JP7503439B2 - Composite Beam - Google Patents

Description

The present invention relates to a composite beam made of wood and reinforced concrete.

Conventionally, hybrid structural materials that combine steel frames or reinforced concrete with wood materials have been used as the framework of building structures.
For example, Patent Document 1 discloses a composite beam structure in which a rigid reinforcing material made of metal and a wooden material are sandwiched and laminated together, and the reinforcing material and the wooden material are fixed together with an adhesive.
In a hybrid structural material such as that disclosed in Patent Document 1, the stress in the direction along the joint surface between the reinforcing material and the wood material is transmitted only by the adhesive force. Therefore, when a large stress acts between the reinforcing material and the wood material, the adhesive may peel off the fixed portion. Although such a structure is suitable for use in a form that mainly supports the load in the layering direction of the reinforcing material and the wood material, it is not suitable for use in a form that supports the load or stress in the direction along the joint surface between the reinforcing material and the wood material. Therefore, it is difficult to use the structure disclosed in Patent Document 1 as, for example, a beam.

In response to this, Patent Document 2 discloses a hybrid structural material that includes a central steel material, a wooden member provided along the central steel material, and a connecting member that connects the central steel material and the wooden member. In this hybrid structural material, the connecting member extends in the longitudinal direction of the central steel material, with one end fixed to the wooden member and the other end fixed to the pressure-receiving part.
In a hybrid structural material such as that disclosed in Patent Document 2, load and stress are transferred between the central steel material and the wooden members, so that the central steel material and the wooden members bear the load and stress, respectively. However, in this structure, the load and stress are not transferred at the joint surface between the side of the central steel material and the wooden steel material. For this reason, it is desired to provide a technology that can improve the bending rigidity and bending strength of the beam.

Patent Document 3 discloses a laminated member having a plurality of coating layers made of wood and a structural layer made of a cement-based composition filled between the coating layers, in which recesses or openings are provided on the side of the coating layers facing the structural layer, and the cement-based composition is filled into the recesses or openings to form a shear key.
In the laminated member disclosed in Patent Document 3, the load and stress are transmitted between the structural layer and the covering layer in the direction along the joint surface between the structural layer and the covering layer through the shear key formed in the recess or opening of the covering layer. However, since the shear key is made of a cement-based composition and is formed in a protruding shape protruding from the surface of the structural layer, it may break when a large load or stress is applied. Therefore, it is desired to provide a technology that can more effectively improve the bending stiffness and bending strength of the beam.

Japanese Patent Application Laid-Open No. 6-226715 JP 2017-179838 A JP 2019-52451 A

The problem that this invention aims to solve is to provide a composite beam made of wood and reinforced concrete that has excellent bending rigidity and bending strength.

The inventors have developed the present invention by focusing on the fact that a composite beam structure capable of being made longer spans can be realized by forming a composite beam with a reinforced concrete section and wooden sections on both sides of the reinforced concrete section and connecting the two with a steel stress distribution means, and thus a wooden composite beam with superior bending rigidity and bending strength compared to a single reinforced concrete beam can be realized because the reinforced concrete section is stiffened by the wooden sections. The reinforced concrete section is formed by conventional reinforced concrete construction in which only reinforcing bars are embedded in the concrete, fiber reinforced concrete construction, or prestressed concrete construction in which concrete is reinforced by applying compressive stress through PC steel.
In order to solve the above problems, the present invention employs the following means.
In other words, the composite beam of the present invention is a composite beam made of wood material and reinforced concrete and extending in the axial direction, comprising a reinforced concrete section in which main beam reinforcement and shear reinforcement are embedded and whose longitudinal cross section perpendicular to the axial direction is T-shaped or rectangular, a wood section provided on at least both side surfaces of the reinforced concrete section, and a steel stress distribution means embedded across and connecting the reinforced concrete section and the wood section, causing the wood section to share the stress acting on the reinforced concrete section, and at least the lower end surface of the reinforced concrete section is exposed.
According to this configuration, a steel stress distribution means is embedded so as to straddle the reinforced concrete portion and the wood portion. This allows the stress acting on the reinforced concrete portion to be effectively transmitted to the wood portion in a direction along the joint between the reinforced concrete portion and the wood portion via the stress distribution means. Therefore, the stress acting on the reinforced concrete portion is shared and borne not only by the reinforced concrete portion but also by the wood portions on both sides. As a result, it is possible to provide a composite beam composed of wood material and reinforced concrete, which has excellent bending rigidity and bending strength.
In this composite beam, a reinforced concrete section with excellent rigidity and strength is provided in the center of the beam cross section, and wooden sections are provided on both sides of the reinforced concrete section as stiffening materials, making it possible to achieve a long span that would be difficult to achieve with wooden materials alone. Furthermore, because both sides of the composite beam in the width direction are formed by wooden sections, it can present a warm appearance that is unique to wood-based materials. In other words, such a composite beam can be used to construct a wood-based composite structural member in which the reinforced concrete section is stiffened and reinforced by the wooden sections on both sides.
In addition, in a composite beam, the reinforced concrete portion and the wooden portion are joined and integrated with a steel stress distribution means, so that the wooden portion acts as a stiffener for the reinforced concrete portion, reducing the warping or deflection that occurs in the reinforced concrete portion. Furthermore, in a composite beam, the lower end surface of the reinforced concrete portion is not covered by the wooden portion, and since the lower end surface is exposed, when the composite beam deflects, the reinforced concrete portion provided at the center of the cross section of the composite beam can deform downward without being affected by the wooden portion. Therefore, the composite beam only needs to have wooden portions on both sides of the reinforced concrete portion, making it possible to realize a composite beam with a highly designed form.

The present invention also provides a composite beam composed of wood material and reinforced concrete and extending in an axial direction, comprising: a reinforced concrete section in which beam main reinforcement and shear reinforcement are embedded and whose longitudinal cross section perpendicular to the axial direction is T-shaped or rectangular; wood material provided on at least both side surfaces of the reinforced concrete section; and steel stress sharing means embedded across and connecting the reinforced concrete section and the wood material to share the stress acting on the reinforced concrete section with the wood material, wherein the wood material comprises side wood material provided on both side surfaces so as to sandwich the reinforced concrete section, and a bottom wood material installed on the underside of the reinforced concrete section in a state not joined to the side wood material.
According to this configuration, a steel stress distribution means is embedded so as to straddle the reinforced concrete portion and the wood portion. This allows the stress acting on the reinforced concrete portion to be effectively transmitted to the wood portion in a direction along the joint between the reinforced concrete portion and the wood portion via the stress distribution means. Therefore, the stress acting on the reinforced concrete portion is shared and borne not only by the reinforced concrete portion but also by the wood portion. As a result, it is possible to provide a composite beam composed of wood material and reinforced concrete, which has excellent bending rigidity and bending strength.
In this composite beam, a reinforced concrete section with excellent rigidity and strength is provided in the center of the beam cross section, and a wooden section is provided as a stiffening material, which allows for a long span that would be difficult to achieve with wooden materials alone. Furthermore, because the composite beam is formed from wooden sections, it can have a warm appearance that is unique to wood-based materials. In other words, such a composite beam can be used to form a wood-based composite structural member in which the reinforced concrete section is stiffened and reinforced by the wooden section.
Furthermore, by providing a composite beam with a reinforced concrete section, side wooden materials provided on both sides of the reinforced concrete section, and a bottom wooden material installed in a non-jointed state with the side wooden materials, when the composite beam reaches a large deformation state, the reinforced concrete section and the bottom wooden material can resist deformation as a whole without being restrained by the side wooden materials. Also, in a composite beam, because the side wooden materials and the bottom wooden material are installed in a non-jointed state, damage and destruction to the joints between the two can be suppressed, and excellent deformation performance can be ensured.

In another aspect of the present invention, the reinforced concrete section is a prestressed concrete structure, and tension is introduced into at least a portion of the beam reinforcement.
According to this structure, by introducing tension into a part of the reinforced concrete section to form a prestressed concrete structure, it is possible to increase the bending stiffness and bending strength compared to a case where the reinforced concrete section is a reinforced concrete structure made of cast-in-place concrete. This makes it possible to realize a composite beam that can be made into a long span.

The present invention makes it possible to provide a composite beam made of wood and reinforced concrete that has excellent bending rigidity and bending strength.

FIG. 1 is a plan view showing an example of a structure including a composite beam according to an embodiment of the present invention. FIG. 2 is a side view of the composite beam of FIG. 3 is a cross-sectional view of the composite beam shown in FIG. 2 taken along the line II. 3 is a cross-sectional view of the composite beam shown in FIG. 2 taken along the line II-II. 3 is a cross-sectional view of the composite beam shown in FIG. 2 taken along the line III-III. FIG. 13 is a cross-sectional view showing the state in which the main beam reinforcement and shear reinforcement are arranged and the formwork is assembled, illustrating the process of the construction method for a composite beam. FIG. 13 is a cross-sectional view showing the process of constructing a composite beam, in which concrete has been poured into the beam forming portion of the reinforced concrete section. FIG. 1 is a cross-sectional view showing a composite beam according to a first modified example of the embodiment of the present invention. 13 is a cross-sectional view showing the state in which the main beam reinforcement and shear reinforcement are arranged and the formwork is assembled, showing the process of the construction method of the composite beam of the first modified example. FIG. FIG. 11 is a cross-sectional view showing a composite beam according to a second modified example of the embodiment of the present invention. FIG. 1 is a diagram showing the installation status of a composite beam test specimen simulating the composite beam of the present invention and a schematic configuration of a bending test device thereof. These are the experimental results of the bending moment and central deflection relationship of a composite beam specimen.

The present invention is a composite beam in which a reinforced concrete section is provided in the center of the beam cross section and wooden sections are provided on both side surfaces, or on both side surfaces and the bottom end surface, and the reinforced concrete section and the wooden sections are joined via a steel stress sharing means.
The first embodiment is a composite beam in which wood parts are provided only on both side surfaces of the reinforced concrete part, and the reinforced concrete part and the wood part are joined by stress sharing means (bolts) that penetrate both. The first modified example is a composite beam that differs from the first embodiment only in the stress sharing means that joins the reinforced concrete part and the wood part, and the stress sharing means is not a bolt that penetrates both, but a structural screw that penetrates the wood part and remains within the cross section of the reinforced concrete part. The second modified example has wood parts provided on both side surfaces and the bottom end surface of the reinforced concrete part. The second modified example is characterized in that the side wood material provided on both side surfaces of the reinforced concrete part that constitutes the wood part and the bottom wood material provided on the bottom end surface are installed in a non-jointed state.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a composite beam according to the present invention will be described with reference to the accompanying drawings.

A plan view showing an example of a structure including a composite beam according to an embodiment of the present invention is shown in Fig. 1. Fig. 2 is a side view of the composite beam of Fig. 1.
As shown in Figure 1, the main body of a structure 1 equipped with a composite beam 10 of this embodiment has an outer periphery frame 2 arranged along the outer periphery of the structure 1, and an inner frame 3 arranged inside the outer periphery frame 2.
The outer perimeter frame 2 comprises a plurality of outer perimeter columns 4 (see Figure 2) arranged at intervals along the outer perimeter of the structure 1, and outer perimeter beams 5 erected between adjacent outer perimeter columns 4.

As shown in FIG. 1, the inner frame 3 mainly includes a plurality of columns 6, a first inner beam 7, and a second inner beam 8. The plurality of columns 6 are arranged inside the outer frame 2 at intervals in a first horizontal direction D1. The first inner beam 7 extends in the first direction D1 and is supported by the plurality of columns 6. The first inner beam 7 is provided so as to connect the outer beams 5A located on both sides of the first direction D1. Two sets of such first inner beams 7 (and the plurality of columns 6 supporting the first inner beams 7) are provided at intervals in the second direction D2 in the center of the structure 1, which is perpendicular to the first direction D1 in the horizontal plane.
The second inner beam 8 extends in the second direction D2 as shown in Fig. 1. The second inner beam 8 is installed between the outer peripheral beam 5B and the first inner beam 7 located on both sides in the second direction D2 (and between the two first inner beams 7 arranged at an interval in the second direction D2). A plurality of sets of the second inner beams 8 are provided at intervals in the first direction D1.

Fig. 3 is a cross-sectional view of the composite beam shown in Fig. 2 taken along line II. Fig. 4 is a cross-sectional view of the composite beam shown in Fig. 2 taken along line II-II. Fig. 5 is a cross-sectional view of the composite beam shown in Fig. 2 taken along line III-III.
Each of the second inner beams 8 is formed of a composite beam 10 according to this embodiment.
The composite beam 10 is made of wood and reinforced concrete. The composite beam 10 is provided so that the axial direction Da extends along the second direction D2. As shown in Figs. 2 to 5, the composite beam 10 has a reinforced concrete part 20, a wood part 30, and a stress sharing means 40.

The reinforced concrete section 20 functions as the main material that mainly bears the load and stress acting on the composite beam 10. Both ends of the reinforced concrete section 20 in the axial direction Da are joined to the outer perimeter beam 5 (or outer perimeter column 4) of the outer perimeter frame 2 or the first inner beam 7 (or column 6). As shown in Figures 3 to 5, the reinforced concrete section 20 mainly comprises a concrete section 21, beam main reinforcement 24, and shear reinforcement 25.

In this embodiment, the reinforced concrete part 20 (concrete part 21) has a vertical cross-sectional shape perpendicular to the axial direction Da, for example, a T-shape. The reinforced concrete part 20 has a web part 22 and a flange part 23 integrally formed therewith. The web part 22 has a vertical cross-sectional shape perpendicular to the axial direction Da that is long in the vertical direction Dv (vertically elongated rectangular shape). The flange part 23 is formed on the web part 22. The flange part 23 extends from the upper end of the web part 22 to both sides in the width direction Dw perpendicular to the axial direction Da and the vertical direction Dv. The flange part 23 forms at least a part of the slab of the upper floor. The flange parts 23 of the composite beams 10 adjacent to each other in the first direction D1 may be butted against each other to form the slab of the upper floor. In addition, the slab of the upper floor may be formed by installing a slab panel made of, for example, wood material, precast concrete material, or steel material so as to straddle the flange portions 23 of the composite beams 10 adjacent to each other in the first direction D1.

The beam main reinforcements 24 and the shear reinforcement bars 25 are embedded in the web portion 22 of the concrete portion 21. A plurality of beam main reinforcements 24 (e.g., four each) are arranged at intervals in the width direction Dw at the upper and lower portions of the web portion 22. Each beam main reinforcement 24 extends in the axial direction Da. At least a portion of the beam main reinforcements 24 (e.g., the beam main reinforcements 24 arranged at the lower portion of the web portion 22) is made of PC steel, and a predetermined tension is introduced to both ends of the concrete portion 21 in the axial direction Da by fixing devices (not shown). As a result, in this embodiment, the reinforced concrete portion 20 has a prestressed concrete structure.
The shear reinforcement bars 25 are provided so as to surround the multiple beam main reinforcements 24. The multiple shear reinforcement bars 25 are arranged at intervals in the axial direction Da.

2 and 4, holes 26 for removing weight (reducing weight) are formed at a plurality of locations spaced apart in the axial direction Da in the reinforced concrete portion 20. Each hole 26 is formed penetrating the reinforced concrete portion 20 in the width direction Dw.
As shown in Fig. 4, the beam main reinforcement bars 24 are arranged above and below each hole 26 so as not to interfere with the holes 26. In addition, the shear reinforcement bars 25 have upper shear reinforcement bars 25A arranged to surround the upper beam main reinforcement bars 24A arranged above the hole 26 and lower shear reinforcement bars 25B arranged to surround the lower beam main reinforcement bars 24B arranged below the hole 26, at the upper and lower parts of the hole 26.

In this embodiment, the wood parts 30 are realized as side wood materials. That is, as shown in Figs. 3 to 5, the wood parts 30 are arranged on both sides of the web part 22 of the reinforced concrete part 20 in the width direction Dw. As shown in Fig. 2, in this embodiment, the wood parts 30 are provided not on the entire length of the composite beam 10, but on a part excluding a predetermined length part at both ends of the composite beam 10 in the axial direction Da. As shown in Figs. 3 to 5, each wood part 30 is provided so as to respectively follow the side surfaces 22s on both sides of the web part 22 of the reinforced concrete part 20 in the width direction Dw. Each wood part 30 has a vertical cross-sectional shape perpendicular to the axial direction Da that is long in the up-down direction Dv (vertically elongated rectangular shape). As shown in Fig. 3, the thickness T2 of each wood part 30 in the width direction Dw is smaller than the thickness T1 of the web part 22 of the reinforced concrete part 20 in the width direction Dw. The wood part 30 is made of, for example, larch laminated lumber having a thickness of 120 mm.
The upper end surface 30a of each wood part 30 is provided in contact with the lower surface 23b of the flange part 23. The upper end surface 30a of the wood part 30 is cut downward on the outer side in the width direction Dw to form a step part 30d. As a result, a gap S is provided in the vertical direction Dv between the wood part 30 and the lower surface 23b of the flange part 23 on the outer side in the width direction Dw of the upper end of each wood part 30. In addition, when constructing a floor slab to be connected to the composite beam 10, a formwork can be installed in this gap S, which can be used to form a floor slab of reinforced concrete construction. Since the upper end surface 30a of each wood part 30 is in contact with the flange part 23, stress is transmitted from the flange part 23 to the wood part 30.
When viewed from below in the vertical direction Dv, the lower end faces 30b of each wood part 30 are exposed on both sides of the web part 22 of the reinforced concrete part 20. In this embodiment, the lower end faces 30b of each wood part 30 protrude downward beyond the lower end faces 22b of the web parts 22 of the reinforced concrete part 20.
In this embodiment, no wood portion is provided on the lower end surface 22b of the reinforced concrete portion 20, and therefore at least the lower end surface 22b of the reinforced concrete portion 20 is exposed to the outside.

As shown in FIG. 4 , the wood part 30 has through holes 33 formed at positions communicating with the holes 26 of the reinforced concrete part 20 .
A waterproof film 32 such as a waterproof coating is formed on at least the portion of the wooden part 30 that faces and contacts the reinforced concrete part 20. The waterproof film 32 prevents moisture contained in concrete from seeping into the wooden part 30 when the concrete that forms the concrete part 21 is poured and cured in the construction process of the composite beam 10, which will be described in detail later.

As shown in Fig. 5, the stress sharing means 40 joins the reinforced concrete part 20 and the wood part 30 on both sides in the width direction Dw of the web part 22 of the reinforced concrete part 20. The stress sharing means 40 is embedded so as to straddle the reinforced concrete part 20 and the wood part 30. The stress sharing means 40 are provided on the upper and lower sides of the reinforced concrete part 20 and the wood part 30, respectively, at predetermined intervals in the axial direction Da. The stress sharing means 40 is made of steel, and has a bolt 41 and a nut 42 in this embodiment. The composite beam 10 including the flange portion 23 shown in Figures 2 and 5 has, for example, a span length of 10.6 m, a thickness of the reinforced concrete flange portion 23 of 130 mm, a height of the reinforced concrete web portion 22 of 620 mm and a width of 270 mm, and wooden portions 30 as side wooden materials of 720 mm and 120 mm in thickness are installed on both sides of the web portion 22. The stress distribution means 40 are, for example, M16 bolts, and are arranged at intervals of 750 mm on the upper and lower sides of the beam center side, and are densely arranged at intervals of 675, 525, and 450 mm toward the beam end side. The vertical distance between the stress distribution means 40 installed on the upper side of the beam height and the stress distribution means 40 installed on the lower side is, for example, 330 mm.
As described above, in the composite beam 10, the shear stress that causes a shift between the reinforced concrete section 20 and the wooden section 30 when the beam bends downward is greater at the end of the beam than at the center of the beam. Therefore, by installing a larger number of stress sharing means 40 at the end of the beam, the joint strength between the reinforced concrete section 20 and the wooden section 30 is increased, thereby aiming to ensure integrity.
The bolt 41 has a screw shaft portion 41a and a screw head portion 41b integrally therewith. The screw shaft portion 41a extends in the width direction Dw. The screw shaft portion 41a has an axial length longer than the width of the web portion 22. The screw head portion 41b is integrally formed at the base end of the screw shaft portion 41a. The bolt 41 has the screw shaft portion 41a penetrating the web portion 22 and the shaft insertion hole 34 formed in the wood portion 30 on both sides, and the screw head portion 41b abuts against the wood portion 30L on one side in the width direction Dw. The wood portions 30 on both sides in the width direction Dw each have a recess 31 recessed inward in the width direction Dw from the outer surface 30s of the wood portion 30 at a position where each bolt 41 is inserted. The screw head portion 41b abuts against the bottom surface of the recess 31. The tip of the screw shaft 41a protrudes into the recess 31 of the wood part 30R on the other side of the width direction Dw. A nut 42 is fastened to the tip of the screw shaft 41a. The nut 42 is abutted against the bottom surface of the recess 31 of the wood part 30R. The steel stress distribution means 40 consisting of the bolt 41 and the nut 42 transmits the stress acting on the reinforced concrete part 20 to the wood part 30. The stress distribution means 40 transmits the stress in the direction along the joint surface (vertical surface perpendicular to the width direction Dw) between the reinforced concrete part 20 and the wood part 30 to the wood part 30. As a result, the wood part 30 shares a part of the stress acting on the reinforced concrete part 20. In addition, the recess 31 in which the screw head 41b and the nut 42 are arranged is blocked from the outside of the screw head 41b and the nut 42 with a blocking material 45 made of wood.
Regarding the number and spacing of the structural screws used as the stress sharing means 40, first, a push-out shear test was conducted on the shear joint where four structural screws (paneled steel, L = 110 mm) were driven in, and the parallel rigidity of 2.45 kN/mm and the orthogonal rigidity of 2.28 kN/mm per structural screw were calculated. Then, a bending test specimen in which the composite beam 10 of the present invention was divided into a mesh was used as the subject, and the structural screws obtained in the preliminary experiment were provisionally installed at a predetermined interval, and the spacing of the structural screws was determined so that the bending behavior of the reinforced concrete part 20 and the wooden part 30 that make up the composite beam 10 being integrated via the structural screws could be reproduced.

In this embodiment, cotters (shear cotters) 50 are provided at intervals determined in the axial direction Da in correspondence with the stress distribution means 40. The cotters 50 are integrally formed with the web portion 22 (concrete portion 21) on both sides of the width direction Dw of the web portion 22. The cotters 50 protrude from the side surfaces 22s on both sides of the width direction Dw of the web portion 22 to the outside in the width direction Dw. The cotters 50 extend continuously in the vertical direction Dv so as to straddle the upper stress distribution means 40P arranged on the upper side of the reinforced concrete portion 20 and the wood portion 30 and the lower stress distribution means 40Q arranged on the lower side of the reinforced concrete portion 20 and the wood portion 30. In the cotters 50, the tip surface 50s on the outside in the width direction Dw is formed parallel to the side surface 22s. The screw shaft portion 41a of the upper stress distribution means 40P and the lower stress distribution means 40Q penetrates the cotter 50 in the width direction Dw. Inclined surfaces 50a, 50b are formed on the top and bottom of the cotter 50. These inclined surfaces 50a, 50b are formed such that the length of the cotter 50 in the up-down direction Dv gradually decreases from the side surface 22s of the web portion 22 toward the outside in the width direction Dw.
A cotter accommodating recess 35 into which the cotter 50 fits is formed on the side of the wood part 30 facing the side surface 22s. The cotter accommodating recess 35 is formed in the wood part 30 so as to be recessed outward in the width direction Dw from the inner surface 30t facing the side surface 22s. The cotter accommodating recess 35 is formed in a shape that complements the cotter 50.

Next, a method for constructing the composite beam 10 will be described.
Fig. 6 is a diagram showing the steps of the construction method of the composite beam, and is a cross-sectional view showing the state in which the beam main reinforcement and shear reinforcement are arranged and the formwork is assembled. Fig. 7 is a diagram showing the steps of the construction method of the composite beam, and is a cross-sectional view showing the state in which concrete is poured into the beam forming part of the reinforced concrete part.
As shown in Fig. 6, to form the composite beam 10, first, the main beam reinforcement 24 and the shear reinforcement 25 are arranged. Next, buttresses (not shown) are provided at positions that will become both end faces in the axial direction Da of the composite beam 10 to be formed, and a predetermined tensile force is introduced to the main beam reinforcement 24 arranged at the lower part of the web portion 22.
Next, a formwork 60 of a predetermined shape is assembled around the arranged beam main reinforcement bars 24 and shear reinforcement bars 25. A part of this formwork 60 is composed of wood that forms the wooden part 30. The wood that forms the wooden part 30 is arranged on both sides of the arranged beam main reinforcement bars 24 and shear reinforcement bars 25 in the width direction Dw. A waterproof membrane 32 such as a waterproof coating is formed in advance on at least the part of the wooden part 30 that faces and contacts the reinforced concrete part 20. A bolt 41 is inserted into the shaft insertion hole 34 formed in the wooden part 30 on both sides in the width direction Dw, and a nut 42 is fastened. The recess 31 in which the screw head 41b and the nut 42 are arranged is blocked with a blocking material 45 made of a wooden material.
The gap between the lower ends of the wooden parts 30 on both sides in the width direction Dw is blocked by lower formwork members 63. In addition, auxiliary formwork members 64 and the like for forming the gap S are attached to the step portions 30d of the wooden parts 30 as appropriate.
After the formwork 60 is assembled, as shown in Fig. 7, concrete for forming at least the web portion 22 is poured into the formwork 60. After the concrete for forming the web portion 22 is poured, concrete for forming the flange portion 23 is poured. Pouring of the concrete for the web portion 22 and pouring of the concrete for the flange portion 23 may be performed consecutively or separately.
The poured concrete is cured for a predetermined period of time, and after the concrete has developed the required strength, the lower formwork members 63, the auxiliary formwork members 64, the buttresses (not shown), etc. are removed. As a result, a composite beam 10 having a predetermined shape is formed, as shown in Figures 3 to 5.

When the composite beam 10 is made to have a large span, a warp is provided when the composite beam 10 is formed. The warp refers to the central part being warped upward with respect to both ends in the axial direction Da in the opposite direction to the bending caused by the weight of the composite beam 10. By introducing tension into the beam main reinforcement 24 arranged at the bottom of the web part 22, the upper end of the web part 22 is placed in a tensile stress state and the lower end of the web part 22 is placed in a compressive stress state. When the concrete poured into the formwork 60 hardens, the amount of warp at the upper end of the web part 22 decreases. Accordingly, the tensile stress level at the upper end of the web part 22 decreases and the compressive stress level at the lower end increases. At this time, the web part 22 is stiffened by the wood part 30 provided on both sides of the web part 22 of the reinforced concrete part 20 in the width direction Dw. This makes it possible to reduce the amount of warp generated in the web part 22. This reduces the amount of the web portion 22 that is embedded in the flange portion 23 due to warping, which is rational from a manufacturing perspective.

(Action and Effect)
The effects of the composite beam 10 of the present invention in this embodiment will be described below.
According to the composite beam 10 as described above, the composite beam 10 is a composite beam 10 made of wood material and reinforced concrete and extending in the axial direction Da, and includes a reinforced concrete section 20 in which the beam main reinforcement bars 24 and the shear reinforcement bars 25 are embedded and whose longitudinal cross section perpendicular to the axial direction Da is T-shaped, a wood section 30 provided on at least both side surfaces 22s of the reinforced concrete section 20, and a steel stress distribution means 40 that is embedded across and connects the reinforced concrete section 20 and the wood section 30 and causes the wood section 30 to share the stress acting on the reinforced concrete section 20, and at least the lower end surface 22b of the reinforced concrete section 20 is exposed.
According to this configuration, by embedding a steel stress sharing means 40 so as to straddle the reinforced concrete section 20 and the wooden sections 30 provided on both sides of the web section 22, the stress acting on the reinforced concrete section 20 is effectively transmitted to the wooden sections 30 in a direction along the joints (joint surfaces) between the reinforced concrete section 20 and the wooden sections 30 via the stress sharing means 40. As a result, the stress acting on the reinforced concrete section 20 is shared and borne not only by the reinforced concrete section 20 but also by the wooden sections 30 on both sides. Therefore, it is possible to provide a composite beam 10 composed of wood material and reinforced concrete, which has excellent bending rigidity and bending strength.
In this composite beam 10, a reinforced concrete section 20 with excellent rigidity and strength is provided in the center of the beam cross section, and wooden sections 30 are provided as stiffening materials on both side surfaces 22s of the reinforced concrete section 20, thereby enabling a long span. Furthermore, since both sides of the width direction Dw of the composite beam 10 are formed by the wooden sections 30, it is possible to present a warm appearance unique to wood-based materials. In other words, such a composite beam 10 can be used to form a wood-based composite structural member in which the reinforced concrete section 20 is stiffened and reinforced by the wooden sections 30 on both sides.
In addition, in the composite beam 10, the reinforced concrete portion 20 and the wood portion 30 are joined and integrated by the steel stress distribution means 40, so that the wood portion 30 acts as a stiffening material for the reinforced concrete portion 20, and the warping or deflection occurring in the reinforced concrete portion 20 can be reduced. Furthermore, in the composite beam 10, the lower end surface 22b of the reinforced concrete portion 20 is not covered by the wood portion 30, and the lower end surface 22b is exposed, so that when the composite beam 10 deflects, the reinforced concrete portion 20 provided at the center of the cross section of the composite beam 10 can deform downward without being affected by the wood portion 30. Therefore, the composite beam 10 only needs to have the wood portion 30 provided on both side surfaces 22s of the reinforced concrete portion 20, and a highly designed composite beam 10 can be realized.

In addition, the reinforced concrete section 20 is a prestressed concrete structure, and tension is introduced into at least a portion of the beam main reinforcement 24 .
According to this configuration, by introducing tension into a part of the reinforced concrete section 20 to form a prestressed concrete structure, it is possible to increase the bending rigidity and bending strength compared to a case in which the reinforced concrete section 20 is a reinforced concrete structure made of cast-in-place concrete. This makes it possible to realize a composite beam 10 that can be made into a long span.

The stress distribution means 40 is a bolt 41, and is provided on the upper and lower sides of the web portion 22 of the reinforced concrete portion 20 and the wood portion 30 at predetermined intervals in the axial direction Da.
According to this configuration, by providing stress distribution means 40 at intervals determined in the axial direction Da of the composite beam 10 on the web portion 22 of the reinforced concrete portion 20 and the upper and lower sides of the wooden portion 30, the reinforced concrete portion 20 and the wooden portion 30 can be well integrated to form the composite beam 10.

In addition, cotters 50 are provided on the web portion 22 of the reinforced concrete portion 20 at predetermined intervals in the axial direction Da in correspondence with the stress sharing means 40, and the wood portion 30 is provided with cotter accommodating recesses 35 in correspondence with the cotters 50, which are formed to accommodate the cotters 50 and engage with the cotters 50.
With this configuration, the reinforced concrete section 20 and the wood section 30 can be further integrated to form a composite beam 10 in which the stress acting on the reinforced concrete section 20 can be shared and borne by the wood section 30.

(First Modification of the Embodiment)
The composite beam of the present invention is not limited to the above-described embodiment explained with reference to the drawings, and various modifications are possible within the technical scope.
For example, in the above embodiment, the bolts 41 (and nuts 42) are used as the stress sharing means 40, and the web portion 22 and the wood portion 30 are engaged with each other by the cotter 50, but the present invention is not limited to this.
Fig. 8 is a cross-sectional view showing a composite beam according to a first modified example of the embodiment of the present invention. Fig. 9 is a cross-sectional view showing a process of a construction method for the composite beam of Fig. 8, in which the beam main reinforcement and the shear reinforcement are arranged and the formwork is assembled.
For example, the composite beam 10B shown in Fig. 8 includes steel structural screws 48 as stress sharing means 40B. The structural screws 48 as the stress sharing means 40B join the reinforced concrete part 20 and the wooden part 30B on both sides of the web part 22 of the reinforced concrete part 20 in the width direction Dw. The structural screws 48 are embedded so as to straddle the reinforced concrete part 20 and the wooden part 30B.
The structural screws 48 extend in the width direction Dw. Both ends of the structural screws 48 are embedded in the web portion 22 and through holes 36 formed in each wood portion 30B. The through holes 36 penetrate the bottom surface of the recess 31B recessed inward in the width direction Dw from the outer surface 30s of the wood portion 30B and the inner surface 30u of the wood portion 30B facing the side surface 22s of the web portion 22. The structural screws 48 are screwed into the recess 31B of the wood portion 30B from the outer surface 30s side toward the inner surface 30u side, and the tip of the structural screw 48 is provided so as to be located inside the web portion 22. The recess 31B is blocked by a blocking material 45B made of wood material.
Specifically, the structural screws 48 are, for example, steel rods with a diameter of 8 mm and a length of 120 mm, and are driven into the upper and lower sides of the beam in sets of three. The structural screws 48 are installed at intervals of, for example, 0.75 m at the center of the beam, and are installed at intervals of 675 mm, 525 mm, and 450 mm from the center of the beam toward the end of the beam.
In the example of FIG. 8, the cotter 50 is not provided, and the wood portion 30B is simply disposed with the inner surface 30u aligned along the side surface 22s of the web portion 22.

To construct such a composite beam 10B, first, the beam main reinforcement bars 24 and the shear reinforcement bars 25 are arranged as shown in FIG. 9, in the same manner as in the above embodiment.
Next, a formwork 60B of a predetermined shape is assembled around the arranged beam main reinforcement 24 and shear reinforcement 25. A part of this formwork 60B is made of wood that forms the wooden part 30B. Through holes 36 are formed in advance in the wooden part 30B, and structural screws 48 are screwed into the wooden part 30B from the outer surface 30s side. In addition, a waterproof film 32 such as a waterproof coating is formed in advance on at least the part of the wooden part 30B that faces and contacts the reinforced concrete part 20. The recess 31B is blocked with a blocking material 45B made of wood material. In addition, the gap between the lower ends of the wooden parts 30B on both sides in the width direction Dw is blocked by a lower formwork material 63. An auxiliary formwork material 64 is placed in the part that forms the gap S.
After the formwork 60 is assembled, concrete is poured into the formwork 60. The poured concrete is cured for a predetermined period of time, and after the concrete has developed a required strength, the lower formwork material 63, the auxiliary formwork material 64, etc. are removed. As a result, a composite beam 10B having a predetermined shape is formed as shown in FIG.

Even with the composite beam 10B described above, the steel stress distribution means 40B is embedded so as to straddle the reinforced concrete section 20 and the wooden sections 30B on both sides of it, so that the stress acting on the reinforced concrete section 20 is shared and borne not only by the reinforced concrete section 20 but also by the wooden sections 30B on both sides. Therefore, it is possible to provide a composite beam 10B composed of wood material and reinforced concrete, which has excellent bending rigidity and bending strength.

(Second Modification of the Embodiment)
FIG. 10 is a cross-sectional view showing a composite beam according to a second modified example of the embodiment of the present invention.
In this modified example, the wood parts 30C, 70 include a side wood material 30C and a bottom wood material 70.
10, the structural screws 48 as the stress distribution means 40C may be screwed from the inner surface 30v of the side wood material 30C facing the side surface 22s of the web portion 22 toward the outside in the width direction Dw. In this case, there is no need to provide the recesses 31B or the plugging material 45B, which makes the construction even easier.
As shown in FIG. 10, the lower wooden material 70 is provided between the side wooden materials 30C protruding downward from the lower end surface 22b of the web portion 22, with the deformation absorbing means 80 sandwiched between them. When a composite beam is constructed by combining reinforced concrete and wooden materials, it is desirable to place them in close contact from the viewpoint of the fire resistance of the composite beam. However, in this modified example, the deformation absorbing means 80 is provided between the wooden materials to prevent the deformation of one wooden material from affecting other wooden materials. In this modified example, the deformation absorbing means 80 is provided with a gap of 3 mm or less, which is small enough to have little effect on the fire resistance. Alternatively, the deformation absorbing means 80 may be a molded body made of a thin layer of wood material or filler material having a lower rigidity than the lower wooden material 70. In this way, the lower surface wooden material 70 is provided so as to be in a non-jointed state with the side surface wooden material 30C by sandwiching the deformation absorbing means 80 between the side surface wooden material 30C and the wooden material 30C, 70 are installed so as to cover the outside of the web portion 22 of the reinforced concrete portion 20 in a U-shape with the wooden material 30C, 70. In this way, the deformation absorbing means 80 geometrically separates the side surface wooden material 30C and the lower surface wooden material 70, realizing a non-jointed state. By installing the lower surface wooden material 70 between the side surface wooden materials 30C facing each other across the reinforced concrete portion 20, even if the reinforced concrete portion and the side surface wooden material 30C bend downward as a unit when the composite beam is bent, the deformation absorbing means 80 is provided between the side surface wooden material 30C and the lower surface wooden material 70, and the lower surface wooden material 70 is installed inside the side surface wooden material 30C, so that the side surface wooden material 30C can be prevented from pushing down the lower surface wooden material 70, and the deformation performance of the composite beam can be improved.
The lower surface wooden material 70 is fixed to the lower end surface 22b of the reinforced concrete section 20 using structural screws 49 or adhesive. The lower surface wooden material 70 is used as part of the formwork 60D when pouring concrete, and is also used as a finishing material. The structural screws 49 also act as stress sharing means 49 that causes the lower surface wooden material 70 to share the stress acting on the reinforced concrete section 20, similar to the stress sharing means 40C that joins the side surface wooden material 30C to the reinforced concrete section 20.
10, the flange portion 23 is not integrally formed with the reinforced concrete portion 20, and the reinforced concrete portion 20 is only a web portion 22 having a rectangular cross section perpendicular to the axial direction Da. In this case, a slab 9 made of other materials such as wood, precast concrete, or steel may be laid on the composite beam 10C.

The composite beam 10C of this modified example is a composite beam 10C made of wood material and reinforced concrete and extending in the axial direction Da, and comprises a reinforced concrete section 20 in which beam main reinforcement bars 24 and shear reinforcement bars 25 are embedded and which has a rectangular cross section perpendicular to the axial direction Da, wood parts 30C, 70 provided on at least both side surfaces 22s of the reinforced concrete section 20, and steel stress distribution means 40C, 49 that are embedded across and connect the reinforced concrete section 20 and the wood parts 30C, 70 to cause the wood parts 30C, 70 to share the stress acting on the reinforced concrete section 20, and the wood parts 30C, 70 comprise side wood material 30C provided on both side surfaces 22s so as to sandwich the reinforced concrete section 20, and a bottom wood material 70 that is installed on the underside of the reinforced concrete section 20 in a non-jointed state with the side wood material 30C.
According to this configuration, the steel stress sharing means 40C, 49 are embedded so as to straddle the reinforced concrete portion 20 and the wooden portion 30C, 70. As a result, the stress acting on the reinforced concrete portion 20 is effectively transmitted to the wooden portion 30C, 70 in the direction along the joint between the reinforced concrete portion 20 and the wooden portion 30C, 70 via the stress sharing means 40C, 49. Therefore, the stress acting on the reinforced concrete portion 20 is shared and borne not only by the reinforced concrete portion 20 but also by the wooden portion 30C, 70. As a result, it is possible to provide a composite beam 10C composed of wood material and reinforced concrete, which has excellent bending rigidity and bending strength.
In this composite beam 10C, the reinforced concrete section 20, which has excellent rigidity and strength, is provided in the center of the beam cross section, and the wooden sections 30C and 70 are provided as stiffening materials, which allows for a long span that would be difficult to achieve with wooden materials alone. Furthermore, since the composite beam 10C is formed of the wooden sections 30C and 70, it can present a warm appearance that is unique to wood-based materials. In other words, such a composite beam 10C can be used to form a wood-based composite structural member that is stiffened and reinforced by the reinforced concrete section 20 and the wooden sections 30C and 70.
Furthermore, the composite beam 10C includes the reinforced concrete section 20, the side wood material 30C provided on both side surfaces 22s of the reinforced concrete section 20, and the bottom wood material 70 installed in a non-jointed state with the side wood material 30C, so that when the composite beam 10C reaches a large deformation state, the deformation of the bottom wood material 70 is not restrained by the side wood material 30C, and the reinforced concrete section 20 and the bottom wood material 70 can resist as one body. Furthermore, in the composite beam 10C, because the side wood material 30C and the bottom wood material 70 are installed in a non-jointed state, damage and destruction to the joints between the two can be suppressed, and excellent deformation performance can be ensured.

(Other Modifications of the Embodiment)
In addition, in the above embodiment, cotters 50 were provided at predetermined intervals in the axial direction Da in correspondence with the bolts 41 serving as the stress sharing means 40. However, while using the bolts 41 as the stress sharing means 40, as in the above first modified example, the cotters 50 may not be provided and the wood part 30 may be positioned such that its inner surface is simply aligned with the side surface 22s of the web part 22.
In this case, compared to the cotter-type joint structure of the above embodiment, it is possible to reduce the cross-sectional defects of the reinforced concrete section 20 and the wooden section 30. This makes it possible to prevent damage or destruction caused by the cross-sectional defects when an unexpected load is applied.

In the above embodiment, tension (prestress) may not be applied to the beam reinforcement 24 below the web portion 22, and the concrete portion 21 of the reinforced concrete portion 20 may be of ordinary reinforced concrete construction.
In addition, the above embodiment and each modified example may be appropriately combined. For example, in the above embodiment, the bolt 41 is installed as the stress sharing means 40 so as to penetrate both the reinforced concrete part 20 and the wood part 30, but the bolt is not limited to the bolt penetrating both of them, and the reinforced concrete part 20 and the wood part 30 may be joined with a structural screw. In addition, in the first modified example and the second modified example, the structural screw 48 is used as the stress sharing means 40B, 40C, but the bolt is not limited to the structural screw, and may be a bolt penetrating both the reinforced concrete part 20 and the wood part 30.
Alternatively, the lower surface wood material 70 may be provided in the configuration of the above embodiment in which the reinforced concrete section 20 has both the web section 22 and the flange section 23, or the configuration of the above second modified example in which the reinforced concrete section 20 has only the web section 22 may not have the lower surface wood material 70, and the lower surface wood material 70 may be omitted.
5, the cotters 50 are provided in one stage on each side of the reinforced concrete section 20, and the cotter receiving recesses 35 into which the cotters 50 fit are formed in the side wood material 30, but the number of cotters provided in the vertical direction is not limited to one stage, and two stages of cotters may be provided on both side surfaces of the reinforced concrete section 20, and two stages of cotter receiving recesses 35 may be formed in the side wood material 30 to correspond to each cotter. When two stages of cotters 50 are provided, the inclined surface forming the cotters 50 is doubled compared to when one stage is provided, and the joint area including the inclined surface between the reinforced concrete section and the side wood material is increased, so that high joint strength can be ensured.
In addition, in the above embodiment and each modified example, the step portion 30d is provided in the wood portion, but this may be omitted and the gap S may not be provided.

(Bending test results)
A bending test was carried out on the configuration shown in the above embodiment, and the results are shown below.
FIG. 11 is a diagram showing a schematic configuration of a test device for performing a bending test on the composite beam shown in the above embodiment. FIG. 12 is a diagram showing the results of the bending test on the composite beam shown in the above embodiment. As shown in FIG. 11, a composite beam 10 (Example) equipped with a bolt 41 and a cotter 50 as a stress sharing means 40 as shown in the above embodiment was prepared as a test specimen. The test specimen was provided with a wood part 30 over a length of 10,000 mm in the axial direction Da, with the center of the test specimen being the center of the axial direction Da. Both ends of the test specimen were placed on a support stand 101 installed at an interval of 12,000 mm in the axial direction Da, and a load applying body W was placed on the center to apply a vertical load. The amount of strain when a vertical load was applied from above to the center of the composite beam 10 by the load applying body W was measured.
The results are shown in Fig. 12. In Fig. 12, the experimental results in the case where bolts 41 and cotters 50 corresponding to the above embodiment were used are shown in Example 1, and the experimental results in the case where structural screws 48 corresponding to the above first modified example were used are shown in Example 2. As a comparative example, a normal reinforced concrete beam without a wooden portion was used.

As shown in Figure 12, it was confirmed that Examples 1 and 2 have significantly higher strength than the Comparative Example that does not have a woody portion. In addition, in both Examples 1 and 2, the maximum strength is reached in the region where deformation increases after the first yield occurs in the beam main reinforcement 24 (tension member) to which tension is introduced. In both Examples 1 and 2, the envelopment of the moment and deflection relationship is almost the same up to the vicinity of the maximum strength, and it is considered that there is almost no superiority or inferiority between the stress distribution means of Examples 1 and 2.
It was confirmed that the wood part 30 shares the stress acting on the reinforced concrete part 20, thereby improving the bending rigidity and strength characteristics of the composite beam 10.

The composite beams shown in Examples 1 and 2 have a beam cross section with wood parts 30 on both sides of the reinforced concrete part 20, and compared to the comparative example in which the beam cross section is composed only of reinforced concrete parts, the moment of inertia, which indicates the resistance of the beam member to deformation against bending moment, is about 4.3 times (2,520,000 ^cm4 / 590,000 ^cm4 ) higher, so the strength increased even after bending cracks occurred in the reinforced concrete part. In particular, by placing the bottom end surface of the wood part 100 mm below the bottom end surface of the reinforced concrete part, it is presumed that the wood part protruding below the reinforced concrete part greatly influenced the increase in bending strength against the bending deformation of the reinforced concrete part. Therefore, the bending experiment results also confirmed the excellent bending strength of the composite beam composed of wood material and reinforced concrete of the present invention.

10, 10B, 10C, Composite beam 30b Lower end surface 20 Reinforced concrete section 40, 40B, 40C Stress distribution means 22 Web section 41 Bolt 22b Lower end surface 48, 49 Structural screw (stress distribution means)
22s Side 70 Wood part (lower wood)
23 Flange portion 80 Deformation absorbing means 24 Beam main reinforcement Da Axial direction 25 Shear reinforcement Dw Width direction 30, 30B, 30C Wood portion (side wood material)

Claims (4)

A composite beam made of wood and reinforced concrete and extending in the axial direction,
A reinforced concrete section in which a beam main bar and a shear reinforcement bar are embedded and whose longitudinal section perpendicular to the axial direction is T-shaped or rectangular;
A wooden part provided on at least both side surfaces of the reinforced concrete part;
a steel stress distribution means that is embedded between the reinforced concrete portion and the wood portion to connect them and distribute the stress acting on the reinforced concrete portion to the wood portion;
At least the lower end surface of the reinforced concrete portion is exposed ,
A composite beam, characterized in that the lower end surface of the wood part protrudes downward below the lower end surface of the reinforced concrete part . A composite beam made of wood and reinforced concrete and extending in the axial direction,
A reinforced concrete section in which a beam main bar and a shear reinforcement bar are embedded and whose longitudinal section perpendicular to the axial direction is T-shaped or rectangular;
A wooden part provided on at least both side surfaces of the reinforced concrete part;
a steel stress distribution means that is embedded between the reinforced concrete portion and the wood portion to connect them and distribute the stress acting on the reinforced concrete portion to the wood portion;
A composite beam characterized in that the wooden part comprises side wooden materials provided on both sides so as to sandwich the reinforced concrete part, and a bottom wooden material installed on the underside of the reinforced concrete part in a non-jointed state with the side wooden materials. A composite beam as described in claim 1 or 2, characterized in that cotters are provided on the reinforced concrete portion at intervals in the axial direction so as to protrude outward in the width direction, and a cotter accommodating recess is provided on the wood portion in correspondence with the cotters, the cotter accommodating recess being formed to accommodate the cotters and engage with them. The reinforced concrete section has a web portion and a flange portion formed on the web portion, the longitudinal section is T-shaped, and the flange portion forms at least a part of a slab;
The wood parts are arranged on both sides of the web part in the width direction,
A composite beam as described in claim 1 or 2, characterized in that the upper end surface of the wood portion is abutted against the lower surface of the flange portion, and a step is formed by cutting downwardly on the outer side in the width direction, thereby providing a gap in the vertical direction between the wood portion and the lower surface of the flange portion.

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