JP5325313B2 - Precast concrete beams - Google Patents

Description

  The present invention relates to a precast concrete beam by a pretension system.

  A precast concrete beam by a pretension method is a beam in which compressive stress is introduced in advance via a tension member disposed at the lower part of the cross section (see, for example, Patent Document 1). A precast concrete beam can be used for a large span because a large lifting force due to an eccentric moment can be expected near the center due to the compressive stress of the tendon.

  A prestressed concrete member is provided with a tension method such as a post-tension method, in which a tension material such as a PC cable or PC steel material is placed, then concrete is placed, and prestress is introduced into the tension material after the concrete is cured. After the tension material is disposed, the concrete is placed, and after the concrete is hardened, the tension material is released to introduce prestress, thereby forming a pre-tension method.

  Since the eccentric moment is proportional to the tension force and the eccentric distance of the tendon material, a larger eccentric moment can be obtained if the eccentric distance can be increased with respect to the similar tension force.

  In order to increase the eccentric distance of the tension members, it is effective to arrange more tension members at positions away from the center of the beam cross section, but the number of tension members that can be arranged in a row is Limited by the interval and the cover size.

  Conventionally, the spacing C between the tendon members 102 in the precast concrete beam 1 has been set to be three times (3D) or more the diameter of the tendon member 102, so the number of tendon members 102 that can be arranged in a row is limited by the width of the beam. It was. Therefore, there has been a case where it is intended to obtain a larger eccentric moment M1 by arranging a plurality of tension members 102 in multiple stages (see FIG. 5).

JP 2007-120002 A

However, when the tension members 102 are arranged in multiple stages, the eccentric distance e1 of the tension members 102 becomes smaller. Therefore, in order to obtain the necessary eccentric moment M1, the number of the tension members 102 is further increased or the beam width is increased. There was a need to do.
For this reason, there are problems such as an increase in the amount of steel material of the tension material 102 and an increase in material cost, and an increase in the number of tension materials 102, which requires time and labor for manufacturing the precast concrete beam 101.
Further, when the interval between the tendons is narrowed, the adhering forces of the adjacent tendons interfere with each other, so that there is a concern that the end of the material will be fixed and broken due to repeated loading during an earthquake, and the prestress will be reduced.

  The present invention has been made to solve the above-described problems, and can be manufactured with high quality by ensuring a large eccentric distance of the tendon material, and can be manufactured easily and inexpensively. The subject is to propose precast concrete beams.

In order to solve the above-mentioned problem, a first invention is a precast concrete beam by a pretension system in which a plurality of tendons are arranged, and the plurality of tendons are below a center of gravity of a beam section. It is eccentric and arranged in a row in the beam cross section, and the interval between the adjacent tendons is set to be 1.5 times or more and less than 3 times the diameter of the tendons. Further, every other means for preventing fixing fracture is provided at both ends of the tendon.
The means for preventing the fixing breakage may be an insulating material covering both ends of the tension material.

  According to such a precast concrete beam, it is possible to increase the number of tension members that can be arranged in one step and increase the eccentric distance by setting the spacing between the tension members to less than three times the diameter. Therefore, the number of tendons for securing the same eccentric moment can be reduced. Therefore, it becomes possible to manufacture a high-quality precast concrete beam easily and inexpensively.

  In addition, since the means for preventing the fixing failure is provided while reducing the interval between the tension members, the fixing failure is prevented from occurring at the end portion of the precast concrete beam.

Moreover, since it is possible to introduce a large amount of prestress with respect to the same cross-sectional dimension, it becomes possible to cope with further long span and heavy load.
In addition, under the same design conditions, it becomes possible to reduce the cross-sectional dimension of the beam and to reduce the beam dimension.

  The second invention is a precast concrete beam by a pretension system in which a plurality of tendons are arranged, and the plurality of tendons are eccentric to the lower side of the center of gravity of the beam cross section and It is arranged in a row in the beam cross-section in the horizontal direction, the spacing between the adjacent tendons is set to be 1.5 times or more and less than 3 times the diameter of the tendons, Means for preventing fixing destruction are provided at both ends of the tension material, and the fixing area between the adjacent tension materials is shifted in the material axis direction.

  The means for preventing the fixing breakage may be, for example, a fixing tool provided on the tension material or an adhesion improving material applied to the tension material.

  According to the precast concrete beam of the present invention, it is possible to manufacture with high quality by securing a large eccentric distance of the tension material, and to be manufactured easily and inexpensively.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the precast concrete beam concerning suitable embodiment of this invention, Comprising: (a) is a general view, (b) is a stress distribution map of a tendon. It is AA sectional drawing of the precast concrete beam shown in FIG. It is a top view of the precast concrete beam which concerns on 1st Embodiment. It is sectional drawing of the precast concrete beam which concerns on 3rd Embodiment. It is sectional drawing which shows the conventional precast concrete beam.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. In the description, the same reference numerals are used for the same elements, and duplicate descriptions are omitted.

<First Embodiment>
A precast concrete beam (hereinafter may be simply referred to as “beam”) 1 according to the first embodiment is a reinforced concrete beam member having a predetermined span length, and has a cross section as shown in FIG. The tension material 2 is arrange | positioned along the longitudinal direction at the lower part.

As shown in FIG. 2, the beam 1 is formed in a rectangular cross section, and four main bars 3 are arranged along the longitudinal direction of the beam 1 at the top and the bottom, and a plurality of main bars 3 are arranged. The reinforcing bars 4 formed in a rectangular shape so as to surround are arranged.
The upper part of the beam 1 according to the present embodiment is formed integrally with the slab B, and the tension material 2 is disposed corresponding to the stress S acting on the part other than the upper part.

As shown in FIG. 2, the tendon 2 is disposed at the lower part of the cross section of the beam 1 and between the upper and lower reinforcing bars 3 and 3.
Although the number of the tension members 2 is not limited, in the present embodiment, seven tension members are arranged at the same interval. Moreover, in this embodiment, although PC steel material shall be used as the tension | tensile_strength 2, if the material which comprises the tension | tensile_strength 2 is not limited and it selects and uses from well-known tension | tensile_strength suitably, it will be used. Good.

  For the purpose of obtaining a larger eccentric moment M, the tendon material 2 has an eccentric distance e from the center of gravity axis CL of the beam 1 as large as possible. In this embodiment, the center of gravity CL of the beam 1 and the beam 1 The tendon material 2 is disposed approximately in the middle of the reinforcing bar 3 disposed on the lower side of the cross section.

  The interval C between the tendon members 2 is equal to or greater than the maximum dimension of the concrete aggregate of the beam 1 for the purpose of securing the adhesion between the tendon member 2 and the concrete and securing the number of the tendon members 2. It is comprised so that it may be 1.5 times or more and less than 3.0 times the diameter of the tendon 2.

  Moreover, in order to prevent the fixing destruction in the fixing area A of the both ends of the tension material 2 and the crack by a bare pressure by making the space | interval C between the tension materials 2 small, in this embodiment, as shown in FIG. By covering every other end of the tension members 2, 2,... With the insulating material 5, the fixing area of the adjacent tension members 2 is shifted in the longitudinal (material axis) direction.

In the present embodiment, the insulating material 5 is constituted by a pipe material 5 a disposed around the tension material 2 and an unbond material 5 b filled in a gap between the pipe material 5 a and the tension material 2.
The insulating material 5 is used to unbond both ends of the tension material 2 every other line, thereby preventing fixing breakage at both ends (fixing area A) of the beam 1.
In addition, the structure of the insulating material 5 is not limited to the said structure, It is possible to set suitably.

  Here, the adhesion split fracture means that when the tensile force P of the tension material 2 is transmitted to the concrete, the concrete around the tension material 2 is forced to spread radially around the tension material 2. 2 is mainly caused when the tension members 2 are densely packed or when the concrete covering thickness is thin.

  Further, the bare pressure is a force acting on the concrete due to the expansion of the tension material 2 when the tension force is introduced (when the tension material is released). That is, the tension material 2 of the pretension member is thinned by introducing a tensile force, but by releasing the tensile force (releasing the tension material), the tensile force at both ends of the tension material 2 is 0 and the diameter returns to the initial diameter. And, in the center side of the fixing area A of the pretension member, the introduction of prestress is constant, and the diameter of the tension material 2 is narrower than both ends. That is, in the fixing area A of the pretension member (straining material 2), the tensioning material 2 expands, and the diameter gradually increases from the center toward the tip. The expansion force (bare pressure) is acting.

As described above, the beam 1 can increase the number of the tension members 2 arranged in a row by setting the interval C between the tension members 2 within the range of 1.5D to 3.0D, and the eccentric distance. e can be increased. As a result, the eccentric moment M proportional to the tension force P and the eccentric distance e can be further increased.
In addition, about the relationship of the load-displacement by the force experiment which assumed the adhesion force in the fixation area, and the load at the time of an earthquake in the case where the space | interval C between the tendons 2 is set to 3.0D and 1.5D, respectively. As a result of experiments, it was found that even if the distance C was narrowed to 1.5D, the structural performance equivalent to that when the distance C was 3.0D was obtained. Therefore, in this embodiment, the number of the tension members 2 arranged in a row is increased by setting the interval C between the tension members 2 to 1.5D or more and less than 3.0D.

In addition, it is preferable because the number of tension members 2 for obtaining the same eccentric moment M can be reduced as compared with a conventional beam in which tension members are arranged in multiple stages (see FIG. 5).
In addition, compared to conventional beams with the same cross-sectional dimensions, it is possible to introduce a large amount of prestress, so it is possible to cope with longer span of beams and heavy load loads. .

  Further, by shifting the fixing area A between the adjacent tendons 2 in the longitudinal direction, the adhesion stress between each other becomes less likely to be affected. Is done.

  In this embodiment, as a method of shifting the fixing area A between the adjacent tension members 2, the insulating material 5 is covered on both ends of every other tension member 2, but only one end portion is covered. The insulating material 5 may be covered. In addition, the range (distance) for shifting the fixing area A varies depending on conditions such as concrete strength, adhesion stress level, and tension member spacing, but generally 15 to 30 times the tension material diameter is sufficient. It is. It should be noted that the range in which the fixing area A is shifted may be larger than this depending on the length of the span.

  The means for shifting the fixing area A between the adjacent tension members 2 in the longitudinal direction is not limited to the insulating material 5 and can be appropriately performed. For example, fixing may be performed by fixing a fixing tool such as a crimping grip to the end of the tension member 2. In this case, the fixing tool is fixed at a position shifted in the longitudinal direction between the adjacent tension members 2. Thereby, the fixing tool functions as a bearing plate, and it is possible to reduce the adhesion stress of the concrete and shorten the fixing area, and the fixing area between the adjacent tension members 2 is shifted.

<Second Embodiment>
The precast concrete beam 1 according to the second embodiment is the first in that an adhesion improving material is applied to the tension member 2 in the fixing area A instead of disposing the insulating material 5 around the tension member 2. It is different from the precast concrete beam 1 according to the embodiment.

  Since the adhesion improving material is applied to the tendon material, the beam 1 has a low adhesion force between the tendon material 2 and the concrete. It is possible to prevent. That is, the precast concrete beam 1 according to the second embodiment prevents the beam 1 from being broken by weakening the adhesive force between the tension material 2 and the surrounding concrete in the fixing area A.

  In addition, since the configuration and operational effects of the precast concrete beam 1 according to the second embodiment are the same as the contents shown in the first embodiment, detailed description thereof is omitted.

<Third Embodiment (Reference Embodiment)>
As shown in FIG. 4, the precast concrete beam 1 according to the third embodiment is arranged in the fixing area A in place of the insulating material 5 around the tension material 2 in the fixing area A. The present embodiment is different from the precast concrete beam 1 according to the first embodiment in that a mesh-like reinforcing member 6 disposed so as to intersect is provided.

  Such a beam 1 is provided with a mesh-like reinforcing material 6 around the tension material 2 against fixing fracture and bare pressure caused by concrete being spread in the radial direction around the tension material 2. In this way, the concrete is prevented from separating from the tendon 2. Therefore, it is prevented that the fixing failure and the crack due to the bare pressure occur. In other words, the precast concrete beam 1 according to the third embodiment prevents the beam 1 from being broken by increasing the adhesive force between the tension material 2 and the surrounding concrete in the fixing area A.

In addition, since the configuration and operational effects of the precast concrete beam 1 according to the third embodiment are the same as the contents shown in the first embodiment, detailed description thereof is omitted.
In addition, the arrangement | positioning location and quantity of the mesh-shaped reinforcing material 6 are not limited, and can be set suitably. In the present embodiment, one place is provided in each of the fixing areas A at both ends of the beam 1 shown in FIG.

<Fourth embodiment (reference embodiment)>
In the precast concrete beam 1 according to the fourth embodiment, as a means for preventing fracturing failure, the average adhesion stress degree at the end of the tension material is set to 1/10 or less of the concrete strength when the tension force is introduced. This is different from the precast concrete beam 1 according to the first embodiment.

In such a beam 1, the adhesion stress degree of the portion corresponding to the fixing area A at the end of the tension material 2 is 1/10 or less of the concrete strength, and is equal to or less than the strength corresponding to the tensile strength of the concrete when the tension force is introduced. Therefore, it is possible to prevent cracking due to anchorage failure or bare pressure during earthquake loading.
In other words, the beam 1 has an adhesion stress degree at the end of the tendon 2 of 1/10 or less of the concrete strength, so that the relationship between the load and the displacement is 3D or more between the conventional tendons 102. A behavior equivalent to that of the beam 101 (see FIG. 5) is shown.

  In addition, since the configuration and operational effects of the precast concrete beam 1 according to the fourth embodiment are the same as the contents shown in the first embodiment, detailed description thereof is omitted.

The preferred embodiments according to the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the spirit of the present invention.
For example, the precast concrete beam according to the present invention is preferably used as a precast member that is produced in advance in a factory or the like. However, in application to a large-scale member that is difficult to transport as a precast member, prestress in the field is used. As long as it is possible to secure the necessary space for installation and installation of equipment necessary for power introduction, construction may be performed by on-site construction.

  Further, in addition to the configuration shown in each embodiment, a more excellent pretension member may be constructed by appropriately combining the configuration shown in each embodiment. For example, in the fixing area, every other tension material may be unbonded, and a mesh-like reinforcing material may be disposed in the fixing area at both ends to improve durability against fixing failure.

  The means for preventing fixing destruction is not limited to those shown in the above embodiments, and can be appropriately performed by known means. For example, it is good also as a structure which prevents separation | separation with a tension material and concrete by using high-strength concrete about the fixing area of both ends, and prevents an adhesion split fracture. In this case, for example, fiber reinforced concrete may be employed as the high-strength concrete.

1 Beam (Precast concrete beam)
2 Tensile material 3 Main reinforcement 5 Insulation material 6 Reinforcement material A Anchorage area M Eccentric moment C Interval e Eccentric distance

Claims (2)

A precast concrete beam with a pretension system in which a plurality of tendons are arranged,
The plurality of tension members are eccentric to the lower side of the center of gravity axis of the beam cross section and are arranged in a row in the transverse direction in the beam cross section,
The spacing between adjacent tendons is set to be 1.5 times or more and less than 3 times the diameter of the tendon,
A precast concrete beam characterized in that every other end portion of the tendon is provided with means for preventing fixing fracture. A precast concrete beam with a pretension system in which a plurality of tendons are arranged,
The plurality of tension members are eccentric to the lower side of the center of gravity axis of the beam cross section and are arranged in a row in the transverse direction in the beam cross section,
The spacing between adjacent tendons is set to be 1.5 times or more and less than 3 times the diameter of the tendon,
A precast concrete beam characterized in that means for preventing fixing destruction are provided at both ends of all the tendons, and the fixing areas of the adjacent tendons are shifted in the direction of the axis of the material. .

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