforcement structure of the present embodiment, and (B) is a vertical cross-sectional view. It is a figure which shows the stress in the reinforced concrete member to which the shear force acted. It is a figure which shows the line element showing adhesion with a steel pipe and a concrete member. It is a figure for demonstrating the load-displacement characteristic of a line element, The figure (A) and (B) shows the displacement condition of a line element, The figure (C) and (D) is each (A). And the relationship between the displacement (horizontal axis) and the stress τ (vertical axis) when displaced as shown in (B) is shown. It is a graph which shows the load displacement relationship in each condition. It is the conventional shear reinforcement structure which provided the fixing tool in the both ends of the shear reinforcement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Reinforced concrete member 11 Main reinforcement 12 Concrete member 13 Power distribution rod 20 Shear reinforcement structure 22 Steel pipe 30 Conventional shear reinforcement structure 31 Fixing tool 32 Shear reinforcement

Claims (6)

A shear reinforcement structure for a reinforced concrete member on which a shear load acts,
A shear reinforcement structure, characterized in that a steel pipe is embedded in the reinforced concrete member in a direction intersecting with a main reinforcing bar embedded in the reinforced concrete member so as to intersect with an oblique crack surface caused by the shear load.   The shear reinforcement structure according to claim 1, wherein the steel pipe has a shear strength greater than a shear load acting on the oblique crack surface.   The shear reinforcement structure according to claim 1 or 2, wherein the steel pipe is embedded in the reinforced concrete member substantially in parallel with the direction of the shear load. It said main reinforcing bars are each are set embedded in a predetermined overburden thickness from opposing surfaces of said reinforced concrete member,
The said steel pipe is arrange | positioned so that the both ends may extend to the surface side of the said reinforced concrete rather than the said main reinforcement, The shear reinforcement structure in any one of Claims 1-3 characterized by the above-mentioned.   A reinforced concrete member comprising the shear reinforcement structure according to any one of claims 1 to 4. A method for reinforcing shear of a reinforced concrete member subjected to a shear load,
A shear reinforcement method comprising embedding a steel pipe in a direction intersecting with a main rebar embedded in the reinforced concrete member so as to intersect with an oblique crack surface generated by the shear load in the reinforced concrete member .

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