# Patent

## Title
Underframe structure of railcar

## Abstract

An underframe structure of a railcar capable of reducing a deformation amount of a cross beam supporting an underfloor equipment upon underfloor fire. The underframe structure of the railcar includes an underframe having a pair of side sills extending in a railcar longitudinal direction and a cross beam arranged between the side sills and extending in a railcar width direction, a structural floor provided on an upper surface of the underframe, and an underfloor equipment suspended down in a center part in the railcar width direction of the cross beam. The underframe structure includes a passenger cabin floor provided on an upper side of the structural floor, the passenger cabin floor forming a lower surface of a passenger cabin S, and floor receiving members supporting the passenger cabin floor and extending in the railcar longitudinal direction between the structural floor and the passenger cabin floor.

## Background
TECHNICAL FIELD
The present invention relates to a underframe structure of a railcar.
BACKGROUND ART
A railcar generally has a underframe structure in which side sills are provided in a rail direction, i.e., a railcar longitudinal direction, and a plurality of cross beams for combining the side sills in a cross sleeper direction, i.e., a railcar width direction, are provided. As shown in Patent Literature 1, an underfloor equipement such as a main transformer is suspended down in a center part in the railcar width direction of the cross beams by suspended bolts.
CITATION LIST
Patent Literature


    [PTL 1] JP 2007-308042 A


SUMMARY OF INVENTION
Technical Problem
Evaluation criteria taking underfloor fire into consideration are provided for the underframe structure of the railcar. For example, in the United States, ASTM E-119 Standard Methods of Fire Tests of Building Construction and Materials specifies a method of fire resistance tests. Under test conditions of the above method, a temperature of the cross beams suspending the underfloor equipement is increased, and as a result, strength of the cross beams is lowered, and a deformation amount of the cross beams supporting the underfloor equipement is increased.
An object of the present invention is to provide a underframe structure of a railcar capable of reducing a deformation amount of a cross beam supporting an underfloor equipement upon underfloor fire.
Solution to Problem
The present invention is a underframe structure of a railcar including a underframe having a pair of side sills extending in a railcar longitudinal direction and a cross beam arranged between the side sills and extending in a railcar width direction, a structural floor provided on an upper surface of the underframe, and an underfloor equipement suspended down in a center part in the railcar width direction of the cross beam, the underframe structure further including a passenger cabin floor provided on an upper side of the structural floor, the passenger cabin floor forming a lower surface of a passenger cabin, and floor receiving members supporting the passenger cabin floor and extending in the railcar longitudinal direction between the structural floor and the passenger cabin floor, wherein among the floor receiving members, a floor receiving member provided in a substantially center part in the railcar width direction is attached to the structural floor so as to bear at least a part of a load of the underfloor equipement.
According to the present invention, the floor receiving member bears at least a part of the load of the underfloor equipement. Thus, a load received by the cross beam supporting the underfloor equipement is reduced. As a result, upon underfloor fire, a deformation amount of the cross beam can be reduced.
Advantageous Effects of Invention
In short, according to the present invention, the underframe structure of the railcar capable of reducing the deformation amount of the cross beam supporting the underfloor equipment upon the underfloor fire can be provided.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic sectional view of a railcar provided with a underframe structure according to the present invention.
FIG. 2 is a schematic perspective view showing side sills and cross beams.
FIG. 3 is a sectional view taken along line of FIG. 1.
FIG. 4 is an enlarged view of a part of a structural floor where no cross beams are provided in FIG. 3.
FIG. 5 is an enlarged view of a part of the cross beam where an underfloor equipement is not suspended in FIG. 3.
FIG. 6 is an enlarged view of a part of the cross beam where the underfloor equipment is suspended in FIG. 3.
FIG. 7 is a view showing a heat insulating structure of the part of the cross beam where the underfloor equipement is suspended, the heat insulating structure being different from FIG. 6.
FIG. 8 is a front view of the cross beam covered with a second heat insulating material.
FIG. 9 is a schematic perspective view of the underframe structure for reducing a bearing load of the cross beams.
FIG. 10 is a schematic front view of the cross beam showing a state before underfloor fire in the underframe structure of FIG. 9.
FIG. 11 is a schematic front view of the cross beam showing a state after the underfloor fire in the underframe structure of FIG. 9.
FIG. 12 is a view in which a metal plate covering a lower surface of a first heat insulating material is seen from the lower side.
FIG. 13 is a sectional view taken along line XIII-XIII of FIG. 12.
FIG. 14 is a partially enlarged view of FIG. 13.
FIG. 15 is a sectional view taken along line XV-XV of FIG. 12.
FIG. 16 is a partially enlarged view of FIG. 15.
FIG. 17 is a graph showing a temperature ratio between a temperature of the structural floor and an in-furnace temperature with respect to thickness of the first heat insulating material.



DESCRIPTION OF EMBODIMENT
FIG. 1 is a schematic sectional view of a railcar provided with a underframe structure according to the present invention. A underframe 1 is provided in a lowermost part of a carbody shell of the railcar. The underframe 1 has a pair of side sills 2 arranged in the rail direction, that is, in the railcar longitudinal direction (Y direction), and a plurality of cross beams 3 for combining the pair of side sills 2 in the cross sleeper direction, that is, in railcar width direction (Z direction). FIG. 2 is a schematic perspective view showing the side sills 2 and the cross beams 3. The cross beams 3 are provided at a pitch of 600 mm to 1,000 mm in the Y direction. In the cross beam 3, a plurality of piping holes 31 into which electric wires, air piping, and the like (hereinafter, simply referred to as the “electric wire and piping etc.”) are inserted are provided in line in the Z direction.
A structural floor 4 serving as an air-tight floor is provided on the underframe 1, and a plurality of floor receiving members 5 extending in the Y direction stand on the structural floor 4 at an interval in the Z direction. The floor receiving members 5 support a passenger cabin floor 6 forming a floor of a passenger cabin S on the upper side spaced from the structural floor 4 by a fixed distance. Seats 7 on which passengers are seated are provided on the passenger cabin floor 6.
FIG. 3 is a sectional view taken along line III-III of FIG. 1. The cross beams 3 have a substantially I shape section. In lower parts of the cross beams 3, rectangular suspending groove portions 3a whose lower end openings are narrowed down are integrally formed. Head parts of a plurality of suspended bolts 8 are inserted into the suspending groove portions 3a. An underfloor equipement 10 is supported by the suspended bolts 8 and nuts 8a via brackets 9.
(Heat Resistant Structure of Structural Floor)
FIG. 4 is an enlarged view of a part of the structural floor 4 where no cross beams 3 are provided in FIG. 3. On the lower side of the structural floor 4, a first heat insulating material 42a is provided via a space (air layer 41a). An upper surface of the first heat insulating material 42a is covered with a second metal plate 43a and a lower surface of the first heat insulating material 42a is covered with a first metal plate 43b. 
The first heat insulating material 42a is preferably formed by using glass fiber or ceramic fiber including alumina fiber. The second metal plate 43a and the first metal plate 43b are preferably stainless steel. Surface finish such as polishing processing is preferably performed to outer surfaces of the second metal plate 43a and the first metal plate 43b. 
Thickness D1 in the up and down direction of the air layer 41a is smaller than thickness D2 in the up and down direction of the first heat insulating material 42a. Specifically, the thickness D1 is about 1⁄3 of the thickness D2.
(Heat Resistant Structure of Cross Beam)
FIG. 5 is an enlarged view of a part of the cross beam 3 where the underfloor equipement 10 is not suspended in FIG. 3. A lower part of the cross beam 3 and at least a part of a side part, that is, a web 3b and the suspending groove portion 3a of the cross beam 3 are covered with a second heat insulating material 42b. An outer surface of the second heat insulating material 42b is covered with a third metal plate 43c having a U shape section. An upper surface of the cross beam 3 is attached to the structural floor 4, and upper side parts of the cross beam 3 are covered with the air layer 41a or the first heat insulating material 42a. The third metal plate 43c is supported by the cross beam 3 via the second heat insulating material 42b, and the first metal plate 43b and the third metal plate 43c are not in contact with each other.
FIG. 6 is an enlarged view of a part of the cross beam 3 where the underfloor equipement 10 is suspended in FIG. 3. The web 3b and the suspending groove portion 3a of the cross beam 3 are covered with the second heat insulating material 42b. The outer surface of the second heat insulating material 42b is covered with the third metal plate 43c. The third metal plate 43c is supported by the suspended bolts 8, and the first metal plate 43b and the third metal plate 43c are not in contact with each other. A collar 32 is provided on the lower side of the cross beam 3 and on the upper side of the third metal plate 43c, and oscillation of the suspended bolts 8 is suppressed by the collar 32.
FIG. 7 is a view showing a heat resistant structure of the part of the cross beam 3 where the underfloor equipement 10 is suspended, the heat resistant structure being different from FIG. 6 (modified example). As shown in FIG. 7, at least a part of the side part of the cross beam 3 may be covered with the second heat insulating material 42b via an air layer 41b. That is, the second heat insulating material 42b is formed so as to have a U shape section, an outside surface is covered with the third metal plate 43c, and an inside surface is covered with a fourth metal plate 43d. The air layer 41b is provided between the fourth metal plate 43d on the inner side and the cross beam 3. The third metal plate 43c and the fourth metal plate 43d covering the second heat insulating material 42b are supported by the suspended bolts 8, the first metal plate 43b and the third metal plate 43c are not in contact with each other, and the first metal plate 43b and the fourth metal plate 43d are not in contact with each other.
FIG. 8 is a front view in the Y direction of the cross beam 3 covered with the second heat insulating material 42b. Among the plurality of piping holes 31 provided in line in the Z direction of the cross beam 3, the electric wire and piping etc. are actually inserted into parts excluding a substantially center part in the Z direction, for example, both ends in the Z direction. Therefore, excluding the parts of several piping holes 31 in both the ends in the Z direction, the cross beam 3 is covered with the second heat insulating material 42b which is covered with the third metal plate 43c. 
The second heat insulating material 42b is preferably the same as the first heat insulating material 42a. The third metal plate 43c and the fourth metal plate 43d are preferably the same as the second metal plate 43a and the first metal plate 43b. 
(Heat Deformation Structure)
As shown in FIG. 8, the underfloor equipement 10 is generally suspended in a center part in the Z direction of the cross beam 3. Among the plurality of holes 31 provided in the Z direction, the electric wire and piping etc. are actually inserted into the parts excluding the substantially center part in the Z direction, for example, both the ends in the Z direction.
Since the electric wire and piping etc. are inserted into several piping holes 31 in both the ends, the piping holes 31 cannot be covered with the second heat insulating material 42b. Therefore, upon the underfloor fire, a temperature is increased in the parts of the piping holes 31 in both the ends of the cross beam 3, and the cross beam 3 is easily deformed (deflected) downward. Thus, in order to prevent large deformation of the cross beams 3 supporting the underfloor equipement 10, there is a need for reducing a bearing load of the cross beams 3.
FIG. 9 is a schematic perspective view of the underframe structure for reducing the bearing load of the cross beams 3. The floor receiving members 5 extending in the Y direction are provided on the structural floor 4 at an interval in the Z direction. Floor receiving members 5a provided in the substantially center part in the Z direction excluding both the ends in the Z direction are welded and fixed to the structural floor 4 over the entire length in the Y direction of the floor receiving members 5a. 
FIGS. 10 and 11 are schematic front views of the cross beams 3 respectively showing a state before the underfloor fire and after the underfloor fire in the underframe structure of FIG. 9. In FIGS. 10 and 11, the third metal plate 43c covering the second heat insulating material 42b is deleted. As shown in FIG. 8, the underfloor equipement 10 is suspended in the center part in the Z direction of the cross beams 3 by the suspended bolts 8. The cross beams 3 are covered with the second heat insulating material 42b excluding the parts of the piping holes 31 in both the ends in the Z direction of the cross beams 3.
Upon the underfloor fire, the temperature is increased in the parts of the piping holes 31 in both the ends in the Z direction of the cross beams 3, the parts not being covered with the second heat insulating material 42b, so that the cross beams 3 are easily deformed. As a result, the cross beams 3 are deflected downward by a load G of the underfloor equipement 10. The upper parts of the cross beams 3 are attached to the structural floor 4, and the floor receiving members 5 are attached to an upper part of the structural floor 4 so as to couple the cross beams 3. The floor receiving members 5a in the substantially center part in the Z direction where the underfloor equipement 10 is suspended are fixed to the structural floor 4 over the entire length in the Y direction of the floor receiving members 5a. Note that the floor receiving members 5a may be fixed to the structural floor 4 by welding or the floor receiving members 5a and the structural floor 4 may be integrated. Therefore, as shown in FIG. 9, the floor receiving members 5a can bear a part of the load G of the underfloor equipement 10. That is, a part of the load G of the underfloor equipement 10 is transmitted in the F1 direction and the F2 direction which are parallel to the Y direction through the floor receiving members 5a. 
(Metal Plate Attachment Structure)
As shown in FIG. 4, the upper surface and the lower surface of the first heat insulating material 42a are covered with the second metal plate 43a and the first metal plate 43b, respectively. An attachment structure of the first metal plate 43b covering the lower surface of the first heat insulating material 42a will be described with reference to FIGS. 12 to 16. FIG. 12 is a view in which the first metal plate 43b covering the lower surface of the first heat insulating material 42a is seen from the lower side. FIG. 13 is a sectional view taken along line XIII-XIII of FIG. 12, FIG. 14 is a partially enlarged view of FIG. 13, FIG. 15 is a sectional view taken along line XV-XV of FIG. 12, and FIG. 16 is a partially enlarged view of FIG. 15.
In FIG. 13, in order to prevent downward deflection of the first metal plate 43b, between the cross beams 3 in the Y direction, the first metal plate 43b is formed by combining two first metal plates 43b1, 43b2 in a substantial center in the Y direction. In upper parts of the cross beams 3, plate-shaped first plate members 432 are attached by welding. To ends of the first metal plate 43b1 and the first metal plate 43b2 on the side of the cross beams 3, first support members 433 formed in a Z shape when seen in the Z direction are attached by welding. By inserting ends of the first support members 433 into gaps between the cross beams 3 and the first plate members 432 and mounting the ends on the first plate members 432, the ends of the first metal plate 43b1 and the first metal plate 43b2 are supported by the cross beams 3. Upon underfloor fire, the first metal plate 43b1 and the first metal plate 43b2 are brought into direct contact with flame. However, the first plate members 432 are attached to the cross beams 3 on the upper side of the first metal plate 43b1 and the first metal plate 43b2. Further, the first metal plate 43b1 and the first metal plate 43b2 extend toward the cross beams 3 on the lower side of the first plate members 432. With such a configuration, direct contact of the first plate members 432 with the flame can be prevented.
In FIG. 12, the plurality of first plate members 432 are provided at an interval in the Z direction. Upon the underfloor fire, since the first plate members 432 are divided and attached to the cross beams 3, a contact area of the first plate members 432 and the cross beams 3 is reduced. As a result, a heat transmission amount from the first metal plates 43b1, 43b2 to the cross beams 3 is reduced. Therefore, a temperature increase of the cross beams 3 can be reduced.
FIG. 14 shows a detail of a combining part of the first metal plate 43b1 and the first metal plate 43b2. In a lower part of the structural floor 4 and in a substantially center part in the Y direction between the cross beams 3, a second plate member 434 extending in the substantially vertical direction from the structural floor 4 is attached by welding. The second plate member 434 and a second support member 435 formed in a substantially L shape when seen in the Z direction are fastened by a bolt 436 and a nut 436a. The second support member 435, the first metal plate 43b1, and the first metal plate 43b2 are fastened by a bolt 437 and a nut 437a. Among the second support member 435, a part to be fastened together with the second plate member by the bolt 436 and the nut 436a is called a first fastened portion, and a part to be fastened together with the first metal plate 43b1 and the first metal plate 43b2 by the bolt 437 and the nut 437a is called a second fastened portion. Note that, although the second plate member 434 is formed in a substantially L shape in FIG. 11, the shape is not limited thereto, and it may take any shape as long as it is fastened to the second plate member 434 and to the first metal plates 43b1, 43b2.
As described above, one end of the divided first metal plates 43b1, 43b2 is inserted between the cross beam 3 and the first plate member 432 and the other end is fastened to the structural floor 4 by the bolt 436 and the bolt 437 via the second support member 435. Therefore, even if, for example, the structural floor 4 is an aluminum alloy and the first metal plate 43b is stainless steel, that is, the structural floor 4 and the first metal plate 43b are made of different types of materials from each other, the first metal plate 43b can be supported by the structural floor 4 by adopting the above attachment structure.
In order to prevent the downward deflection of the first metal plate 43b, the first metal plate 43b is divided into two of the first metal plate 43b1 and the first metal plate 43b2. However, further in order to improve rigidity of the first metal plates 43b1, 43b2, as shown in FIG. 16, stiffeners 438 having an L shape section are preferably attached to upper surfaces of the first metal plates 43b1, 43b2 by welding. The plurality of stiffeners 438 extend in the Y direction and are provided at an interval in the Z direction.
In FIG. 16, on the lower side of the structural floor 4 and on an upper surface of the second metal plate 43a covering the upper surface of the first heat insulating material 42a, third support members 439 supporting the structural floor 4 are provided. The plurality of third support members 439 are provided at an interval in the Z direction and the Y direction.
According to the present embodiment, the following effects can be obtained.
(1) Since the floor receiving members 5a are welded and fixed to the structural floor 4 over the entire length in the Y direction of the floor receiving members 5a, the floor receiving members 5a can receive a part of the load G of the underfloor equipement 10. Therefore, even in a case where the temperature of both the ends of the cross beams 3 is increased by the underfloor fire and the cross beams 3 are easily deformed downward, a part of the load G of the underfloor equipement 10 is distributed to the floor receiving members 5a and a load received by the cross beams 3 is reduced. Thus, a downward deformation amount of the cross beams 3 can be reduced. By reducing the downward deformation amount of the cross beams 3, a downward deformation amount of the structural floor 4 and further the passenger cabin floor 6 can be reduced.
(2) The structural floor 4 is covered with the first heat insulating material 42a via the air layer 41a. Thus, while maintaining a heat insulating effect, thickness in the up and down direction (D1+D2) of both the air layer 41a and the first heat insulating material 42a can be shortened. As a result, a heat insulating structure on the lower side of the structural floor 4 can be downsized, so that the large underfloor equipement 10 can be attached.
Detailed reasons why the heat insulating structure on the lower side of the structural floor 4 can be downsized are as follows.
In general, a heat transmission mode is classified into heat conduction, heat transfer, and heat emission (radiation). Upon the underfloor fire of the railcar, the heat conduction and the radiation are major. A relationship between the heat conduction and the radiation differs depending on a temperature. The radiation is dominant over the heat conduction at a high temperature (500° C. or more) and the heat conduction is dominant over the radiation at a low temperature (500° C. or less). When the air layer 41a and the first heat insulating material 42a are compared, a heat conduction property is lower in the air layer 41a than the first heat insulating material 42a. Meanwhile, a property for blocking the radiation is higher in the first heat insulating material 42a than the air layer 41a. Therefore, in the case of underfloor fire, a temperature on the lower side is high and a temperature on the upper side is low. Thus, by arranging the first heat insulating material 42a having a high property for blocking the radiation on the lower side and arranging the air layer 41a having a low heat conduction property on the upper side, the thickness in the up and down direction of both the air layer 41a and the first heat insulating material 42a (hereinafter, referred to as the “thickness”) can be thinnest. When a temperature of the flame is about 1,000° C., a temperature of the lower surface of the first heat insulating material 42a becomes about 800° C. In order to make a temperature of a lower surface of the air layer 41a about 500° C. (by heat insulating with the first heat insulating material 42 at the temperature at which the radiation is dominant and by heat conduction with the air layer 41a at the temperature at which the heat conduction is dominant) and to make a temperature of the structural floor 4 about 350° C. (for example, in a case where a light aluminum alloy is used for the structural floor 4, the temperature of the structural floor 4 is preferably suppressed to be about 350° C.), the thickness D1 of the air layer 41a is preferably smaller than the thickness D2 of the first heat insulating material 42a. Further, the thickness D1 of the air layer 41a is preferably about 1⁄3 of the thickness D2 of the first heat insulating material 42a. FIG. 17 is a graph showing a temperature ratio between the temperature of the structural floor 4 and an in-furnace temperature (corresponding to the temperature of the underfloor fire) with respect to the thickness of the first heat insulating material 42a in a case where the sum of the thickness D1 of the air layer 41a and the thickness D2 of the first heat insulating material 42a is 20 mm. From FIG. 17, for example when the sum of the thickness D1 of the air layer 41a and the thickness D2 of the first heat insulating material 42a is about 20 mm, the thickness D1 of the air layer 41a is preferably about 2.5 to 5 mm, and the thickness D2 of the first heat insulating material 42a is preferably about 17.5 to 15 mm.
(3) Since the first metal plate 43b is provided on the lower surface of the first heat insulating material 42a, the first heat insulating material 42a can be protected from the flame upon the underfloor fire. Since the first heat insulating material 42a can be supported by the first metal plate 43b, there is no need for providing a special member for supporting the first heat insulating material 42a. 
(4) Since the second metal plate 43a is provided on the upper surface of the first heat insulating material 42a, radiation heat to the structural floor 4 from the lower side by the underfloor fire can be reduced.
(5) The lower part of the cross beam 3 and at least a part of the side part are covered with the second heat insulating material 42b or covered with the second heat insulating material 42b via the air layer 41b. Thus, fire resistance and a heat insulating property of the cross beams 3 can be improved upon the underfloor fire. By covering the cross beams 3 with the second heat insulating material 42b via the air layer 41b, as well as the heat insulating structure of the structural floor 4 described above, the thickness of both the air layer 41b and the second heat insulating material 42b can be shortened. As a result, the heat insulating structure around the cross beams 3 can be downsized.
(6) Since the second heat insulating material 42b is covered with the third metal plate 43c, the second heat insulating material 42b can be protected from the flame upon the underfloor fire. Since the second heat insulating material can be supported by the third metal plate 43c and the fourth metal plate 43d, there is no need for providing a special member for supporting the second heat insulating material 42b. 
(7) The first metal plate 43b and the third metal plate 43c are not in contact with each other, and the first metal plate 43b and the fourth metal plate 43d are not in contact with each other. Thus, heat strain can be prevented from being generated between the first metal plate 43b and the third metal plate 43c and between the first metal plate 43b and the fourth metal plate 43d, and large deformation, cracking, or the like can be prevented from being generated between the first metal plate 43b and the third metal plate 43c and between the first metal plate 43b and the fourth metal plate 43d. 
(8) Since the first metal plate 43b is divided into two of the first metal plate 43b1 and the first metal plate 43b2, a downward deflection amount of the first metal plate 43b can be reduced.
(9) The first metal plate 43b is inserted into the gaps between the cross beams 3 and the first plate members 432 and mounted on and supported by the first plate members 432. The first metal plate 43b is fastened to the structural floor 4 by the bolts 436, 437 via the second support member 435. Therefore, different materials from the cross beams 3 and the structural floor 4 can be used for the first metal plate 43b. For example, the cross beams 3 and the structural floor 4 can be a light aluminum alloy, and the first metal plate 43b can be stainless steel having high fire resistance.
(10) Since the stiffeners 438 are attached to the upper surface of the first metal plate 43b, the rigidity of the first metal plate 43b can be improved. As a result, the downward deflection amount of the first metal plate 43b can be reduced.
(11) Since the third support members 439 are provided on the upper surface of the second metal plate 43a, the third support members 439 support the structural floor 4 so as to reduce the downward deflection amount of the structural floor 4.
(12) The piping holes 31 into which piping is placed are provided in the Y direction in both the ends in the z direction of the cross beams 3, and the second heat insulating material 42b is formed such that the piping holes 31 are exposed. Thus, the electric wire and piping etc. of the underfloor equipement 10 and the like can be placed in both the ends in the z direction of the cross beam 3, so that a wiring structure can be prevented from being complicated.
(13) Since the surface finish such as the polishing processing is performed to the outer surfaces of the second metal plate 43a, the first metal plate 43b, the third metal plate 43c, and the fourth metal plate 43d, emissivity of the outer surfaces of the second metal plate 43a, the first metal plate 43b, the third metal plate 43c, and the fourth metal plate 43d is low. As a result, heat emission from the second metal plate 43a, the first metal plate 43b, the third metal plate 43c, and the fourth metal plate 43d can be reduced.
As well as the cross beams 3 and the structural floor 4, the side sills 2 are preferably covered with a heat insulating material, and further preferably covered with a heat insulating material via an air layer.
In the present embodiment, the floor receiving members 5a in the substantially center part in the Z direction where the underfloor equipement 10 is suspended are welded and fixed to the structural floor 4 over the entire length in the Y direction of the floor receiving members 5a. However, the present invention is not limited to the floor receiving members 5a in the substantially center part in the Z direction, but all the floor receiving members 5 may be welded and fixed to the structural floor 4 over the entire length in the Y direction of the floor receiving members 5. Although the floor receiving members 5a are welded and fixed to the structural floor 4, a fixing method thereof is not limited to welding, but any method can be used as long as the floor receiving members 5a are attached to the structural floor 4 so as to bear a part of the load of the underfloor equipement 10. For example, the floor receiving members 5a may be integrated with the structural floor 4 or the floor receiving members 5a may be fastened to the structural floor 4 by bolts and nuts. The floor receiving members 5a may be attached to the structural floor 4 via connection members serving as separate bodies from the floor receiving members 5a. 
In the present embodiment, the piping holes 31 are provided in both the ends in the Z direction of the cross beams 3. However, the piping holes 31 may be provided anywhere in the cross beams 3 as long as it is within a range not corresponding to a part substantially immediately below the floor receiving members 5a in the substantially center part in the Z direction where the underfloor equipement 10 is suspended.
The present invention is not limited to the configuration described in the above embodiment, but can include various modified examples that those skilled in the art can anticipate without departing from the contents described in the claims.
INDUSTRIAL APPLICABILITY
In the present invention, the underframe structure of the railcar capable of reducing the deformation amount of the cross beams supporting the underfloor equipement upon the underfloor fire can be provided. Thus, an industrial utility value is high.

## Claims

1. An underframe structure of a railcar comprising:
an underframe having a pair of side sills extending in a railcar longitudinal direction and a cross beam arranged between the side sills and extending in a railcar width direction;
a structural floor provided on an upper surface of the underframe; and
an underfloor equipment suspended down in a center part in the railcar width direction of the cross beam,
the underframe structure further comprising:
a passenger cabin floor provided on an upper side of the structural floor, the passenger cabin floor forming a lower surface of a passenger cabin; and
floor receiving members supporting the passenger cabin floor and extending in the railcar longitudinal direction between the structural floor and the passenger cabin floor, wherein
among the floor receiving members, a floor receiving member provided in a substantially center part in the railcar width direction is attached to the structural floor so as to bear at least a part of a load of the underfloor equipment, and
the underframe structure further comprising a piping hole extending in the railcar longitudinal direction in the cross beam within a range not corresponding to a part substantially immediately below the floor receiving member which is provided in the substantially center part in the railcar width direction, wherein
among the floor receiving members, the floor receiving member provided in the substantially center part in the railcar width direction is fixed to the structural floor over the entire length in the railcar longitudinal direction of the floor receiving members by welding.

2. The underframe structure of the railcar according to claim 1, further comprising a first heat insulating material arranged on a lower side of the structural floor via an air layer for the structural floor.

3. The underframe structure of the railcar according to claim 2, further comprising a first metal plate provided on a lower surface of the first heat insulating material, wherein
the structural floor, the air layer for the structural floor, the first heat insulating material, and the first metal plate are arranged in order from the structural floor side to the lower side.

4. The underframe structure of the railcar according to claim 3, further comprising a second metal plate provided on an upper surface of the first heat insulating material, wherein
the structural floor, the air layer for the structural floor, the second metal plate, the first heat insulating material, and the first metal plate are arranged in order from the structural floor side to the lower side.

5. The underframe structure of the railcar according to claim 2, wherein at least a part of a side part of the cross beam is covered with a second heat insulating material.

6. The underframe structure of the railcar according to claim 2, wherein at least a part of a side part of the cross beam is covered with a second heat insulating material via an air layer for the cross beam.

7. The underframe structure of the railcar according to claim 5, wherein the second heat insulating material is covered with a metal plate.