OPENING STEEL COMPOSITE GIRDER AND METHOD FOR

MANUFACTURING THE SAME

Technical Field

[1] The present invention relates to an opening steel composite girder and a method of manufacturing the same, which uses, in consideration of construction field conditions and load sizes, various methods of manufacturing positive and negative moment opening type steel composite girders that can strongly resist against and support a load depending on the bending moment distribution resulting from the load acting on the girder installed on building structures, and selectively connects the positive and negative moment opening type steel composite girders. Background Art

[2] In general, a steel girder or a girder in which prestressing was introduced into concrete were employed for building structures, however, it was not sufficient to rapid cope with situations depending on various loads or field conditions, and in particular, when the girder is applied to the building structure having no posts, there exists a limited span to make it difficult to be applied to the desired structure. Disclosure of Invention Technical Problem

[3] In view of the problems mentioned above, an object of the invention is to provide positive and negative moment opening steel composite girders and a method of manufacturing the same, which employs various methods taking construction field conditions and operation and size of a load into consideration.

[4] The steel composite girders as manufactured above are installed based on the distribution of bending moment acting on the girders, and are assembled to manufacture the opening type steel composite girder.

[5] The opening type steel composite girder is then installed on a structure, and an upper slab is placed thereon to manufacture the structure.

[6] With the girder manufactured above, a girder having a longer span can be manufactured, so that a structure having a larger space can be installed and an amount of steel used can be reduced with the reduced compressive and tensile stresses acting on the girder. Technical Solution

[7] In order to achieve the objects mentioned above, one aspect of the present invention is to provide an opening steel composite girder, which includes: an opening type steel girder including reversed trapezoidal-shaped side steels installed as webs on both sides of the opening type steel girder, a bottom steel welded to a bottom of the side steels, and U-shaped steels or L-shaped steels installed on the respective side steels; positive moment opening type steel composite girders having reinforced bars arranged within the U-shaped steels and cast by concrete to have respective opening type cross- sectional concretes; and a negative moment opening type steel composite girder including the L-shaped steels installed to face each other on the respective side steels with a space between the L-shaped steels being arranged with reinforced bars, anchorages installed at both ends of a longitudinal direction of the opening type steel girder, a prestressed (PS) tendon connected to the anchorages, a closed cross-sectional concrete cast by concrete and prestressed by a prestressed force on the PS tendon, a web and a bottom concrete simultaneously installed by reinforced bars and cast by concrete at inner surfaces of the side steels and the bottom steel of the opening type steel girder, and an end- finished steel plate installed on the web and both ends of the bottom concrete, wherein the positive moment opening type steel composite girder is installed at right and left sides where a positive moment is generated by the distribution having positive and negative bending moments, the negative moment opening type steel composite girder is installed at a central position between the right and left sides, and the positive moment opening type steel composite girder and the negative moment opening type steel composite girder are assembled by means of welding or bolt and nut.

[8] Another aspect of the present invention is to provide a method of manufacturing an opening steel composite girder, which includes: forming an opening type steel girder including reversed trapezoidal- shaped side steels installed as webs on both sides of the opening type steel girder, a bottom steel welded to a bottom of the side steels, and U- shaped steels or L-shaped steels installed on the respective side steels; forming positive moment opening type steel composite girders having reinforced bars arranged within the U-shaped steel and cast by concrete to have respective opening type cross-sectional concrete; and forming a negative moment opening type steel composite girder including L-shaped steels installed to face each other on the respective side steels having reinforced bars installed in a space between the L-shaped steels, anchorages installed at both ends in a longitudinal direction of the opening type steel girder, a prestressed (PS) tendon connected to the anchorages installed at both ends and cast by concrete, a closed cross-sectional concrete prestressed by a prestressed force on the PS tendon, a web and a bottom concrete simultaneously installed by reinforced bars and cast by concrete at inner surfaces of the side steels and the bottom steel of the opening type steel girder, and an end-finished steel plate installed on the web and both ends of the bottom concrete, wherein the positive moment opening type steel composite girder is installed at right and left sides where a positive moment is generated by distribution having positive and negative bending moments, the negative moment opening type steel composite girder is installed at a central position between the right and left sides, and the positive moment opening type steel composite girder and the negative moment opening type steel composite girder are assembled by means of welding or bolt and nut.

Advantageous Effects

[9] According to the present invention, an opening type steel as a steel plate is installed, a U-shaped steel used also as a mold is installed on top of the opening type steel as a web to manufacture an opening type steel girder, reinforced bars are arranged within the U-shaped steel and concrete is cast therein to form U-shaped steel cross-sectional concrete synthesized with the U-shaped steel, thereby manufacturing a positive moment opening type steel composite girder.

[10] In the meantime, an opening type steel as a steel plate is installed, a U-shaped steel used also as a mold is installed on top of the opening type steel as a web to manufacture an opening type steel girder, reinforced bars are arranged within the U- shaped steel and concrete is cast therein to form U-shaped steel cross-sectional concrete synthesized with the U-shaped steel, and concrete is cast on a bottom and both webs or a bottom only of the opening type steel girder, thereby manufacturing a negative moment opening type steel composite girder, or an L-shaped steel is installed on top of the opening type steel as a web to manufacture an opening type steel girder, reinforced bars are arranged within the L-shaped steels facing each other and concrete is cast therein to form closed concrete that is synthesized with the L-shaped steels and is introduced by prestressing, and concrete is cast on a bottom and both webs or a bottom only of the opening type steel girder, thereby manufacturing a negative moment opening type steel composite girder.

[11] The negative moment opening type steel composite girder is installed between the positive moment opening type steel composite girders, which are then assembled together to manufacture the opening type steel composite girder.

[12] The opening type steel composite girder manufactured as described above is synthesized and integrated with steel and concrete so that it can behave in a body.

[13] According to the present invention, a method of manufacturing a steel girder synthesizes the steel with concrete while partially introducing prestressing to the steel girder taking construction field conditions and constructability into consideration to install a structure, so that a magnitude of stress to be applied can be reduced, an amount of steel used can be reduced, the girder having a long span can be installed at a low cost, and the structure can be constructed in more effective, economical, and enhanced constructability manner. Brief Description of the Drawings

[14] FIG. 1 is a diagram illustrating the cross-section of an opening steel composite girder according to an embodiment of the present invention.

[15] FIG. 2 is a diagram illustrating the cross-section taken along line A-A of FIG. 1.

[16] FIG. 3 is a diagram illustrating the cross-section taken along line B-B of FIG. 1.

[17] FIG. 4 is a diagram illustrating the cross-section of an opening type steel composite girder according to another embodiment of the present invention.

[18] FIG. 5 is a diagram illustrating the cross-section taken along line A-A of FIG. 4.

[19] FIG. 6 is a diagram illustrating the cross-section taken along line B-B of FIG. 4.

[20] FIG. 7 is a diagram illustrating the cross-section of an opening steel composite girder according to yet another embodiment of the present invention.

[21] FIG. 8 is a diagram illustrating the cross-section taken along line A-A of FIG. 7.

[22] FIG. 9 is a diagram illustrating the cross-section taken along line B-B of FIG. 7.

[23] FIG. 10 is a diagram illustrating the cross-section of an opening type steel composite girder according to still yet another embodiment of the present invention.

[24] FIG. 11 is a diagram illustrating the cross-section taken along line A-A of FIG. 10.

[25] FIG. 12 is a diagram illustrating the cross-section taken along line B-B of FIG. 10.

[26] FIG. 13 is a diagram illustrating the cross-section of an opening steel composite girder according to another embodiment of the present invention.

[27] FIG. 14 is a diagram illustrating the cross-section taken along line A-A of FIG. 13.

[28] FIG. 15 is a diagram illustrating the cross-section taken along line B-B of FIG. 13.

[29] FIG. 16 is a diagram illustrating the cross-section of an opening steel composite girder according to yet another embodiment of the present invention.

[30] FIG. 17 is a diagram illustrating the cross-section taken along line A-A of FIG. 16.

[31] FIG. 18 is a diagram illustrating the cross-section taken along line B-B of FIG. 16.

Best Mode for Carrying Out the Invention

[32] Hereinafter, configuration and operation of the present invention will be described in detail with reference to accompanying drawings.

[33] FIGS. 1, 4, 7, 10, 13, and 16 are diagrams illustrating the cross-section of an opening steel composite girder manufactured by various manufacturing methods according to the present invention, FIG. 2 is a diagram illustrating the cross-section taken along line A-A of FIG. 1, FIG. 3 is a diagram illustrating the cross-section taken along line B-B of FIG. 1, FIG. 5 is a diagram illustrating the cross-section taken along line A-A of FIG. 4, FIG. 6 is a diagram illustrating the cross-section taken along line B-B of FIG. 4, FIG. 8 is a diagram illustrating the cross-section taken along the line A-A of FIG. 7, FIG. 9 is a diagram illustrating the cross-section taken along the line B-B of FIG. 7, FIG. 11 is a diagram illustrating the cross-section taken along the line A-A of FIG. 10, FIG. 12 is a diagram illustrating the cross-section taken along the line B-B of FIG. 10, FIG. 14 is a diagram illustrating the cross-section taken along the line A-A of FIG. 13, FIG. 15 is a diagram illustrating the cross-section taken along the line B-B of FIG. 13, FIG. 17 is a diagram illustrating the cross-section taken along the line A-A of FIG. 16, and FIG. 18 is a diagram illustrating the cross-section taken along the line B-B of FIG. 16.

[34] First, reversed trapezoidal-shaped side steels 21 formed of a steel plate are installed as webs on both sides of an opening type steel girder 20, a bottom steel 22 as a steel plate is welded to a bottom of the side steels 21, and a U-shaped steel 23 or an L- shaped steel 25 is installed on the side steels 21, thereby manufacturing the opening type steel girder 20.

[35] U-shaped steels 23 are installed on top of the respective side steels 21 acting as the webs in the opening type steel girder 20, reinforced bars are arranged within the U- shaped steels 23 and concrete is cast therein to form opening type cross-sectional concretes 24 integrated and synthesized with the U-shaped steels 23, reinforcedd bars (not shown), and concrete, thereby manufacturing a positive moment opening type steel composite girder 30.

[36] In the meantime, the U-shaped steels 23 are installed on top of the respective side steels 21 acting as the webs of the opening type steel girder 20, reinforced bars are arranged within the U-shaped steels 23 and concrete is cast therein to form the opening type cross-sectional concretes 24 integrated and synthesized with the U-shaped steels 23 and reinforced bars, concrete is cast on both webs and a bottom or a bottom only of the opening type steel girder 20 to install a web 41 and a bottom concrete 42 or to install the bottom concrete 42 only, thereby manufacturing a negative moment opening type steel composite girder 40, or L-shaped steels 25 facing each other are installed on top of the respective side steels 21 acting as the webs of the opening type steel girder 20, reinforced bars are arranged between the L-shaped steels 25, a PS tendon 12 is installed to be connected to the anchorage 13 installed at both ends of the longitudinal direction of the opening type steel girder 20, concrete is cast and cured therein, a prestressed force is introduced into the PS tendon 12 to introduce prestressing into the closed cross-sectional concrete 43, reinforced bars are arranged within inner surfaces of the bottom steel 22 and the side steels 21 of the opening type steel girder 20 and concrete is cast therein to simultaneously form the web 41 and the bottom concrete 42 or the bottom concrete 42 only, thereby manufacturing the negative moment opening type steel composite girder 40.

[37] The positive moment opening type steel composite girders 30 as manufactured above are installed at right and left sides where a positive moment is generated by the distribution having positive and negative bending moments resulting from the load usually acting on a girder, the negative moment opening type steel composite girder 40 is installed at a central position where a negative moment is generated between the right and left sides, and the positive moment opening type steel composite girders 30 and the negative moment opening type concrete steel girder 40 are assembled by means of welding or bolt and nut, thereby manufacturing the opening type steel composite girder 10.

[38] Hereinafter, the steel composite girder manufactured by various methods will be described.

[39] Reversed trapezoidal-shaped side steels 21 formed of a steel plate are installed as webs on both sides of the opening type steel girder 20, the bottom steel 22 as a steel plate is welded to a bottom of the side steels 21, and the U-shaped steel 23 or the L- shaped steel 25 is installed on the side steels 21 acting as the webs, thereby manufacturing the opening type steel girder 20.

[40] When the U-shaped steels 23 are installed on top of the respective side steels 21 in the opening type steel girder 20, reinforced bars are arranged within the U-shaped steels 23 and concrete is cast therein to form the opening type cross-sectional concretes 24 integrated and synthesized with the U-shaped steels 23, reinforcedd bars (not shown), and concrete, thereby manufacturing the positive moment opening type steel composite girder 30.

[41] In the meantime, the L-shaped steels 25 facing each other are installed on top of the respective side steels 21 acting as the webs of the opening type steel girder 20, reinforced bars are arranged between the L-shaped steels 25, the PS tendon 12 is installed to be connected to the anchorage 13 installed at both ends of the longitudinal direction of the opening type steel girder, concrete is cast and cured therein, a prestressed force is introduced into the PS tendon 12 to introduce prestressing into the closed cross-sectional concrete 43, reinforced bars are arranged within inner surfaces of the bottom steel 22 and the side steels 21 of the opening type steel girder 20 and concrete is cast therein to simultaneously form the web 41 and the bottom concrete 42, and the end-finished steel plate 44 is installed on the web and the bottom concrete end, thereby manufacturing the negative moment opening type steel composite girder 40.

[42] The positive moment opening type steel composite girders 30 as manufactured above are installed at right and left sides where a positive moment is generated by the distribution having positive and negative bending moments resulting from the load usually acting on a girder, the negative moment opening type steel composite girder 40 is installed at a central position where a negative moment is generated between the right and left sides, and the positive moment opening type steel composite girders 30 and the negative moment opening type concrete steel girder 40 are assembled by means of welding or bolt and nut, thereby manufacturing the opening type steel composite girder 10.

[43] After the opening type steel composite girder 10 is placed on the structure, reinforced bars are arranged and concrete is cast thereon, and an upper slab 11 is installed to install the structure, which is shown in FIGS. 1 to 3.

[44] The positive moment opening type steel composite girder 30 is characterized in that the U-shaped steels 23 also used as the mold are installed on top of the respective side steels 21 acting as the webs to form the opening type cross-sectional concrete 24 therein, which acts to enhance the coupling force with the upper slab 11 while strengthening the force of supporting the side steels 21.

[45] In addition, the negative moment opening type steel composite girder 40 is characterized in that the negative moment opening type steel composite girder is also used as the mold and allows the closed cross-sectional concrete 41 to be installed between adjacent L-shaped steels 25, introduces prestressing into the closed cross-sectional concrete 41, and allows concrete to be cast within the side steels 21 and the bottom steel 22 to form the web 41 and the bottom concrete 42 for resisting more against the negative moment.

[46] A method of introducing prestressing into the closed cross-sectional concrete 43 employs a method of introducing a prestressed force into the PS tendon 12, and casting and curing the closed cross-sectional concrete to introduce the prestressing, or a method of installing a sheath, casting and curing the closed cross-sectional concrete, and prestressing the PS tendon installed within the sheath that is already installed to introduce the prestressing.

[47] The end-finished steel plate 44 installed on the bottom and the end of the side concrete acts to enhance the synthetic force between the concrete and the steel girder.

[48] In addition, the end-finished steel plate may act to allow the anchorage to be installed on the end of the girder.

[49] The steel girder 10 manufactured by another method is shown in FIGS. 4 to 6.

[50] Reversed trapezoidal-shaped side steels 21 formed of a steel plate are installed as webs on both sides of an opening type steel girder 20, a bottom steel 22 as a steel plate is welded to a bottom of the side steels 21, and a U-shaped steel 23 or an L-shaped steel 25 is installed on the side steels 21 acting as the webs, thereby manufacturing the opening type steel girder 20.

[51] U-shaped steels 23 are installed on top of the respective side steels 21 acting as the webs in the opening type steel girder 20, reinforced bars are arranged within the U- shaped steels 23 and concrete is cast therein to form opening type cross-sectional concretes 24 integrated and synthesized with the U-shaped steels 23, reinforcedd bars (not shown), and concrete, thereby manufacturing a positive moment opening type steel composite girder 30. [52] In the meantime, the L-shaped steels 25 facing each other are installed on top of the respective side steels 21 acting as the webs of the opening type steel girder 20, reinforced bars are arranged between the L-shaped steels 25, anchorages 13 are installed at both ends of the longitudinal direction of the girder, concrete is cast therein, a prestressed force is introduced into the PS tendon 12 to introduce prestressing into the closed cross-sectional concrete 43, reinforced bars are arranged within inner surfaces of the bottom steel 22 of the opening type steel girder 20 and concrete is cast therein to form the bottom concrete 42, and the end-finished steel plate 44 is installed on both ends of the installed bottom concrete, thereby manufacturing the negative moment opening type steel composite girder 40.

[53] The positive moment opening type steel composite girders 30 as manufactured above are installed at right and left sides where a positive moment is generated by the distribution having positive and negative bending moments resulting from the load usually acting on a girder, the negative moment opening type steel composite girder 40 is installed at a central position where a negative moment is generated between the right and left sides, and the positive moment opening type steel composite girders 30 and the negative moment opening type concrete steel girder 40 are assembled by means of welding or bolt and nut, thereby manufacturing the opening type steel composite girder 10.

[54] After the opening type steel composite girder 10 is placed on the structure, reinforced bars are arranged and concrete is cast thereon, and an upper slab 11 is installed to install the structure.

[55] The positive moment opening type steel composite girder 30 is characterized in that the U-shaped steels 23 also used as the mold are installed on top of the respective side steels 21 to form the opening type cross-sectional concrete 24 therein, which acts to enhance the coupling force with the upper slab 11 while strengthening the force of supporting the side steels 21.

[56] In the meantime, the negative moment opening type steel composite girder 40 is characterized in that the closed cross-sectional concrete 41 also acting as a mold is installed between adjacent L-shaped steels 25, prestressing is introduced into the closed cross-sectional concrete 41, and concrete is cast within the inner bottom to form the bottom concrete 42 for resisting more against the negative moment.

[57] The girder 10 is employed for a lighter load when the stiffness is weak than the girder manufactured as shown in FIG. 1.

[58] A method of introducing prestressing into the closed cross-sectional concrete 43 employs a method of introducing a prestressed force into the PS tendon, and casting and curing the closed cross-sectional concrete to introduce the prestressing, or a method of installing a sheath, casting and curing the closed cross-sectional concrete, and prestressing the PS tendon installed within the sheath that is already installed to introduce the prestressing.

[59] The end- finished steel plate installed on the end of the bottom concrete acts to enhance the synthetic force between the concrete and the steel girder.

[60] In addition, the end-finished steel plate may act to allow the anchorage to be installed on the end of the girder.

[61] The steel girder 10 manufactured by another method is shown in FIGS. 7 to 9.

[62] Reversed trapezoidal-shaped side steels 21 formed of a steel plate are installed as webs on both sides of an opening type steel girder 20, a bottom steel 22 as a steel plate is welded to a bottom of the side steels 21, and a U-shaped steel 23 is installed on the side steels 21 acting as the webs, thereby manufacturing the opening type steel girder 20.

[63] U-shaped steels 23 are installed on top of the respective side steels 21 acting as the webs in the opening type steel girder 20, reinforced bars are arranged within the U- shaped steels 23 and concrete is cast therein to form opening type cross-sectional concretes 24 integrated and synthesized with the U-shaped steels 23, reinforcedd bars (not shown), and concrete, thereby manufacturing a positive moment opening type steel composite girder 30.

[64] In the meantime, the U-shaped steels 23 are installed on top of the respective side steels 21 acting as the webs of the opening type steel girder 20, reinforced bars are arranged between the U-shaped steels 23 and concrete is cast therein to form opening type cross-sectional concretes 24 integrated and synthesized with the U-shaped steels 23, reinforcedd bars (not shown), and concrete, reinforced bars are arranged within inner surfaces of the side steels 21 and the bottom steel 22 of the opening type steel girder 20 to simultaneously install the web 41 and the bottom concrete 42, and end- finished steel plates 44 are installed at both ends of bottom concrete 42 and the web 41, thereby manufacturing the negative moment opening type steel composite girder 40.

[65] The positive moment opening type steel composite girders 30 as manufactured above are installed at right and left sides where a positive moment is generated by the distribution having positive and negative bending moments resulting from the load usually acting on a girder, the negative moment opening type steel composite girder 40 is installed at a central position where a negative moment is generated between the right and left sides, and the positive moment opening type steel composite girders 30 and the negative moment opening type concrete steel girder 40 are assembled by means of welding or bolt and nut, thereby manufacturing the opening type steel composite girder 10.

[66] After the opening type steel composite girder 10 as manufactured above is installed on the structure, anchorages 13 are installed at both ends of the longitudinal direction of the negative moment opening type concrete steel girder 40 installed where the negative moment occurs, the PS tendon 12 is connected to the anchorages, concrete is cast on the positive and negative moment opening type steel composite girders 30 and 40 to install the upper slab 11, and a prestressed force is introduced into the PS tendon connected to the anchorages for introducing prestressing into the upper slab.

[67] The positive moment opening type steel composite girder 30 is characterized in that the U-shaped steels 23 also used as the mold are installed on top of the respective side steels 21 acting as the webs to form the opening type cross-sectional concrete 24 therein, which acts to enhance the coupling force with the upper slab 11 while strengthening the force of supporting the side steels 21.

[68] In the meantime, the negative moment opening type steel composite girder 40 is characterized in that the closed cross-sectional concrete 41 also acting as a mold is installed in the positive moment opening type steel composite girder 30, concrete is cast at an inner side surface and a bottom of the opening type steel girder 20 to install the web 41 and the bottom concrete 42, and prestressing is introduced only into the upper slab 11 when the upper slab 11 is installed on top of the negative moment opening type steel girder 40 for resisting more against the negative moment.

[69] The magnitude of the girder stiffness lies at a medium value between those of the girders described above, and the magnitude of the load is also employed for the structure taking the substantially medium value of the load.

[70] The end- finished plate installed on the side and the end of the bottom concrete acts to enhance the synthetic force between the concrete and the steel girder.

[71] In addition, the end- finished steel plate may act to allow the anchorage to be installed on the end of the girder.

[72] The steel girder 10 manufactured by another method is shown in FIGS. 10 to 12.

[73] Reversed trapezoidal-shaped side steels 21 formed of a steel plate are installed as webs on both sides of an opening type steel girder 20, a bottom steel 22 as a steel plate is welded to a bottom of the side steels 21, and a U-shaped steel 23 is installed on the side steels 21 acting as the webs, thereby manufacturing the opening type steel girder 20.

[74] U-shaped steels 23 are installed on top of the respective side steels 21 acting as the webs in the opening type steel girder 20, reinforced bars are arranged within the U- shaped steels 23 and concrete is cast therein to form opening type cross-sectional concretes 24 integrated and synthesized with the U-shaped steels 23, reinforcedd bars (not shown), and concrete, thereby manufacturing a positive moment opening type steel composite girder 30.

[75] In the meantime, the U-shaped steels 23 are installed on top of the respective side steels 21 acting as the webs of the opening type steel girder 20, reinforced bars are arranged between the U-shaped steels 23 and concrete is cast therein to form opening type cross-sectional concretes 24 integrated and synthesized with the U-shaped steels 23, reinforcedd bars (not shown), and concrete, reinforced bars are arranged within inner surfaces of the bottom steel 22 of the opening type steel girder 20 to install the bottom concrete 42, and end-finished steel plates 44 are installed at both ends of bottom concrete 42, thereby manufacturing the negative moment opening type steel composite girder 40.

[76] The positive moment opening type steel composite girders 30 as manufactured above are installed at right and left sides where a positive moment is generated by the distribution having positive and negative bending moments resulting from the load usually acting on a girder, the negative moment opening type steel composite girder 40 is installed at a central position where a negative moment is generated between the right and left sides, and the positive moment opening type steel composite girders 30 and the negative moment opening type concrete steel girder 40 are assembled by means of welding (not shown) or bolt and nut, thereby manufacturing the opening type steel composite girder 10.

[77] After the opening type steel composite girder 10 as manufactured above is installed on the structure, anchorages 13 are installed at both ends of the longitudinal direction of the negative moment opening type concrete steel girder 40 installed where the negative moment occurs, the PS tendon 12 is connected to the anchorages, concrete is cast on the positive and negative moment opening type steel composite girders 30 and 40 to install the upper slab 11, and a prestressed force is introduced into the PS tendon 12 connected to the anchorages for introducing prestressing into the upper slab.

[78] The positive and negative moment opening type steel composite girders 30 and 40 are characterized in that the U-shaped steels 23 are installed on the side steels 21 also acting as the mold to install the opening cross-sectional concrete 24, which acts to enhance the coupling force with the upper slab 11 while strengthening the force of supporting the side steels 21.

[79] The negative moment opening type steel composite girder 40 is such that concrete is cast on the inner bottom of the opening type steel girder 20 to form the bottom concrete 42, and prestressing is introduced only to the upper slab 11 positioned on the negative moment opening type steel composite girder 40 for resisting against the negative moment when the upper slab 11 is installed.

[80] The magnitude of the girder stiffness lies at a medium value between those of the girders described above, and the magnitude of the load is also employed for the structure taking the substantially medium value of the load in consideration of the con- structability.

[81] The end- finished plate installed on the end of the bottom concrete acts to enhance the synthetic force between the concrete and the steel girder.

[82] Another steel girder according to another embodiment is shown in FIGS. 13 to 15.

[83] The steel girder is characterized in that it further includes a positive moment high- intensity added concrete 31 integrated on the opening type cross-sectional concrete 24 of the positive moment opening type steel composite girder 30 manufactured as shown in FIGS. 1 to 3, and a negative moment high-intensity added concrete 45 integrated on the bottom concrete 42 of the negative moment opening type steel composite girder 40.

[84] A manufacturing method will now be described as follows.

[85] Reversed trapezoidal-shaped side steels 21 formed of a steel plate are installed as webs on both sides of an opening type steel girder 20, a bottom steel 22 as a steel plate is welded to a bottom of the side steels 21, and a U-shaped steel 23 or an L-shaped steel 25 is installed on the side steels 21 acting as the webs, thereby manufacturing the opening type steel girder 20.

[86] U-shaped steels 23 are installed on top of the respective side steels 21 acting as the webs in the opening type steel girder 20, reinforced bars are arranged within the U- shaped steels 23 and concrete is cast therein to form opening type cross-sectional concretes 24 integrated and synthesized with the U-shaped steels 23, reinforcedd bars (not shown), and concrete, and the positive moment high-intensity added concrete 31 having a predetermined height is integrated and installed thereon, thereby manufacturing a positive moment opening type steel composite girder 30.

[87] In the meantime, when the L-shaped steel 25 is installed on top of the side steels 21 acting as the webs of the opening type steel girder 20, reinforced bars are arranged between the L-shaped steels 25 facing each other on the side steels 21, anchorages 13 are installed at both ends of the longitudinal direction of the girder, the PS tendon 12 is connected to the anchorages 13 and concrete is cast therein, a prestressed force is introduced into the PS tendon 12 to install the closed cross-sectional concrete 43 with the prestressing, reinforced bars are arranged at inner surfaces of the bottom steel 22 and the side steels of the opening type steel girder 20 and concrete is cast therein to simultaneously install the web 41 and the bottom concrete 42, the negative moment high-intensity added concrete 45 having a predetermined height is integrated with and on the bottom concrete 42, and the end- finished steel plate 44 is installed at both ends of the bottom concrete and the web, thereby manufacturing the negative moment opening type steel composite girder 40.

[88] The positive moment opening type steel composite girders 30 as manufactured above are installed at right and left sides where a positive moment is generated by the distribution having positive and negative bending moments resulting from the load usually acting on a girder, the negative moment opening type steel composite girder 40 is installed at a central position where a negative moment is generated between the right and left sides, and the positive moment opening type steel composite girders 30 and the negative moment opening type concrete steel girder 40 are assembled by means of welding or bolt and nut, thereby manufacturing the opening type steel composite girder 10.

[89] After the manufactured opening type steel composite girder 10 is placed on the structure, reinforced bars are arranged thereon and concrete is cast to install the upper slab 11 so that the structure is installed.

[90] The positive and negative moment opening type steel composite girders 30 and 40 are characterized in that the positive moment high-intensity added concrete and the negative moment high-intensity added concrete are additionally installed on the steel girders manufactured as shown in FIGS. 1 to 3.

[91] Additionally installing the high-intensity added concretes acts to prevent the steel girder installed on the structure from being deformed due to the load acting on the girder as much as possible, and also acts to exert stronger resistance when the high- intensity added concretes are integrated with the upper slab to be installed later.

[92] A method of introducing prestressing into the closed cross-sectional concrete employs a method of introducing a prestressed force into the PS tendon, and casting and curing the closed cross-sectional concrete to introduce the prestressing, or a method of installing a sheath, casting and curing the closed cross-sectional concrete, and prestressing the PS tendon installed within the sheath that is already installed to introduce the prestressing.

[93] The end-finished plate installed on the side and the end of the bottom concrete acts to enhance the synthetic force between the concrete and the steel girder.

[94] In addition, the end-finished steel plate may act to allow the anchorage to be installed on the end of the girder.

[95] The steel girder 10 manufactured by another method is shown in FIGS. 16 to 18.

[96] The steel girder is characterized in that side corrugated steels 51 are employed to make the side steels acting as the webs of the steel girders manufactured as shown in FIGS. 1 to 3 become the opening type corrugated steel girder 50, the PS tendon 12 is installed within the bottom concrete 42 of the positive moment opening type steel composite girder 30, and a prestressed force is introduced to allow prestressing to be introduced into the bottom concrete.

[97] A manufacturing method will now be described as follows.

[98] Reversed trapezoidal-shaped side steels formed of a corrugated steel plate are installed as side corrugated steels 51 acting as webs on both sides of an opening type corrugated steel girder 50, a bottom steel 22 as a steel plate is welded to a bottom of the side steels 51, and a U-shaped steel 23 or an L-shaped steel 25 is installed on the side corrugated steels 51, thereby manufacturing the opening type corrugated steel girder 50.

[99] The U-shaped steels 23 are installed on top of the side corrugated steels 51 acting as the webs in the opening type corrugated steel girder 50, reinforced bars are arranged within the U-shaped steels 23 and concrete is cast to install the opening cross-sectional concrete 24 integrated and synthesized with the U-shaped steels 23, reinforced bars (not shown), and concrete, anchorages 13 are installed at both ends of the opening type corrugated steel girder 50, the PS tendon 12 is connected to the anchorages, concrete is cast on the bottom steel 22 to form the bottom concrete 42, a prestressed force is introduced into the PS tendon 12 for introducing prestressing into the bottom concrete 42, thereby manufacturing the positive moment opening type steel girder 30.

[100] In the meantime, the L-shaped steels 25 facing each other are installed on top of the respective side corrugated steels 51 acting as the webs of the steel girder 20, reinforced bars are arranged between the L-shaped steels 25 facing each other on the side corrugated steels 51, anchorages 13 are installed at both ends of the longitudinal direction of the girder, the PS tendon 12 is connected to the anchorages, concrete is cast therein, a prestressed force is introduced into the PS tendon 12 to form the closed cross-sectional concrete 42 with the prestressing, reinforced bars are arranged within inner surfaces of the bottom steel 22 and the side steels 21 of the opening type steel girder 20 and concrete is cast therein to simultaneously form the web 41 and the bottom concrete 42, and the end- finished steel plate 44 is installed on both ends of the installed bottom concrete and the web, thereby manufacturing the negative moment opening type steel composite girder 40.

[101] The positive moment opening type steel composite girders 30 as manufactured above are installed at right and left sides where a positive moment is generated by the distribution having positive and negative bending moments resulting from the load usually acting on a girder, the negative moment opening type steel composite girder 40 is installed at a central position where a negative moment is generated between the right and left sides, and the positive moment opening type steel composite girders 30 and the negative moment opening type concrete steel girder 40 are assembled by means of welding or bolt and nut, thereby manufacturing the opening type steel composite girder 10.

[102] After the manufactured opening type steel composite girder 10 is placed on the structure, reinforced bars are arranged thereon and concrete is cast to install the upper slab 11 so that the structure is installed.

[103] In order to prevent the steel girder manufactured using the corrugated steel as the side steel from being deformed while strengthening the resistance, concrete is cast on the bottom steel of the positive moment opening type steel girder to form the bottom concrete where prestressing is introduced, and concrete is cast into the negative moment opening type steel composite girder to cast the web and the bottom concrete.

[104] A method of introducing prestressing into the closed cross-sectional concrete employs a method of introducing a prestressed force into the PS tendon, and casting and curing the closed cross-sectional concrete to introduce the prestressing, or a method of installing a sheath, casting and curing the closed cross-sectional concrete, and prestressing the PS tendon installed within the sheath that is already installed to introduce the prestressing.

[105] The end- finished steel plate installed at the side and the end of the bottom concrete acts to enhance a synthetic force between concrete and steel.

[106] In addition, the end- finished steel plate may act to allow the anchorage to be installed at an end of the girder.