[0001]The present disclosure relates to a joining structure, a method fr producing a joining structure, and a vehicle body. BACKGROUND ART [0002] For example, a body panel of an automobile is attached to a vehicle body member by joining a fange that is provided in the body panel and a flange that is provided in a diferent vehicle body member which is adjacent to the relevant body panel. These fanges are sometimes joined by being spot-welded to each other in a state in which an adhesive has been applied between the fanges (fr example, see Patent Document 1). In the structure disclosed in Patent Document 1, by causing a fange of a vehicle body panel and a fange of a vehicle body member to abut against each other in a state in which an adhesive has been applied between the two fanges, adhesive is interposed between the entire area of the respective surfces that oppose each other, and the fanges are frmly joined and united using the adhesive. LIST OF PRIOR ART DOCUMENTS PATENT DOCUMENT [0003] Patent Document 1: JP2013-13910A SUMMARY OF INVENTION TECHNICAL PROBLEM 2 [0004] In this connection, with regard to steel sheets that constitute the vehicle bodies of automobiles, development of techniques fr compatibly achieving both improvements in collision safty by increasing the tensile strength, and reductions in weight by making the steel sheets thinner is proceeding. However, when the thickness of a steel sheet constituting a vehicle body becomes thinner, NV perfrmance (anti-noise perfrmance and anti-vibration perfrmance) decreases. In other words, if the thickness of a steel sheet constituting a vehicle body member is made thinner, when vibrations are received, the vibrations become large, and the noise in the vehicle cabin also becomes large. [0005] However, in Patent Document 1, no suggestion is made fom the viewpoint of improving anti-noise perfrmance and anti-vibration perfrmance. Further, the demand for improving anti-noise perfrmance and anti-vibration perfrmance is not limited to the vehicle body, but also exists with respect to other general joining structures which receive vibrations. [0006] In consideration of the above situation, one objective of the present invention is, with respect to a joining structure including a structure that joins two flanges together as well as a vehicle body that includes the joining structure, to enable securement of suficient anti-noise perfrmance and anti-vibration perfrmance even when the sheet thickness is made thin. SOLUTION TO PROBLEM [0007] The gist of the present invention is a joining structure, a method for producing a joining structure, and a vehicle body which are described hereunder. [0008] (1) Ajoining structure, including: a frst fange; 3 a second flange arranged opposing the frst fange; a joint portion frmed by the frst fange and the second fange being joined to each other in a state in which at least one of the frst flange and the second fange is collapsed to a side of the other of the first fange and the second flange; and a contact portion where the frst fange and the second fange slidably contact each other at a position that is separated fom the joint portion; wherein: at a position between the joint portion and the contact portion, the frst fange and the second fange are separated fom each other and a gap is frmed between the first fange and the second fange. [0009] (2) The joining structure according to the above (1 ), wherein: the frst flange includes a curved portion which extends so that a distance fom the second flange increases as a distance fom the contact portion increases, and the contact portion is provided at one end of the curved portion. [0010] (3) The joining structure according to the above (1), wherein: the contact portion is arranged at an edge part of the first flange. [0011] ( 4) The joining structure according to the above (3), wherein: the frst fange includes a curved portion which extends so that a distance fom the second fange increases as a distance fom the contact portion increases, and the joint portion is arranged between the contact portion and the curved portion. [0012] (5) The joining structure according to any one of the above (1) to (4), wherein: each of the fanges extends in a predetermined longitudinal direction, and the contact portion is arranged between two of the joint portions. [0013] (6) A method fr producing the joining structure according to any one of the 4 above (1) to (5), including: preparing a frst fange starting material as a starting material of the first fange, and a second fange starting material as a starting material of the second fange, wherein: in at least one of the frst flange starting material and the second fange starting material, a recess is provided which is a portion where the first flange starting material and the second flange starting material are separated when the frst flange starting material and the second flange starting material are butted against each other, the recess is deformed by abutting the frst fange starting material and the second fange starting material against each other at the recess, and the joint portion is formed by joining an abutted portions, and the frst flange starting material and the second fange starting material are caused to slidably contact at the contact portion that is at a position which is separated from the joint portion. [0014] (7) A vehicle body including: the joining structure according to any one of the above (1) to (5), a panel in which the first fange is provided, and a framework member in which the second flange is provided. [0015] (8) The vehicle body according to the above (7), wherein the framework member has: a frst half portion in which the second flange is provided; a second half portion which has a third flange arranged opposing the second flange, and which is combined with the first half portion; and a half-portion joint portion which is formed by the second flange and the third flange being joined to each other, and which restricts relative sliding of the frst flange and the third flange. [0016] (9) The vehicle body according to the above (8), wherein: by the joint portion and the half-portion joint portion being formed at a place 5 where the frst fange, the second fange, and the third fange are superimposed on each other, the joint portion and the half-portion joint portion are arranged overlapping each other in a thickness direction of the panel. [0017] (10) The vehicle body according to the above (8) or the above (9), wherein: each of the fanges extends in a predetermined longitudinal direction; and by the second flange and the third fange being separated fom each other at a position between two of the half-portion joint portions, a half-portion gap is frmed as a gap between the second flange and the third flange. ADVANTAGEOUS EFFECTS OF INVENTION [0018] According to the present invention, in a joining structure including a structure that joins two fanges together, even in a case where the sheet thickness is made thin, suffcient anti-noise perfrmance and anti-vibration perfrmance can be secured, fr example, without reducing the sense of rigidity with respect to the vehicle body when the driver is steering. BRIEF DESCRIPTION OF DRAWINGS [0019] [Figure 1] Figure 1 is a schematic perspective view illustrating a part of an automobile vehicle body including a joining structure according to an embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional diagram illustrating a part of the vehicle body, and shows a state as viewed from a longitudinal direction. [Figure 3] Figure 3(A) and Figure 3(B) are schematic cross-sectional diagrams fr describing a process for joining a frst fange of the vehicle body to a second fange by Jommg. [Figure 4] Figure 4(A) is a view illustrating a frst modifcation of a frst embodiment, and shows a cross section as viewed fom the longitudinal direction. Figure 4(B) is a 6 view illustrating a second modifcation of the frst embodiment, and shows a cross section as viewed fom the longitudinal direction. [Figure 5] Figure 5(A) is a view illustrating a third modification of the first embodiment, and shows a cross section as viewed from the longitudinal direction. Figure 5(B) is a view illustrating a furth modifcation of the first embodiment, and shows a cross section as viewed fom the longitudinal direction. [Figre 6] Figure 6(A) and Figre 6(B) are schematic cross-sectional diagrams fr describing a process fr joining a frst fange to a second fange in the furth modifcation of the frst embodiment. [Figure 7] Figure 7(A) is a view illustrating a ffth modifcation of the frst embodiment, and shows a cross section as viewed from the longitudinal direction. Figure 7(B) is a view illustrating a sixth modifcation of the frst embodiment, and shows a cross section as viewed fom the longitudinal direction. [Figure 8] Figure 8 is a view illustrating a seventh modification of the frst embodiment, and shows a cross section as viewed fom the longitudinal direction. [Figure 9] Figure 9 is a view illustrating an eighth modification of the frst embodiment, and shows a cross section as viewed fom the width direction. [Figure 1 OJ Figre 10 is a schematic perspective view fr describing a process fr joining a frst fange to a second fange in the eighth modifcation of the first embodiment. [Figure 11] Figure 11(A) and Figure 11(B) are schematic cross-sectional diagrams fr describing the process fr joining the frst flange to the second fange in the eighth modifcation of the first embodiment. [Figre 12] Figure 12 is a schematic perspective view illustrating one part of an automobile vehicle body according to a second embodiment of the present invention. [Figure 13] Figure 13 is a view illustrating one part of the vehicle body illustrated in Figure 12, and shows a state as viewed from the longitudinal direction. [Figre 14] Figure 14 is a schematic diagram fr describing a process fr joining a frst fange of the vehicle body to a second fange. [Figure 15] Figure l 5(A) is a view illustrating a frst modifcation of the second 7 embodiment, and shows a state as viewed from the longitudinal direction. Figure 15(8) is a schematic diagram fr describing a process fr joining a frst flange to a second fange in the frst modification of the second embodiment. [Figure 16] Figure 16(A) is a view illustrating a second modification of the second embodiment, and shows a state as viewed from the longitudinal direction. Figre 16(8) is a schematic diagram fr describing a process fr joining a frst fange to a second fange in the second modifcation of the second embodiment. [Figure 17] Figure 17(A) is a view illustrating a third modification of the second embodiment, and shows a state as viewed from the longitudinal direction. Figre 17(8) is a schematic diagram fr describing a process fr joining a frst fange to a second flange in the third modifcation of the second embodiment. [Figure 18] Figure 18 is a view illustrating a furth modifcation of the second embodiment, and shows a view as viewed fom a longitudinal direction X. [Figure 19] Figure 19(A) is a view illustrating a ffth modifcation of the second embodiment, and shows a view as viewed fom the longitudinal direction X. Figure 19(8) is a schematic diagram fr describing a process for joining a first fange to a second fange in the ffth modification of the second embodiment. [Figure 20] Figure 20(A) is a view illustrating a sixth modifcation of the second embodiment, and shows a view as viewed fom the longitudinal direction. Figure 20(8) is a schematic diagram fr describing a process fr joining a frst fange to a second fange in the sixth modifcation of the second embodiment. [Figure 21] Figure 21 is a schematic perspective view illustrating one part of an automobile vehicle body according to a third embodiment of the present invention. [Figre 22] Figre 22 is a cross-sectional diagram illustrating one part of the vehicle body of the third embodiment, and shows a state as viewed fom the longitudinal direction. [Figre 23] Figure 23(A) and Figure 23(8) are schematic cross-sectional diagrams fr describing a process fr joining a frst fange of the vehicle body to a second fange in the third embodiment. [Figre 24] Figre 24(A) 1s a view illustrating a frst modifcation of the third 8 embodiment, and shows a cross section as viewed fom the longitudinal direction. Figure 24(B) is a view illustrating a second modification of the third embodiment, and shows a cross section as viewed fom the longitudinal direction. [Figre 25] Figre 25(A) is a view illustrating a third modifcation of the third embodiment, and shows a cross section as viewed fom the longitudinal direction. Figure 25(B) is a view illustrating a fourth modification of the third embodiment, and shows a cross section as viewed fom the longitudinal direction. [Figure 26] Figre 26(A) and Figure 26(B) are schematic cross-sectional diagrams fr describing a process fr joining a frst fange to a second flange in the furth modifcation of the third embodiment. [Figure 27] Figure 27(A) is a view illustrating a fifh modifcation of the third embodiment, and shows a cross section as viewed fom the longitudinal direction. Figre 27(B) is a view illustrating a sixth modification of the third embodiment, and shows a cross section as viewed fom the longitudinal direction. [Figure 28] Figure 28 is a view illustrating a seventh modifcation of the third embodiment, and shows a cross section as viewed fom the longitudinal direction. [Figure 29] Figure 29 is a view illustrating an eighth modifcation of the third embodiment and shows a cross section as viewed fom the width direction. [Figure 30] Figre 30 is a schematic perspective view fr describing a process fr joining a frst fange to a second fange in the eighth modifcation of the third embodiment. [Figure 31] Figure 31(A) and Figure 31(B) are schematic cross-sectional diagrams fr describing a process fr joining a first fange to a second fange in the eighth modifcation of the third embodiment. DESCRIPTION OF EMBODIMENTS [0020] Hereunder, embodiments of the present invention are described while refrring to the accompanying drawings. [0021] 9 Figure 1 is a schematic perspective view illustrating one part of an automobile vehicle body 100 (hereinafer, also refrred to as simply "vehicle body 100") including a joining structure 30 according to a frst embodiment of the present invention. Figure 2 is a cross-sectional diagram illustrating one part of the vehicle body 100, and shows a state as viewed fom a longitudinal direction X. Refrring to Figure 1 and Figure 2, vehicle body 100 is the vehicle body of an automobile. [0022] Note that, hereunder, the longitudinal direction of the joining structure 30 shown in Figure 1 is refrred to as "longitudinal direction X". In the longitudinal direction X, the side fcing away fom the viewer in Figure 2 is taken as the positive side. Further, the width direction of the joining structure 30 is refrred to as "width direction Y". The width direction Y is the transverse direction in Figure 1 and Figure 2, and the lef direction on the page surfce is taken as the positive side. Further, the direction orthogonal to both the longitudinal direction X and the width direction Y is refrred to as "height direction Z". In the height direction Z, the upper side on the page surfce in Figure 1 and Figure 2 is taken as the positive side. The longitudinal direction X, the width direction Y, and the height direction Z may match the vehicle length direction, the vehicle width direction, and the vehicle height direction of the vehicle body 100, respectively, or need not match these directions, respectively. Hereinafter, one of the sides in the width direction Y is refrred to as "one end side", and the other side is referred to as "the other end side". [0023] The vehicle body 100 has a frst member 1 and a second member 2. [0024] In the present embodiment, the frst member 1 is, fr example, an exterior member of the vehicle body 100, and is not a famework member which bears the weight of the automobile and receives an exteral frce fom the suspension. Examples of such an exterior member that can be mentioned include an outer panel, a rear quarter panel, a roof panel, a door panel ( door inner panel, door outer panel), and a 10 bonnet hood (hood inner panel, hood outer panel) of an automobile. Note that, the first member 1 may be a member other than the members mentioned as examples above. [0025] The second member 2 is, fr example, an exterior member or a famework member of the vehicle body 100. Examples of such a famework member that can be mentioned include a font side member, an A pillar, a B pillar, a C pillar, a side sill, a rear side member and a cross member. Note that, it sufices that the second member 2 is a member constituting the vehicle body 100, and the second member 2 may be a member other than the members mentioned as examples above. [0026] The frst member 1 is frmed in a sheet shape by subjecting a sheet to press working. The sheet constituting the frst member 1 is, for example, a mild steel sheet. The materials constituting the first member 1 and the second member 2 are sheets or tubes made of steel, aluminum, magnesium, and resin including resin reinfrced with fber, and the material quality and shape of the frst member 1 and the second member 2 may difer fom each other. The frst member 1 and the second member 2 may each be frmed of a single material, or may each be frmed of a composite material. Methods for joining the frst member 1 and the second member 2 include welding such as spot welding, laser welding, arc welding, or seam welding, mechanical joining such as riveting, caulking, or bolt fstening, and bonding using an adhesive or the like. [0027] The frst member 1 has a frst main body 11, a frst vertical wall 12 and a first fange 13. [0028] The second member 2 has a second main body 21, a second vertical wall 22 and a second fange 23. [0029] The frst vertical wall 12 extends from the frst main body 11. The frst main body 11 is continuous with the other end of the frst vertical wall 12, and the frst fange 13 is continuous with one end of the first vertical wall 12. The frst flange 13 is joined 11 to the second fange 23 of the second member 2. [0030] In the second member 2, the second vertical wall 22 extends fom the second main body 21. The second main body 21 is continuous with the other end of the second vertical wall 22, and the second flange 23 is continuous with one end of the second vertical wall 22. The frst flange 13 and the second flange 23 are arranged opposing each other in the height direction Z. [0031] The joining structure 30 which includes the frst flange 13 and the second flange 23 is provided in the vehicle body 100. [0032] The joining structure 30 has the frst flange 13, the second flange 23, a gap forming portion 31, a joint portion 32, and a contact portion 33. [0033] The first flange 13 has a first curved portion 41, a frst contact portion 45, a frst gap forming portion 42, and a frst edge part 43. [0034] The frst curved portion 41 is formed in a curved shape as viewed from the longitudinal direction X, and is formed in an arc shape that is convex toward the second member 2. The frst curved portion 41 extends to one side in the height direction Z so that the distance from the second flange 23 increases as the distance from the contact portion 33 to the other end side increases. The other end of the first curved portion 41 is continuous with the frst vertical wall 12, and one end of the first curved portion 41 is continuous with the first gap forming portion 42 via the first contact portion 45. [0035] The first gap forming portion 42 forms the gap 34 in cooperation with a second gap frming portion 52, to be described later, of the second fange 23. The gap forming portion 31 is frmed by the frst gap forming portion 42 and the second gap forming portion 52. The frst gap frming portion 42 is formed, for example, in a substantially U-shape as viewed fom the longitudinal direction X. One end and the 12 other end of the frst gap frming portion 42 in the width direction Y are in contact with the second fange 23, while on the other hand, an intermediate portion of the first gap forming portion 42 is separated fom the second fange 23. The gap 34 is frmed between the interediate portion of the first gap frming portion 42 as the afrementioned separated portion and the second gap frming portion 52 of the second fange 23. The one end of the frst gap frming portion 42 is continuous with the first edge part 43. [0036] The frst edge part 43 is the edge part ( edge portion) of the frst member 1 in the width direction Y The first edge part 43 is also the font end portion of the frst fange 13 in the width direction Y The other end (base end) of the first edge part 43 is continuous with the frst gap frming portion 42. The one end (font end) of the frst edge part 43 is a free end. [0037] The second flange 23 has a second curved portion 51, a second contact portion 55, the second gap forming portion 52, and a second edge part 53. [0038] The second curved portion 51 is frmed in a curved shape as viewed fom the longitudinal direction X, and is frmed in an arc shape that is convex toward the frst member 1. The second curved portion 51 extends to the other side in the height direction Z so that the distance fom the frst fange 13 increases as the distance fom the contact portion 33 to the other end side increases. The other end of the second curved portion 51 is continuous with the second vertical wall 22, and the one end of the second curved portion 51 is continuous with the second gap frming portion 52 via the second contact portion 55. [0039] The second gap frming portion 52 is frmed, fr example, in a substantially U-shape as viewed fom the longitudinal direction X. One end 52a and the other end 52b of the second gap frming portion 52 in the width direction Y are in contact with the frst gap frming portion 42, while on the other hand, an intermediate portion of the 13 second gap frming portion 52 is separated fom the frst flange 13. As mentioned above, at a position between the joint portion 32 and the contact portion 33, the gap 34 is frmed between the frst fange 13 and the second fange 23 as a result of the frst flange 13 and the second flange 23 (the frst gap frming portion 42 and the second gap frming portion 52) being separated fom each other. The width and height of the gap 34 are appropriately set according to the target fictional frce and the like between the fanges 13 and 23 at the contact portion 33. The one end of the second gap frming portion 52 is continuous with the second edge part 53. [0040] The second edge part 53 is the edge part ( edge portion) of the second member 2 in the width direction Y. The second edge part 53 is also the front end portion of the second fange 23 in the width direction Y. The one end (base end) of the second edge part 53 is continuous with the second gap frming portion 52, and the one end (font end) of the second edge part 53 is a free end. In the present embodiment, the second edge part 53 extends along the width direction Y. In the present embodiment, a clearance is frmed between the frst edge part 43 and the second edge part 53. [0041] The joint portion 32 is frmed by joining the frst flange 13 and the second fange 23 ( a frst fange starting material and a second flange starting material which are described later) to each other in a state in which at least one of the frst fange 13 and the second fange 23 is collapsed to the side of the other of the frst fange 13 and the second flange 23. In the present embodiment, the joint portion 32 is frmed by joining the first fange 13 and the second fange 23 to each other in a state in which the frst fange 13 is collapsed to the second fange 23 side, and the second fange 23 is collapsed to the frst fange 13 side. Spot welding can be mentioned as an example of the joining method in this case. The joint portion 32 is frmed by, fr example, intermittently perfrming spot welding in the longitudinal direction X. Note that, the joint portion 32 may be frmed by joining the frst fange 13 and the second fange 23 over the entire area in the longitudinal direction X in a state in which these fanges 13 and 23 are pressed against each other. 14 [0042] The joint portion 32 has a first joint portion 44 which is frmed in the first fange 13, artd a second joint portion 54 which is frmed in the second fange 23. [0043] In the present embodiment, the first joint portion 44 is provided at one end 42a of the frst gap frming portion 42 that is the end closer to the first edge part 43, and extends in the width direction Y. The frst gap frming portion 42 is formed by plastically deforming a frst fange starting material that is the starting material of the first flange 13 by causing the first fange starting material to be collapsed to the side of a second fange starting material that is the starting material of the second flange 23, and presses the other end 42b (first contact portion 45) of the first gap forming portion 42 to the side of the second contact portion 55 of the second fange 23. The second joint portion 54 is a portion of the second fange 23 that is joined to the first joint portion 44 by joining, and is formed at the one end 52a of the second gap forming portion 52 that is the end closer the second edge part 53, and extends in the width direction Y. The second gap foring portion 52 is formed by causing a second fange starting material that is the starting material of the second fange 23 to be collapsed and deformed to the side of the first fange starting material that is the starting material of the frst flange 13, and presses the other end 52 (second contact portion 55) of the second gap forming portion 52 to the side of the first contact portion 45 of the frst fange 13. [0044] The contact portion 33 is formed by the frst fange 13 and the second fange 23 slidably contacting at a position that is separated from the joint portion 32. [0045] The contact portion 33 has the frst contact portion 45 which is formed in the first flange 13, and the second contact portion 55 which is formed in the second flange 23. [0046] In the present embodiment, the frst contact portion 45 is provided at the other end 42b which is on the frst curved portion 41 side in the first gap forming portion 42, 15 and extends in the width direction Y. It can also be said that the frst contact portion 45 is frmed at one end of the frst curved portion 41. As mentioned above, the frst contact portion 45 is pressed to the side of the second contact portion 55 of the second flange 23. In the present embodiment, the second contact portion 55 is provided at the other end 52b side on the second curved portion 51 side of the second gap frming portion 52, and extends in the width direction Y. It can also be said that the second contact portion 55 is provided at the other end of the second curved portion 51. The second contact portion 55 is a portion of the second flange 23 that is pressed against the first contact portion 45, and by rubbing against the first contact portion 45, the second contact portion 55 converts vibration energy into thermal energy to thereby attenuate the vibration energy. The frst contact portion 45 and the second contact portion 55 are in direct contact with each other, without an adhesive interosed therebetween. In this case, the term "direct" means that any of a steel sheet constituting the frst fange 13, a coating layer frmed on a surfce of the steel sheet, a plating layer frmed on a surfce of the steel sheet, and a paint layer frmed on a surfce of the plating layer is in contact with any of a steel sheet constituting the second fange 23, a coating layer frmed on a surface of the steel sheet, a plating layer frmed on a surfce of the steel sheet, and a paint layer frmed on a surfce of the plating layer. [0047] The vehicle body 100 including the joining structure 30 having the confguration described above receives an exciting frce due to vibration fom the engine, vibration fom the suspension, and vibrations generated by pressure fuctuations in air at the vehicle surfce. The exciting frce propagates through the famework of the vehicle body 100, and is transmitted to the joining structure 30. In the joining structure 30, the frst contact portion 45 and the second contact portion 55 slide against each other due to the exciting frce, thereby attenuating the vibrations. That is, when the first contact portion 45 slides with respect to the second contact portion 55, the afrementioned exciting frce is. consumed as thermal energy and attenuated. As a result, vibration sound (panel vibration sound) can be suppressed. By utilizing the vibration energy attenuation effect produced by fiction between the sheets of the joined 16 fanges 13 and 23 in this way, even in a case where the sheet thickness of the frst member 1 and the second member 2 is made thin, vehicle body vibrations can be suppressed and noise emitted by the automobile can also be suppressed. [0048] Further, in the present embodiment, the contact portion 33 is provided at one end of the curved portions 41 and 51. With this confgration, by the contact portions 45 and 55 being provided at one end of the curved portions 41 and 51 as places at which a contact frce between the fanges 13 and 23 is particularly high, the amount of energy attenuation due to frictional sliding between the frst contact portion 45 and the second contact portion 55 can be increased. [0049] The fregoing describes the schematic confguration of the vehicle body 100. Next, an example of a method for producing the vehicle body 100 will be described. [0050] Figre 3(A) and Figure 3(B) are schematic cross-sectional diagrams for describing a process fr joining the first fange 13 of the vehicle body 100 to the second flange 23 by joining. When joining the frst flange 13 to the second fange 23, frst, a frst flange starting material 61 and a second fange starting material 62 illustrated in Figure 3(A) are prepared. The first fange starting material 61 is the starting material of the frst fange 13, and the second fange starting material 62 is the starting material of the second fange 23. [0051] The first fange starting material 61 is frmed in approximately the same shape as the frst member 1 except that a portion of the first fange 13 which is located on the one end side in the width direction Y from the intermediate portion of the frst gap frming portion 42 is frmed in a fat shape. That is, the first fange starting material 61 has the frst main body 11, the frst vertical wall 12, and a frst planned fange portion 71. The first planned fange portion 71 has the frst curved portion 41, the frst contact portion 45, the other end 42b of the frst gap frming portion 42, and a first fat sheet portion 72 extending to the one end side in the width direction Y from the 17 intermediate portion of the frst gap frming portion 42. A frst recess 73 is frmed by the other end 42b of the frst gap frming portion 42 and the first fat sheet portion 72. The frst recess 73 is a portion at which the first fange starting material 61 and the second fange starting material 62 are separated fom each other when the frst flange starting material 61 and the second fange starting material 62 are butted against each other. [0052] Similarly, the second flange starting material 62 is frmed in the same shape as the second member 2 except that a portion of the second fange 23 which is located on the one end side in the width direction Y fom the intermediate portion of the second gap forming portion 52 is frmed in a fat shape. That is, the second fange starting material 62 has the second main body 21, the second vertical wall 22, and a second planned flange portion 81. The second planned fange portion 81 has the second curved portion 51, the second contact portion 55, the other end 52b of the second gap frming portion 52, and a second fat sheet portion 82 extending to the one end side in the width direction Y fom the intermediate portion of the second gap frming portion 52. Further, a second recess 83 is frmed by the other end 52b of the second gap frming portion 52 and the second flat sheet portion 82. The second recess 83 is a portion where the first fange starting material 61 and the second fange starting material 62 are separated fom each other when the frst contact portion 45 of the frst flange starting material 61 and the second contact portion 55 of the second fange starting material 62 are butted against each other. [0053] After preparing the frst flange starting material 61 and the second fange starting material 62, the frst contact portion 45 of the frst fange starting material 61 and the second contact portion 55 of the second fange starting material 62 are positioned to oppose each other. At such time, the fat sheet portions 72 and 82 are arranged in parallel with each other, or are arranged non-parallel to each other so that a clearance therebetween expands toward the side of the corresponding edge parts 43 and 53. Then, by abutting the frst fange starting material 61 and the second fange 18 starting material 62 against each other at the recesses 73 and 83, the recesses 73 and 83 are deformed, as illustrated in Figure 3(B). Specifcally, a clamp of a spot welding gun 90 sandwiches the fange starting materials 61 and 62 so that the places in the recesses 73 and 83 which are the places to serve as the joint portion 32 contact each other. By this means, the portions of the fange starting materials 61 and 62 which serve as the joint portion 32 are abutted, and by joining the abutted portions by spot welding or the like, the joint portion 32 is frmed. At this time, at the contact portion 33 which is at a position that is separated fom the joint portion 32, the frst contact portion 45 and the second contact portion 55 are slidably pressed against each other by defrmation of the fat sheet portions 72 and 82. [0054] In this way, the flange starting materials 61 and 62 are formed so that a clearance (recesses 73 and 83) can be fred in the vicinity of the portions which serve as the joint portion 32 prior to spot welding, and joining is performed while forcibly causing the flange starting materials 61 and 62 to come in contact with each other while the fange starting materials 61 and 62 are being sandwiched by the spot welding gun 90. By this means, the frst contact portion 45 and the second contact portion 55 frmly come in contact at the contact portion 33 which is a place other than the joint portion 32. [0055] By the above process, the frst fange 13 is frmed and the second fange 23 is formed, and frthermore, the fanges 13 and 23 are joined to each other at the joint portion 32. Note that, either one of the recess 73 of the fange starting material 61 and the recess 83 of the fange starting material 62 need not be provided. In such a case, the planed fange portion of the fange starting material in which a recess is not provided is formed in a fat shape. [0056] As described above, according to the present embodiment, by the simple operation of perfrming joining while sandwiching the recesses 73 and 83 with the clamp of the spot welding gun 90, the joint portion 32 and the contact portion 33 which 19 is capable of attenuating vibration energy can be frmed. [0057] Note that, although a frm in which the contact portion 33 is provided at one end of the curved portions 41 and 51 is described as an example in the above embodiment, the frm in which the contact portion 33 is provided may be diferent fom the above example. Hereinafer, structures which are different fom the fregoing embodiment will be mainly described, and structures which are the like in the fregoing embodiment are denoted by the like refrence numerals in the drawings and a detailed description thereof may be omitted. [0058] Figure 4(A) is a view illustrating a first modifcation, and shows a cross section as viewed from the longitudinal direction X. Although the above embodiment is described by taking a confguration in which a curved portion (the second curved portion 51) is frmed in the second member 2 as an example, a diferent confguration may also be adopted. As illustrated in Figure 4(A), a second member 2A in which a curved portion is not provided may be provided instead of the second member 2. A second fange 23A of the second member 2A is frmed, fr example, in a fat shape. Further, in the afrementioned embodiment the second gap frming portion 52 of the second fange 23 is frmed in a U-shape as viewed fom the longitudinal direction X. On the other hand, in a joining structure 30A of the frst modifcation, a second gap frming portion 52 of the second fange 23A of the second member 2A is frmed in a flat shape that extends straight along the width direction Y [0059] Figure 4(B) is a view illustrating a second modifcation, and shows a cross section as viewed fom the longitudinal direction X. In the above frst modification, a curved portion is not provided in the second fange 23A. In contrast, in a joining structure 30B of the second modification, the second curved portion 51 and the second vertical wall 22 are provided in the second flange 23B. 20 [0060] Figre 5(A) is a view illustrating a third modifcation, and shows a cross section as viewed fom the longitudinal direction X. Although the second modifcation is described by taking a frm in which the frst curved portion 41 and the frst vertical wall 12 are provided in the frst member 1 as an example, a diferent frm may also be adopted. As illustrated in Figure 5(A), a frst member 1 C in which a curved portion and a vertical wall are not provided may be provided instead of the frst member 1. In this joining structure 30C, the frst main body 11 of the frst member 1 C is directly continuous with the frst contact portion 45. [0061] Figure 5(8) is a view illustrating a furth modifcation, and shows a cross section as viewed fom the longitudinal direction X. In the embodiment described above, the curved portions 41 and 51, the contact portion 33, the gap frming portion 31, and the joint portion 32 are arranged in that order fom the other end to the one end along the width direction Y However, a diferent confguration may also be adopted. In a joining structure 30D of the furth modifcation illustrated in Figure 5(8), the curved portions 41 and 51, the joint portion 32, the gap forming portion 31, and the contact portion 33 are arranged in that order fom the other end to the one end along the width direction Y In this furth modifcation, the contact portion 33 is arranged at the edge parts 43 and 53 of fanges 13D and 23D. The length of the contact portion 33 in the width direction Y is appropriately set according to the pressure for the target fictional resistance frce between the frst contact portion 45 and the second contact portion 55 and the like. Further, the joint portion 32 is aranged between the contact portion 33 and the curved portions 41 and 51. [0062] The above is a description of the schematic confgration of the furth modifcation. Next, an example of a method fr producing the furth modification will be described. 21 [0063] Figure 6(A) and Figure 6(8) are schematic cross-sectional diagrams fr describing a process fr joining the frst fange 13D to the second fange 23D. When joining the frst fange 13D to the second fange 23D, frst, a frst fange starting material 61D and a second fange starting material 62D illustrated in Figure 6(A) are prepared. [0064] The frst fange starting material 61 D is the starting material of the frst fange 13D, and the second flange starting material 62D is the starting material of the second fange 23D. The frst fange starting material 61D is frmed in the same shape as the frst member ID except that a portion of the frst fange 13D fom the intermediate portion of the frst gap frming portion 42 to the first curved portion 41 is frmed in a fat shape. That is, the frst fange starting material 61 D has the frst main body 11, the first vertical wall 12, and a first planned fange portion 71D. The frst planned fange portion 71D has the one end 42a of the frst gap frming portion 42, the frst contact portion 45 that is frmed at the one end 42a (first edge part 43), a frst fat sheet portion 72D extending fom the intermediate portion of the frst gap frming portion 42 to the other end side in the width direction Y, and the first curved portion 41. Further, a frst recess 73D is frmed by the one end 42a of the frst gap frming portion 42 and the frst flat sheet portion 72D. The first recess 73D is a portion where the frst fange starting material 61D and the second fange starting material 62D are separated fom each other when the frst flange starting material 61 D and the second fange starting material 62D are butted against each other. [0065] Similarly, the second fange starting material 62D is frmed in the same shape as the second member 2D except that a portion of the second flange 23D fom the intermediate portion of the second gap frming portion 52 to the second curved portion 51 is frmed in a fat shape. That is, the second fange starting material 62D has the second main body 21, the second vertical wall 22, and a second planed fange portion 8 ID. The second planned fange portion 8 ID has the one end 52a of the second gap 22 frming portion 52, the second contact portion 55 that is frmed at the one end 52a (second edge part 53), a second fat sheet portion 82D extending from the intermediate portion of the second gap forming portion 52 to the other end side in the width direction Y, and the second curved portion 51. Further, a second recess 83D is frmed by the one end 52a of the second gap frming portion 52 and the second fat sheet portion 82D. The second recess 83D is a porion where the frst flange starting material 61D and the second flange starting material 62D are separated fom each other when the frst fange starting material 61D and the second flange starting material 62D are butted against each other. [0066] After preparing the first fange starting material 61D and the second flange starting material 62D, the frst contact portion 45 of the frst flange starting material 61D and the second contact portion 55 of the second fange starting material 62D are caused to oppose each other. At such time, the flat sheet portions 72D and 82D are arranged in parallel with each other, or are arranged non-parallel to each other so that a clearance therebetween narrows toward the side of the corresponding edge parts 43 and 53, or are arranged in a state such that a curved portion is frmed in the vicinity of the edge parts 43 and 53. Then, by abutting the frst fange starting material 61D and the second fange starting material 62D against each other at the recesses 73D and 83D, the recesses 73D and 83D are deformed, as illustrated in Figure 6(B). Specifcally, the clamp of the spot welding gun 90 sandwiches the flange starting materials 61D and 62D so that the places to serve as the joint portion 32 contact each other. By this means, the portions of the flange starting materials 6 lD and 62D which become the joint portion 32 are abutted, and by subjecting the abutted portions to spot welding, the joint portion 32 is frmed. At this time, at the contact portion 33 which is at a position that is separated from the joint portion 32, the frst flange starting material 61D and the second flange starting material 62D are slidably pressed against each other. [0067] In this way, the fange starting materials 61D and 62D are formed so that a clearance ( clearance of recesses 73D and 83D) can be formed in the vicinity of the 23 portions which become the joint portion 32 prior to spot welding, and joining is perfrmed while forcibly causing the fange starting materials 61D and 62D to come in contact with each other while sandwiching the fange starting materials 61D and 62D using the spot welding gun 90. By this means, the first contact portion 45 and the second contact portion 55 firmly come in contact at a place other than the joint portion 32. [0068] Figure 7(A) is a view illustrating a fifth modifcation, and shows a cross section as viewed fom the longitudinal direction X. Although the foregoing furth modifcation was described by taking a confguration in which a curved portion (second curved portion 51) is frmed in the second member 2D as an example, a diferent confguration may also be adopted. As illustrated in Figure 7(A), a fat-shaped second member 2E in which a curved portion is not provided may be provided in a joining structure 30E instead of the second member 2D. [0069] Figure 7(B) is a view illustrating a sixth modifcation, and shows a cross section as viewed from the longitudinal direction X. In the afrementioned fifth modifcation, the second member 2E is a fat member in which a curved portion and a vertical wall are not formed. On the other hand, in a second member 2F of a joining structure 30F of the sixth modification, the second curved portion 51 and the second vertical wall 22 are provided. [0070] Figure 8 is a view illustrating a seventh modifcation, and shows a cross section as viewed from the longitudinal direction X. In the afrementioned sixth modifcation, the frst member 1D has the frst curved portion 41 and the frst vertical wall 12. In contrast, in a frst member 1G of a joining structure 3 OG of the seventh modification, a curved portion and a vertical wall are not provided. In the frst member lG, on the 24 other end side of the frst joint portion 44, an inclined portion that rises slightly to one side in the height direction Z as it advances toward the other end side along the width direction Y is frmed, and the first main body 11 is continuous with the other end of the inclined portion. [0071]