[BACKGROUND ART] In general, for various structures, structural steel and concrete are typically used as a structural member that resists a bending moment.

Concrete is most widely used because it is cheap and easy to be formed in various shapes and provides protection against vibrations. Concrete has great compressive strength, but little tensile strength. Thus, a structure subject to deflection where both compression and tension are generated requires reinforcement with respect to the tension. To do this, reinforced concrete beams which are designed such that steel reinforcement bars resist the tension in the tension zone irrespective of the strength of concrete or

prestressed concrete beams (hereinafter, called"PSC beams") which allow concrete in the tension zone to be effectively used due to pre-applied compressed prestress in the tension zone is being used.

Since most PSC structures as well as the PSC beams use a tension member made from high-strength steel tendons, they have similar elastic coefficients with generally used steel but has four to six times greater strength than the generally used steel. Thus, they are very suitable to be harmonized with concrete. Since the tension member has a high strength against an elastic coefficient, that is, having a very high elongation ratio, very large deformation should be accompanied in order to make the most use of the strength. Therefore, the tension member is not appropriate to be directly applied to a structure and support a dynamic load. However, if the tension member is used as a material for the applying of prestress to concrete, it is very useful and has the advantage that internal stress loss is minimal due to the long-term plastic deformation such as drying shrinkage or a creep of the concrete. That is, when the tension member is embedded into the tension zone in a state that the tension member is deformed with the large amount of deformation and has a tensile stress, a compressive force is applied to the concrete as a reaction force. Compressed prestress applied to concrete allows the concrete in the tension zone to withstand a tensile load, thereby increasing a supportive rigidity.

Meanwhile, an attempt to use PSC beams for low height structures

and large spans has been continuously made according to changes in market environments. According to this, the application of only compressed prestress in the tension zone of concrete is sometimes not enough. To reduce the amount of variation in stresses generated in the tension zone due to loads such as the weight of the structure itself or an external force, there have been attempts to design a neutral axis, which is a boundary surface between the compression zone and the tension zone, at a location that is closer to the tension zone by minimizing the compression zone and maximizing the tension zone. However, such a design causes problems because excessive compressive stresses are applied in the compression zone. In addition, similar problems are caused when repetitive prestressing is carried out according to an increase of loads on all phases of construction.

As for a prestressing method using tension members, the application of compression zone in the tension zone is relatively easy, while the application of tensile prestress in the compression prestress is relatively very difficult.

Moreover, a small amount of tensile force can be applied to concrete in the compression zone opposite to an eccentric direction by enlarging eccentricity, a distance between the center of the cross-section and the tension member, but there are limitations of a maximum eccentricity. That is, as shown in Figure 6, which illustrates the forces applied to a structural member according to where the tension members are anchored and illustrates a moment diagram, the forces applied to the structural member vary according

to how the tension members are arranged and where the tension members are located. Particularly, a moment applied to a specific cross-section varies according to the location of the tension members in the cross-section and the magnitude of a tensile force.

Herein, the magnitude of the moment is obtained by multiplying <BR> <BR> eccentricity (i. e. , a distance between the tension member and the neutral axis of the cross-section) by the tensile force. Thus, in order to enlarge eccentricity, the member should be heightened, that is, the height should be increased. However, in order to maintain the height to a certain degree, a tensile force of the tension member should be increased. In this case, the moment is increased but more compressive force than is necessary is applied to the member, causing the problem that the compression zone of the member is destroyed first.

As stated above, the applying compressed prestress in the tension zone of the structural member has limitation in that no more than an effect to make up for lack of tensile strength can be obtained, and therefore has a limit in an aspect of efficiency in designing a cross-section by using prestressing. Accordingly, in order to support a much greater external force, <BR> <BR> it is necessary to pre-apply (i. e. , apply in advance) a moment in a direction that is opposite to a moment by the external force to the cross-section of the structural member by applying not only an eccentric compressive force but also a compressive force and a tensile force at the same time by using both

a compression member and a tension member in the cross-section of the structural member.

A technique of applying tensile prestress in the compression zone of a structural member by using compression members is disclosed in Japanese Laid Open Publication No. 10-220009, entitled"METHOD OF PUSHING AND ANCHORING COMPRESSED PC STEEL ROD". That is, as shown in Figure 7, the method is as follows : a mold made of steel is embedded to penetrate an upper portion of a PSC beam, which is the compression zone, in order to apply a compression force to a compression member of high strength, then cut portions are formed at upper surfaces in the vicinity of both ends of the PSC beam, then a compression member 13 is anchored to the steel mold, and the compression member 13 is pushed into the mold made of steel by means of compression jacks 30 formed at both sides. In addition, if a prestressing procedure is completed, the spaces between a sheath pipe and the compression member are filled with grout and the cut portions are filled with concrete or mortar.

That is, compressed prestress is applied to a lower portion of the PSC beam, which is a structural member 10 subject to deflection by a bending moment, by tensioning a tension member 12 in advance and then anchoring the tensioning member, and tensile prestress is applied to an upper portion of the PSC beam by disposing the compression member 13 passing by an anchoring cut portion 32 to a position where the compression member 13

does not reach a working cut portion 31. In addition, by putting the compression jack 30 into the working cut portion 31, the compression member 13 is pushed in at the support of the rear concrete and then the compressed compression member 13 is fixed by tightening a fixing bolt at the anchoring cut portion 32. Since the end of the compression member 13 is laid in concrete between the working cut portion 31 and the anchoring cut portion 32, the force is indirectly applied by inserting a separate steel bar.

However, such a technique has not only low constructability and economical efficiency but also has technical limitations. That is, local stresses are concentrated on a portion where a reaction force of the compression jack is applied and a portion where the compression member is anchored. In general, local stresses are concentrated on the anchoring part of the tension member but compressive stresses are mainly generated, whereby proper reinforcement may resolve this problem. However, it is very difficult to achieve proper reinforcement for completely preventing cracks because tensile stresses are generated when the compression member is anchored.

Additionally, problems are also created because the work must be done at an upper surface of the PSC beam. According to the trend of efficiently designing a cross-section, materials of high strength for prestressing are designed to withstand more dead loads, while concrete is designed to support and withstand live loads requiring a stiffness property

against vibration or deflection by bending moment. In order to realize those objects, a prestressing procedure should be performed after dead loads such as slabs are additionally generated in addition to the weight of the PSC beam itself. However, in the conventional art, in case that the slabs are constructed, as a sufficient working area for the prestressing procedure is not provided, it was very difficult to work the prestressing job.

In addition, since a job of tensioning a tension member and a procedure of compressing a compression member are separately done, the procedures are complicated, analysis is required according to each phase of construction, respective anchoring parts for the tension member and the compression member are designed, and a tension jack and a compression jack are respectively necessary for the procedures.

[DISCLOSURE OF THE INVENTION Therefore, it is an object of the present invention to provide a method of applying prestress and to provide a device used therein which can apply deflection in an opposite direction to loads without applying an axial force to a structural member subject to deflection, by a simple tensioning procedure by implementing tension of a tension member and compression of compression members at the same time.

It is another object of the present invention to make it unnecessary to provide the separate reinforcement of an anchoring part to the structural

member as the compression members and the tension member connected by means of an anchoring device receive each other's reaction forces.

To achieve the above object, there is provided a method of applying prestress, comprising: disposing a tension member in the tension zone of the structural member in a longitudinal direction thereof such that the tension member is not attached to the structural member and exposing the tension member to the end of the structural member; disposing compression members in the compression zone of the structural member in the longitudinal direction thereof such that the tension member is not attached to the structural member; fixedly installing an anchoring device for connecting the compression members with the tension member at the compression members, and tensioning the tension member penetrating the anchoring device, wherein a reaction force against a tensile force of the tension member is applied to the compression members through the anchoring device as a compression force, so that a tensile force is applied to the tension member and a compressive force is applied to the compression members at the same time. That is, the structural member receives an upward force at the center and a downward force at the end according to an arrangement of the tension member and the compression members without being affected by the anchorage of the tension member and the compression members. At this time, the anchoring device should be formed, to which the compression members and the tension member can be anchored and in

which forces generated from the tension member and the compression members are balanced of themselves.

Here, preferably, the method further comprises injecting grouting materials through a prearranged grouting hose connected to the spaces between the tension member, the compression members and the structural member and exposed to the outside, hardening the grouting materials, and then releasing the anchoring device after the tensioning step, so that the anchoring device can be recycled.

Meanwhile, the present invention provides an anchoring device used to apply prestress to a structural member provided with a tension member and compression members, comprising: a body having a first hole which the bundled tension member penetrates and second holes formed at both sides of the first hole of the tension member, which the compression members penetrate; fixing bolts for fixing the compression members penetrating the body at the front and rear of the body; an anchor plate having a plurality of third holes the tension member can penetrate wire by wire and closing the first hole ; wedges for anchoring the tension member to the third holes of the anchoring plate after the tension member is tensioned, wherein a reaction force is transferred to the anchoring plate and the body during the tensioning of the tension member and the transferred reaction force is transferred to the compression members through the fixing bolts to thereby apply a compressive force. Through this, an axial force is not applied to the structural

member, deflection is generated according to an arrangement of the compression members and the tension member, the separate reinforcement for anchoring the tension member and the compression members is not required for the structural member, and a large moment can be applied to the structural member by one tensioning procedure.

In addition, in order to achieve the above object, there is also provided a prestress concrete beam, comprising : concrete ; compression members buried in an upper portion of said concrete in a longitudinal direction by means of a sheath pipe such that the compression members are not attached to a structural member; a tension member with a curvature whose center faces upward buried in a lower portion of said concrete in a longitudinal direction; an anchoring device for fixing the tension member and the compression members at the end of said concrete, wherein the tension member penetrates the anchoring device and is exposed to the outside, the compression members are fixed to the anchoring device, and a compressive force is applied to the compression members through the anchoring device by pulling the tension member.

In addition, in applying prestress in an opposite direction to deflection due to loads such as the weight of the structural member or an external force applied thereto in case that a material having weakness in tension such as concrete are used for the material of the structural member, the strength of such material having weakness in tension can be reinforced by applying

prestress by using the conventional prestressing method together.

[BRIEF DESCRIPTION OF THE DRAWINGS] Figure 1 illustrates forces applied to a structural member when a tension member is tensioned by a method according to the present invention and a moment diagram corresponding to the forces; Figure 2 shows views illustrating a force applied to the structural member when a tension member is tensioned for continuity in a state that one end of a compression member is attached to the structural member and a moment diagram due to the force ; Figure 3 is a front view illustrating a prestressed concrete beam in accordance with one embodiment of the present invention; Figure 4 is a side view of Figure 3; Figure 5 illustrates one embodiment of an anchoring device fixed to the compression members for anchoring the tension member, which is shown in different directions; Figure 6 illustrates forces applied to the structural member according to where the tension members are anchored according to the conventional prestressing method and a moment diagram; Figure 7 illustrates the conventional construction for applying tensile prestress; and Figure 8 shows a comparison between stresses induced over the

structural member in accordance with the conventional prestressing method and one embodiment of the present invention.

(MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS] Hereinafter, the preferred embodiments of the present invention will described in detail with reference to the accompanying drawings.

As shown in Figures 1 to 4, a method of applying prestress in accordance with one embodiment of the present invention comprises : sinking a tension member 12 with a downward curvature into a sheath pipe 11 at a lower portion of a structural member 10, the tension zone in a longitudinal direction of the structural member 10, and disposing the tension member 12 not to be attached to the structural member 10, and simultaneously exposing the tension member 12 to the. end of the structural member 10; sinking compression members 13 into a sheath pipe 11 at an upper portion of the structural member 10, the compression zone in a longitudinal direction of the structural member 10, and disposing the compression members 13 not to be attached to the structural member 10, and simultaneously exposing the compression members 13 to the end of the structural member 10; fixedly installing an anchoring device 20 for connecting the tension member 12 with the compression members 13 at the compression members 13, and tensioning the tension member 12 penetrating the anchoring device 20; and injecting grouting materials through a prearranged grouting hose connected

to the spaces between the tension member 12, the compression members 13 and the structural member 10 and exposed to the outside, hardening the grouting materials, and then releasing the anchoring device 20.

Herein, the tension member 12 and the compression members 13 are made from materials of high strength, lowered into the sheath pipes 11 and fixed inside the structural member 10 such that the tension member 12 and the compression members 13 can apply a tensile force and a compressive force, not attached to the structural member 10.

The anchoring device 20 is exposed to the end of the structural member 10 subject to deflection and serves as an anchoring device of the tension member 12 and the compression members 13. Forces applied to the anchoring device 20 by the tension member 12 and the compression members 13 are balanced. The compression member 13 exposed to the end is firmly fixed to the anchoring device 20 by a fixing means such as a fixing bolt 21. As for the tension member 12, several wires of tension members thick enough to be bent are used to allow various arrangements. The tension member 12 penetrates the anchoring device 20 and penetrates the holes made in an anchor plate 22 one by one. The tension member 12 penetrating the anchor plate 22 is tensioned by a general tension device for prestressing, and is anchored to the anchor plate 22 by using wedges 23.

Since the tension device supports the anchor plate 22 and tensions the tension member 12, a reaction force against a tensile force is transferred

to the compression members 13 through the anchoring device 20 and the fixing bolt 21, and compressive forces equal to the tensile forces applied to the tension member act on the compression members 13. During a tensioning procedure, the compression members become shorter in length and therefore the anchoring device is preferably installed to be sufficiently separated from the structural member. The tensioning procedure may be carried out additionally according to an increase of loads. After finishing a final tensioning procedure, grouting materials are injected through the grouting hose 24 to thereby attach the compression members and the tension members to the structural member.

Figure 1 illustrates forces applied to a structural member when a tension member is tensioned according to the present invention and a moment diagram corresponding to the forces. The compression members 13 and the tension member 12 are disposed not to be attached to the structural member 10 subject to deflection, exposed to the end, and anchored to the anchoring device 20 in equilibrium. Even though a spacer is used for buckling prevention or supportive conditions are made at certain intervals by another method, freedom of arrangement cannot be allowed because the compression members 13 should be able to resist the minimum deflection.

Accordingly, the compression members 13 are arranged nearly in a straight line, preferably. Controlling an arrangement of the tension member 12 facilitates the controlling of the moment applied to a corresponding

cross-section.

The tension member 12 passes the lowest portion at the maximum moment point and disposed in parallel with the compression members 13 at the end thereof. In addition, a tensile force applied to the tension member 12 and a compressive force applied to the compression members 13 as a reaction force against the tensile force at the anchoring device 20 are balanced. At this time, fixing the compression members 13 to the anchoring device 20 with a clearance to allow deformation of the compression members 13 is effective. Unlike the conventional prestressing method using only tension members, eccentricity causing moments to the structural member 10 is determined by a distance between the compression member 13 and the tension member 12 regardless of a neutral axis of the structural member. An upward or downward force applied to the structural member is determined according to a rate of change in the eccentricity. As a result, a moment applied to the structural member by prestressing is proportional to the magnitude of the eccentricity, and an arrangement of the tension member 12 is identical with that of the moment when the compression members 13 are arranged completely in a straight line.

Meanwhile, in order to make structural members subject to deflection continuous over two spans or to integrally form the structural members and a pillar, prestress needs to be applied such that a continuous portion can resist a negative moment due to loads. Figure 2 shows views illustrating a force

applied to a structural member when a tension member is tensioned for continuity in a state that one end of a compression member is attached to the structural member and a moment diagram due to the force. One span of the structural members being continuous over two spans is illustrated in Figure 2, and tendons have a symmetrical arrangement on the basis of a continuous point (the right end in Figure 2).

The implementation of such a continuous prestress beam comprises: arranging a plurality of beams in which buried sheath pipes having a U-shaped curvature are exposed to both ends of the beams, and then putting the beams in a continuous line and connecting the exposed sheath pipes; making the beams continuous by placing concrete at connection portions of the beams and then inserting steel wires of tension members into the sheath pipes continuously buried to the plurality of the beams; and tensioning the tension member. That is, since the tension member with U-shaped curvature is buried in the prestress beam and receives a tensile force, a compressive force is applied to the connection portion of the prestress beam by the curvature of the tension member to thereby implement a connection portion of higher strength.

More specifically, the tension members 12 are continuously disposed in a continuous structure. The compression members 13 are disposed to the point where they are separated from the continuous point with a certain distance, and their ends are attached to the structural member 10. There can

be various methods of attaching or anchoring compression members to a structural member according to the materials and shapes of the structural member. However, in case of the PSC beam, the compression members 13 can be easily attached to the structural member by placing concrete in a state that the ends of the compression members 13 to be attached to concrete are exposed with a certain length so as not to be encompassed by the sheath pipes. In such a state, if the tension member 12 exposed to the end is supported by the anchoring device 20 and tensioned, the structural member experiences a bending moment and simultaneously receives a compressive force in the vicinity of the continuous point, which is opposite to the center of the span. A distance between the compression members 13 and the tension member 12 is eccentric at the center of the span. However, in the vicinity of the continuous point where there is no compression member, a distance between the center of a cross-section shown as a dotted line in the Figures and the tension member 12 is eccentric and the tension member passes above the center of the cross-section. Accordingly, a moment opposite to that of the center of the span occurs.

A prestressing method in accordance with one embodiment of the present invention can be properly applied to materials having similar strength against tension and compression and to concrete, which is most widely used for the prestress beam. Accordingly, it is more effective that when the above method is applied to a prestressed concrete beam, the conventional

prestressing method using only tension members is also used in order to make up for properties of materials having weakness in tension. Especially, in a flexible member used for a bridge which experiences heavy live loads such as traffic loads as well as the weight of a structure itself, stresses of the upper and lower flanges of the structural member should not exceed an allowable tensile stress no matter what loads the structural member experiences. Thus, another tension member in addition to compression members matched with a tension member are necessary only for applying a moment. Figures 3 and 4 illustrate a front view and a side view of a prestressed concrete beam proposed in one embodiment of the present invention. The compression members 13 are buried in the upper portion of the PSC beam 10, and the tension members 12 are buried in the lower portion of the PSC beam 10. Some compression members 13 and the tension member 12 are installed not to be attached to the PSC beam 10 by means of sheath pipes, exposed to the end of the PSC beam 10 and connected to each other by the anchoring device 20. Other tension members not in connection with the compression members are attached to the PSC beam in a state of being tensioned by a pretension method, or are buried by means of sheath pipes in a state of not being attached to the PSC beam, pass through general anchoring devices 33 installed at the end of the PSC beam and are exposed to the outside such that the tension members can be tensioned by a post-tension method.

When a material of a structural member has weakness in tension like concrete, compressed prestressing is more greatly carried out by making a tensile force of the tension member greater than a compressive force of the compression member, preferably.

Hereinafter, an operational principle with respect to one embodiment of the present invention will be described.

According to a prestressing method in accordance with the present invention, both a compression member and a tension member of high strength are used for a prestressing member. The compression member and the tension member receive a compressive force and a tensile force by each other's forces of restitution at the end of the structural member. On the assumption that the structural member is horizontally laid to receive vertical loads, the structural member receives an upward or downward force according to an arrangement of the compression members and the tension member but does not receive an axial force. As a result, a moment obtained by multiplying a distance between the compression member and the tension member by a prestressing force is generated on a specific section of the structural member. Since a sign of the generated moment is opposite to that of the structural member which experiences due to loads, the load-carrying capacity of the structural member with regard to loads is increased.

In previously available prestressing methods using only tension members, the moment which can be applied is small compared to the

magnitude of a tension force because the moment is applied by using eccentricity between a neutral axis of the cross-section with and a tension member. In addition, anchorage of tension members acts as an average compressive force of an entire section of the structural member. That is, a desired compressive force can be applied to a portion which experiences tension due to loads, but it is difficult to control the tension at a portion which experiences compression due to loads. It is most important to apply compressed prestress to a portion which experiences a tensile stress in case of a structural member using materials having weakness in tension such as concrete. However, if the cross-section of a structural member gets smaller and more tension members are used according to the trend of a slim design, destruction of the structural member is affected by a compressive force.

Meanwhile, for the application of tensile stresses to a portion carrying excessive compressive stresses developed by loads, a method of applying tensile prestress in which compression members are installed at an upper portion of a PSC beam has been developed and used. However, it is inconvenient to apply a compressive force to the compression members, and a portion to which a reaction force the compression jacks is applied and a portion to which the compression members are anchored are required for the reinforcements. In addition, construction phases are increased because a procedure of tensioning the tension members and a procedure of compressing compression members are separately done, which causes

inefficiency. Also, it is very difficult to apply prestressing according to an increase of loads in case that loads increase step by step. Finally, if slabs are constructed, a prestressing job cannot be done any longer because the procedure should be done at the upper portion of a structural member.

However, a prestressing method in accordance with the present invention can apply a compressive force and a tensile force at the same time by one tensioning procedure, prestressing can be implemented corresponding to the phased application of the loads because such a procedure is done at the end of the structural member, and a reinforcing procedure for anchoring tension members and compression members are unnecessary.

In addition, since the most widely used concrete in applying prestress and manufacturing a structural member resisting deflection has great compressive strength, but little tensile strength, some compressed prestress should be additionally applied to make up for weak tensile strength in the PSC beam. That is, it is very ideal that the. PSC beam is subjected to deflection due to loads and deflection opposite to said deflection is applied by the prestressing method in accordance with one embodiment of the present invention using the anchoring device. However, in order to make the structural member withstand variable live loads smoothly, a predetermined axial load needs to be applied such that concrete having weakness in tension should be in compression to a certain degree. Accordingly, provided is a PSC beam in which another tension members are installed in addition to

tension members matched to compression members.

Figure 8 represents prestress generated in a structural member when a compressive force alone is applied to the structural member by using only tension members and when a compressive force and a tensile force are all applied to the structural member by using compression members. An upper diagram of Figure 8 represents a stress induced over the cross-section where a positive moment of a structural member is applied when prestressing by using only tension members is applied. A lower diagram of Figure 8 represents a stress induced over the cross-section of the structural member when prestressing is applied by disposing compression members at the upper portion of the structural member and tension members at the lower portion of the structural member.

In the upper diagram of Figure 8, a compressive force equal to a tensile force of the tension members is applied to the cross-section of the structural member, and a position of resultant of the forces is a position where the tension members pass. The forces are eccentric and therefore apply compressive forces and moments to the structural member. As a result, a high compressive stress is applied at the lower portion, a low tensile stress is applied to the upper portion in case of small eccentricity and a high tensile stress in case of large eccentricity. In case the compressive force of the compression members is identical to the tensile force of the tension member, the compressive force is applied to the cross-section of the structural

member where a lower tension member is located and the tensile force is applied to the cross-section of the structural member where upper compression members are located. The two forces are offset by each other, whereby an axial force is not applied to the structural member. But moments alone are applied due to a difference between positions of the moment applications, so that prestress can be applied to be precisely opposite to the moments developed by loads.

As so far described, the present invention implements the application of the optimum prestress by a simple and easy procedure such that a structural member can resist deflection.

Simultaneously, in the present invention, forces can be applied to compression members and tension members at the same time by one tensioning procedure and additional prestress can be applied according to steps of loads. In addition, since a distance between the compression member and the tension member is eccentric, a large moment can be applied with little force. Since loads in an axial direction are not applied to the structural member, the capability for responding to very large loads is enabled by increasing the prestressing force freely. In addition, designing and manufacturing of a structural member is facilitated because designing of an anchoring part for stress concentration is not required.

In addition, when the present invention in combination with the conventional prestressing method using only tension members is applied to a

PSC beam for a bridge, an economical and beautiful bridge with a low height and a long span can be constructed.

In one embodiment of the present invention, one tension member 12 is matched with two compression members 13, but a plurality of tension members 12 can be matched with a plurality of compression members 13 according to the shape and width of a structural member.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.