Patent Publication Number: US-11019930-B2

Title: Load support structure for chair, load support body for chair, and chair

Description:
TECHNICAL FIELD 
     The present invention relates to a load support structure for a chair, a load support body for a chair, and a chair. 
     Priority is claimed on Japanese Patent Application No. 2016-116273, filed Jun. 10, 2016, and Japanese Patent Application No. 2016-116274, filed Jun. 10, 2016, the contents of which are incorporated herein by reference. 
     BACKGROUND ART 
     In the related art, a load support structure for a chair and a load support body for a chair, such as a backrest member or a seat member, including a frame member as a strength member and a tensile material having an elastic resistance (repulsive force) against a load from a surface perpendicular direction are generally known. 
     For example, as described in Patent Document 1, a chair in which a frame-like seat frame is fixed to a frame-like clamping frame, and an end portion of a net member is caught in a fixing portion between the clamping frame and the seat frame is known. In the fixing portion between the clamping frame and the seat frame, protrusions and recessions provided on the clamping frame and the seat frame are engaged with each other and they are screwed together. 
     In such a configuration, the fixing portion between the clamping frame and the seat frame is firmly fixed by being fitted and screwed to each other. Therefore, only the tensile material stretched on the frame member is displaced in the surface perpendicular direction, and the frame member itself such as the clamping frame or the seat frame does not sufficiently deform against the load of a seated person and is not able to stably support the body of the seated person. In addition, when the load of the seated person acts on a position eccentric from the center of the tensile material, the frame member may come into contact with the body of the seated person and make the seated person feel pain or discomfort. 
     Thus, as described in Patent Document 2, a structure which includes a tensile material, a pair of vertical frame sections to which the tensile material is attached and which are elastically deformable in response to a force acting from the tensile material, an upper frame section for connecting upper end portions of the pair of vertical frame sections, and a backrest rear part support member for connecting and supporting the upper frame section and lower parts of the vertical frame sections, and in which the vertical frame sections and the backrest rear part support member are annularly formed in a side view has been proposed. In this configuration, since a space is formed in a front-rear direction between the vertical frame section and the backrest rear part support member, when a load from the seated person acts on the tensile material, the vertical frame sections which can be elastically deformed deform greatly rearward to follow the back of the seated person. 
     DOCUMENT OF RELATED ART 
     Patent Document 
     Patent Document 1: Japanese Patent No. 4061160 
     Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2014-79510 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the configuration described in Patent Document 2, the support section such as the vertical frame section to which the tensile material is attached and the backrest rear part support member for supporting the annular body are disposed at the center of the backrest in a width direction, and when a large load acts on an end portion side in the width direction of the backrest, there is a possibility of the vertical frame section being excessively displaced backward. For this reason, a stable feeling of seating while the frame member such as the vertical frame sections are flexibly deformed is desired. 
     The present invention has been made in view of the above circumstances, and an object thereof is to provide a load support structure for a chair and a chair that can suppress excessive displacement, while permitting elastic deformation of a support section to which a tensile material is attached. 
     Further, the present invention has been made in view of the above circumstances, and another object thereof is to provide a load support body for a chair and a chair which can suppress excessive displacement, while permitting elastic deformation of an annular body to which a tensile material is attached. 
     Solution to Problem 
     A load support structure for a chair according to the present invention includes: a tensile material on which a load support surface configured to receive a load of a seated person is formed; a pair of support sections to which the tensile material is attached, and which is elastically deformable in response to a force acting from the tensile material; a pair of first reinforcing sections which extends along an extending direction of the pair of support sections and is disposed to be spaced apart from the pair of support sections in a surface perpendicular direction perpendicular to the load support surface, the first reinforcing section being located on a side opposite to the load support surface; and a connecting body which connects each of both end portion sides of the support section with a corresponding end portion side of both end portion sides of the first reinforcing section, in which the support section is disposed outside the first reinforcing section in a view of the surface perpendicular direction from the load support surface side. 
     In the load support structure for a chair configured as described above, the support sections are disposed to be spaced apart from the first reinforcing section in the surface perpendicular direction. Therefore, the support sections are elastically deformed to follow the body of the seated person, corresponding to a separation distance in the surface perpendicular direction, by the load acting from the seated person. Further, since the support sections are disposed outside the first seat reinforcing rod when the load support surface is viewed in the surface perpendicular direction from the load support surface side, the support sections are pulled by the tensile material, are displaced to the central side of the load support surface, and are displaced so as to rise toward the body side of the seated person and wrap the body from the sides. Therefore, the seated person can sit in a stable state. 
     Further, even if the seated person sits at a position deviated from the center of the load support surface of the tensile material, since the support section itself is elastically deformed and bent, the user does not feel the hardness of the support section itself and does not feel uncomfortable. 
     Further, both end portion sides of the support section are connected to the corresponding end portion sides of the first reinforcing section disposed along the support section via the connecting body. Thus, since the support section is supported by the first reinforcing section over the extending direction, excessive displacement is suppressed. 
     Further, in the load support structure for a chair according to the present invention, each support section may be formed in a plate shape in which the surface perpendicular direction is set as a thickness direction of the support section. 
     In the load support structure for a chair configured as described above, since the support section is formed in a plate shape in which the surface perpendicular direction is set as the thickness direction, the support section itself is easily deformed by the load support surface. Therefore, the support sections are pulled by the tensile material, and are more easily deformed to rise toward the body side of the seated person and wrap the body from the sides. 
     Further, in the load support structure for a chair according to the present invention, each support section may be formed such that a thickness in the surface perpendicular direction decreases toward the other support section of the pair of support sections. 
     In the load support structure for a chair configured as described above, the support section is formed such that the thickness thereof in the surface perpendicular direction becomes thinner toward the other support section of the pair of support sections. Therefore, one side (the inner edge side) of the support section closer to the other support section is pulled by the tensile material and displaced in a load input direction, and the opposite side (the outer edge side) of the support section is easily displaced in the direction of rising against the displacement of the inner edge side. 
     Further, the load support structure for a chair according to the present invention may further include a pair of connecting sections which connects end portions of the pair of support sections to each other. 
     In the load support structure for a chair configured as described above, since the end portions of the pair of support sections are connected by the connecting section, excessive displacement of the support section is further suppressed. 
     The load support structure for a chair according to the present invention may further include a pair of second reinforcing sections which connects end portions of the pair of first reinforcing sections to each other and supports the pair of connecting sections. 
     In the load support structure for a chair constituted as described above, since the second reinforcing section for supporting the connecting section is provided, the connecting section can be strongly reinforced. Therefore, it is possible to reliably bend the support sections connected to the connecting section, while suppressing the deflection of the connecting section by the load from the seated person. 
     Further, since the first reinforcing section and the second reinforcing section form an annular shape, the rigidity is enhanced, and the support section can be stably supported. 
     Further, a chair according to the present invention includes: a support body disposed on a floor surface, and a seat body and a backrest supported on the support body, in which at least one of the seat body and the backrest includes the load support structure for a chair according to any one of the above aspects. 
     In the chair configured as described above, since at least one of the seat body and the backrest is constituted by the load support structure for a chair according to any one of the above-mentioned aspects, it is possible to suppress excessive displacement, while allowing the elastic deformation of the support section. 
     A load support body for a chair according to the present invention includes: a tensile material on which a load support surface configured to receive a load of a seated person is formed; and an annular body which is annularly arranged around the tensile material and to which the tensile material is attached, in which the annular body includes: a pair of first parts which is disposed to be spaced apart from each other along the load support surface and is elastically deformable in response to a force acting from the tensile material; and a pair of second parts which is disposed between the pair of first parts in an extending direction of the annular body, and a pair of rigidity reinforcing sections configured to enhance rigidity is provided only on the pair of second parts among the first parts and the second parts. 
     In the load support body for a chair configured as described above, the tensile material is bent flexibly in the load input direction at the central side of the load support surface, and the first parts of the annular body, which are disposed to be spaced from each other along the load support surface, elastically deform to follow the body of the seated person by the load acting from the seated person. Therefore, the first parts can receive the seated person together with the tensile material by wrapping the seated person. 
     In addition, since the rigidity reinforcing section for enhancing the rigidity is provided only on the second part among the first parts and the second part of the annular body, the second part can be strongly reinforced. Therefore, excessive displacement and bending of the first parts can be suppressed by the second part disposed between the pair of first parts. 
     Further, in the load support body for a chair according to the present invention, the rigidity reinforcing section and the second part may be integrally formed in a surface perpendicular direction which is perpendicular to the load support surface. 
     In the load support body for a chair configured as described above, the integrated body can be formed by integrally forming the rigidity reinforcing section and the second part while increasing the thickness, in the surface perpendicular direction of the load support surface, of the integrated body. Therefore, it can easily be reinforced over a wide range in the extending direction (longitudinal direction) of the second part. 
     In the load support body for a chair according to the present invention, the rigidity reinforcing section may be configured as a separate body from the second part. 
     In the load support body for a chair thus configured, since the rigidity reinforcing section is formed as a separate body from the second part, the rigidity reinforcing section is simply connected to the second part by a screw or the like, and the rigidity reinforcing section can be easily manufactured. In addition, the shapes of the rigidity reinforcing section and the second part can be simplified, and the volumes of the rigidity reinforcing section and the second part can be reduced. As a result, it is possible to prevent defective molding of the rigidity reinforcing section and the second part. 
     Further, in the load support body for a chair according to the present invention, the first part may be disposed on a side closer to an input direction of the load of the seated person than the second part. 
     In the load support body for a chair configured as described above, since the first parts are disposed on the side closer to the input direction of the load than the second part, the first parts are easily displaced to rise to the body side of the seated person and wrap the body from the sides. 
     Further, in the load support body for a chair according to the present invention, the annular body may have a pair of connection reinforcing sections which connects end portions of the pair of rigidity reinforcing sections to each other and is disposed to be spaced apart from the pair of first parts in the surface perpendicular direction perpendicular to the load support surface. 
     In the load support body for a chair configured as described above, since the annular body is formed in an annular shape by the rigidity reinforcing sections and the connection reinforcing sections, the rigidity is enhanced and the first parts of the annular body can be stably supported. 
     Further, since the first parts are disposed to be spaced apart from the connection reinforcing section in the surface perpendicular direction of the load support surface, the first parts can be elastically deformed sufficiently to correspond to a separation distance in the surface perpendicular direction. 
     Further, in the load support body for a chair according to the present invention, the first part may be disposed outside the connection reinforcing section in a view of the surface perpendicular direction from the load support surface side. 
     In the load support body for a chair configured as described above, since the first parts are disposed outside the connection reinforcing section when the load support surface is viewed in the surface perpendicular direction from the load support surface side, the first parts are pulled by the tensile material to easily displace toward the central side of the load support surface, and are easily displaced to rise to the body side of the seated person and wrap around the body from the sides. 
     Further, in the load support body for a chair according to the present invention, each first part may be formed in a plate shape in which the surface perpendicular direction perpendicular to the load support surface is set as a thickness direction of the first part. 
     In the load support body for a chair configured as described above, since each first part is formed in a plate shape in which the surface perpendicular direction of the load support surface is set as the thickness direction, the first parts themselves are easily deformed along the load support surface. Therefore, the first parts are pulled by the tensile material, and are more easily displaced to rise toward the body side of the seated person and wrap the body from the sides. 
     Further, in the load support body for a chair according to the present invention, each first part may be formed such that a thickness in the surface perpendicular direction perpendicular to the load support surface decreases toward the other first part of the pair of first parts. 
     In the load support body for a chair constituted as described above, each first part is formed such that the thickness thereof in the surface perpendicular direction becomes thinner toward the other first part of the pair of first parts. Therefore, one side (the inner edge side) of the first part closer to the other first part is pulled by the tensile material and displaced to a side away from the input direction of the load, and the opposite side (the outer edge side) of the first part is easily displaced in the direction of rising (to a side close to the input direction of the load) against the displacement on the inner edge side. 
     Further, a chair according to the present invention includes a support body disposed on a floor surface; and a seat body and a backrest supported on the support body, in which at least one of the seat body and the backrest includes the load support body for a chair according to any one of the above aspects. 
     In the chair constituted as described above, since at least one of the seat body and the backrest is constituted by the load support body for a chair as described in any one of the above-mentioned aspects, it is possible to suppress excessive displacement while allowing the elastic deformation of the frame rod. 
     Advantageous Effects of Invention 
     According to the load support structure for a chair and the chair according to the present invention, it is possible to suppress excessive displacement while allowing elastic deformation of a support section to which a tensile material is attached. 
     Further, according to the load support body for a chair and the chair according to the present invention, it is possible to suppress excessive displacement, while allowing elastic deformation of an annular body to which a tensile material is attached. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a chair according to a first embodiment of the present invention as viewed from a lateral side. 
         FIG. 2  is a perspective view of the chair according to the first embodiment of the present invention as viewed from behind (a backrest side). 
         FIG. 3  is a vertical cross-sectional view of a seat body of the chair according to the first embodiment of the present invention taken along a left-right direction. 
         FIG. 4  is a vertical cross-sectional view of the seat body of the chair according to the first embodiment of the present invention taken along a front-rear direction. 
         FIG. 5  is a vertical cross-sectional view of the seat body of the chair according to the first embodiment of the present invention taken along the front-rear direction and taken at an outer side in the left-right direction of the seat body compared to  FIG. 4 . 
         FIG. 6  is a cross-sectional view taken along a line A-A of  FIG. 2 . 
         FIG. 7  is a cross-sectional view taken along a line B-B of  FIG. 2 . 
         FIG. 8  is a side perspective view of a chair according to a second embodiment of the present invention as viewed from a lateral side. 
         FIG. 9  is a perspective view of the chair according to the second embodiment of the present invention as viewed from behind (the backrest side). 
         FIG. 10  is a vertical cross-sectional view of a seat body of the chair according to the second embodiment of the present invention taken along the left-right direction. 
         FIG. 11  is a vertical cross-sectional view of the seat body of the chair according to the second embodiment of the present invention taken along the front-rear direction. 
         FIG. 12  is a vertical cross-sectional view of the seat body of the chair according to the second embodiment of the present invention taken along the front-rear direction and taken at an outer side in the left-right direction of the seat body compared to  FIG. 11 . 
         FIG. 13  is a cross-sectional view taken along a line C-C of  FIG. 9 . 
         FIG. 14  is a cross-sectional view taken along a line D-D of  FIG. 9 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Hereinafter, a chair according to a first embodiment of the present invention will be described with reference to the drawings. 
       FIG. 1  is a perspective view of a chair according to the first embodiment of the present invention as viewed from a lateral side.  FIG. 2  is a perspective view of the chair according to the first embodiment of the present invention as viewed from behind (backrest side). 
     As shown in  FIGS. 1 and 2 , a chair  100  has a leg section  1  installed on a floor surface F, a box-like support base  2  (not shown) installed on an upper part of the leg section  1 , a seat receiving member  3  attached to an upper part of the support base  2 , a seat body (a load support structure of the chair)  4  that is slidably supported by the seat receiving member  3  and on which a seated person sits, and a backrest (a load support structure for a chair)  7  extending from the support base  2  to support the back of the seated person seated on the seat body  4 . 
     In the following description, for convenience, a direction in which the seated person seated on the seat body  4  faces forward is referred to as “forward”, and an opposite direction thereof is referred to as “rearward”. Further, a direction connecting the floor surface F side on which the chair  100  is installed and an opposite side thereto is referred to as a “vertical direction”. Further, a width direction of the chair  100 , that is, a horizontal direction orthogonal to the front-rear direction, is referred to as a “left-right direction”. In the drawings, the forward direction is indicated by an arrow FR, the upward direction is indicated by an arrow UP, and the leftward direction is indicated by an arrow LH. 
     The leg section  1  has a multi-legged bar  11  with casters  11 A, and a leg pillar  12  which stands up from a central part of the multi-legged bar  11  and incorporates a gas spring (not shown) as an elevating mechanism. 
     An outer cylinder  13 , which constitutes a lower part of the leg pillar  12 , is fitted and supported on the multi-legged bar  11  in a non-rotatable manner. The support base  2  is fitted and supported on an upper end portion of an inner cylinder  14  which constitutes an upper part of the leg pillar  12 , and a lower part of the inner cylinder  14  is supported by the outer cylinder  13  to be rotatable in the horizontal direction. 
     The support base  2  incorporates an elevating movement adjustment mechanism of the leg pillar  12 , and a tilting adjustment mechanism of the backrest  7 . 
     The seat receiving member  3  has four link arms (not shown) attached to the upper part of the support base  2 , and a pair of right and left fixed frames  31  (see a broken line shown in  FIG. 3 ) which connect the link anus to each other. 
     In this embodiment, the leg section  1 , the support base  2 , and the seat receiving member  3  constitute a support body  30 . 
     The seat body  4  has a seat frame  40  and an elastically deformable tensile material  60  stretched over the seat frame  40 . An upper surface of the tensile material  60  serves as a load support surface  60 U that receives the load of the seated person. 
       FIG. 3  is a vertical cross-sectional view of the seat body  4  of the chair  100  taken along the left-right direction.  FIG. 4  is a vertical cross-sectional view of the seat body  4  of the chair  100  taken along the front-rear direction.  FIG. 5  is a vertical sectional view of the seat body  4  of the chair  100  taken along the front-rear direction.  FIG. 5  is a cross-sectional view taken on the outer side in the left-right direction of the seat body  4  compared to  FIG. 4 . In  FIGS. 3 to 5 , the tensile material  60  is not shown. 
     As shown in  FIGS. 3 to 5 , the seat frame  40  has a seat bottom frame  40 D supported by the fixed frames  31 , and a seat top frame  50 U fixed to an upper surface of the seat bottom frame  40 D. Each of the seat bottom frame  40 D and the seat top frame  50 U is annularly formed. 
     The seat bottom frame  40 D has first seat reinforcing rods (a first reinforcing section)  41  slidably provided on the pair of fixed frames  31 , respectively, and second seat reinforcing rods (a second reinforcing section)  42  each of which connects end portions  41 E of the first seat reinforcing rods  41  to each other. The first seat reinforcing rods  41  and the second seat reinforcing rods  42  are integrally formed of, for example, a resin or the like, and have a predetermined strength. 
     As shown in  FIG. 3 , the first seat reinforcing rod  41  extends in the front-rear direction. The first seat reinforcing rod  41  has a downward U shape in a cross section along a surface perpendicular direction, which is a direction perpendicular to the load support surface  60 U (see  FIG. 1 , the same applies hereinafter). In other words, a concave section  41 C that is recessed upward is formed in a lower part of the first seat reinforcing rod  41 . The fixed frame  31  is disposed in the concave section  41 C. 
     Both end portions  41 E of the first seat reinforcing rod  41  are formed to have a larger width in the left-right direction than a portion of the first seat reinforcing rod  41  on a central side in the front-rear direction. Both end portions  41 E of the first seat reinforcing rod  41  are gradually inclined upward toward a distal end side. 
     As shown in  FIG. 4 , the second seat reinforcing rod  42  extends in the left-right direction. The second seat reinforcing rod  42  has a plate shape wider in the front-rear direction, in a cross section along the surface perpendicular direction (a vertical cross section along the front-rear direction). 
     As shown in  FIGS. 3 to 5 , the seat top frame  50 U includes a pair of frame rods (a support section)  51  disposed to be spaced apart from each other in the left-right direction (in a direction along the load support surface  60 U), and connecting rods (a connecting section)  52  each of which connects end portions of the frame rods  51  to each other. The frame rods  51  and the connecting rods  52  are integrally formed of, for example, a resin or the like, and configured to be elastically deformable in response to a force acting from the tensile material  60  (see  FIG. 1 , the same applies hereinafter). 
     As shown in  FIG. 3 , the frame rod  51  extends in the front-rear direction. The frame rod  51  has a plate shape extending along the load support surface  60 U and wider in the left-right direction, in a cross section along the surface perpendicular direction (a vertical cross section along the left-right direction). 
     The frame rod  51  is formed such that the thickness thereof in the surface perpendicular direction becomes thinner toward an inner edge (an inner end portion in the left-right direction)  51 J. Further, the inner edge  51 J of the frame rod  51  is inclined downward. 
     A groove  53  recessed inward is formed in an outer edge (an outer end portion in the left-right direction)  51 K of the frame rod  51 . An end portion of the tensile material  60  is caught in the groove  53 . 
     As shown in  FIG. 4 , the connecting rod  52  extends in the left-right direction. The connecting rod  52  has a plate shape wider in the front-rear direction, in a cross section along the surface perpendicular direction (a vertical cross section along the front-rear direction). 
     The rear connecting rod  52  is gradually inclined downward toward the rear. 
     The rear connecting rod  52  is formed such that the thickness thereof in the surface perpendicular direction becomes thinner toward an inner edge (an inner end portion in the front-rear direction)  52 J. A reinforcing plate section  54  having a plate shape extending along the horizontal plane is provided on the inner edge  52 J of the front connecting rod  52 . 
     Both end portions of the reinforcing plate section  54  in the left-right direction are connected to the respective frame rods  51 . Therefore, a front part of the seat top frame  50 U including a boundary region between the frame rod  51  and the connecting rod  52  is prevented from hanging down forward and downward due to the load that is input from the body of the seated person. 
     A cushion body having elasticity (not shown, the same applies hereinafter) may be placed on an upper surface of the reinforcing plate section  54 . As a result, a front part of the tensile material  60  stretched over the seat top frame  50 U is supported by the cushion body and urged upward. The seated person feels a good seating comfort while thighs of the seated person are flexibly supported on the tensile material  60 , and because the thighs do not come into direct contact with an inner peripheral edge of the connecting rod  52 , the seated person does not feel the hardness of the connecting rod  52  and does not feel uncomfortable. 
     The groove  53  recessed inward is formed on an outer edge (an outer end portion in the front-rear direction)  52 K of the connecting rod  52 . The end portion of the tensile material  60  is caught in the groove  53 . 
     The second seat reinforcing rod  42  is provided on a lower part on the inner edge  52 J side of the connecting rod  52 . Both end portions of the connecting rod  52  are screwed to the respective end portions of the second seat reinforcing rod  42  by screws  52 X. 
     The length of the connecting rod  52  is longer than the length of the second seat reinforcing rod  42  of the seat bottom frame  40 D. As a result, the frame rod  51  connected to the end portion of the connecting rod  52  is disposed on the outer side (the outer side in the left-right direction) than the first seat reinforcing rod  41  connected to the end portion of the second seat reinforcing rod  42  when the load support surface  60 U is viewed in the surface perpendicular direction from the load support surface  60 U side. 
     In the present embodiment, the end portions of the connecting rods  52 , the end portions of the second seat reinforcing rods  42 , and the screws  52 X constitute a connecting body  5  which connects the frame rod  51  and the first seat reinforcing rod  41 . Since the end portion  41 E of the first seat reinforcing rod  41  is gradually inclined upward toward the distal end side, the frame rod  51  is disposed above the first seat reinforcing rod  41 . 
     Further, the end portion of the connecting rod  52  is gradually inclined upward toward the outer side in the left-right direction. As a result, the frame rod  51  is disposed above the connecting rod  52 . 
     As shown in  FIGS. 1 and 2 , the backrest  7  includes a back frame  70 , and a tensile material  90  stretched over the back frame  70 . A front surface of the tensile material  90  serves as a load support surface  90 F that receives the load of the seated person. 
     The back frame  70  has a back rear frame  70 B connected to the support base  2 , and a back front frame  80 F provided in front of the back rear frame  70 B. 
     The back rear frame  70 B has lower side portions  71 , lateral side portions (a first reinforcing section)  72 , and an upper side portion  73 . The lower side portions  71 , the lateral side portions  72 , and the upper side portion  73  are formed integrally by, for example, a metal such as aluminum or a resin having a predetermined strength. 
     The lower side portions  71  are connected to the tilting adjustment mechanism in the support base  2  and extend from both the left and right sides of the rear part of the support base  2 . The lower side portion  71  is gradually inclined rearward toward the upper part. Also, an armrest  74  extending sideways is provided in each lower side portion  71 . 
     The lateral side portion  72  is connected to the upper end portion of each lower side portion  71 . Each lateral side portion  72  is gradually inclined outward in the left-right direction toward the upper part. 
     A lower part of the lateral side portion  72  is gradually inclined forward toward the upper part. 
     An upper part of the lateral side portion  72  is gradually inclined rearward toward the upper side. The upper parts of the lateral side portions  72  are connected to each other by the upper side portion  73 . 
       FIG. 6  is a cross-sectional view taken along the line A-A of  FIG. 2 .  FIG. 7  is a cross-sectional view taken along the line B-B of  FIG. 2 . 
     As shown in  FIGS. 1, 2, 6, and 7 , the back front frame  80 F has upper arm sections (a connecting body)  81  connected to the upper parts of the lateral side portions  72  of the back rear frame  70 B, lower arm sections (a connecting body)  82  connected to the lower parts of the lateral side portions  72 , a pair of vertical rods (a support section)  86  disposed to be spaced apart from each other in the left-right direction (along load support surface  60 U), and an upper rod (a connecting section)  87  which connects the upper ends of the pair of vertical rods  86 . The upper arm sections  81 , the lower arm sections  82 , the vertical rods  86 , and the upper rod  87  are integrally formed of, for example, resin or the like. The vertical rods  86  and the upper rod  87  are configured to be elastically deformable in accordance with the force acting from the tensile material  90 . 
     As shown in  FIG. 6 , the upper arm section  81  is fixed to the upper part of the lateral side portion  72  of the back rear frame  70 B by a bolt  81 X. The upper arm section  81  extends forward from the lateral side portion  72  of the back rear frame  70 B, and gradually extends outward in the left-right direction toward the front part. 
     As shown in  FIG. 7 , a fixed piece  83  is fixed to the lower part of the lateral side portion  72  of the back rear frame  70 B with a bolt  83 X. The lower arm section  82  externally fits the fixed piece  83 . The lower arm section  82  and the fixed piece  83  are fixed by a retaining pin  84 . The lower arm section  82  extends forward from the lateral side portion  72  of the back rear frame  70 B and gradually extends outward in the left-right direction toward the front part. 
     As shown in  FIG. 1 , the upper arm section  81  is connected to the upper part of the vertical rod  86 , and the lower arm section  82  is connected to the lower part of the vertical rod  86 . 
     As shown in  FIG. 2 , each vertical rod  86  extends in the vertical direction. In detail, the vertical rod  86  is gradually inclined inward in the left-right direction toward the lower part. The lower ends of the pair of vertical rods  86  are connected to each other. 
     As shown in  FIG. 1 , a lower part  86 A of the vertical rod  86  is gradually inclined forward toward the upper part. An upper part  86 B of the vertical rod  86  is gradually inclined rearward toward the upper part. Accordingly, in a side view, a boundary section  86 C between the lower part  86 A and the upper part  86 B has a shape protruding forward. The lower arm section  82  is connected to a rear surface of the boundary section  86 C. 
     As shown in  FIGS. 6 and 7 , the vertical rod  86  has a plate shape extending along the load support surface  90 F and wider in the left-right direction, in a cross section along the surface perpendicular direction, which is a direction perpendicular to the load support surface  90 F (see  FIG. 1 ) (a horizontal cross section along the left-right direction). 
     As shown in  FIG. 7 , the lower part of the vertical rod  86  is formed such that the thickness thereof in the surface perpendicular direction becomes thinner toward an inner edge (an inner end portion in the left-right direction)  86 J. 
     A groove  88  recessed inward is formed in an outer edge (an outer end portion in the left-right direction)  86 K of the vertical rod  86 . The end portion of the tensile material  90  is caught in the groove  88 . 
     Since the upper arm section  81  and the lower arm section  82  gradually extend outward in the left-right direction toward the front, the vertical rod  86  is disposed outside the lateral side portion  72  in the left-right direction. 
     Next, the deformation of the seat body  4  when the seated person sits on the seat body  4  of the chair  100  will be described. 
     First, a description will be given of a case (hereinafter, this case will be referred to as a first seated state) in which the seated person sits on the rear part of the central part in the left-right direction (width direction) of the load support surface  60 U of the seat body  4 . 
     Since the load support surface  60 U is made up by the elastically deformable tensile material  60 , the tensile material  60  elastically deforms to sink downward by the load acting from the seated person. 
     Since the rear connecting rod  52  on which the tensile material  60  is stretched gradually inclines downward toward the rear, the connecting rod  52  is easy to elastically deform downward. Here, since the second seat reinforcing rod  42  is provided at the lower part of the connecting rod  52 , bending of the central part in the left-right direction of the connecting rod  52  is suppressed. 
     Both the left and right sides of the front end portion of the rear connecting rod  52  and both the left and right sides of the rear end portion of the front connecting rod  52  are connected by the first seat reinforcing rods  41 , respectively. Therefore, the left and right frame rods  51 , which are disposed outside in the left-right direction than the connecting rods  52 , are restrained by the connecting rod  52  and elastically deform gradually upward from the rear part. 
     Next, the description will be given of a case (hereinafter, this case will be referred to as a second seated state) in which the seated person sits slightly in front of a central part in the front-rear direction of the load support surface  60 U of the seat body  4  and the central part in the left-right direction (width direction) of the load support surface  60 U. 
     In the second seated state, since the seating position is ahead of the first seated state, the amount of elastic deformation of the rear connecting rod  52  toward the lower side is smaller than in the case of the first seated state. 
     However, the frame rods  51 , each of which has a plate shape in the cross-sectional view taken along the surface perpendicular direction of the tensile material  60 , are pulled by the tensile material  60  elastically deforming in the surface perpendicular direction, rise toward the body side of the seated person, and elastically deform to wrap the body from the sides. At this time, the pair of front and rear connecting rods  52  suppress excessive elastic deformation of the frame rods  51 . 
     Next, the deformation of the backrest  7  when the seated person puts his back against the backrest  7  will be described. 
     When the back is put against the load support surface  90 F of the backrest  7  made up of the tensile material  90 , the load in the surface perpendicular direction acting on the tensile material  90  is not so large as the load acting on the load support surface  60 U of the seat body  4 . 
     Further, the vicinity of the boundary sections  86 C that protrude forward in a side view makes contact with the back. 
     From these facts, as the vertical rods  86  are pulled by the tensile material  90 , the vertical rods  86  rise toward the body side of the seated person, and elastically deform to wrap the body from the sides. That is, the vertical rods  86  are elastically deformed, without being caused by the rearward elastic deformation of the upper rod  87  connecting the upper ends of the vertical rods  86 , the connecting section of the lower ends of the vertical rods  86 , or the like. At this time, the upper rod  87  suppresses excessive elastic deformation of the vertical rods  86 . 
     As described above, with the frame rods  51  of the seat top frame  50 U of the seat body  4  constituting the support section of the present invention, and the vertical rods  86  of the back front frame  80 F of the backrest  7  constituting the support section of the present invention, elasticity deformation is promoted while suppressing excessive deformation, due to complex factors such as the cross-sectional shape thereof, the tension of the tensile materials  60  and  90  constituting the load supporting surface, and the engagement with the other parts of the seat top frame  50 U and the other parts of the back front frame  80 F. 
     In the chair  100  configured as described above, in the seat body  4 , the frame rods  51  are disposed above the first seat reinforcing rods  41 . Therefore, the frame rods  51  elastically deform to follow the body of the seated person, corresponding to a separation distance in the vertical direction between the frame rod  51  and the first seat reinforcing rod  41 , by the load applied from the seated person as described above. Further, since the frame rods  51  are disposed outside the first seat reinforcing rods  41  when the load support surface  60 U is viewed in the surface perpendicular direction from the load support surface  60 U side, the frame rods  51  are pulled by the tensile material  60 , are displaced to the central side of the load support surface  60 U, rise toward the body side of the seated person and are displaced so as to wrap the body from the sides. Therefore, the seated person can sit in a stable state. 
     Further, in the backrest  7 , the vertical rods  86  are disposed in front of the lateral side portions  72 . Therefore, the vertical rods  86  elastically deform to follow the body of the seated person, corresponding to a separation distance in the front-rear direction between the vertical rod  86  and the lateral side portion  72 , by the load applied from the seated person. Further, since the vertical rods  86  are disposed outside the side edge portions  72  when the load support surface  90 F is viewed in the surface perpendicular direction from the load support surface  90 F side, the vertical rods  86  are pulled by the tensile material  90 , are displaced to the central side of the load support surface  90 F, rise toward the body side of the seated person and are displaced so as to wrap the body from the sides. Therefore, the seated person can sit in a stable state. 
     Even if the seated person sits at a position displaced from the center of the load support surfaces  60 U and  90 F of the tensile materials  60  and  90 , since the frame rods  51  and the vertical rods  86  themselves are elastically deformed and bent, the user does not feel the hardness of the frame rod  51  and the vertical rod  86  and does not feel uncomfortable. 
     In the seat body  4 , both end portions of the frame rod  51  are connected to both end portions  41 E of the first seat reinforcing rod  41  disposed along the frame rod  51  via the end portions of the connecting rods  52 , the end portions of the second seat reinforcing rods  42  and the screws  52 X. Therefore, since the frame rod  51  is supported by the first seat reinforcing rod  41  over the extending direction (the front-rear direction), excessive displacement is suppressed. 
     Further, in the backrest  7 , both end portions of the vertical rod  86  are connected to both end portion sides of the lateral side portion  72  disposed along the vertical rod  86  via the upper arm section  81  and the lower arm section  82 . Therefore, since the vertical rod  86  is supported by the lateral side portion  72  over the extending direction (the vertical direction), excessive displacement is suppressed. 
     Since the frame rod  51  and the vertical rod  86  are formed in a plate shape in which the surface perpendicular direction of the load support surfaces  60 U and  90 F is set as the thickness direction of the load support surfaces  60 U and  90 F, respectively, the frame rod  51  and the vertical rod  86  themselves are easily deformed by the load support surfaces  60 U and  90 F. Therefore, the frame rods  51  and the vertical rods  86  are pulled by the tensile materials  60  and  90 , rise toward the body side of the seated person, and more easily deform to wrap the body from the sides. 
     Further, the frame rod  51  and the vertical rod  86  are formed such that the thickness thereof in the surface perpendicular direction becomes thinner toward the inner edge side. Therefore, the inner edge sides of the frame rod  51  and the vertical rod  86  are pulled by the tensile material  60  and displaced in a load input direction (downward in the case of the frame rod  51  and rearward in the case of the vertical rod  86 ), and the outer edge sides of the frame rod  51  and the vertical rod  86  are easily displaced in a direction of rising (upward in the case of the frame rod  51  and forward in the case of the vertical rod  86 ) against the displacement of the inner edge sides. 
     In addition, in the seat body  4 , since the end portions of the pair of frame rods  51  are connected by the connecting rod  52 , excessive displacement of the frame rods  51  is further suppressed. 
     Further, in the seat body  4 , since the second seat reinforcing rod  42  is provided at the lower part of the connecting rod  52 , the connecting rod  52  can be strongly reinforced. Therefore, it is possible to reliably bend the frame rods  51  connected to the connecting rod  52 , while suppressing the deflection of the connecting rod  52  by the load from the seated person. 
     In addition, in the seat body  4 , since the first seat reinforcing rods  41  and the second seat reinforcing rods  42  form an annular shape, the rigidity is enhanced, and the frame rods  51  can be stably supported. 
     Further, the shapes and combinations of the constituent members shown in the above-described embodiments are merely examples, and various modifications can be made on the basis of design requirements or the like, within the scope that does not depart from the gist of the present invention. 
     For example, in the above-described embodiment, both the seat body  4  and the backrest  7  are made up of the load support structure for a chair according to the present invention, but the present invention is not limited thereto, and only at least one of them may be made up of the load support structure for a chair of the present invention. 
     In the aforementioned embodiment, the frame rod  51  and the vertical rod  86  are each formed in a plate shape along the load support surfaces  60 U and  90 F, but the present invention is not limited thereto, and the plate rod  51  and the vertical rod  86  may have a shape other than a plate shape. 
     Although the seat bottom frame  40 D and the seat top frame  50 U are configured as separate bodies in the above-described embodiment, the seat bottom frame  40 D and the seat top frame  50 U may be integrally formed. In this case, by adopting means such as two-color molding of resin, it is possible to make the strength of the seat bottom frame  40 D and the seat top frame  50 U different from each other, or it is also possible to make the strengths of both the same. When the strengths of both are the same, as the seat bottom frame  40 D is supported by the seat receiving member  3 , the first seat reinforcing rod  41  and the second seat reinforcing rod  42  of the seat bottom frame  40 D function as the first reinforcing section and the second reinforcing section, respectively. 
     Second Embodiment 
     Hereinafter, a chair according to the second embodiment of the present invention will be described with reference to the drawings. 
       FIG. 8  is a perspective view of a chair according to the second embodiment of the present invention as viewed from a lateral side.  FIG. 9  is a perspective view of the chair according to the second embodiment of the present invention as viewed from behind (the backrest side). 
     As shown in  FIGS. 8 and 9 , a chair  200  has a leg section  201  installed on a floor surface F, a box-like support base  202  (not shown) installed on an upper part of the leg section  201 , a seat receiving member  203  attached to an upper part of the support base  202 , a seat body (a load support body for a chair)  204  that is slidably supported by the seat receiving member  203  and on which a seated person sits, and a backrest  207  extending from the support base  202  to support the back of the seated person seated on the seat body  204 . 
     In the following description, for convenience, a direction in which the seated person seated on the seat body  204  faces forward is referred to as a “forward”, and an opposite direction thereof is referred to as a “rearward”. Further, a direction connecting the floor surface F side on which the chair  200  is installed and an opposite side thereto is referred to as a “vertical direction”. Further, a width direction of the chair  200 , that is, a horizontal direction orthogonal to the front-rear direction, is referred to as a “left-right direction”. In the drawings, the forward direction is indicated by an arrow FR, the upward direction is indicated by an arrow UP, and the leftward direction is indicated by an arrow LH. 
     The leg section  201  has a multi-legged bar  211  with casters  211 A, and a leg pillar  212  which stands up from a central part of the multi-legged bar  211  and incorporates a gas spring (not shown) as an elevating mechanism. 
     An outer cylinder  213 , which constitutes a lower part of the leg pillar  212 , is fitted and supported on the multi-legged bar  211  in a non-rotatable manner. The support base  102  is fitted and supported on an upper end portion of an inner cylinder  214  which constitutes an upper part of the leg pillar  212 , and a lower part of the inner cylinder  214  is supported by the outer cylinder  213  to be rotatable in the horizontal direction. 
     The support base  202  incorporates an elevating movement adjustment mechanism of the leg pillar  212 , and a tilting adjustment mechanism of the backrest  207 . 
     The seat receiving member  203  has four link arms (not shown) attached to the upper part of the support base  202 , and a pair of right and left fixed frames  231  (see a broken line shown in  FIG. 10 ) which connect the link arms to each other. 
     In this embodiment, the leg section  201 , the support base  202 , and the seat receiving member  203  constitute a support body  230 . 
     The seat body  204  has a seat frame (an annular body)  240 , and an elastically deformable tensile material  260  stretched over the seat frame  240 . An upper surface of the tensile material  260  serves as a load support surface  260 U that receives the load of the seated person. 
       FIG. 10  is a vertical cross-sectional view of the seat body  204  of the chair  200  taken along the left-right direction.  FIG. 11  is a vertical cross-sectional view of the seat body  204  of the chair  200  taken along the front-rear direction.  FIG. 12  is a vertical sectional view of the seat body  204  of the chair  200  taken along the front-rear direction.  FIG. 12  is a cross-sectional view taken on the outer side in the left-right direction of the seat body  204  compared to  FIG. 11 . In  FIGS. 10 to 12 , the tensile material  260  is not shown. 
     As shown in  FIGS. 10 to 12 , the seat frame  240  has a seat bottom frame  240 D supported by the fixed frames  231 , and a seat top frame  250 U fixed to an upper surface of the seat bottom frame  240 D. Each of the seat bottom frame  240 D and the seat top frame  250 U is annularly formed. 
     The seat bottom frame  240 D has first seat reinforcing rods (a connection reinforcing section)  241  slidably provided on the pair of fixed frames  231 , respectively, and second seat reinforcing rods (an elastic reinforcing section)  242  each of which connects end portions  241 E of the first seat reinforcing rods  241  to each other. The first seat reinforcing rods  241  and the second seat reinforcing rods  242  are integrally formed of, for example, a resin or the like, and have a predetermined strength. 
     As shown in  FIG. 10 , the first seat reinforcing rod  241  extends in the front-rear direction. The first seat reinforcing rod  241  has a downward U shape in a cross section along a surface perpendicular direction, which is a direction perpendicular to the load support surface  260 U (see  FIG. 8 , the same applies hereinafter). In other words, a concave section  241 C that is recessed upward is formed in a lower part of the first seat reinforcing rod  241 . The fixed frame  231  is disposed in the concave section  241 C. 
     Both end portions  241 E of the first seat reinforcing rod  241  are formed to have a larger width in the left-right direction than a portion of the first seat reinforcing rod  241  on a central side in the front-rear direction. Both end portions  241 E of the first seat reinforcing rod  241  are gradually inclined upward toward a distal end side. 
     As shown in  FIG. 11 , the second seat reinforcing rod  242  extends in the left-right direction. The second seat reinforcing rod  242  is has a plate shape wider in the front-rear direction, in a cross section along the surface perpendicular direction (a vertical cross section along the front-rear direction). 
     As shown in  FIGS. 10 to 12 , the seat top frame  250 U includes a pair of frame rods (a first part)  251  disposed to be spaced apart from each other in the left-right direction (in a direction along the load support surface  260 U), and connecting rods (a second part)  252  each of which connects end portions of the frame rods  251  to each other. The frame rods  251  and the connecting rods  252  are integrally formed of, for example, a resin or the like, and configured to be elastically deformable in response to a force acting from the tensile material  260  (see  FIG. 8 , the same applies hereinafter). 
     As shown in  FIG. 10 , the frame rod  251  extends in the front-rear direction. The frame rod  251  has a plate shape extending along the load support surface  260 U and wider in the left-right direction, in a cross section along the surface perpendicular direction (a vertical cross section along the left-right direction). 
     The frame rod  251  is formed such that the thickness thereof in the surface perpendicular direction becomes thinner toward an inner edge (an inner end portion in the left-right direction)  251 J. Further, the inner edge  251 J of the frame rod  251  is inclined downward. 
     A groove  253  recessed inward is formed in an outer edge (an outer end portion in the left-right direction)  251 K of the frame rod  251 . An end portion of the tensile material  260  is caught in the groove  253 . 
     As shown in  FIG. 11 , the connecting rod  252  extends in the left-right direction. The connecting rod  252  has a plate shape wider in the front-rear direction, in a cross section along the surface perpendicular direction (a vertical cross section along the front-rear direction). 
     The rear connecting rod  252  is gradually inclined downward toward the rear. 
     The rear connecting rod  252  is formed such that the thickness thereof in the surface perpendicular direction becomes thinner toward an inner edge (an inner end portion in the front-rear direction)  252 J. A reinforcing plate section  254  having a plate shape extending along the horizontal plane is provided on the inner edge  252 J of the front connecting rod  252 . 
     Both end portions of the reinforcing plate section  254  in the left-right direction are connected to the respective frame rods  251 . Therefore, a front part of the seat top frame  250 U including a boundary region between the frame rod  251  and the connecting rod  252  is prevented from hanging down forward and downward due to the load that is input from the body of the seated person. 
     A cushion body having elasticity (not shown, the same applies hereinafter) may be placed on an upper surface of the reinforcing plate section  254 . As a result, a front part of the tensile material  260  stretched over the seat top frame  250 U is supported by the cushion body and urged upward. The seated person feels a good seating comfort while thighs of the seated person are flexibly supported on the tensile material  260 , and because the thighs do not come into direct contact with an inner peripheral edge of the connecting rod  252 , the seated person does not feel the hardness of the connecting rod  252  and does not feel uncomfortable. 
     The groove  253  recessed inward is formed on an outer edge (an outer end portion in the front-rear direction)  252 K of the connecting rod  252 . The end portion of the tensile material  260  is caught in the groove  253 . 
     The second seat reinforcing rod  242  is provided on a lower part on the inner edge  252 J side of the connecting rod  252 . Both end portions of the connecting rod  252  are screwed to the respective end portions of the second seat reinforcing rod  242  by screws  252 X. 
     The length of the connecting rod  252  is longer than the length of the second seat reinforcing rod  242  of the seat bottom frame  240 D. As a result, the frame rod  251  connected to the end portion of the connecting rod  252  is disposed on the outer side (the outer side in the left-right direction) than the first seat reinforcing rod  241  connected to the end portion of the second seat reinforcing rod  242  when the load support surface  260 U is viewed in the surface perpendicular direction from the load support surface  260 U side. 
     In the present embodiment, the end portions of the connecting rods  252 , the end portions of the second seat reinforcing rods  242 , and the screws  252 X constitute a connecting body  205  which connects the frame rod  251  and the first seat reinforcing rod  241 . Since the end portion  241 E of the first seat reinforcing rod  241  is gradually inclined upward toward the distal end side, the frame rod  251  is disposed above the first seat reinforcing rod  241 . 
     Further, the end portion of the connecting rod  252  is gradually inclined upward toward the outer side in the left-right direction. As a result, the frame rod  251  is disposed above the connecting rod  252 . 
     As shown in  FIGS. 8 and 9 , the backrest  207  includes a back frame  270 , and a tensile material  290  stretched over the back frame  270 . A front surface of the tensile material  290  serves as a load support surface  290 F that receives the load of the seated person. 
     The back frame  270  has a back rear frame  270 B connected to the support base  202 , and a back front frame  280 F provided in front of the back rear frame  270 B. 
     The back rear frame  270 B has lower side portions  271 , lateral side portions  272 , and an upper side portion  273 . The lower side portions  271 , the lateral side portions  272 , and the upper side portion  273  are formed integrally by, for example, a metal such as aluminum or a resin having a predetermined strength. 
     The lower side portions  271  are connected to the tilting adjustment mechanism in the support base  202  and extend from both the left and right sides of the rear part of the support base  202 . The lower side portion  271  is gradually inclined rearward toward the upper part. Also, an armrest  274  extending sideways is provided in each lower side portion  271 . 
     The lateral side portion  272  is connected to the upper end portion of each lower side portion  271 . Each lateral side portion  272  is gradually inclined outward in the left-right direction toward the upper part. 
     A lower part of the lateral side portion  272  is gradually inclined forward toward the upper part. 
     An upper part of the lateral side portion  272  is gradually inclined rearward toward the upper side. The upper parts of the lateral side portions  272  are connected to each other by the upper side portion  273 . 
       FIG. 13  is a cross-sectional view taken along the line C-C of  FIG. 9 .  FIG. 14  is a cross-sectional view taken along the line D-D of  FIG. 9 . 
     As shown in  FIGS. 8, 9, 13, and 14 , the back front frame  280 F has upper arm sections  281  connected to the upper parts of the lateral side portions  272  of the back rear frame  270 B, lower arm sections  282  connected to the lower parts of the lateral side portions  272 , a pair of vertical rods  286  disposed to be spaced apart from each other in the left-right direction (along load support surface  260 U), and an upper rod  287  which connects the upper ends of the pair of vertical rods  286 . The upper arm sections  281 , the lower arm sections  282 , the vertical rods  286 , and the upper rod  287  are integrally formed of, for example, resin or the like. The vertical rods  286  and the upper rod  287  are configured to be elastically deformable in accordance with the force acting from the tensile material  290 . 
     As shown in  FIG. 13 , the upper arm section  281  is fixed to the upper part of the lateral side portion  272  of the back rear frame  270 B by a bolt  281 X. The upper arm section  281  extends forward from the lateral side portion  272  of the back rear frame  270 B, and gradually extends outward in the left-right direction toward the front part. 
     As shown in  FIG. 14 , a fixed piece  283  is fixed to the lower part of the lateral side portion  272  of the back rear frame  270 B with a bolt  283 X. The lower arm section  282  externally fits the fixed piece  283 . The lower arm section  282  and the fixed piece  283  are fixed by a retaining pin  284 . The lower arm section  282  extends forward from the lateral side portion  272  of the back rear frame  270 B and gradually extends outward in the left-right direction toward the front part. 
     As shown in  FIG. 8 , the upper arm section  281  is connected to the upper part of the vertical rod  286 , and the lower arm section  282  is connected to the lower part of the vertical rod  286 . 
     As shown in  FIG. 9 , each vertical rod  286  extends in the vertical direction. In detail, the vertical rod  286  is gradually inclined inward in the left-right direction toward the lower part. The lower ends of the pair of vertical rods  286  are connected to each other. 
     As shown in  FIG. 8 , a lower part  286 A of the vertical rod  286  is gradually inclined forward toward the upper part. An upper part  286 B of the vertical rod  286  is gradually inclined rearward toward the upper part. Accordingly, in a side view, a boundary section  286 C between the lower part  286 A and the upper part  286 B has a shape protruding forward. The lower arm section  282  is connected to a rear surface of the boundary section  286 C. 
     As shown in  FIGS. 13 and 14 , the vertical rod  286  has a plate shape extending along the load support surface  290 F wider in the left-right direction, in a cross section along the surface perpendicular direction, which is a direction perpendicular to the load support surface  290 F (see  FIG. 8 ) (a horizontal cross section along the left-right direction). 
     As shown in  FIG. 14 , the lower part of the vertical rod  286  is formed such that the thickness thereof in the surface perpendicular direction becomes thinner toward an inner edge (an inner end portion in the left-right direction)  286 J. 
     A groove  288  recessed inward is formed in an outer edge (an outer end portion in the left-right direction)  286 K of the vertical rod  286 . The end portion of the tensile material  290  is caught in the groove  288 . 
     Since the upper arm section  281  and the lower arm section  282  gradually extend outward in the left-right direction toward the front, the vertical rod  286  is disposed outside the lateral side portion  272  in the left-right direction. 
     Next, the deformation of the seat body  204  when the seated person sits on the seat body  204  of the chair  200  will be described. 
     First, a description will be given of a case (hereinafter, this case will be referred to as a first seated state) in which the seated person sits on the rear part of the central part in the left-right direction (the width direction) of the load support surface  260 U of the seat body  204 . 
     Since the load support surface  260 U is made up by the elastically deformable tensile material  260 , the tensile material  260  elastically deforms to sink downward by the load acting from the seated person. 
     Since the rear connecting rod  252  on which the tensile material  260  is stretched gradually inclines downward toward the rear, the connecting rod  252  is easy to elastically deform downward. Here, since a second seat reinforcing rod  242  is provided at the lower part of the connecting rod  252 , it is possible to prevent the central part in the left-right direction of the connecting rod  252  from being excessively descended downward and being bent. 
     Both the left and right sides of the front end portion of the rear connecting rod  252  and both the left and right sides of the rear end portion of the front connecting rod  252  are connected by the first seat reinforcing rods  241 , respectively. Therefore, the left and right frame rods  251 , which are disposed outside in the left-right direction than the connecting rods  252 , are restrained by the connecting rod  252  and elastically deform gradually upward from the rear part. 
     Next, the description will be given of a case (hereinafter, this case will be referred to as a second seated state) in which the seated person sits slightly in front of a central part in the front-rear direction of the load support surface  260 U of the seat body  204  and the central part in the left-right direction (the width direction) of the load support surface  260 U. 
     In the second seated state, since the seating position is ahead of the first seated state, the amount of elastic deformation of the rear connecting rod  252  toward the lower side is smaller than in the case of the first seated state. 
     However, the frame rods  251 , each of which has a plate shape in the cross-sectional view taken along the surface perpendicular direction of the tensile material  260 , are pulled by the tensile material  260  elastically deforming in the surface perpendicular direction, rise toward the body side of the seated person, and elastically deform to wrap the body from the sides. At this time, the pair of front and rear connecting rods  252  suppress excessive elastic deformation of the frame rod  251 . 
     Next, the deformation of the backrest  207  when the seated person puts his back against the backrest  207  will be described. 
     When the back is put against the load support surface  290 F of the backrest  207  made up of the tensile material  290 , the load in the surface perpendicular direction acting on the tensile material  290  is not so large as the load acting on the load support surface  260 U of the seat body  204 . Further, the vicinity of the boundary sections  286 C that protrude forward in a side view makes contact with the back. From these facts, since the vertical rods  286  are pulled by the tensile material  290 , the vertical rods  286  rise toward the body side of the seated person, and elastically deform to wrap the body from the sides. That is, the vertical rods  286  are elastically deformed, without being caused by the rearward elastic deformation of the upper rod  287  connecting the upper ends of the vertical rods  286 , the connecting section of the lower ends of the vertical rods  286 , and the like. At this time, the upper rod  287  suppresses excessive elastic deformation of the vertical rods  286 . 
     As described above, with the frame rods  251  of the seat top frame  250 U of the seat body  204  constituting the support section of the present invention, and the vertical rod  286   s  of the back front frame  280 F of the backrest  207 , elasticity deformation is promoted while suppressing excessive deformation, due to complex factors such as the cross-sectional shape thereof, the tension of the tensile materials  260  and  290  constituting the load supporting surface, and the engagement with the other parts of the seat top frame  250 U and the other parts of the back front frame  280 F. 
     In the chair  200  having such a configuration, the tensile material  260  is flexibly bent at the central side of the load support surface  260 U in a load input direction, and the frame rods  251 , which are arranged opposite to each other, elastically deform to follow the body of the seated person by the load acting from the seated person. Therefore, the frame rods  251  can receive the seated person together with the tensile material  260  by wrapping the seated person. 
     In addition, since the second seat reinforcing rods  242  for enhancing the rigidity are provided only on the connecting rods  252  among the frame rods  251  and the connecting rods  252 , the connecting rods  252  can be strongly reinforced. Therefore, excessive displacement and bending of the frame rods  251  can be suppressed by the connecting rods  252  arranged between the pair of frame rods  251 . 
     In addition, since the frame rods  251  are disposed on a side (upper side) closer to an input direction of the load than the connecting rods  252 , the frame rods  251  are easily displaced to rise toward the body side of the seated person and wrap the body from the sides. 
     In addition, since the first seat reinforcing rods  241  and the second seat reinforcing rods  242  form an annular shape, the rigidity is enhanced, and the frame rods can be stably supported. 
     Further, since the frame rod  251  is disposed to be spaced apart from the first seat reinforcing rod  241  in the surface perpendicular direction of the load support surface  260 U, the frame rod  251  can be elastically deformed sufficiently to correspond to the separation distance in the surface perpendicular direction. 
     Further, since the frame rods  251  are disposed outside the first seat reinforcing rods  241  when the load support surface  260 U is viewed in the surface perpendicular direction from the load support surface  260 U side, when the frame rods  251  are pulled by the tensile material  260 , the frame rods  251  are easily displaced toward the central side of the load support surface  260 U to rise toward the body side of the seated person and wrap the body from the sides. 
     Further, since the frame rod  251  is formed in a plate shape along the load support surface  260 U, the frame rod  251  itself is easily deformed along the load support surface  260 U. Therefore, when the frame rods  251  are pulled by the tensile material  260 , the frame rods  251  are more easily displaced to rise toward the body side of the seated person and wrap the body from the sides. 
     Further, the frame rod  251  is formed such that the thickness thereof in the surface perpendicular direction becomes thinner toward the inner edge side. Therefore, the inner edge sides of the frame rod  251  are pulled by the tensile material  260  and displaced to a side (downward) away from the input direction of the load, and the outer edge sides of the frame rod  251  are easily displaced in a direction of rising (a side close to the input direction of the load, upward) against the displacement of the inner edge sides. 
     Since the second seat reinforcing rod  242  is formed as a separate body from the connecting rod  252 , the second seat reinforcing rod  242  is simply connected to the connecting rod  252  by the screw  252 X, and the second seat reinforcing rod  242  can be easily manufactured. In addition, the shapes of the second seat reinforcing rod  242  and the connecting rod  252  can be simplified, and the volumes of the second seat reinforcing rod  242  and the connecting rod  252  can be reduced. As a result, it is possible to prevent defective molding of the second seat reinforcing rod  242  and the connecting rod  252 . 
     Further, the shapes and combinations of the constituent members shown in the above-described embodiments are merely examples, and various modifications can be made on the basis of design requirements or the like in the scope that does not depart from the gist of the present invention. 
     For example, in the above-described embodiment, the seat body  204  is constituted by the load support body for a chair according to the present invention, but the present invention is not limited thereto, and the backrest may be configured by the load support body for a chair according to the present invention. 
     Further, in the above-described embodiment, the second part and the reinforcing section are formed as separate bodies, but the present invention is not limited thereto, and the second part and the reinforcing section may be formed as a single body. In this case, the body is constituted by increasing the thickness in the surface perpendicular direction of the integrated second part and reinforcing section. Therefore, it can easily be reinforced over a wide range in the extending direction (longitudinal direction) of the second part. 
     INDUSTRIAL APPLICABILITY 
     According to the load support structure for a chair and the chair according to the present invention, it is possible to suppress excessive displacement, while allowing elastic deformation of a support section to which a tensile material is attached. 
     Further, according to the load support body for a chair and the chair according to the present invention, it is possible to suppress excessive displacement, while allowing elastic deformation of the annular body to which the tensile material is attached. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Leg section 
               2  Support base 
               3  Seat receiving member 
               4  Seat body (load support structure for chair) 
               5  Connecting body 
               7  Backrest (load support structure for chair) 
               30  Support body 
               40  Seat frame 
               40 D Seat bottom frame 
               41  First seat reinforcing rod (first reinforcing section) 
               42  Second seat reinforcing rod (second reinforcing section) 
               50 U Seat top frame 
               51  Frame rod (support section) 
               52  Connecting rod (connecting section) 
               60  Tensile material 
               60 U Load support surface 
               70  Back frame 
               70 B Back rear frame 
               71  Lower side portion 
               72  Lateral side portion (first reinforcing section) 
               73  Upper side portion 
               80 F Back front frame 
               81  Upper arm section (connecting body) 
               82  Lower arm section (connecting body) 
               86  Vertical rod (support section) 
               87  Upper rod (connecting section) 
               90  Tensile material 
               100  Chair 
               201  Leg section 
               202  Support base 
               203  Seat receiving member 
               204  Seat body (load support body for chair) 
               205  Connecting body 
               207  Backrest 
               230  Support structure 
               240  Seat frame (annular body) 
               240 D Seat bottom frame 
               241  First seat reinforcing rod (connection reinforcing section) 
               242  Second seat reinforcing rod (rigidity reinforcing section) 
               250 U Seat top frame 
               251  Frame rod (first part) 
               252  Connecting rod (second part) 
               260  Tensile material 
               260 U Load support surface 
               270  Back frame 
               270 B Back rear frame 
               271  Lower side portion 
               272  Lateral side portion 
               273  Upper side portion 
               280 F Back front frame 
               281  Upper arm section 
               282  Lower arm section 
               286  Vertical rod 
               287  Upper rod 
               290  Tensile material 
               200  Chair