Title of Invention	MANUFACTURING METHOD FOR PRESTRESSED STEEL COMPOSITE GIRDER AND PRESTRESSED STEEL COMPOSITE GIRDER THEREBY
Abstract	A prestressed steel composite girder and a method of manufacturing the prestressed steel composite girder are provided by using a steel beam and a concrete. The method includes steps of: placing the steel beam above the ground; installing a form, into which the concrete is to be inserted, to surround at least a portion of the steel beam, the form being suspended by the steel beam; inserting the concrete into an internal space of the form and curing it; and removing the form to compose the steel beam and the concrete. The prestressed steel composite girder includes a steel beam and a concrete composed to surround a portion of the steel beam so that stress caused by its self-weight can be applied on only the steel beam.

Title of Invention

MANUFACTURING METHOD FOR PRESTRESSED STEEL COMPOSITE GIRDER AND PRESTRESSED STEEL COMPOSITE GIRDER THEREBY

Abstract

A prestressed steel composite girder and a method of manufacturing the prestressed steel composite girder are provided by using a steel beam and a concrete. The method includes steps of: placing the steel beam above the ground; installing a form, into which the concrete is to be inserted, to surround at least a portion of the steel beam, the form being suspended by the steel beam; inserting the concrete into an internal space of the form and curing it; and removing the form to compose the steel beam and the concrete. The prestressed steel composite girder includes a steel beam and a concrete composed to surround a portion of the steel beam so that stress caused by its self-weight can be applied on only the steel beam.

Full Text	WO 2006/065085 PCT/KR2005/004320 MANUFACTURING METHOD FOR PRESTRESSED STEEL COMPOSITE GIRDER AND PRESTRESSED STEEL COMPOSITE GIRDER THEREBY BACKGROUND OF THE INVENTION (a) Field of the Invention The present invention relates to a method of manufacturing a prestressed steel composite girder having a lower flange of the steel girder reinforced with concrete, and a steel composite girder manufactured using the same, and more particularly, to a method of manufacturing a prestressed steel composite girder for previously introducing compressive prestress on concrete in order to compensate for tensile stress generated during common use and a steel composite girder manufactured using the same. (b) Description of the Related Art Generally, it is known in the art that concrete is resistant to compressive stress but not resistant to tensile stress. A prestressed steel composite girder has been designed to compensate for the tensile stress generated when applying live and dead loads for the compressive prestress. Conventional engineering methods for previously introducing compressive stress to concrete to provide a resistive cross-section can be classified into the following three kinds of technologies depending on a method of introducing the compressive prestress and material composition for the resistive cross-section. First, as a most common and fundamental engineering method for introducing the compressive prestress into a concrete by using only tension (i.e., a prestress force) of a tendon, a prestressed concrete (PSC) beam has been known in the art. In a conventional PSC beam engineering method, a resistant force is given to the concrete by artificially estimating stress distribution and strength and adopting a high strength steel (generally referred to as a tendon) for compensating for the tensile stress generated by an external force up to a certain point. In order to overcome mechanical shortcomings of the conventional PSC beam, in other words, in order to increase resistance strength for a tension crack that can occur in an upper surface of the beam cross-section when introducing tension 1 WO 2006/065085 PCT/KR2005/004320 and reduce the height of the beam with respect to the same effective span, another improved technology has been proposed in a Korean unexamined patent application publication No. 10-2004-0058542, entitled "A Prestressed Steel Reinforced Concrete Unit Beam and Manufacturing Method Thereof". In this technology, a T-shaped steel plate is inserted into upper and lower flanges of the conventional prestressed concrete beam. Specifically, steel strands are provided in sheath pipes installed in the steel assembly, and the T-shaped steel plates are provided on the upper and lower flanges, a guide pipe is provided in the T-shaped steel plate installed in the center of the lower flange, steel strands are further provided in the guide pipe, the guide pipe is jointed with a lower reinforcing plate installed under the T shape steel plate using nuts to integrate and fix it, and then, the concrete is placed and cured. Lastly, the steel strands are settled on both ends of the beam after a prestress force is introduced into the steel strands. Unlike the aforementioned PSC beam or the prestressed steel reinforced concrete unit beam, a structure in which die steels are inserted into a cross-section of the concrete has been proposed in a Korean unexamined patent application publication No. 10-2004-0004197, entitled "Composite Beam Stiffened with Prestressed Concrete Panel Having Embedded Lower Flange and Multi-stepped Jacking Structure", wherein this structure is generally referred to as an MSP structure in the art. In this structure, unlike the aforementioned technologies, a precasted concrete panel composite beam is made by combining a steel beam with a precasted concrete panel. Specifically, a protrusion is provided on an upper surface of the precasted concrete panel to bury the lower flange of the steel beam; first and second tendons are provided on the precasted concrete panel, wherein the first tendon is disposed on left and right sides of a position where the protrusion is provided under the center axis of the precasted concrete panel near the center axis, and the second tendon is spaced far from the center axis of the composite cross- section after integrated under the protrusion; the first tendon is firstly prestressed before the lower flange of the steel beam is positioned in the protrusion of the precasted concrete panel, and then, secondly prestressed after the steel beam is disposed on the protrusion and second concrete is placed in the protrusion, so that compressive stress is also applied to the second concrete by introducing the second 2 WO 2006/065085 PCT/KR2005/004320 prestress; the second tendon is thirdly prestressed and settled in the state that the self-weights of the steel beam and the panel is reflected on the entire load after the steel beam is combined with the precasted concrete panel, so that third prestress can be applied on the panel and additionally applied to the second concreted. A second conventional technology is to introduce the compressive prestress into concrete only by a recovery force of the steel beam. This technology stems from a Belgian engineering method invented in 1950's, and is frequently adopted in the Northeast Asia. The resultant girder manufactured by this technology is called "a preflex beam" in the art. In this technology, while slope deflection is generated by applying a predetermined load on the steel girder, concrete is placed on the lower flange of the steel girder and cured. The compressive prestress is introduced into the lower flange concrete in the process of releasing the slope deflection by removing the load on the steel girder (i.e., a releasing process). A third conventional technology is to introduce the compressive prestress into the concrete by using both the recovery force of the steel beam and the tension of the tendon. The resultant girder manufactured by this technology is call "a re- prestressed preflex (RPF) girder" in the art as disclosed in Korean Patent Publication No. 10-024084. In this technology, the RPF steel complex girder is manufactured by placing the concrete in the lower flange and cured with the preflexion load applied to the steel girder as the aforementioned preflex girder and then introducing the second prestress into the lower flange concrete using the tension of the tendon in the state that the compressive prestress is initially introduced by the recovery force of the steel beam. Specifically, this technology relates to a method of manufacturing a re-prestressed steel composite beam, in which a load generating bending moment having a predetermined strength (i.e., a Pf load) is previously applied to an I-shaped beam; a concrete is placed in the lower flange of the beam and cured, the previously applied load (Pf) is removed to introduce first compressive prestress into the lower flange concrete; and second compressive prestress is introduced by a tendon installed in the lower flange concrete, wherein unbonded strands are used as the tendon; a plurality of strands are disposed with a constant interval in upper and/or lower portions of the lower flange and installed 3 WO 2006/065085 PCT/KR2005/004320 in the lower flange concrete before concrete is placed in the lower flange of the beam and cured; after the lower flange concrete is cured, the strands are installed in a prestressed state using a compressive strength of 450 kgf/cm, so that the lower flange concrete is perfectly prestressed. In the aforementioned conventional methods (i.e., the aforementioned PSC beam or the prestressed steel reinforced concrete unit beam) for previously introducing compressive prestress to constitute a resistance cross-section, although they have a cross-section consisting of reinforced bars, a high rigidity of concrete, and tendons, and allow a more economical construction in comparison with other conventional methods for manufacturing a composite beam with the I-shaped beam installed in its cross-section, they may be limited by the height of the beam and particularly, by the effective span due to a structural limitation that the self-weight is dominant among external forces applied to the cross-section. Therefore, the bridges based on the aforementioned methods are applicable to constructions having an effective span more or less than 30m, and particularly, to constructions not limited by overhead clearance or discharge capacity. In order to compensate for the limitation of the height of the beam or the effective span, a steel composite beam adopting both advantages of a high rigidity of concrete as well as the I-shaped beam has been proposed. Among aforementioned engineering methods, the preflex girder and the re-prestressed preflex steel composite girder (RPF) correspond to such a thing. However, in these engineering methods, since the compressive stress for the concrete surrounding the steel beam is introduced using a recovery force of the steel beam, the upper and lower flanges of the beam must be enlarged. Also, additional processes and costs should be prepared for the preflexion and release. Further, since large bending deformation occurs in the beam during the manufacturing process, it is very difficult to manage a camber of a finally manufactured product. Particularly, in the aforementioned preflex beam, since a typical steel beam is used to introduce compressive stress, such a composite cross-section is vulnerable to creep of the concrete. In other words, the concrete experiences creep deformation as time goes by, and the compressive prestress introduced in the manufacturing process is lost due to deformation confinement of the concrete composite beam. Meanwhile, in 4 WO 2006/065085 PCT/KR2005/004320 the preflex girder, since the prestress is applied to the concrete by dominantly using the recovery force of the steel beam, the area of the lower flange should be large. Therefore, loss of the compressive prestress resulted from dry shrinkage deformation and creep deformation in the concrete becomes big problems in the art. Also, construction may become difficult and its cost may increase because an amount of shear connections should be provided for the lower flange of the steel girder. In order to compensate for the shortcomings of the preflex girder from the view point of a long-time behavior, a re-prestressed preflex steel composite beam (RPF) has been developed. In this technology, secondary prestress is further applied to the conventional preflex girder. As a result, it is possible to compensate for an amount of creep loss generated during a suspending period until the preflex girder is installed in a bridge or a building, and to apply sufficient prestress to the lower concrete. Also, it is possible to reduce the size of the flange of the beam due to a tendon. However, similar to the conventional preflex girder, cumbersome processes such as preflexion and release should be also applied to the RPF girder. In addition, a prestress process using a tendon should be further applied. As a result, manufacturing cost is never reduced. Although a secondary prestress process using a tendon can be performed just before the girder is installed in a target structure, a primary prestress process is introduced in a release process. Therefore, similar to the conventional preflex girder, the creep loss is inevitably generated during a suspending period. In addition, problems of the conventional preflex girder, such as relating to a number of shear connections and camber management, still exist. Recently, a multi-stage prestressed (MSP) precasted concrete panel composite girder having a lower flange buried in a single connection structure has been developed in order to overcome problems caused by introducing compressive stress into the concrete using an elastic force of the steel beam. However, although this engineering method solves problems of the conventional technologies, its construction is very complicated. Therefore, construction cost increases, and particularly, quality control becomes very difficult because it has a construction joint in lower casing concrete. 5 WO 2006/065085 PCT/KR2005/004320 In addition, all the aforementioned conventional methods of manufacturing steel composite girders have a structural problem that the stress caused by the self-weight of the steel composite girder (including a self-weight of an I-shaped beam and a self-weight of the concrete) acts as tensile stress of the lower flange concrete. This fact means that additional stress for compensating for the tensile stress caused by the self-weight of the composite girder should be previously introduced before the compressive stress caused by bending deformation in the steel beam or tension of the tendon is introduced. Furthermore, in all the aforementioned conventional steel composite girders, since the concrete experiences a predetermined strength of compressive stress during they are suspended in a bridge or a abutment before a slab is composed, compressive stress loss caused by the creep deformation is inevitable as time goes by. SUMMARY OF THE INVENTION The present invention has been made to solve the aforementioned problems, and an object of the present invention is to provide a method of manufacturing a prestressed steel composite girder allowing stress caused by the self-weight of the girder to be applied to a steel beam and not to be applied to the concrete, and a steel composite girder manufactured using the same. In other words, the present invention provides a method of manufacturing a prestressed steel composite girder, in which the stress caused by the self-weight of the concrete is not generated in a cross-section of the concrete by allowing the self- weight of the concrete positioned around the lower flange of the steel beam to be supported by only the steel beam, and loss of compressive stress caused by creep deformation of the concrete can be minimized by previously introducing compressive stress into the concrete before it is placed on a bridge or an abutment, and a steel composite girder manufactured using the same. According to an aspect of the present invention, there is provided a method of manufacturing a prestressed steel composite girder by using a steel beam and a concrete, the method comprising steps of: placing the steel beam above the ground; installing a form, into which the concrete is to be inserted, to surround at 6 WO 2006/065085 PCT/KR2005/004320 least a portion of the steel beam, the form being suspended by the steel beam; inserting the concrete into an internal space of the form and curing it; and removing the form to compose the steel beam and the concrete. In the above aspect, the method may further comprises steps of: installing a reinforcement bar and a sheath pipe for inserting a tendon in the steel beam before placing the concrete and curing it; and introducing compressive prestress into the concrete by tensioning the tendon in the sheath pipe after composing the concrete. In addition, in the installation of the sheath pipe, the steel beam may be an I-shaped beam comprising an upper flange, a lower flange, and a web; and the sheath pipe may be arranged around the lower flange of the steel beam along a length of the steel beam. In addition, in the installation of the sheath pipe, the sheath pipe may be extended in a parabolic shape via the web adjacent to a support and a circumference of the lower flange in the center of the steel beam. In addition, in the placing the steel beam above the ground, the steel beam may be supported at both ends thereof. In addition, the steel beam may be suspended by a beam-suspending end supports disposed at both ends of the steel beam. In addition, an intermediate support may be further provided between the beam-suspending end supports to avoid lateral buckling or swaying of the steel beam. In addition, the reinforcement bar and the form may surround the lower flange of the steel beam. In addition, the reinforcement bar and the form may surround the lower flange and the web of the steel beam. In addition, the reinforcement bar and the form may surround the entire steel beam. In addition, the method may further comprise: placing a weighting member on an upper surface of the steel beam to generate positive moment on the steel beam before composing the concrete and the steel beam; and removing the weight member after composing the steel beam and the concrete, thereby introducing compressive prestress into the concrete. In addition, the steel composite girder may be segmented into more than three segments, the segments of the steel composite girder may be connected with one another before introducing the compressive prestress, and the concrete may be 7 WO 2006/065085 PCT/KR2005/004320 inserted into connection portions of the segments and cured. In addition, the steel beam may be an I-shaped beam comprising an upper flange, a lower flange, and a web connecting the upper flange and the lower flange, and an area of the upper flange may be larger than that of the lower flange. According to another aspect of the present invention, there is provided a method of manufacturing a prestressed steel composite girder by composing steel beams and a concrete in a single body, the method comprising steps of: placing the steel beams above the ground, the steel beams are separated from each other; installing a form, into which the concrete is to be inserted, to surround a portion of two or more steel beams, the form being suspended by the steel beam; inserting the concrete into an internal space of the form and curing it; and removing the form to composing two or more steel beams and the concrete. In addition, the form may surround a portion of the steel beam in a U- shape. In addition, the form may surround a portion of all the steel beams to compound the concrete. In addition, the method may further comprise: installing a sheath pipe for inserting a reinforcement bar and a tendon into the steel beam before inserting the concrete and curing it; and tensioning the tendon in the sheath pipe to introduce compressive prestress in the concrete after composing the concrete. In addition, the steel beam may be an I-shaped beam comprising an upper flange, a lower flange, and a web connecting the upper and lower flanges, and an area of the upper flange may be larger than that of the lower flange. According to still another aspect of the present invention, there is provided a prestressed steel composite girder, comprising: a steel beam; a concrete composed to surround a portion of the steel beam so that stress caused by its self-weight can be applied on only the steel beam; a tendon installed in the steel beam and /or the concrete to provide the concrete with compressive prestress; and a reinforcement bar installed in the steel bar and/or the concrete to reinforce strength of the concrete. According to further still an aspect of the present invention, there is provided a prestressed steel composite girder, comprising: a plurality of steel beams separated from each other; a concrete formed to surround a portion of the 8 WO 2006/065085 PCT/KR2005/004320 plurality of steel beams together, so that stress caused by its self-weight is applied on only the steel beams; a tendon installed in the steel beam and/or the concrete to provide the concrete with compressive stress; and a reinforcement bar installed in the steel beam and/or the concrete to reinforce strength of the concrete. In addition, the steel beam may be an I-shaped beam comprising an upper flange, a lower flange, and a web connecting the upper and lower flanges. In addition, the upper flange of the steel beam may have a large area than the lower flange of the steel beam. In addition, the concrete may surround the lower flange of the steel beam. In addition, the concrete may surround the lower flange and the web of the steel beam. In addition, the concrete may surround the entire I-shaped beam. In addition, the tendon may be extended in a parabolic shape via the web adjacent to a support and a circumference of the lower flange in the center of the steel beam. In summary, the present invention relates to a prestressed steel composite girder comprising a reinforced concrete unit formed to apply stress caused by a self- weight and an I-shaped steel beam to only the I-shaped steel beam and a tendon providing the reinforced concrete unit with compressive prestress. The advantages of the present invention can be summarized as follows: First, in the steel composite girder structure formed by composing the concrete around the I-shaped steel beam, the reinforced concrete unit is manufactured to allow stress caused by the self-weight of the girder to be applied on only the I-shaped beam. Therefore, unlike conventional engineering methods, there is no tensile stress caused by the self-weight of the concrete of the girder. Secondly, the compressive stress for the reinforced concrete unit composed with the I-shaped beam is introduced by a tendon just before the slab concrete is placed, and the concrete previously constructed in the manufacturing process has no stress. Therefore, unlike conventional engineering methods, there is no stress loss caused by creep deformation that progresses in proportion to the strength of the stress applied during the girder is placed. 9 WO 2006/065085 PCT/KR2005/004320 Thirdly, according to the present invention, the lower flange of the I- shaped beam has a smaller area than the upper flange. Therefore, the amount of loss of the compressive stress caused by creep or dry shrinkage deformation of the reinforced concrete unit can be minimized while the compressive stress is introduced into the reinforced concrete unit. As a result, it is possible to improve structural performance and safety of the steel composite girder. Fourthly, the steel composite girder according to the present invention is not required to comprise preflexion and release processes for the I-shaped beam, in which compressive stress is introduced into the concrete by using a recovery force of the steel beam. Also, an excessive amount of shear connections are not required to use. Therefore, it is possible to significantly reduce the amount of materials and construction cost. In addition, it is possible to exclude a work classification which is dangerous in relation to the preflexion and release processes, and thus to significantly reduce possibility of a safety accident. Fifthly, in the steel composite girder according to the present invention, a tendon and an I-shaped steel beam having a significant strength of bending stiffness are installed in the concrete. Therefore, a long span can be established while the height of the beam is low. Particularly, applicability may be remarkable when there is limitation to overhead clearance or discharge capacity. BRIEF DESCRIPTION OF THE DRAWINGS The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: FIGS. 1 to 7 are schematic diagrams for describing a method of manufacturing a prestressed steel composite girder according to a first embodiment of the present invention; FIG. 8 is a perspective view illustrating a prestressed steel composite girder manufactured by a method of manufacturing the prestressed steel composite girder according to a first embodiment of the present invention; FIG. 9 is a front view schematically illustrating a simple support state of a prestressed steel composite girder according to the present embodiment; 10 WO 2006/065085 PCT/KR2005/004320 FIG. 10 is a horizontal cross-sectional view schematically illustrating a prestressed steel composite girder manufactured by a method of manufacturing a prestressed steel composite girder according to a second embodiment of the present invention; FIG. 11 is a horizontal cross-sectional view schematically illustrating a prestressed steel composite girder manufactured by a method of manufacturing a prestressed steel composite girder according to a third embodiment of the present invention; FIG. 12 is a horizontal cross-sectional view schematically illustrating a prestressed steel composite girder manufactured by a method of manufacturing a prestressed steel composite girder according to a fourth embodiment of the present invention; FIG. 13 is a horizontal cross-sectional view schematically illustrating a prestressed steel composite girder manufactured by a method of manufacturing a prestressed steel composite girder according to a fifth embodiment of the present invention; FIGS. 14 and 15 are front views schematically illustrating a prestressed steel composite girder manufactured by a method of manufacturing a prestressed steel composite girder according to a sixth embodiment of the present invention; FIGS. 16 to 18 are front views schematically illustrating a prestressed steel composite girder for describing a method of manufacturing a prestressed steel composite girder according to a seventh embodiment of the present invention; FIG. 19 illustrates a configuration of an end portion support for supporting a steel beam according to the present invention; and FIG. 20 is a side view illustrating a steel beam installed on the end portion support shown in FIG. 19. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The prestressed steel composite girder according to the present invention is structured by casting a concrete in a portion of the steel beam (e.g., a lower flange of 11 WO 2006/065085 PCT/KR2005/004320 the I-shaped steel beam if a T-shaped steel beam is used) and introducing compressive prestress of a predetermined quantity into the concrete using tension of a tendon. Such a prestressed steel composite girder is placed on an abutment or a bridge pier to support a concrete slab while compensate for the tensile stress generated when dead and live loads are applied for the aforementioned compressive prestress. FIGS. 1 to 7 are schematic diagrams for describing a method of manufacturing a prestressed steel composite girder according to a first embodiment of the present invention. Now, a method of manufacturing a prestressed steel composite girder 100 according to the embodiment of the present invention will be described. As shown in FIG. 1, an I-shaped steel beam 10 comprising an upper flange 11, a lower flange 13, and a web 15 for connecting the flanges 11 and 13 with each other is prepared. As shown in FIG. 2, this I-shaped steel beam 10 is placed in a simply supported position by providing temporary supports at both ends of the beam 10 (Step S10). In this case, it is preferable that the lower flange 13 of the I-shaped steel beam 10 has a smaller area than the lower flange 11 while a plurality of shear connections are provided on an upper surface of the upper flange 11. Placing the I-shaped steel beam 10 in a simply supported position at both ends by supports 20 may be achieved by suspending the beam 10 by a beam- suspending end support 9110 at both ends as shown in FIGS. 19 and 20. In other words, the beam-suspending end support 9110 comprises two vertical members 911 erected on the ground; a horizontal member 9111 placed on and supported by the vertical members 9111; a hydraulic jack 9113 installed on an upper end of the vertical member 9111 to lift up and down the horizontal member 9112; a bracing member 9114 slanted by the side of the vertical member 911; a vertical reinforcing member 9115 interposed between the upper and lower flanges 11 and 13 to reinforce elasticity of the I-shaped beam 10 when the I-shaped beam is connected to the horizontal member 912; and a turn-buckle (9116) of which both ends are hinge- connected between the vertical reinforcing member 9115 and the horizontal member 9112 with bolts and the like to support the I-shaped beam 10. As a result, the I- shaped beam 10 can be suspended by the beam-suspending end support 9110 in a 12 WO 2006/065085 PCT/KR2005/004320 both-ends-supported shape by fixing the vertical reinforcing member 9115 installed on both ends of the I-shaped beam 10 with the turn-buckle 9116. Meanwhile, an intermediate support (not shown) having a shape similar to the beam-suspending end support 9110 may be preferably provided between the beam-suspending end supports 9110 to avoid lateral buckling or swaying of the beam during a manufacturing process of the beam. Then, as shown in FIG. 3, a reinforcement bar assembly 70 is provided by cross-connecting vertical and horizontal bars on the lower flange 13 of the I-shaped beam 10. The reinforcement bar assembly 70 is integrated to the beam 10 in a single body by welding the assembly 70 with the web 15 of the I-shaped beam 10 so that it can be supported by the I-shaped beam 10 (Step S20). Subsequently, as shown in FIG. 4, a plurality of sheath pipes 60 for installing tendons 50 (see FIG. 7) are disposed in the lower flange 13 and the bar assembly 70 (Step S30). In this case, the sheath pipe 60 is preferably installed in an internal space of the reinforcement bar assembly 70 around the lower flange 13 along a length of the I-shaped beam. Then, as shown in FIG. 5, a form 40 for placing the concrete is installed to be supported by only the I-shaped beam 10. For this purpose, a separate support member 80 as shown in a one-dotted chain line in FIG. 5 is used to integrate the form 40 into the I-shaped beam 10. In this case, the support member 80 may comprise: a first support 81 for transferring the load of the form 40 to the upper flange of the I-shaped beam 10; a second support 82 for substantially connecting the first support 81 and the form 40 to transfer a vertical load; and a third support 83 connected to the I-shaped beam 10 to transfer the horizontal load applied on the form 40. As a result, as shown in FIGS. 19 and 20, since the I-shaped beam 10 is suspended from the ground with its both ends supported, the self-weight of the form 40 is supported by the I-shaped beam 10 and the support member 80 while the form 40 surrounds the bar assembly 70 and the sheath pipes 60. Subsequently, as shown in FIG. 6, a predetermined amount of the concrete is inserted into the internal space of the form 40, and then cured during a predetermined time period (Step S40) (see FIG. 6). In this state, it is noted that 13 WO 2006/065085 PCT/KR2005/004320 bending moment is generated in the I-shaped beam 10 by the load of the I-shaped beam 10 and the concrete itself, and compressive stress is applied on the upper flange while the tensile stress is applied on the lower flange 13. After the concrete surrounding the lower flange of the I-shaped beam 10 is completely cured, the form 40 is removed from the I-shaped beam 10. Then, as shown in FIG. 7, tendons 50 are inserted into the inside of the sheath pipes 60. As a result, it is possible to provide a reinforced concrete unit 30 having no stress on the lower flange 13 while the lower flange 13 is sufficiently tensioned by the self- weights of the I-shaped beam 10 and the concrete. Through the aforementioned process, it is possible to manufacture a prestressed steel composite girder 100 according to a first embodiment of the present invention, in which the reinforced concrete unit 30 is built in the lower flange 13 of the I-shaped beam 10 with no stress while only the I-shaped beam 10 experiences the stress caused by the self-weights of the I-shaped beam 10 and the concrete. FIG. 8 is a perspective view illustrating a prestressed steel composite girder manufactured according to a method of manufacturing a prestressed steel composite girder according to a first embodiment of the present invention, and FIG. 9 is a front view schematically illustrating a simple support state of a prestressed steel composite girder according to the present embodiment. Referring to FIGS. 8 and 9, just before or after the steel composite girder 100 manufactured as the described above is placed on a bridge or an abutment, the tendons 50 are tensioned by using a tension device such as a hydraulic jack as shown in FIG. 7, and both ends of the tendon 50 are anchored on both ends of the reinforced concrete unit 30 using an anchorage 90. As a result, a predetermined strength of compressive stress is introduced into the reinforced concrete unit 30. Now, the prestressed steel composite girder 100 configured as described above will be described in more detail. The prestressed steel composite girder 100 comprises: an I-shaped steel beam 10; a reinforced concrete unit 30 mixed with the I- shaped beam 10 to be supported by the I-shaped beam 10 with no stress; and a tendon 50 installed in the reinforced concrete unit 30 to provide prestress with the reinforced concrete unit 30. 14 WO 2006/065085 PCT/KR2005/004320 The I-shaped beam 10, as described above, comprises: an upper flange 11; a lower flange 13; and a web 15 for connecting the flanges 11 and 13 with each other. The upper and lower flanges 11 and 13 are connected to upper and lower sides of the web 15 which horizontally elongated and thus also horizontally elongated. Preferably, the lower flange 13 of the I-shaped beam 10 has a smaller area than the upper flange 11. In the I-shaped beam 10 having such a shape, since a neutral axis is substantially high for the upper and lower flanges 11 and 13, the lower flange 13 can be subjected to sufficient tensile stress by the self-weights of the I-shaped beam 10 and the reinforced concrete unit 30. In other words, in the I- shaped beam 10, the upper flange experiences compressive stress and the lower flange experiences tensile stress by the self-weights of the I-shaped beam 10 and the reinforced concrete unit 30. As shown in FIG. 9, the reinforced concrete unit 30 (referred to as a lower flange concrete in the art) is combined with the lower flange 13 of the I-shaped beam 10 by using the reinforcement bar assembly 70 and the form 40 (see FIG. 5) supported by only the I-shaped beam 10 while both ends of the I-shaped beam 10 are simply supported by the support 20. More specifically, in the process of manufacturing the steel composite girder according to the present, Since the reinforced concrete unit 30 is manufactured in such a way that both ends of the I-shaped beam 10 are simply supported by supports 20, and the form 40 is supported by only the I-shaped beam 10, the entire self-weight of the concrete placed in the form 40 is transferred to the I-shaped beam 10. In other words, the reinforced concrete unit 30 is combined with the lower flange 13 while the lower flange 13 experiences sufficient tensile stress by the self-weights of the I- shaped beam 10 and the concrete itself. Therefore, since the I-shaped beam 10 is substantially responsible for the self-weights of the I-shaped beam 10 and the reinforced concrete unit 30, if the concrete is cured and the form 40 is removed, the reinforced concrete unit 30 is supported by the lower flange 13 of the I-shaped beam 10 with no stress. As a result, in the steel composite girder 100 according to a first embodiment of the present invention, the stress caused by the self-weights of the I- 15 WO 2006/065085 PCT/KR2005/004320 shaped beam 10 and the reinforced concrete unit 30 is applied on only the I-shaped beam 10 while its both ends are simply supported by the supports 20, but the stress caused by the self-weights is not applied on the reinforced concrete unit 30. In this case, the stress applied on the I-shaped beam 10 is generated by the weights of the I- shaped beam 10 and the reinforced concrete unit 30, and includes compressive stress applied on the upper flange and tensile stress applied on the lower flange. The tendon 50 which provides prestress on the reinforced concrete unit 30 is inserted into the sheath pipe 60 distributed around the reinforced bar assembly 70 and the lower flange 13 along the length of the I-shaped beam 10. Both ends of the tendon 50 may be installed on both ends of the reinforced concrete unit 30 by twisting strands in a single one and tensioning it with a tensioning device such as a hydraulic jack. For this purpose, as shown in FIG. 8, an anchorage 90 is provided on both ends of the reinforced concrete unit 30 for anchoring both ends of the tendon 50 in both ends of the reinforced concrete unit 30. In this case, the anchorage 90 has a typical jointing structure that can joint the tendon 50 at both ends of the reinforced concrete unit 30 by installing a wedge with an anchor cone (not shown). Now, advantages of the prestressed steel composite girder 100 according to the embodiment of the present invention will be described below. Since the prestressed steel composite girder 100 is manufactured by sufficiently tensioning the I-shaped beam 10 and combining the reinforced concrete unit 20 with the lower flange 13 of the I-shaped beam 10 without stress, no stress is generated by the self- weight of the steel composite girder 100. Also, since the stress generated by the self-weight of the steel composite girder 100 is not applied on the reinforced concrete unit 30 while both ends of the girder 100 is simply supported by the supports 20, the loss of compressive stress caused by the self-weight is not generated, and particularly, since the concrete experiences no stress, there is no stress loss caused by creep deformation that progresses in proportion to the strength of the applied stress. In addition, it is possible to consider additional loads that will be applied on the girder 100 after completing construction of a bridge by combining slab concrete. Also, since tension is introduced by the tendon just before the slab concrete is placed, and the applied stress is not large in a common 16 WO 2006/065085 PCT/KR2005/004320 use, the loss of compressive stress caused by creep of the concrete with the slab mixed is negligible. Furthermore, if the steel composite girder is collapsed, and the reinforced concrete unit 30 is completely broken down so that the girder loses its function, the lower flange 13 of the I-shaped beam 10 does not experience much marginal stress. As a result, its cross-section can be efficiently used. Further, in the prestressed steel composite girder 100 according to the present embodiment, the lower flange of the I-shaped beam 10 has a smaller area than the upper flange 11. Therefore, it is possible to reduce loss of the compressive prestress caused by dry shrinkage deformation of the reinforced concrete unit 30 after the compressive prestress is introduced into the reinforced concrete unit 30. Furthermore, in the prestressed steel composite girder 100 according to the present embodiment, the upper flange 11 of the I-shaped beam 10 experiences relatively less compressive stress in comparison with the tensile stress applied on the lower flange 13. Therefore, it is possible to have a large margin for additional loads. FIG. 10 is a horizontal cross-sectional view schematically illustrating a prestressed steel composite girder manufactured by a method of manufacturing a prestressed steel composite girder according to a second embodiment of the present invention. Now, a method of manufacturing a prestressed steel composite girder according to a second embodiment of the present invention will be described with reference to the accompanying drawings. Similar to the steps S20 and S30 described above, the reinforcement bar assembly 170 and the form 140 are installed in the I-shaped beam 110. However, according to the second embodiment, the reinforcement bar assembly 170 and the form 140 surrounds the lower flange 113 and the web 115 of the I-shaped beam 110 as shown in FIG. 10, and they are supported by only the I-shaped beam 110. In this state, concrete is placed in an internal space of the form 140 and cured, and the form 140 is removed. Through this manufacturing method, a prestressed steel composite girder 200 according to a second embodiment of the present invention can be manufactured by combining the reinforced concrete unit 130 with the lower flange 17 WO 2006/065085 PCT/KR2005/004320 113 and the web 115 of the I-shaped beam 110. It should be noted that the tendon 150 is also installed between the opposite sheath pipes 160 of the reinforced concrete unit 130. In the second embodiment, since other manufacturing procedures, structures, and effectiveness are similar to those of the aforementioned first embodiment, their descriptions will be omitted. FIG. 11 is a horizontal cross-sectional view schematically illustrating a prestressed steel composite girder manufactured by a method of manufacturing a prestressed steel composite girder according to a third embodiment of the present invention. Now, a method of manufacturing the prestressed steel composite girder according to a third embodiment of the present invention will be described with reference to FIG. 11. Similar to the steps S20 and S30 of the aforementioned first embodiment, the reinforcement bar assembly 270 and the form 240 are installed in the I-shaped beam 210. However, according to the third embodiment, the reinforcement bar assembly 270 and the form 240 surrounds the entire I-shaped beam 110 as shown in FIG. 11, and they are supported by only the I-shaped beam 110. In this state, concrete is placed in an internal space of the form 240 and cured, and the form 240 is removed. According to the method of manufacturing the prestressed steel composite girder according to the third embodiment, the reinforced concrete unit 230 surrounds the entire I-shaped beam 210, or preferably, the entire surfaces excluding an upper surface of the upper flange 211 of the I-shaped beam. It should be noted that the tendon 250 is also installed between the opposite sheath pipes 260 of the reinforced concrete unit 230. In the third embodiment, since other manufacturing procedures, structures, and effectiveness are similar to those of the aforementioned first embodiment, their descriptions will be omitted. FIG. 12 is a horizontal cross-sectional view schematically illustrating a prestressed steel composite girder manufactured by a method of manufacturing a 18 WO 2006/065085 PCT/KR2005/004320 prestressed steel composite girder according to a fourth embodiment of the present invention. Now, a method of manufacturing the prestressed steel composite girder according to a fourth embodiment of the present invention will be described with reference to FIG. 12. Similar to the steps S20 of the aforementioned first embodiment, the sheath pipe 360 is installed. However, according to the fourth embodiment, the sheath pipe 360 is installed in a parabolic shape as shown in the one-dotted chain line of FIG. 12, so that the sheath pipe 360 can be extended via the web 315 of the I-shaped beam 310 corresponding to the support 320 and a circumference of the I-shaped beam 310 in the center of the lower flange 313. In this state, concrete is placed in the lower flange 313 of the I-shaped beam 310 and portions of the web 315 corresponding to the supports 320, and cured. Then, a tensioning device such as a hydraulic jack is used to tension the tendon 350 while the tendon 350 (shown as a one-dotted chain line in FIG. 12) is installed in the internal space of the sheath pipe 360. Subsequently, both ends of the tendon 350 are fixed at both ends of the concrete unit 330 through the anchorage 390. The fourth embodiment of the present invention is not limited to the configuration of installing the anchorage 390 in both ends of the concrete unit. Alternatively, the anchorage 390 may be installed in an inner side separated from the concrete unit 390 with a predetermined distance. According to the fourth embodiment of the present invention, it is possible to manufacture a prestressed steel composite girder 400 having a sheath pipe 360 extending in a parabolic shape via the web 315 adjacent to the supports 320 and the lower flange 313 in the center of the I-shaped beam 310. In the fourth embodiment, since other manufacturing procedures, structures, and effectiveness are similar to those of the aforementioned first embodiment, their descriptions will be omitted. FIG. 13 is a horizontal cross-sectional view schematically illustrating a prestressed steel composite girder manufactured by a method of manufacturing a prestressed steel composite girder according to a fifth embodiment of the present invention. 19 WO 2006/065085 PCT/KR2005/004320 Now, a method of manufacturing the prestressed steel composite girder according to a fifth embodiment of the present invention will be described with reference to FIG. 13. Similar to the steps S10 of the aforementioned first embodiment, the I-shaped beam 410 is provided. However, according to the fifth embodiment of the present invention, at least two I-shaped beams 410, or preferably, a pair of I-shaped beams 410 are provided in such a way that they can be lined up with a predetermined interval. In this state, the reinforcement bar assembly 470 and the form 440 are installed in the I-shaped beam 410 as shown in FIG. 13. Specifically, the reinforcement bar assembly 470 and the form 440 surrounds the lower flanges 113 and the webs 115 of two I-shaped beams 410 together, so that they can be supported by only the I-shaped beams 410. Then, concrete is placed in an internal space of the form 440 and cured, and the form 440 is removed. In the fifth embodiment of the present invention, since the reinforced concrete unit 430 is manufactured to surround a pair of I-shaped beams 410 together, a cross-sectional shape of the girder 500 can have a U-shape. In this case, it should be noted that the sheath pipe 460 is also provided in the reinforced concrete unit 430, and the tendon 450 is also inserted into the sheath pipe 460. If the prestressed steel composite girder 500 according to the fifth embodiment of the present invention is employed in a deck bridge, the cross- sectional shape of the bridge after applying concrete slabs may be a closed shape. As a result, it is possible to increase torsional stiffness allowing for a long span of a bridge. In addition, the prestressed steel composite girder according to the fifth embodiment of the present invention can be used as a deck bridge. In the fifth embodiment, since other manufacturing procedures, structures, and effectiveness are similar to those of the aforementioned first embodiment, their descriptions will be omitted. FIGS. 14 and 15 are front views schematically illustrating a prestressed steel composite girder manufactured by a method of manufacturing a prestressed steel composite girder according to a sixth embodiment of the present invention. 20 WO 2006/065085 PCT/KR2005/004320 Now, a method of manufacturing the prestressed steel composite girder according to a sixth embodiment of the present invention will be described with reference to FIGS. 14 and 15. As shown in FIG. 14, after the Step S30 in the aforementioned first embodiment, a weighting member W having a predetermine weight is disposed on the I-shaped beam 510 to generate positive moment on the I- shaped beam 510. In this state, concrete is placed in an internal space of the former 540 shown as a dashed line in FIG. 14 and cured, and the weight member W and the former 540 are removed. As a result, as shown in FIG. 15, it is possible to introduce additional compressive stress into the reinforced concrete unit 530 by the weighting member W. The prestressed steel composite girder 600 according to the sixth embodiment of the present invention is manufactured by a manufacturing process similar to that of the first embodiment. However, since the self-weight of the weighting member W is applied on the I-shaped beam 510, it is possible to more easily compensate for the tensile stress generated in a negative moment cross- section when a design load is applied. FIGS. 16 to 18 are front views schematically illustrating a prestressed steel composite girder for describing a method of manufacturing a prestressed steel composite girder according to a seventh embodiment of the present invention. Now, a method of manufacturing the prestressed steel composite girder according to a seventh embodiment of the present invention will be described with reference to FIGS. 16 through 18. As shown in FIG. 16, taking the structure of the I- shaped beam and a delivery condition into account, three girder members 610a, 610b, and 610c that have been previously manufactured in a factory are prepared. The three girder members 610a, 610b, and 610c are combined with one another in a single body to provide an I-shaped beam 610 according to the seventh embodiment of the present invention. In this process, connecting plates 617 are provided at the connecting areas a and b (i.e., adjoining portions of the girder members 610a, 610b, and 610c in an upper flange 611a, a lower flange 613a, and a web 615a), and then, fixing members such as bolts are engaged in the connecting plate 617, so that each of the girder members 610a, 610b, and 610c are connected with one another in a single body. 21 WO 2006/065085 PCT/KR2005/004320 In this state, as shown in FIG. 17, the reinforced concrete unit 630 is formed in the lower flange 613a except for the connection areas a and b of the girder members 610a, 610b, and 610c through a process similar to that of the first embodiment. Then, the connecting plates 617 provided in the connecting areas a and b are removed from the girder members 610a, 610b, and 610c, so that three pieces of segmented girders 600a, 600b, and 600c are manufactured. Then, the segmented girders 600a, 600b, and 600c are delivered to a construction site, the connecting plates 617 are installed in each of the connecting areas a and b of the segmented girders 600a, 600b, and 600c, so that the each of the segmented girders 600a, 600b, and 600c are connected in a single body. Subsequently, as shown in FIG. 18, the reinforcement bar assemblies 670a and the sheath pipes 650a shown as a dashed line are also installed in the connecting areas a and b between the segmented girders 600a, 600b, and 600c (i.e., between the reinforced concrete units 630 of each segmented girder 600a, 600b, and 600c). The reinforcement bar assembly 670a may be connected to the opposite reinforcement bar assembly 670 installed in the reinforced concrete unit 630 of each segmented girder 600a, 600b, and 600c by using a typical connection method such as a welding. Similarly, the sheath pipe 650a may be connected to the opposite sheath pipe 650 installed in the reinforced concrete unit 630 of each segmented girder 600a, 600b, and 600c by using a jointing member (not shown). Subsequently, the forms (not shown) are installed in each connection area a and b between the segmented girders 600a, 600b, and 600c. Then, concrete is placed in the forms and cured for a predetermined time period, and the forms are removed. As a result, it is possible to manufacture a prestressed steel composite girder 700 having a segmented structure according to the seventh embodiment of the present invention, in which the reinforced concrete unit 630 is connected along a plurality of lower flanges (not shown) of all the I-shaped beams 610. While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein 22 WO 2006/065085 PCT/KR2005/004320 without departing from the spirit and scope of the present invention as defined by the appended claims. 23 WO 2006/065085 PCT/KR2005/004320 WHAT IS CLAIMED IS: 1. A method of manufacturing a prestressed steel composite girder by using a steel beam and a concrete, the method comprising steps of: placing the steel beam above the ground; installing a form, into which the concrete is to be inserted, to surround at least a portion of the steel beam, the form being suspended by the steel beam; inserting the concrete into an internal space of the form and curing it; and removing the form to compose the steel beam and the concrete. 2. The method of claim 1, further comprising steps of: installing a reinforcement bar and a sheath pipe for inserting a tendon in the steel beam before placing the concrete and curing it; and introducing compressive prestress into the concrete by tensioning the tendon in the sheath pipe after composing the concrete. 3. The method of claim 2, wherein in the installation of the sheath pipe, the steel beam is an I-shaped beam comprising an upper flange, a lower flange, and a web; and the sheath pipe is arranged around the lower flange of the steel beam along a length of the steel beam. 4. The method of claim 3, wherein in the installation of the sheath pipe, the sheath pipe is extended in a parabolic shape via the web adjacent to a support and a circumference of the lower flange in the center of the steel beam. 5. The method of claim 1, wherein in the placing the steel beam above the ground, the steel beam is supported at both ends thereof. 6. The method of claim 5, wherein the steel beam is suspended by a beam-suspending end supports disposed at both ends of the steel beam. 24 WO 2006/065085 PCT/KR2005/004320 7. The method of claim 5 or 6, wherein an intermediate support is further provided between the beam-suspending end supports to avoid lateral buckling or swaying of the steel beam. 8. The method of claim 3, wherein the reinforcement bar and the form surrounds the lower flange of the steel beam. 9. The method of claim 3, wherein the reinforcement bar and the form surrounds the lower flange and the web of the steel beam. 10. The method of claim 2, wherein the reinforcement bar and the form surrounds the entire steel beam. 11. The method of any one of claims 1 to 6 and 8 to 10, further comprising: placing a weighting member on an upper surface of the steel beam to generate positive moment on the steel beam before composing the concrete and me steel beam; and removing the weight member after composing the steel beam and the concrete, thereby introducing compressive prestress into the concrete. 12. The method of any one of claims 1 to 6 and 8 to 10, wherein the steel composite girder is segmented into more than three segments, and wherein the segments of the steel composite girder are connected with one another before introducing the compressive prestress, and the concrete is inserted into connection portions of the segments and cured. 13. The method of any one of claims 1 to 6 and 8 to 10, wherein the steel beam is an I-shaped beam comprising an upper flange, a lower flange, and 25 WO 2006/065085 PCT/KR2005/004320 wherein a web connecting the upper flange and the lower flange, and an area of the upper flange is larger than that of the lower flange. 14. A method of manufacturing a prestressed steel composite girder by composing steel beams and a concrete in a single body, the method comprising steps of: placing the steel beams above the ground, the steel beams are separated from each other; installing a form, into which the concrete is to be inserted, to surround a portion of two or more steel beams, the form being suspended by the steel beam; inserting the concrete into an internal space of the form and curing it; and removing the form to composing two or more steel beams and the concrete. 15. The method of claim 14, wherein the form surrounds a portion of the steel beam in a U-shape. 16. The method of claim 14, wherein the form surrounds a portion of all the steel beams to compound the concrete. 17. The method of claim 14, further comprising: installing a sheath pipe for inserting an reinforcement bar and a tendon into the steel beam before inserting the concrete and curing it; and tensioning the tendon in the sheath pipe to introduce compressive prestress in the concrete after composing the concrete. 18. The method of any one of claims 14 to 17, wherein the steel beam is an I-shaped beam comprising an upper flange, a lower flange, and a web connecting the upper and lower flanges, and an area of the upper flange is larger than that of the lower flange. 26 WO 2006/065085 PCT/KR2005/004320 19. A prestressed steel composite girder, comprising: a steel beam; a concrete composed to surround a portion of the steel beam so that stress caused by its self-weight can be applied on only the steel beam; a tendon installed in the steel beam and /or the concrete to provide the concrete with compressive prestress; and a reinforcement bar installed in the steel bar and/or the concrete to reinforce strength of the concrete. 20. A prestressed steel composite girder, comprising: a plurality of steel beams separated from each other; a concrete formed to surround a portion of the plurality of steel beams together, so that stress caused by its self-weight is applied on only the steel beams; a tendon installed in the steel beam and/or the concrete to provide the concrete with compressive stress; and a reinforcement bar installed in the steel beam and/or the concrete to reinforce strength of the concrete. 21. The prestressed steel composite girder of claim 19 or 20, wherein the steel beam is an I-shaped beam comprising an upper flange, a lower flange, and a web connecting the upper and lower flanges. 22. The prestressed steel composite girder of claim 21, wherein the upper flange of the steel beam has a large area than the lower flange of the steel beam. 23. The prestressed steel composite girder of claim 21, wherein the concrete surrounds the lower flange of the steel beam. 27 WO 2006/065085 PCT/KR2005/004320 24. The prestressed steel composite girder of claim 21, wherein the concrete surrounds the lower flange and the web of the steel beam. 25. The prestressed steel composite girder of claim 21, wherein the concrete surrounds the entire I-shaped beam. 26. The prestressed steel composite girder of any one of claims 19 to 25, wherein the tendon is extended in a parabolic shape via the web adjacent to a support and a circumference of the lower flange in the center of the steel beam. 28 A prestressed steel composite girder and a method of manufacturing the prestressed steel composite girder are provided by using a steel beam and a concrete. The method includes steps of: placing the steel beam above the ground; installing a form, into which the concrete is to be inserted, to surround at least a portion of the steel beam, the form being suspended by the steel beam; inserting the concrete into an internal space of the form and curing it; and removing the form to compose the steel beam and the concrete. The prestressed steel composite girder includes a steel beam and a concrete composed to surround a portion of the steel beam so that stress caused by its self-weight can be applied on only the steel beam.

Full Text

WO 2006/065085 PCT/KR2005/004320
MANUFACTURING METHOD FOR PRESTRESSED STEEL COMPOSITE
GIRDER AND PRESTRESSED STEEL COMPOSITE GIRDER THEREBY
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a method of manufacturing a prestressed
steel composite girder having a lower flange of the steel girder reinforced with
concrete, and a steel composite girder manufactured using the same, and more
particularly, to a method of manufacturing a prestressed steel composite girder for
previously introducing compressive prestress on concrete in order to compensate
for tensile stress generated during common use and a steel composite girder
manufactured using the same.
(b) Description of the Related Art
Generally, it is known in the art that concrete is resistant to compressive
stress but not resistant to tensile stress. A prestressed steel composite girder has
been designed to compensate for the tensile stress generated when applying live
and dead loads for the compressive prestress.
Conventional engineering methods for previously introducing
compressive stress to concrete to provide a resistive cross-section can be classified
into the following three kinds of technologies depending on a method of
introducing the compressive prestress and material composition for the resistive
cross-section.
First, as a most common and fundamental engineering method for
introducing the compressive prestress into a concrete by using only tension (i.e., a
prestress force) of a tendon, a prestressed concrete (PSC) beam has been known in
the art. In a conventional PSC beam engineering method, a resistant force is given
to the concrete by artificially estimating stress distribution and strength and
adopting a high strength steel (generally referred to as a tendon) for compensating
for the tensile stress generated by an external force up to a certain point.
In order to overcome mechanical shortcomings of the conventional PSC
beam, in other words, in order to increase resistance strength for a tension crack that
can occur in an upper surface of the beam cross-section when introducing tension
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and reduce the height of the beam with respect to the same effective span, another
improved technology has been proposed in a Korean unexamined patent
application publication No. 10-2004-0058542, entitled "A Prestressed Steel
Reinforced Concrete Unit Beam and Manufacturing Method Thereof". In this
technology, a T-shaped steel plate is inserted into upper and lower flanges of the
conventional prestressed concrete beam. Specifically, steel strands are provided in
sheath pipes installed in the steel assembly, and the T-shaped steel plates are
provided on the upper and lower flanges, a guide pipe is provided in the T-shaped
steel plate installed in the center of the lower flange, steel strands are further
provided in the guide pipe, the guide pipe is jointed with a lower reinforcing plate
installed under the T shape steel plate using nuts to integrate and fix it, and then,
the concrete is placed and cured. Lastly, the steel strands are settled on both ends
of the beam after a prestress force is introduced into the steel strands.
Unlike the aforementioned PSC beam or the prestressed steel reinforced
concrete unit beam, a structure in which die steels are inserted into a cross-section of
the concrete has been proposed in a Korean unexamined patent application
publication No. 10-2004-0004197, entitled "Composite Beam Stiffened with
Prestressed Concrete Panel Having Embedded Lower Flange and Multi-stepped
Jacking Structure", wherein this structure is generally referred to as an MSP
structure in the art. In this structure, unlike the aforementioned technologies, a
precasted concrete panel composite beam is made by combining a steel beam with a
precasted concrete panel. Specifically, a protrusion is provided on an upper
surface of the precasted concrete panel to bury the lower flange of the steel beam;
first and second tendons are provided on the precasted concrete panel, wherein the
first tendon is disposed on left and right sides of a position where the protrusion is
provided under the center axis of the precasted concrete panel near the center axis,
and the second tendon is spaced far from the center axis of the composite cross-
section after integrated under the protrusion; the first tendon is firstly prestressed
before the lower flange of the steel beam is positioned in the protrusion of the
precasted concrete panel, and then, secondly prestressed after the steel beam is
disposed on the protrusion and second concrete is placed in the protrusion, so that
compressive stress is also applied to the second concrete by introducing the second
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prestress; the second tendon is thirdly prestressed and settled in the state that the
self-weights of the steel beam and the panel is reflected on the entire load after the
steel beam is combined with the precasted concrete panel, so that third prestress can
be applied on the panel and additionally applied to the second concreted.
A second conventional technology is to introduce the compressive
prestress into concrete only by a recovery force of the steel beam. This technology
stems from a Belgian engineering method invented in 1950's, and is frequently
adopted in the Northeast Asia. The resultant girder manufactured by this
technology is called "a preflex beam" in the art. In this technology, while slope
deflection is generated by applying a predetermined load on the steel girder,
concrete is placed on the lower flange of the steel girder and cured. The
compressive prestress is introduced into the lower flange concrete in the process of
releasing the slope deflection by removing the load on the steel girder (i.e., a
releasing process).
A third conventional technology is to introduce the compressive prestress
into the concrete by using both the recovery force of the steel beam and the tension
of the tendon. The resultant girder manufactured by this technology is call "a re-
prestressed preflex (RPF) girder" in the art as disclosed in Korean Patent Publication
No. 10-024084. In this technology, the RPF steel complex girder is manufactured
by placing the concrete in the lower flange and cured with the preflexion load
applied to the steel girder as the aforementioned preflex girder and then
introducing the second prestress into the lower flange concrete using the tension of
the tendon in the state that the compressive prestress is initially introduced by the
recovery force of the steel beam. Specifically, this technology relates to a method
of manufacturing a re-prestressed steel composite beam, in which a load generating
bending moment having a predetermined strength (i.e., a Pf load) is previously
applied to an I-shaped beam; a concrete is placed in the lower flange of the beam
and cured, the previously applied load (Pf) is removed to introduce first
compressive prestress into the lower flange concrete; and second compressive
prestress is introduced by a tendon installed in the lower flange concrete, wherein
unbonded strands are used as the tendon; a plurality of strands are disposed with a
constant interval in upper and/or lower portions of the lower flange and installed
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in the lower flange concrete before concrete is placed in the lower flange of the beam
and cured; after the lower flange concrete is cured, the strands are installed in a
prestressed state using a compressive strength of 450 kgf/cm, so that the lower
flange concrete is perfectly prestressed.
In the aforementioned conventional methods (i.e., the aforementioned PSC
beam or the prestressed steel reinforced concrete unit beam) for previously
introducing compressive prestress to constitute a resistance cross-section, although
they have a cross-section consisting of reinforced bars, a high rigidity of concrete,
and tendons, and allow a more economical construction in comparison with other
conventional methods for manufacturing a composite beam with the I-shaped beam
installed in its cross-section, they may be limited by the height of the beam and
particularly, by the effective span due to a structural limitation that the self-weight
is dominant among external forces applied to the cross-section. Therefore, the
bridges based on the aforementioned methods are applicable to constructions
having an effective span more or less than 30m, and particularly, to constructions
not limited by overhead clearance or discharge capacity.
In order to compensate for the limitation of the height of the beam or the
effective span, a steel composite beam adopting both advantages of a high rigidity
of concrete as well as the I-shaped beam has been proposed. Among
aforementioned engineering methods, the preflex girder and the re-prestressed
preflex steel composite girder (RPF) correspond to such a thing. However, in these
engineering methods, since the compressive stress for the concrete surrounding the
steel beam is introduced using a recovery force of the steel beam, the upper and
lower flanges of the beam must be enlarged. Also, additional processes and costs
should be prepared for the preflexion and release. Further, since large bending
deformation occurs in the beam during the manufacturing process, it is very
difficult to manage a camber of a finally manufactured product. Particularly, in the
aforementioned preflex beam, since a typical steel beam is used to introduce
compressive stress, such a composite cross-section is vulnerable to creep of the
concrete. In other words, the concrete experiences creep deformation as time goes
by, and the compressive prestress introduced in the manufacturing process is lost
due to deformation confinement of the concrete composite beam. Meanwhile, in
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the preflex girder, since the prestress is applied to the concrete by dominantly using
the recovery force of the steel beam, the area of the lower flange should be large.
Therefore, loss of the compressive prestress resulted from dry shrinkage
deformation and creep deformation in the concrete becomes big problems in the art.
Also, construction may become difficult and its cost may increase because an
amount of shear connections should be provided for the lower flange of the steel
girder.
In order to compensate for the shortcomings of the preflex girder from the
view point of a long-time behavior, a re-prestressed preflex steel composite beam
(RPF) has been developed. In this technology, secondary prestress is further
applied to the conventional preflex girder. As a result, it is possible to compensate
for an amount of creep loss generated during a suspending period until the preflex
girder is installed in a bridge or a building, and to apply sufficient prestress to the
lower concrete. Also, it is possible to reduce the size of the flange of the beam due
to a tendon. However, similar to the conventional preflex girder, cumbersome
processes such as preflexion and release should be also applied to the RPF girder.
In addition, a prestress process using a tendon should be further applied. As a
result, manufacturing cost is never reduced. Although a secondary prestress
process using a tendon can be performed just before the girder is installed in a
target structure, a primary prestress process is introduced in a release process.
Therefore, similar to the conventional preflex girder, the creep loss is inevitably
generated during a suspending period. In addition, problems of the conventional
preflex girder, such as relating to a number of shear connections and camber
management, still exist.
Recently, a multi-stage prestressed (MSP) precasted concrete panel
composite girder having a lower flange buried in a single connection structure has
been developed in order to overcome problems caused by introducing compressive
stress into the concrete using an elastic force of the steel beam. However, although
this engineering method solves problems of the conventional technologies, its
construction is very complicated. Therefore, construction cost increases, and
particularly, quality control becomes very difficult because it has a construction
joint in lower casing concrete.
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In addition, all the aforementioned conventional methods of
manufacturing steel composite girders have a structural problem that the stress
caused by the self-weight of the steel composite girder (including a self-weight of an
I-shaped beam and a self-weight of the concrete) acts as tensile stress of the lower
flange concrete. This fact means that additional stress for compensating for the
tensile stress caused by the self-weight of the composite girder should be previously
introduced before the compressive stress caused by bending deformation in the
steel beam or tension of the tendon is introduced.
Furthermore, in all the aforementioned conventional steel composite
girders, since the concrete experiences a predetermined strength of compressive
stress during they are suspended in a bridge or a abutment before a slab is
composed, compressive stress loss caused by the creep deformation is inevitable as
time goes by.
SUMMARY OF THE INVENTION
The present invention has been made to solve the aforementioned
problems, and an object of the present invention is to provide a method of
manufacturing a prestressed steel composite girder allowing stress caused by the
self-weight of the girder to be applied to a steel beam and not to be applied to the
concrete, and a steel composite girder manufactured using the same.
In other words, the present invention provides a method of manufacturing
a prestressed steel composite girder, in which the stress caused by the self-weight of
the concrete is not generated in a cross-section of the concrete by allowing the self-
weight of the concrete positioned around the lower flange of the steel beam to be
supported by only the steel beam, and loss of compressive stress caused by creep
deformation of the concrete can be minimized by previously introducing
compressive stress into the concrete before it is placed on a bridge or an abutment,
and a steel composite girder manufactured using the same.
According to an aspect of the present invention, there is provided a
method of manufacturing a prestressed steel composite girder by using a steel beam
and a concrete, the method comprising steps of: placing the steel beam above the
ground; installing a form, into which the concrete is to be inserted, to surround at
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least a portion of the steel beam, the form being suspended by the steel beam;
inserting the concrete into an internal space of the form and curing it; and removing
the form to compose the steel beam and the concrete.
In the above aspect, the method may further comprises steps of: installing a
reinforcement bar and a sheath pipe for inserting a tendon in the steel beam before
placing the concrete and curing it; and introducing compressive prestress into the
concrete by tensioning the tendon in the sheath pipe after composing the concrete.
In addition, in the installation of the sheath pipe, the steel beam may be an
I-shaped beam comprising an upper flange, a lower flange, and a web; and the
sheath pipe may be arranged around the lower flange of the steel beam along a
length of the steel beam.
In addition, in the installation of the sheath pipe, the sheath pipe may be
extended in a parabolic shape via the web adjacent to a support and a circumference
of the lower flange in the center of the steel beam.
In addition, in the placing the steel beam above the ground, the steel beam
may be supported at both ends thereof. In addition, the steel beam may be
suspended by a beam-suspending end supports disposed at both ends of the steel
beam. In addition, an intermediate support may be further provided between the
beam-suspending end supports to avoid lateral buckling or swaying of the steel
beam.
In addition, the reinforcement bar and the form may surround the lower
flange of the steel beam. In addition, the reinforcement bar and the form may
surround the lower flange and the web of the steel beam. In addition, the
reinforcement bar and the form may surround the entire steel beam.
In addition, the method may further comprise: placing a weighting
member on an upper surface of the steel beam to generate positive moment on the
steel beam before composing the concrete and the steel beam; and removing the
weight member after composing the steel beam and the concrete, thereby
introducing compressive prestress into the concrete.
In addition, the steel composite girder may be segmented into more than
three segments, the segments of the steel composite girder may be connected with
one another before introducing the compressive prestress, and the concrete may be
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inserted into connection portions of the segments and cured. In addition, the steel
beam may be an I-shaped beam comprising an upper flange, a lower flange, and a
web connecting the upper flange and the lower flange, and an area of the upper
flange may be larger than that of the lower flange.
According to another aspect of the present invention, there is provided a
method of manufacturing a prestressed steel composite girder by composing steel
beams and a concrete in a single body, the method comprising steps of: placing the
steel beams above the ground, the steel beams are separated from each other;
installing a form, into which the concrete is to be inserted, to surround a portion of
two or more steel beams, the form being suspended by the steel beam; inserting the
concrete into an internal space of the form and curing it; and removing the form to
composing two or more steel beams and the concrete.
In addition, the form may surround a portion of the steel beam in a U-
shape.
In addition, the form may surround a portion of all the steel beams to
compound the concrete.
In addition, the method may further comprise: installing a sheath pipe for
inserting a reinforcement bar and a tendon into the steel beam before inserting the
concrete and curing it; and tensioning the tendon in the sheath pipe to introduce
compressive prestress in the concrete after composing the concrete. In addition,
the steel beam may be an I-shaped beam comprising an upper flange, a lower flange,
and a web connecting the upper and lower flanges, and an area of the upper flange
may be larger than that of the lower flange.
According to still another aspect of the present invention, there is provided
a prestressed steel composite girder, comprising: a steel beam; a concrete composed
to surround a portion of the steel beam so that stress caused by its self-weight can
be applied on only the steel beam; a tendon installed in the steel beam and /or the
concrete to provide the concrete with compressive prestress; and a reinforcement
bar installed in the steel bar and/or the concrete to reinforce strength of the concrete.
According to further still an aspect of the present invention, there is
provided a prestressed steel composite girder, comprising: a plurality of steel
beams separated from each other; a concrete formed to surround a portion of the
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WO 2006/065085 PCT/KR2005/004320
plurality of steel beams together, so that stress caused by its self-weight is applied
on only the steel beams; a tendon installed in the steel beam and/or the concrete to
provide the concrete with compressive stress; and a reinforcement bar installed in
the steel beam and/or the concrete to reinforce strength of the concrete.
In addition, the steel beam may be an I-shaped beam comprising an upper
flange, a lower flange, and a web connecting the upper and lower flanges.
In addition, the upper flange of the steel beam may have a large area than
the lower flange of the steel beam.
In addition, the concrete may surround the lower flange of the steel beam.
In addition, the concrete may surround the lower flange and the web of the
steel beam.
In addition, the concrete may surround the entire I-shaped beam.
In addition, the tendon may be extended in a parabolic shape via the web
adjacent to a support and a circumference of the lower flange in the center of the
steel beam.
In summary, the present invention relates to a prestressed steel composite
girder comprising a reinforced concrete unit formed to apply stress caused by a self-
weight and an I-shaped steel beam to only the I-shaped steel beam and a tendon
providing the reinforced concrete unit with compressive prestress. The advantages
of the present invention can be summarized as follows:
First, in the steel composite girder structure formed by composing the
concrete around the I-shaped steel beam, the reinforced concrete unit is
manufactured to allow stress caused by the self-weight of the girder to be applied
on only the I-shaped beam. Therefore, unlike conventional engineering methods,
there is no tensile stress caused by the self-weight of the concrete of the girder.
Secondly, the compressive stress for the reinforced concrete unit composed
with the I-shaped beam is introduced by a tendon just before the slab concrete is
placed, and the concrete previously constructed in the manufacturing process has
no stress. Therefore, unlike conventional engineering methods, there is no stress
loss caused by creep deformation that progresses in proportion to the strength of the
stress applied during the girder is placed.
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Thirdly, according to the present invention, the lower flange of the I-
shaped beam has a smaller area than the upper flange. Therefore, the amount of
loss of the compressive stress caused by creep or dry shrinkage deformation of the
reinforced concrete unit can be minimized while the compressive stress is
introduced into the reinforced concrete unit. As a result, it is possible to improve
structural performance and safety of the steel composite girder.
Fourthly, the steel composite girder according to the present invention is
not required to comprise preflexion and release processes for the I-shaped beam, in
which compressive stress is introduced into the concrete by using a recovery force
of the steel beam. Also, an excessive amount of shear connections are not required
to use. Therefore, it is possible to significantly reduce the amount of materials and
construction cost. In addition, it is possible to exclude a work classification which
is dangerous in relation to the preflexion and release processes, and thus to
significantly reduce possibility of a safety accident.
Fifthly, in the steel composite girder according to the present invention, a
tendon and an I-shaped steel beam having a significant strength of bending stiffness
are installed in the concrete. Therefore, a long span can be established while the
height of the beam is low. Particularly, applicability may be remarkable when
there is limitation to overhead clearance or discharge capacity.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features and advantages of the present invention will
become more apparent by describing in detail exemplary embodiments thereof with
reference to the attached drawings in which:
FIGS. 1 to 7 are schematic diagrams for describing a method of
manufacturing a prestressed steel composite girder according to a first embodiment
of the present invention;
FIG. 8 is a perspective view illustrating a prestressed steel composite girder
manufactured by a method of manufacturing the prestressed steel composite girder
according to a first embodiment of the present invention;
FIG. 9 is a front view schematically illustrating a simple support state of a
prestressed steel composite girder according to the present embodiment;
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FIG. 10 is a horizontal cross-sectional view schematically illustrating a
prestressed steel composite girder manufactured by a method of manufacturing a
prestressed steel composite girder according to a second embodiment of the present
invention;
FIG. 11 is a horizontal cross-sectional view schematically illustrating a
prestressed steel composite girder manufactured by a method of manufacturing a
prestressed steel composite girder according to a third embodiment of the present
invention;
FIG. 12 is a horizontal cross-sectional view schematically illustrating a
prestressed steel composite girder manufactured by a method of manufacturing a
prestressed steel composite girder according to a fourth embodiment of the present
invention;
FIG. 13 is a horizontal cross-sectional view schematically illustrating a
prestressed steel composite girder manufactured by a method of manufacturing a
prestressed steel composite girder according to a fifth embodiment of the present
invention;
FIGS. 14 and 15 are front views schematically illustrating a prestressed
steel composite girder manufactured by a method of manufacturing a prestressed
steel composite girder according to a sixth embodiment of the present invention;
FIGS. 16 to 18 are front views schematically illustrating a prestressed steel
composite girder for describing a method of manufacturing a prestressed steel
composite girder according to a seventh embodiment of the present invention;
FIG. 19 illustrates a configuration of an end portion support for supporting
a steel beam according to the present invention; and
FIG. 20 is a side view illustrating a steel beam installed on the end portion
support shown in FIG. 19.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, embodiments of the present invention will be described in detail
with reference to the accompanying drawings.
The prestressed steel composite girder according to the present invention is
structured by casting a concrete in a portion of the steel beam (e.g., a lower flange of
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WO 2006/065085 PCT/KR2005/004320
the I-shaped steel beam if a T-shaped steel beam is used) and introducing
compressive prestress of a predetermined quantity into the concrete using tension of
a tendon. Such a prestressed steel composite girder is placed on an abutment or a
bridge pier to support a concrete slab while compensate for the tensile stress
generated when dead and live loads are applied for the aforementioned
compressive prestress.
FIGS. 1 to 7 are schematic diagrams for describing a method of
manufacturing a prestressed steel composite girder according to a first embodiment
of the present invention.
Now, a method of manufacturing a prestressed steel composite girder 100
according to the embodiment of the present invention will be described. As shown
in FIG. 1, an I-shaped steel beam 10 comprising an upper flange 11, a lower flange
13, and a web 15 for connecting the flanges 11 and 13 with each other is prepared.
As shown in FIG. 2, this I-shaped steel beam 10 is placed in a simply supported
position by providing temporary supports at both ends of the beam 10 (Step S10).
In this case, it is preferable that the lower flange 13 of the I-shaped steel beam 10 has
a smaller area than the lower flange 11 while a plurality of shear connections are
provided on an upper surface of the upper flange 11.
Placing the I-shaped steel beam 10 in a simply supported position at both
ends by supports 20 may be achieved by suspending the beam 10 by a beam-
suspending end support 9110 at both ends as shown in FIGS. 19 and 20. In other
words, the beam-suspending end support 9110 comprises two vertical members 911
erected on the ground; a horizontal member 9111 placed on and supported by the
vertical members 9111; a hydraulic jack 9113 installed on an upper end of the
vertical member 9111 to lift up and down the horizontal member 9112; a bracing
member 9114 slanted by the side of the vertical member 911; a vertical reinforcing
member 9115 interposed between the upper and lower flanges 11 and 13 to
reinforce elasticity of the I-shaped beam 10 when the I-shaped beam is connected to
the horizontal member 912; and a turn-buckle (9116) of which both ends are hinge-
connected between the vertical reinforcing member 9115 and the horizontal member
9112 with bolts and the like to support the I-shaped beam 10. As a result, the I-
shaped beam 10 can be suspended by the beam-suspending end support 9110 in a
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WO 2006/065085 PCT/KR2005/004320
both-ends-supported shape by fixing the vertical reinforcing member 9115 installed
on both ends of the I-shaped beam 10 with the turn-buckle 9116.
Meanwhile, an intermediate support (not shown) having a shape similar to
the beam-suspending end support 9110 may be preferably provided between the
beam-suspending end supports 9110 to avoid lateral buckling or swaying of the
beam during a manufacturing process of the beam.
Then, as shown in FIG. 3, a reinforcement bar assembly 70 is provided by
cross-connecting vertical and horizontal bars on the lower flange 13 of the I-shaped
beam 10. The reinforcement bar assembly 70 is integrated to the beam 10 in a
single body by welding the assembly 70 with the web 15 of the I-shaped beam 10 so
that it can be supported by the I-shaped beam 10 (Step S20).
Subsequently, as shown in FIG. 4, a plurality of sheath pipes 60 for
installing tendons 50 (see FIG. 7) are disposed in the lower flange 13 and the bar
assembly 70 (Step S30). In this case, the sheath pipe 60 is preferably installed in an
internal space of the reinforcement bar assembly 70 around the lower flange 13
along a length of the I-shaped beam.
Then, as shown in FIG. 5, a form 40 for placing the concrete is installed to
be supported by only the I-shaped beam 10. For this purpose, a separate support
member 80 as shown in a one-dotted chain line in FIG. 5 is used to integrate the
form 40 into the I-shaped beam 10. In this case, the support member 80 may
comprise: a first support 81 for transferring the load of the form 40 to the upper
flange of the I-shaped beam 10; a second support 82 for substantially connecting the
first support 81 and the form 40 to transfer a vertical load; and a third support 83
connected to the I-shaped beam 10 to transfer the horizontal load applied on the
form 40.
As a result, as shown in FIGS. 19 and 20, since the I-shaped beam 10 is
suspended from the ground with its both ends supported, the self-weight of the
form 40 is supported by the I-shaped beam 10 and the support member 80 while the
form 40 surrounds the bar assembly 70 and the sheath pipes 60.
Subsequently, as shown in FIG. 6, a predetermined amount of the concrete
is inserted into the internal space of the form 40, and then cured during a
predetermined time period (Step S40) (see FIG. 6). In this state, it is noted that
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bending moment is generated in the I-shaped beam 10 by the load of the I-shaped
beam 10 and the concrete itself, and compressive stress is applied on the upper
flange while the tensile stress is applied on the lower flange 13.
After the concrete surrounding the lower flange of the I-shaped beam 10 is
completely cured, the form 40 is removed from the I-shaped beam 10. Then, as
shown in FIG. 7, tendons 50 are inserted into the inside of the sheath pipes 60. As a
result, it is possible to provide a reinforced concrete unit 30 having no stress on the
lower flange 13 while the lower flange 13 is sufficiently tensioned by the self-
weights of the I-shaped beam 10 and the concrete.
Through the aforementioned process, it is possible to manufacture a
prestressed steel composite girder 100 according to a first embodiment of the
present invention, in which the reinforced concrete unit 30 is built in the lower
flange 13 of the I-shaped beam 10 with no stress while only the I-shaped beam 10
experiences the stress caused by the self-weights of the I-shaped beam 10 and the
concrete.
FIG. 8 is a perspective view illustrating a prestressed steel composite girder
manufactured according to a method of manufacturing a prestressed steel
composite girder according to a first embodiment of the present invention, and FIG.
9 is a front view schematically illustrating a simple support state of a prestressed
steel composite girder according to the present embodiment.
Referring to FIGS. 8 and 9, just before or after the steel composite girder
100 manufactured as the described above is placed on a bridge or an abutment, the
tendons 50 are tensioned by using a tension device such as a hydraulic jack as
shown in FIG. 7, and both ends of the tendon 50 are anchored on both ends of the
reinforced concrete unit 30 using an anchorage 90. As a result, a predetermined
strength of compressive stress is introduced into the reinforced concrete unit 30.
Now, the prestressed steel composite girder 100 configured as described
above will be described in more detail. The prestressed steel composite girder 100
comprises: an I-shaped steel beam 10; a reinforced concrete unit 30 mixed with the I-
shaped beam 10 to be supported by the I-shaped beam 10 with no stress; and a
tendon 50 installed in the reinforced concrete unit 30 to provide prestress with the
reinforced concrete unit 30.
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The I-shaped beam 10, as described above, comprises: an upper flange 11; a
lower flange 13; and a web 15 for connecting the flanges 11 and 13 with each other.
The upper and lower flanges 11 and 13 are connected to upper and lower sides of
the web 15 which horizontally elongated and thus also horizontally elongated.
Preferably, the lower flange 13 of the I-shaped beam 10 has a smaller area
than the upper flange 11. In the I-shaped beam 10 having such a shape, since a
neutral axis is substantially high for the upper and lower flanges 11 and 13, the
lower flange 13 can be subjected to sufficient tensile stress by the self-weights of the
I-shaped beam 10 and the reinforced concrete unit 30. In other words, in the I-
shaped beam 10, the upper flange experiences compressive stress and the lower
flange experiences tensile stress by the self-weights of the I-shaped beam 10 and the
reinforced concrete unit 30.
As shown in FIG. 9, the reinforced concrete unit 30 (referred to as a lower
flange concrete in the art) is combined with the lower flange 13 of the I-shaped beam
10 by using the reinforcement bar assembly 70 and the form 40 (see FIG. 5)
supported by only the I-shaped beam 10 while both ends of the I-shaped beam 10
are simply supported by the support 20.
More specifically, in the process of manufacturing the steel composite
girder according to the present,
Since the reinforced concrete unit 30 is manufactured in such a way that
both ends of the I-shaped beam 10 are simply supported by supports 20, and the
form 40 is supported by only the I-shaped beam 10, the entire self-weight of the
concrete placed in the form 40 is transferred to the I-shaped beam 10. In other
words, the reinforced concrete unit 30 is combined with the lower flange 13 while
the lower flange 13 experiences sufficient tensile stress by the self-weights of the I-
shaped beam 10 and the concrete itself.
Therefore, since the I-shaped beam 10 is substantially responsible for the
self-weights of the I-shaped beam 10 and the reinforced concrete unit 30, if the
concrete is cured and the form 40 is removed, the reinforced concrete unit 30 is
supported by the lower flange 13 of the I-shaped beam 10 with no stress.
As a result, in the steel composite girder 100 according to a first
embodiment of the present invention, the stress caused by the self-weights of the I-
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WO 2006/065085 PCT/KR2005/004320
shaped beam 10 and the reinforced concrete unit 30 is applied on only the I-shaped
beam 10 while its both ends are simply supported by the supports 20, but the stress
caused by the self-weights is not applied on the reinforced concrete unit 30. In this
case, the stress applied on the I-shaped beam 10 is generated by the weights of the I-
shaped beam 10 and the reinforced concrete unit 30, and includes compressive
stress applied on the upper flange and tensile stress applied on the lower flange.
The tendon 50 which provides prestress on the reinforced concrete unit 30
is inserted into the sheath pipe 60 distributed around the reinforced bar assembly 70
and the lower flange 13 along the length of the I-shaped beam 10.
Both ends of the tendon 50 may be installed on both ends of the reinforced
concrete unit 30 by twisting strands in a single one and tensioning it with a
tensioning device such as a hydraulic jack.
For this purpose, as shown in FIG. 8, an anchorage 90 is provided on both
ends of the reinforced concrete unit 30 for anchoring both ends of the tendon 50 in
both ends of the reinforced concrete unit 30. In this case, the anchorage 90 has a
typical jointing structure that can joint the tendon 50 at both ends of the reinforced
concrete unit 30 by installing a wedge with an anchor cone (not shown).
Now, advantages of the prestressed steel composite girder 100 according to
the embodiment of the present invention will be described below. Since the
prestressed steel composite girder 100 is manufactured by sufficiently tensioning
the I-shaped beam 10 and combining the reinforced concrete unit 20 with the lower
flange 13 of the I-shaped beam 10 without stress, no stress is generated by the self-
weight of the steel composite girder 100. Also, since the stress generated by the
self-weight of the steel composite girder 100 is not applied on the reinforced
concrete unit 30 while both ends of the girder 100 is simply supported by the
supports 20, the loss of compressive stress caused by the self-weight is not
generated, and particularly, since the concrete experiences no stress, there is no
stress loss caused by creep deformation that progresses in proportion to the strength
of the applied stress. In addition, it is possible to consider additional loads that
will be applied on the girder 100 after completing construction of a bridge by
combining slab concrete. Also, since tension is introduced by the tendon just
before the slab concrete is placed, and the applied stress is not large in a common
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WO 2006/065085 PCT/KR2005/004320
use, the loss of compressive stress caused by creep of the concrete with the slab
mixed is negligible. Furthermore, if the steel composite girder is collapsed, and the
reinforced concrete unit 30 is completely broken down so that the girder loses its
function, the lower flange 13 of the I-shaped beam 10 does not experience much
marginal stress. As a result, its cross-section can be efficiently used.
Further, in the prestressed steel composite girder 100 according to the
present embodiment, the lower flange of the I-shaped beam 10 has a smaller area
than the upper flange 11. Therefore, it is possible to reduce loss of the compressive
prestress caused by dry shrinkage deformation of the reinforced concrete unit 30
after the compressive prestress is introduced into the reinforced concrete unit 30.
Furthermore, in the prestressed steel composite girder 100 according to the
present embodiment, the upper flange 11 of the I-shaped beam 10 experiences
relatively less compressive stress in comparison with the tensile stress applied on
the lower flange 13. Therefore, it is possible to have a large margin for additional
loads.
FIG. 10 is a horizontal cross-sectional view schematically illustrating a
prestressed steel composite girder manufactured by a method of manufacturing a
prestressed steel composite girder according to a second embodiment of the present
invention.
Now, a method of manufacturing a prestressed steel composite girder
according to a second embodiment of the present invention will be described with
reference to the accompanying drawings. Similar to the steps S20 and S30
described above, the reinforcement bar assembly 170 and the form 140 are installed
in the I-shaped beam 110. However, according to the second embodiment, the
reinforcement bar assembly 170 and the form 140 surrounds the lower flange 113
and the web 115 of the I-shaped beam 110 as shown in FIG. 10, and they are
supported by only the I-shaped beam 110.
In this state, concrete is placed in an internal space of the form 140 and
cured, and the form 140 is removed.
Through this manufacturing method, a prestressed steel composite girder
200 according to a second embodiment of the present invention can be
manufactured by combining the reinforced concrete unit 130 with the lower flange
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WO 2006/065085 PCT/KR2005/004320
113 and the web 115 of the I-shaped beam 110. It should be noted that the tendon
150 is also installed between the opposite sheath pipes 160 of the reinforced concrete
unit 130.
In the second embodiment, since other manufacturing procedures,
structures, and effectiveness are similar to those of the aforementioned first
embodiment, their descriptions will be omitted.
FIG. 11 is a horizontal cross-sectional view schematically illustrating a
prestressed steel composite girder manufactured by a method of manufacturing a
prestressed steel composite girder according to a third embodiment of the present
invention.
Now, a method of manufacturing the prestressed steel composite girder
according to a third embodiment of the present invention will be described with
reference to FIG. 11. Similar to the steps S20 and S30 of the aforementioned first
embodiment, the reinforcement bar assembly 270 and the form 240 are installed in
the I-shaped beam 210. However, according to the third embodiment, the
reinforcement bar assembly 270 and the form 240 surrounds the entire I-shaped
beam 110 as shown in FIG. 11, and they are supported by only the I-shaped beam
110.
In this state, concrete is placed in an internal space of the form 240 and
cured, and the form 240 is removed.
According to the method of manufacturing the prestressed steel composite
girder according to the third embodiment, the reinforced concrete unit 230
surrounds the entire I-shaped beam 210, or preferably, the entire surfaces excluding
an upper surface of the upper flange 211 of the I-shaped beam. It should be noted
that the tendon 250 is also installed between the opposite sheath pipes 260 of the
reinforced concrete unit 230.
In the third embodiment, since other manufacturing procedures, structures,
and effectiveness are similar to those of the aforementioned first embodiment, their
descriptions will be omitted.
FIG. 12 is a horizontal cross-sectional view schematically illustrating a
prestressed steel composite girder manufactured by a method of manufacturing a
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WO 2006/065085 PCT/KR2005/004320
prestressed steel composite girder according to a fourth embodiment of the present
invention.
Now, a method of manufacturing the prestressed steel composite girder
according to a fourth embodiment of the present invention will be described with
reference to FIG. 12. Similar to the steps S20 of the aforementioned first
embodiment, the sheath pipe 360 is installed. However, according to the fourth
embodiment, the sheath pipe 360 is installed in a parabolic shape as shown in the
one-dotted chain line of FIG. 12, so that the sheath pipe 360 can be extended via the
web 315 of the I-shaped beam 310 corresponding to the support 320 and a
circumference of the I-shaped beam 310 in the center of the lower flange 313.
In this state, concrete is placed in the lower flange 313 of the I-shaped beam
310 and portions of the web 315 corresponding to the supports 320, and cured.
Then, a tensioning device such as a hydraulic jack is used to tension the tendon 350
while the tendon 350 (shown as a one-dotted chain line in FIG. 12) is installed in the
internal space of the sheath pipe 360. Subsequently, both ends of the tendon 350
are fixed at both ends of the concrete unit 330 through the anchorage 390. The fourth
embodiment of the present invention is not limited to the configuration of installing
the anchorage 390 in both ends of the concrete unit. Alternatively, the anchorage
390 may be installed in an inner side separated from the concrete unit 390 with a
predetermined distance.
According to the fourth embodiment of the present invention, it is possible
to manufacture a prestressed steel composite girder 400 having a sheath pipe 360
extending in a parabolic shape via the web 315 adjacent to the supports 320 and the
lower flange 313 in the center of the I-shaped beam 310.
In the fourth embodiment, since other manufacturing procedures,
structures, and effectiveness are similar to those of the aforementioned first
embodiment, their descriptions will be omitted.
FIG. 13 is a horizontal cross-sectional view schematically illustrating a
prestressed steel composite girder manufactured by a method of manufacturing a
prestressed steel composite girder according to a fifth embodiment of the present
invention.
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WO 2006/065085 PCT/KR2005/004320
Now, a method of manufacturing the prestressed steel composite girder
according to a fifth embodiment of the present invention will be described with
reference to FIG. 13. Similar to the steps S10 of the aforementioned first
embodiment, the I-shaped beam 410 is provided. However, according to the fifth
embodiment of the present invention, at least two I-shaped beams 410, or preferably,
a pair of I-shaped beams 410 are provided in such a way that they can be lined up
with a predetermined interval.
In this state, the reinforcement bar assembly 470 and the form 440 are
installed in the I-shaped beam 410 as shown in FIG. 13. Specifically, the
reinforcement bar assembly 470 and the form 440 surrounds the lower flanges 113
and the webs 115 of two I-shaped beams 410 together, so that they can be supported
by only the I-shaped beams 410.
Then, concrete is placed in an internal space of the form 440 and cured, and
the form 440 is removed.
In the fifth embodiment of the present invention, since the reinforced
concrete unit 430 is manufactured to surround a pair of I-shaped beams 410 together,
a cross-sectional shape of the girder 500 can have a U-shape. In this case, it should
be noted that the sheath pipe 460 is also provided in the reinforced concrete unit 430,
and the tendon 450 is also inserted into the sheath pipe 460.
If the prestressed steel composite girder 500 according to the fifth
embodiment of the present invention is employed in a deck bridge, the cross-
sectional shape of the bridge after applying concrete slabs may be a closed shape.
As a result, it is possible to increase torsional stiffness allowing for a long span of a
bridge. In addition, the prestressed steel composite girder according to the fifth
embodiment of the present invention can be used as a deck bridge.
In the fifth embodiment, since other manufacturing procedures, structures,
and effectiveness are similar to those of the aforementioned first embodiment, their
descriptions will be omitted.
FIGS. 14 and 15 are front views schematically illustrating a prestressed
steel composite girder manufactured by a method of manufacturing a prestressed
steel composite girder according to a sixth embodiment of the present invention.
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WO 2006/065085 PCT/KR2005/004320
Now, a method of manufacturing the prestressed steel composite girder
according to a sixth embodiment of the present invention will be described with
reference to FIGS. 14 and 15. As shown in FIG. 14, after the Step S30 in the
aforementioned first embodiment, a weighting member W having a predetermine
weight is disposed on the I-shaped beam 510 to generate positive moment on the I-
shaped beam 510.
In this state, concrete is placed in an internal space of the former 540 shown
as a dashed line in FIG. 14 and cured, and the weight member W and the former 540
are removed. As a result, as shown in FIG. 15, it is possible to introduce additional
compressive stress into the reinforced concrete unit 530 by the weighting member W.
The prestressed steel composite girder 600 according to the sixth
embodiment of the present invention is manufactured by a manufacturing process
similar to that of the first embodiment. However, since the self-weight of the
weighting member W is applied on the I-shaped beam 510, it is possible to more
easily compensate for the tensile stress generated in a negative moment cross-
section when a design load is applied.
FIGS. 16 to 18 are front views schematically illustrating a prestressed steel
composite girder for describing a method of manufacturing a prestressed steel
composite girder according to a seventh embodiment of the present invention.
Now, a method of manufacturing the prestressed steel composite girder
according to a seventh embodiment of the present invention will be described with
reference to FIGS. 16 through 18. As shown in FIG. 16, taking the structure of the I-
shaped beam and a delivery condition into account, three girder members 610a,
610b, and 610c that have been previously manufactured in a factory are prepared.
The three girder members 610a, 610b, and 610c are combined with one another in a
single body to provide an I-shaped beam 610 according to the seventh embodiment
of the present invention.
In this process, connecting plates 617 are provided at the connecting areas
a and b (i.e., adjoining portions of the girder members 610a, 610b, and 610c in an
upper flange 611a, a lower flange 613a, and a web 615a), and then, fixing members
such as bolts are engaged in the connecting plate 617, so that each of the girder
members 610a, 610b, and 610c are connected with one another in a single body.
21

WO 2006/065085 PCT/KR2005/004320
In this state, as shown in FIG. 17, the reinforced concrete unit 630 is formed
in the lower flange 613a except for the connection areas a and b of the girder
members 610a, 610b, and 610c through a process similar to that of the first
embodiment.
Then, the connecting plates 617 provided in the connecting areas a and b
are removed from the girder members 610a, 610b, and 610c, so that three pieces of
segmented girders 600a, 600b, and 600c are manufactured.
Then, the segmented girders 600a, 600b, and 600c are delivered to a
construction site, the connecting plates 617 are installed in each of the connecting
areas a and b of the segmented girders 600a, 600b, and 600c, so that the each of the
segmented girders 600a, 600b, and 600c are connected in a single body.
Subsequently, as shown in FIG. 18, the reinforcement bar assemblies 670a
and the sheath pipes 650a shown as a dashed line are also installed in the
connecting areas a and b between the segmented girders 600a, 600b, and 600c (i.e.,
between the reinforced concrete units 630 of each segmented girder 600a, 600b, and
600c). The reinforcement bar assembly 670a may be connected to the opposite
reinforcement bar assembly 670 installed in the reinforced concrete unit 630 of each
segmented girder 600a, 600b, and 600c by using a typical connection method such as
a welding. Similarly, the sheath pipe 650a may be connected to the opposite sheath
pipe 650 installed in the reinforced concrete unit 630 of each segmented girder 600a,
600b, and 600c by using a jointing member (not shown).
Subsequently, the forms (not shown) are installed in each connection area a
and b between the segmented girders 600a, 600b, and 600c. Then, concrete is
placed in the forms and cured for a predetermined time period, and the forms are
removed. As a result, it is possible to manufacture a prestressed steel composite
girder 700 having a segmented structure according to the seventh embodiment of
the present invention, in which the reinforced concrete unit 630 is connected along a
plurality of lower flanges (not shown) of all the I-shaped beams 610.
While the present invention has been particularly shown and described
with reference to exemplary embodiments thereof, it will be understood by those
skilled in the art that various changes in form and details may be made therein
22

WO 2006/065085 PCT/KR2005/004320
without departing from the spirit and scope of the present invention as defined by
the appended claims.
23

WO 2006/065085 PCT/KR2005/004320
WHAT IS CLAIMED IS:
1. A method of manufacturing a prestressed steel composite girder by
using a steel beam and a concrete, the method comprising steps of:
placing the steel beam above the ground;
installing a form, into which the concrete is to be inserted, to
surround at least a portion of the steel beam, the form being suspended by the steel
beam;
inserting the concrete into an internal space of the form and curing
it; and
removing the form to compose the steel beam and the concrete.
2. The method of claim 1, further comprising steps of:
installing a reinforcement bar and a sheath pipe for inserting a
tendon in the steel beam before placing the concrete and curing it; and
introducing compressive prestress into the concrete by tensioning
the tendon in the sheath pipe after composing the concrete.
3. The method of claim 2, wherein in the installation of the sheath
pipe, the steel beam is an I-shaped beam comprising an upper flange, a lower flange,
and a web; and the sheath pipe is arranged around the lower flange of the steel
beam along a length of the steel beam.
4. The method of claim 3, wherein in the installation of the sheath
pipe, the sheath pipe is extended in a parabolic shape via the web adjacent to a
support and a circumference of the lower flange in the center of the steel beam.
5. The method of claim 1, wherein in the placing the steel beam above
the ground, the steel beam is supported at both ends thereof.
6. The method of claim 5, wherein the steel beam is suspended by a
beam-suspending end supports disposed at both ends of the steel beam.
24

WO 2006/065085 PCT/KR2005/004320
7. The method of claim 5 or 6, wherein an intermediate support is
further provided between the beam-suspending end supports to avoid lateral
buckling or swaying of the steel beam.
8. The method of claim 3, wherein the reinforcement bar and the form
surrounds the lower flange of the steel beam.
9. The method of claim 3, wherein the reinforcement bar and the form
surrounds the lower flange and the web of the steel beam.
10. The method of claim 2, wherein the reinforcement bar and the form
surrounds the entire steel beam.
11. The method of any one of claims 1 to 6 and 8 to 10, further
comprising:
placing a weighting member on an upper surface of the steel beam
to generate positive moment on the steel beam before composing the concrete and
me steel beam; and
removing the weight member after composing the steel beam and
the concrete,
thereby introducing compressive prestress into the concrete.
12. The method of any one of claims 1 to 6 and 8 to 10,
wherein the steel composite girder is segmented into more than
three segments, and
wherein the segments of the steel composite girder are connected
with one another before introducing the compressive prestress, and the concrete is
inserted into connection portions of the segments and cured.
13. The method of any one of claims 1 to 6 and 8 to 10,
wherein the steel beam is an I-shaped beam comprising an upper
flange, a lower flange, and
25

WO 2006/065085 PCT/KR2005/004320
wherein a web connecting the upper flange and the lower flange,
and an area of the upper flange is larger than that of the lower flange.
14. A method of manufacturing a prestressed steel composite girder by
composing steel beams and a concrete in a single body, the method comprising
steps of:
placing the steel beams above the ground, the steel beams are
separated from each other;
installing a form, into which the concrete is to be inserted, to
surround a portion of two or more steel beams, the form being suspended by the
steel beam;
inserting the concrete into an internal space of the form and curing
it; and
removing the form to composing two or more steel beams and the
concrete.
15. The method of claim 14, wherein the form surrounds a portion of
the steel beam in a U-shape.
16. The method of claim 14, wherein the form surrounds a portion of
all the steel beams to compound the concrete.
17. The method of claim 14, further comprising:
installing a sheath pipe for inserting an reinforcement bar and a
tendon into the steel beam before inserting the concrete and curing it; and
tensioning the tendon in the sheath pipe to introduce compressive
prestress in the concrete after composing the concrete.
18. The method of any one of claims 14 to 17, wherein the steel beam is
an I-shaped beam comprising an upper flange, a lower flange, and a web connecting
the upper and lower flanges, and an area of the upper flange is larger than that of
the lower flange.
26

WO 2006/065085 PCT/KR2005/004320
19. A prestressed steel composite girder, comprising:
a steel beam;
a concrete composed to surround a portion of the steel beam so that
stress caused by its self-weight can be applied on only the steel beam;
a tendon installed in the steel beam and /or the concrete to provide
the concrete with compressive prestress; and
a reinforcement bar installed in the steel bar and/or the concrete to
reinforce strength of the concrete.
20. A prestressed steel composite girder, comprising:
a plurality of steel beams separated from each other;
a concrete formed to surround a portion of the plurality of steel
beams together, so that stress caused by its self-weight is applied on only the steel
beams;
a tendon installed in the steel beam and/or the concrete to provide
the concrete with compressive stress; and
a reinforcement bar installed in the steel beam and/or the concrete
to reinforce strength of the concrete.
21. The prestressed steel composite girder of claim 19 or 20, wherein
the steel beam is an I-shaped beam comprising an upper flange, a lower flange, and
a web connecting the upper and lower flanges.
22. The prestressed steel composite girder of claim 21, wherein the
upper flange of the steel beam has a large area than the lower flange of the steel
beam.
23. The prestressed steel composite girder of claim 21, wherein the
concrete surrounds the lower flange of the steel beam.
27

WO 2006/065085 PCT/KR2005/004320
24. The prestressed steel composite girder of claim 21, wherein the
concrete surrounds the lower flange and the web of the steel beam.
25. The prestressed steel composite girder of claim 21, wherein the
concrete surrounds the entire I-shaped beam.
26. The prestressed steel composite girder of any one of claims 19 to 25,
wherein the tendon is extended in a parabolic shape via the web adjacent to a
support and a circumference of the lower flange in the center of the steel beam.
28

A prestressed steel composite girder and a method
of manufacturing the prestressed steel composite girder are provided
by using a steel beam and a concrete. The method includes steps of:
placing the steel beam above the ground; installing a form, into which
the concrete is to be inserted, to surround at least a portion of the steel
beam, the form being suspended by the steel beam; inserting the concrete
into an internal space of the form and curing it; and removing
the form to compose the steel beam and the concrete. The prestressed
steel composite girder includes a steel beam and a concrete composed
to surround a portion of the steel beam so that stress caused by its self-weight can be applied on only the steel beam.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=4sDgZEfM6mExe9vJ/Hnj/Q==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

272485

Indian Patent Application Number

2446/KOLNP/2007

PG Journal Number

15/2016

Publication Date

08-Apr-2016

Grant Date

04-Apr-2016

Date of Filing

02-Jul-2007

Name of Patentee

RESEARCH INSTITUTE OF INDUSTRIAL SCIENCE & TECHNOLOGY

Applicant Address

SAN 32, HYOJA-DONG, NAM-KU, POHANG-CITY, KYUNGSANGBUK-DO

Inventors:

#	Inventor's Name	Inventor's Address
1	LEE PIL GOO	101-101 HANVITSAMAUNG APT., SEOCHO-DONG, SEOCHO-KU, SEOUL 137-070

PCT International Classification Number

E01D 2/00

PCT International Application Number

PCT/KR2005/004320

PCT International Filing date

2005-12-15

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	102005-0079067	2005-08-26	Republic of Korea
2	102005-0079069	2005-08-26	Republic of Korea
3	102004-0106173	2004-12-15	Republic of Korea
4	102004-0106230	2004-12-15	Republic of Korea