KR100650158B1 - Prefabricated steel girder with void web, lower member of a box type and opened upper member and the construction method using the same - Google Patents

Abstract

A prefabricated steel girder composed of a hollow web, a reduced box type lower chord and an opened upper flange is provided to manufacture a girder for a bridge economically by planning the cross section of a girder effectively and economically and reducing weight. A prefabricated steel girder(100) composed of a hollow web, a reduced box type lower chord and an opened upper flange comprises: web members(110) functioning as a web for a bridge girder using L-shaped steel and containing vertical members installed to face each other horizontally, spaced out vertically and provided with one or more through-holes(111) to increase composite efficiency with slab concrete; a double base panel member(120) divided into an upper double base panel member(121) and a lower double base panel member(122) and connected to the inner bottom of the web member using a folding member(150) to have a hollow(S); an upper flange member(130) coupled to the inner/outer sides of the top of the web member and extended vertically using a fastener(300) composed of a bolt and a nut; and slab concrete formed to bury the top of the web member. A construction method of a bridge using a prefabricated steel girder comprises the steps of manufacturing many prefabricated steel girders in a factory, carrying to a construction site, assembling with a coupler containing a bolt and a nut and re-assembling in the appointed length, and installing on a lower structure of a bridge vertically; installing an additional slab form panel(170) between outer upper flange members installed on both outer sides of the prefabricated steel girders; and forming a slab by placing slab concrete on the slab form panel.

Description

Prefabricated Steel Girder with Void Web, Lower Member of a Box Type and Opened Upper Member And the Construction Method Using the Same }

Figure 1a is a cross-sectional view showing a conventional plate girder with a slab bending moment diagram according to the construction step.

Figure 1b shows a conventional asymmetric plate girder.

1c illustrates an example in which concrete is formed at a predetermined height under a steel box girder located in a conventional point portion.

Figure 2a and 2b is a sectional view showing the assembled steel girder and its installation state of the present invention.

<Description of the symbols for the main parts of the drawings>

100: assembled steel girder 110: abdominal member

111: Through hole 120: Double bottom plate member

121: upper double bottom plate member 122: lower double bottom plate member

130: upper flange member 140: slab concrete

150: foldable member 160: abdominal slope reinforcement member

170: slab formwork plate 180: shear connector

190: lower reinforcing member 200: slab

300: fastener 400: bridge undercarriage

The present invention relates to an assembled steel girder consisting of a hollow abdomen, a lower chord and an open upper flange of a reduced box shape, and a bridge construction method using the same. More specifically, the present invention relates to a composite girder for bridges, which is manufactured by synthesizing a steel girder with slab concrete, but having a more efficient cross-sectional configuration.

FIG. 1a shows a conventional plate girder 10 along with a slab 20 in cross-sectional view, and shows the girder weight, the girder and the slab combined with each other, and the bending moment diagrams for live loads according to the construction stage.

First, in the case of the bending moment diagram (BMD1) due to the weight of the girder before being installed on the bridge substructures, bridges, and the like, the upper edge (upper flange) and the lower edge (lower flange) of the girder based on the neutral axis CL It can be seen that compressive stress (+ a1) and compressive stress (-a1) of the same magnitude are generated.

After installation on the bridge undercarriage, in the case of the bending moment diagram (BMD2) in the state where the girder and the slab are combined, the neutral axis CL is moved upward by slab formation, and the compressive stress (+ a2) at the upper edge and the compressive stress at the lower edge It can be seen that (-(a2 + Δa2)) is generated,

After the completion of the bridge, when the live load is loaded on the slab, there is no change in the neutral shaft, but it can be seen that the compressive stress (+ a3) at the upper edge and the compressive stress (-(a3 + Δa3)) at the upper edge.

That is, compressive stress A1 (+ (a1 + a2 + a3)) accumulates at the upper edge of the girder, and tensile stress A2 (-(a1 + a2 + a3)-(Δa2 + Δa3)) accumulates at the lower edge. (The absolute values of a1, a2, and a3 are the same).

At this time, as the slab and the girder are synthesized and the neutral axis is moved upward, A2 becomes quantitatively larger than A1, so when designing the girder section, it is necessary to secure a cross-sectional area where the lower edge, not the upper edge of the girder, can resist the design load. The criteria will be set to help.

Since the girder having the same cross sectional area as the upper and lower edges of plate girder or steel box girder is manufactured and sold, the girder section is designed based on the girder having the same cross sectional area as the upper edge based on the cross sectional area of the lower girder. Overdesign has led to the problem of being very inefficient and inefficient.

In order to solve this problem, an improved asymmetric plate girder (Korean Patent No. 10-2004-26408, 30) having a lower thickness and / or width than the upper edge has been introduced as shown in FIG. 1B. However, it was pointed out that such girders are difficult to manufacture, and their practical use is limited.

In addition, steel box girders of trapezoidal cross-sectional shape in which the upper surface is opened and the lower edge is formed with a relatively large cross-sectional area have been introduced. However, the structural problem was pointed out that this method could not be expected in terms of the effect.

In other words, in the upper stage of girder, the change of compressive stress is not large until fabrication stage, slab and compounding stage, live load loading stage, whereas in the case of lower edge, the change of tensile stress is very large. In order to minimize the upward movement of the neutral axis, it is desirable to improve the cross-sectional area of the girder by simply adopting a method that can secure a large cross-sectional area of the lower edge of the girder. The need for technology development has emerged.

Therefore, in the steel box girder, in particular, the method of forming the concrete 40 at a predetermined height in the lower portion of the steel box girder located at the point (Korean Patent No. 328318) has also been introduced as shown in FIG. 1C, thereby increasing the rigidity of the lower girder. Although it can be said that it can have an effect, but in the case of the girder where the lower part of the girder corresponds to the compression part, the technical effect for effectively resisting the tensile stress of the lower edge of the girder cannot be expected in the case of the girder filled with concrete at the point. In addition, above all, there was a limit that the movement of the neutral shaft can not be lowered fundamentally, and there was a problem that it is not easy to secure the constructability in the concrete filling.

Therefore, the present invention is to provide a means for enabling a more efficient cross-sectional design of the composite girder,

An object of the present invention is to reduce the size of the design dominant stress generated in the girder by lowering the neutral axis of the girder for the bridge in the manufacturing step of the girder to be synthesized with the slab, the synthesis step of the girder and the slab and the action of the live load is more economical It is to provide bridge girders that can efficiently design cross sections.

Another object of the present invention is to provide a bridge girders that can be manufactured and installed more economically in the manufacture and construction of bridge girders.

Another object of the present invention is to enable efficient cross-sectional design by reducing the weight of the girder for the manufacture of bridge girders, and to optimize the design of the girder cross section by minimizing the member forming the upper flange portion of the girder. .

In order to achieve the above technical problem, the present invention is manufactured by using a steel material that can be manufactured by the assembly method for bridge girders,

First, the assembled steel girder is formed at the bottom of the double bottom member spaced up and down in its entire longitudinal direction, and has a reduced box shape such as the overall shape of the girder, and thus has different behavior characteristics from the existing lower flange. By constructing the chord to represent the axial stress governing characteristics, the neutral axis of the assembled steel girder is lowered while increasing the local stiffness.

Second, since the overall shape of the assembled steel girder 100 is made in the shape of ㅂ, it is easy to manufacture and box-shaped, so that it has sufficient resistance to warping, sagging, buckling, and vibration caused by live loads. By manufacturing the assembled steel girder using the shape steel member to make it more economical and easy to manufacture, the upper end of the assembled steel girder 100 is not installed other members except the upper flange member 130 installed on both sides. When synthesizing the slab concrete 140 and the abdomen member 110, the neutral axis upward movement was minimized.

Third, since the neutral axis of the assembled steel girder is already lowered and lowered at the manufacturing stage by the double bottom member 120, the burden on the design governing stress at the bottom of the assembled steel girder is greatly reduced, so that the mold height is lowered for the same bending stress. In consideration of the fact that the compressive stress of the upper part of the assembled steel girder does not vary significantly by construction stages, the upper part of the abdomen is not installed on the lower surface of the slab, but it is embedded into the slab and synthesized so that the height of the girder is further increased. It was possible to lower stably.

Fourth, in the case of the conventional bridge girders in the load transfer path, although the slab and the girder are combined with each other, a connection configuration for integrally behaving is required, but in the present invention, the upper part of the abdomen is embedded into the slab concrete and the slab is embedded. And fully integrated behavior of the assembled steel girder is enabled. Fifth, the upper portion of the assembled steel girder is further opened, the slab concrete 140 is to be poured using only the slab formwork thin plate so that the neutral shaft upward by the installation of the upper flange member 130 is minimized.

Hereinafter, the assembly steel girder 100 consisting of a hollow abdomen, a reduced box-shaped lower chord and an open upper flange according to the present invention will be described in detail with reference to the embodiment shown in the drawings.

Figure 2a shows the assembled steel girder of the present invention, the assembled steel girder 100,

An abdominal member 110 installed to face each other in a transverse direction and including a plurality of vertical members spaced apart in the longitudinal direction and having a through hole formed at an upper end thereof;

A double bottom plate member 120 connected between the bottom inner side of the abdominal member 110 and installed in the longitudinal direction, the horizontal bottom plate having a horizontal plate member spaced vertically to be formed as a hollow portion S;

An upper flange member 130 including an L-shaped steel which is fastened to both inner and outer sides of the upper part of the abdomen member 110 and installed in a longitudinal direction; And

It is configured to include; slab concrete 140 is formed so that the upper end of the abdomen member 110 is embedded.

The abdominal member 110 is to have the function of the abdomen (WEB) constituting the bridge girders (GIERDER) using the L-beams, and install the L-beams in the form of a vertical beam to face each other in the lateral direction, each The L-shaped steel is spaced apart in the longitudinal direction so that the assembled steel girder (bridge girder) can be installed discontinuously with a predetermined length in the longitudinal direction.

In the design of the flange section of the upper and lower edges of the girder, the abdominal function is insignificant in the flexural stiffness role, but rather the abdominal part in the general position except for the point is thin like L-shaped steel because it causes the design stress to increase due to the increase in self-weight. It can be used as a member, and it is also possible to use a beam having a shape of a square such as a simple square bar without using L-shaped steel.

At this time, the upper end of the abdomen member 110, the abdominal member upper end is embedded in the slab concrete 140, as will be described later to at least one concrete communication through-hole 111 to increase the synthetic performance with the slab concrete 140 To be formed.

The double bottom plate member 120 is connected between the lower inner side of the abdomen member 110 and is installed to be dividedly assembled or integrally extended in the longitudinal direction, and is responsible for the function of the box-shaped lower chord in the overall assembly steel girder form. Done.

The double bottom plate member 120 may be divided into an upper double bottom plate member 121 and a lower double bottom plate member 122, and an upper double bottom plate member 121 installed on the lower double bottom plate member 122 may be installed at the installation position thereof. By adjusting the serves to adjust the height of the formation of the hollow portion (S).

At this time, in order to connect and install the upper double bottom member 121 to the abdominal member 110, which is L-shaped steel, the folding member 150, which is L-shaped steel, is used in the present invention.

That is, first install the folding member 150 of the L-shaped steel at the position where the upper double bottom plate member 121 is to be installed as the fastener 300, and the side portion of the upper double bottom plate member 121 is located within the folding member 150. By fastening to the fastener 300 including the side portion and also bolts and nuts to facilitate the installation of the upper double bottom plate member 121.

Also in the case of the lower double bottom plate member 122 is installed using the folding member 150 and the fastener 300, which is L-shaped steel, and the side portion of the lower double bottom plate member 122 in the folding member 150 Fasten with a fastener 300 including the side and bolts and nuts.

Furthermore, the plurality of lower reinforcing members 190 are spaced apart in the longitudinal direction on both side surfaces of the double bottom plate member 120 to further install using fasteners including bolts and nuts, such as bending rigidity of the hollow part S. It can be promoted, the installation and disassembly is facilitated by installing using the fastener so as to protrude on both sides of the double bottom plate member 120 in the installation.

Since the upper and lower double bottom members 121 and 122 are installed to form the hollow portion S as described above, the assembled steel girder 100 of the present invention has a double box shape in which an abdominal space and a lower end are formed as an empty space as a whole. It can be manufactured, and can be manufactured by a simple fastener 300, such as bolts and nuts, so that the production, transportation and transportation is very easy, light weight, and very efficient in torsion, buckling and vibration due to the box shape It can be produced in a cross section.

In addition, the length of the longitudinal direction in the assembled steel girder may be long, so that the abdominal inclination reinforcement member 160 is installed diagonally between the abdominal member and the abdominal member in the longitudinal direction by welding or fasteners (bolts and nuts). Thereby allowing longitudinal reinforcement of the abdomen member 110. At this time, the abdominal slope reinforcing member is preferably connected to the pin in the form of a truss.

The assembled steel girder 100 manufactured as described above has a box-shaped lower chord formed by the configuration of the upper and lower double bottom members 120 and 121 installed at the lower end of the abdominal member 110 due to the application of the X-shape as a whole. Can be.

In other words, due to the reduced box bottom chord, the girder's stiffness increases due to the local chord stiffness increased locally compared to the existing lower flange, and the behavior characteristic also causes the axial deformation instead of the bending deformation. Induces the behavior of dispersing the energy due to the movement of the neutral shaft, and even if the slab 200 is formed in the upper abdomen member 110 in the future to sufficiently suppress the upward movement of the neutral shaft, resulting in the lower edge of the girder It is possible to effectively control the magnitude of design governing stress acting on

At this time, the upper end of the assembled steel girder constituting the upper edge of the girder is fastened to the inside / outside of the upper end of the abdomen member 110 so that the upper flange member 130 including the L-shaped steel extending in the longitudinal direction is installed.

The upper flange member 130 is fastened by the fastener 300 including the bolt 310 and the nut 320 to the inside and outside of the upper end of the abdomen member 110, so that the upper flange of the assembled steel girder is simply To form.

That is, the role of the girder top (the top of the assembled steel girder) can be minimized so that unnecessary overdesign is not performed at the top of the girder which has less stress burden than the lower edge depending on the construction stage in the bridge girder.

The fabricated steel girder 100 manufactured as described above is installed on the bridge lower structure 400 including the pier, the upper slab 200 is formed, in order to pour the slab concrete 140, the assembled steel girder The slab formwork is needed between the 100 and the slab 200.

Thus, the assembled steel girder 100 of the present invention allows the slab formwork plate 170 to be mounted on the folding member 150 to serve as a slab formwork for placing the slab concrete 140.

The folding member 150 is for supporting the slab formwork plate 170 and is installed at a position spaced slightly downward from the inner upper end of the abdominal member 110, and the upper double bottom member installed at the lower end of the abdominal member 110. It may be installed in the same manner as the folding member 150 is an L-shaped steel for installing (120).

That is, the slab formwork plate 170 is between the upper inner side of the abdomen member 110 including the L-shaped steel, the side member is in contact with the abdomen member 110, the folding member 150 including the L-shaped steel extending in the longitudinal direction installed The side end portion is installed to be fastened by the fastener 300 including the bolt or nut, and may be installed using a thin wood plate or the like, otherwise there is no material limitation and may have a formwork function.

As a result, the slab formwork plate 170 is installed continuously in the longitudinal direction, where the slab formwork may be divided and installed when the length is long in the longitudinal direction. As a result, the slab formwork serves as the bottom formwork of slab concrete and may be removed later.

Thus, by installing only the slab formwork plate 170 made of a thin wooden plate other than the folding member 150, by the construction stage in the bridge girder to avoid unnecessary overdesign at the stage of the assembly steel girder without any stress burden according to the construction stage It can optimize the role and minimize the upward movement of the neutral axis of the assembled steel girder by slab formation.

As such, the upper end of the assembled steel girder 100 of the present invention is formed in an open structure except for the slab formwork plate 170, thereby lowering the self-weight of the assembled steel girder and minimizing the upward movement of the neutral shaft to the bottom of the assembled steel girder. The amount of tensile stress applied can be reduced.

In addition, after installing the additional slab formwork plate 170 for forming the slab 200 between the upper flange member 130 of the plurality of assembled steel girder 100 in the transverse direction, the slab concrete 140 is poured. .

At this time, the upper end of the abdomen member 110 is embedded in the slab concrete 140, and the slab concrete 140 is in communication with the through-hole 111 of the abdomen member (110). Thus, as compared with the slab 200 is formed in contact with the upper surface of the conventional abdominal member as shown in Figure 2b, the height of the slab 200 is much lower, the effect of the top of the assembly steel girder synthesized with the slab 200 Will occur.

That is, due to the slab formation, the neutral axis of the cross section of the assembled steel girder moves the neutral axis somewhat upward, which is a factor that may increase the magnitude of tensile stress generated at the lower edge of the assembled steel girder.

However, because the pre-assembled steel girders act as cross-sections already synthesized with the slab, the flexural stiffness that can withstand the live loads in the construction stage is increased, so the increased tensile stress that occurs at the lower edge of the girder even if the girder cross section is reduced. Will be able to resist enough

In the present invention, it has been further adopted to reduce the height of the girder by the assembly steel girder, the height of the girder in forming the slab, so that the abdomen of the girder, rather than the upper surface of the girder is buried inside the slab To achieve.

That is, the upper end portion of the abdominal member 110 of the present invention is to be protruded into the slab, and the slab concrete 140 to communicate with the through-hole 111 of the abdominal member 110 to lower the overall height of the girder. . This reduces the mold height of the girder cross section and enables a more rational design of the girder cross section.

At this time, in order to improve the adhesion performance with the slab concrete 140, if the folding member 150 or the upper flange member upper surface allows space may be provided with a shear connector (180).

Bridge construction method using the assembled steel girder 100 of the present invention

In the bridge construction method of installing a bridge undercarriage including a bridge and a bridge, and installing a girder and a slab on the bridge undercarriage,

An abdominal member 110 installed to face each other in a transverse direction and including a plurality of vertical members spaced apart in the longitudinal direction and having a through hole formed at an upper end thereof; A double bottom plate member 120 connected between the bottom inner side of the abdominal member 110 and installed in the longitudinal direction, the horizontal bottom plate having a horizontal plate member spaced vertically to be formed as a hollow portion S; An upper flange member 130 including an L-shaped steel which is fastened to the inner and outer sides of the upper end of the abdominal member 110 and installed in a longitudinal direction; A folding member 150 including an L-shaped steel installed inside the upper abdomen member; Slab formwork plate 170 provided between the folding member; An abdominal slope reinforcing member 160 in a diagonal direction between the longitudinally spaced abdominal member and the abdominal member; After fabricating the assembled steel girder 100, including; and the lower reinforcing member 190 is installed in a plurality spaced apart in the longitudinal direction so as to connect between the upper double bottom member and the lower double bottom member of the double bottom member vertically; Installed in parallel in the longitudinal direction on the upper surface of the bridge substructure 400 (s1),

Further installing the slab formwork plate 170 between the outer upper flange member 130 of the assembled steel girder 100 (s2),

The slab concrete 140 is poured into the upper part of the slab formwork plate so as to form the slab 200 (s3).

The step s1 may be referred to as a step to be installed in the factory by manufacturing the assembly steel girder 100 of the present invention in advance in the factory. In this case, when the longitudinal length is long, it may be manufactured and transported and installed as a prefabricated steel segment. That is, since the longitudinal length of the assembled steel girder 100 may be limited in transporting, a plurality of assembled steel girder 100 may be manufactured first based on the longitudinal length possible, and then simply transported to the site to easily bolt and After reassembling to a predetermined length by a fastener including a nut, it can be installed on the bridge substructure 400.

The assembled steel girder 100 is composed of the abdomen member 110, the upper and lower double bottom plate members 121, 22, as shown in Figure 2b, the double installed on the lower end of the abdomen member 110 by the folding member 150 Bottom plate member 120, upper flange member 130, folding member (150, for double bottom plate member and slab formwork plate), abdominal slope reinforcement member 160, slab formwork plate 170, lower reinforcement member 180 is included It is produced in the state.

Therefore, a plurality of such steel girder 100 is installed using a bridge support (not shown) in parallel (lateral direction) on the upper surface of the bridge substructure 400 including a bridge or alternating bridge installed in a conventional manner.

Step s2 is a step of installing additional slab formwork plate 170 for forming a slab between the upper flange member 130 installed on both outer sides of the assembly steel girder 100 installed in parallel in the lateral direction. This is to form a slab formed between the assembly steel girder (100).

Step s3 is a step of forming the slab 200 by pouring and curing the slab concrete 140 on the slab formwork plate 170 installed between the upper assembly steel girder 100 and the assembled steel girder.

At this time, the slab concrete 140 is in communication with the through-hole 111 formed in the upper portion of the abdomen member 110 to be formed. As a result, the upper portion of the abdomen member 110 of the assembled steel girder 100 may be embedded in the slab 200.

Further, both outer upper ends of the assembled steel girder 100 may be continuously cast in the transverse direction by the other slab formwork plate 170 installed between the upper flange member 130.

When using the assembled steel girder of the present invention for bridge girders,

First, due to the increase in flexural stiffness of the lower edge of the assembled steel girder and the slab synthesis at the top, the increase of the neutral axis according to the construction stage can be restrained to the maximum, thereby reducing the magnitude of the tensile stress generated at the lower edge of the assembled steel girder, thus making the girder cross section more efficient. Economical design is possible, and the self-weight of the assembled steel girder is reduced, thereby making it possible to manufacture and install the economical assembled steel girder.

That is, in the fabrication step of the assembled steel girder, it is possible to reduce the magnitude of the tensile stress of the lower edge of the girder due to the suppression of the rise of the neutral shaft, which enables an optimized design of the girder cross section.

Referring to Figure 1a, by forming a relatively small size of-(Δa2 + Δa3) due to the rise of the neutral axis in the lower edge of the girder can reduce the magnitude of the tensile stress generated in the lower edge of the girder.

Second, considering that the upper part and the abdomen of the assembled steel girder according to the construction stage do not need excessive design of unnecessary cross section in its role, the ready-made product can be used, and the transportation and construction are easy, and the assembly fabrication The L-shaped steel can be assembled and installed, but the abdominal member is embedded inside the slab so that the upper edge of the girder can be combined with the slab to reduce the overall height of the girder, thereby enabling efficient sectional design of the girder cross section.

Third, the assembled steel girder forms a box-shaped structure in a U-shape, so that it can sufficiently resist phenomena such as warping or buckling, and offsets the weakness of the girder of the conventional I-type or H-shaped cross section. Unlike the related art, the lower girder of the girder, which is governed by bending stress, is provided as a truss type bottom chord, which is a structure governed by axial force, thereby converting the behavior characteristics, thereby reducing the stress generated at the lower edge due to its design dominant stress, thereby improving durability. It will have an effect. An embodiment of the present invention described above and illustrated in the drawings should not be construed as limiting the technical spirit of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those skilled in the art can change and change the technical idea of the present invention in various forms. Therefore, such improvements and modifications fall within the protection scope of the present invention as long as it will be apparent to those skilled in the art.

Claims (10)

The abdomen is formed as a hollow space, and the overall shape is an assembled steel girder made of a rectangular cuboid, An abdominal member installed to face each other in a transverse direction and including a plurality of vertical members spaced apart in the longitudinal direction and having a through hole formed at an upper end thereof; A double bottom member connected between the lower inner side of the abdominal member and installed in a longitudinal direction, the horizontal bottom member including a horizontal plate member spaced vertically to be formed as a hollow part S; An upper flange member including an L-shaped steel fastened to the inside and the outside of the upper end of the abdominal member and installed in a longitudinal direction; And Slab concrete formed so that the upper end portion of the abdomen member; Assembly hollow steel girder consisting of a hollow abdomen, a reduced box-shaped lower chord and an open upper flange. 2. The folding member according to claim 1, wherein the double bottom member comprises an upper and a lower bottom member, and the upper and lower bottom members include an L-shaped steel extending in a longitudinal direction in contact with an abdominal member including the L-shaped steel. Assembly side girder consisting of a hollow abdomen, a reduced box-shaped lower chord and an open upper flange, characterized in that the side end is fastened by a fastener including a bolt and a nut. The method of claim 2, wherein the folding member including an L-shaped steel installed inside the upper abdomen member; And a slab formwork plate installed between the folding member; a hollow abdomen, a reduced box-shaped lower chord, and an open upper flange. 4. The hollow abdominal cavity according to any one of claims 1 to 3, wherein an abdominal inclination reinforcing member is further disposed between the longitudinally spaced abdominal members and the abdominal member in a diagonal direction. Prefabricated steel girder consisting of current and open top flanges. 5. The hollow abdominal cavity according to claim 4, wherein a plurality of lower reinforcing members are vertically spaced apart from each other to vertically connect between the upper double bottom member and the lower double bottom member of the double bottom member. Prefabricated steel girder consisting of a bottom pulley and an open top flange. 6. The assembled steel girder according to claim 5, wherein at least the upper surface of the folding member or the upper flange member is further provided with a shear connector. The hollow abdomen according to any one of claims 1 to 3, wherein the prefabricated steel girder is segmented by a fastener including a bolt and a nut in the longitudinal direction, and then can be prefabricated. Prefabricated steel girder with box bottom chord and open top flange. In the bridge construction method of installing a bridge undercarriage including a bridge and a bridge, and installing a girder and a slab on the bridge undercarriage, An abdominal member installed to face each other in a transverse direction and including a plurality of vertical members spaced apart in the longitudinal direction and having a through hole formed at an upper end thereof; A double bottom member connected between the bottom inner side of the abdominal member 110 and installed in the longitudinal direction, the horizontal bottom member including a horizontal plate installed to form a hollow portion S; An upper flange member including an L-shaped steel fastened to the inside and the outside of the upper end of the abdomen member 110 and installed in a longitudinal direction; A foldable member including an L-shaped steel installed inside the upper abdomen member; Slab formwork plate provided between the folding member; An abdominal slope reinforcing member in a diagonal direction between the longitudinally spaced abdominal member and the abdominal member; After fabricating the assembled steel girder including; and the lower reinforcing member spaced in the longitudinal direction so as to connect the upper double bottom member and the lower double bottom member of the double bottom member vertically spaced up and down; Installed in parallel in the longitudinal direction, Further installing slab formwork plate between the outer upper flange member of the assembled steel girder, Bridge construction method using the assembled steel girder, characterized in that the slab is formed by placing the slab concrete so that the upper portion of the abdominal member is embedded in the upper slab formwork plate. 9. The folding member according to claim 8, wherein the double bottom member is composed of an upper and a lower bottom member, and the upper and lower bottom members include an L-shaped steel extending in the longitudinal direction in contact with an abdominal member including the L-shaped steel. Bridge construction method using the assembled steel girder, characterized in that the side end is fastened by a fastener including a bolt and a nut. 10. The bridge construction method according to claim 8 or 9, wherein the assembled steel girder is segmented by a fastener including a bolt and a nut in the longitudinal direction, and then installed in a prefabricated manner.

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