Bridge structure

Abstract

The present invention improves the wind resistance performance of a long-span bridge using a bridge girder comprising two end main box girders or two end main I-shaped girders. The bridge structure of the present invention comprises a bridge girder 13 having a deck slab 21 and a main girder 22 that includes I-shaped girders 23, 24 or box girders supporting the deck slab 21 from below at both ends in the width direction of the deck slab 21, the bridge structure being characterized in that the span length of the bridge girder 13 exceeds 100 m, the total width of the bridge girder 13 is 15 m or less, the height of the main girder 22 is 1.2 m or more, the ratio W1 / H3 of the total width W1 of the bridge girder 13 to the height H3 of the main girder 22 is seven or more, and a steel material with a yield strength of 380 N / mm2 or more is used for at least a lower flange of the main girder.

Description

Bridge structure

[0001] The present invention relates to a bridge structure using a bridge girder composed of, for example, two main box girders at the ends or two main I-shaped members at the ends.

[0002] Bridges are important structures in constructing social infrastructure. In recent years, the development of bridges with long spans (hereinafter sometimes referred to as long-span bridges) has been promoted. Since the sectional forces acting on the bridge girder of a long-span bridge are large, the girder height is increased to ensure the rigidity of the bridge itself. Also, like in cable-stayed bridges and suspension bridges, long-span bridges have a structure that is supported by cables to withstand sectional forces. Such long-span bridges are used, for example, in cable-stayed bridges and suspension bridges using a bridge girder having a full width with four or more lanes. Note that the full width is the length (width) in the transverse direction of the bridge girder.

[0003] In the 1970s, for example, truss girders (see Fig. 6(a)) with high rigidity and wind stability were used in cable-stayed bridges and suspension bridges. In the 1980s, with the progress of manufacturing technology and wind resistance evaluation technology, a single box girder section (see Fig. 6(b)) came to be used. In Japan, a streamlined single box girder bridge girder with fairings has become the mainstream. On the other hand, overseas, two main box girders at the ends (see Fig. 6(c)) having a sectional shape with reduced steel weight and a bridge girder composed of two main I-shaped members at the ends called edge girders (see Fig. 6(d)) are adopted.

[0004] Steel Structure Series 20 Steel Cable-Stayed Bridge - Technology and Changes - [2010 Edition], Japan Society of Civil Engineers, (2010)Irwin, P. A.: 12th Congress IABSE (1984) 689-696H.Yamada: Journal of Wind Engineering. JAWE 30 (1986) 41-55

[0005] To ensure wind resistance stability in long-span bridges, it is necessary to consider both the structural mechanical challenges of the bridge itself and the aerodynamic challenges of the bridge girders. For example, wind resistance performance is generally evaluated using the dimensionless wind speed U / fB (U: wind speed, f: frequency, B: total width) obtained from wind tunnel experiments. For example, if the total width is narrow, the wind speed converted from the dimensionless wind speed will also be small. In other words, bridge girders with a narrow total width are evaluated as having low wind resistance performance. Furthermore, bridge girders with a narrow total width have low rigidity and low frequency, and a decrease in wind resistance performance is unavoidable. Therefore, in order to ensure high wind resistance performance, it is necessary to widen the total width of the bridge girders. Accordingly, in long-span bridges, from the viewpoint of wind resistance performance, bridge girders with a total width that can accommodate, for example, two lanes on each side for a total of four lanes or more, are used. Note that when using bridge girders for a road with one lane on each side for a total of two lanes in a long-span bridge, it is necessary to widen the total width of the bridge girders, for example, in order to ensure wind resistance stability.

[0006] Incidentally, while end-type box girders and end-type I-shaped bridge girders have the advantage of lower manufacturing costs compared to box girders, they have lower torsional rigidity and wind resistance. Therefore, bridge girders consisting of end-type box girders or end-type I-shaped bridge girders are less likely to be used in weather conditions where strong winds occur, such as typhoons, and have the problem of limiting their installation locations.

[0007] This invention has been made in view of the above problems, and aims to improve the wind resistance performance of long-span bridges that use bridge girders consisting of two end main box girders or two end main I-shaped girders.

[0008] A bridge structure according to one aspect of the present invention is a bridge structure comprising a bridge girder having a deck slab and main girders including I-beams or box girders that support the deck slab from below at both ends in the width direction of the deck slab, wherein the span length of the bridge girder exceeds 100 m, the total width of the bridge girder is 15 m or less, the height of the main girder is 1.2 m or more, the ratio of the total width of the bridge girder to the height of the main girder is 7 or more, and at least the lower flange of the main girder has a yield strength of 380 N / mm ２ It is characterized by the use of the above-mentioned steel materials.

[0009] Furthermore, it is preferable that the bridge girder be a composite girder formed by combining the deck slab and the main girder.

[0010] Furthermore, a cable-stayed bridge in one aspect of the present invention is characterized by having the bridge structure described above.

[0011] According to the present invention, the wind resistance performance of long-span bridges using bridge girders consisting of two end box girders or two end I-shaped girders can be improved.

[0012] Figure 1(a) is a schematic side view showing one configuration of the cable-stayed bridge shown in this embodiment, and Figure 1(b) is a front view of the cable-stayed bridge shown in Figure 1(a). Figure 2 is a cross-sectional view showing the configuration of the bridge girder at position P1 of the cable-stayed bridge. Figure 3 is a cross-sectional view showing the configuration of the bridge girder. Figure 4(a) is a diagram showing the stress distribution in a non-composite girder, and Figure 4(b) is a diagram showing the stress distribution in a composite girder. This is a diagram showing the results of comparing the main girder height of a non-composite girder with the main girder height of a composite girder. Figure 6 is a cross-sectional view illustrating bridge girders of different structures.

[0013] The cable-stayed bridge shown in this embodiment will be described below with reference to the drawings. While the bridge structure of the present invention will be described below using a cable-stayed bridge, the bridge is not limited to a cable-stayed bridge; other types of bridges, such as girder bridges, may also be used.

[0014] As shown in Figure 1, the cable-stayed bridge 10 comprises main towers 11 and 12, a bridge girder 13, and a bridge pier 14. Although not shown in the figure, the bridge girder 13 is supported from below by bearings provided on the main towers 11 and 12 and on the bridge pier 14, and is also supported by multiple cables 15 that radiate from the upper ends of the main towers 11 and 12. The cables 15 are products commonly used in cable-stayed bridges, and their outer diameter is approximately 95 to 120 mm.

[0015] The main towers 11 and 12 are, for example, A-type towers used to increase the torsional rigidity of the cable-stayed bridge 10. Although A-type towers are used for the main towers 11 and 12, it is also possible to use single-column towers, independent two-column towers, inverted Y-type towers, H-type towers, etc. The height H1 of the main towers 11 and 12 is, for example, H1 = 97 m.

[0016] In the following, the distance from the support of the main tower 11 to the support of the main tower 12 that supports the bridge girder 13 from below will be referred to as the span length L1. In the cable-stayed bridge 10, it is preferable that the span length L1 is, for example, L1 > 100 m. As an example, the span length L1 is L1 = 300 m. The height H2 of the bridge girder 13 supported by the main towers 11 and 12 from the ground is, for example, H2 = 18 m.

[0017] Figure 2 is a cross-sectional view of the bridge girder 13 at position P1 of the cable-stayed bridge 10 shown in Figure 1. As shown in Figure 2, for example, a bridge girder with two end main H girders is used as the bridge girder 13. The bridge girder 13 is a composite girder having, for example, a reinforced concrete deck slab 21 and main girders 22. The main girders 22 also have I-shaped girders 23 and 24 and transverse girders 25. Hereinafter, the reinforced concrete deck slab 21 may be simply referred to as the deck slab 21.

[0018] In this embodiment, two end main H girders are shown as bridge girders 13, but it is also possible to use two end main box girders as bridge girders, for example, as shown in Figure 6(c).

[0019] The I-beams 23 and 24 are positioned at both ends of the deck slab 21 in the width direction (the transverse direction of the bridge girder 13), along the extension direction of the deck slab 21 (the longitudinal direction of the bridge girder 13) which is perpendicular to the width direction of the deck slab 21. The I-beam 23 has a web 23a, an upper flange 23b, a lower flange 23c, and reinforcing ribs 23d. Since the I-beam 24 has the same configuration as the I-beam 23, the configuration of the I-beam 24 is omitted here.

[0020] The transverse beams 25 are members arranged along the width direction of the floor slab 21. Multiple transverse beams 25 are arranged at predetermined intervals in the extending direction of the floor slab 21.

[0021] The bridge girder 13 described above is configured to have a two-lane road, and the total width W1 of the bridge girder 13 is preferably 15 m or less. For example, the total width W1 is W1 = 11.3 m. The thickness TH1 of the deck slab 21 is, for example, TH1 = 350 mm. The total width W1 of the bridge girder 13 is a value set according to the width W2 of the main girder.

[0022] Furthermore, the height of the main girder 22, that is, the I-shaped girders 23 and 24, is preferably, for example, H3 ≥ 1.2 m.

[0023] The main components of the main girder 22 are shown in Table 1.

[0024]

[0025] As described above, the main girder 22 has I-beams 23 and 24 and crossbeams 25. The steel material used for the I-beams 23 and 24 is, for example, SM570. Below, we will describe the I-beam 23, and omit the description of the I-beam 24.

[0026] The dimensions of the web 23a, upper flange 23b, lower flange 23c, and rib 23d that constitute the I-beam 23 are as follows: The height and thickness of the web 23a are, for example, 1500 mm and 22 mm in thickness. The width and thickness of the upper flange 23b are, for example, 500 mm and 20 mm in thickness. The width and thickness of the lower flange 23c are, for example, 750 mm and 30 mm in thickness. The width and thickness of the rib 23d are, for example, 200 mm and 15 mm in thickness.

[0027] The steel material used for the crossbeam 25 is, for example, SM490Y. The dimensions of the upper flange 25b and lower flange 25c that make up the crossbeam 25 are as follows: The height and thickness of the web 25a are, for example, 1250 mm in height and 22 mm in thickness. The width and thickness of the upper flange 25b and lower flange 25c are, for example, 500 mm in width and 40 mm in thickness.

[0028] In the cable-stayed bridge 10 described above, one way to improve wind resistance stability is to lower the height of the main girder 22 and make the overall cross-section of the bridge girder 13 a streamlined cross-section. A streamlined cross-section refers to a cross-section in which the ratio W1 / H3 of the total width W1 of the bridge girder 13 to the height H3 of the main girder 22 is large. On a two-lane road, the total width W1 is small, but the height H3 of the bridge girder 13 calculated from the load conditions is large, and the ratio W1 / H3 of the total width W1 to the height H3 tends to be small. This makes it difficult to ensure wind resistance stability.

[0029] In this embodiment, by using steel with high yield strength for the I-beams 23, 24 and the crossbeams 25, the limit value of the stress acting on the I-beams 23, 24 and the crossbeams 25 is improved, and at the same time, the wind resistance stability is improved by lowering the height H3 of the main girder 22. Hereinafter, steel with high yield strength will be referred to as high-strength steel.

[0030] For example, if high-strength steel is used for the I-beams 23 and 24 and the transverse girders 25 that make up the main girder 22, the deflection rigidity of the cable-stayed bridge 10 will decrease. However, the deflection rigidity of the cable-stayed bridge 10 can be increased by adjusting the diameter of the cables 15 that support the bridge girder 13 and the number of cables used (to support the bridge girder 13).

[0031] Next, we will explain the height H3 of the main girder 22, that is, the I-shaped girders 23 and 24, which are made of high-strength steel. The following explanation will take into account the bending stress of the lower flange 23c. For example, the height H3 of the main girder 22 is proportional to the section modulus. Also, the increase in stress is inversely proportional to the square of the height H3 of the main girder 22. That is, as shown in equation (1) below, the square root of the stress ratio is proportional to the ratio of the total width W1 to the height H3 of the main girder 22.

[0032] (δ² / δ¹) １ / ２ =α×(W1 / H3)...(1)

[0033] In equation (1) above, δ1 is the stress before the change, δ2 is the stress after the change, and α is a coefficient.

[0034] Therefore, the steel material used for the lower flanges of the I-shaped girders 23 and 24 that constitute the main girder 22 was SM490Y (yield strength 355 N / mm²). ２ The ratio W1 / H3 of the total width W1 of the bridge girder 13 to the height H3 of the main girder 22 was calculated using equation (1) when the steel material was changed to one with a yield strength higher than SM490Y. For example, SM570 (yield strength 450 N / mm ２ ), SBH500 (yield strength 500N / mm ２ ), SBHS700 (yield strength 630N / mm ２The formula used was (1) above. It was found that the ratios W1 / H3 obtained from formula (1) above are 1.13 times, 1.19 times, and 1.4 times the values ​​obtained when SM490Y is used as the material for the lower flanges of I-beams 23 and 24.

[0035] For example, in a bridge girder 13 for a two-lane road, if the material of the I-shaped girders 23 and 24 is SM490Y, the width W1 of the deck slab 21 is W1 = 12 m, and the height H3 of the main girder 22, i.e., the I-shaped girders 23 and 24, is H3 = 2 m, then the ratio W1 / H3 is W1 / H3 = 6. For example, if the material of the I-shaped girders 23 and 24 is the aforementioned SBHS700, and the height H3 of the main girder 22 is H3 = 1.43 m, then the ratio W1 / H3 is W1 / H3 = 8.4. In this way, by using steel with high yield strength, the height H3 of the I-shaped girders 23 and 24 can be lowered, and the ratio W1 / H3 can be increased. As a result, the cross-section of the bridge girder 13 becomes a streamlined cross-section, and wind resistance safety can be ensured in the cable-stayed bridge 10.

[0036] Incidentally, the I-beams 23 and 24, which are the main girders of the cable-stayed bridge 10, are used as composite girders integrated with the deck slab 21. As shown in Figure 4(a), for example, in the case of a non-composite girder 51 composed of a deck slab 52 and an I-beam 53, compressive stress S1 and tensile stress S2 due to the bending moment acting on the non-composite girder 51 act on each of the deck slab 52 and the I-beam 53. On the other hand, as shown in Figure 4(b), in the case of a composite girder 61 composed of a deck slab 62 and an I-beam 63 made of steel, for example, the compressive stress S1 due to the bending moment acting on the composite girder 61 acts on the deck slab 62 and the tensile stress S2 acts on the I-beam 63, so a more rational design is possible compared to the non-composite girder 51. By using a composite girder, the advantage of applying steel with high yield strength to the lower flange becomes greater.

[0037] The following describes the results obtained by simulation of the height H3 of the main girder 22, that is, the I-shaped girders 23 and 24, when the full span W1 is set to W1 = 12 m and the span length L1 is set to L1 = 200, 300, 400 m. Here, in Fig. 5, the horizontal axis represents the span length L1, and the vertical axis represents the height H3 of the main girder 22. A case where the floor slab 21 is a concrete floor slab and the thickness of the floor slab 21 is 350 mm is being simulated. In Fig. 5, the height of the main girder 22 is obtained for each of the non-composite girder and the composite girder. Also, if the span length exceeds 100 m and is 200 m or less, it can be realized with the same girder height as a span length of 200 m in a cable-stayed bridge. Also, in this region, even without a cable support structure, a girder height of 1.2 m can be realized with high-yield-strength steel.

[0038] As shown in Fig. 5, the black squares indicate non-composite girders, and the black triangles indicate composite girders. In the non-composite girder, when the span length L1 is L1 = 400 m, the stress that the I-shaped girder constituting the non-composite girder can bear is insufficient, so it does not hold as a non-composite girder. Therefore, in Fig. 5, the result when the span length L1 is L1 = 400 m is shown by white squares instead of black squares.

[0039] As shown in Fig. 5, when the span length L1 in the non-composite girder is L1 = 200 m, the ratio W1 / H3 is W1 / H3 = 4.5. Also, when the span length L1 in the non-composite girder is L1 = 300 m, the ratio W1 / H3 is W1 / H3 = 4.0. Further, when the span length in the non-composite girder is 400 m, the ratio W1 / H3 is W1 / H3 = 4.0.

[0040] On the other hand, when the span length in the composite girder is 200 m, the ratio W1 / H3 is W1 / H3 = 9.4. Also, when the span length in the composite girder is 300 m, the ratio W1 / H3 is W1 / H3 = 7.5. Further, when the span length in the composite girder is 400 m, the ratio W1 / H3 is W1 / H3 = 7.5. That is, in the composite girder, even if the height of the main girder 22, that is, the I-shaped girders 23 and 24, is 1200 mm or more and 1500 mm or less, the ratio W1 / H3 becomes 7 or more, and it is possible to obtain a cross-sectional shape with high wind resistance safety.

[0041] The girder height of 1.2 m is the minimum girder height in the current design. When higher-yield-strength steel materials appear or the design system changes, it is possible to reduce the girder height. Considering the constraints in manufacturing, erection, and even maintenance management, it is preferable that the minimum value of the girder height is about 1.0 m.

[0042] <Summary of Effects> The wind-resistant bridge structure of this embodiment is a wind-resistant bridge structure provided with a bridge truss 13 having a floor slab 21 and main girders 22 made of I-shaped girders or box girders that support the floor slab 21 from below at both ends in the width direction of the floor slab 21. The span length of the bridge truss 13 exceeds 100 m, the total width W1 of the bridge truss 13 is 15 m or less, the height H3 of the main girder is 1.2 m or more, and the ratio W1 / H3 of the total width W1 of the bridge truss 13 to the height H3 of the main girder is 7 or more. At least the lower flanges 23c of the I-shaped girders 23 and 24 constituting the main girder 22 are made of steel with a yield strength of 380 N / mm ２ or more.

[0043] According to this, the wind-resistant stability of the bridge truss 13 having two end main box girders, two end main I-shaped girders, etc. can be improved.

[0044] Further, the bridge truss 13 is characterized in that it is a composite girder formed by combining the floor slab 21 and the main girder 22.

[0045] According to this, since the compressive stress S1 due to the bending moment acting on the composite girder 61 acts on the floor slab 62 and the tensile stress S2 acts on the I-shaped girder 63, it is possible to perform a more reasonable design compared to the non-composite girder 51 in which the compressive stress S1 and the tensile stress S2 act on the floor slab 52 and the I-shaped girder 53 respectively.

[0046] Further, according to the cable-stayed bridge of the present invention, since it becomes a cable-stayed bridge having the above-described bridge structure, the wind-resistant stability of the bridge can be improved.

[0047] 10 Cable-stayed bridge 11, 12 Main tower 13 Bridge truss 14 Bridge pier 15 Cable 21 Reinforced concrete floor slab 22 Main girder 23, 24 I-shaped girder 25 Cross girder 51 Non-composite girder 61 Composite girder

Claims

1. A bridge structure comprising a bridge girder having a deck slab and main girders including I-beams or box girders that support the deck slab from below at both ends in the width direction of the deck slab, wherein the span length of the bridge girder exceeds 100 m, the total width of the bridge girder is 15 m or less, the height of the main girder is 1.2 m or more, the ratio of the total width of the bridge girder to the height of the main girder is 7 or more, and at least the lower flange of the main girder has a yield strength of 380 N / mm ２ A bridge structure characterized by the use of the above-mentioned steel materials.

2. The bridge structure according to claim 1, characterized in that the bridge girder is a composite girder formed by combining the deck slab and the main girder.

3. A cable-stayed bridge having the bridge structure described in claim 1 or claim 2.

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