JP2005120702A - Composite concrete member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a half precast member provided with bending proof stress and deformation property substantially equal to those of a completely integral cast-in-place concrete member for vertical load. <P>SOLUTION: A pair of precast concrete form members 2, 2 constituted by burying a plurality of steps of assembly bars 6 extending in parallel along the longitudinal direction are arranged by separating them to the left and right, and a plurality of sets of form members having the same configuration as that of them are arranged in the longitudinal direction through a join part 5 to connect and integrate them by a main bar 3 arranged over the whole length and cast-in-place concrete 4 in this half precast member. The join part is provided at substantially center in the direcion of its span length in left and right shearing regions formed in cross section of the member by bending stress of the member. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a composite concrete member. More specifically, the present invention is a half precast member formed by integrating a plurality of precast concrete formwork materials and cast-in-place concrete cast in the formwork material, and has improved bending strength. It relates to members.

In recent years, the half precast method has attracted attention as a method that incorporates the advantages of cast-in-place concrete and precast concrete members. In this half precast method, a part of the member is pre-manufactured with precast concrete and assembled on site,
This is a construction method in which cast-in-place concrete is driven into the precast concrete formwork and the final member is completed while being integrated.

According to such a half precast method, it has been established as a method that does not require skilled workers, requires a small number of workers, and improves productivity. In addition, it can be considered as one of the construction methods that enables energy reduction throughout the entire building life cycle in the process from production to disposal of formwork.

However, since the final member formed by this half precast method is a composite structure composed of precast concrete formwork and cast-in-place concrete, it is necessary to ensure the structural integrity of both, Continuity must be ensured at the joint between the precast concrete formwork materials. In particular, since there is a limit to the length of the precast concrete formwork material, in the case of a long object such as a beam, a joint portion is generated between the formwork materials. Therefore, the bending strength / deformation properties, etc. are not impaired by the influence of this joint, that is, it has continuity with bending strength / deformation properties equal to or better than the cast-in-place integrated member formed by cast-in-place concrete. It needs to be designed to be something.

Conventionally, in a composite concrete member formed by a half precast method having a joint in the direction perpendicular to the material axis in the middle, and as an improvement in bending strength at the joint,
For example, in the invention according to Japanese Patent Application Laid-Open No. 5-321324, the bottom main bar protrudes from one end or both ends of the member by notching the bottom wall of one end or both ends of the precast concrete member having a bowl shape of the top opening to expose the bottom main bar. Half that overlaps each other in the notch part, or arranges connecting bars so as to straddle both lower end main bars exposed in the notch part, and places concrete in the hook-like part to connect A precast beam is disclosed.

In addition, in the invention according to Japanese Patent Laid-Open No. 11-61979, a method for constructing a reinforced concrete structure by a precast formwork method in which the joint position between the precast embedded formwork members and the joint of the cast-in-place concrete is separated by 10 cm or more is proposed. Furthermore, JP-A-20
In the invention according to No. 00-141328, a permeable earth and sand spill prevention sheet is bonded to the end joint portion of the precast formwork member, and concrete is placed thereon, so that unevenness for improving adhesion is provided. A formwork method for jointing precast concrete members has been proposed.

JP-A-5-321324 Japanese Patent Laid-Open No. 11-61979 JP 2000-141328 A

However, each of these proposals is merely a reinforced part of the joint by adding a device to the structure of the joint or the surface of the joint. No proposals for improving deformation properties are disclosed. That is, in a composite concrete member formed by a half precast method having a joint in the middle, in order to improve the bending strength of the member, this integrity is verified while verifying the integrity of the composite member with respect to a vertical load. Development of general-purpose bending strength improvement means related to the position of the joints to secure, the distance between the joints, the joint surface orthogonal reinforcing bars, etc. is required, but the above-mentioned conventional proposals do not disclose any of these points. Absent.

In general, in designing a precast concrete member at a material axis orthogonal joint, it is necessary to confirm that the bending strength M or shear strength Q in each state of the joint exceeds the design bending moment Md or the design shear force Qd. . The design bending moment Md or the design shearing force Qd determines the type of stress transmission of the joining element according to the applied stress and the allowable deformation, and the transmission of the axial force acting on the reinforcing bar is from a direct joint or an indirect joint. It is necessary to make a selection (The Architectural Institute of Japan “In-Situ Equivalent Precast Reinforced Concrete Structural Design Guidelines (Draft) / Comment 2002”)

The present invention is a half-precast composite concrete member, and has been subjected to various experiments on the position of the joint, the spacing of the joint, the size of the joint surface orthogonal reinforcement, etc. to ensure the integrity to the vertical load. The purpose of the present invention is to provide a composite concrete member having bending strength and deformation properties almost equal to those of the in-situ integrated member.

In order to achieve the above object, the invention according to claim 1 of the present application is arranged with a pair of precast concrete formwork members separated from each other in the left and right directions, each of which is formed by embedding a plurality of assembly bars extending in parallel along the longitudinal direction. This is a half precast member in which a plurality of mold materials having the same structure as these are arranged in the longitudinal direction via joints and are connected and integrated with the main bars arranged over the entire length by cast-in-place concrete. Thus, in the left and right shear regions formed in the member cross section by the bending stress of the member, the joint portion is provided at the center of the span length direction.

In addition, the invention according to claim 2 of the present application is that when a pair of precast concrete formwork members formed by embedding a plurality of assembly bars extending in parallel along the longitudinal direction are arranged apart from each other on the left and right sides,
A half precast member in which a plurality of sets of mold materials having the same configuration are arranged in the longitudinal direction via joints, and are connected and integrated with main bars arranged over the entire length by using cast-in-place concrete. A composite concrete member characterized in that a reinforcing bar whose diameter is set to be equal to or greater than a total of the moments of section with respect to the compression edge is disposed and connected at a tensile main bar position across the joint. It is.

Furthermore, the invention according to claim 3 of the present application is the composite concrete member according to claim 1 or 2, wherein the interval between the joints is 1. which is the maximum dimension of the coarse aggregate used for the cast-in-place concrete. 3 to 2.5 times or less, or 30 mm to 50 mm or less.

The invention according to claim 4 of the present application is the invention according to claims 1 to 3, wherein the composite concrete member is a beam or a foundation beam.

Since the composite concrete member according to the present invention can be formed by a half precast method, there is an advantage in that it does not require a skilled worker, requires a small number of workers, and improves productivity. According to the invention according to the above, it is possible to obtain a composite concrete member that is easy to connect between the half precast mold materials and that has a bending strength almost equivalent to that of the in-situ integrated member.

Further, according to the invention according to claim 2, the composite having bending strength / deformation properties almost equal to those of the in-situ integrated member, regardless of the position of the joining portion connecting the half precast mold materials to each other. When a concrete member can be obtained, it is possible to obtain a composite concrete member having even greater bending strength than the composite concrete member according to claim 1.

Furthermore, according to the invention which concerns on Claim 3, on-site concrete is fully filled also between the end surfaces in the junction part between half precast formwork materials. Therefore, it is not directly affected by the surface properties of the end face of the mold material, and there is no risk that this joint will become a cross-sectional defect. Will improve. Moreover, since the space | interval of a junction part can be determined easily, connection of half precast mold materials can be performed easily, and manufacture of a composite concrete member is easy.

Moreover, according to the invention which concerns on Claim 4, the beam or foundation beam provided with bending strength and a deformation | transformation property substantially equivalent to an in-situ integrated member can be obtained.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. In the figure, reference numeral 1 denotes a composite concrete member made of a half precast structure. As shown in FIGS. 1 and 2, a precast made of a pair of left and right horizontal rectangular plates facing each other at a predetermined interval. When the concrete mold materials 2 and 2 and the precast concrete mold materials 2 and 2 having the same structure as those at one end are arranged in the longitudinal direction with a predetermined distance D, they are arranged over the entire length inside. An upper end main bar 3a and a lower end main bar 3b, and a cast-in-place concrete 4 in which the upper and lower main bars 3a and 3b are respectively arranged inside, are integrated via a joint portion 5 (hereinafter referred to as a half). A precast member).

Inside the precast concrete formwork 2, a plurality of assembly bars 6, 6 extending in parallel in the horizontal direction and arranged in multiple stages, and a vertical direction fixed by welding or binding to the assembly bars 6, 6. A plurality of gluteal muscles 7, 7 extending in the direction are embedded. Each of the barbs 7 has a substantially C shape, and when the pair of left and right precast concrete formwork materials 2 and 2 are arranged to face each other, Form material 2 on the other side from the upper and lower ends
The upper and lower horizontal bent portions 8a and 8b projecting toward the upper side and the upper and lower vertical bent portions 9a and 9b facing the inner side surface of the counterpart mold material 2 are provided.

In addition, as described above, a plurality of upper main bars (compression side main bars) 3a, 3a extending in the horizontal direction over the entire length of the half precast member 1 are provided inside the cast-in-place concrete 4 as described above.
The same number of lower main bars (tensile side main bars) 3b and 3b are embedded, the upper main bar 3a is a horizontal bent portion 8a above the gluteal barb 7, and the lower main bar 3b is a lower horizontal bar. The bent portion 8b is fixed to each other by welding or binding.

Here, the interval D of the joint portion 5 was set to 1.3 times to 2.5 times the maximum dimension of the coarse aggregate used for the cast-in-place concrete 4 or 30 mm to 50 mm. The reason is that when the end faces of the precast formwork materials 2 and 2 are in contact with each other,
This is because it is directly affected by the surface properties of the end faces of the precast mold frames 2 and 2, and this portion becomes a cross-sectional defect. The concrete is sufficiently filled between the end surfaces of the frame members 2 and 2. On the other hand, if an excessive interval width is provided, as shown in FIG. 3, when the cast-in-place concrete 4 is placed, the side frame plates B _{1 and} B ₁ arranged on the joint 5 become large and work is performed. It is not preferable. In FIG. 3, B ₂
Is a bottom frame plate.

Basically, the joining strength is equivalent to that of an in-situ concrete integrated member (hereinafter referred to as an in-situ integrated member), and it is not desirable from the viewpoint of cost to provide an excessive joining means. Therefore, it is most desirable to provide an interval so that the concrete to be placed later functions as a wet joint as it is. Therefore, when the maximum dimension of the coarse aggregate is 20 mm, for example, the distance D of the joint portion 3 is set to 30 to 50 mm. Actually, it may be set from 1.3 times to 2.5 times that of the coarse aggregate maximum dimension.

Moreover, in the half precast member 1 used in a place where a load load is applied as shown in FIGS. 4A and 4B, the position where the joint portion 5 is provided depends on the bending stress of the half precast member 1. In the case of the half precast member 1 used in a shear region Y formed in the cross section or a place where a load is applied as shown in FIG. 4C, the cross section is formed in the member cross section by the bending stress of the half precast member 1. It is necessary to provide each at a position off the center of the central bending region C. More preferably, the shear region Y is provided at the center in the span length direction, and the central bending region C is provided at a position off the center where the ultimate bending moment is obtained.

The reason is that the half precast member 1 provided with the joint 5 in the center in the span length direction in the shear region Y exhibits a bending strength almost equivalent to that of the in-situ integrated member, and the central bending region. The ground is that the half precast member 1 in which the joint 5 is provided at a position deviating from the center position where the final bending moment is present in C exhibits the same integral deformation characteristics as the in-situ integrated member. Also, in the structure type in which shearing force acts, there is no influence on the integrity due to the joint, and the ultimate fracture strength is slightly different depending on the shearing force ratio, but it is also the same as the in-situ integrated member. one of.

As described above, in the half precast member 1, there is no influence of the joint portion on the shearing force, but the influence appears significantly on the bending depending on the position of the joint portion.
That is, when the joint portion is provided at the center of the bending region C, the bending shape becomes a V shape when the bending yield strength of the defect cross section is reached. Therefore, in the half precast member, in order to make the bending strength equivalent to that of the in-situ cast integrated member, it is necessary to form the joint at a position deviating from the position where the ultimate bending moment is obtained.

However, even when the joint portion 5 is provided at the center of the bending region C, a half precast member that can ensure a bending strength substantially equivalent to that of the on-site integrated member by adopting the structure shown in FIGS. 1 can be obtained. That is, in the figure, reference numeral 10 denotes a reinforcing bar embedded in the joint portion 5, and has a diameter that is a magnitude of a cross-sectional primary moment that is equal to or greater than the sum of the cross-sectional primary moments with respect to the compression edges of the assembly bars 6 and 6. The lower bent main bars 3b are arranged along the lower end main bars 3b and straddling the joint 5, and the horizontal bent parts 8b below the lower main bars 3b and the heel bars 7 are arranged.
It is fixed by welding or binding.

Here, it is desirable that the reinforcing bars 10 are provided with a predetermined fixing length on both sides of the axial length at the center of the joint portion 5. In other words, “Reinforced Concrete Structural Calculation Standards and Explanation” (Architectural Institute of Japan,
1999), the primary moment of section is set to coincide with the calculation formula of the adhesion fixing length defined in Article 16. Therefore, if the cross section and the reinforcing bar diameter are different, the fixing length may be calculated according to this. Further, the reinforcing bar 10 abuts the precast formwork 2 with each other,
It can be easily installed before the on-site concrete 4 is placed.

Next, the reasons for the above limitation regarding the position of the joint portion 5 of the half precast member 1 according to the present invention, the distance D of the joint portion 5 and the size of the joint surface orthogonal reinforcing bars 10 will be described below based on experimental results. To do. As shown in FIGS. 1 and 2, the half precast member (hPCa) subjected to the experiment has a thickness of 300 mm, a height of 800 mm, and a length of 7000 mm. SD 295 D 22 was used for the upper main bar 3a and lower main bar 3b, and D 295 of SD 295 was used for the assembly bar 6 and the heel bar 7, respectively. G 3112).

The main muscle ratio is 0.38% and the gluteal muscle ratio is 0.24%. The upper and lower horizontal bent portions 8a and 8b are fixed to the cast-in-place concrete 4 in accordance with JASS 5, and the length of the upper and lower vertical bent portions 9a and 9b is 8D. Established. The half precast member (hPCa)
As a comparison object, as shown in FIG. 7, an in-situ integrated test body (RC) by a conventional method was manufactured with the same material and the same dimensions.

Table 1 shows the composition and strength of the precast concrete formwork material 2 and the cast-in-place concrete 4. In addition, Table 2 shows the position of the joint of each specimen, the distance between the joints, the joint surface orthogonal reinforcing bars (reinforcing bars)
The list is shown.

FIG. 4C shows a loading method for the bending test. Loading was divided into several stages, and loading and unloading were repeated while increasing the maximum loading floor, and finally continued until the specimen was destroyed. In addition, using a gauge and displacement meter, the specimen surface, reinforcing bar strain, load, crack width, curvature (center position in the bending span, 300 mm length in the axial direction of the specimen, compressive strain and tensile strain at the top and bottom of the specimen) Of the absolute amount of the two parts divided by the distance between the vertical displacement measurements), and the change of these displacements with respect to the test load, the integrity of the half precast member (hPCa) based on the in-situ integrated member (RC) Evaluated.

Table 3 shows the test results for each specimen. As is apparent from Table 3, those having no joint (seam) show a bending strength almost equal to that of the cast-in-place integrated member (RC) even in the half precast member (hPCa). However, when the joint 5 is provided in the center of the loading point, or when the joint 5 is a wedge joint, the half precast member (hPCa) is 60 to 70% of the bending strength of the in-situ integrated member (RC). It shows only the bending strength.

However, even if the joint 5 is in the center of the loading point, the reinforcing bar (D16 of SD 295) 10 is arranged and connected at the position of the tension main bar 3b so that the first moment of section coincides with the compression edge of the assembly bar 6. In this case, the bending strength almost equal to that of the in-situ integrated member (RC) is shown. In addition, in the shear region formed in the cross section of the member by the bending stress of the half precast member (hPCa), even when the joint portion 5 having a predetermined interval is provided at the center in the span length direction, the in-situ integrated member (RC) Shows almost the same bending strength. In this test example, since the coarse aggregate maximum dimension was 20 mm, the interval between the joints was set to 30 to 50 mm.

Next, in the present invention, “variability” and “similarity” are introduced as indicators of the integrity of the half precast member (hPCa). “Variability” is an evaluation of the variation of local deformation state of the test specimen.
(Amax−Amin) / 2Aave (1)
However, Amax, Amin, and Aave indicate the maximum value, minimum value, and average value of the measurement target A.
And is evaluated as a variation coefficient.

“Similarity” is an evaluation of the integrity of a half precast member (hPCa) to an in-situ integrated member (RC).
Aave-pca / Aave-rc (2)
However, Aave-pca and Aave-rc are a half precast member
The average value of the measurement object A is shown.
And is evaluated as a similarity coefficient.
For each measurement object such as crack, displacement, strain, etc., by introducing the variation coefficient and similarity coefficient calculated by the above formulas (1) and (2), Integrity can be evaluated.

FIG. 8 shows the results of evaluation by introducing a similarity coefficient regarding the load and a variation coefficient regarding the total crack width in order to evaluate the integrity of the half precast member (hPCa) under bending stress. The variation coefficient of the cast-in-place integrated member (RC) is within 10% for each loading step, while the half precast member (hPCa) becomes remarkably large after the fifth step in which the compressive strain on the specimen surface exceeds 3000 μm. . However, it has been clarified that the similarity coefficient regarding the strength characteristics (load and deflection) is not affected.

From the above, the half precast member (hPCa) when the reinforcing bar 10 is disposed and connected to the position of the tension side main bar (lower bar main bar) 3b so that the primary moment of section coincides with the compression edge of the assembled reinforcing bar 6 In addition to the bending strength being almost equivalent to the cast-in-place integrated member (RC),
It was found that the deformation characteristics with respect to the vertical load can be regarded as almost the same as the in-situ integrated member.

By the way, even in the case where the joint 5 having a predetermined interval is provided at the center in the span length direction in the left and right shear regions formed in the member cross section by the bending stress of the half precast member (hPCa), In order to clarify the grounds for showing a bending strength almost equal to RC), the deformation characteristics during the bending test were compared between the half precast member (hPCa) and the cast-in-place integrated member (RC).

FIG. 9 summarizes the relationship between the half precast member (hPCa) and the cast-in-place integrated member (RC) with respect to the position of the joint 5 with respect to the specimen surface strain, rebar strain, total crack width and curvature when the specimen is crushed. It is a thing. According to this result, an integral deformation characteristic can be obtained as in the case of the cast-in-place integrated member (RC) by shifting the position of the joint portion 5 from the position (center) where the ultimate bending moment is obtained under the condition where bending stress acts. It can be seen that

Separately from this, as shown in FIGS. 4 (a) and 4 (b), a shear test was performed with a shear span ratio of 1.0 to 0.5. The results are shown in Table 4. According to this result, in the structure type in which the shearing force acts, there is no influence on the integrity by the joint portion 5, and the ultimate breaking strength varies slightly depending on the shear ratio, but is almost the same as the cast-in-place integral member (RC). It turns out that it becomes.

Next, the diameter of the reinforcing bar 10 will be described in more detail with reference to FIG. 5. In the test specimen, two reinforcing bars 10 of D16 are provided at the position of the tensile main bar 3b. The assembly bar 6 is D
A total of five of the 16 types are provided with a distance of 177.5 mm between 45 mm of left and right top and bottom cover. Therefore, considering the distance from the compression edge, which is the bending load surface,
In the reinforcing bar 10,
755 x AD16 x 2 = 755 x 198.6 x 2 = 299,886mm ³
In the assembly muscle 6,
(45 +222.5 +400 +577.5 +755) x AD10 x 2 = 2000 x 71.33 x2 = 285,320 mm ³
However, 198.6 and 71.33 indicate the nominal cross-sectional areas of AD16 and AD10.
It becomes. Therefore, since the cross-sectional primary moment of the reinforcing bar 10 is larger than the sum of the cross-section primary moments of the assembly bars 6, a sufficient reinforcing effect can be obtained.

It is a partially cutaway perspective view of a composite concrete member according to the present invention. It is a cross-sectional enlarged view of the junction part in the same member. It is the top view (a) and front view (b) of the principal part which show a manufacturing method. It is explanatory drawing which shows a loading test method. It is a cross-sectional enlarged view which shows other embodiment of a junction part. It is a partially notched perspective view which shows the bar arrangement state in the junction part. It is a cross-sectional enlarged view of the cast-in-place concrete member used for the test body. It is a graph which shows the relationship between the similarity coefficient and variation coefficient of the half precast member used for the test body. It is a graph which shows the test result about the relationship between the position of a junction part with respect to bending stress and a deformation characteristic in a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Composite concrete member 2 Precast concrete formwork material 3a Top main reinforcement 3b Lower bottom main reinforcement 4 On-site concrete 5 Joint part 6 Assembly reinforcement 7 Reinforcing bar 8a Upper horizontal bent part 8b Lower horizontal bent part 9a Upper vertical bent part 9b Lower vertical bent portion 10 Reinforcement bar Y Shear region

Claims (4)

When a pair of precast concrete formwork members, each of which is formed by embedding a plurality of assembly bars extending in parallel along the longitudinal direction, are spaced apart from each other on the left and right sides, the same formwork formwork material is inserted through the joints. A half precast member that is arranged in a plurality of lengths in the longitudinal direction and is integrated by connecting the main bars arranged over the entire length with cast-in-place concrete, and the left and right shear regions formed in the member cross section by the bending stress of the member The composite concrete member according to claim 1, wherein the joint portion is provided at the center of the span length direction. When a pair of precast concrete formwork members, each of which is formed by embedding a plurality of assembly bars extending in parallel along the longitudinal direction, are spaced apart from each other on the left and right sides, the same formwork formwork material is inserted through the joints. A half precast member that is arranged in a plurality in the longitudinal direction and is integrated by connecting the main bars arranged over the entire length with cast-in-place concrete, and with respect to the sum of the cross-sectional primary moments with respect to the compression edges of the assembly bars A composite concrete member characterized in that reinforcing bars whose diameters are equal to or greater than each other are arranged and connected at the position of the tensile main bar across the joint. The distance between the joints is 1.3 of the maximum size of the coarse aggregate used for the cast-in-place concrete.
The composite concrete member according to claim 1 or 2, wherein the composite concrete member is not less than 2.5 times and not more than 2.5 times or not less than 30 mm and not more than 50 mm. The composite concrete member according to claim 1, wherein the composite concrete member is a beam or a foundation beam.

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