GYPSUM-BASED LOAD-BEARING BOARD, LOAD-BEARING WALL STRUCTURE, AND LOAD-BEARING WALL CONSTRUCTION METHOD FOR WOODEN CONSTRUCTION BUILDING

Abstract

An object of the present invention is to provide a gypsum-based load-bearing board for wood structural load-bearing walls which is capable of increasing the co-efficient of effective wall length without additionally using reinforcement materials or stiffening materials, and without increasing the specific gravity and/or the thickness of the gypsum-based board. The gypsum-based load-bearing board (10) for wood structural load-bearing walls includes a main member or a core member formed from a board-shaped hardened gypsum containing an inorganic fiber and an organic-based strength enhancer that exert a lateral nail resistance of 500 N or more, and a paper covering at least front and back sides of the main member or the core member to constitute the load-bearing board. The load-bearing board has a surface density of 6.5 kg/m.sup.2 to 8.9 kg/m.sup.2, exhibits an ultimate displacement (?u2) of the load-bearing wall measured by an in-plane shear test of greater than 20?10.sup.3 rad (?u2), and exerts an ultimate strength (correction value) (Pu) of greater than 7.6 kN. According to the wooden structural load-bearing walls using the load-bearing board can obtain short-term reference shear strength (P.sub.0) greater than the wooden structural load-bearing walls using similar load-bearing board having a surface density of greater than 9.0 kg/m.sup.2.

Claims

1. A wooden load-bearing wall having a structure in which a gypsum-based load-bearing board is to be fastened to a wooden wall base used in a wooden framework construction method or a framework wall construction method by a fastener, the wooden load-bearing wall comprising: a main member or a core member formed from a board-shaped hardened gypsum containing an inorganic fiber and an organic-based strength enhancer that exert a lateral nail resistance of 500 N or more, and a paper covering at least front and back sides of the main member or the core member, the main member and the paper or the core member and the paper constituting the load-bearing board, wherein a surface density or a surface weight of the load-bearing board specified as a mass per unit area of a wall surface is in a range from 6.5 kg/m.sup.2 to 8.9 kg/m.sup.2. wherein an ultimate displacement value (?u2) of greater than 20?10.sup.?3 rad as a value of the ultimate displacement value (?u2) of the load-bearing wall measured by an in-plane shear test using a test piece with a wall length of 1.82 m, and wherein a correction value (Pu) is greater than 7.6 kN as the correction value (Pu) of an ultimate strength (Pu) determined based on the ultimate strength (Pu) and a plasticity (?) of the load-bearing wall measured by the in-plane shear test.

2. The wooden load-bearing wall according to claim 1, wherein a measurement value of a yield strength (Py) by the in-plane shear test is greater than 7.6 kN.

3. The wooden load-bearing wall according to claim 1, wherein the correction value (Pu) of the ultimate strength (Pu) is 8.0 kN or more, the measurement value of the yield strength (Py) of the load-bearing wall measured by the in-plane shear test is 8.0 kN or more, or both the correction value (Pu) and the measurement value of the yield strength (Py) are 8.0 kN or more.

4. The wooden load-bearing wall according to claim 1, wherein a plate thickness of the gypsum-based load-bearing board is set to be less than 12 mm, a specific gravity of the gypsum-based load-bearing board is set to be 0.96 or less, or the thickness of the gypsum-based load-bearing board is set to be less than 12 mm and the specific gravity of the gypsum-based load-bearing board is set to be 0.96 or less.

5. A method of constructing a wooden load-bearing wall fastening a gypsum-based load-bearing board to a wooden wall base used in a wooden framework construction method or a framework wall construction method by a fastener, the method comprising: fastening the gypsum-based load-bearing board to the wooden wall base, in which a surface density or a surface weight of the load-bearing board specified as a mass per unit area of a wall surface is in a range from 6.5 kg/m.sup.2 to 8.9 kg/m.sup.2, and the gypsum-based load-bearing board is constituted by a main member or a core member formed from a board-shaped hardened gypsum containing an inorganic fiber and an organic-based strength enhancer that exert a lateral nail resistance of 500 N or more, and a paper covering at least front and back sides of the main member or the core member; and obtaining a correction value (Pu) of greater than 7.6 kN as the correction value (Pu) of an ultimate strength (Pu) determined based on the ultimate strength (Pu) and a plasticity (?) of the load-bearing wall measured by the in-plane shear test in addition to obtain an ultimate displacement (?u2) of the load-bearing wall measured by an in-plane shear test using a test piece with a wall length of 1.82 which is greater than 20?10.sup.?3 rad (?u2).

6. The method according to claim S, wherein a plate thickness of the gypsum-based load-bearing board is set to be less than 12 mm, a specific gravity of the gypsum-based load-bearing board is set to be 0.96 or less, or the plate thickness of the gypsum-based load-bearing board is set to be less than 12 mm and the specific gravity of the gypsum-based load-bearing board is set to be 0.96 or less.

7. The method according to claim 5, wherein a measurement value of a yield strength (Py) as measured by the in-plane shear test is greater than 7.6 kN.

8. The method according to claim 5, wherein the correction value (Pu) of the ultimate strength (Pu) is increased to 8.0 kN or more, the measurement value of the yield strength (Py) measured by the in-plane shear test is increased to 8.0 kN or more, or the correction value (Pu) is increased to 8.0 kN or more and the measurement value of the yield strength (Py) is 8.0 kN or more.

9-12. (canceled)

13. A gypsum-based load-bearing board of wooden load-bearing wall fastened to a wooden wall base used in a wooden framework construction method or a framework wall construction method by a fastener, the gypsum-based load-bearing board comprising: a main member or a core member formed from a board-shaped hardened gypsum containing an inorganic fiber and an organic-based strength enhancer that exert a lateral nail resistance of 500 N or more, and a paper covering at least front and back sides of the main member or the core member to constitute the load-bearing board, wherein a surface density or a surface weight of the load-bearing board specified as a mass per unit area of the wall surface is in a range from 6.5 kg/m.sup.2 to 8.9 kg/m.sup.2, wherein an ultimate displacement (?u2) of the load-bearing wall measured by an in-plane shear test using a test piece with a wall length of 1.82 m is greater than 20?10.sup.?3 rad (?u2), and wherein a correction value (Pu) is greater than 7.6 kN as the correction value (Pu) of an ultimate strength (Pu) determined based on the ultimate strength (Pu) and a plasticity (?) of the load-bearing wall measured by the in-plane shear test.

14. The gypsum-based load-bearing board according to claim 13, wherein a plate thickness of the load-bearing board is set to be less than 12 mm, a specific gravity of the load-bearing board is set to be 0.96 or less, or the plate thickness of the load-bearing board is set to be less than 12 mm and the specific gravity of the load-bearing board is set to be 0.96 or less.

15. The gypsum-based load-bearing board according to claim 13, wherein the gypsum-based load-bearing board has a laminated structure in which a surface or a surface layer of the core material is covered with a gypsum board paper.

16. The gypsum-based load-bearing board according to claim 13, wherein the main material or the core material of the gypsum-based load-bearing board contains an organopolysiloxane compound as an anti-degradation agent to prevent deterioration of the load-bearing strength.

17. The gypsum-based load-bearing board according to claim 13, wherein the gypsum-based load-bearing board has a lateral nail resistance of 980 N or less.

18. The gypsum-based load-bearing board according to claim 13, wherein the measurement value (Py) of the yield strength measured by the in-plane shear test is greater than 7.6 kN.

19. The gypsum-based load-bearing board according to claim 13, wherein the correction value (Pu) of the ultimate strength (Pu) is increased to 8.0 kN or more, the measurement value (Py) of the yield strength measured by the in-plane shear test is increased to 8.0 kN or more, or the correction value (Pu) is increased to 8.0 kN or more and the measurement value (Py) is 8.0 kN or more.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG. 1 is a front view schematically illustrating a structure of a load-bearing wall of a wooden construction building;

[0048] FIG. 2 is a front view illustrating of a structure of a load-bearing wall test piece used in an in-plane shear test for the load-bearing wall structure illustrated in FIG. 1;

[0049] FIG. 3 is a diagram illustrating the physical properties and compounding of a gypsum plate of Examples and Comparative Example of the present invention;

[0050] FIG. 4 is a diagram illustrating the load-deformation angle curve obtained by the in-plane shear test. FIG. 4(A) illustrates the in-plane shear test results of the gypsum plate of Comparative Example in the present invention, and FIG. 4(B) illustrates the in-plane shear test results of the gypsum plate of Examples in the present invention;

[0051] FIG. 5 is a diagram illustrating an envelope made based on the load-deformation angle curve illustrated in FIG. 4; and

[0052] FIG. 6 is a perspective view illustrating a summary of the lateral nail resistance test specified in JIS A 6901.

DETAILED DESCRIPTION OF THE INVENTION

[0053] Hereinafter, the structure of the load-bearing wall of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0054] FIG. 1 is a front view schematically illustrating a structure of a load-bearing wall of a wooden construction building.

[0055] The load-bearing wall 1 illustrated in FIG. 1 is a wooden structural load-bearing wall of the wooden framework construction method constructed by obtaining the load-bearing board 10 to a wooden frame on a fabric foundation F of the reinforced concrete (RC) structure. The load-bearing board 10 has dimensions of 9.5 mm in thickness, 910 mm in width, and about in a range from 2,800 to 3,030 mm in height (e.g., 2,900 mm) and has a surface density in the range from 6.5 kg/m.sup.2 to 8.9 kg/m.sup.2 (e.g., a surface density of 7.1 kg/m.sup.2). The surface density (also called the surface weight) is the mass (weight) per unit area of the wall in front view of the wall. The load-bearing board 10 is a gypsum-based board that is constituted from a board-shaped gypsum core (gypsum core material) containing a predetermined amount of inorganic fiber (glass fiber) and an organic strength enhancer (starch) and a base paper (paper) for a gypsum board that covers both sides of the gypsum core.

[0056] The load-bearing wall 1 has a foundation 2 secured to the upper surface of the fabric foundation F by anchor bolts B. The load-bearing wall 1 is generally constituted from the foundation 2, pillars 3 placed vertically on the foundation 2 at predetermined intervals, studs 4 and joint pillar 4, a lateral frame (beams, girts, outriggers, and gable outriggers) 5 supported on the upper end (or intermediate portion) of the pillars 3, and the aforementioned load-bearing board 10. The foundation 2, the pillars 3, the studs 4, the joint pillar 4, and the lateral frame 5 constituting the framework are wood (square timber) of the cross-section of the member employed in conventional wooden construction buildings.

[0057] The load-bearing board 10 is secured to the foundation 2, the pillars 3, the studs 4, the joint stud 4, and the lateral frame 5 by nails 20. The nails 20 are, for example, a plated iron nail (NZ nail: JIS A 5508). In this example, the nails 20 are used, for example, NZ50 nails (50 mm in length, 6.6 mm in head diameter, and 2.75 mm in shaft diameter). The nails 20 are spaced S1 apart in the four outer circumferential areas of the load-bearing board 10 and spaced S2 apart in the central area of the load-bearing board 10 extending vertically. Preferably, the spacing S1 is set to a dimension in the range from 50 mm to 200 mm (e.g., 75 mm), and the spacing S2 is set to a dimension in the range from 50 mm to 300 mm (e.g., 150 mm).

[0058] The gypsum core of the load-bearing board 10 contains a predetermined amount of inorganic fibers and organic strength enhancers and has a lateral nail resistance of 500 N or more. An amount of inorganic fibers is 0.3 to 5 parts by weight, preferably 2 to 4 parts by weight based on 100 parts by weight of calcined gypsum. Examples of the inorganic fibers compounded include glass fibers, carbon fibers, and the like. If the glass fibers are used, glass fibers having 5 to 25 ?m in diameter and 2 to 25 mm in length may be suitably used. Further, the amount of the organic strength enhancer compounded is 0.3 to 15 parts by weight, and preferably 1 to 13 parts by weight per 100 parts by weight of calcined gypsum. Examples of the organic strength enhancers compounded include starch, polyvinyl acetate, polyvinyl alcohol, polyacrylic, and the like. As starch, both unprocessed starch and processed starch may be used. The processed starches include starches that have been physically, chemically, or enzymatically treated. As the physically treated starch, a-modified starch may be preferably used. As the chemically treated starch, oxidized starch, phosphate esterified starch, urea phosphate esterified starch, hydroxyethylated starch, hydroxypropylated starch, and acetylated starch may be preferably used.

[0059] The composition and structure of the load-bearing board 10 are similar to that of the structural gypsum board defined in JIS A 6901. However, the surface density of the load-bearing board 10 is in the range from 6.5 kg/m.sup.2 to 8.9 kg/m.sup.2 (e.g., 7.1 kg/m.sup.2). Accordingly, the load-bearing board 10 is basically different from the Structural Gypsum Board of JIS A 6901, which requires a surface density of 9.4 kg/m.sup.2 or more as described above. In addition, although the reinforced gypsum board specified in JIS A 6901 is known, the load-bearing board 10 is basically different from the reinforced gypsum board because the surface density of the reinforced gypsum board is 9.4 kg/m.sup.2 or more. In addition, the load-bearing board 10 differs from other gypsum boards in terms of having a main or core material that is compounded with inorganic fibers and organic strength enhancer to provide lateral nail resistance of 500 N or more. That is, the load-bearing board 10 does not correspond to any gypsum board specified in the current JIS A 6901. In this specification, the load-bearing board 10 is specified or expressed as a gypsum-based board or gypsum plate.

[0060] Generally, gypsum-based board (including gypsum boards) are manufactured by a general-purpose gypsum board manufacturing apparatus. A gypsum board manufacturing apparatus includes a mixer for preparing gypsum slurry by mixing raw materials such as a calcined gypsum, an auxiliary adhesive, a curing accelerator, foams (or foam agents) with kneading water required for slurring the calcined gypsum as described in WO 2019/058936, for example. The gypsum slurry is cast onto a gypsum board base paper (bottom sheet) on a conveyor belt of a gypsum board manufacturing apparatus, and the gypsum board base paper (top sheet) is laminated onto the gypsum slurry. The consecutive laminate of the strip-like and three-layer structure thus formed is processed by the gypsum board manufacturing device including a coarse cutting device, a forced drying device, a cutting device, or the like, and formed into a gypsum-based board having a predetermined dimension of a gypsum product, i.e., both sides of a hardened body of the gypsum slurry (i.e., a gypsum core) covered with a base paper for a gypsum board. The specific gravity of the gypsum-based board is controlled primarily by the amount of foam in the gypsum slurry.

[0061] With respect to the wooden structural load-bearing wall using the structural gypsum board, reinforced gypsum board, and (regular) gypsum board as the load-bearing board specified in JIS A 6901, the co-efficient of effective wall length of the load-bearing board of okabe-zukuri of the wooden framework structure as specified in the aforementioned Ministry of Construction Notification No. 1100 is as follows. [0062] Structural gypsum board (Class A) 1.7 [0063] Structural gypsum board (Class B) 1.2 [0064] Reinforced gypsum board 0.9 [0065] (Regular) gypsum board 0.9

[0066] In addition, an example of the co-efficient of effective wall length (Load-bearing walls with a vertical frame spacing of more than 50 cm) of the load-bearing walls for framework wall constructions specified in the aforementioned Ministry of Land, Infrastructure, Transport and Tourism Notification No. 1541 is as follows. [0067] Structural gypsum board (Class A) 1.7 [0068] Structural gypsum board (Class B) 1.5 [0069] Reinforced gypsum board 1.3 [0070] (Regular) gypsum board 1.0

[0071] Thus, the co-efficient of effective wall lengths specified in the Ministry of Construction or Ministry of Land, Infrastructure, Transport and Tourism Notification are generally acceptable without performing individual performance tests. However, when new materials are used or when co-efficient of effective wall length other than the above is used, it is necessary to set the co-efficient of effective wall length by performing the performance tests described above.

[0072] As mentioned above, the above-mentioned structural gypsum boards and reinforced gypsum boards specified in JIS A 6901 require physical properties with a surface density of 9.4 kg/m.sup.2 or more and a specific gravity of 0.75 or more. This is considered to be an important condition for increasing the maximum load that the board can withstand and ensuring a high short-term allowable shear strength (and thus a high co-efficient of effective wall length) of wooden structural load-bearing walls. In particular, in structural gypsum board, which exhibits higher lateral nail resistance than reinforced gypsum board, it has been thought that the surface density and specific gravity of a gypsum board for structural use cannot be reduced. In other words, obtaining the physical properties with a surface density of 9.4 kg/m.sup.2 or more and a specific gravity of 0.75 or more was considered to be a prerequisite for further increasing the co-efficient of effective wall length of the load-bearing wall test (wooden structure load-bearing wall) obtained in the in-plane shear test described above. However, in recent experiments by the inventors of the present invention, it has been found that, in the gypsum-based board having a physical property (lateral nail resistance) comparable to that of the structural gypsum board by adding an inorganic fiber or an organic-based strength enhancer, the plate thickness of the board is reduced, or the foam amount is adjusted to reduce the specific gravity of the gypsum core, thereby reducing the surface density, and as a result, the toughness or the deformation tracking potentially possessed by the board itself becomes apparent. As a result, the ultimate strength of the board can be effectively utilized and the plasticity of the board can be increased, thereby further improving the short-term allowable shearing strength of the wooden structure load-bearing wall. The inventors of the present invention have arrived at the present invention based on the findings obtained from such experiments. Hereinafter, the experiment (in-plane shear test) performed by the inventors will be described in detail.

[0073] FIG. 2 is a front view illustrating of a structure of a load-bearing wall test piece used in an in-plane shear test for the load-bearing wall structure illustrated in FIG. 1. FIGS. 3 to 5 are diagrams illustrating the test results of in-plane shear tests.

[0074] In FIG. 2, the components or members of the bearing wall test piece corresponding to or similar to the components or members illustrated in FIG. 1 are designated by the same reference numerals. The inventors of the present invention

[0075] manufactured a load-bearing wall test piece with a wall width of 1,820 mm and a height of 2,730 mm illustrated in FIG. 2 (hereinafter, simply referred to as the test piece) as a test piece of the load-bearing wall structure illustrated in FIG. 1, and performed an in-plane shear test using a non-loading test device in accordance with the test piece specification described in the Performance Test and Evaluation Methodology for Wood-Frame Load-bearing walls and Their Co-efficient of effective wall length.

[0076] The test piece illustrated in FIG. 2 has the main structure of a wooden framework assembly including a cedar foundation 2 and pillars 3 with a cross-section of 105 mm?105 mm; and a lateral frame 5 of pine lumber with a cross-section of 180 mm?105 mm supported by the pillars 3. In the center between the pillars 3, a cedar joint stud 4 with a cross-section of 45?105 mm is disposed, and cedar studs 4 with a cross-section of 27 mm?105 mm are disposed between the pillars 3 and the joint stud 4. Cedar or pine lumber of noggings 5 are disposed between the pillars 3 and the studs 4 and is also provided between the studs 4 and the joint stud 4. As a test jig, a pull-on bracket 40 is provided at the joint of the foundation 2 and the pillars 3 and is also provided at the joint of the lateral frame 5 and the pillars 3. The foundation 2, the pillars 3, the joint stud 4, the studs 4, the lateral frame 5, and the noggings 5 constitute the framework members of the load-bearing wall structure, and rectangular-shaped framework assemblies are formed by these members (framework members).

[0077] In the test piece illustrated in FIG. 2, the length between the foundation 2 and the beam 3 in the vertical direction h1, the length between the foundation 2 and the noggings 5 in the vertical direction h2, and the relative length of the beam 3 with respect to the noggins 5 in the vertical direction h3 were set to be h1=2,625 mm, h2=1,790 mm, and h3 =835 mm, respectively. The distance between the pillar 3 and the joint stud 4 (distance between the core pillars) w1 was set to be w1=910 mm. The wall length L was set to be 1.82 m. The board 10 is divided into upper and lower sections by the noggings 5, the lower board 10a having a dimension of 910 mm in width and 1,820 mm in height, and the upper board 10b having a dimension of 910 mm in width and 865 mm in height. The overlapped length h4 and h5 of the boards 10a and 10b were set at 30 mm.

[0078] In the test piece illustrated in FIG. 2, the nails 20 for fastening the boards 10a and 10b to the foundation 2, the pillars 3, the joint stud 4, the lateral frame 5, and the noggings 5 were arranged at equal intervals (space S1=75 mm) throughout the peripheral portion of the boards 10a and 10b. The nails 20 for fastening the boards 10a and 10b to the studs 4 were arranged at equal intervals (space S2=150 mm) in the vertical center zone of the boards 10a and 10b. NZ50 nails (50 mm in length, 6.6 mm in head diameter, and 2.75 mm in shaft diameter) were used as the nails 20.

[0079] The present inventors manufactured gypsum plates according to Examples 1 to 5 and Comparative Example illustrated in FIG. 3 as samples and performed in-plane shear tests using a non-loaded test apparatus. As described above, the gypsum plates according to Examples 1 to 5 are a gypsum-based board including a sheet-shaped gypsum core (gypsum core material) containing a predetermined amount of inorganic fibers (glass fibers) and an organic strength enhancing material (starch) and a base paper (paper) for the gypsum plate covering both sides of the gypsum core. The board of Comparative Example is a gypsum-type board equivalent to the EX board (9.5 mm in plate thickness) described above, which is equivalent to the gypsum plate of Examples 1 to 5, or is composed of a board-shaped gypsum core (gypsum core material) containing less amount of inorganic fiber (glass fiber) and an organic strength enhancer (starch) than that of Examples 1 to 5, and a base paper (paper member) for a gypsum board covering both sides of the gypsum core.

[0080] As illustrated in FIG. 3, the gypsum plates of Examples 1 to 5 have a surface density in the range from 7.3 to 8.7 kg/m.sup.2, and the gypsum plate of Comparative Example has a surface density of 9.8 kg/m.sup.2.

[0081] The ultimate displacement ?u2 of the gypsum plates in Examples 1 to 5 obtained by the in-plane shear test was in a range from 26.8?10.sup.?3 rad to 36.0?10.sup.?3 rad, and the ultimate displacement ?u1 of the gypsum plate of Comparative Example obtained by the in-plane shear test was 20.0?10.sup.?3 rad. As illustrated in FIG. 3, in the gypsum plates of Examples 1 to 5 and the gypsum plate in Comparative Example, the yield strength Py was greater than the ultimate strength (correction value) Pu. Therefore, the short-term reference shear strength P.sub.0 and the co-efficient of effective wall length were specified by the ultimate strength (correction value) Pu. In the gypsum plates of Examples 1 to 5, the value of the ultimate strength (correction value) Pu was larger than that of the gypsum plate of Comparative Example, and the difference between the yield strength Py and the ultimate strength (correction value) Pu was less than 2.0 kN (1.6 or less), indicating that the difference between the yield strength Py and the ultimate strength (correction value) Pu was relatively small. That is, as far as reference is made to the test results illustrated in FIG. 3, in both Comparative Example and Examples 1 to 5, the ultimate strength (correction value) Pu is relatively smaller than the yield strength Py.

[0082] However, in Examples 1 to 5, the difference between the yield strength Py and the ultimate strength (correction value) Pu is reduced, and a tendency for both to level off numerically is observed. Since the load-bearing (load) and displacement (shear deformation angle) of each gypsum plate of Examples 1 to 5 obtained by the in-plane shear test have substantially the same tendency or characteristics, the characteristics of the gypsum plate of the present invention will be described below based on the test results of the gypsum plate of Example 1, which indicates generally intermediate ultimate displacement (33.1?10.sup.?3 rad).

[0083] FIG. 4 is a diagram illustrating the load-deformation angle curve obtained by the in-plane shear test. FIG. 4(A) illustrates the in-plane shear test result of the gypsum plate in Comparative Example. FIG. 4(B) illustrates the in-plane shear test result of the gypsum plate in Example 1. FIG. 5 is a diagram illustrating an envelope created based on the load-deformation angle curve illustrated in FIG. 4. The envelope is a characteristic line of the load (load-bearing) and displacement (shear deformation angle) based on the load-deformation angle curve on the side that ultimately lead to breakage.

[0084] As illustrated in FIG. 4(A), the gypsum plate of Comparative Example reached the maximum load (maximum load-bearing) Pmax at the deformation angle=about 20?10.sup.?3 rad, but was substantially broken by the subsequent horizontal force acting immediately thereafter. As a result, the load (load-bearing) of the gypsum-based board immediately dropped to a value less than 0.8 Pmax. In FIG. 4(A), the load level at the maximum load Pmax is indicated by a dashed-and-dotted line, and the load level at 0.8 Pmax load drop range is indicated by a dashed-and-double dotted line. In FIG. 4(A), the load-deformation angle curve during repeated application just after the maximum load Pmax is indicated below the load level at 0.8 Pmax that illustrated by the dashed-and-double dotted line. This curve is specified by the load difference AP with the 0.8 Pmax load level.

[0085] As illustrated in FIGS. 4(A) and 5, when the gypsum plate in Comparative Example, the gypsum plate is broken at the deformation angle=about 20?10.sup.?3 rad at once at the time of maximum load Pmax, so that the ultimate displacement ?u1 is substantially equal to the deformation angle at the time of the maximum load Pmax. Therefore, it is not possible to increase the short-term allowable shear strength of the gypsum plate relying on the toughness or deformation tracking of the gypsum plate. In order to increase the short-term allowable shear strength of the gypsum plate, it is necessary to increase the surface density and increase the maximum load, which had been recognized as virtually the only method to increase co-efficient of effective wall length. However, as is obvious from the load-deformation angle curve of Example 1 illustrated in FIG. 4(B) and FIG. 5, when the surface density is reduced while obtaining the minimum physical properties (lateral nail resistance: 500 N or more) as the gypsum-based load-bearing board, the potential properties such as toughness or deformation tracking of the gypsum plate itself become obvious, and as a result, the short-term reference shear strength P.sub.0 can be specified based on the ultimate strength Pu and the plasticity u. This point will be further described below.

[0086] As illustrated in FIG. 4(B), the gypsum plate of Example 1 was reached to a maximum load (maximum load-bearing) at a deformation angle=about 20?10.sup.?3 rad. After that, applying force repeatedly caused the deformation angle in the 0.8 Pmax load reduction zone, i.e., the ultimate displacement ?u2 was obtained as the ultimate displacement ?u2=33.1?10.sup.?3 rad. As described above, the ultimate displacement ?u2 of each gypsum plate of Examples 1 to 5 is within the range from 26.8?10.sup.?3 rad to 36.0?10.sup.?3 rad as illustrated in FIG. 3, and the ultimate displacement ?u2 generally equivalent to that of Example 1 was obtained in Examples 2 to 5. That is, after the gypsum plates of Examples 1 to 5 reached to the maximum load (maximum load-bearing) at the deformation angle=about 20?10.sup.?3 rad, the plastic deformation by the repeated force was continued until causing about 1.3 to 1.8 times deformation angles of the deformation angle at the maximum load Pmax. Accordingly, the plasticity u was relatively largely increased.

[0087] As explained at the beginning of this specification, the co-efficient of effective wall length is the value obtained by dividing the short-term allowable shear strength Pa by the predetermined reference shear strength (L?1.96. The short-term allowable shear strength Pa is the value obtained by multiplying the short-term reference shear strength P.sub.0 by the predetermined reduction coefficient ?, as can be understood from the equation illustrated in FIG. 5. Similar to many previous in-plane shear tests of gypsum-based boards, the short-term reference shear strength P.sub.0 of each Example and Comparative Example is specified as a value determined by multiplying the correction value of the ultimate strength Pu (i.e., the ultimate strength (correction value) Pu) obtained by correction based on the plasticity u by the variation coefficient ?. Accordingly, the short-term reference shear strength P.sub.0 is proportional to the value of the ultimate strength Pu and increases in conjunction with the increase in plasticity ?, as can be readily understood from the equation of FIG. 5. The plasticity ? is proportional to the ultimate displacement ?u, and the short-term reference shear strength P.sub.0 increases in conjunction with the increase in the ultimate displacement ?u if the yield displacement ?v is assumed to be almost the same value. That is, by increasing the ultimate displacement ?u, the short-term reference shear strength P.sub.0 can be increased. In order to simplify the explanation, the variation coefficient ? is assumed to be 1.0.

[0088] As illustrated in the table in FIG. 5, the short-term reference shear strength P.sub.0 obtained from the gypsum plate of Example 1 is significantly greater than the value of the short-term reference shear strength P.sub.0 obtained from the gypsum plate of Comparative Example. This means that the ultimate displacement ?u2 is increased by the decrease in surface density, thereby increasing the short-term reference shear strength P.sub.0. As a result, this means that an increased co-efficient of effective wall length is obtained. It should be noted that the reduction coefficient ? is a value artificially set, and by multiplying the short-term reference shear strength P.sub.0 by the reduction coefficient ?, a short-term allowable shear strength (Pa) is obtained, thereby obtaining the final co-efficient of effective wall length value. For example, if the reduction coefficient is set to 0.75, the co-efficient of effective wall length of the wooden structural load-bearing wall using the gypsum plate of Example 1 is 2.25, which is approximately 1.4 times the co-efficient of effective wall length (1.60) of Comparative Example. The value of the co-efficient of effective wall length is significantly larger than the co-efficient of effective wall length (co-efficient of effective wall length of the aforementioned: 0.9 to 1.7) of the wooden structural load-bearing walls such as structural gypsum boards specified in Ministry of Construction Notification No. 1100 and the like.

[0089] As described above, according to the load-bearing wall 1 of the above-described structure, the load-bearing board 10 is composed of a main material or a core material formed from a board-shaped hardened gypsum containing inorganic fibers and organic-based strength enhancers to exert the lateral nail resistance of 500 N or more, and a paper covering at least the front and back sides of the main material or the core material. The surface density or the surface weight of the load-bearing board 10 specified as the mass per unit area of the wall is set at a value within the range of 6.5 kg/m.sup.2 to 8.9 kg/m.sup.2. The ultimate displacement ?u2 of the load-bearing wall 1 obtained by the in-plane shear test using a load-bearing wall test piece with a wall length of 1.82 m is, for example, 33.1?10.sup.?3 rad (Example 1), which is greater than 20?10.sup.?3 rad (Comparative Example). The ultimate strength (Correction value) Pu obtained by the in-plane shear test is, for example, 10.7 kN (Example 1), which is greater than 7.6 kN (Comparative Example). Assuming that the variation coefficient ? is 1, the short-term allowable shear strength Pa is, for example, 10.7 kN (Example 1), which is greater than 7.6 kN (Comparative Example). The co-efficient of effective wall length is, for example, 2.25 (Example 1), which is greater than 1.60 (Comparative Example). Thus, according to the load-bearing wall 1 having the structure in which the load-bearing board 10 is fastened to the wooden wall base of the wooden framework construction method by the nails 20, the short-term reference shear strength P.sub.0 can be increased and the co-efficient of effective wall length can be increased without additionally using the reinforcement materials or stiffening materials, without increasing the specific gravity and/or the plate thickness of the load-bearing board 10, by improving the toughness and deformation tracking of the gypsum-based board and increasing the ultimate strength (correction value) Pu while obtaining the minimum physical properties (lateral nail resistance=500 N or more) as a gypsum-based load-bearing board.

[0090] While the preferred embodiments and Examples of the present invention have been described in detail, the present invention is not limited to the above-described embodiments and Examples, and that various modifications or variations may be made within the scope of the present invention as defined in the claims.

[0091] For example, the above-described embodiments and Examples relate to first floor level bearing walls of a wooden construction building, but the present invention is equally applicable to second or third floor level bearing walls. In the case of the second or third floor level bearing walls, the lower end of the bearing board is fastened to the second or third floor level lateral frame material.

[0092] The above-described embodiments and Examples relate to the wooden framework construction method and the load-bearing wall structure of Okabe-zukuri. However, the present invention may be applied to a Shinkabe-zukuri, a Yukagachi (floor preceding method), and Okabe-zukuri of a wooden framework construction method. Alternatively, the present invention may be applied to a load-bearing wall structure of a framework wall construction method. In this case, a load-bearing board is fastened to a vertical frame, a lower frame, an upper frame, or the like, instead of a foundation, pillars, and lateral frames.

[0093] In addition, the test piece illustrated in FIG. 4 has a structure in which a gypsum plate is divided into upper and lower portions and noggings are arranged at an intermediate position in the height direction, but an in-plane shear test may be performed using a gypsum plate of substantially the same height as the total height of the wooden framework assembly.

[0094] In the latter case, it is considered that the short-term reference shear strength may be increased.

[0095] Also, in the above-described embodiments and Examples, the load-bearing board is fastened to the wooden framework assembly, such as pillars, lateral frames, and the like, by nails, but the load-bearing board may be fastened to the wooden framework assembly by other types of fasteners, such as screws.

INDUSTRIAL APPLICABILITY

[0096] The present invention is applied to gypsum-based load-bearing boards in wooden construction buildings. In particular, the present invention is applied to a gypsum-based load-bearing board, in which the load-bearing board is constituted by a main member or a core member formed from a board-shaped hardened gypsum containing inorganic fibers and organic-based strength enhancers that exert a lateral nail resistance of 500 N or more, and a paper covering at least front and back sides of the main member or core member. The present invention is also applied to a method of increasing a co-efficient of effective wall length of a wooden structural load-bearing wall using such gypsum-based load-bearing board. The present invention further applies to a load-bearing wall structure and a load-bearing wall construction method of a wooden construction building configured to fasten such gypsum-based load-bearing board to a wooden wall base by a wooden framework wall construction method or a framework wall construction method, thereby integrally retaining the load-bearing board by a wooden wall base. According to the present invention, the practical value or effect thereof is significant since the co-efficient of effective wall length of the wooden structural load-bearing wall can be increased without additionally using the reinforcement materials or stiffening materials and without increasing the specific gravity and/or plate thickness of the gypsum-based board.

EXPLANATION OF REFERENCE NUMERALS

[0097] 1 Load-bearing wall [0098] 2 Foundation [0099] 3 Pillar [0100] 4 Stud [0101] 4 Joint stud [0102] 5 Lateral frame (beams, girts, outriggers, and gable outriggers) [0103] 5 Nogging [0104] 10, 10a, and 10b Gypsum-based load-bearing board [0105] 20 Nails (fasteners]