Abstract:
A double floor structure capable of being adapted to the conditions of construction and the needs of users at low cost. A double floor structure (K) provided with support legs ( 1 ) which are provided on a lower floor and rows of beams which form an upper floor. The support legs ( 1 ) are each provided with an upper member ( 14 ) which supports a beam from the lower side, an intermediate member ( 13 ) which supports the upper member ( 14 ) from the lower side, and a lower member ( 12 ) which supports the intermediate member ( 13 ) from the lower side. The upper member ( 14 ), the intermediate member ( 13 ), and the lower member ( 12 ) consist of metallic, extruded shape material and are disposed in such a manner that the direction of the extrusion is aligned with the top-bottom direction.

Description:
TECHNICAL FIELD 
     The present invention relates to a double floor structure and a support leg for a double floor structure, where the support leg is used for constructing a double floor. 
     BACKGROUND ART 
     Patent Literature 1 discloses a double floor structure in which beams (as constituent members for an upper floor) are arranged on support legs, which are extruded shapes of an aluminum alloy and placed on a lower floor. The support legs disclosed in Patent Literature 1 are formed by assembly of upper, intermediate, and lower members, which are extruded shapes of the aluminum alloy. In the case where a double floor structure is constructed by use of the above support legs, it is possible to comply with various requirements from customers and execution conditions at low cost. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent Laid-open No. 2009-150088 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     According to the Patent Literature 1, the extrusion direction of the upper member (which supports a beam in the double floor structure) is parallel to the extrusion direction of the beam. On the other hand, the extrusion directions of the intermediate and lower members are the vertical direction, which is perpendicular to the extrusion direction of the upper member. Therefore, the rigidity of the upper member depends on the cross-sectional profile of the extruded shape, so that it is necessary to design the cross-sectional profile of the extruded shape for each of various requirements from customers and execution conditions. 
     The object of the present invention is to provide a double floor structure and a support leg for a double floor which can comply with various needs of customers and execution conditions at low cost. 
     Solution to Problem 
     In order to solve the above problem, according to the present invention, a double floor structure is provided. The double floor structure according to the present invention is a double floor structure having a plurality of support legs to be placed on a lower floor and a plurality of beams which are arranged in a plurality of rows and constitute an upper floor. The double floor structure according to the present invention is characterized in that each of the support legs includes an upper member supporting the beams from a lower side, a lower member arranged below the upper member, and an intermediate member arranged between the upper member and the lower member, and each of the upper member, the intermediate member, and the lower member is formed of a metal extruded shape, and is to be positioned in such a manner that an extrusion direction coincides with the vertical direction. 
     According to the present invention, the rigidity of the upper members can be varied by changing the cut lengths in which the upper members are cut from a primary extruded shape. Therefore, it is possible to easily adjust the maximum load or the earthquake resistance of the double floor structure. Although it is preferable to form the extruded shapes of one or more aluminum alloys, alternatively, the extruded shapes may be formed of another material as long as extrusion is possible. 
     In addition, it is preferable to insert an upper portion of the intermediate member into the upper member, and insert a lower portion of the intermediate member into the lower member. In this case, positioning for fixing the upper member to the intermediate member becomes easy, and positioning for fixing the lower member to the intermediate member also becomes easy. 
     Although there is no limitation on the connection between the upper member and the beams, for example, the upper member and the beams can be connected by use of bolts and nuts. In this case, the upper member may be fixed to the beams by forming one or more latching grooves extending in the length directions of the beams on the lower surfaces of the beams in advance, and screw engaging the one or more shanks of one or more bolts inserted through the upper member with one or more nuts held in the one or more latching grooves or screw engaging the one or more shanks of one or more bolts having one or more heads held in the one or more latching grooves with one or more nuts arranged on the lower side of the upper member. The use of the one or more latching groove enables fixing of each support leg at an arbitrary position in the length direction of each beam, and further enables easy adjustment of the maximum load or earthquake resistance of the double floor structure. 
     The double floor structure according to the present invention may include one or more connection members which connect adjacent one of the beams. In this case, the support legs supporting one of the adjacent beams are connected to the other of the adjacent beams through the one or more connection members and the adjacent beams, so that the rigidity of the double floor structure can be increased. 
     It is preferable to use the one or more latching grooves formed on the lower surfaces of the beams for fixing the one or more connection members to the beams. That is, it is preferable to fix the one or more connection members to the beams by screw engaging the shanks of bolts inserted through the one or more connection members with nuts held in the one or more latching grooves or screw engaging the shanks of bolts having heads held in the one or more latching grooves with nuts arranged on the lower sides of the one or more connection members. In this case, the connection member can be fixed at an arbitrary position in the length direction of each beam. 
     In the case where the double floor structure is formed for placing one or more pieces of equipment, it is preferable to arrange multiple beams under each piece of equipment, and provide seat members realizing seats for each piece of equipment. In this case, it is preferable to form seat-attachment grooves extending in the length directions of the beams on the upper surfaced of the beams in advance, and fix the seat members on the beams by using at least two seat-attachment grooves. When the double floor structure is arranged as above, the seat members can be fixed at arbitrary positions in the length directions on the beams. 
     In the case where the seat members are arranged between the beams and the equipment, it is preferable to arrange in the seat members a bolt-holding portion for holding the head of an equipment-fixing bolt (which is used for fixing the equipment to the seats) in advance, and form, in the upper wall of the bolt-holding portion, a plurality of equipment-fixing holes or a set of longer and shorter elongated holes through which the shank of the equipment-fixing bolt can be inserted. In this case, it is possible to easily cope with even a situation in which the pitch of bolt-insertion holes formed in each piece of equipment is different. 
     In the case where the plurality of equipment-fixing holes are formed in the upper wall of the bolt-holding portion, it is preferable to set the positions of the equipment-fixing holes in such a manner that the arrangement of the equipment-fixing holes when the bolt-holding portion is turned around to the opposite direction in the horizontal plane is different from the arrangement of the equipment-fixing holes before the bolt-holding portion is turned around. In this case, the seat members can cope with a greater variety of equipment. 
     In addition to the seat members, it is preferable to provide supplementary members which transfer the weight of the equipment to the beams. In this case, it is preferable to arrange the supplementary members to straddle the seat members, so that the equipment can be stably supported. 
     It is possible to arrange covering panels in the areas on which no equipment is placed. In the case where conditioned air for cooling the equipment flows in the underfloor space (i.e., the space between the upper floor and the lower floor) in the double floor structure having the covering panels, dissipation loss of the conditioned air for can be prevented, so that the equipment can be efficiently cooled. It is preferable to detachably arrange the covering panels so as to cover the spaces between adjacent beams. In this case, installation of new equipment on the areas on which no equipment is placed yet is easy. 
     Further, in order to solve the aforementioned problem, according to the present invention, a support leg to be placed on a lower floor in the double floor structure is provided. The support leg according to the present invention is characterized in that the support leg includes an upper member which supports an upper floor structure constituting an upper floor, a lower member which is arranged below the upper floor, and an intermediate member arranged between the upper member and the lower member, and each of the upper member, the intermediate member, and the lower member is formed of a metal extruded shape, and is to be positioned in such a manner that an extrusion direction coincides with a vertical direction. 
     The height of the support leg according to the present invention can be varied by merely changing the cut lengths in which each of the upper member, the intermediate member, and the lower member is cut from a primary extruded shape. Therefore, it is possible to easily change the vertical dimension of the underfloor space, and comply with execution conditions and the customers&#39; needs. The constituent members of the upper floor which can be supported by the support leg according to the present invention include planar members such as floor panels as well as the beams. Although the extruded shapes are preferably formed of aluminum alloys, the extruded shapes may be formed of other metals as long as extrusion is possible. 
     Although there is no limitation on the cross-sectional profile of the intermediate member, it is preferable that the intermediate member have a cylindrical shape. When conditioned air for cooling the equipment flows in the underfloor space, the intermediate member having a cylindrical shape makes the flow of the conditioned air smooth, so that the equipment is efficiently cooled. In addition, the intermediate member having a cylindrical shape does not have any protrusion or the like on the peripheral surface (i.e., the peripheral surface of the intermediate member has a shape conformable to cables). Therefore, the underfloor cables are less likely to be damaged, and wiring operations can be performed smoothly. Further, since the profile of the intermediate member is directionally uniform, the manufacturing error can be easily absorbed. 
     Although there is no limitation on the manner of connecting the upper member, the intermediate member, and the lower member, it is preferable to join, by welding, the upper member and the intermediate member, and the intermediate member and the lower member. Although bolt connection needs drilling of parts, tightening of bolts, and other work, such work can be dispensed with by use of the welding. 
     It is preferable to form a female screw in the side wall of the intermediate member. In this case, optional parts (for example, cable trays, jigs, and the like for fixing wiring and piping) can be easily fixed. 
     Effect of Invention 
     The double floor structure and the support leg for the double floor structure according to the present invention make it possible to comply with execution conditions and the customers&#39; needs. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating a double floor including a double floor structure according to an embodiment of the present invention. 
         FIG. 2  is a front view of a support leg according to the embodiment of the present invention. 
         FIG. 3  is an exploded perspective view of the support leg according to the embodiment of the present invention. 
         FIG. 4A  is a perspective view illustrating a method for production of an upper member of members constituting the support leg. 
         FIG. 4B  is a perspective view illustrating a method for production of an intermediate member of the members constituting the support leg. 
         FIG. 4C  is a perspective view illustrating a method for production of a lower member of the members constituting the support leg. 
         FIG. 5  is a cross-sectional view of the support leg according to the embodiment of the present invention. 
         FIG. 6  is a partially-exploded perspective view of the double floor structure according to the embodiment of the present invention. 
         FIG. 7A  is a perspective view of a first seat member. 
         FIG. 7B  is a top view of the first seat member. 
         FIG. 8A  is a perspective view of a second seat member. 
         FIG. 8B  is a top view of the second seat member. 
         FIG. 9  is a perspective view, from the lower side, of the double floor structure according to the embodiment of the present invention. 
         FIG. 10  is a perspective view illustrating a variation of the double floor structure according to the embodiment of the present invention. 
         FIG. 11A  is a side view of the variation of the double floor structure. 
         FIG. 11B  is a top view of the variation of the double floor structure. 
         FIG. 12A  is a top view of a supplementary member. 
         FIG. 12B  is a top view illustrating a situation in which the supplementary member is turned around. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The double floor F illustrated in  FIG. 1  is constructed on the lower floor (floor slabs) S, for example, in a data center. The double floor F includes equipment-installation areas F 1  and passage areas F 2 . The pieces of equipment C are placed on the equipment-installation areas F 1 , and the passage areas F 2  are arranged adjacent to the equipment-installation areas F 1 . There is no limitation on the type and size of the pieces of equipment C and the standards with which the pieces of equipment C are required to comply. The pieces of equipment C include not only apparatuses and instruments, and also containers and racks for the apparatuses and instruments. 
     The equipment-installation areas F 1  are formed with double floor structures K according to the present embodiment. The passage areas F 2  are formed with multiple floor panels P 1 , P 2 , . . . arranged between adjacent ones of the double floor structures K. One or more covering panels P are arranged over the areas on which no equipment is placed (uninstalled areas) even in the equipment-installation areas F 1 . Conditioned air flows in the underfloor space, and blows upward to cool the pieces of equipment C. 
     Each double floor structure K includes a plurality of support legs  1 , beams  2  in two rows, first seat members  3 , second seat members  4 , and connection members  5 . The support legs  1  are arranged on the lower floor S. The beams  2  in two rows constitute an upper floor. The first seat members  3  and the second seat members  4  realize one or more seats for the pieces of equipment C. The connection members  5  indirectly connect the beams  2  in two rows. In the following explanations, the expressions “front” and “front and rear” are used with respect to the length direction of each of the beams  2 . For example, the front-rear direction is the length direction of each of the beams  2 . 
     First, the structure of each of the support legs  1  is explained in detail. 
     Each of the support legs  1  includes a pair of legs  11 , a lower member  12 , an intermediate member  13 , an upper member  14 , and protection covers  15 , as illustrated in  FIG. 3 . The pair of legs  11  are arranged to stand on the lower floor S. The lower member  12  is arranged between the pair of legs  11 . The intermediate member  13  is supported by the lower member  12 . The upper member  14  is supported by the intermediate member  13 . The protection covers  15  are attached to the lower member  12  (as illustrated in  FIG. 3 ). 
     As illustrated in  FIG. 2 , each of the legs  11  includes a base plate  11   a , a column portion  11   b , a lower nut  11   c , and an upper nut  11   d . The base plate  11   a  is fixed onto the lower floor S. The column portion  11   b  is arranged to stand on the base plate  11   a . The lower nut  11   c  and the upper nut  11   d  are screw engaged with male screws on the column portion  11   b  in such a manner that the lower nut  11   c  and the upper nut  11   d  sandwich the lower member  12 . The base plate  11   a  is fixed to the upper surface of the lower floor S with anchor bolts S 1 , which are buried in the lower floor S from the upper side of the lower floor S. 
     The lower member  12  is a member for supporting the intermediate member  13  from the lower side, and is arranged below the upper member  14 . The lower member  12  is supported by the legs  11  in such a manner that the lower member  12  is raised above the lower floor S. As illustrated in  FIG. 3 , the lower member  12  is realized by an extruded shape of an aluminum alloy having a hollow cross section, and is positioned in such a manner that the extrusion direction coincides with the vertical direction. In other words, the lower member  12  is arranged so that hollows formed in a primary extruded shape from which the lower member  12  is cut continuously extend in the vertical direction in the lower member  12  and produces openings on the upper and lower sides of the lower member  12 . As illustrated in  FIG. 4C , the lower member  12  can be produced by cutting the primary extruded shape  12 ′ having the same cross section as the lower member  12  along a plane perpendicular to the extrusion direction (i.e., the horizontal plane in  FIG. 4C ). 
     As illustrated in  FIG. 3 , the lower member  12  in the present embodiment includes a frame portion  12   a , leg-connection portions  12   b , and ribs  12   c . The intermediate member  13  is connected to the frame portion  12   a . The leg-connection portions  12   b  are respectively connected to the legs  11 . The leg-connection portions  12   b  are respectively connected to the frame portion  12   a  through the ribs  12   c , respectively. 
     The frame portion  12   a  has a shape corresponding to the intermediate member  13 . Since the intermediate member  13  has a cylindrical shape in the present embodiment, the frame portion  12   a  also has a cylindrical shape corresponding to the intermediate member  13 . The bottom portion of the intermediate member  13  is inserted into the hollow of the frame portion  12   a . The inner diameter of the frame portion  12   a  is slightly greater than the outer diameter of the intermediate member  13 . 
     The leg-connection portions  12   b  are arranged on both sides of the frame portion  12   a . Although there is no limitation on the shapes of the leg-connection portions  12   b , the leg-connection portions  12   b  in the present embodiment each have a tubular shape. The column portions  11   b  of the pair of legs  11  are respectively inserted through the hollows in the leg-connection portions  12   b . The hollows (holes) in the leg-connection portions  12   b  may be formed when the primary extruded shape  12 ′ (from which the lower member  12  is cut as illustrated in  FIG. 4C ) is produced by extrusion, or may be formed by drilling after extrusion. The leg-connection portions  12   b  need not have a closed cross section, and may have an open cross section (e.g., a C-shaped cross section) as long as the column portions  11   b  can be inserted through the leg-connection portions  12   b.    
     The ribs  12   c  are laterally projected from the frame portion  12   a . In each of the ribs  12   c  in the present embodiment, a hollow continuously extending in the vertical direction is formed. 
     The lower member  12  is fixed to the pair of legs  11  as follows. First, the lower nut  11   c  is screw engaged with the column portion  11   b  in each of the pair of legs  11 . Then, the column portions  11   b  are inserted through the leg-connection portions  12   b  of the lower member  12  so that the leg-connection portions  12   b  are placed on the lower nuts  11   c . Thereafter, the upper nuts  11   d  are screwed onto the column portions  11   b  (as illustrated in  FIG. 2 ) and tightened. Since the elevation of the lower member  12  can be finely adjusted by controlling the positions of the lower nuts  11   c  and the upper nuts  11   d , it is possible to easily cope with unevenness, inclination, or the like of the finished surface of the lower floor S. 
     As illustrated in  FIG. 2 , the intermediate member  13  is a member for supporting the upper member  14  from the lower side, and is arranged between the lower member  12  and the upper member  14 . As illustrated in  FIG. 3 , the intermediate member  13  is formed of an extruded shape of an aluminum alloy having a hollow cross section, and is positioned in such a manner that the extrusion direction coincides with the vertical direction. In other words, the intermediate member  13  is arranged so that hollows formed in a primary extruded shape from which the intermediate member  13  is cut produces openings on the upper and lower sides of the intermediate member  13 . As illustrated in  FIG. 4B , the intermediate member  13  can be produced by cutting the primary extruded shape  13 ′ having the same cross section as the intermediate member  13  along a plane perpendicular to the extrusion direction (i.e., the horizontal plane in  FIG. 4B ). 
     The intermediate member  13  has a cylindrical shape. As illustrated in  FIG. 13 , female screws  13   a  are formed on the side wall of the intermediate member  13 . Although not shown, male-screwed parts for fixing optional parts (for example, cable trays, jigs, and the like for fixing wiring and piping) are screw engaged with the female screws. 
     The intermediate member  13  and the lower member  12  can be joined by welding after the bottom portion of the intermediate member  13  is inserted into the frame portion  12   a  in the lower member  12  as illustrated in  FIG. 5 . In the present embodiment, the bottom face of the intermediate member  13  is maintained above the bottom face of the frame portion  12   a , and the bottom face of the intermediate member  13  is welded to the inner surface of the frame portion  12   a  in the entire circle (as indicated by the reference W 1 ). In addition, the top face of the frame portion  12   a  is welded to the outer surface of the intermediate member  13  in the entire circle (as indicated by the reference W 2 ). Although the lower member  12  and the intermediate member  13  are joined by welding at the upper and lower positions (indicated by the references W 1  and W 2 ) in the illustrated example, alternatively, the lower member  12  and the intermediate member  13  may be joined by welding at only one of the upper and lower positions. Further, although the entire circle is welded in the illustrated example, the weld may be performed intermittently. 
     As illustrated in  FIG. 2 , the upper member  14  is a member for supporting one of the beams  2  from the lower side, and is arranged between the intermediate member  13  and the beam  2 . As illustrated in  FIG. 3 , the upper member  14  is formed of an extruded shape of an aluminum alloy having a hollow cross section, and is positioned in such a manner that the extrusion direction coincides with the vertical direction. In other words, the upper member  14  is arranged so that hollows formed in a primary extruded shape from which the upper member  14  is cut produces openings on the upper and lower sides of the upper member  14 . As illustrated in  FIG. 4A , the upper member  14  can be produced by cutting the primary extruded shape  14 ′ having the same cross section as the upper member  14  along a plane perpendicular to the extrusion direction (i.e., the horizontal plane in  FIG. 4A ). 
     As illustrated in  FIG. 3 , the upper member  14  in the present embodiment includes a frame portion  14   a , projecting portions  14   b , and insert-receiving portions  14   c . The intermediate member  13  is connected to the frame portion  14   a . The projecting portions  14   b  radially project from the frame portion  14   a . The insert-receiving portions  14   c  are respectively arranged around the frame portion  14   a.    
     The frame portion  14   a  has a shape corresponding to the intermediate member  13 . The frame portion  14   a  also has a cylindrical shape corresponding to the intermediate member  14 . The top portion of the intermediate member  13  is inserted into the hollow of the frame portion  14   a . The inner diameter of the frame portion  14   a  is slightly greater than the outer diameter of the intermediate member  13 . 
     The projecting portions  14   b  are formed on the periphery of the frame portion  14   a , Hollows continuously extending in the vertical direction are formed in the projecting portions  14   b.    
     The insert-receiving portions  14   c  are portions for guiding the shanks of beam-fixing bolts B 1  (as illustrated in  FIG. 2 ), and respectively have hollows continuously extending in the vertical direction. In the present embodiment, four insert-receiving portions  14   c  are arranged on each of the left and right sides of the frame portion  14   a . Part of the insert-receiving portions  14   c  arranged on the right side are aligned along a straight line, and part of the insert-receiving portions  14   c  arranged on the left side are also aligned along a straight line. Each of the insert-receiving portions  14   c  in the present embodiment has a C-shaped cross section, and a slit continuously extending in the vertical direction is formed in the side surface of each of the insert-receiving portions  14   c . The insert-receiving portions  14   c  is designed to have an open cross section in order to facilitate manufacture of the primary extruded shape  14 ′ (from which the upper member  14  is cut as illustrated in  FIG. 4A ). However, the insert-receiving portions  14   c  need not have an open cross section, and may have a closed cross section as long as the shanks of the bolts can be inserted through the insert-receiving portions  14   c . The insert-receiving portions  14   c  may be formed when the primary extruded shape  14 ′ (from which the upper member  14  is cut as illustrated in  FIG. 4A ) is produced by extrusion, or may be formed by drilling after extrusion. 
     The upper member  14  and the lower member  12  can be joined by welding after the top portion of the intermediate member  13  is inserted into the frame portion  14   a  in the upper member  14  as illustrated in  FIG. 5 . In the present embodiment, the top face of the intermediate member  13  is maintained below the top face of the frame portion  14   a , and the top face of the intermediate member  13  is welded to the inner surface of the frame portion  14   a  in the entire circle (as indicated by the reference W 3 ). In addition, the bottom face of the frame portion  14   a  is welded to the outer surface of the intermediate member  13  in the entire circle (as indicated by the reference W 4 ). Although the upper member  14  and the intermediate member  13  are joined by welding at the upper and lower positions (indicated by the references W 3  and W 4 ) in the illustrated example, alternatively, the upper member  14  and the intermediate member  13  may be joined by welding at only one of the upper and lower positions. Further, although the entire circle is welded in the illustrated example, the weld may be performed intermittently. 
     The protection covers  15  illustrated in  FIG. 3  covers at least a portion of the edges of the lower member  12 , and is formed of synthetic resin. Each of the protection covers  15  in the present embodiment includes an insertion portion  15   a , a cover portion  15   b , and edge-cover portions  15   c . The insertion portion  15   a  is inserted into the hollow in each of the ribs  12   c . The cover portion  15   b  covers the upper surface of each of the ribs  12   c . The edge-cover portions  15   c  cover the edges of each of the ribs  12   c . The edge-cover portions  15   c  are formed to have a round-shaped upper surface. Since the lower member  12  is formed by cutting from a primary extruded shape, the ribs  12   c  are likely to have sharp edges. However, the edge-cover portions  15   c  covering the edges can prevent contact of the wiring (not shown) with the edges. Therefore, it is possible to prevent damaging to wiring by the edges. Further, in the case where the edges of the lower member  12  are chamfered, or in the case where a countermeasure against the damaging to the wiring is taken, the protection cover  15  may be dispensed with, although the cost of the provision of the protection cover  15  is lower than the cost of the chamfering of the edges of the lower member  12 . 
     Next, the structure of the beams  2  is explained in detail. 
     As illustrated in  FIG. 1 , the beams  2  are a kind of constituent members of the upper floor. In the present embodiment, the beams  2  constitute a part of the floor face in the equipment-installation areas F 1 , and support the covering panels P 1  (arranged over the uninstalled areas) and floor panels P 2  (constituting the floor face in the passage areas F 2 ). 
     Each of the beams  2  is arranged over ones (three in the present embodiment) of the support legs  1 , which are arranged at intervals. The beams  2  in the present embodiment are formed of an extruded shape of an aluminum alloy having a hollow cross section. 
     As illustrated in  FIG. 6 , in each of the beams  2 , multiple rows (two rows in the present embodiment) of latching grooves  2   a  extending in the length direction (in the extrusion direction) of the beam  2  are arranged on the lower surface of the beam  2 , and multiple rows (three rows in the present embodiment) of seat-attachment grooves  2   b  extending in the length direction (in the extrusion direction) of the beam  2  are arranged on the upper surface of the beam  2 . 
     The heads of the beam-fixing bolts B 1  are held in the latching grooves  2   a . The opening widths of the latching grooves  2   a  are arranged to be smaller than the widths across flats (i.e., the minimum widths) of the beam-fixing bolts B 1  so that the heads of the beam-fixing bolts B 1  held in the latching grooves  2   a  do not fall off the latching grooves  2   a . The one of the latching grooves  2   a  on the right side is formed at the position corresponding to the four insert-receiving portions  14   c  aligned on the right side, and the one of the latching grooves  2   a  on the left side is formed at the position corresponding to the four insert-receiving portions  14   c  aligned on the left side. 
     Female-screw members N 2  for fixing the seats are held in the seat-attachment grooves  2   b . The opening widths of the seat-attachment grooves  2   b  are arranged to be smaller than the widths of the female-screw members N 2  so that the female-screw members N 2  held in the seat-attachment grooves  2   b  do not fall off the seat-attachment grooves  2   b.    
     Each of the beams  2  can be fixed to the support legs  1  by placing the beam  2  on the upper members  14  of the support legs  1 , and joining the upper member  14  to the beam  2  by using the beam-fixing bolts B 1  and beam-fixing nuts N 1 . Specifically, the beam  2  can be fixed to the support legs  1  by inserting the heads of the beam-fixing bolts B 1  into the latching grooves  2   a  from an end of the beam  2 , inserting the shanks of the beam-fixing bolts B 1  into the insert-receiving portions  14   c  from the upper side, screwing the beam-fixing nuts N 1  onto portions of the shanks of the beam-fixing bolts B 1  which protrude from the lower ends of the insert-receiving portions  14   c , and tightening the beam-fixing nuts N 1  (as illustrated in  FIG. 2 ). It is possible to appropriately select ones of the insert-receiving portions  14   c  for use, for example, according to the strengths of the beam-fixing bolts B 1  and the position at which each of the support legs  1  is placed. For example, it is preferable to use all the four insert-receiving portions  14   c  on each of the left and right sides of each upper member  14  located at the ends of the beam  2 , and use two of the four insert-receiving portions  14   c  on each of the left and right sides of each upper member  14  located at the center of the beam  2 . Although not shown, alternatively, each of the beams  2  can be fixed to the support legs  1  by inserting the shanks of the beam-fixing bolts B 1  into the insert-receiving portions  14   c  from the lower side of the upper members  14 , and screw engaging the beam-fixing bolts B 1  with the beam-fixing nuts N 1  held in the latching grooves  2   a.    
     Next, the structures of the first seat members  3  and the second seat members  4  illustrated in  FIG. 1  are explained. The first seat members  3  and the second seat members  4  are members realizing the seats for the pieces of equipment C. The first seat members  3  are arranged on a first one of the beams  2 , and the second seat members  4  are arranged on a second one of the beams  2 . 
     As illustrated in  FIG. 7A , the first seat members  3  are arranged to straddle the two seat-attachment grooves  2   b  which are adjacent to each other in the lateral direction, and the first seat members  3  are fixed to the upper surface of the first one of the beams  2  by using the two seat-attachment grooves  2   b . Each of the first seat members  3  is constituted by a bolt holder  31  and flanges  32 . The bolt holder  31  holds the head of an equipment-fixing bolt B 3 . The flanges  32  are formed on the front and rear sides of the bolt holder  31 . A plurality of equipment-attachment holes  3   a  being arrayed in the direction perpendicular to the seat-attachment grooves  2   b  are arranged in the upper wall of the bolt holder  31 . The shank of the equipment-fixing bolt B 3  can be inserted through the equipment-attachment holes  3   a . In addition, a pair of through holes  3   b  spaced by the distance between the two adjacent seat-attachment grooves  2   b  are formed in each of the flanges  32 . The shanks of seat-fixing bolts B 2  are inserted into the through holes  3   b . The first seat members  3  in the present embodiment are formed of a steel plate which is press molded to a convex shape. (The steel may include stainless steel.) Alternatively, the first seat members  3  may be formed of an extruded shape of an aluminum alloy. 
     As illustrated in  FIG. 7B , the equipment-attachment holes  3   a  in each first seat members  3  are formed in an arrangement asymmetric in the lateral (left-right) direction. The positions of the equipment-fixing holes  3   a  are set in such a manner that the arrangement of the equipment-fixing holes  3   a  after the first seat members  3  is turned 180 degrees around in the horizontal plane is different from the arrangement of the equipment-fixing holes  3   a  before the first seat members  3  is turned 180 degrees around in the horizontal plane. In the present embodiment, the center of one of the equipment-fixing holes  3   a  at an end of the array of the equipment-fixing holes  3   a  is located on a reference line P 1 , and the center of one of the equipment-fixing holes  3   a  at the other end of the array of the equipment-fixing holes  3   a  is located offset from a reference line P 2  (toward the reference line P 1 ). The offset amount d a  from the reference line P 2  is equal to half of the distance between the centers of the adjacent ones of the equipment-fixing holes  3   a . When each of the first seat members  3  having the above arrangement of the equipment-fixing holes  3   a  is turned 180 degrees around in the horizontal plane, the positions of the equipment-fixing holes  3   a  are shifted by the offset amount d a  from the positions of the equipment-fixing holes  3   a  before the 180-degree turn around. Therefore, even in the case where the positions of bolt-insertion holes formed in a piece of equipment C do not fit the positions of the equipment-fixing holes  3   a , it is possible to easily cope with such a case by turning around the first seat members  3  to the opposite direction. The reference line P 1  is a straight line passing through the centers of the through holes  3   b  which are arranged along one of the two seat-attachment grooves  2   b , and the reference line P 2  is a straight line passing through the centers of the through holes  3   b  which are arranged along the other of the two seat-attachment grooves  2   b . In  FIG. 7B , the seat-fixing bolts B 2  are not illustrated. 
     The first seat members  3  can be fixed to the beam  2  by selecting two of the three seat-attachment grooves  2   b , placing the first seat members  3  on the beam  2 , inserting the shanks of the seat-fixing bolts B 2  through the through holes  3   b  from the upper side of the first seat members  3 , and screw engaging the shanks of the seat-fixing bolts B 2  with the female-screw members N 2  held in the seat-attachment grooves  2   b . Alternatively, although not shown, it is possible to hold the heads of the seat-fixing bolts B 2  in the seat-attachment grooves  2   b , and screw engage the shanks of the seat-fixing bolts B 2  protruding from the seat-attachment grooves  2   b , with nuts arranged on the upper side of the flanges  32 . The positions at which the first seat members  3  are attached can be moved in the front-rear direction by moving the positions at which the seat-fixing bolts B 2  are screw engaged with the female-screw members N 2 , along the direction in which the seat-attachment grooves  2   b  extend. Further, the position at which each of the first seat members  3  is attached can be moved in the lateral direction by changing the seat-attachment groove to which the first seat member  3  is attached. 
     As illustrated in  FIG. 2 , each piece of equipment C can be fixed to ones of the first seat members  3  by placing the piece of equipment C on the upper surface of the first seat members  3  and joining the piece of equipment C to the first seat members  3  by use of the equipment-fixing bolt B 3  and equipment-fixing nuts N 3 . 
     As illustrated in  FIG. 8A , the second seat members  4  are arranged to straddle the two seat-attachment grooves  2   b  which are adjacent to each other in the lateral direction of the second one of the beams  2 , and fixed to the upper surface of the beam  2  by use of the seat-attachment grooves  2   b . Each of the second seat members  4  is constituted by a bolt holder  41  and flanges  42 . The bolt holder  41  holds the head of an equipment-fixing bolt B 3 . The flanges  42  are formed on the front and rear sides of the bolt holder  41 . A shorter elongated hole  4   a  and a longer elongated hole  4   b , which are elongated in the direction perpendicular to the seat-attachment grooves  2   b , are arranged in the upper wall of the bolt holder  41 . The shank of the equipment-fixing bolt B 3  can be inserted through the elongated hole  4   a  or  4   b . In addition, a pair of through holes  4   b  spaced by the distance between the two adjacent seat-attachment grooves  2   b  are formed in each of the flanges  42 . The shanks of the seat-fixing bolts B 2  are inserted into the through holes  4   b . The second seat members  4  in the present embodiment are formed of a steel plate which is press molded to a convex shape. (The steel may include stainless steel.) Alternatively, the second seat members  4  may be formed of an extruded shape of an aluminum alloy. 
     As illustrated in  FIG. 8B , the (shorter) elongated hole  4   a  is elongated toward another reference line P 4  from a position at which the elongated hole  4   a  intersects with a reference line P 3 . The (longer) elongated hole  4   b  is elongated toward the reference line P 4  from a position at which the elongated hole  4   b  intersects with a center line P 5  extending in the center of the width of the second seat members  4 . The end of the elongated hole  4   a  on the reference line P 3  side is shaped into a semicircular shape. The central position of the semicircular portion of the shorter elongated hole  4   a  is located on the reference line P 3 . The end of the elongated hole  4   b  on the reference line P 4  side is shaped into a semicircular shape. The central position of the semicircular portion of the shorter elongated hole  4   b  is located offset from the reference line P 4  toward the reference line P 3 . The offset amount d b  from the reference line P 4  is equal to the radius of the semicircular portion of the elongated hole  4   b . That is, the elongated hole  4   b  is formed not to intersect with the reference line P 4 . When the second seat members  4  having the above arrangement of the elongated holes  4   a  and  4   b  is turned 180 degrees around in the horizontal plane, the positional relationship between the shorter elongated holes  4   a  and  4   b  is inverted as illustrated on the right side in  FIG. 8B , and the position of the end of the shorter elongated hole  4   a  after the 180-degree turn around is offset by the offset amount d b  from the position of the end of the elongated hole  4   b  before the 180-degree turn around. Therefore, it is possible to adjust the position at which insertion of the equipment-fixing bolt B 3  is allowed. Thus, even in the case where the positions of bolt-insertion holes formed in a piece of equipment C do not fit the positions of the elongated holes  4   a  and  4   b , it is possible to easily cope with such a case by turning around the second seat members  4  to the opposite direction. The reference line P 3  is a straight line passing through the centers of the through holes  4   c  which are arranged along one of the two seat-attachment grooves  2   b , and the reference line P 2  is a straight line passing through the centers of the through holes  4   c  which are arranged along the other of the two seat-attachment grooves  2   b . In  FIG. 8B , the seat-fixing bolts B 2  are not illustrated. 
     The second seat members  4  can be fixed to the beam  2  by selecting two of the three seat-attachment grooves  2   b , placing the second seat members  4  on the beam  2 , inserting the shanks of the seat-fixing bolts B 2  through the through holes  4   c  from the upper side of the second seat members  4 , and screw engaging the shanks of the seat-fixing bolts B 2  with the female-screw members N 2  held in the seat-attachment grooves  2   b . Alternatively, although not shown, it is possible to hold the heads of the seat-fixing bolts B 2  in the seat-fixing grooves  2   b , and screw engage the shanks of the seat-fixing bolts B 2  protruding from the seat-fixing grooves  2   b , with nuts arranged on the upper side of the flanges  42 . The positions at which the second seat members  4  are attached can be moved in the front-rear direction by moving the positions at which the seat-fixing bolts B 2  are screw engaged with the female-screw members N 2 , along the direction in which the seat-attachment grooves  2   b  extend. Further, the position at which each of the second seat members  4  is attached can be moved in the lateral direction by changing the seat-attachment groove to which the second seat member  4  is attached. 
     Female screws in the number corresponding to the number of the seat-fixing bolts B 2  inserted through the seat-attachment grooves  2   b  (two in the present embodiment) are formed in each of the female-screw members N 2 . In this case, the first and second seat members  3  and  4  can be attached to the beams  2  simply and quickly. 
     The pieces of equipment C (illustrated in  FIG. 1 ) can also be fixed to ones of the second seat members  4  in a similar manner to the first seat members  3 . 
     Next, the structures of the connection members  5  are explained in detail.  FIG. 9  is a perspective view, from the lower side, of the double floor structure K according to the present embodiment. 
     As illustrated in  FIG. 9 , the connection members  5  are arranged in the direction perpendicular to the length direction of the beams  2 , and fixed to the lower surfaces of the beams  2  on the left and right sides. Each of the connection members  5  includes an abutting portion  51  and side walls  52  and  53 . The abutting portion  51  abuts the lower surfaces of the beams  2 . The side walls  52  and  53  extend downward from both side edges of the abutting portion  51 . As illustrated in  FIG. 6 , a pair of through holes  5   a  spaced by the distance between the adjacent latching grooves  2   a  in each beam  2  are formed at each end portion of the connection member  5 . The shanks of connection bolts B 4  are inserted through the through holes  5   a.    
     The connection members  5  can be joined to the beams  2  by use of the connection bolts B 4  and connection nuts N 4 . Specifically, the connection members  5  are joined to the lower surfaces of the beams  2  by inserting the heads of the connection bolts B 4  into the latching grooves  2   a  from ends of the beams  2 , inserting the shanks of the connection bolts B 4  through the through holes  5   a , screwing the shanks of the connection bolts B 4  into the connection nuts N 4  arranged on the lower side of the connection members  5 , and tightening the screws. Although not shown, alternatively, the connection members  5  can be joined to the beams  2  by inserting the shanks of the connection bolts B 4  through the through holes  5   a  from the lower side of the connection members  5 , and screw engaging the shanks of the connection bolts B 4  with the connection nuts N 4  held in the latching grooves  2   a.    
     Although the pieces of equipment C are installed on the double floor structures K, the covering panels P 1  are arranged over the areas on which the pieces of equipment C are not installed, as illustrated in  FIG. 1 . The covering panels P 1  are detachably arranged to cover the spaces between adjacent beams  2 , and are removed when a piece of equipment C is additionally installed. As illustrated in  FIG. 2 , the covering panels P 1  in the present embodiment are placed on projecting supports  21 , which are formed on the side surfaces of the beams  2 . Engagement members  22  which can engage with the covering panels P 1  from the lower side are attached to the projecting supports  21 . The engagement members  22  can prevent movement of the covering panels P 1  in the front-rear direction (in the direction perpendicular to paper plane in  FIG. 2 ). 
     The arrangement of the covering panels P 1  can prevent dissipation of the conditioned air, which flows in the underfloor space for cooling the pieces of equipment C. Therefore, the arrangement of the covering panels P 1  enables efficient cooling of the pieces of equipment C. Although the detachable arrangement of the covering panels P 1  is realized in the present embodiment by placement of the covering panels P 1  on the projecting supports  21  formed on the side surfaces of the beams  2 , alternatively, the covering panels P 1  may be fixed to the beams  2  by using a detachable fixing means (bolts, screws, and the like) or an detachable engagement mechanism. 
     Although the floor panels P 2  are arranged to cover the passage areas F 2  as illustrated in  FIG. 1 , the floor panels P 2  include two types, a perforated type (having a number of through holes) and an unperforated type (having no holes). It is possible to appropriately select the perforated type or the unperforated type according to the heat generation rates of the pieces of equipment C, the air flows in the room, and other conditions. 
     According to the double floor structure K having the above structure, the rigidity of the upper members  14  can be varied by changing the cut length in the primary extruded shape  14 ′ (from which the upper members  14  are cut). Therefore, the maximum load or the earthquake resistance of the double floor structure K can be easily controlled. That is, the maximum load or the earthquake resistance of the double floor structure K can be adjusted without changing the cross-sectional profile of the primary extruded shape  14 ′ (from which the upper members  14  are cut). In addition, the elevation of the underfloor space can be easily changed by simply changing the cut length in at least one of the primary extruded shape  12 ′ (from which the lower member  12  are cut), the primary extruded shape  13 ′ (from which the intermediate member  13  are cut), and the primary extruded shape  14 ′ (from which the upper members  14  are cut). Further, the double floor structure K can cope with the execution conditions and customers&#39; needs at low cost. Alternatively, the strengths of the support legs  1  (and therefore the max load and the earthquake resistance of the double floor structure K) can be adjusted by changing the cross-sectional profiles and/or thicknesses of the extruded shapes  12 ′,  13 ′, and  14 ′. 
     According to the support legs  1  in the present embodiment, the bottom portion of the intermediate member  13  is inserted into the lower member  12 , and the top portion of the intermediate member  13  is inserted into the upper member  14 . Therefore, the intermediate member  13  can be easily positioned when the intermediate member  13  is fixed to the lower member  12  or to the upper member  14 . 
     In the support legs  1 , the lower member  12  and the intermediate member  13  are joined by welding, instead of bolt connection, and the intermediate member  13  and the lower member  12  are also joined by welding, instead of bolt connection. Therefore, it is possible to simplify the operations for assembling the support legs  1  (since drilling, screwing of bolts, and the like are unnecessary). 
     The support legs  1  are formed by using the hollow members. Therefore, the flow of the conditioned air in the underfloor space for cooling the pieces of equipment C becomes smooth, so that the pieces of equipment C can be efficiently cooled. 
     In the double floor structure K according to the present embodiment, the support legs  1  are fixed to the beams  2  by using the latching grooves  2   a  formed in the beams  2 . The use of the latching grooves  2   a  enables fixing of the support legs  1  at arbitrary positions in the length direction of the beams  2 , easy increase or decrease in the intervals at which the support legs  1  are arranged, and easy adjustment of the maximum load and the earthquake resistance of the double floor structure K. 
     In the double floor structure K, the support legs  1  supporting one of two adjacent beams  2  and the support legs  1  supporting the other of the two adjacent beams  2  are connected through the two adjacent beams  2  and the connection members  5 . Therefore, it is possible to achieve high rigidity of the double floor structure K. 
     In the double floor structure K, the connection members  5  are fixed to the beams  2  by using the latching grooves  2   a . Therefore, the positions at which the connection members  5  are fixed can be arbitrarily changed along the length direction of the beams  2 , and the number of the connection members  5  can be easily increased. 
     Although the pieces of equipment C are placed on the first and second seat members  3  and  4  in the present embodiment, it is possible to arrange supplementary members  6  and  7  between the pieces of equipment C and the beams  2  as illustrated in  FIG. 10 . In the case where the supplementary members  6  and  7  are arranged and the pieces of equipment C are placed on the supplementary members  6  and  7 , it is possible to support the pieces of equipment C more stably. Since the supplementary members  6  are arranged plane symmetric (mirror symmetric) to the supplementary members  7 , the following explanations are focused on the supplementary members  6 . 
     The supplementary members  6  transfer the weights of the pieces of equipment C to the beams  2  (as illustrated in  FIG. 10 ). The supplementary members  6  are arranged to straddle the first seat members  3  (or the second seat members  4 ). The supplementary members  6  in the present embodiment are formed of an extruded shape of an aluminum alloy. As illustrated in  FIG. 11B , each of the supplementary members  6  includes a pair of supports  61  and a table portion  62 . The supports  61  are respectively arranged on the front and rear sides. 
     The supports  61  are arranged on the front and rear sides of the first seat members  3  so as to project from the lower surface of the table portion  62 . The supports  61  is arranged to have the same height as the first seat members  3 . 
     The upper surface of the table portion  62  abuts the lower surface of one of the pieces of equipment C (illustrated in  FIG. 10 ), and the lower surface of the table portion  62  abuts the upper surface of the bolt holder  31  in the first seat members  3 . As illustrated in  FIG. 11A , the table portion  62  has a planar shape. A plurality of elongated adjustment holes  6   a  being arrayed in the lateral direction of the beams  2  are formed in the table portion  62 . The shank of the equipment-fixing bolt B 3  can be inserted through the elongated adjustment holes  6   a . It is possible to appropriately select one of the elongated adjustment holes  6   a  through which the equipment-fixing bolt B 3  is to be inserted, according to the depth of the piece of equipment C (or the dimension of the beams  2  in the lateral direction). Since the elongated adjustment holes  6   a  are elongated in the direction along the length direction of the beams  2 , it is possible to adjust the position of the insertion of the equipment-fixing bolt B 3  according to the width of the piece of equipment C (or the dimension of the beams  2  in the length direction). 
     As illustrated in  FIGS. 12(   a ) and  12 ( b ), the plurality of elongated adjustment holes  6   a  are asymmetrically arranged in the lateral (left-right) direction. That is, the positions of the elongated adjustment holes  6   a  are set in such a manner that the arrangement of the elongated adjustment holes  6   a  after the supplementary members  6  (illustrated in  FIG. 12B)  is turned 180 degrees around in the horizontal plane is different from the arrangement of the elongated adjustment holes  6   a  before the supplementary members  6  (illustrated in  FIG. 12A ) is turned 180 degrees around in the horizontal plane. In the present embodiment, the supplementary members  6  are arranged so that the distance d 1  between a side edge of each of the supplementary members  6  and the center line of one of the elongated adjustment holes  6   a  located at an end the array of the elongated adjustment holes  6   a  is greater than the distance d 2  between the opposite side edge of the supplementary member  6  and the center line of one of the elongated adjustment holes  6   a  located at the other end the array of the elongated adjustment holes  6   a . The difference (d 1 -d 2 ) between the distance d 1  and the distance d 2  is equal to half of the distance d 3  between the centers of the adjacent ones of the elongated adjustment holes  6   a . When each of the supplementary members  6  having the above arrangement of the elongated adjustment holes  6   a  is turned 180 degrees around in the horizontal plane, the positions of the opposite ends of the supplementary member  6  are shifted by the difference (d 1 -d 2 ) between the distance d 1  and the distance d 2  (which is equal to d 3 /2). Therefore, it is possible to finely adjust the positions of the supplementary members  6  according to the shape and the like of each piece of equipment C. 
     REFERENCE SIGNS LIST 
     
         
         K: double floor structure 
           1 : support legs (support legs for double floor) 
           11 : legs 
           12 : lower member 
           13 : intermediate member 
           14 : upper member 
           2 : beams (member constituting upper floor) 
           2   a : latching grooves 
           2   b : seat-fixing grooves 
           3 ,  4 : seat members 
           3   a : equipment-fixing holes 
           4   a ,  4   b : elongated holes 
           5 : connection members 
         P 1 : covering panels