Main tower for bridge and bridge provided therewith

Abstract

An object is to provide a main tower of a bridge having a rectangle-shaped cross section which can effectively reduce oscillation for wind blowing in the direction normal to the bridge axis. A cross sectional shape of a tower column is a rectangle shape with a direction normal to the bridge axis dimension smaller than a bridge-axis direction dimension. A slit passing through in the direction normal to the bridge axis is formed in a substantially central position, and a ratio of the bridge-axis direction dimension of the slit with respect to the bridge-axis direction dimension of the cross section is between 0.2 and 0.3.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a main tower of a bridge, and particularly to a main tower that is suitable for use in cable-supported bridges (suspension bridge, cable-stayed bridge).

DESCRIPTION OF RELATED ART

[0002] FIG. 8 schematically shows a part of a suspension bridge.

[0003] The suspension bridge is constructed with a main tower 101, provided standing in a substantially vertical direction, a bridge girder 102, which extends in the bridge-axis direction, main cables 103 supported at the top of the main tower 101, and hangers 104 suspended from the main cables 103. The bridge girder 102 is supported by the main tower 101 via the main cables 103 and the hangers 104.

[0004] When the main tower becomes larger as the bridge becomes longer and larger, oscillation caused by wind can no longer be ignored. This oscillation must be considered not only after the completion of bridge construction, but also during the construction.

[0005] As a method for reducing such oscillation, the cross sectional shape of the main tower is changed.

[0006] For example, in "Wind resistant stability of Sugaharashirokita bridge" (bridges and foundations), page 90-7, page 29-34), a technique is disclosed for reducing oscillation in a direction normal to the bridge axis, caused by wind blowing towards the bridge-axis direction, by forming slits in the bridge-axis direction.

[0007] However, in the technique disclosed in the above document, the cross sectional shape of the main tower is a square shape, and the effect in the case where this is a rectangle shape is not disclosed. In the case of a main tower having a rectangle-shaped cross section, even when slits are formed, it is difficult to predict a dimension that gives wind resistant stability. Particularly, for limited-amplitude oscillation where the wind velocity is relatively low (for example, vortex-induced oscillations), it can be predicted that a bridge will exhibit a constant wind resistant stability, as shown in the above document. However, for a range with a relatively high wind velocity showing divergence of the oscillation amplitude, it cannot be easily predicted.

[0008] Furthermore, slits formed along the direction of wind flow are expected to effectively give wind resistant stability. However, it is predicted that the slits will not produce a desirable effect for wind that is orthogonal to the direction in which they are formed.

BRIEF SUMMARY OF THE INVENTION

[0009] The present invention has been achieved in consideration of such circumstances, with an object of providing a main tower of a bridge having a rectangle-shaped section, which can effectively reduce oscillation, and a bridge provided therewith.

[0010] Moreover, it is an object of the present invention to provide a main tower of a bridge having a rectangle-shaped cross section that has wind resistant stability for wind blowing not only in the direction normal to the bridge axis, but also in the bridge-axis direction, and a bridge provided therewith.

[0011] In order to solve the above problem, the main tower of a bridge of the present invention and a bridge provided therewith employ the following solutions.

[0012] That is to say, in a main tower of a bridge according to a first aspect of the present invention where a cross sectional shape of a tower column is a rectangle shape with a direction normal to the bridge axis dimension smaller than a bridge-axis direction dimension, a slit passing through in the direction normal to the bridge axis is formed in a substantially central position, and a ratio of the bridge-axis direction dimension of the slit with respect to the bridge-axis direction dimension of the cross section is between 0.2 and 0.3.

[0013] By forming a slit passing through in the direction normal to the bridge axis with respect to the cross section of the main tower of a bridge, oscillation in the bridge-axis direction caused by wind blowing towards the direction normal to the bridge axis can be suppressed. Specifically, oscillation amplitude which occurs when dimensionless wind velocity that has been made dimensionless by dividing the wind velocity by the natural frequency of the main tower, and the direction normal to the bridge axis dimension of the main tower cross section, is 10 or less, can be suppressed.

[0014] If the width of the slit is increased, the slit can suppress limited oscillation for wind in the direction normal to the bridge axis. However, as a result of further detailed examination, the present inventors have discovered that oscillation amplitude actually increases when the slit width is increased above a predetermined value, in the case where wind velocity further increases. That is to say, as a result of carrying out dedicated wind tunnel testing relating to a main tower having a rectangle-shaped cross section, the present inventors have discovered that a minimum value exists in a maximum amplitude that occurs in dimensionless wind velocity between 20 to 30, when the width of the slit is changed. Specifically, by making a ratio of the bridge-axis direction dimension of the slit with respect to the bridge-axis direction dimension of the cross section to be between 0.2 and 0.3, the maximum amplitude that occurs in a dimensionless wind velocity of 20 to 30 can also be made small accordingly.

[0015] Preferably, the ratio of the bridge-axis direction slit width to the bridge-axis direction dimension is substantially 0.25.

[0016] Furthermore, in the main tower of a bridge relating to a second aspect of the present invention, where an envelope shape of a tower column cross section is a rectangle shape with a direction normal to the bridge axis dimension smaller than a bridge-axis direction dimension; a slit passing through in the direction normal to the bridge axis is formed in a substantially central position; in four corners of the envelope shape, is formed cutout parts with a cut out section which is cut out from a bridge-axis direction cutout position positioned on one side in the bridge-axis direction, to a direction normal to the bridge axis cutout position positioned on an other side in the direction normal to the bridge axis that is orthogonal to the one side, and a bridge-axis direction cutout dimension from a corner part of the envelope shape to the bridge-axis direction cutout position is greater than a direction normal to the bridge axis cutout dimension from the corner part to the direction normal to the bridge axis cutout position.

[0017] Providing cutout parts in the four corners improves wind resistant stability. Furthermore, as a result of carrying out dedicated wind tunnel testing with respect to a main tower with an envelope shape of the cross section in a rectangle shape, the present inventors have discovered the existence of an optimal shape for the cutout part. That is to say, by providing a cutout part in which the bridge-axis direction cutout dimension is greater than the direction normal to the bridge axis cutout dimension, oscillation caused by wind blowing in the bridge-axis direction can be suppressed to the greatest possible extent.

[0018] Furthermore, since a slit which passes through in the direction normal to the bridge axis is formed, oscillation caused by wind blowing towards the direction normal to the bridge axis can also be suppressed to the greatest possible extent.

[0019] Moreover, the shape of the cutout part is typically a rectangle shape. However, it is not limited to this, and for example it may be a triangle shape with chamfered corners.

[0020] Furthermore, the ratio of the bridge-axis direction dimension of the slit, to the bridge-axis direction dimension of the cross section is preferably between 0.2 and 0.3.

[0021] Moreover, in a main tower of a bridge according to a third aspect of the present invention, where a cross section is a rectangle shape with a direction normal to the bridge axis dimension smaller than a bridge-axis direction dimension, a slit passing through in the direction normal to the bridge axis is formed in a substantially central position, and a slit passing through in the bridge-axis direction is formed in a substantially central position.

[0022] By forming a slit passing through in the direction normal to the bridge axis, in the cross section of the main tower of a bridge, oscillation caused by wind blowing in the direction normal to the bridge axis can be suppressed. Furthermore, by forming a slit which passes through in the bridge-axis direction, oscillation caused by wind blowing in the bridge-axis direction can be suppressed.

[0023] Moreover, in the slit of the main tower of a bridge according to the first to third aspects, viscoelastic members are arranged.

[0024] By arranging viscoelastic members in the slit, oscillation in the main tower can be suppressed even lower. Furthermore, if the widths of the slits are made in a size that can accommodate an operator, workability at the time of installation increases.

[0025] Also, a bridge of the present invention is characterized in that it is provided with a main tower of a bridge according to any of the first to third aspects.

[0026] By providing a main tower having a cross section that reduces oscillation, the wind resistant stability of the bridge can be improved.

[0027] According to the present invention, by providing slits of optimal dimensions, a reduction in oscillation can be achieved not only in limited oscillation when the dimensionless wind velocity is 10 or less, but also in oscillation when the dimensionless wind velocity is 20 to 30.

[0028] Moreover, by optimizing the shape of the cutout part, oscillation caused by wind blowing not only in the direction normal to the bridge axis, but also in the bridge-axis direction, can be suppressed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0029] FIG. 1A is a perspective view showing a main tower of a bridge of the present invention.

[0030] FIG. 1B is a cross sectional view showing a main tower according to a first embodiment of the main tower of a bridge of the present invention.

[0031] FIG. 2 is a cross sectional view showing a main tower that illustrates a second embodiment of the present invention.

[0032] FIG. 3 is a cross sectional view showing a main tower that illustrates a third embodiment of the present invention.

[0033] FIG. 4 is a cross sectional view showing a condition in which dampers have been installed in the slit.

[0034] FIGS. 5A and B are diagrams which illustrate examples of the present invention, showing wind resistant stability due to the slit.

[0035] FIGS. 6A and B are diagrams which illustrate examples of the present invention, showing wind resistant stability due to cutout parts.

[0036] FIG. 7 is a diagram which illustrate examples of the present invention, showing variation in maximum amplitude with respect to slit width.

[0037] FIG. 8 is a perspective view showing a part of conventional cable-supported bridge.

DETAILED DESCRIPTION OF THE INVENTION

[0038] Hereunder, embodiments according to the present invention are described, with reference to the drawings.

First Embodiment

[0039] FIG. 1A shows a main tower which is used for cable-supported bridges such as a cable-stayed bridge and a suspension bridge. As shown in FIG. 8, this main tower 1 constitutes a bridge by having a bridge girder and cables attached thereto.

[0040] The main tower 1 is provided standing in a substantially vertical direction, and two tower columns are provided, one on each side of the bridge girder. In the upper part of the main tower 1, a cross member 8 is provided, enhancing the rigidity of the main tower 1. The cross member 8 may be omitted.

[0041] Slits 10 are formed in the main tower 1, passing through in the direction normal to the bridge axis Y, orthogonal to the bridge-axis direction X. A plurality of the slits 10 is provided in the direction in which the main tower 1 is standing.

[0042] FIG. 1B shows a cross section of the main tower 1. The cross section of the main tower 1 is a rectangle shape in which a dimension B in the direction normal to the bridge axis Y is smaller than a dimension D in the bridge-axis direction X. As shown in the same diagram, the slits 10 are formed in a substantially central position of the cross section. A slit width s is set such that its ratio to the dimension D in the bridge-axis direction X, is between 0.2 and 0.3, and is more preferably 0.25.

[0043] By having such slit dimension s, oscillation generated by the wind blowing in the direction normal to the bridge axis Y can be suppressed. Specifically, not only a oscillation amplitude, which occurs when dimensionless wind velocity (=U/fD; U is wind velocity), which is made dimensionless by dividing the wind velocity by a natural frequency f of the main tower 1 and by the dimension D of the main tower cross section in the bridge-axis direction, is 10 or less, but also a maximum oscillation which occurs when the dimensionless wind velocity is 20 to 30, can be reduced accordingly.

Second Embodiment

[0044] FIG. 2 shows a second embodiment of the present invention. This diagram shows a cross section of the main tower 1. The present embodiment differs from the first embodiment in that cutout parts 15 are formed in addition to the slits in the first embodiment.

[0045] As shown in the same diagram, the envelope shape of the cross section is a rectangle shape in which a dimension B in the direction normal to the bridge axis Y is smaller than a dimension D in the bridge-axis direction X. As with the above embodiment, a slit 10 that passes through in the direction normal to the bridge axis Y is formed in a substantially central position. The slit width s is set such that its ratio to the dimension D in the bridge-axis direction X is between 0.2 and 0.3, and is more preferably 0.25.

[0046] In four corners of the main tower 1 having the rectangle shape envelope shape, is formed cutout parts 15 with a cut out section cutout from a bridge-axis direction cutout position 11 positioned on one side in the bridge-axis direction X, to a direction normal to the bridge axis cutout part 12 positioned on an other side in the direction normal to the bridge axis Y that is orthogonal to the one side. A bridge-axis direction cutout dimension D2 from a corner part 13 of the envelope shape to the bridge-axis direction cutout position 11 is greater than a direction normal to the bridge axis cutout dimension B2 from the corner part 13 to the direction normal to the bridge axis cutout position 12. Specifically, the cutout parts 15 have rectangle shapes when seen in a cross sectional view as shown in FIG. 2. Instead of the rectangular shape, for example, the cut out part may be a triangle shape with chamfered corners, giving an overall shape having an octagon shape in a cross sectional view.

[0047] According to the present embodiment, since the cutout parts 15 are formed in a rectangle shape with the bridge-axis direction cutout dimension D2 greater than the direction normal to the bridge axis cutout dimension B2, oscillation caused by wind blowing towards the bridge-axis direction X can be suppressed to the greatest possible extent.

[0048] Furthermore, in the present embodiment, since a slit 10 that passes through in the direction normal to the bridge axis Y is formed, oscillation caused by wind blowing towards the direction normal to the bridge axis Y can also be suppressed to the greatest possible extent.

Third Embodiment

[0049] FIG. 3 shows a third embodiment of the present invention. This diagram shows a cross section of the main tower 1. The present embodiment differs from the first embodiment in that a slit in the bridge-axis direction is formed, in addition to the slit in the first embodiment.

[0050] As shown in FIG. 3, in addition to the slit 10 formed in the direction normal to the bridge axis Y, a slit 20 that passes through in the bridge-axis direction X is formed in a substantially central position.

[0051] By having such a construction, not only can oscillation caused by wind blowing in the direction normal to the bridge axis Y be suppressed, but also oscillation caused by wind blowing in the bridge-axis direction X can be suppressed.

[0052] Each embodiment described above may have a construction in which dampers (viscoelastic member) 25 are arranged in the slits 10 and 20 as shown in FIG. 4. Accordingly, oscillation of the main tower 1 can be suppressed even lower. Furthermore, if the widths of the slits 10 and 20 are made of a size that can accommodate an operator, workability at the time of installation increases.

EXAMPLES

[0053] FIGS. 5A, 5B, 6A, 6B and 7 illustrate examples of the present invention.

[0054] Each diagram shows results of wind tunnel tests using a model of the main tower 1.

[0055] In the tables in FIGS. 5A, 5B, 6A and 6B, the first column shows the sample number, the second column shows cross sectional shapes of the main tower, and the third and fourth columns show V-A diagrams (wind velocity--response amplitude diagrams).

[0056] The cross sectional shape of the main tower is such that a bridge-axis direction dimension D is for example 16m, and a direction normal to the bridge axis dimension B is for example 12 m (B=0.75 D).

[0057] The V-A diagrams are shown for angles of attack of 0.degree. and 90.degree. respectively. The definition of the angle of attack is shown in FIG. 1B, with flow along the direction normal to the bridge axis Y taken as being 0.degree., and flow along the bridge-axis direction X taken as being 90.degree.. The horizontal axis in the V-A diagrams uses dimensionless wind velocity. The wind velocity is made dimensionless by dividing the wind velocity U by the natural frequency f of the main tower and by the bridge-axis direction dimension D (U/fD). The vertical axis in the V-A diagram shows dimensionless amplitude which is made dimensionless by dividing by the bridge-axis direction dimension D.

[0058] In FIGS. 5A and 5B, sample numbers S-0, 1, 2, 4, 5 are comparative examples, and S-3 is the present invention. For a basic sectional shape S-0 with no slit, the dimensionless amplitude is approximately 0.14 in the limited oscillation where the dimensionless wind velocity is 10 or less. Furthermore, the dimensionless amplitude becomes divergent and cannot be measured when the dimensionless wind velocity is 13 or more.

[0059] For S-1, in which a slit s/D=0.05 (s is the slit width and D is the bridge-axis direction dimension of the cross section) is inserted into the basic sectional shape S-0, the dimensionless amplitude in limited oscillation is 0.16 or more, and an effect of the slit is not observed. When the dimensionless wind velocity is 20 or more, divergent oscillation is suppressed to a some degree. However, when the dimensionless wind velocity is greater than 30, the oscillation becomes divergent.

[0060] For S-2, in which a slit s/D=0.1 is inserted, the dimensionless amplitude in limited oscillation is suppressed to 0.04 or less, and an effect of the slit is obtained. However, in the range of the dimensionless wind velocity of 20 to 30, the dimensionless amplitude is approximately 0.08, and the oscillation cannot be said to be sufficiently suppressed.

[0061] For S-3 of the present invention, in which a slit s/D=0.25 is inserted, the dimensionless amplitude in limited oscillation is suppressed to 0.02 or less, and furthermore, the dimensionless amplitude is suppressed to approximately 0.02 in the range of the dimensionless wind velocity of 20 to 30.

[0062] For S-4, in which a more enlarged slit s/D=0.4 is inserted, limited oscillation is suppressed. However, the dimensionless amplitude in the range of the dimensionless wind velocity of 20 to 30 increases to approximately 0.04.

[0063] For S-5, in which a slit s/D=0.5 is inserted, limited oscillation is suppressed as with S-4. However, the dimensionless amplitude in the range of the dimensionless wind velocity of 20 to 30 is not suppressed.

[0064] FIG. 7 is a plot of limited oscillation amplitudes and maximum amplitudes in the range of the dimensionless wind velocity of 20 to 30, of the respective samples No. S-0 to S-5.

[0065] As can be seen from FIG. 7, the limited oscillation amplitude can be reduced by increasing the slit width. However it can be seen that there is an optimal value of the slit width for the maximum amplitudes in the range of the dimensionless wind velocity of 20 to 30. Specifically, the maximum amplitude can be suppressed with a slit width s/D between 0.2 and 0.3, and preferably 0.25. This is a new finding obtained as a result of wind tunnel testing, and it is beyond the prediction of a person skilled in the art.

[0066] Next, the case in which cutout parts are formed is considered.

[0067] Sample No. C-1 in FIG. 5B is a comparative example, in which rectangle-shaped cutout parts, where B2/D2=1/2 (D2 is a bridge-axis direction cutout part dimension, and B2 is a direction normal to the bridge axis cutout dimension: refer to FIG. 2) are formed in the basic cross section of S-0. Oscillation with an angle of attack of 0.degree. is not suppressed. However, limited oscillation is suppressed to approximately 0.04 for wind blowing with an angle of attack of 90.degree., which is the bridge-axis direction. When compared to the result of the angle of attack of 90.degree. in S-3, it can be said that an effect is obtained due to the cutout parts.

[0068] Sample No. CS-3 is the present invention, and has a cross section combining C-1 and S-3. The dimensionless amplitude at the angle of attack of 90.degree. is slightly increased. However, it is clear that oscillation at the angle of attack of 0.degree. is drastically decreased. This CS-3 is also shown in FIG. 6A.

[0069] FIGS. 6A and 6B show the cases in which the shapes of the cutout parts are changed.

[0070] CS-1 and CS-2 are comparative examples, and CS-3 to CS-5 are the present invention.

[0071] CS-1 is a case where the rectangle-shaped cutout parts used extend sideways in the diagram and have B2/D2=2, and a slit is inserted with s/D=0.15. In this case, limited oscillation with an angle of attack of 0.degree. is suppressed. However, oscillation becomes divergent in the range of the dimensionless wind velocity of 20 or more, and cannot be measured.

[0072] CS-2 has sideways rectangle-shaped cutout parts as with CS-1, and has a slit s/D=0.25. Oscillation is sufficiently suppressed at an angle of attack of 0.degree.. However, the dimensionless amplitude of limited oscillation becomes 0.12 at an angle of attack of 90.degree., and the effect of the cutout parts is not observed.

[0073] According to the results of CS-1 and CS-2, it can be seen that sideways rectangle-shaped cutout parts, that is, cutout parts which are wide in the direction of the wind blowing in the bridge-axis direction of 90.degree. angle of attack, cannot produce sufficient wind resistant stability with respect to wind with an angle of attack of 90.degree..

[0074] CS-3 to CS-5 of the present invention are cases where the slit width is the same as that of CS-2, and the cut out parts are lengthwise rectangles. As can be seen from these results, oscillation at an angle of attack of 0.degree. can be suppressed, while oscillation at an angle of attack of 90.degree. can be suppressed to 0.08 or less (for CS-4 and CS-5, 0.04 or less). Accordingly, when combining the cutout part and the slit, it is preferable to provide a cutout part in which the bridge-axis direction dimension D2 is long.

[0075] When comparing CS-3 and CS-4, even though B2/D2 are both 0.5, CS-4 with its smaller cutout part area has better wind resistant stability at an angle of attack of 90.degree..

[0076] Moreover, as with CS-5 with B2/D2 of 0.75, it shows that even with a rectangle shape wider than that of CS-3 and CS-4, sufficient wind resistant stability can be obtained.

[0077] Furthermore, as with CS-6, cutout parts may be provided in the entry and exit of the slit in addition to the cut outs of CS-5. Accordingly, even when cutout parts are provided in the entry and exit of the slit, sufficient wind resistant stability can be obtained.

Claims

1. A main tower of a bridge where a cross sectional shape of a tower column is a rectangle shape with a direction normal to the bridge axis dimension smaller than a bridge-axis direction dimension, wherein a slit passing through in said direction normal to the bridge axis is formed in a substantially central position, and a ratio of said bridge-axis direction dimension of said slit with respect to said bridge-axis direction dimension of said cross section is between 0.2 and 0.3.

2. A main tower of a bridge according to claim 1, wherein a viscoelastic member is arranged in said slit.

3. A bridge provided with a main tower of a bridge according to claim 1.

4. A main tower of a bridge where an envelope shape of a tower column cross section is a rectangle shape with a direction normal to the bridge axis dimension smaller than a bridge-axis direction dimension; wherein a slit passing through in said direction normal to the bridge axis is formed in a substantially central position; in four corners of said envelope shape, is formed cutout parts with a cut out section which is cut out from a bridge-axis direction cutout position positioned on one side in the bridge-axis direction, to a direction normal to the bridge axis cutout position positioned on an other side in the direction normal to the bridge axis that is orthogonal to said one side, and a bridge-axis direction cutout dimension from a corner part of said envelope shape to said bridge-axis direction cutout position is greater than a direction normal to the bridge axis cutout dimension from said corner part to said direction normal to the bridge axis cutout position.

5. A main tower of a bridge according to claim 4, wherein a ratio of said bridge-axis direction dimension of said slit with respect to said bridge-axis direction dimension of said cross section is between 0.2 and 0.3.

6. A main tower of a bridge according to claim 4, wherein a viscoelastic member is arranged in said slit.

7. A bridge provided with a main tower of a bridge according to claim 4.

8. A main tower of a bridge where a cross section is a rectangle shape with a direction normal to the bridge axis dimension smaller than a bridge-axis direction dimension, wherein a slit passing through in said direction normal to the bridge axis is formed in a substantially central position, and a slit passing through in said bridge-axis direction is formed in a substantially central position.

9. A main tower of a bridge according to claim 8, wherein a viscoelastic member is arranged in said slit.

10. A bridge provided with a main tower of a bridge according to claim 8.