WO2006065085A1

WO2006065085A1 - Manufacturing method for prestressed steel composite girder and prestressed steel composite girder thereby

Info

Publication number: WO2006065085A1
Application number: PCT/KR2005/004320
Authority: WO
Inventors: Pil Goo Lee
Original assignee: Research Institute Of Industrial Science & Technology; Sam Hyun P F. Co., Ltd
Priority date: 2004-12-15
Filing date: 2005-12-15
Publication date: 2006-06-22

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.

Description

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 i 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 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 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/cπf, 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 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. 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 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 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 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. hi 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. 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 rninimized 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; 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 QF 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 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 SlO). 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 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 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. 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. hi 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- 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 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 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 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. hi 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. 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 SlO 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. 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. 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 without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

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.

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 the 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 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.

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.

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.