Column head of box girder bridge and construction method of the same

Abstract

To make it possible to construct a column head of a box girder bridge without using a large bracket unit when a width of a box girder is larger than that of a bridge footing.SOLUTION: A column head 8 of a box girder bridge 10 comprises: a cross beam 17 constructed integrally at an upper end of a bridge footing 3 and having a pair of extension parts 16 extending from side surfaces 3a of the bridge footing 3 to both sides; and a pair of additional beams 19 constructed integrally on the bridge footing 3 so as to extend from upper parts of the side surfaces 3a of the bridge footing 3 sideward below the extension parts 16 and supporting the corresponding extension parts 16.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a column capital of a box girder bridge and a method for constructing the same, and more particularly to a column capital of a box girder bridge constructed so as to protrude on both sides from a pier and a method for constructing the same. [Background technology]

[0002] One method for erecting a concrete box girder bridge is the so-called cantilever erection method, in which the box girder is constructed by projecting a specified length of construction block from the column head, which is part of the box girder constructed integrally on the pier, to both sides in the bridge axis direction. In the cantilever erection method, in order to secure space for locating mobile work vehicles, the column head is constructed so that it has a large cross-section part (cross girder) constructed on the pier, and a pair of projections (box girder base parts) that project from the cross girder on both sides in the bridge axis direction.

[0003] In order to construct a column head equipped with a cross beam and a pair of overhanging parts, it is necessary to provide large brackets on both sides of the bridge pier in the bridge axis direction. In order to eliminate the need to assemble these brackets, a column head construction method has been proposed that enables the overhanging erection of a bridge body (bridge girder) from a small column head (Patent Document 1). In this construction method, in a side view of the bridge, the main structure of the right-facing erection work vehicle constructed on the column head is set to a specified width, and the main structure of the left-facing erection work vehicle is set to a width narrower than the specified width and is arranged so as to be intertwined inside the main structure of the right-facing erection work vehicle. Both work vehicles move forward in accordance with the overhanging erection of the bridge body, and the main structure of the left-facing erection work vehicle is changed to the specified width after it leaves the main structure of the right-facing erection work vehicle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-218316 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conventional technology described in the above Patent Document 1 is for constructing the first part of the girder bridge section from the column capital part, which has a small dimension in the bridge axis direction. In other words, this technology can be used only after constructing a column capital part with the same dimension as the pier's dimension in the bridge axis direction, and it is based on the premise that the column capital part has been constructed.

[0006] In box girder bridges, the width of the pier (the dimension perpendicular to the bridge axis) is sometimes designed to be smaller than the width of the box girder (the dimension perpendicular to the bridge axis). Also, when two parallel box girder bridges are supported by a common pier, the width of the pier may be smaller than the width of both box girders.

[0007] When the overhanging part of the upper deck overhangs to the side from the pier at the column head, there is a method of erecting a bracket unit on the upper side of the pier and constructing shoring or scaffolding on the bracket unit to construct the overhanging part of the upper deck at the column head. This method can be used when the width of the box girder itself is larger than that of the pier. However, when the width of the box girder itself is larger than that of the pier, the load that the bracket unit must support is larger than when only the overhanging part of the upper deck is constructed. As a result, the bracket unit becomes very large, or it becomes necessary to reconsider the design of the pier itself in order to support a large bracket unit.

[0008] In view of the above background, an objective of the present invention is to provide a column capital of a box girder bridge that can be constructed without using large bracket units when the width of the box girder is larger than the width of the pier, and a construction method thereof. [Means for solving the problem]

[0009] In order to solve the above problems, one embodiment of the present invention is a column capital (8) of a box girder bridge (10), which comprises a cross beam (17) constructed integrally with the upper end of a pier (3) and having a pair of protrusions (16) protruding outward on both sides from the pier, and a pair of additional beams (19) constructed integrally with the pier so as to extend laterally below the protrusions from the upper parts of both side surfaces (3a) of the pier, and which support the corresponding protrusions.

[0010] According to this embodiment, the additional beam is constructed first, and the overhanging portion of the cross beam can be constructed using the additional beam. Therefore, the column capital of the box girder bridge can be constructed without using a large bracket unit. In addition, the shear force transmitted from the box girder bridge is transmitted to the pier through not only the cross beam of the column capital but also the additional beam. In other words, the flow of the shear force becomes smooth, and the shear stress of the cross beam is reduced. Therefore, even if the width of the box girder is larger than that of the pier, it is not necessary to make the bridge axis direction dimension of the cross beam larger than that of the pier in order to ensure shear resistance.

[0011] In the above aspect, each of the additional beams (19) may have a tapered shape that decreases in height toward the tip end.

[0012] According to this embodiment, the volume (amount of concrete) of the additional beam can be reduced while ensuring the necessary shear strength of the additional beam, thereby further reducing the shear stress of the additional beam.

[0013] In the above aspect, it is preferable that the width dimension (W19) in the bridge axis direction of the additional beam (19) and the dimension (W17) in the bridge axis direction of the cross beam (17) are less than or equal to the dimension (W3) in the bridge axis direction of the upper part of the pier to which the additional beam is connected.

[0014] Because the area of ​​the cross beam in the bridge axis direction is larger than that of the additional beam, when the cross beam dimension in the bridge axis direction increases, the volume (amount of concrete) increases significantly. With this configuration, the amount of concrete in the column capital is reduced. This also reduces the need for large bracket units.

[0015] In the above-mentioned aspect, each of the additional beams (19) may be composed of a plurality of half precast members (21) divided in the extension direction and a cast-in-place concrete section (22) poured inside the half precast members.

[0016] According to this embodiment, since the weight of the half precast members is smaller than when full precast members are used, the lifting equipment required to construct the additional beams is smaller, thereby reducing construction costs.

[0017] In the above aspect, it is preferable that reinforcing bars (31) are assembled inside the cast-in-place concrete portion (22).

[0018] According to this aspect, the shear strength of the additional beam can be improved.

[0019] In order to solve the above-mentioned problems, another aspect of the present invention is a method for constructing a column capital (8) of a box girder bridge (10) having a cross beam (17) constructed integrally with the upper end of a pier (3) and having a pair of overhanging portions (16) overhanging both sides from a side surface (3a) of the pier, and a pair of additional beams (19) constructed integrally with the pier so as to extend laterally from the upper portion of each side surface of the pier below the overhanging portions and supporting the corresponding overhanging portions, the method comprising the steps of: dividing each of the additional beams in the extension direction to form a plurality of half precast concrete beams; The method includes a step (ST1) of preparing a precast member (21), an arrangement step (ST3, ST5) of arranging the half-precast member on the side of the pier, a pouring step (ST9) of pouring concrete into the half-precast member arranged on the side of the pier, construction steps (ST3 to ST11) of repeating the arrangement step and the pouring step to construct a pair of the additional beams, and a step (ST12) of constructing the cross beam on the pier and the pair of the additional beams.

[0020] According to this embodiment, since the overhanging portion of the cross beam can be constructed on the additional beam, even if the width of the box girder is larger than that of the pier, the column capital of the box girder bridge can be constructed without using a large bracket unit. Also, since each additional beam is constructed using multiple half precast members, there is no need to assemble a large bracket support that can support the load of the additional beam.

[0021] In the above-mentioned embodiment, the placement steps (ST3, ST5) are repeated to place a plurality of the half-precast members (21) on the sides of the pier, and then in the pouring step (ST9), concrete is poured inside the plurality of the half-precast members.

[0022] According to this aspect, the number of times concrete is poured can be reduced, thereby shortening the construction period.

[0023] In the above aspect, the construction method may further include an assembly step (ST7) of placing a reinforcing bar cage inside the half precast member and assembling reinforcing bars (31) after the placement steps (ST3, ST5) and before the pouring step (ST9).

[0024] According to this aspect, the shear strength of the additional beam can be improved by arranging the reinforcing bars, while the construction period can be shortened by using the reinforcing bar cage.

[0025] In the above aspect, the construction method may further include, after the placement steps (ST3, ST5), a primary tensioning step (ST6) of attaching the half-precast member (21) to the pier (3) by tensioning a primary tension member (29) arranged to penetrate the half-precast member (21).

[0026] According to this embodiment, the half precast member can be easily and reliably attached to the pier by tensioning the primary tendon.

[0027] In the above aspect, the construction method may further include a secondary tensioning step (ST10) of placing a secondary tensioning member (30) on the upper part of the additional beam (19) and tensioning the secondary tensioning member after the casting step (ST9).

[0028] According to this embodiment, the bending strength of the additional beam, which is a cantilever beam, can be effectively improved by tensioning the secondary tendon arranged on the upper part of the additional beam. Effect of the Invention

[0029] According to the above aspect, when the width of the box girder is larger than the width of the pier, the column capital of the box girder bridge can be constructed without using a large bracket unit. [Brief description of the drawings]

[0030] [Figure 1] Side view of a bridge according to an embodiment [Diagram 2] Cross-sectional view of II-II in Fig. 1 [Diagram 3] Front view of the top of the capital after construction [Figure 4] Cross-sectional view taken along the line IV-IV in FIG. [Diagram 5] Cross-sectional view of half precast members that make up the additional beam [Figure 6] Flowchart showing the construction steps for the column capital [Figure 7] Diagram showing the construction procedure of the column capital [Figure 8] FIG. 1 is an explanatory diagram of the effect of the column capital part according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0032] Fig. 1 is a side view of a bridge 1 according to an embodiment. As shown in Fig. 1, the bridge 1 comprises a pair of abutments 2, at least one pier 3 (two in the illustrated example) disposed between the abutments 2, and a bridge section 4 (superstructure) spanning the abutments 2 and pier 3. Each pier 3 comprises a foundation section 6 constructed on the ground 5, a column section 7 rising from the foundation section 6, and a column capital section 8 integrally formed with the upper end of the column section 7 and constituting a part of the bridge section 4.

[0033] Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. As shown in Fig. 2, the bridge section 4 is composed of a pair of box girder bridges 10 arranged close to each other and parallel to each other. One box girder bridge 10 constitutes a road bridge for the up lane, and the other box girder bridge 10 constitutes a road bridge for the down lane. Each box girder bridge 10 comprises a box girder 11, a deck slab 12 (upper deck) integrally formed with the upper part of the box girder 11, and a balustrade 13 provided at the end of the deck slab 12 in the width direction. The deck slab 12 is formed wider than the box girder 11, and has left and right deck slab overhangs 14 that overhang from the side edges of the box girder 11.

[0034] The width between the box girders 11 of both box girder bridges 10 is approximately equal to the width of the column parts 7 of the piers 3. Therefore, the box girders 11 of both box girder bridges 10 protrude significantly to the left and right from the column parts 7 of the piers 3. The column capital parts 8 of the piers 3 have cross beams 17 having a pair of protruding parts 16 protruding to the left and right from the column parts 7 to form part of the box girders 11 of both box girder bridges 10. The protruding parts 16 of the column capital parts 8 corresponding to both box girders 11 have a pair of passages 18 for maintenance formed so as to penetrate the cross beams 17 in the bridge axis direction.

[0035] The column capital 8 of this embodiment further has a pair of additional beams 19 constructed integrally with the pier 3 so as to extend laterally below the overhanging portion 16 from the upper portion of both side surfaces 3a of the pier 3. Each additional beam 19 is constructed to support the corresponding overhanging portion 16 when constructing the cross beam 17, and supports the corresponding overhanging portion 16 from below.

[0036] Each additional beam 19 has a tapered shape with its height decreasing towards its tip when viewed in the bridge axis direction in Fig. 2. The upper surface of the additional beam 19 that matches the underside of the box girder 11 is roughly horizontal. Therefore, the underside of the additional beam 19 is an inclined surface that slopes upward towards the extended end. As shown in Fig. 1, the width dimension W19 of the additional beam 19 in the bridge axis direction is the same as the dimension W3 of the upper part of the pier 3 in the bridge axis direction.

[0037] Fig. 3 is a front view of the upper part of the column capital 8 before the bridge section 4 is constructed and after the pier 3 is constructed, and Fig. 4 is a cross-sectional view taken along the line IV-IV in Fig. 3. As shown in Figs. 3 and 4, the column capital 8 has the above-mentioned cross beam 17 and additional beam 19, and a box girder base 20 that protrudes from the cross beam 17 on both sides in the bridge axis direction.

[0038] As shown in Fig. 4, the thickness dimension W17 in the bridge axis direction of the cross girder 17 is approximately the same as the dimension W3 in the bridge axis direction of the upper part of the pier 3. Therefore, the width dimension W19 in the bridge axis direction of the additional beam 19 is approximately the same as the thickness dimension W17 in the bridge axis direction of the cross girder 17. It is preferable that the width dimension W19 in the bridge axis direction of the additional beam 19 and the thickness dimension W17 in the bridge axis direction of the cross girder 17 are equal to or smaller than the dimension W3 in the bridge axis direction of the upper part of the pier 3 to which the additional beam 19 is connected. Also, it is preferable that the thickness dimension W17 in the bridge axis direction of the cross girder 17 is equal to or smaller than the width dimension W19 in the bridge axis direction of the additional beam 19.

[0039] The additional beam 19 is composed of multiple (seven in the illustrated example) half precast members 21 divided by dividing lines shown by imaginary lines in Figure 3, and a cast-in-place concrete section 22 (Figure 5) poured inside the half precast members 21.

[0040] Fig. 5 is a cross-sectional view of the half precast member 21 that constitutes the additional beam 19. As shown in Fig. 5, the half precast member 21 has a W-shaped cross-sectional shape, and defines two upwardly open grooves 23 therein. Both grooves 23 are also open at both ends of the half precast member 21. In other words, the half precast member 21 has three vertical walls 24 and a bottom wall 25 that connects the lower ends of these vertical walls 24.

[0041] Four vertical ribs 26 protruding from the vertical wall 24 toward the groove 23 are formed in the middle of the half precast member 21 in the extension direction. A plurality of shear keys 27 are formed on the end faces of the half precast member 21 in order to increase the shear resistance against vertical loads between the half precast member 21 and other half precast members 21 arranged adjacently.

[0042] The vertical ribs 26 of the half precast member 21 are formed with through holes through which a plurality of pulling PC steel bars 28 pass, for pulling the half precast member 21 toward the pier 3 when placing the half precast member 21 in a predetermined position. The vertical walls 24 and bottom wall 25 of the half precast member 21 are formed with through holes through which a plurality of primary tendons 29 pass, for primarily tensioning the half precast member 21 toward the pier 3. In other words, the primary tendons 29 are arranged to pass through the half precast member 21. A plurality of secondary tendons 30 are arranged inside the half precast member 21, i.e., in the upper part of the groove 23.

[0043] After the half precast member 21 is placed in a predetermined position, reinforcing bars 31 are assembled inside the half precast member 21, i.e., in the groove 23, and then cast-in-place concrete is poured to construct the cast-in-place concrete section 22. Before the cast-in-place concrete is poured into the groove 23, a formwork is assembled to close the open end of the groove 23. The secondary tendon 30 is tensioned after the cast-in-place concrete section 22 is constructed.

[0044] Next, a method for constructing the column capital 8 of the pier 3 having such a configuration will be described with reference to Figures 6 and 7. Figure 6 is a flow chart showing the construction procedure for the column capital 8, and Figure 7 is an explanatory diagram showing the construction procedure for the column capital 8. The column capital 8 is constructed by workers in charge of each process.

[0045] First, workers fabricate half precast members 21 (see FIG. 5) at a precast factory (step ST1). Workers also construct the main body of the pier 3, i.e., the column portion 7, at the site (step ST2). Either step ST1 or step ST2 may be performed first, or they may be performed in parallel.

[0046] After constructing the column 7, as shown in FIG. 7(A), the worker places the half precast members 21 on both sides of the pier 3 (step ST3). After placing the half precast members 21, the worker uses the pull-in PC steel rods 28 (FIG. 5) to pull the half precast members 21 toward the column 7 and fasten them (step ST4). Then, as shown in FIG. 7(B), the worker places another half precast member 21 on the side of the half precast member 21 that has already been placed (step ST5). In this placement step, the worker also pulls and fastens using the pull-in PC steel rods 28. Next, the worker uses the primary tendons 29 (FIG. 5) that are provided so as to penetrate the half precast member 21 that has already been placed to perform primary tensioning of the half precast member 21 (step ST6).

[0047] After arranging the multiple half precast members 21, workers place reinforcing bars 31 (FIG. 5) inside the half precast members 21 (step ST7). Next, workers assemble forms to close the grooves 23 at the ends of the half precast members 21 (step ST8). After that, workers perform a pouring step to pour concrete inside the multiple half precast members 21 (step ST9) as shown in FIG. 7(C), and construct a part of the cast-in-place concrete section 22. After the concrete hardens, workers use secondary tendons 30 (FIG. 5) arranged on the top of the additional beam 19 to secondarily tension the constructed part of the additional beam 19 (step ST10).

[0048] Thereafter, if the half precast member 21 has not been completed up to the predetermined block (seven blocks in this embodiment) (step ST11: No), the worker repeats the work of steps ST3 to ST10. As shown in FIG. 7(D), when the half precast member 21 has been completed up to the predetermined block and the step of constructing the additional beam 19 is completed (step ST11: Yes), the worker constructs the cross beam 17 on the constructed additional beam 19 (step ST12). This completes the construction of the column capital part 8.

[0049] Next, the effect of the column capital 8 of the pier 3 constructed in this manner will be described. Fig. 8 is an explanatory diagram of the effect of the column capital 8 according to the embodiment. Fig. 8(A1) shows a front view of the column capital 8 of this embodiment, and Fig. 8(A2) shows a side view of the column capital 8 of this embodiment. Fig. 8(B1) shows a front view of a conventional column capital 108 according to a comparative example, and Fig. 8(A2) shows a side view of the conventional column capital 108.

[0050] As shown in Fig. 8(B1), in the conventional column capital 108, a pair of overhanging parts 16 of the cross beam 17 overhangs largely to both sides from the side surface 3a of the pier 3, and both overhanging parts 16 are connected perpendicularly to the column part 7. Therefore, the load of the box girder bridge 10 acting on the cross beam 17 via the box girder base 20 is transmitted horizontally from the overhanging parts 16 to the center of the cross beam 17 as shown by the arrows, and then transmitted vertically to the column part 7 of the pier 3. For this reason, as shown by the hatched area in Fig. 8(B2), it was necessary to increase the thickness dimension W17 of the cross beam 17 in the bridge axis direction to accommodate the flow of the shear force transmitted from the box girder bridge 10, which resulted in a large increase in the volume of concrete.

[0051] In contrast, in this embodiment, as shown in Fig. 8 (A1), a pair of additional beams 19 are constructed integrally with the pier 3 so as to extend laterally from the upper part of both side surfaces 3a of the pier 3 below the overhanging part 16, and each additional beam 19 supports the corresponding overhanging part 16. Therefore, the shear force transmitted from the box girder bridge 10 is transmitted to the column part 7 of the pier 3 through not only the cross beam 17 of the column capital part 8 but also the additional beam 19 as shown by the arrow. In other words, the flow of the shear force becomes smoother, and the shear stress of the cross beam 17 is reduced.

[0052] Therefore, even if the width of the box girder 11 is greater than the width of the column portion 7 of the pier 3, it is not necessary to make the dimension of the cross girder 17 in the bridge axis direction greater than that of the pier 3 in order to ensure shear strength, as shown in FIG. 8 (A2). Although the volume of concrete increases in order to construct the additional beam 19, this increase is smaller than the increase due to the conventional increase in the thickness of the cross girder 17. In this embodiment, the increase in concrete volume is approximately 500 m 37(D), by constructing the additional beam 19 first, the overhanging portion 16 of the cross beam 17 can be constructed using the additional beam 19.

[0053] In this embodiment, each of the additional beams 19 has a tapered shape in which the height decreases toward the tip side. This reduces the volume (amount of concrete) of the additional beams 19 while ensuring the necessary shear strength of the additional beams 19. Therefore, the shear stress of the additional beams 19 is further reduced.

[0054] As shown in Fig. 8, the area of ​​the cross girder 17 as viewed in the bridge axis direction is larger than the area of ​​the additional beam 19, so when the dimension of the cross girder 17 in the bridge axis direction increases, the volume (amount of concrete) increases significantly. In contrast, in this embodiment, as described with reference to Fig. 4, the width dimension W19 of the additional beam 19 in the bridge axis direction and the thickness dimension W17 of the cross girder 17 in the bridge axis direction are set to be equal to or smaller than the dimension W3 in the bridge axis direction of the upper part of the pier 3 to which the additional beam 19 is connected. This reduces the amount of concrete in the column capital 8. This also reduces the need for large bracket units.

[0055] As shown in Fig. 5, each additional beam 19 is composed of multiple half precast members 21 divided in the extension direction, and cast-in-place concrete sections 22 poured inside the half precast members 21. This configuration makes the half precast members 21 lighter than when full precast members are used. Therefore, the lifting equipment required to construct the additional beams 19 can be made smaller, reducing construction costs.

[0056] In this embodiment, reinforcing bars 31 are assembled inside the cast-in-place concrete portion 22. This improves the shear strength of the additional beam 19.

[0057] Next, the effect of the method for constructing the capital part 8 described with reference to Figs. 6 and 7 will be described.

[0058] In the method for constructing the column capital 8, a pair of additional beams 19 are constructed by repeating steps ST3 and ST5 of placing half precast members 21 on the sides of the pier 3 and step ST9 of pouring concrete. In the subsequent step ST12, a cross beam 17 is constructed on the pier 3 and the pair of additional beams 19. In this way, since the overhanging portion 16 of the cross beam 17 can be constructed on the additional beam 19, the column capital 8 of the box girder bridge 10 can be constructed without using a large bracket unit even if the width of the box girder 11 is larger than the width of the pier 3. In addition, since each of the additional beams 19 is constructed using a plurality of half precast members 21, there is no need to assemble a large bracket support capable of supporting the load of the additional beam 19.

[0059] In this embodiment, after repeating steps ST3 and ST5 to place multiple half precast members 21 on the sides of the pier 3, in step ST9, concrete is poured into the multiple half precast members 21. Therefore, the number of times concrete is poured is reduced compared to the case where concrete is poured for each block of half precast members 21, and the construction period is shortened.

[0060] In an assembly step (ST7) following steps ST3 and ST5 in which the half precast members 21 are arranged and before step ST9 in which concrete is poured, a reinforcing bar cage is placed inside the half precast members 21 and reinforcing bars 31 are assembled. Therefore, the shear strength of the additional beam 19 can be improved by placing the reinforcing bars 31, while the construction period can be shortened by using the reinforcing bar cage.

[0061] In a primary tensioning step (ST6) following steps ST3 and ST5 in which the half precast member 21 is placed, the half precast member 21 is attached to the pier 3 by tensioning the primary tendons 29 provided so as to penetrate the half precast member 21. In this way, by tensioning the primary tendons 29, the half precast member 21 can be attached to the pier 3 simply and reliably.

[0062] In a secondary tensioning step (ST10) following step ST9 of pouring concrete, a secondary tensioning member 30 is placed on the upper part of the additional beam 19, and the secondary tensioning member 30 is tensioned. The tensioning of the secondary tensioning member 30 placed on the upper part of the additional beam 19 effectively improves the bending strength of the additional beam 19, which is a cantilever beam.

[0063] Although the description of the specific embodiment is finished above, the present invention is not limited to the above embodiment and modified examples, and can be widely modified and implemented. For example, in the above embodiment, the bridge 1 has two rows of box girder bridges 10, but it may have one box girder bridge 10 configured to be wide. In this case, the box girder bridge 10 may be a multi-main girder box girder bridge having two or more box cross-sectional parts, a multiple box girder bridge with continuous box cross-sectional parts, etc., instead of a single box girder bridge having one box cross-sectional part. In addition, instead of using the half precast member 21, a full precast member may be used. Furthermore, the cross-sectional shape of the half precast member 21 is not limited to the one shown in the figure, and various shapes can be adopted. In addition, the specific configuration and arrangement of each member and part, the quantity, materials, construction procedure, etc. can be appropriately changed within the scope of the purpose of the present invention. In addition, all of the components shown in the above embodiment are not necessarily required, and can be selected appropriately. [Explanation of symbols]

[0064] 1: Bridge 3: Bridge pier 3a: Side 7: Pillar part 8: Column head 10: Box girder bridge 11: Box girder 12: Floor slab 16: Overhang 17: Crossbeam 19:Additional beam 21: Half precast members 22: Cast-in-place concrete section 29 :Primary tendon material 30:Secondary tendon material 31: Reinforced concrete W3: Dimension of the upper part of pier 3 in the bridge axis direction W17: Thickness of cross beam 17 in the bridge axis direction W19: Width dimension of additional beam 19 in the bridge axis direction

Claims

1. A column capital of a box girder bridge, A cross girder integrally constructed on the upper end of the pier and having a pair of overhanging portions overhanging both sides from the pier; A pair of additional beams constructed integrally with the pier so as to extend laterally from the upper portions of both sides of the pier below the overhanging portion and support the corresponding overhanging portion.

2. The column capital of a box girder bridge according to claim 1 , wherein each of the additional beams has a tapered shape having a smaller height toward the tip side.

3. The column capital of a box girder bridge according to claim 1, wherein the width dimension of the additional beam in the bridge axis direction and the dimension of the cross beam in the bridge axis direction are equal to or less than the dimension in the bridge axis direction of the upper part of the pier to which the additional beam is connected.

4. The column head of a box girder bridge according to any one of claims 1 to 3, wherein each of the additional beams is composed of a plurality of half precast members divided in the extension direction and a cast-in-place concrete section poured inside the half precast members.

5. The column capital of a box girder bridge according to claim 4, wherein a reinforcing bar is assembled inside the cast-in-place concrete section.

6. A method for constructing a column capital of a box girder bridge, comprising: a cross girder constructed integrally with the upper end of a pier, the cross girder having a pair of overhanging portions overhanging from the pier on both sides; and a pair of additional beams constructed integrally with the pier so as to extend from the upper portions of both sides of the pier below the overhanging portions to the sides, the pair of additional beams supporting the corresponding overhanging portions, A step of preparing a plurality of half precast members each formed by dividing each of the additional beams in an extension direction; A placement step of placing the half precast member on the side of the pier; A pouring step of pouring concrete into the inside of the half precast member arranged on the side of the pier; A construction step of repeating the placing step and the casting step to construct a pair of the additional beams; and constructing the cross beam on the pier and a pair of the additional beams.

7. 7. The method for constructing a column capital of a box girder bridge according to claim 6, wherein the placing step is repeated to place a plurality of the half precast members on the sides of the pier, and then in the pouring step, concrete is poured into the interiors of the plurality of half precast members.

8. The method for constructing a column capital of a box girder bridge according to claim 6 or 7, further comprising an assembly step of assembling a reinforcing bar by placing a reinforcing bar cage inside the half precast member after the placing step and before the casting step.

9. The method for constructing a column capital of a box girder bridge according to claim 6 or 7, further comprising, after the placing step, a primary tensioning step of attaching the half precast member to the pier by tensioning a primary tension member provided to penetrate the half precast member.

10. The method for constructing a column capital of a box girder bridge according to claim 9, further comprising a secondary tensioning step of placing a secondary tension member on the top of the additional beam and tensioning the secondary tension member after the casting step.

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