Inverted trapezoidal box girder bridge and method of installing inverted trapezoidal box girder bridge

Abstract

To provide an inverted trapezoidal box girder bridge capable of facilitating work while maintaining the quality of concrete.SOLUTION: An extra-dosed box girder bridge 1 has a concrete upper floor slab 6, a concrete lower floor slab 7, and four concrete webs 8 connecting the upper floor slab 6 and the lower floor slab 7, and includes an inverted trapezoidal box girder 3 having an inverted trapezoidal cross-sectional shape as a whole. The web 8 includes two middle webs 8I disposed on the inner side in a widthwise direction, and two outer webs 8O disposed on the outer side of the middle webs 8I. One central chamber 9 having a trapezoidal cross-sectional shape is formed between the middle webs 8I, and a side chamber 10 having an inverted triangular cross-sectional shape is formed in each between each middle web 8I and the corresponding outer web 8O. The two outer webs 8O are inclined relative to the middle webs 8I and include precast webs 11 made of precast concrete.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an inverted trapezoidal box girder bridge and a method for erecting an inverted trapezoidal box girder bridge.

Background Art

[0002] A box girder bridge includes an upper floor slab, a lower floor slab, and a plurality of webs connecting the upper floor slab and the lower floor slab, and has a box-shaped cross-sectional shape. The box girder bridge includes a composite box girder bridge in which the web and the lower floor slab are made of steel and the upper floor slab is made of concrete, or the web is made of steel and the lower floor slab and the upper floor slab are made of concrete, and a concrete box girder bridge in which the web, the lower floor slab, and the upper floor slab are all made of concrete.

[0003] In a concrete box girder bridge, a composite girder is known in which a precast prestressed concrete slab is used for the web, and in-situ concrete is used for the upper floor slab and the lower floor slab integrated above and below the web (Patent Document 1). When constructing this box girder bridge, a lower floor slab formwork is assembled, a precast PC slab manufactured at a factory or the like is erected thereon, an upper floor slab formwork is assembled at the upper end of the precast PC slab, reinforcing bars are assembled in the lower floor slab part and the upper floor slab part, and concrete is placed on the lower floor slab and the upper floor slab to manufacture a box girder. After curing the concrete, prestress is introduced into the manufactured box girder, and the wagon is moved forward. By repeating this process and sequentially manufacturing box girders, the box girder bridge is erected.

[0004] In a concrete box girder bridge, in addition to a configuration having one box-shaped cross-sectional part (also referred to as a single box girder bridge or a one-room box girder bridge), there are configurations having a plurality of separated box-shaped cross-sectional parts (multi-main girder box girder bridge, multi-room box girder bridge), configurations having a plurality of continuous box-shaped cross-sectional parts (multi-box girder bridge, multi-room box girder bridge), etc. Further, there is also a multi-configuration box girder bridge having one trapezoidal box-shaped cross-sectional part and two inverted triangular cross-sectional parts continuous thereto on both sides thereof, and having an inverted trapezoidal cross-sectional shape as a whole (hereinafter referred to as an inverted trapezoidal box girder bridge) (see Non-Patent Document 1). Furthermore, in addition to a structure in which the box girder alone supports the load, the box girder bridge also has a structure in which the load is supported by a combination with other structures such as the wires of a cable-stayed bridge or the wires of an extradosed bridge.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non - Patent Documents

[0006]

Non - Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in an inverted trapezoidal box girder bridge, the inclination angle of the outermost web is large. When constructing the web with in - place concrete, air bubbles remain along the upper formwork, easily causing poor compaction (so - called janka) on the surface of the web. Therefore, the concrete placement work takes a great deal of time, additional equipment such as formwork vibrators is required, and the work is complicated.

[0008] In view of the above background, an object of the present invention is to provide an inverted trapezoidal box girder bridge and a method for erecting the same that can facilitate the work while maintaining the quality of concrete.

Means for Solving the Problems

[0009] In order to solve the above problems, an aspect of the present invention is an inverted trapezoidal box girder bridge (1), comprising a concrete upper floor slab (6), a concrete lower floor slab (7), and four concrete webs (8) connecting the upper floor slab and the lower floor slab, and having an inverted trapezoidal box girder (3) with an overall inverted trapezoidal cross-sectional shape. The webs include two middle webs (8I) arranged on the inner side in the width direction and two outer webs (8O) arranged outside the middle webs. A central chamber (9) with a trapezoidal cross-sectional shape is formed between the middle webs, and side chambers (10) with an inverted triangular cross-sectional shape are formed between each middle web and the corresponding outer web. The two outer webs are inclined compared to the middle webs and include precast webs (11) made of precast concrete.

[0010] According to this aspect, since the outer webs that are inclined compared to the middle webs include precast webs, the outer webs can be easily constructed while maintaining the quality of the concrete of the outer webs.

[0011] In the above aspect, it is preferable that the two outer webs include a plurality of the precast webs arranged at intervals in the bridge axis direction.

[0012] According to this aspect, the precast webs can be designed to have a desired size and weight, and the placement work of the precast webs is easy.

[0013] In the above aspect, it is preferable that the two precast webs arranged in the bridge axis direction are connected to each other by in-situ concrete.

[0014] According to this aspect, it is easier to ensure the required rigidity of the outer web composed of the precast web and the in-situ concrete.

[0015] In the above aspect, it is preferable that the two middle webs are made of in-situ concrete.

[0016] Generally, the use of precast concrete members is advantageous in terms of quality improvement and construction period shortening, while it is often disadvantageous in terms of cost reduction. According to this aspect, by constructing the middle web with cast-in-place concrete, it is possible to reduce the construction cost of the inverted trapezoidal box girder bridge while maintaining the quality of the concrete.

[0017] In the above aspect, it is preferable that the two middle webs include the precast web.

[0018] According to this aspect, even if the box girder bridge has a structure in which the middle web is inclined in the design, the middle web can be easily constructed while maintaining the quality of the concrete of the middle web.

[0019] In the above aspect, the inverted trapezoidal box girder bridge further includes a main tower (4) constructed above the pier (P) and a diagonal member (5) stretched between the main tower and the inverted trapezoidal box girder to form an extradosed box girder bridge. It is preferable that a diagonal member fixing protrusion (14) for fixing the lower end of the diagonal member is formed at the upper part of the central chamber.

[0020] According to this aspect, in a box girder having a lightweight structure with a small cross-sectional area, a box girder structure that is rationally supported by the diagonal member is realized by transmitting the load of the box girder to the diagonal member without generating local stress.

[0021] Another aspect of the present invention for solving the above problems is an erection method for erecting an inverted trapezoidal box girder bridge according to any one of claims 1 to 6 by a cantilever erection method using a wagen (17), comprising: a step of assembling a bottom slab formwork (21) on the wagen (Fig. 5(A)); a step of assembling bottom slab reinforcing bars (22) on the bottom slab formwork (Fig. 5(B)); a step of arranging two precast webs in an inclined posture at the positions of the corresponding outer webs using a support pedestal (23) (Fig. 5(B)); a step of placing bottom slab concrete (26) with the two precast webs arranged at the positions of the corresponding outer webs and integrating the lower ends of the precast webs with the bottom slab (Fig. 6(C)); a step of assembling shoring for the upper slab (28) on the bottom slab and the two precast webs and assembling an upper slab formwork (29) on the shoring for the upper slab (Fig. 6(D)); a step of assembling upper slab reinforcing bars (31) on the upper slab formwork (Fig. 6(D)); and a step of placing upper slab concrete (32) and integrating the upper ends of the precast webs with the upper slab (Fig. 7(E)).

[0022] According to this aspect, two precast webs can be arranged at the positions of the outer webs that are inclined compared to the middle web using a support pedestal. Further, by assembling shoring for the upper slab above the inclined precast webs, an upper slab formwork can be assembled and upper slab concrete can be placed. By using precast webs for the outer webs, the quality of the concrete for the outer webs is maintained and the work becomes easier.

Advantages of the Invention

[0023] According to the above aspects, it is possible to provide an inverted trapezoidal box girder bridge and an erection method thereof that can facilitate the work while maintaining the quality of the concrete.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0026] FIG. 1 is a side view of an extradosed box girder bridge 1 according to an embodiment. As shown in FIG. 1, the extradosed box girder bridge 1 is a multi-span continuous bridge erected between the first pier P1 to the fourth pier P4 provided at positions spaced apart in the bridge axis direction. Hereinafter, when the first pier P1 to the fourth pier P4 are collectively referred to or not distinguished, they are simply referred to as pier P. Each pier P is constructed on a foundation 2 having an appropriate structure. The extradosed box girder bridge 1 includes an inverted trapezoidal box girder 3 forming a continuous box girder having an inverted trapezoidal cross-sectional shape, two main towers 4 constructed on the second pier P2 and the third pier P3, and a plurality of diagonal members 5 extending from each main tower 4 to both sides in the bridge axis direction. The diagonal members 5 are stretched between the main tower 4 and the inverted trapezoidal box girder 3, and an upward tensile force is applied to the inverted trapezoidal box girder 3. Note that the extradosed box girder bridge 1 is an example of an extradosed box girder bridge.

[0027] Figure 2 is a cross-sectional view of the extradosed box girder bridge 1 shown in Figure 1, showing the cross-section II-II in Figure 1. As shown in Figure 2, the inverted trapezoidal box girder 3 has a concrete upper floor slab 6, a concrete lower floor slab 7, and four concrete webs 8 (8I, 8O) that connect the upper floor slab 6 and the lower floor slab 7. The width of the lower floor slab 7 is about 1 / 3 to 1 / 4 of the width of the upper floor slab 6, and the inverted trapezoidal box girder 3 as a whole has an inverted trapezoidal cross-sectional shape. The four webs 8 include two inner webs 8I arranged on the inner side in the width direction and two outer webs 8O arranged outside the inner web 8I. Hereinafter, when the inner web 8I and the outer web 8O are collectively referred to or not distinguished, they are called the web 8.

[0028] The lower ends of the inner web 8I and the outer web 8O arranged on the left side of the cross-section are connected near the left end of the lower floor slab 7. The lower ends of the inner web 8I and the outer web 8O arranged on the right side of the cross-section are connected near the right end of the lower floor slab 7. The two inner webs 8I are slightly inclined in a direction where the upper sides approach each other. Therefore, the central chamber 9 formed between the inner webs 8I has a trapezoidal cross-sectional shape. The two outer webs 8O are inclined in a direction where the upper sides move away from each other, with an inclination angle larger than the inclination angle of the inner web 8I. Since the lower ends of the adjacent inner web 8I and outer web 8O are close to each other, the side chambers 10 formed between the inner web 8I and the outer web 8O each have an inverted triangular cross-sectional shape. As a result, the inverted trapezoidal box girder 3 as a whole has an inverted trapezoidal cross-sectional shape.

[0029] The upper floor slab 6 and the lower floor slab 7 are composed of cast-in-place concrete. The two inner webs 8I are also composed of cast-in-place concrete. The two outer webs 8O are mainly composed of precast webs 11 made of precast concrete. The lower end and the upper end of the outer web 8O are composed of cast-in-place concrete and are integrated with the lower floor slab 7 and the upper floor slab 6. Note that in other embodiments, the inner web 8I may also be mainly composed of the precast web 11 like the outer web 8O.

[0030] On the lower surface of the upper deck 6, a plurality of horizontal ribs 12 are integrally formed. The horizontal ribs 12 are arranged at predetermined intervals in the bridge axis direction and are constructed by in-situ concrete during the construction of the upper deck 6. On the upper surface of the upper deck 6, a plurality of parapets 13 extending in the bridge axis direction are provided. Two parapets 13 are provided at the left and right ends of the upper deck 6. In this embodiment, two more parapets 13 are provided near the center of the upper deck 6, and the uphill lane and the downhill lane are separately provided on the left side and the right side of the upper deck 6. The parapet 13 may be formed by in-situ concrete or may be composed of precast parapets made of precast concrete.

[0031] FIG. 3 is a (A) cross-sectional view and (B) longitudinal sectional view of the extrados box girder bridge 1 at the diagonal member connection part. The diagonal member 5 is arranged at the center in the width direction of the upper deck 6. On the lower surface of the upper deck 6, a diagonal member fixing protrusion 14 for fixing the lower end of the diagonal member 5 is integrally provided so as to protrude into the central chamber 9. The left and right ends of the diagonal member fixing protrusion 14 are connected to the two middle webs 8I. Further, on each inner surface of the middle web 8I on the central chamber 9 side, vertical ribs 15 extending vertically and connecting the left and right ends of the diagonal member fixing protrusion 14 and the lower deck 7 are integrally formed. The diagonal member 5 is arranged so as to penetrate the upper deck 6 and the diagonal member fixing protrusion 14, and the lower end is fixed to the diagonal member fixing protrusion 14 by a fixture 16 provided on the diagonal member fixing protrusion 14.

[0032] As shown in FIG. 3(B), the vertical force of the tensile force of the diagonal member 5 is transmitted to the diagonal member fixing protrusion 14. As shown in FIG. 3(A), the vertical force from the diagonal member 5 transmitted to the diagonal member fixing protrusion 14 supports the central portion of the upper deck 6. Further, this vertical force is transmitted to the lower deck 7 as a tensile force in the middle web 8I and the vertical rib 15, and is transmitted as a compressive force in the outer web 8O, thereby supporting both side portions of the upper deck 6. In this way, the inverted trapezoidal box girder 3 includes the left and right middle webs 8I and outer webs 8O that respectively define the inverted left-angled side chambers 10, thereby constituting a stress transmission mechanism that converts the vertical force from the diagonal member 5 into the supporting force of the entire upper deck 6 without generating local stress. That is, the inverted trapezoidal box girder 3 has a reasonable structure capable of transmitting a large force with a small member cross-section and exhibits excellent stress transmission characteristics.

[0033] As described with reference to FIG. 1, the inverted trapezoidal box girder 3 further includes a main tower 4 constructed above the pier P and diagonal members 5 stretched between the main tower 4 and the inverted trapezoidal box girder 3 to form the extradosed box girder bridge 1. As shown in FIG. 3, a diagonal member fixing projection 14 for fixing the lower end of the diagonal member 5 is formed above the central chamber 9. Thereby, in a box girder having a small cross-sectional area and a lightweight structure, a box girder structure that is rationally supported by the diagonal member 5 is realized because the load of the box girder is transmitted to the diagonal member 5 without generating local stress.

[0034] FIG. 4 is a side view of a main part of the extradosed box girder bridge 1 shown in FIG. 1. As shown in FIG. 4, the outer web 8O of the inverted trapezoidal box girder 3 includes a plurality of precast webs 11 arranged at a predetermined interval in the bridge axis direction. The intermediate portion 8a of the outer web 8O between the adjacent precast webs 11 is constructed of cast-in-place concrete. The interval between the precast webs 11 may be, for example, about 500 mm. One precast web 11 may be arranged for each construction block of the lower floor slab 7 and the upper floor slab 6, or two or three precast webs 11 may be arranged.

[0035] When one precast web 11 is arranged for each construction block, the length (dimension in the bridge axis direction) of the precast web 11 may be about the dimension obtained by subtracting the interval (500 mm) from the dimension in the bridge axis direction of the construction block. For example, when the dimension in the bridge axis direction of the construction block is 3 m, the length of the precast web 11 may be 3 - 0.5 = 2.5 m. An inclined outer formwork and inner formwork are assembled between the adjacent precast webs 11, and concrete is placed into the formwork from the upper floor slab 6 side before placing the upper floor slab concrete. Since the outer formwork and the inner formwork are inclined, it takes time to place the concrete so that no bubbles remain, but since the length (axial length) of the concrete placing portion is short, complicated work is reduced.

[0036] When two or more precast webs 11 are arranged for each construction block, the length (dimension in the bridge axis direction) of the precast web 11 may be approximately the dimension obtained by subtracting the intervals for the number of sheets from the dimension in the bridge axis direction of the construction block and then dividing by the number of sheets. For example, when the dimension in the bridge axis direction of the construction block is 6 m and two precast webs 11 are arranged in one construction block, the length of the precast web 11 may be (6 - 0.5×2) / 2 = 2.5 m. In this case, when placing the concrete for one construction block, the concrete is placed into the inclined forms provided at two locations. Also in this case, since the length (axial length) of the concrete placement part is shorter compared to the case where the precast web 11 is not used, less complicated work is required.

[0037] Thus, since each outer web 8O includes a plurality of precast webs 11 arranged at intervals in the bridge axis direction, the precast webs 11 can be designed to have a desired size and weight, and the work of arranging the precast webs 11 is easy.

[0038] Also, when two precast webs 11 arranged in the bridge axis direction are connected to each other by in-place concrete, it is easy to ensure the required rigidity for the outer web 8O composed of the precast webs 11 and the in-place concrete.

[0039] Next, with reference to FIGS. 5 to 7, the erection method of the inverted trapezoidal box girder 3 in the extradosed box girder bridge 1 according to the embodiment will be described. The inverted trapezoidal box girder 3 is erected by a cantilever erection method in which the box girder is constructed for each construction block using wagons 17 (mobile working vehicles) on both sides in the bridge axis direction from the bridge piers P. As shown in FIG. 5(A), the wagon 17 includes a cross beam 18 arranged above the upper floor slab 6 and a lower working platform 20 supported by the cross beam 18 via a suspension member 19. The cross beam 18 is arranged above the upper floor slab 6 of the construction block to be constructed by a support base (not shown) fixed to the cross girder on the bridge pier P or the upper surface of the already constructed upper floor slab 6. The erection work described below is performed by workers.

[0040] First, the operator assembles the formwork 21 for the lower floor slab on the lower working platform 20. Although not shown in the figure, the formwork 21 for the lower floor slab is provided with a height that can be changed so that it can be removed after the concrete is placed. Next, as shown in FIG. 5(B), the operator assembles the reinforcing bars 22 for the lower floor slab on the formwork 21 for the lower floor slab. The operator also arranges two trapezoidal support brackets 23 on the formwork 21 for the lower floor slab and arranges the two precast webs 11 in an inclined posture at the positions corresponding to the outer webs 8O. At the lower end of the precast web 11, the outer web reinforcing bars 24 protrude, and the outer web reinforcing bars 24 are connected to the reinforcing bars 22 for the lower floor slab by lap joints. Further, the operator assembles the middle web reinforcing bars 25 at the positions where the middle web 8I is to be constructed. The lower end of the middle web reinforcing bars 25 is similarly connected to the reinforcing bars 22 for the lower floor slab by lap joints.

[0041] Next, as shown in FIG. 6(C), the operator places the concrete 26 for the lower floor slab inside the formwork 21 for the lower floor slab and integrates the lower end of the precast web 11 with the lower floor slab 7. Subsequently, as shown in FIG. 6(D), the operator assembles the formwork 27 for the middle web, assembles the shoring 28 (28A, 28B) for the upper floor slab on the lower working platform 20, the lower floor slab 7, and the two precast webs 11, and assembles the formwork 29 for the upper floor slab on the shoring 28 for the upper floor slab. The shoring 28 for the upper floor slab includes a first shoring 28A for the upper floor slab assembled on the lower working platform 20 and the lower floor slab 7, and a second shoring 28B for the upper floor slab assembled on the two precast webs 11. The second shoring 28B for the upper floor slab is provided with an inclined lower base 30 so that it can be assembled on the inclined precast web 11. After assembling the formwork 29 for the upper floor slab, the operator assembles the reinforcing bars 31 for the upper floor slab on the formwork 29 for the upper floor slab. The upper ends of the outer web reinforcing bars 24 and the middle web reinforcing bars 25 protruding from the upper ends of the precast webs 11 are connected to the reinforcing bars 31 for the upper floor slab by lap joints.

[0042] Thereafter, as shown in FIG. 7(E), the operator places the concrete 32 for the upper floor slab inside the formwork 27 for the middle web and inside the formwork 29 for the upper floor slab, constructs the middle web 8I and the upper floor slab 6, and integrates the upper end of the precast web 11 with the upper floor slab 6.

[0043] After the concrete is cured and hardened, as shown in Fig. 7(F), the worker disassembles and removes the shoring 28 for the upper floor slab, the formwork 29 for the upper floor slab, the formwork 27 for the middle web, the support gantry 23, and the formwork 21 for the lower floor slab. Thereby, one block of the inverted trapezoidal box girder 3 having the above configuration is constructed. Note that the railing 13 is constructed later.

[0044] According to this erection method, as shown in Fig. 5(B), two precast webs 11 can be arranged at the position of the outer web 8O inclined with respect to the middle web 8I by using the support gantry 23. Further, as shown in Fig. 6(D), by assembling the second shoring 28B for the upper floor slab above the inclined precast web 11, the formwork 29 for the upper floor slab can be assembled and the concrete 32 for the upper floor slab can be placed. By using the precast web 11 for the outer web 8O, the quality of the concrete of the outer web 8O is maintained and the work becomes easier.

[0045] As described with reference to Fig. 2, the two outer webs 8O are inclined with respect to the middle web 8I and include the precast web 11 made of precast concrete. Therefore, the outer web 8O can be easily constructed while maintaining the quality of the concrete of the outer web 8O.

[0046] Generally, when using precast concrete members, it is advantageous in terms of quality improvement and construction period shortening, but it is often disadvantageous in terms of cost reduction. In this embodiment, the two middle webs 8I are made of cast-in-place concrete, and the middle webs 8I are constructed by cast-in-place concrete. Thereby, it is possible to reduce the construction cost of the inverted trapezoidal box girder 3 while maintaining the quality of the concrete.

[0047] The description of the specific embodiments ends here. However, the present invention is not limited to the above embodiments and modifications, and can be widely modified and implemented.

[0048] For example, the two middle webs 8I may include the precast web 11. By configuring the inverted trapezoidal box girder 3 in such a structure, even if the inverted trapezoidal box girder 3 is designed with an inclined middle web 8I, the middle web 8I can be easily constructed while maintaining the quality of the concrete in the middle web 8I.

[0049] In the above embodiment, the inverted trapezoidal box girder 3 constitutes the extradosed box girder bridge 1. However, the inverted trapezoidal box girder 3 may be configured as a cable-stayed bridge or as an inverted trapezoidal box girder bridge without diagonal members 5. In addition, the specific configurations, arrangements, quantities, materials of each member and part, and the specific operations and sequences of each erection work can be appropriately changed as long as they do not deviate from the gist of the present invention. Also, not all of the constituent elements shown in the above embodiment are necessarily essential and can be appropriately selected.

Explanation of Reference Numerals

[0050] 1: Extradosed box girder bridge (inverted trapezoidal box girder bridge) 3: Inverted trapezoidal box girder 4: Main tower 5: Diagonal member 6: Upper floor slab 7: Lower floor slab 8: Web 8I: Middle web 8O: Outer web 9: Central chamber 10: Side chamber 11: Precast web 14: Diagonal member fixing protrusion 17: Wagen 21: Formwork for lower floor slab 22: Reinforcement for lower floor slab 23: Support pedestal 26: Concrete for lower floor slab 27: Formwork for middle web 28: Shoring for upper floor slab 28A: First shoring for upper floor slab 28B: Second shoring for upper floor slab 29: Formwork for upper floor slab 30: Lower base 31: Reinforcement for upper floor slab 32: Concrete for the upper bed P: Bridge pier P2: Second bridge pier P3: Third bridge pier

Claims

1. An inverted trapezoidal box girder bridge, comprising: a top slab made of concrete, a bottom slab made of concrete, and four webs made of concrete connecting the top slab and the bottom slab, and having an inverted trapezoidal box girder with an overall inverted trapezoidal cross-sectional shape; the webs include two middle webs arranged on the inner side in the width direction and two outer webs arranged outside the middle webs, a central chamber having a trapezoidal cross-sectional shape is formed between the middle webs, and side chambers having an inverted triangular cross-sectional shape are formed between each middle web and the corresponding outer web; an inverted trapezoidal box girder bridge, wherein the two outer webs include precast webs made of precast concrete.

2. The inverted trapezoidal box girder bridge according to claim 1, wherein the two outer webs include a plurality of the precast webs arranged at intervals in the bridge axis direction.

3. The inverted trapezoidal box girder bridge according to claim 2, wherein the two precast webs arranged in the bridge axis direction are connected to each other by cast-in-place concrete.

4. The inverted trapezoidal box girder bridge according to claim 1, wherein the two middle webs are made of cast-in-place concrete.

5. The inverted trapezoidal box girder bridge according to claim 1, wherein the two middle webs include the precast webs.

6. a main tower constructed above the pier; and a plurality of diagonal members stretched between the main tower and the inverted trapezoidal box girder to form an extrados box girder bridge, The inverted trapezoidal box girder bridge according to claim 1, wherein a diagonal member fixing protrusion for fixing the lower end of the diagonal member is formed above the central chamber.

7. An erection method for erecting the inverted trapezoidal box girder bridge according to any one of claims 1 to 6 by a cantilever erection method using a wagon, comprising: assembling a formwork for the bottom slab on the wagon; assembling bottom slab reinforcement on the formwork for the bottom slab; arranging the two precast webs in an inclined posture at the positions of the corresponding outer webs using a support gantry; placing concrete for the bottom slab in a state where the two precast webs are arranged at the positions of the corresponding outer webs, and integrating the lower ends of the precast webs with the bottom slab; assembling supports for the top slab on the bottom slab and the two precast webs, and assembling a formwork for the top slab on the supports for the top slab; assembling top slab reinforcement on the formwork for the top slab; A method for erecting an inverted trapezoidal box girder bridge, comprising the step of placing concrete for the upper bed slab and integrating the upper end of the precast web with the upper bed slab.

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