Bridge Structure

Abstract

To improve the wind resistance performance of long-span bridges using bridge girders consisting of two end box girders or two end I-shaped girders. [Solution] The present invention provides a bridge structure comprising a bridge girder 13 having a deck slab 21 and main girders 22 including I-shaped girders 23, 24 or box girders that support the deck slab 21 from below at both ends in the width direction of the deck slab 21, wherein the span length of the bridge girder 13 exceeds 100m, the total width of the bridge girder 13 is 15m or less, the height of the main girder 22 is 1.2m or more, the ratio of the total width W1 of the bridge girder 13 to the height H3 of the main girder 22 W1 / H3 is 7 or more, and at least the lower flange of the main girder has a yield strength of 380N / mm 2 It is characterized by the use of the above-mentioned steel materials.

Description

Technical Field

[0001] The present invention relates to a bridge structure using a bridge girder made of, for example, a double main box girder or a double main I-girder at the ends.

Background Art

[0002] Bridges are important structures that make up social infrastructure. In recent years, the development of bridges with long spans (hereinafter sometimes referred to as long-span bridges) has been underway. 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 cable-stayed bridges and suspension bridges, long-span bridges have a structure that is supported by cables and can 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 that secures 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 resistance stability were used in cable-stayed bridges and suspension bridges. In the 1980s, due to 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, double main box girders (see Fig. 6(c)) having a sectional shape with reduced steel weight and bridge girders made of double main I-girders called edge girders (see Fig. 6(d)) are adopted.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

[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 velocity 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 velocity 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. [Means for solving the problem]

[0008] A bridge structure in 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. [Effects of the Invention]

[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. [Brief explanation of the drawing]

[0012] [Figure 1] 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] Figure 2 is a cross-sectional view showing the configuration of the bridge girder at location P1 of the cable-stayed bridge. [Figure 3] Figure 3 is a cross-sectional view showing the structure of the bridge girder. [Figure 4] Figure 4(a) shows the stress distribution in the non-composite girder, and Figure 4(b) shows the stress distribution in the composite girder. [Figure 5] This figure shows a comparison of the main girder heights of non-composite girders and composite girders. [Figure 6] Figure 6 is a cross-sectional view illustrating bridge girders of different structures. [Modes for carrying out the invention]

[0013] Hereinafter, the cable-stayed bridge shown in this embodiment will be described with reference to the drawings. Hereinafter, the bridge structure of the present invention will be described using a cable-stayed bridge, but the bridge does not necessarily have to be limited to a cable-stayed bridge, and may be other bridges such as a girder bridge.

[0014] As shown in FIG. 1, the cable-stayed bridge 10 includes main towers 11, 12, a bridge girder 13, and bridge piers 14. Although illustration is omitted, the bridge girder 13 is supported from below by supports provided on the main towers 11, 12 and supports provided on the bridge piers 14, and is supported by a plurality of cables 15 that radiate from the upper ends of the main towers 11, 12. The cable 15 is a product generally used in cable-stayed bridges, and the outer diameter is approximately 95 to 120 mm.

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

[0016] Hereinafter, the distance from the support of the main tower 11 that supports the bridge girder 13 from below to the support of the main tower 12 will be referred to as the span length L1. The span length L1 in the cable-stayed bridge 10 is preferably, 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, 12 from the ground is, for example, H2 = 18 m.

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

[0018] In this embodiment, two end main H girders are shown as example 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-shaped girders 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-shaped girder 23 has a web 23a, an upper flange 23b, a lower flange 23c, and a reinforcing rib 23d. Since the I-shaped girder 24 has the same configuration as the I-shaped girder 23, the configuration of the I-shaped girder 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 15m or less. For example, the total width W1 is W1 = 11.3m. The thickness TH1 of the deck slab 21 is, for example, TH1 = 350mm. The total width W1 of the bridge girder 13 is a value set according to the main girder width W2.

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

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

[0024] [Table 1]

[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 transverse beams 25, the limit value of the stress acting on the I-beams 23, 24 and the transverse beams 25 is improved, and at the same time, the wind resistance stability is improved by lowering the height H3 of the main beam 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, i.e., 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 the coefficient.

[0034] Therefore, the steel 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 / mm²) was used as an example of a steel material with a yield strength higher than SM490Y. 2 ), SBH500 (yield strength 500N / mm 2 ), SBHS700 (yield strength 630N / mm 2 The 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, for example, SM490Y is used as the material for the lower flange 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 21 is W1 = 12m, and the height H3 of the main girder 22, i.e., the I-shaped girders 23 and 24, is H3 = 2m, 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 = 1.43m, 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 a composite girder 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 and tensile stress 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 due to the bending moment acting on the composite girder 61 acts on the deck slab 62 and the tensile stress 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 of simulations to determine the height H3 of the main girders 22, i.e., I-beams 23 and 24, when the total width W1 is set to W1 = 12m and the span length L1 is set to L1 = 200, 300, and 400m. In Figure 5, the horizontal axis represents the span length L1, and the vertical axis represents the height H3 of the main girder 22. The simulation was conducted for a case where the deck slab 21 is a concrete slab with a thickness of 350mm. In Figure 5, the heights of the main girders 22 and 23 are determined for both non-composite girders and composite girders. Furthermore, if the span length exceeds 100m but is 200m or less, it is possible to achieve the same girder height as a cable-stayed bridge with a span length of 200m. Also, in this range, a girder height of 1 or 2m can be achieved with high yield strength steel without using a cable support structure.

[0038] As shown in Figure 5, black squares represent non-composite girders, and black triangles represent composite girders. Note that when the span length L1 is L1 = 400m in a non-composite girder, the I-beams constituting the non-composite girder cannot withstand the stress, and therefore it does not function as a non-composite girder. Accordingly, in Figure 5, the result when the span length L1 is L1 = 400m is shown with a white square instead of a black square.

[0039] As shown in Figure 5, when the span length L1 of the non-composite girder was L1 = 200m, the ratio W1 / H3 was W1 / H3 = 4.5. Furthermore, when the span length L1 of the non-composite girder was L1 = 300m, the ratio W1 / H3 was W1 / H3 = 4.0. Moreover, when the span length of the non-composite girder was 400m, the ratio W1 / H3 was W1 / H3 = 4.0.

[0040] On the other hand, when the span length of the composite girder was 200m, the ratio W1 / H3 was W1 / H3 = 9.4. Furthermore, when the span length of the composite girder was 300m, the ratio W1 / H3 was W1 / H3 = 7.5. Moreover, when the span length of the composite girder was 400m, the ratio W1 / H3 was W1 / H3 = 7.5. In other words, in the composite girder, even if the height of the main girder 22, i.e., the I-beams 23 and 24, is set to between 1200mm and 1500mm, the ratio W1 / H3 is 7 or higher, making it possible to obtain a cross-sectional shape with high wind resistance safety.

[0041] A girder height of 1.2m is the minimum girder height under current design. If steel materials with higher yield strength become available or if the design system changes, the girder height can be reduced. Considering constraints in manufacturing, erection, and maintenance, it is preferable that the minimum girder height be around 1.0m.

[0042] <Summary of effects> The wind-resistant bridge structure of this embodiment is a bridge girder 13 having a deck slab 21 and main girders 22 consisting of I-shaped girders or box girders that support the deck slab 21 from below at both ends in the width direction of the deck slab 21, wherein the span length of the bridge girder 13 exceeds 100m, the total width W1 of the bridge girder 13 is 15m or less, the height H3 of the main girders is 1.2m or more, the ratio of the total width W1 of the bridge girder 13 to the height H3 of the main girders W1 / H3 is 7 or more, and the lower flanges 23c of at least the I-shaped girders 23,24 constituting the main girders 22 have a yield strength of 380N / mm 2 It is characterized by the use of the above-mentioned steel materials.

[0043] According to this, the wind resistance stability of the bridge girder 13, which has two end box girders, two end I-shaped girders, etc., can be improved.

[0044] Furthermore, the bridge girder 13 is characterized by being a composite girder formed by combining the deck slab 21 and the main girder 22.

[0045] According to this, the compressive stress due to the bending moment acting on the composite girder 61 acts on the deck slab 62, and the tensile stress acts on the I-beam girder 63. Therefore, it is possible to perform a more rational design compared to a non-composite girder 51, where the compressive and tensile stresses act on the deck slab 52 and the I-beam girder 53 respectively.

[0046] Furthermore, the cable-stayed bridge of the present invention is a cable-stayed bridge having the above-described bridge structure, which improves the wind resistance stability of the bridge. [Explanation of Symbols]

[0047] 10 Cable-stayed bridge 11,12 Main tower 13 Bridge girders 14 Bridge piers 15 Cables 21 Reinforced concrete slab 22 Main digit 23, 24 Type I girder 25 crossbeam 51 Non-composite digits 61 composite digits

Claims

1. A bridge structure comprising a deck slab and main girders including I-shaped girders or box girders that support the deck slab from below at both ends in the width direction of the deck slab, The span length of the aforementioned bridge girder exceeds 100m. The total width of the aforementioned bridge girder is 15m or less. The height of the main beam is 1.2m or more. The ratio of the total width of the bridge girder to the height of the main girder is 7 or more. 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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