JP4394048B2 - Concrete beam and manufacturing method thereof - Google Patents

Description

 The present invention relates to a reinforced concrete beam or a steel reinforced concrete beam having a through hole, and a method for manufacturing the same.

When installing equipment piping in a building with concrete beams or from the inside of the building to the outside, a piping through hole is provided in the abdomen of the beam so that the piping does not affect the floor height setting. The method is common.
When a through-hole is provided in a beam, the shear strength of the beam decreases due to a decrease in cross-section, stress concentration around the hole, etc. Is generally used.
For example, as shown in FIG. 8, a quadrilateral shear reinforcing bar (shear reinforcing member) 5 is disposed around a through hole 4 provided in the beam 1. This is because the initial shear crack 7 generated when shear stress is applied to the beam 1 propagates along a 45-degree line passing through the vicinity of the center of the through hole 4 as shown in the figure. This is because the shear reinforcement member 5 oriented in the direction perpendicular to the direction 7 is arranged to enhance the reinforcement effect. The shear reinforcement member 5 suppresses the progress of the shear crack 7 by the adhesive force with the concrete.

Moreover, the technique which processes and arrange | positions the shear reinforcement member in circular, a rectangle, etc. is also disclosed (for example, refer patent document 1).
JP-A-5-321404

However, according to the results of the structural experiment, the initial shear crack propagates in the 45 degree direction as described above, but after that, the reinforcing effect of the shear reinforcing member is exhibited, and the crack propagates so as to avoid that portion. I know what to do. In the example shown in FIG. 8, finally, another shear crack 8 expands at a portion where the reinforcing effect of the shear reinforcing member 5 is small, that is, at the upper and lower portions of the through hole 4, leading to shear failure at a stretch. That is, another shear crack 8 proceeds from a portion where the reinforcing effect of the shear reinforcing member 5 is low, and accordingly, the adhesive force between the shear reinforcing member and the concrete decreases.
For this reason, when a big earthquake etc. generate | occur | produce, there exists a problem that the beam 1 will reach a final state (destruction) in the stage where the reinforcement effect of the shear reinforcement member 5 is not exhibited 100%.
It is desirable for the shear reinforcement member to exert its maximum reinforcement effect against shear cracks from the viewpoint of economic design of the beam, and also from the viewpoint of facilitating structural calculation for calculating the proof stress of the beam.

Therefore, in order to prevent the cracks from progressing and breaking at the upper and lower portions of the through hole, a method of arranging another shear reinforcement member at the upper and lower portions of the through hole can be designed.
However, it is not preferable to arrange a number of shear reinforcement members according to a plurality of sites where cracks are expected to occur because the construction is troublesome and the bar arrangement becomes complicated. In addition, when the length of the beam is small, there may be a case where many such shear reinforcement members cannot be arranged.

  Furthermore, especially when the shear reinforcement member 5 as shown in FIG. 8 is not disposed around the through-hole, the stirrup of the beam opposes the shear crack. However, at that time, there is a problem that the shear cracks proceed at the upper and lower portions of the through hole as described above without intersecting the stirrup.

  Then, this invention makes it a subject to demonstrate the reinforcement effect with respect to a shear crack to the stirrup or the shear reinforcement member arrange | positioned around a through-hole to the maximum.

In order to solve the above-mentioned problems, the present invention dares to induce the occurrence of shear cracks at the position and orientation in which the stirrup or shear reinforcing member can exert its reinforcing effect to the maximum.
In this way, since the shear crack is always induced to propagate at the position, the stirrup or the shear reinforcement member related to the induced portion maximizes the reinforcement effect from the initial stage of the crack to the ultimate state. It can be used as much as possible.
The occurrence of shear cracks in a beam in service is usually not preferable. For this reason, there is also a conventional technique for inducing cracking to a location that does not affect the yield strength of the structure. However, in the present invention, the initial shear crack generated by seismic force or the like is advanced to maximize the effect of the shear reinforcing member and improve the beam proof stress. That is, on the premise of the occurrence of cracks, by intentionally guiding the cracks to a predetermined part, it is confirmed that cracks are generated in parts other than the part where the arranged stirrup or shear reinforcement member can exert its reinforcement effect to the maximum. It suppresses.

As a specific configuration of the above means, the progress of shear cracks that occur when shear stress is applied to the beam in the middle of the height direction of the stirrup adjacent to the through-hole provided in the beam is measured. A crack guiding means for guiding in the axial direction is provided.
Further, as another means, in a concrete beam in which a shear reinforcement member that intersects an initial shear crack generated when a shear stress is applied to the beam is arranged around a through hole provided in the beam, the shear reinforcement member Further, a crack guiding means for guiding the progress of the initial shear crack is provided.
In this way, tensile stress is generated in the stirrup or shear reinforcement member due to the shear crack, and the tensile stress always contradicts the middle of the stirrup or reinforcement member from the initial stage of the crack to the ultimate state. Therefore, the stirrup or shear reinforcing member can exert its reinforcing effect to the maximum.
The crack guiding means may be provided in a state of being attached to the stirrup or shear reinforcing member, or the effect can be exhibited even if it is provided in the concrete separately from the stirrup or shear reinforcing member.

Further, as the crack guiding means, it is possible to adopt a configuration in which a notch on the beam surface that is long in the guiding direction, a gap inside the beam, or a member embedded in the beam. If it does in this way, it will become easy to guide a shear crack along the induction direction from the crack initial stage to the final state.
Further, in the configuration in which the shear reinforcement member is disposed, the effect of the shear reinforcement member can be exhibited more efficiently if the guide direction of the crack guiding means is provided in a direction orthogonal to the shear reinforcement member. .

Furthermore, the following specific configurations can be adopted as a method for producing a concrete beam by the above means.
In other words, in the middle of the height direction of the stirrup adjacent to the through hole provided in the beam, the crack induction means for guiding the progress of the shear crack generated when the shear stress is applied to the beam in the beam axis direction of the beam. Is provided, and concrete is cast in that state.
As another means, in a method of manufacturing a concrete beam, a shear reinforcement member that intersects an initial shear crack generated when a shear stress is applied to the beam is disposed around a through hole provided in the beam. The reinforcing member may be provided with a crack guiding means for inducing the progress of the initial shear crack and the concrete may be cast.
In this way, tensile stress is generated in the stirrup or the shear reinforcement member due to the shear crack, and the stress always contradicts the middle of the stirrup or shear reinforcement member from the initial stage of the crack to the ultimate state. Therefore, the stirrup or the shear reinforcing member can exert its reinforcing effect to the maximum.
The crack guiding means may be provided in a state of being attached to the stirrup or shear reinforcing member, or the effect can be exhibited even if it is provided in the concrete separately from the stirrup or shear reinforcing member.

In the concrete beam manufacturing method described above, as the crack guiding means, it is possible to adopt a structure in which a notch on the beam surface that is long in the guiding direction, a gap inside the beam, or an embedded member in the beam. If it does in this way, it will become easy to guide a shear crack along the induction direction from the crack initial stage to the final state.
Further, in the configuration in which the shear reinforcement member is disposed, the effect of the shear reinforcement member can be exhibited more efficiently if the guide direction of the crack guiding means is provided in a direction orthogonal to the shear reinforcement member. .

  Since the present invention is configured as described above, the stiffening effect on the shear crack can be exhibited to the maximum with respect to the stirrup or the shear reinforcing member arranged around the through hole.

An embodiment will be described with reference to FIGS.
FIG. 1 shows a state in which pipes 14 a are respectively inserted into through holes 14 provided in a concrete beam 10 connecting the columns 11 and 11.
FIG. 2 shows a bar arrangement state of the column 11 and the beam 10. Reference numeral 16 shown in FIG. 2 indicates a main bar of the beam 10, and reference numeral 17 indicates a staggered bar.

The through hole 14 of the beam 10 is provided perpendicular to the beam axis direction of the beam 10, and is arranged in parallel with the length direction of the through hole 14 (width direction of the beam 10) around the through hole 14. Two shear reinforcement bars (shear reinforcement members) 15 and 15 are arranged (see FIG. 2B).
As shown in FIG. 2 (a), the two parallel shear reinforcement bars 15 and 15 are formed in a quadrilateral shape surrounding the through hole 14, and both are symmetrical in the beam axis direction and the vertical direction. . Further, as shown in FIG. 2B, a predetermined covering is secured from the front and back surfaces 12 and 13 of the beam 10, and each is fixed to the corresponding stirrup 17. As shown in FIG. 2A, a plurality of reinforcing bars 15, 15 may be provided in parallel in each part to enhance the effect of reinforcement.

  In addition, crack guiding means 20 is provided around the through hole 14. The crack guiding means 20 is provided for the purpose of giving priority to the generation of shear cracks in the portion, and is provided in the middle of both shear reinforcement bars 15 and 15. The middle part of the shear reinforcement 15 provided with the crack guiding means 20 may be a position in contact with the shear reinforcement 15 or may not be in contact with each other with a slight distance in the width direction of the beam 10. It may be a position.

As a specific configuration of the crack guiding means 20, for example, as shown in FIG. 3A, a planar wire mesh or lath mesh or an iron plate facing the guiding direction can be adopted.
This wire net, lath net, or iron plate may be attached to a sleeve or the like embedded in the beam 10 in order to form the through hole 14, or may be attached to the shear reinforcement 15.
Further, as shown in FIG. 3B, the crack guiding means 20 may be a notch in the beam front and back surfaces 12, 13 that is long in the guiding direction. The notch is formed by embedding a spacer for forming the notch in the mold when placing the concrete of the beam 10 and removing the spacer after the beam 10 is completed.
Furthermore, the crack guiding means 20 may be a rod-like embedded member inside the beam as shown in FIG. The embedding member may be attached to the sleeve for forming the through hole 14 or may be attached to the shear reinforcement 15.
Moreover, the crack induction means 20 can also be made into the space | gap inside a beam by making the said embedded member into a raw material soluble in concrete. 3A and 3B, the shear reinforcement 15 is not shown.

The case where shear stress acts on the beam 10 will be described. As shown in FIG. 4, near the front and back surfaces 12 and 13 of the beam 10, shear cracks (initial shear cracks) 18 and 18 are respectively in the beam axis direction. It occurs in the 45 degree direction.
These shear cracks 18 and 18 will continue to propagate in the guiding direction due to the effect of the crack guiding means 20 even if the acting shear force increases thereafter, so that the beam reaches the final state. Large shear cracks that affect 10 breaks are not produced elsewhere.

  At this time, in any of the crack guiding means 20, the guiding direction is preferably a direction orthogonal to the shear reinforcement 15. This is because, by making the shear reinforcement 15 and the guiding direction orthogonal to each other, an equal tensile force is generated in the opposite direction to the shear reinforcement 5, and due to the adhesive force with the concrete, the shear reinforcement 5 is This is because the reinforcing effect can be maximized.

Moreover, the aspect shown in FIG. 5 can also be employ | adopted as other embodiment. The concrete beam 10 of this embodiment is provided with a long crack guiding means 20 in the beam axis direction in the middle of the rib height 17 of the rib 17 adjacent to the through hole 14, and when shear stress acts on the beam 10. The progress of the shear crack 18 that occurs in is induced in the beam axis direction.
By this induction, the shear crack proceeds in a direction perpendicular to the stirrup 17, and a tensile stress is generated in the stirrup 17. Since the stress is always generated in the opposite direction from the middle of the crack to the final state, the rib 17 can exert its reinforcing effect to the maximum.
It should be noted that the crack guiding means 20 may be provided in a state of being attached to the stirrup 17, or the effect can be exhibited even if it is provided in the concrete of the beam 10 separately from the stirrup 17.
At this time, as shown in FIG. 5, the shear reinforcing bars 15 may be arranged around the through holes 14.

Furthermore, as another embodiment, each aspect shown in FIGS. 6 and 7 may be employed. Each embodiment shown in FIGS. 6 and 7 employs a different form as a shear reinforcement (shear reinforcement member) 15 in each embodiment shown in FIGS.
In FIG. 6, a shear reinforcing member 15 having a circular shape in front view is provided around the through hole 14, and the crack guiding member 20 is provided in a 45 ° direction shown in the figure so as to intersect the shear reinforcing member 15. .
FIG. 7 shows a plate-like shear reinforcement member 15 fitted around the through hole 14 provided in the beam 10, in which a crack guiding member 20 is provided in the 45 ° direction shown in the figure. The plate-like shear reinforcing member 15 is provided with a rib 15 ′ surrounding the through hole 14, and the crack guiding means 20 is provided orthogonal to the rib 15 ′.

Explanatory drawing showing an installation example of concrete beams with through holes The bar arrangement state of one embodiment is shown, (a) is an overall front view of the beam, (b) is a cut side view of the beam. It is a detailed view of the crack guiding member of the embodiment, (a) is a perspective view when a wire mesh is used, (b) is a perspective view when a notch is provided, and (c) is a case where an embedded member is used Perspective view Front view showing after the occurrence of cracks in the same embodiment The bar arrangement state and arrangement | positioning of a crack induction member of other embodiment are shown, (a) is the whole front view of a beam, (b) is the cut | disconnected side view of a beam Furthermore, the front view which shows after the crack generation | occurrence | production of other embodiment Detailed view of crack induction member of still another embodiment Front view of the conventional example after cracking

Explanation of symbols

1,10 beams (concrete beams)
4,14 Through hole 5,15 Shear reinforcement (shear reinforcement member)
7, 8, 18 Shear crack 11 Column 12 Front surface 13 Back surface 16 Main bar 17 Stirrup 20 Guide means

Claims (4)

  In the middle of the height direction of the stirrup 17 adjacent to the through hole 14 provided in the beam 10, the progress of the shear crack 18 generated when the shear stress is applied to the beam 10 is caused in the beam axis direction of the beam 10. A concrete beam provided with a crack guiding means 20 for guiding. In a concrete beam in which a shear reinforcement member 15 that intersects an initial shear crack 18 generated when a shear stress is applied to the beam 10 is disposed around a through hole 14 provided in the beam 10.
A concrete beam characterized in that a crack guiding means 20 for guiding the progress of the initial shear crack 18 is provided around the through hole 14.   3. The concrete beam according to claim 1, wherein the crack guiding means 20 is a notch on the beam surface that is long in the guiding direction, a gap inside the beam, or an embedded member in the beam.   The crack guiding means 20 is a notch on the beam surface that is long in the guiding direction, a gap inside the beam, or an embedded member in the beam. The guiding direction of the crack guiding means 20 is the same as the shear reinforcing member 15. The concrete beam according to claim 2, wherein the concrete beam is in an orthogonal direction.

Images