KR20050009589A - Apparatus for decreasing section force installed between girders in plate girder bridge for reduction of bending moment stress and introduction of re-tension force, and construction method thereof - Google Patents

Abstract

PURPOSE: A section force reducer and a construction method thereof are provided to prevent the falling of a girder by reducing the size of a negative moment and to reinforce the load capacity of a bridge by inducing the prestressing force when the load capacity is reduced. CONSTITUTION: A section force reducer(200) comprises a negative moment reducer(30) and an upward force inducer(100). The negative moment reducer is installed by connecting girders(20) in a bridge(11) to reduce the size of the negative moment on the girders. The upward force inducer induces upward force to the girders by inducing prestressing force to strands to be connected with tensile brackets(50) and plural auxiliary tensile brackets(40) for additionally inducing the prestressing force when the load capacity of the bridge is reduced. The tensile brackets are installed in the upper part of bellies in the girders. The auxiliary tensile brackets are installed in the center lower part of the girders at regular intervals. Thereby, the height and the load capacity are reinforced by reducing the section force on a plate girder bridge(10).

Description

Apparatus for decreasing section force installed between girders in plate girder bridge for reduction of bending moment stress and introduction of plate bending bridge to reduce bending moment stress and re-tension re-tension force, and construction method

In the present invention, in the plate girder bridge, the bending moment acting on the plate girders vertically mounted to the continuous point portion, that is, the parent moment is installed by connecting the constant length of both girders that can reduce the size of the secondary moment It is possible to reduce the size of the bending moment acting on the center of the plate girder mounted between the reduction device and the ground, and to add additional tension when there is a need to introduce additional tension due to the reduced load capacity of the bridge. Sectional force consisting of an owner's bracket installed at the top of the abdomen and an upward force introduction device to introduce upward force into the girder by introducing tension force to the strands installed respectively connected to a plurality of saddle-assisted auxiliary tension brackets installed at a plurality of intervals at regular intervals. Install a reduction device to act on the plate girder bridge It is reduced by reducing the type of choices danmyeonryeok and also to reinforce the middle finger ganhwa and load carrying capacity of the span.

The present invention is to install a cross-section force reducing device equipped with steel rods and strands to reduce the size and cross-sectional force of the parent moment in the plate girder bridge to reduce the mold height of the girder by introducing a tension force to the steel rods and strands If long span between the bridges is possible and the load capacity needs to be increased due to the aging of the bridge, the tension force is introduced to the strand installed in the upward force introduction device, and the upward compression force is introduced to the girder to add the load capacity additionally. The construction method of the section force reduction device that can reduce the construction cost by reducing the cost of the steel can be saved by increasing the endurance life and preventing the unnecessary bridge construction by using the old bridges. To provide.

Conventionally, a fixing device is installed at the bottom of a plate girder and the strands are connected to each other to introduce a tension force to introduce a compressive force to the girder, or to cast concrete or resin inside a box-type girder such as a steel box, or to install a rib to weld the parent cement. However, when the concrete or resin and steel plate placed in the steel box is attached over time, and the cumulative load acts, the concrete or resin is cracked and separated from the steel plate. The steel box bridge should be periodically managed because it is not sufficient to bear the stress caused by the load that is not generated or the ribs alone.In addition, when the tension force is applied to the strand installed under the plate girder, Exposed to the outside, the atmosphere, Due to the corrosion and temperature difference, the elastic force acts on the strand and the loss of the tension force introduced in the strand becomes large, and the cases frequently fall short of the required tension force in the design are frequently caused. Problems such as sag due to inability to properly cope with problems and working loads have been generated, and problems that fall short of the endurance of required bridges have frequently occurred.

In order to solve the above problems, the present invention provides an owner's bracket on the abdomen between adjacently installed unit plate girders, and a saddle combined auxiliary tension bracket under the lower flange between adjacently installed unit plate girders. After connecting the strands and connecting the strands, the tension force is applied to distribute the tension force, so that the upper part of the girders do not concentrate the tensile stress, and the upper compressive force is applied to the girders, and the continuous moment reduction device is installed between the girders installed consecutively. By installing a certain length, it reduces the size of the parent moment generated at the continuous point to reduce the cross-sectional force acting on the girder to prevent the girder from sagging and to reduce the cross-sectional area of the steel, thereby reducing the amount of steel used and reducing the height of the bridge, To keep the space wider, The present invention relates to a method of introducing a tension force to a girder through the installation of a cross-sectional force reduction device that can reinforce a bridge's load capacity by introducing a retension force when the load capacity decreases.

1 is a view showing that the sectional force reducing device of the present invention installed on the plate girder bridge.

Figure 2 is a sectional view showing that the parental reduction device of Figure 1 is installed in section A-A.

3 is a view showing in detail the owner of the bracket of Figure 1;

Figure 4 is a view showing in detail the saddle dual support bracket of Figure 1;

FIG. 5 is a unit plate in which the saddle combined auxiliary tension bracket of FIG.

A diagram showing the installation over the lower flange of the girder.

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

10 ... plate girder bridge 11 ... pier

12 ... shift 13 ... gear

14 ... strand 15 ... slab

16 ... steel rod 17 ... pavement

18 ... anchor bolt 19 ... bolted

20 ... Unit Plate Girder 21 ... Steel Plate

22 ... Bracing 23 ... Lower Flange

24 ... upper flange 25 ... abdomen

26 ... "L" section 27 ... clearance

28 ... anchorage 29 ... vertical bracing

30 ... Parental Reduction Device

40. Saddles for both saddles 41 ... Saddles

42 ... support plate 43 ... support plate

44 ... box bracket 45 ... holder

50 ... Host Bracket 51 ... Unit Box Bracket

60 ... unit box plate 61 ... longitudinal rib

62 ... stud bolt 63 ... space

64 ... Connections

100 ... Upward force introduction device 200 ... Sectional force reduction device

In the present invention, in the plate girder bridge 10, both girders 20 which can reduce the size of the bending moment, that is, the minor moment, acting on the plate girder 20 which is vertically mounted at the pier 11 which is the continuous point portion. It can reduce the size of the bending moment acting in the center of the parent moment reduction device 30 and the plate girder 20 mounted between the fixed length connected to each other, and the additional tension due to the reduction of the load capacity of the bridge When necessary to introduce additional saddle combined auxiliary tension brackets installed in a plurality of spaced at regular intervals and the host bracket 50 installed on the top of the abdomen 25 of both sides of the plate girder 20 to be introduced additionally Cross section force reduction device consisting of an upward force introduction device 100 for introducing a tension force to the stranded wires respectively connected to the 40 to introduce the upward force to the girder 20 It is characterized in that to install the 200 to reduce the cross-sectional force acting on the plate girder bridge 10 to reinforce the mold and load-bearing force.

By installing the cross-sectional force reduction device 200 is a method of increasing the load capacity to the plate girder 20 as follows.

a) In the plate girder bridge 10, while installing the unit box-shaped plate 60 to be attached to the upper flange 24 and the abdomen 25 of the girder 20 longitudinally adjacent to the pier 11 that is a continuous point The steel plate 21 is installed above and below the connecting portion 64 of the unit box-shaped plate 60 installed at the lower portion of the adjacent upper flange 24, and the unit box-shaped plate 60 and the slab 15 are anchor bolts 18. Connecting to each other;

b) filling the interior of the unit box-shaped plate (60) with urethane foam and filling the gap (27) between the slab (15) and the upper portion of the unit box-shaped plate (60) with epoxy;

c) installing a plurality of fixing units 28 on the lower surface of the unit box-shaped plate 60 and connecting the steel bars 16 to each other;

d) Steel plate 21 is installed on one side of each abdomen 25 adjacently installed, and the “L” shaped steel 26 is installed on the other side, that is, the unit box-shaped plate 60 is installed, and the bolt connection 19 is connected. Welding the steel plate 21 to the inside of the “L” shaped steel 26;

e) The unit box-shaped plate 60 is installed inside the lower flange 23 and the abdomen 25 of the plate girder 20, and the steel plates 21 are installed at the upper and lower portions of the connecting portion 64, and then bolted ( 19) connecting the bolt box 19 with the steel plate 21 installed above and below the unit box-shaped plate 60 and the lower flange 23;

f) Fill the unit box-shaped plate 60 with lightweight concrete or foamed urethane, install a plurality of fixing units 28 on the upper surface of the unit box-type plate 60, and connect the steel bars 16 to each other to reduce the parental moment ( 30) completing the installation;

g) One side of the unit box-type bracket 51 is welded to the upper end of the abdomen 25 of both side ends of the unit plate girder 20 installed laterally adjacently on the pier 11 and the alternating 12 to form the unit box. The steel plate 21 is bolted or welded to the upper and lower portions of the connecting portion 64 where the brackets 51 meet each other, and the mounting bracket 45 is installed outside the inside of the unit box-type bracket 51, and the fixing unit is mounted on the mounting bracket. Installing a plurality of 28 and then filling the inside of the unit box bracket with mortar;

h) Fixing and installing a plurality of box-shaped brackets 44, which are installed in a plurality at regular intervals, in the center of the lower portion of the lower flange 23 of the unit plate girder 20 installed on the pier or alternating side under the adjacent lower flange 23. After the mounting brackets 28 are installed on both outer sides of the box-shaped bracket 44, the fixing unit 28 is installed, and one side of the fan-shaped support 43 is spaced apart from the inside of the box-shaped bracket 44. Installing a saddle combined auxiliary tension bracket 40 attached to one side and attached to the support plate 42 with a groove formed on the fan-shaped surface;

i) The stranded wire on the anchors 28 of the host bracket 50 installed on the upper sides of the unit plate girder 20 and the saddle 41 of the saddle combined auxiliary tension bracket 40 installed on the lower portion of the girder 20 14) while fixing the strand wire 14 to the anchorage 28 installed in the saddle combined auxiliary tension bracket 40 installed at regular intervals in the lower center of the plate girder 20 while fixing the mounting of the box-shaped bracket 44 Filling the inside tightly with mortar;

j) installing the bracing 22 to cross at both sides of the inner space where the abdomen 25 and the unit box-shaped plate 60 are installed; And

k) the saddle combined auxiliary tension bracket 40 while introducing and fixing the tension force to the strand 28 of the host bracket 50 after the fixed force is introduced and fixed to the steel rod 16 of the parent reduction device 30. It is characterized in that it consists of the step of introducing and fixing the tension force in the strand (28) installed in the fixing device, and the load-bearing force on the plate girder bridge (10) by the anti-rust treatment and peripheral cleansing on each device.

Hereinafter, the configuration and operation of the present invention will be described in detail by the accompanying drawings.

1 is a view showing that the sectional force reducing device of the present invention is installed on the plate girder bridge.

Parent cement is installed by connecting a certain length of both girders 20 that can reduce the size of the parent cement acting on the plate girders 20 mounted longitudinally in the continuous point portion of the plate girder bridge 10 A plurality of owner brackets 50 installed on the upper part of the abdomen 25 at both ends of the plate girder 20 mounted between the reduction device 30 and the shift 12 and the pier 11 at regular intervals in the lower part of the center. It is to install a cross-sectional force introduction device 200 is connected to each of the strands 14 to the installed saddle combined auxiliary tension bracket 40 installed.

FIG. 2 is a cross-sectional view showing that the parent moment reduction device of FIG. 1 is installed at a cross section AA. Between the plate girders 20 and the girders 20 are installed successively in the longitudinal and transverse directions on top of the pier 11 as the continuous point portion. In the upper part of the upper plate 24 and the lower part of the abdomen 25 the unit box-shaped plate 60, which is provided with a plurality of longitudinal ribs 61 inside the abdomen 25 of the plate girder and the inner side of the lower part of the upper flange 24 at regular intervals. ) Is installed to contact the upper plate 24 so as to extend a predetermined distance from the point where the inner surface of the cross) cross each other to form a connecting portion 64 to meet another unit box-shaped plate 60 installed inside the adjacent plate girder 20 The steel box 21 is welded or bolted to the upper and lower portions of the connecting portion, and fixedly installed to the unit box-shaped plate 60 and the slab 15 using anchor bolts 18, and the unit box-shaped plate 60 The inner space 63 is filled tightly with urethane foam, and the gap 27 between the upper portion of the unit box-shaped plate 60 and the lower part of the slab 15 is tightly filled with epoxy, and the adjacently installed The unit box-shaped plate 60 in which a plurality of longitudinal ribs 61 and stud bolts 62 installed in the longitudinal direction on the inner side of the lower flange 23 and the abdomen 25 of the unit plate girder 20 are provided at regular intervals. Is installed in close contact with the upper portion of the lower plate 23 while the steel plate 21 is installed in the upper and lower portions of the connecting portion 64 with the other unit box-shaped plate 60 adjacently installed and welded or bolted to connect the lower flange 23 ) And bolt fastening (19), and bolts (19) on one side of the abdomen (25) and the "L" shaped steel (26) on each side of the unit box-shaped plate 60 is installed inside (19) and The steel plate 21 is welded and attached to the inner side of the “L” shaped steel 26 while the steel plate 21 is installed at the upper and lower portions of the lower flange 23 and connected with the bolted fastening 19. The space 63 is filled with lightweight concrete or foamed urethane, and a plurality of anchorages 28 are provided on the upper and lower portions of the unit box-shaped plate 60 installed above and below the upper and lower flanges 23 and 24, and then the steel rod 16 is installed. Each plate girder 20 installed adjacent to each other vertically and horizontally at the continuous point portion is installed by connecting a predetermined distance to each other, the momentum reduction device 30 having the bracing 22 in the X-shape while fixing and connecting to each other.

Tension force is introduced into the steel box 16 connected to the fixing rod 28 respectively installed on the upper portion of the unit box-shaped plate 60 of the parent reduction device 30 to the unit box-shaped plate 60 This is to ensure the reduction of the size of the parent moment generated in the continuous point portion to be introduced.

In addition, only the longitudinal ribs 61 are installed in the unit box-shaped plate 60 installed on the upper flange 24, and the inner space 63 is filled with foam urethane to prevent corrosion of the interior of the steel bar 16. In order to ensure the tension force is introduced into the unit box-shaped plate 60 so that the longitudinal rib 61 and the foamed urethane are integrated when the tension force is introduced into the unit box, the unit box-shaped plate 60 installed on the lower flange 23 is provided. At the same time, the longitudinal ribs 61 and the stud bolts 62 are installed at the same time, and the light concrete or epoxy is filled in the inside, which is transmitted to the lower part than the size of the parent delivered to the unit box type plate 60 installed at the upper part. As the size of the parental cement is large, it is integrated with the filling filled inside while introducing rigidity to effectively reduce it. While reducing the open negative moment is also intended to be a tensile force is securely introduced passes than introduced into the steel rod attached to the upper.

On the other hand, the unit box-shaped plate 60 is installed in the upper and lower portions of the upper and lower flanges (23, 24) by 1/2, respectively, so that the unit box-shaped plate is heavy and installed between the plate girders. It is to make installation easier by reducing the weight because the place is narrow.

After the installation of the parental reduction device 30 between the girders 20, the bracing 22 is installed to cross each other diagonally using steel materials so that the parental reduction device 30 is uniformly rigid throughout. This is to allow delivery.

3 is a view showing in detail the host bracket of FIG. 1, each of the unit box type on the upper end of the abdomen 25 of both sides of the unit plate girders 20 installed laterally adjacent to the pier (11) and the alternating (12) One side of the bracket 51 is welded and bolted or welded to the steel plate 21 above and below the connecting portion 64 where the unit box-type bracket 51 meets each other, and on the outside of the inside of the unit box-type bracket 51. The holder 45 is installed and the owner bracket 50 having a plurality of anchorages 28 installed on the holder is installed.

The host bracket 50 is installed on the abdomen 25 between the unit plate girders 20, and divides the unit box-shaped bracket 51 by half and connects them to each abdomen 25, and then connects them to each other. One is that the unit box-type bracket 51 is heavy, so it is very difficult to install between the girders 20, so that the unit box bracket 51 is divided in half to reduce the weight, and then each of them is connected to each other.

In addition, the inside of the unit box-shaped bracket 51 is filled with mortar to protect from corrosion.

FIG. 4 is a detailed view illustrating the saddle combined auxiliary raising bracket of FIG. 1, wherein a plurality of box-shaped brackets 44 are provided at regular intervals at a central portion of a lower portion of the lower flange 23 of the unit plate girder 20 adjacent to each other. ) Is fixed to the bottom of the adjacent lower flange (23) and then the fixing unit 28 is installed while installing the supporters 45 on both sides of the box-shaped bracket (44) and the support of the fan-shaped at regular intervals inside ( 43) one side of the box-shaped bracket 44 is attached to one side of the box-shaped bracket 44, and the unit plate girder after installing the saddle combined auxiliary tension bracket 40 with the support plate 42 having a groove formed on the fan-shaped surface The strands 14 in the grooves of the anchorage bracket 28 of the host bracket 50 installed on both sides of the 20 and the saddle 41 of the saddle combined auxiliary tension bracket 40 installed on the bottom of the girder 20. While fixing the steel wire (14) to the anchoring hole (28) installed in the saddle combined auxiliary tension bracket (40) installed at regular intervals in the lower center of the plate girder 20 while fixing to the inside of the box-shaped bracket (44) Fill tightly with mortar.

5 is a view showing that the saddle combined auxiliary tension bracket of Figure 4 is installed across the lower flange of the unit plate girder adjacently installed, the unit plate girders 20 are horizontally adjacent in the bridge installed vertically and horizontally The unit plate girder 20 installed laterally adjacently while installing the saddle combined auxiliary tensioning device 40 by connecting the box-shaped bracket 44 to the lower portion of the lower flange 23 of the unit plate girder 20 installed. The buckling connecting the lower part of the slab 15 and the upper center part of the box-shaped bracket 44 while installing the bracing 22 so as to intersect at the center at the intersection where the upper and lower flanges 23, 24 and the abdomen 25 meet each other Install a vertical bracing 29 for prevention. The lower flange 23 and the box-shaped bracket 44 are in contact with each other to be bolted to the connection 19 or welded.

As shown in FIG. 1, the saddle combined auxiliary tensioning device 40 is installed in pairs at a predetermined distance from the center of the lower flange 23 of the unit plate girder 20, and the saddle 41 and the fixing unit 28 are installed. The strands 14 connected to each of the strands 14 are respectively mounted on the saddle 41, the strands (14) when the tensile force is applied to the strands (14) fixed to the host bracket (50) 14) is installed in the lower portion of the lower flange 23 of the central portion of the unit plate girders 20 adjacently installed so that the upward compressive force acts so that the upward compressive force acts on the unit plate girder 20. Fixtures 28 are provided at regular intervals in the lower central portion of the lower flange 23 of the plate girder 20 to connect and install the strands 14, respectively. Settling the strand (14) In order to compensate for the compressive force reduced by the constant loss by allowing the compressive force to be actuated in addition to the upward compressive force acted by the saddle 41 to ensure that the upward compressive force acts. When (10) is deteriorated and the load bearing force is lowered to introduce additional upward compressive force, the pair of anchorages 28 and the saddles 41 respectively provided on the pair of box-shaped brackets 44 installed under the lower flange 23 are provided. In order to extend the durability of the aged bridges by introducing a tensile force to each of the stranded wires 14, which are connected to each other, to add a compressive force upward.

After the installation of FIG. 2 to FIG. 5 is completed, a tension force is introduced into the steel bar 21 of the parent reduction device 30 to fix and fix the tension rod, and then a tension force is introduced into the strand 14 of the host bracket 50. While fixing, the tension force is introduced into the strand wire 14 installed in the saddle combined auxiliary tension bracket 40 to fix and fix the load force of the plate girder bridge 10 using the cross-sectional force reducing device 200.

The present invention uses the cross-sectional force reduction device installed between the plate girders installed in the continuous point portion by introducing a tension force to the girder to reduce the size of the parent moment generated in the continuous point portion to enhance the load capacity of the aged bridge while increasing the load capacity of the bridge It is possible to reduce the height by reducing the cross-sectional force, and it is a construction method using a very useful device that can manage the bridge economically and effectively to reduce the amount of steel used.

Claims (5)

Parent-receiving device installed by connecting a certain length to both sides of the plate girders mounted vertically on the continuous point of the plate girder bridge, and the owner's bracket installed on the upper part of the abdomen at both ends of the plate girders mounted between the bridge and the bridge And a stranded wire to the saddles installed in the plurality of saddles installed auxiliary saddle bracket installed at a plurality of intervals at the bottom of the center and connected to the anchor wire installed in the anchorage bracket installed in the host bracket, and to the saddles combined saddle bracket installed at regular intervals Cross section force reduction device for reducing the bending moment stress and re-tension force installed between the girder and the girder of the plate girder bridge characterized by connecting and fixing the stranded wire to the installed anchorage. The method of claim 1, The parental reduction device is installed in a plurality of units at a constant interval inside the abdomen of the plate girder between the plate girder and the girder between the plate girders installed in the longitudinal, lateral direction in the upper portion of the pier as a continuous point portion at regular intervals The box-shaped plate is installed to be in contact with the upper plate to extend a predetermined distance from the point where the lower side of the upper plate and the inner side of the abdomen cross each other to form a connecting portion that meets another unit box-shaped plate installed inside the adjacent plate girder, and the upper and lower portions of the connecting plate The steel plate is fixed to the unit box-shaped plate and the slab while welding or bolted using anchor bolts, and the space inside the unit box-shaped plate is tightly filled with urethane foam, and the upper part of the unit box-type plate and the lower part of the slab and Of The lower part is filled with a unit box-type plate in which a plurality of unit ribs and stud bolts are installed in the inner part at regular intervals after the lower part of the unit plate girder and the longitudinal ribs installed in the inner part of the abdomen are tightly filled with epoxy. Steel plate is installed in the upper and lower portions of the connection portion with the other unit box-shaped plate adjacently installed while being installed in close contact with the bolt, and bolted connection with the lower flange while connecting or welding by bolting, the steel plate is connected to the unit box-shaped plate on one side of the abdomen After installing the "L" section steel on the inner side of each side, bolts are fastened, and the steel plate is welded and attached to the inner side of the "L" section, while the steel plate is installed on the upper and lower parts of the lower flange and connected by bolts, Space is lightweight concrete or foot In the upper and lower parts of the unit box-shaped plate filled with urethane and installed above and below the upper and lower flanges, a plurality of anchorages are installed, and then the steel rods are connected to each other to fix the plate girder between the girder and the girder of the plate girder bridge. Sectional force reducing device for reducing bending moment stress and introducing re-tension. The method of claim 1, The saddle combined auxiliary tension bracket is mounted on both sides of the box-type bracket after fixing and installing a plurality of box-type brackets installed at a predetermined distance from the lower part of the lower flange of the unit plate girder adjacently and horizontally. Install the anchorage and install one side of the fan-shaped support on one side of the box-shaped bracket at regular intervals inside, and attach the support plate formed with the groove on the fan-shaped surface to install the saddle combined supporter bracket Later, the anchor rods are installed on both sides of the unit plate girder and the saddles of the saddle combined supporter brackets installed on the bottom of the girder are fixed to the saddles, and the saddle combined supporter installed at regular intervals in the lower center of the plate girder. Bro The bracing and the vertical bracing supporting the upper part of the slab bottom and the upper part of the box-type bracket while connecting and fixing each other are characterized in that the mortar is securely filled with the mortar inside the box-type bracket while fixing the strand in the anchorage installed in the bracket. Cross section force reduction device for reducing the bending moment stress and re-tension introduced between the girder and the girder of the plate girder bridge characterized by the installation. The method of claim 1, The host bracket is attached to the upper and lower sides of the connecting portion where the unit box brackets meet each other by welding and attaching one side of the unit box bracket to the upper part of the abdomen of both sides between the unit plate girders installed laterally adjacently on the piers and the alternating bolts. Or welded and installed between the girders of the girder and the girders of the plate girder bridge, characterized in that the mounting bracket is installed on the outside of the inside of the unit box bracket, and a plurality of anchorages are installed in the mounting box, and then the mortar is filled inside the unit box bracket. Section force reducing device for reducing moment stress and introducing re-tension. a) In the plate girder bridge, the steel plate is placed above and below the connection with the unit box plate installed at the bottom of the adjacent upper flange while the unit box plate is installed to be attached to the upper flange and abdomen of the girder longitudinally adjacent to the continuous piers. Installing and connecting the unit box-shaped plate and the slab with anchor bolts; b) filling the inside of the unit box type plate with foamed urethane and filling the gap between the slab and the unit box type plate with epoxy; c) installing a plurality of fixtures on the lower surface of the unit box-shaped plate and connecting the steel bars to each other; d) installing steel plate on one side of each abdomen provided adjacent to each other, that is, installing the "L" section steel on the other side, that is, the unit box-shaped plate, bolted connection and welding the steel plate inside the "L" section steel; e) installing the unit box-shaped plates on the inner side of the lower flange and the abdomen of the plate girder, and then installing the steel plates on the upper and lower portions of the connecting portion and bolting them, and bolt-connecting the steel plates provided on the upper and lower portions of the unit box-shaped plate and the lower flange, respectively; f) filling the inside of the unit box-shaped plate with lightweight concrete or foamed urethane, installing a plurality of anchorages on the upper surface of the unit box-type plate, and connecting steel bars to each other to complete the installation of the parent reduction device; g) Weld and attach one side of the unit box bracket to the upper part of the abdomen of both side ends of the unit plate girders installed laterally adjacent to the pier and the alternating iron plate above and below the connection where the unit box brackets meet each other. And installing a cradle on the outside of the inside of the unit box bracket, and installing a plurality of fixing holes on the cradle, and filling the inside of the unit box bracket with mortar; h) Install a plurality of box-shaped brackets installed at fixed intervals in the center of the lower part of the lower flange of the unit plate girder installed on the piers or alternating parts at the bottom of the adjacent lower flange, and then install the mounts on both sides of the box-shaped bracket. While installing the fixing unit and installing one side of the fan-shaped support at regular intervals inside the box-shaped bracket on one side of the box-shaped bracket, and forming a support plate formed with a groove on the fan-shaped surface; i) Saddle combined support installed at regular intervals in the lower center of the plate girder while anchoring the steel wire to the anchorage of the host holder bracket installed on the upper sides of the unit plate girder and the saddle of the saddle combined support bracket installed on the bottom of the girder Filling the inside of the box-shaped bracket with mortar while fixing the strand in the anchorage installed in the tension bracket; j) installing bracing to cross at both sides of the inner space where the abdomen and the unit box-shaped plate are installed; And k) introducing and fixing the tension force to the steel bar of the parental reduction device, and then introducing and fixing the tension force to the strand of the host bracket, while introducing and fixing the tension force to the strand wire installed on the saddle dual support tension bracket. A method of constructing a cross-sectional force reduction device for reducing the bending moment stress and introducing re-tensioning force installed between the girder and the girder of the plate girder bridge, characterized in that the step of improving the load capacity on the plate girder bridge by rust prevention treatment and peripheral cleanup.